Plaunol A and B,new anti-ulcer diterpenelactones from Crotonsublyratus

Two new diterpenelactones named plaunol A ($\text{2}$) and B ($\text{3}$) exhibiting anti-Shay ulcer activity were isolated from Thai medicinal plant, $\text{Croton}$$\text{sublyratus}$. Structure of $\text{2}$ was determined by X-ray analysis of its $\text{p}$-bromobenzoate and structure of $\text{3}$ was deduced from the results of chemical correlation and the spectral data.     

Semiconductor laser fluorimetry for enzyme and enzymatic assays

Near-infrared semiconductor laser fluorimetry is applied to assays of xanthine and xanthine oxidase. The fluorescence of indocyanine green in the near-infrared region is quenched by hydrogen peroxide. Xanthine is converted to uric acid by xanthine oxidase, in a reaction which also produces hydrogen peroxide; xanthine can be determined by measuring the decrease in fluorescence intensity of the dye added to the sample solution. The calibration graph for xanthine is linear from 5 × 10^?5 M to 5 × 10^?7 M. The enzyme activity can also be determined.     

A study of molecular vibrational relaxation mechanism in condensed phase based upon mixed quantum-classical molecular dynamics. I. A test of IBC model for the relaxation of a nonpolar solute in nonpolar solvent at high density

In order to investigate vibrational relaxation mechanism in condensed phase, a series of mixed quantum-classical molecular dynamics calculations have been executed for nonpolar solute in nonpolar solvent and polar solute in polar solvent. In the first paper (Paper I), relaxation mechanism of I2 in Ar, where Lennard-Jones force is predominant in the interaction, is investigated as a function of density and temperature, focusing our attention on the isolated binary collision (IBC) model. The model was originally established for the relaxation in gas phase. A key question, here, is "can we apply the IBC model to the relaxation in the high-density fluid?" Analyzing the trajectory of solvent molecule as well as its interaction with the solute, we found that collisions between them may be defined clearly even in the high-density fluid. Change of the survival probability of the vibrationally first excited state on collision was traced. The change caused by collisions with a particular solvent molecule was also traced together with the interaction between them. Each collision makes a contribution to the relaxation by a stepwise change in the probability. The analysis clearly shows that the relaxation is caused by collisions even in the high-density fluid. The difference between stepwise relaxation and the continuous one found for the total relaxation in the low-density fluid and in the high-density one, respectively, was clarified to come from just the difference in frequency of the collision. The stronger the intensity of the collision is, the greater the relaxation caused by the collision is. Further, the shorter the collision time is, the greater the resultant relaxation is. The discussion is followed by the succeeding paper (Paper II), where we report that molecular mechanism of the relaxation of a polar molecule in supercritical water is significantly different from that assumed in the IBC model despite that the density dependence of the relaxation rate showed a linear correlation with the local density of water around the solute, the linear correlation being apparently in good accordance with the IBC model. The puzzle will be solved in Paper II.     

Selective permeation of CO2 through poly 2-(N,N-dimethyl)aminoethyl methacrylate membrane prepared by plasma-graft polymerization technique

A membrane having an amine moiety was prepared by plasma-grafting 2-(N,N-dimethyl)aminoethyl methacrylate (DAMA) onto a microporous polyethylene substrate. Permselectivity of the membrane for CO₂ over N₂ was achieved in both dry and water swollen conditions. When the CO₂ partial pressure in the feed gas was 0.047 atm, the selectivity of CO₂ over N₂ reached 130 for the highly swollen water containing membrane. This value was found to agree with that obtained with a mobile carrier membrane (supported liquid membrane) using DAMA as the carrier. The effects of several experimental conditions such as degree of grafting, feed partial pressure and temperature on the membrane performance were studied. It was suggested that the membrane acted as a fixed carrier membrane for CO₂ facilitated transport in under the dry condition and acted as a fixed reaction site membrane in the water swollen condition. The carrier transport mechanism is discussed for dry and aqueous membranes.     

Electronic structures of exohedral lanthanide-C60 clusters

We have studied the electronic structures of several gas phase exohedral lanthanide (Ln)-C(60) clusters, Ln(n)C(60) (Ln=Pr, Ho, Tb, Tm, Eu, and Yb) with n=1-4, by photoionization spectroscopy of the neutrals and photoelectron spectroscopy of their anions. Both of the spectroscopic analyses reveal that most of the Ln atoms preferably take +3 oxidation states, while Eu atoms alone assume +2 oxidation states, and that C(60) accepts up to twelve donated electrons in Ln(n)C(60). An additional photoionization examination of the oxygen atom mixing into the Ln(n)C(60) clusters demonstrated that each oxygen atom reduces two electrons from C(60). This result implies that the number of accepted electrons in C(60) can be varied by a suitable choice of the number of Ln atoms and O atoms.     

Synthesis, structure, and reactivity of novel 3,4-diphosphacyclobutenes bearing silyl groups

[reaction: see text] Copper-mediated homocoupling of sterically hindered 2-(2,4,6-tri-tert-butylphenyl)-1-trialkylsilyl-2-phosphaethenyllithiums afforded 1,2-bis(trialkylsilyl)-3,4-diphosphacyclobutenes (1,2-dihydrodiphosphetenes) through a formal electrocyclic [2+2] cyclization in the P=C-C=P skeleton as well as 2-trimethylsilyl-1,4-diphosphabuta-1,3-diene. Reduction of 1,2-bis(trimethylsilyl)-3,4-diphosphacyclobutenes followed by quenching with electrophiles afforded ring-opened products, (E)-1,2-bis(phosphino)-1,2-bis(trimethylsilyl)ethene and (Z)-2,3-bis(trimethylsilyl)-1,4-diphosphabut-1-ene. The structures of the ring-opened products indicated E/Z isomerization around the C=C bond after P-P bond cleavage of 5, and the isomerization of the P-C=C skeleton. Ring opening of 1,2-bis(trimethylsilyl)-3,4-diphosphacyclobutenes affording (E,E)- and (Z,Z)-1,4-diphosphabuta-1,3-dienes was observed upon desilylation.     

2 alpha-(3-hydroxypropyl)- and 2 alpha-(3-hydroxypropoxy)-1 alpha,25-dihydroxyvitamin D3 accessible to vitamin D receptor mutant related to hereditary vitamin D-resistant rickets

Hereditary vitamin D-resistant rickets (HVDRR) is a genetic disorder caused by mutations in the vitamin D receptor, which lead to resistance to 1alpha,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)]. We found that the A ring-modified analogues, 2alpha-(3-hydroxypropyl)- and 2alpha-(3-hydroxypropoxy)-1alpha,25(OH)(2)D(3), (O1C3 and O2C3) can bind better than the natural hormone to the mutant VDR (R274A), which similar to the HVDRR mutant, R274L, had lost the hydrogen bond to the 1alpha-hydroxyl group of 1alpha,25(OH)(2)D(3).     

Effect of dose rate on the radiation-induced polymerization of ethylene in tert-butyl alcohol

The dependence of the dose rate on the rate of radiation-induced polymerization of ethylene in tert-butyl alcohol containing 5 vol-% water was studied. The reaction was carried out by use of a reactor with a capacity of 100 ml under the following conditions: pressure, 200 kg/cm²; temperature, 24 ± 3°C; dose rate, 3.7 × 10⁴?1.6 × 10⁵ rad/hr; amount of medium, 70 ml. The dose rate exponents for rate of the polymerization, the molecular weight, and the number of polymer chain were found to be about 0.8, ?0.1, and 0.9, respectively. These results were well explained with kinetic results (obtained by a novel analytical method) for the polymerization which contain both first-order and second-order terminations for the concentrations of propagating radical. The individual values of the rate constants in each elementary reaction were also obtained.     

Synthesis and properties of the first stable silylene-isocyanide complexes

The first stable silylene-isocyanide complexes, [Tbt(Mes)SiCNAr] (5 c: Ar=Tip, 5 d: Ar=Tbt, 5 e: Ar=Mes*; Tbt=2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, Mes=mesityl, Tip=2,4,6-triisopropylphenyl, Mes*=2,4,6-tri-tert-butylphenyl) were successfully synthesized by the reaction of a kinetically stabilized disilene, [Tbt(Mes)Si=Si(Mes)Tbt] (1), with bulky isocyanides, ArNC (3c-e). The spectroscopic data of 5 c-e and theoretical calculations for a model molecule indicated that 5 c-e are not classical cumulative compounds but the first stable silylene-Lewis base complexes. The reactions of 5 c-e with triethylsilane and 1,3-dienes gave the corresponding silylene adducts, and they underwent isocyanide-exchange reactions in the presence of another isocyanide at room temperature. These results indicate dissociation of complexes 5 c-e to the corresponding silylene 2 and isocyanides 3 c-e under very mild conditions. The reaction of 5 c with methanol gave the MeOH adduct 16, [Tbt(Mes)SiHC(OMe)NTip], which has a hydrogen atom on the silicon atom. This regioselectivity can be explained in terms of the contribution of zwitterionic resonance structures D and E, which have an anion on the silicon atom. This result indicates that 5 c is not a classical cumulene having Si=C double bonds that should react with methanol to give adducts bearing a methoxyl group on the silicon atom. Although the reactions of 5 c-e with electrophilic reagents such as methanol, hydrogen chloride, and methyl iodide gave the formal silylene adducts, the studies on the reaction mechanism by trapping experiments and the observation of the intermediate suggested that the reaction mainly or partially proceeds by initial nucleophilic attack of the silicon atom, as is the case in the formation of 16 in the reaction of 5 c with methanol. It was revealed that 5 c-e show the nucleophilicity of the silicon atom, most likely resulting from the contribution of the zwitterionic resonance structures D and E.     

Chiral separation of trimetoquinol hydrochloride and related compounds by micellar electrokinetic chromatography using sodium taurodeoxycholate solutions and application to optical purity determination

The chiral separation of trimetoquinol hydrochloride, which is a bronchodilator (Inolin), and three related compounds by micellar electrokinetic chromatography was investigated using a bile salt as a chiral surfactant. Enantiomers of these compounds, except laudanosoline, were successfully separated within 12 min using a separation tube of effective length 500 mm × 0.05 rum i.d. and a 0.05 M sodium taurodeoxycholate solution of pH 7.0. The observed theoretical plate numbers of the peaks were ca. 150000. Chiral recognition was affected by the structure of bile salts, the pH of the buffer solutions used and the structure of the solutes. Of four kinds of bile salts, successful chiral separation was achieved only using sodium taurodeoxycholate solution under neutral conditions. The method was applied to the optical purity determination of trimetoquinol hydrochloride. The effects of surfactant concentrations and some additives to the micellar solution are briefly described.