Kinetics and mechanism of biodegradation of (co)polyglycolide sutures

Biodegradation in vivo of modified and unmodified PG (polyglycolide) and PGL (copolymer glycolide — L — lactide) monofilament sutures were studied using ¹H- NMR, wide and small angle X-ray scattering, differential scanning calorimetry (DSC), electron microscopy (EM), Fourier transform (FT) Raman spectroscopy methods. It was found that the process includes a steady-state and accelerated stages of biodegradation. The suture biostability depends on polymer morphology changing widely over the suture draw ratio. The modification of polymer chain results in an increase in suture useful lifetime without significant changes of complete polymer degradation time. It was also established the important role of weak intermolecular hydrogen bonds such as CH–-O=C in the suture stability.     

The structure of the boundary element matrix for the three-dimensional Dirichlet problem in elasticity

The algebraic properties of the matrix arising for the three-dimensional Dirichlet problem for Lamé equations in a rotational domain by the boundary element method are considered. The use of the special basis leads to a matrix having a block structure with sparse blocks. The possible strategies for the efficient solution of the above problem are discussed. © 1998 John Wiley & Sons, Ltd.     

Azabrendanes. II. Chemo-, regio- and stereoselective transformation of 3-oxatricyclo[3.2.1.02,4]octane-endo-6-carbonitrile in reaction with lithium aluminum hydride

The reduction of 3-oxatricyclo[3.2.1.0^2,4]octane-endo-6-carbonitrile by lithium aluminum hydride is completed by the formation of exo-2-hydroxy-4-azatricyclo[4.2.1.0^3,7]nonane with the structure confirmed (1) by the analysis of ¹H, ¹³C, ¹⁴N, and ¹⁷O NMR spectra and the two-dimensional spectra (COSY-experiment); (2) by comparison with ¹H and ¹³C NMR spectra of the corresponding oxygen analog of heterobrendane; (3) by the calculation of the vicinal constants for the spin-spin interaction in the molecules of both analogs by the MMX program; and (4) by transformation into N-(p-bromophenylsulfonyl)-exo-2-hydroxy-4-azatricyclo[4.2.1.0^3,7]nonane prepared by an alternative synthesis, viz., epoxidation of N-(p-bromophenylsulfonyl)bicyclo-[2.2.1]hept-2-en-endo-5-methylamine. The reduction of 3-oxatricyclo [3.2.1.0^2,4]octane-exo-6-carbonitrile affords the epoxide, 3-oxatricyclo[3.2.1.0^2,4]octane-exo-6-methylamine. Different behaviors of stereoisomers are discussed; analysis of the coefficients of the atomic orbitals in the MO LCAO equation (AM1 method) has been made, and the strengths of the C(SINGLE BOND)O bonds in the epoxy ring has been analyzed. © 1997 John Wiley & Sons, Inc.     

Ordering and mobility of ferroelectric liquid crystal dimer as studied by FT-IR spectroscopy with 2D-IR correlation analysis

Both a conservative rapid-scan FT-IR technique and a novel step-scan FT-IR technique with 2D correlation analysis were used to study the orientation and the mobility of a ferroelectric liquid crystal dimer during switching under an electric field. The detailed mutual arrangements of different molecular segments (mesogen, poly(methylene) chain, polysiloxane chain) in a smectic C* phase were derived from the static spectra. It was shown that the long mesogen axis, the average poly(methylene) and the average polysiloxane chain axes do not coincide with each other. The hindered rotation of the carbonyl group is confirmed. Time-resolved FT-IR technique was used to follow the segmental motion with a time resolution of 5 μs. The temperature and electric field strength dependencies of the mobility of these segments are discussed. 2D correlation analysis of time-resolved data reveals small differences in the behavior of the carbonyl and the benzoic rings in the mesogen moieties, that can be explained as differences in the orientation distribution functions of these moieties.     

A Parallel Preconditioned Iterative Realization of the Panel Method in 3D

The parallel version of precondition iterative techniques is developed for matrices arising from the panel boundary element method for three-dimensional simple connected domains with Dirichlet boundary conditions. Results were obtained on an nCube-2 parallel computer showing that preconditioned iterative methods are very well suited also in three-dimensional cases for implementation on an MIMD computer and that they are much more efficient than usual direct solution techniques.     

Carbenoid reactions of trifluoromethylelement compounds. Part 4. Reactions of trifluoromethylzinc bromide with enamines and methylene bases

The reactions of ZnBr(CF₃)·2CH₃CN with 1-morpholinocyclo-pentene and -hexene have been investigated and found to yield mixtures of two isomers of 1-morpholino-1-cyanomethyl-2-difluoromethyl-cyclopentane and -hexane, respectively. The interaction with methylene bases of nitrogen heterocycles leads to the formation of trimethinecyanine dyes. This reaction sequence includes the formation of two carbon-carbon bonds in a one-pot operation. The mechanism of the reactions is discussed.     

Analysis of oligonucleotides using coupled high performance liquid chromatography-electrospray mass spectrometry

Summary Improved HPLC and ESMS conditions have been established, allowing the separation and analysis of oligodesoxyribonucleotides by coupled HPLC-ESMS.     

Trifluoromethyl-substituted hydantoins, versatile building blocks for rational drug design

Preparatively simple, one-pot syntheses of trifluoromethyl-substituted hydantoins starting from Boc-protected imines of hexafluoroacetone and trifluoropyruvate are described. They represent valuable building blocks for the construction of constrained peptides or as scaffolds for the synthesis of highly potent VLA-4 antagonists.