Dielectric relaxation studies of 1-hexanol and 1,2-hexanediol in heptane

Solutions of 1-hexanol and 1,2-hexanediol in heptane have been investigated tigated by means of dielectric time domain spectroscopy (TDS). The permittivity spectrum of 1-hexanol in heptane is characterized by a model function containing a sum of three elementary Debye dispersions, while 1,2-hexanediol in heptane is best described by a Cole-Davidson model function. It is shown that dilute solutions of 1-hexanol in heptane have a completely different behavior to that of 1,2-hexanediol. For the diol, the relaxation time levels off at a high value indicating an existence of higher hydrogen bonded complexes. It is possible to quantify the relative amount of monomeric 1-alcohol molecules from the dielectric spectrum. The monomerization rate for 1-hexanol upon dilution with heptane is initially low, but increases rapidly for mole fractions of heptane exceeding 0.4.     

Superpositioned dielectrophoresis for enhanced trapping efficiency

One of the major applications for dielectrophoresis is selective trapping and fractionation of particles. If the surrounding medium is of low conductivity, the trapping force is high, but if the conductivity increases, the attraction decreases and may even become negative. However, high-conductivity media are essential when working with biological material such as living cells. In this paper, some basic calculations have been performed, and a model has been developed which employs both positive and negative dielectrophoresis in a channel with interdigitated electrodes. The finite element method was utilized to predict the trajectories of Escherichia coli bacteria in the superpositioned electrical fields. It is shown that a drastic improvement of trapping efficiency can be obtained in this way, when a high conductivity medium is employed.     

Reactions of the ionized enol tautomer of acetanilide: elimination of HNCO via a novel rearrangement

The reactions of ionised acetanilide, C(6)H(5)NH(=O)CH(3)(.+), and its enol, C(6)H(5)NH(OH)=CH(2)(.+), have been studied by a combination of tandem mass spectrometric and computational methods. These two isomeric radical cations have distinct chemistries at low internal energies. The keto tautomer eliminates exclusively CH(2)=C=O to give ionised aniline. In contrast, the enol tautomer loses H-N=C=O, via an unusual skeletal rearrangement, to form predominantly ionised methylene cyclohexadiene. Hydrogen atom loss also occurs from the enol tautomer, with the formation of protonated oxindole. The mechanisms for H-N=C=O and hydrogen atom loss both involve cyclisation; the former proceeds via a spiro transition state formed by attachment of the methylene group to the ipso position, whereas the latter entails the formation of a five-membered ring by attachment to the ortho position. The behaviour of labelled analogues reveals that these two processes have different site selectivities. Hydrogen atom loss involves a reverse critical energy and is subject to an isotope effect. Surprisingly, attempts to promote the enolisation of ionised acetanilide by proton-transport catalysis were unsuccessful. In a reversal of the usual situation for ionised carbonyl compounds, ionised acetanilide is actually more stable than its enol tautomer. The enol tautomer was resistant to proton-transport catalysed ketonisation to ionised acetanilide, possibly because the favoured geometry of the encounter complex with the base molecule is inappropriate for facilitating tautomerisation.     

A Role for Neuropeptides in UVB-Induced Systemic Immunosuppression

The aim of this study was to investigate the possible role of sensory nerves in UV light-induced systemic immunomodulation. Contact hypersensitivity to the low molecular weight compound picrylchloride was used as a model for cellular immunity that can be suppressed by low (i.e. suberythemal) doses of UV light even after exposure at a distant locus (i.e. systemic immunosuppression). In sensory nerve-depleted mice, achieved by two subcutaneous injections with the neurotoxin capsaicin before the age of 4 weeks, UV light exposure failed to inhibit contact hypersensitivity responses to picrylchloride. This indicates that sensory nerves are at least partially involved in the induction of systemic immunosuppression by UV light. In order to analyze whether sensory neuropeptides, such as calcitonin gene-related peptide (CGRP) and tachykinins, are involved in UV light-induced systemic immunosuppression, mice were pretreated with selective antagonists prior to each UV light exposure. These experiments indicated that CGRP but not the tachykinins plays a crucial role in the UV light-induced systemic immunosuppression.     

Investigation of the formation process of MCs+-molecular ions during sputtering

In secondary ion mass spectrometry, the detection of MCs+ clusters (with M an element of the specimen) under a Cs bombardment is frequently used for the quantification of major elements. Despite some very good results obtained by this method, some problems still remain. In order to gain some more insight into these problems, the formation mechanism of the MCs+ clusters is investigated using a Monte Carlo model. It is shown that the majority of the constituent particles of the formed clusters are initially first or second neighbor atoms at the surface and that the velocity distribution of the MCs+ clusters becomes broader and peaked at higher velocities with increasing surface binding energy of the M atom. In addition, it is demonstrated that the interaction potential between the M and Cs+ particle has no influence on the velocity distribution of the MCs+ clusters. On the other hand, the cluster formation probability, defined as the probability that a sputtered M and Cs+ particle will form a MCs+ cluster, is extremely sensitive to this interaction potential. It is also shown that the cluster formation probability decreases with increasing surface binding energy. Finally, a good correspondence is obtained between the calculated and experimental velocity distributions of MCs+ clusters sputtered from different monoatomic materials. As a consequence, the Monte Carlo model and the discussed results can be validated.     

Extraction of proteins from plant tissues for two-dimensional electrophoresis analysis

To increase the number of proteins detectable by two-dimensional electrophoresis (2-DE) in plants, we present a new procedure for extracting total proteins from plant tissue. This method avoids any loss of proteins in the course of sample preparation and results in two different fractions, one comprising mainly the cytoplasmatic proteins, the other one containing predominantly structure bond proteins. 2-DE patterns obtained from these two fractions show that the total number of different protein spots detected exceeds the degree of resolution commonly reported for plant proteins threefold.     

Analytical pyrolysis of carbohydrates: I. Chemical interpretation of matrix influences on pyrolysis-mass spectra of amylose using pyrolysis-gas chromatography-mass spectrometry

Inorganic additives, viz. Na₂CO₃, NaOH, HCl, ZnC₂, NaH₂PO₄, Na₂HPO₄, NaCl. MgSO₄ and sea salt, to the pyrolysis matrix change the pyrolysis-mass spectrum of amylose significantly. Carbonyl compounds, acids and their lactones, furans, pyranones anhydrosugars and aromatic substances are found in different ratios under the various conditions, as determined by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS).Carbonyl compounds, acids and lactones are released from alkaline and neutral matrices. Furans and anhydrohexoses are particularly formed under neutral and acidic conditions. Pyranones are specific for phosphate matrices. Unsaturated hydrocarbons and aromatic substances arise from strongly alkaline or dehydrating matrices. Degradation pathways are proposed for various compound categories.The results of pyrolysis-mass spectrometry and Py-GC-MS are highly compatible.