Dephasing Dynamics across Different Local Vibrational Modes and Crystalline Environments.

The perturbed free induction decay (PFID) observed in ultrafast infrared spectroscopy was used to unveil the rates at which different vibrational modes of the same atomic-scale defect can interact with their environment. The N_{3}VH^{0} defect in diamond provided a model system, allowing a comparison of stretch and bend vibrational modes within different crystal lattice environments. The observed bend mode (first overtone) exhibited dephasing times T_{2}=2.8(1) ps, while the fundamental stretch mode had surprisingly faster dynamics T_{2}<1.7 ps driven by its more direct perturbation of the crystal lattice, with increased phonon coupling. Further, at high defect concentrations the stretch mode's dephasing rate was enhanced. The ability to reliably measure T_{2} via PFID provides vital insights into how vibrational systems interact with their local environment.

Towards elucidating the photochemistry of the sunscreen filter ethyl ferulate using time-resolved gas-phase spectroscopy.

Ultrafast time-resolved ion yield (TR-IY) and velocity map imaging spectroscopies are employed to reveal the relaxation dynamics after photoexcitation in ethyl 4-hydroxy-3-methoxycinnamate (ethyl ferulate, EF), an active ingredient in commercially available sunscreens. In keeping with a bottom-up strategy, the building blocks of EF, 2-methoxy-4-vinylphenol (MVP) and 4-hydroxy-3-methoxycinnamyl alcohol (coniferyl alcohol, ConA), were also studied to assist in our understanding of the dynamics of EF as we build up in molecular complexity. In contrast to the excited state dynamics of MVP and ConA, which are described by a single time constant (>900 ps), the dynamics of EF are described by three time constants (15 ± 4 ps, 148 ± 47 ps, and >900 ps). A mechanism is proposed involving internal conversion (IC) between the initially excited S1(11ππ*) and S2(11nπ*) states followed by intramolecular vibrational redistribution (IVR) on both states, in competition with intersystem crossing onto neighbouring triplet states (15 ± 4 ps). IVR and IC within the triplet manifold then ensues (148 ± 47 ps) to populate a low-lying triplet state (>900 ps). Importantly, the fluorescence spectrum of EF at the S1 origin, along with the associated lifetime (6.9 ± 0.1 ns), suggests that population is trapped, during initial IVR, on the S1(11ππ*) state. This serves to demonstrate the complex, competing dynamics in this sunscreen filter molecule.

Torsional Motion of the Chromophore Catechol following the Absorption of Ultraviolet Light.

The ability to probe energy flow in molecules, following the absorption of ultraviolet light, is crucial to unraveling photophysical phenomena. Here we excite a coherent superposition of vibrational states in the first excited electronic state (S1) in catechol, resulting in a vibrational wave packet. The observed quantum beats, assigned to superpositions of the low-frequency, and strongly mixed, O-H torsional mode τ2, elegantly demonstrate how changes in geometry upon photoionization from the S1 state to the ground state of the cation (D0) enables one to probe energy flow at the very early stages of photoexcitation in this biological chromophore.

Probing Rotational Motion in 4-tert-Butylcatechol through H Atom Photofragmentation: Deviations from Axial Recoil.

The time-resolved photofragmentation dynamics of 4-tert-butylcatechol were studied following one photon excitation to the S1 (1(1)ππ*) state with ultraviolet radiation in the range 260 ≤ λ ≤ 286 nm. The preparation of an aligned molecular ensemble via photoexcitation leads to anisotropy in the H atom photofragments. These H atoms originate from the decay of the S1 state through coupling onto the S2 ((1)πσ*) state, which is dissociative along the nonintramolecular hydrogen bonded "free" O-H bond. The degree of anisotropy of these photogenerated H atoms decreases with increasing pump-probe time delay. This is attributed to rotational dephasing of the initially aligned molecular ensemble. The measured dephasing occurs on a time scale akin to the appearance time of these H atoms, which likely places an intrinsic lower bound on the dephasing lifetime. The present work demonstrates how a careful balance between the appearance time of the H atoms, determined by the S1 lifetime, and the rotational dephasing in 4-tert-butylcatechol provides an opportune window to probe rotational motion in real time.

Once-weekly intravenous paricalcitol in the treatment of secondary hyperparathyroidism in hemodialysis patients.

BACKGROUND: Paricalcitol, a vitamin D analog, is commonly administered three times weekly to control secondary hyperparathyroidism in hemodialysis patients. Less frequent dosing would be more convenient, require less nursing time, and be an option in other dialysis modalities. No studies have examined the efficacy of once-weekly dosing of paricalcitol. METHODS: Chronic hemodialysis patients receiving a stable dose of paricalcitol three times weekly with intact PTH (iPTH) 100-500 ng/l were monitored during a two-week baseline, then were converted to a single mid-week paricalcitol dose equal to the previous cumulative weekly dose. Serum calcium and phosphorus were monitored weekly and iPTH levels determined during study Weeks 4 and 8. A single paricalcitol dose adjustment was made during study Week 5 based on iPTH to achieve a target value of 150-300 ng/l. Phosphate binders and calcium dialysate bath were kept constant during the study. RESULTS: In the 25 patients, mean iPTH was 295 +/- 107 ng/l at baseline, and not significantly different at Week 4 (307 +/- 111 ng/l) or Week 8 (285 +/- 98 ng/l). Paricalcitol dose increases mid-study were almost exclusively in patients with iPTH > 300 ng/l. Calcium, phosphorus, and calcium x phosphorus product were not significantly different on weekly therapy. (Only one patient developed a calcium > 2.55 mmol/l during the study.) CONCLUSION: Once-weekly dosing of paricalcitol is an effective option in treatment of secondary hyperparathyroidism. Less frequent dosing may better allocate nursing time and potentially benefit other patient populations with CKD and ESRD.

Determination of encapsulated menthol flavour using thermal desorption gas chromatography.

The analysis of menthol in encapsulated products is challenging due to the nature of the encapsulating matrices and the volatility of the analyte. Normal sampling/extraction procedures cannot be applied to the different types of menthol encapsulated products, due to variable extraction efficiencies of the analyte. This paper details the extraction and analysis of menthol flavour using a two stage thermal desorption GC process. This two stage thermal desorption system, using a Tenax TR packed cold trap, enables a narrow band of the extracted menthol to be focused onto the GC column. The method showed linearity in the range of 0.2-0.8 mg of menthol with a correlation coefficient greater than 0.999. Average instrumental precision of 3% RSD was determined and method precision was in the range of 2.1-9.4% RSD. This method was specific to menthol showing no interfering peaks. All the menthol was extracted in one extraction step. The specific analysis of menthol in encapsulated products allowed comparison of the efficiency of encapsulating processes, by comparing menthol loading values. RSD values for the different microparticles also indicate the relative homogeneity of the systems.

Pharmacological study of a new anti-inflammatory steroid, tixocortol pivalate (JO 1016).

Some pharmacological activities of pregn-4-ene-3,20-dione-21-thiol-11 beta,17 alpha-dihydroxy-21-pivalate (tixocortol pivalate, JO 1016 Pivalone), a new steroidal anti-inflammatory compound, are described. The anti-inflammatory activity of tixocortol pivalate has been clearly demonstrated in various tests using adrenalectomised and intact animals. Of particular interest is the dissociation of its local and systemic activities. Comparison with hydrocortisone acetate indicates a similar or greater anti-inflammatory activity, by either the local or topical routes, but tixocortol pivalate is between 60 and 300 times less active than hydrocortisone acetate after oral or subcutaneous administration. Glucocorticoid activity was only detected at very high oral doses of tixocortol pivalate and the highest tested subcutaneous dose (300 mg/kg) failed to induce significant activity. Hydrocortisone acetate exerted glucocorticoid effects at much lower doses. It is possible therefore the local or topical use of tixocortol pivalate in therapy may not cause the unwanted side effects of many of the corticosteroids in current use.