Free-radical polymerization of methyl methacrylate in presence of the Cr(C5H7O2)3–Al(i-C4H9)3 catalyst system

Polymerization of methyl methacrylate has been studied with the chromium acetylacetonate–triisobutyl aluminum catalyst system in benzene medium at 40°C. These studies have been carried out at an Al/Cr ratio of 12 to compare the behavior with the previously studied chromium acetyl acetonate–triethyl aluminum catalyst system. The enhanced yield and gelling of polymer suggests a free-radical mechanism of polymerization. Further, the kinetics of polymerization and the heterotactic structure of polymer as determined by NMR examination have led to confirmation of the freeradical mechanism of polymerization of methyl methacrylate by an excess of triisobutylaluminum in the presence of catalyst complex.     

Kinetics and mechanism of polymerization yielding stereoblock poly(methyl methacrylate) with VCl4-Al(C2H5)3 catalyst system

Methyl methacrylate was polymerized at 40°C with the VCl₄–AlEt₃ catalyst system in n-hexane. The rate of polymerization was proportional to the catalyst and monomer concentration at Al/V ratio of 2, indicating a coordinate anionic mechanism of polymerization. NMR spectra were further used to confirm the mechanism of polymerization and stability of active sites responsible for isotacticity.     

Polymerization of acrylonitrile with VCl4–Al(C2H5)3 catalyst system in presence of acetonitrile

The polymerization of acrylonitrile with the homogeneous catalyst system of VCl₄–AlEt₃ in acetonitrile at 40°C has been investigated. The rate of polymerization is found to be first-order with respect to monomer and inversely proportional to the catalyst concentration. The overall activation energy for this catalyst system is 10.97 kcal/mole. The inverse proportionality of rate of polymerization with the catalyst concentration is attributed to the permanent complex formation between the catalyst complex and acrylonitrile, and a reaction scheme is proposed.     

Design and development of a common synthetic strategy for a variety of 1-N-iminosugars

[formula: see text] A new synthetic strategy has been developed for a general approach toward the synthesis of a variety of 1-N-iminosugar-type glycosidase inhibitors utilizing precursors developed by the PET-mediated cyclization of alpha-trimethylsilylmethylamine radical cation to a tethered pi-functionality.     

Polymerization of styrene with chromium acetylacetonate and triethylaluminum and diethylaluminum bromide

Kinetics of the polymerization of styrene in the presence of benzene at 30°C., with chromium acetylacetonate in combination with triethylaluminum and also in combination with diethylaluminum bromide as catalyst, have been studied. Chromium acetylacetonate forms a homogeneous system with triethylaluminum, and chromium acetylacetonate with diethylaluminum bromide behaves as a heterogeneous system. This homogeneous catalyst system, though reported inactive in the polymerization of α-olefins, has been found effective with styrene. Depending on the homogeneity and heterogeneity of the system, the rate of polymerization is proportional to half order and first order of catalyst concentration. A probable reason for the effect of homogeneity on the order of reaction has been discussed. A study of the effect of diethylzinc as a chain-transfer agent has helped to confirm the mechanism of polymerization.     

A new access to polyhydroxy piperidines of the azasugar class: synthesis and glycosidase inhibition studies

A new synthetic strategy has been devised to access a variety of polyhydroxylated piperidines belonging to the azasugar class of glycosidase inhibitors. The key precursor (3aR, 7aR)-5-benzyl-2,2-dimethyl-7-methylenehexahydro[1,3]dioxo[4,5-c]pyridine is obtained by photoinduced electron transfer (PET) cyclization of the corresponding alpha-trimethylsilylmethylamine radical cation to the tethered acetylene functionality. The new molecules have been evaluated for inhibitory properties for certain beta-glycosidases and have been found to be moderate to weak inhibitors of the enzymes under study.     

Alkoxy Derivatives of Tricyclopentadienyl Cerium (IV)

Tricyclopentadienyl cerïum(IV) chloride has been treated with various primary and secondary alcohols in benzene medium in the presence of triethylamine to give compounds, (C₅H₅)₃Ce(OR) wherein R may be CH₃ C₂H₃, n-C₂H₃, iso-C₃H₇, N-C₄H₉, iso-C₄H₉ and iso-C₃H₁₁. Infrared spectra and some physical characteristics of all these compounds and reported.     

Observation of daunomycin and nogalamycin complexes with duplex DNA using electrospray ionisation mass spectrometry

The noncovalent binding of the antitumour drugs daunomycin and nogalamycin to duplex DNA has been studied using electrospray ionisation mass spectrometry (ESI-MS). The conditions for the preparation of drug/duplex DNA complexes and for their detection by ESI-MS have been optimised. Ions corresponding to these complexes were most abundant relative to free DNA when prepared in the pH range 8-9, and using gentle ESI interface conditions. Self-complementary oligonucleotides, 5'-d(GGCTAGCC)-3' or 5'-d(CGGCGCCG)-3', annealed in the presence of a 5-fold molar excess of either nogalamycin or daunomycin gave ESI mass spectra in which the most intense ions corresponded to three molecules of drug bound to duplex DNA, with some evidence for four drug molecules bound. For binding to 5'-d(TGAGCTAGCTCA)(2)-3', complexes containing up to four nogalamycin and six daunomycin molecules were observed. These data are consistent with the neighbour exclusion principle whereby intercalation occurs between every other base pair such that up to four bound drugs would be expected for the 8 mers and up to six for the 12 mer. Competition experiments involving a single drug in an equimolar mixture of two oligonucleotides (5'-d(TGAGCTAGCTCA)(2)-3' with either 5'-d(CGGCGCCG)(2)-3' or 5'-d(GGCTAGCC)(2)-3') showed ions arising from complexes of drug/5'-d(CGGCGCCG)(2)-3' were more intense than complexes of drug/5'-d(GGCTAGCC)(2)-3', relative to those from the 12 mer in each mixture. While this suggests ESI-MS has the potential to detect differences in sequence selectivity, more detailed experiments involving a comparison of the relative ionisation efficiency of different oligonucleotides and a wider range of intercalators are required to establish this definitively. ESI mass spectra from experiments in which both drugs were reacted with the same oligonucleotide were more complex, such that a clear preference for one drug could not be established.     

Nucleophilic dephosphorylation of p-nitrophenyl diphenyl phosphate in cationic micellar media

The kinetics of nucleophilic dephosphorylation of p-nitrophenyl diphenyl phosphate by hydroxamate ions (R'(C=O)N(RO-)) have been investigated in aqueous cationic micellar media at pH 9.12 and 27 degrees C. The pseudo-first-order rate constant-surfactant profiles show micelle-assisted bimolecular reactions involving interfacial ion exchange between bulk aqueous media and micellar pseudophase. N-Substituted hydroxamate ion shows higher reactivity over the unsubstituted hydroxamate ions in cationic micellar media. The kinetic data are discussed in terms of the pseudophase ion exchange model.