Theoretical calculations of the effects of 2-heavier group 14 element and substituents on the singlet-triplet energy gap in cyclopentane-1,3-diyls and computational prediction of the reactivity of singlet 2-silacyclopentane-1,3-diyls

UDFT and CASSCF calculations with the 6-31G(d) basis set were performed to investigate the heavier group 14 element (M) effect on the ground-state spin multiplicity of cyclopentane-1,3-diyls and their reactivity. The calculations find that 2-metallacyclopentane-1,3-diyls (M = Si, Ge) that possess a variety of substituents (X = H, Me, F, OR, SiH(3)) at M(2) are singlet ground-state molecules. The energies of the 1,3-diphenyl-substituted singlet 2-silacyclopentane-1,3-diyls are calculated to be ca. 5 kcal/mol lower than those of the intramolecular ring-closure products, i.e., 1,4-diphenyl-5-silabicyclo[2.1.0]pentanes, at the B3LYP/6-31G(d) level of theory. The energy barrier for the disrotatory ring closure of singlet 2,2-dimethyl-1,3-diphenyl-2-silacyclopentane-1,3-diyl (lambda(calcd) = 757 nm, f = 1.01 at RCIS/6-31G(d)) to the corresponding 5-silabicyclo[2.1.0]pentane is computed to be 11.6 kcal/mol, which is 13.1 kcal/mol lower in energy than that for the conrotatory ring-opening to a 3-silapenta-1,4-diene. The computational work predicts that singlet 1,3-diaryl-2-silacyclopentane-1,3-diyls are persistent molecules under conditions without trapping agents.     

Properties of low temperature swelling hydrogels prepared with partially saponified PVA and drug release using the hydrogels

The hydrogels prepared by the crosslinking of partially saponified poly(vinyl alcohol) (PVA) which has low critical solution temperature (LCST) in water showed characteristics of swelling at low temperature and shrinkage at high temperature. The hydrogels showed repeatable swelling–shrinking behavior. The hydrogels containing release substances such as cyanocobalamin, p‐acetamidophenol, insulin and ovalbumin were prepared by dipping these aqueous solutions and the release substances were studied. Insulin and ovalbumin were not absorbed by the hydrogels when the use of partially PVA with the degrees of polymerization (DPs) of 540 were prepared, but absorbed by the hydrogels with DPs of 1860. The size of the polymer network prepared with a higher DP was suitable for the absorption of insulin and ovalbumin. In accordance with release substances, the release patterns were different. In this way, the polymer network sizes and their swelling behaviors of partially saponified PVAs were estimated. Copyright © 2003 John Wiley & Sons, Ltd.     

Facile and convenient synthesis of 2,6-disubstituted 4H-1,3-oxazin-4-one derivatives

Facile and convenient methods for the preparation of a variety of 2,6-disubstituted 4H-1,3-oxazin-4-ones 3 by three complementary methods are described. Treatment of the branched aliphatic imidate 2c,d with diketene 1 in the presence of a catalytic amount of acetic acid affords 2-substituted 6-methyl-1,3-oxazin-4-ones 3c,d , whereas the unbranched imidate 2b,e gave oxazines 3b,e and pyrimidines 4b,e (Method A). The reaction of acyl Meldrum's acid 5 with imidate 2 afford 2,6-disubstituted oxazine 3, though the alkylimidate with acetyl Meldrum's acid yielded 3 and 5-acetyl-1,3-oxazine-4,6-dione 8 (Method B). The cylodehydration of acylacetylcarboxamide 13 with acid, such as 70% perchloric acid or fluorosulfonic acid, afforded 1,3-oxazines 3 (Method C).     

Immunological properties of type IV collagen from mouse kidney

Some immunological properties of mouse kidney type IV collagen (MKIVC) were investigated. In enzyme-linked immunosorbent assay (ELISA), rabbit anti-MKIVC antiserum reacted strongly with MKIVC but not at all with type I collagen or laminin of mouse origin. Thus, the purified MKIVC preparation was not contaminated with detectable amounts of other constituents of the extracellular matrix and the basement membrane including interstitial collagens, as suggested previously (T. Oikawa et al., Chem. Pharm. Bull., 34, 789 (1986)). In ELISA inhibition assay, human kidney type IV collagen (HKIVC) only partially inhibited the binding of MKIVC to anti-MKIVC antiserum. Similarly, HKIVC showed a far weaker binding capacity to the antiserum compared to MKIVC in ELISA direct binding assay. After the anti-MKIVC antiserum was absorbed with acetone powder of human kidney, the resulting antiserum still possessed a considerable binding activity to MKIVC but did not react with HKIVC. In accord with these findings, anti-MKIVC antiserum immunostained both mouse and human renal basement membranes, while it stained the former but not the latter after being absorbed with human kidney. Taken together, these results suggest that MKIVC possesses at least two antigenic determinants; one but not the other cross-reacts with human kidney basement membrane collagen.     

Drawing behavior and characteristics of laser‐drawn polypropylene fibers

Drawing behavior, flow drawing, and neck drawing, was studied for isotacticpolypropylene fibers in CO₂ laser drawing system, and the fiber structure and the mechanical properties of drawn fibers were analyzed. For a certain laser power, flow drawing of polypropylene (PP) was possible up to draw ratio (DR) 19.5. Though the drawing stress was very low, the flow‐drawn PP fiber exhibited oriented crystal structure and improved mechanical properties. On the other hand, neck‐drawing was accomplished from DR 4 to 12, with significant increase in drawing stress that enhanced the development of fiber structure and mechanical properties. Unlike PET, the drawing stress depends not only on the DR, but on irradiated laser power also. The 10–12 times neck‐drawn fibers were highly fibrillated. The fibers having tensile strength 910 MPa, initial modulus 11 GPa, and dynamic modulus 14 GPa were obtained by single‐step laser drawing system. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 398–408, 2006     

Investigation of molecular motions of crosslinked polyepichlorohydrin by nuclear magnetic resonance spectroscopy

The molecular motion of crosslinked polyepichlorohydrin (PECH) is studied qualitatively by NMR techniques. The results of temperature dependence of ¹H T₂ and T₁ indicate that the crosslinking (crosslink density < 3%) restricts molecular motions of the polymer even far above its T_g. The ¹H T₁ minimum, corresponding to the large-scale chain-motion of crosslinked PECH, shifts to higher temperatures with increasing crosslink density. ¹H T₂ data also show that the crosslinking hinders free chain motions of the polymer above its T_g. The ¹³C T₁ relaxation time is sensitive to such motional changes as well. ¹³C linewidths of crosslinked PECHs vary with the crosslink density in both the swollen state and the solid state. The mechanism of ¹³C linewidth broadening of crosslinked polymers is discussed in detail. In the case of PECH, the linewidth broadening is caused by changing molecular environment due to crosslinking (such as presence of various chemical shift structures and freezing effects in conformational environment as chain mobility decreases), rather than increasing correlation times, which shorten the relaxation time (T₂) of polymer chains. © 1994 John Wiley & Sons, Inc.     

Gate-voltage dependence of zero-bias anomalies in multiwall carbon nanotubes

Temperature dependence of zero-bias conductance of the vanadium (V)/multiwall carbon nanotube (MWNT)/V structure is studied. As temperature is reduced, the conductance decreases with a functional form consistent with a power law. For the first time, we find that the exponent depends significantly on gate voltage. This exponent dependence cannot be explained by Luttinger-liquid theory for ballistic MWNTs. We interpret the obtained results within the framework of the nonconventional Coulomb blockade theory for strongly disordered MWNTs.     

Ionization of long-lived highly excited atoms by collision with molecules. II

A theoretical treatment of the collisional ionization of a highly excited atom with a molecule is improved by use of the exact form factor of the hydrogen atom in highly excited states. The present treatment is still based on the previously proposed mechanism in which the Rydberg electron is ionized by gain of energy from rotational de-excitation of the molecule in a rotationally excited state. Closer comparison of experiment with theory is made for symmetric- as well as asymmetric-top molecules.     

Mechanische Denaturierung von Hochpolymeren in L?sung. 33. Mitt. Einflu? von Antischaumreagentien auf die flie?induzierte Kristallisation von Polyvinylalkohol aus dessen w?llriger L?sung

Ohne Zusammenfassung     

Einflu? der Syndiotaktizit?t auf die Reaktion von Polyvinylalkoholen mit Jod

Ohne Zusammenfassung