Thermal characterization and thermal degradation of poly(norbornene-2,3-dicarboxylic acid dialkyl esters) synthesized by vinyl addition polymerization

The thermal properties and degradation behaviors of poly(norbornene-2,3-dicarboxylic acid dialkyl esters) (PNB-dialkyl esters) (alkyl = Me (PNB-Me), Et (PNB-Et), Pr (PNB-Pr), and Bu (PNB-Bu)) were investigated by thermogravimetric analysis (TGA) in dynamic conditions and by infrared (IR) spectroscopy. The PNB-dialkyl esters show good thermal stability up to 350 °C, and the thermal stability decreases in the order Me > Et > Pr > Bu with the increase in size of side chain. The effect of side-chain size on the thermal degradation behaviors of PNB-dialkyl esters is evidenced by one-step thermal degradation profile for PNB-Me while two-step thermal degradation profile for PNB-Et, PNB-Pr, and PNB-Bu. Transformation is deduced to undergo β-hydrogen elimination and formation of anhydride group in the first stage of thermal degradation reaction according to TGA and IR results for PNB-Et, PNB-Pr, and PNB-Bu. The apparent activation energy and thermal degradation model of PNB-dialkyl esters are estimated by means of Ozawa-Flynn-wall method and Phadnis-Deshpande method, respectively.     

Detection of bilayer packing stress and its release in lamellar-cubic phase transition by time-resolved fluorescence anisotropy

An introduction of nonlamellar-forming lipids into planar bilayers generates packing stress, which is important for the biological functions of plasma membranes and is a driving force for the lamellar-nonlamellar phase transition. We have investigated the phase behavior of a binary system consisting of egg yolk phosphatidylcholine and monoolein (MO) and the changes in the local orientation order of lipids in a lamellar-bicontinuous cubic phase transition. Small-angle X-ray scattering has revealed that the lamellar-bicontinuous cubic phase transition occurs at an MO molar fraction (X(MO)) between 0.6 and 0.7. These phases were dispersed to form liposomes and cubosomes to monitor the anisotropy of the incorporated fluorescence probe, in which Pluronic F127, used as a dispersion stabilizer of the cubic phase, has been proven not to alter the cubic structure and the location of the probes. Time-resolved fluorescence anisotropy measurements on these dispersions have revealed that the order parameter of the probe in the lamellar phase increases with increasing X(MO), and that it decreases during the transition to the cubic phase. This observation suggests that packing stress generated by the addition of the nonlamellar-forming lipid is released by the phase transition.     

Clinical significance of molecular genetic changes in sporadic invasive pituitary adenomas

Several molecular and genetic changes have been found in pituitary adenomas. We looked for correlations between these changes and the degree of invasiveness of the tumors. The invasiveness of 11 pituitary adenomas was graded by Hardy classification. We examined the retinoblastoma gene (RB1.20 on chromosome 13q) and the region around the MEN1 locus (chromosome 11q13.1-5) for loss of heterozygosity. Also examined are p53 mutations using single strain conformation polymorphism, p53 protein overexpression using immuno cytochemistry, homozygous deletions of p15 and p16 by polymerase chain reaction, and cellular proliferative activity using MIB-1 antibody. Six tumors (54.5%) had an LOH at either RB1.20 or the MEN1 locus. LOHs were found more frequently in Grade 4 and stage E tumors (72% and 67%) than in Grade 3 and stage D tumors (25% and 40%). However, no mutation or overexpression of p53 was found. No homozygous deletions of p15 or p16 were identified. The cell proliferative index ranged from 0 to 3%. LOH at 11q13 and 13q may be valuable in predicting the invasiveness of pituitary adenomas.     

Idealized collision model for reactive scattering: Energy dependence of the cross section for CH3I + K → CH3 + Kl

The energy and temperature dependence of the reaction cross section for CH₃I + K → CH₃ + KI have been calculated using the reaction probability obtained from the idealized model of collinear, impulsive interaction between the atoms K and I and between the group CH₃ and I. Calculated values of the cross section agree very closely with the postmaximum data by Gersh and Berastein.     

Crucial role of three-center hydrogen bonding in a challenging chiral molecular recognition

The enantio-discrimination of beta-chiral primary ammonium ions is achieved by a rational approach that utilizes three-center (bifurcated) hydrogen bonding. The extraction experiments on various selected guests reveal that the bifurcated H-bonding plays a crucial role for the chiral discrimination. The X-ray data obtained for an inclusion complex substantiate such interactions. Using the bifurcated H-bonding, the chiral molecular recognition with our C(3)-symmetric tripodal oxazoline receptors is extended generally toward ammonium ions of alpha-, beta-, and alpha,beta-chiral amines. Simple molecular models, evoking the bifurcated H-bonding, explain the chiral discrimination modes.     

A new synthetic pathway of segmented tri-block copolyether

A new synthetic pathway of A–B–A tri-block copolyether which is composed of a hydrophilic poly(oxyethylene) unit as an A part and a hydrophobic poly(oxy-2-methyl-trimethylene) unit as a B part is proposed. Telechelic α-tosyl-ω-tosyloxypoly(oxy-2-methyl-trimethylene) derived from tosylation of poly(oxy-2-methyl-trimethylene glycol) (PMTG) was allowed to react with poly(ethylene glycol) (PEG) in the presence of sodium hydroxide. T_g of the resulting A–B–A tri-block copolyether (PEMG) (M?_n = 1600) was ?72°C and its specific gravity [D₄¹⁵] was 1.055.     

Improved expression by cytomegalovirus promoter/enhancer and behavior of vascular endothelial growth factor gene after myocardial injection of naked DNA

Direct injection of the vascular endothelial growth factor (VEGF) gene plasmid DNA into the myocardium was shown to induce development of new blood vessels to increase the circulation in the heart of patients with coronary artery diseases. However, such angiogenic gene therapy (via naked DNA) was limited by low level of gene expression. Furthermore, the temporal and spatial characteristics of VEGF gene transfer in the heart are not known. In this study, we demonstrated that a plasmid vector, containing the human cytomegalovirus immediate early (HCMV IE) promoter and enhancer, induces greater expression of gene in the rat heart monitored by gene fused to the chloramphenicol acetyl transferase (CAT) reporter, than four different viral and cellular promoters. Interestingly, expression of VEGF121 protein showed an earlier peak, a shorter duration, and a wider distribution than that of CAT only. Therefore, a plasmid vector with an HCMV IE promoter/enhancer provides clear advantages over other previously developed plasmids. Furthermore, expression profile of VEGF121 gene may provide useful information in the design of angiogenic gene therapy in the heart.     

Sequential Injection Photometric Determination of Molybdenum Using Organic Wetting Film Extraction

Wetting film extraction was combined with colorimetry to determine nanogram amounts of molybdenum(VI). The simple extraction procedure enhanced sensitivity and selectivity while maintaining a high sample throughput. Extraction and back extraction steps were exploited to exclude interference from the 31 metal species and 11 anions tested. In the first step, molybdenum(VI) was extracted into a toluene film as an ion paired complex. Molybdenum(VI) reacted with thiocyanate to form anionic molybdenum(V) and/or molybdenum(VI) thiocyanate complexes. The complexes were extracted into a toluene film containing tetraheptylammonium bromide as ion pairing reagent. The thiocyanate ligands were displaced by 1,5-diphenylcarbazone (DPC) to form a more intensely colored complex (λ_max= 540 nm). DPC was introduced in the back extraction solvent, methanol. The relative standard deviation was 2.5% for 50 ng ml⁻¹of molybdenum(VI) (n= 10) at a rate of 25 samples h⁻¹. The detection limit (3 × baseline noise) was 2.5 × 10⁻⁸M.     

Increased transport of theophylline into gastrointestinal lumen and gastrointestinal dialysis by activated charcoal in rats with hepatic cirrhosis

The characteristics of exsorption and/or excretion of theophylline into the small intestinal lumen in rats with hepatic cirrhosis (HC rats) induced by carbon tetrachloride were investigated by an in situ single-pass perfusion technique. The serum concentrations of theophylline after i.v. administration of aminophylline (10 mg/kg) in the HC rats were significantly higher than those in normal rats during the experimental period. Moreover, the exsorption of theophylline from blood into the intestinal lumen was significantly increased in the HC rats compared with the normal rats. Treatments with oral activated charcoal reduced the serum theophylline levels in the HC rats. Consequently, gastrointestinal dialysis by oral administration of activated charcoal may be a useful method to remove poisonous drugs from the blood in patients with hepatic failure (including cirrhosis), which decreases the systemic clearance.