Chromophores, absorption spectra

One aspect of the research will examine equilibrium aspects of solvation at hydro-phobic and hydrophilic interfaces. In these experiments, solvent dependent shifts in chromophore absorption spectra will be used to infer interfacial polarity. Preliminary results from these studies are presented. The polarity of solid-liquid interfaces arises from a complicated balance of anisotropic, intermolecular forces. It is hoped that results from these studies can aid in developing a general, predictive understanding of dielectric properties in inhomogeneous environments. 

However, low-temperature spectroscopy reveals that the chromophore absorption spectrum is heterogeneously broadened, and Frauenfelder has shown that there is a functional link between the spectral line position and the recombination rate. Agmon and Hopfield pointed out that the protein myoglobin is photolyzed into a strained configuration and must undergo conformational relaxation to reach the true deoxy configuration, and that the recombination rate is slowest in the fully relaxed deoxy... 

In Pedersen s early experiments, the relative binding of cations by crown ethers was assessed by extraction of alkali metal picrates into an organic phase. In these experiments, the crown ether served to draw into the organic phase a colored molecule which was ordinarily insoluble in this medium. An extension and elaboration of this notion has been developed by Dix and Vdgtle and Nakamura, Takagi, and Ueno In efforts by both of these groups, crown ether molecules were appended to chromophoric or colored residues. Ion-selective extraction and interaction with the crown and/or chromophore could produce changes in the absorption spectrum. Examples of molecules so constructed are illustrated below as 7 7 and 18 from refs. 32 and 131, respectively. 

The photoprotein is non-fluorescent. The absorption spectrum of purified photoprotein shows a very small peak at 410 nm, in addition to the protein peak at 280 nm (Fig. 10.2.5). The peak height at 410 nm appears to be proportional to the luminescence activity of the protein. The protein also shows extremely weak absorption peaks at about 497, 550 and 587nm (not shown). These absorption peaks, except the 280 nm peak, might be due to the presence of a chromophore that is functional in the light emission. 

The absorption and fluorescence spectra of a neat film made of RdB-den-drimer are shown in Fig. 2. The absorption spectrum in visible-wavelength region was similar to that obtained from a solution of RdB with a concentration less than 0.1 mmol/1. Interpretation of the fluorescence in terms of the Frank-Condon mechanism indicated that the core RdB chromophore behaved with a site-isolation effect and had little interaction with the neighboring chro-... 

A method suitable for quantification of the functional class of bis(ethanol)amine antistatics, which lack UV chromophores, consists of reaction with methyl orange [53]. Atmer 163 (alkyl-diethanol amine) has been determined as a yellow complex at 415 nm after interaction with a bromophenol/cresole mixture [64]. Hilton [65] coupled extracted phenolic antioxidants with diazotised p-nitroaniline in strongly acidic medium and carried out identification on the basis of the visible absorption spectrum in alkaline solution. The antioxidant Nonox Cl in... 

Of experimental methods for studying the metal in enzymes, light absorption in the visible region from molybdenum chromophores is likely to be weak and frequently masked by stronger absorption from other enzyme constituents. Indeed only recently has a small molybdenum contribution to the absorption spectrum of even the most studied of these enzymes, xanthine oxidase, been demonstrated 33, see Section V F). 

Another possible source of modification of the HBI optical properties arises from cis-trans (or, more properly, Z-E) isomerization around its exocyclic ethylene bridge (dihedral angle x as depicted in Fig. 3a) [74, 75]. The absorption spectrum of trans HBI in different solvents is red-shifted by 5-10 nm compared to that of the cis conformation [76]. While the trans conformation is thermodynamically unfavorable and contributes only a minor population at room temperature, cis-trans isomerization seems to take place regardless of the chromophore ionization state, and involves a relatively low energy barrier of about 50 kJ/mol [75], a value that appears significantly lower than initially predicted from quantum mechanics [77, 78]. 

The absorption spectrum of folded AvGFP in the visible region displays two well-separated peaks at 395 nm and 475 nm, whose relative intensity depends on pH (Fig. 4b). The chromophore states associated to these two peaks have been termed, respectively, A and B [81]. Although this has been initially debated [78, 82, 83], accumulated spectroscopic and theoretical evidences indicate that these two absorption bands, respectively, arise from the neutral (A) and anionic (B) forms of the HBI chromophore [10, 11, 69-71, 84-87]. 

Voityuk AA, MichelBeyerle ME, Rosch N (1997) Protonation effects on the chromophore of green fluorescent protein. Quantum chemical study of the absorption spectrum. Chem Phys... 

FRET is a nonradiative process that is, the transfer takes place without the emission or absorption of a photon. And yet, the transition dipoles, which are central to the mechanism by which the ground and excited states are coupled, are conspicuously present in the expression for the rate of transfer. For instance, the fluorescence quantum yield and fluorescence spectrum of the donor and the absorption spectrum of the acceptor are part of the overlap integral in the Forster rate expression, Eq. (1.2). These spectroscopic transitions are usually associated with the emission and absorption of a photon. These dipole matrix elements in the quantum mechanical expression for the rate of FRET are the same matrix elements as found for the interaction of a propagating EM field with the chromophores. However, the origin of the EM perturbation driving the energy transfer and the spectroscopic transitions are quite different. The source of this interaction term... 

The pyrene-like aromatic chromophore of BaPDE is characterized by a prominent and characteristic absorption spectrum in the A 310-360 nm spectral region, and a fluorescence emission in the X 370-460 nm range. These properties are sensitive to the local microenvironment of the pyrenyl chromophore, and spectroscopic techniques are thus useful in studies of the structures of the DNA adducts and in monitoring the reaction pathways of BaPDE and its hydrolysis products in DNA solutions. 

We give here only a brief summary of the electronic absorption spectrum of the diene chromophore which has been extensively treated by Gross and Schnepp5 with reference to a- and /1-phellandrene. 

Fig. 2.11 Absorption spectrum of a DH6/PMMA thin film after it is exposed to DNT vapor at 65°C for various periods of time. The peak at about 630 nm is the characteristic absorption peak of the chromophore. Reprinted from Ref. 33 with permission. 2008 American Chemical Society...

Figure 15. Temperature dependence of absorption spectrum of the viologen bilayer membrane having biphenyl chromophore, CnBphCfV 2Br in water.

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