Cadmium iodide complexes with dimethylsulphoxide,and their crystal structures

The crystalline compounds [{CdI₂(dmso)}_n] ( 1 ,) and [Cd₂I₄(dmso)₄] ( 2 ,) provide a structural sequence illustrating the conversion of CdI₂ into the ionic derivatives [Cd(dmso)₆]²⁺ [Cd(dmso)I₃]₂^? · EtOH ( 3 ,) and [Cd(dmso)₆]²⁺ CdI₄^2? ( 4 ,), with increasing proportions of dmso. ( 1 ,) comprises polymeric chains with Cd centres linked by bridging iodide atoms, and alternately in four- and six-coordination. ( 2 ,) is a binuclear segment of the chains and can be seen as the structural forerunner of the ionic compounds ( 3 ,) and ( 4 ,). The ion packing in ( 3 ,) is loose, with lattice ethanol.     

Kinetic isotope effects on the dissolution kinetics of solid salicylic acid in aqueous solution: evidence for solubilisation via a proton dissociation-recombination mechanism

Quantitative Atomic Force Microscopy measurements made on the dissolving surface of solid salicylic acid in H2O and D2O reveal a kinetic isotope effect (kH/kD = 2.3 +/- 0.6) on the dissolution rate consistent with a transition state in which the proton is dissociated from the dissolving molecule.     

Determination of long-lived radionuclides in environmental media around a nuclear fuel reprocessing plant

Methods for the analysis of¹²⁹I and²⁴¹Pu are described briefly. Neutron activation is necessary to achieve an adequate degree of sensitivity for the measurement of¹²⁹I, but otherwise all laboratory manipulations are straightforward and use commonly-found, well-tried techniques. With these methods, both radionuclides can be measured easily in the terrestrial environment around a nuclear fuel reprocessing plant;²⁴¹Pu is measureable elsewhere in integrating media such as undisturbed soil.     

Use of electrokinetic measurements for characterization of columns used in capillary electrochromatography

The separation mechanism in capillary electrochromatography (CEC) is a hybrid differential migration process, which entails the features of both high-performance liquid chromatography (HPLC) and capillary zone electrophoresis (CZE), i.e., chromatographic retention and electrophoretic migration. The focus of this paper is on the use of electrokinetic data, such as current, electroosmotic flow (EOF) and column efficiency measurements, that are readily available, for an improved understanding of CEC separations. A framework is presented here for the use of this data for evaluation of a variety of performance parameters including, conductivity ratio, interstitial EOF mobility, porosity, and zeta potential. This framework is applied for characterization of two monolithic columns with different chemistry that were manufactured in-house. The above-mentioned performance parameters were calculated for the two columns and it is found that the poly(VBC-EGDMA-SWNT) monolithic column with the GPTMS-PEI coating offers a significantly improved flow distribution in comparison to the poly(VBC-EGDMA) monolithic column. This observation is confirmed by performing separation of peptides on the two columns and height equivalent of a theoretical plate (HETP) measurements on the resulting peaks. It is shown that following our approach leads to an improved understanding of the separations achieved with the columns and to better column design.     

The NaK 1 1,3delta states: theoretical and experimental studies of fine and hyperfine structure of rovibrational levels near the dissociation limit

Earlier high-resolution spectroscopic studies of the fine and hyperfine structure of rovibrational levels of the 1 3delta state of NaK have been extended to include high lying rovibrational levels with v < or = 59, of which the highest levels lie within approximately 4 cm(-1) of the dissociation limit. A potential curve is determined using the inverted perturbation approximation method that reproduces these levels to an accuracy of approximately 0.026 cm(-1). For the largest values of v, the outer turning points occur near R approximately 12.7 angstroms, which is sufficiently large to permit the estimation of the C6 coefficient for this state. The fine and hyperfine structure of the 1 3delta rovibrational levels has been fit using the matrix diagonalization method that has been applied to other states of NaK, leading to values of the spin-orbit coupling constant A(v) and the Fermi contact constant b(F). New values determined for v < or = 33 are consistent with values determined by a simpler method and reported earlier. The measured fine and hyperfine structure for v in the range 44 < or = v < or = 49 exhibits anomalous behavior whose origin is believed to be the mixing between the 1 3delta and 1 1delta states. The matrix diagonalization method has been extended to treat this interaction, and the results provide an accurate representation of the complicated patterns that arise. The analysis leads to accurate values for A(v) and b(F) for all values of v < or = 49. For higher v (50 < or = v < or = 59), several rovibrational levels have been assigned, but the pattern of fine and hyperfine structure is difficult to interpret. Some of the observed features may arise from effects not included in the current model.     

Host-guest interactions at self-assembled monolayers of cyclodextrins on gold

We have developed synthesis routes for the introduction of short and long dialkylsulfides onto the primary side of alpha-, beta-, and gamma-cyclodextrins. Monolayers of these cyclodextrin adsorbates were characterized by electrochemistry, wettability studies, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and atomic force microscopy (AFM). The differences in thickness and polarity of the outerface of the monolayers were measured by electro-chemistry and wettability studies. On average about 70% of the sulfide moieties were used for binding to the gold, as measured by XPS. Tof-SIMS measurements showed that the cyclodextrin adsorbates adsorb without any bond breakage. AFM measurements revealed for beta-cyclodextrin monolayers a quasi-hexagonal lattice with a lattice constant of 20.6 A, which matches the geometrical size of the adsorbate. The alpha-cyclodextrin and gamma-cyclodextrin monolayers are less ordered. Interactions of the anionic guests 1-anilinonaphthalene-8-sulfonic acid (1,8-ANS) and 2-(p-toluidinyl)naphthalene-6-sulfonic acid (2,6-TNS) and the highly ordered monolayers of heptapodant beta-cyclodextrin adsorbates were studied by surface plasmon resonance (SPR) and electrochemical impedance spectroscopy. The SPR measurements clearly showed interactions between a beta-cyclodextrin monolayer and 1,8-ANS. Electrochemical impedance spectroscopy measurements gave high responses even at low guest concentrations (< or = 5 microM). The association constant for the binding of 1,8-ANS (K = 289,000 +/- 13,000M-1) is considerably higher than the corresponding value in solution. (Partial) methylation of the secondary side of the beta-cyclodextrin strongly decreases the binding.     

Kinetic analysis of cyclic CMP-specific and multifunctional phosphodiesterases by quantitative positive-ion fast-atom bombardment mass spectrometry

Two enzymes, cyclic CMP-specific phosphodiesterase and multifunctional phosphodiesterase, are responsible for the hydrolysis of cytidine 3',5'-cyclic monophosphate in living cells. Quantitation of both enzymes has been carried out by positive-ion fast-atom bombardment mass spectrometric analysis of the enzyme incubates after termination of the reaction. The kinetic data obtained are in close agreement with parallel data obtained by the conventional radiometric assay. The extra facility of the mass spectrometry based assay to monitor several incubation components simultaneously has been exploited to study the concurrent hydrolysis of alternate cyclic nucleotide substrates and provides kinetic parameters of significance in interpreting substrate-enzyme interactions. This is extended by the use of collisionally-induced dissociation of the protonated molecules of the liberated products to identify the mononucleotide isomers resulting from the cyclic nucleotide hydrolysis.     

Molecular structure of carbonyl fluoride as studied by gas electron diffraction and microwave data

The molecular structure of carbonyl fluoride has been determined by electron diffraction. The results have been used in conjunction with the rotational constants reported by Carpenter in a combined structure analysis. The values so obtained are r_z (C=O) = 1.1717 ± 0.0013 Å, r_z (C-F) = 1.3157 ± 0.0005 Å, and ∠_zF-C-F = 107.71 ± 0.08°. These agree with the corresponding parameters estimated by Carpenter from the rotational constants alone. The effective constants, α₃, representing the cubic anharmonicity of bond stretching vibrations have been estimated.     

Electroanalytical exploitation of quinone-thiol interactions: application to the selective determination of cysteine

Square wave voltammetry was applied to the detection of cysteine through the use of an indirect assay that exploits the reaction of the thiol with a quinone indicator. Voltammetric discrimination between unreacted quinone and the corresponding quinone-cysteine adduct is possible with clear resolution of the latter peak providing a linear response from 5 to 47 microM. The selectivity of the approach was assessed with no interference from cystine, lysine, paracetamol or 4-aminophenol. The response recorded in the presence of a massive excess of ascorbic acid was also investigated and the integrity of the approach confirmed. The effects of other sulfhydryl thiols, homocysteine and glutathione, were also assessed and found to present no appreciable change in the voltammetric profile. The practical utility of the approach was investigated through examining the response to cysteine in urine.