Spiro(benzoxasilole) catalyzed polymerization of oxetane derivatives

A spiro(benzoxasilole) catalyst, 3,3,3′,3′-tetrakis(trifluoromethyl)-1,1′-(3H,3H′)-spirobis(1,2-benzoxasilole) was used to polymerize 3,3-R,R′-oxetanes: BEMO (R, R′ = ethoxymethyl), AMMO (R = azidomethyl, R′ = methyl), NMMO (R = nitratomethyl, R′ = methyl), BAMO (R, R′ = azidomethyl), and BCMO (R, R′ = chloromethyl) with descending rates in this order. ³¹P-NMR of polymerization mixtures quenched using Bu₃P are consistent with an oxonium ion propagating species. Water is not a cocatalyst because it increases the induction period which is not eliminated by the proton trap 2,6-di-t-bu-tylpyridine. The propagating chains were terminated by transfer with the ether oxygen of the polymer either intermolecularly or intramolecularly. The index of propagation to chain transfer, Kk_ik_p/k_tr, varies over more than three orders of magnitude for BEMO > AMMO > NMMO > BAMO. However, k_p/k_tr for the four monomers differ by less than a factor of five indicating the same factors are affecting propagation and chain transfer. Addition of benzyl alcohol and propandiol produced poly(BEMO) having one and two hydroxyl termini, respectively. These telechelic polymers can be used to synthesize linear triblock or multiblock copolymers of oxetane derivatives. © 1992 John Wiley & Sons, Inc.     

ansa-Zirconocenium catalysis of syndiospecific polymerization of propylene: Theory and experiment

The syndiospecific propylene polymerizations catalyzed by isopropylidene(cyclopentadienyl)(fluorenyl)- and (2,2-dimethylpropylidene)(cyclopentadienyl)(fluorenyl)-zirconocenium ( 1 ⁺ and 2 ⁺) have been investigated theoretically and compared with experimental observations. With the ab initio calculated structures for the transition state (TS) of 1 ⁺(M)P and 2 ⁺(M)P (M = propylene, P = 2-methylpentyl), their steric energies (E°) have been computed using MM2 force-field. The difference between steric energies E°(m) and E°(r) for the meso and racemic enchainment of propylene, respectively, is defined as the stereocontrol energy [δE°(m ? r)] for syndiotactic propagation. The δE°(m ? r) for the TS of 1 ⁺ (M)P is about 2.1 kcal/mol, the value is 1 kcal/mol greater for 2 ⁺(M)P. The observed steric pentad distributions of the syndiotactic poly(propylene) obtained by these catalysts are consistent with smaller effective stereocontrol energy, which is about two-third as large as δE°(m ? r) values calculated for the MM2 optimized structure. Syndiotactic enchainment is favored over isotactic enchainment for all combinations of site configurations in the catalyst. α-Agostic interaction seems to enhance syndioselectivity, whereas γ-agostic interaction changes the stereoselectivity to meso enchainment. The mirror plane symmetry of the syndiotactic propagating species renders the stereoselectivity of the polymerization insensitive to reaction conditions. These catalysts are also highly regiospecific. © 1995 John Wiley & Sons, Inc.     

Determination of terazosin by cloud point extraction-fluorimetric combined methodology

A new sensitive and selective preconcentration-fluorimetric method for determination of terazosin based on its native fluorescence was developed. The analyte, initially present in aqueous matrix, was treated with an extractive non-ionic surfactant solution and separated by the clouding phenomenon. The optimum analytical conditions for terazosin assay were established. Under these conditions, linear calibration curves were obtained over the range of 1 × 10⁻⁵ to 7.0 μg mL⁻¹ with detection and quantification limits of 1.11 × 10⁻⁵ and 3.7 × 10⁻⁵ μg mL⁻¹, respectively. Additionally, the binding constant (K_B) for the terazosin-PONPE 7.5 system was determined given a value of 1028 L mol⁻¹. The developed coupled methodology, which thoroughly satisfies the typical requirements for pharmaceutical control processes, was proved to be appropriate for monitoring terazosin in actual pharmaceutical formulations and biological fluid sample. The results were validated by recovery test and by comparison with other reported methods, being highly satisfactory.     

Four new podocarpane-type trinorditerpenes from the bark of Taiwania cryptomerioides

Further studies on the bark of Taiwania cryptomerioides found four new podocarpane derivatives, 1beta,13-dihydroxy-8,11,13-podocarpatriene (1), 14,18-dihydroxy-13-methoxy-8,11,13-podocarpatriene (2), 1beta,14-dihydroxy-13-methoxy-8,11,13-podocarpatriene-2,7-dione (3), and 3beta,14-dihydroxy-13-methoxy-8,11,13-podocarpatrien-7-one (4), together with a known 1beta,13,14-trihydroxy-8,11,13-podocarpatrien-7-one (5). Those structures were elucidated principally from spectral evidence.     

Development of enzyme biosensor based on pH-sensitive field-effect transistors for detection of phenolic compounds.

This article describes a biosensor based on pH-sensitive field-effect transistors (pH-FETs) as transducer, and immobilised enzyme tyrosinase as biorecognition element, which was used for the determination of phenolic compounds in water solutions. The biologically active membrane was formed by cross-linking of tyrosinase with bovine serum albumin (BSA) in saturated glutaraldehyde (GA) vapours on the sensitive transducer surface. The main analytical characteristics were studied under different conditions as well as the possibility to optimise these working parameters. Different factors such as the pH of immobilisation, the enzyme loading, the time of exposition to glutaraldehyde vapours were investigated in regards to the influence on sensitivity, limit of detection, dynamic range, and operational and storage stability.     

In vivo activation analysis of organ cadmium using the Tsing Hua Mobile Educational Reactor

This work describes a nuclear facility forin vivo prompt gamma activation analysis (IVPGAA) using a moderated neutron beam from a 0.1 W Tsing-Hua Mobile Educational Reactor (THMER). The IVPGAA measurement is a new technique for toxic cadmium determination in organs, which can efficiently be used in clinical diagnosis. The low-power nuclear reactor provides a total neutron flux of 3.3·10⁴ n·cm^–2·s^–1 on the surface of the central vertical neutron beam tube to which a liquid phantom is positioned. The capability of such partial-body irradiation facility is demonstrated. The detection limit of cadmium in the left kidney for a skin dose equivalent of 1.66 mSv (166 mrem) was 1.34 mg in a 500-s irradiation/counting period, and the sensitivity in the left kidney was 103 counts mg^–1·mSv^–1. The performance of IVPGAA system using the THMER nuclear facility therefore has the advantages of mobility and feasibility with high sensitivity under low neutron and gamma doses.     

Synthesis,Characterization and Catalysis of Ce‐MCM‐41

The cerium‐containing MCM‐41 (Ce‐MCM‐41) has been synthesized by direct hydrothermal method. The low‐angle XRD patterns revealed the typical five major peaks of MCM‐41 type hexagonal structures. The interplanar spacing d₁₀₀ = 38.4 Å was obtained that can be indexed on a hexagonal unit cell parameter with a_o = 44.3 Å which was larger than that of pure siliceous MCM‐41 (Si‐MCM‐41). Transmission electron micrograph shows the regular hexagonal array of uniform channel characteristics of MCM‐41. The BET surface area of Ce‐MCM‐41 was 840 m²/g, which is much reduced as compared to that of Si‐MCM‐41, with the pore size of 26.9 Å and mesopore volume of 0.78 cm³/g were measured by nitrogen adsorption‐desorption isotherm at 77 K. Along with the results, the synthesized Ce‐MCM‐41 exhibited a well‐ordered MCM‐41‐type mesoporous structure with the incorporation of cerium. Using Ce‐MCM‐41 as a support, the Rh (0.5 wt%) catalyst exhibited very high activity for the NO/CO reactions.     

Syntheses and photophysical properties of some 5(2)-aryl-2(5)-(4-pyridyl)oxazoles and related oxadiazoles and furans

A number of 5-aryl-2-(4-pyridyl)oxazoles, a 2-aryl-5-(4-pyridyl)oxazole, the related oxadiazole and furan, several 2-(4-pyridyl)cycloalkano[d]oxazoles, and many of their quaternary salts were prepared. No single standard synthesis was effective for preparation of more than a few of the 25 free bases described; methods often unique to a base were employed. Minor variations in structure sometimes produced large differences in absorption and emission wavelengths, as well as in the magnitude of the extinction coefficient. The salts are of interest as laser dyes, scintillation fluors, biological stains, and shifters for luminescent solar concentrators.     

New Clerodane Diterpenoids from Casearia membranacea

Bioassay‐guided fractionation of an AcOEt extract of Casearia membranacea resulted in the isolation of six new clerodane diterpenes, caseamembrins G–L ( 1 – 6 ). The structures of the new compounds, including their relative configurations, were established by an extensive study of their spectral data, especially 2D NMR. The cytotoxic activities of the isolated diterpenes against human oral epidermoid (KB), cervical epitheloid (Hela), and liver (Hep59T/VGH) carcinoma cell lines were investigated.     

The Synthesis of Alanine Oligopeptides

The oligopeptides of alanine (penta-, deca-, and pentadeca-) were synthesized by solid phase method and new peptide-resin cleaving reagent TFA-BBr₃ was used to cleave the peptides from resin-support. Penta-alanine was also synthesized by liquid phase for the comparision and FAB-Mass method was used to determine the molecular weight of penta-alanine. HPLC separation of these new oligopeptides were described.