Preparation and properties of silicon containing polyamides

Silicon containing polyamides were prepared by melt polycondensation method with a 1,3-bis(3-aminopropyl)tetramethyldisiloxane and aliphatic dicarboxylic acids having various numbers of methylene groups. Only one endothermic peak appeared in the DTA curve of the quenched sample for polyamides having an even number of methylene groups in the repeating unit. Two endothermic peaks, however, appeared for the sample kept for a week in dry air at ambient temperature after quenching: the peak at the higher temperature is called peak I; and the peak at the lower one, peak II. By heat treatment at the higher temperature, peak II shifted to a higher temperature and increased its peak area, and peak I decreased its peak area while keeping its temperature unchanged. This behavior suggests the existence of two types of crystalline states. The peak temperature of peak I alternatively decreased with the increase of the number of methylene groups. The Young's modulus and the tensile strength increased with increase of annealing time at ambient temperature. The solubilities in various solvents, the resistance to alkali solution, and the thermal stability were acceptable. Both the permeation coefficient of oxygen (P) and the separation ratio (P/P) increased with the increase of silicon content in the repeating unit.     

Thermodynamics of solutions of methanol and solvating components

A model is proposed to correlate the excess Gibbs free energies and excess enthalpies of binary solutions of methanol and a solvating component. Solution nonideality from ideal solutions is given by the sum of the chemical contribution term, which is due to self-association of methanol and solvation between methanol and a nonassociating component, and the physical contribution term with allowance for the NRTL equation. The model uses the following data for methanol: two enthalpies for formation of the hydrogen bonds for the dimer and all larger polymeric species, three equilibrium constants of stepwise association for the dimer, trimer and other polymeric species, and an equilibrium constant for cyclic species of more than tetramer. The association model further includes an additional solvation equilibrium to allow for the interaction between the terminal hydroxyl group of methanol polymeric species and a solvating component. The model is extended to predict vapor—liquid equilibria, liquid—liquid equilibria and excess enthalpies for ternary solutions containing methanol and two nonassociating components from only binary information. Calculated results are in good agreement with experimental data as shown by selected illustrative examples.     

Near-IR absorption and fluorescence spectra and AFM observation of the light-harvesting 1 complex on a mica substrate refolded from the subunit light-harvesting 1 complexes of photosynthetic bacteria Rhodospirillum rubrum

The subunit light-harvesting 1 (LH 1) complexes isolated from photosynthetic bacteria Rhodospirillum rubrum using n-octyl-beta-glucoside were reassociated and adsorbed on a mica substrate using spin-coat methods with the aim of using this LH complex in a nanodevice. The near-IR absorption and fluorescence spectra of the LH 1 complexes indicated that the LH 1 complex on the mica was stable, and efficient energy transfer from a carotenoid to a bacteriochlorophyll a was observed. Atomic force microscopy of the reassociated LH 1 complexes, under air, showed the expected ringlike structure. The outer and inner diameters of the ringlike structure of the LH 1 complex were approximately 30 and 8 nm, respectively, and the ringlike structure protruded by 0.2-0.6 nm.     

Products of the reaction between alpha- or gamma-tocopherol and nitrogen oxides analyzed by high-performance liquid chromatography with UV-visible and atmospheric pressure chemical ionization mass spectrometric detection

The reaction products of alpha- or gamma-tocopherol with nitric oxide in the presence of molecular oxygen were isolated and characterized. The consumption of tocopherols and the formation of the major products were monitored by high-performance liquid chromatography (HPLC) by a gradient elution method. The quantitative analysis of these compounds with UV-Vis detectors, however, was interfered by several minor products having similar UV spectra and retention times as those of the major ones. In order to establish a quantitative analytical method for the products, we investigated other detection methods, and found that atmospheric pressure chemical ionization (APCI), LC-MS was a more selective and better analytical method for these compounds.     

CA 19-9 like epitope(s) on carcinoembryonic antigen molecules

CA 19-9 epitope(s) on carcinoembryonic antigen (CEA) was studied by a method designated the hybrid immunoradiometric-assay (hybrid IRMA) using solid phase CEA antibody to capture the CEA molecule and radio-labeled NS 19-9 antibody as a detector. The radioactivities of the hybrid IRMA of respective sera with certain cancers differed from that of normal sera. The specific radioactivities of hybrid IRMA did not disappear on washing with a reaction mixture containing Triton X-100 as a detergent. Treatment of the sample with neuraminidase or periodate diminished the specific bound radioactivities, similar to CA 19-9 antigen. Furthermore, the treatment of CEAs by PI-PLC had no effect on the radioactivities. Taken together, it was suggested that CEA sugar moieties contain CA 19-9 like epitope(s).     

Reduction of sulfoxides and sulfilimines catalyzed by metalloporphins

Reduction of sulfoxides and sulfilimines to the corresponding sulfides by both BNAH and NaBH₄ have been found to proceed in the presence of a catalytic amount of metallo-mesotetraphenylporphins.     

Alteration of protein composition in mouse thymocytes by signals through T-cell receptor

To avoid destructive autoimmunity, T-cell precursors (thymocytes) expressing autoreactive T-cell receptor are deleted in the thymus via an apoptotic process by the signals from the T-cell receptor-CD3 complexes. In order to analyze the apoptotic mechanism, we established a cell-free system using the lysates from mouse thymocytes treated in vivo with anti-CD3 monoclonal antibody (mAb). The soluble cytosolic high molecular mass protein fraction from the anti-CD3-treated thymocytes revealed an activity that directly induces nuclear apoptotic morphological changes and DNA fragmentation. This fragmentation activity was not observed in the fraction from the thymocytes without anti-CD3 treatment. Proteins in both fractions were separated by two-dimensional electrophoresis. The silver-stained gels revealed differences in protein spots. These protein spots were identified by database searching of mass spectrometric (MS) and tandem mass spectrometric (MS/MS) data obtained from in-gel tryptic digests of the spots, using an integrated system of liquid chromatography/electrospray ionization/ion-trap mass spectrometry. In this study, the high mobility group protein HMG2 was identified as one of the cytosolic proteins that is increased by the signals from the T-cell receptor, and heterogeneous nuclear ribonucleoprotein A2/B1 and glyceraldehyde 3-phosphate dehydrogenase were found to be decreased by the signals.     

13C NMR Spectroscopy on the Complexation of α-Cyclodextrin with 1-Alkanols and 1-Alkanoate Ions

Binding constants for -cyclodextrin ( -CD) complexes with 1- alkanols and 1- alkanoate ions were determined by analyzing changes ( ) in chemical shifts of guest ¹³C NMR signals with -CD concentration. The guests gave well-separated ¹³C NMR signals. The curve-fitting analyses of for individual carbons upon assumption of a simple 1:1 complexation gave virtually the same binding constants (K₁) in the cases of guests with relatively short alkyl chains, such as 1-propanol, 1-butanol, 1- pentanol , 1- butanoate , 1- pentanoate , and 1-hexanoate. However, thus obtained individual K₁ values were significantly different from one another, when the guests had relatively long alkyl chains such as 1- hexanol , 1- heptanol , and 1-octanoate. In these guests, satisfactorily consistent K₁ values were obtained by the curve-fitting analyses of for individual carbons upon an assumption that not only 1:1 but also 2:1 (host:guest) complexation occurs.     

An ab initio molecular orbital study on the stacking interaction between nucleic acid bases: Dependence on the sequence and relation to the conformation

The stacking interaction energies between nucleic acid bases in A DNA and B DNA are calculated by means of the ab initio molecular orbital method. The calculated values agree well with the experimental values of stacking enthalpy changes. The stacking interaction energy is shown to be highly sequence dependent, particularly when the sequence includes guanine or cytosine. The possibility is shown that the conformation of a DNA double helix fragment is determined by the constituent stacking interaction. Electrostatic energy is the cause of the sequence dependency of the stacking energy, while charge transfer and dispersion energies contribute to the overall stability.     

Protected amino acids as a nonbonding source of chirality in induction of single-handed screw-sense to helical macromolecular catalysts

Chiral nonbonding interaction with N-protected amino acid methyl esters used as chiral additives in achiral solvents allows dynamic induction of single-handed helical conformation in poly(quinoxaline-2,3-diyl)s (PQX) bearing only achiral substituents. Ac-l-Pro-OMe, for instance, allows induction of energy preference of 0.16 kJ mol⁻¹ per monomer unit for the M-helical structure over the P-helix in t-butyl methyl ether (MTBE). With this new mode of screw-sense induction, homochiral screw-sense has been induced in virtually achiral poly(quinoxaline-2,3-diyl)s 1000-mer containing phosphine pendants (PQXphos). Use of PQXphos as a helically dynamic ligand along with Ac-Pro-OMe (l or d) as a chiral additive in MTBE allowed a highly enantioselective Suzuki–Miyaura coupling reaction with up to 95% enantiomeric excess.

Achiral poly(quinoxaline-2,3-diyl) containing Ar₂P groups undergo dynamic induction of M-helical conformation through nonbonding interaction with protected AA such as Ac-l-Pro-OMe, serving as a chiral ligand in asymmetric cross-coupling with up to 95% ee.