[en] Two oxime-cyclophosphazenes were prepared from the hexakis(4-formylphenoxy)cyclotriphosphazene and hexakis(4-acetylphenoxy)cyclotriphosphazene. The reactions of these oximes with ethyl bromide, allyl bromide, propanoyl chloride, and acriloyl chloride were studied. Hexasubstituted compounds were obtained from the reactions of hexakis{4-[(hydroxyimino)methyl]phenoxy}cyclotriphosphazene with ethyl bromide, allyl bromide, and propanoyl chloride, however, the oxime groups on 3 rearranged to nitrile in the reaction of 3 with acriloyl chloride. Hexasubstituted compounds were also obtained from the reactions of hexakis{4-[(1)-N-hydroxyethaneimidoyl]phenoxy}cyclotriphosphazene with allyl bromide and propanoyl chloride. Tetra- and penta-substituted products were obtained from the reactions of 9 with ethyl bromide and acriloyl chloride, respectively. All products were generally obtained in high yields. The structures of the compounds were defined by elemental analysis, IR, ¹H, ¹³C, and ³¹P NMR spectroscopy. (author)

[en] Application of hydrostatic pressure to phospholipid bilayers increases acyl chain order and raises the main transition temperature. ²H NMR spectra and quadrupole echo decay times were obtained at ambient pressure and pressures of 85 MPa and 196.1 MPa for ordered phase bilayers of a zwitterionic phospholipid : 16:0-16:0 PC-d₆₂ (DPPC-d₆₂) and an anionic phospholipid : 16:0-16:0 PG-d₆₂ (DPPG-d₆₂). The extent to which deuterium magnetization following an RF pulse is refocused in the echo after a second pulse is limited by the motions that modulate the orientation-dependent quadrupole interaction. The q-CPMG pulse sequence is used to separate the contribution of slow and fast motions to the echo decay rate. This work provides insight into how chain packing affects local motion.

[en] Kinetic isotope effect studies have been applied to a class of reactions involving acyl transfer. Initially studies were made of relatively well understood reactions of methyl formate. These measurements were then used as a basis for interpreting the kinetic isotope effects observed during chymotrypsin-catalyzed reactions. Values of k/sub ¹⁶O//K/sub ¹⁸O/ were measured for several reactions of methyl formate-methoxyl-¹⁸O. The ratios for acid-catalyzed hydrolysis, alkaline hydrolysis, and general base catalyzed hydrolysis in succinate buffer were determined. The extremely small kinetic isotope effect observed for acid-catalyzed hydrolysis suggests a mechanism in which equilibrium protonation of the ester is counter-balanced by the normal kinetic isotope effect for the attack of water on the oxocarbonium ion. The small but significant isotope effects observed for alkaline hydrolysis, general base catalyzed hydrolysis, and hydrazinolysis at high pH suggest a transition state in which the order of the acyl carbon-methoxyl oxygen bond of 1.15 in the ester is only slightly reduced in the transition state. Oxygen-18 leaving group kinetic isotope effects were also used to elucidate the transition state structure in the acylation of chymotrypsin by the two specific ester substrates, CH₃CO-L-Trp-¹⁸OC₂H₅ (AcTrpEE) and CH₃OCO-L-Trp-¹⁸OC₂H₅ (MocTrpEE). These differ in that AcTrpEE can in principle form an oxazoline en route to the acyl enzyme. The kinetic isotope effects were measured at three values of pH and, for AcTrpEE, at two substrate concentrations, and were found to be independent of these parameters. The values of k/sub ¹⁶O//k/sub ¹⁸O/ were also measured. An alternative technique using doubly labeled substrates was investigated and discarded because of its relatively poor precision. Numerous new computer programs used in the data analysis are listed and described in an appendix

No abstract available

[en] Paramagnetic contact shifts and relaxation rate enhancements from molecular oxygen dissolved in a model membrane, were studied by nuclear magnetic resonance spectroscopy. The model membrane system was an isotropic bicelle formed using 1-myristelaidoyl-2-myristoyl-d27-sn- glycero-3-phosphocholine (MLMPC), a custom phospholipid, and 1-2-dihexanoyl-d22-sn-glycero-3-phosphocholine (DHPC). The ¹³C and ¹H spectra of MLMPC were assigned. Molecular oxygen was delivered at external pressures of 20 and 50 atm. Paramagnetic contact shifts were found to scale with the oxygen solubility gradient in the lipid bilayer, were found to be invariant to temperature changes in the region studied (288K to 331K), and scaled linearly with changes in oxygen pressure. Relaxation rate enhancements from oxygen were low in the headgroup region and increased to a roughly constant rate in the acyl chain region. Rates were comparable to values predicted by simple thermodynamic theories which take into account the observed gradients in diffusion rates and solubility of oxygen in bilayers. (author)

[en] Our study is devoted to the development of an optimal protocol for lipolysis and lipogenesis assessment using ¹⁴C-labeled glucose. We confirmed the utility of the developed method for the analysis of lipogenesis and lipolysis rates in adipocytes using insulin and isoproterenol. The present study describes rapid, cheap and simple techniques for the assessment of lipids metabolism and storage in adipocytes. Upgraded methods of ¹⁴C-labeled TAG extraction and saponification allow to investigate mechanisms of lipolysis, lipogenesis and TAG-cycling. (author)

[en] An efficient method for the synthesis of acylals from different aldehydes and acetic anhydride in the presence of Keggin-type stannum (IV) phosphomolybdate under ultrasound irradiation at room temperature was achieved. This method provides a new and efficient protocol in terms of cost effective of catalyst, a wide scope of substrates, and simple work-up procedure. (author)

No abstract available

[en] The acylation of TMS-2-lithiomalonates gives rise to ketones. Since [1-¹⁴C] acyl halides are easily prepared from [¹⁴COOH] acids accessible directly from ¹⁴CO₂ or via the [¹⁴C-cyanide] route we applied this reaction to a wide variety of labelled acyl halides and a large array of bis-TMS malonates or monoethyl, mono TMS malonates. The resulting ketones were then subjected to appropriate chemical transformations resulting in the high yielding preparation of ¹⁴C biochemicals. (author). 11 refs.; 1 tab

[en] The 2-monoacylglycerol acyltransferase (EC 2.3.1.22, acylglycerol palmitoyl transferase) catalyzes the synthesis of X-1,2-diacylglycerols from 2-monoacylglycerol and acyl CoA with an apparently variable stereochemical specificity. A microassay for determining the ratio of sn-1,2- and sn-2,3-diacylglycerol formed by the acylation of radioactive 2-monoacylglycerol in intact cell or in cell-free systems in the presence of free fatty acids and cofactors has been developed. The diacyglycerols isolated by thin-layer chromatography using nonradioactive racemic diacylglycerols as carriers. The enantiomer content is determined following a chemical synthesis of X-1,2-diacylphosphatidylcholines and a stereospecific stepwise release of the sn-1,2- and sn-2,3-diacylglycerols by phospholipase C. By using thin-layer chromatography for the isolation of the hydrolysis products, known samples ranging in enantiomer ratios from 0.05 to 20 and containing 5000 to 200,000 cpm can be assayed to within 1% of the major and within 10% of the minor enantiomer content. The method is applicable to the determination of the enantiomer content of X-1,2-diacylglycerols generated via other acyltransferases and via lipolysis of triacylglycerols and diacylglycerolphospholipids in other biological systems