High-performance liquid chromatographic method for monitoring leupeptin in mouse serum and muscle by pre-column fluorescence derivatization with benzoin

A high-performance liquid chromatographic method is described for the determination of leupeptin, a possible therapeutic drug for muscular dystrophy, in mouse serum and muscle. Leupeptin is reduced with sodium borohydride to leupeptinol, and then converted to a fluorescent derivative with benzoin. The derivative is separated on a reversed-phase column (LiChrosorb RP-18) with isocratic elution and determined with fluorescence detection. The detection limits of leupeptin in serum and muscle are 250 pmol/ml (107 ng/ml) and 500 pmol/g (214 ng/g), respectively, corresponding to approximately 150 fmol each in a 100-microliters injection volume. This method is simple and sensitive enough to permit the quantification of leupeptin in biological samples from mice dosed with leupeptin.     

Characterization of diffusion-controlled mass transport through nanoporous and nanothin films plasma polymerized on a sputtered platinum electrode

We demonstrate the diffusion mode of various redox chemical species through a plasma-polymerized nanothin coating with nanometer-sized pores on a sputtered platinum (Pt) electrode. In this work, hexamethyldisiloxane plasma-polymerized films (PPFs) were added onto the sputtered platinum film, both of which were sequentially deposited in the same vacuum chamber. Results of atomic force microscopy, X-ray photoelectron spectroscopy, and electrochemical studies showed that the PPF provided the platinum electrode with a coating with a complete surface coverage. Sub-nanometer-sized pores (less than 1 nm) responsible for a highly crosslinked polymer network in the PPF coatings offered diffusivity-controlled permeation of redox molecules (i.e., size-exclusivity) rather than solubility-controlled permeation (i.e., chemoselectivity). Consequently, variation of the plasma power could give control over the size of the nanometer-sized cavities.     

Bicyclic dioxetanes bearing a 4-(benzoazol-2-yl)-3-hydroxyphenyl moiety: chemiluminescence profile for base-induced decomposition in aprotic medium and in aqueous medium

Four bicyclic dioxetanes bearing a 4-(benzothiazol-2-yl)-3-hydroxyphenyl or 4-(benzoxazol-2-yl)-3-hydroxyphenyl group were synthesized. These dioxetanes underwent base-induced decomposition with accompanying emission of light with high efficiency in NaOH/H₂O as well as in tetrabutyl ammonium fluoride (TBAF)/acetonitrile. Among them, benzothiazol-analogs decomposed faster in the aqueous solution than in acetonitrile.     

Construction of chiral α-tert-amine scaffolds via amine-catalyzed asymmetric Mannich reactions of alkyl-substituted ketimines

Stereoselective Mannich reactions of aldehydes with ketimines provide chiral β-amino aldehydes that bear an α-tert-amine moiety. However, the structural variation of the ketimines is limited due to the formation of inseparable E/Z isomers, low reactivity, and other synthetic difficulties. In this study, a highly diastereodivergent synthesis of hitherto difficult-to-access β-amino aldehydes that bear a chiral α-tert-amine moiety was achieved using the amine-catalyzed Mannich reactions of aldehydes with less-activated Z-ketimines that bear both alkyl and alkynyl groups.

Stereoselective Mannich reactions of aldehydes with ketimines provide chiral β-amino aldehydes that bear an α-tert-amine moiety.     

Indium(III) chloride-promoted intramolecular addition of allylstannanes to alkynes

In the presence of an equimolar amount of InCl(3), 8-tributylstannyl-6-octen-1-ynes (allylstannanes bearing an alkynyl group) were efficiently cyclized to 2-allyl-1-methylenecyclopentanes. In contrast, catalytic use of InCl(3) gave 2-allyl-1-(tributylstannylmethylene)cyclopentanes mainly by intramolecular allylstannylation. These cyclizations could proceed via intramolecular addition of an allylindium intermediate.     

ULTRAVIOLET RESONANCE RAMAN STUDY ON PURPLE AND BLUE MEMBRANES OF Halobacterium halobium

Abstract— Two hundred and forty and 213 nm excited resonance Raman spectra of purple membrane (PM) and blue membrane (BM) of Halobacterium halobiurn were studied. Generally intense Trp scattering and a strong relative intensity of the W3 band at 1553 cm^-1 in the 240 nm spectrum of PM indicate red-shifted B_b absorptions of some Trp sidechains. A high intensity ratio of Trp doublet at 1360 and 1340 cm^-1 suggests interactions with highly hydrophobic Trp environments. These Trp are not strongly H-bonded and their N₁ sites are located in positions easily reached by solvent water molecules. Tyrosines are also in very hydrophobic environments and H-bonded. The mainchain consists of normal and distorted α-helices whose amide NH are hardly deuterated in D₂O suspension, and some NH exchangeable irregular segments on the membrane surface. Upon acidification, the ratio of Trp doublet with 240 nm excitation decreases concomitant with increase in retinal absorbance at 600 nm, and the W3 relative intensity and overall Trp scattering also decrease. These observations strongly indicate that the counterpart of Trp interactions in PM is the retinal and that the interactions partly diminish upon acidification. The Tyr environment also changes with the color. Although the 240 nm amide I intensity is greater in acid BM than in PM, the change is not related to the color change because the amide I intensity of deionized BM is practically the same as that of PM. The amide I intensity increase in acid BM is ascribable to a structural change of the surface peptides due to acid induced aggregation.     

Microporous poly(vinyl methyl ether) hydrogels prepared by γ-ray irradiation at different heating rates

We prepared thermoresponsive and microporous polymer hydrogels by γ-ray irradiation of aqueous solutions poly(vinyl methyl ether) (PVME) at different heating rates. Under all temperature programs, opaque and heterogeneous PVME gels formed, which swelled at temperatures below the lower critical solution temperature and shrank at temperatures above it. All of the samples contained porous and phase-separated structures. The shape and size of the gel pores varied depending on the temperature programs. Gels having a sponge-like continuous porous structure formed only when the radiation-induced crosslinking was carried out at an optimum heating rate, which we found to be 0.11–0.13°C min⁻¹. For temperature changes between 10°C and 40°C, gels with this structure showed rapid volume transitions on a time scale of about a minute.     

Regio- and stereoselective homolytic hydrostannylation of propargyl alcohols and ethers with dibutylchlorostannane

The Et3B-initiated reaction of gamma-unsubstituted propargyl alcohols with dibutylchlorostannane (Bu2SnClH) at low temperature gave (Z)-vinylstannanes with high regio- and stereoselectivity. The corresponding alkyl propargyl ethers also underwent regio- and stereoselective homolytic hydrostannylation with Bu2SnClH; however, the regioselectivity was not so high as that with the propargyl alcohols.     

Micellar chromatographic separation of vanadium(V) chelate with 2-(2-thiazolylazo)-5-dimethylaminophenol

Summary In reversed phase—high performance liquid chromatography for metal chelates with 2-(2-thiazolylazo)-5-dimethylaminophenol, an aqueous non-ionic surfactant solution is used as a mobile phase. Among V(V), Fe(III), Cu(II), Co(II), Ni(II), Cd(II), Zn(II), Mn(II), and Al(III), only the V(V) chelate gave a resolved peak by using 0.8% w/w poly(oxyethylene)_n-4-nonylphenyl ether (n=20) solution buffered at pH 3.8. V(V) can be selectively separated and sensitively determined.     

Electron affinities, excitation energies and ionization potentials of the transition metals (I) Sc and Ti

The electron affinities of the Sc and Ti atoms have been obtained by configuration interaction calculations. Energy convergence with respect to the systematic expansion of both the one-electron basis set and the configuration space was investigated for valence electrons, and the inclusion of correlation contributions from core electrons and relativistic effects gave the electron affinities of 0.181 eV and 0.163 eV for Sc and Ti, respectively. These are in excellent agreement with the observed values of 0.189 ± 0.020 eV and 0.080 eV. The same approach was applied for the first excited states and positive ions of both atoms. Excellent agreement with the experimental results was also obtained for these states. Received: 16 February 1998 / Accepted: 2 April 1998 / Published online: 23 June 1998