Synthesis of ethyl 2-alkylthio-2-oxazoline-5-carboxylate

Glycidic esters react with excess alkyl thiocyanates in the presence of equimolar amounts of boron trifluoride etherate to give esters of 2-alkylthio-2-oxazoline-5-carboxylic acids. The structure of the products was confirmed by the data from the PMR and IR spectra.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 460–461, April, 1979.     

Stereoisomerism of the matrine alkaloids

The stereoisomerism of compounds of the matrine series is considered on the basis of the authors' own x-ray structural studies of these alkaloids. A corrected series of eight stereoisomers has been drawn up. It has been shown that the numbers of theoretically possible stereoisomers of matrine is thirty-two.     

Crystal structure of a mutant of archaeal ribosomal protein L1 from Methanococcus jannaschii

The crystal structure of a mutant of archaeal ribosomal protein L1 from Methanococcus jannaschii with the deletion of a nonconserved positively charged cluster consisting of eight C-terminal amino acid residues is determined by the molecular replacement method at 1.75 Å resolution. This mutant is shown to form more stable and ordered crystals belonging to a space group other than that of the wild-type protein crystals. The positively charged C-terminal region has only a slight effect on the interaction between protein L1 and RNA molecules. Hence, this mutant can be used to prepare protein-RNA complexes and obtain their crystals.     

Standardization of pH measurements based on the ion interaction approach

The Pitzer method was used to calculate the pH values on the conventional and “true” scales for the TRIS—TRIS·HCl−NaCl−H₂O buffer system in the 0–40 °C temperature region and 0–4 NaCl molality interval. This buffer can be used as a standard for pH measurements in a wide range of ionic strengths. The conventional scale is used in cells without a salt bridge. The “true” scale is recommended for pH measurements using cells with a salt bridge. At the same concentrations of the buffer solution, the “true” scale is essentially transformed into the scale of the National Bureau of Standards (NBS) of the USA. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 676–680, April, 2000.     

Optimizing the performance of the multiconfiguration molecular mechanics method

Multiconfiguration molecular mechanics (MCMM) is a general algorithm for constructing potential energy surfaces for reactive systems (Kim, Y.; Corchado, J. C.; Villà, J.; Xing, J.; Truhlar, D. G. J. Chem. Phys. 2000, 112, 2718). This paper illustrates how the performance of the MCMM method can be improved by adopting improved molecular mechanics parameters. We carry out calculations of reaction rate constants using variational transition state theory with optimized multidimensional tunneling on the MCMM PESs for three hydrogen transfer reactions, and we compare the results to direct dynamics. We find that the MCMM method with as little as one electronic structure Hessian can describe the dynamically important regions of the ground-electronic state PES, including the corner-cutting-tunneling region of the reaction swath, with practical accuracy.     

Molecular and crystal structure of sophoridine N-oxide

The spatial structure of natural sophoridine N-oxide has been studied by x-ray structural analysis. It has been shown that when sophoridine is oxidized, rings B and C, which have the boat form, are deformed in the direction of the twist form.     

How well can density functional methods describe hydrogen bonds to pi acceptors?

We employed four newly developed density functional theory (DFT) methods for the calculation of five pi hydrogen bonding systems, namely, H2O-C6H6, NH3-C6H6, HCl-C6H6, H2O-indole, and H2O-methylindole. We report new coupled cluster calculations for HCl-C6H6 that support the experimental results of Gotch and Zwier. Using the best available theoretical and experimental results for all five systems, our calculations show that the recently proposed MPW1B95, MPWB1K, PW6B95, and PWB6K methods give accurate energetic and geometrical predictions for pi hydrogen bonding interactions, for which B3LYP fails and PW91 is less accurate. We recommend the most recent DFT method, PWB6K, for investigating larger pi hydrogen bonded systems, such as those that occur in molecular recognition, protein folding, and crystal packing.     

Mechanism of the oxidation reaction of Cu with N2O via nonadiabatic electron transfer

We treat the present work as an attempt to elucidate the mechanism of the oxidation reaction of the Cu atom by nitrous oxide based on our recent work (Kryachko, E. S.; Vinckier, C.; Nguyen, M. T. J Chem Phys 2001, 114, 7911) on the electron attachment to this molecule. We suggest that the title reaction in its Arrhenius regime occurs via the nonadiabatic electron transfer from Cu to the oxygen atom at the crossing of the potential energy surfaces Cu(4s ²S_1/2) + N₂O(X ¹Σ⁺) and Cu⁺ + N₂O^?, where the latter is linked to the complex N₂O^? originated from the higher‐energy T‐shape N₂O molecule and discovered in the aforementioned work. The calculations performed in the present work using a variety of quantum chemical methods support the proposed model. We also show the existence of other reaction pathways of the title reaction that, we believe, contribute to its non‐Arrhenius behavior observed experimentally at T > 1190 K. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Molecular and crystal structure of sophoridine

The three-dimensional structure of the alkaloid sophoridine C₁₅H₂₄ON₂ has been studied by x-ray structural analysis; the parameters of the elementary cell are: a=5.458, b=10.640, c=11.989 Å; =99.7°; z=2; space group P2₂. The experimental set was obtained on a Sinteks-P2₁ diffractometer, the structure being determined by the direct method with refinement by the method of least squares in the anisotropic approximation taking the hydrogen atoms into account to R=0.059. Ring A has the chair conformation, rings B and C the boat conformation, and ring D the half-chair conformation. The linkages of rings A/B, B/C, and C/D are trans, and of B/C cis. There are no shortened intermolecular contacts in the crystal structure of the compound.Institute of Bioorganic Chemistry, Academy of Sciences of the Uzbek SSR, Tashkent. Institute of Crystallography, Academy of Sciences of the USSR, Moscow. V. I. Lenin Tashkent State University. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 355–362, May–June, 1979.     

Synthesis and products of hydrolysis of 2-methyl-5-(β-arylacrylyl)-2-oxazolines

The condensation of 2-methyl-5-acetyl-2-oxazolines with p-R-substituted benzaldehydes in the presence of bases gave the corresponding 2-methyl-5-(-aryl-acrylyl)-2-oxazolines, the hydrolysis of which with hydrochloric acid leads to hydrochlorides of alkyl-substituted 1-(p-R-styryl)-2-acetoxy-3-aminobutan-1-ones. Treatment of the latter with bases gives 1-(p-R-styryl)-2-hydroxy-3-N-acetyl-2, 3-alkylbutan-1-ones.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1025–1027, August, 1982.