Complex 2 plane bundles over CP(n)

The purpose of this note is to construct examples of non-trivial rank 2 complex bundles over CP(n) with vanishing Chern classes for all n5.     

The spectrophotometric determination of chromium in ilmenite

A new diphenylcarbazide procedure free from iron interference is described for the determination of chromium in low-chrome ilmenite. After fusion of the sample, chromium is oxidised with permanganate and most of the iron is eliminated by extraction of chromium(VI) with MIBK Residual iron causes fading of the final colour, this can be avoided by using a phosphoric acid medium at temperatures below 15°. When iron levels are less than 200 μg, temperature control (10°) suffices to prevent iron interference if the concentration of the usual sulphuric acid medium is increased to 0.2 M. However, the phosphoric acid-low temperature method gives wider tolerance to acidity variations and maximum stability with time.     

Time-dependent master equation simulation of complex elementary reactions in combustion: application to the reaction of 1CH2 with C2H2 from 300-2000 K

Computational simulations of the title reaction are presented, covering a temperature range from 300 to 2000 K. At lower temperatures we find that initial formation of the cyclopropene complex by addition of methylene to acetylene is irreversible, as is the stabilisation process via collisional energy transfer. Product branching between propargyl and the stable isomers is predicted at 300 K as a function of pressure for the first time. At intermediate temperatures (1200 K), complex temporal evolution involving multiple steady states begins to emerge. At high temperatures (2000 K) the timescale for subsequent unimolecular decay of thermalized intermediates begins to impinge on the timescale for reaction of methylene, such that the rate of formation of propargyl product does not admit a simple analysis in terms of a single time-independent rate constant until the methylene supply becomes depleted. Likewise, at the elevated temperatures the thermalized intermediates cannot be regarded as irreversible product channels. Our solution algorithm involves spectral propagation of a symmetrized version of the discretized master equation matrix, and is implemented in a high precision environment which makes hitherto unachievable low-temperature modelling a reality.     

Water adsorption, desorption, and clustering on FeO(111)

The adsorption of water on FeO(111) is investigated using temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS). Well-ordered 2 ML thick FeO(111) films are grown epitaxially on a Pt(111) substrate. Water adsorbs molecularly on FeO(111) and desorbs with a well resolved monolayer peak. IRAS measurements as a function of coverage are performed for water deposited at 30 and 135 K. For all coverages (0.2 ML and greater), the adsorbed water exhibits significant hydrogen bonding. Differences in IRAS spectra for water adsorbed at 30 and 135 K are subtle but suggest that water adsorbed at 135 K is well ordered. Monolayer nitrogen TPD spectra from water covered FeO(111) surfaces are used to investigate the clustering of the water as a function of deposition or annealing temperature. Temperature dependent water overlayer structures result from differences in water diffusion rates on bare FeO(111) and on water adsorbed on FeO(111). Features in the nitrogen TPD spectra allow the monolayer wetting and 2-dimensional (2D) ordering of water on FeO(111) to be followed. Voids in a partially disordered first water layer exist for water deposited below 120 K and ordered 2D islands are found when depositing water above 120 K.     

QCM/HCC as a platform for detecting the binding of warfarin to an immobilized film of human serum albumin

Quartz crystal microbalance/heat conduction calorimetry (QCM/HCC) is a new measurement technology that has been used to monitor simultaneously the mass and motional resistance of a thin film in conjunction with the heat flow produced by a chemical change in the film initiated by reaction with a gas. In this work we examine the applicability of the QCM/HCC in detecting chemical changes at the solution/thin film interface. Human serum albumin (HSA) was bound to the gold electrode of a 5 MHz AT-cut quartz resonator using three types of linkers and then exposed to buffered solutions of the anticoagulant drug warfarin. Changes in resonator frequency and motional resistance as well as changes in heat flow produced by warfarin binding to HSA were monitored as a function of the warfarin concentration. Differences in frequency and motional resistance changes depend upon the linker and vary both in magnitude and sign, whereas the integrated heat signal is proportional to the concentration of warfarin and independent of the linker chemistry. Quartz crystal microbalance/heat conduction calorimetry can thus be a useful tool for studying protein-ligand interactions at the solution-surface interface, even though the quartz resonator does not behave as a microbalance.     

Synthesis of 17β-hydroxy-1′-H-5α-androst-2-eno[3,2-b]pyrrole and 17β-hydroxy-1′-H-5α-androst-3-eno[3,4-b]pyrrole from O-(2-hydroxyethyl)ketoxime precursors

Pyrrolosteroids such as 17β-hydroxy-1′-H-5α-androst-2-eno[3,2-b]pyrrole ( 1 ) and the novel 17β-hydroxy-1′-H-5α-androst-3-eno[3,4-b]pyrrole ( 12 ) can be synthesized from the corresponding O-(2-hydroxyethyl)ketoxime precursors. In the case of 1 , yields compare favourably with previously reported literature methods.     

Lysine peroxycarbamates: free radical-promoted peptide cleavage

Strategies are reported that combine in one step a predictable chemical-based protein digestion with mass spectrometry. Lysine residue amino groups in peptides and proteins are modified by reaction with a peroxycarbonate derived from p-nitrophenol, and tert-butyl hydroperoxide. The peroxycarbonate reacts with lysine residues in peptides and proteins, and the resulting lysine peroxycarbamates undergo homolytic fragmentation under conditions of low-energy collision-induced dissociation (CID). Observed fragmentation of the peptides involves apparent free radical processes including Hofmann-L?ffler-type rearrangements that lead to peptide chain fragmentation. Strategies for directed cleavage of peptides by free radical promoted processes are feasible, and such strategies may well simplify schemes for protein analysis.     

PROTECTION OF ESCHERICHIA COLI CELLS AGAINST THE LETHAL EFFECTS OF ULTRAVIOLET AND X IRRADIATION BY PRIOR X IRRADIATION: A GENETIC AND PHYSIOLOGICAL STUDY

Abstract— When log phase cells of wild-type E. coli K-12 were maintained in growth medium after X irradiation, they became progressively more resistant to a subsequent exposure to UV or X radiation. The time to achieve maximum resistance was about 60 min. The uvrB, uvrD, polA and certain exrA strains (W3110 background) also demonstrated this X ray-induced resistance to subsequent UV or X irradiation but recA, recB, lex (AB1157 or W3110 backgrounds) and other exrA strains (AB1157 background) did not. The resistance induced in wild-type, uvrB and uvrD cells was characterized by the production or enhancement of a shoulder on the survival curves obtained for the second irradiation, while the resistance induced in the W3110 exrA strains was expressed only as a change in slope. The induction of resistance in the W3110 exrA strain was not inhibited by the presence of chloramphenicol, but that in the wild-type cells appeared to be. The production or enhancement of a shoulder on the survival curves of the rec ⁺ lex ⁺ exr ⁺ cells is consistent with the concept of the radiation induction of repair enzymes. Alternative explanations, however, are discussed.     

SINGLE-STRAND BREAKS IN THE DNA OF THE uvrA AND uvrB STRAINS OF ESCHERICHIA COLI K-12 AFTER ULTRAVIOLET IRRADIATION

Abstract— DNA single-strand breaks were produced in uvrA and uvrB strains of E. coli K-12 after UV (254 nm) irradiation. These breaks appear to be produced both directly by photochemical events, and by a temperature-dependent process. Cyclobutane-type pyrimidine dimers are probably not the photoproducts that lead to the temperature-dependent breaks, since photoreactivation had no detectable effect on the final yield of breaks. The DNA strand breaks appear to be repairable by a process that requires DNA polymerase I and polynucleotide ligase, but not the recA, recB, recF, lexA 101 or uvrD gene products. We hypothesize that these temperature-dependent breaks occur either as a result of breakdown of a thermolabile photoproduct, or as the initial endonucleolytic event of a uvrA , uvrB -independent excision repair process that acts on a UV photoproduct other than the cyclobutane-type pyrimidine dimer.     

Application of a simple high-performance liquid chromatographic method for the determination of melphalan in the presence of its hydrolysis products

A procedure for the separation and quantitation of melphalan (L-PAM) and its hydrolysis products by high-performance liquid chromatography is described. The hydrolysis of L-PAM at 25 +/- 0.1 degrees and 41 +/- 0.1 degrees was studied between pH 3.0 and 9.0. The pattern of hydrolysis suggested that L-PAM decomposes via two consecutive pseudo first-order reactions. Pseudo first-order rate constants (k1) were determined for the disappearance of L-PAM at various pH values in buffered solutions and in a formulated product. At both temperatures L-PAM solutions were found to be most stable at low pH. Chloride ion was found to reduce the rate of hydrolysis.