Component Crystallization and Physical Collapse during Freeze-Drying of L-Arginine-Citric Acid Mixtures

Component crystallization and physical collapse during freeze-drying of aqueous solutions containing protein-stabilizing L-arginine and citric acid mixtures were studied. Freeze-drying microscopy (FDM) and thermal analysis of the solute-mixture frozen solutions showed collapse onset at temperatures (T(c)) approximately 10°C higher than their T(g)'s (glass transition temperatures of the maximally freeze-concentrated solute phase). Experimental freeze-drying of these solutions at a low chamber pressure showed the occurrence of physical collapse at shelf temperatures close to or slightly higher than the T(c). Slower ice sublimation at higher chamber pressures induced the physical collapse from lower shelf temperatures. The large effect of chamber pressures on the collapse-inducing shelf temperatures confirmed significance of the sublimation-related heat loss on the sublimation interface temperature during the primary drying. Drying of the single-solute L-arginine solution resulted in cake-structure solids composed of its anhydrous crystal. Thermal and powder X-ray diffraction (PXRD) analysis suggested slow crystal nucleation of L-arginine dihydrate in the frozen solutions. Characterization of the frozen solutions and freeze-dried solids should enable rational formulation design and process control of amino acid-containing lyophilized pharmaceuticals.     

Manipulating double-decker molecules at the liquid-solid interface

We have used a scanning tunneling microscope (STM) to manipulate heteroleptic phthalocyaninato, naphthalocyaninato, and porphyrinato double-decker (DD) molecules at the liquid-solid interface between 1-phenyloctane solvent and graphite. We employed nanografting of phthalocyanines with eight octyl chains to place these molecules into a matrix of heteroleptic DD molecules; the overlayer structure is epitaxial on graphite. We have also used nanografting to place DD molecules in matrices of single-layer phthalocyanines with octyl chains. Rectangular scans with a STM at low bias voltage resulted in the removal of the adsorbed DD molecular layer and substituted the DD molecules with bilayer-stacked phthalocyanines from phenyloctane solution. Single heteroleptic DD molecules with lutetium sandwiched between naphthalocyanine and octaethylporphyrin were decomposed with voltage pulses from the probe tip; the top octaethylporphyrin ligand was removed, and the bottom naphthalocyanine ligand remained on the surface. A domain of decomposed molecules was formed within the DD molecular domain, and the boundary of the decomposed molecular domain self-cured to become rectangular. We demonstrated a molecular "sliding block puzzle" with cascades of DD molecules on the graphite surface.     

Two new dioxopiperazine derivatives, arestrictins A and B, isolated from Aspergillus restrictus and Aspergillus penicilloides

In the course of searching for bioactive substances, two new dioxopiperazine derivatives, arestrictins A (1) and B (2), were isolated along with the known dioxopiperazine, cristatin A (3), and the known peptide, asperglucide (4), from the organic extract of the xerophilic fungi, Aspergillus restrictus and Aspergillus penicilloides. The absolute structures of 1 and 2, except for the configuration of the secondary alcohol in 1, were established by spectroscopic and chemical investigation. The absolute configuration of cristatin A (3) was also determined.     

Dynamical valence fluctuation at the charge-density-wave phase boundary in iodide-bridged Pt compound [Pt(chxn)2I]I2

We synthesized a novel iodo-bridged linear chain platinum compound, having the quasi-two-dimensional charge-density-wave (CDW) ground state and the smallest band gap. In this compound, we discovered an anomalous valence state in the boundary region at which the CDW phase alternates in the crystal by means of ESR, X-ray diffuse scattering, STM, and electrical resistivity. This anomalous state can be explained by the fast fluctuation between Pt(IV)-I...Pt(II) and Pt(II)...I-Pt(IV) in the double well potential. This is the first observation of the dynamical fluctuation of the CDW phase among the quasi one-dimensional halogen-bridged complexes.     

Chain conformations of poly(gamma-benzyl-L-glutamate) pre and post an electrospinning process

In order to reveal mechanisms for the electrospinning of proteins, this study focuses on the polymer chain conformation, which is considered to be a critical factor for successful electrospinning. Poly(gamma-benzyl-L-glutamate) (PBLG) is employed and the relationships between the chain conformations of the pre-spun PBLG molecules and the morphologies of the post-spun PBLG fibers are investigated. By combining viscosity measurements, and circular dichroism and FT-IR spectroscopies, chain conformations of the pre- and post-spun PBLG are characterized. The chain conformations of the pre-spun PBLG changes from an alpha-helix to a random coil upon changing the solvent ratios of dichloromethane (CH(2)Cl(2)) and trifluoroacetic acid (CF(3)COOH) from 100:0 to 0:100. In an alpha-helix conformation, the morphology of PBLG fibers is relatively thick, while that of the random coil is thin and homogenous. The mean fiber diameters decrease when the chain conformations change from an alpha-helix to a random coil. FT-IR spectroscopy and wide-angle X-ray diffraction measurements reveal that electrospinning predominantly induces an alpha-helical conformation in post-spun PBLG fibers, and more highly crystallized fibers are generated as the alpha-helical content in the pre-spun solution increases.     

Structures and properties of dendrimers having peripheral 2,3-difluorobiphenyl mesogenic units: effects of dendrimer generation

1st-5th generation poly(propyleneimine) dendrimers having peripheral 2,3-difluorobiphenyl mesogenic groups have been synthesized. They exhibited smectic liquid crystalline behaviour. All the liquid crystalline dendrimers exhibited a smectic A (SmA) phase and a crystal E (E) phase. The SmA-isotropic phase transition temperature increased with increasing generation. In addition, a homeotropic structure was spontaneously formed on a glass plate in the SmA phase for the 2nd, 3rd, and 4th generation dendrimers. The hometropic structure remained unchanged in the phase.     

On sharp triangle inequalities in Banach spaces

We shall present a couple of norm inequalities which will much improve the sharp triangle inequality with n elements and its reverse inequality in a Banach space shown recently by the last three authors.     

Characterization of a d-Stereoselective Aminopeptidase (DamA) Exhibiting Aminolytic Activity and Halophilicity from Aspergillus oryzae

β-Aminopeptidases exhibit both hydrolytic and aminolytic (peptide bond formation) activities and have only been reported in bacteria. We identified a gene encoding the β-aminopeptidase homolog from a genome database of the filamentous fungus Aspergillus oryzae. The gene was overexpressed in A. oryzae, and the resulting recombinant enzyme was purified. Apart from bacterial homologs [β-Ala-para-nitroanilide (pNA)], the enzyme preferred d-Leu-pNA and d-Phe-pNA as substrates. Therefore, we designated this gene as d-stereoselective aminopeptidase A (damA). The purified recombinant DamA was estimated to be a hexamer and was composed of two subunits with molecular masses of 29.5 and 11.5 kDa, respectively. Optimal hydrolytic activity of DamA toward d-Leu-pNA was observed at 50 °C and pH 8.0. The enzyme was stable up to 60 °C and from pH 4.0–11.0. DamA also exhibited aminolytic activity, producing d-Leu-d-Leu-NH₂ from d-Leu-NH₂ as a substrate. In the presence of 3.0 M NaCl, the amount of pNA liberated from d-Leu-pNA by DamA was 3.1-fold higher than that in the absence of NaCl. Thus, DamA is a halophilic enzyme. The enzyme was utilized to synthesize several hetero-dipeptides containing a d-amino acid at the N-terminus as well as physiologically active peptides.     

End-on double azido bridged copper (II) complex with (N, N, O) schiff base: synthesis, structure and magnetic study

A rare asymmetric end-on double-bridged copper (II) azido complex with ∠Cu-N(azide)-Cu=89.1°, has been synthesized and characterized structurally and magnetically. The Cu-N(azide)-Cu angle is unusually low in the complex reported here in comparison to the same in other similar complexes. The magnetic study reveals that the interaction between metal centers in this complex is antiferromagnetic in nature. Though a ferromagnetic interaction between the metal centers is expected in the complex the coupling has actually been found to be antiferromagnetic, instead.     

Effect of methyl substituents on permeability and permselectivity of gases in polyimides prepared from methyl-substituted phenylenediamines

Permeability and solubility coefficients for H₂, CO₂, O₂, CO, N₂, and CH₄ in polyimides prepared from 6FDA and methyl-substituted phenylenediamines were measured to investigate effects of the substituents on gas permeability and permselectivity. The methyl substituents restrict internal rotation around the bonds between the phenyl rings and the imide rings. The rigidity and nonplanar structure of the polymer chain, and the bulkiness of methyl groups make chain packing inefficient, resulting in increases in both diffusion and solubility coefficients of the gases. Polyimides from tetramethyl-p-phenylenediamine and trimethyl-m-phenylenediamine display very high permeability coefficients and very low permselectivity due to very high diffusion coefficients and very low diffusivity selectivity, as compared with the other polyimides having a similar fraction of free space. This suggests that these polyimides have high fractions of large-size free spaces.