Ab initio study of the He(1S)-Li2(X̃, 1∑) interaction by the SCF and MP2 methods

Ab initio electronic structure calculations have been carried out for the He(¹S)-Li₂ (X?, ¹∑) interaction both by the single-configuration SCF and correlated second-order MP2 methods using an extended basis set. From these calculations, an estimate of the isotropic (V₀) and first two anisotropic (V₂ and V₄) terms of the He-Li₂ potential surface has been obtained. An assessment of the leading induced-dipole-induced-dipole dispersion energy is presented from the MP2 energies. Where possible, a comparison is made with previous unpublished ab initio calculations by Staemmler and Stahl using the CEPA method.     

Lifetime measurements of the 2p 3d 3 D 1, 2, 3 0 and 2p 3d 1 P 1 0 levels in NII by beam-foil-laser spectroscopy

Accurate lifetimes measured by means of the cascade-free method based on laser excitation of a fast ion beam preexcited in a carbon foil are reported for four 2p 3d levels in NII. The lifetime results are: τ(2p 3d ³ D ₁ ⁰ )=0.209±0.007 ns, τ(2p 3d ³ D ₂ ⁰ )=0.219±0.007 ns, τ(2p 3d ³ D ₃ ⁰ )=0.217±0.005 ns, and τ(2p 3d ¹ P ₁ ⁰ )=0.410±0.017 ns. These results are compared to theoretical and experimental lifetimes reported previously.     

A SCF Xα MO study of the optical and Ti2p core photoemission spectra of TiCl4

SCF Xα MO calculations on the ground state and optical excitation transition states of TiCl₄ accurately predict the energies of its UV absorption peaks. Calculations on the Ti2p core ion state and associated transition states indicate that the recently observed low energy (4.0 eV) Ti2p satellite arises from ligand to metal charge transfer excitations while the satellite at high energy (9.4 eV), similar to those previously observed in Ti(IV) compounds, can be attributed to transitions from the highest filled orbitals to empty orbitals with Cl3pTi4s. 4p antibonding character.     

Radiative lifetimes of the 6p 2 P 1 2/0 and 6p 2 P 3 2/0 levels in Yb II

Radiative lifetimes have been determined for the 6² P ₁ ^2/0 and 6² P ₃ ^2/0 levels in Yb II using the method of laser-induced fluorescence from sputtered metal vapour. The results, 8.0(2)ns (6² P ₁ ^2/0 ) and 6.3(3)ns (6² P ₃ ^2/0 ), are compared with lifetimes obtained from ab initio manybody perturbation calculations.     

Accurate variational calculations of the ground 2Po(1s22s22p) and excited 2S(1s22s2p2) and 2Po(1s22s23p) states of singly ionized carbon atom

In this article we report accurate nonrelativistic variational calculations of the ground and two excited states of C(+) ion. We employ extended and well optimized basis sets of all-electron explicitly correlated Gaussians to represent the wave functions of the states. The optimization of the basis functions is performed with a procedure employing the analytic gradient of the energy with respect to the nonlinear parameters of the Gaussians. The calculations explicitly include the effects due to the finite nuclear mass. The calculated transition energies between the three states are compared to the experimentally derived values. Finally, we present expectation values of some small positive and negative powers of the interparticle distances and contact densities.     

Mutation and expression of the p27KIP1 and p57KIP2 genes in human gastric cancer

Cyclin-dependent kinase inhibitors (CDKI) are negative regulators of cell cycle progression by binding the cyclin-CDK complex and inhibiting the CDK activity. Genetic alteration in the CDKI genes has been implicated for carcinogenesis. To test the genetic alteration in the p27 and p57 genes, KIP family CDKI genes, 30 gastric tumor-normal pairs and 8 gastric cancer cell lines were analyzed for mutations by polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP). No mutation was detected in these genes although length polymorphisms in the proline-alanine repeat of the p57 gene were detected. When the p27 and p57 mRNAs were analyzed in gastric cancer cell lines by RT-PCR, the p27 mRNA was expressed considerably high in tumor cells but expression of the p57 mRNA was much low in gastric cancer cell lines compared to that of normal cells. The result suggests that inactivation of gene expression rather than mutations in the p57 gene accounts possibly for the involvement of this gene in tumorigenesis of gastric cancer. However, expression of the p27 gene seems to be essential for cell survival.     

Identification of selenium-containing proteins in selenium-rich yeast aqueous extract by 2D gel electrophoresis, nanoHPLC-ICP MS and nanoHPLC-ESI MS/MS

An approach based on the consecutive use of nanoHPLC-ICP collision cell MS and nanoHPLC-electrospray MS was proposed for the analysis of water-soluble selenium-containing proteins in selenium-rich yeast after their separation by 2D gel electrophoresis (GE). An ultrasonic probe was employed for fast protein extraction avoiding sample heating and thus reducing the risk of protein degradation. The efficiency of different extraction steps were critically evaluated by total selenium analysis and size-exclusion chromatography (SEC)-ICP MS. Prior to electrophoresis proteins were purified by acetone precipitation. The protein-containing spots from 2D GE were excised and digested with trypsin. The digests obtained were analyzed by nanoHPLC-ICP MS in order to check for the presence of selenium-containing peptides; this allowed the detection of target proteins for further analyses (two out of five spots). The subsequent analyses of the selected digests by nanoHPLC-ES MS/MS allowed the attribution of amino acid sequences to peaks detected by ICP MS revealing the presence of two selenium-containing proteins: SIP 18 and HSP 12.     

Effect of the exchange integral K2s2p on the 2p-orbitals of the 1P and 3P states of the beryllium isoelectronic sequence arising from the configuration (1s)2(2s)(2p)

The ¹P and ³P states arising from the configuration (1s)²(2s)(2p) of the Be isoelectronic sequence are investigated. In the single configuration approximation, the energies of the two states are expressed as E⁰ + K_2s2p and E⁰ - K_2s2p, respectively. K_2s2p is the exchange integral between the 2s and 2p electrons and E⁰ is the energy of a model in which K_2s2p is deleted. First we calculate the 2s- and 2p-orbitals in this model. Second, by taking account of K_2s2p in this model, effects of this term on the 2p-orbitals in the ^1,3P states are investigated. In this manner, an explanation is given for the following facts which are obtained from a minimal Slater-type orbital set; (1) for Be and B⁺, the 2p-orbital of the ¹P state is broader than that of the ³P state; (2) for C²⁺, the extension of the 2p-orbital in the two states is almost the same; (3) for O⁴⁺ and Ne⁶⁺, in contrast to Be and B⁺, the 2p-orbital of the ¹P state is tighter than that of the ³P state.     

Binding energies of CH3F and CH2F2 calculated by the overlapping sphere SCF MS Xα method

Multiple scattering Xα calculations with overlapping spheres were performed on CH₃F and CH₂F₂ for all-valence region ionization potentials. Comparison with previous Xα calculations shows a substantial improvement.     

Theoretical study of the 1:1 and 2:1 (homo- and heterochiral) complexes of XOOX' (X, X' = H, CH3) with lithium cation

A theoretical study of the 1:1 and 2:1 complexes of XOOX' (X, X' = H, CH(3)) with the lithium cation has been carried out by means of ab initio computational methods up to the MP2/aug-cc-pVTZ level. The optical rotatory power and NMR parameters (absolute chemical shielding and indirect coupling constants) have been calculated. In addition, the racemization barriers within the complexes formed have been evaluated. Special attention has been paid concerning the differences between the 2:1 homo- and heterochiral complexes.     

HFS constants of Be I 1s22s2p 3p0, B I 1s22s2p24P and B I 1s22s2p22D obtained from the non-closed shell many-electron theory for excited states

Using the non-closed shell many-electron theory for excited states of Sinano?lu we compute the hyperfine structure constants of Be I 1s²2s2p ³P⁰, B I 1s²2s2p²⁴P and B I 1s²2s2p²²D. The quadrupole moment of ⁹Be is also newly determined to be, Q = 0.05494 barns.     

The large effects of electron correlation on the multiplet generalized oscillator strengths of non-closed shell systems: Be 1s22s21S → 1s22s2p 1P0 and B 1s22s22p 2p0 → 1s22s2p22D

Correlation effects are shown to change generalized oscillator strengths and inelastic form factors by large factors as large as 10, from the Hartree-Fock values. The effects are fully included in the charge wavefunctions of the non-closed shell many-electron theory by Sinano?lu. We calculate the charge wavefunctions and obtain from the generalized oscillator strength F_0η(q) versus ln q² and the integrated cross section σ_0η(E) versus lnE₁ for BeI 2s²¹S → 2s2p ¹P⁰ and BI 2s²2p ²P⁰ → 2s2p²²D cases, exemplifying the method.     

Determination of the oligomeric number and intermolecular distances of membrane protein assemblies by anisotropic 1H-driven spin diffusion NMR spectroscopy

Determination of the high-resolution quaternary structure of oligomeric membrane proteins requires knowledge of both the oligomeric number and intermolecular distances. The centerband-only detection of exchange (CODEX) technique has been shown to enable the extraction of the oligomeric number through the equilibrium exchange intensity at long mixing times. To obtain quantitative distances, we now provide an analysis of the mixing-time-dependent CODEX intensities using the 1H-driven spin diffusion theory. The exchange curve is fit to a rate equation, where the rate constants are proportional to the square of the dipolar coupling and the spectral overlap integral between the exchanging spins. Using a number of 13C- and 19F-labeled crystalline model compounds with known intermolecular distances, we empirically determined the overlap integrals of 13C and 19F CODEX for specific spinning speeds and chemical shift anisotropies. These consensus overlap integral values can be applied to structurally unknown systems to determine distances. Applying the 19F CODEX experiment and analysis, we studied the transmembrane peptide of the M2 protein (M2TMP) of influenza A virus bound to 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine bilayers. The experiment proved for the first time that M2TMP associates as tetramers in lipid bilayers, similar to its oligomeric state in detergent micelles. Moreover, the nearest-neighbor interhelical F-F distance between (4-19F)Phe30 is 7.9-9.5 angstroms. This distance constrains the orientation and the packing of the helices in the tetrameric bundle and supports the structural model derived from previous solid-state NMR 15N orientational data. Thus, the CODEX technique presents a general method for determining the oligomeric number and intermolecular distances in the approximately 10 angstroms range in membrane proteins and other complex biological assemblies.     

Conversion of indoles into quinolines through the n-1-c-2 fission by singlet-oxygen as a model experiment of biomimetic synthesis of quinine alkaloids

Photo-oxygenation of indole-3-acetaldehydes (28–30) followed by treatments with dimethyl sulphide and then dilute acetic acid gave 4-acylquinolines (13,31 and 32), respectively.     

Efficient large-scale purification of non-histone chromosomal proteins HMG1 and HMG2 by using Polybuffer-exchanger PBE94

A method for the efficient and practical large-scale purification of high-mobility group (HMG) non-histone chromosomal proteins, HMG1 and HMG2, from porcine thymus applying Polybuffer-exchanger PBE94 gel as anion-exchanger has been developed. This method affords higher resolution, purity and yield, than the conventional procedure of CM-Sephadex C-25 ion-exchange column chromatography. Furthermore, use of Polybuffer-exchanger PBE94 column chromatography led to direct preparation of HMG1 and HMG2 from loosely bound non-histone chromosomal protein fraction of chromatin without prefractional precipitation with trichloroacetic acid or prior extraction with perchloric acid. Thus, the application of PBE94 gel as an anion-exchanger to the subfractionation of other kinds of homologous protein is possible.     

Solid-state NMR study of amyloid nanocrystals and fibrils formed by the peptide GNNQQNY from yeast prion protein Sup35p

Sup35p is a prion protein found in yeast that contains a prion-forming domain characterized by a repetitive sequence rich in Gln, Asn, Tyr, and Gly amino acid residues. The peptide GNNQQNY7-13 is one of the shortest segments of this domain found to form amyloid fibrils, in a fashion similar to the protein itself. Upon dissolution in water, GNNQQNY displays a concentration-dependent polymorphism, forming monoclinic and orthorhombic crystals at low concentrations and amyloid fibrils at higher concentrations. We prepared nanocrystals of both space groups as well as fibril samples that reproducibly contain three (coexisting) structural forms and examined the specimens with magic angle spinning (MAS) solid-state nuclear magnetic resonance. 13C and 15N MAS spectra of both nanocrystals and fibrils reveal narrow resonances indicative of a high level of microscopic sample homogeneity that permitted resonance assignments of all five species. We observed variations in chemical shift among the three dominant forms of the fibrils which were indicated by the presence of three distinct, self-consistent sets of correlated NMR signals. Similarly, the monoclinic and orthorhombic crystals exhibit chemical shifts that differ from one another and from the fibrils. Collectively, the chemical shift data suggest that the peptide assumes five conformations in the crystals and fibrils that differ from one another in subtle but distinct ways. This includes variations in the mobility of the aromatic Tyr ring. The data also suggest that various structures assumed by the peptide may be correlated to the "steric zipper" observed in the monoclinic crystals.     

Accurate lifetime measurements of the 2p 3d 1 D 0 and 2p 3d 3 P 2 0 levels in N II with the beam-foil-laser method

We have obtained accurate values for the radiative lifetimes of the 2p 3d ¹ D ⁰ and 2p 3d ³ P ₂ ^o levels in NII by the cascade-free beam-foil-laser spectroscopy method. Our results are (2p 3d ¹ D ⁰)=0.346±0.012 ns and (2p 3d ³ P ₂ ^o )=0.457±0.020 ns. Comparison of these results with experimental and recent theoretical lifetimes reported previously is also made.Senior Research Associate of the Belgian FNRS     

Experimental and theoretical studies of the quenching of Li(3p,4p) by N2

Quenching mechanisms of the Li3p and Li4p states in collision with the nitrogen molecule are studied by laser-induced fluorescence spectroscopy and by a quantum chemical calculation. The Li3p state is observed to be efficiently quenched to the Li3s state detected as intense 3s-->2p emission. The Li4p state is efficiently quenched to the Li4s and Li3d states detected as 4s-2p and 3d-2p emissions, respectively. The potential-energy surfaces for the Li(2s-4p)N2 states show a large number of conical intersections and avoided crossings resulting from the couplings between the ionic [Li+(N2)-] and covalent configurations. There are a large number of stable excited states, and we give here the spectroscopic constants for the lowest two stable isomers correlating to Li2p+N2.     

Systematic determination of the Slater-Condon parameters of atoms and ions with 1s 2 2s m 2p n configurations

Semiempirical values of the Slater parameters F ²(2p,2p) and G ¹(2s, 2p) have been determined for the atoms and ions with the electron configurations 1s ²2s ^m2p ⁿ from the experimental atomic energy levels. Particular attention has been paid to get the values of the parameters to be used for semiempirical calculations on molecular electronic structure. The calculation has also yielded E _av's, the average energies of configurations of these atoms. Evaluation of the semiempirical or effective value of F ⁰ from E of an appropriate electron-transfer reaction, based on the idea presented by Anno [15], is also referred to in the present paper. The semiempirical values of the Slater parameters as well as those of E's and E _av's show almost linear dependence upon atomic number Z through isoelectronic series. From the overall tendency of the correlation lines, it is pointed out that the assignment of atomic energy levels of Na⁵⁺ (1s ²2p ⁴) must be wrong.

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Zusammenfassung Semiempirische Werte der Slater-Parameter F ²(2p,2p) und G ¹(2s, 2p) wurden für die Atome und Ionen mit der Elektronenkonfiguration 1s ²2s ^m2p ⁿ aus den experimentellen atomaren Energietermen bestimmt. Insbesondere wurden die Parameter bestimmt, die für semiempirische Berechnungen der Elektronenstruktur von Molekülen benötigt werden. Die Berechnung ergibt weiterhin Werte von E _av, der Durchschnittsenergie der Konfigurationen der genannten Atome. Die vorliegende Arbeit geht auch auf die Bestimmung des semiempirischen bzw. effektiven Wertes von F ⁰ aus E einer geeigneten Elektronenübertragungsreaktion ein, die auf die Arbeit von Anno [15] zurückgeht. Die semiempirischen Werte der Slater-Parameter sowie der E und E _av zeigen annähernd lineare Abhängigkeit von der Atomnummer Z innerhalb isoelektronischer Reihen. Aus dem Gesamtverhalten der genannten Kurven wird geschlossen, da die Zuordnung der atomaren Energieterme von Na⁵⁺(1s ²2p ⁴) falsch sein dürfte.

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Résumé Détermination à partir des niveaux d'énergie atomiques expérimentaux des valeurs semi-empiriques des paramètres de Slater F ²(2p, 2p) et G ¹(2s, 2p) pour les atomes et les ions ayant les configurations 1s ²2s ^m2p ⁿ. On a fait particulièrement attention d'obtenir les valeurs des paramètres à utiliser pour des calculs moléculaires semi-empiriques. Le calcul a aussi fourni les énergies moyennes des configurations de ces atomes. On évoque aussi le calcul de la valeur semi-empirique ou effective de F ⁰ à partir du E d'une réaction appropriée de transfert électronique, selon une idée de Anno [15]. Les valeurs semiempiriques des paramètres de Slater, ainsi que celles des E et E _moy, montrent une dépendance presque linéaire au nombre atomique Z à travers les séries isoélectroniques. A partir des tendances générales des lignes de corrélation, on remarque que l'attribution des niveaux d'énergie atomiques de Na⁵⁺(1s ²2p ⁴) doit être fausse.