James Terner

Microwave synthesis of graphene sheets supporting metal nanocrystals in aqueous and organic media

We have developed a facile and scalable chemical reduction method assisted by microwave irradiation for the synthesis of chemically converted graphene sheets and metal nanoparticles dispersed on the graphene sheets. The method allows rapid chemical reduction of exfoliated graphite oxide (GO) using a variety of reducing agents in either aqueous or organic media. It also allows the simultaneous reduction of GO and a variety of metal salts thus resulting in the dispersion of metallic and bimetallic nanoparticles supported on the large surface area of the thermally stable 2D graphene sheets.

Ultrasmall Gold Nanoparticles Anchored to Graphene and Enhanced Photothermal Effects by Laser Irradiation of Gold Nanostructures in Graphene Oxide Solutions

In this work we demonstrate the coupling of the photothermal effects of gold nanostructures of controlled size and shape with graphene oxide nanosheets dispersed in water. The enhanced photothermal effects can be tuned by controlling the shape and size of the gold nanostructures, which result in a remarkable increase in the heating efficiency of the laser-induced size reduction of gold nanostructures. The Raman spectra of the Au-graphene nanosheets provide direct evidence for the presence of more structural defects in the graphene lattice induced by laser irradiation of graphene oxide nanosheets in the presence of Au nanostructures. The large surface areas of the laser-reduced graphene oxide nanosheets with multiple defect sites and vacancies provide efficient nucleation sites for the ultrasmall gold nanoparticles with diameters of 2-4 nm to be anchored to the graphene surface. This defect filling mechanism decreases the mobility of the ultrasmall gold nanoparticles and, thus, stabilizes the particles against the Ostwald ripening process, which leads to a broad size distribution of the laser-size-reduced gold nanoparticles. The Au nanostructures/graphene oxide solutions and the ultrasmall gold-graphene nanocomposites are proposed as promising materials for photothermal therapy and for the efficient conversion of solar energy into usable heat for a variety of thermal, thermochemical, and thermomechanical applications.

Stereochemistry of the chloroperoxidase active site: crystallographic and molecular-modeling studies

BACKGROUND Chloroperoxidase (CPO) is the most versatile of the known heme enzymes. It catalyzes chlorination of activated C-H bonds, as well as peroxidase, catalase and cytochrome P450 reactions, including enantioselective epoxidation. CPO contains a proximal heme-thiolate ligand, like P450, and polar distal pocket, like peroxidase. The substrate-binding site is formed by an opening above the heme that enables organic substrates to approach the activated oxoferryl oxygen atom. CPO, unlike other peroxidases, utilizes a glutamate acid-base catalyst, rather than a histidine residue. RESULTS The crystal structures of CPO complexed with exogenous ligands, carbon monoxide, nitric oxide, cyanide and thiocyanate, have been determined. The distal pocket discriminates ligands on the basis of size and pKa. The refined CPO-ligand structures indicate a rigid active-site architecture with an immobile glutamate acid-base catalyst. Molecular modeling and dynamics simulations of CPO with the substrate cis-beta methylstyrene and the corresponding epoxide products provide a structural and energetic basis for understanding the enantioselectivity of CPO-catalyzed epoxidation reactions. CONCLUSIONS The various CPO-ligand structures provide the basis for a detailed stereochemical mechanism of the formation of the intermediate compound I, in which Glu183 acts as an acid-base catalyst. The observed rigidity in the active site also explains the relative instability of CPO compound I and the formation of the HOCI chlorinating species. Energetics of CPO-substrate/ product molecular modeling provides a theoretical basis for the P450-type enantioselective epoxidation activities of CPO.

Observation of the FeIVO stretching vibration of ferryl myoglobin by resonance Raman spectroscopy

Abstract We have directly observed the oxyferryl group of ferryl myoglobin by resonance Raman spectroscopy. The Fe IV O stretching vibration is observed at 797 cm −1 and confirmed by an 18 O-induced isotopic shift to 771 cm −1 . The porphyrin center-to-nitrogen distance of ferryl myoglobin is significantly less than that previously observed for horseradish peroxidase compound II, which also contains an Fe IV O heme. The Fe III -CN − stretch of myoglobin (Fe III ) cyanide is observed at 454 cm − , which shifts to 449 cm −1 upon substitution with [ 13 C]cyanide.

Resonance Raman spectroscopic characterizations of horseradish peroxidase. Observations of the FeIV = O stretching vibration of Compound II

Abstract Resonance Raman spectra of the various six-coordinate low-spin forms of horseradish peroxidase isoenzymes are studied in the 600 to 1000 cm−1 vibrational region. Bands are observed which are sensitive to coordinating ligands and the identity of isoenzymes. The FeIV = O stretching vibration of Compound II is observed at 779 cm−1 and confirmed by an 18O-induced isotopic shift to 743 cm−1.

Measurement of hemoglobin oxygen saturation using Raman microspectroscopy and 532-nm excitation.

The resonant Raman enhancement of hemoglobin (Hb) in the Q band region allows simultaneous identification of oxy- and deoxy-Hb. The heme vibrational bands are well known at 532 nm, but the technique has never been used to determine microvascular Hb oxygen saturation (So(2)) in vivo. We implemented a system for in vivo noninvasive measurements of So(2). A laser light was focused onto areas of 15-30 microm in diameter. Using a microscope coupled to a spectrometer and a cooled detector, Raman spectra were obtained in backscattering geometry. Calibration was performed in vitro using blood at several Hb concentrations, equilibrated at various oxygen tensions. So(2) was estimated by measuring the intensity of Raman signals (peaks) in the 1,355- to 1,380-cm(-1) range (oxidation state marker band nu(4)), as well as from the nu(19) and nu(10) bands (1,500- to 1,650-cm(-1) range). In vivo observations were made in microvessels of anesthetized rats. Glass capillary path length and Hb concentration did not affect So(2) estimations from Raman spectra. The Hb Raman peaks observed in blood were consistent with earlier Raman studies using Hb solutions and isolated cells. The correlation between Raman-based So(2) estimations and So(2) measured by CO-oximetry was highly significant for nu(4), nu(10), and nu(19) bands. The method allowed So(2) determinations in all microvessel types, while diameter and erythrocyte velocity could be measured in the same vessels. Raman microspectroscopy has advantages over other techniques by providing noninvasive and reliable in vivo So(2) determinations in thin tissues, as well as in solid organs and tissues in which transillumination is not possible.

Resonance Raman characterization of heme Fe(IV)=O groups of intermediates of yeast cytochrome C peroxidase and lactoperoxidase

Abstract Resonance Raman Fe(IV)=O stretching vibrations of intermediates of cytochrome c peroxidase and lactoperoxidase are identified on the basis of 18 O-induced frequency shifts. For cytochrome c peroxidase compounds ES a broad Fe(IV)=O peak centered at 753 cm −1 is identified by an 18 O-shift to 725 cm −1 . For lactoperoxidase compound II, a broad feature at 745 cm −1 , identified by spectral subtraction, undergoes an 18 O-induced shift to 712 cm −1 . Previous ferryl heme protein Fe(IV)=O frequencies have been found in the range from 770 to 800 cm −1 . The present Fe(IV)=O frequencies are thus the lowest Fe(IV)=O frequencies reported to date for ferryl (compound II type) heme enzyme intermediates and imply stronger hydrogen bond donation from distal amino acids to the oxo-ferryl group than for previously reported peroxidases. Concomitant with the lowered frequencies is a considerably higher Fe(IV)=O oxygen exchange efficiency with solvent water than previously observed for horseradish peroxidase compound II.

Oxidative Metalation as a Route to Size‐Mismatched Macrocyclic Complexes: Osmium Corroles

Heavy-element corroles are of great interest as optical sensors, near-IR dyes, phosphors, organic light-emitting diodes, and anticancer compounds. Insertion of 5d metals into corroles, however, is often a difficult and unpredictable process. Against this backdrop, oxidative metalation of meso triarylcorroles with [Os3 (CO)12 ]/NaN3 in refluxing 1:2 diethylene glycol monomethyl ether/glycol has provided a convenient and relatively high-yielding route to nitridoosmium(VI) corroles, three of which could be characterized with single-crystal X-ray structure analysis.

Resonance Raman spectroscopy: a new technology for tissue oxygenation monitoring.

Objective:To evaluate resonance Raman spectroscopy for the detection of changes in sublingual mucosal hemoglobin oxygen saturation (Smo2) in response to hemorrhage and resuscitation, and to compare Smo2 with other indicators of tissue oxygenation including central venous oxygen saturation (Scvo2), lactate, base excess, and shed blood volume. Design:Prospective single group pilot study. Setting:University laboratory. Subjects:Five Sprague-Dawley rats. Interventions:Animals were anesthetized and instrumented for measurement of arterial and central venous blood gases. Raman spectroscopy was performed using a krypton ion laser providing excitation at 406.7 nm (5 mW). A 1-mm2 region of the sublingual tongue surface was chosen for investigation. Animals were subjected to stepwise hemorrhage until approximately 50% of the blood volume was removed. At each hemorrhage and resuscitation interval, Raman spectroscopy was performed and corresponding arterial and central venous blood gas and lactate measurements were made. Smo2 was calculated as the ratio of the oxygenated heme spectral peak height to the sum of the oxy- and deoxyhemoglobin spectral peak heights. Raman spectroscopy-derived Smo2 measurements were compared with Scvo2 as well as with other indicators of oxygenation. Measurements and Main Results:The mean difference between Smo2 and Scvo2 for all paired measurements was 5.8 ± 11.7 absolute saturation points. Smo2 was significantly (p < .0001) correlated with Scvo2 (r = .80), lactate (r = −.78), base excess (r = .80), and shed blood volume (r = −.75). Smo2 and Scvo2 showed similar levels of precision for predicting elevated lactate and base deficit. Conclusions:These studies demonstrate the ability of Raman spectroscopy to noninvasively track microvascular hemoglobin oxygenation in tissue and favorably correlate with other important indicators of tissue oxygenation such as Scvo2, lactate, base deficit, and shed blood volume. The technique shows promise as a method to noninvasively monitor tissue oxygenation.

Resonance raman spectroscopic characterization of the heme coordination and spin state in the alkaline form of horseradis peroxidase

Abstract Resonance Raman spectra of the alkaline forms of horseradish peroxidase isoenzymes are indicative of six-coordinate low-spin hemes. Comparisons are made with resonance Raman spectra of horseradish peroxidase Compounds II and X. The v4 porphyrin frequencies of the Fe(IV) derivatives, that are used as oxidation state marker bands, have been found to be not significantly higher than those of the low-spin Fe(III) hemes of the alkaline forms.