Solute–Solvent Hydrogen Bond Formation in the Excited State. Experimental and Theoretical Evidence

Abstract

Hydrogen bonds (H-bonds) are of great importance in biological systems, as they are responsible for the secondary structure of proteins and nucleic acids and are also involved in the mechanisms of enzyme catalysis. Supramolecular chemistry makes use of H-bonds in building up novel compounds of various architectures.The identification of these interactions and the analysis of their influence on the photophysical properties are also important in designing new fluorophores for different applications, the processes involved being rather complex in nature and often only partially understood.The main feature reflecting H-bond interaction in both the ground and excited states is the solvatochromic effect on the absorption and fluorescence spectra. This implies that changes in the solvent nature or composition produce shifts in the position, shape and intensity of the spectral bands. The source of solvatochromic shifts is the different solvation of the ground and excited states: depending on the relative stabilization of these states by solvents, bathochromic (positive)or hypsochromic (negative)shifts of the maximum of the band can be observed experimentally. Thus, such changes are indicative of the interactions occurring between the solute and the solvent in its immediate vicinity. The solute-solvent interactions are classified into:1. non-specific interactions caused by polarity/polarizability effects; 2. specific interactions, such as H-bonds.

Studies of the solvatochromic emission properties of N-aroylurea derivatives II: influence of hydrogen-bonding interactions

“…7,35 This assumption is in agreement with the increasing red-shift of the emission maximum of the derivatives 2a-d with increasing AN or SA value of the solvent, which is characteristic of molecules that form H-bonds in the excited state. 36 In addition, the dependence of the emission properties of 2a-d on the temperature and on the viscosity of the solvent provides further evidence that conformational changes and solvent relaxation are involved in excited-state processes of these compounds. Firstly, the increasing fluorescence quantum yields of the aroylurea derivatives 2b-d with increasing viscosity of the glycerol solution (Fig.…”

Deciphering Spectroscopic and Structural Insights into the Photophysical Behavior of 2,2′-Dipyridylamine: An Efficient Environment Sensitive Fluorescence Probe

“…This is because the polar protic solvents like water can interact with the heterocyclic organic compounds either through hydrogen bond donation acidity (HBD) or hydrogen bond acceptance basicity (HBA) (typically defined by the parameters α and β, respectively). 26 Under these situations even the uniparametric scale E T (30) the large negative absorption of Betaine dye in hydrogen bond donor solvents, is no longer applicable to quantify the specific solvent effect. Multiparametric linear solvation energy relationship (LSER)originally developed by Kamlet, Taft, and coworkers 28 takes into account of the nonspecific interaction term due to solvent dipolarity/polarizability (π*) along with the specific solvent contributors like α and β (with their contribution as s, a, and b, respectively) to interpret the modulation of a spectroscopic property (P) from its corresponding value in the gas phase (P 0 ) through the following relation:…”

“…However, in the presence of specific solvent interaction with the fluorophores, the situation becomes more complex and needs careful data handling. This is because the polar protic solvents like water can interact with the heterocyclic organic compounds either through hydrogen bond donation acidity (HBD) or hydrogen bond acceptance basicity (HBA) (typically defined by the parameters α and β, respectively) . Under these situations even the uniparametric scale E T (30),developed by Dimroth and Reichard based on the large negative absorption of Betaine dye in hydrogen bond donor solvents, is no longer applicable to quantify the specific solvent effect.…”

In‐depth insight into the methods of plasma protein‐drug interaction studies: Comparison of capillary electrophoresis‐frontal analysis, isothermal titration calorimetry, circular dichroism and equilibrium dialysis

“…The K bi was determined by adjusting the experimental data using nonlinear regression (with MS Excel) according to the following Eq. : where Δθ is the ellipticity change due to complex formation (absolute value) and k = 32982.1 · Δε · l ( Δε is the extrinsic molar circular dichroic absorption coefficient of the drug bound to HSA in M –1 cm –1 and l is the path length in cm).…”