The solvation dynamics for deoxygenated and oxygenated Vaska's complex, bis(triphenylphosphene) iridium(I) carbonyl chloride, (deoxy-VC and oxy-VC) were characterized using twodimensional infrared (2D-IR) spectroscopy in d 6 -benzene, chloroform, and DMF. The iridium-bound carbonyl was used as a probe of the static and dynamic chemical environments in each solvent system. The linear IR spectra of the complexes were consistent with CO frequency modulation through dÀπ* backbonding interactions. The deoxy-VC center frequencies were insensitive to the solvent type, but those of oxy-VC were sensitive to the surrounding solvent, presumably due to the indirect influence of the dioxygen ligand on the carbonyl vibrational frequency. The vibrational lifetimes of the VC carbonyls were consistent with intramolecular relaxation through the metal dÀπ orbitals. 2D-IR spectra were analyzed using the inverse centerline slope (CLS) as a representative of the normalized frequencyÀfrequency correlation function. Multiexponential fits to the CLS decays revealed solvation dynamics on several time scales, ranging from a few to tens of picoseconds, with a shift of the relative proportion of the slower dynamics for the oxygenated complexes. The measured dynamics were compared to previously determined oxidative addition rate constants to hypothesize the potential role of solvent shell fluctuations in the overall reaction rate.

This double-blind prospective study was designed to determine the best dose variables for patient-controlled epidural analgesia (PCEA)

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The vibrational solvatochromism of bis(triphenylphosphine) iridium(I) carbonyl chloride (Vaska's complex, VC) was investigated by FTIR spectroscopy. The carbonyl stretching frequency (ν(CO)) was measured in 16 different organic solvents with a wide range of Lewis acidities for VC and its dioxygen (VC-O(2)), hydride (VC-H(2)), iodide (VC-I(2)), bromide (VC-Br(2)), and sulfide (VC-S(X)) adducts. The ν(CO) of the VC-O(2) complex was sensitive to the solvent electrophilicity, whereas minimal correlation was found for VC and the other adducts. The stretching frequency of the trans-O(2) ligand on VC-O(2) was measured to be anticorrelated with ν(CO), supporting a model in which this ligand indirectly affects the carbonyl frequency by modulating the extent of metal-to-CO back-bonding. The ν(CO) values obtained from DFT calculations on VC adducts with solvent continua and explicit hydrogen bonds were used to aid the interpretations of the experimental results. The O(2) ligand is more susceptible to stronger specific solvent interactions and it binds in a fundamentally different mode from the monatomic ligands, providing a more direct communication channel with those metal d-orbitals that have the appropriate symmetry to back-bond into the carbonyl π*-orbital.

A vibrational pump-probe and FTIR study was performed on two different adducts of Vaska's complex in two different sets of binary solvent mixtures. The carbonyl vibrational mode in the oxygen adduct exhibits solvatochromic shifts of ~10 cm(-1) in either benzyl alcohol or chloroform relative to benzene-d6, whereas this vibration is nearly unchanged for the iodine adduct for the same three solvents. The width and center frequency of the carbonyl stretch for each adduct are compared to its vibrational lifetime in binary mixtures of benzene-d6 with either benzyl alcohol or chloroform. In neat solvents, the trends in line width, frequency, and vibrational lifetime are consistent for the two adducts, but complex relationships emerge when the trends in each property are compared as a function of mixed solvent composition. ν(CO) is more sensitive to the solvation environment around the trans ligand, whereas the line width and lifetime depend on the environment around the CO group itself. The carbonyl frequency and width vary nonlinearly across the two binary solvent series, indicating preferential solvation. In contrast, the vibrational lifetime changes linearly with solvent composition and is correlated with the mole fraction of chloroform but anticorrelated with the mole fraction of benzyl alcohol. The results are explained by differences in the densities of solvent modes that affect intermolecular relaxation of the carbonyl mode.

Although the science behind the soda geyser demonstration is well known, describing the microscopic origins of this dramatic, sticky demonstration can be difficult. In this experiment, an apparatus was designed to contain the reaction, thereby allowing for quantitative analysis of the amount of CO 2 released after dropping in various initiating objects. The exploratory studies were tested with a moderate sized group of 12−17 year old participants at a summer learning event, and their data confirmed that the difference in the surface area of the initiators was a primary factor for the release of dissolved gas. Additional studies were performed to relate the soda temperature to the amount of dissolved CO 2 . In this laboratory experiment, students gained a greater understanding of surface area and its effect on gas nucleation and bubble formation as well as gas solubility its temperature dependence. The experimental approach provided a dramatic yet contained format for students to form and test their own hypotheses about the chemical processes behind this popular classroom demonstration.

Porous sol–gel matrices were synthesized with IR-active Si–H vibrational chromophores integrated into the silica network. The Si–H vibrational mode was found to be highly accessible to solvents within the nanoscopic pores. Vibrational solvatochromism of the silane vibration was controlled largely by interactions between infiltrating solvents and the oxygen and hydroxide sites in the silica. Exchanging solvents in the silica matrices produced reversible solvatochromic shifts in some cases but led to irreversible shifts when strongly interacting solvents were tested, suggesting that a layer of solvent was not exchangeable. 2D-IR spectroscopy was used to monitor spectral diffusion and extract the homogeneous line widths of the Si–H mode for a range of infiltrating solvents as well as solvent-free aerogel samples. It was demonstrated that the silane vibration is sensitive to the nature of the infiltrating solvent, making these vibrationally active sol–gel films a general platform for solvent dynamics in nanoscopic confined volumes.

This study evaluated partial antagonism of tiletamine-zolazepam (TZ) anesthesia in cheetahs (Acinonyx jubatus) and differences between two benzodiazepine antagonists, flumazenil and sarmazenil, in this species. Four cheetahs were anesthetized three times at an interval of 14 days with an average intramuscular dose of 4.2 mg/kg TZ. In trials 2 and 3 flumazenil at 0.031 mg/kg and sarmazenil at 0.1 mg/kg, respectively, were applied intramuscularly 30 min after initial TZ injection. There was a highly significant difference between the duration of TZ anesthesia with and without antagonist. Use of the antagonists significantly shortened duration and recovery and eliminated excitatory behavior during the recovery phase. No significant differences could be determined between the two antagonists. We recommend the use of sarmazenil and flumazenil to antagonize TZ anesthesia in cheetahs.