Characterization of biosynthesized P(3HB-co-3HA)s swellable in organic solvents

Polyhydroxyalkanoate (PHA) copolymers consisting of (R)-3-hydroxybutyrate (3HB) and medium-chain-length (R)-3-hydroxyalkanoate (3HA), P(3HB-co-3HA), are usually solved in chloroform. However, we found that some of the P(3HB-co-3HA) aged for more than 1 month under ambient conditions were not solved in chloroform, but instead swelled when the 3HA fraction was over 14 mol%. On the basis of differential scanning calorimetry and wide-angle x-ray diffraction analyses, we predicted that swellable P(3HB-co-3HA) contained numerous P(3HB) microcrystals, which may form physical crosslinks between adjacent PHA polymer chains.     

Existence of a Global Solution for a Scalar Conservation Law with a Source Term

We are concerned with a scalar conservation law with a source term. This equation is proposed to describe the qualitative behavior of waves for a general system in resonance with the source term by T.P. Liu. In addition to this, the scalar conservation law is used in various areas such as fluid dynamics, traffic problems etc.In the present paper, we prove the global existence and stability of entropy solutions to the Cauchy problem. The difficult point is to obtain the bounded estimate of solutions. To solve it, we introduce some functions as the lower and upper bounds. Therefore, our bounded estimate depends on the space variable. This idea comes from the generalized invariant region theory for the compressible Euler equation. The method is also applicable to other nonlinear problems involving similar difficulties. Finally, we use the vanishing viscosity method to construct approximate solutions and derive the convergence by the compensated compactness.     

Relationship between physicochemical properties and chemical stability of muramyldipeptide derivative B30-MDP in liposomal solutions

The muramyldipeptide derivative B30-MDP has immunoadjuvant activity and vesicle-forming ability in aqueous environments. It is therefore important to evaluate the relationship between its physicochemical properties and chemical stability for use as a vaccine adjuvant. We studied the effects of octyl--D-glucoside (O.G.) incorporation on the physicochemical properties and chemical stability in aqueous solution at pH 7.4. The changes in particle size and in the membrane fluidity of B30-MDP liposomes, which were induced by the addition of O.G., were measured to confirm the transition from micelle phase to vesicle phase. The degradation of B30-MDP in both liposomal and mixed micellar solutions was measured by reverse-phase high-performance liquid chromatography. This degradation occurred by a pseudo first-order reaction at 313, 323 and 333 K. The shelf-life of the B30-MDP solution supplemented with O.G. was approximately one-seventh of that of B30-MDP alone in the liposomal solution. The changes in thek _obs values of B30-MDP correlated well with those in membrane fluidity induced by O.G. incorporation. These results indicate that an increase in membrane fluidity labilizes B30-MDP in liposomal solution.     

Synthesis and properties of rhodium(III) porphyrin cyclic tetramer and cofacial dimer

Rhodium(III) porphyrin complexes, [Rh(4-PyT(3)P)Cl](4) (1) and [Rh(2-PytB(3)P)Cl](2) (2) (4-PyT(3)P = 5-(4-pyridyl)-10,15,20-tritolylporphyrinato dianion, 2-PytB(3)P = 5-(2-pyridyl)-10,15,20-tri(4-tert-butyl)phenylporphyrinato dianion), were self-assembled and characterized by (1)H nuclear magnetic resonance spectroscopy, infrared spectroscopy, and electron spray ionization-mass spectroscopy methods. The spectroscopic results certified that the rhodium porphyrin complexes 1 and 2 have a cyclic tetrameric structure and a cofacial dimeric structure, respectively. The X-ray structure analysis of 1 confirmed the cyclic structure of the complex. The Soret bands of both oligomers were significantly broadened by excitonic interactions between the porphyrin units, compared to those observed for a corresponding analogue of Rh(TTP)(Py)Cl (TTP = 5,10,15,20-tetratolylporphyrinato dianion, Py = pyridine). Stepwise oxidation of the porphyrin rings in the oligomers was observed by cyclic voltammetry. The oligomers 1 and 2 are very stable in solution, and they slowly undergo reactions with pyridine to give corresponding monomer complexes only at high temperatures (approximately 80 degrees C).     

Biosynthesis of polyhydroxyalkanoate (PHA) copolymer from fructose using wild-type and laboratory-evolved PHA synthases

Eleven laboratory-evolved polyhydroxyalkanoate (PHA) synthases which originated from Pseudomonas sp. 61-3 enzyme (PhaC1(Ps)), together with the wild-type enzyme, were applied for PHA synthesis from fructose using Ralstonia eutropha PHB(-)4 as a host strain. The evolved PhaC1(Ps) mutants had amino acid substitution(s) at position 325 and/or position 481. In these mutants, serine-325 (S325) was replaced by cysteine (C) or threonine (T), while glutamine-481 (Q481) was replaced by lysine (K), methionine (M) or arginine (R). All recombinant strains harboring the genes of the evolved PhaC1(Ps) mutants produced a significantly increased amount of PHA (55-68 wt.-%) compared with the one harboring the wild-type gene (49 wt.-%). Particularly, those evolved PhaC1(Ps) mutants having multiple amino acid substitutions showed higher activities for PHA synthesis. Characterization of the PHA by NMR spectroscopy revealed that they were copolymers consisting of (R)-3-hydroxybutyrate (98-99 mol-%) and medium-chain-length comonomers (1-2 mol-%). This study also confirmed that amino acid substitution at position 481 in PhaC1(Ps) led to an increasing molecular weight of PHA. The number-average molecular weight (Mn) of PHA (Mn = 240,000) synthesized by the evolved PhaC1(Ps) (Q481K) mutant was 4.6-fold greater than that (Mn = 52,000) synthesized by the wild-type enzyme.     

Guest encapsulation and self-assembly of a cavitand-based coordination capsule

The synthesis and spectroscopic characterization of a cavitand-based coordination capsule 14 BF4 of nanometer dimensions is described. Encapsulation studies of large aromatic guests as well as aliphatic guests were performed by using 1H NMR spectroscopy in [D1]chloroform. In addition to the computational analysis of the shape and geometry of the capsule, an experimental approach to estimate the interior size of the cavity is discussed. The cavity provides a highly rigid binding space in which molecules with lengths of approximately 14 A can be selectively accommodated. The rigid cavity distinguished slight structural differences in the flexible alkyl-chain guests as well as the rigid aromatic guests. The detailed thermodynamic studies revealed that not only CH-pi interactions between the methyl groups on the guest termini and the aromatic cavity walls, but also desolvation of the inner cavity play a key role in the guest encapsulation. The cavity preferentially selected the hydrogen-bonded heterodimers of a mixture of two or three carboxylic acids 18-20. The chiral capsule encapsulated a chiral guest to show diastereoselection.     

Jet spectroscopy of arylmethyl radicals in the visible region: assignment of low-frequency vibrational modes in diphenylmethyl and chlorodiphenylmethyl radicals

The D(1)-D(0) transitions of diphenylmethyl (DPM) and chlorodiphenylmethyl (CDPM) radicals were studied by laser induced fluorescence (LIF) spectroscopy in a supersonic jet. Laser induced fluorescence excitation and dispersed fluorescence (DF) spectra were obtained for DPM and CDPM radicals produced by ArF excimer laser (193 nm) photolyses of their chlorides. With the aid of the density functional theory (DFT) calculation, vibronic bands are assigned by comparing the observed LIF excitation spectra of the jet-cooled radicals with the single vibronic level DF spectra. Low-frequency vibrations of 55 and 53 cm(-1) in the ground and excited states, respectively, are assigned to the symmetric phenyl torsional mode of the DPM radical. The geometries of DPM in the ground and excited states are discussed with regards to observed spectra and DFT calculations. Similarly for the CDPM radical, symmetric phenyl torsional and Ph-C-Ph bending modes are assigned and the halogen-substitution effect in equilibrium geometry is discussed.