The vibrational excitation of hydrogen fluoride behind incident shock waves

The vibrational excitation of HF occurring behind incident shock waves has been studied in the temperature range of 1400°K to 4100°K. The extent of excitation was determined as a function of time by continuously monitoring the emission intensity from the 1–0 band of HF centered at 2.5 μ. The data were interpreted in terms of the process and gave a value of for M = HF. The corresponding result for (τp)^?1_Ar was found to be insignificant in comparison to this result. Data were also obtained for the effect of F atoms upon the relaxation rate, i.e., it was found that      

Ultrafast dynamics in the dispersed phase of oil-in-water microemulsions: monosubstituted benzenes incorporated into dodecyltrimethylammonium bromide (DTAB) aqueous micelles

Time-resolved optical Kerr effect spectroscopy has been used to probe the molecular environment afforded by the hydrophobic core of oil-in-water microemulsions. This was achieved by measuring the ultrafast dynamics of a series of benzene derivatives (benzonitrile, nitrobenzene, fluorobenzene, styrene, and toluene) incorporated as the oil phase within oil-in-water microemulsions and comparing them to the dynamics in neat liquid and the liquid diluted in nonpolar solvent. Polar and strongly interacting liquids (benzonitrile and nitrobenzene) showed dynamics in the microemulsion that are similar to those in the solution phase, while weakly interacting and mildly polar liquids (fluorobenzene, styrene and toluene) reveal dynamics more similar to those of the neat liquid. This suggests stabilization of the polar dispersed phase in polar regions of the micelle.     

Soft X‐ray characterization technique for Li batteries under operating conditions

O K‐edge and Co L‐edge near‐edge X‐ray absorption fine structure has been used to examine the cathode of an intact solid‐state lithium ion battery. The novel technique allowed for the simultaneous acquisition of partial electron yield and fluorescence yield data during the first charge cycle of a LiCoO₂‐based battery below the intercalation voltage. The chemical environments of oxygen and cobalt at the surface are shown to differ chemically from those in the bulk. The present design enables a wide variety of in situ spectroscopies, microscopies and scattering techniques.     

Direct observation of phenylalanine orientations in statherin bound to hydroxyapatite surfaces

Extracellular biomineralization proteins such as salivary statherin control the growth of hydroxyapatite (HAP), the principal component of teeth and bones. Despite the important role that statherin plays in the regulation of hard tissue formation in humans, the surface recognition mechanisms involved are poorly understood. The protein-surface interaction likely involves very specific contacts between the surface atoms and the key protein side chains. This study demonstrates for the first time the power of combining near-edge X-ray absorption fine structure (NEXAFS) spectroscopy with element labeling to quantify the orientation of individual side chains. In this work, the 15 amino acid N-terminal binding domain of statherin has been adsorbed onto HAP surfaces, and the orientations of phenylalanine rings F7 and F14 have been determined using NEXAFS analysis and fluorine labels at individual phenylalanine sites. The NEXAFS-derived phenylalanine tilt angles have been verified with sum frequency generation spectroscopy.     

Ring current effects in the active site of medium-chain Acyl-CoA dehydrogenase revealed by NMR spectroscopy

Medium-chain acyl-CoA dehydrogenase (MCAD) catalyzes the flavin-dependent oxidation of fatty acyl-CoAs to the corresponding trans-2-enoyl-CoAs. The interaction of hexadienoyl-CoA (HD-CoA), a product analogue, with recombinant pig MCAD (pMCAD) has been studied using (13)C NMR and (1)H-(13)C HSQC spectroscopy. Upon binding to oxidized pMCAD, the chemical shifts of the C1, C2, and C3 HD carbons are shifted upfield by 12.8, 2.1, and 13.8 ppm, respectively. In addition, the (1)H chemical shift of the C3-H is also shifted upfield by 1.31 ppm while the chemical shift of the C4 HD-CoA carbon is unchanged upon binding. These changes in chemical shift are unexpected given the results of previous Raman studies which revealed that the C3=C2-C1=O HD enone fragment is polarized upon binding to MCAD such that the electron density at the C3 and C1 carbons is reduced, not increased (Pellet et al. Biochemistry 2000, 39, 13982-13992). To investigate the apparent discrepancy between the NMR and Raman data for HD-CoA bound to MCAD, (13)C NMR spectra have been obtained for HD-CoA bound to enoyl-CoA hydratase, an enzyme system that has also previously been studied using Raman spectroscopy. Significantly, binding to enoyl-CoA hydratase causes the chemical shifts of the C1 and C3 HD carbons to move downfield by 4.8 and 5.6 ppm, respectively, while the C2 resonance moves upfield by 2.2 ppm, in close agreement with the alterations in electron density at these carbons predicted from Raman spectroscopy (Bell, A. F.; Wu, J.; Feng, Y.; Tonge, P. J. Biochemistry 2001, 40, 1725-33). The large increase in shielding experienced by the C1 and C3 HD carbons in the HD-CoA/MCAD complex is proposed to arise from the ring current field from the isoalloxazine portion of the flavin cofactor. The flavin ring current, which is only present when the enzyme is placed in an external magnetic field, also explains the differences in (13)C NMR chemical shifts for acetoacetyl-CoA when bound as an enolate to MCAD and enoyl-CoA hydratase and is used to rationalize the observation that the line widths of the C1 and C3 resonances are narrower when the ligands are bound to MCAD than when they are free in the protein solution.     

Pectin substances ofChara aculeolata

Summary The carbohydrate complex of the Chara algaChara aculeolata Kütz includes an acid polysaccharide similar to the pectin substances of higher plants. It is based on a fragment constructed of -14 bound residues of D-galacturonic acid in the pyranose form. The pectin is characterized by a high homogeneity, a considerable content of D-galacturonic acid, and a low degree of acidification of the carboxy groups.M. V. Lomonosov Odessa Technological Institute of the Food Industry. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 702–705, November–December, 1976.     

Investigation of antirelaxation coatings for alkali-metal vapor cells using surface science techniques

Many technologies based on cells containing alkali-metal atomic vapor benefit from the use of antirelaxation surface coatings in order to preserve atomic spin polarization. In particular, paraffin has been used for this purpose for several decades and has been demonstrated to allow an atom to experience up to 10?000 collisions with the walls of its container without depolarizing, but the details of its operation remain poorly understood. We apply modern surface and bulk techniques to the study of paraffin coatings in order to characterize the properties that enable the effective preservation of alkali spin polarization. These methods include Fourier transform infrared spectroscopy, differential scanning calorimetry, atomic force microscopy, near-edge x-ray absorption fine structure spectroscopy, and x-ray photoelectron spectroscopy. We also compare the light-induced atomic desorption yields of several different paraffin materials. Experimental results include the determination that crystallinity of the coating material is unnecessary, and the detection of C[Double Bond]C double bonds present within a particular class of effective paraffin coatings. Further study should lead to the development of more robust paraffin antirelaxation coatings, as well as the design and synthesis of new classes of coating materials.