Vibrational Fine Structures Research Articles

Stability and structure-activity relationship of the SPA4 peptide under ambient and stressed conditions of lung injury.

Lung inflammation and injuries are major health problems. The SPA4 peptide (amino acid sequence GDFRYSDGTPVNYTNWYRGE) binds to Toll-like receptor-4 and exerts anti-inflammatory activity. In this study, we have determined the stability of the structure and structure-activity relationship of the SPA4 peptide under ambient and stressed conditions of lung injury. The SPA4 peptide was maintained at different pH and temperatures, in solutions of different ionic strengths, and simulated lung fluids. The primary and secondary structure of the SPA4 peptide was determined by ultraviolet-visible (UV-VIS) and circular dichroism (CD) spectroscopy. The activity of the SPA4 peptide was determined by measurement of secreted levels of chemokine C-X-C motif ligand 1/keratinocyte-derived chemokine (CXCL1/KC) and lactate by primary mouse lung epithelial cells against lipopolysaccharide (LPS) stimuli. Our results demonstrate the stability of the structure of the SPA4 peptide at room temperature and 4 °C over 10 days. The original UV-VIS spectra of the SPA4 peptide followed a typical pattern when incubated in solutions of pH 5.7, 7.0, and 8.0 at different temperatures, simulated lung fluids, and most of the chemical components. Slight shifts in the absorbance peaks, derivative values, and vibrational fine structures were noted in the fourth-derivative spectra of the SPA4 peptide under some conditions. An increased level of lactate is the hallmark of lung injury. The SPA4 peptide on its own and in the presence of lactate exerts anti-inflammatory activity. The primary and secondary structure and the activity of the SPA4 peptide remain intact when pre-incubated in 2 mM sodium lactate solution. The results provide important insights about the stability and structure-activity relationship of the SPA4 peptide.

Electron affinities and lowest triplet and singlet state properties of para-oligophenylenes (n = 3-5): theory and experiment.

We apply photodetachment-photoelectron spectroscopy to measure the electron affinities and the energetics of the lowest excited electronic states of the neutral molecules para-terphenyl (p3P), para-quaterphenyl (p4P) and para-quinquephenyl (p5P), including especially the triplet states below S1. The interpretation of the experimental data is based on the comparison to calculated 0-0 energies and Dyson norms, using density functional theory and multireference configuration interaction methods, as well as Franck-Condon patterns. The comparison between calculated and experimental vibrational fine-structures reveals a twisted benzoid-like molecular structure of the S0 ground state and nearly planar quinoid-like nuclear arrangements in the S1 and T1 excited states as well as in the D0 anion ground state. For all para-oligophenylenes (ppPs) in this series, at least two triplet states have been identified in the energy regime below the S1 state. The large optical S0-S1 cross sections of the ppPs are rationalised by the nodal structure of the molecular orbitals involved in the transition. The measured electron affinities range from 380 meV (p3P) over 620 meV (p4P) to 805 meV (p5P). A saturation of the electron binding energy with the increasing number of phenyl units is thus not yet in sight.

Vibrationally Broadened Optical Spectra of Selected Radicals and Cations Derived from Adamantane: A Time-Dependent Correlation Function Approach.

Diamondoids are hydrogen-saturated molecular motifs cut out of diamond, forming a class of materials with tunable optoelectronic properties. In this work, we extend previous work on neutral, closed-shell diamondoids by computing with hybrid density functional theory and time-dependent correlation functions vibrationally broadened absorption spectra of cations and radicals derived from the simplest diamondoid, adamantane, namely, the neutral 1- and 2-adamantyl radicals (C10H15), the 1- and 2-adamantyl cations (C10H15+), and the adamantane radical cation (C10H16+). For selected cases, we also report vibrationally broadened emission, photoelectron, and resonance Raman spectra. Furthermore, the effect of the damping factor on the vibrational fine-structure is studied. The following trends are found: (1) Low-energy absorptions of the adamantyl radicals and cations, and of the adamantane cation, are all strongly red-shifted with respect to adamantane; (2) also, emission spectra are strongly red-shifted, whereas photoelectron spectra are less affected for the cases studied; (3) vibrational fine-structures are reduced compared to those of adamantane; (4) the spectroscopic signals of 1- and 2-adamantyl species are significantly different from each other; and (5) reducing the damping factor has only a limited effect on the vibrational fine-structure in most cases. This suggests that removing hydrogen atoms and/or electrons from adamantane leads to new optoelectronic properties, which should be detectable by vibronic spectroscopy.

High-Resolution Near-Edge X-ray Absorption Fine Structure Study of Condensed Polyacenes

We present a systematic study of high-resolution near-edge X-ray absorption fine structure (NEXAFS) spectra of well-ordered films of condensed benzene and polyacenes, namely naphthalene, anthracene, tetracene, and pentacene. Increased spectral complexity with increasing molecular size is observed: NEXAFS features decrease in intensity and move to lower photon energy (red shift) as the size of the aromatic system grows. Moreover, a second group of transitions arises. The dichroism in the C K-edge spectra increases with molecular size. While benzene molecules are randomly oriented, the polyacenes preferentially lie flat with increasing molecular size. Vibrational fine structures coupled to the C 1s π* transitions are apparent for all investigated molecules. The energy position of the onset of the first resonance decreases from 284.86 eV for benzene to 283.26 eV for pentacene. Calculations of absolute band envelopes with time-dependent density functional theory (TDDFT), followed by analysis of the transition...

Enhanced visible photoluminescence of V_2O_5 via coupling ZnO/V_2O_5 composite nanostructures

V(2)O(5) films capped by a thin ZnO layer had been prepared by sputtering method at room temperature. The initial smooth films transferred to porous composite nanocrystals and nanorods after annealed at 500 degrees C, and enhanced visible light emission was observed. This tremendous enhancement was attributed to the coupling between V(2)O(5) nanorods and ZnO nanoparticles as well as the improved V(2)O(5) crystallinity. Prominent vibrational fine structures of the photoluminescence spectra were also observed.

Vibrational Fine Structures Revealed by the Frequency-to-Time Fourier Transform of the Transient Spectrum in Bacteriorhodopsin

A vibrational progression that is hidden in a featureless spectrum of induced absorption and stimulated emission was found in time-resolved absorption change spectra. The ultrahigh time resolution of the pump-probe measurement made by using an ultrashort laser pulse localizes the wave packet along the potential multimode hyper surfaces, represented by a vibrational progression. The transition energy of the induced absorption and stimulated emission corresponds to a localized point (space) on the hyper surface, which is visited by the wave packets with fixed phases.

Synthesis, Thermal, and Light-Emitting Properties of Anthracene Derivatives

Several anthracene derivatives were prepared by a single-step reaction and characterized their thermal properties by differential scanning calorimetry (DSC) and thermogravimetric analyses. Their photoluminescence properties were examined in a large number of organic solvents of increased polarity that included toluene, chloroform, tetrahydrofuran, acetone, methanol, acetonitrile, and dimethyl sulfoxide. Some compounds exhibited emission spectra with vibrational fine structures in organic solvents; and other compounds exhibited structureless emission spectra in organic solvents.

Vibrational fine structures revealed by the real-time vibrational phase and amplitude in MEH-PPV using few cycle pulses

It was found that the vibronic transition peaks hidden in a featureless spectrum of induced absorption could be clearly revealed by utilizing the spectra of phases and amplitudes of the molecular vibrational modes. Some of the peaks were also found in a second derivative of a transition spectrum integrated over a delay time from 100 to 700 fs. This is because of the localization of a wave packet in a limited region along the potential multimode hypersurfaces. The transition energy of an induced absorption or an induced emission corresponds to some localized point (space) on the potential hypersurface to which the wave packets visit with some fixed phases.

Unusual CD couplet pattern observed for the π*←n transition of enantiopure (Z)‐8‐methoxy‐4‐cyclooctenone: An experimental and theoretical study by electronic and vibrational circular dichroism spectroscopy and density functional theory calculation

Ultraviolet absorption (UV) and electronic circular dichroism (ECD) spectra of enantiopure (Z)-8-methoxy-4-cyclooctenone (MCO) were measured in hexane to give a normal single UV absorption band at 298 nm, which is assigned to the carbonyl's pi*<--n transition. Unexpectedly, the ECD spectrum exhibited an apparent couplet pattern with vibrational fine structures. Obviously, the conventional CD exciton coupling mechanism cannot be applied to this bisignate CD signal observed for single-chromophoric MCO. Variable temperature-ECD and vibrational circular dichroism (VCD) spectral measurements, simultaneous UV and ECD spectral band resolution, and density functional theory (DFT) calculations of energy and structure revealed that this apparent CD couplet originates from a rather complicated spectral overlap of more than three conformers of MCO, two of which exhibit mirror-imaged ECD spectra at appreciably deviated wavelengths. In the simultaneous band-resolution analysis, the observed UV and ECD spectra were best fitted to four overlapping bands. Two major conformers were identified by comparing the experimental IR and VCD spectra with the simulated ones, and the other two by comparing the observed UV and ECD spectra with the theoretical ones obtained by time-dependent DFT calculations. It was shown that the combined use of experimental ECD and VCD spectra and theoretical DFT calculations can give a reasonable interpretation for the Cotton effects of the conformationally flexible molecule MCO.

2,4,5-Triphenylimidazole Nanowires with Fluorescence Narrowing Spectra Prepared through the Adsorbent-Assisted Physical Vapor Deposition Method

The single crystalline nanowires have been fabricated from a small organic functional molecule, 2,4,5-triphenylimidazole (TPI), through an adsorbent-assisted physical vapor deposition (PVD) method. The introduction of the absorbents can significantly improve the dimensional uniformity of the as-prepared TPI nanowires. The TPI nanowires displayed interesting size-dependent optical properties, that is, the absorption spectra of the wires exhibit an obvious blue shift with the decrease of diameter, and simultaneously, the vibrational fine structures of the emission spectra emerge and become more pronounced with the diameter decreasing from 500 to 40 nm even at room temperature, which are usually observed only under cryogenic conditions. The emergence and enhancement of the vibrational structures are contributed to the increase of the long-range order and the degree of orientation with the decrease of diameter. The strategy described here should give a useful enlightenment for the fabrication of wirelike nano...

The C 1s NEXAFS spectrum of benzene below threshold: Rydberg or valence character of the unoccupied σ-type orbitals

High-resolution C 1s near edge X-ray absorption fine structure (NEXAFS) spectra of benzene and benzene-d 6 were measured and compared with the results of state-of-the-art density functional theory (DFT) calculations demonstrating excellent agreement. The spectrum below threshold is dominated by four resonances, each two of them with σ- and π-type final-state orbitals. The π-type resonances have been ascribed in previous work unanimously to antibonding valence orbitals while the character of the σ-type resonances is still the subject of discussion. Based on the present theoretical results and the observed vibrational fine structures both σ-type orbitals are assigned to be valence type with minor admixtures of Rydberg character.

Effect of the addition of propane and distortion of tetrahedral vanadium(V) species in VSiβ zeolites on the photodecomposition of NO

VxSiβ catalysts with x=0.05, 0.2 and 1.75 V wt%, prepared by a two-step post-synthesis method, have been characterised by physical techniques and their photocatalytic reactivity investigated in the decomposition of NO. XRD and diffuse reflectance UV-Vis spectroscopy show that vanadium is incorporated as tetrahedral Vv species, a result confirmed by XANES and EXAFS. Photoluminescence spectra of V x Siβ catalysts show well-resolved vibrational fine structures due to three different kinds of tetrahedral VV (α, β, γ) species, with different degrees of distortion. Their relative amounts depend on V content and calcination/hydration treatments. Calcined-hydrated V1.75Siβ, calcined V1.75Siβ and calcined V0.05Siβ exhibit mainly the α, γ and β kind of tetrahedral vanadium, respectively. These samples are active in the decomposition of NO under UV-irradiation, leading mainly to N2 and O2. The decomposition of NO is strongly enhanced in presence of propane, leading to higher yield of N2. The latter strongly depends on the distortion of tetrahedral V species. The highest activity is found for the catalyst with tetrahedral V of highest distortion, lowest V=O bond length and biggest lifetime of its excited triplet state.

Effects of High Pressure on the Luminescence and Upconversion Properties of Ti2+-Doped NaCl

The luminescence and upconversion properties of 0.8% Ti2+-doped NaCl at 15 K are studied as a function of external hydrostatic pressure. Luminescence band maxima shifts are analyzed with a ligand field point charge model, allowing an estimate of the compressibility of the spectroscopically active TiCl64- unit in the NaCl host matrix. The pressure dependencies of the vibrational fine structures in the two Ti2+ luminescence bands are analyzed and interpreted in terms of pressure-induced changes in equilibrium distortions and force constants of the emitting electronic states 3T2g(t2geg) and 3T1g(t2geg). Time-resolved luminescence measurements are used to study the effects of pressure on the excited-state dynamics. 15 K near-infrared excitation at 9399 cm-1 leads to upconversion luminescence in the red spectral region both at ambient pressure and 34 kbar. On the basis of time-dependent upconversion luminescence experiments, two fundamentally different upconversion mechanisms are found to be dominant under these two experimental conditions. In particular, pressure is found to switch on an efficient upconversion mechanism, which is inactive at ambient pressure, leading to an estimated order-of-magnitude enhancement of the overall upconversion efficiency at 34 kbar. This additional mechanism involves energy transfer (ET) between two excited Ti2+ ions. Its occurrence only at high pressure is interpreted in terms of a strongly pressure-dependent spectral overlap integral governing the efficiency of the ET step.

Vibrational fine structures in photoelectron spectra of carbon ring clusters

Based on first-principles calculations, we study the vibrational fine structures of photoelectron spectroscopy used as a tool to identify carbon clusters. The hybrid density functional theory is used to perform electronic-structure calculations, then the fine structure is obtained based on the generalized harmonic oscillator model including displacement, frequency change, and mode mixing between the initial and final charge states. Calculational results for carbon-ring anion clusters enable clear identification of spectra observed in the past.

Electronic structure of haloalkanes: a high resolution photoelectron spectroscopic study

High resolution He(I) photoelectron spectra (PES) of a number of bromo- and iodoalkanes have been measured. Linear relationships between ionization energies (Ei) and 1/n (where n is the number of carbon atoms in the chain) describe the trends reasonably well if n = 1 is excluded for dihaloalkanes. This property (i.e. line slopes) when joined the alternation of halogen lone pair bandwidths within a given spin—orbit doublet, can be used to provide a fully empirical assignment of the four non-bonding orbital ionizations of dihaloalkanes. The interactions between the halogen lone pair orbitals and the alkane σ orbitals dominate in dihaloalkanes for which n⩾2, while through-space interaction is important only in dihalomethanes (n = 1). Vibrational fine structures were used to infer the existence of hyperconjugative effects.

Vibrationally resolved carbon core excitations in alkane molecules.

Core-excitation spectra at the carbon K threshold of methane, ethane, and propane, as well as of the deuterated molecules, were studied by high-resolution photoabsorption using synchrotron radiation from the SX700/II monochromator at BESSY. The spectra contain signals from excitations to C 1${\mathit{s}}^{\mathrm{\ensuremath{-}}1}$np Rydberg states and their vibrational substates, as well as from transitions to C 1${\mathit{s}}^{\mathrm{\ensuremath{-}}1}$ns Rydberg states. The latter excitation is dipole forbidden in methane, but rendered possible by strong vibronic coupling. Transitions to vibrational substates could be identified via the observed isotope effects. The C 1${\mathit{s}}^{\mathrm{\ensuremath{-}}1}$np Rydberg states were found to be split by a Jahn-Teller effect or by molecular-field interaction. C-H and C-C equilibrium distances as well as vibrational frequencies in the core-excited molecular states were derived within the Franck-Condon model from the vibrational fine structures of the C 1${\mathit{s}}^{\mathrm{\ensuremath{-}}1}$3p Rydberg excitations.

Origin of the multiple fluorescence emission of unsymmetrical squaraines

Multiple fluorescence emission bands are observed for unsymmetrical squaraines, a class of unsymmetrical donor-acceptor-donor molecules, in organic solvents at room temperature and are shown to be vibrational fine structures of the emissions of the excited states of the unsymmetrical squaraine and its solute-solvent complex.

Darstellung, Reaktionen und spektroskopische Charakterisierung von [Os2X8]2-, X = Cl, Br, I, und Kristallstruktur von (PPN)2[Os2I8] · 2 CH2Cl2 / Preparation, Reactions and Spectroscopic Characterization of [Os2X8]2-, X = Cl, Br, I, and Crystal Structure of (PPN)2[Os2I8] · 2 CH2Cl2

The triply bonded octahalogenodiosmate(III) anions [Os2X8]2-, previously known with X = Cl, Br, have now been extended to include the iodide with two staggered OsI4 units. This compound was prepared by treating [Os2Cl8]2- with Nal at room temperature in acetone solution. The structure determination by X-ray diffractometry on single crystals of (PPN)2[Os2I8] · 2 CH2Cl2, reveals crystallization in the monoclinic system, space group P21/c with Z = 4. The Os-Os triple bond is with 2.212(1) Å the longest within the three octahalogenodiosmates(III). The Raman spectra show ν(OsOs) at 285, [Os2Cl8]2-; at 287, [Os2Br8]2- and for the iodo compound at 270.1 cm-1 with up to three overtones. The spectroscopic constants are calculated to be ω1 = 270.9 cm-1; X11 = -0.50 cm-1. The 10 Κ UV-VIS spectra of solid [(n-C4H9)4N]2[Os2X8] exhibit δ-π* transitions with maxima at 723, 690 and 643 nm, superimposed by vibrational fine structures with long progressions of 195, 211 and 183 cm-1 for X = Cl, Br, I, respectively. Oxidation of [Os2X8]2-, X = Cl, Br with the corresponding halogen leads to the cleavage of the Os-Os bond, and the dekahalogenodiosmates(IV), [Os2X10]2-, are formed

Luminescence of Ce 3+-doped aluminoborates, M 3Al 6B 8O 24 (M = Mg, Ca, Sr, Ba)

Newer dielectric materials doped with appropriate impurities are often sought for tunable blue laser applications. Thus, the luminescence properties of Ce 3+ in the novel ternary borates, M 3Al 6B 8O 24 (M = Mg, Ca, Sr, Ba) have been investigated. The single excitation band centred around 310 nm and the broad emission band maximising around 400 nm are devoid of the characteristic Ce 3+ doublet and the vibrational fine structures, even at low temperatures. These luminescence features are due to the extensive crystal-field splitting of the 4f ground state. The large Stokes shift of ∼7000 cm −1 and the half-band-widths are influenced by M 2+ ions.

Validity of Franck—Condon analysis procedures for deduction of excited state and ionic geometries I. The X2Π and A2Σ + states of N 2O

Three Franck—Condon analysis procedures, namely the generating function method, the method of Coon et al. and the Duschinsky matrix method were applied to vibrational fine structures observed in the photoelectron bands of N 2O. The ionic geometries thus deduced for the X 2Π and A 2Σ + states of N 2O are in good agreement with experimental data. Criteria for the determination of signs for changes in bond lengths have been studied. Furthermore, the Duschinsky effect on vibrational intensity distributions accompanying electronic transitions are discussed in detail.