Condensation of all-cis-tetraphenylcyclotetrasiloxanetetraol in ammonia: new method for preparation of ladder-like polyphenylsilsesquioxanes

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Thermally induced solid-state transformation of cimetidine. A multi-spectroscopic/chemometrics determination of the kinetics of the process and structural elucidation of one of the products as a stable N3-enamino tautomer

Exposure of cimetidine (CIM) to dry heat (160–180 °C) afforded, upon cooling, a glassy solid containing new and hitherto unknown products. The kinetics of this process was studied by a second order chemometrics-assisted multi-spectroscopic approach. Proton and carbon-13 nuclear magnetic resonance (NMR), as well as ultraviolet and infrared spectroscopic data were jointly used, whereas multivariate curve resolution with alternating least squares (MCR-ALS) was employed as the chemometrics method to extract process information. It was established that drug degradation follows a first order kinetics.     

Multicriteria decision making under uncertainty

Formalization for problems of multicriteria decision making under uncertainty is constructed in terms of guaranteed and weak estimates. A relevant definition of the vector maximinimax value is given. Parameterization and approximation of maximum, minimax, and maximinimax values based on the inverse logical convolution are suggested. An application for multicommodity networks is considered. Received: December 13, 2000 / Accepted: August 21, 2001?Published online May 8, 2002     

Tribute to Endre Csáki and Pál Révész

Summary This article provides a glimpse of some of the highlights of the joint work of Endre Csáki and Pál Révész since 1979. The topics of this short exploration of the rich stochastic milieu of this inspiring collaboration revolve around Brownian motion, random walks and their long excursions, local times and additive functionals, iterated processes, almost sure local and global central limit theorems, integral functionals of geometric stochastic processes, favourite sites--favourite values and jump sizes for random walk and Brownian motion, random walking in a random scenery, and large void zones and occupation times for coalescing random walks.     

Path properties of l_p-valued Gaussian random fields

General limit theorems are established for l~p-valued Gaussian random fields indexed by a multidimensional parameter,which contain both almost sure moduli of continuity and limits of large increments for the l~p-valued Gaussian random fields under(?)explicit conditions.     

Mechanism of the cyclization of dimethyl diethynyl silane with selenium tetrabromide: Computational and structural studies, and monitoring

The structure of 2,4-dibromo-2-dibromomethyl-3,3-dimethyl-1-selena-3-silacyclopentene-4, formed by regioselective electrophilic addition of SeBr₄ to dimethyl diethynyl silane, has been determined using X-ray analysis technique. Quantum chemistry methods were used to study elementary stages of the reaction. It was found that the first stage consisted of SeBr₄ conversion into bimolecular complex Br₂?SeBr₂, initiated by dimethyl diethynyl silane. Possible formation of five-membered and six-membered heterocycles involves different cyclization mechanisms. The formation of only five-membered heterocycle is explained by kinetically preferable ring closure through four-center transition state. The conclusions obtained by calculations were confirmed by monitoring of the reaction using ¹H NMR method.     

Electrochemical and spectral studies on the reductive nitrosylation of water-soluble iron porphyrin

The reaction of iron(III) (meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (Fe(III)TMPyP) with nitric oxide (NO) was studied by electronic absorption spectroscopy, ESR, and electrochemical and spectroelectrochemical techniques in aqueous solutions with pH from 2.2 to 12.0. Fe(III)TMPyP has been found to undergo a reductive nitrosylation in all pHs, and the product of nitric oxide binding to the porphyrin has been determined as iron(II) porphyrin nitrosyl complex ([Fe(II)(NO)TMPyP]). The rate of the reductive nitrosylation exhibits a tendency to get faster with increase in pH. An intermediate species was observed around neutral pH by spectroelectrochemical technique and was proposed to be the iron(II) nitrosyl complex of the mu-oxo dimeric form of FeTMPyP, which is known to be a predominant in neutral solutions.     

Synthesis of hydroporphyrins based on comparative studies of palladium-catalyzed and non-catalyzed approaches

Hydroporphyrins have been synthesized using both Pd-catalyzed and non-catalyzed approaches. Comparative studies of the reaction of tetrasubstituted porphyrins with organolithium reagents in the presence of and without palladium catalysts showed that depending on reagents, the catalyst structure and reactivity of the corresponding porphyrins, chlorins (β-hydroporphyrins) and/or porphodimethenes (meso hydroporphyrins) of 5,10-type can be prepared in reasonable yields. In the absence of Pd catalysts, the formation of chlorins is predominant in the reactions with aliphatic RLi while porphodimethenes are the main products in reactions with PhLi. The use of a palladium catalyst resulted in the formation of both types of hydroporphyrins and the selective formation of either β-mono- or disubstituted chlorins. Of special interest was the reaction of octaethylporphyrin. Here, reaction with t-BuLi in the presence of Pd(PPh₃)₄/CuI proceeded with complete regioselectivity for 5,10-porphodimethenes.     

Oligonucleotides containing new fluorescent 1-phenylethynylpyrene and 9,10-bis(phenylethynyl)anthracene uridine-2′-carbamates: synthesis and properties

The synthesis of two novel fluorescent uridine-2′-carbamate phosphoramidites is described. The reagents carrying fluorescent polyaromatic hydrocarbons 1-phenylethynylpyrene (PEPy) or 9,10-bis(phenylethynyl)anthracene (BPEA) are suitable for oligonucleotide synthesis. Prepared oligonucleotide conjugates show strong dye emissions at 401 and 485 nm, but low FRET rate when located in the oligonucleotide duplex. The dyes show considerable compensation of the usual carbamate duplex destabilization. The possible explanation of both effects is binding of PEPy and BPEA to the minor groove of the DNA duplex.