Vibrational spectra and structure of zinc phthalocyanine

Semi-empirical molecular orbital calculations using PM3 Hamiltonian were employed to determine qualitative assignments of the vibrational spectrum of zinc phthalocyanine (ZnPc). The assignments are from the potential energy distribution calculations in the normal coordinate analysis and optimized geometry in the PM3 calculations. The structure of the ZnPc molecule is also deduced. (C) 1999 Elsevier Science B.V. All rights reserved.

Probing lanthanide ions binding on tRNA(Phe) by H-1 NMR

The structure of phenylalanine transfer ribonucleic acid (tRNA(Phe)) in solution was explored by H-1 NMR spectroscopy to evaluate the effect of lanthanide ion on the structural and conformational change. It was found that La3+ ions possess specific effects on the imino proton region of the H-1 NMR spectra for yeast tRNA(Phe). The dependence of the imino proton spectra of yeast tRNA(Phe) as a function of La3+ concentration was examined, and the results suggest that the tertiary base pair G(15). C-48, which is located in the terminal in the augmented dihydrouridine helix (D-helix), was markedly affected by La3+ (shifted to downfield by as much as 0.35). Base pair U-8. A(14) in yeast tRNA(Phe), which are stacked on G(15). C-48, was also affected by added La3+ when 1 similar to 2 Mg2+ were also present. Another imino proton that may be affected by La3+ in yeast tRNA(Phe) is that of the tertiary base pair G(19). C-56. The assignment of this resonance in yeast tRNA(Phe) is tentative since it is located in the region of highly overlapping resonances beween 12.6 and 12.2. This base pair helps to anchor the D-loop to the T Psi C loop. The binding of La3+ caused conformational change of tRNA, which is responsible for shifts to upfield or downfield in H-1 NMR spectra.

The influence of muffin-tin approximation on energy band gap

The influence of muffin-tin approximation on energy band gap was studied using LMTO-ASA (Linear Muffin-Tin Orbital-Atomic Sphere Approximation) approach. Since the diverse data are available for LaX(X=N, P, As, Sb), they are presented in our research as an example in order to test the reliability of our results. Four groups of muffin-tin radii were chosen, they were the fitted muffin-tin radii based on the optical properties of the crystals (the first), 1 : 1 for La : X(the second), 1.5 : 1 for La : X(the third), and a group of radii derived by making the charge in the interstitial space to be zero(the fourth). The results show that the fitted muffin-tin radii (the first group) give the best results compared with experimental values, and the predicted energy band gaps are very sensitive to the choice of muffin-tin radius in comparison with the other groups. The second and the third delivered results somewhere in between, while the fourth provided the worst results compared with the other groups. For the same crystal, with the increase of muffin-tin radius of lanthanum, the calculated energy band gaps decreased, going from semi-conductor to semimetal. This again clearly indicated the sensitivity of energy band structure on muffin-tin approximation.

Effect of lanthanum ions on tRNA(Phe) structure: Imino proton NMR spectroscopy

The effect of lanthanum ions on the structural and conformational change of yeast tRNA(Phe) was studied by H-1 NMR. The results suggest that the tertiary base pair (G-15)(C-48), which was located in the terminal in the augmented dihydrouridine helix (D-helix), was markedly affected by adding La3+ and shifted 0.33 downfield. Based pair (U-8)(A-14), which is associated with a tertiary interaction, links the base of the acceptor stem to the D-stem and anchors the elbow of the L structure, shifted 0.20 upfield. Another imino proton that may be affected by La3+ in tRNA(Phe) is the tertiary base pair (G-19)(C-56). The assignment of this resonance is tentative since it is located in the region of highly overlapping resonances between 12.6 and 12.2. This base pair helps to anchor the D-loop to the T psi C loop.

Three dimensional solution structure of neurotoxin CM-11 from the Ophiophagus hannah

The Ophiophagus hannah (King Cobra) neurotoxin CM-11 is a small protein with 72 amino acid residues, Based on complete assignments of H-1-NMR resonances and determination of secondary structures of CM-11, 349 distance and 27 dihedral angle constraints including 19 phi's and 8 chi's were collected from NOESY and DQF-COSY , and the chemical stereospecific assignment of beta(1)H was partially achieved, Twelve structures with lower energy was obtained via metric matrix distance geometry and refinement with simulated annealing, These structures have a low RMSD of 0.14 nm for backbone atoms and 0.20 nm for heavy atoms, with no distance constraint violation more than 0.05 nm, and no dihedral angle violation more than 3 degrees.

Bond-charge calculation of nonlinear optical susceptibilities of LiXO3 type complex crystals

Second order nonlinear optical (NLO) tensor coefficients of LiXO3 (X = I, Nb, Ta) type crystals have been evaluated on the basis of the dielectric theory of complex crystals and the modified bond charge model. The current method is capable of calculating single bond contributions to the total second order NLO susceptibility. The tenser values thus calculated agree well with experimental data. By introducing the subformula equation and the concept of the effective charge of one valence electron, we are able to successfully treat such complex crystals as LiXO3 type compounds. In addition, the bond charge expression is modified to a more reasonable form for complex crystals. (C) 1998 Elsevier Science B.V.

Theoretical study on the unimolecular fragmentation of ionized tetrahydroimidazole-substituted methylene beta-diketones

Semiempirical molecular orbital calculations on the unimolecular mass spectrometric fragmentation of tetrahydroimidazole-substituted methylene beta-diketones are carried out by Austin Model 1 method, and the calculated results give a strong support to our experimental results reported previously. The optimum of the investigated molecular configuration indicates that the two hydrogen atoms attached to nitrogen atom have different activities due to their chemical environment; the relative energies of the ions in fragmentation pathway of ionized tetrahydroimidazole-substituted methylene beta-diketones provide indirectly an evidence for both the existence of ion/neutral complex and the stabilities of these ions.

Gas-phase ion-molecule reactions of C-60 and theoretical studies of [C60C2H3O](+) adduct cations

Gas-phase ion-molecule reactions of buckminsterfullerene (C-60) with the acetyl cation CH3-C-+=O (m/z 43) and formylmethyl cation (CH2)-C-+-CH=O (m/z 43, or oxiranyl cation), generated from the self-chemical ionization of acetone and vinyl acetate, respectively, were studied in the ion source of a mass spectrometer. Adduct cations [C60C2H3O](+) (m/z 763) and protonated C-60, [C60H](+) (m/z 721), were observed as the major products. AM1 semiempirical molecular orbital calculations on the possible structures, stabilities and charge locations of the isomers of the adducts [C60C2H3O](+) were carried out at the restricted Hartree-Fock level. The results indicated that the sigma-addition product [C-60-COCH3](+) is the most stable adduct for the reaction of C-60 with CH3-C-+=O rather than that resulting from the [2+2] cycloaddition. The [2+3] cycloadduct and the sigma-adduct [C60CH2CHO](+) might be the most possible coexisting products for the reactions of C-60 with (CH2)-C-+-CH=O or oxiranyl cation. Other [C60C2H3O](+) isomers are also discussed. (C) 1997 by John Wiley & Sons, Ltd.

Relationship between the dissolution behaviours and current efficiencies of La, Ce, Pr and Nd in their chloride molten salts

The dissolution behaviours of La and Nd in their chloride molten salts were studied by means of the see-through cell, electrochemical weak polarization and quantum chemistry (extended Huckel molecular orbital). The reasons for the low current efficiencies of rare earth metals and the difference between La and Nd in their own chloride electrolytes on the basis of the solubility, rate of dissolution, and existing state of the metals dissolved as well as the structure of the melts, are discussed.

FORMATION OF [C60C5H5] ADDUCT CATIONS AND THEORETICAL-STUDY OF THE ISOMERS

We study here the reactions between C-60 and planar C5H5+ cations that lead to the formation of [C60C5H5](+) adduct cations in the chemical ionization source of the mass spectrometer. The structures, stabilities and charge locations of some possible isomers of [C60C5H5](+): sigma-adduct, pi-complex, [1,4]- and [1,2]-addition cations, are studied by AM1 semiempirical molecular orbital calculations. We find that the most stable is the sigma-addition cation. Another interesting and stable structure is the pi-complex cation which is bonded by the electrostatic interaction at the inter-ring distance of 1.589 Angstrom with the C-5v symmetry. The C5H5+ cyclopentadienium cation seems to be an ''inverted umbrella'' sitting on a five-membered ring of the C-60 cage.

COORDINATION CHEMISTRY AND SUPERCONDUCTIVITY

Analysing the coordination state of copper ions in cuprate superconductors, it is found that the larger the energy splitting between d(x2-y2) and d(z2) orbitals of Cu or the higher the energy of the d(x2-y2) orbital, the higher the Tc. Thus, appropriate coordination structures and strong-field ligands must be chosen for expanding the energy splitting and increasing the energy of the d(x2-y2) orbital when searching for new high-Tc superconductors. Summarizing the experimental results of ESR and XPS, it is considered that the [Cu2+ - O open-square-box 2- - Cu3+] resonance exists in cuprate superconductors and the electron field breathing mode is present. Analysing the mechanism and the relationship between the coordination state of Cu and Tc, we consider that the two dimensional Cu-O planes are responsible for the superconductivity of YBa2Cu3O7-y.

Cold event at 5 500 a BP recorded in mud sediments on the inner shelf of the East China Sea

A 700-year record (1.0-1.5 a resolution) of the East Asian winter monsoon (EAWM), based on grain-size analysis and AMS(14)C dating of Core EC2005 from the inner-shelf mud wedge of the East China Sea (ECS), was compared with the Dongge stalagmite delta O-18 record during the mid-Holocene. The upper muddy section of Core EC2005 has been formed mainly by suspended sediments derived from the Changjiang (Yangtze) River mouth since 7.3 ka BP. High precipitation and a strengthened EAWM might have played key roles in the high sedimentation rate (1 324-1 986 cm/ka) between 5.9-5.2 ka BP. The EAWM strengthened when the Asian summer monsoon weakened, especially around 5 500 a BP, which corresponded to a worldwide cold event. The EAWM during the mid-Holocene shows statistically significant solar periodicities at 62 and 11 a. The 5 500 a BP cold event might be resulted from orbital forcing and changes in solar activity.

Evolution and variability of the East Asian summer monsoon during the Pliocene: Evidence from clay mineral records of the South China Sea

The Late Pliocene is thought to be characterized by the simultaneous intensification of both the East Asian winter monsoon (EAWM) and East Asian summer monsoon (EASM). However, the evolution of the EASM during the Pliocene remains still controversial and only little is known about the dynamics of the EASM during the Pliocene on orbital time scales. Here we use clay mineral assemblages in sediments from Ocean Drilling Program (ODP) Site 1143 in the southern South China Sea (SCS) to obtain proxy records of past changes in the EASM climate during the Pliocene. Provenance analysis suggests that illite, chlorite and kaolinite originated mainly from the Mekong River drainage area. Smectite was derived mainly from the Indonesian islands. The kaolinite/illite ratio and the chemical index of alteration (CIA) of siliciclastic sediments allowed us to reconstruct the history of chemical weathering and physical erosion of the Mekong River drainage area and thus, the evolution of,the EASM during the Pliocene. Our clay minerals proxy data suggests a stronger EASM during the Early Pliocene than during the Late Pliocene. We propose that the long-term evolution of the EASM has been driven by global cooling rather than the uplift of the Tibetan Plateau. Spectral analysis of kaolinite/ illite ratio displays a set of strong periodicities at 100 ka, 30 ka, 28 ka, 25 ka, and 22 ka. with no clear obliquityrelated signal. Our study suggests that the Pliocene EASM intensity on orbital time scales is not only controlled by the Northern Hemisphere summer insolation, but also strongly influenced by equatorial Pacific ENSO-like ocean atmosphere dynamics. (C) 2010 Elsevier B.V. All rights reserved.

A unified criterion for initiation of sediment motion and inception of sheet flow under water waves

A unified criterion is developed for initiation of non-cohesive sediment motion and inception of sheet flow under water waves over a horizontal bed of sediment based on presently available experimental data. The unified threshold criterion is of the single form, U-o = 2 pi C[1 + 5(T-R/T)(2)](-1/4), where U-o is the onset velocity of sediment motion or sheet flow, T is wave period, and C and T-R are the coefficients. It is found that for a given sediment, U-o initially increases sharply with wave period, then gradually approaches the maximum onset velocity U-o = 2 pi C and becomes independent of T when T is larger. The unified criterion can also be extended to define sediment initial motion and sheet flow under irregular waves provided the significant wave orbital velocity and period of irregular waves are introduced in this unified criterion.

Near-Space Wide-Swath Radar Imaging With Multiaperture Antenna

Near-space, defined as the altitude region between 20 and 100 km, offers many capabilities that are not accessible for low Earth-orbit (LEO) satellites or airplanes because it is above storm and not constrained by orbital mechanics and high fuel consumption. Hence, a high flying speed can be obtained for the maneuvering vehicles operating in near-space. This offers a promising solution to simultaneous high-resolution and wide-swath synthetic aperture radar (SAR) imaging. As such, one near-space wide-swath SAR imaging technique is presented in this letter. The system configuration, signal model, and imaging scheme are described. An example near-space SAR system is designed, and its imaging performance is analyzed. Simulation results show that near-space maneuvering vehicle SAR indeed seems to be a promising solution to wide-swath SAR imaging.