DETECTION OF DNA-PSORALEN PHOTOADDUCTS in situ

Abstract— An immunological method, with the use of specific immune serum, has been developed for detection of 8-methoxypsoralen (8-MOP) photoadducts to DNA, formed in situ in cell nuclei, after combined treatment with 8MOP and UV-A irradiation (Zarçbska et al. , 1978). Lymphocytes fixed on slides or in suspension, and cryostat sections of different mammalian tissues, served as antigenic substrate, after treatment with 8-MOP and UV-A in vitro. Specific fluorescence in these substrates was detected in the nuclei after treatment with 30 ˜ 140 kJ/m² UV-A in the presence of 0.1-0.3 μg/cm² 8-MOP. PHA-stimulated-lymphocytes appeared to be the most sensitive substrate.
However, hairless mice treated with high doses of UV-A in vivo , 70 ˜ 360 kJ/m² did not reveal a specific fluorescence of epidermal nuclei, unless a high local concentration of 8-MOP was attained.
The apparent discrepancy in the level of photoadduct detection between the in vitro and in vivo treated specimens was explained by the low number of DNA-8-MOP-photoadducts formed in vivo under these experimental conditions. The relevance of these findings to the role of DNA-8-MOP-photoadducts formed during PUVA photochemotherapy is discussed.     

ON QUOTIENTS OF BRAID GROUPS

ABSTRACT.

Let G be the group ?[t, t ^?1] x ?. By studying the action of the braid group B_n on the set Gⁿ , we obtain representations of B_n into a wreath product of the symmetric group and the general linear group over ?[t, t ^?1]. This in particular recovers the Burau representation of the braid group. Furthermore, some quotients of the braid group are obtained by using the representations found.     

A split microchannel design and analytical model to compensate for electroosmotic instabilities in micro-separations

Organic polymers offer many advantages as materials for the construction of microfluidic devices but suffer frequently from the limitation that the electrodynamic flow they support can exhibit considerable instability. This article describes a split-channel microfluidic device that can be used to compensate for changes in electroosmotic flow. The design of the separation system divides an analyte plug after injection between two separation channels of differing length. The two channels are later recombined for single point detection, eliminating the need for a scanning optical detection system. The utility of this simple design lies in the fact that the migration time of any analyte can be referenced to its twin in the parallel separation channel. This eliminates the need for a separate electroosmotic marker and allows mobilities measured in multiple devices to be compared quantitatively. Using a model adopted from the literature, the data from the split channel system can be used to precisely account for the drift that characterizes electrophoretic separations made in a polymer chip. The relative standard deviations of the analyte mobilities measured for replicate runs on multiple devices were reduced from values as high as 20% to ca. 1% RSD. This internal standardization procedure also appears to address other sources of drift in the electroosmotic flow (EOF) supported by the polymer microchannel, eliminating the need for careful monitoring of either the temperature or reservoir pH between separation runs.     

Characterization of partially transesterified poly(beta-hydroxyalkanoate)s using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) was used for the characterization of a partially transesterified poly(beta-hydroxyalkanoate), PHA, polymer produced by the bacterial strain Alcaligenes eutrophus using saponified vegetable oils as the sole carbon sources. The transesterification was carried out separately under acidic and basic conditions to obtain PHA oligomers weighing less than 10 kDa. The intact oligomers were detected in their cationized [M + Na](+) and [M + K](+) forms by MALDI-TOFMS. A composition analysis, using the MALDI-TOF spectra, indicate that the oligomers obtained via acid catalysis were terminated with a methyl 3-hydroxybutyrate end group, and those obtained by base catalysis had a methyl crotonate (olefinic) termination. In addition to HB (hydroxy butyrate), the oligomers were found to contain a small percentage of HV (hydroxy valerate). This was independently confirmed using gas chromatography/mass spectrometry (GC/MS). In comparison, the analysis of a commercial PHA polymer, transesterified under identical conditions, only showed the presence of HB, i.e. a pure PHB homopolymer. Copyright 1999 John Wiley & Sons, Ltd.     

More efficient Brownian dynamics algorithms

We examine the relative efficiencies of three- algorithms for performing Brownian Dynamics simulations without many-body hydrodynamics. We compare the conventional Brownian Dynamics algorithm of Ermak (CBD), Smart Monte Carlo (SMC) which incorporates Boltzmann sampling into essentially a CBD procedure, and the Stochastic Runge Kutta (SRK) method. We show, using the repulsive potential φ(r) = ε(σ/r) ⁿ , where n = 36 and 72, that the SRK algorithm gives the most accurate short-time dynamics for the mean-square displacements. The SRK algorithm static and dynamical properties converge better with a reducing time step to the exact values, than those generated by the CBD algorithm; giving efficiency gains typically of a factor of 3–4. Both CBD and SMC have the incorrect sign for the first correction term to the mean square displacement in a time step, whereas the SRK algorithm gives essentially the exact solution to order Δt ², where Δt is the simulation time step. In fact, these correction terms are almost equal and opposite in sign. Expressions for these terms were derived in terms of the average interaction energy per particle. The force, shear and bulk stress autocorrelation functions were calculated. The average energy per particle and time correlation functions at short time have values in excess of the exact values, while the corresponding quantities for SRK are below this. This difference in behaviour can be traced back to the extent of compliance of the particle trajectories with the exact expansion of the Smoluchowski equation. The accuracy, at a given value of the time step, of the stochastic algorithms can significantly depend on the form of the interaction potential between particles. It is also demonstrated that the long time limits of various correlation functions are fairly insensitive to a particular scheme (SRK or CBD) used in the simulations. All the correlation functions have a stretched exponential region at intermediate to long times, and the values of the exponents on density and force law steepness have been determined.     

Adsorption of linear alkanes on Cu(111): temperature and chain-length dependence of the softened vibrational mode

The vibrational spectra of linear alkanes, with lengths ranging from n-propane to n-octane, were examined on a copper surface by reflection-absorption infrared spectroscopy. The appearance and frequency of the "soft mode," a feature routinely seen in studies of saturated hydrocarbons adsorbed on metals, were examined and compared between the different adsorbates. The frequency of the mode was found to be dependent on both the number of methylene units of each alkane as well as specific aspects of the order of the monolayer phase. Studies of monolayer coverages at different temperatures provide insights into the nature of the two-dimensional (2D) melting transitions of these adlayer structures, ones that can be inferred from observed shifts in the soft vibrational modes appearing in the C-H stretching region of the infrared spectrum. These studies support recently reported hypotheses as to the origins of such soft modes: the metal-hydrogen interactions that mediate them and the dynamics that underlay their pronounced temperature dependencies. The present data strongly support a model for the 2D to one-dimensional order-order phase transition arising via a continuous rather than discrete first-order process.     

Effect of random and block copolymer additives on a homopolymer blend studied by small-angle neutron scattering

Small-angle neutron scattering (SANS) has been employed to study a blend of polystyrene and polybutadiene modified by copolymer additives. SANS data from the one-phase region approaching the phase boundary has been acquired for blends modified by random and diblock copolymers that have equal amounts of styrene and butadiene monomers as well as a random copolymer with an unequal monomer composition. The binary blend is near the critical composition, and the copolymer concentrations are low at 2.5% (w/w). The data have been fitted with the random-phase approximation model (binary and multicomponent versions) to obtain Flory–Huggins interaction parameters (χ) for the various monomer interactions. These results are considered in the context of previous light scattering data for the same blend systems. The SANS cloud points are in good agreement with previous results from light scattering. The shifts in the phase boundary are due to the effects of the additives on the χ parameter at the spinodal. All the additives appear to lower the χ parameter between the homopolymers; this is in conflict with the predicted Flory–Huggins behavior. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3191–3203, 2004