Cooperative hydrogen-bonding effects in a water square: a single-crystal neutron and partial atomic charges and hardness analysis study

Four isomorphous complexes of formula [M(L)(4)(H(2)O)(2)]SO(4).2H(2)O (M = Co, 1a; Ni, 1b; Cu, 1c; Zn, 1d) have been isolated and characterized by single-crystal X-ray diffraction and neutron diffraction using the quasi-Laue diffractometer VIVALDI at the Institut Laue-Langevin as well as by thermogravimetric analysis. The structures contain a discrete, strongly hydrogen-bonded water tetramer which causes a significant distortion of the metal coordination sphere in each case. Partial atomic charges and hardness analysis (PACHA) calculations reveal that the shortest hydrogen bonds are not the strongest in this constrained, cyclic solid-state structure and show that the distortion at the metal center is caused by the drive to maintain the integrity of the water tetramer. The system undergoes a disorder-order transition on slow cooling that provides insight into the nature of communication between water squares.     

Stoichiometric and catalytic deuterium and tritium labeling of "unactivated" organic substrates with cationic Ir(III) complexes

[reaction: see text] Ir(III) complex [Cp(PMe(3))IrMe(CH(2)Cl(2))][BAr(f)] (1) was used to introduce deuterium stoichiometrically into substituted naphthalene/benzene templates and several "drug-like" entities. The exchange process is tolerant of a wide array of functional groups. Labeling of warfarin using subatmospheric pressures of T(2) led to specific activities and total activities rivaling current functional group directed tritium labeling methods. When paired with the appropriate deuterium donor, Cp(PMe(3))Ir(H(3))OTf (4) was found to deuterate a number of organic compounds catalytically.     

Oxidation of formic acid and carbon monoxide on gold electrodes studied by surface-enhanced Raman spectroscopy and DFT.

The oxidation of formic acid and carbon monoxide was studied at a gold electrode by a combination of electrochemistry, in situ surface-enhanced Raman spectroscopy (SERS), differential electrochemical mass spectrometry, and first-principles DFT calculations. Comparison of the SERS results and the (field-dependent) DFT calculations strongly suggests that the relevant surface-bonded intermediate during oxidation of formic acid on gold is formate HCOO- ad*. Formate reacts to form carbon dioxide via two pathways: at low potentials, with a nearby water to produce carbon dioxide and a hydronium ion; at higher potentials, with surface-bonded hydroxyl (or oxide) to give carbon dioxide and water. In the former pathway, the rate-determining step is probably related to the reaction of surface-bonded formate with water, as measurements of the reaction order imply a surface almost completely saturated with adsorbate. The potential dependence of the rate of the low-potential pathway is presumably governed by the potential dependence of formate coverage. There is no evidence for CO formation on gold during oxidation of formic acid. The oxidation of carbon monoxide must involve the carboxyhydroxyl intermediate, but SERS measurements do not reveal this intermediate during CO oxidation, most likely because of its low surface coverage, as it is formed after the rate-determining step. Based on inconclusive spectroscopic evidence for the formation of surface-bonded OH at potentials substantially below the surface oxidation region, the question whether surface-bonded carbon monoxide reacts with surface hydroxyl or with water to form carboxyhydroxyl and carbon dioxide remains open. The SERS measurements show the existence of both atop and bridge-bonded CO on gold from two distinguishable low-frequency modes that agree very well with DFT calculations.     

Chemical removal of humic substances interfering with the on-line solid-phase extraction—Liquid chromatographic determination of polar water pollutants

Summary Different methods for removing interference by humic substances in the analysis of polar pollutants have been compared in the analysis of environmental water by solid-phase extraction (SPE) with a chemically modified polymeric resin coupled on-line to liquid chromatography with UV detection. The methods were based on the use of chemical reagents. The best method was found to be addition of sodium sulphite to humic-containing water before SPE. The appropriate amount of sulphite depends on the amount of humic substances dissolved in the sample—for analysis of 50 mL tap and Ebro river water, respectively, 250 μL and 500 μL 10 % Na₂SO₃ solution had to be added. In both cases, the recovery values after chemical treatment were similar to those when a Milli-Q-quality water standard was analysed.     

Transformation of acridines and azepines into the corresponding 3-oxo-heterocycles by means of hypervalent aromatic iodine compounds

Summary The acridines3,5, and6, as well as the dibenzo[b,f]-azepine4 were converted into the 3-oxo-derivatives7–10 using hypervalent iodine compounds (iodosylbenzene and bis-(trifluoroacetoxy)iodopentafluorobenzene).

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Oxidation von Acridinen und Azepinen in ihre 3-Oxoderivate mit Hilfe von hypervalenten aromatischen Jodverbindungen (Kurze Mitt.)

Zusammenfassung Die Acridine3,5 und6 sowie das Dibenzo[b,f]azepin4 wurden mit Hilfe der beiden hypervalenten Jod-Verbindungen Jodosobenzol (1) und Bis-trifluoroacetoxyiodbenzol (2) zu den entsprechenden 3-Acridinonen7,9 und10 sowie zum Dibenzoazepin-3-on8 oxidiert.

     

The type of group measure space von Neumann algebras

LetG be a countable discrete group acting by measure-preserving automorphisms of a finite measure space (M, ) and let (G,M) be the corresponding group measure space von Neumann algebra, which will be a finite von Neumann algebra. Necessary and sufficient conditions are given for (G,M) to have a non-zero type I part, and the projection on the type I part is explicitly described.This research was supported in part by National Science Foundation Grant MCS 74-19876.     

Unexpected reactivity of PdCl(2) and PtCl(2) complexes of the unsaturated diphosphine o-Me(2)TTF(PPh(2))(2) toward chloride abstraction with thallium triflate

Attempted thallium triflate abstraction of chloride anions from the MCl(2) complexes of the unsaturated chelating diphosphines o-dimethyl-bis(diphenylphosphino)tetrathiafulvalene (P2) (M = Pd, Pt) and cis-1,2-bis(diphenylphosphino)ethylene (dppen) (M = Pd) affords, surprisingly, a Tl(OTf) adduct in the case of (P2)PdCl(2) and (P2)PtCl(2), with no chloride abstraction, and a dicationic bis(palladium) bis(triflate) salt in the case of (cis-dppen)PdCl(2), in which only one Cl anion was removed. The crystal structures of these complexes were determined by X-ray analysis, which established the formulations (P2)MCl(2).Tl(OTf) (M = Pd, Pt) and [(dppen)PdCl](2)(OTf)(2), respectively. These compounds can be seen as possible intermediates in the general chloride abstraction process between (P-P)MCl(2) (M = Pd, Pt) and thallium triflate.     

Preparation of Neutral Ionophores for Alkali and Alkaline Earth Metal Cations and their application in ion selective membrane electrodes

The preparation of a series of non-cyclic, uncharged ligands able to selectively complex alkali and alkaline earth metal cations is described. These molecules are designed to be used as carriers for cations through membranes. Some of the compounds show high Ca²⁺ and Na⁺ selectivity, respectively, in liquid membrane electrodes.     

Characterization of single- and double-stranded DNA on gold surfaces

Single- and double-stranded deoxy ribonucleic acid (DNA) molecules attached to self-assembled monolayers (SAMs) on gold surfaces were characterized by a number of optical and electronic spectroscopic techniques. The DNA-modified gold surfaces were prepared through the self-assembly of 6-mercapto-1-hexanol and 5'-C(6)H(12)SH -modified single-stranded DNA (ssDNA). Upon hybridization of the surface-bound probe ssDNA with its complimentary target, formation of double-stranded DNA (dsDNA) on the gold surface is observed and in a competing process, probe ssDNA is desorbed from the gold surface. The competition between hybridization of ssDNA with its complimentary target and ssDNA probe desorption from the gold surface has been investigated in this paper using X-ray photoelectron spectroscopy, chronocoulometry, fluorescence, and polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS). The formation of dsDNA on the surface was identified by PM-IRRAS by a dsDNA IR signature at approximately 1678 cm(-)(1) that was confirmed by density functional theory calculations of the nucleotides and the nucleotides' base pairs. The presence of dsDNA through the specific DNA hybridization was additionally confirmed by atomic force microscopy through colloidal gold nanoparticle labeling of the target ssDNA. Using these methods, strand loss was observed even for DNA hybridization performed at 25 degrees C for the DNA monolayers studied here consisting of attachment to the gold surfaces by single Au-S bonds. This finding has significant consequence for the application of SAM technology in the detection of oligonucleotide hybridization on gold surfaces.