首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
Aqueous solutions of fac- and mer-isomers of [Co(NH2C2H4O)3] · 3H2O were investigated by the 13C NMR spectroscopy method. The spectrum of the fac-isomer exhibited only two signals with 47.08 (CN) and 63.87 (CO) ppm, which points to a high symmetry of the compound and to the presence of a complex in the solution (unlike the crystal) with one type of polyhedron (probably, of a trigonal-prismatic type). The spectrum of the mer-isomer solution is more complicated: the CNand COsignals are split into three components with 48.81, 47.18, and 46.11 ppm and 64.70, 64.45, and 64.23 ppm, respectively. This fact confirms deterioration of the symmetry of the coordination polyhedron due to nonequivalence of -aminoethylate ions bound to the central atom. The successive protonation of the complexes does not affect either the symmetry of the coordination sphere of the fac-isomer or the asymmetry of the coordination sphere of the mer-isomer. The 1H, 13C, 59Co NMR and IR spectroscopy data made it possible to suggest that both fac-[Co(NH2C2H4O)3] fragments in the binuclear fac-[H3(Co(NH2C2H4O)3)2](NO3)3complex are linked together by three symmetrical hydrogen bridges.  相似文献   

2.
Raman spectroscopic measurements on aqueous solutions of poly(dG) · poly(dC)indicate that the conformation of the polynucleotides in this double helicalcomplex are distributed between the A and B types at room temperature, the Aform being predominant at –15°C and decreasing progressively upon raising thetemperature to 65°C. A reversible pretransition has been found in this complexnear 70°C. Modifications in the spectra at this temperature indicate no majorconformational changes, but rather suggest altered base pairing and hydration ofthe carbonyl groups, accompanied by a slight distortion of the double helix,resulting in a slightly reduced stacking of the cytosine bases. Measurements inself-pressurized solutions of the complex at high temperature show that it meltsat 103°C in 0.1M NaCl solution (107°C in 0.5M NaCl). These values are somewhatlower than those we have determined in the same manner for the complexpoly(dG-dC) · poly(dG-dC): 117°C in 0.1M MgCl2 and 113°C or higher in 0.1MNaCl solution.  相似文献   

3.
l.IntroductionAsalatelydeveloPedsensihveandsimPleelectroanalghcalmethod,adsorptivedrippingvoltanUneto'(AdSV)receivesincreasingattenhonIl,2a].lnorgamcionscanbedetetrinedincomPlexformb}'AdSV,andmoStligandsusedaresmal1orgtricmoleculeswhichcanbeadsoIbedonthesdriceofelectrodereadily[2b]fforinStance,beryllonIIIisfitforthedetenTiltalonofboron[31.AJthoughwater-solublePOlyInerssuchasPOly(vinylalcohol)WVA)areusedasenhancingreagentSinvoltaInInetryformetalcomPlexesofotherligands[4],therearenor…  相似文献   

4.
Summary: The thermal degradation behavior of poly(ε-caprolactone) (PCL) and poly(L-lactic acid) (PLA) have been studied in different environment. It was found that these polymers undergo completely different degradation processes in nitrogen and oxygen atmosphere. In oxygen environment PCL and PLA mainly decompose to CO2, CO, water and short-chain acids. In nitrogen atmosphere PCL releases 5-hexenioc acid, CO2, CO and ε-caprolactone, whereas PLA decomposes to acetaldehyde, CO2, CO and lactide. The polymer blends of poly(3-hydroxybutyrate) (PHB) with PCL and PLA decompose similar to the individual homopolymers with crotonic acid as the initial decomposition product of PHB.  相似文献   

5.
Homogeneous blends of poly(L-lactide) (M n = 30 000 to 40 000) and poly(β-propiolactone) or poly(ε-caprolactone) were prepared in solution. The solvent-free blends were subjected to transesterification catalyzed by means of methyl triflate, triflic acid, boron trifluoride, or tributyltin methoxide at 100 or 150°C. At 100°C, transesterification was barely detectable even after 96 h. When poly(β-propiolactone) was used as the reactant at 150°C, degradation was faster than transesterification regardless of the catalyst. The same negative result was obtained for heterogeneous blends of poly(L-lactide) and poly(glycolide). In the case of poly(ε-caprolactone), copolyesters with slightly blocky sequences were obtained with tributyltin methoxide as catalyst, whereas the acidic catalysts caused rapid degradation. The copolyesters were characterized by means of 1H-NMR spectroscopy with regard to their molar composition, by means of 13C-NMR spectroscopy with regard to their sequences, and by means of differential scanning calorimetry with regard to crystallinity.  相似文献   

6.

Nanoscale poly(cyclohexyl methacrylate) (PCHMA) particles were prepared by a modified microemulsion polymerization procedure. 13C‐NMR analysis suggested that such PCHMA samples were higher in syndiotactic content (61–72% rr) and lower in isotactic content (1–3% mm). The glass transition temperatures (Tg's) of the products were also higher than that reported in the literature. The polymer properties, such as particle size, molecular weight, tacticity, and Tg were affected by the reaction conditions. The smaller the particle size, the higher the syndiotacticity, the lower the isotacticity and the greater the molecular weight, then the higher the Tg of the PCHMA samples. Possible mechanism of rich‐syndiotacticity was also discussed.  相似文献   

7.
Naproxen is a poorly soluble anti-inflammatorydrug, the solubility of which canbe enhanced by complexation withbeta-cyclodextrin. Besides that, the inclusioncomplex reduces the incidence of gastrointestinal side effects of the drug. The aim of this work was to compare the physicochemical characteristics of the solid complexes prepared by traditional methods (kneading, freeze-drying and spray-drying) and using a supercritical fluid technology. The unusual solvent properties of carbon dioxide above their critical temperature and pressure were exploited in order to prepare inclusion compounds. Complexes prepared using supercritical fluid technology showed similar properties to those of freeze-drying andspray-drying complexes as proved by DSC, FT-IRand UV.  相似文献   

8.
Abstract

A series of mixed ligand complexes of the type [Fe(CO)3L1L2] (L1=tri-phenylphosphite and L2=phosphine or phosphite) have been prepared to study the Fe-P bond. The 57Fe Mössbauer spectra of trans-[Fe(CO)3L1L2] showed a quadrupole splitting doublet characteristic of the disubstituted iron carbonyls in trigonal bipyramidal symmetry. The linear dependence of the quadrupole splittings on the isomer shifts with a positive slope has revealed that the iron-to-phosphorus σ-donation is offset by the phosphorus-to-iron π-back donation. The 31P{1H} NMR spectra showed a couple of doublets assigned to the coordinated phosphite and the coordinated phosphine. The doublet of the phosphite site was generally observed at the down field compared with that of the phosphine site. The coordination shifts increase with the Mössbauer isomer shifts, suggesting that the iron-to-phosphorus π-back donation plays an important role in the Fe-P bond of trans-[Fe(CO)3L1L2]. The relatively large coupling constants due to 2J(P,P) have demonstrated that there exists a strong interaction between trans phosphorus ligands through the dπ orbitals of the central iron. The coupling constant is a measure of the bond strength between Fe-P, while the Mössbauer isomer shift reflects the electron density at the iron nucleus. Thus, a linear correlation has been established between these two spectroscopic parameters.  相似文献   

9.
Duetoitschemicalstabilib'andcapability'toincorporaterelati\'e1}'largeamountofelectroactivespecies.thepeffiuorinatedion-exchangepolymer.Nallon.hasbeenwidel}'usedascoahngfilminfabricatingchenuca1modiliedelectrodesMmp'exPenmentalresultsindicatethatheNallonInatrixpossessesremarkablermnity'forhydIoPhobiccationsl1-2].However.uPlodae.ven'littleworkhasbeende`o[edtotheinveStigationoftheinteractionbetweenthehydrophobiccountenonsandtheNallonmatrixlnth1spaper.wereporttheUV-viSandrnRstudiesofCoL,'-an…  相似文献   

10.
2-Methyl-3-trichlorostannylpropionate, Cl3SnCH2CH(CH3)CO2R, a novel type of mono- organotin compounds containing ester group, have received considerable attention since Hutton et al. reported their synthesis because of the variety of coordination geometry about tin atom1-4. Organotin compounds5 like organotin carboxylates or oxides were already used as transesterification catalysts, however, little attention was paid to transestrifications of 2-methyl-3-trichlorostannylpropionate complexe…  相似文献   

11.
In recent years,the organic ferromagnets have drawn growing attention due to their characteristics of structural diversities,low density,and readily processing1-3.Design and synthesis of magnetic polymers are one of great challenges in today′s magnetic material research,and some significant achievements have been made in this field4,5.In this article,we describe the synthesis of acrylamide-type polymer with pendent thiazolyl groups(Scheme1).The as-prepared polymer exhibited better solubility …  相似文献   

12.
Biodegradation of blends of poly(ϵ-caprolactone) [PCL] with poly(vinyl butyral) [PVB] was studied in the soil and by bacterial strains of Bacillus subtilis and Escherichia Coli isolated from the soil. Miscibility of the blends was also analyzed using FT-IR and optical microscopy at room temperature. Biodegradation of the blends was followed by weight loss, visual observations and scanning electron microscopy [SEM]. Blends with low polyester concentration, i.e., 30 wt% PCL and less, were clear and transparent and no spherulite formation was observed. Above 30 wt% PCL spherulites appeared, the size of which increased with increasing PCL concentration. Infra-red studies of the blends with less than 30 wt% PCL showed that only the amorphous phase of PCL was present. Above 30 wt% PCL indicated the presence of both crystalline and blended PCL. The second derivative of the carbonyl peak of PCL also supported the presence of two phases in blends with more than 30 wt% PCL and only one peak for blends with 30 wt% or less PCL. Weight loss was observed in all the blends. PCL rich blends showed more degradation, which was faster in the natural environment than in the laboratory. Physical appearance and microscopic examination showed the films deteriorated in soil. Blends in the Bacillus subtilis strain showed more degradation as compared to the E. Coli. strain.  相似文献   

13.
A novel sensitizer with imidazole zinc porphyrin as electron donor has been synthesized. The structure has been characterized by UV-Vis, elemental analyses and 1 H NMR.UV-Vis and fluorescence spectra show that it has good light absorbing properties in the range of visible light and suggests that it has potential applications in dye-sensitized solar cells.  相似文献   

14.
Chemical transformations resulting from irradiation of the poly(vinyl chloride) (PVC)–triallyl cyanurate (TAC) system were studied by IR spectroscopy. It was shown that crosslinking was accompanied by scission of the network structure formed in the initial dose range, and the scission process occurred even at small irradiation doses. The scission is assumed to be localized at the interface boundary between PVC and poly(iso-TAC) or poly(TAC).  相似文献   

15.

Single step polymerization of poly(o‐toluidine) was carried out by using ammonium persulphate as an oxidizing agent. Formation of the conducting emeraldine salt phase of the polymer was confirmed by the UV‐visible and FT‐IR spectroscopic analysis. The elemental composition of the polymer was evaluated by using a CHNS analyzer. Thermal stability of these polymers was investigated by the thermogravimetric analysis. Among the three polymeric acids used for doping purposes, poly(acrylic acid) doped material was found to show less thermal stability compared to poly(styrene sulphonic acid) and poly(vinyl sulphonic acid) doped poly(o‐toluidine).  相似文献   

16.
Abstract

Raman spectra of benzaldehyde, vanillin and trans-cinnamaldehyde, and of their complexes in β-cyclodextrin are presented and discussed. The guest molecules provide both an aromatic ring for privileged interaction with the cyclodextrin cavity, and characteristic vibrations (e.g., vC=O, vC=C, vCC? (?=phenyl), vC-H?) with group frequencies in spectral regions free from cyclodextrin bands which are useful for probing the guest perturbed by complex formation with β-cyclodextrin. In particular, the C=O bond is shown to be a good vibrational spectroscopic probe to monitor the effects of both the medium, through its dielectric constant, and of specific interactions, namely of the hydrogen bonding type. The first of these effects is evaluated theoretically and a Kirkwood-Bauer-Magat plot for benzaldehyde is used to estimate the effective dielectric constant for the guest in the benzaldehyde-β-cyclodextrin complex. The above mentioned Raman spectroscopic results are interpreted and discussed.  相似文献   

17.
N-saliCylidenchnoacidcomplexesInayserveasmodelsfOrN-bodoXylidenedoacidcomp1exSystmschcharebelieVedtObetheintermediatesinthetranboIlationprocessl'l.ThecoordinaionOfametaJiontosuchSchiffbasesstabilizestheazomethine1inkag,underconditionsthatwouldothendsepromotebondcleaVag[2-5].Inaddition,thecomplexesOftalnoeddScAfbasesareconsideredtobeanewldndOfpoentialanhbactrialandanhcanceragentsl6].However,littleattentionhasbeengiventoSystemsinwhchtheScusbasesarederivedfromsimPlepePtides.ThispoprrePO…  相似文献   

18.
19.
The effect of the complexation of polyacrylic (PAA) and polymethacrylic (PMAA) acids with poly(N-vinyl pyrrolidone) (PVP) on their surface properties was studied by measuring surface tension, conductivity, and the viscosity of aqueous mixed polymer solutions, as well as by the potentiometric titration at 293.15 K. The values of relaxation times and the surface activity of polycomplexes were calculated from kinetic data and the surface tension isotherms of the solutions. The complexation was found to increase the surface layer relaxation time, surface activity, and the ability of the macromolecules to reduce the surface tension of solvent. The values of adsorption free energy were calculated for PVP and polycomplexes. They were equal to –22.0, –23.0, and –24.8 kJ/base-mole (per one mole of PVP monomer unit) for PVP and PMAA–PVP and PAA–PVP polycomplexes, respectively.  相似文献   

20.
In recent years, X-ray emission spectroscopy (XES) in the Kβ (3p-1s) and valence-to-core (valence-1s) regions has been increasingly used to study metal active sites in (bio)inorganic chemistry and catalysis, providing information about the metal spin state, oxidation state and the identity of coordinated ligands. However, to date this technique has been limited almost exclusively to first-row transition metals. In this work, we present an extension of Kβ XES (in both the 4p-1s and valence-to-1s [or VtC] regions) to the second transition row by performing a detailed experimental and theoretical analysis of the molybdenum emission lines. It is demonstrated in this work that Kβ2 lines are dominated by spin state effects, while VtC XES of a 4d transition metal provides access to metal oxidation state and ligand identity. An extension of Mo Kβ XES to nitrogenase-relevant model complexes shows that the method is sufficiently sensitive to act as a spectator probe for redox events that are localized at the Fe atoms. Mo VtC XES thus has promise for future applications to nitrogenase, as well as a range of other Mo-containing biological cofactors. Further, the clear assignment of the origins of Mo VtC XES features opens up the possibility of applying this method to a wide range of second-row transition metals, thus providing chemists with a site-specific tool for the elucidation of 4d transition metal electronic structure.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号