Structure of the hydrated and dimethyl sulfoxide solvated rubidium ions in solution

The structure of the hydrated and the dimethyl sulfoxide solvated rubidium ions in solution has been determined by means of large-angle X-ray scattering (LAXS) and extended X-ray absorption fine structure (EXAFS) studies. The models of the hydrated and dimethyl sulfoxide solvated rubidium ions fitting the experimental data best are square antiprisms with Rb-O bond distances of 2.98(2) and 2.98(3) A, respectively. The EXAFS data show a significant asymmetry in the Rb-O bond distance distribution with C(3) values of 0.0076 and 0.015 A(3), respectively. No second hydration sphere is observed around the hydrated rubidium ion. The dimethyl sulfoxide solvated rubidium ion displays a Rb-O-S bond angle of ca. 130 degrees, which is typical for a medium hard electron acceptor such as rubidium.     

LC Determination of Propylene Glycol in Human Plasma After Pre-Column Derivatization with Benzoyl Chloride

A simple high-performance liquid chromatographic method, using photodiode array detection was developed for the determination of propylene glycol in human plasma and in the fluid retreived after continuous veno-venous hemofiltration. The method entailed alkaline derivatization with benzoyl chloride and ethylene glycol as internal standard. The separation of the compounds, after extraction with pentane, was carried out on a Pursuit C8 column with UV-detection at 230 nm. Validation samples were analyzed with an accuracy between 95 and 105%, and intra- and inter-day coefficients of variation of less than 8%. The calibration curve was linear over a concentration range of 5–100 mg L⁻¹ with a detection limit of 1 mg L⁻¹. Blood plasma samples of several patients were analysed by using the prescribed method with propylene glycol concentrations varying from 5 to 98 mg L⁻¹. Compared to previously described LC methods, this method is ten times more sensitive and thus suitable for use in pharmacokinetic studies of propylene glycol.     

Study of Hg22+ and complexes of NpO2+ and UO22+ in solution. examples of cation-cation interactions

Density functional theory (BPW91/TZ2P) is used to explore the nature of cation-cation interactions (CCIs) that exist between two actinyl cations in solution. Solvation, which is modeled using COSMO, favors the complexes (ONpO-ONpO)2+ and (ONpO-OUO)3+ over separated NpO2+(aq) and UO2(2+)(aq) cations because of the quadratic dependence of solvation on charge. For (OUO-OUO)4+, solvation effects, even though very large, are unable to overcome intrinsic electrostatic repulsion between the units. The actinyl-actinyl complexes are T-shaped, with the oxygen of one unit coordinated to the actinide metal of the other unit. The association free energies of (ONpO-ONpO)2+ and (ONpO-OUO)3+ are calculated as -42.1 and -29.2 kcal/mol. Explicit consideration of the first solvation shell at the B3LYP/LANL2DZ level suggests that the free energies of binding may be overestimated. The Hg2(2+) dication, though not considered a "traditional" CCI, is very similar to the actinyl-actinyl interaction. The binding free energy of Hg2(2+) in solution is calculated as -16.0 kcal/mol.     

Hydrogen bonds of RNA are stronger than those of DNA, but NMR monitors only presence of methyl substituent in uracil/thymine

Recently, Vakonakis and LiWang (J. Am. Chem. Soc. 2004, 126, 5688) reported experimental evidence for stronger hydrogen bonds in RNA A:U than in DNA A:T base pairs, which was based on differences in NMR shielding for adenine C2. We have analyzed the proposed correlation between NMR shielding and hydrogen-bond strength using density functional theory. Although we agree with the conclusion that A:U is more strongly bound, we find no correlation between the hydrogen-bond strength and the NMR shielding of C2. Our study shows that NMR merely probes the presence/absence of the methyl group in thymine/uracil, without any relation to the strength of the hydrogen bonds involved. In other words, one cannot infer the Watson-Crick hydrogen-bond strength from the NMR shielding constant of adenine C2.     

Experimental and quantum chemical studies of structure and reaction mechanisms of dioxouranium(VI) complexes in solution

This perspective article describes the combination of experimental data and quantum chemical methods for the determination of structure and reaction mechanisms of uranyl(vi) complexes in aqueous solution. The first part assesses the accuracy of the chemical and thermodynamic properties of solvated uranyl(vi) complexes as obtained by various quantum chemical methods. The second part discusses structure determination, mechanisms for ligand exchange and the lability of coordinated water molecules for various uranyl(vi) complexes using a combination of NMR and quantum chemical data.     

On the escape process during phase inversion of an emulsion

This paper deals with a phenomenon which plays an important role in the phase inversion process of emulsions. This process is governed by the interplay of coalescence of droplets, often leading to double emulsions, and the escape of those internal droplets. The latter process retards the inversion process. Coalescence has been the subject of many studies, contrary to the escape event. This paper addresses the escape process both theoretically and experimentally. The model developed analyses the rate of the escape of internal droplets from the mother droplet via a coalescence process, where the internal flow, as generated by the external flow, generates the viscous force for coalescence. Incomplete mixing in the droplet has been assumed. Experimental data on the escape rate of oil droplets from O/W/O emulsions have been analysed using a Computational Fluid Dynamics approach, where the model as indicated above has been incorporated. Experimental data and simulations compare very well. Data have been compared on varying the size of the inner droplets and the rotational speed of the vessel where the double emulsion has been formed and where the escape took place.     

Isotachophoresis of beta-blockers in a capillary and on a poly(methyl methacrylate) chip

Analysis of the beta-blockers oxprenolol, atenolol, timolol, propranolol, metoprolol, and acebutolol in human urine by a combination of isotachophoresis (ITP) and zone electrophoresis (ZE) was investigated. Methods were developed with a conventional capillary electrophoresis (CE) apparatus and a poly(methyl methacrylate) (PMMA) microchip system. With CE the separation of oxprenolol, atenolol, timolol, and acebutolol from a standard solution containing 5 microg/mL of each compound was accomplished by performing ZE with transient ITP. The electrolyte system consisted of 10 mM sodium morpholinoethane sulfonate (pH 5.5) and 0.1% methylhydroxyethylcellulose as the leading electrolyte and 30 mM ortho-phosphoric acid (pH 2.0) as both the terminating and the ZE background electrolyte. With the microchip system the separation of oxprenolol and acebutolol from a standard solution containing 10 microg/mL of each compound was accomplished by a coupled-channel ITP-ZE device using the same leading electrolyte solution as the CE system but 5 mM glutamic acid (pH 3.4) as terminating and background electrolytes. The systems were used for analyses of patient urine samples. Water-soluble hydrophilic matrix compounds were removed from the urine samples by solid-phase extraction (SPE). Limits of quantification below 5 microg/mL could be achieved. The PMMA ITP-ZE chip has not earlier been used for analyses of any drugs from urine samples.