Selective hydrophobic pocket binding observed within the carbonic anhydrase II active site accommodate different 4-substituted-ureido-benzenesulfonamides and correlate to inhibitor potency

4-Substituted-ureido benzenesulfonamides showing inhibitory activity against carbonic anhydrase (CA, EC 4.2.1.1) II between 3.3-226 nM were crystallized in complex with the enzyme. Hydrophobic interactions between the scaffold of the inhibitors in different hydrophobic pockets of the enzyme were observed, explaining the diverse inhibitory range of these derivatives.     

Development of a quantitative high-performance liquid chromatography-photodiode array detection measurement system for phenolic acids

A quantitative high-performance liquid chromatography-photodiode array detection method separating 16 phenolic acids was achieved. Six columns and several mobile phases were investigated. Resolution was achieved with a high-purity silica Phenomenex Luna C18 column (150 mm x 4.6 mm, 5 microm) and a binary gradient consisting of CH3OH-water (with 0.1% formic acid) and flow rate set at 0.7 ml/min. Acids were detected and quantitation performed at wavelength representing the lowest energy lambda(max) for individual acids. Extraction procedure from wine was optimized and yields ranged from 79 to 87% based on internal standard recovery. To confirm our quantitative results, identical samples were analyzed both in-house and by a collaborating laboratory. Correlation of two data sets generated linear regression equations that approached unity (0.93-0.98) and R2 values ranging from 0.990 to 0.999.     

Determination of the anomeric configuration of 2′-deoxy-D-ribonucleosides by 1H NMR and by crystallographic studies of a novel 2′-deoxy C-nucleoside

2′-Deoxy-D-ribonucleoside analogs of biologically active 2-β-D-ribofuranosylthiazole-4-carboxamide were synthesized and the structure of the β anomer was determined by X-ray crystallography and ′¹H nmr. 2′-Methylene protons of α- and β-deoxyribonucleosides were observed to exhibit characteristic patterns in the ¹H nmr which was used to distinguish between the two anomers. The method could be used to determine the anomeric configuration of both N- and C-2′-deoxyribonucleosides.     

Vibrational spectra of germanium-carbon clusters. II. GeC(7) and GeC(9)

Experimental and theoretical studies of a novel family of germanium-carbon clusters (Ge(n)C(m)) that were initiated with our earlier identification of the GeC(3)Ge cluster have now been extended to the GeC(7) and GeC(9) chains. The new clusters, which were formed by laser ablation and trapped in solid Ar at approximately 10 K, have been identified using Fourier-transform infrared (FTIR) measurements coupled with density-functional theory (DFT) calculations. The nu(1)(sigma) vibrational fundamental of linear GeC(7) has been identified at 2063.6 cm(-1), and an absorption at 1928.3 cm(-1) has been assigned to the nu(4)(sigma) fundamental of linear GeC(9). FTIR measurements of the isotopic shifts for the assignments are in good agreement with the DFT predictions.     

Nitrogen speciation of polar petroleum compounds by compound class separation and on-line liquid chromatography – mass spectrometry (LC-MS)

Chromatography on Attapulgus clay and on silicic acid has been used to isolate ‘neutral’ and ‘basic’ nitrogen fractions from the 650–1050 °F distillate of an off-shore Californian crude oil. These polar compounds were subjected to on-line liquid chromatography – mass spectrometric (LC-MS) analysis using low voltage electron-impact ionization high resolution mass spectrometry (LVEI HRMS) and deuterated ammonia chemical ionization (ND₃ Cl) to determine the molecules' elemental composition and number of exchangeable hydrogen atoms. On-line separation of heavy oils into saturated, 1–4 ring aromatic, and polar compounds was performed by normal phase high performance liquid chromatography (HPLC) on a dinitroanilinopropyl (DNAP) silica column.     

Multichannel time-reversal processing for acoustic communications in a highly reverberant environment

The development of time-reversal (T/R) communication systems is a recent signal processing research area dominated by applying T/R techniques to communicate in hostile environments. The fundamental concept is based on time-reversing the impulse response or Green's function characterizing the uncertain communications channel to mitigate deleterious dispersion and multipath effects. In this paper, we extend point-to-point to array-to-point communications by first establishing the basic theory to define and solve the underlying multichannel communications problem and then developing various realizations of the resulting T/R receivers. We show that not only do these receivers perform well in a hostile environment, but they also can be implemented with a "1 bit" analog-to-digital converter design structure. We validate these results by performing proof-of-principle acoustic communications experiments in air. It is shown that the resulting T/R receivers are capable of extracting the transmitted coded sequence from noisy microphone array measurements with zero-bit error.     

Junction phenomena for optimal control with state-variable inequality constraints of third order

It is known that extremal arcs governed by inequality constraints of third order (constraint relations that must be differentiated three times to generate a control equation) cannot join an unconstrained arc, except in special cases. But a control problem is exhibited, for which every extremal includes a constrained arc of third order. The constrained arc joins the end of an infinite sequence of consecutive unconstrained arcs of finite total duration. Evidence (but not proof) is given that this phenomenon is typical, rather than exceptional. An analogous phenomenon is well known for optimal control problems with singular arcs of second order.     

Evidence for exciton binding at Ni impurity sites in ZnSe

A broad charge transfer band is observed in the photoluminescence excitation (PLE) spectrum of the 2.5 μ Ni²⁺ luminescence in ZnSe : Ni. This band lies above the highest energy d-d excitation bands and exhibits a ZPL at 1.8163 eV and LO(#38;0lambda;) phonon replicas at higher energy. In contrast, PLE spectra of Co²⁺ luminescence in ZnSe:Co contain only d-d excitation bands. The charge transfer band in ZnSe:Ni is interpreted as evidence for bound exciton formation at the Ni site. The recombination energy of this exciton is transferred efficiently to the excited d-band states of the Ni ion, leading to characteristic Ni²⁺d-d luminescence.