Inhibition of aggregation of a biomimic peptidolipid Langmuir monolayer by Congo red studied by UV-vis and infrared spectroscopies

A synthetic peptidolipid consisted of a hydrocarbon chain with a chain length of C18 and a peptide moiety of IIGLM terminated with an amine group, designated as C18IIGLM-NH2, has been employed as a biomimic model compound of amyloid peptide for exploring molecular interaction and orientation with the use of the Langmuir monolayer and Langmuir-Blodgett film techniques. Inspired by a well-known fact that a stain reagent, Congo red (CR), binds well to the amyloid-mimic part (IIGLM), inhibition of molecular aggregation of C18IIGLM-NH2 by interaction with CR was expected, and it has been investigated by use of surface pressure-area isotherm, surface dipole moment-area isotherm, Brewster-angle microscopy, and UV-vis/infrared spectroscopies. It has been revealed that monomeric CR molecules whose long axis is parallel to the Langmuir monolayer surface are penetrating the C18IIGLM-NH2 Langmuir monolayer, which plays a role of inhibition of molecular aggregation via hydrogen bonding.     

Microfluidic thermodynamics of the shift in thermal stability of DNA duplex in a microchannel laminar flow

This paper reports the shift in thermal stability of DNA duplex and its thermodynamics spectroscopically, caused by stretching and orientation of DNA strands in a microchannel laminar flow. For direct spectroscopic measurement of the microchannel, we prepared an in-house temperature-controllable microchannel-type flow cell. The melting curves of DNA oligomers in a microchannel laminar flow were measured. For DNA oligomers with more than 10 base pairs, the melting curve shifted to the high-temperature side with higher flow speed. However, for 8-base-pair DNA oligomers, a change in the melting profile was not observed in batchwise and microchannel flows. We undertook microfluidic thermodynamic analysis to elucidate details of the shift in thermal stability of the DNA duplex in a microchannel laminar flow. Enthalpy-entropy compensation is applicable to the microfluidic thermal stability shift. We studied the relationships between the enthalpy-entropy compensation and DNA strand length or flow speed. Results showed that the enthalpy-entropy compensation was influenced by both DNA strand length and flow speed, and the penalties of enthalpy were 2-12% greater than the benefits of entropy.     

Aqueous chromatographic system for separation of biomolecules using thermoresponsive polymer modified stationary phase

We have investigated a new method for HPLC using packing materials modified with a functional polymer, such as thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm). PNIPAAm-modified silica exhibits temperature-controlled hydrophilic-hydrophobic surface property changes in aqueous systems. Temperature-responsive chromatography is performed with an aqueous mobile phase without using an organic solvent. We designed ternary copolymers of NIPAAm introduced 2-(dimethyl-amino) ethyl methacrylate (DMAEMA) as a cationic monomer and butyl methacrylate (BMA) as a hydrophobic monomer. A cationic thermoresponsive hydrogel grafted surface would produce an alterable stationary phase with both thermally regulated hydrophobicity and charge density for separation of bioactive compounds. In this study, we achieved successful separation of lysozyme without the loss of bioactivity by temperature-responsive chromatography. The electrostatic and hydrophobic interactions could be modulated simultaneously with the temperature in an aqueous mobile phase, thus the separation system would have potential applications in the separation of biomolecules.     

First chemical synthesis of antioxidative metabolites of sesamin

The first chemical synthesis of two metabolites ((1R,2S,5R,6S)-6-(3,4-dihydroxyphenyl)-2-(3,4-methylenedioxyphenyl)-3,7-dioxabicyclo[3,3,0]octane (SC-1) and (1R,2S,5R,6S)-2,6-bis(3,4-dihydroxyphenyl)-3,7-dioxabicyclo[3,3,0]octane (SC-2)) of sesamin was achieved by a simple two-step approach from sesamin. The approach consists of acetoxylation of the methylenedioxy moiety(ies) with lead(IV) tetraacetate and acid hydrolysis of the resulting hemiorthoester to SC-1 and SC-2.     

Determination of diazepam and its metabolites in human urine by liquid chromatography/tandem mass spectrometry using a hydrophilic polymer column

Diazepam and its major metabolites, nordazepam, temazepam and oxazepam, in human urine samples, were analyzed by liquid chromatography (LC)/tandem mass spectrometry (MS/MS) using a hydrophilic polymer column (MSpak GF-310 4B), which enables direct injection of crude biological samples. Matrix compounds in urine were eluted first from the column, while the target compounds were retained on the polymer stationary phase. The analytes retained on the column were then eluted into an acetonitrile-rich mobile phase using a gradient separation technique. All compounds showed base-peak ions due to [M+H]+ ions on LC/MS with positive ion electrospray ionization, and product ions were produced from each [M+H]+ ion by LC/MS/MS. Quantification was performed by selected reaction monitoring. All compounds spiked into urine showed method recoveries of 50.1-82.0%. The regression equations for all compounds showed excellent linearity in the range of 0.5-500 ng/mL of urine. The limits of detection and quantification for each compound were 0.1 and 0.5 ng/mL of urine, respectively. The intra- and inter-day coefficients of variation for all compounds in urine were not greater than 9.6%. The data obtained from actual determination of diazepam and its three metabolites, oxazepam, nordazepam and temazepam, in human urine after oral administration of diazepam, are also presented.     

Direct analysis of ultra-trace semiconductor gas by inductively coupled plasma mass spectrometry coupled with gas to particle conversion-gas exchange technique

An inductively coupled plasma mass spectrometry (ICPMS) coupled with gas to particle conversion-gas exchange technique was applied to the direct analysis of ultra-trace semiconductor gas in ambient air. The ultra-trace semiconductor gases such as arsine (AsH₃) and phosphine (PH₃) were converted to particles by reaction with ozone (O₃) and ammonia (NH₃) gases within a gas to particle conversion device (GPD). The converted particles were directly introduced and measured by ICPMS through a gas exchange device (GED), which could penetrate the particles as well as exchange to Ar from either non-reacted gases such as an air or remaining gases of O₃ and NH₃. The particle size distribution of converted particles was measured by scanning mobility particle sizer (SMPS) and the results supported the elucidation of particle agglomeration between the particle converted from semiconductor gas and the particle of ammonium nitrate (NH₄NO₃) which was produced as major particle in GPD. Stable time-resolved signals from AsH₃ and PH₃ in air were obtained by GPD-GED-ICPMS with continuous gas introduction; however, the slightly larger fluctuation, which could be due to the ionization fluctuation of particles in ICP, was observed compared to that of metal carbonyl gas in Ar introduced directly into ICPMS. The linear regression lines were obtained and the limits of detection (LODs) of 1.5 pL L⁻¹ and 2.4 nL L⁻¹ for AsH₃ and PH₃, respectively, were estimated. Since these LODs revealed sufficiently lower values than the measurement concentrations required from semiconductor industry such as 0.5 nL L⁻¹ and 30 nL L⁻¹ for AsH₃ and PH₃, respectively, the GPD-GED-ICPMS could be useful for direct and high sensitive analysis of ultra-trace semiconductor gas in air.     

Applications of spectral-Representation model as a potential method for Cu clusters

We applied the spectral-representation technique developed by Katsuki and Huzinaga as a model potential in calculating the electronic structure of Cu clusters. The characteristics of this potential were closely investigated in Cu and Cu₂. For Cu, Cu₂, Cu₅, Cu₉, and Cu₁₃, we performed all-electron ab initio self-consistent field calculations and model-potential calculations where 3p, 3d, and 4s electrons, and 3d and 4s electrons are treated as valence electrons. The ionization potentials (IPs) given by the all-electron calculations were 6.26, 5.55, 4.52, 4.02, and 4.08 eV for Cu, Cu₂, Cu₅, Cu₉, and Cu₁₃, respectively. The IPs given by the model-potential calculations were 6.25, 5.56, 4.62, 4.09, and 4.23 eV for the 3p-, 3d-, and 4s-valence electrons, and 6.26, 5.68, 4.71, 4.07, and 4.19 eV for the 3d- and 4s-valence electrons. The IPs given by the model-potential calculations agree well with those of the all-electron calculations. We also performed model-potential calculations where only the 4s electrons were treated as valence electrons. The calculated IPs were 6.47, 5.98, 5.38, 4.63, and 4.88 eV for Cu, Cu₂, Cu₅, Cu₉, and Cu₁₃, respectively. These are ca. 0.8 eV higher than the IPs by the all-electron calculation for the larger clusters of Cu₅, Cu₉, and Cu₁₃. The higher IPs originate from the expulsion of the 3d electrons from the valence electrons. We also performed model-potential calculations with 4s electrons for Cu₇₄. The calculated IP is 4.61 eV, which is estimated to be 0.8 eV larger than that obtained by the all-electron calculation. The IPs with correlation corrections are 7.7, 7.4, 6.3, 5.8, 5.9, and 5.6 eV for Cu, Cu₂, Cu₅, Cu₉, Cu₁₃, and Cu₇₄, respectively. Experimental values are 7.73, 7.37, 6.30, 5.37, 5.67, and 5.26 eV. The agreement between the two is fairly good. The electron affinities are also discussed. © 1996 by John Wiley & Sons, Inc.     

Synthesis of nitrogen‐containing heterocycles 9. Preparation and carbon‐carbon bond cleavage of spiro[cycloalkane[1′,2′,4′]‐triazolo[1′,5′‐a][1′,3′,5′]triazine] derivatives and related compounds

Diaminomethylenehydrazones of cyclic ketones 1–5 reacted with ethyl N‐cyanoimidate (I) at room temperature or with bis(methylthio)methylenecyanamide (II) under brief heating to give directly the corresponding spiro[cycloalkane[1′,2′,4′]triazolo[1′,5′,‐a][1′,3′‐5′]triazine] derivatives 7–12 in moderate to high yields. Ring‐opening reaction of the spiro[cycloalkanetriazolotriazine] derivatives occurred at the cycloalkane moiety upon heating in solution to give 2‐alkyl‐5‐amino[1,2,4]triazolotriazines 13–16. Diaminomethylenehydrazones 17–19, of hindered acyclic ketones, gave 2‐methyl‐7‐methylthio[1,2,4]‐triazolo[1,5‐a][1,3,5]triazines 21–23 by the reaction with II as the main products with apparent loss of 2‐methylpropane from the potential precursor, 2‐tert‐butyl‐2‐methyl‐7‐methylthio[1,2,4]triazolo[1,5‐a]‐[1,3,5]triazines 20, in good yields. In general, bis(methylthio)methylenecyanamide II was found to be a favorable reagent to the one‐step synthesis of the spiro[cycloalkanetriazolotriazine] derivatives from the diaminomethylenehydrazones. The spectral data and structural assignments of the fused triazine products are discussed.