Helicity amplitudes A1/2 and A3/2 for the D13(1520) resonance obtained from the gamma-->p-->-->ppi(0) Reaction

The helicity dependence of the gamma-->p-->-->ppi(0) reaction has been measured for the first time in the photon-energy range from 550 to 790 MeV. The experiment, performed at the Mainz microtron MAMI, used a 4pi-detector system, a circularly polarized, tagged photon beam, and a longitudinally polarized frozen-spin target. These data are predominantly sensitive to the D13(1520) resonance and are used to determine its helicity amplitudes.     

Multiple defect-core hexagonal photonic crystal fiber with flattened dispersion and polarization maintaining properties

In this paper, we present a dispersion controlling technique with a multiple defect-core hexagonal photonic crystal fiber (MD-HPCF). By omitting air holes in the core region of the conventional HPCF and adjusting the size of air holes around the newly formed core, we can successfully design low flattened dispersion PCF with low confinement loss, as well as high birefringence. The low flattened dispersion feature, as well as the low confinement losses and high birefringence are the main advantages of the proposed PCF structure, making it suitable as chromatic dispersion controller, dispersion compensator, and/or polarization maintaining fiber.     

Stabilities and isomeric equilibria in solutions of monomeric metal-ion complexes of guanosine 5'-triphosphate (GTP4-) and inosine 5'-triphosphate (ITP4-) in comparison with those of adenosine 5'-triphosphate (ATP4-)

Under experimental conditions in which the self-association of the purine-nucleoside 5'-triphosphates (PuNTPs) GTP and ITP is negligible, potentiometric pH titrations were carried out to determine the stabilities of the M(H;PuNTP) and M(PuNTP)2-complexes where M2+ = Mg2+, Ca2+, Sr2+. Ba2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, or Cd2+ (I = 0.1 M, 25 degrees C). The stabilities of all M(GTP)2- and M(ITP)2- complexes are significantly larger than those of the corresponding complexes formed with pyrimidine-nucleoside 5'-triphosphates (PyNTPs), which had been determined previously under the same conditions. This increased complex stability is attributed, in agreement with previous 1H MNR shift studies, to the formation of macrochelates of the phosphate-coordinated metal ions with N7 of the purine residues. A similar enhanced stability (despite relatively large error limits) was observed for the M(H;PuNTP) complexes, in which H+ is bound to the terminal y-phosphate group, relative to the stability of the M(H;PyNTP)- species. The percentage of the macrochelated isomers in the M(GTP)2- and M(ITP)2- systems was quantified by employing the difference log KMM(PuNTP)-log KMM(PyNTP); the lowest and highest formation degrees of the macrochelates were observed for Mg(ITP)2- and Cu(GTP)2- with 17 +/- 11% and 97 +/- 1%, respectively. From previous studies of M(ATP)2- complexes, it is known that innersphere and outersphere macrochelates may form; that is, in the latter case a water molecule is between N7 and the phosphate-coordinated M2+. Similar conclusions are reached now by comparisons with earlier 1H MNR shift measurements, that is, that Mg(GTP)2- (21 +/- 11%), for example, exists largely in the form of an outersphere macrochelate and Zn(GTP)2- (68 +/- 4%) as an innersphere one. Generally, the overall percentage of macrochelate falls off for a given metal ion in the order M(GTP)2- > M(ITP)2- > M(ATP)2-; this is in accord with the decreasing basicity of N7 and the steric inhibition of the (C6)NH2 group in the adenine residue. Furthermore, although the absolute stability constants of the previously studied M(GMP), M(IMP), and M(AMP) complexes differ by about two to three log units from the present M(PuNTP)2- results, the formation degrees of the macrochelates are astonishingly similar for the two series of nucleotides for a given metal ion and purine-nucleobase residue. The conclusion that N7 of the guanine residue is an especially favored binding site for metal ions is also in accord with observations made for nucleic acids.     

A platinum-ruthenium dinuclear complex bridged by bis(terpyridyl)xanthene

4,5-Bis(terpyridyl)-2,7-di-tert-butyl-9,9-dimethylxanthene (btpyxa) was prepared to serve as a new bridging ligand via Suzuki coupling of terpyridin-4'-yl triflate and 2,7-di-tert-butyl-9,9-dimethylxanthene-4,5-diboronic acid. The reaction of btpyxa with either 1 equiv or an excess of PtCl(2)(cod) (cod = 1,5-cyclooctadiene) followed by anion exchange afforded mono- and dinuclear platinum complexes [(PtCl)(btpyxa)](PF(6)) ([1](PF(6))) and [(PtCl)(2)(btpyxa)](PF(6))(2) ([2](PF(6))(2)), respectively. The X-ray crystallography of [1](PF(6)).CHCl(3) revealed that the two terpyridine units in the ligand are nearly parallel to each other. The heterodinuclear complex [(PtCl)[Ru((t)Bu(2)SQ)(dmso)](btpyxa)](PF(6))(2) ([4](PF(6))(2)) (dmso = dimethyl sulfoxide; (t)Bu(2)SQ = 3,5-di-tert-butyl-1,2-benzosemiquinone) and the monoruthenium complex [Ru((t)Bu(2)SQ)(dmso)(trpy)](PF(6)) ([5](PF(6))) (trpy = 2,2':6',2' '-terpyridine) were also synthesized. The CV of [2](2+) suggests possible electronic interaction between the two Pt(trpy) groups, whereas such an electronic interaction was not suggested by the CV of [4](2+) between Pt(trpy) and Ru((t)Bu(2)SQ) frameworks.     

化学与环境污染

科学技术的进步可以促进生产事业的发展,使人民生活更为丰富,更加方便,但也会因而发生各种公害以及破坏自然环境等问题。在众多的环境污染问题之中,以由化学品所造成的污染最为严重。本文目的是阐明由于人类的活动如何造成大气、水、土壤等自然环境的化学污染。只有当人们普遍树立起环境意识之时,才能形成社会力量来共同保护自身的生活环境。要积极发扬化学为人类的造福作用,同时注意防止化学品对环境污染之害。     

Calixarene-coated water-soluble CdSe-ZnS semiconductor quantum dots that are highly fluorescent and stable in aqueous solution

A simple method for the preparation of highly fluorescent and stable, water-soluble CdSe-ZnS quantum dots is reported using calix[4]arene carboxylic acids as surface coating agents; the coating of the surface with the calixarene and the conjugation of antibodies to the quantum dots are confirmed by fluorescence correlation spectroscopy.     

Multi-Photon Fluorescence Correlation Spectroscopy: a Quantification of Tryptophan Methylester Solutions by Visible Emission

A multi-photon excitation fluorescence correlation system has been developed. The emission from tryptophan methylester solution was observed by this system and analyzed by the intensity correlation function of the visible emission, which originates from the two-photon excitation of photo products generated through a five-photon process. The intensity and the product concentration were proportional to the concentration of tryptophan methylester at a lower concentration range and thus the generation process is a single molecular reaction. The correlation analysis determined the concentration of tryptophan methylester down to 5 μM. The photo product generation from tryptophan solution was enhanced by a potassium iodide addition. These results suggest a new quantification method of tryptophan derivatives.     

A monoterpene alkaloid from incarvillea sinensis

A novel monoterpene alkaloid, named incarvillateine E, possessing three moles of incarvilline moieties, has been obtained from the aerial parts of Incarvillea sinensis LAM. (Bignoniaceae). On the basis of spectroscopic evidence, the structure of incarvillateine E has been characterized.     

Transport at surface nanostructures measured by four-tip STM

For in situ measurements of local electrical conductivity of well-defined crystal surfaces in ultrahigh vacuum, we have developed two kinds of microscopic four-point probe methods. One is a ‘four-tip STM prober’, in which independently driven four tips of scanning tunneling microscope (STM) are used for four-point probe conductivity measurements. The probe spacing can be changed from 500 nm to 1 mm. The other one is monolithic micro-four-point probes, fabricated on silicon chips, whose probe spacing is fixed around several μm. These probes were installed in scanning-electron-microscopy/electron-diffraction chambers, in which the structures of sample surfaces and probe positions were in situ observed. The probes can be positioned precisely on aimed areas on the sample with aid of piezo-actuators. With these machines, the surface sensitivity in conductivity measurements has been greatly enhanced compared with macroscopic four-point probe method. Then the conduction through the topmost atomic layers (surface-state conductivity) and influence of atomic steps upon conductivity could be directly measured. The STM prober is mainly described here.