Crotonase catalysis enables flexible production of functionalized prolines and carbapenams

The biocatalytic versatility of wildtype and engineered carboxymethylproline synthases (CMPSs) is demonstrated by the preparation of functionalized 5-carboxymethylproline derivatives methylated at C-2, C-3, C-4, or C-5 of the proline ring from appropriately substituted amino acid aldehydes and malonyl-coenzyme A. Notably, compounds with a quaternary center (at C-2 or C-5) were prepared in a stereoselective fashion by engineered CMPSs. The substituted-5-carboxymethyl-prolines were converted into the corresponding bicyclic β-lactams using a carbapenam synthetase. The results demonstrate the utility of the crotonase superfamily enzymes for stereoselective biocatalysis, the amenability of carbapenem biosynthesis pathways to engineering for the production of new bicyclic β-lactam derivatives, and the potential of engineered biocatalysts for the production of quaternary centers.     

Dynamics of drying in 3D porous media

The drying dynamics in three dimensional porous media are studied with confocal microscopy. We observe abrupt air invasions in size from single particle to hundreds of particles. We show that these result from the strong flow from menisci in large pores to menisci in small pores during drying. This flow causes air invasions to start in large menisci and subsequently spread throughout the entire system. We measure the size and structure of the air invasions and show that they are in accord with invasion percolation. By varying the particle size and contact angle we unambiguously demonstrate that capillary pressure dominates the drying process.     

Comparison of acoustic and perceptual measures of voice in male-to-female transsexuals perceived as female versus those perceived as male

The present study explored significant differences between male-to-female transgendered speakers perceived as male and those perceived as female in terms of speaking fundamental frequency (SFF) and its variability, vowel formants for /a/ and /i/, and intonation measures. Fifteen individuals who identified themselves as male-to-female transsexuals served as speaker subjects, in addition to 6 biological female control subjects and 3 biological male control subjects. Each subject was recorded reading the Rainbow Passage and producing the isolated vowels /a/ and /i/. Twenty undergraduate psychology students served as listeners. Results indicated that subjects perceived as female had a higher mean SFF and higher upper limit of SFF than subjects perceived as male. A significant correlation between upper limit of SFF and ratings of femininity was achieved.     

Investigation of high sensitivity GC-FTIR as an analytical tool for structural identification

As part of a detailed investigation into the application of GC-FTIR in industrial and environmental analysis, representative sets of samples have been analyzed in parallel using commercial high-sensitivity instruments. Two of the instruments utilize low temperature storage of the GC eluate to extend the time available for FTIR analysis, yielding greater sensitivity than that possible by conventional ‘light-pipe’ GC-FTIR. In certain circumstances, instruments using both types of sample storage give rise to spectra exhibiting features characteristic of the interface used. Chromatographic resolution was found not to be significantly degraded by use of either sample storage interface. Particular advantages were found in having parallel flame ionization detection and mass spectrometry; this enabled the location of smaller components and gave greater certainty of identification.     

Simultaneous determination of sub-mg/1 levels of sulphur and chlorine in liquid hydrocarbons by a coupled combustion—ion chromatography technique

A method for elemental analysis that employs a novel coupled combustion—ion chromatography (C---IC) apparatus is described in detail. The samples are combusted and the products collected in a dilute peroxide solution. This solution is loaded onto a concentrator column which is then introduced into the injection position of a suppressed conductivity anion chromatography system. The method is rapid, reliable, free from interferences and has the capacity for simultaneous determination of sulphur and chlorine in organic liquids at concentrations down to 0.03 mg/1. Provided that the capacity of the concentrator column is not exceeded, the recovery for organic standards of both chlorine and sulphur in a variety of organic solvents is greater than 93%, irrespective of the solvent and the sample volume and concentration. Repeatability is only slightly worse than that observed for conventional direct IC analysis of aqueous solutions. At concentrations of 0.4 mg/1 C1 and 0.5 mg/1 S, the % standard deviations (n = 10) were found to be 2.9 and 3.5% respectively. The results obtained with the C---IC analyser for both standards and petroleum-based samples are in good agreement with those obtained by microcoulometry.     

Mode-coupling theory for multiple-time correlation functions of tagged particle densities and dynamical filters designed for glassy systems

The theoretical framework for higher-order correlation functions involving multiple times and multiple points in a classical, many-body system developed by Van Zon and Schofield [Phys. Rev. E 2002, 65, 011106] is extended here to include tagged particle densities. Such densities have found an intriguing application as proposed measures of dynamical heterogeneities in structural glasses. The theoretical formalism is based upon projection operator techniques which are used to isolate the slow time evolution of dynamical variables by expanding the slowly evolving component of arbitrary variables in an infinite basis composed of the products of slow variables of the system. The resulting formally exact mode-coupling expressions for multiple-point and multiple-time correlation functions are made tractable by applying the so-called N-ordering method. This theory is used to derive for moderate densities the leading mode coupling expressions for indicators of relaxation type and domain relaxation, which use dynamical filters that lead to multiple-time correlations of a tagged particle density. The mode coupling expressions for higher order correlation functions are also successfully tested against simulations of a hard sphere fluid at relatively low density.     

Cation–π Interactions Contribute to Substrate Recognition in γ‐Butyrobetaine Hydroxylase Catalysis

γ‐Butyrobetaine hydroxylase (BBOX) is a non‐heme Fe^II‐ and 2‐oxoglutarate‐dependent oxygenase that catalyzes the stereoselective hydroxylation of an unactivated C?H bond of γ‐butyrobetaine (γBB) in the final step of carnitine biosynthesis. BBOX contains an aromatic cage for the recognition of the positively charged trimethylammonium group of the γBB substrate. Enzyme binding and kinetic analyses on substrate analogues with P and As substituting for N in the trimethylammonium group show that the analogues are good BBOX substrates, which follow the efficiency trend N⁺>P⁺>As⁺. The results reveal that an uncharged carbon analogue of γBB is not a BBOX substrate, thus highlighting the importance of the energetically favorable cation–π interactions in productive substrate recognition.     

Electronic effects induced by single hydrogen atoms on the Ge(001) surface

The properties of an isolated dangling bond formed by the chemisorption of a single hydrogen atom on a dimer of the Ge(001) surface are investigated by first-principles density functional theory (DFT) calculations, and scanning tunneling microscopy (STM) measurements. Two stable atomic configurations of the Ge-Ge-H hemihydride with respect to the neighboring bare Ge-Ge dimers are predicted by DFT. For both configurations, the unpaired electron of the HGe(001) system is found to be delocalized over the surface, rendering the isolated dangling bond of the hemihydride unoccupied. However, local surface charge accumulation, such as may occur during STM imaging, leads to the localization of two electrons onto the hemihydride dangling bond. The calculated surface densities of states for one of the charged Ge-Ge-H hemihydride configurations are found to be in good agreement with atomic-resolution STM measurements on n-type Ge(001). Comparison with a Si-Si-H hemihydride of the Si(001) surface shows similarities in structural properties, but substantial differences in electronic properties.