Structural Characterization and Enzymatic Degradation of α‐, β‐, and γ‐Crystalline Forms for Poly(β‐propiolactone)

A structural comparison of three different crystalline forms of poly(β‐propiolactone) (PPL) was carried out by wide‐angle X‐ray diffraction, Fourier‐transform infrared spectroscopy, and differential scanning calorimetry. The α‐form in a hot‐drawn and annealed film represents a 2₁ helix conformation. The β‐form in a cold‐drawn and annealed film represents a planar zigzag conformation. The γ‐form in an oriented sedimented mat of solution‐grown chain‐folded lamellar crystals also implies a planar zigzag conformation. The solution‐cast film depicts similar outlines with the γ‐form in lamellar crystals in all the experimental measurements, suggesting that the molecular chain in the solution‐cast film has a planar zigzag conformation. While elongation at break decreased, tensile strength and Young's modulus increased with an increase in the crystallinity, independent of the crystalline forms. The influence of the enzymatic degradation of these crystal structures has been investigated by using an extracellular PHB depolymerase purified from Ralstonia pickettii T1. The rate of degradation was in the order of β‐form > α‐form > solution‐cast (γ‐form) film, and the different surface morphologies after partial enzymatic degradation were observed in scanning electron micrographs. It is suggested that the crystal structure is one of the important factors for determining the rate of degradation together with crystallinity.

Enzymatic degradation profiles of poly(β‐propiolactone) films.     

Synthesis and characterization of radioiodinated MD-230254: a new ligand for potential imaging of monoamine oxidase B activity by single photon emission computed tomography

A series of iodinated analogues of MD-230254 was synthesized and evaluated for inhibitory potency and selectivity toward monoamine oxidase B (MAO-B). Among them, 5-[4-(2-iodobenzyloxy)phenyl]-3-(cyanoethyl)-1,3,4-oxadiazole-2(3H)one (2-IBPO) was found to have high inhibitory potency and selectivity toward MAO-B (IC50=2.0 nM, MAO-A/MAO-B >50000). Analysis of the inhibition kinetics indicated that 2-IBPO acts in a two-step mechanism as a competitive, slow, and tight-binding inhibitor of MAO-B with a Ki value of 2.4 nM and an overall Ki* value at an equilibrium of 3.8 nM. The new radioligand for MAO-B, [125I]2-IBPO was conveniently synthesized from a tributylstannyl precursor by an iododestannylation reaction using sodium [125I]iodide and hydrogen peroxide with high radiochemical yield. The in vivo tissue distribution studies of [125I]2-IBPO demonstrated its high initial uptake and prolonged retention in the brain. A selective interaction of [125I]2-IBPO with MAO-B was confirmed by the pretreatment experiment with well known MAO specific inhibitors, l-deprenyl, Ro-16-6491, clorgyline, and Ro-41-1049. These very desirable characteristics of [125I]2-IBPO suggested that a 123I-labeled counterpart, [123I]2-IBPO, would have great potential in in vivo studies of MAO-B in the human brain with single photon emission computed tomography (SPECT).     

High-molecular-weight polyterephthalamide by direct polycondensation reaction in the presence of poly(ethylene oxide)

Polyterephthalamides of high molecular weight (η_inh up to 1.9) were obtained by the direct polycondensation reaction of terephthalic acid and aromatic diamines in the presence of poly(ethylene oxide) (PEO) with triphenyl phosphite in a N-methylpyrrolidone (NMP)–pyridine solution that contained lithium chloride. The molecular weights of the polymers produced varied with the amount and molecular weight of PEO, which showed maximum values when PEO with a molecular weight of 2.0 × 10⁴?5.0 × 10⁵ was used in a concentration of about 0.5 wt % in the solvent. The polycondensation reaction was significantly affected by the level of pyridine in a mixed solvent of NMP and pyridine and by the concentration of the lithium chloride added.     

Characteristics of InAlGaAs/InAlAs Superlattice Avalanche Photodiodes for Ultra-low Optical Power Detection in the Near Infrared

Static characteristics of two different structured InAlGaAs/InAlAs superlattice avalanche photodiodes (SLAPDs) cooled by liquid nitrogen were evaluated at a wavelength of 1.5 μm. The dark current of the SLAPD having a thick superlattice layer of 0.504 μm was 5 × 10⁻¹³ A. This was successively reduced by four orders of magnitude compared to that of the thin layer SLAPD of 0.231 μm at a breakdown voltage of around 20 V. The thickened layer was effective in suppressing tunneling dark current. An output current of 1.7×l0⁻¹² A at a bias voltage of 15 V was measured for an optical input with a wavelength of 1.5 μm and a signal power of 1 × 10⁻¹² W. This showed a sharp distinction from the dark current.     

High-efficiency longitudinally-pumped miniature Nd:YVO4 laser

We report on fundamental and intracavity frequency-doubled emission in a miniature Nd:YVO₄ (3×3×1 mm) laser. A maximum slope efficiency of η_s=58.6%, with optical efficiency of η₀=53.0% at 780 mW pump power was realized in a TEM₀₀ output beam. To obtain the optimum pump-beam focusing conditions we applied a new formalism in which the pump-beam propagation in the active medium was described by its M² factor. A good agreement between theoretical predictions and experimental results was observed. In second-harmonic regime, obtained by a KTP crystal, 230 mW green power that corresponds to 54% nonlinear conversion efficiency was reached.     

SCMTR: a chloride-selective, membrane-anchored peptide channel that exhibits voltage gating

The design, synthesis, and characterization of a synthetic chloride membrane transporter, SCMTR (synthetic chloride membrane transporter, "scimitar"), are presented. The compound [CH3(CH2)17]2NCOCH2OCH2CO-GGGPGGG-OBzl inserts rapidly into liposomes and planar lipid bilayers. SCMTR has a 1.3 +/- 0.01 nS chloride diffusion pathway (>10:1 Cl/K selectivity). Evidence was also obtained for voltage gating behavior.