Raman spectroscopic study of polar aprotic molecule and its molecular associations with chemical and isotopic solvents: Comparative study with quantum-chemical calculations

Electrochemical Behavior of Symmetric Electrical Double-Layer Capacitors and Pseudocapacitors and Identification of Transport Anomalies in the Interconnected Ionic and Electronic Phases Using the Impedance Technique

A double-channel transmission line impedance model was applied to the study of supercapacitors to investigate the charge transport characteristics in the ionic and electronic conductors forming the electrode/solution interface. The macro homogeneous description of two closely mixed phases (Paasch-Micka-Gersdorf model) was applied to study the influence of disordered materials on the charge transport anomalies during the interfacial charge-discharge process. Different ex situ techniques were used to characterize the electrode materials used in electrical double-layer (EDLC) and pseudocapacitor (PC) devices. Two time constants in the impedance model were adequate to represent the charge transport in the different phases. The interfacial impedance considering frequency dispersion and blocked charge transfer conditions adequately described the charge storage at the interface. Deviations from the normal (Fickian) transport involving the ionic and electronic charge carriers were identified by the dispersive parameters (e.g., n and s exponents) used in the impedance model. The ionic and electronic transports were affected when the carbon-based electrical double-layer capacitor was converted into a composite with strong pseudocapacitive characteristics after the decoration process using NiO. The overall capacitance increased from 2.62 F g-1 to 536 F g-1 after the decoration. For the first time, the charge transport anomalies were unequivocally identified in porous materials used in supercapacitors with the impedance technique.

Phase transition-induced changes in the Raman properties of DMSO/benzene binary systems

The Raman spectra of dimethylsulfoxide (DMSO)/benzene binary mixtures were studied by decreasing the temperature from 333 K to 263 K with the aim to reveal the molecular interaction properties during phase transition. The intensity of the Raman band for benzene at 992 cm-1 showed an increasing trend in the liquid and solid phases, while it exhibited a highly decreasing trend during the liquid-solid phase transition. The potential energy was calculated to study the effect of intermolecular interaction distance between DMSO and benzene on Raman intensity. The observations indicated that the blueshift of the low-frequency bands of DMSO was significantly different from the redshift of its high-frequency bands. The hydrogen bond generated between DMSO and benzene was well formed in the binary systems. This interaction inducing an enhanced hydrogen bond between the binary systems and attenuated C-H bonds led to opposite Raman shift variations with decreasing temperature. The Raman bands of DMSO at 1425 cm-1, 2899 cm-1, and 2992 cm-1 each split into two peaks after phase transition. The splitting of the Raman bands of DMSO at 1417 cm-1, 2895 cm-1, and 2982 cm-1 cropped up as the temperature dropped to the transformation point of 288 K. This is attributed to the phase transition-induced latent def.(C7) atomic vibrations corresponding to the individual methyl groups of DMSO. The implications of these analyses are expected to be helpful to understand the effect of phase transition on the Raman properties of binary solutions.

Vibrational Relaxation of the Backbone and Base Modes in LacDNA Complexes by UV Resonance Raman Spectroscopy

Vibrational band shape analysis through time correlation function concept is widely used to obtain experimental information on the molecular dynamics of medium-size molecules in different environments. Interesting details are revealed by extending this technique to biomolecules such as functional groups of the nucleic acids in media approaching the physiological conditions. In this work a study into the UV resonance Raman (UVRR) vibrational half bandwidths of functional groups in LacDNA, upon lowering the pH (pH 6.4, pH 3.45) and in the presence of Mn²⁺ and Ca²⁺ ions, respectively, was of interest. The corresponding global relaxation times have been derived. Also, the 793 cm^-1 UVRR band, corresponding to ν (backbone O-P-O, dT) oscillator of LacDNA in aqueous solutions, was selected for band shape-analysis. Vibrational relaxation appears as the dominant relaxation process for this mode, with vibrational dephasing being the most efficient for this oscillator. Current theories developed for vibrational dephasing have been applied to this profile, and relevant relaxation parameters have been obtained and discussed. To our knowledge this is the first study on DNA oligomers vibrational band shape analysis through time correlation function concept.