Experimental and Theoretical Study of the Broadening and Shifting of N2H+ Rotational Lines by Helium

Pressure broadening and pressure shift of N₂H⁺ rotational lines perturbed by collisions with He are studied for the first time using experiment and theory. Results are reported from measurements at 88 K for the rotational transitions ${j = 3 \leftarrow 2}$ , ${4 \leftarrow 3}$ , ${5 \leftarrow 4}$ and ${6 \leftarrow 5}$ with frequencies ranging from 0.28 to 0.56 THz. The agreement between experiment and theoretical data derived from close coupling calculations confirms the reliability of a theoretical framework used for state‐to‐state transition rates of interest in the interpretation of spectroscopic data from interstellar molecular clouds. The influence of hyperfine effects on shifts and widths of the rotational lines is discussed in detail. Although in principle possible, experiment and theoretical considerations lead to the conclusion that hyperfine effects only play a minor role.     

Vibrational spectrum of solid picene (C22H14)

Recently, Mitsuhashi et al observed superconductivity with a transition temperature up to 18 K in potassium doped picene (C(22)H(14)), a polycyclic aromatic hydrocarbon compound (Mitsuhashi et al 2010 Nature 464 76). Theoretical analysis indicates the importance of electron-phonon coupling in the superconducting mechanisms of these systems, with different emphasis on inter- and intra-molecular vibrations, depending on the approximations used. Here we present a combined experimental and ab initio study of the Raman and infrared spectrum of undoped solid picene, which allows us to unambiguously assign the vibrational modes. This combined study enables the identification of the modes which couple strongly to electrons and hence can play an important role in the superconducting properties of the doped samples.     

8-Bromo-7-hydroxyquinoline as a photoremovable protecting group for physiological use: mechanism and scope

Two-photon excitation (2PE) of "caged" biomolecules represents a powerful method to investigate the temporal and spatial relevance of physiological function in real time and on living tissue, because the excitation volume can be restricted to 1 fL. Additionally, low-energy IR light is used, which minimizes tissue destruction and enables deeper penetration into tissue preparations. Exploitation of this technology for studying cell physiology requires the further development of photoremovable protecting groups with sufficient sensitivity to 2PE for use in "caged" compounds. 8-Bromo-7-hydroxyquinoline (BHQ) is efficiently photolyzed by classic 1PE (365 nm) and 2PE (740 nm) under simulated physiological conditions (aqueous buffer of high ionic strength, pH 7.2) to release carboxylates, phosphates, and diols-functional groups commonly found on bioactive molecules such as neurotransmitters, nucleic acids, and drugs. It is stable in the dark, soluble in water, and exhibits low levels of fluorescence, which will enable use in conjunction with fluorescent indicators of biological function. BHQ-protected effectors are synthetically accessible. Stern-Volmer quenching, time-resolved infrared (TRIR), and (18)O-labeling experiments suggest that the photolysis occurs through a solvent-assisted photoheterolysis (S(N)1) reaction mechanism on the sub-microsecond time scale. BHQ has the requisite photochemical and photophysical properties as a photoremovable protecting group to regulate the action of biological effectors in cell and tissue culture with light, especially 2PE.     

Analytical characterization of corrosion products of copper and its alloys on stained stone surfaces

Monuments, where stone and metals or metallic alloys are used together, are very frequently met in all historical periods and in all countries. In the case of bronze and other copper alloys, their corrosion products can be dissolved by the action of acid rain and thus reach the porous building materials in contact with (or near to) the metallic structures. Once absorbed by the stone, they precipitate on the external stone surface and inside its porous space. As the majority of these products are coloured, their precipitates may produce stains, which are perceived as unpleasant alterations of the original ‘values’ of the stone monuments. The removal of stains is therefore required on the occasion of conservation treatments. The paper reports on the characterisation of copper corrosion products found on two, very different, monuments in Rome: ‘Fontana delle Tartarughe’ (by T. Landini, last quarter of the 16th century) and ‘Statua dello Studente’ (by A. Cataldi, 1920). To identify the speciation of copper compounds in their carbonate matrices, different techniques [X‐ray diffraction, X‐ray fluorescence, SEM/energy‐dispersive X‐ray spectroscopy (EDS), micro‐Raman and XPS] had to be employed. To further confirm the identification of the chemical species, SEM/EDS data were also processed by principal component analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Light-Activated Serotonin for Exploring Its Action in Biological Systems

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Rotational Spectroscopy of HBS: The Quadrupole Coupling Constant of S in Thioborine

The unstable HBS molecule has been produced in the gas phase by a high-temperature reaction between crystalline boron and hydrogen sulfide. Ground state rotational spectra have been observed in the millimeter-wave region, from 75 to 460 GHz, for the previously unobserved H¹¹B³³S and H¹⁰B³³S isotopic species. The analysis of the hyperfine structure produced by the ^10/11B and ³³S nuclear spins in the low-J rotational transitions has yielded the first evaluation of the quadrupole coupling constant of 33S in the thioborine molecule, which was 6.361(15) MHz in H¹¹B³³S and 6.329(17) MHz in H¹⁰B³³S. In addition, further measurements have been performed for the most abundant isotopomers H^10/11B^32/34S, for which improved values of rotational, centrifugal, and hyperfine structure constants have been determined.     

Structural studies of liquid alcohols by neutron diffraction

Neutron diffraction measurements have been made on methyl alcohol at room temperature for an incident wavelength of 0·94 Å. Cross sections have been obtained for CD₃OD, CD₃OH, and mixtures of these compounds. These data are subtracted to obtain the separated structure factors for intermolecular H₀H₀, the hydroxyl components, and the non-hydroxyl components. The Fourier transformations of the structure factors show components of both intra- and intermolecular distribution functions. Width parameters obtained from model fits are too large for thermal vibrations and are interpreted as geometrical broadening due to the stretching of bonds, variations in bond angles, and rotation of the methyl group. Differences in the real space distribution function between hydrogen and deuterium are noted.     

The structure factor for liquid nitrogen and liquid oxygen by neutron scattering

The structure factor S(Q) has been measured for liquid nitrogen at 77 K by neutron diffraction at four wavelengths. The effects of Placzek corrections on the self [1, 2] and interference [3] components of the observed differential scattering cross-sections at 0·35, 0·7, 0·84 and 1·06 Å [4] have been investigated. Effective molecular masses and internuclear bond lengths have been obtained by fitting a modified Placzek model to the observed data. It is concluded that after correction the different structure factors agree satisfactorily within the statistical errors of the measurements and the internuclear bond length is close to that measured in the gas phase.     

Neutron diffraction studies of liquid carbon suboxide

The structure factor S _m(Q) for liquid carbon suboxide has been determined for a Q-value range of 0·4 to 60 Å^-1 by neutron diffraction measurements using a steady-state (reactor) and a pulsed (linac) neutron source. The bond lengths of the molecule have been determined from the data and give good agreement with the results of electron diffraction measurements on the vapour phase after application of a molecular recoil correction term. The quasi-linear nature of the molecule is confirmed but the shape of the form factor indicates that large amplitude bending motion probably occurs in the liquid phase.

Oscillations in the intermolecular pair correlation function are observed to have a regular periodicity extending to 12 Å but details of orientational effects cannot be established from a single diffraction measurement.