Spectroscopic studies of solute–solvent interactions

Rao, C. N. R.; Singh, Samrendra; Senthilnathan, V. P.

doi:10.1039/cs9760500297

Cited by 79 publications

(41 citation statements)

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“…[36,37] Taking matrix effects due to changes in Dn into account (see Table 2), only a small increase in Dt F by up to 12 % and a reduction in Dl by up to 14 % is expected. Thus, a net effect of Dt F = À22 ps and Dl = 1.25 nm can be unambiguously attributed to force.…”

Section: Overall Discussionmentioning

confidence: 94%

Fluorophores as Optical Sensors for Local Forces

et al. 2009

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The main aim of this study is to investigate correlations between the impact of an external mechanical force on the molecular framework of fluorophores and the resultant changes in their fluorescence properties. Taking into account previous theoretical studies, we designed a suitable custom-tailored oligoparaphenylenevinylene derivative (OPV5) with a twisted molecular backbone. Thin foils made of PVC doped with 100 nM OPV were prepared. By applying uniaxial force, the foils were stretched and three major optical effects were observed simultaneously. First, the fluorescence anisotropy increased, which indicates a reorientation of the fluorophores within the matrix. Second, the fluorescence lifetime decreased by approximately 2.5% (25 ps). Finally, we observed an increase in the emission energy of about 0.2% (corresponding to a blue-shift of 1.2 nm). In addition, analogous measurements with Rhodamine 123 as an inert reference dye showed only minor effects, which can be attributed to matrix effects due to refractive index changes. To relate the observed spectroscopic changes to the underlying changes in molecular properties, quantum-chemical calculations were also performed. Semiempirical methods had to be used because of the size of the OPV5 chromophore. Two conformers of OPV5 (C(2) and C(i) symmetry) were considered and both gave very similar results. Both the observed blue-shift of fluorescence and the reduced lifetime of OPV5 under tensile stress are consistent with the results of the semiempirical calculations. Our study proves the feasibility of fluorescence-based local force probes for polymers under tension. Improved optical sensors of this type should in principle be able to monitor local mechanical stress in transparent samples down to the single-molecule level, which harbors promising applications in polymer science and nanotechnology.

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Section: Overall Discussionmentioning

confidence: 94%

Fluorophores as Optical Sensors for Local Forces

et al. 2009

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“…An approximately linear dependence of the C-D stretching frequency on solvent dielectric was immediately apparent. Correspondingly, the data are not well fit by models that predict a nonlinear relationship between frequency and the dielectric constant or refractive index of the solvent, including the KBM equation, the modified KBM equation, or the Buckingham equation 42,43 (Supporting Information). In addition, no correlation was found with Gutmann's solvent acceptor numbers, 44 as is found for other IR probes, such as cyano groups 32,34 A linear least square fit was performed using the program Origin (squared correlation coefficient = 0.94 for all of the data and 0.98 when limited to just the free amino acid) and a t-test at the 95% confidence level shows the linear correlation to be significant (t value of 35 compared to a critical value of ~2 45 ).…”

Section: Resultsmentioning

confidence: 99%

Carbon−Deuterium Bonds as Probes of Dihydrofolate Reductase

2008

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Much effort has been directed towards understanding the contributions of electrostatics and dynamics to protein function and especially to enzyme catalysis. Unfortunately, these studies have been limited by the absence of direct experimental probes. We have been developing the use of carbon-deuterium bonds as probes of proteins and now report the application of the technique to the enzyme dihydrofolate reductase, which catalyzes a hydride transfer and has served as a paradigm for biological catalysis. We observe that the stretching absorption frequency of (methyl-d 3 ) methionine carbon-deuterium bonds show an approximately linear dependence on solvent dielectric. Solvent and computational studies support the empirical interpretation of the stretching frequency in terms of local polarity. To begin to explore the use of this technique to study enzyme function and mechanism, we report a preliminary analysis of (methyl-d 3 ) methionine residues within dihydrofolate reductase. Specifically, we characterize the IR absorptions at Met16 and Met20, within the catalytically important Met20 loop, and Met42, which is located within the hydrophobic core of the enzyme. The results confirm the sensitivity of the carbon-deuterium bonds to their local protein environment, demonstrate that dihydrofolate reductase is electrostatically and dynamically heterogeneous, and lay the foundation for the direct characterization protein electrostatics and dynamics, and potentially, their contribution to catalysis.

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“…The dependence of (Jco)">m on the £(co"m) or n2 i w nm) i n Eq. (19) can, for all practical purposes, be replaced by £(0) or nv 2 . This would simplify correlation of experimentally observed solvent shifts of the spectra of non-polar molecules in non-polar solvents.…”

Section: -«Vacuum (B V'; Co)]f (V'-r)mentioning

confidence: 99%

Theory of Dispersion Energy and Solvent Effects on Molecular Spectra

Mahanty

Rao

1976

Zeitschrift Für Naturforschung A

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The theory of dispersion energy has been shown to directly give an explicit expression for the solvent shifts in the spectra of non-polar solute molecules.Solvent effects on the spectra of molecules arise from various interactions between the solute and solvent molecules 2 . Dispersion effects are primarily responsible for the influence of non-polar solvents on the spectra of non-polar solutes and can in the simplest form be regarded as arising from London dipole interactions. Such effects on spectra are generally discussed in the literature 2 in terms of Onsager's reaction field. In this paper we analyze solvent effects on spectra from the viewpoint of the dispersion energy 3 of the solute molecule in the solvent medium and show that in this way an explicit relation for solvent-induced spectral shifts similar to that obtained from perturbation theory can be derived. The MethodThe dispersion energy of a molecule arises from the change in the energy of the electromagnetic field due to the presence of the molecule. If we consider a fluctuating dipole moment p (co) on the molecule located at R, the electric field due to that can be written as e(r,co)=4nG(r,R;oj)p(oj)where 4aG(r, R; co) is the diadic Green's function giving the electric field at V with a unit dipole source at R. The dipole moment of the molecule can be considered as being due to the same field at R, i. e., p(co) =a(

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Spectroscopic studies of solute–solvent interactions

Cited by 79 publications

References 0 publications

Fluorophores as Optical Sensors for Local Forces

Fluorophores as Optical Sensors for Local Forces

Carbon−Deuterium Bonds as Probes of Dihydrofolate Reductase

Theory of Dispersion Energy and Solvent Effects on Molecular Spectra

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