Kinetics of Chromic Acid Oxidation of Thioglycollic, Thiolactic & Thiomalic Acids

1082-108

Excited-state proton transfer from pyranine to acetate in methanol

Excited-state proton transfer (ESPT) of pyranine (8-hydroxypyrene-1,3,6-trisulphonate, HPTS) to acetate in methanol has been studied by steady-state and time-resolved fluorescence spectroscopy. The rate constant of direct proton transfer from pyranine to acetate (k1) is calculated to be ~1 × 109 M-1 s-1. This is slower by about two orders of magnitude than that in bulk water (8 × 1010 M-1 s-1) at 4 M acetate

The development and validation of a scoring tool to predict the operative duration of elective laparoscopic cholecystectomy

Background: The ability to accurately predict operative duration has the potential to optimise theatre efficiency and utilisation, thus reducing costs and increasing staff and patient satisfaction. With laparoscopic cholecystectomy being one of the most commonly performed procedures worldwide, a tool to predict operative duration could be extremely beneficial to healthcare organisations. Methods: Data collected from the CholeS study on patients undergoing cholecystectomy in UK and Irish hospitals between 04/2014 and 05/2014 were used to study operative duration. A multivariable binary logistic regression model was produced in order to identify significant independent predictors of long (> 90 min) operations. The resulting model was converted to a risk score, which was subsequently validated on second cohort of patients using ROC curves. Results: After exclusions, data were available for 7227 patients in the derivation (CholeS) cohort. The median operative duration was 60 min (interquartile range 45–85), with 17.7% of operations lasting longer than 90 min. Ten factors were found to be significant independent predictors of operative durations > 90 min, including ASA, age, previous surgical admissions, BMI, gallbladder wall thickness and CBD diameter. A risk score was then produced from these factors, and applied to a cohort of 2405 patients from a tertiary centre for external validation. This returned an area under the ROC curve of 0.708 (SE = 0.013, p  90 min increasing more than eightfold from 5.1 to 41.8% in the extremes of the score. Conclusion: The scoring tool produced in this study was found to be significantly predictive of long operative durations on validation in an external cohort. As such, the tool may have the potential to enable organisations to better organise theatre lists and deliver greater efficiencies in care

Kinetic and mechanistic studies on the oxidation of D-glucose by MnO2 nanoparticles. Effect of microheterogeneous environments of CTAB, Triton X-100 and Tween 20

The kinetics of electron transfer reaction between D-glucose and MnO2 nanoparticles has been studied in weakly acid medium. In the colloidal solution of MnO2, ultrafine nanoparticles of MnO2 remain supported on two-dimentional gum acacia sheets in the form of crumbled paper ball assuming the form of spherical particulates of size 60-200 nm as detected by TEM. The nanoparticles are found to be amorphous. Apart from the inhibition, due to adsorption of reaction products on the surface of the nanoparticles, the reaction is first order with respect to MnO2, but complex order with respect to glucose as well as H. Glucose is oxidized to 6-lactone through a one-step two-electron transfer process and the latter is rapidly hydrolyzed to gluconic acid. The oxidation of glucose in absence of surfactant is entropy-controlled. In the presence of surfactants of cetyl trimethyl ammonium bromide (CTAB), Triton X-100 (TX-100) and Tween 20, the reaction rate passes through a maximum around the CMC. Both the reactants are distributed between the aqueous and the micellar pseudophases and then react, following Berezin's model. Ion-dipole interaction and H-bonding appear to play an important role in the binding between glucose and the surfactant molecules while protonated MnO2 remains at the periphery of the Stern layer within the micelle. The binding of glucose with the surfactants is controlled by the entropy changes associated with the glucose-water interaction, micelle-water interaction and glucose-micelle interaction. (C) 2017 Elsevier B.V. All rights reserved

Vibration-Assisted Intersystem Crossing in the Ultrafast Excited-State Relaxation Dynamics of Halocoumarins

Due to its numerous applications, triplet formation and resulting phosphorescence remain a frontier area of research for over eight decades. Facile intersystem crossing (ISC) is the primary requirement for triplet formation and observation of phosphorescence. The incorporation of a heavy atom in molecules is one of the common approaches employed to facilitate ISC. A detailed study of the excited state dynamics that governs ISC is necessary to understand the mechanism of heavy atom effect (HAE). Incorporation of iodine at the 3 position of coumarin-1 reduces fluorescence quantum yield (ϕ ) drastically as expected, whereas bromine substitution at the same position increased the ϕ . Such a contrasting effect of the two heavy atoms suggests that there are other features yet to be discovered to fully understand the HAE. Detailed steady state and femtosecond transient absorption studies along with theoretical calculations suggest that the C3-X (X = Br, I) bond vibration plays an important role in the ISC process. The study reveals that while in the case of the iodo-derivative there is no energy barrier in the singlet triplet crossing path, there is a barrier in the case of the bromo-derivative, which slows the ISC process. Such an unexpected phenomenon is not limited to halocoumarins as this rationalizes the photobehavior of 1-bromo-/iodo-substituted naphthalenes as well

A femtosecond study of photoinduced electron transfer from dimethylaniline to coumarin dyes in a cetyltrimethylammonium bromide micelle

Ultrafast photoinduced electron transfer (PET) from N,N-dimethylaniline to coumarin dyes in cetyltrimethylammonium bromide (CTAB) micelle is studied using femtosecond upconversion spectroscopy. The rate of PET in a CTAB micelle is found to be highly nonexponential with components much faster (~10 ps) than the slow components of solvation dynamics. The ultrafast components of electron transfer exhibits a bell-shaped dependence on the free energy change which is similar to the Marcus inversion

Crystal structure and Hirshfeld surface analysis of (E)-2-[1-hydroxy-2-(pyridin-2-yl)ethyl]-4-[2-(4-methoxyphenyl)diazen-1-yl]phenol

In the title compound, C20H19N3O3, the configuration about the azo N=N bond is E, and the central benzene ring is inclined to the pyridine ring by 31.43 (8)° and to the 4-methoxyphenyl ring by 4.73 (8)°. In the crystal, molecules are linked by pairs of O—H...N hydrogen bonds, forming inversion dimers with an R22(12) ring motif. The dimers are linked by O—H...O and C—H...O hydrogen bonds, forming layers parallel to the ac plane. There are C—H...π interactions present within the layers and between the layers, leading to the formation of a supramolecular framework. The layers are also linked by offset π–π interactions, with an interplanar distance of 3.416 (2) Å

Hydration dynamics of a protein in the presence of urea and sodium dodecyl sulfate

The antagonistic effects of unfolding of a protein (lysozyme) by urea and refolding by sodium dodecyl sulfate (SDS), have been studied by solvation dynamics and circular dichroism. Efficient fluorescence resonance energy transfer from tryptophan to coumarin 153 (C153) indicates that the solvation probe, C153 is located near tryptophan 62 and 108 of lysozyme. The average solvation time of C153 bound to lysozyme in 7 M urea and 3 mM SDS is quite close to that in the native state of lysozyme while in 28 mM SDS and 7 M urea the average solvation time is nearly three times slower

Excited state proton transfer of pyranine in a γ-cyclodextrin cavity

Excited state proton transfer of pyranine (8-hydroxypyrene-1,3,6-trisulfonate, HPTS) in γ-cyclodextrin (γ-CD) is studied using picosecond and femtosecond fluorescence spectroscopy. It is shown that confinement of pyranine in γ-CD cavity accelerates recombination of the geminate ion pair and slows down the initial proton transfer step and the dissociation of the geminate ion pair. This results in enhanced emission from the protonated species

Fluorescence anisotropy decay and solvation dynamics in a nanocavity: coumarin 153 in methyl β -cyclodextrins

Fluorescence anisotropy decay and solvation dynamics of coumarin 153 (C153) are studied in dimethyl β -cyclodextrin (DIMEB) and trimethyl β-cyclodextrin (TRIMEB) nanocavity in water. C153 binds to DIMEB and TRIMEB to form both 1:1 and 1:2 (C153:cyclodextrin) complexes. The anisotropy decays of C153 in DIMEB and TRIMEB are found to be biexponential. The fast component of anisotropy decay (~1000 ps) is attributed to the 1:1 complex and the slower one (~2500 ps) to the 1:2 complex. From the components of the anisotropy decay, the length of the 1:1 and 1:2 complexes are estimated. Solvation dynamics of C153 in DIMEB exhibits a very fast (2.4 ps) component (41%) and two slower components of 50 ps (29%) and 1450 ps (30%). Solvation dynamics in TRIMEB is described by three slow components of 10.3 ps (24%), 240 ps (45%), and 2450 ps (31%). Possible origins of the ultraslow components are discussed