Articoli di riviste: "Enantiomeric purification"

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Choi, Hwa-Jin, e Dong-Yeun Koh. "Homochiral Metal-Organic Framework Based Mixed Matrix Membrane for Chiral Resolution". Membranes 12, n. 4 (24 marzo 2022): 357. http://dx.doi.org/10.3390/membranes12040357.

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Efficient separation of enantiomers is critical in the chemical, pharmaceutical, and food industries. However, conventional separation methods, such as chromatography, crystallization, and enzymatic kinetic resolution, require high energy costs and specific reaction conditions for the efficient purification of one enantiomer. In contrast, membrane-based processes are continuous processes performed with less energy than conventional separation processes. Enantioselective polymer membranes have been developed for the chiral resolution of pharmaceuticals; however, it is difficult to generate sufficient enantiomeric excess (ee) with polymer membranes. In this work, a homochiral filler of L-His-ZIF-8 was synthesized by the ligand substitution method and mixed with polyamide(imide) (i.e., Torlon®) to fabricate an enantioselective mixed-matrix membrane (MMM). The enantio-selective separation of R-1-phenylethanol over S-1-phenylethanol was demonstrated with a 25 wt% loaded L-His-ZIF-8/Torlon® MMM in an organic solvent nanofiltration (OSN) mode.

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Xu, Hong Yu, Zhao Jie Cui e Jing Liu. "Enantioselective Trace Analysis of Polychlorinated Biphenyl Enantiomers in Soils by GC-ECD/MS". Advanced Materials Research 183-185 (gennaio 2011): 1928–32. http://dx.doi.org/10.4028/www.scientific.net/amr.183-185.1928.

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A simple method for qualitative and quantitative determination of PCB95, 132, 149 and 174 enantiomers in soils and sediments using GC-ECD/MS was proposed. On the promise of good purification efficiency, high recovery and easy operability, H2SO4 washing and a multi-layer column filled with 1 g anhydrous sodium sulfate, 2 g 10% silver nitrate-impregnated silica gel, 4 g 3.3% water-deactivated silica gel and 1.5 g anhydrous sodium sulfate were selected as purification procedures. The chromatographic conditions were optimized to obtain the best enantiomeric separation. Complete baseline separations were achieved for PCB95, 132 and 149, as well as approximate baseline separation was obtained for PCB174. This method was proved to have highly satisfactory accuracy, precision and sensitivity with mean recoveries of target PCB enantiomers in range of 71.42−80.12% and RSD<6%. The detection limits of the method were 11.37−25.36 pg•g−1.

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Wzorek, Alicja, Magdalena Kwiatkowska, Mariusz Urbaniak e Barbara Gawdzik. "PROCES SAMO-DYSPROPORCJONOWANIA ENANCJOMERÓW PODCZAS CHROMATOGRAFII KOLUMNOWEJ". Wiadomości Chemiczne 77, n. 5 (9 giugno 2023): 425–48. https://doi.org/10.53584/wiadchem.2023.05.2.

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The review is devoted to self-disproportionation of enantiomers (SDE) phenomenon which has been observed for many different classes of chiral organic compounds. The SDE phenomenon occurs when the fractionation of an enantioenriched sample due the application of a physicochemical process under achiral conditions results in the variation of the proportion of the enantiomers present across the fractions, though the overall composition in terms of the sample ee remains unchanged. The SDE process can be considered in terms of separating the excess enantiomer from the racemate. The basic terminology related to SDE was described. The formation of the SDE under chromatographic conditions is the result of an association process occurring in a solution of a chiral, non-racemic compound. Information on preferred interactions leading to homo-/heterochiral supramolecules can be provided by quantum chemical calculations, NMR spectroscopy and comparison of crystal structures of the racemic and enantiomeric crystals. Several examples of the chromatographic experiments with different classes of compounds were given in two purposes 1) to highlight the possibility of application SDE during column chromatography as the method for enantiopurification of the chiral, non-racemic compounds; 2) to demonstrate that a standard workup (chromatographic purification, evaporation) can alter the stereochemical outcome of asymmetric reactions

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Vieira, Lucas C. C., Bianca T. Matsuo, Lorena S. R. Martelli, Mayara Gall, Marcio W. Paixão e Arlene G. Corrêa. "Asymmetric synthesis of new γ-butenolides via organocatalyzed epoxidation of chalcones". Organic & Biomolecular Chemistry 15, n. 29 (2017): 6098–103. http://dx.doi.org/10.1039/c7ob00165g.

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Bosits, Miklós Hunor, Emese Pálovics, János Madarász e Elemér Fogassy. "New Discoveries in Enantiomeric Separation of Racemic Tofisopam". Journal of Chemistry 2019 (7 aprile 2019): 1–10. http://dx.doi.org/10.1155/2019/4980792.

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Resolution process of tofisopam has been re-evaluated now based on our new investigations. Originally, it was carried out in the water-chloroform system, where the intermediate salt of high diastereomeric excess was described as (R)-TOF·(R,R)-DBTA·(H2O)3. Opposed to previous assumptions, we have actually found that a different solvate composition, (R)-TOF‐(R,R)-DBTA-CHCl3, forms with chloroform, in which molecules of CHCl3 are captured and held with different strengths. Moreover, resolution of TOF with (R,R)-DBTA is possible (and favourable) in water-free solvent and solvent mixture. However, presence of chloroform is essential, and thus, chloroform is also a suitable solvent alone. Among the tested solvents, toluene-chloroform mixture results in the highest resolution efficiency, while the highest enantiomeric purity was achieved when acetonitrile was in the system too. Resolution efficiency can be also increased by using the quasi-racemic resolving agent and thermodynamic control. Purification of enantiomeric mixtures was examined, and recrystallization of the diastereomeric salt was found to be the most efficient solution. Instructive behaviour of the complex enantiomer-conformer system of tofisopam is emphasized.

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Zheng, Ming. "(Invited) Purification of Enantiomeric Pairs of DNA-Wrapped Carbon Nanotubes and Their Use in Bilateral Chiral Sensing". ECS Meeting Abstracts MA2024-01, n. 8 (9 agosto 2024): 833. http://dx.doi.org/10.1149/ma2024-018833mtgabs.

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This presentation will focus on our recent progress in purifying enantiomeric pairs of DNA-wrapped carbon nanotubes (DNA-CNTs) via the aqueous two-phase extraction method. We will also discuss a potential application of enantiomeric pairs of DNA-CNTs in bilateral chiral sensing.

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Varga e Bagi. "Preparation of Enantiomerically Enriched P-Stereogenic Dialkyl-Arylphosphine Oxides via Coordination Mediated Optical Resolution". Symmetry 12, n. 2 (2 febbraio 2020): 215. http://dx.doi.org/10.3390/sym12020215.

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Optical resolution of several dialkyl-arylphosphine oxides was elaborated using the Ca2+ salt of (−)-O,O’-dibenzoyl-(2R,3R)-tartaric acid as the resolving agent. The conditions of crystallization and purification of the enantiomerically enriched phosphine oxides were optimized. Ethyl-phenyl-propylphosphine oxide and butyl-methyl-phenylphosphine oxide were prepared with an enantiomeric excess higher than 93%, whereas, three other dialkyl-arylphosphine oxides were obtained with an enantiomeric excess of 37–85%. It was also found that the sterically demanding alkyl chains hinder the formation of stable diastereomeric complexes, which consequently led to less efficient resolution procedures.

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Frishman, Einat, Moshe Shapiro, David Gerbasi e Paul Brumer. "Enantiomeric purification of nonpolarized racemic mixtures using coherent light". Journal of Chemical Physics 119, n. 14 (8 ottobre 2003): 7237–46. http://dx.doi.org/10.1063/1.1603732.

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Meyer, Elazar. "Optimization of Process for Enzymatic Resolution of Racemic Amines using Continuous Flow Bioreactor". Technium: Romanian Journal of Applied Sciences and Technology 20 (22 marzo 2024): 56–79. http://dx.doi.org/10.47577/technium.v20i.10794.

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The optimization of enzymatic process for the resolution of chemically and pharmaceutically important racemic amines is described using a continuous flow bioreactor. Also described are the isolation and purification methods of the reaction products and the various parameters affecting the optimal reaction conditions for the enzymatic resolution to afford the products in high chemical purity and enantiomeric excess (ee) of over 90%.

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Gerbasi, David, Paul Brumer, Ioannis Thanopulos, Petr Král e Moshe Shapiro. "Theory of the two step enantiomeric purification of 1,3 dimethylallene". Journal of Chemical Physics 120, n. 24 (22 giugno 2004): 11557–63. http://dx.doi.org/10.1063/1.1753552.

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Belardini, Alessandro, Emilija Petronijevic, Ramin Ghahri, Daniele Rocco, Fabiana Pandolfi, Concita Sibilia e Leonardo Mattiello. "Fluorescence Spectroscopy of Enantiomeric Amide Compounds Enforced by Chiral Light". Applied Sciences 11, n. 23 (1 dicembre 2021): 11375. http://dx.doi.org/10.3390/app112311375.

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Chirality, the absence of mirror symmetry, governs behavior in most biologically important molecules, thus making the chiral recognition of great importance in the pharmaceutical and agrochemical industries, as well as medicine. Chiral molecules can be characterized by means of optical experiments based on chiro-optical excitation of molecules. Specifically, chiral absorptive materials differently absorb left- and right-circular polarized light, i.e., they possess circular dichroism (CD). Unfortunately, the natural CD of most molecules is very low and lies in the ultraviolet range. Fluorescence-detected CD is a fast and sensitive tool for investigation of chiral molecules which emit light; ultralow CD in absorption can be detected as the difference in emission. In this work, we perform fluorescence-detected CD on novel chiral amide compounds, designed specifically for visible green emission; we synthesize two enantiomeric fluorescent compounds using low-cost starting compounds and easy purification. We investigate different solutions of the enantiomers at different concentrations, and we show that the fluorescence of the intrinsically chiral compounds depends on the polarization state of the penetrating light, which is absorbed at 400 nm and emits across the green wavelength range. We believe that these compounds can be coupled with plasmonic nanostructures, which further shows promise in applications regarding chiral sensing or chiral emission.

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Kőrösi, Márton, Csaba Varga, Péter Tóth, Noémi Buczkó, Erzsébet Varga e Edit Székely. "Experimental Determination of a Chiral Ternary Solubility Diagram and Its Interpretation in Gas Antisolvent Fractionation". Molecules 28, n. 5 (24 febbraio 2023): 2115. http://dx.doi.org/10.3390/molecules28052115.

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Although crystallization has been widely applied for the enantiomeric enrichment of non-racemates both in research and in industrial applications, the physical–chemical background of chiral crystallizations is not as frequently discussed. A guide for the experimental determination of such phase equilibrium information is lacking. In the current paper, the experimental investigation of chiral melting phase equilibria, chiral solubility phase diagrams and their application in atmospheric and supercritical carbon dioxide-assisted enantiomeric enrichment is described and compared. Benzylammonium mandelate is a racemic compound; it shows eutectic behavior when molten. A similar eutonic composition was observed in its methanol phase diagram at 1 °C. The influence of the ternary solubility plot could be unequivocally discovered in atmospheric recrystallization experiments, which proved that the crystalline solid phase and the liquid phase were in an equilibrium. The interpretation of the results obtained at 20 MPa and 40 °C, using the methanol–carbon dioxide mixture as a pseudo-component, was more challenging. Although the eutonic composition was found to be the limiting enantiomeric excess value in this purification process as well, the high-pressure gas antisolvent fractionation results were only clearly thermodynamically controlled in certain concentration ranges.

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Metcalf, James S., Sandra Anne Banack, Peter B. Wyatt, Peter B. Nunn e Paul A. Cox. "A Direct Analysis of β-N-methylamino-l-alanine Enantiomers and Isomers and Its Application to Cyanobacteria and Marine Mollusks". Toxins 15, n. 11 (1 novembre 2023): 639. http://dx.doi.org/10.3390/toxins15110639.

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Of the wide variety of toxic compounds produced by cyanobacteria, the neurotoxic amino acid β-N-methylamino-l-alanine (BMAA) has attracted attention as a result of its association with chronic human neurodegenerative diseases such as ALS and Alzheimer’s. Consequently, specific detection methods are required to assess the presence of BMAA and its isomers in environmental and clinical materials, including cyanobacteria and mollusks. Although the separation of isomers such as β-amino-N-methylalanine (BAMA), N-(2-aminoethyl)glycine (AEG) and 2,4-diaminobutyric acid (DAB) from BMAA has been demonstrated during routine analysis, a further compounding factor is the potential presence of enantiomers for some of these isomers. Current analytical methods for BMAA mostly do not discriminate between enantiomers, and the chiral configuration of BMAA in cyanobacteria is still largely unexplored. To understand the potential for the occurrence of D-BMAA in cyanobacteria, a chiral UPLC-MS/MS method was developed to separate BMAA enantiomers and isomers and to determine the enantiomeric configuration of endogenous free BMAA in a marine Lyngbya mat and two mussel reference materials. After extraction, purification and derivatization with N-(4-nitrophenoxycarbonyl)-l-phenylalanine 2-methoxyethyl ester ((S)-NIFE), both L- and D-BMAA were identified as free amino acids in cyanobacterial materials, whereas only L-BMAA was identified in mussel tissues. The finding of D-BMAA in biological environmental materials raises questions concerning the source and role of BMAA enantiomers in neurological disease.

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Zhang, Shi-Yuan, Cheng-Xiong Yang, Wei Shi, Xiu-Ping Yan, Peng Cheng, Lukasz Wojtas e Michael J. Zaworotko. "A Chiral Metal-Organic Material that Enables Enantiomeric Identification and Purification". Chem 3, n. 2 (agosto 2017): 281–89. http://dx.doi.org/10.1016/j.chempr.2017.07.004.

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Johansson, Henrik, Thomas Cailly, Alex Rojas Bie Thomsen, Hans Bräuner-Osborne e Daniel Sejer Pedersen. "Synthesis of the calcilytic ligand NPS 2143". Beilstein Journal of Organic Chemistry 9 (9 luglio 2013): 1383–87. http://dx.doi.org/10.3762/bjoc.9.154.

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(R)-3 (NPS 2143) is a negative allosteric modulator of the human calcium-sensing receptor (CaSR) and as such represents an important pharmacological tool compound for studying the CaSR. Herein, we disclose for the first time a complete experimental description, detailed characterisation and assessment of enantiomeric purity for (R)-3. An efficient, reproducible and scalable synthesis of (R)-3 that requires a minimum of chromatographic purification steps is presented. (R)-3 was obtained in excellent optical purity (er > 99:1) as demonstrated by chiral HPLC and the pharmacological profile for (R)-3 is in full accordance with that reported in the literature.

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Chen, Alex M., Yaling Wang e Robert M. Wenslow. "Purification of Partially Resolved Enantiomeric Mixtures with the Guidance of Ternary Phase Diagram". Organic Process Research & Development 12, n. 2 (marzo 2008): 271–81. http://dx.doi.org/10.1021/op7002387.

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Waśniowski, Paweł, Jolanta Czuczejko, Michał Chuchra, Mateusz Wędrowski, Dawid Marciniak, Stanisław Sobiak e Bogdan Małkowski. "Automatic Production of [18F]F-DOPA Using the Raytest SynChrom R&D Module". Pharmaceuticals 16, n. 1 (22 dicembre 2022): 10. http://dx.doi.org/10.3390/ph16010010.

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[18F]F-DOPA is widely used in PET diagnostics. Diseases diagnosed with this tracer are schizophrenia, Parkinson’s disease, gliomas, neuroendocrine tumors, pheochromocytomas, and pancreatic adenocarcinoma. It should be noted that the [18F]F-DOPA tracer has been known for over 30 years. However, the methods of radiosynthesis applied in the past did not allow its clinical use due to low efficiency and purity. Currently, in the market, one encounters different types of radiosynthesis using the fluorine 18F isotope and variants of the same method. The synthesis and its modifications were carried out using a Raytest Synchrom R&D module. The synthesis consists of the following steps: (a) binding of the fluoride anion 18F− on an anion exchange column; (b) elution with TBAHCO3−; (c) nucleophilic fluorination to the ABX 1336 precursor; (d) purification of the intermediate product on the C18ec column; (e) Baeyer–Villiger oxidation; (f) hydrolysis; and (gfinal purification of the crude product on a semipreparative column. The nucleophilic synthesis of [18F]F-DOPA was successfully performed in 120 min, using the ABX 1336 precursor on the Raytest SynChrom R&D module, with a radiochemical yield (RCY) of 15%, radiochemical purity (RCP) ≥ 97%, and enantiomeric purity (ee) ≥ 96%.

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Thanopulos, Ioannis, Petr Král e Moshe Shapiro. "Theory of a two-step enantiomeric purification of racemic mixtures by optical means: The D2S2 molecule". Journal of Chemical Physics 119, n. 10 (8 settembre 2003): 5105–16. http://dx.doi.org/10.1063/1.1597491.

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Zeng, Lu, Rongda Xu, Yinong Zhang e Daniel B. Kassel. "Two-dimensional supercritical fluid chromatography/mass spectrometry for the enantiomeric analysis and purification of pharmaceutical samples". Journal of Chromatography A 1218, n. 20 (maggio 2011): 3080–88. http://dx.doi.org/10.1016/j.chroma.2011.03.041.

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Martens, Jürgen, e Ravi Bhushan. "Purification of Enantiomeric Mixtures in Enantioselective Synthesis: Overlooked Errors and Scientific Basis of Separation in Achiral Environment". Helvetica Chimica Acta 97, n. 2 (febbraio 2014): 161–87. http://dx.doi.org/10.1002/hlca.201300392.

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Singh, Ankita, PalakVarma .., Arpita Singh, Shuchi .., Anakshi .., Neha Sharma, Kajal Rawat et al. "Applications of Microbial Enzymes: The Need of an Hour". Indian Journal of Genetics and Molecular Research 12, n. 2 (15 dicembre 2023): 19–32. http://dx.doi.org/10.21088/ijgmr.2319.4782.12223.3.

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A growing need for sustainable solutions is one of the primary drivers of the demand for industrial enzymes. One of the most significant and beneficial sources of many enzymes has been and still is the microbial world. Numerous industrial procedures, such as chemical synthesis used to create chemicals and pharmaceuticals, have a number of drawbacks: Lack of enantiomeric specificity for chiral synthesis, low pH, high pressure, high temperature, and low catalytic efficiency. Enzyme research and interest are still advancing, which helps industrial biocatalysis succeed even more. There should be a lot of intriguing discoveries in the field of biotransformation over the coming years. The value of biotechnologically and industrially significant microbial enzymes is the main topic of this study, which comprises 44 papers, including research studies and review articles. Also, it offers novel insights into the micro-organisms that manufacture these enzymes as well as the procedures employed for their purification and separation.

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Cumbicus, Carolina, Omar Malagón, Nixon Cumbicus e Gianluca Gilardoni. "The Leaf Essential Oil of Gynoxys buxifolia (Kunth) Cass. (Asteraceae): A Good Source of Furanoeremophilane and Bakkenolide A". Plants 12, n. 6 (15 marzo 2023): 1323. http://dx.doi.org/10.3390/plants12061323.

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The present study describes the chemical and enantiomeric composition of a new essential oil, distilled from the dry leaves of Gynoxys buxifolia (Kunth) Cass. The chemical analysis was conducted by GC-MS and GC-FID, on two orthogonal capillary columns. A total of 72 compounds were detected and quantified with at least one column, corresponding to about 85% by weight of the whole oil mass. Of the 72 components, 70 were identified by comparing the respective linear retention indices and mass spectra with data from the literature, whereas the two main constituents were identified by preparative purification and NMR experiments. The quantitative analysis was carried out calculating the relative response factor of each compound according to their combustion enthalpy. The major constituents of the EO (≥3%) were: furanoeremophilane (31.3–28.3%), bakkenolide A (17.6–16.3%), caryophyllene oxide (6.0–5.8%), and (E)-β-caryophyllene (4.4%). Additionally, the hydrolate was also analyzed with respect to the dissolved organic phase. About 40.7–43.4 mg/100 mL of organic compounds was detected in solution, of which p-vinylguaiacol was the main component (25.4–29.9 mg/100 mL). Finally, the enantioselective analysis of some chiral terpenes was carried out, with a capillary column based on β-cyclodextrin chiral stationary phase. In this analysis, (1S,5S)-(−)-α-pinene, (1S,5S)-(−)-β-pinene, (S)-(+)-α-phellandrene, (S)-(+)-β-phellandrene, and (S)-(−)-terpinen-4-ol were detected as enantiomerically pure, whereas (S)-(−)-sabinene showed an enantiomeric excess of 69.2%. The essential oil described in the present study is a good source of two uncommon volatile compounds: furanoeremophilane and bakkenolide A. The former lacks bioactivity information and deserves further investigation, whereas the latter is a promising selective anticancer product.

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Rösener, Nadine S., Lothar Gremer, Elke Reinartz, Anna König, Oleksandr Brener, Henrike Heise, Wolfgang Hoyer, Philipp Neudecker e Dieter Willbold. "A d-enantiomeric peptide interferes with heteroassociation of amyloid-β oligomers and prion protein". Journal of Biological Chemistry 293, n. 41 (21 agosto 2018): 15748–64. http://dx.doi.org/10.1074/jbc.ra118.003116.

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Alzheimer's disease (AD) is a progressive neurodegenerative disorder that affects millions of people worldwide. One AD hallmark is the aggregation of β-amyloid (Aβ) into soluble oligomers and insoluble fibrils. Several studies have reported that oligomers rather than fibrils are the most toxic species in AD progression. Aβ oligomers bind with high affinity to membrane-associated prion protein (PrP), leading to toxic signaling across the cell membrane, which makes the Aβ–PrP interaction an attractive therapeutic target. Here, probing this interaction in more detail, we found that both full-length, soluble human (hu) PrP(23–230) and huPrP(23–144), lacking the globular C-terminal domain, bind to Aβ oligomers to form large complexes above the megadalton size range. Following purification by sucrose density–gradient ultracentrifugation, the Aβ and huPrP contents in these heteroassemblies were quantified by reversed-phase HPLC. The Aβ:PrP molar ratio in these assemblies exhibited some limited variation depending on the molar ratio of the initial mixture. Specifically, a molar ratio of about four Aβ to one huPrP in the presence of an excess of huPrP(23–230) or huPrP(23–144) suggested that four Aβ units are required to form one huPrP-binding site. Of note, an Aβ-binding all-d-enantiomeric peptide, RD2D3, competed with huPrP for Aβ oligomers and interfered with Aβ–PrP heteroassembly in a concentration-dependent manner. Our results highlight the importance of multivalent epitopes on Aβ oligomers for Aβ–PrP interactions and have yielded an all-d-peptide–based, therapeutically promising agent that competes with PrP for these interactions.

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Peters, Christin, e Rebecca Buller. "Linear enzyme cascade for the production of (–)-iso-isopulegol". Zeitschrift für Naturforschung C 74, n. 3-4 (25 febbraio 2019): 63–70. http://dx.doi.org/10.1515/znc-2018-0146.

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Abstract Biocatalysis has developed enormously in the last decade and now offers solutions for the sustainable production of chiral and highly functionalised asset molecules. Products generated by enzymatic transformations are already being used in the food, feed, chemical, pharmaceutical and cosmetic industry, and the accessible compound panoply is expected to expand even further. In particular, the combination of stereo-selective enzymes in linear cascade reactions is an elegant strategy toward enantiomeric pure compounds, as it reduces the number of isolation and purification steps and avoids accumulation of potentially unstable intermediates. Here, we present the set-up of an enzyme cascade to selectively convert citral to (–)-iso-isopulegol by combining an ene reductase and a squalene hopene cyclase. In the initial reaction step, the ene reductase YqjM from Bacillus subtilis selectively transforms citral to (S)-citronellal, which is subsequently cyclised exclusively to (–)-iso-isopulegol by a mutant of the squalene hopene cyclase from Alicyclobacillus acidocaldarius (AacSHC). With this approach, we can convert citral to an enantiopure precursor for isomenthol derivatives.

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Gu, Xuyuan, John M. Ndungu, Wei Qiu, Jinfa Ying, Michael D. Carducci, Hank Wooden e Victor J. Hruby. "Large scale enantiomeric synthesis, purification, and characterization of ω-unsaturated amino acids via a Gly-Ni(II)-BPB-complex". Tetrahedron 60, n. 37 (settembre 2004): 8233–43. http://dx.doi.org/10.1016/j.tet.2004.06.087.

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Martens, Juergen, e Ravi Bhushan. "ChemInform Abstract: Purification of Enantiomeric Mixtures in Enantioselective Synthesis: Overlooked Errors and Scientific Basis of Separation in Achiral Environment". ChemInform 45, n. 17 (10 aprile 2014): no. http://dx.doi.org/10.1002/chin.201417256.

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Inoue, Kousuke, Yoshihide Makino e Nobuya Itoh. "Purification and Characterization of a Novel Alcohol Dehydrogenase from Leifsonia sp. Strain S749: a Promising Biocatalyst for an Asymmetric Hydrogen Transfer Bioreduction". Applied and Environmental Microbiology 71, n. 7 (luglio 2005): 3633–41. http://dx.doi.org/10.1128/aem.71.7.3633-3641.2005.

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ABSTRACT To find microorganisms that could reduce phenyl trifluoromethyl ketone (PTK) to (S)-1-phenyltrifluoroethanol [(S)-PTE], styrene-assimilating bacteria (ca. 900 strains) isolated from soil samples were screened. We found that Leifsonia sp. strain S749 was the most suitable strain for the conversion of PTK to (S)-PTE in the presence of 2-propanol as a hydrogen donor. The enzyme corresponding to the reaction was purified homogeneity, characterized and designated Leifsonia alcohol dehydrogenase (LSADH). The purified enzyme had a molecular weight of 110,000 and was composed of four identical subunits (molecular weight, 26,000). LSADH required NADH as a cofactor, showed little activity with NADPH, and reduced a wide variety of aldehydes and ketones. LSADH catalyzed the enantioselective reduction of some ketones with high enantiomeric excesses (e.e.): PTK to (S)-PTE (>99% e.e.), acetophenone to (R)-1-phenylethanol (99% e.e.), and 2-heptanone to (R)-2-heptanol (>99% e.e.) in the presence of 2-propanol without an additional NADH regeneration system. Therefore, it would be a useful biocatalyst.

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López-Gómez, José Pablo, Peter Unger, Roland Schneider e Joachim Venus. "From Upstream to Purification: Production of Lactic Acid from the Organic Fraction of Municipal Solid Waste". Waste and Biomass Valorization 11, n. 10 (28 febbraio 2020): 5247–54. http://dx.doi.org/10.1007/s12649-020-00992-9.

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Abstract The implementation of an efficient and sustainable management of the organic fraction of municipal solid wastes (OFMSW) is a topic of intensive discussion in EU countries. Recently, the OFMSW has been investigated as a potential substrate for the production of lactic acid (LA) through fermentation. Nevertheless, none of the reports available in the literature covers all the stages of the conversion process. The present research article is a comprehensive study which includes the upstream, fermentation and downstream for the conversion of OFMSW into LA. Several batches of OFMSW were analysed for the evaluation of sugars released and LA content before the fermentation. Fermentations were performed to study the effect of hydrolysate quality on the LA production using Bacillus coagulans A166. Purification of LA, based on electrodialysis, was carried out after pilot scale fermentation of OFMSW hydrolysates. Results showed that variations in the concentrations of sugars and LA are observed from batch to batch of OFMSW. More specifically, LA can reach high concentrations even before the substrates are hydrolysed, limiting the potential applications of the final product due to low enantiomeric purities. In general, fermentations of the hydrolysate were efficient, with conversion yields of 0.65 g g−1 without the addition of extra nutrients. Downstream is still a challenging stage of the process. A LA recovery of 55% was obtained, with the most significant losses observed during the micro- and nanofiltrations. Overall, a conversion of 10% from OFMSW substrate (dry basis) to LA was achieved. Graphic Abstract

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Sheldon, R. A. "Cross-linked enzyme aggregates (CLEA®s): stable and recyclable biocatalysts". Biochemical Society Transactions 35, n. 6 (23 novembre 2007): 1583–87. http://dx.doi.org/10.1042/bst0351583.

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The key to obtaining an optimum performance of an enzyme is often a question of devising an effective method for its immobilization. In the present review, we describe a novel, versatile and effective methodology for enzyme immobilization as CLEAs (cross-linked enzyme aggregates). The method is exquisitely simple (involving precipitation of the enzyme from aqueous buffer followed by cross-linking of the resulting physical aggregates of enzyme molecules) and amenable to rapid optimization. We have shown it to be applicable to a wide variety of enzymes, including, in addition to a wide variety of hydrolases, lyases, e.g. nitrile hydratases and oxynitrilases, and oxidoreductases such as laccase and galactose oxidase. CLEAs are stable, recyclable catalysts exhibiting high catalyst productivities. Because the methodology is essentially a combination of purification and immobilization into one step, the enzyme does not need to be of high purity. The technique is also applicable to the preparation of combi-CLEAs, containing two or more enzymes, for use in one-pot, multistep syntheses, e.g. an oxynitrilase/nitrilase combi-CLEA for the one-pot conversion of benzaldehyde into (S)-mandelic acid, in high yield and enantiomeric purity.

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30

Pennacchio, Angela, Biagio Pucci, Francesco Secundo, Francesco La Cara, Mosè Rossi e Carlo A. Raia. "Purification and Characterization of a Novel Recombinant Highly Enantioselective Short-Chain NAD(H)-Dependent Alcohol Dehydrogenase from Thermus thermophilus". Applied and Environmental Microbiology 74, n. 13 (2 maggio 2008): 3949–58. http://dx.doi.org/10.1128/aem.00217-08.

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ABSTRACT The gene encoding a novel alcohol dehydrogenase (ADH) that belongs to the short-chain dehydrogenase/reductase (SDR) superfamily was identified in the extremely thermophilic, halotolerant gram-negative eubacterium Thermus thermophilus HB27. The T. thermophilus ADH gene (adh Tt) was heterologously overexpressed in Escherichia coli, and the protein (ADHTt) was purified to homogeneity and characterized. ADHTt is a tetrameric enzyme consisting of identical 26,961-Da subunits composed of 256 amino acids. The enzyme has remarkable thermophilicity and thermal stability, displaying activity at temperatures up to ∼73°C and a 30-min half-inactivation temperature of ∼90°C, as well as good tolerance to common organic solvents. ADHTt has a strict requirement for NAD(H) as the coenzyme, a preference for reduction of aromatic ketones and α-keto esters, and poor activity on aromatic alcohols and aldehydes. This thermophilic enzyme catalyzes the following reactions with Prelog specificity: the reduction of acetophenone, 2,2,2-trifluoroacetophenone, α-tetralone, and α-methyl and α-ethyl benzoylformates to (S)-(−)-1-phenylethanol (>99% enantiomeric excess [ee]), (R)-α-(trifluoromethyl)benzyl alcohol (93% ee), (S)-α-tetralol (>99% ee), methyl (R)-(−)-mandelate (92% ee), and ethyl (R)-(−)-mandelate (95% ee), respectively, by way of an efficient in situ NADH-recycling system involving 2-propanol and a second thermophilic ADH. This study further supports the critical role of the D37 residue in discriminating NAD(H) from NADP(H) in members of the SDR superfamily.

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31

Pogorevc, Mateja, e Kurt Faber. "Purification and Characterization of an Inverting Stereo- and Enantioselective sec-Alkylsulfatase from the Gram-Positive Bacterium Rhodococcus ruber DSM 44541". Applied and Environmental Microbiology 69, n. 5 (maggio 2003): 2810–15. http://dx.doi.org/10.1128/aem.69.5.2810-2815.2003.

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Abstract (sommario):

ABSTRACT Whole cells of Rhodococcus ruber DSM 44541 were found to hydrolyze (±)-2-octyl sulfate in a stereo- and enantiospecific fashion. When growing on a complex medium, the cells produced two sec-alkylsulfatases and (at least) one prim-alkylsulfatase in the absence of an inducer, such as a sec-alkyl sulfate or a sec-alcohol. From the crude cell-free lysate, two proteins responsible for sulfate ester hydrolysis (designated RS1 and RS2) were separated from each other based on their different hydrophobicities and were subjected to further chromatographic purification. In contrast to sulfatase RS1, enzyme RS2 proved to be reasonably stable and thus could be purified to homogeneity. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a single band at a molecular mass of 43 kDa. Maximal enzyme activity was observed at 30°C and at pH 7.5. Sulfatase RS2 showed a clear preference for the hydrolysis of linear secondary alkyl sulfates, such as 2-, 3-, or 4-octyl sulfate, with remarkable enantioselectivity (an enantiomeric ratio of up to 21 [23]). Enzymatic hydrolysis of (R)-2-octyl sulfate furnished (S)-2-octanol without racemization, which revealed that the enzymatic hydrolysis proceeded through inversion of the configuration at the stereogenic carbon atom. Screening of a broad palette of potential substrates showed that the enzyme exhibited limited substrate tolerance; while simple linear sec-alkyl sulfates (C7 to C10) were freely accepted, no activity was found with branched and mixed aryl-alkyl sec-sulfates. Due to the fact that prim-sulfates were not accepted, the enzyme was classified as sec-alkylsulfatase (EC 3.1.6.X).

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32

Faigl, Ferenc, Kálmán Simon, Antal Lopata, Éva Kozsda, Richárd Hargitai, Mátyás Czugler, Mária Ács e Elemér Fogassy. "A combined DSC, X-ray diffraction, and molecular modelling study of chiral discrimination in the purification of enantiomeric mixtures of cis-permethrinic acid". J. Chem. Soc., Perkin Trans. 2, n. 1 (1990): 57–63. http://dx.doi.org/10.1039/p29900000057.

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33

Hu, Shaoqiang. "Copper (II) Ions Induced Self-Disproportionation of Enantiomers in Capillary Electrophoresis for the Quantification of Atenolol Enantiomers". Molecules 28, n. 15 (6 agosto 2023): 5908. http://dx.doi.org/10.3390/molecules28155908.

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Abstract (sommario):

Despite the fact that the self-disproportionation of enantiomers (SDE) has been found for several decades and has been widely used in crystallization, sublimation and chromatography for the purification or separation of nonracemic compounds, the phenomenon of SDE in capillary electrophoresis (CE) has never been reported up to now. Here, a new approach to separate enantiomers in CE based on SDE was demonstrated by introducing copper (II) ions into the separation media. The enantiomers of atenolol interact with copper ions to produce positively charged complexes with different electrophoretic mobilities from the single molecules. The dynamic equilibrium between homo- or heterochiral complexes (associates) and single molecules of atenolol enantiomers supports the manifestation of SDE. Different mobilities of the single molecules and associates, and different distribution of two enantiomers between the single molecules and associates caused by their different concentrations, produce a net difference in electrodriven migration velocities of the two enantiomers. The relative movement of two enantiomers causes a zone depleted in one enantiomer at the rear end of sample segment, giving a trapezoidal CE curve with a step at the end. Quantification of enantiomers is achieved according to the step height. The analysis does not rely on the use of enantiomerically pure chiral selector and the result agrees with that obtained by conventional chiral CE using a chiral selector.

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34

Aly, Ashraf A., Stefan Bräse, Alaa A. Hassan, Nasr K. Mohamed, Lamiaa E. Abd El-Haleem e Martin Nieger. "Synthesis of New Planar-Chiral Linked [2.2]Paracyclophanes-N-([2.2]-Paracyclophanylcarbamoyl)-4-([2.2]Paracyclophanylcarboxamide, [2.2]Paracyclophanyl-Substituted Triazolthiones and -Substituted Oxadiazoles". Molecules 25, n. 15 (22 luglio 2020): 3315. http://dx.doi.org/10.3390/molecules25153315.

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Abstract (sommario):

The manuscript describes the synthesis of new racemic and chiral linked paracyclophane assigned as N-5-(1,4(1,4)-dibenzenacyclohexaphane-12-yl)carbamoyl)-5’-(1,4(1,4)-dibenzenacyclohexaphane-12-yl)carboxamide. The procedure depends upon the reaction of 5-(1,4(1,4)-dibenzenacyclohexaphane-12-yl)hydrazide with 5-(1,4(1,4)-dibenzenacyclohexaphane-12-yl)isocyanate. To prepare the homochiral linked paracyclophane of a compound, the enantioselectivity of 5-(1,4(1,4)-dibenzenacyclohexaphane-12-yl)carbaldehyde (enantiomeric purity 60% ee), was oxidized to the corresponding acid, which on chlorination, gave the corresponding acid chloride of [2.2]paracyclophane. Following up on the same procedure applied for the preparation of racemic-carbamoyl and purified by HPLC purification, we succeeded to obtain the target Sp-Sp-N-5-(1,4(1,4)-dibenzenacyclohexaphane-12-yl)carbamoyl)-5’-(1,4(1,4)-dibenzenacyclohexaphane-12-yl)carboxamide. Subjecting N-5-(1,4(1,4)-dibenzenacyclohexaphane-12-yl)hydrazide to various isothiocyanates, the corresponding paracyclophanyl-acylthiosemicarbazides were obtained. The latter compounds were then cyclized to a new series of 5-(1,4(1,4)-dibenzenacyclohexaphane-12-yl)-2,4-dihydro-3H-1,2,4-triazol-3-thiones. 5-(1,4(1,4)-Dibenzenacyclohexaphane-12-yl)-1,3,4-oxadiazol-2-amines were also synthesized in good yields via internal cyclization of the same paracyclophanyl-acylthiosemicarbazides. NMR, IR, and mass spectra (HRMS) were used to elucidate the structure of the obtained products. The X-ray structure analysis was also used as an unambiguous tool to elucidate the structure of the products.

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35

Calvopiña, Karyna, Omar Malagón, Francesca Capetti, Barbara Sgorbini, Verónica Verdugo e Gianluca Gilardoni. "A New Sesquiterpene Essential Oil from the Native Andean Species Jungia rugosa Less (Asteraceae): Chemical Analysis, Enantiomeric Evaluation, and Cholinergic Activity". Plants 10, n. 10 (4 ottobre 2021): 2102. http://dx.doi.org/10.3390/plants10102102.

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Abstract (sommario):

As part of a project devoted to the phytochemical study of Ecuadorian biodiversity, new essential oils are systematically distilled and analysed. In the present work, Jungia rugosa Less (Asteraceae) has been selected and some wild specimens collected to investigate the volatile fraction. The essential oil, obtained from fresh leaves, was analysed for the first time in the present study. The chemical composition was determined by gas chromatography, coupled to mass spectrometry (GC-MS) for qualitative analysis, and to flame ionization detector (GC-FID) for quantitation. The calculation of relative response factors (RRF), based on combustion enthalpy, was carried out for each quantified component. Fifty-six compounds were identified and quantified in a 5% phenyl-polydimethylsiloxane non-polar column and 53 compounds in a polyethylene glycol polar column, including four undetermined compounds. The main feature of this essential oil was the exclusive sesquiterpenes content, both hydrocarbons (74.7% and 80.4%) and oxygenated (8.3% and 9.6%). Major constituents were: γ-curcumene (47.1% and 49.7%) and β-sesquiphellandrene (17.0% and 17.9%), together with two abundant undetermined oxygenated sesquiterpenes, whose abundance was 6.7–7.2% and 4.7–3.3%, respectively. In addition, the essential oil was submitted to enantioselective evaluation in two β-cyclodextrin-based enantioselective columns, determining the enantiomeric purity of a minor component (1S,2R,6R,7R,8R)-(+)-α-copaene. Finally, the AChE inhibition activity of the EO was evaluated in vitro. In conclusion, this volatile fraction is suitable for further investigation, according to two main lines: (a) the purification and structure elucidation of the major undetermined compounds, (b) a bio-guided fractionation, intended to investigate the presence of new sesquiterpene AChE inhibitors among the minor components.

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36

Pietrusiewicz, K. Michał, Mariusz Borkowski, Dorota Strzelecka, Katarzyna Kielar, Wioleta Kicińska, Sergei Karevych, Radomir Jasiński e Oleg M. Demchuk. "A General Phenomenon of Spontaneous Amplification of Optical Purity under Achiral Chromatographic Conditions". Symmetry 11, n. 5 (17 maggio 2019): 680. http://dx.doi.org/10.3390/sym11050680.

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Abstract (sommario):

This work explores the behavior of chiral compound mixtures enriched in one of the enantiomers whilst a typical chromatography on the achiral stationary phase is employed. The influence of several factors, such as the eluent composition, ratio of the compound to the stationary phase, and the initial enatiomeric purity of the compound used on the distribution of the enantiomers in the collected chromatographic fraction, was studied. The obtained results indicate that the phenomenon of Self Disproportionation of Enantiomer (SDE) occurred in all cases, and some of the collected fractions got higher optical purities than the initial one. Thus, achiral column chromatography could be applied in some cases as the simplest approach for chiral purification. Based on the experimental results and DFT calculations, an alternative concept explaining the SDE phenomenon was proposed. Due to its generality and simplicity, SDE may also be responsible for the formation of the first chiral non-racemic compounds on the early Earth.

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37

Nolte, Johannes Christoph, Marc Schürmann, Catherine-Louise Schepers, Elvira Vogel, Jan Hendrik Wübbeler e Alexander Steinbüchel. "Novel Characteristics of Succinate Coenzyme A (Succinate-CoA) Ligases: Conversion of Malate to Malyl-CoA and CoA-Thioester Formation of Succinate AnaloguesIn Vitro". Applied and Environmental Microbiology 80, n. 1 (18 ottobre 2013): 166–76. http://dx.doi.org/10.1128/aem.03075-13.

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ABSTRACTThree succinate coenzyme A (succinate-CoA) ligases (SucCD) fromEscherichia coli,Advenella mimigardefordensisDPN7T, andAlcanivorax borkumensisSK2 were characterized regarding their substrate specificity concerning succinate analogues. Previous studies had suggested that SucCD enzymes might be promiscuous toward succinate analogues, such as itaconate and 3-sulfinopropionate (3SP). The latter is an intermediate of the degradation pathway of 3,3′-dithiodipropionate (DTDP), a precursor for the biotechnical production of polythioesters (PTEs) in bacteria. ThesucCDgenes were expressed inE. coliBL21(DE3)/pLysS. The SucCD enzymes ofE. coliandA. mimigardefordensisDPN7Twere purified in the native state using stepwise purification protocols, while SucCD fromA. borkumensisSK2 was equipped with a C-terminal hexahistidine tag at the SucD subunit. Besides the preference for the physiological substrates succinate, itaconate, ATP, and CoA, high enzyme activity was additionally determined for both enantiomeric forms of malate, amounting to 10 to 21% of the activity with succinate.Kmvalues ranged from 2.5 to 3.6 mM forl-malate and from 3.6 to 4.2 mM ford-malate for the SucCD enzymes investigated in this study. Asl-malate-CoA ligase is present in the serine cycle for assimilation of C1compounds in methylotrophs, structural comparison of these two enzymes as members of the same subsubclass suggested a strong resemblance of SucCD tol-malate-CoA ligase and gave rise to the speculation that malate-CoA ligases and succinate-CoA ligases have the same evolutionary origin. Although enzyme activities were very low for the additional substrates investigated, liquid chromatography/electrospray ionization-mass spectrometry analyses proved the ability of SucCD enzymes to form CoA-thioesters of adipate, glutarate, and fumarate. Since all SucCD enzymes were able to activate 3SP to 3SP-CoA, we consequently demonstrated that the activation of 3SP is not a unique characteristic of the SucCD fromA. mimigardefordensisDPN7T. The essential role ofsucCDin the activation of 3SPin vivowas proved by genetic complementation.

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38

Nishihara, M., e Y. Koga. "Purification and Properties of sn-Glycerol-1 -Phosphate Dehydrogenase from Methanobacterium thermoautotrophicum: Characterization of the Biosynthetic Enzyme for the Enantiomeric Glycerophosphate Backbone of Ether Polar Lipids of Archaea". Journal of Biochemistry 122, n. 3 (1 settembre 1997): 572–76. http://dx.doi.org/10.1093/oxfordjournals.jbchem.a021791.

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39

Ueki, Hisanori, Manabu Yasumoto e Vadim A. Soloshonok. "Rational application of self-disproportionation of enantiomers via sublimation—a novel methodological dimension for enantiomeric purifications". Tetrahedron: Asymmetry 21, n. 11-12 (giugno 2010): 1396–400. http://dx.doi.org/10.1016/j.tetasy.2010.04.040.

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40

Souness, J. E., e L. C. Scott. "Stereospecificity of rolipram actions on eosinophil cyclic AMP-specific phosphodiesterase". Biochemical Journal 291, n. 2 (15 aprile 1993): 389–95. http://dx.doi.org/10.1042/bj2910389.

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Abstract (sommario):

The stereospecificity of rolipram inhibition of particulate cyclic AMP-specific phosphodiesterase (PDE IV) from guinea-pig eosinophils has been investigated. (-)-Rolipram (IC50 = 0.22 +/- 0.08 microM) was 2.5-fold more potent than (+)-rolipram (IC50 = 0.58 +/- 0.05 microM) in inhibiting membrane-bound PDE IV. Solubilization of PDE IV with deoxycholate (0.5%) and NaCl (100 mM) increased rolipram stereospecificity [IC50 (-)-rolipram = 0.020 +/- 0.002 microM; IC50 (+)-rolipram = 0.33 +/- 0.07 microM]. Partial purification of this solubilized PDE IV by DEAE-trisacryl anion-exchange chromatography reduced the enantiomeric potency difference compared with the pre-chromatographed activity, with (-)-rolipram (IC50 = 0.20 +/- 0.02 microM) being only 2.9-fold more potent than (+)-rolipram (IC50 = 0.57 +/- 0.14 microM). Vanadate-glutathione complex (V-GSH) stimulated membrane-bound PDE IV activity and increased the potency of (-)-rolipram (IC50 = 0.014 +/- 0.006 microM) but not (+)-rolipram (IC50 = 0.32 +/- 0.07 microM). In intact eosinophils, (-)-rolipram (EC50 = 0.19 +/- 0.02 microM) was 10-fold more potent than (+)-rolipram (EC50 = 1.87 +/- 0.09 microM) in enhancing isoprenaline (10 microM)-stimulated cyclic AMP accumulation. Strong correlations were demonstrated for displacement of [3H]rolipram binding to brain membranes by several PDE inhibitors and their inhibition of solubilized PDE IV (r = 0.98, P < 0.001, n = 7) and stimulation of cyclic AMP accumulation in intact cells (r = 0.98, P < 0.001, n = 6). Rolipram was a relatively weak inhibitor of partially purified pig aortic PDE IV and only slight stereospecificity was exhibited [IC50 (-)-rolipram = 1.47 +/- 0.09 microM; IC50 (+)-rolipram = 2.73 +/- 0.38 microM]. The results indicate the presence of a partially concealed stereospecific site (Sr) on eosinophil PDE IV possibly similar to the high-affinity rolipram-binding site in brain through which rolipram can potently inhibit enzyme activity. This site, which apparently is not present on partially purified pig aortic PDE IV, is concealed in freshly prepared eosinophil membranes but is exposed by solubilization or V-GSH treatment and is important in regulating intracellular cyclic AMP accumulation in intact cells.

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41

Shiau, Lie-Ding, Keng-Fu Liu e Pin-Hao Huang. "Purification of hydrobenzoin enantiomers by stripping crystallization". Journal of the Taiwan Institute of Chemical Engineers 44, n. 5 (settembre 2013): 707–12. http://dx.doi.org/10.1016/j.jtice.2013.01.020.

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42

Gee, N. S., C. I. Ragan, K. J. Watling, S. Aspley, R. G. Jackson, G. G. Reid, D. Gani e J. K. Shute. "The purification and properties of myo-inositol monophosphatase from bovine brain". Biochemical Journal 249, n. 3 (1 febbraio 1988): 883–89. http://dx.doi.org/10.1042/bj2490883.

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Abstract (sommario):

1. An inositol monophosphatase was purified to homogeneity from bovine brain. 2. The enzyme is a dimer of subunit Mr 29,000. 3. The enzyme hydrolyses both enantiomers of myo-inositol 1-phosphate and both enantiomers of myo-inositol 4-phosphate, but has no activity towards inositol bisphosphates, inositol trisphosphates or inositol 1,3,4,5-tetrakisphosphate. 4. Several non-inositol-containing monophosphates are also substrates. 5. The enzyme requires Mg2+ for activity, and Zn2+ supports activity to a small extent. 6. Other bivalent cations (including Zn2+) are inhibitors, competitive with Mg2+. 7. Phosphate, but not inositol, is an inhibitor competitive with substrate. 8. Li+ inhibits hydrolysis of inositol 1-phosphate and inositol 4-phosphate uncompetitively with different apparent Ki values (1.0 mM and 0.26 mM respectively).

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43

Zhou, Shengde, T. B. Causey, A. Hasona, K. T. Shanmugam e L. O. Ingram. "Production of Optically Pure d-Lactic Acid in Mineral Salts Medium by Metabolically Engineered Escherichia coli W3110". Applied and Environmental Microbiology 69, n. 1 (gennaio 2003): 399–407. http://dx.doi.org/10.1128/aem.69.1.399-407.2003.

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Abstract (sommario):

ABSTRACT The resistance of polylactide to biodegradation and the physical properties of this polymer can be controlled by adjusting the ratio of l-lactic acid to d-lactic acid. Although the largest demand is for the l enantiomer, substantial amounts of both enantiomers are required for bioplastics. We constructed derivatives of Escherichia coli W3110 (prototrophic) as new biocatalysts for the production of d-lactic acid. These strains (SZ40, SZ58, and SZ63) require only mineral salts as nutrients and lack all plasmids and antibiotic resistance genes used during construction. d-Lactic acid production by these new strains approached the theoretical maximum yield of two molecules per glucose molecule. The chemical purity of this d-lactic acid was ∼98% with respect to soluble organic compounds. The optical purity exceeded 99%. Competing pathways were eliminated by chromosomal inactivation of genes encoding fumarate reductase (frdABCD), alcohol/aldehyde dehydrogenase (adhE), and pyruvate formate lyase (pflB). The cell yield and lactate productivity were increased by a further mutation in the acetate kinase gene (ackA). Similar improvements could be achieved by addition of 10 mM acetate or by an initial period of aeration. All three approaches reduced the time required to complete the fermentation of 5% glucose. The use of mineral salts medium, the lack of antibiotic resistance genes or plasmids, the high yield of d-lactate, and the high product purity should reduce costs associated with nutrients, purification, containment, biological oxygen demand, and waste treatment.

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44

Izatt, Neil E., Ronald L. Bruening, Krzysztof E. Krakowiak, Reed M. Izatt e Jerald S. Bradshaw. "ChemInform Abstract: Nonchromatographic Solid-Phase Purification of Enantiomers". ChemInform 32, n. 29 (25 maggio 2010): no. http://dx.doi.org/10.1002/chin.200129267.

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45

Metzger, Tzuriel S., Yair Tokatly, Eytan Avigad, Shira Yochelis e Yossi Paltiel. "Selective enantiomer purification using magnetic oriented interacting microparticles". Separation and Purification Technology 239 (maggio 2020): 116501. http://dx.doi.org/10.1016/j.seppur.2020.116501.

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46

Doumani, Jacques, Rui Xu, Minhan Lou, Nina Hong, Andrey Baydin, Yohei Yomogida, Riichiro Saito et al. "(Invited) Wafer-Scale Probing of Natural and Synthetic Chirality in Carbon Nanotubes". ECS Meeting Abstracts MA2024-01, n. 9 (9 agosto 2024): 907. http://dx.doi.org/10.1149/ma2024-019907mtgabs.

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Abstract (sommario):

Harnessing chirality can advance diverse technologies, encompassing displays, quantum light sources, secured communication, and biosensing. We have investigated chirality-induced processes in carbon nanotube (CNT) ensembles, based on both natural and synthetic chirality, on macroscopic scales. Firstly, through enantiomer purification [1] combined with nanotube alignment [2], we demonstrated second harmonic generation in an aligned film of (6,5)+ single enantiomer-enriched CNTs. Enantiomer purification using mixed-surfactant gel chromatography and CNT alignment through controlled vacuum filtration (CVF) resulted in a resonance-enhanced second-order nonlinear optical susceptibility χ(2) of ~2 nm/V at the E11 exciton transition. Secondly, we engineered artificial chiral assemblies from achiral mixtures of CNTs to create chiral structures, achieving a record high deep-ultraviolet ellipticity of 40 mdeg/nm [3]. Our orbital shaking-assisted CVF methodology enabled the fabrication of a macroscopic assembly of synthetic optical isomers, so-called “tornado” films, obtaining both types of handedness within a single film by fine-tuning a shaking-filtration recipe. References: [1] X. Wei, T. Tanaka, Y. Yomogida, N. Sato, R. Saito, H. Kataura, Experimental determination of excitonic band structures of single-walled carbon nanotubes using circular dichroism spectra, Nature Communications 7 (2016) 12899. https://doi.org/10.1038/ncomms12899. [2] X. He, W. Gao, L. Xie, B. Li, Q. Zhang, S. Lei, J.M. Robinson, E.H. Hároz, S.K. Doorn, W. Wang, R. Vajtai, P.M. Ajayan, W.W. Adams, R.H. Hauge, J. Kono, Wafer-scale monodomain films of spontaneously aligned single-walled carbon nanotubes, Nature Nanotechnology 11 (2016) 633–638. https://doi.org/10.1038/nnano.2016.44. [3] J. Doumani, M. Lou, O. Dewey, N. Hong, J. Fan, A. Baydin, K. Zahn, Y. Yomogida, K. Yanagi, M. Pasquali, R. Saito, J. Kono, W. Gao, Engineering chirality at wafer scale with ordered carbon nanotube architectures, Nature Communications 14 (2023) 7380. https://doi.org/10.1038/s41467-023-43199-x.

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47

Gu, Binbin, Anwei Hou e Jeroen S. Dickschat. "The stereochemical course of 2-methylisoborneol biosynthesis". Beilstein Journal of Organic Chemistry 18 (8 luglio 2022): 818–24. http://dx.doi.org/10.3762/bjoc.18.82.

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Abstract (sommario):

Both enantiomers of 2-methyllinalyl diphosphate (2-Me-LPP) were synthesized enantioselectively using Sharpless epoxidation as a key step and purification of enantiomerically enriched intermediates through HPLC separation on a chiral stationary phase. Their enzymatic conversion with 2-methylisoborneol synthase (2MIBS) demonstrates that (R)-2-Me-LPP is the on-pathway intermediate, while a minor formation of 2-methylisoborneol from (S)-2-Me-LPP may be explained by isomerization to 2-Me-GPP and then to (R)-2-Me-LPP.

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48

Rudolf, Philip R., Larry Kershner e Jim Tai. "Probing Structure-Property Relationships in a Family of Aryloxyphenoxy Propionate Herbicides Using Single Crystal X-Ray Diffraction Techniques". Advances in X-ray Analysis 35, A (1991): 641–43. http://dx.doi.org/10.1154/s0376030800009368.

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Aryloxyphenoxy propionates are a widely manufactured class of highly active grass-selective herbicides for use in various crops. Examples include VERDICT (1a), FUSILADE (1b), WHIP (1c), and ASSURE (1d). Figure 1 shows the general structure of aryloxyphenoxy propionates. All of these compounds contain a chiral center and each enantiomer of the optical pair exhibits significantly different herbicidal activity. The optically active isomers can be prepared by reacting the corresponding substituted phenoxyphenol with the S-(-)methyl lactate sulfonate ester (2). However, the optical yield from this type of reaction is usually less than 85%. Optical purification can be achieved by control of the crystallization.

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49

Shiau, Lie-Ding, Keng-Fu Liu e Yu-Chao Hsu. "Chiral purification of S-ibuprofen from ibuprofen enantiomers by stripping crystallization". Chemical Engineering Research and Design 117 (gennaio 2017): 301–8. http://dx.doi.org/10.1016/j.cherd.2016.10.019.

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50

Sidana, Jasmeen, e Lokesh Kumar Joshi. "Recycle HPLC: A Powerful Tool for the Purification of Natural Products". Chromatography Research International 2013 (6 novembre 2013): 1–7. http://dx.doi.org/10.1155/2013/509812.

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Abstract (sommario):

Natural compounds occur as various isomeric or closely related structures in biological matrices. These compounds are difficult to separate from the complex mixtures, and hence, the need for effective and innovative separation techniques arises. Recycle HPLC allows the recycling of sample, in part or full, and increases the separation efficiency of the process while keeping the peak dispersion to a minimum. Recycling in an HPLC system has been used in the isolation and purification of different types of natural products including enantiomers, diastereomers, epimers, positional isomers, and structurally related or unrelated compounds having similar retention characteristics. The present paper overviews the development of instrumentation and setup of recycle HPLC and its applications in the separation of natural products.

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