Nuclear magnetic relaxation dispersion measurement of water mobility at a silica surface

Nuclear magnetic relaxation rates are measured as a function of magnetic field strength corresponding to proton Larmor frequencies ranging from 0.01 to 42 MHz for silica gel samples with a nitroxide free radical covalently attached at the surface. The field dependence of the relaxation rate is interpreted using a translational model for the relaxation equation to yield a translational diffusion coefficient for the water, in the immediate vicinity of the radical attached to the surface, of 2.1 × 10^?6 cm² s^?1 at 278 K for Si-4000 silica.     

Fluorescence quantum yields and their relation to lifetimes of rhodamine 6G and fluorescein in nine solvents: improved absolute standards for quantum yields

Absolute fluorescence quantum yields are reported for the rhodamine 6G cation and the fluorescein dianion dyes in nine solvents. This information is combined with previously reported fluorescence lifetimes to deduce radiative and nonradiative decay rates. Along the alcohol series from methanol to octanol, rhodamine 6G displays an increasing radiative rate, in parallel with the square of the refractive index increase, and a slightly decreasing nonradiative rate. Fluorescein is different: the apparent radiative rate actually decreases, suggesting that the emissive species is perturbed in some fashion. For both dyes, fluorescence yields are enhanced in D2O, rising to 0.98, in parallel with a corresponding increase in lifetimes. Protonated solvents invariably give shorter lifetimes and lower quantum yields, contrary to some previous speculation. From this work and an analysis of existing literature values, more precise values have been obtained for two previously proposed absolute quantum yield standards. The yield of fluorescein in 0.1 N NaOH(aq) is 0.925+/-0.015, and for rhodamine 6G in ethanol, it is 0.950+/-0.015. In both cases, the solutions are assumed to be in the limit of low concentration, excited close to their long-wave absorption band and at room temperature but may be either air-saturated or free of oxygen.     

Molecular structure and spectral properties of bromo(2-acetylpyridine4 N-methylthiosemicarbazonato)copper(II)

Summary The anion (loss of³ N hydrogen) of 2-acetylpyridine⁴ N-methylthiosemicarbazone coordinates in a planar conformation to copper(II) through the pyridyl nitrogen, azomethine nitrogen and thiolato sulphur atoms. The fourth coordination site is occupied by a bromo ligand and the complex is mononuclear and essentially planar. Bond distances and angles, as well as solid state and solution spectral properties, are compared to other recently reported copper(II) thiosemicarbazone complexes.     

Spectral and biological studies of copper(II) complexes of 2-acetyl-pyridine thiosemicarbazones with bulky 4N-substituents

Summary Copper(II) complexes of a large number of 2-acetylpyridine ⁴N-alkyl thiosemicarbazones were prepared and characterized. I.r., electronic and e.s.r. spectra of the complexes, as well as ¹H and ¹³C n.m.r. spectra of the thiosemicarbazones, were obtained. Both the thiosemicarbazones and their complexes show either modest or no growth inhibitory activity against Aspergillus niger, but many have considerable activity against Paecilomyces variotii. There is a relationship between the antifungal activity and size of the ⁴N-substituent for both the thiosemicarbazones and their copper(II) complexes.     

Fast automatic registration of images using the phase of a complex wavelet transform: application to proteome gels

Image registration describes the process of manipulating a distorted version of an image such that its pixels overlay the equivalent pixels in a clean, master or reference image. The need for it has assumed particular prominence in the analysis of images of electrophoretic gels used in the analysis of protein expression levels in living cells, but also has fundamental applications in most other areas of image analysis. Much of the positional information of a data feature is carried in the phase of a complex transform, so a complex transform allows explicit specification of the phase, and hence of the position of features in the image. Registration of a test gel to a reference gel is achieved by using a multiresolution movement map derived from the phase of a complex wavelet transform (the Q-shift wavelet transform) to dictate the warping directly via movement of the nodes of a Delaunay-triangulated mesh of points. This warping map is then applied to the original untransformed image such that the absolute magnitude of the spots remains unchanged. The technique is general to any type of image. Results are presented for a simple computer simulated gel, a simple real gel registration between similar "clean" gels with local warping vectors distributed about one main direction, a hard problem between a reference gel and a "dirty" test gel with multi-directional warping vectors and many artifacts, and some typical gels of present interest in post-genomic biology. The method compares favourably with others, since it is computationally rapid, effective and entirely automatic.     

A rigid cavity containing tetra-cobalt(III) [2 x 2] grid complex

The synthesis and structure of a rigid, cavity containing tetra-cobalt(III) [2 x 2] grid complex using an unusual bis(bipyridine)dimethoxynaphthyridine ligand is described.     

Electrogenerated chemiluminescence using solution phase and immobilized tris(4,7-diphenyl-1,10-phenanthrolinedisulfonic acid)ruthenium(II)

Electrogenerated chemiluminescence (ECL) with tris(4,7-diphenyl-1,10-phenanthrolinedisulfonic acid)rathenium(II) (RuBPS) in solution and immobilized on an electrode surface is investigated. Flow injection analysis with a thin layer electrochemical cell modified for ECL detection is used to determine the analytical utility of solution phase RuBPS and RuBPS immobilized in a cationic polypyrrole derivative. The solution phase reaction of RuBPS with oxalate is investigated with regard to the dependence of ECL emission on RuBPS concentration, carrier stream flow rate, and pH. In the parameter range studied, ECL intensity is not linear with the concentration of RuBPS in the sample. A maximum ECL intensity is observed with a RuBPS concentration of approximately 250 M. Slower linear velocities give greater ECL intensities which is the opposite of what is observed for Ru(bpy) ₃ ³⁺ and oxalate. Greater ECL intensity is observed at lower pHs for oxalate and at higher pHs for proline. RuBPS ECL with oxalate yields a working curve with a linear range from 0.1–100 M oxalate. Solution phase ECL is observed for RuBPS and other amines such as NADH, proline, tripropylamine, and antibiotics including streptomycin and gentamicin. RuBPS is also immobilized by electrochemical polymerization of 1-methyl-3-(pyrrol-1-ylmethyl)pyridinium chloride (MPP) in the presence of RuBPS. This polymer-modified electrode yields ECL for oxalate and for amines.Deceased     

Preconcentration of trace metal ions by combined complexation-anion exchange : Part 2. Cobalt,zinc, cadmium and lead with 8-hydroxyquinoline-5-sulfonic acid [1]

The ligand, 8-hydroxyquinoline-5-sulfonic acid, forms anionic complexes with cobalt(II), zinc(II), cadmium(II), and lead(II), each resulting complex showing a high affinity for anion-exchange resins. The effect of pH, ligand/metal ratio, volume, and concentration on percent retention of the anionic complexes by an anion-exchange resin are reported. At optimum conditions, all four metals are quantitatively retained by the column. Zinc, cadmium and lead(II) ions are completely eluted with 11 ml or less of 2 M HN0₃; cobalt(II) is totally removed by 12 M HCl and 2 M HNO₃. Concentration enhancements of 100-fold are easily achieved. All four anionic complexes can be left on the column for 7 days and still be quantitatively (99%) recovered. A ligand-loaded resin column can also remove all four metals quantitatively. Distribution coefficients for the metal complexes and their ligand/metal ratios were determined by using batch methods that may also serve as the isolation procedure.     

Mndo study of bond orders in some conjugated BI- and tri-cyclic hydrocarbons

MNDO calculations have been carried out on a number of conjugated bicyclic and tricyclic hydrocarbons. For reference purposes some acenes and monocyclic non-benzenoid hydrocarbons are also mentioned. While the influence of 2 or 6 π-electron systems in stabilising, and of 4 π-electron systems in destabilising, structures is readily evident, it is clear that arrays of 10 or more π-electrons have markedly less effect, and the balance between fixation of bonds and delocalisation in many compounds possessing such systems is subtle.     

Octaphenylbiphenylene and dodecaphenyltriptycene

Octaphenylbiphenylene, the expected dimer of tetraphenylbenzyne, has been prepared in low yield by diazotization of 3,4,5,6-tetraphenylanthranilic acid, and its X-ray structure has been determined. The X-ray structure of a second, abnormal dimer of tetraphenylbenzyne, 1,2,3,8,9,10-hexaphenyldibenzo[fg,op]naphthacene has also been determined; this is a saddle-shaped polycyclic aromatic hydrocarbon. 1,2,3,4,5,6,7,8,13,14,15,16-Dodecaphenyltriptycene, perhaps the most crowded triptycene derivative yet prepared, has been made by the reaction of tetraphenylbenzyne with 1,2,3,4,5,6,7,8-octaphenylanthracene, which in turn was synthesized in two steps from commercial starting materials. The X-ray structure of the dodecaphenyltriptycene nonabenzene solvate is a remarkable channel containing structure in which more than 50% of the unit cell volume is occupied by the benzene molecules.