Aggregation and photoisomerization of amphiphilic crown-ether styryl dye in monolayers at the interface

The molecules oftrans-isomer of styryl dye1a, containing the benzo-18-crown-6 moiety and the methoxybenzothiazole residue with theN-octadecyl substituent, were shown to form stable, highly ordered monolayers at the water/air interface. Increasing the surface pressure of the monolayer results in the formation of the H-aggregated molecules of compound1a. The H-aggregates tend to dissociate to the monomerictrans-form, when the monolayer forms in the Langmuir-Blodgett film (LB film). The light irradiation of the LB films leads to the partially reversibletrans-cis-photoisomerization of compound1a, whose efficiency is much lower than that observed in an acetonitrile solution of1a. The aggregation of cis-1a isomers in the LB film is suggested to hamper the reversecis-trans-isomerization. The aggregation oftrans-1a molecules in the LB films does not occur in air, but, after dipping in an aqueous solution, molecules of the LB film slowly form J-aggregates. A model of the structural organization oftrans-1a molecules in the LB films was proposed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2490–2496, October, 1996.     

Crystal-Chemical Classes of “Cambridge” Crystal Structures: Statistical Analysis of Topology

Crystals structures with organic carbon, i.e., organic and organometal compounds and coordination compounds with organic ligands are systematized based on the results of a statistical treatment of CSD (Cambridge Structural Database) data. The overwhelming majority of CSD structures are molecular crystals, which may be homomolecular or heteromolecular; the latter, in turn, are classified into molecular complexes, salts, crystal solvates, and crystal hydrates. Polymeric (nonmolecular) crystals occur much more rarely. For substances belonging to different crystal-chemical classes, distributions according to space groups and structural classes have been studied; considerable differences between the distributions have been found. In particular, it was established that chiral structures (with P2₁2₁2₁, P2₁, etc. symmetry) are met much more rarely among inorganic CSD structures with metals and metalloids than among organic structures consisting exclusively of organogen elements; the most striking examples are hydrates and salts containing Cl^–, Br^–, and I^– ions.     

Structure of Supramers Formed by the Amphiphile Biotin-CMG-DOPE

The synthetic function-spacer-lipid (FSL) amphiphile biotin-CMG-DOPE is widely used for delicate ligation of living cells with biotin residues under physiological conditions. Since this molecule has an “apolar-polar-hydrophobic” gemini structure, the supramolecular organization is expected to differ significantly from the classical micelle. Its organization is investigated with experimental methods and molecular dynamics simulations (MDS). Although the linear length of a single biotin-CMG-DOPE molecule is 9.5 nm, the size of the dominant supramer globule is only 14.6 nm. Investigations found that while the DOPE tails form a hydrophobic core, the polar CMG spacer folds back upon itself and predominantly places the biotin reside inside the globule or planar layer. MDS demonstrates that <10 % of biotin residues on the highly water dispersible globules and only 1 % of biotin residues in layer coatings are in an linear conformation and exposing biotin into the aqueous medium. This explains why in biotin-CMG-DOPE apolar biotin residues both in water dispersible globules and coatings on solid surfaces are still capable of interacting with streptavidin.     

Concurrent measurements on conductivity and hall coefficient tensor components of anisotropic semiconductor films

The problem of distribution of the electric-field potential in anisotropic semiconductor films in the case of proble measurements is discussed. Models for distributions of the potential and streamlines in test specimens, clearly demonstrating features of the passage of electric current through anisotropic media, are presented. A concurrent measurement procedure for conductivity and Hall coefficient tensor components of rectangular semiconductor films, using a four-point probe technique, is introduced. Lipetsk State Pedagogical Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 89–95, June, 2000.