ABSTRACT
The inclusion of explicit polarization in molecular dynamics simulation has gained increasing interest during the last several years. An understudied area is the role of polarizability in computer simulations of solvation dynamics around chromophores, particularly for the large solutes used in experimental studies. In this work, we present fully polarizable ground and excited state force fields for the common fluorophores N-methyl-6-oxyquinolium betaine and Coumarin 153. While analyzing the solvation responses in water, methanol, and the highly viscous ionic liquid 1-ethyl-3-methylimidazolium trifluoromethanesulfonate we found that the inclusion of solute polarizability considerably increases the agreement of the obtained Stokes shift relaxation functions with experimental data. Solute polarizability slows down the inertial solvation response in the femtosecond time regime and enables the chromophore to adapt its dipole moment to the environment. Furthermore, the developed chromophore force field reproduces the solute dipole moments in both the electronic ground and excited state in environments ranging from gas phase to highly polar media correctly. Based on these studies it is anticipated that polarizable models of chromophores will lead to an improved understanding of the relationship of their environment to their spectroscopic properties.
ABSTRACT
The local changes in protein hydration dynamics upon encapsulation of the protein or macromolecular crowding are essential to understand protein function in cellular environments. We were able to obtain a spatially-resolved picture of the influence of confinement and crowding on the hydration dynamics of the protein ubiquitin by analyzing the time-dependent Stokes shift (TDSS), as well as the intermolecular Nuclear Overhauser Effect (NOE) at different sites of the protein by large-scale computer simulation of single and multiple proteins in water and confined in reverse micelles. Besides high advanced space resolved information on hydration dynamics we found a strong correlation of the change in NOE upon crowding or encapsulation and the change in the integral TDSS relaxation times in all investigated systems relative to the signals in a diluted protein solution.
ABSTRACT
Multivariate curve resolution methods aim at recovering the underlying chemical components from spectroscopic data on chemical reaction systems. In most cases the spectra and concentration profiles of the pure components cannot be uniquely determined from the given spectral data. Instead continua of possible factors exist. This fact is known as rotational ambiguity. The sets of all possible pure component factors can be represented in the so-called area of feasible solutions (AFS). This paper presents an AFS study of the pure component reconstruction problem for a series of UV/Vis spectra taken from an acid-base titration of N-methyl-6-oxyquinolone. Additional information on the equilibrium concentration profiles for a varying acid concentration is taken from fluorescence measurements. On this basis chemometric duality arguments lead to the construction of a unique final solution.
ABSTRACT
We developed a procedure to use the highly sensitive dye N-methyl-6-oxyquinolone as an acidity probe in molecular solvents and protic ionic liquids. The combination of well-established stationary UV-vis absorption and the mathematical algorithm of singular value decomposition allows the determination of the amount of acidic protons even in complex solvents like ionic liquids.
ABSTRACT
We have incorporated the dye N-methyl-6-oxyquinolone [6MQz] in its protonated form as a cation into an ionic liquid (IL) and thus to synthesize an IL dye. The IL dye N-methyl-6-hydroxyquinolinium bis(trifluoromethylsulfonyl) imide [6MQc][NTf2 ] was characterized by NMR, ATR IR spectroscopy and X-ray crystallography. The fluorescence of the IL dye has a large Stokes shift of Δλ=116â nm and a quantum yield of φF =0.56 in acetonitrile. Characteristic solvent dependent shifts can be detected in the emission spectra. In other ILs, acetonitrile and THF we observe a bathochromic shift of up to 28â nm compared to the pure IL dye at 467â nm. For stronger polar solvents the fluorescence signals are strongly red-shifted to 650â nm indicating proton transfer to the solvent molecules in the excited state. This underlines the importance of the IL building block [MQc]+ as photo acid.
