Expanding diversity in dynamic combinatorial libraries: simultaneous exchange of disulfide and thioester linkages

Dynamic combinatorial libraries have been prepared which feature two simultaneous covalent exchange reactions in aqueous solution at neutral pH. This allows for diversity, not only of the subunits that are linked, but also of the linkage itself.     

Circular dichroism of 5α-deuteriocholesta-1,3-diene

Replacement of the 5α-hydrogen by deuterium in 5α-cholesta-1,3-diene decreased the Δ at 262 nm (in hexane) from ?2.37 ± 0.06 to ?2.18 ± 0.04.     

Magnetostatic modes in antiferromagnetic resonance

Measurements of the antiferromagnetic resonance (AFMR) spectra of MnF₂ spheres are reported, and the principal magnetostatic modes (MSMs) in these spectra are identified. To interpret the observed spectra it is necessary to take into account, in addition to the theoretical MSM solution, the effects of impurities, finite sample size (propagation effects), and radiation damping. Expressions for the predicted relative intensities of the modes are developed for particular choices of symmetry of the exciting rf field and compared to observations. The observed shifts and intensities are larger than predicted. This discrepancy is explained by analysis of the role of the magnetic susceptibility of a sample near resonance. New observations are reported which improve the understanding of radiation damping in AFMR.     

A note on optimal fish harvest

Some relatively simple techniques are applied to a singular control problem arising in bioeconomics. First, Stokes' theorem is applied to the fixed-endpoint problem. This reduces the free-endpoint problem to a problem in ordinary calculus. It is then possible to find an explicit expression for the switching manifold, which generalizes the results obtained by Cliff and Vincent (Ref. 1).     

The reductive metalation of 1,2-dihalobenzocyclobutenes by NaFe(CO)2Cp and HFe(CO)2Cp

The reactions between cis- and trans-1,2-dibromo- or 1,2-diidobenzocyclobutene and NaFe(CO)₂Cp (NaFp) were investigated. The mechanism of formation of 1,2-bis(cyclopentadienyldicarbonyliron)benzocyclobutene (I) and 1-(cyclopentadienyldicarbonyliron)benzocyclobutene (II) is thought to involve initial formation of benzocyclobutadiene, addition of a Fp radical to benzocyclobutadiene and subsequent addition of a second Fp radical to form I, or hydrogen abstraction from FpH to form II.     

Single molecule spectroscopy studies of diffusion in mesoporous silica thin films

Single molecule spectroscopy is applied in studies of diffusion and surface adsorption in sol-gel-derived mesoporous silica thin films. Mesoporous films are obtained by spin casting surfactant-templated sols onto glass substrates. Small-angle X-ray diffraction results are consistent with hexagonally ordered mesophases in as-synthesized (i.e., surfactant-containing) films. Upon calcination, a 30% contraction and disordering of these structures occurs. Nile Red is used as a fluorescent probe of both the as-synthesized and calcined films. It is loaded into the samples at subnanomolar levels either prior to spin casting or after calcination. Fluorescence imaging and single-point fluorescence time transients show the dye molecules to be relatively mobile in the as-synthesized samples. In contrast, the molecules appear entrapped at fixed locations in dry calcined films. In calcined films rehydrated under high humidity conditions, the Nile Red molecules again become mobile. Time transients obtained from the as-synthesized and rehydrated samples provide clear evidence for frequent reversible adsorption of the dye to the silica surfaces. Autocorrelations of the time transients provide quantitative data on the mean diffusion coefficients (D = 2.4 x 10(-10) and 2.6 x 10(-10) cm2/s) and mean desorption times (1/k = 25 and 40 s) for the as-synthesized and rehydrated films, respectively. The results prove both water and surfactant play important roles in governing matrix interactions and mass transport.     

Development of an on-line automated sample clean-up method and liquid chromatography–tandem mass spectrometry analysis: application in an in vitro proteolytic assay

Fluorescence detection has been a method of choice in industry for screening assays, including identification of enzyme inhibitors, owing to its high-throughput capabilities, excellent reproducibility, and sensitivity. Occasionally, inhibitors are identified that challenge the fluorescence assay limit, necessitating the development of more sensitive detection methods to assess these compounds. For data mining purposes, however, original assay conditions may be required. A direct method transfer to highly sensitive and specific LC-MS-based methods has not always been possible due to the presence of MS-incompatible neutral detergents and non-volatile salts in the assay matrix. Utilizing an in vitro proteolytic screening assay for the serine protease hepatitis C virus (HCV) nonstructural (NS) 3 protease as a test case, we report the development of an automated sample clean-up procedure implemented on-line with liquid chromatography–tandem mass spectrometry (LC-MS/MS) analysis to complement fluorescence detection. Ion exchange and peptide microtraps were employed to remove MS-incompatible assay matrix components. Three protease inhibitors were used to validate the MS/MS method. Comparable potencies were achieved for these compounds when assessed by fluorescence and MS/MS detection. Furthermore, four-fold less enzyme could be utilized when employing the MS/MS method compared to fluorescence detection. The longer analysis time, however, resulted in reduced sample capacity. The potency of our designed HCV NS3 protease inhibitors are thus routinely evaluated using a continuous fluorescence-based assay. Only pertinent inhibitors approaching the fluorescence assay sensitivity limit are subsequently analyzed further by LC-MS/MS. This methodology allows us to maintain a database and to compare results independent of the detection method. Despite the relatively slow sample turnaround time of this LC-MS approach, the versatility of the automated on-line clean-up procedure and sample analysis can be applied to assays containing reagents which were historically considered to be MS incompatible.     

The Influence of Dung Amendments on Dissolved Organic Matter in Grassland Soil Leachates - Preliminary Results from a Lysimeter Study

Abstract

Understanding the carbon (C) cycle in grassland pasture systems requires more information about the fate of decomposing dung material within the soil. In this soil lysimeter study we successfully applied the natural ¹³C abundance labelling technique to trace dung-C within a temperate grassland soil. Dung was collected from beef steers fed on either maize (a C₄ plant) or perennial ryegrass (a C₃ plant) silages, and applied to a freely draining (C₃) grassland soil. Leachates were collected from soil lysimeters (0–2.5) and (0–10 cm soil depth) to determine the organic carbon and ¹³C content of < 0.7 μm filtered solution. Leachates were taken from (i) control, no dung added, (ii) C₃ dung and (iii) C₄ dung amended soil. Results showed that, (i) the addition of dung resulted in a tenfold increase in C lost from the lysimeters in drainage waters, (ii) up to 50% of the C present in the leachates was ‘native’ soil C and (iii) the application of dung produced a ‘priming’ effect. Further work is required to verify; (i) whether increased leaching of native C following dung application is a ‘true priming’ phenomenon, or merely the result of ‘displacement’ or ‘pool substitution’ of soil C, and (ii) the precise conditions and mechanisms under which organic amendments induce a true ‘priming’ effect in grassland and other agricultural soils.     

METHODS OF HEAT LOSS MEASUREMENT FOR A THERMOHYDRAULIC FACILITY

Three methods, using different thermal transients, are proposed to measure the heat loss of a thermohydraulic facility. They can he used for loop-type facilities, with circulation pumps, and for vessel-type facilities, with fluid at saturation. The analysis of uncertainties of the measurement results can help to design a heat loss experiment for a specific application. Examples are presented of heat loss measurements at the LOBI-MOD2 facility, which is an integral system thermohydraulic test facility for safety investigations of pressurized water reactor (PWR) nuclear power plants.