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51.
Johannes Siemons 《Journal of Geometry》1984,22(2):178-182
We show that 2-designs with given parameters v, k, are in one-to-one correspondence to polynomials that solve a certain differential equation and have coefficients equal to zero or one. From this result we derive an existence theorem whereby designs correspond to integer points on a sphere in Euclidean space. 相似文献
52.
Johannes Häusler 《Monatshefte für Chemie / Chemical Monthly》1982,113(10):1213-1216
Meldrum's acid (2) is acylated by diketen affording the acylMeldrum's acid3. In aqueous bicarbonate its 3-oxogroup is selectively reduced by sodium tetrahydroborate giving the alcohol4, which readily undergoes cyclization in refluxing dioxane leading to the title pyrone7. Under identical conditions3 produces the pyrone6 with the pyrone carboxylic acid5 as intermediate. 相似文献
53.
Gary D. Jaycox Roger Sinta Johannes Smid 《Journal of polymer science. Part A, Polymer chemistry》1982,20(6):1629-1638
Insoluble complexes are formed in acidic aqueous media when poly(acrylic acid) (PAA) and poly-(vinylbenzo-18-crown-6) (P18C6) or polyvinylbenzoglymes are mixed. Complex formation results from hydrogen bonding between carboxyl groups and crown ether- or glyme–oxygen atoms as well as from hydrophobic interactions. The precipitation is pH dependent and was determined as a function of the ratio PAA to P18C6 or to polyglyme at different HCl concentrations in 10?4M solutions of polycrown or polyglyme. Precipitation is nearly quantitative in 0.01N HCl. The compositions of PAA/P18C6 precipitates were determined as a function of the initial PAA/P18C6 ratio in solution. The complexes with P18C6 can be solubilized in acidic media when crown-complexable cations (K+, Cs+, Ba2+) are added, but the charged P18C6 reprecipitates in basic solution as a polysalt complex with the PAA–polyanion. More stable PAA–P18C6 complexes in the form of fibers can be obtained by interfacial complex formation. Poly(methacrylic acid) is less effective as a complex former. 相似文献
54.
Johannes Siemons 《Archiv der Mathematik》1984,43(6):483-487
55.
Keyes TE Leane D Forster RJ Coates CG McGarvey JJ Nieuwenhuyzen MN Figgemeier E Vos JG 《Inorganic chemistry》2002,41(22):5721-5732
A detailed spectroscopic and electrochemical study of a series of novel phenolate bound complexes, of general formulas [M(L-L)(2)(box)](PF(6)), where M is Os and Ru, L-L is 2,2-bipyridine or 2,2-biquinoline, and box is 2-(2-hydroxyphenyl)benzoxazole, is presented. The objectives of this study were to probe the origin of the LUMOs and HOMOs in these complexes, to elucidate the impact of metal and counter ligand on the electronic properties of the complex, and to identify the extent of orbital mixing in comparison with considerably more frequently studied quinoid complexes. [M(L-L)(2)(box)](PF(6)) complexes exhibit a rich electronic spectroscopy extending into the near infrared region and good photostability, making them potentially useful as solar sensitizers. Electrochemistry and spectroscopy indicate that the first oxidation is metal based and is associated with the M(II)/(III) redox states. A second oxidative wave, which is irreversible at slow scan rates, is associated with the phenolate ligand. The stabilities of the oxidized complexes are assessed using dynamic electrochemistry and discussed from the perspective of metal and counter ligand (LL) identity and follow the order of increasing stability [Ru(biq)(2)(box)](+) < [Ru(bpy)(2)(box)](+) < [Os(bpy)(2)(box)](+). Electronic and resonance Raman spectroscopy indicate that the lowest energy optical transition for the ruthenium complexes is a phenolate (pi) to L-L (pi) interligand charge-transfer transition (ILCT) suggesting the HOMO is phenolate based whereas electrochemical data suggest that the HOMO is metal based. This unusual lack of correlation between redox and spectroscopically assigned orbitals is discussed in terms of metal-ligand orbital mixing which appears to be most significant in the biquinoline based complex. 相似文献
56.
The primary all-trans to 13-cis chromophore isomerization of the light driven chloride pump halorhodopsin has been studied by means of transient absorption spectroscopy in the visible and mid-infrared regime at a time resolution of better than 100 and 220 fs, respectively. The picosecond vibrational dynamics are dominated by two time constants, i.e., 2 and 7.7 ps in accordance with the biphasic decay of the retinal excited electronic state and electronic ground state formation with 1.5 and 6.6 ps. The transient vibrational spectra of the participating electronic states strongly suggest the existence of two distinct S1 populations as a result of an early branching reaction. It is shown that the 13-cis product is formed with the fast time constant, whereas the all-trans educt state is repopulated via both time constants. Concomitant protein dynamics are indicated by spectral changes on a similar time scale in the amide region. 相似文献
57.
Yano J Pushkar Y Glatzel P Lewis A Sauer K Messinger J Bergmann U Yachandra V 《Journal of the American Chemical Society》2005,127(43):14974-14975
The biological generation of oxygen by the oxygen-evolving complex in photosystem II (PS II) is one of nature's most important reactions. The recent X-ray crystal structures, while limited by resolutions of 3.2-3.5 A, have located the electron density associated with the Mn4Ca cluster within the multiprotein PS II complex. Detailed structures critically depend on input from spectroscopic techniques, such as EXAFS and EPR/ENDOR, as the XRD resolution does not allow for accurate determination of the position of Mn/Ca or the bridging and terminal ligand atoms. The number and distances of Mn-Mn/Ca/ligand interactions determined from EXAFS provide important constraints for the structure of the Mn4Ca cluster. Here, we present data from a high-resolution EXAFS method using a novel multicrystal monochromator that show three short Mn-Mn distances between 2.7 and 2.8 A and, hence, the presence of three di-mu-oxo-bridged units in the Mn4Ca cluster. This result imposes clear limitations on the proposed structures based on spectroscopic and diffraction data and provides input for refining such structures. 相似文献
58.
Carstens MG van Nostrum CF Ramzi A Meeldijk JD Verrijk R de Leede LL Crommelin DJ Hennink WE 《Langmuir : the ACS journal of surfaces and colloids》2005,21(24):11446-11454
Methoxypoly(ethylene glycol)-b-oligo-L-lactate (mPEG-b-OLA) diblock oligomers with monodisperse OLA blocks were obtained by fractionation of polydisperse block oligomers using preparative HPLC. The fractionated oligomers were composed of an mPEG block with a molecular weight of 350, 550, or 750 and an OLA block with a degree of polymerization of 4, 6, 8, or 10. The diblock oligomers with a low PEG content were fully amorphous, with glass transition temperatures ranging from -60 to -20 degrees C, indicating that the blocks were miscible. Upon heating aqueous dispersions of the block oligomers, cloud points, depending on the PEG/OLA ratio of the block oligomer, were observed at temperatures above 40 degrees C. The monodispersity of the hydrophobic block enabled the amphiphilic molecules to form nanoparticles in water with a hydrodynamic radius of 130-300 nm, at concentrations above the critical aggregation concentration (0.4-1 mg/mL), whereas polydisperse mPEG-b-OLAs gave formation of large aggregates. Static light scattering measurements showed that the nanoparticles have a low density (0.6-25 mg/mL), indicating that the particles are highly hydrated. In agreement herewith, the (1)H NMR spectra of nanoparticles in D2O closely resembled spectra in a good solvent for both blocks (CDCl3). It is therefore suggested that the nanoparticles contain a hydrated core of mPEG-b-OLA block oligomers, stabilized by a thin outer PEG layer. The particles were stable for two weeks, except for the mPEG350 series and mPEG750-b-OLA4, indicating that both the PEG block size and the PEG weight fraction of the oligomers determine their stability. The evident self-emulsifying properties of mPEG-b-oligo-l-lactates with monodisperse hydrophobic blocks as demonstrated in this study, together with their expected biocompatibility and biodegradability, make these systems well suitable for pharmaceutical applications. 相似文献
59.
N,N-Dimethylformamide () and N,N-dimethylpivalamide () react with carbonyl chloride isocyanate () in the presence of antimony pentachloride to afford the amino substituted 1-oxa-3-azabutatrienium hexachloroantimonates ,. An X-ray diffraction analysis of confirms the proposed structure. The heterocumulenes , react with aldehydes, ketones and tertiary carboxamides to give the amino substituted 2-azaallenium salts - in high yields. 相似文献
60.
By the phase transfer catalyzed reaction of 9(10H)-acridinone with 1-bromo-2-propyne, 10-(2-propynyl)-9(10H)-acridinone is synthesized. As prototropic rearrangement products of this 10-(1,2-propadienyl)-9(10H)-acridinone and 10-(1-propynyl)-9(10H)-acridinone are obtained, Under the given conditins 1-bromo-2butyne leads to 10-(2-butynyl)-9(10H)-acridinone and 2-chloro-3-butyne leads to 10-(1-methyl-1,2-propddienyl)-9(10H)-acridinone, 10-(1-methyl-2-propynyl)-9(10H)-acridinone, 9-(1-methyl-2-propynyloxy)acridine and 10-[1-methyl-3-(3,4-dimethylphenyl-2-propynyl)]-9(10H)-acridinone. The formation of the products is experimentally confirmed and with published work compared. 相似文献