Consistent assignment of the vibrations of symmetric and asymmetric para-disubstituted benzene molecules

We give a description of the phenyl-ring-localized vibrational modes of the ground states of the para-disubstituted benzene molecules including both symmetric and asymmetric cases. In line with others, we quickly conclude that the use of Wilson mode labels is misleading and ambiguous; we conclude the same regarding the related ones of Varsányi. Instead we label the modes consistently based upon the Mulliken (Herzberg) method for the modes of para-difluorobenzene (pDFB). Since we wish the labelling scheme to cover both symmetrically- and asymmetrically-substituted molecules, we apply the Mulliken labelling under C2v symmetry. By studying the variation of the vibrational wavenumbers with mass of the substituent, we are able to identify the corresponding modes across a wide range of molecules and hence provide consistent assignments. Particularly interesting are pairs of vibrations that evolve from in- and out-of-phase motions in pDFB to more localized modes in asymmetric molecules. We consider the para isomers of the following: the symmetric dihalobenzenes, xylene, hydroquinone, the asymmetric dihalobenzenes, halotoluenes, halophenols and cresol

Distinct Populations of Hepatic Stellate Cells in the Mouse Liver Have Different Capacities for Retinoid and Lipid Storage

Hepatic stellate cell (HSC) lipid droplets are specialized organelles for the storage of retinoid, accounting for 50–60% of all retinoid present in the body. When HSCs activate, retinyl ester levels progressively decrease and the lipid droplets are lost. The objective of this study was to determine if the HSC population in a healthy, uninjured liver demonstrates heterogeneity in its capacity for retinoid and lipid storage in lipid droplets. To this end, we utilized two methods of HSC isolation, which leverage distinct properties of these cells, including their vitamin A content and collagen expression. HSCs were isolated either from wild type (WT) mice in the C57BL/6 genetic background by flotation in a Nycodenz density gradient, followed by fluorescence activated cell sorting (FACS) based on vitamin A autofluorescence, or from collagen-green fluorescent protein (GFP) mice by FACS based on GFP expression from a GFP transgene driven by the collagen I promoter. We show that GFP-HSCs have: (i) increased expression of typical markers of HSC activation; (ii) decreased retinyl ester levels, accompanied by reduced expression of the enzyme needed for hepatic retinyl ester synthesis (LRAT); (iii) decreased triglyceride levels; (iv) increased expression of genes associated with lipid catabolism; and (v) an increase in expression of the retinoid-catabolizing cytochrome, CYP2S1. Conclusion: Our observations suggest that the HSC population in a healthy, uninjured liver is heterogeneous. One subset of the total HSC population, which expresses early markers of HSC activation, may be “primed” and ready for rapid response to acute liver injury

Topology of molecular machines of the endoplasmic reticulum: a compilation of proteomics and cytological data

The endoplasmic reticulum (ER) is a key organelle of the secretion pathway involved in the synthesis of both proteins and lipids destined for multiple sites within and without the cell. The ER functions to both co- and post-translationally modify newly synthesized proteins and lipids and sort them for housekeeping within the ER and for transport to their sites of function away from the ER. In addition, the ER is involved in the metabolism and degradation of specific xenobiotics and endogenous biosynthetic products. A variety of proteomics studies have been reported on different subcompartments of the ER providing an ER protein dictionary with new data being made available on many protein complexes of relevance to the biology of the ER including the ribosome, the translocon, coatomer proteins, cytoskeletal proteins, folding proteins, the antigen-processing machinery, signaling proteins and proteins involved in membrane traffic. This review examines proteomics and cytological data in support of the presence of specific molecular machines at specific sites or subcompartments of the ER

Broadband Coupling into a Single-Mode, Electroactive Integrated Optical Waveguide for Spectroelectrochemical Analysis of Surface-Confined Redox Couples

Pushing the sensitivity of spectroelectrochemical techniques to routinely monitor changes in spectral properties of thin molecular films (i.e., monolayer or submonolayer) adsorbed on an electrode surface has been a goal of many investigators since the earliest developments in this field. 1 It was initially recognized that exploiting the evanescent field generated by total internal reflection at the interface of an optically transparent electrode (such as a thin film of tin oxide or indium tin oxide (ITO) on glass or quartz) has the inherent advantage of selectively probing only the near-surface region, as opposed to bulk sampling with transmission based techniques. Furthermore, by utilizing the multiple reflections in an attenuated total reflectance (ATR) geometry, an enhancement in sensitivity can be realized, and as the thickness of the ATR element is decreased, the number of reflections increases, yielding a substantial sensitivity enhancement. [2][3][4][5][6] Itoh and Fujishima were the first to show the advantages of reducing the thickness of an ATR element overcoated with a transparent conductive oxide to the integrated optical waveguide (IOW) regime. Using a four-mode, gradient index waveguide coated with a transparent, conductive tin oxide layer, they demonstrated large sensitivity enhancements, relative to a single pass transmission experiment, for spectroelectrochemical measurements of methylene blue. 7,8 Other research groups subsequently described similar gradient index, multilayer, electroactive waveguide structures, but they did not make use of the technology to explore the spectroelectrochemistry of (sub)monolayer coverage films. [9][10][11][12][13] We recently described a single-mode, electroactive planar IOW (the EA-IOW) having a step refractive index profile. It was fabricated by sputtering a Corning 7059 glass layer (400 nm) over soda lime glass or quartz, followed by a 200-nm layer of SiO 2

THE 1B2(ΠΠ∗)←1A1^{1}B_{2} (\Pi\Pi^{*}) \leftarrow ^{1}A_{1} ELECTRONIC BAND SYSTEM OF TOLUENE

Author Institution:The $^{1}B_{2}(\Pi \Pi ^{*})\leftarrow ^{1}A_{1}$ electronic band system of the normal isotope of toluene has been photographed and measured at high resolution. Analysis of the strong vibronic components has led to identification of active $^{1}B_{2}$ state fundamentals. The rotational definition of the strong bands near the origin, $\nu_{00} = 37478.76 cm^{-1}$, suggests that a band contour computation including internal rotation of the methyl group should be attempted. Preliminary results of such as asymmetric top/internal rotation computation will be presented

IDENTIFICATION OF TORSIONAL TRANSITIONS IN THE SUPERSONIC JET SPECTRUM OF MONO-METHYL TETRAZINE

1. C.A. Haynam and D.H. Levy, J. Phys. Chem. 87, 2091 (1983). 2. M.A. Leugers and C.J. Seliskar, J. Mol. Spectrosc. 91, 150-164 (1982). 3. S.M. Beck, M.G. Liverman, D.L. Monts and R.E. Smalley, J. Chem. Phys. 70, 232-237 (1979).Author Institution: Department of Chemistry, University of CincinnatiIdentification of the strong torsional transitions, with $m^{\prime}=m^{\prime\prime}=\pm 1$ and delta m equal to zero, in the high-resolution laser excitation molecular beam spectrum of the methyl tetrazine 5613 {\AA} origin band recently published by Haynam and Levy (1) has been made. Use of their published tetrazine frame rotational constants with $A_{T} = 5.3403 cm^{-1}, \triangle A_{T} = -0.034 cm^{-1}$ results in predicting the positions of the torsional transitions for J up to 3 to within about $.001 cm^{-1}$ precision. However, line positions for larger values of J are not adequately calculated using these constants in the asymmetric top/free internal rotor model (2), the fit worstening with increasing J. Reasons for this discrepancy are discussed. Assumption of an equilibrium distribution over both rotation and torsion states for a specified temperature does not quantitatively reproduce the observed molecular beam spectrum intensities. However, a simple model based on a suggestion of Smalley, et al. (3) does produce the observed spectral intensities in at least the simplest of the Haynam and Levy (1) spectra. Indeed, this simple model, with $T_{rot} = 0.50K$ and $T_{m=1} = 5.0K$ reproduces the published 500 PSI backing-pressure spectrum on a line-for-line basis

ELECTRONIC BAND CONTOUR CALCULATION OF TOLUENE

$^{1}$ E. B. Wilson, JR., C. C. Lin, and D. R. Lide, JR., J. Chem. Phys. 23, 136--142 (1955).Author Institution:The rotational contour of the origin band of toluene has been computed within the framework of the asymmetric top with free internal rotation (1). With the basis |J, Ka, Kc, M, m $>$ and the barrier height equal to zero, the energy matrix becomes diagonal in the torsional quantum number, m, and the secular equation is then factorable into even and odd K sub-blocks. The selection rules for dipole radiation are the same as for the rigid asymmetric top with the additional constraint that $\Delta m =$O. A general program has been written so that the rotational band contour for any molecule in this class may be computed