Sergey A. Pisarev

Self-assembly in double-tailed surfactants in dilute aqueous solutions

Abstract The phase behavior and aggregation of dialkyldimethylammonium bromides (alkyl chain lengths 8, 10, 12 and 16) in dilute aqueous solutions (concentrations below 1 wt.%) were investigated by static light scattering, densitometry and freeze-fracture electron microscopy. Surface and interfacial tension measurements were performed by use of the drop weight and spinning drop methods. Phase diagrams of dialkylammonium bromide/water systems in the temperature range 20–60°C were obtained, and it was found that four areas are present on the phase diagrams: (1) molecular solution; (2) vesicular solution with small unilamellar vesicles (D = 30–70 nm, depending on the alkyl chain length); (3) a two-phase region, where two populations of aggregates coexist: small vesicles and large liposomes; (4) a random lamellar L3 phase. It is important to note that vesicle and liposome formation occurred spontaneously on consecutive dilutions of the L3 phase. Surface and interfacial tension measurements have shown that aggregation in the bulk solutions were accompanied by unusually sharp decreases of the surface and interfacial tensions; the tension at the L3 phase/octane interface dropped to an ultralow value (0.01 mN m−1). Langmuir balance studies of diC12 derivative and diC16 derivative monolayers on the aqueous subphase were performed, and some hysteresis in the compression-decompression cycles was observed, probably due to partial dissolution of amphiphiles. The minimum area per surfactant molecule in the condensed monolayers was found to be independent of the alkyl chain length, being equal to 68 A2. The structural transformation vesicles/large liposomes/lamellar phase was illustrated by electron microscopy.

Fast tools for calculation of atomic charges well suited for drug design.

Two novel approaches to construct empirical schemes for partial atomic charge calculation were proposed. The charge schemes possess important benefits. First, they produce both topologically symmetrical and environment dependent charges. Second, they can be parameterised to reasonably reproduce ab initio molecular electrostatic potential (MEP), which guarantees their successful use in molecular modelling. To validate the approaches, the parameters of the proposed charge schemes were fitted to best reproduce MEP simultaneously on grids around a set of 227 diverse organic compounds. The residual errors in MEP reproduction due to calculated atomic charges were compared to those due to charges from known charge schemes. 1Presented at CMTPI 2007: Computational Methods in Toxicology and Pharmacology Integrating Internet Resources (Moscow, Russia, September 1–5, 2007).

A novel highly efficient nanostructured organosilicon luminophore with unusually fast photoluminescence

Synthesis and theoretical and experimental investigations of a novel nanostructured organosilicon luminophore (NOL) containing six 2,2′-bithienyl donor units connected via silicon atoms to a 1,4-bis(5-phenylthienyl-2-yl)-benzene acceptor unit with efficient intramolecular Forster resonance energy transfer are reported. The NOL shows a unique combination of optical properties: a high photoluminescence (PL) quantum yield of up to 91%, a fast PL decay time of down to 800 ps, a large pseudo-Stokes shift of 101 nm and a huge molar extinction coefficient of 1.4 × 105 M−1 cm−1. These peculiarities caused by the specific arrangement of the donor and acceptor fragments at the nanoscale distance within the NOL were correlated with the molecular structure of the NOL using theoretical calculations, which for the first time allowed successful prediction of the oscillator strength, PL decay time and intramolecular energy transfer efficiency. A comparison of the photophysical properties of the NOL with the standard laser dye POPOP in THF and toluene solutions revealed its huge application potential in organic photonics and high energy physics.

General Purpose Electronegativity Relaxation Charge Models Applied to CoMFA and CoMSIA Study of GSK-3 Inhibitors

Two fast empirical charge models, Kirchhoff Charge Model (KCM) and Dynamic Electronegativity Relaxation (DENR), had been developed in our laboratory previously for widespread use in drug design research. Both models are based on the electronegativity relaxation principle (Adv. Quantum Chem. 2006, 51, 139–156) and parameterized against ab initio dipole/quadrupole moments and molecular electrostatic potentials, respectively. As 3D QSAR studies comprise one of the most important fields of applied molecular modeling, they naturally have become the first topic to test our charges and thus, indirectly, the assumptions laid down to the charge model theories in a case study. Here these charge models are used in CoMFA and CoMSIA methods and tested on five glycogen synthase kinase 3 (GSK‐3) inhibitor datasets, relevant to our current studies, and one steroid dataset. For comparison, eight other different charge models, ab initio through semiempirical and empirical, were tested on the same datasets. The complex analysis including correlation and cross‐validation, charges robustness and predictability, as well as visual interpretability of 3D contour maps generated was carried out. As a result, our new electronegativity relaxation‐based models both have shown stable results, which in conjunction with other benefits discussed render them suitable for building reliable 3D QSAR models.

Synthesis and photovoltaic effect in red/near-infrared absorbing A-D-A-D-A-type oligothiophenes containing benzothiadiazole and thienothiadiazole central units

Abstract. Two π-conjugated acceptor-donor-acceptor-donor-acceptor-type (A-D-A-D-A) oligothiophenes, TT-(2T-DCV-Hex)2 and BT-(2T-DCV-Hex)2 were designed and synthesized with thienothiadiazole (TT) or benzothiadiazole (BT) as the core and dicyanovinyl (DCV) as the terminal acceptor groups for comprehensively investigating and understanding structure–property relationships. The resulting oligomers were first characterized by thermal analysis, UV-Vis spectroscopy, and cyclic voltammetry. By simply changing the BT to TT core in these two oligothiophenes, the highest occupied molecular orbital levels were varied from −5.55  eV for BT-(2T-DCV-Hex)2 to −5.11  eV for TT-(2T-DCV-Hex)2, and the optical band gaps were varied from 1.72 eV for BT-(2T-DCV-Hex)2 to 1.25 eV for TT-(2T-DCV-Hex)2, ascribed to the stronger electron accepting character of the TT core. However, the power conversion efficiency of bulk heterojunction organic solar cells (OSCs) with TT-(2T-DCV-Hex)2 as donor and [6,6]-phenyl C70-butyric acid methyl ester (PC71BM) as acceptor was measured to be 0.04% only, which is much lower than that of BT-(2T-DCV-Hex)2:PC71BM (1.54%). Compared to the TT-(2T-DCV-Hex)2 system, the BT-(2T-DCV-Hex)2 based device shows smoother film surface morphology, and superior charge generation and charge carrier mobilities. Therefore, the results clearly demonstrate that in addition to modifying the alkyl side chains and π-bridge lengths, the design of new small molecules for high-performance OSCs should also aim to choose suitable acceptor units.

Multipole models of sulphur for accurate anisotropic electrostatic interactions within force fields

Abstract Nowadays, as computing has become much more available, a fresh momentum has been observed in the field of re-visioning and re-parameterizing the usual tools, as well as estimating for the incorporation of new qualitative capabilities, aimed at making more accurate and reliable predictions in drug discovery processes. Inspired by the success of modelling the electrostatic part of the halogen bonding (XB) by means of the distributed multipole expansion, a study is presented which attempts to extend this approach to a tougher case of σ-hole interaction: sulphur-based chalcogen bonding. To that end, 11 anisotropic models have been derived and tested for their performance in the reproduction of reference ab initio molecular electrostatic potential. A careful examination resulted in three models which have been selected for further examination as a part of the molecular mechanics force field (GAFF). The combined force field was used to estimate inter- and intra-molecular interactions for the molecular systems, capable of differentiating the binding from the σ-hole and other directions. The anisotropic models proposed were generally able to correct the wrong predictions of the sulphur models based only on isotropic charges and, thus, are a promising direction for further development of the refined electrostatics force fields.

Intramolecular Strain and Conformational Energy of Some Symmetric Heteroanalogues of Bicyclo[3.3.1]nonane

131 For solving one of the important problems of con formational analysis—to relate the trends in the con formational behavior of saturated heterocyclic com pounds to the positions of the heteroatoms in the skel eton, it is not sufficient to start from the corresponding conformational energies, which are the differences between the energies of individual conformers. To do this, it is vital to have a detailed picture of the effect of heteroatoms on the intramolecular strain of each con former.