Characterization of hydrogen bonding in the complex of adenosine deaminase with a transition state analogue: a Raman spectroscopic study

The Raman spectra of purine ribonucleoside as well as a stable model compound (1-methoxyl-1,6-dihydropurine ribonucleoside), free in solution and bound into its complex with adenosine deaminase (ADA), have been studied by Raman difference spectroscopy. Using purine riboside analogues labeled with 15N1 or 13C6 and the theoretical frequency normal-mode analyses of these molecules using ab initio quantum mechanic methods, we have positively identified many of the Raman bands in the enzyme-bound inhibitor. The spectrum of the enzyme-bound inhibitor is consistent with the enzyme-catalyzed hydration of the purine base to yield 1-hydroxyl-1,6-dihydropurine ribonucleoside, as suggested earlier by X-ray crystallographic studies. In addition, the Raman data and subsequent vibrational analyses show that the binding-induced Raman spectral changes of the inhibitor can be modeled by the formation of a strong hydrogen bond to its N1-H bond. This hydrogen bond, apparently between the N1-H of the inhibitor and the Odelta1 of Glu217 in ADA, causes a substantial N1-H bending frequency increase of about 50-100 cm-1 compared to its solution value, and this results in an estimated enthalpy of the hydrogen bond of 4-10 kcal/mol. The relationship of transition state stabilization in the catalytic strategy of this efficient enzyme to such a bonding pattern is discussed.     

Tire-wear particles as a source of zinc to the environment

Tire-tread material has a zinc (Zn) content of about 1 wt %. The quantity of tread material lost to road surfaces by abrasion has not been well characterized. Two approaches were used to assess the magnitude of this nonpoint source of Zn in the U.S. for the period 1936-1999. In the first approach, tread-wear rates from the automotive engineering literature were used in conjunction with vehicle distance-driven data from the U.S. Department of Transportation to determine Zn releases. A second approach calculated this source term from the volume of tread lost during lifetime tire wear. These analyses showed that the quantity of Zn released by tire wear in the mid-1990s was of the same magnitude as that released from waste incineration. For 1999, the quantity of Zn released by tire wear in the U.S. is estimated to be 10 000-11 000 metric tons. A specific case study focused on Zn sources and sinks in an urban-suburban watershed (Lake Anne) in the Washington, DC, metropolitan area for a time period of the late 1990s. The atmospheric flux of total Zn (wet deposition) to the watershed was 2 microg/cm2/yr. The flux of Zn to the watershed estimated from tire wear was 42 microg/cm2/yr. The measured accumulation rate of total Zn in age-dated sediment cores from Lake Anne was 27 microg/cm2/yr. These data suggest that tire-wear Zn inputs to urban-suburban watersheds can be significantly greater than atmospheric inputs, although the watershed appears to retain appreciable quantities of vehicular Zn inputs.     

Liquid core modal interferometer integrated with silica waveguides

An integrated structure is demonstrated as a refractive index sensor. The structure consists of a liquid-filled elliptical microchannel embedded in silica glass and integrated with waveguides. The microchannel features entry points that are open to the top surface of the device and distinct from the optical input. The structure allows light to couple from a solid-core input waveguide to the liquid-core waveguide formed by the microchannel, and back to a solid-core output waveguide. Bimodal interference allows the structure to be sensitive to the refractive index of the liquid, with a full beat corresponding to a refractive index change of /spl sim/10/sup -4/. The structure allows the direct integration of optical fluids with silica waveguides for sensing and optical processing applications.     

Usefulness of tomography in the evaluation of patients with temporomandibular disorders: a retrospective clinical study

OBJECTIVES: To evaluate the effect of temporomandibular joint tomography on the diagnosis and management of temporomandibular disorders and to determine whether there were any clinical predictors of usefulness of tomography in providing new information helpful in the treatment of these patients. STUDY DESIGN: The charts of 116 patients with temporomandibular joint tomograms were reviewed retrospectively for presenting signs and symptoms, initial clinical diagnosis, and alterations in diagnosis and management as a result of tomography. RESULTS: Common clinical diagnoses included osteoarthrosis (54%) and internal derangement (42%). Tomography changed the diagnosis in 24%, mainly adding or subtracting osteoarthrosis, and altered the management in 17%. Most of the latter were minor changes in treatment recommendations. There were few clinical variables that were related to whether tomography changed diagnosis or management. CONCLUSIONS: Tomography seems to have a minimal effect on the diagnosis or management of temporomandibular disorders based on the results of this retrospective study.     

Long-range surface plasmon polariton waveguides embedded in fluorinated polymer

Low-attenuation waveguides based on the propagation of long-range surface plasmon polaritons (LRSPPs) along thin Au stripes embedded in low absorption perfluorocyclobutane (PFCB) polymer are presented. A new low in propagation loss of <2.0 dB/cm was achieved for a 4 microm wide waveguide by optimizing the cladding material and fabrication process. The coupling efficiency between the LRSPP waveguide and the optical fiber is studied theoretically and experimentally for different widths of Au stripes and various cladding thicknesses. Lower coupling loss is found when the cladding thickness is close to the mode diameter of the butt-coupled fiber. Based on the 2D distribution of SPP modes calculated by a finite-difference mode solver, a symmetric structure of multilayer claddings with different refractive indices is proposed to optimize device insertion loss.     

Structure of the complex between pyridoxal 5'-phosphate and the tyrosine 225 to phenylalanine mutant of Escherichia coli aspartate aminotransferase determined by isotope-edited classical Raman difference spectroscopy

The azomethine (Schiff base) linkage between the epsilon-amino group of active-site lysine 258 and the carbonyl moiety of enzyme-bound pyridoxal 5'-phosphate (PLP) normally exhibits absorbance maxima at ca. 360 (high-pH form) or ca. 430 nm (low-pH form). However, the absorbance maximum is shifted from 358 to 386 nm, a value which is similar to that of free PLP (lambda max = 388 nm), in a mutant form of Escherichia coli aspartate aminotransferase (AATase) in which tyrosine 225, which normally donates a hydrogen bond to the phenolate function of PLP, has been replaced with phenylalanine (Y225F). This spectral shift suggested that PLP binds to Y225F as the free aldehyde. The following evidence from isotope-edited classical Raman spectroscopy proves conclusively that the near-UV spectrum is anomalous and that PLP is bound to Y225F as a Schiff base: (1) A strong cofactor peak at 1630 cm-1 in the holoenzyme-minus-apoenzyme difference spectrum of the unprotonated form of Y225F is red-shifted by 18 cm-1 in enzyme labeled with 15N at lysine 258 and other positions. (2) This isotope-induced red shift is similar to that observed in the unprotonated form of the model Schiff base, PLP-valine. (3) The Raman spectrum of Y225F is unchanged in H(2)18O, while peaks at ca. 1670 cm-1 in the spectrum of free PLP or in that of a mutant of AATase in which Lys-258 is replaced with Ala, are red-shifted by ca. 30 cm-1 in H(2)18O.(ABSTRACT TRUNCATED AT 250 WORDS)     

A note on the sampling variance of the mean uncorrected correlation in meta-analysis and validity generalization.

Compares the accuracy of several formulas for the standard error of the mean uncorrected correlation in meta-analytic and validity generalization studies. The effect of computing the mean correlation by weighting the correlation in each study by its sample size is also studied. On the basis of formal analysis and simulation studies, it is concluded that the common formula for the sampling variance of the mean correlation, Vr ?=?Vr/K where K is the number of studies in the meta-analysis, gives reasonably accurate results. This formula gives accurate results even when sample sizes and ρs are unequal and regardless of whether or not the statistical artifacts vary from study to study. It is also shown that using sample-size weighting may result in underestimation of the standard error of the mean uncorrected correlation when there are outlier sample sizes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Electrolysis of weak black liquor Part II: Effect of process parameters on the energy efficiency of the electrolytic cell

A laboratory study of the effects of process parameters on the performance of weak black liquor (WBL) electrolysis cells showed that anode material, current density and temperature are critical to the operation. The two latter variables showed an interaction effect upon the operation of the cell. In terms of energy efficiency, the IrO₂ anode performed better than the Pt anode. The addition of sodium sulfate to the WBL was beneficial to the energy efficiency. No chlorine gas was produced when electrolyzing WBL containing sodium chloride within the pH range 5.4 to 13.     

Formation and evaluation of highly uniform aluminate interface coatings for sapphire fiber reinforced ceramic matrix composites (FRCMCs) using carboxylate-alumoxane nanoparticles

Sapphire fibers have been dip-coated in aqueous and CHCl₃ solutions of carboxylate-alumoxane nanoparticles and calcium-, lanthanum-, and yttrium-doped carboxylate-alumoxane nanoparticles and fired up to 1400°C to form uniform, conformal and contiguous, aluminate coatings. Optimum solvent, dip/dry, and firing sequences were determined for the formation of crack-free coatings. Both carboxylate-alumoxane and ceramic coated fibers were examined by field emission scanning electron and transmission electron microscopy, microprobe analysis and optical microscopy. Coatings produced were stable to thermal cycling in air up to a temperature of 1400°C. The ability of the carboxylate-alumoxanes to provide crack infiltration and repair was demonstrated. Sapphire fiber/alumina matrix FRCMCs have been prepared with calcium-, lanthanum-, and yttrium-aluminate interphase layers. Microscopy and fiber push-out data confirm that the calcium- and lanthanum-aluminate coatings provide a means for controlling failure properties at the fiber-matrix interface. However, FRCMCs containing YAG-coated fibers failed catastrophically before interfacial debonding and/or sliding occurred.     

Hurter and Driffield: The Widnes Partnership in Photographic History

Since integral photography was first proposed by Lippmann in 1908 researchers and investigators have attempted to overcome the techni¬cal difficulties inherent in the production of integral images in order to realize the full potential of the system as a 3-dimensional recording and display medium.

While integral photography may not achieve the extremely high resolving power of holography, nevertheless it does have distinct advantages in certain industrial situations.

Hitherto, a major drawback has been that integral imaging has been a two stage process. However, an optical unit which inverts the spatial sense of the scene and increases the resolution when compared to previous techniques has created the prospect of a one-step single-exposure system. This optical unit has also made possible the direct optical transfer of 3-D information.