Effect of amines on the ceric ion-initiated polymerization of vinyl monomers. I. Polymerization of acrylonitrile by ceric ion–triethylamine catalyst system

The polymerization of acrylonitrile was studied in aqueous solution with ceric ammonium sulfate in the presence of triethylamine as initiator at 30, 40, and 50°C. The rate of polymerization was found to be linear with the concentration of the amine and independent of ceric ion concentration. A reaction scheme involving initial complex formation between ceric ion and the amine and subsequent disproportionation of the conplex to produce free radicals is proposed for the initiation reaction. The termination step is postulated as involving oxidation of the polymer chains by ceric ions. The results have been explained in the light of the proposed reaction scheme.     

Constrained self-consistent-field wave functions with improved long-range behavior

The recent suggestion that the long-range behavior of energy-optimized Gaussian basis sets can be improved by augmenting them with a Gaussian chosen to satisfy a constraint involving a linearly averaged position moment is explored. Calculations indicate that the high-order moments 〈r^k〉, with k > 4, in He, Be, and Li^?, and 〈x^kz^L?k〉, with L > 4 and k ≤ L, in H₂ are improved by the constraint, but that lower-order moments and dipole polarizabilities are not. In H₂, the higher moments with a given L improve by different amounts for different k, and, hence, the multipole moments do not improve. The basis-set superposition error in He? He and Be? Be interaction energy calculations decreases if the internuclear distance is large enough. Thus, the constraint procedure improves the very long range behavior of the self-consistent-field wave functions. © 1992 John Wiley & Sons, Inc.     

Functionalization and extraction of large fullerenes and carbon-coated metal formed during the synthesis of single wall carbon nanotubes by laser oven, direct current arc, and high-pressure carbon monoxide production methods

Large fullerenes and carbon-coated metal nanoparticles that are formed during the synthesis of carbon nanotubes have been functionalized by the addition of alkyl radicals and isolated by extraction into chloroform. The soluble, functionalized fullerenes have been isolated from raw single-wall carbon nanotube (SWNT) material prepared by laser oven, direct current arc, and high-pressure carbon monoxide production methods. Analyses of the extracted large fullerenes were carried out by thermogravimetric analysis, UV-vis-near-IR, laser desorption ionization mass spectrometry, and high-resolution transmission electron microscopy.     

Structure and synthesis of SSZ-63: toward an ordered form of zeolite beta

The synthesis, characterization, and structure elucidation of the borosilicate zeolite SSZ-63 are described. SSZ-63 is synthesized using the 1-cyclodecyl-1-methylpyrrolidinium cation as a structure-directing agent. The structural model for SSZ-63 was determined by comparison of its powder X-ray diffraction pattern with those of zeolite beta and its polytype structures. Whereas conventional zeolite beta may be described as a random intergrowth of polytypes A and B, SSZ-63 is more accurately described as a random intergrowth of polytypes B and C(H) (the hypothetical polytype C proposed by Higgins). Polytype C(H) is essentially an ordered intergrowth (of polytypes A and B) in which one of the crystallographic projections is equivalent to those in polytype A and another projection is equivalent to those in polytype B. Unlike zeolite beta, which possesses significant disorder related to layer shifts along both the a- and b-crystallographic axes, the structure of SSZ-63 has little disorder associated with the translations of layers in the a-direction. DIFFaX simulations of the powder diffraction patterns, electron diffraction, and high-resolution transmission electron microsocopy data all support the proposed model.     

A simple polyacrylamide gel electrophoresis procedure for separation of polyamidoamine dendrimers

A simple, inexpensive, and rapid electrophoresis technique was developed for use as a routine tool for evaluating purity of polyamidoamine (PAMAM) dendrimers. A variety of factors influencing migration of generations 0-7 dendrimers on nongradient polyacrylamide gels were evaluated. The low generation dendrimers were found to be very sensitive to diffusion during or after electrophoresis. The proposed method incorporates steps that minimize diffusion, in order to obtain improved resolution and sensitivity, especially for the lower-molecular-weight dendrimers. This was accomplished by inclusion of a dendrimer fixation step with glutaraldehyde and performing the electrophoresis separation, fixation, staining, and destaining at 4 degrees C. PAMAM dendrimer separation was studied under basic and acidic conditions. Electrophoresis under acidic conditions gave increased resolution and sensitivity over separation at alkaline pH. Oligomers and trailing generations could be clearly separated and visualized under these conditions. The smallest PAMAM dendrimer, generation 0, was visible at 1.5 microg under the optimized acidic conditions. With slight modifications, this technique should be applicable to separation of other water-soluble dendrimers.     

Schiff-base derivatives of molybdenum carbonyl

Summary Reactions of five Schiff bases (SB),viz.,N,N-ethylenebis(benzalideneimine) (SB¹),N,N-ethylenebis(p-anisylideneimine) (SB²),N,N-ethylenebis(methylphenylketimine) (SB³),N,N-ethylenebis(diphenylketimine) (SB⁴) andN,N-ethylenebis (salicylideneimine) (SB⁵) with molybdenum hexacarbonyl have been studied. The first four Schiff bases yieldcis-disubstituted derivatives whereas a non-carbonyl complex is obtained for the last one (SB⁵). [(Ph₃E)Mo(CO)₅] (E = P or As) after reaction with SB give SB-bridged dinuclear [(Ph₃E)(CO)₄Mo--(SB)-Mo(CO)₄(Ph₃E)] derivatives. Halogen-oxidation and nitrosylation ofcis-[(SB)Mo(CO)₄] have also been studied.     

Discrete spatial symmetries in energy derivatives

Based upon the invariance of N-particle systems under discrete operations of reflection, inversion, and rotation by 2π/n, a method for obtaining complete sets of relations among energy derivatives of all orders has been presented. The method is based on the criterion that, for a discrete symmetry operation such as reflection across a plane; the change in energy due to simultaneous arbitrary displacements of each particle is equal to another set of “conjugate” displacements of all particles. Applications of the above relations for particular molecular systems possessing a combination of symmetry operations is also presented. Here, via the row echelon analysis, the number of independent derivatives are found, and simple symmetry relations that allow determination of the remaining derivatives are presented. For example, for a homonuclear diatomic molecule with D_2h symmetry only 1 of the 6 first derivatives and 1 of the 21 second derivatives need to be independently calculated.     

Polyacrylamide gel electrophoresis separation and detection of polyamidoamine dendrimers possessing various cores and terminal groups

Detection and separation of polyamidoamine dendrimers possessing various cores and surface groups was studied by polyacrylamide gel electrophoresis. Although many dyes and staining techniques were able to detect dendrimers on polyacrylamide gels, Coomassie Blue was found to be the most sensitive and convenient. Amine and hydroxyl terminated dendrimers were best separated under acidic conditions, while dendrimers with carboxyl surfaces required alkaline buffers. Some dendrimers were very susceptible to diffusion that could occur during their separation, staining or destaining steps. In the absence of an appropriate fixation step, dendrimers could be resolved by using small pore size gels and low voltage or current. Increasing core lengths did not significantly affect migration of a given dendrimer generation but exhibited improved separation and staining characteristics. Polyacrylamide gel electrophoresis was found to be a rapid, inexpensive, and reliable procedure to characterize many different water-soluble dendritic macromolecules.