Oleg Lukin

Two‐Dimensional Polymers: Just a Dream of Synthetic Chemists?

In light of the considerable impact synthetic 2D polymers are expected to have on many fundamental and applied aspects of the natural and engineering sciences, it is surprising that little research has been carried out on these intriguing macromolecules. Although numerous approaches have been reported over the last several decades, the synthesis of a one monomer unit thick, covalently bonded molecular sheet with a long-range ordered (periodic) internal structure has yet to be achieved. This Review provides an overview of these approaches and an analysis of how to synthesize 2D polymers. This analysis compares polymerizations in (initially) a homogeneous phase with those at interfaces and considers structural aspects of monomers as well as possibly preferred connection modes. It also addresses issues such as shrinkage as well as domain and crack formation, and briefly touches upon how the chances for a successful structural analysis of the final product can possibly be increased.

Drug- and Lead-likeness, Target Class, and Molecular Diversity Analysis of 7.9 Million Commercially Available Organic Compounds Provided by 29 Suppliers

A database of 7.9 million compounds commercially available from 29 suppliers in 2008-2009 was assembled and analyzed. 5.2 million structures of this database were identified to be unique and were subjected to an assessment of physical and biological properties and estimation of molecular diversity. The rules of Lipinski and Veber were applied to the molecular weight, the calculated water/n-octanol partition coefficients (Clog P), the calculated aqueous solubility (log S), the numbers of hydrogen-bond donors and acceptors, and the calculated Caco-2 membrane permeability to identify the drug-like compounds, whereas the toxicity/reactivity filters were used to remove the structures with biologically undesired functional groups. This filtering resulted in 2.0 million (39%) structures perfectly suitable for high-throughput screening of biological activity. Modified filters applied to identify lead-like structures revealed that 16% of the unique compounds could be potential leads. Assessment of the biological activities, the analysis of diversity, and the sizes of exclusive sets of compounds are presented.

Synthesis, Conformation, and Binding Properties of Resorcarene Tetrasulfonates. Asymmetric Reorganization of Pendant Sulfonyl Groups via Intramolecular SO- - -H−O Hydrogen Bonds

The regioselective reaction of resorcarene octaols 1 with 4 equiv of arylsulfonyl chlorides and Et3N in MeCN gives in 30−60% yield the C2v symmetrical tetrasulfonates 3. The mild electrophilic substitution (aminomethylation, bromination) of resorcarene tetrasulfonates 3 and tetraphosphates 2 takes place only in the 2-positions of unsubstituted resorcinol rings yielding distally disubstituted resorcarenes 4. The acylation of hydroxy groups in compounds 2 and 3 gives C2v symmetrical octaesters 5 including large resorcarene tetracrown-ethers. In the minimized boat conformation of tetrasulfonates 3 the two unsubstituted resorcinol rings are vertical and the sulfonyl fragments are arranged in a C2 symmetrical manner via intramolecular SO- - -H−O hydrogen bonds. This structure is proved by NMR and IR spectroscopy. In the case of tetrasulfonate 3c the two enantiomeric conformations interconvert in CDCl3 with ΔG* = 11.6 kcal/mol. This is in agreement with the ΔE* value predicted by molecular mechanics in vacuo.

Ab initio calculations of the NMR spectra of [1.1.1] propellane and bicyclo [1.1.1] pentane

New high-level ab initio values of all the NMR shielding and spin–spin coupling constants in [1.1.1]propellane and bicyclo[1.1.1]pentane are obtained and compared with previous theoretical results and available experimental data. Electron correlation effects are taken into account and large basis sets suitable for NMR studies are applied. The results for the shielding constants depend primarily on the basis set, while the spin–spin coupling constants, in particular for the carbon–carbon coupling, are very sensitive to electron correlation effects. The computed NMR parameters agree well with the known experimental values, with the exception of the bridgehead–bridgehead carbon coupling constant in [1.1.1]propellane. Our best estimates of this constant differ from the experimental value for a substituted [1.1.1]propellane, and possible explanations of this discrepancy are discussed.

Molecular mechanics study of endohedral fullerene complexes with small molecules

Abstract Molecular mechanics calculations using CFF91, ESFF and CVFF force fields have been carried out for endohedral complexes of fullerenes C 60 , C 70 , C 76 (of D 2 and T d symmetry), C 80 (of C 2v , C 2v′ , D 2 , D 3 , D 5d , D 5h and I h symmetry), C 82 (of C 2v , two isomers of C 3v , three isomers of C 2 , and three isomers of C s symmetry), with several hydrocarbons, ketones, amines and other small molecules. The results obtained depend on the force field applied. Nevertheless, they indicate that much bigger fullerenes are needed to obtain complexes of practical importance.

Selective Acylation of Calixresorcinolarene

Abstract Selective acylation of calixresorcinolarene 1 has been performed. The reaction with mild acylating agents such as arylsulfonylchlorides leads to the tetrasubstituted compounds. Stereochemistry of the compounds obtained has been investigated in detail by means of 1 H- and 13 C-NMR.

Dependence of the average energy between the 1:2 complexes of enantiomeric α-pinenes with α-cyclodextrin on the length of dynamic simulation

Abstract Molecular dynamics is frequently used in studies of chiral recognition by cyclodextrins. Although the free energy difference for complexes involving enantiomeric guests is a measure of this effect, the difference between the corresponding average energies is used instead in the pertaining literature with simulation times mostly not exceeding 2 ns. In continuation of our program of evaluation of theoretical methods applied in cyclodextrin studies, we have carried out simulations for 12 ns for the 1:2 complexes of α-pinenes with α-cyclodextrin in water and analyzed how the average energy differences depended on the length of simulation time. Surprisingly, not only the value of energy difference but also its sign changed during the simulations. This result indicates that much longer simulation times are necessary to obtain reliable results from dynamic simulations.

First generation TREN dendrimers functionalized with naphthyl and/or dansyl units. Ground and excited state electronic interactions and protonation effects

We report the photophysical properties (absorption and emission spectra, quantum yield, and lifetime) of five dendrimers of first generation based on a TREN (tris(2-aminoethyl)amine) skeleton functionalized at the periphery with naphthyl and/or 5-dimethylamino-1-naphthalenesulfonamide (hereafter called dansyl) chromophores. Each dendrimer comprises one tertiary amine unit in the core and three branches carrying a sulfonimido unit at the periphery, each one substituted by two identical or different moieties. In particular, TD6 and TN6 contain dansyl (D) or naphthyl (N) units, respectively, while TD3B3, TN3B3 and TN3D3 contain dansyl, naphthyl or benzyl (B) units at the periphery. The spectroscopic behaviour of these dendrimers has been investigated in acetonitrile solution and compared with that of reference compounds. For all dendrimers the absorption bands are red shifted compared to those of monomeric naphthyl and dansyl reference compounds. Moreover, the intense naphthyl and dansyl fluorescence is greatly quenched because of strong interactions between the two aromatic moieties linked by a sulfonimido unit. Protonation of the amine units of the dendrimers by addition of CF(3)SO(3)H (triflic) acid causes a decrease in intensity of the luminescence and a change in the shape of the emission bands. The shapes of the titration curves depend on the dendrimer, but in any case the effect of acid can be fully reversed by successive addition of base (tributylamine). The obtained results reveal that among the intradendrimer interactions the most important one is that taking place (via mesomeric interaction) between the various chromophores and a pair of sulfonimido groups.

Facile Synthesis of 4H-1,2,4-Benzothiadiazine-1,1-dioxides

Abstract o-Bromoarylsulfonylated amidines prepared either by acylation of amidine with o-bromoarylsulfonyl chloride or through the reaction of o-bromoarylsulfoamide with lactime ether underwent Cu(I)-catalyzed intramolecular cyclization to give 4H-1,2,4-benzothiadiazine-1,1-dioxides in good yield. By varying substituents on arylsulfonyl moieties, amidines, and lactime ethers, a small library of structurally diverse 4H-1,2,4-benzothiadiazine-1,1-dioxide derivatives was prepared.

Ease of formation of nested fullerenes

Abstract Molecular mechanics calculations using CVFF force field for isolated fullerenes C 60 , C 240 , C 540 , C 960 and the nested ones they form indicate that the process of buckyonion formation is cooperative and driven by nonbonded interactions. The calculations for the nested fullerenes involving all isomers of C 70 , C 76 and C 80 satisfying isolated pentagon rule indicate that the complex formation with these guests is less efficient than that with the C 60 . Molecular dynamics simulations for C 60 , C 240 , C 540 , C 960 and for the quaternary complex C 60 @C 240 @C 540 @C 960 support the cooperativity of the process of nested fullerenes formation.