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1.
Results of ab initio self-consistent-field (SCF) and density functional theory (DFT) calculations of the gas-phase structure, acidity (free energy of deprotonation, ΔGo), and aromaticity of 1,2-diseleno-3,4-dithiosquaric acid (3,4-dithiohydroxy-3-cyclobutene-1,2-diselenone, H2C4Se2S2) are reported. The global minimum found on the potential energy surface of 1,2-diseleno-3,4-dithiosquaric acid presents a planar conformation. The ZZ isomer was found to have the lowest energy among the three planar conformers and the ZZ and ZE isomers are very close in energy. The optimized geometric parameters exhibit a bond length equalization relative to reference compounds, cyclobutanediselenone, and cyclobutenedithiol. The computed aromatic stabilization energy (ASE) by homodesmotic reaction (Eq 1) is −20.1 kcal/mol (MP2(fu)/6-311+G** //RHF/6-311+G**) and −14.9 kcal/mol (B3LYP//6-311+G**//B3LYP/6-311+G**). The aromaticity of 1,2-diseleno-3,4-dithiosquaric acid is indicated by the calculated diamagnetic susceptibility exaltation (Λ) −17.91 (CSGT(IGAIM)-RHF/6-311+G**//RHF/6-311+G**) and −31.01 (CSGT(IGAIM)-B3LYP/6-311+G**//B3LYP/6-311+G**). Thus, 1,2-diseleno-3,4-dithiosquaric acid fulfils the geometric, energetic and magnetic criteria of aromaticity. The calculated theoretical gas-phase acidity is ΔGo 1(298K)=302.7 kcal/mol and ΔGo 2(298K)=388.4 kcal/mol. Hence, 1,2-diseleno-3,4-dithiosquaric acid is a stronger acid than squaric acid(3,4-dihydroxy-3-cyclobutene-1,2-dione, H2C4O4). Received: 11 April 2000 / Accepted: 7 July 2000 / Published online: 27 September 2000  相似文献   

2.
Syntheses of 3-Hydroxy-4-methyl-3-cyclobutene-1,2-dione (Methylmoniliformin) New routes to 3-hydroxy-4-methyl-3-cyclobutene-1,2-dione (9) , the lowest homologue of the mycotoxine moniliformin are described. A common feature of all pathways is the synthesis of methylcyclobutanes having the oxidation level 6. Precursors, which are easily transformed to 9 by acid catalyzed hydrolysis, include [2+2]-cycloadducts of in situ generated methyl ketene to tetraethoxyethylene and [2+2]-photocycloadducts of dichlorovinylenecarbonate with 1,1-dichloro-1-propene. The acid hydrolysis of [2+2]-cycloadducts of chlorotrifluoroethylene to N, N-diethyl-1-propynylamine yields the diethylamide of 9 (=22) in 50% overall yield. In addition, a convenient one-pot-two-steps synthesis of a new electronrich ethylene, 1,1,2-triethoxy-2-trimethylsilyloxy-ethylene (11) , is described.  相似文献   

3.
《Tetrahedron》1987,43(5):959-970
Esters of oxalic acid, 3,4-dihydroxy-3-cyclobutene-1,2-dione (squaric acid), and oxamic acid, are reduced cathodically at modest potentials. In aprotic solvent, and on the cyclic voltammetric time scale, the esters are cleaved to the corresponding alkane. For oxalates, the mechanism of cathodic cleavage was investigated thoroughly by voltammetry, coulometry, and detailed product analysis. On the time scale of controlled potential electrolysis the rapid electrogenerated base-catalysed hydrolysis of the esters by adventitious water competes with cathodic cleavage. Similarly, rapid base-catalysed transesterification involving oxalates and added alcohols is observed which provides a practical method of reductively cleaving alcohols to alkanes by co-electrolysis of a mixture of alcohol and readily available oxalate (e.g. diethyloxalate). The leaving group in such cathodic fragmentation is the half-ester anion and the efficiency of reaction depends on the stability of the other, radical, fragment.  相似文献   

4.
1 INTRODUCTION In the past decades, there have been great efforts to research on the molecules nonlinear opti- cal (NLO) properties in which theoretical calcu- lation[1~3] became a powerful tool because it not only explains the micro-mechanism of the mo…  相似文献   

5.
周立新 《中国化学》2000,18(6):808-814
Results of ab initio self-consistent-field (SCF) and density functional theory (DFT) calculations of the gas-phase structure,acidity (free energy of deprotonation,G0) and aro-maticity of tetraselenosquaric acid (3,4-diselenyl-3-cy-dobutene-1,2-diselenone,H2C4Se4) are reported.The global minimum found on the potential energy surface of tetraselenosquaric acid presents a planar conformation.The ZZ iso-mer was found to have the lowest energy among the three planar conformers and the ZZ and ZE isomers are very dose in energy.The optimized geometric parameters exhibit a bond length equalization relative to reference compounds,cyclobu-tanediselenone,and cydobutenediselenol.The computed aromatic stabilization energy (ASE) by homodesmotic reaction is -77.4 (MP2(fu)/6 - 311 G //RHF/6 - 311 G) and - 54.8 kJ/mol (B3LYP/6 - 311 G //B3LYP/6 -311 G).The aromaticity of tetraselenosquaric add is indicated by the calculated diamagnetic susceptibility exaltation (A) - 19.13 (CSGT(IGAEM) - RHF/6 - 311 G// RHF/6-  相似文献   

6.
Magnetic resonance angiography (MRA) has put forth an impetus for the development of macromolecular GdIII complexes that have a prolonged lifetime in the vascular system. Herein, we report the synthesis and GdIII complexation of a new sugar conjugate based on inulin and the DO3A ligand (DO3A = 1,4,7,10-tetraazacyclododecan-1,4,7-triacetic acid). Two API-DO3ASQ conjugates (API = O-(aminopropyl)inulin, SQ = squaric acid = 3,4-dihydroxy-3-cyclobutene-1,2-dione) with different degrees of substitution (ds = 0.7 and ds = 1.5) were prepared from API by using the diethyl ester of squaric acid as a linking agent for the DO3A chelate. The efficacies of the resulting GdIII compounds were evaluated by investigation of their water 1H longitudinal-relaxation-rate enhancements at variable field (NMRD). A dramatic increase in relaxivity was observed in the more highly substituted conjugate (ds = 1.5); this prompted us to do a variable-temperature (17)O study in order to further characterize the relaxation parameters involved in this system. [Gd(API-DO3ASQ)] shows promising properties for application as a contrast agent for MRI.  相似文献   

7.
The laser desorption mass spectrometry of the oxocarbon squaric acid (3,4-dihydroxy-3-cyclobutene-1,2-dione) and its salts of the form A2C4O4 (A = cation) is described. Both positive and negative ion spectra were obtained. The positive ion spectrum of the acid is characterized by an ion corresponding to loss of CO from [M + H]+. The negative ion spectrum shows an intense [M ? H]? peak in addition to a dimer species. The alkali salt spectra contain [M + A]+ in the positive mode and [M ? A]? and an intense [C4HO4]? in the negative mode. The smaller alkali salts also have an [M + H]+ adduct ion. Unlike the alkali squarates, the ammonium salt shows ions corresponding to losses of neutrals from the molecular adduct in the positive ion spectrum and a dimer species in the negative ion spectrum. Molecular weight information was obtained in all cases. A (bis) dicyanomethylene derivative of potassium squarate was also studied. Some field desorption mass spectrometry results are presented for comparison.  相似文献   

8.
Four new pyrrolidine alkaloids, broussonetines M, O, P, and Q, were isolated from the branches of Broussonetia kazinoki SIEB, (Moraceae). Broussonetines M, O, P, and Q were formulated as (2R,3R,4R,5R)-2-hydroxymethyl-3,4-dihydroxy-5-[(10S)-10,13-dihydroxy-tri decyl]pyrrolidine (1), (2R,3R,4R,5R)-2-hydroxymethyl-3,4-dihydroxy-5-[(E)9-oxo-13-hydroxy-3- tridecenyl]pyrrolidine (2), (2R,3R,4R,5R)-2-hydroxymethyl-3,4-dihydroxy-5-[(E)10-oxo-13-hydroxy-3-++ +tridecenyl]pyrrolidine (3), and (2R,3S,4R,5R)-2-hydroxymethyl-3-hydroxy-4-(beta-D-glucopyranosyloxy++ +)-5-[10-oxo-13-(beta-D-glucopyranosyloxy)tridecyl]pyrrolidine (4) respectively, by spectroscopic and chemical methods. 1-4 inhibited beta-glucosidase, beta-galactosidase and beta-mannosidase.  相似文献   

9.
Three novel conjugated polymers bearing 3,4-bis(4-hexylthiophen-2-yl)-3-cyclobutene-1,2-dione unit in their main chain have been synthesized successfully in good yields through Suzuki or Stille coupling reaction.Their molecular structures have been confirmed by FT-IR,~1H NMR and ~(13)C NMR.All these copolymers exhibit broad and strong absorption bands in UV-vis region,and their optical band gaps are calculated to be 1.6-2.0 eV.suggesting that they have good coverage with the solar spectrum.These polymers...  相似文献   

10.
11.
Lewis JA  Cohen SM 《Inorganic chemistry》2004,43(21):6534-6536
The lead(II) ion is regarded as a serious environmental contaminant. A considerable need exists to develop selective ligands for remediation of this metal ion. Herein, the coordination chemistry of lead(II) is investigated with three O,S donor ligands: thiomaltol, 3-hydroxy-1-methyl-2(1H)-pyridinethione (3,2-HOPTO), and 3-hydroxy-1,2-dimethyl-4(1H)-pyridinethione (3,4-HOPTO). The X-ray structures of [Pb(thiomaltolato)(2)] and [Pb(3,4-HOPTO)(2)] have been solved, revealing the expected 4-coordinate geometries. Electronic spectra have been obtained for the lead(II) complexes with all three ligands. Preliminary solution studies show that the thiomaltol ligand binds lead(II) preferentially over magnesium(II) and calcium(II); however, [Pb(thiomaltolato)(2)] is not stable in the presence of 1 equiv of EDTA. Tetradentate ligands derived from these O,S chelators are expected to generate higher affinity ligands for lead(II) sequestration.  相似文献   

12.
Two new polyketides: 2Z-(heptadec-12-enyl)-4-hydroxy-3,4,7,8-tetrahydro-2H-chromen-5(6H)-one (1) and 2-(heptadec-12-enyl)-5-hydroxy-5,6,7,8-tetrahydrochromen- 4-one (2), together with eleven known compounds: 4-hydroxy-2-[(3,4-methylenedioxy- phenyl)tridecanoyl] cyclohexane-1,3-dione (3), oleiferinone (4), 4-hydroxy-2-[(3,4- methylenedioxyphenyl)undecanoyl]cyclohexane-1,3-dione (5), 4-hydroxy-2-[(11-phenyl- undecanoyl)cyclohexane-1,3-dione (6), proctorione C (7), surinone C (8), 5-hydroxy- 7,8,4'-trimethoxyflavone (9), 5-hydroxy-7,8,3',4'-tetramethoxyflavone (10), 5-hydroxy- 7,3',4'-trimethoxyflavone (11), 5,8-dihydroxy-7,3',4'-trimethoxyflavone (12) and cepharanone B (13) were isolated from the whole plant of Peperomia dindygulensis Miq. Their structures were elucidated by spectroscopic methods, including 2D-NMR techniques. Compounds 2, 3, 5 and 8 inhibited human umbilical vein endothelial cell (HUVEC) proliferation and compounds 5 and 8 sharply suppressed HUVEC tube formation.  相似文献   

13.
Piperazine and 1,2-diaminobenzene have been previously used as anchoring molecules to synthesize 3-hydroxy-4-pyridinone (3,4-HPO) tetradentate ligands affording ligands with different flexibility and coordination properties. In order to have a relatively rigid and hindered structure, a porphyrin platform was selected to anchor one or two 3,4-HPO chelating units. This platform provides an additional N4 coordination sphere and also very interesting optical properties to the synthesized conjugates. Depending on the metal ion present in the porphyrin core, conjugates with different spectroscopic properties are obtained. EPR spectroscopy has been used to characterize the copper(II) metalloporphyrins and to monitor and identify the species formed upon addition of copper(II) to solutions of two porphyrin conjugates with one and two 3,4-HPO arms. The porphyrin conjugates having two 3,4-HPO units are ligands that provide two separate binding sites with N4 and O4 coordination spheres, which allow accommodation of two metal ion centers that may be distinguished by spectroscopic methods.  相似文献   

14.
The electrochemical oxidation of 4,5,6,7-tetrahydro-1H-pyrazolo[3,4-d] pyrimidine-4,6-dione (oxipurinol) at the pyrolytic graphite electrode (PGE) has been studied. Oxipurinol exhibits up to three voltammetric oxidation peaks at the PGE between pH 1–12. The first pH-dependent peak (peak Ia) is proposed to be an initial, irreversible 2e-2H+ reaction to give 5,6-dihydro-4H-pyrazolo[3,4-d] pyrimidine-4,6-dione. This primary product further reacts by two routes. The major route, accounting for ca. 90% of the latter compound, involves a Michael addition of water followed by further electrochemical oxidation and hydrolysis to give 5,6-dihydro-5,6-dihydroxy-5-carboxy-6-diazenouracil. The minor route involves further electrochemical oxidation of 5,6-dihydro-4H-pyrazolo[3,4-d]-pyrimidine-4,6-dione in a 2e-2H+ reaction to give 4,5,6,7-tetrahydro-3H-pyrazolo[3,4-d]-pyrimidine-3,4,6-trione.Decomposition and, generally, additional electrochemical reactions of 5,6-dihydro-5,6-dihydroxy-5-carboxy-6-diazenouracil result in the formation of alloxan, parabanic acid, 6-diazo-isobarbituric acid and 5′-hydroxy-5-carboxy-6,6′-azouracil. The two latter compounds have never previously been reported. Decomposition of 4,5,6,7-tetrahydro-3H-pyrazolo[3,4-d]pyrimidine-3,4,6-trione results in formation of uracil-5-carboxylic acid.Detailed reaction schemes have been proposed to explain the observed electrochemistry and the formation of the observed products.  相似文献   

15.
Six new xanthones, 4,6-dihydroxy-2,3-dimethoxyxanthone (1), 2,6-dihydroxy-3,4-dimethoxyxanthone (2), 6-hydroxy-2,3,4-trimethoxyxanthone (3), 3,6-dihydroxy-1,2-dimethoxyxanthone (4), 4,7-dihydroxy-2,3-dimethoxyxanthone (5), and 3,7-dihydroxy-2,4-dimethoxyxanthone (6) were isolated from the stems of Hypericum chinense, together with four known xanthones. Their structures were established based on spectroscopic studies.  相似文献   

16.
Complexation of VO(2+) ion with the most abundant class of human immunoglobulins, immunoglobulin G (IgG), was studied using EPR spectroscopy. Differently from the data in the literature which report no interaction of IgG with vanadium, in the binary system VO(2+)/IgG at least three sites with comparable strength were revealed. These sites, named 1, 2, and 3, seem to be not specific, and the most probable candidates for metal ion coordination are histidine-N, aspartate-O or glutamate-O, and serinate-O or threoninate-O. The mean value for the association constant of (VO)(x)IgG, with x = 3-4, is log β = 10.3 ± 1.0. Examination of the ternary systems formed by VO(2+) with IgG and human serum transferrin (hTf) and human serum albumin (HSA) allows one to find that the order of complexing strength is hTf ? HSA ≈ IgG. The behavior of the ternary systems with IgG and one insulin-enhancing agent, like [VO(6-mepic)(2)], cis-[VO(pic)(2)(H(2)O)], [VO(acac)(2)], and [VO(dhp)(2)], where 6-mepic, pic, acac, and dhp indicate the deprotonated forms of 6-methylpicolinic and picolinic acids, acetylacetone, and 1,2-dimethyl-3-hydroxy-4(1H)-pyridinone, is very similar to the corresponding systems with albumin. In particular, at the physiological pH value, VO(6-mepic)(IgG)(OH), cis-VO(pic)(2)(IgG), and cis-VO(dhp)(2)(IgG) are formed. In such species, IgG coordinates nonspecifically VO(2+) through an imidazole-N belonging to a histidine residue exposed on the protein surface. For cis-VO(dhp)(2)(IgG), log β is 25.6 ± 0.6, comparable with that of the analogous species cis-VO(dhp)(2)(HSA) and cis-VO(dhp)(2)(hTf). Finally, with these new values of log β, the predicted percent distribution of an insulin-enhancing VO(2+) agent between the high molecular mass (hTf, HSA, and IgG) and low molecular mass (lactate) components of the blood serum at physiological conditions is calculated.  相似文献   

17.
A novel cyclobutenedione-containing poly(phenylenevinylene) (PPV) was obtained from 3,4-bis(4-bromomethylphenyl)-3-cyclobutene-1,2-dione via modified 1,12-polydehydrohalogenation. This resultant polymer, soluble in polar aprotic solvents, exhibits a regioregular structure of alternating cis- and trans-vinylene units. The present polymer exhibits photoluminescence with a maximum at 472 nm, corresponding to the blue emission region, in DMAc solution, and a red-shift emission at 574 nm in the film.  相似文献   

18.
Reaction of VO(acac)(2) with 1,2-dithiols in the presence of triethylamine gives pentacoordinate oxovanadium complexes [HNEt(3)](2)[VO(bdt)(2)] (1), [HNEt(3)](2)[VO(tdt)(2)] (2), and [HNEt(3)](2)[VO(bdtCl(2))(2)] (3) (where H(2)bdt = 1,2-benzenedithiol, H(2)tdt = 3,4-toluenedithiol, and H(2)bdtCl(2) = 3,6-dichloro-1,2-benzenedithiol). Compounds 1-3 have been characterized by IR, UV/visible, EPR, and mass spectroscopies. The X-ray crystal stuctures of 1 and 2 show hydrogen-bonding interactions between the terminal oxo atom and triethylammonium counterions and between ligand sulfur atoms and the counterions. These interactions are comparable with those found at the active sites of mononuclear molybdenum enzymes.  相似文献   

19.
Two Pyrone Derivatives from Fungus Phellinus Igniarius   总被引:3,自引:0,他引:3  
Two new pyrone derivatives phelligridins A 1 and B 2 were isolated from the fruit body of Phellinus igniarius. Their structrues were elucidated as 8, 9-dihydroxy-3-methyl- 1H,6H-pyrano[4,3-c][2]benzopyran-l,6-dione and 4-hydroxy-6-(3‘,4‘-dihvdroxystyryl)-3-methoxycarbon-yl-2-pyrone, respectively, by means of spectral methods,including IR, MS, 1D and 2DNMR spectra.  相似文献   

20.
Abstract

Reaction of two equivalents of N-mono- or di-substituted 3-amino-4-(n-butoxy)-3-cyclobutene-1,2-diones with a 1,2-diaminoethane gave N-mono- or di-substituted 1,2-bis((2-amino-1-cyclobutene-3,4-dione)amino)-ethane derivatives (bis(squaramides)). Reaction of the bis(squaramides) with excess P4S10 gave the analogous tetrathio derivatives (bis(dithiosquaramides), LH2) of formula (NR1R2)C4S2(NHCH2CH2NH)-C4S2(NR1R2) (R1=n-Bu, R2=H; R1=R2=Et, n-Bu). The new bis(dithiosquaramide) ligands were characterized by elemental analysis, IR, 1H NMR, 13C NMR, electronic, and mass spectroscopic methods. The complexes of these ligands with nickel(II) were prepared, isolated and characterized. The isolated complexes are neutral 2:2 species of formula Ni2L2, as evidenced by results from mass spectrometry, and they exhibit thermochromic behaviour in pyridine solution. Additional spectroscopic data (IR, NMR) are consistent with the ligands being coordinated only through sulfur donor atoms and a structure for the complexes is proposed.  相似文献   

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