No abstract available

[en] The explicit form of the zeroth Green's function in the Hückel model, approximated by the negative of the inverse of the Hückel matrix, has direct quantum interference consequences for molecular conductance. We derive a set of rules for transmission between two electrodes attached to a polyene, when the molecule is extended by an even number of carbons at either end (transmission unchanged) or by an odd number of carbons at both ends (transmission turned on or annihilated). These prescriptions for the occurrence of quantum interference lead to an unexpected consequence for switches which realize such extension through electrocyclic reactions: for some specific attachment modes the chemically closed ring will be the ON position of the switch. Normally the signs of the entries of the Green's function matrix are assumed to have no physical significance; however, we show that the signs may have observable consequences. In particular, in the case of multiple probe attachments – if coherence in probe connections can be arranged – in some cases new destructive interference results, while in others one may have constructive interference. One such case may already exist in the literature

[en] The literature on the spectral properties of ketocyanine dyes are reviewed from the viewpoint of chromophore interaction theory. It is shown that this theory can be used to describe the properties of a number of bichromophoric polyene donor–acceptor compounds and to predict their molecular configurations and spectral features.

[en] Polymerization of a monomeric crystal is obtained by slow electron irradiation

No abstract available

No abstract available

[en] A theory has been described of solvents effects on radiative rate constants using first-order perturbation theory with vibrionic coupling along with solvent-dependent energy denominators. The fixed expression of this theory contained no provisions for solvent effects on the wave functions. However, if all decay channels are properly taken into account, the direct solvent contribution to the radiative rate constant should be nonzero

[en] 

This review summarizes main advances achieved by Russian researchers in the synthesis and characterization of semi-synthetic antibiotics of a new generation in the period from 2004 to 2019. The following classes of compounds are considered as the basis for modification: polycyclic antibacterial glycopeptides of the vancomycin group, classical macrolides, antifungal polyene macrolides, the antitumour antibiotic olivomycin A, antitumour anthracyclines and broad-spectrum antibiotics, in particular, oligomycin A, heliomycin and some other. Main trends in the design of modern anti-infective and antitumour agents over this period are considered in relation to original natural antibiotics, which have been independently discovered by Russian researchers. It is shown that a new type of hybrid structures can, in principle, be synthesized based on glycopeptides, macrolides and other antibiotics, including heterodimers containing a new benzoxaborole pharmacophore. The review addresses the influence of the length of the spacer between two antibiotic molecules on the biological activity of hybrid structures. A combination of genetic engineering techniques and methods of organic synthesis is shown to be useful for the design of new potent antifungal antibiotics based on polyenes of the amphotericin B group. Many new semi-synthetic analogues exhibit important biological properties, such as a broad spectrum of activity and low toxicity. Emphasis is given to certain aspects related to investigation of a broad range of biological activity and mechanisms of action of new derivatives.

The bibliography includes 101 references. (paper)

[en] Measurements of the rate coefficients for ternary association reactions between unsaturated hydrocarbon ions C_nH_m⁺ (4≤ n≤ 6, 0≤ m≤6) and CO in a SIFT apparatus have been used to deduce rate coefficients for the corresponding radiative association processes. These latter rate coefficients have been used to estimate the relative abundances of a variety of unusual chemical species and their isomers with the chemical formulae C_nO, HC_nO, and H₂C_nO in dense interstellar clouds such as TMC-1. Two of these species -C₃O and HC₂ CHO (propynal)- have already been detected in this source

[en] The knowledge of the intersection space topography of electronic states is essential for deciphering and predicting photoinduced reactions. Michl and Bonacic-Koutecky developed a two-electron two-orbital model that allowed first systematic studies of the chemical origin of conical intersections in strongly polar systems. We generalize this approach to arbitrary functionalized and unfunctionalized polyene systems. For the extended model, a set of mathematical conditions for the formation of conical intersections are derived. These conditions are translated into geometrical motions and electronic effects, which help to explain and predict the structure and energetics of conical intersections. A three-step strategy for the conceptual search of conical intersections is outlined. Its universal validity is demonstrated using the textbook example cyclohexadiene and its functionalized derivative trifluoromethyl-indolylfulgide, a chromophore studied for possible application as a molecular switch.