Determination of liposome permeability of ionizable carbamates of zidovudine by steady state fluorescence spectroscopy

In the present paper the relative permeabilities of AZT-Pyp and AZT-Ethy across a phospholipid bilayer were estimated by the means of fluorescence spectroscopy.

The center of spectral mass of both non-encapsulated AZT-derivatives (AZT-der) emission spectra increased as a function of the illumination time inside the spectrofluorimeter cell. This phenomenon was even more evident when drugs were incubated under an UV mercury lamp, suggesting its photolytic origin. AZT-der were protected from photolysis inside liposomes and decomposed upon irradiation when they were free in the aqueous phase. The time-dependent decrease in the fluorescence intensity at a constant wavelength was fitted to a two-exponential equation and the values of rate constants for permeability and photolysis were calculated. It was concluded that AZT-Pyp but not AZT-Ethy diffused across the bilayer. This behavior correlated with the molecular volumes of AZT-Pyp (379.6 Å³) and AZT-Ethy (450.5 Å³), determined from the minimum energy conformations but not with previously reported log P values. These results reinforce the concept that not only lipophilicity but also membrane structure and AZT-der molecular size had a critical influence in passive diffusion across bilayers and may help in future refinements of other AZT-der molecular design.     

Quantifying the Interactions in the Aggregation of Thermoresponsive Polymers: The Effect of Cononsolvency

The aggregation kinetics of thermoresponsive core–shell micelles with a poly(N‐isopropyl acrylamide) shell in pure water or in mixtures of water with the cosolvents methanol or ethanol at mole fractions of 5% is investigated during a temperature jump across the respective cloud point. Characteristically, these mixtures give rise to cononsolvency behavior. At the cloud point, aggregates are formed, and their growth is followed with time‐resolved small‐angle neutron scattering. Using the reversible association model, the interaction potential between the aggregates is determined from their growth rate in dependence on the cosolvents. The effect of the cosolvent is attributed to the interaction potential on the structured layer of hydration water around the aggregates. It is surmised that the latter is perturbed by the cosolvent and thus the residual repulsive hydration force between the aggregates is reduced. The larger the molar volume of the cosolvent, the more pronounced is the effect. This framework provides a molecular‐level understanding of solvent‐mediated effective interactions in polymer solutions and new opportunities for the rational control of self‐assembly in complex soft matter systems.

     

Synthesis and crystal structure of 2‐isocyano‐4‐methylphenyl diphenylacetate: a rare case of an easily accessible odourless isocyanide

Acidic hydrogen containing 2‐isocyano‐4‐methylphenyl diphenylacetate, C₂₂H₁₇NO₂, (I), was synthesized by the base‐promoted reaction between 5‐methylbenzoxazole and diphenylacetyl chloride. Achiral (I) crystallizes in the chiral P2₁2₁2₁ space group. The C[triple‐bond]N bond length is 1.164 (2) Å and the angle between the OCO and 2‐isocyano‐4‐methylphenyl planes is 69.10 (16)°. Molecules are linked via C=O...H_phenyl and bifurcated N[triple‐bond]C...H_phenyl/N[triple‐bond]C...H_methine hydrogen bonds, forming one‐dimensional arrays.     

New 3,3′[2,2′‐oxy‐bis‐(oxazaborolidine)]‐ethylenes. Structural studies by NMR,X‐ray,and quantum chemistry methods

3,3′‐[2,2′‐Oxy‐bis‐(4S‐methyl, 5R‐phenyl‐1,3,2‐oxazaborolidine)]ethylene ( 4a ) and 3,3′‐[2, 2′‐oxy‐(4S‐methyl‐5R‐phenyl‐1,3,2‐oxazaborolidine)‐ (1,3,2‐benzoxazaborolidine)]ethylene ( 4b ) were synthesized by the reaction of N,N′‐bis‐[(1R,2S)‐norephedrine]oxalyl ( 3a ) or N,N′‐[((1R,2S)‐norephedrine, o‐hydroxyphenylamine]oxalyl ( 3b ) with BH₃‐THF. The molecular structure of these compounds was established by NMR and infrared spectroscopy. The molecular geometry for 4 was studied by means of theoretical methods, resulting in structures that were in total agreement with those obtained by spectroscopy data and X‐ray diffraction. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:513–519, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20151     

Penny-shaped crack at the interface between elastic half-spaces under the action of a shear wave

The three-dimensional problem of elasticity for a bimaterial body with a penny-shaped crack at the interface under the action of a normal harmonic shear wave is solved by the boundary-element method. The distribution of displacements of crack faces and tractions and displacements at the interface is analyzed     

Magnetic phase transitions and the dynamic electric polarization in the LaMn<Subscript>2</Subscript>O<Subscript>5</Subscript> compound

Possible phase transitions to the ferromagnetic phase in the LaMn₂O₃ compound have been studied in the framework of a phenomenological approach based on a symmetry analysis. The conditions that parameters of the thermodynamic potential must satisfy to realize a second-order transition have been found. The line of the first-order phase transitions in this system and the critical point of the second-order phase transition line have been determined. It was shown that a dynamic electric polarization can form in the antiferromagnetic phase.     

Experimental and theoretical structural study of 2‐pyridyl‐ and 4‐hydroxyphenyl‐1,4‐dihydropyridine derivatives

A series of substituted 1,4‐dihydropyridines (1,4‐DHPs) has been synthesised following the well‐known Hantzsch's procedure for symmetrical 1,4‐DHP. The structures of these compounds have been thoroughly studied by X‐ray crystallographic analysis and semiempirical (AMI) calculations. A good agreement is found between the theoretical and experimental results. In all cases, the most stable conformation fulfils all the requirements needed for exhibiting an antagonist calcium effect.     

The antiferromagnetic photovoltaic effect

It is established that the photovoltaic effect may occur in centroantisymmetric antiferromagnets. It is due to nontrivial transformations of the antiferromagnetic vector upon atomic transposition under the action of crystallochemical symmetry group elements of a medium. The direction of the photovoltaic current is shown to be governed by the crystal symmetry, its exchange magnetic structure, and the orientation of the antiferromagnetic vector about the crystallographic axes.