Crosslinking structure of keratin. VI. Number,type, and location of disulfide crosslinkages in low-sulfur protein of wool fiber and their relation to permanent set

Crosslinked structures of the permanent set wool fiber treated with boiling water at a 40% extension state and the control fiber were studied by analyzing the rubberlike force-extension curve of the swollen fiber in a mixed solution composed of equal volumes of 8M LiBr and butyl carbitol. The thiol and disulfide contents of set fibers were also determined. It was found that (1) the disulfide (SS) bonds in low-sulfur (LS) microfibril protein transform into new crosslinkages in boiling water, but the SS bonds in high-sulfur matrix protein remain intact, (2) the SS bonds in α-helical segments becomes reactive only at the extension state of fiber and produces a free thiol group, and (3) intramolecular SS bonds may exist in the α-helical segments. Discussion was also made about the closeness of the number of crosslinkage sites of SS bonds obtained from the present rubber elasticity theory and from the theoretical analysis of the amino acid sequence of the intermediate filament. The cross-linking structure model in LS protein was proposed. It was suggested further that the setting mechanism for new crosslinkage theory seems to be unsatisfactory, since the new crosslinkages do not contribute to stabilize the extended conformation of the wool chain. © 1996 John Wiley & Sons, Inc.     

The Relationship Between the Rigidity of the Liposomal Membrane and the Absorption of Insulin After Nasal Administration of Liposomes Modified with an Enhancer Containing Insulin in Rabbits

The relationship between the rigidity of the liposomal membrane and the absorption of insulin after nasal administration of liposomes modified with an enhancer containing insulin was investigated for the nasal delivery of peptide drugs in rabbits. The rigid liposomal membrane makes liposomes stable, protecting insulin from enzymatic degradation. Soybean-derived sterol (SS) or its sterylglucoside (SG) was used as an enhancer. Dipalmitoylphosphatidylcholine (DPPC) liposomes modified with SG had increased fluidity of the hydrophobic group of the liposome bilayer compared with the liposomes modified with cholesterol (Ch) or SS, as shown by measurements of the steady-state fluorescence anisotropy of 1,6-diphenyl-1,3,5,-hexatriene (DPH); however, the fluidity of the polar group of the liposome bilayer was decreased according to measurements of steady-state fluorescence anisotropy of dansylhexadecylamine (DSHA) at 37°C. These findings suggest that the fluidity of the hydrophobic group of the liposome bilayer is responsible for the increase of liposomal leakage and instability of the liposomes. When insulin was administered nasally to rabbits as a solution, no hypoglycemic effect was observed. The administration of insulin contained in DPPC/SG (7/4, mole) liposomes with high fluidity caused a high glucose reduction of long duration (8 hr). DPPC/SS and DPPC/Ch (7/4) liposomes with low fluidity caused low glucose reductions. These results demonstrated that liposomes modified with SG can be useful as carriers of insulin administered nasally.     

Forced convective heat transfer in uniformly heated horizontal tubes (2nd report, theoretical study)

Effects of buoyancy force on forced laminar convective heat transfer in a uniformly heated horizontal tube may not be neglected at large Re Ra. This 2nd report deals with a theoretical investigation of this problem on a fully developed laminar flow and compares the results with experimental results reported in the 1st report.

In order to back up assumptions made in the following analysis, patterns of secondary flow due to buoyancy are observed in flow visualization experiments. An approximate solution for very large Re Ra is obtained. Nusselt numbers are shown as a function of Re Ra and Pr and are shown to be in fairly good agreement with experimental results on air. Resistance coefficients are also obtained as a function of Re Ra and Pr.     

Construction of reversible crosslinking–decrosslinking system consisting of a polymer bearing vicinal tricarbonyl structure and poly(ethylene glycol)

In this article, we report a novel reversible crosslinking–decrosslinking system consisting of a polymer bearing vicinal tricarbonyl moieties in its side chains and poly(ethylene glycol) (PEG). A mixture of the tricarbonyl polymer and PEG (0.1 equiv of OH groups relative to the vicinal tricarbonyl moieties) in CH₂Cl₂ spontaneously turned into an orange-colored gel, in which a network structure was formed through hemiketal linkages. Conversely, the resulting networked polymer could be decrosslinked by treatment with water-containing solvent to recover the linear vicinal tricarbonyl polymer as its hydrate in 90 % yield. Following dehydration process by heating at 100 °C under reduced pressure regenerated the original vicinal tricarbonyl polymer.     

A case of progressive multifocal leukoencephalopathy with methionine uptake demonstrated by PET]

We report here a 55-year-old man with progressive multifocal leukoencephalopathy (PML) associated with chronic adult T cell leukemia (ATL). Neurological examination revealed mild dementia, right homonymous hemianopsia and visual agnosia. Serologically anti-HTLV-I antibody was positive. Peripheral blood analysis showed ATL cells up to 23% in white blood cells. Because he did not have symptoms or signs directly related to ATL, it was considered that he had chronic ATL. T2-weighted cranial MRI demonstrated multiple hyperintensity lesions confined to the white matter from the bilateral occipital to parietal lobes, without enhancement after gadolinium administration or mass effect. We performed stereotactic biopsy of the left occipitoparietal white matter. Histological examination of the biopsied specimens showed demyelinated lesions, containing foamy macrophages and bizarre astrocytes. Oligodendrocytes contained nuclear inclusions which reacted with an antibody against the JC virus (JCV) antigen. These findings were consistent with those of PML. The genomic analysis of JCV from the biopsied brain revealed deletions in the regulatory region. We investigated cerebral blood flow, glucose and amino acid metabolism in this patient using positron emission tomography, and obtained the following three characteristic findings in the lesions: 1) luxury perfusion state, 2) decreased fluorodeoxyglucose (FDG) uptake, and 3) increased methionine (Met) uptake. These findings resembled those of low grade tumors.     

Crosslinking structure of keratin. I. Determination of the number of crosslinks in hair and wool keratins from mechanical properties of the swollen fiber

Hair and wool keratin fibers which had been treated with an 11 M LiBr solution containing N-ethyl maleimide showed typical rubberlike elasticity in a solution composed of equal volume of 8 M LiBr and diethylene glycol mono-n-butyl ether. Stress–strain curves and equilibrium force–temperature relations were measured for swollen hair and wool fibers. The non-Gaussian effects on deformation and the energy component in retractive forces were analyzed. On the basis of rubber elasticity theory, a method for estimation of the number of mechanically effective crosslinks in keratin fibers was proposed. A linear relationship between the crosslink density and the disulfide content was obtained from the data for a variety of keratin fibers (i.e., two different human hairs, horse hair, and 17 different wools). From the results of thermodynamical and non-Gaussian treatments for swollen keratin, it was suggested that the swollen fiber consists of a two-phase structure: a mechanically stable phase of higher crosslinked domains and rubbery phase with lower crosslink density. It was further found that considerable amounts of nondisulfide covalent crosslinks are present in wool and hair keratins.     

Nano‐scaled ordering of hyperbranched and star‐hyperbranched polymers

Hyperbranched polystyrenes (HPS) were prepared by living radical polymerization of 4‐vinylbenzyl N,N‐diethyldithiocarbamate (VBDC) as an inimer under UV irradiation. These HPS exhibited large amounts of photofunctional diethyldithiocarbamate (DC) groups on their outside surfaces. We derived star‐HPS (SHPS) by grafting from such HPS macroinitiator with methyl methacrylate (MMA) or ethyl methacrylate (EMA). The ratios of radius of gyration to hydrodynamic radius R_g/R_h for HPS and SHPS in tetrahydrofuran (THF) were in the range of 0.74–0.90 and 1.05–1.12, respectively. HPS and SHPS behaved in a good solvent as hard and soft spheres, respectively. We demonstrated the structural ordering of both branched polymers in THF through small‐angle X‐ray scattering (SAXS), by varying the polymer concentration. As a result, HPS and SHPS formed face‐centered‐cubic (fcc) and body‐centered‐cubic (bcc) structures, respectively, near the overlap threshold (C*). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3340–3345, 2006     

Mechanism and Kinetics of Aluminum Nitride Powder Degradation in Moist Air

Aluminum nitride (AlN) powders manufactured via three major commercial processes, namely, chemical vapor deposition from triethyl aluminum, carbothermal reduction and nitridation of alumina, and direct nitridation of aluminum, were exposed to moist air at room temperature to investigate the degradation mechanism and kinetics. In the degradation, the powders were initially hydrolyzed to amorphous aluminum oxyhydroxide, which subsequently transformed into mixtures of crystallized aluminum trihydroxide (Al(OH)₃) polymorphs, i.e., bayerite, nordstrandite, and gibbsite, forming agglomerates around the unreacted AlN. The data were fitted by using the unreacted-core model. Three stages were found in the degradation: the stage of an induction period at the beginning, followed by a stage of fast hydrolysis with the chemical reaction being rate controlling, and finally, with gradual closing of pores in the structure of Al(OH)₃ around AlN, changing to a stage of slow hydrolysis that was controlled by mass diffusion through Al(OH)₃. The existence of an induction period was attributed to slow hydrolysis of the surface oxide/oxyhydroxide layer. The powder produced by the carbothermal process showed the longest induction period, which was attributed to its surface structure being different from other powders.