Quantum chemical investigation of the electronic spectra of the keto, enol, and keto-imine tautomers of cytosine

The low-lying excited singlet states of the keto, enol, and keto-imine tautomers of cytosine have been investigated employing a combined density functional/multireference configuration interaction (DFT/MRCI) method. Unconstrained geometry optimizations have yielded out-of-plain distorted structures of the pi --> pi and n --> pi excited states of all cytosine forms. For the keto tautomer, the DFT/MRCI adiabatic excitation energy of the pi --> pi state (4.06 eV including zero-point vibrational energy corrections) supports the resonant two-photon ionization (R2PI) spectrum (Nir et al. Phys. Chem. Chem. Phys. 2002, 5, 4780). On its S1 potential energy surface, a conical intersection between the 1pipi state and the electronic ground state has been identified. The barrier height of the reaction along a constrained minimum energy path amounts to merely 0.2 eV above the origin and explains the break-off of the R2PI spectrum. The 1pipi minimum of the enol tautomer is found at considerably higher excitation energies (4.50 eV). Because of significant geometry shifts with respect to the ground state, long vibrational progressions are expected, in accord with experimental observations. For the keto-imine tautomer, a crossing of the 1pipi potential energy surface with the ground-state surface has been found, too. Its n --> pi minimum (3.27 eV) is located well below the conical intersection between the pi --> pi and S0 states, but it will be difficult to observe because of its small transition moment. The identified conical intersections of the pi --> pi excited states of the keto cytosine tautomers are made responsible for the ultrafast decay to the electronic ground states and thus may explain their subpicoseconds lifetimes.     

Synthesis, Structure, and Antimicrobial Activity of Complexes of Pt(II), Pd(II), and Ni(II) with the Condensation Product of 2-(Diphenylphosphino)benzaldehyde and Semioxamazide

Summary. Complexes of Pt(II), Pd(II), and Ni(II) with the condensation derivative of 2-(diphenylphosphino)benzaldehyde and semioxamazide were synthesized, characterized, and their antimicrobial activity was evaluated. The ligand and the complexes were characterized by spectroscopic methods with the particular accent on NMR spectral analysis. For the palladium(II) complex, the crystal structure was determined by X-ray analysis. In all the complexes the ligand is coordinated as a tridentate via a P, N, O donor set. The Pd(II) and Pt(II) complexes have a square planar geometry, whereas the geometry of the Ni(II) complex is tetrahedral. The ligand showed antibacterial and antifungal activity, which was enhanced upon complexation.     

Accreditation of GMO detection laboratories: Improving the reliability of GMO detection

Reliable and efficient methods for detecting genetically modified organisms (GMOs) are essential for establishing an effective system for traceability all along the supply chain from seed producers to final consumers. The latter is especially meaningful in European Union and other countries where strict legislations on GMOs were set up. Performance of the methods used in laboratories around the world should be uniform, in order to obtain reliable and comparable results. Accreditation is a suitable system for harmonising procedures in each testing laboratory. In this paper, key elements for the accreditation of molecular biology methods for GMO detection according to ISO/IEC 17025 are described. The procedures described are also valuable for the accreditation of molecular methods for all laboratory diagnostics where qualitative and quantitative characterisation of nucleic acids is needed.     

Sodium citrate dihydrate doped with Mn3+ ions

Sodium citrate dihydrate doped with Mn³⁺ ions, namely trisodium(I) managnese(III) citrate(3−) dihydrate, [Na₃Mn_0.011(C₆H₅O₇)(H₂O)₂]_n, was obtained during attempts to prepare some complex Mn^III citrates from a concentrated strong alkaline solution containing Na⁺, Mn³⁺ and citrate ions. The compound is isostructural with the recently described Na₃(C₆H₅O₇)·2H₂O [Fischer & Palladino (2003). Acta Cryst. E 59 , m1080–m1082]. The essential difference between these two structures is the presence of a very small proportion (0.205 wt%) of Mn³⁺ ions, which are positioned at the special 4e Wyckoff position in C2/c, where they are in a highly distorted octahedral environment of O atoms from two citrate anions.     

Simulations and Velocity Measurements for a Microparticle in an Evanescent Field

We report theoretical calculations and experimental data for guiding of polystyrene microspheres in the evanescent field of an optical waveguide. The waveguides used in our experiments were made using Cs⁺ ion-exchange in soda lime glass, which gives efficient trapping and high guiding velocities. The computations were done using a generalized version of Mie scattering theory, which gives good agreement with our experimental results. © 2005 The Optical Society of Japan     

Identification of Tmem10/Opalin as a novel marker for oligodendrocytes using gene expression profiling

Background  

During the development of the central nervous system, oligodendrocytes generate large amounts of myelin, a multilayered insulating membrane that ensheathes axons, thereby allowing the fast conduction of the action potential and maintaining axonal integrity. Differentiation of oligodendrocytes to myelin-forming cells requires the downregulation of RhoA GTPase activity.     

The Crystal Structure of the NH4NCS Complex of Nonactin

The NH₄NCS complex of the macrotetrolide antibiotic nonactin crystallizes in the space group P1 , a = 12.565, b = 13.115, c = 14.999 Å, α= 91.22, β= 90.10, γ= 104.97°. The X-ray crystal structure analysis shows that the NH ion is coordinated by hydrogen bonds to the four ether oxygen atoms (NH … O, 2.86 Å). These four atoms and the four carbonyl oxygen atoms (N … O, 3.08 Å) enclose the NH ion in a somewhat distorted cube.     

Applicability of Hydrated Iron(III) Oxide and Dithiocarbamates as Colloid Collectors for Flotation Preconcentration of Manganese in Traces Before its ETAAS Determination

 The applicability of tetramethylenedithiocarbamate (TMDTC⁻) and hexamethylenedithiocarbamate (HMDTC⁻) for colloid flotation separation of manganese in traces from fresh (spring, well and tap) water was studied. The experimental conditions for the successful manganese separation and preconcentration before electrothermal atomic absorption spectrometric (ETAAS) determination were optimised. Higher enrichment of manganese was achieved when a larger amount of HMDTC⁻ is used. Applying iron(III) hexamethylenedithiocarbamate, Fe(HMDTC)₃, as a precipitate collector, manganese was determined at μg/L levels singly or simultaneously with lead and zinc in 1 L of water sample. The applicability of the proposed procedure have been verified by analyses of fresh water samples using the method of standard addition, as well as by comparing the results obtained by ETAAS with those obtained by inductively coupled plasma-atomic emission spectrometry (ICP-AES). The detection limit of manganese using this method is 0.025 μg/L. Received August 30, 1999. Revision May 15, 2000     

Solid state and solution structures of Cd(II) complexes with two N-heteroaromatic Schiff bases containing ester groups

Two novel cadmium(II) complexes with condensation derivatives of 2-acetylpyridine or 2,6-diacetylpyridine with ethyl hydrazinoacetate hydrochloride were synthesized. X-ray crystal structures of the complexes revealed a bidentate coordination of the 2-acetylpyridine derivative, while the symmetric 2,6-diacetylpyridine derivative was coordinated tridentately. It was found that the oxygen atoms were not coordinated to the cadmium ions, despite the fact that they are the position to form six membered chelate rings. NMR spectroscopy investigations showed that the coordination properties of the ligands do not change in solution. Both complexes possess cytotoxic potential, as determined by the toxicity test to Artemia salina.