Efficiency of visual peak detection in X‐ray photoelectron spectra

We report initial results of a VAMAS/TWA2 project to evaluate procedures for automated peak detection in X‐ray photoelectron spectra. As a reference for investigations of the efficiency of automated peak‐detection software, we report the efficiency of visual peak detection in three test spectra. It was found that (i) characteristics of analysts are grouped into four categories using principal component analysis (PCA); the first participant group to detect large numbers of peaks for the three test spectra, the second one to detect small numbers of peaks for them, the third one to detect similar numbers of peaks, and the fourth one to detect a relatively large number of peaks for one of them and small numbers for two of them, (ii) scattering of detected peak numbers seems to depend on detection of medium‐intensity peaks because of participants' subjectivity or ambivalence for judgment of intensity, and (iii) the peaks that are detected by the analysts with a detectability more than 75% almost correspond to the peak signal‐to‐noise(S/N) ratio of more than 10 in logarithmic expression. Copyright © 2008 John Wiley & Sons, Ltd.     

Thermally changing lattice distance of lamella in the hydrated solid of octadecyltrimethylammonium chloride

A temperature scanning small-angle X-ray scattering measurement was carried out for the hydrated solids of octadecyltrimethylammonium chloride (OTAC). A gradual change of the lattice spacing of lamella-like structure from 40 nm at 5 degrees C to 20 nm at 18 degrees C was observed in the melting process of the hydrated solid that was incubated at 4 degrees C for a period of 24 h in the aqueous solution, while little change of the lattice spacing of about 20 nm was observed in the same process of the hydrated solid that was incubated at 4 degrees C for a period about 10 min. This indicates structural changes of the hydrated solid during the incubation at 4 degrees C and in the melting process. Corresponding to the nanostructure changes, broad endothermic peaks were observed at temperatures from 13 to 22 degrees C for the former hydrated solid and at temperatures from 15 to 21 degrees C for the latter hydrated solid in difference scanning calorimetry measurements. The structure change at temperatures below 13 degrees C is considered to be athermal from the fact that no endothermic peak is observed there. Large dielectric dispersions at frequencies at about 10 kHz were observed for the suspensions of hydrated solids but not for the solutions of dissolved solids. It was found that the electric conductance of the hydrated solid suspensions was much lower than that of the solutions of dissolved solids. The observed electric properties indicate that an amount of the free chloride ion is very small and that the chloride ions binding to the ammonium groups are movable in the hydrated solids by responding to an applied electric field. The electric conductance of suspension of the hydrated solid being incubated at 4 degrees C for 10 min was 4 times as large as that of a suspension of the hydrated solid being incubated at the same temperature for 24 h. This indicates that the structural change of the OTAC hydrated solid at 4 degrees C is related to the chloride ion binding to the hydrated solid. The experimental results described above suggest that the lamella in the hydrated solid of OTAC is undulated and that the wavelength of undulation increases with the incubation at a temperature much lower than the melting temperature.     

Development of a N-acetyl-β-D-glucosaminidase (NAG) assay on a centrifugal lab-on-a-compact-disc (Lab-CD) platform

A centrifugal microfluidic platform, which is also known as lab-on-a-compact-disc (Lab-CD), was developed for use as a urinary N-acetyl-β-D-glucosaminidase (NAG) activity assay. In this work, Lab-CD design, centrifugal operations and analytical procedures were established. Automated liquid handling on Lab-CD processes, such as fluid transport, sample metering, mixing, and fluorescence detection are accomplished using a portable Lab-CD system. The linearity of the NAG assay using 4-methylumbelliferyl-N-acetyl-β-D-glucosaminide (4-MU-GlcNAc) was found to be acceptable in the range of 2.5 to 20 U L(-1); the relative standard deviations for the fluorescence intensity of eight samples (7.5 U L(-1)) was 6.4%. Clinical diagnostics is one of the most promising applications for Lab-CD technologies. All the benefits of miniaturization, such as reduced sample requirement, reduced reagent consumption and automation, are realized in this investigation.     

Exciton localization of single-walled carbon nanotubes revealed by femtosecond excitation correlation spectroscopy

Photoluminescence (PL) dynamics in single-walled carbon nanotubes (SWNTs) has been studied by the femtosecond excitation correlation method with a 150 fs time resolution. The SWNT samples were synthesized by different methods and suspended in gelatin films or D2O solutions. The PL dynamics of SWNTs depends on the local environment surrounding the SWNTs rather than the synthesis methods. The very weak temperature dependence of tauPL and the environment-dependent tauPL reveal that the PL relaxation process is dominated by the interplay between free excitons and weakly localized excitons.     

Mechanism of O2-accelerated sonolysis of bisphenol A

The effects of dissolved gases on the sonochemical degradation of bisphenol A (BPA) were studied at a frequency of 500 kHz. BPA degradation rate increased in the order O(2)>Ar>air>N(2). The rate constant for oxygen (2.6 h(-1)) was approximately two fold higher than that for argon (1.2 h(-1)). A primary intermediate (2,3-dihydro-2-methylbenzofuran), a typical intermediate of BPA formed during attack by OH radicals, was detected only in the presence of oxygen, revealing that a different reaction path was responsible for the enhancement of decomposition.     

Photoreactions of β-aziridinylacrylonitriles and acrylates with alkenes: the substituent effects on the formation of [3+2] cycloadducts

The photochemical C,C-bond cleavage of trisubstituted aziridines 3-6 and consequent [3+2] cycloaddition with electron-deficient alkenes afforded the novel head-to-head adducts (1,2,3,5-tetrasubstituted pyrrolidines) selectively and efficiently. The aziridines 3 and 5 reacted with molecular oxygen, affording dioxazolidine 26 and cleaved products, respectively. The results may suggest that the C,C-bond of aziridine cleaves biradically. The photoreactions of N-tritylaziridines 7-9 possessing diester, dinitrile, and butadiene groups in the side chain with electron-deficient alkenes yielded 2,3-cis-pyrrolidine derivatives 29, 30, and 33 exclusively. In particular, the dinitrile 8 also reacted with non-electron-deficient alkenes. The formal synthesis of the indolizidine fragment 10 of stellettamides starting from the pyrrolidine (E)-33 was achieved in a convenient manner.     

Incorporation of selective population transfer and homo-spin decoupling into selective one-dimensional experiments

The incorporation of selective population transfer (SPT) and homo-spin decoupling (HSD) into selective one-dimensional (1D) experiments has been shown to be very useful in obtaining information on the elucidation of the structure of organic compounds. To demonstrate this, the determination of the relative configuration of the sugar moiety of Mi-saponins has been presented.     

Quantitative analysis of the structure-hydrophobicity relationship for di- and tripeptides based on voltammetric measurements with an oil/water interface

The transfer of 18 di- and 27 tripeptides with un-ionizable amino acid side chains at a nitrobenzene/water (NB/W) interface was studied by cyclic voltammetry. The reversible half-wave potential (E(r)(1/2)), i.e., the midpoint potential could be accurately determined at pH 2 for both the facilitated and non-facilitated transfers, respectively, in the presence and absence of dibenzo-18-crown-6 (DB18C6) in NB. A multiple linear regression analysis was then performed for the E(r)(1/2) using the 'corrected' Dubois steric parameter for amino acid side chain substitutents. The result shows that the hydrophobicity of the peptides is governed not only by the intrinsic hydrophobicity of the peptide backbone and side chains, but also by the steric effects of side chain substituents. For the non-facilitated transfer of peptides, the steric effect of a bulky side chain is more significant at the N-terminus than at the C-terminus (and central for tripeptides). The more bulky the side chain at the N-terminus, the less hydrophobic the peptide becomes due to inhibition of the solvation of a terminal -NH(3)(+) group by organic solvents. For the facilitated transfer by DB18C6, however, the steric effect of a bulky side chain is the most significant at the central position of a tripeptide. A MOPAC calculation of optimized structures of DB18C6-peptide complexes has also shown that there is a notable steric hindrance between the central side chain and the benzene rings of DB18C6, which would reduce the 'apparent' hydrophobicity or transferability of the tripeptide.     

Synthesis of 2,4,6-trisubstituted chiral piperidines and (-)-dendroprimine by one-pot asymmetric azaelectrocyclization protocol

[reaction: see text] Stereocontrolled synthesis of 2,4,6-trisubstituted piperidine diastereomers has been realized from common intermediates, obtained by a one-pot azaelectrocyclization protocol. Based on the method, the asymmetric synthesis of an indolizidine alkaloid, (-)-dendroprimine, was achieved.