Novel bifunctional probe for radioisotope-free photoaffinity labeling: compact structure comprised of photospecific ligand ligation and detectable tag anchoring units

A novel method for radioisotope-free photoaffinity labeling was developed, in which a bifunctional ligand is connected to a target protein by activation of a photoreactive group, such as an aromatic azido or 3-trifluoromethyl-3H-diazirin-3-yl group, and identification of the ligated product is achieved by anchoring of a detectable tag through the Staudinger-Bertozzi reaction with an alkyl azido moiety that survives photolysis. The chemical ground of this method was confirmed using model compounds with the bifunctional group under photoirradiation in the presence of trapping agents for reactive intermediates. The utility of the method has been demonstrated by specific labeling of the catalytic portion of human HMG-CoA reductase.     

Synthesis and polymerization of N-(p-vinylbenzyl)-3-carbamoyl-1,4-dihydropyridine and redox behavior of the oligomer

In order to prepare a soluble dihydropyridine-type redox polymer, N-(p-vinylbenzyl)-3-carbamoyl-1,4-dihydropyridine was synthesized and characterized by elemental analysis, infrared spectroscopy, and nuclear magnetic resonance spectroscopy. The polymerization of the vinyl monomer in N,N-dimethylformamide or chloroform was also studied. Only oligomers were obtained by radical polymerization. The reduction of various compounds by the oligomer thus prepared was examined in heterogeneous or homogeneous solution.     

Polyelectrolyte gel transitions: experimental aspects of charge inhomogeneity in the swelling and segmental attractions in the shrinking

This paper aims to provide a systematic discussion based on our experimental results both previously published and unpublished, to promote better understanding of volume-phase transitions in polyelectrolyte gels. Special attention was paid to the distribution of network charges as well as to the attractive interaction among polymer segments. From looking at how these effects appear in the swelling curves, an exploration of the nature of polyelectrolyte gel transitions was attempted. Two sorts of polyelectrolyte gels, temperature-responsive ionic gels based on N-isopropylacrylamide (NIPA) and cationic poly(ethyleneimine) (PEI) gels, were mainly employed with various modifications. The charge inhomogeneity within the gel phase was created by surfactant binding, immobilized enzyme reaction and physical entrapment of polyions. The attractive interactions holding the gel in a collapsed state were studied in comparison with phase separations of the corresponding linear polyelectrolyte. The main conclusions are summarized as follows: (i) The charge inhomogeneity exhibits a large influence on the volume transition in ionic gels. (ii) Hydrogen bonding and hydrophobic association, other than electrostatic attraction, can be considered to play an important role in the segmental association. (iii) Stably associated segments via one or more of these attractive interactions causes a large hysteresis in the swelling process, in which the repulsive interaction among the fixed charges on the network is dominant as shown in the Katchalsky's model. (iv) A distribution of "neutral but hydrophilic" moieties (e.g., ion pair or salt-linkage formed between the opposite charged groups) within the gel shows a marked effect on the temperature-induced volume collapse, the aspect of which is similar to that observed in the gels with a charge inhomogeneity.     

Dynamic and electrophoretic light scattering of poly(dimethyldiallylammonium chloride) in salt-free solutions

Dynamic and electrophoretic light scattering were used to study the diffusion and electrophoretic mobility of poly(dimethyldiallylammonium chloride) as a function of polymer molecular weight in salt-free solutions. Two relaxation modes characterized as fast diffusion (D_f) and slow diffusion (D_s) were obtained from dynamic light scattering. Although the slow diffusion coefficient D_s strongly depends on molecular weight (M_w), the fast diffusion coefficient D_f was found to be independent of M_w over the range in the study. The fast diffusion was considered as the diffusion of a part of the polymer chain; the slow diffusion was interpreted by multichain diffusion. Electrophoretic light scattering results in the salt-free solution show that the electrophoretic mobility of the polymer is independent of M_w. © 1996 John Wiley & Sons, Inc.     

Viscometric,light scattering,and size‐exclusion chromatography studies on the structural changes of aqueous poly(vinyl alcohol) induced by γ‐ray irradiation

The crosslinking processes of aqueous poly(vinyl alcohol) (PVA) by γ‐ray irradiation were studied by viscometry, dynamic and static light scattering (DLS and SLS), as well as size exclusion chromatography (SEC). Increases in the intrinsic viscosity ([η]), molecular weight (M_w), hydrodynamic radius (R_h), and radius of gyration (R_g), and a decrease in second virial coefficient (A₂) were observed after γ‐ray irradiation. However, both the values of [η] and A₂ for irradiated PVA fell below the data of unirradiated PVA solutions, suggesting a conformational change of PVA chains after γ‐ray irradiation. This structural change of PVA as a result of γ‐ray irradiation was also indicated by the decreases in R_g/R_h from 1.5 to 1.39 by SLS and DLS, and in Mark–Houwink exponent α_η from 0.54 to 0.26 by SEC‐Viscometry. The broadening of the M_w distribution (MWD) as indicated by the polydispersity index increased from 2.2 to 6.5 because of γ‐ray irradiation. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 214–221, 2000     

Effects of substituent groups of polyimides on sorption and diffusion of gases

Sorption rate curves of CO₂, N₂, and He gases below 1 atm were measured for polyimide films prepared from benzophenone tetracarboxylic dianhydride (BTDA) with 3,5-diaminotoluene trifluoride (DATF), 2,4-diaminotoluene (DAT), m-phenylenediamine (MPD), and diaminobenzoic acid (DABA). The molecular structures of these four polyimides differ only in the substituent groups of the diamine structure. These polyimides exhibit dualmode type sorption isotherms for carbon dioxide that are concave to the pressure axis, typical of glassy polymer/gas system. The apparent diffusion coefficients below 1 atm pressure of carbon dioxide for this series of compounds decrease in the order: BTDA-DATF > BTDA-DAT > BTDA-MPD > BTDA-DABA. A linear relation between the logarithm of the apparent diffusion coefficient and the reciprocal of free volume, calculated by the method of Bondi using density data, is found for these polyimides. However, this tendency is not observed for the other two gases. The activation energies of the apparent diffusion coefficients at 20 cmHg pressure of carbon dioxide increase with increasing cohesive energy density of the polyimides. The energy per mole of free volume elements in a liquidlike structure in each cohesive energy density may be equated to the activation energy and used to calculate the free volume. The values from the activation energy are almost the same as those from Bondi's method.     

Sorption and diffusion of gases in a polyimide

Sorption and diffusion of gases (CO₂, N₂, and He) in a polyimide (PI2080) film were measured by using an apparatus which gives the sorption rate curves from the initial state to the equilibrium state. Nonlinear isotherms observed for CO₂ sorption were interpreted successfully in terms of the dual-mode model for sorption in glassy polymers. Linear isotherms observed for N₂ and He seemed to obey Henry's law. Two diffusion coefficients (D_I and D_E) were obtained using the short-time method and the long-time method for a Fickian diffusion model, together with the equilibrium solubility (C_e) from each experiment. The initial sorption rate curves agreed with the calculated curves using D_I, however near sorption equilibrium the curves are in accord with the calculated curves using D_E. These observations suggest that some relaxation process is superimposed on the diffusion process. The non-Fickian transport data were correlated successfully with a model that combines time-dependent diffusion and the Fickian model.     

Evaluation of dispersion state of the two racemic compounds of troglitazone in pharmaceutical granules using IR-to-THz imaging

Troglitazone exists as four isomers in equal amount and these isomers compose two racemic compounds, RR/SS and RS/SR. The objective of this study was to discriminate between the racemic compounds and between the crystal and amorphous forms of troglitazone in solid dispersions (SDs) using IR-to-THz imaging. SDs of troglitazone with polyvinylpyrrolidone (PVP, carrier) were prepared by the closed melting method. SDs were heated at various temperatures and water content. The mid-to-far infrared measurements for the powder samples were performed by using the synchrotron radiation source at the BL43IR in SPring-8. Crystalline RR/SS (L) and RS/SR (H) showed different spectra, that is, each form had a specific peak, respectively. However, amorphous forms prepared from each crystalline form exhibited the same spectra. Using the chemo-metric analysis, the existing component was decided in each pixel and the distribution of crystalline L, H and amorphous troglitazone in SDs could be illustrated. For the sample heated at 105 °C, 75%RH, scattered plots of H and amorphous against PVP showed the trend for H was negative; on the other hand, amorphous showed positive correlation. This result suggested that H existed separately, whereas amorphous would be dissolved in PVP. Based on these evaluations, it was clear that the physical state and distribution of troglitazone in SDs, including the discrimination between L, H, and amorphous, reflect the preparation conditions. Chemical imaging can observe a difference in the dispersed state of drug and ingredient in a visible image by performing statistical processing.     

The preparation of di- and tri-phenylstannyl esters of aromatic dithio acids,and some of their reactions

Some crystalline di- and tri-phenylstannyl esters [ArCS₂SnPh₃ and (ArCS₂)₂SnPh₂] of aromatic dithio acids have been prepared in good yields and characterized. Preferential cleavage of the SnS bond of the ester was observed by treating them with primary and secondary amines as well as with phenacylidenetetramethylenesulfurane.