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Spectral Shift (spectral + shift)
Selected AbstractsMulticolor Emission on Prepatterned Substrates Using a Single Dye Species,ADVANCED MATERIALS, Issue 16 2007W. Hu A new strategy for realizing patterned surfaces with different emission colors is demonstrated. This approach relies on the gas-phase deposition of dye molecules onto solid substrates that are prepatterned by nanoimprint lithography (see figure). Only a single molecular species is involved. Thus, the observed color change and corresponding spectral shift in the emission properties depends on the substrate used and can be tuned by surface engineering. [source] Glu 87 of Channelrhodopsin-1 Causes pH-dependent Color Tuning and Fast Photocurrent Inactivation,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2009Satoshi P. Tsunoda Channelrhodopsins (ChR1 and ChR2) are directly light-gated ion channels acting as sensory photoreceptors in the green alga Chlamydomonas reinhardtii. These channels open rapidly after light absorption and both become permeable for cations such as H+, Li+, Na+, K+ and Ca2+. Km for Ca2+ is 16.6 mm in ChR1 and 18.3 mm in ChR2 whereas the Km values for Na+ are higher than 100 mm for both ChRs. Action spectra of ChR1 peak between 470 and 500 nm depending on the pH conditions, whereas ChR2 peaks at 470 nm regardless of the pH value. Now we created two chimeric ChRs possessing helix 1,5 of ChR1 and 6, 7 of ChR2 (ChR1/25/2), or 1, 2 from ChR1 and 3,7 from ChR2 (ChR1/22/5). Both ChR-chimera still showed pH-dependent action spectra shifts. Finally, a mutant ChR1E87Q was generated that inactivated only slowly in the light and showed no spectral shift upon pH change. The results indicate that protonation/deprotonation of E87 in helix 1 alters the chromophore polarity, which shifts the absorption and modifies channel inactivation accordingly. We propose a trimodal counter ion complex for ChR1 but only a bimodal complex for ChR2. [source] Systematic Investigation of Molecular Arrangements and Solid-State Fluorescence Properties on Salts of Anthracene-2,6-disulfonic Acid with Aliphatic Primary AminesCHEMISTRY - A EUROPEAN JOURNAL, Issue 33 2009Yuji Mizobe Dr. Abstract Organic salts of anthracene-2,6-disulfonic acid (ADS) with a wide variety of primary amines have been fabricated, and their arrangements of anthracene molecules and solid-state fluorescence properties investigated. Single-crystal X-ray studies reveal that the salts show seven types of crystal forms and corresponding molecular arrangements of anthracene moieties depending on the amine, while anthracene shows only one form and arrangement in the solid state. Depending on the molecular arrangements, the ADS salts exhibit various solid-state fluorescence properties: spectral shift (30,nm) and suppression and enhancement of the fluorescence intensity. Especially the ADS salt with n -heptylamine (nHepA), which shows discrete anthracene moieties in the crystal, exhibits the highest quantum yield (,F=46.1±0.2,%) in the series of ADS salts, which exceeds that of anthracene crystal (,F=42.9±0.2,%). From these systematic investigations on the arrangements and the solid-state properties, the following factors are essential for high fluorescence quantum yield in the solid state: prevention of contact between , planes of anthracene moieties and immobilization of anthracene rings. In addition, such organic salts have potential as a system for modulating the molecular arrangements of fluorophores and the concomitant solid-state properties. Thus, systematic investigation of this system constructs a library of arrangements and properties, and the library leads to remarkable strategies for the development of organic solid materials. [source] Structural Identification of Spectroscopic Substates in NeuroglobinCHEMPHYSCHEM, Issue 1 2010Karin Nienhaus Dr. Abstract The structural origins of infrared absorptions of photodissociated CO in murine neuroglobin (Ngb) are determined by combining Fourier transform infrared (FTIR) spectroscopy and molecular dynamics (MD) simulations. Such an approach allows to identify and characterize both the different conformations of the Ngb active site and the transient ligand docking sites. To capture the influence of the protein environment on the spectroscopy and dynamics, experiments and simulations are carried out for the wild type protein and its F28L and F28W mutants. It is found that a voluminous side chain at position 28 divides site B into two subsites, B' and B". At low temperatures, CO in wt Ngb only migrates to site B' from where it can rebind, and B" is not populated. The spectra of CO in site B' for wt Ngb from simulations and experiments are very similar in spectral shift and shape. They both show doublets, red-shifted with respect to gas-phase CO and split by,8 cm,1. The FTIR spectra of the F28L mutant show additional bands which are also found in the simulations and can be attributed to CO located in substate B". The different bands are mainly related to different orientations of the His64 side chain with respect to the CO ligand. Large red-shifts arise from strong interactions between the HistidineNH and the CO oxygen. After dissociation from the heme iron, the CO ligand visits multiple docking sites. The locations of the primary docking site B and a secondary site C, which corresponds to the Mb Xe4 cavity, could be identified unambiguously. Finally, by comparing experiment and simulations it is also possible to identify protonation of its , position (His,64 NgbCO) as the preferred heme-bound conformation in the wild type protein with a signal at 1935 cm,1. [source] Self-association of cromolyn sodium in aqueous solution characterized by nuclear magnetic resonance spectroscopyJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 5 2004Xuan Ding Abstract The major objective of this study was to investigate and characterize the solution properties of cromolyn sodium (in D2O or D2O/H2O phosphate buffer at pH 7.5) using nuclear magnetic resonance (NMR) spectroscopy. The self-association of cromolyn molecules was examined primarily via one-dimensional 1H and 13C, and two-dimensional homonuclear NOESY NMR. Significant spectral shifts were observed for a majority of cromolyn 1H and 13C resonances, and are attributed to inter-molecular ring-stacking association accompanied by intra-molecular conformational changes. The critical self-association concentration was determined to be 10 mg/mL at pH 7.5 and 25°C by measuring the chemical shift of a specific cromolyn 1H resonance. The observed magnitude and sign changes of NOESY correlations indicate the formation of cromolyn aggregates with restricted molecular mobility. Mesomorphic liquid crystal formation is suggested by uniformly pronounced line broadening in concentrated cromolyn solutions; the transition concentration was approximately 60 mg/mL at 25°C, which is consistent with literature findings based on other techniques. A stronger tendency toward association was observed at lower temperature but aggregation appeared to be independent of pH. Lastly, it was concluded that self-association of cromolyn is promoted by the presence of monovalent cations as a result of reduced electrostatic repulsive forces. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:1351,1358, 2004 [source] Ultraviolet Absorption Spectra of Substituted Phenols: A Computational Study,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2006Lei Zhang ABSTRACT Vertical excitation energies for electronic transitions from the ground state to the first two excited states of phenol, mono- and disubstituted methoxyphenols and methyl-substituted phenols have been characterized with the Time-Dependent Density Functional Theory (TD-DFT), the Complete Active Space Self-Consistent Field method (CASSCF) and the Coupled Cluster with Single and Double Excitations Equation-of-Motion approach (CCSD-EOM) to simulate and interpret experimental ultraviolet absorption spectra. While CASSCF excitation energies for the first two transitions either are grossly overestimated or exhibit a weak correlation with experimental data, both TD-DFT and CCSD-EOM perform very well, reproducing the spectral shifts of both the primary band and secondary band observed upon substitution. The conformational dependence of the calculated excitation energies is generally smaller than the shifts caused by substitution. [source] On Spectral Relaxation in Proteins,,§PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2000Joseph R. Lakowicz ABSTRACT During the past several years there has been debate about the origins of nonexponential intensity decays of intrinsic tryptophan (trp) fluorescence of proteins, especially for single tryptophan proteins (STP). In this review we summarize the data from diverse sources suggesting that time-dependent spectral relaxation is a ubiquitous feature of protein fluorescence. For most proteins, the observations from numerous laboratories have shown that for trp residues in proteins (1) the mean decay times increase with increasing observation wavelength; (2) decay associated spectra generally show longer decay times for the longer wavelength components; and (3) collisional quenching of proteins usually results in emission spectral shifts to shorter wavelengths. Additional evidence for spectral relaxation comes from the time-resolved emission spectra that usually shows time-dependent shifts to longer wavelengths. These overall observations are consistent with spectral relaxation in proteins occurring on a subnanosecond timescale. These results suggest that spectral relaxation is a significant if not dominant source of nonexponential decay in STP, and should be considered in any interpretation of nonexponential decay of intrinsic protein fluorescence. [source] 18O Isotope Substitution, Vibrational Coupling and Protein Structure: A Theoretical ApproachCHEMPHYSCHEM, Issue 2 2004Thorsten Koslowski Prof. Dr. Site-specific 18O substitution of two amino acids that are in a close spatial vicinity, but far apart in the primary sequence, exhibits characteristic IR fingerprints; the corresponding spectral shifts of the absorption bands are shown color-coded in the figure. This approach can be used to obtain detailed structural information, for example, about membrane proteins which are difficult to crystallize. [source] | ||||||||||