Novel transformations of nitraminodiol diacetates

A novel scission reaction of nitraminodiol diacetates of the formula AcO[CH₂N(NO₂) _x CH₂OAc (x = 1–4) in concentrated sulfuric acid to form formaldehyde, nitramide, and 2-nitro-2-azapropane-1,3-diol disulfate was found.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 3, pp 761–762, March, 1996.     

Steroid compounds from ophiuroids. I. New steroid sulfate from Ophiura sarsi

The sulfate of a steroid polyol has been isolated from the Far Eastern ophiuroidOphiura sarsi, and its structure has been established by chemical and spectral methods as cholest-5-ene-3,4,21-diol 3-(sodium sulfate). No steroid compounds of such structure from ophiuroids have been described previously.Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Branch, USSR Academy of Sciences, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 375–379, May–June, 1988.     

DNA-phospholipid recognition: modulation by metal ion and lipid nature. Complexes structure and stability calculated by molecular mechanics

The structures and formation energies of nucleic acid-phospholipid complexes both in the absence and in the presence of Mg(2+) ions were calculated taking double-stranded trinucleoside diphosphates NpNpN or heptanucleotides ApAp(NpNpN)pApA, composed of 64 possible combinations of genetic code, and phosphatidylcholine (PC) and sphingomyelin (SM) as model compounds. The dependence of intramolecular interactions on the primary structure of nucleic acid molecules and on the presence of a cationic bridge was revealed. The formation energies and structure of oligonucleotides were found by molecular mechanics calculations with the AMBER force field. The structures of phospholipid and MgCl(2) molecules were calculated by the semiempirical PM3 method, while the energies of phospholipid-oligonucleotide complexes were calculated by the molecular mechanics method. Calculations of complexes were carried out with consideration of solvation effects. Considerable gain in the formation energy of triple complexes is achieved due to the presence of the electroneutral metal bridge. A tendency toward increasing the stability of "triple" PC complexes (but not SM ones), containing guanosine- and cytidine-enriched triplets was revealed. Depending on the structure of NpNpN trinucleotides, the formation energy values of NpNpN-MgCl(2)-PC and ApAp(NpNpN)pApA-MgCl(2)-PC complexes differ by 1.7-2.6 kcal mol(-1), which can be considered as the atomic-scale manifestation of the recognition phenomenon. Presence of metal (II) ion bridge results in a greater stabilization of the phospholipid-nucleic acid complexes for SM in comparison to PC (the total energy difference equals to 4-16 kcal mol(-1)). Depending on the structure of NpNpN trinucleotides, the formation energies of NpNpN-MgCl(2)-SM and ApAp(NpNpN)pApA-MgCl(2)-SM complexes differ by 1.7-2.1 kcal.mol(-1), which is essential at physiological conditions and can also be considered as the recognition effect.     

HIV fusion inhibitor peptide T-1249 is able to insert or adsorb to lipidic bilayers. Putative correlation with improved efficiency

T-1249 is a HIV fusion inhibitor peptide under clinical trials. Its interaction with biological membrane models (large unilamellar vesicles) was studied using fluorescence spectroscopy. A gp41 peptide that includes one of the hydrophobic terminals of T-1249 was also studied. Both peptides partition extensively to liquid-crystalline POPC (1-palmitoyl-2-oleyl-sn-glycero-3-phosphocholine) (DeltaG = -7.0 kcal/mol and -8.7 kcal/mol, for T-1249 and terminal peptide, respectively) and are located at the interface of the membrane. T-1249 is essentially in a random coil conformation in this lipidic medium, although a small alpha-helix contribution is present. When other lipid compositions are used (DPPC, POPG + POPC, and POPC + cholesterol) (DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) and POPG (1-palmitoyl-2-oleyl-sn-glycero-3-[phospho-rac-(1-glycerol)), partition decreases, the most severe effect being the presence of cholesterol. Partition experiments and fluorescence resonance energy transfer analysis show that T-1249 adsorbs to cholesterol-rich membranes. The improved clinical efficiency of T-1249 relative to enfuvirtide (T20) may be related to its bigger partition coefficient and ability to adsorb to rigid lipidic areas on the cell surface, where most receptors are inserted. Moreover, adsorption to the sterol-rich viral membrane helps to increase the local concentration of the inhibitor peptide at the fusion site.     

Synthesis and multitopic complex formation of a photochromic bis(crown ether) based on benzobis(thiazole)

2,7-Bis[2-(6,7,9,10,12,13,15,16-octahydro-5,8,11,14,17-pentaoxabenzocyclopentadecen-2-yl)vinyl]-benzo[1,2-d;3,4-d']bisthiazole, 2, with crown ether styryl moieties substituted on a heterocyclic core, was synthesized and its complex forming ability with several metal cations was evaluated in acetonitrile by absorption and fluorescence spectroscopy. The results are compared to those for the analogous ligand possessing a single crown ether styryl moiety. Selective binding of the metal cation at the heterocyclic core of both ligands was observed only for Hg2+. Alkali and alkaline earth cations bind selectively at the crown ether moieties. Stability constants and pure spectra of defined stoichiometry were determined with the use of HYPERQUAD, a least-squares fitting program, and the results were validated in one case by subjecting the titration spectral matrix to singular value decomposition with self-modeling (SVD-SM). The multitopic ligand 2 forms relatively strong 2:2 stoichiometric complexes with K+, among the alkali metal cations, and Ba2+, among the alkaline earth metal cations, and is a promising selective optical sensor for these ions.     

Reduction of arsenic trichloride with hydrogen

The composition of an equilibrium vapor-gas mixture in the range 700–1100 K was estimated for the reaction of arsenic trichloride with hydrogen taken in excess of a = 1.0–2.5 as compared to the stoichiometry. The temperatures of the onset of arsenic condensation (dew point) were found. Kinetic parameters of the chemical reaction were determined. Optimal conditions for the reduction of arsenic trichloride with hydrogen were refined and conditions for the condensation of arsenic with the minimum fraction of the amorphous modification were found. Original Russian Text ? N.A. Potolokov, A.V. Serov, V.N. Potolokov, A.V. Zhuravlev, V.P. Kolganov, E.G. Zhukov, V.A. Fedorov, V.I. Kholstov, 2007, published in Zhurnal Prikladnoi Khimii, 2007, Vol. 80, No. 1, pp. 3–8.     

Determination of the Inductive Constant of the Succinimide Group from the Reaction Series of Thermolysis of Nitro Esters

The inductive constant σ* of the succinimide group was determined using the previously obtained equation correlating the rate constant k _l ofliquid-phase homolysis of the O-NO₂ bond in nitro esters with the σ* constants of electronegative substituents. The kinetics of thermolysis of N-nitroxymethyl- and N-(2-nitroxyethyl)succinimide in the melt and solutions was studied manometrically. Adequate data for k _l were obtained. The σ* constant of the succinimide group was determined to be 4.5. The σ* constants for the phthalimide group and some other imide substituents were determined by a similar procedure.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 6, 2005, pp. 954–957.Original Russian Text Copyright © 2005 by Goncharov, Dubikhin, Nazin, Fedorov, Shastin.     

Rhenium complexes with pyrazoles. Synthesis and crystal structure of trans-[Re(O)(OMe)L4]Br2·L·4H2O (L is 3,5-dimethylpyrazole)

The first mononuclear Re^V complex with four pyrazole ligands, viz., [Re(O)(OMe)L₄]Br₂ (L is 3,5-dimethylpyrazole), and its molecular adduct with L, viz., [Re(O)(OMe)L₄]Br₂·L·4H₂O, were synthesized. The complex is resistant to hydrolysis in a neutral aqueous solution. The structure of the adduct was established by X-ray diffraction analysis.