Academic literature on the topic 'C–X bond'
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Journal articles on the topic "C–X bond"
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Xu, Da-Zhen, Ren-Ming Hu, and Yi-Huan Lai. "Iron-Catalyzed Aerobic Oxidative Cross-Dehydrogenative C(sp3)–H/X–H (X = C, N, S) Coupling Reactions." Synlett 31, no. 18 (July 21, 2020): 1753–59. http://dx.doi.org/10.1055/s-0040-1707195.
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The direct functionalization of C(sp3)–H bonds is an attractive research topic in organic synthetic chemistry. The cross-dehydrogenative coupling (CDC) reaction provides a simple and powerful tool for the construction of C–C and C–heteroatom bonds. Recently, some progress has been made in the iron-catalyzed aerobic oxidative CDC reactions. Here, we present recent developments in the direct functionalization of C(sp3)–H bonds catalyzed by simple iron salts with molecular oxygen as the terminal oxidant.1 Introduction2 C(sp3)–C Bond Formation3 C(sp3)–N Bond Formation4 C(sp3)–S(Se) Bond Formation5 Conclusion and Outlook
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Robertson, Katherine N., Osvald Knop, and T. Stanley Cameron. "C-H···H-C interactions in organoammonium tetraphenylborates: another look at dihydrogen bonds." Canadian Journal of Chemistry 81, no. 6 (June 1, 2003): 727–43. http://dx.doi.org/10.1139/v03-080.
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The crystal structures of the tetraphenylborates of the dabcoH+, guanidinium (MeCN solvate), and biguanidinium cations are shown to contain a variety of C-H···H-C dihydrogen (DB) bonds of nominally zero polarity, as well as a variety of N-H···N, C-H···N, N-H···Ph, and C-H···Ph hydrogen (HB) bonds. These intermolecular bonds have been characterized topologically after multipole refinement of the structures. The coexistence of the DBs and HBs in each of the structures makes it possible to establish their relative strength hierarchy. It also illustrates the importance of the DBs in satisfying the tendency of these structures to maximize the total intermolecular bonding engagement. To compare the above DBs with other DBs, the results of an extensive set of MP2/6-31G(d,p) calculations (supplied by I. Alkorta) were analyzed for reference correlations between the bond-critical parameters. Thus, for an X-H···H-Y bond, the difference Δε(H)m between the Mulliken charges on the H atoms in the uncomplexed X-H and H-Y components correlates quite well with the X-H···H-Y parameters and can be used for predicting the topological strength of an X-H···H-Y bond. The use of the difference Δε(H)c in the bond does not appear to change the correlation significantly; closer correlations are observed when the amount of charge transferred on formation of the H···H bond is used instead of Δε(H)m or Δε(H)c. Bonding interactions are obtained even between like or symmetry-related H atoms as a consequence of induced-dipole interactions, which accounts for the existence of the above intermolecular C-H···H-C bonds with d(H···H) = 2.182.57 Å, electron density at the bond-critical point of ~0.050.08 e/Å3, and a rough estimate of the H···H binding energy of ~1-5 kcal/mol. Examination of the bond-critical parameters of X-H···H-Y bonds also suggests a criterion of stability of these bonds with respect to the transition from non-shared (closed-shell) X-H···H-Y interaction to covalent (shared-shell) X···H-H···Y interaction. This transition appears to be discontinuous.Key words: bond-critical parameters, bond topology, dihydrogen bonds, hydrogen bonds, organoammonium tetraphenylborates.
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Liu, Dong, Chao Liu, and Aiwen Lei. "Carbon-Centered Radical Addition to C=X Bonds for C−X Bond Formation." Chemistry - An Asian Journal 10, no. 10 (June 23, 2015): 2040–54. http://dx.doi.org/10.1002/asia.201500326.
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Valentini, Federica, Oriana Piermatti, and Luigi Vaccaro. "Metal and Metal Oxide Nanoparticles Catalyzed C–H Activation for C–O and C–X (X = Halogen, B, P, S, Se) Bond Formation." Catalysts 13, no. 1 (December 22, 2022): 16. http://dx.doi.org/10.3390/catal13010016.
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The direct functionalization of an inactivated C–H bond has become an attractive approach to evolve toward step-economy, atom-efficient and environmentally sustainable processes. In this regard, the design and preparation of highly active metal nanoparticles as efficient catalysts for C–H bond activation under mild reaction conditions still continue to be investigated. This review focuses on the functionalization of un-activated C(sp3)–H, C(sp2)–H and C(sp)–H bonds exploiting metal and metal oxide nanoparticles C–H activation for C–O and C–X (X = Halogen, B, P, S, Se) bond formation, resulting in more sustainable access to industrial production.
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Allwohn, Jürgen, Ralf Hunold, Monika Pilz, Rolf-Günter Müller, Werner Massa, and Armin Berndt. "Nachweis starker C – Sn-Hyperkonjugation über Kristallstruktur und NMR-Daten eines C-Stannylmethylenborans / Evidence for Strong C–Sn-Hyperconjugation by Crystal Structure and NMR Data of a C-Stannylmethyleneborane." Zeitschrift für Naturforschung B 45, no. 3 (March 1, 1990): 290–98. http://dx.doi.org/10.1515/znb-1990-0304.
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Strong C—Sn hyperconjugation in C-stannylmethyleneborane 3 is indicated by (1) a small B—sp2C—Sn bond angle (105.6°), (2) a long sp2C—Sn bond (216 pm), (3) a very short B=C double bond (131 pm), (4) a very small coupling constant 1J(119Sn-13C) = 125 Hz for the sp2C—Sn bond and (5) shielding of the boron atom of the B=C double bond by 20 ppm as compared to methyleneboranes without strong hyperconjugation. The boron atoms of the B=C double bond of 3 and related methyleneboranes act as π-donor and σ-acceptor, the substituents X at the carbon atom of the B=C double bond as π-acceptors and, through their C—X σ-bonds, as σ-donors. The partly bridged methyleneborane 3 closes the gap between unbridged and bridged methyleneboranes. Relationships to non-classical carbocations are pointed out.
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Nagorny, Pavel, and Zhankui Sun. "New approaches to organocatalysis based on C–H and C–X bonding for electrophilic substrate activation." Beilstein Journal of Organic Chemistry 12 (December 23, 2016): 2834–48. http://dx.doi.org/10.3762/bjoc.12.283.
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Hydrogen bond donor catalysis represents a rapidly growing subfield of organocatalysis. While traditional hydrogen bond donors containing N–H and O–H moieties have been effectively used for electrophile activation, activation based on other types of non-covalent interactions is less common. This mini review highlights recent progress in developing and exploring new organic catalysts for electrophile activation through the formation of C–H hydrogen bonds and C–X halogen bonds.
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Liu, Dong, Chao Liu, and Aiwen Lei. "ChemInform Abstract: Carbon-Centered Radical Addition to C=X Bonds for C-X Bond Formation." ChemInform 46, no. 46 (October 27, 2015): no. http://dx.doi.org/10.1002/chin.201546253.
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Luo, Tian, Shanghui Tian, Jie-Ping Wan, and Yunyun Liu. "Recent Advances in Transition Metal-Free Halogenation of C(sp2)-H Bonds." Current Organic Chemistry 25, no. 10 (June 1, 2021): 1180–93. http://dx.doi.org/10.2174/1385272825666210122094423.
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C-X (X = halogen) bonds are indispensable functional groups in organic synthesis by mediating a massive number of important organic reactions. While a variety of different catalytic strategies are available for generating C-X bonds, those methods enabling the C-X bond formation under transition metal-free conditions via the C-H bond functionalization are particularly interesting because of the inherent atom economy and environmental friendliness associated with such methods. Herein, the advancements in the transition metal-free halogenation of C(2)-H bond are reviewed.
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Hao, Wenyan, and Yunyun Liu. "C–H bond halogenation catalyzed or mediated by copper: an overview." Beilstein Journal of Organic Chemistry 11 (November 9, 2015): 2132–44. http://dx.doi.org/10.3762/bjoc.11.230.
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Carbon–halogen (C–X) bonds are amongst the most fundamental groups in organic synthesis, they are frequently and widely employed in the synthesis of numerous organic products. The generation of a C–X bond, therefore, constitutes an issue of universal interest. Herein, the research advances on the copper-catalyzed and mediated C–X (X = F, Cl, Br, I) bond formation via direct C–H bond transformation is reviewed.
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Liu, Nan-nan, and Yi-hong Ding. "A metal–metal bond passing through the arene ligand: a theoretical study on inverse sandwiches X[Sc–C8H8–Sc]nX (X = F, Cl, Br; n = 1, 2)." New Journal of Chemistry 39, no. 3 (2015): 1558–62. http://dx.doi.org/10.1039/c4nj01832j.
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In X[Sc–C8H8–Sc]2X (X = F–Br), Sc–Sc bonds between two [Sc–C8H8–Sc] units and the Sc–Sc bond through C8H8 form the uninterrupted Sc–Sc–Sc–Sc bond-chain.
Dissertations / Theses on the topic "C–X bond"
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Taylor, Dawn. "Palladium-catalysed C-X bond formations." Thesis, University of Bath, 2006. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.437449.
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Vuong, Khuong Quoc Chemistry Faculty of Science UNSW. "Metal complex catalysed C-X (X = S, O and N) bond formation." Awarded by:University of New South Wales. Chemistry, 2006. http://handle.unsw.edu.au/1959.4/23015.
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This thesis describes the catalysed addition of X-H bonds (X = S, O and N) to alkynes using a range of novel rhodium(I) and iridium(I) complexes containing hybrid bidentate phosphine-pyrazolyl, phosphine-imidazolyl and phosphine-N heterocyclic carbene (NHC) donor ligands. The synthesis of novel bidentate phosphine-pyrazolyl, phosphine-imidazolyl (P-N) and phosphine-NHC (PC) donor ligands and their cationic and neutral rhodium(I) and iridium(I) complexes [M(P N)(COD)]BPh4, [M(PC)(COD)]BPh4, [Ir(P-N)(CO)2]BPh4 and [M(P-N)(CO)Cl] were successfully performed. An unusual five coordinate iridium complex with phosphine-NHC ligands [Ir(PC)(COD)(CO)]BPh4 was also obtained. Seventeen single crystal X-ray structures of these new complexes were determined. A range of these novel rhodium and iridium complexes were effective as catalysts for the addition of thiophenol to a variety of alkynes. Iridium complexes were more effective than rhodium analogues. Cationic complexes were more effective than neutral complexes. Complexes with hybrid phosphine-nitrogen donor were more effective than complexes containing bidentate nitrogen donor ligands. An atom-economical, efficient method for the synthesis of cyclic acetals and bicyclic O,O-acetals was successfully developed based on the catalysed hydroalkoxylation. Readily prepared terminal and non-terminal alkyne diols were cyclised into bicyclic O,O-acetals in quantitative conversions in most cases. The efficiency of a range of rhodium and iridium complexes containing bidentate P-N and PC donor ligands as catalysts for the cyclisation of 4-pentyn-1-amine to 2-methyl-1-pyrroline varied significantly. The cationic iridium complexes with the bidentate phosphine-pyrazolyl ligands, [Ir(R2PyP)(COD)]BPh4 (2.39-2.42) were extremely efficient as catalysts for this transformation. Increasing the size of the substituent on or adjacent to the donor led to improvement in catalytic activity of the corresponding metal complexes. The mechanism of the catalysed hydroalkoxylation was proposed to proceed by the initial activation of the alkyne via ?? coordination to the metal centre. The ?? binding of both aliphatic and aromatic alkynes to [Ir(PyP)(CO)2]BPh4 (2.44) was observed by low temperature NMR and no reaction between 2.44 and alcohols was observed. In contrast, the facility in which thiol and amine oxidatively added to 2.44 led the proposal that in the hydrothiolation and hydroamination reaction, the catalytic cycle commences with the activation of the X-H bond (X = S, N) by an oxidative addition process.
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Mata, Campaña Yvette Angela. "Screening of Modular Carbohydrate Ligand Libraries in Asymmetric Metal-catalyzed C-C and C-X Bond Formation Reactions." Doctoral thesis, Universitat Rovira i Virgili, 2007. http://hdl.handle.net/10803/9090.
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En els últims anys, la creixent demanda de compostos enantiomèricament purs (fàrmacs, agroquímics...) ha impulsat el desenvolupament de la catàlisi asimètrica, sobretot emprant compostos organometàl·lics quirals com a catalitzadors. En aquest context, la síntesi de nous lligands quirals és essencial per descobrir bons sistemes catalítics en catàlisis asimètrica. Els sucres són una font important de lligands per l'elevada disponibilitat i baix preu. A més, són compostos altament funcionalitzats amb centres esterogènics. Això permet la síntesi de sèries sistemàtiques de lligands amb l'objectiu d'obtenir altes activitats i selectivitats per cada reacció en particular.Aquesta tesi s'ha centrat en la síntesi de compostos derivats de la D-(+)-glucosa, de la D-(+)-fructosa i la D-(+)-galactosa i l'aplicació com a lligands de catalitzadors homogenis quirals en quatre reaccions asimètriques: substitució al·lílica, Heck, addició 1,2 i addició conjugada 1,4. Per assolir aquest objectiu, s'ha plantejat la síntesi de tres famílies de compostos: fosfit-oxazolina (L1-L5), fosfit-fosforoamidit (L6) i monofosfit (L7-L11) (Figura 1).
Després de la introducció (Capítol 1) i els objectius (Capítol 2), al capítol 3 es discuteix la síntesi i caracterització de les tres llibreries de compostos (L1-L11) i s'estudia l'aplicació de les tres llibreries a la reacció de substitució al·lílica asimètrica catalitzades per pal·ladi.
La primera llibreria de compostos fosfit-oxazolina (L1-L5) ha mostrat altes enantioselectivitats (fins a un 99%) i bones activitats en un ampli ventall de substrats amb diferents propietats electròniques i estèriques. S'han observat importants efectes al variar els substituents de l'anell oxazolina, de la quiralitat axial i dels diferents substituents del biaril. L'estudi de diferents intermedis de reacció pal·ladi al·lil mitjançant espectroscòpia de ressonància magnètica nuclear ha permès entendre el comportament catalític d'aquests compostos. L'estudi també ha indicat que l'atac nuclèofil té lloc preferentment al carboni al·lílic terminal localitzat trans al fosfit.
Figura 1. Fosfit-oxazolina (L1-L5), fosfit-fosforamidit (L6) i monofosfit (L7-L11).
Les reaccions de substitució asimètrica utilitzant els compostos fosfit-fosforoamidit (L6) han mostrat que l'excés enantiomèric depèn preferentment dels substituents de les posicions en para dels bifenils. Aquests efectes han estat diferents segons el tipus de substrat. S'han obtingut excessos enantiomèrics fins a un 89% i altes activitats utilitzant el substrat rac-1,3-difenil-acetoxipropè, rac-(E)-etil-2,5-dimetil-3-hex-4-enilcarbonat i el rac-3-acetoxicicloheptè. Pel substrat lineal 1-(1-naftil)al·lil acetat, aquests lligands han mostrat no ser útils en termes de regioselectivitat però s'han obtingut bons excessos enantiomèrics de fins a un 72%.
Si comparem aquests resultats amb els obtinguts amb els compostos fosfit-oxazolina (L1-L5) s'observa que el canvi de la funció oxazolina per la funció fosforoamidit té un efecte negatiu en la reacció de substitució al·lílica i en general decreixen les enantioselectivitats i la versalitat d'aquests compostos.
L'aplicació de la llibreria de compostos monofosfit (L7-L11) en la reacció de substitució al·lílica asimètrica ha mostrat moderades enantioselectivitats (fins a un 46%). Els resultats en la catàlisi es veuen afectats en gran mesura per la diferència en la mida de l'anell carbohidrat, de les configuracions del carboni-3 i del carboni-4 de l'esquelet del lligand i pel tipus de substituents de l'anell biaril.
El capítol 4 descriu l'aplicació dels compostos fosfit-oxazolina (L1-L5) com a lligands en la reacció de Heck asimètrica intermolecular. Una selecció correcta dels substituents en la funció oxazolina i del fosfit han permès obtenir excel·lents activitats (fins un 100% de conversió en 10 minuts), regioselectivitats i enantioselectivitats (fins un 99%) en un ampli rang de substrats utilitzant diferents fonts de triflat.
El capítol 5 descriu l'aplicació de les tres llibreries de compostos (L1-L11) a les reaccions d'addició 1,2 a aldehids catalitzades per níquel. En primer lloc, s'ha estudiat l'aplicació dels compostos L1-L6. S'ha observat que la selectivitat del procés depèn principalment del grup funcional unit a l'esquelet del lligand, de les propietats estèriques del substituent en la funció oxazolina i de l'estructura del substrat. S'ha obtingut fins a un 59% d'excés enantiomèric utilitzant el precursor de catalitzador que conté el lligand L3a. En canvi, la utilització de la llibreria de compostos monofosfit (L7-L11) ha mostrat elevades enantioselectivitats (fins a 94%) i activitats en diferents tipus de substrat utilitzant baixes concentracions de catalitzador i sense excés de lligand.
El capítol 6 descriu l'aplicació de les tres famílies de compostos (L1-L11) com a lligands en la reacció d'addició 1,4 catalitzada per coure de compostos organometàl·lics a diferents enones amb diferents propietats estèriques.
L'ús de les llibreries de compostos fosfit-oxazolina (L1-L5) i fosfit-fosforamidit (L6) han proporcionat bones enantioselectivitats (fins a 78%) en l'addició de reactius de trialquilalumini a diferents enones. En canvi, la llibreria de compostos monofosfit (L7-L11) ha mostrat bones activitats però enantioselectivitats fins a 57%.
The growing demand for enantiomerically pure compounds for the development of pharmaceuticals, agrochemicals and flavors has captured the interest of the chemist in the last few decades. Of the various methods for producing enantiopure compounds, enantioselective homogeneous metal catalysis is an attractive one. In this context, carbohydrates have many advantages: they are readily available, are highly functionalized and have several stereogenic centers. This enables series of chiral ligands to be synthesized and screened in the search for high activities and selectivities for each particular reaction.
In this context, this thesis focuses on the development of new chiral ligand libraries derived from carbohydrates, the synthesis of new catalyst precursors and their application in the Pd-catalyzed asymmetric allylic substitution, Pd-catalyzed asymmetric Heck reactions, Ni-catalyzed asymmetric addition of trialkylaluminium to aldehydes, and Cu-catalyzed asymmetric 1,4-conjugated addition of trialkylaluminium reagents to enones.
For this porpose, we have designed and syntezied 3 new sugar based ligand libraries: phosphite-oxazoline (L1-L5), phosphite-phosphoroamidite (L6) i monophosphite (L7-L11) (Figure 1).
After introduction (Chapter 1) and objectives (Chapter 2), in chapter 3 is discussed the synthesis and characterization of the ligand libraries (L1-L11) and and their application in the asymetric Pd-catalyzed allylic substituion reactions.
Using phosphite-oxazoline ligands (L1-L5) we observed important effects of the oxazoline substituents and the axial chirality and the substituents of the biaryl moieties. However, the effects of these parameters depended on each substrate. High enantioselectivities (up to 99%) and good activities have been achieved in a wide range of substrates with different steric and electronic properties.
The study of the Pd-1,3-diphenyl, 1,3-dimethyl and 1,3-cyclohexenyl allyl intermediates by NMR spectroscopy made it possible to understand the catalytic behaviour observed. This study also indicated that the nucleophilic attack takes place predominantly at the allylic terminal carbon atom located trans to the phosphite moiety.
Figura 1. Fosfit-oxazolina (L1-L5), fosfit-fosforamidit (L6) i monofosfit (L7-L11).
Asymmetric substitution reactions with catalyst precursors containing the phosphite-phosphoroamidite ligands showed that enantiomeric excesses depend strongly on the substituents at the para positions of the biphenyl moieties. However, these effects were different depending on the substrate in study. Enantiomeric excesses of up to 89% with high activities were obtained for rac-1,3-diphenyl-3-acetoxyprop-1-ene, rac-(E)-ethyl-2,5-dimethyl-3-hex-4-enylcarbonate and rac-3-acetoxycycloheptene. For the monosubstituted linear substrate 1-(1-naphthyl)allyl acetate, these ligands proved to be inadequate in terms of regioselectivities. However, we obtained good enantioselectivity by carefully selecting the substituents on the para position of the biphenyl moieties (ee's up to 72%).
If we compare these results with those from the catalyst precursors containing the previous phosphite-oxazoline ligands (L1-L5), we found that the replacement of the oxazoline moiety by a phosphoroamidite group decreased enantioselectivities and versatibility.
Asymmetric allylic alkylation with catalyst precursors containing the sugar-based monophosphite ligand library showed that the catalytic performance is highly affected by the size of the sugar backbone, the configurations at C-3 and C-4 of the ligand backbone and the type of substituents/configurations in the biaryl phosphite moiety. Low-to-moderate enantioselectivities (up to 46%) were obtained.
In the asymmetric Pd-catalyzed Heck reactions (Chapter 4) with catalysts precursors based on phosphite-oxazoline ligands, we obtained excellent activities (up to 100% conversion in 10 minutes), regio- (up to >99%) and enantioselectivities (up to 99%) were obtained in a wide range of substrates and triflate sources.
In the asymmetric Ni-catalyzed 1,2-addition of trialkylaluminium to aldehydes (Chpater 5) with catalysts precursors based on phosphite-oxazoline and phosphite-phosphoroamidite ligands, we found that the selectivity depends strongly on the type of functional group attached to the carbohydrate backbone, on the steric properties of the oxazoline substituents and on the substrate structure. Enantioselectivities up to 59% were obtained using the catalyst precursor containing the phosphite-oxazoline ligand L3a. In contrast to what we observed with the previous two ligand libraries, using sugar-based monophosphite ligands (L7-L11) provides high enantioselectivities (up to 94% ee) and activities in different substrate types, with low catalysts loadings and without excess of ligand.
In Chapter 6, we described the phosphite-oxazoline and phosphite-phosphoroamidite ligands as chiral auxiliaries in the asymmetric Cu-catalyzed 1,4-conjugated addition of trialkylaluminium reagents to several enones provides good enantioselectivities (up to 80% ee).
In the asymmetric Cu-catalyzed asymmetric 1,4-conjugated addition of trialkylaluminium reagents to several enones with catalysts precursors based on sugar monophosphite ligands, we found good activites and enantioselectivities up to 57% ee.
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Borràs, Noguera Carlota. "Sustainable and cost-effective development of chiral metal-catalysts for C-H and C-X bond forming reactions." Doctoral thesis, Universitat Rovira i Virgili, 2018. http://hdl.handle.net/10803/664741.
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L’obtenció de compostos enantiomèricament purs ha esdevingut una necessitat que ha conduit a un important progrés en la catàlisi asimètrica, principalment usant compostos organometàl•lics quirals. Entre les diferents estratègies en l’optimització dels catal•litzadors per aconseguir elevades selectivitats i activitats, el disseny i correcta selecció de lligands quirals, modificant-ne les seves propietats és fonamental i la més utilitzada. Que un lligand sigui fàcil de sintetitzar a partir de compostos de partida accessibles i que aquests lligands siguin estables i fàcils de manipular, tenen un elevat interès en la industria.
En aquest context, el principal objectiu d’aquesta tesi és la síntesi de diferents famílies de lligands quirals, acomplint els requisits prèviament esmentats, i la seva posterior aplicació a diverses reaccions asimètriques d’elevat interès industrial: hidrogenació d’olefines funcionalitzades i no funcionalitzades catalitzada per Rh i Ir, hidrogenació de cetones catalitzada per Ir, reaccions de substitució al•lílica catalitzades per Pd i reaccions de substitució propargílica catalitzada per Cu. S’han sintetitzat diverses famílies fosfit/fosfinit-tioèter/selenoèter, carbè-tioèter, amino-fosfit/fosfinit/fosfina, i varies famílies de lligands tridentats.La obtención de compuestos enantioméricamente puros se ha convertido una necesidad que ha conducido a un importante progreso en la catálisis asimétrica, principalmente usando compuestos organometalicos quirales. Entre las diferentes estrategias en la optimización de los catalizadores para conseguir elevadas selectividades y actividades, el diseño y la correcta selección de ligandos quirales, modificando sus propiedades es fundamental y la más utilizada. Que un ligando sea fácil de sintetizar a partir de compuestos de partida accesibles y que estos ligandos sean estables y fáciles de manipular, tienen un elevado interés en la industria. En este contexto, el principal objetivo de esta tesis es la síntesis de distintas familias de ligandos quirales, cumpliendo con los requisitos previamente mencionados, y su posterior aplicación en distintas reacciones asimétricas de alto interés industrial: hidrogenación de alquenos funcionalizados y no funcionalizados catalizados por Rh y Ir, hidrogenación de cetonas catalizada por Ir, reacciones de substitución alílica catalizada por Pd y reacciones de substitución propargílica catalizada por Cu. Se han sintetizado diferentes familias de ligandos Fosfito/fosfinito-tioéter/selenoéter, carbeno-tioéter, amino-fosfito/fosfinito/fosfina, y varias familias de ligandos tridentados.
The obtaining of enantiomerically pure compounds has become a need that led to an important progress in asymmetric catalysis, mainly using organometallic chiral compounds. Among different strategies to optimize catalysts in order to obtain high selectivities and activities, the design and the correct selection of chiral ligands, modifying their properties, is fundamental and the most used strategy. Ligands easy to synthesize from readily accessible starting material and stable and easy to manipulate ligands, have a high interest in the industry. In this context, the main objective of this thesis is the synthesis of different chiral ligand families, according to the previously mentioned requirements, and their application in different asymmetric reactions with high industrial interest: Rh- and Ir-catalyzed hydrogenation of functionalized and minimally functionalized olefins; Ir-catalyzed hydrogenation of simple ketones; Pd-catalyzed asymmetric substitution of allylic acetates and Cu-catalyzed propargylic substitution. There have been synthesized different phosphite/phosphinite-thioether/selenoether, carbene-thioether, amino-phosphite/phosphinite/phosphine and various tridentated ligand families.
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Mazuela, Aragón Javier. "Design and screening of biaryl phosphite-based ligand libraries for asymmetric reduction and c-c and c-x bond forming reactions." Doctoral thesis, Universitat Rovira i Virgili, 2012. http://hdl.handle.net/10803/96665.
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Durant els últims anys, els compostos fosfit han demostrat ser lligands eficients en diverses reaccions catalitzades por metalls de transició. En aquest context, hem desemvolupat diverses lligandoteques fosfit per la seva aplicació en reaccions per obtenit productes enantiomericament purs. Més concretament hem estudiat:
(a) La síntesis i aplicació de 9 lligandoteques fosfit-nitrogen en l’hidrogenació d’olefines mínimament funcionalizades catalitzada per iridi i les reaccions de substitució al•lílica i Heck catalitzades per pal•ladi. Aquests lligands s’han dissenyat mitjançant variacions sistemàtiques de diversos paràmetres del lligand. En tots els casos s’han obtingut activitats i selectivitats excel•lents (ee’s superiors als 99%) per un ampli rang de substrats. Els resultats competeixen favorablement amb els publicats prèviament en la bibliografia.
(b) L’aplicació de diversos tipus de lligandoteques fosfit en la hidrofomilació de vinilarens, olefines heterocícliques i enol esters terminals catalitzada per rodi obtenint resultats prometedors (ee’ de fins el 76%).During the last years, phosphite-containing compounds have proved to be efficient ligands for several metal-catalyzed transformations. In this context, we have developed several phosphite-containing ligand libraries for their application in reactions leading to enantiomerically pure products. More concretely we have studied: (a) the synthesis and screening of 9 phosphite-nitrogen ligand libraries in the Ir-catalyzed hydrogenation of minimally functionalized olefins, Pd-catalyzed allylic substitution and Heck reactions. These ligand libraries have been designed by systematic modification of several ligand parameters. In all cases excellent activities, regio- and enantioselectivities (ee’s up to >99%) have been obtained for a broad range of substrates. These results compete favorably with those reported previously in the literature. (b) the screening of several types of phosphite containing ligand libraries in the Rh-catalyzed hydroformylation of vinylarenes, heterocyclic olefins and 1,1’-terminal enol esters obtaining promising results (ee’s up to 76%).
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Esswein, Arthur J. "Late transition metal bimetallics for photocatalytic hydrogen production, M-X and C-H bond activation." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/40970.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2007.Vita.
Includes bibliographical references.
Broadly defined this thesis has focused on the design and study of molecular catalysts that engender multi-electron reactions and photoreactions on small molecule substrates relevant to solar energy conversion. Specifically the molecular design elements employed have focused on bimetallic complexes of late transition metals that exhibit an unusual two-electron mixed valence ground state. Initial studies focused on the mechanistic elucidation of the reported photocatalytic production of hydrogen from homogeneous hydrohalic acid solution using a two-electron mixed valence dirhodium complex. Studies aimed at understanding and improving the photochemical quantum efficiency for challenging M-X (X = CI, Br-) bond photoactivations were undertaken by incorporating gold into a heterobimetallic rhodium-gold construct. Additionally the organometallic reactivity of two-electron mixed valence diiridium cores was explored with a specific emphasis on C-H bond activations in order to extend the cooperative bimetallic reactivity observed in the dirhodium systems beyond HX and H2 substrates to alkanes and arenes.
by Arthur J. Esswein.
Ph.D.
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Margalef, Pallarès Jèssica. "Screening of modular and readily available ligand libraries for C-X (X=H, C, N and O) bond forming reactions. The use of DFT studies for catalysts optimization." Doctoral thesis, Universitat Rovira i Virgili, 2016. http://hdl.handle.net/10803/386578.
Full textAbstract:
El creixent interès per a l’obtenció de compostos enantiomèricament purs, ha conduït a un important desenvolupament de la catàlisi asimètrica. En aquest context, aquesta tesis és centra en la síntesis de vàries famílies de lligands quirals altament modulars a partir de compostos de fàcil disponibilitat. Concretament, s'ha treballat en la síntesis de lligands fosfit-tioèter, fosfit-piridina, fosfit-triazola i lligands hidroaximida i tioamida. Tots ells tenen en comú que són sòlids, estables i per tant de fàcil manipulació. Aquests lligands s'han aplicat en la hidrogenació d’olefines funcionalitzades i no funcionalitzades catalitzada per Rh i Ir, en la reducció de cetones mitjançant transferència d’hidrogen catalitzada per Rh i Ru, en reaccions de substitució alílica catalitzada per Pd i en l'addició d'organoaluminats a aldehids catalitzada per Ni. A més a més, en alguns casos s'han realitzat estudis DFT per tal d'agilitzar el procés d'optimització dels lligands. Així doncs, s'ha aconseguit l'obtenció de diferents compostos químics quirals d'alt interès sintètic (alcohols, alcans funcionalitzats i no funcionalitzats, al·lils substituits) en grans enantioselectivitats i en el millor dels casos s'han aconseguit els productes en la seva forma enantiomèricament pura (>99% ee).El creciente interés para la obtención de compuestos enantioméricamente puros para la obtención de compuestos enantioméricamente puros, ha conducido a un importante desarrollo de la catálisis asimétrica. En este contexto, esta tesis se centra en la síntesis de varias familias de ligandos quirales altamente modulares a partir de compuestos de fácil disponibilidad. Concretamente, se ha trabajado en la síntesis de ligandos fosfito-tioéter, fosfito-piridina, fosfito-triazoles y ligandos hidroaximida y tioamida. Todos ellos tienen en común que son sólidos, estables y por lo tanto de fácil manipulación. Estos ligandos se han aplicado en la hidrogenación de olefinas funcionalizadas y no funcionalizadas catalizada por Rh e Ir, en la reducción de cetonas mediante transferencia de hidrógeno catalizada por Rh y Ru, en reacciones de sustitución alílica catalizada por Pd y en el adición de organoaluminiatos a aldehídos catalizada por Ni. Además, en algunos casos se han realizado estudios DFT para agilizar el proceso de optimización de los ligandos. Así pues, se ha logrado la obtención de diferentes compuestos químicos quirales de alto interés sintético (ej. alcoholes, alcanos funcionalizados y no funcionalizados, alilos sustituidos) en grandes enantioselectividades y en el mejor de los casos se han conseguido los productos en su forma enantioméricamente pura (> 99% ee).
The growing interest in obtaining enantiomerically pure compounds in obtaining enantiomerically pure compounds has led to a significant development in the field of asymmetric catalysis. In this context, this thesis is focused on the synthesis of several families of highly modular chiral ligands from readily available compounds. Specifically, we worked on the synthesis of thioether-phosphite ligands, phosphite-pyridine, phosphite-triazole and hidroaximide and thioamide ligands. They all have in common that are solid, stable and therefore easy to handle. These ligands have been applied in the Rh- and Ir-catalyzed hydrogenation of functionalized and unfunctionalized olefins, in the Ru- and Rh-catalyzed asymmetric transfer hydrogenation of ketones, in Pd-catalyzed allylic substitution reactions and in the Ni-catalyzed addition of organoalumininum to aldehydes. Moreover, in some cases DFT studies have been performed to speed up the optimization of ligands. Hence, a variety of chiral chemical compounds of high synthetic interest (i. e. alcohols, functionalized and non-functionalized alkanes, substituted allyl) lhigh enantioselectivities were achieved and in some cases the products were obtained in their enantiomerically pure form(> 99% ee).
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Mazloomi, Zahra. "New approaches to perfluoroalkylation of aromatic compounds, and tailor-made catalysts for C-X bond forming and water oxidation reactions. Mechanistic insights." Doctoral thesis, Universitat Rovira i Virgili, 2017. http://hdl.handle.net/10803/450517.
Full textAbstract:
Aquesta tesis esta dividida en dos parts: la primer part es va realizar a l’Institut Català d’Invstigació Química (ICIQ) desde 2012 fins a 2015, aquesta part tracta sobre la perfluoroalquilació de substrats aromatics i inclou dos projectes principals. L’objectiu del primer projecte era la producción en flux continu de CuCF3 com a reactiu trifluorometilat i la confirmació de la seva eficacia en la trifluorometilacio de diversos halurs aromatics, els quals van ser tractats amb CuCF3 i es van convertir selectivament en composotos trifluorometilats.
En el segon projecte, l’objectiu era transformar diferents halurs vinílics a anàlegs trifluorometilats i pentafluoroetilats emprant els reactius nucleòfils CuCF3 i CuC2F5, el quals ja havien estat utilitzats prèviament en el mateix grup.
La segona part s’ha dut a terme a la Universitat Rovira i Virgili (URV) a partir de 2015 fins al 2017. Aquesta part tracta sobre diferents reaccions catalítiques de formació d’enllaços C-X i estudis mecanístics sobre d’aquestes. Aquesta part conté 4 projectes d’investigació. Tres d’ells tracten sobre la síntesi i l’aplicació en varies reaccions catalítiques de gran rellevància de diversos complexes de carbens anormals amb Ir (I), Ir (III) i Ru (II). Aquests catalitzadors altament eficaços s’han aplicat amb èxit en la hidrogenació per transferència d’enllaços C = O, C = N i C = C, també en la deshidrogenació d’alcohols i l’oxidació amb aigua. L’últim projecte tracta sobre la formació catalítica asimètrica d’enllaços C-C amb una nova i versàtil lligandoteca de lligands P-N quirals. Tots els objectius d’aquesta segona part de la tesis s’han realitzat amb èxit.
En resum, en aquesta tesis s’ha realitzat diverses transformacions químiques importants, totes elles de gran interès en la formació de productes farmacèutics, agroquímics, naturals i de química fina y en ala producció d’energia neta. El treball realitzat en aquesta tesis conté aspectes fonamentals de la química i des del punt de vista química i industrial, existeix una gran demanda en el desenvolupament i millora de tots els processos mencionats.Esta tesis está dividida en dos partes: la primera parte se realizó en el Instituto Catalán de Investigación Química (ICIQ) desde 2012 hasta 2015, esta parte trata sobre la perfluoroalquilación de sustratos aromáticos e incluye dos proyectos principales. El objetivo del primer proyecto era la producción en flujo continuo de CuCF3 como reactivo trifluorometilado y la confirmación de su eficacia en la trifluorometilación de algunos haluros aromáticos, los cuales fueron tratados con CuCF3 y se convirtieron selectivamente en compuestos trifluorometilados. En el segundo proyecto, el objetivo era transformar varios haluros vinílicos a análogos trifluorometilados y pentafluoroetilados usando los reactivos nucleófilos CuCF3 y CuC2F5, los cuales habían sido utilizados previamente en el mismo grupo. La segunda parte se ha llevado a cabo en la Universidad de Rovira i Virgili (URV) a partir de 2015 hasta 2017. Esta parte trata sobre diferentes reacciones catalíticas de formación de enlaces C-X y estudios mecanísticos sobre de estas. Esta parte contiene 4 proyectos de investigación. Tres de ellos tratan sobre la síntesis y aplicación en varias reacciones catalíticas de gran relevancia de varios complejos de carbeno anormales con Ir (I), Ir (III) y Ru (II). Estos catalizadores altamente eficaces se aplicaron con éxito en la hidrogenación por transferencia de enlaces C = O, C = N y C = C, también en la deshidrogenación de alcoholes y la oxidación con agua. El último proyecto trata sobre la formación catalítica asimétrica de enlaces C-C con una nueva y versátil biblioteca de ligandos P-N quirales. Todos los objetivos de la segunda parte de la tesis se realizaron con éxito. En resumen, en esta tesis se han realizado diversas transformaciones químicas importantes, todas ellas de gran interés en la formación de productos farmacéuticos, agroquímicos, naturales, de química fina y en la producción de energía limpia. El trabajo hecho en esta tesis contiene aspectos fundamentales de la química y desde el punto de vista químico e industrial existe una gran demanda en el desarrollo y mejora de los procesos mencionados.
This dissertation divided into two main parts: the first part which had been done from 2012 until 2015 in Institute of chemical research of Catalonia (ICIQ) is about perfluoroalkylation of aromatic substrate including two main works. In the first project the goal was continuous flow production of CuCF3 as a trifluoromethylated reagent and confirming its efficiency in trifluoromethylation of some aromatic halides which were treated with batch made CuCF3 reagent and selectively converted to trifluoromethylated conterparts. In the second project the target was transforming several vinylic halides to trifluoromethylated and pentafluoroethylated analoges with nucleophilic CuCF3 and CuC2F5 reagents which were demonstrated previously in the same group. The later part has been carried out in the University of Rovira I Virgili (URV) from 2015 until 2017. Generally this part is about different catalytic C-X bond forming reactions with mechanistic insights which contains 4 research projects. Three of them are about synthesis and catalytic application of several Ir(I), Ir(III) and Ru(II) abnormal carbene complexes in several important and challenging catalytic reactions. These highly efficient catalysts successfully applied in transfer hydrogenation of C=O, C=N and C=C functionalities, alcohol dehydrogenation and water oxidation. The last project is asymmetric catalytic formation of C-C bond with a new and versatile chiral P-N ligand library. All of the objectives for the second part of thesis were performed successfully. In conclusion, various important chemical transformation were made in this thesis which all of them are vital in pharmaceuticals, agrochemicals, fine and natural products and the production of clean energy. The total works in this thesis are so important in chemistry and there is a huge demand about developing and improving the mentioned processes from the chemical and industrial point of view.
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Smith, Daniel L. "Selective incorporation of the C-F bond as a conformational tool in quadruplex DNA ligand design." Thesis, University of St Andrews, 2012. http://hdl.handle.net/10023/3169.
Full textAbstract:
Chapter 1 provides a general introduction to organofluorine chemistry and focuses on recent developments in fluorination techniques. It also details how the C–F bond influences conformational and physiochemical properties of organic molecules. Chapter 2 highlights the biological role of the telomere, telomerase and quadruplex DNA in cells. It discusses the inhibition of telomerase with small molecules that stabilise quadruplex DNA as a treatment for cancer. An overview of the development of structurally related telomerase inhibitors and recent X-ray crystallographic structural data with BSU6039 and BRACO-19 telomeric DNA is presented. Chapter 3 discusses the synthesis of fluorinated BSU6039 analogues for the investigation of the conformational effects of fluorine in 5-membered rings and its influence on binding with quadruplex DNA. These compounds have been successfully co-crystallised with telomeric DNA and their relative stabilisation of telomeric DNA has been assessed. The latter half of this chapter focuses on the co-crystal structures between (S,S)- and (R,R)-144 with Oxytricha nova telomeric DNA, discussing the key differences between the two stereoisomers. Chapter 4 details the synthesis of fluorinated BRACO-19 analogues. The syntheses of such fluorinated analogues were achieved through a base mediated coupling between 3,6-diaminoacridone and an α-fluorinated-β-amino ester. The α-fluorinated-β-amino ester was synthesised through a deoxyfluorination-mediated approach, using the stereochemistry of natural amino acids. Chapter 5 describes the stereo- and regio- selectivity of deoxyfluorination reactions with dipeptides bearing the β-amino alcohol functionality. Understanding this selectivity enabled the development of a method towards α-fluorination of tertiary amides. The application of this fluorination method with an orthogonally protected tertiary amide is described.
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Biosca, Brull Maria. "Fitting the catalysts for effective enantioselective C-X bond forming reactions. Theoretically guided ligand design and mechanistic investigations." Doctoral thesis, Universitat Rovira i Virgili, 2018. http://hdl.handle.net/10803/665121.
Full textAbstract:
La creixent demanda de compostos enantiomèricament purs, ha incrementat l’interès pel desenvolupament de metodologies per l’obtenció d'aquests compostos. Entre elles, la catàlisi asimètrica és la tècnica més emprada. En aquesta metodologia, l'elecció lligand quiral és clau per l'obtenció de elevades activitats i enantioselectivitats. En aquest context, aquesta tesis és centra en la síntesis de diferents famílies de lligands quirals altament modulars a partir de productes de partida d'elevada disponibilitat. Més concretament, s’han sintetitzat diverses famílies de lligands heterodadors P-oxazolina (P= fosfina, fosfinit, fosfit, fosforamidit), P-altres grups N-dadors (P= fosfit, fosforamidit, fosfonit i N= tiazol, sulfoximina, hidrazona, amina, piridina), P-tioèter (P= fosfina, fosfinit, fosfit) i una família de lligands fosfina quiral-fosfit. Aquests lligands s'han aplicat en la reacció d’hidrogenació d’olefines funcionalitzades i mínimament funcionalitzades catalitzada per Rh i Ir, la reacció de substitució al·lílica i la reacció de protonació descarboxilativa d’oxindoles ambdues catalitzades per Pd. A més a més, en alguns casos, s'han dut a terme estudis computacionals en combinació amb assajos experimentals per estudiar l'origen de les enantioselectivitats obtingudes o bé per guiar l'optimització dels lligand.La creciente demanda de compuestos enantioméricamente puros, ha incrementado el interés por el desarrollo de metodologías para la obtención de dichos compuestos. Entre ellas, la catálisis asimétrica es la técnica mas utilizada. En dicha metodología, la elección del ligando quiral es clave para la obtención de elevada actividades i enantioselectividades. En este contexto, esta tesis se centra en la síntesis de diferentes familias de ligandos quirales altamente modulares a partir de productos de partida de elevada disponibilidad. Más concretamente, se ha trabajado en la síntesis de ligandos heterodadores P-oxazoline (P= fosfina, fosfinito, fosfito, fosforamidito), P-otros grupos N-dadores (P= fosfito, fosforamidito, fosfonito y N= tiazol, sulfoximina, hidrazona, amina, piridina), P-tioéter (P= fosfina, fosfinito, fosfito) i una familia de ligandos fosfina quiral-fosfito. Estos ligandos se han aplicado en la reacción de hidrogenación de olefinas funcionalitzadas i mínimamente funcionalitzadas catalizada por Rh i Ir, la reacción de substitución alílica y la reacción de protonación descarboxilativa de oxindolas ambas catalizadas por Pd. Además, en algunos casos, se han realizado cálculos computacionales en combinación con ensayos experimentales para estudiar el origen de las enantioselectividades obtenidas o bien para guiar la optimización de los ligandos.
The growing demand on enantiomerically pure compounds has stimulated the interest for the development of methodologies to obtain these compounds. Among them, asymmetric catalysis is one of the most employed tools. In this technic, the choice of the chiral ligand is fundamental to obtain high levels of activity and enantioselectivity. In this context, this thesis is focused on the synthesis of several families of highly modular chiral ligands from readily available starting materials. Particularly, we worked on the synthesis of P-oxazoline (P= phosphine, phosphinite, phosphite, phosphoroamidite), P-other N-donor groups (P= phosphite, phosphoroamidite, phosphonite and N= thiazole, sulfoximine, hydrazone, amine, pyridine), P-thioether (P= phosphine, phosphinite, phosphite) and a family of P*-stereogenic phosphine-phosphite ligands. These ligands have been applied in the Rh- and Ir-catalyzed hydrogenation of functionalized and minimally functionalized olefins, Pd-catalyzed allylic substitution reaction and Pd-catalyzed decarboxylative protonation. Furthermore, in some cases, DFT studies in combination with experimental ones have been performed to better understand the origin of the obtained enantioselectivities or in order to guide the ligand optimization.
Books on the topic "C–X bond"
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Vigalok, Arkadi, ed. C-X Bond Formation. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-12073-2.
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C-X bond formation. Heidelberg: Springer, 2010.
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Ribas, Xavi, ed. C-H and C-X Bond Functionalization. Cambridge: Royal Society of Chemistry, 2013. http://dx.doi.org/10.1039/9781849737166.
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Vigalok, Arkadi. C-X Bond Formation. Springer, 2012.
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Ma, Dawei, Ian J. S. Fairlamb, Guosheng Liu, Xavi Ribas, and Livi Mirica. C-H and C-X Bond Functionalization: Transition Metal Mediation. Royal Society of Chemistry, The, 2013.
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Andersson, Pher G. Innovative Catalysis in Organic Synthesis: Oxidation, Hydrogenation, and C-X Bond Forming Reactions. Wiley & Sons, Incorporated, John, 2012.
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Andersson, Pher G. Innovative Catalysis in Organic Synthesis: Oxidation, Hydrogenation, and C-X Bond Forming Reactions. Wiley & Sons, Limited, John, 2012.
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Andersson, Pher G. Innovative Catalysis in Organic Synthesis: Oxidation, Hydrogenation, and C-X Bond Forming Reactions. Wiley & Sons, Incorporated, John, 2012.
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Andersson, Pher G. Innovative Catalysis in Organic Synthesis: Oxidation, Hydrogenation, and C-X Bond Forming Reactions. Wiley & Sons, Incorporated, John, 2012.
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Trost, Barry M. Additions to C-X ?-Bonds. Elsevier Science & Technology Books, 1992.
Find full textBook chapters on the topic "C–X bond"
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Eisen, Moris S. "Catalytic C–N, C–O, and C–S Bond Formation Promoted by Organoactinide Complexes." In C-X Bond Formation, 157–84. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-12073-2_7.
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Muñiz, Kilian. "Transition Metal Catalyzed Electrophilic Halogenation of C–H Bonds in Alpha-Position to Carbonyl Groups." In C-X Bond Formation, 1–18. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-12073-2_1.
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Vigalok, Arkadi, and Ariela W. Kaspi. "Late Transition Metal-Mediated Formation of Carbon–Halogen Bonds." In C-X Bond Formation, 19–38. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-12073-2_2.
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Bichler, Paul, and Jennifer A. Love. "Organometallic Approaches to Carbon–Sulfur Bond Formation." In C-X Bond Formation, 39–64. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-12073-2_3.
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Glueck, David S. "Recent Advances in Metal-Catalyzed C–P Bond Formation." In C-X Bond Formation, 65–100. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-12073-2_4.
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Vedernikov, Andrei N. "C–O Reductive Elimination from High Valent Pt and Pd Centers." In C-X Bond Formation, 101–21. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-12073-2_5.
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Hintermann, Lukas. "Recent Developments in Metal-Catalyzed Additions of Oxygen Nucleophiles to Alkenes and Alkynes." In C-X Bond Formation, 123–55. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-12073-2_6.
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Mani, Devendra, and E. Arunan. "The X-C…Y Carbon Bond." In Challenges and Advances in Computational Chemistry and Physics, 323–56. Cham: Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-14163-3_11.
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Ohno, Hiroaki. "Intramolecular CX Bond Formation between CX or XH and Alkynes." In Transition-Metal-Mediated Aromatic Ring Construction, 485–536. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2013. http://dx.doi.org/10.1002/9781118629871.ch19.
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Deuss, Peter J., Megan V. Doble, Amanda G. Jarvis, and Paul C. J. Kamer. "Hybrid Catalysts for Other CC and CX Bond Formation Reactions." In Artificial Metalloenzymes and MetalloDNAzymes in Catalysis, 285–319. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA, 2018. http://dx.doi.org/10.1002/9783527804085.ch10.
Full textConference papers on the topic "C–X bond"
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Nakrachi, Aziz, and Genevieve Dauphin-Tanguy. "A Distributed Parameter Pseudo Bond Graph for Heat Conduction Modelling: Notion of Cellular Bond Graph." In ASME 2003 International Mechanical Engineering Congress and Exposition. ASMEDC, 2003. http://dx.doi.org/10.1115/imece2003-41751.
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The paper presents a new procedure for building a pseudo bond graph model representing 1D and 2D heat conduction phenomena, in their distributed parameter form. The heat conduction equation is written in such a way that conjugate variables, temperature T(t,x,y) and heat flow rate Q⃗˙(t,x,y), and their space derivatives appear explicitly in the equation. New conjugations between variables are introduced as (T,div(Q⃗˙)) and (gradT,Q⃗˙). We define new bond graph elements named “distributed C- and R-elements”, and we build a “Distributed Parameter Bond Graph” (DPBG), with a form slightly different from the classical one. The approximation of the space derivatives leads to submodels we call “cellular bond graphs”, new notion which could be compared to the cellular automata. Moreover, we show how this representation enables to easily build classical finite difference or finite volume schemes.
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Subramanian, Raghavendran, and Kazem Kazerounian. "Improved Molecular Model of a Peptide Unit for Proteins." In ASME 2006 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2006. http://dx.doi.org/10.1115/detc2006-99315.
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Pauling, Corey and Branson in their seminal paper in 1951 reported numerical values for the bond lengths and bond angles for a peptide unit in proteins. These values became the standard model for several decades after that. This classic peptide model was either confirmed or improved upon by other researchers over the years, by using more advanced X-Ray diffraction equipments. In this paper, we have made an attempt to calibrate the values of these bond lengths and bond angles based on a systematic and deterministic approach applied to a collection of proteins defined structurally in the Protein Data Bank (PDB). Our method is based on the assumption that a peptide chain is a serial chain of identical rigid bodies connected by revolute joints (i.e. dihedral angles). The proposed procedure first computes the best estimate for the dihedral angles in the presence of inaccuracies in the atoms’ coordinates data. Then these values are used to find the conformation of the peptide chain using the calibrated model of the peptide unit. Through an optimization process, the structural error (RMSD of all atoms) between the resultant conformation and the PDB data is minimized to yield the best values for the bond length and bond angles in the calibrated peptide unit. Our numerical experiments indicate that by making small changes in the Pauling-Corey peptide model parameters (0.15% to 8.7%) the structural error is reduced significantly (3.0% to 57.4%). The optimum values for the bond angles and bond lengths are as follow: Bond Lengths: N-C(A): 1.4721Å, C(A)-C: 1.6167Å, C-N: 1.2047Å, C=O: 1.1913Å and N-H: 0.9621Å. Bond Bending Angles: N-C(A)-C: 109.6823°, C(A)-C=0: 119.518°, C(A)-C-N: 114.5553°, O=C-N: 125.9233°, C-N-H: 123.5155°, C-N-C(A): 121.5756°, C(A)-N-H: 114.901°. Peptide bond torsion angle: ω: 179.4432°.
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Jay, Raphael M., Ambar Banerjee, Torsten Leitner, Robert Stefanuik, Ru-Pan Wang, Jessica Harich, Emma Beale, et al. "From Femtosecond Excited-State and Dissociation Dynamics to Nanosecond Reaction Kinetics: Following C-H Bond Activation with X-rays." In International Conference on Ultrafast Phenomena. Washington, D.C.: Optica Publishing Group, 2022. http://dx.doi.org/10.1364/up.2022.tu1a.2.
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Using ultrafast X-ray absorption spectroscopy, we observe how a rhodium carbonyl catalyst is formed on femtosecond timescales and reveal the decisive orbital interactions which facilitate the efficient cleavage of an alkane C-H bond from solution.
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Musalek, Radek, Jan Medricky, Zdenek Pala, Ondrej Kovarik, Libor Tomek, Nicholas Curry, and Stefan Bjorklund. "Fatigue Performance of TBCs on Hastelloy X Substrate during Cyclic Bending." In ITSC2015, edited by A. Agarwal, G. Bolelli, A. Concustell, Y. C. Lau, A. McDonald, F. L. Toma, E. Turunen, and C. A. Widener. ASM International, 2015. http://dx.doi.org/10.31399/asm.cp.itsc2015p0406.
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Abstract Our previous experiments with low-cost steel substrates confirmed that individual steps of conventional thermal barrier coating (TBC) deposition may influence fatigue properties of the coated samples differently. In this study, testing was carried out for TBC samples deposited on industrially more relevant Hastelloy X substrates. Samples were tested after each step of TBC deposition process: as-received (non-coated), grit-blasted, bond-coated (NiCoCrAlY) and bondcoated + top-coated (yttria-stabilized zirconia - YSZ). Conventional atmospheric plasma spraying (APS) with gas stabilized plasma torch was used for deposition of both bond coat and top coat. In addition, for one half of the samples, bond coat was prepared by consecutive combination of HVAF (High Velocity Air Fuel) and APS processes. Samples were tested both in as-sprayed condition and after 100 hours annealing at 980 °C, which simulated in-service conditions. Obtained results showed that different fatigue performance may be expected for various stages of the TBC deposition as well as due to the variation of the deposition process and sample temperature history.
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Yuan, K., K. P. Jonnalagadda, Y. Yu, R. L. Peng, X. H. Li, X. Ji, and J. Shen. "Thermal Fatigue Failure of Thermal Barrier Coatings with a High-Cr MCrAlY Bond Coat." In ITSC 2016, edited by A. Agarwal, G. Bolelli, A. Concustell, Y. C. Lau, A. McDonald, F. L. Toma, E. Turunen, and C. A. Widener. DVS Media GmbH, 2016. http://dx.doi.org/10.31399/asm.cp.itsc2016p0273.
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Abstract Thermal barrier coatings (TBCs) consisting of a MCrAlY bond coat and a YSZ topcoat were air plasma sprayed onto Hastelloy X substrates. Samples were thermally cycled between 100 °C and 1100 °C and thermal fatigue failures were investigated via microstructure analyses. Final fatigue failure was caused by the formation of interface-parallel cracks in the topcoat, which was found to strongly related to the oxidation behavior of the bond coat. The development of oxide layers was therefore studied in detail and a thermo-kinetic model was used to explore the role of elemental diffusion in oxide formation.
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Tiwari, Santosh K., and Brian K. Paul. "Application of Nickel Nanoparticles in Diffusion Bonding of Stainless Steel Surfaces." In ASME 2008 International Manufacturing Science and Engineering Conference collocated with the 3rd JSME/ASME International Conference on Materials and Processing. ASMEDC, 2008. http://dx.doi.org/10.1115/msec_icmp2008-72151.
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In this study, the effect of nickel nanoparticles (NiNPs) interlayer application to transient liquid-phase diffusion brazing was investigated. The primary focus was to bond stainless steel 316L laminae in a stack using a Nickel nanoparticles interlayer and to compare the bond line of the sample with the conventionally bonded and nickel-phosphorous interlayer (NiP) brazed samples for microstructure evolution and bond strength. The bonding was carried out in a vacuum hot press and the bonding parameters were kept same for all the samples: bonding temperatures 1000°C, bonding pressure 1000 psi, heating rate 10°C/min and dwell time of 2 hrs. The cross sections of the bonded samples were investigated for microstructure evolution using optical microscopy and scanning electron microscopy (SEM). The inter-diffusion of the diffusing species across the bond line (interface) was evaluated by wavelength dispersive spectroscopy (WDS). X-ray diffraction technique (XRD) is proposed to determine the formation of any brittle intermetallic phases along the bond line and transmission electron microscopy (TEM) to confirm the same. Bond strength will be measured with the help of samples bonded according to ASTM standards.
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Zhang, Q., C. J. Li, C. X. Li, G. J. Yang, X. R. Wang, H. T. Wang, and S. C. Lui. "Preliminary Study of Oxidation Behavior of Cold Sprayed Nanostructured NiCrAlY Bond Coatings." In ITSC2007, edited by B. R. Marple, M. M. Hyland, Y. C. Lau, C. J. Li, R. S. Lima, and G. Montavon. ASM International, 2007. http://dx.doi.org/10.31399/asm.cp.itsc2007p0457.
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Abstract Nanostructured NiCrAlY coating was deposited by cold spray, using a milled powder for applications as a bond coat to thermal barrier coating. A shot-peening treatment was then applied to the as-sprayed coating to modify the coating surface morphology. The oxidation behavior of the coating with the shot-peened surface was investigated under isothermal oxidation at 900°C and 1,000°C for different times. The oxidation behavior of the coating was characterized through surface morphology and cross-sectional microstructure by scanning electron microscopy and X-ray diffraction analysis. It was found that a uniform oxide layer was formed on the surface of the shot-peened nanostructured NiCrAlY coating during oxidation at temperatures of 900°C and 1,000°C. The nanostructure of the initial coating possibly promoted rapid formation of α-Al2O3 oxide. It was clearly revealed that the surface morphology of the coating significantly impacted the morphology of the oxide. The surface geometry of the cold-sprayed MCrAlY coating must be modified to promote formation of a protective oxide film during oxidation, through application of a post-treatment process such as shot-peening.
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Fernández, J., M. Gaona, and J. M. Guilemany. "The Influence of Thermal Treatment on Hydroxyapatite Coatings Obtained by HVOF." In ITSC2006, edited by B. R. Marple, M. M. Hyland, Y. C. Lau, R. S. Lima, and J. Voyer. ASM International, 2006. http://dx.doi.org/10.31399/asm.cp.itsc2006p0011.
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Abstract Hydroxyapatite (HAp) is known to be bioactive, i.e. able to bond to bone. This makes HAp very suitable to be applied as coatings on bone-metallic implants. In this work high velocity oxy-fuel spraying (HVOF) was used successfully for obtaining hydroxyapatite coatings on Ti-6Al-4V substrates. With optimized HVOF process parameters, coatings with similar bond strength to plasma sprayed HAp coatings, good microstructure and higher crystallinity degree than atmospheric plasma sprayed ones were obtained. As-deposited HAp coatings contains amorphous calcium phosphate (ACP) that can be crystallized by a heat-treatment of 60 minutes at 700 °C, resulting in a more stable coating when they are immersed in simulated body fluid (SBF).Coating structural characteristics of as-sprayed and post heat treated coatings were analysed with X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy analyser (EDS), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Furthermore, in vitro tests were done in order to evaluate the coating response. Surface changes were observed for as-sprayed coating but not after a post heat treatment. Moreover, the strength of the coatings were evaluated after in vitro leaching. The high degree crystallinity of the post heat treated coating improves the adhesion between the coating and the substrate after an in vitro test in a free-protein simulated body fluids (SBF). Consequently a relation between the amorphicity, the in vitro response and mechanical degradation of the coating was found.
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Suzuki, Koji, Yoshihiro Deyashiki, Junji Nishioka, Kazunori Toma, and Shuji Yamamoto. "THE INHIBITOR OF ACTIVATED PROTEIN C: STRUCTURE AND FUNCTION." In XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1642963.
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In the final step of protein C pathway, activated protein C (APC) is neutralized with a plasma inhibitor, termed protein C inhibitor (PCI). PCI was first described by Marlar and Griffin (1980) and then isolated from human plasma as a homogeneous form and characterized by the authors (1983). PCI is a single chain glycoprotein with M 57,000 and a plasma concentration of 5 ug/ml. Analysis of a cDNA nucleotide sequence has clarified that a precursor of human PCI consists of a mature protein of 387 amino acid residues (M 43,759) and a signal peptide of 19 amino acid residues. Only one cysteine residue is present in the entire protein as in α1antitrypsin (α1AT) and α1antichymotrypsin (α1ACT). Three Asn-X-Ser/Thr sequences and two Ser/Thr-X-X-Pro sequences are present as potential attachment sites of carbohydrate chains. Based on the amino acid sequence of the carboxyl-terminal peptide released from the inhibitor by APC digestion, the reactive site peptide bond of PCI was found to be Arg(354)-Ser(355). It is similar to the reactive sites of the other serine protease inhibitors which are located to their carboxyl-terminal Arg(393)-Ser (394), Met(358)-Ser(359) and Leu(358)-Ser(359) in antithrombin III, α1AT and α1ACT, respectively. The alignment of the amino acid sequence of PCI with heparin cofactor II, α1plasmin inhibitor, ovalbumin, angiotensinogen and the above noted plasma inhibitors showed that PCI is a member of serine protease inhibitor superfamily. PCI inhibits APC noncompetitively in a 1:1 stoichiometry and forms a covalent acyl-bond with a Ser residue in the active center of APC. The half life of APC in plasma approximately 30 min, which is rather slow compared with the other protease inhibitors. However, optimal concentrations of heparin, dextran sulfate and its derivatives potentiate the rate of inhibition 30-60 fold. PCI has Ki of 10-8m for APC, and can inhibit thrombin, Factor Xa, urokinase and tissue plasminogen activator as well in the presence of heparin or dextran sulfate, though the Ki for these enzymes is slightly higher. During the complex formation with APC, PCI is cleaved by the complexed APC to form a modified form with M 54,000. PCI is synthesized in several hepatoma cell lines and decreased in plasma of patients with liver cirrhosis. It is also decreased in patients with DIC or those during cardiopulmonary bypass in parallel with the decrease in protein C, suggesting that PCI participates in regulation of the protein C pathway in intravascular coagulation. Recently, we have obtained the recombinant PCI from COS-1 cells which were transfected with expression vector pSV2 containing the cDNA of PCI. The recombinant PCI had the same Mr and specific activity as the protein purified from plasma. It also had an affinity for heparin and dextran sulfate. Moreover, we have predicted a three dimentional structure of the proteolytically modified PCI with computer graphics based on its amino acid sequence homology with the modified α1AT whose structure had been elucidated with X-ray crystallography. All potential carbohydrate attachment sites were estimated to exist on the surface of the protein. Succesively we have constructed the interaction model between the intact PCI predicted from the modified form and the active center of APC which was simulated from that of trypsin. From the model, it was observed that the amino-group of Arg (354, PI site) of PCI could strongly interact with the carboxy1-group of Asp (88, SI site) of the heavy chain of APC at the base of the active center pocket of the enzyme.
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Karaoglanli, A. C., A. Turk, Ð. Ozdemir, and F. Ustel. "Oxidation Behavior of Thermal Barrier Coatings With Cold Gas Dynamic Sprayed CoNiCrAlY Bond Coats." In 13th International Conference on Plasma Surface Engineering September 10 - 14, 2012, in Garmisch-Partenkirchen, Germany. Linköping University Electronic Press, 2013. http://dx.doi.org/10.3384/wcc2.420-423.
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The paper presents the results of investigation into the oxidation resistance and thermally grown oxide (TGO) of thermal barrier coatings (TBC). TGO occurred during in service affect the lifetime of the component by introducing several kinds of degradation mechanisms such as decreasing bonding strength, initiation of stress concentration and thermal stresses which lead to crack initiation and propagation associated with delamination or spallation failure. Therefore, TGO plays important role on TBC durability. In this study, TBCs that consist of a typical bond layer / top layer system (CoNiCrAlY bond layers and YSZ top layers) are deposited on Inconel 718 superalloy substrates. The metallic bond coatings are applied via Cold Gas Dynamic Spraying (CGDS); the ceramic top coatings via Atmospheric Plasma Spraying (APS). Investigations are done concerning the oxidation behavior of this TBC system at 1100 °C in normal atmosphere for 8h, 24h, 50 h and 100 hours. The oxidation behaviour and microstructural properties during the oxidation test were evaluated and compared, and TGO growth behavior was also investigated under high temperature oxidation. The microstructural features and oxidation behaviours were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. Phase stability of TBCs were evaluated by means of X-ray diffraction method.
Reports on the topic "C–X bond"
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McFarland, Eric, Horia Metiu, and Michael Gordon. Fundamental Mechanisms of C-X bond Transformations on Complex Molten Surfaces. Office of Scientific and Technical Information (OSTI), July 2019. http://dx.doi.org/10.2172/1580080.
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Litaor, Iggy, James Ippolito, Iris Zohar, and Michael Massey. Phosphorus capture recycling and utilization for sustainable agriculture using Al/organic composite water treatment residuals. United States Department of Agriculture, January 2015. http://dx.doi.org/10.32747/2015.7600037.bard.
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Objectives: 1) develop a thorough understanding of the sorption mechanisms of Pi and Po onto the Al/O- WTR; 2) determine the breakthrough range of the composite Al/O-WTR during P capturing from agro- wastewaters; and 3) critically evaluate the performance of the composite Al/O-WTR as a fertilizer using selected plants grown in lysimeters and test-field studies. Instead of lysimeters we used pots (Israel) and one- liter cone-tainers (USA). We conducted one field study but in spite of major pretreatments the soils still exhibited high enough P from previous experiments so no differences between control and P additions were noticeable. Due to time constrains the field study was discontinued. Background: Phosphorous, a non-renewable resource, has been applied extensively in fields to increase crop yield, yet consequently has increased the potential of waterway eutrophication. Our proposal impetus is the need to develop an innovative method of P capturing, recycling and reuse that will sustain agricultural productivity while concurrently reducing the level of P discharge from and to agricultural settings. Major Conclusions & Achievements: An innovative approach was developed for P removal from soil leachate, dairy wastewater (Israel), and swine effluents (USA) using Al-based water treatment residuals (Al- WTR) to create an organic-Al-WTR composite (Al/O-WTR), potentially capable of serving as a P fertilizer source. The Al-WTR removed 95% inorganic-P, 80% to 99.9% organic P, and over 60% dissolved organic carbon from the agro-industrial waste streams. Organic C accumulation on particles surfaces possibly enhanced weak P bonding and facilitated P desorption. Analysis by scanning electron microscope (SEM- EDS), indicated that P was sparsely sorbed on both calcic and Al (hydr)oxide surfaces. Sorption of P onto WW-Al/O-WTR was reversible due to weak Ca-P and Al-P bonds induced by the slight alkaline nature and in the presence of organic moieties. Synchrotron-based microfocused X-ray fluorescence (micro-XRF) spectrometry, bulk P K-edge X-ray absorption near edge structure spectroscopy (XANES), and P K-edge micro-XANES spectroscopy indicated that adsorption was the primary P retention mechanism in the Al- WTR materials. However, distinct apatite- or octocalciumphosphatelike P grains were also observed. Synchrotron micro-XRF mapping further suggested that exposure of the aggregate exteriors to wastewater caused P to diffuse into the porous Al-WTR aggregates. Organic P species were not explicitly identified via P K-edge XANES despite high organic matter content, suggesting that organic P may have been predominantly associated with mineral surfaces. In screen houses experiments (Israel) we showed that the highest additions of Al/O-WTR (5 and 7 g kg⁻¹) produced the highest lettuce (Lactuca sativa L. var. longifolial) yield. Lettuce yield and P concentration were similar across treatments, indicating that Al/O- WTR can provide sufficient P to perform similarly to common fertilizers. A greenhouse study (USA) was utilized to compare increasing rates of swine wastewater derived Al/O-WTR and inorganic P fertilizer (both applied at 33.6, 67.3, and 134.5 kg P₂O₅ ha⁻¹) to supply plant-available P to spring wheat (TriticumaestivumL.) in either sandy loam or sandy clay loam soil. Spring wheat straw and grain P uptake were comparable across all treatments in the sandy loam, while Al/O-WTR application to the sandy clay loam reduced straw and grain P uptake. The Al/O-WTR did not affect soil organic P concentrations, but did increase phosphatase activity in both soils; this suggests that Al/O-WTR application stimulated microorganisms and enhance the extent to which microbial communities can mineralize Al/O-WTR-bound organic P. Implications: Overall, results suggest that creating a new P fertilizer from Al-WTR and agro-industrial waste sources may be a feasible alternative to mining inorganic P fertilizer sources, while protecting the environment from unnecessary waste disposal.
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Rafaeli, Ada, Russell Jurenka, and Chris Sander. Molecular characterisation of PBAN-receptors: a basis for the development and screening of antagonists against Pheromone biosynthesis in moth pest species. United States Department of Agriculture, January 2008. http://dx.doi.org/10.32747/2008.7695862.bard.
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The original objectives of the approved proposal included: (a) The determination of species- and tissue-specificity of the PBAN-R; (b) the elucidation of the role of juvenile hormone in gene regulation of the PBAN-R; (c) the identificationof the ligand binding domains in the PBAN-R and (d) the development of efficient screening assays in order to screen potential antagonists that will block the PBAN-R. Background to the topic: Moths constitute one of the major groups of pest insects in agriculture and their reproductive behavior is dependent on chemical communication. Sex-pheromone blends are utilised by a variety of moth species to attract conspecific mates. In most of the moth species sex-pheromone biosynthesis is under circadian control by the neurohormone, PBAN (pheromone-biosynthesis-activating neuropeptide). In order to devise ideal strategies for mating disruption/prevention, we proposed to study the interactions between PBAN and its membrane-bound receptor in order to devise potential antagonists. Major conclusions: Within the framework of the planned objectives we have confirmed the similarities between the two Helicoverpa species: armigera and zea. Receptor sequences of the two Helicoverpa spp. are 98% identical with most changes taking place in the C-terminal. Our findings indicate that PBAN or PBAN-like receptors are also present in the neural tissues and may represent a neurotransmitter-like function for PBAN-like peptides. Surprisingly the gene encoding the PBAN-receptor was also present in the male homologous tissue, but it is absent at the protein level. The presence of the receptor (at the gene- and protein-levels), and the subsequent pheromonotropic activity are age-dependent and up-regulated by Juvenile Hormone in pharate females but down-regulated by Juvenile Hormone in adult females. Lower levels of pheromonotropic activity were observed when challenged with pyrokinin-like peptides than with HezPBAN as ligand. A model of the 3D structure of the receptor was created using the X-ray structure of rhodopsin as a template after sequence alignment of the HezPBAN-R with several other GPCRs and computer simulated docking with the model predicted putative binding sites. Using in silico mutagenesis the predicted docking model was validated with experimental data obtained from expressed chimera receptors in Sf9 cells created by exchanging between the three extracellular loops of the HezPBAN-R and the Drosophila Pyrokinin-R (CG9918). The chimera receptors also indicated that the 3ʳᵈ extracellular loop is important for recognition of PBAN or Diapause hormone ligands. Implications: The project has successfully completed all the objectives and we are now in a position to be able to design and screen potential antagonists for pheromone production. The successful docking simulation-experiments encourage the use of in silico experiments for initial (high-throughput) screening of potential antagonists. However, the differential responses between the expressed receptor (Sf9 cells) and the endogenous receptor (pheromone glands) emphasize the importance of assaying lead compounds using several alternative bioassays (at the cellular, tissue and organism levels). The surprising discovery of the presence of the gene encoding the PBAN-R in the male homologous tissue, but its absence at the protein level, launches opportunities for studying molecular regulation pathways and the evolution of these GPCRs. Overall this research will advance research towards the goal of finding antagonists for this important class of receptors that might encompass a variety of essential insect functions.
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Shomer, Ilan, Ruth E. Stark, Victor Gaba, and James D. Batteas. Understanding the hardening syndrome of potato (Solanum tuberosum L.) tuber tissue to eliminate textural defects in fresh and fresh-peeled/cut products. United States Department of Agriculture, November 2002. http://dx.doi.org/10.32747/2002.7587238.bard.
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The project sought to understand factors and mechanisms involved in the hardening of potato tubers. This syndrome inhibits heat softening due to intercellular adhesion (ICA) strengthening, compromising the marketing of industrially processed potatoes, particularly fresh peeled-cut or frozen tubers. However, ICA strengthening occurs under conditions which are inconsistent with the current ideas that relate it to Ca-pectate following pectin methyl esterase (PME) activity or to formation of rhamnogalacturonan (RG)-II-borate. First, it was necessary to induce strengthening of the middle lamellar complex (MLX) and the ICA as a stress response in some plant parenchyma. As normally this syndrome does not occur uniformly enough to study it, we devised an efficient model in which ICA-strengthening is induced consistently under simulated stress by short-chain, linear, mono-carboxylic acid molecules (OAM), at 65 oC [appendix 1 (Shomer&Kaaber, 2006)]. This rapid strengthening was insufficient for allowing the involved agents assembly to be identifiable; but it enabled us to develop an efficient in vitro system on potato tuber parenchyma slices at 25 ºC for 7 days, whereas unified stress was reliably simulated by OAMs in all the tissue cells. Such consistent ICA-strengthening in vitro was found to be induced according to the unique physicochemical features of each OAM as related to its lipophilicity (Ko/w), pKa, protonated proportion, and carbon chain length by the following parameters: OAM dissociation constant (Kdiss), adsorption affinity constant (KA), number of adsorbed OAMs required for ICA response (cooperativity factor) and the water-induced ICA (ICAwater). Notably, ICA-strengthening is accompanied by cell sap leakage, reflecting cell membrane rupture. In vitro, stress simulation by OAMs at pH<pKa facilitated the consistent assembly of ICAstrengthening agents, which we were able to characterize for the first time at the molecular level within purified insoluble cell wall of ICA-strengthened tissue. (a) With solid-state NMR, we established the chemical structure and covalent binding to cell walls of suberin-like agents associated exclusively with ICA strengthening [appendix 3 (Yu et al., 2006)]; (b) Using proteomics, 8 isoforms of cell wall-bound patatin (a soluble vacuolar 42-kDa protein) were identified exclusively in ICA-strengthened tissue; (c) With light/electron microscopy, ultrastructural characterization, histochemistry and immunolabeling, we co-localized patatin and pectin in the primary cell wall and prominently in the MLX; (d) determination of cell wall composition (pectin, neutral sugars, Ca-pectate) yielded similar results in both controls and ICA-strengthened tissue, implicating factors other than PME activity, Ca2+ or borate ions; (e) X-ray powder diffraction experiments revealed that the cellulose crystallinity in the cell wall is masked by pectin and neutral sugars (mainly galactan), whereas heat or enzymatic pectin degradation exposed the crystalline cellulose structure. Thus, we found that exclusively in ICA-strengthened tissue, heat-resistant pectin is evident in the presence of patatin and suberinlike agents, where the cellulose crystallinity was more hidden than in fresh control tissue. Conclusions: Stress response ICA-strengthening is simulated consistently by OAMs at pH< pKa, although PME and formation of Ca-pectate and RG-II-borate are inhibited. By contrast, at pH>pKa and particularly at pH 7, ICA-strengthening is mostly inhibited, although PME activity and formation of Ca-pectate or RG-II-borate are known to be facilitated. We found that upon stress, vacuolar patatin is released with cell sap leakage, allowing the patatin to associate with the pectin in both the primary cell wall and the MLX. The stress response also includes formation of covalently bound suberin-like polyesters within the insoluble cell wall. The experiments validated the hypotheses, thus led to a novel picture of the structural and molecular alterations responsible for the textural behavior of potato tuber. These findings represent a breakthrough towards understanding of the hardening syndrome, laying the groundwork for potato-handling strategies that assure textural quality of industrially processed particularly in fresh peeled cut tubers, ready-to-prepare and frozen preserved products.