ESR SPECTRA OF VO(NCS)_n~((2-n) ) COMPLEXES AND DETERMINATION OF THEIR STABILITY CONSTANTS

The ESR spectra of VO(NCS)_n~((2-n) ) complexes have been studied in this paper. It is shown that four complexes ions of various compositions, VO(NCS)~ , VO(NCS)_2, VO(NCS)_3~- and VO(NCS)_4~(2-), are formed in glyeol-water-mixed media. The parameters of the ESR spectra have been determined. We established a linear correlation between the hyperfine coupling constant and the coordination number n. n=117.66-3.41n (gauss). All the stability constants for various complexes formulated as VO(NCS)_n~((2-n) )(n=1,2,3,4) have been calculated from the ESR spectra, log K_1=2.15; log K_2=1.55; log K_3=0.87; log K_4=0.22. K_3and K_4 have not been reported in literature up to now.     

Complexation of radionuclide ~(152+154)Eu(Ⅲ) with alumina-bound fulvic acid studied by batch and time-resolved laser fluorescence spectroscopy

To contribute to the understanding of Eu(Ⅲ)interaction properties on hydrous alumina particles in the absence and presence of fulvic acid(FA),the complexation properties of Eu(Ⅲ)with hydrous alumina,FA and FA-alumina hybrids are studied by batch and time-resolved laser fluorescence spectroscopy(TRLFS)techniques.The continuous increase in the fluorescence lifetime of Eu-alumina and Eu-FA with increasing pH indicates that the complexation is accompanied by decreasing number of hydration water in the first coordination sphere of Eu(Ⅲ).Eu(Ⅲ)is adsorbed onto alumina particles as outer-sphere surface complexes of≡(Al-O)-Eu·(OH)·7H_2O and≡(Al-O)-Eu·6H_2O at low pH values,and as inner-sphere surface complexes as≡(Al-O)_2-Eu~+·4H_2O at high pH.In FA solution,Eu(Ⅲ)forms complexes with FA as(COO)_2Eu~+(H_2O)_x and the hydration water number in the first coordination sphere decreases with pH increasing.The formation of≡COO-Eu-(O-Al≡)·4H_2O is observed on FA-alumina hybrids,suggesting the formation of strong inner-sphere surface complexes in the presence of FA.The surface complexes are also characterized by their emission spectra[the ratio of emission intensities of~5D_0→~7F_1(λ=594nm)and~5D_0→~7F_2(λ=619nm)transitions]and their fluorescence lifetime.The findings is important to understand the contribution of FA in the complexation properties of Eu(Ⅲ)on FA-alumina hybrids that the clarification of the environmental behavior of humic substances is necessary to understand fully the behavior of Eu(Ⅲ),or its analogue trivalent lanthanide and actinide ions in natural environment.     

TERNARY COMPLEXES OF Cu(ATP)AND HETEROAROMATIC N BASE-ISOQUINOLINE AND BENZIMIDAZOLE:STABILITY CONSTANT AND STACKING EFFECT

The stability constants of the binary complexes ofCu~(2+) with isoquinoline and benzimidazole as well as the ternarycomplexes of Cu(ATP)with the same ligands have been measuredin aqueous solution spectrophotometrically and a strongstacking interaction between the heteroaromatic ring of theligands and the purine moiety of ATP has been found.The factof this stacking interaction is much stronger than that in thesystems of Cu(ATP)with pyridine and imidazole shows thatthe stacking interaction increases with the size of theheteroaromatic ring of the ligands.     

THE ESR STUDY OF SOME DICYCLOPENTA-DIENYL TITANIUM HALIDE COMPLEXES

The ESR spectra of some [Cp_2Ti(L)X] complexes (Cp: C_5H_5, MeC_5H_4; L: phosphane,isocyanide, pyridine, amine and carbon monoxide; X: F, Cl, Br, I) have been obtained.When X is Cl, Br or I, the linear relationships between the g value and hyperfine couplingcoustant a(Ti) are explained in terms of the electron character of the L ligand and the ESRspectral trends of the complexes are studied.     

SIMULTANEOUS DETERMINATION OF NEODYMIUM AND PRASEODYMIUM BY ZERO-ORDER AND FOURTH-ORDER DFRIVATIVE SPECTROPHOTOMETRY

With derivative spectrophotometric method,the complexes oflanthanides with 2-(5-bromo-2-pyridylazo)-5-diethylaminophen-ol(5-Br-PADAP)in the presence of octylphenol poly(ethyleneg-lycol)ether(TX-100)were studied.It is found that the maximumabsorption of fourth-order derivative spectra of the neodymiumcomplex by 4f electron transitions is at 579(+)nm and 582(-)nmwith molar derivative absorptivities of 5.2×10~3 1.mol~(-1).cm~(-1).The maximum absorption of the zero-order derivative spectra ofthe complexes for neodymium and praseodymium is at 580hm,themolar absorptivities are 1.47×10~5 l.mol~(-1).cm~(-1)for Nd and 1.26×10~5 l.mol~(-1).cm~(-1)for Pr.The component ratio of the complexis Nd:5-Br-PADAP=1:4.Beer's law is obeyed in the range of0-3.75μg of Nd and Pr in 25ml of solution.The method has beenused for the simultaneous determination of Nd and Pr in foursynthetic samples and the results obtained are satisfactory.     

STUDY ON THE STRUCTURE AND SPECTRA OF BINUCLEAR BRIDGED COMPLEX μ-4,4-bipy [VO(acac)_2]_2

The synthesis and ~1H NMR, ESR, IR, UV spectra of binuclear bridged complex μ-4,4-bipy[VO-(acac)_2]_2 are reported in this paper. The structure of the complex is discussed using measured spectral parameters.It is deemed that 4,4-bipy as a bridge passing through its two N atoms combined respectively with two V atoms at its sixth position, forming a binuclear bridged complex.The spectra are explained satisfactorily and coefficients of molecular orbitals,β_1,β_2 and 8_m,are calculated from the results of ESR and UV etc.     

Interaction of Copper in CuZn-Superoxide Dismutase With Histidine

The interaction of CuZn-superoxide dismutase ( CuZn-SOD ) with the external histidine in aqueous solution has been studied in this work by ESR and NMR. It is found that the Cu(Ⅱ) of CuZn-SOD makes an exchanging interaction with the external substance in aqueous solution. Unlike in solid state, the Cu(Ⅱ) forms complex with external histidine, and keeps a motional equilibrium between the active centers and the complexes. Enzyme activity is also affected by this interaction. Some other amino acids are also discussed in this paper.     

SOLVENT EFFECT ON CONFORMATIONS OF α,ω-BIS(4-NITROPHENOXY)-ALKANES

Solvent effect on the conformations of-bis(4-nitrophenoxy)-alkanesw th different chain Lengths(Nn)was studied by UV spectra.In poor solvents such asEG-H_2O and THF-H_2O,with the water content higher than 50%,the K-bands of N_4.N,N_6 and N_(10)in the UV absorption spectra shifted to longer wavelengths as comparedwth 4-nitrophenoxyethane(N_0).It is suggested that in poor solvents the two aromaticgrps are close to each other in parallel,forming ground state complexes.The K-bead of N_4 showed a blue shift from that of N_0 when the water content was around5%,probably attributable to a conformation with the nitro group of one benzene ringsiting on the plane of the other benzene ring.     

THE CRYSTAL STRUCTURE AND SPECTROSCOPIC PROPERTIES OF THE COMPLEXES FORMED BY TiCl_4 AND MgCl_2 WITH ESTERS——A RESEARCH ON THE STRUCTURE OF HIGHLY EFFICIENT CATALYSTS FOR POLYPROPYLENE

The complexes of TiCl_4, MgCl_2 and esters which are significant in industry have beenstudied by X-ray diffraction, IR and uv spectra. Their single crystal structures have also beendetermined. TiCl_4 and PhCOOEt can form two complexes, TiCl_4·L and TiCl_4·2L·MgGl_2, CH_3COOEtand H_2O form complex MgCl_2·2CH_3COOEt·2H_2O. All of them are molecular crystals. Theirspacial groups are C_(2h)~5-P2_1/c, C_(2h)~5-P2_1/n and C_(2h)~6-C_2/c respectively. From the XRD powderpattern, it has been ascertained that TiCl_4·L is formed in the process of the catalyst prepara-tion with milling-soaking method. Comparison between the IR spectra of the catalyst and Mgcomplex indicates that the coordinative bonds of the surface complex of the catalyst are verysimilar to that of the complex.     

Structure effect of nucleotides in terbium(Ⅲ)-nucleotide fluorescent reaction—-New evidence for the binding sites of terbium(Ⅲ) on nucleotides

Upon addition of Tb~(3+) to 16 nucleotides and homopolynucleotides, all of them showeda characteristic green emission from Tb~(3+), but with much different intensity, upon excitation inthe aromatic region of bases. The result suggested that nucleotides with at least one carbonylgroup in nucleotide bases are better enhancers to the fluorescence of Tb3+. The complexes of ATP,GDP and GTP with T5~(3+) are synthesized as two types of models. Guanine tpye nucleotides withone carbonyl group in the bases are the best enhancers, while adenine type nucleotides with nocarbonyl group in the bases are poorest enhancers to the fluorescence of Tb~(3+). Comparing theIR spectra of ATP, GTP, GDP and their Tb~(3+) complexes suggested that C-6 carbonyl group inGTP and GDP may be involved in complex formation, which may be responsible for the effectiveenergy transfer. This is further supported by comparing the UV spectra of ATP, Poly(A), GTP,and Poly(G) with their Tb~(3+) complexes in water solution.     

SCIENTIFIC PRINCIPLES FOR MODIFICATION OF WATER-SOLUBLE POLYMERS. FORMATION OF MACROMOLECULAR COMPLEXES

The study of nanosecond dynamics of macromolecules with the lumines-cent methods make it possible to investigate the formation and functioning of polymericcomplexes, polymeric conjugates and macromolecular metal complexes, which are widelyused for solving many practical tasks. The nanosecond dynamics of macromolecules are ahighly sensitive indicator of interpolymer complexes (IPC) formation. It enables us to solvethe problems of studying IPC formation and stability and to investigate the interpolymerreactions of exchange and substitution. The investigation of changes in the rotational mo-bility of globular protein molecules as a whole makes it possible to determine the complexcomposition and its stability, and to control the course of polymer-protein conjugate forma-tion reaction. The nanosecond dynamics of polymers interacting with surfacants' ions (S)are the sensitive indicator of the S-polymer complex formation. A method for determin-ing the equilibrium constants of the S-polymer complex formation was developed on thebasis of the study of polymer chains mobility. It is established that nanosecond dynamicsinfluences the course of chemical reactions in polymer chains. Moreover, the marked effectof the nanosecond dynamics is also revealed in the study of photophysical processes (theformation of excimers and energy migration of electron excitation) in polymers with pho-toactive groups. It was found that the efficiency of both processes increases with increasingthe mobility of side chains, the carriers of photoactive groups.     

REACTION MECHANISM OF BENZOPHENONE-PHOTOINITIATED CROSSLINKING OF POLYETHYLENE

The radical intermediates, the crosslink microstructures, and the reaction mechanism of benzophenone (BP)-photoinitiated crosslinking of low-density polyethylene (LDPE) and model compounds (MD) have been reviewed in detail.The spin-trapping electron spin resonance (ESR) spectra obtained from the LDPE/BP systems with spin-trap agents showthat two kinds of polymer radical intermediates are mainly formed: tertiary carbon and secondary carbon radicals. The spin-trapping ESR studies of MD/BP systems give further evidence that photocrosslinking reactions of PE predominantly takeplace at sites of tertiary carbon, secondary carbon, and especially allylic carbon when available. The high resolution ~(13)C-NMR spectra obtained from LDPE and MD systems show that the crosslink microstructures have H- and Y-type links andthat their concentrations are of the same order. The fluorescence, ESR ~(13)C and ~1H-NMR spectra from the PE and MDsystems demonstrate that the main photoreduction product of BP(PPB) is benzpinacol formed by the recombination of twodiphenylhydroxymethyl (K·) radical intermediates. Two new PPB products: an isomer of benzpinacol with quinoid structure,1-phenylhydroxymethylene-4-diphenylhydroxymethyl-2, 5-cyclohexadiene and three kinds of α-alkyl-benzhydrols have beendetected and identified. These results provide new experimental evidence for elucidating the reaction mechanism in the BP-photoinitiated crosslinking of polyethylene.     

Effect of urea on synchronous fluorescence spectra and electrochemical behaviour of cytochrome

The changes of the synchronous fluorescence spectra and the electrochemical behaviour of cytochrome c with the urea concentration are studied. It has been found that with the increase of urea concentration, there occur sequentially the deaggregation of cytochrome c molecules, the increase of exposure extent of the heme group to the solvent, the disruption of Fe-S bond of the heme group and the change in the electrochemical behaviour of cytochrome c. It is suggested that the reason why the electrochemical reaction of cytochrome c is irreversible is that cytochrome c molecules exist in the concentrated solution as oligomers which are electrochemically inactive.     

STUDIES ON BIO-ANTIOXIDANTS——MICELLAR EFFECTS ON THE REDUCTION OF NITROXIDES BY VITAMIN C

The kinetics of reduction of nitroxides including 4-hydroxy-TEMPO, 4-methoxy-TEMPOand 4-hexanoyloxy-TEMPO, which are of different lipophilicities, by vitamin C in cationic,non-ionic and anionic micelles, i. e. CTAB, Triton X-100 and SDS, respectively, have beenstudied by ESR spectroscopy by a stopped-flow technique. A mechanism for the reactionconducted in micelles is proposed and the rate constants for the elementary reactions areevaluated. It is found that the rates of single electron transfer reactions involving the ni-troxides are dependent on the nature of the micelle and the lipophilicity of the nitroxide.The rates are increased in CTAB, decreased in SDS, whereas unaffected in Triton X-100.And the greater the lipophilicity of the nitroxide, the more pronounced the rate variation.As high as a 3600-fold increase in the rate was observed for 4-hexanoyloxy-TEMPO in CTABover that in SDS. The micellar effects are rationalized on the basis of analysis of parame-ters and line shape of the ESR spectra for     

ENDOR AND ESR STUDIES OF RADICALS FORMED IN FRIEDEL-CRAFTS REACTIONS

The present study deals with the study of some Friedel-Crafts alkylating system and the accurate measurement of hyperfine coupling constants by ESR and ENDOR techniques. The results indicate that the observed ESR spectra are due to polycyclic aromatic radical cations formed from their parent hydrocarbons.It is suggested that benzyl halides produced in the Friedel-Crafts alkylating reaction undergo Scholl condensation reaction to give polycyclic aromatic hydrocarbons, which were converted into the corresponding polycyclic aromatic radical cations in the presence of aluminum chloride.     

XPS STUDY ON THE ROLE OF CO_2 IN LOW-PRESSURE METHANOL SYNTHESIS

Surface characterization of CuO-ZnO-Al_2O_3 catalysts for low pres-sure methanol synthesis was carried out by using X-ray photoelectron spec-troscopy(XPS)combined with reaction chamber under simulated industrialoperating condition.Under the reduction and reaction conditions,no stableCu~(2+) or Cu~+ ions were found,only Cu~0 species was detected.ZuO could be re-duced with result of forming oxygen-deficient structure ZnO_x(X<1)andoxygen vacancy on the surface.The presence of enough amount of CO_2 infeed gas enhanced copper dispersion.It is believed that highly dispersed Cu~0 in intimate contact with ZnO is one of the active components for methanol syn-thesis and the optimal structure of the active unit is Cu——Zn—O(“□”is oxygen vacancy).It is proposed that the main role of CO_2 is to establish anoxidation potential of syngas so as to accelerate the oxidation-reduction cyclebetween Cu~0 and Cu~(δ+)/or Cu~+ during methanol synthesis as well as to preventCu~0 crystallites from aggregating and thus to maintain the catalyst in high ac-tivity and have long life.     

Synthesis,Crystal Structure of Cis—dioxo—catecholatotungsten（VI） Complex and Its NMR Studies on the Interaction with ATP

Cis-dioxo-catecholatotungsten(VI) complex anion[W^(VI)O2-(OC6H4O)2]^2- was obtained with discrete protonated ethylenediamine (NH2CH2CH2NH3)^ cations by the reaction of tetrabutyl ammonium decatungstate with catechol in the mixed solvent of CH3OH,CH3CN and ethylenediamine,and compared with its molybdenum anaogue [Mo^(V) O2(OC6H4O)2]^3- by crystal structure,UV,EPR,The results of the UV and EPR spectra show that tungsten is less redox active than molybdenum since the molybdenum is reduced from Mo(VI) to Mo(V) but tungsten stays in the original highest oxidized state Mo(VI) when they are crystallized from the solution above.It is worthy to note that [W^(VI)O2(OC6H4O)]^2- shows the same coordination structure as its molybdenum analogue in which the metal center exhibits distorted octahedral coordination geometry with two cis-dioxocatecholate ligands and might have the related coordination structure feature with the cofactor of flavoenzyme because [Mo^(V)O2(OC6H4O)2]^3- presented essentially the same EPR spectra as flavoenzyme.The NMR studies on the interaction of the title complex with ATP reveal that the reduction of W(VI) to W(V) occurs when the title complex is dissolved in D2O and the W(V) is oxidized again when ATP solution is mixed with original solution and the hydrolysis of the catecholato ligand take places at mean time being monitored by ^1H NMR and ^13C NMR spectra.     

SYNTHESIS OF POLYCATECHOL WITH ELECTROCHEMICAL ACTIVITY AND ITS PROPERTIES

The electrochemical polymerization of catechol on platinum has been carried out using repeated potential cyclingbetween-0.2 and 1.1 V (versus SCE). The electrolytic solution consisted of 0.2 mol dm~(-3) catechol, 0.5 mol dm~(-3) NaCl and0.1 mol dm~(-3) Na_2HPO_4 with pH 8.72. Catechol can not be polymerized at pH≥10.12. Polycatechol has an electrochemicalactivity at pH≤4. The anodic and cathodic peak potentials of polycatechol shift towards more negative values as the pH ofthe solution increases from 1 to 4. The electrochemical activity of polycatechol hardly changes in this pH region, but itdecreases slowly with time. This is caused by oxygen in air, which leads to an irreversible oxidation of polycatechol. Thisproperty is favorable for protecting metals from corrosion. Raman and FTIR spectra of polycatechol and catechol are quitedifferent. AFM images of polycatechol films provide evidence that the image of the oxidized state of polycatechol ismarkedly different from that of the reduced one. This difference is caused by doping and dedoping of polycatechol.     

Synthesis, Characterization and Weak Intramolecular Interactions of Porphyrins Bearing Nucleobases

5,10, 15-Triphenyl-20-{2- [α- (adenine-9 ) acetylamino]} phenyl porphyrin ( 1 ), 5,10, 15-triphenyl-20-{2-[α-(cytosine-1)acetylamino]} phenyl porphyrin (2), 5, 10, 15-triphenyl-20-{4-[α-(cytosine-1)ethoxy]} phenyl porphyrin (3) and their zinc complexes Zn-1, Zn-2 and Zn-3 have been prepared and characterized by ^1H NMR spectra, elemental analyses, electronic absorption spectra and mass spectra (FAB). Intramolecular π-π interactions and intramolecular metal-~ interaction for 1, 2, Zn-1,and Zn-2 have been investigated by several methods. ^1H NMR studies demonstrate that the porphyrin π-system in 1 and 2 is parallel to the adenine and the cytosine aromatic ring, respectively. The electronic absorption spectral properties of free porphyrin derivatives and their zinc complexes have been compared with those of H2TPP and ZnTPP. The results show that the UV-vis spectra of 1 and 2 are the same as that of H2TPP,whereas the spectra of their zinc complexes show 7 nm red shifts of the Soret bands compared to that of ZnTPP. The emission spectra of Zn-1 and Zn-2 are independent of excitation wavelength. From combination of the evidence of absorption and emission spectra it is suggested the existence of intramolecular metal-π interaction in Zn-1 and Zn-2. The results of conformational analysis agreed quite nicely with that of experiments, thus it was further to validate the experimental conclusions.     

APPLICATIONS OF DSCPCF MODEL IN RARE EARTH COMPLEXES (Ⅳ)——ANALYSIS OF ABSORPTION SPECTRA FOR Pr~(3+)- AND Tm~(3+)-2-THENOYLTRIFLUOROACETONE-PIPERIDINE COMPLEXES

The new complexes, RE(TTA)_4·HP(RE are Pr~(3+) and Tm~(3+)), have been prepared, and their UV-VIS-NIR absorption spectra measured. All the matrix element formulas of f~2 and f~(12) configurations in D_4 symmetry field have been derived with the Double Sphere Coordination Point Charge Field Model, and the influence of the symmetry change of the complex unit, REO_3, on the forbital levels of Pr~(3+) is discussed. And based on the theoretical calculations, the transition peaks in the absorption bands are assigned.