Vibrational Relaxation in EDTA Is Ion-Dependent

Ion binding by carboxylate groups is common in biomolecules such as metalloproteins, but dynamical aspects of ion binding are not fully understood. We present ultrafast spectroscopic measurements of vibrational relaxation in the ion-coordinating carboxylate groups of EDTA, which we use as a model of carboxylate-mediated ion binding, as EDTA binds a series of divalent and trivalent metal ions with high affinity. The measurements are interpreted using a Redfield-based anharmonic model of vibrational relaxation that rationalizes trends in vibrational lifetimes in terms of vibrational energy transfer between EDTA’s asymmetric carboxylate stretching vibrational modes and lower-lying modes. Results show ion-dependent changes in complex structure and dynamics well outside the temporal and spatial resolution of common structural methods and demonstrate how vibrational relaxation measurements may contribute to exploration of ion-binding dynamics on ultrashort length and time scales

An Empirical IR Frequency Map for Ester CO Stretching Vibrations

We present an approach for parametrizing spectroscopic maps of carbonyl groups against experimental IR absorption spectra. The model correlates electric fields sampled from molecular dynamics simulations with vibrational frequencies and line shapes in different solvents. We perform an exhaustive search of parameter combinations and optimize the parameter values for the ester carbonyl stretching mode in ethyl acetate by comparing to experimental FTIR spectra of the small molecule in eight different solvents of varying polarities. Hydrogen-bonding solvents require that the peaks are fit independently for each hydrogen bond ensemble to compensate for improper sampling in molecular dynamics simulations. Spectra simulated using the optimized electrostatic map reproduce CO IR absorption spectra of ethyl acetate with a line center RMSD error of 4.9 cm^–1 over 12 different solvents whose measured line centers span a 45 cm^–1 range. In combination with molecular dynamics simulations, this spectroscopic map will be useful in interpreting spectra of ester groups in heterogeneous environments such as lipid membranes

A study of stabilization of P3HT/PCBM organic solar cells by photochemical active TiOx layer

We describe a study of the stabilization behavior of P3HT/PCBM organic solar cells under air and UV irradiation using a 20 nm thin TiOx protection layer made by partial hydrolysis of a Ti-alkoxide and spin coating in air. Data on the degradation of solar cell performance under air and under UV exposure are presented indicating that significant improvements are observed with TiOx layer protection. The protection mechanism has been investigated by transmission IR and UV spectroscopy and by ESR spectroscopy. The results of this study suggest how sol–gel derived TiOx films containing organic functionalities serve as effective passivation films for protection from oxygen when excited by photons, where the photooxidation of the bound organic moieties causes oxygen gas scavenging