Articles de revues : « M-L bond »

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Chintalacharuvu, K. R., et S. L. Morrison. « Residues critical for H-L disulfide bond formation in human IgA1 and IgA2. » Journal of Immunology 157, n^o 8 (15 octobre 1996) : 3443–49. http://dx.doi.org/10.4049/jimmunol.157.8.3443.

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Abstract There are two subclasses of human IgA, IgA1 and IgA2. IgA2 exists as two known allotypes, IgA2 m(1) and IgA2 m(2) with a recently reported novel IgA2 (IgA2(n)) possibly representing a third allotype. The variants of human IgA differ in their H and L chain disulfide-bonding pattern; in IgA1, IgA2(n), and IgA2 m(2), a disulfide bond connects a cysteine residue in CH1 of the H chain with the L chains while human IgA2 m(1) has been reported to lack a covalent bond between the H and L chains. Here we have used site-directed mutagenesis to demonstrate that Cys133 is essential for the formation of the H-L disulfide bond in IgA1. However, IgA2 m(2) and the IgA2(n) but not IgA2 m(1) form an H-L disulfide in the absence of Cys133. IgA2 m(1) differs from IgA2 m(2) and the IgA2(n) at two positions in CH1; IgA2 m(1) has Pro212 and Pro221 whereas IgA2 m(2) and the IgA2(n) have Ser212 and Arg221. Our studies demonstrate that it is the presence of Pro221 in IgA2 m(1) that interferes with the H-L disulfide in the absence of Cys133. Contrary to what has been previously reported, protein purified from culture supernatants of IgA2 m(1) show some HL, H2L2, and H4L4J, suggesting that IgA2 m(1) can exist either as a form lacking H-L disulfide bonds or as a form with H-L disulfides.

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Calhorda, Maria J., Alberto R. Dias, Adelino M. Galvão et José A. Martinho Simões. « Estimation of stepwise M-L bond dissociation enthalpies in M(η-C5H5)2L2 complexes ». Journal of Organometallic Chemistry 307, n^o 2 (juin 1986) : 167–76. http://dx.doi.org/10.1016/0022-328x(86)80471-5.

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Yang, Ming-Chung, et Ming-Der Su. « Theoretical investigations of the reactivity of neutral molecules that feature an MM (M = B, Al, Ga, In, and Tl) double bond ». New Journal of Chemistry 43, n^o 24 (2019) : 9364–75. http://dx.doi.org/10.1039/c9nj01294j.

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The geometry, the electronic structure and the reactivity of compounds that feature a central MM (M = group 13 element) double bond with two sterically bulky ligands (L₁ = ^tBu₂MeSi and L₂ = NHC^iPr), L₁L₂MML₁L₂ (Rea-MM) are studied at the B3LYP-D3(BJ)/def2-SVP level of theory.

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He, Fen, Xin Yang, Zhi-Yue Tian, Han-Guang Wang et Ying Xue. « Theoretical investigation on the structures and bonding properties of Pd(II), Pt(II) and Ni(II) complexes with tridentate CNC-pincer N-heterocyclic carbene ligands ». Journal of Theoretical and Computational Chemistry 15, n^o 05 (août 2016) : 1650037. http://dx.doi.org/10.1142/s0219633616500371.

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The density functional theory (DFT) has been applied for the analysis of the bond between group 10 metals and N-heterocyclic carbene (NHC) in complexes (MCl(L-X): M [Formula: see text] Pd(II), Pt(II), and Ni(II), L-X[Formula: see text][2-(3-methylimidazolin-4,5-bisX-2-yliden-1-yl)-4-phenyl] amido, X [Formula: see text]H, Cl and CN). Full geometry optimizations have been performed for all the ligands (L-X[Formula: see text] anions), MCl[Formula: see text] cations, and the complexes. In the ligands, the energy levels of the carbon [Formula: see text] lone-pair orbitals suggest the trend L-H[Formula: see text] L-Cl[Formula: see text] L-CN[Formula: see text] for the donor strength. The role of the M–NHC interaction in complexes was investigated by natural bond orbital (NBO) analysis. The results show that the NHC–M bond consists of the components originating from the L[Formula: see text]M donation and the M[Formula: see text]Carbene C back-donation and the metal[Formula: see text]the ring of NHC back-donation. The transition-metal strongly affects the donation and back-donation. The interaction between the metal and the NHC ligand can be influenced by the central metal and the substituent on the ring of NHC.

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Delmas, Claude, Marie Guignard et Francois Weill. « (Invited) Overview of the Ordering Phenomena in Li and Na Layered Oxide Electrode Materials ». ECS Meeting Abstracts MA2022-02, n^o 1 (9 octobre 2022) : 23. http://dx.doi.org/10.1149/ma2022-02123mtgabs.

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AX(M)O2 layered oxides (A = Li, Na) are considered as the best positive electrode materials either for Li ion and Na ion batteries. In most of the systems, the shape of the voltage curve shows change in slope of the curve which indicate the occurrence of structural transitions due to: (i) electronic configuration modification in the MO2 slab, (ii) change in the slab packing, (iii) alkali ion-vacancy ordering. Moreover, in AX(M,L)O2 materials a M/L ordering can occur within the (M,L)O2 slab for the pristine material. Lithium and sodium tends to be ordered in the deintercalated materials for peculiar compositions. Nevertheless, due to the larger ionic radii of Na+ vs Li+, the repulsive interaction between sodium ions are stronger for sodium, leading to many Na+/vacancy patterns in the interslab space. Moreover, transition element orderings can occur within the (L,M)O2 slab if the difference in size is significant and if the cation ratio corresponds to a specific composition (1/3, ½, 2/3...). Then an interesting behaviour is observed as the sodium/vacancy ordering in the interslab space can be st superimposed to the cation ordering. Another original situation is also observed for cations (d2 or d3) which like to form M-M bonds. In this case, the pattering of short bond and long bond in the MO2 slab is directly related to the Na+/vacancy distribution and to the M3+/M4+ ratio.

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Aguilar, Charles M., et Willian R. Rocha. « The nature of the M–NO bond in [M(Imidazole)(PPIX)(L)]q complexes (M=Fe2+, Ru2+ ; L=NO+, NO and NO− ; PPIX=Protoporphyrin IX) ». Inorganica Chimica Acta 408 (novembre 2013) : 18–26. http://dx.doi.org/10.1016/j.ica.2013.08.002.

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Altabe, Silvia G., Pablo Aguilar, Gerardo M. Caballero et Diego de Mendoza. « The Bacillus subtilis Acyl Lipid Desaturase Is a Δ5 Desaturase ». Journal of Bacteriology 185, n^o 10 (15 mai 2003) : 3228–31. http://dx.doi.org/10.1128/jb.185.10.3228-3231.2003.

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ABSTRACT Bacillus subtilis was recently reported to synthesize unsaturated fatty acids (UFAs) with a double bond at positions Δ5, Δ7, and Δ9 (M. H. Weber, W. Klein, L. Muller, U. M. Niess, and M. A. Marahiel, Mol. Microbiol. 39:1321-1329, 2001). Since this finding would have considerable importance in the double-bond positional specificity displayed by the B. subtilis acyl lipid desaturase, we have attempted to confirm this observation. We report that the double bond of UFAs synthesized by B. subtilis is located exclusively at the Δ5 position, regardless of the growth temperature and the length chain of the fatty acids.

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Walsh, Eoin F., Vladimir K. Popov, Michael W. George et Martyn Poliakoff. « Photoacoustic Calorimetry at High Pressure : A New Approach to Determination of Bond Strengths. Estimation of the M-L Bond Dissociation Energy of M(CO)5L (M = Cr, Mo ; L = H2, N2) in n-Heptane Solution ». Journal of Physical Chemistry 99, n^o 31 (août 1995) : 12016–20. http://dx.doi.org/10.1021/j100031a033.

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Yang, Chao, Yong Luo, Xie Li et Jiaolin Cui. « N-type thermoelectric Ag8SnSe6 with extremely low lattice thermal conductivity by replacing Ag with Cu ». RSC Advances 11, n^o 6 (2021) : 3732–39. http://dx.doi.org/10.1039/d0ra10454j.

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The point defects and the bond energy can be increased by replacing Ag with Cu, which have diverse effects on κ_L respectively, thus attaining the minimum κ_L ∼ 0.12 W K⁻¹ m⁻¹ at 645 K.

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Jansson, R. K., S. H. Lecrone et R. Lance. « Management of Lepidopterous Pests on Cabbage, 1991 ». Insecticide and Acaricide Tests 18, n^o 1 (1 janvier 1993) : 97–100. http://dx.doi.org/10.1093/iat/18.1.97.

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Abstract ‘Rio Verde’ cabbage seeds were incorporated into a germination mix (Pro-Mix) and direct seeded into a Rockdale soil at the University of Florida’s Tropical Research and Education Center on 19 Dec 1990. The soil was fumigated with Terr-O-Gas (75% methyl bromide, 25% chloropicrin; 246 kg/ha) and covered with white on black plastic mulch on 12 Dec. Plants were spaced 0.3 m apart within rows and 0.76 m apart between rows on 1.8 m-center beds. Fertilizer (1680 kg/ha of granular 6:12:12) was applied and incorporated into the soil on 11 Dec. Goal 2 EC was applied (0.56 kg (AI)/ha) between the beds on 17 Dec for weed control. Plants were irrigated 4 h/day using a turbo T-tape drip irrigation system (model 40) which delivered 5.0 liters of water/m of dripline/h. Twelve insecticide treatments and a control were compared. Treatments were: RH-5922 2F (0.14 kg (AI)/ha) in combination with Triton B-1956 (568 ml/ha); the above in combination with Cutlass WP (1.1 kg/ha) or Phosdrin 4 EC (0.56 kg (AI)/h); RH-5992 OS (0.14 kg (AI)/ha) in combination with Triton B-1956; RH-2485 2F (0.14 kg (AI)/ha) in combination with Triton B-1956; CME 13406 15 SC (0.03 6 kg (AI)/ha) in combination with Bond (2.3 liter/ha); MYX 1111 L (4.7 liter/ha) and MYX 1112 L (7.0 liter/ha) in combination with Bond; CGA 106630 (0.74 kg (AI)/ha) in combination with Bond; Cutlass WP (2.2 kg/ha) in combination with Bond; Javelin WG (1.1 kg ha) in combination with Bond; Phosdrin 4 EC (0.56 kg (AI)/ha) in combination with Cutlass WP (2.2 kg/ha) and Bond; and a nontreated check.

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Malisch, Wolfgang, Martin Märkl, Sandro Amann, Ulrich Hirth et Martin Schmeußer. « Phosphorus Metal Double Bond Complexes : Functional and Chiral Species Cp(L)(L′)M=PR2(M = Mo, W) and the Iron Derivative Cp (CO) Fe = PMes2 ». Phosphorus, Sulfur, and Silicon and the Related Elements 49-50, n^o 1-4 (mai 1990) : 441–44. http://dx.doi.org/10.1080/10426509008038998.

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Korkmaz, Yonca, Nuray Attar et Meral Ozalp. « Comparison of the Antibacterial Activity of Different Self-etching Primers and Adhesives ». Journal of Contemporary Dental Practice 9, n^o 7 (2008) : 57–64. http://dx.doi.org/10.5005/jcdp-9-7-57.

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Aim The aim of this study was to evaluate the antibacterial effects of different one-step and two-step selfetching primer/adhesives on Streptococcus mutans (S. mutans), Lactobacillus casei (L. casei), and Lactobacillus acidophilus (L. acidophilus). Methods and Materials The antibacterial effects of Clearfil Protect Bond Primer and Bonding agent; AdheSE Primer and Bonding agent; Adper Prompt L-Pop; Futurabond NR; Clearfil Tri S Bond; and Cervitec (positive control, 1% chlorhexidine varnish) were tested against standard strains of S. mutans, L. Casei, and L. acidophilus using the disk diffusion method. Standard filter paper disks (n=5) impregnated with 20 microL of each material were prepared. After incubation at 37°C for 48 hours in a 5-10% CO2 atmosphere, the diameter of inhibition zones were measured in millimeters. Data were analyzed using one way analysis of variance (ANOVA) and multivariate analysis of variance (MANOVA). Duncan's Multiple Range Test was used for pairwise comparison. Results The size of inhibition zones produced by primer/adhesives varied among the brands. AdheSE Primer: S. mutans (20.6±1.51); L. casei (14.8±1.78); L. acidophilus (11.4±0.54). Adper Prompt L-Pop: S. mutans (19.6±1.51); L. casei (13.8±1.64); L. acidophilus (13.8±1.09). Cervitec: S. mutans (23±0.00); L. casei (27±0.70); L. acidophilus (22.4±0.54). Clearfil Protect Bond Primer: S. mutans (17±0.00); L. casei (17.6±0.54); L. acidophilus (22.4±0.54). Futurabond NR was found effective only against S. mutans (14.6±1.67). Of all the materials tested, AdheSE Bonding agent, Clearfil Protect Bond Bonding agent, and Clearfil Tri S Bond exhibited no inhibition zone (-) for all bacteria tested. Conclusion Among the adhesives tested Clearafil Protect Bond Primer based upon monomer methacryloyloxydodecylpyridiniium bromide (MDPB) was found to be the most potent material against L. acidophilus and L. casei. AdheSE Primer and Adper Prompt L-Pop are highly effective against S. mutans. Clinical Significance Compared with other adhesive systems, Clearfil Protect Bond Primer (containing MDPB) showed a high antibacterial effect against all microorganizms tested. Two-step, self-etching primer/ adhesive system Clearfil Protect Bond might be a suitable choice under minimally invasive restorations. The recently developed one-step, self-etching system Clearfil Tri S Bond showed no antibacterial effect against microorgazims tested. Citation Korkmaz Y, Ozalp M, Attar N. Comparison of the Antibacterial Activity of Different Self-etching Primers and Adhesives. J Contemp Dent Pract 2008 November; (9)7:057-064.

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Muraoka, Takako, Keisuke Abe, Haruhiko Kimura, Youhei Haga, Keiji Ueno et Yusuke Sunada. « Synthesis, structures, and reactivity of the base-stabilized silanone molybdenum complexes ». Dalton Trans. 43, n^o 44 (2014) : 16610–13. http://dx.doi.org/10.1039/c4dt02159b.

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Gryko, Daniel T., Rafał Orłowski, John Clark, Harry B. Gray, Valentine I. Vullev et Agnieszka Szumna. « Polypeptide Oligomers Comprised of Corroles – Hydrogen Bonding Provides “Short-Circuit” Coupling Pathways for Electron Transfer ». ECS Meeting Abstracts MA2022-01, n^o 14 (7 juillet 2022) : 974. http://dx.doi.org/10.1149/ma2022-0114974mtgabs.

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Electron flow through proteins is a crucial factor, which decides about their multiple functions in living organisms. Incorporating polypeptides as bridges in donor-bridge-acceptor (DBA) conjugates allows for examining how various structural features in proteins affect the kinetics of the CT processes they mediate. Based on the premise that hydrogen-bonds formation could serve to modify geometry and special orientation of donor and acceptor scaffolds in covalently linked bichromophoric system we designed and synthesized series of dyads comprised of perylene-bisimide and free-base corrole. Specifically, the object of the study was hydrogen-bonded discrete assemblies of corroles possessing core-NH as hydrogen bond donor and amide groups located at position meso-10 as hydrogen bond acceptor. The three dyads differ in type and number of bridging aminoacids’ moieties: L-alanine and L-phenylalanine and one or four respectively. These complex corroles were prepared via synthesis of perylenebisimide-amino acid conjugate possessing free NH2 group followed by amidation of COOH-corrole. Combined steady-state and time-resolved photophysical studies identified that electron-transfer occurs in all four bichromophoric systems. Our focus was on alanine tetramer that is long enough not to mediate too efficiently through-bond CT. A corrole moiety serves as an electron donor, and a perylenediimide as an acceptor. The picosecond rates of electron transfer suggests that the electronic-coupling pathways cannot be through-bond and most likely involve through-hydrogen bond interaction. References Orłowski, R.; Vakuliuk, O.; Gullo, M. P.; Danylyuk, O.; Ventura, B.; Koszarna, B.; Tarnowska, A.; Jaworska, N.; Barbieri, A.; Gryko, D. T. Commun. 2015, 51, 8284-8287. Orłowski, R.; Cichowicz, G.; Staszewska-Krajewska, O.; Schilf, W.; Cyrański, M. K.; Gryko, D. T. Eur. J. 2019, 25, 9658-9664. Figure 1

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Lashanizadegan, Maryam, et Marzieh Sarkheil. « Solvent-dependent synthesis and mono-hydrolysis of di-Schiff base of (+/-)trans-1,2-cyclohexanediamine and 2-pyridinecarboxaldehyde in Cu(II), Co(II) and Zn(II) complexes ». Journal of the Serbian Chemical Society 77, n^o 11 (2012) : 1589–97. http://dx.doi.org/10.2298/jsc111203035l.

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The Schiff base ligand trans-N,N?-bis[2-pyridinecarboxylidene] cyclohexane-1,2-diamine (L) was synthesized. This ligand when stirred with 1 equiv of MCl2.xH2O (M = Cu, Co, Zn) in ethanol, undergoes partial hydrolysis of the imino bond and the result tridentate ligand (L') and immediately forms the complexes with N3 coordination sphere. The reactions of L with MCl2.xH2O (M = Cu, Co, Zn) in THF give complexes [ML]Cl2. The ligand (L), complexes [M(L')Cl]Cl and [ML]Cl2 were characterized by elemental analysis, UV-Vis, FT-IR, 1H NMR, GC/MS and luminescence properties. The 1H NMR spectra of the ligand and its diamagnetic complexes were recorded in CDCl3 and DMSO solvents, respectively. Obtained data confirm that the donor atoms N in ligand coordinated to the metal ions. The luminescence studies show ligands and their complexes display intraligand (?- ?

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Chisholm, Malcolm H. « Mixed valence complexes involving MM quadruple bonds (M=Mo or W) ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 366, n^o 1862 (10 septembre 2007) : 101–12. http://dx.doi.org/10.1098/rsta.2007.2143.

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The MM quadruple bond of configuration MM σ 2 π 4 δ 2 is redox active and in many ways ideally suited for studies of mixed valency when two or more such centres are linked by a bridging ligand. In this account, the mechanism of electronic coupling is examined for complexes of the type [L 3 M 2 bridgeM 2 L 3 ] 0/+ where L, a pivalate; bridge, a dicarboxylate or related ligand and M, Mo or W. The represented examples allow us to probe electronic factors close to the class II/III border and readily distinguish between electron and hole transfer in the superexchange mechanism. The potential for mixed valence organic radical anions mediated by the M 2 centre is also raised and one specific example of class III behaviour is described.

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Rodman, Gary S., et Kent R. Mann. « Variable temperature 1H NMR studies of [M(COD)(μ-L)]2 (M  Rh, Ir ; L = substituted hydroxypyridinate). Facile intramolecular bridging ligand exchange and metal-metal bond cleavage ». Journal of Organometallic Chemistry 378, n^o 2 (décembre 1989) : 255–77. http://dx.doi.org/10.1016/0022-328x(89)80014-2.

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Ziegler, Tom, Vincenzo Tschinke, Liangyou Fan et Axel D. Becke. « Theoretical study on the electronic and molecular structures of (C5H5)M(L) (M = rhodium, iridium ; L = carbonyl, phosphine) and M(CO)4 (M = ruthenium, osmium) and their ability to activate the carbon-hydrogen bond in methane ». Journal of the American Chemical Society 111, n^o 26 (décembre 1989) : 9177–85. http://dx.doi.org/10.1021/ja00208a007.

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Kehrer, Armin, Shi-qi Dou et Alarieh Weiss. « The Electric Field Gradient at the Site of the Halogen Ion and Structure of Amino Acid Hydrobromides and Hydroiodides ». Zeitschrift für Naturforschung A 47, n^o 7-8 (1 août 1992) : 887–917. http://dx.doi.org/10.1515/zna-1992-7-815.

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Abstract The 79,81Br and 127I NQR spectra of several hydrobromides, respectively hydroiodides, of amino acides and dipeptides were studied, mostly as functions of temperature in the range 77 < T/K <420. The investigated compounds are: L-Arg • HBr • H2O, L-Cys • HBr • H2O , L - Cys - S - S - L - Cys • 2HBr, ethanolamine • HBr, L-Glu • HBr, L-His • HBr, L-His • 2HBr, L-Ile HBr • H2O , Sar • HBr, (Sar)2 • HBr, L-Val • HBr • H2O , Gly • LiBr, Gly-Gly • LiBr, ethanolamine HI, Sar • HI, (Sar)2 • HI, (Gly)2 • HI, (L-Val)2 • HI, Gly-L-Leu • HI • H2O . A phase transition with hysteresis was observed for L-Val • HBr • H2O (Tc.up = 318 K, Tc.down = 242 K). Two solid phases of Sar • HI have been studied by NQR, one crystallized from melt, the other one from aqueous solution. For three of the title compounds the crystal structure was determined at room temperature: L-His - 2HBr, P212121 , Z = 4, aj pm = 1652, b/pm = 916, c/pm = 721; L-Cys HBr H2O , P212121 , Z = 4, a/pm = 1955, b/pm = 746, c/pm = 550; Gly-L-Leu • HI • H2O , P2X, Z = 2, a / p m = 1289, b/pm = 914, c/pm = 615, ß/° = 99.In most cases the halogen ion in the studied hydrohalides is polycoordinated by hydrogen bonds of the type N - H • • • X⊖ and O - H • • • X⊖ , X = Br, I. The NQR frequencies and, for iodine, the nuclear quadrupole coupling constants depend on this coordination. A low frequency (coupling constant) region is found for pure N - H • • • X⊖ coordination. Replacing one N - H • • • X⊖ bond by O - H • • • X⊖ rises the electric field gradient, EFG, respectively the resonance frequencies. The dependence of the EFG on the hydrogen bond coordination N - H • • • X⊖ plus O - H • • • X⊖ is discussed for the title compounds including information from literature

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Santoro, Amedeo, Carlo Sambiagio, Patrick C. McGowan et Malcolm A. Halcrow. « Synthesis and coordination chemistry of 1,1,1-tris-(pyrid-2-yl)ethane ». Dalton Transactions 44, n^o 3 (2015) : 1060–69. http://dx.doi.org/10.1039/c4dt02824d.

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The complexes [ML₂]ⁿ⁺(Mⁿ⁺= Fe²⁺, Co²⁺, Co³⁺, Cu²⁺and Ag⁺), [PdCl₂L] and [CuI(L)] are described. [AgL₂]⁺is an unusual square planar silver(i) centre (left). Exposure of [CuI(L)] to air affords mono- or dinuclear copper(ii)/carbonato products. Two of the copper complexes form crystalline hydrates with complicated hydrogen bond networks (right).

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Abbattista, Ramona, Ilario Losito, Cosima Damiana Calvano et Tommaso R. I. Cataldi. « Exploring the Isomeric Precursors of Olive Oil Major Secoiridoids : An Insight into Olive Leaves and Drupes by Liquid-Chromatography and Fourier-Transform Tandem Mass Spectrometry ». Foods 10, n^o 9 (31 août 2021) : 2050. http://dx.doi.org/10.3390/foods10092050.

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Secoiridoids play a key role in determining health benefits related to a regular consumption of extra-virgin olive oil (EVOO), in which they are generated from precursors of the same class naturally occurring in drupes and leaves of the olive (Olea europaea L.) plant. Here, reversed-phase liquid chromatography coupled to electrospray ionization and Fourier-transform single/tandem mass spectrometry (RPLC-ESI-FTMS and MS/MS) was employed for a structural elucidation of those precursors. The presence of three isoforms in both matrices was assessed for oleuropein ([M-H]− ion with m/z 539.1770) and was emphasized, for the first time, also for ligstroside (m/z 523.1821) and for the demethylated counterparts of the two compounds (m/z 525.1614 and 509.1665, respectively). However, only the prevailing isoform included an exocyclic double bond between carbon atoms C8 and C9, typical of oleuropein and ligstroside; the remaining, less abundant, isoforms included a C=C bond between C8 and C10. The same structural difference was also observed between secoiridoids named elenolic acid glucoside and secoxyloganin (m/z 403.1246). This study strengthens the hypothesis that secoiridoids including a C8=C10 bond, recently recognized as relevant species in EVOO extracts, arise mainly from specific enzymatic/chemical transformations occurring on major oleuropein/ligstroside-like precursors during EVOO production, rather than from precursors having that structural feature.

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Samerjai, Wachirawit, Piyada Jittangprasert et Pan Tongraung. « Colorimetric Detection of Iron(III) Ion Based on 4-Aminothiophenol and Schiff Base Naphthalene-2-ol Modified Silver Nanoparticles ». Asian Journal of Chemistry 32, n^o 2 (30 décembre 2019) : 287–92. http://dx.doi.org/10.14233/ajchem.2020.22301.

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A facile, highly selective colorimetric sensor based on 4-aminothiophenol (4-ATP) and Schiff base naphthalene-2-ol (L) modified silver nanoparticles (4-ATP-L-AgNPs) for detection of Fe(III) ion in aqueous solution. The presence of Fe(III) ion induced the aggregation of AgNPs that caused the red-shift from 430 to 440 nm, through a cooperative metal-ligand interaction from the coordination bond between Fe(III) ion and functional groups on AgNPs surface resulting in a colour change from dark brown to dark yellow with increasing absorption at 365 nm. The absorbance at 365 nm is linear with the concentration of Fe(III) ion ranging from 9.0 × 10-6 M to 9.0 × 10-3 M with a correlation coefficient of 0.9991. The detection limit of the developed method was 7.9 × 10-6 M. The practical application of 4-ATP-L-AgNPs for selective sensor for Fe(III) ion in various drinking water samples were demonstrated.

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Witkowska, H. Ewa, Zbigniew Bialy, Marian Jurzysta et George R. Waller. « Analysis of Saponin Mixtures from Alfalfa (Medicago Sativa L.) Roots using Mass Spectrometry with MALDI Techniques ». Natural Product Communications 3, n^o 9 (septembre 2008) : 1934578X0800300. http://dx.doi.org/10.1177/1934578x0800300904.

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This model study demonstrates the value of Matrix Assisted Laser Desorption Ionization (MALDI) MS in global analysis of mixtures of saponin isolates. Unfractionated saponin extract derived from alfalfa [Medicago sativa L.] roots was analyzed. In addition, a few saponin fractions that were purified from the same extract by a series of chromatographic steps were also studied. MALDI mass spectrometry utilized TOF, TOF/TOF and QqTOF analyzers. Low-resolution fingerprints of the mixture characterized the sample in terms of a minimal number of distinct saponin components. The main species observed under MALDI-TOF and oMaldi-QqTOF MS positive ion mode conditions were sodiated pseudomolecular ions [M+Na]+. No protonated molecular ions [M+H]+ were detected. The MS/MS spectra acquired on [M+Na]+ precursor ions under conditions of collision induced dissociation (CID) were dominated by cleavages at glycosidic bonds. Product ions representing free aglycones were either absent or present at low intensities and were never observed for structures carrying an oligosaccharide bound to a sapogenin at the C3- O-position. In general, product ion series generated from CID fragmentation of glycans bound via an ether bond ( e.g., C3- O-position in medicagenic acid) were consistent with the gas phase cleavages of each of the glycosidic bonds within the oligosaccharide, thus revealing the primary structure. In contrast, glycans bound via an ester bond ( e.g., C28- O-position in MA) were released as intact sodiated species. A total of 78 pseudomolecular ions demonstrating signal-to-noise ratios above 5 were observed in the MALDI-TOF mass spectrum of unfractionated root extract from M. sativa. Molecular masses of 52 out of 78 were consistent with at least one known or novel saponin structure, with 10 of those 52 likely representing doubly sodiated saponin species. Calculated masses of the majority of the known M. sativa saponin structures were matched to experimental pseudomolecular ion masses. MS/MS analysis of unfractionated extract allowed us to propose putative structures for 51 saponins: 15 of these corresponded to the known M. sativa species, 8 to other Medicago genus species and 26 were not reported before for Medicago genus. We submit that the approach described here might serve as a high throughput strategy for evaluating effects of stressors or genetic manipulation on the overall composition of the saponin content of an organism.

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Forni, Alessandra, Elena Cariati, Lucia Carlucci, Elena Lucenti, Daniele Marinotto, Stefano Pieraccini et Maurizio Sironi. « Interpreting the different emissive properties of cyclic triimidazole-based Cu^I and Ag^I coordination polymers : a QTAIM and IQA study ». Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 77, n^o 6 (5 novembre 2021) : 865–70. http://dx.doi.org/10.1107/s2052520621009707.

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A QTAIM and IQA investigation on model compounds of two isostructural AgI and CuI coordination polymers (CPs) based on cyclic triimidazole (L), i.e. the [MIL] n 1D double-stranded stair chain and the [MClL] n 3D network (M = Cu, Ag), has allowed light to be shed on the different emissive behaviour associated with the two metal ions. According to a previously reported investigation [Malpicci et al. (2021). Inorg. Chem. Front. 8, 1312–1323], AgI CPs showed both fluorescence and multiple ligand-centred room-temperature phosphorescences, whereas CuI CPs displayed non-thermally equilibrated halogen and metal-to-ligand charge transfer and two ligand-centred phosphorescences, the latter observed only by their selective activation. Analysis of both local and integral QTAIM descriptors, including delocalization indices and source function, of the Ag—N and Cu—N bonds reveals a higher covalent and local character for the latter, explaining the greater metal–ligand electronic communication observed for the Cu compounds. Moreover, IQA investigation shows that the Cu—N bond is characterized by higher interaction energy, due to both higher electrostatic and exchange-correlation contributions. Analysis on the M—X (M = Ag, Cu; X = I, Cl) bonds, also present in these structures, highlights a much higher covalent and local character with respect to the M—N bonds.

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Kawano, Yasuro, Kazunori Yamaguchi, Shun-ya Miyake, Taeko Kakizawa et Mamoru Shimoi. « Investigation of the Stability of the M-H-B Bond in Borane σ Complexes [M(CO)5(η1-BH2R⋅L)] and [CpMn(CO)2(η1-BH2R⋅L)] (M=Cr, W ; L=Tertiary Amine or Phosphine) : Substituent and Lewis Base Effects ». Chemistry - A European Journal 13, n^o 24 (17 août 2007) : 6920–31. http://dx.doi.org/10.1002/chem.200601883.

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INOUYE, Kuniyo, Soo-Bok LEE et Ben'ichiro TONOMURA. « Effect of amino acid residues at the cleavable site of substrates on the remarkable activation of thermolysin by salts ». Biochemical Journal 315, n^o 1 (1 avril 1996) : 133–38. http://dx.doi.org/10.1042/bj3150133.

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The activity of thermolysin in the hydrolysis of N-[3-(2-furyl)acryloyl]-glycyl-L-leucine amide and N-carbobenzoxy-L-aspartyl-L-phenylalanine methyl ester is remarkably enhanced in the presence of high concentrations (1–5 M) of neutral salts [Inouye (1992) J. Biochem. (Tokyo) 112, 335–340]. In this study, the effect of salts on such activity has been examined using a series of substrates, furylacryloyl dipeptide amides, which have various hydrophobic amino acids at the cleavable bond. Although the enzyme activity varies widely depending on the substrate employed, the degree of activation at a given concentration of NaCl is considerably similar. This indicates that the degree of activation is not dependent on the hydrophobicity of the amino acid side chains at the scissile bond of the substrates. The molecular activity, kcat, and Michaelis constant, Km, were evaluated separately for substrates N-[3-(2-furyl)acryloyl]-L-leucyl-L-alanine amide and N-[3-(2-furyl)acryloyl]-L-phenylalanyl-L-alanine amide, and the activation was found to be brought about only by an increase in kcat. The effectiveness of monovalent cations on the increase of kcat was determined to follow the order of Na+ > K+ > Li+.

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Chagas, J. R., F. C. V. Portaro, I. Y. Hirata, P. C. Almeida, M. A. Juliano, L. Juliano et E. S. Prado. « Determinants of the unusual cleavage specificity of lysyl-bradykinin-releasing kallikreins ». Biochemical Journal 306, n^o 1 (15 février 1995) : 63–69. http://dx.doi.org/10.1042/bj3060063.

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Kinetic data for the hydrolysis by human tissue kallikrein of fluorogenic peptides with o-aminobenzoyl-Phe-Arg (Abz-FR) as the acyl group and different leaving groups demonstrate that interactions with the S′1, S′2 and S′3 subsites are important for cleavage efficiency. In addition, studies on the hydrolysis of fluorogenic peptides with the human kininogen sequence spanning the scissile Met-Lys bond [Abz-M-I-S-L-M-K-R-P-N-(2,4-dinitrophenyl)ethylenediamine] and analogues with different residues at positions P′1, P′2 and P′3 showed that (a) the presence of a proline residue at P′3 and the interactions with the tissue kallikrein-binding sites S2 to S′2 are determinants of Met-Lys bond cleavage and (b) residues P3, P4 and/or P5 arc important for cleavage efficiency. The substitution of phenylalanine for methionine or arginine in substrates with scissile Met-Lys or Arg-Xaa bonds demonstrated that lysyl-bradykinin-releasing tissue kallikreins also have a primary specificity for phenylalanine. The replacement of arginine by phenylalanine in (D)P-F-R-p-nitroanilide (pNA) produced an efficient and specific chromogenic substrate, (D)P-F-F-pNA, for the lysyl-bradykinin-releasing tissue kallikreins as it is resistant to plasma kallikrein and other arginine hydrolases.

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Torres, Luciana Sarmento, Levy Anderson César Alves, Marcelo Fava et Rebeca Di Nicoló. « Effects of thermomechanical and thermocycling on the shear bond strength of brackets to bovine enamel bonded with conventional and self-etching adhesive systems ». Brazilian Dental Science 18, n^o 3 (21 septembre 2015) : 98. http://dx.doi.org/10.14295/bds.2015.v18i3.1152.

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Several adhesive systems have been developed in the last decade. T<span lang="EN-US"><span lang="EN-US">he aim of the current study was to evaluate the shear bond strength of orthodontic brackets bonded with conventional primers or self-etching primers, artificially aged by means of thermocycling and thermomechanical procedures.90 bovine incisors were used in the investigation. The roots were sectioned in the amelo-cementary junction. </span></span>All samples were randomly divided in 2 groups ( n= 45), according to the primer used for bracket bonding. XT Group–hydrophobic conventional primer (Transbond XT, 3M unitek, Monrovia, Calif); SEP Group –self-etching primer (Transbond Plus SEP, 3 M Unitek, Monrovia, Calif). All specimens were bonded with XT Transbond resin adhesive (3 M Unitek, Monrovia, Calif). A Universal Testing Machine EMIC DL2000 (EMIC Equip. Sist. Ensaio Ltda., São José dos Pinhais, PR, Brazil) was used for the collection of the values of SBS resistance. The results of the current study were: (Prompt L-Pop 1.72±0.13 MPa; Clearfil SE Bond 1.75±0.19 MPa; FL Bond 1.71±0.22 MPa; One-Up Bond 1.77±0.14 MPa; XT Control 10.5±0.86 MPa). In conclusion: the number of cycles in thermal and thermo mechanical cycling did not influence shear bond strength values for any of the primers tested;SEP Transbond Plus showed the greatest values for bond strength of orthodontic brackets.

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Knop, Osvald, T. Stanley Cameron, D. Adhikesavalu, Beverly R. Vincent et James A. Jenkins. « Crystal chemistry of complex indium(III) and other M(III) halides, with a discussion of M—Cl bond lengths in complex M(III) chlorides and of the structures of and hydrogen bonding in (NH4)2[InCl5(H2O)], K3InCl6•nH2O, (MeNH3)4[InCl6]Cl, and (Me2NH2)4[InCl6]Cl ». Canadian Journal of Chemistry 65, n^o 7 (1 juillet 1987) : 1527–56. http://dx.doi.org/10.1139/v87-261.

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The crystal chemistry of complex In(III) halides is discussed and compared with that of other Group III elements and Fe(III), with critical comments and analysis of the available information. The cation/anion packing types occurring among A+[M3+X4] halides are classified according to volume per formula unit and the relative ionic sizes of M, X, and A, and the structural trends in this class of compounds are identified. The effect of systematic factors responsible for variation in M(III)—Cl bond lengths is examined in detail. It is shown that the mean M(III)—Cl bond lengths in [MClnLm]ε(M = Al, Ga, Fe, In, Tl; L = Cl or a neutral ligand) complexes can be approximated, to within about 0.02 Ă, by a linear function of the coordination number CN = n + m and the charge ε over the range 3 ≤ CN ≤ 6 and.−3 ≤ ε ≤2. This analytical expression provides a norm for comparing M(III)—Cl bond lengths and demonstrates that the CN is always a more important factor than ε in determining the variation in the mean bond length and that it becomes dominant when M is small. The crystal structure of (Me2NH2)4[InCl6]Cl (P21212, a = 10.156(4) Å, b = 13.007(4) Å, c = 8.751(3) Å, Z = 2) has been determined and those of (NH4)2InCl5(H2O)] (Pnma, a = 13.953(4) Å, b = 10.086(5) Å, c = 7.152(3) Å, Z = 4), K3InCl6•nH2O (I4mm, a = 15.659(8) Å, c = 18.106(5) Å, Z = 14) and (MeNH3)4[InCl6]Cl (P2/n, a = 16.113(3) Å, b = 7.446(2) Å, c = 16.163(4) Å, β = 103.75(2)°, Z = 4) redetermined. The water in K3InCl6•nH2O appears to be in part zeolitic; the hydrate examined contained more water than the monohydrate reported previously. Hydrogen bonding in these and related structures is described and discussed in detail; descriptions of the hydrogen-bonding schemes in (NH4)2[InCl5(H2O)] and (MeNH3)4[InCl6]Cl constitute the main improvement over earlier structure determinations.

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Liu, Jia-Bao, Muhammad Kashif Shafiq, Haidar Ali, Asim Naseem, Nayab Maryam et Syed Sheraz Asghar. « Topological Indices of mth Chain Silicate Graphs ». Mathematics 7, n^o 1 (4 janvier 2019) : 42. http://dx.doi.org/10.3390/math7010042.

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A topological index is a numerical representation of a chemical structure, while a topological descriptor correlates certain physico-chemical characteristics of underlying chemical compounds besides its numerical representation. A large number of properties like physico-chemical properties, thermodynamic properties, chemical activity, and biological activity are determined by the chemical applications of graph theory. The biological activity of chemical compounds can be constructed by the help of topological indices such as atom-bond connectivity (ABC), Randić, and geometric arithmetic (GA). In this paper, Randić, atom bond connectivity (ABC), Zagreb, geometric arithmetic (GA), ABC4, and GA5 indices of the mth chain silicate S L ( m , n ) network are determined.

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Беленков, Максим Евгеньевич, et Владимир Михайлович Чернов. « SIMULATION OF POLYMORPHIC VARIETIES OF HEXAGONAL GRAPHENE FUNCTIONALIZED BY HYDROXYL GROUPS ». Physical and Chemical Aspects of the Study of Clusters, Nanostructures and Nanomaterials, n^o 13 (23 décembre 2021) : 541–51. http://dx.doi.org/10.26456/pcascnn/2021.13.541.

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Моделирование кристаллической и электронной структуры слоев гексагонального графена, на поверхность которых были химически адсорбированы гидроксильные группы, было выполнено методом теории функционала плотности. В результате расчетов была установлена возможность устойчивого существования пяти структурных разновидностей COH - L слоев. Слоевая плотность изменяется от 1,62 до 1,72 мг/м. Длина водород-кислородной связи варьируется в диапазоне от 1,046 до 1,079 Å, а углерод-кислородной связи - от 1,455 до 1,465 Å. Ориентация O - H связей относительно плоскости слоев может варьироваться в зависимости от выбора элементарной ячейки слоя. Минимальной энергией сублимации и равной 18,69 эВ/(COH) обладает слой COH-L - T4, а максимальную энергию сублимации 18,93 эВ/(COH) имеет слой COH - L - T1. Электронная структура всех COH слоев характеризуется наличием прямой запрещенной зоны на уровне энергии Ферми, изменяющейся в диапазоне от 3,02 до 4,56 эВ. Computer simulation of the crystal and electronic structure of hexagonal graphene layers, on the surface of which hydroxyl groups, chemically adsorbed, was performed by the density functional theory method. As a result of calculations, the possibility of the stable existence of five structural varieties of COH - L layers was established. The layer density varies from 1,62 to 1,72 mg/m. The length of the hydrogen-oxygen bond varies in the range from 1,046 to 1,079 Å, and the carbon-oxygen bond-from 1,455 to 1,465 Å. The orientation of the -OH bonds relative to the surface of the layers can vary depending on the choice of the unit cell of the layer. Layer COH - L - T4 has the minimum sublimation energy equal to 18,69 eV/(COH), and layer COH - L - T1 has the maximum sublimation energy 18,93 eV/(COH). The electronic structure of all COH layers is characterized by the presence of a direct band gap at the Fermi energy level, varying in the range from 3,02 to 4,56 eV.

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Sweed, Ayman M. K., Mathias O. Senge, Sanaa M. Sh Atta, Dalia S. Farrag, Abdel-Rahman H. Abdel-Rahman et Yasser M. Shaker. « Synthesis of amphiphilic meso-tetrasubstituted porphyrin-L-amino acid and -heterocyclic conjugates based on m-THPP ». Journal of Porphyrins and Phthalocyanines 22, n^o 11 (18 octobre 2018) : 997–1009. http://dx.doi.org/10.1142/s1088424618500979.

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Two series of amphiphilic meso-tetrasubstituted porphyrin conjugates based on 5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin ([Formula: see text]-THPP) covalently linked to L-amino acids and heterocycles were synthesized efficiently in the context of a program targeting new photosensitizers for PDT. 5,10,15-Tris(3-hydroxyphenyl)-20-(3-oxyacetic acid)phenyl]porphyrin and the respective trihexyl ether derivatives were conjugated with polar and non-polar natural L-amino acids such as glycine, L-proline, and L-tyrosine via an amide bond linker using [Formula: see text]-tetramethyl-[Formula: see text]-(1H-benzotriazol-1-yl)uroniumhexafluorophosphate in diisopropylethylamine (HBTU/DIPEA). [Formula: see text]-THPP was also conjugated with heterocyclic systems such as indole 3-acetic acid, 4-methylthiazole-5-carboxylic acid, and thiophene-2-carboxylic acid via ester linker using [Formula: see text]-(3-dimethylaminopropyl)-[Formula: see text]-ethylcarbodiimide hydrochloride in [Formula: see text]-hydroxysuccinamide or 1-hydroxybenzotriazole (EDCI, NHS or HOBt). The members of the two series were obtained in good yields and characterized by UV-vis, HRMS MALDI-TOF, 1H NMR and 13C NMR spectroscopy.

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LOTO, Roland, et Cleophas LOTO. « Data on Evaluation of the Corrosion Inhibition Effect of L-alpha-aminoisocaproate on High Carbon Steel Corrosion in Dilute Acid Media ». Materials Science 25, n^o 4 (27 juin 2019) : 422–26. http://dx.doi.org/10.5755/j01.ms.25.4.21347.

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Corrosion inhibition performance of l-alpha-aminoisocaproate on high carbon steel in 1 M HCl solution has been studied by weight loss measurement, open circuit potential measurement, optical microscopy and ATF-FTIR spectral analysis. The results showed the inhibition performance of l-alpha-aminoisocaproate is time dependent attaining an optimal value of 85.88 % at 5.63 % l-alpha-aminoisocaproate concentration (highest concentration) after 288 h of exposure. The corrosion potential plots of the high carbon steel at 0.91 % (lowest concentration) and 5.63 % l-alpha-aminoisocaproate concentration were more electropositive than the plots at 0% l-alpha-aminoisocaproate concentration due to the effective inhibition performance of l-alpha-aminoisocaproate in counteracting the oxidation of the carbon steel in the presence of chloride anions. Identified functional groups of alcohols, phenols, primary and secondary amines and amides, carboxylic acids, alkynes, aromatics, alkenes and alkanes consisting of O–H stretch, free hydroxyl, H–bonded, N–H stretch, –C(triple bond)C–H: C–H stretch, C–H stretch and =C–H stretch bonds where responsible for the corrosion inhibition. The optical morphology of the carbon steel after 7200 s of exposure in the acid solution without l-alpha-aminoisocaproate was severely corroded in contrast to the morphology of the steel in the presence of l-alpha-aminoisocaproate which underwent minor deterioration due to the time dependent action of the inhibitor.

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Choi, S. C., Russell J. Boyd et Osvald Knop. « A 6-31G* chemistry of isoelectronic tetrahedral XL4ε and YL4ε (X = Li to F ; Y = Na to Cl ; L = H, F, Cl) species. Part 2. Energies, bond lengths, and critical radii ». Canadian Journal of Chemistry 66, n^o 9 (1 septembre 1988) : 2465–75. http://dx.doi.org/10.1139/v88-388.

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The 6-31G* ab initio treatment of isoelectronic tetrahedral species now covers the complete XL4ε and YL4ε series (X = Li to F; Y = Na to Cl; L = H, F, Cl). The optimized equilibrium molecular parameters comprise the total electronic energy E, bond lengths, critical radii rc, MO energy levels, net charges, and electron densities at the bond critical points; only the first four are discussed in this part. The stability in terms of E, of the tetrahedral species relative to some competing systems, is examined. The energy requirements associated with the transfer of electronic charge from L to the central atom are reflected in the variation of the critical radii with the oxidation state m of X and Y, with important differences between the first- and the second-row elements. In an appendix it is shown that the E~HF limit energies of isoelectronic He-core (Li+ ff.), Ne-core (Na+ ff.), and Ar-core (K+ ff.) series of ions can be represented analytically by quadratic polynomials in m to an accuracy of ~0.0023% of the E~HF limit range or better, and that these approximations for the three series are qualitatively of the type E = −a(Z − b)2.

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ALMEIDA, MARLUS QUEIROZ, LIDIANNE SALVATIERRA et JOSÉ WELLINGTON DE MORAIS. « A new species of Masteria L. Koch, 1873 (Dipluridae : Masteriinae) from Guyana ». Zootaxa 4434, n^o 2 (15 juin 2018) : 366. http://dx.doi.org/10.11646/zootaxa.4434.2.6.

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Mygalomorphs are a diverse spider group with primitive characteristics composed of the largest spider species in the world, however some species may be very small (Bond et al. 2012; Rogerio et al. 2013). The small spiders of the subfamily Masteriinae (Dipluridae, Mygalomorphae) can be found in Asia and South America (Raven 1981; Pedroso et al. 2015; WSC 2017). The subfamily is represented by two genera: Masteria L. Koch, 1873 and Striamea Raven, 1981. Masteria species can be identified by the following combination of characters: absence of cuspules in endites and labium; zero, two, six or eight eyes; and with or without paraembolic apophysis on the male palpal bulb (Raven 1981, 1985, 1991; Alayón 1995; Bertani et al. 2013; Pedroso et al. 2015). Currently, 24 species of Masteria are described, with 6 species found in South America: Masteria colombiensis, Raven, 1981 from Colombia; M. manauara Bertani, Cruz & Oliveira 2013 and M. emboaba Pedroso, Baptista & Bertani, 2015 from Brazil; M. cyclops (Simon 1889), M. tovarensis (Simon, 1889) and M. lucifuga (Simon, 1889) from Venezuela (WSC 2017). We document herein the first record and description of a new species of the genus Masteria from Guyana.

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Chuang, Yu-Chun, Chou-Fu Sheu, Gene-Hsiang Lee, Yu-Sheng Chen et Yu Wang. « Charge density studies of 3dmetal (Ni/Cu) complexes with a non-innocent ligand ». Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 73, n^o 4 (25 juillet 2017) : 634–42. http://dx.doi.org/10.1107/s2052520617007119.

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High-resolution X-ray diffraction experiments and atom-specific X-ray absorption experiments are applied to investigate a series of square planar complexes with the non-innocent ligand of maleonitriledithiolate (mnt), [S2C2(CN)2]z−, containingM—S bonds. Four complexes of (PyH)z[M(mnt)2]z−, whereM= Ni or Cu,z= 2 or 1 and PyH+= C5NH6+, were studied in order to clarify whether such one-electron oxidation–reduction, [M(mnt)2]2−/[M(mnt)2]1−, is taking place at the metal or the ligand site. Combining the techniques of metalK-,L-edge and SK-edge X-ray absorption spectroscopy with high-resolution X-ray charge density studies, it is unambiguously demonstrated that the electron redox reaction is ligand based and metal based for Ni and Cu pairs, respectively. The bonding characters in terms of topological properties associated with the bond critical points are compared between the oxidized form [ML]−and the reduced form [ML]2−. In the case of Ni complexes, the formal oxidation state of Ni remains as Ni2+and each mnt ligand carries a 2− charge in [Ni(mnt)2]2−, but only one of the ligands is formally oxidized in [Ni(mnt)2]1−. In contrast, in the case of Cu complexes, the mnt remains as 2− in both complexes, but the formal oxidation states of the metal are Cu2+and Cu3+. Bond characterizations andd-orbital populations will be presented. The complementary results of XAS, XRD and DFT calculations will be discussed. The conclusion on the redox reactions in these complexes can be firmly established.

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Balu, Perumal, Venu Kannappan et Rathinavelu Kumar. « Structural Analysis and Reactivity of Tetramethylcopper(III) Complex towards Nitrogen Donor Ligands by Density Functional Theory ». Advances in Chemistry 2016 (14 juillet 2016) : 1–8. http://dx.doi.org/10.1155/2016/8962695.

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DFT studies are carried out on some ligand substitution reactions of tetramethylcuprate(III) (TMC) complex with five different nitrogen donor ligands as probe ligands. The geometry optimization of the possible nine model systems and the frequency calculations are carried out at DFT level using LANL2DZ basis set. The selected structural parameters of optimized model systems of Cu(III) complexes are reported and discussed. The change in the M-C bond distance in TMC due to substitution by probe ligands is explained. Natural population analysis (NPA) has been carried out for these complexes to establish the charge of copper in these complexes. A detailed population analysis of valence orbitals of copper complexes supports the existence of d8 configuration for metal in complexes and there is evidence for the transmission of electrons from the nitrogen donor atom to dxy, dx2-y2, and 4s orbitals. Bond order calculations have been performed for all the complexes to probe the interaction between Cu(III) and the ligand. The stability of the complexes is ascertained from the computed chemical hardness. In order to understand the nature of Cu(III)-L (L = N donors) and Cu(III)-Me bonds in different complexes, Energy Decomposition Analysis (EDA) has been carried out for all the complexes chosen in the theoretical study. Thermodynamic feasibility of these reactions is investigated in terms of free energy changes of these reactions.

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O’Hair, Richard A. J. « Gas-phase studies of metal catalyzed decarboxylative cross-coupling reactions of esters ». Pure and Applied Chemistry 87, n^o 4 (1 avril 2015) : 391–404. http://dx.doi.org/10.1515/pac-2014-1108.

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AbstractMetal-catalyzed decarboxylative coupling reactions of esters offer new opportunities for formation of C–C bonds with CO2as the only coproduct. Here I provide an overview of: key solution phase literature; thermochemical considerations for decarboxylation of esters and thermolysis of esters in the absence of a metal catalyst. Results from my laboratory on the use of multistage ion trap mass spectrometry experiments and DFT calculations to probe the gas-phase metal catalyzed decarboxylative cross-coupling reactions of allyl acetate and related esters are then reviewed. These studies have explored the role of the metal carboxylate complex in the gas phase decarboxylative coupling of allyl acetate proceeding via a simple two-step catalytic cycle. In Step 1, an organometallic ion, [CH3ML]+/–(where M is a group 10 or 11 metal and L is an auxillary ligand), is allowed to undergo ion-molecule reactions with allyl acetate to generate 1-butene and the metal acetate ion, [CH3CO2ML]+/–. In Step 2, the metal acetate ion is subjected to collision-induced dissociation to reform the organometallic ion and thereby close the catalytic cycle. DFT calculations have been used to explore the mechanisms of these reactions. The organometallic ions [CH3CuCH3]–, [CH3Cu2]+, [CH3AgCu]+and [CH3M(phen)]+(where M = Ni, Pd and Pt) all undergo C–C bond coupling reactions with allyl acetate (Step 1), although the reaction efficiencies and product branching ratios are highly dependant on the nature of the metal complex. For example, [CH3Ag2]+does not undergo C–C bond coupling. Using DFT calculations, a diverse range of mechanisms have been explored for these C–C bond-coupling reactions including: oxidative-addition, followed by reductive elimination; insertion reactions and SN2-like reactions. Which of these mechanisms operate is dependant on the nature of the metal complex. A wide range of organometallic ions can be formed via decarboxylation (Step 2) although these reactions can be in competition with other fragmentation channels. DFT calculations have located different types of transition states for the formation of [CH3CuCH3]–, [CH3Cu2]+, [CH3AgCu]+and [CH3M(phen)]+(where M = Ni, Pd and Pt). Of the catalysts studied to date, [CH3Cu2]+and [CH3Pd(phen)]+are best at promoting C–C bond formation (Step 1) as well as being regenerated (Step 2). Preliminary results on the reactions of [C6H5M(phen)]+(M = Ni and Pd) with C6H5CO2CH2CH=CH2and C6H5CO2CH2C6H5are described.

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Law, David J., Glen Bigam et Ronald G. Cavell. « Preparation and properties of rhodium(I) and iridium(I) diolefin complexes of heterodifunctional phosphorus–imine chelating ligands and a related iminophosphine. 103Rh NMR parameters of the rhodium complexes obtained via indirect two-dimensional 31P, 103Rh{1H} NMR spectroscopy ». Canadian Journal of Chemistry 73, n^o 5 (1 mai 1995) : 635–42. http://dx.doi.org/10.1139/v95-082.

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Treatment of [M(cod)Cl]2 (M = Rh, Ir) with iminophosphoranophosphine ligands of the type Ph2PQP(Ph2)=NSiMe3 (Q = CH2, CH2CH2, 1,2-C6H4) afforded the new metallacycles [Formula: see text] through elimination of Me3SiCl, ultimately "anchoring" the ligand to the metal through a metal–nitrogen σ bond. The phosphine functionality completes the chelate. Cationic complexes of the type [M(cod)L2]+PF6− (M = Rh or Ir; L2 = Ph2PQPPh2NR where Q = CH2, CH(CH3), 1,2-C6H4, and R = p-C6F4CN, C6H2F(NO2)2, and C6H3(NO2)2 or L = Ph2PN=C(H)Ph) were readily prepared by treating [M(cod)Cl]2 with L2 and KPF6. The detection and chemical shift determination of the insensitive 103Rh nucleus was easily accomplished via 31P detected indirect two-dimensional 31P, 103Rh{1H} NMR spectroscopy. The 103Rh, 1H, and 31P NMR data are discussed. Keywords: rhodium, iridium, phosphoranimine, iminophosphine, Rh NMR.

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Ching, Yao-Cheng, Che-Sheng Chung, Cheng-Yen Huang, Yu Hsia, Yin-Liang Tang et Wen Chang. « Disulfide Bond Formation at the C Termini of Vaccinia Virus A26 and A27 Proteins Does Not Require Viral Redox Enzymes and Suppresses Glycosaminoglycan-Mediated Cell Fusion ». Journal of Virology 83, n^o 13 (15 avril 2009) : 6464–76. http://dx.doi.org/10.1128/jvi.02295-08.

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ABSTRACT Vaccinia virus A26 protein is an envelope protein of the intracellular mature virus (IMV) of vaccinia virus. A mutant A26 protein with a truncation of the 74 C-terminal amino acids was expressed in infected cells but failed to be incorporated into IMV (W. L. Chiu, C. L. Lin, M. H. Yang, D. L. Tzou, and W. Chang, J. Virol 81:2149-2157, 2007). Here, we demonstrate that A27 protein formed a protein complex with the full-length form but not with the truncated form of A26 protein in infected cells as well as in IMV. The formation of the A26-A27 protein complex occurred prior to virion assembly and did not require another A27-binding protein, A17 protein, in the infected cells. A26 protein contains six cysteine residues, and in vitro mutagenesis showed that Cys441 and Cys442 mediated intermolecular disulfide bonds with Cys71 and Cys72 of viral A27 protein, whereas Cys43 and Cys342 mediated intramolecular disulfide bonds. A26 and A27 proteins formed disulfide-linked complexes in transfected 293T cells, showing that the intermolecular disulfide bond formation did not depend on viral redox pathways. Finally, using cell fusion from within and fusion from without, we demonstrate that cell surface glycosaminoglycan is important for virus-cell fusion and that A26 protein, by forming complexes with A27 protein, partially suppresses fusion.

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Kunze, Udo, et Roland Burghardt. « Phosphinsubstituierte Chelatliganden, XXV [1] Diastereoselektive Komplexierung chiraler Phosphinothioformamide mit entferntem Asymmetriezentrum ». Zeitschrift für Naturforschung B 42, n^o 7 (1 juillet 1987) : 860–66. http://dx.doi.org/10.1515/znb-1987-0711.

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Abstract For further studies of the diastereoselective complex formation of ambidentate chiral chelating ligands, we prepared the racemic phosphinothioformamides. Ph2P(X )C(S)NHC*HR 1R2, with X = 2e- (R1 = Ph,R2 = Et: 1a;R1 = Ph,R2 = iPr:2a; R2 = Me,R2 = Et:3a) and X = O (1b ,2b ) according to a previously reported route. The coordination of 1a -3a to CpM (CO)3Cl (M = Mo, W) in m ethanol gives the diastereomeric P.S-chelate complexes, (Mo: 4-6, W: 7-9). In solution, epimerisation proceeds to an equilibrium ratio of B/A = 1,5 in case of 4, 5, 7, and 8, but less than 1,1 with 6 and 9. A reduced diastereoselectivity (d.e. 10 -20%) is also observed during the formation of the analogous molybdenum complexes 10a-d with phosphine ligands derived from α-amino acid esters. Ph2PC(S)NHC*H(R)COOMe [R = Me (L-Ala), CH2Ph (L-Phe). CHMe2 (L-Val). Ph (D-phenylglycine)]. The results indicate a significant asymmetric induction despite of the four bond distance of the chiral centres.

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Herold, D. A., P. K. Anonick, M. Kinter et F. G. Hayden. « Measurement of rimantadine in plasma by capillary gas chromatography/mass spectrometry with a deuterium-labeled internal standard. » Clinical Chemistry 34, n^o 8 (1 août 1988) : 1597–99. http://dx.doi.org/10.1093/clinchem/34.8.1597.

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Abstract Rimantadine is a synthetic antiviral agent used in prophylaxis and in treating the early stages of uncomplicated influenza A illness. We describe a stable isotope-dilution assay involving capillary gas chromatography/mass spectrometry. We used 200 ng of d3-rimantadine, added to 1 mL of plasma, as the internal standard. The rimantadine was extracted from the plasma with a Bond-Elut CN column, the column was washed with water, and the rimantadine was eluted with methanol, dried, and treated to form the t-butyldimethylsilyl derivative. The mass spectrometer was operated in the selected ion monitoring mode. Ions at m/z 236 and m/z 239 were monitored, corresponding to the loss of C4H9 from the rimantadine derivative and d3-rimantadine, respectively. Within-run precision (CVs) ranged from 8.9% at 29 micrograms/L to 3.2% at 1666 micrograms/L. Corresponding data for between-run precision were 5.4% and 1.7%. Treated volunteers (n = 86) provided plasma samples with a concentration range of 153 to 1127 micrograms/L. This simplified method allows rapid, precise assay of rimantadine in plasma.

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Boonanunwong, Phachongkit, Pimpawee Keawpapasson, Chayanee Tippayasam, Parjaree Thavorniti, Prinya Chindaprasirt et Duangrudee Chaysuwan. « Properties of Geopolymer Paste from Fly Ash Blended with Metakaolin as Pervious Concrete ». Key Engineering Materials 690 (mai 2016) : 179–86. http://dx.doi.org/10.4028/www.scientific.net/kem.690.179.

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The purpose of this research was to study pervious geopolymer concrete with different amounts of lignite fly ash (F), metakaolin (M), sodium silicate (NS) and 8 mol/L sodium hydroxide (NH) solution. Constant NS/NH ratio of 0.5, three alkali liquid/pozzolan (L/P) ratios viz., 0.5, 0.6 and 0.7 and pozzolan to coarse aggregate ratio of 1:8 were used. The compressive strengths of 50×50×50 mm3 cube specimens were tested at the age of 28 days. In addition, compressive strengths of 100 mm in diameter and 200 mm in height cylindrical specimens were tested at the age of 7, 14, 21 and 28 days. The chemical compositions and microstructures of specimens were characterized by X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM), respectively.The mixture with 50%F+50%M and L/P ratio of 0.7 was the best proportion for pervious geopolymer concrete according to the compressive strength, good permeability and microstructural images. The bond of Si-O-Al and Si-O-Si characterized by Fourier Transform Infrared Spectroscopy (FTIR) spectra confirmed the developed geopolymeric structure.

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Basu, Manju, Patrick Kelly, Peter O'Donnell, Maria Miguel, Mathew Bradley, Sandro Sonnino, Sipra Banerjee et Subhash Basu. « Ceramide Glycanase Activities in Human Cancer Cells ». Bioscience Reports 19, n^o 5 (1 octobre 1999) : 449–60. http://dx.doi.org/10.1023/a:1020220524180.

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Ceramide glycanase (CGase) activities have been detected in different human tumor cells (colon, carcinoma Colo-205; neuroblastoma, IMR-32; breast cancer lines, SKBr3 and MCF7). However, the level of enzymatic activity is lower in these cells compared to that present in other mammalian tissues reported before (Basu, M., Kelly, P., Girzadas, M. A., Li, Z., and Basu, S. Methods Enzymol. (in press)). The majority of CGase activity was found in the 100,000g soluble supernatant fraction isolated from all these cell lines and tissues. Using the soluble enzyme, the requirement for optimum CGase activity was found to be consistent with previous observations found for rat and rabbit tissues (Basu, M., Dastgheib, S., Girzadas, M. A., O'Donnell, P. H., Westervelt, C. W., Li, Z., Inokuchi, J. I., and Basu, S. (1998) Acta Pol. Biochim. 42:327). The CGase activities from both Colo-205 and IMR-32 cells are optimum at a protein to detergent ratio of one. All the mammalian CGases, including human cancer cells, show an optimum pH between 5.5 and 5.8 in sodium acetate buffer. The CGase activities from cancer cells are found to be cation-independent; however, mercury, zinc, and copper ions seem to inhibit the enzyme activity substantially in both tumor cells lines. The mercury ion inhibition of CGase activities from all different sources indicates a possible structural homology in the CGase proteins. Radiolabeled substrates, labeled at the sphingosine double bond or at the 3-position of sphingosine without modifying double bond of sphingosine were used in this investigation. Both were active substrates with all enzyme preparations isolated from different cancer cells (apparent Km, 500 μM for nLcOse5[3H-DT]Cer and 350 μM for GgOse4[sph-3-3H]Cer with Colo-205 enzyme). Structural analogues of ceramide and sphingosine (L-PPMP, L-PDMP, alkylamines, and Tamoxifen) inhibited cancer cell CGase activities in vitro.

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Chiba, Erika Kiyoko, André Luiz Fraga Briso, Rodrigo Sversut De Alexandre, Mariana Dias Moda, Paulo Henrique Dos Santos et Ticiane Cestari Fagundes. « Bond strength to dentin of low-shrinkage composite resin restorations after thermocycling and mechanical loading ». ARCHIVES OF HEALTH INVESTIGATION 9, n^o 6 (22 décembre 2020) : 641–47. http://dx.doi.org/10.21270/archi.v9i6.4906.

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Objective: This study evaluated the in vitro bond strength of Class I restorations to dentin, using four restorative systems. Materials and Methods: Ninety-six molars were used, and a Class I cavity was prepared on the occlusal surface. Next, tooth were divided into 4 groups (n=24), Single Bond Universal + Filtek Z350 XT (SFZ); Single Bond Universal + Filtek Bulk Fill (SFB); AdheSE + Tetric N-Ceram (ATC) and AdheSE + Tetric N-Ceram Bulk Fill (ATB).Thus, the teeth were divided into 3 subgroups (n = 8): 1) storage in water for 24h (control); 2) submitted to thermocycling; 3) mechanical loading. After challenges, teeth were cut into beams 0.8mm², being 3 to 4 sticks per tooth. Then, the specimens were submitted to microtensile testing (μTBS). The data were submitted to Kruskal Wallis and Dunn tests for multiple comparisons, with a significance level of 5%. Results: No significant differences were observed between the restorative systems after thermal cycling challenge (p> 0.05). However, the SFZ group presented the highest μTBS values, with a statistical difference when compared to the ATC, SFB and ATB groups after mechanical loading (p> 0.05). Conclusion: The dentin bond strength of low-shrinkage composite resin restorations was negatively influenced by mechanical loading in class I cavities. Descriptors: Dental Materials; Permanent Teeth; Resin Composite; Restoration; Substrate Cycling. References Bedran-Russo A, Leme-Kraus AA, Vidal CMP, Teixeira EC. An overview of dental adhesive systems and the dynamic tooth-adhesive interface. Dent Clin N Am. 2017; 61:713-31. Rosatto CM, Bicalho AA, Veríssimo C, Bragança GF, Rodrigues MP, Tantbirojn D, et al. Mechanical properties, shrinkage stress, cuspal strain and fracture resistance of molars restored with bulk-fill composites and incremental filling technique. J Dent. 2015;43:1519-28. Ilie N, Bucuta S, Draenert M. Bulk-fill resin-based composites: an in vitro assessment of their mechanical performance. Oper Dent. 2013;38:18-25. Caixeta RV, Guiraldo RD, Kaneshima EN, Barbosa AS, Picolotto CP, Lima AE, et al. Push-out bond strength of restorations with bulk-fill, flow, and conventional resin composites. ScientificWorldJournal 2015; 2015:452976. Amaral FL, Colucci V, Palma-Dibb RG, Corona SA. Assessment of in vitro methods used to promote adhesive interface degradation: a critical review. J Esthet Restor Dent. 2007;19:340-53. Daneshkazemi A, Davari A, Akbari MJ, Davoudi A, Badrian H. Effects of thermal and mechanical load cycling on the dentin microtensile bond strength of Single Bond-2. J Int Oral Health 2015;7:9-13. Poptani B, Gohil KS, Ganjiwale J, Shukla M.Microtensile dentin bond strength of fifth with five seventh-generation dentin-bonding agents after thermocycling: An in vitro study. Contemp Clin Dent. 2012;3(Suppl 2):S167-71. Heintze SD, Monreal D, Peschke A. Marginal quality of Class II composite restorations placed in bulk compared to an incremental technique: Evaluation with SEM and Stereomicroscope. J Adhes Dent. 2015;17:147-54. Soares CJ, Pizi EC, Fonseca RB, Martins LR. Influence of root embedment material and periodontal ligament simulation on fracture resistance tests. Braz Oral Res. 2005;19:11-6. Aguiar TR, André CB, Correr-Sobrinho L, Arrais CA, Ambrosano GM, Giannini M. Effect of storage times and mechanical load cycling on dentin bond strength of conventional and self-adhesive resin luting cements. J Prosthet Dent. 2014;111:404-10. Assunção WG, Jorge JR, Dos Santos PH, Barão VA, Gomes EA, Delben JA. The effect of mechanical cycling and different misfit levels on Vicker's microhardness of retention screws for single implant-supported prostheses J Prosthodont. 2011;20:523-27. De Munck J, Luehrs AK, Poitevin A, Van Ende A, Van Meerbeek B. Fracture toughness versus micro-tensile bond strength testing of adhesive-dentin interfaces. Dent Mater. 2013;29:635-44. Armstrong S, Breschi L, Özcan M, Pfefferkorn F, Ferrari M, Van Meerbeek B. Academy of Dental Materials guidance on in vitro testing of dental composite bonding effectiveness to dentin/enamel using micro-tensile bond strength (μTBS) approach. Dent Mater. 2017;33:133-43. Tjäderhane L, Nascimento FD, Breschi L, Mazzoni A, Tersariol IL, Geraldeli S et al. Strategies to prevent hydrolytic degradation of the hybrid layer- A review. Dent Mater. 2013; 29:999-11. Taneja S, Kumar P, Kumar A. Comparative evaluation of the microtensile bond strength of bulk fill and low shrinkage composite for different depths of Class II cavities with the cervical margin in cementum: An in vitro study. J Conserv Dent. 2016;19:532-35. Campos EA, Ardu S, Lefever D, Jassé FF, Bortolotto T, Krejci iI. Marginal adaptation of class II cavities restored with bulk-fill composites. J Dent. 2014;42;575-81. Mandava J, Vegesna DP, Ravi R, Boddeda MR, Uppalapati LV, Ghazanfaruddin MD. Microtensile bond strength of bulk-fill restorative composites to dentin. J Clin Exp Dent. 2017;9:e1023-28. Costa T, Rezende M, Sakamoto A, Bittencourt B, Dalzochio P, Loguercio AD, et al. Influence of adhesive type and placement technique on postoperative sensitivity in posterior composite restorations. Oper Dent. 2017;42:143-54. Jayaseel A, Niranjan N, Pamidi H, Suryakanth MB. Comparative evaluation of shear bond strength of universal dental adhesives - An in vitro study. J Clin Exp Dent. 20171;9:e892-e96. Silame FDJ, Geraldeli GP, Sinhoreti MAC, Pires-de-Souza FCP, Roulet JF, Geraldeli S. Dentin µTBS and hardness of bulk-fill and conventional composites placed in a box-shaped cavity preparation. J Adhes Dent. 2017;19:395-400. Han SH, Park SH. Comparison of internal adaptation in class II bulk-fill composite restorations using micro-CT. Oper Dent. 2017;42:203-14. Al-Harbi F, Kaisarly D, Michna A, ArRejaie A, Bader D, El Gezawi M. Cervical interfacial bonding effectiveness of class II bulk versus incremental fill resin composite restorations Oper Dent. 2015;40:622-35. Amaral FL, Colucci V, Palma-Dibb RG, Corona SA. Assessment of in vitro methods used to promote adhesive interface degradation: a critical review J Esthet Restor Dent. 2007; 19:340-53. Lezaja Zebic M, Dzeletovic B, Miletic V. Microtensile bond strength of universal adhesives to flat versus Class I cavity dentin with pulpal pressure simulation J Esthet Restor Dent. 2018;30:240-48. Yazici AR, Antonson SA, Kutuk ZB, Ergin E. Thirty-six-month clinical comparison of bulk fill and nanofill composite restorations. Oper Dent. 2017;42:478-85.

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Lassila, Lippo, Anna-Maria Le Bell-Rönnlöf, Milla Lahdenperä et Pekka Vallittu. « Bond Strength of Composite Resin Luting Cements to Fiber-reinforced Composite Root Canal Post ». Journal of Contemporary Dental Practice 8, n^o 6 (2007) : 17–24. http://dx.doi.org/10.5005/jcdp-8-6-17.

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Abstract Aims The aim of this study was to compare the attachment of different composite resin luting cements to a fiber-reinforced composite (FRC) post with a semi-interpenetrating polymer network polymer matrix. Methods and Materials Six different brands of composite resin luting cement stubs were applied on the surface of FRC post material and light-cured for 40 seconds. Shear bond strengths of luting cement stubs were measured using a universal testing machine. Results The differences in shear bond strengths between the cements were not statistically significant. Conclusion All of the tested composite resin luting cements provided acceptable attachment to the tested FRC post. The tested FRC post material is suitable to use with different composite resin luting cements. Citation Le Bell-Rönnlöf AM, Lahdenperä M, Lassila L, Vallittu P. Bond Strength of Composite Resin Luting Cements to Fiber-reinforced Composite Root Canal Post. J Contemp Dent Pract 2007 September; (8)6:017-024.

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Garcia, Rubens Nazareno, Mario Fernando de Goes et Marcelo Giannini. « Effect of Water Storage on Bond Strength of Self-etching Adhesives to Dentin ». Journal of Contemporary Dental Practice 8, n^o 7 (2007) : 46–53. http://dx.doi.org/10.5005/jcdp-8-7-46.

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Abstract Aim The objective of this study was to evaluate the bond strength of self-etching adhesive systems one week and one year after storage in water. Methods and Materials Fragments from the buccal surfaces of 45 bovine teeth were prepared (12 mm in length X 5 mm in width X 1.0 mm in thickness). Dentin surfaces were wet-abraded with 600-grit SiC paper to create a standardized smear layer. Samples were randomly assigned to 18 experimental groups (n=5), according to nine adhesive systems tested (Single Bond; Adper Prompt L-Pop; iBond; One-Up Bond F; Xeno III; Clearfil SE Bond; Optibond Solo Plus SE; Tyrian SPE/One-Step Plus; and UniFil Bond) and two waterstorage times (one week and one year). Adhesives were applied according to the manufacturers’ instructions. Z250 composite was applied into the molds to fill up the internal diameter volume of a Tygon tubing mold (1.0 mm high / 0.7 mm internal diameter). Micro-shear bond strengths were determined using an apparatus attached to an Instron Universal Testing Machine (0.5 mm/min). Data were statistically analyzed using a twoway analysis of variance (ANOVA) and the Tukey's test (5%). Results One year after water storage the dentin bond strength of all adhesive systems reduced significantly, except for One-Up Bond F. Conclusion Water-storage time decreased the bond strength for most dentin bonding agents tested. Citation Garcia RN, de Goes MF, Giannini M. Effect of Water Storage on Bond Strength of Self-etching Adhesives to Dentin. J Contemp Dent Pract 2007 November; (8)7:046-053.

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Debarbieux, Laurent, et Jon Beckwith. « On the Functional Interchangeability, Oxidant versus Reductant, of Members of the Thioredoxin Superfamily ». Journal of Bacteriology 182, n^o 3 (1 février 2000) : 723–27. http://dx.doi.org/10.1128/jb.182.3.723-727.2000.

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ABSTRACT Escherichia coli thioredoxin 1 has been characterized in vivo and in vitro as one of the most efficient reductants of disulfide bonds. Nevertheless, under some conditions, thioredoxin 1 can also act in vivo as an oxidant, promoting formation of disulfide bonds in the cytoplasm (E. J. Stewart, F. Åslund, and J. Beckwith, EMBO J. 17:5543–5550, 1998). We recently showed that when a signal sequence is attached to thioredoxin 1 it is exported to the periplasm, where it can also act as an oxidant, replacing the normal periplasmic catalyst of disulfide bond formation, DsbA, in oxidizing cell envelope proteins (L. Debarbieux and J. Beckwith, Proc. Natl. Acad. Sci. USA 95:10751–10756, 1998). Here we report pulse-chase studies of the efficiency of disulfide bond formation in strains exporting thioredoxin 1 and more-oxidizing variants of it. While the exported thioredoxin 1 itself substantially speeds up the kinetics of disulfide bond formation, a version of this protein containing the DsbA active site exhibits kinetics that are indistinguishable from those of the DsbA protein itself. Further, we confirm the findings of Jonda et al. (S. Jonda, M. Huber-Wunderlich, R. Glockshuber, and E. Mössner, EMBO J. 18:3271–3281, 1999), who found that DsbB is responsible for the oxidation of exported thioredoxin 1, and we report the detection of a disulfide-bonded DsbB-thioredoxin 1 complex. Finally, we have found that under conditions of high-level expression of exported thioredoxin 1, the protein can act as both an oxidant and a reductant.

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NGUYEN, VAN LIEN, et ENRIQUE CANESSA. « FINITE-SIZE SCALING IN TWO-DIMENSIONAL CONTINUUM PERCOLATION MODELS ». Modern Physics Letters B 13, n^o 17 (20 juillet 1999) : 577–83. http://dx.doi.org/10.1142/s0217984999000737.

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We test the universal finite-size scaling of the cluster mass order parameter in two-dimensional (2D) isotropic and directed continuum percolation models below the percolation threshold by computer simulations. We found that the simulation data in the 2D continuum models obey the same scaling expression of mass M to sample size L as generally accepted for isotropic lattice problems, but with a positive sign of the slope in the ln–ln plot of M versus L. Another interesting aspect of the finite-size 2D models is also suggested by plotting the normalized mass in 2D continuum and lattice bond percolation models versus an effective percolation parameter, independent of the system structure (i.e., lattice or continuum) and of the possible directions allowed for percolation (i.e., isotropic or directed) in regions close to the percolation thresholds. Our study is the first attempt to map the scaling behavior of the mass for both lattice and continuum model systems into one curve.

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,, Fernande D., Corinne Bensimon et André L. Beauchamp. « Multinuclear NMR spectra of [Pt(L)Cl3]− (L = pyridine derivatives) complexes and crystal structure of trans-Pt(2,6-di(hydroxymethyl)pyridine)2Cl2•2H2O ». Canadian Journal of Chemistry 74, n^o 11 (1 novembre 1996) : 2121–30. http://dx.doi.org/10.1139/v96-241.

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Complexes of the type [Pt(L)Cl3]− (L = pyridine derivative) were synthesized and studied by 13C and 195Pt NMR spectroscopies. The 195Pt signals were observed between −1720 and −1897 ppm. No correlation between the δ(Pt) and the pKa of the protonated pyridine derivatives was found. The chemical shifts vary with the substituents on the pyridine ligand. Compounds with substituents in ortho positions were observed at lower fields, except for complexes containing hydroxy or amine groups. The latter compounds were observed at higher fields, close to the signals of the Pt-unsubstituted pyridine compound. These results were explained in terms of the solvent effect. The chemical shifts δ(C) and the coupling constants J(13C–195Pt) were measured and the results interpreted with a view of obtaining information on the nature of the Pt—N bond. The possibility of π-bonding between platinum and the pyridine ligand is examined. The conformation of the pyridine ring in relation to the platinum plane and the energies of the rotation barriers around the Pt—N bond in these types of platinum(II) complexes are briefly discussed. The crystal structure of trans-Pt(2,6-(HOCH2)2py)2Cl2•2H2O was determined by X-ray diffraction. The compound is monoclinic, C2/m, a = 7.022(6), b = 15.646(13), c = 8.344(10) Å, β = 93.35(8)°, Z = 2, R = 0.037. The platinum atom is located at the junction of the twofold axis and the mirror plane, the N atoms and the para-C atom of the pyridine ring are situated on the twofold axis, and the chloride ligands are on the mirror plane. The compound crystallizes with molecules of water, which are H-bonded to the hydroxy groups. The Pt—Cl bond distance is 2.306(2) Å, and that of the Pt—N bond is 2.041 (6) Å. The dihedral angle between the platinum and the pyridine planes is 79.8°. Key words: platinum, pyridine derivatives, NMR, crystal structure.

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