Spectroscopic and electrochemical study of Rose Bengal in aqueous solutions of cyclodextrins

The interaction of Rose Bengal (RB) in aqueous solution of LiClO4 0.1 M with alpha-cyclodextrin (alpha-CD), hydroxypropyl-beta-cyclodextrins (HP-beta-CD) and hydroxypropyl-gamma-cyclodextrins (HP-gamma-CD) were studied by spectrophotometric measurements. The presence of Induced Circular Signals and the results of the analysis of the modifications in the absorbance spectra of RB produced by the presence of CDs in solution indicate that RB forms inclusion complexes only with HP-beta-CD and with HP-gamma-CD.     

Self-assembly of insoluble porphyrins on Au(111) under aqueous electrochemical control

Self-assembled monolayers of a water-insoluble porphyrin, tetraphenyl porphyrin (TPP), in the presence of an aqueous electrolyte were characterized in situ with electrochemical scanning tunneling microscopy (EC-STM) at working electrode potentials of between 0.5 and -0.2 V. Isolated domains of TPP monolayers with differing orientation were observed on Au(111) in 0.1 M HClO(4) over this entire potential window. Individual TPP molecules could be resolved over a range of 700 mV, from open circuit potential (OCP) to near the hydrogen evolution potential. The unit cell is square, and the distance between neighboring molecules is about 1.4 ± 0.1 nm. High-resolution images allow the internal molecular structure to be discerned. No changes in the STM contrast of individual molecules were observed as the potential was changed. In a neutral electrolyte (0.1 M KClO(4), pH ~6), the potential range of stability of ordered structures is reduced. On HOPG, TPP forms ordered hexagonal structures with a lattice constant of about 2.6 nm in the double-layer potential region in 0.1 M HClO(4).     

Modulating the redox properties of an osmium-containing metallopolymer through the supporting electrolyte and cross-linking

Thin films of the perchlorate salt of an [Os(N,N'-alkylated-2,2'-biimidazole3)2+/3+-containing polymer have been formed on planar platinum microelectrodes. The electrochemical response associated with the Os2+/3+ couple occurs at -0.19 V. In aqueous perchlorate media at near-neutral pH the voltammetric response is close to that expected for an electrochemically reversible reaction involving a surface-confined reactant. Chronoamperometry conducted on a microsecond time scale indicates that the film and solution resistances are comparable for low concentrations of supporting electrolyte. However, for LiClO4 concentrations greater than 0.4 M, RFilm contributes less than 25% of the overall cell resistance. These results suggest that when the film is dehydrated and the density of redox centers is increased, electron or hole hopping dominates the rate of homogeneous charge transport through the film. The rate of homogeneous charge transport, characterized by D(CT)1/2Ceff, where DCT is the homogeneous charge transport diffusion coefficient and Ceff is the effective concentration of osmium centers within the film, depends weakly on the concentration of LiClO4 as supporting electrolyte decreasing from (8.1 +/- 0.16) x 10(-9) to (4.7 +/- 0.4) x 10(-9) mol cm(-2) s(-1/2) as the perchlorate concentration increases from 0.1 to 1.0 M. These values are about 2 orders of magnitude lower than those of the chemically cross-linked chloride salt of the polymer. The rate of heterogeneous electron transfer is unusually rapid in this system and increases from (5.2 +/- 0.4) x 10(-3) to (7.8 +/- 0.4) x 10(-3) cm s(-1) on going from 0.1 to 0.4 M LiClO4 before becoming independent of the supporting electrolyte concentration at (9.2 +/- 0.6) x 10(-3) cm s(-1) for [LiClO4] > or = 0.6 M.     

Modulation of tautomeric equilibria by ionic clusters. Acetylacetone in solutions of lithium perchlorate-diethyl ether

Acetylacetone (2,4-pentanedione, 1) is a molecule whose tautomeric forms are in dynamic equilibrium. Concentrated salt solutions in nonaqueous solvents exert a remarkable influence on the keto-enol ratio of this beta-diketone. The keto content of 1 increases from 5% in pure diethyl ether to 84.5% in a 4.14 M lithium perchlorate-diethyl ether (LPDE) solution, a nearly 17-fold increase. The equilibrium expression, K = [keto]/[enol] = k(f)/k(r), exhibits a linear dependence on [LiClO(4)], with the formal order of participation of lithium ion in the equilibrium being 1.0. A kinetic analysis reveals that k(f) is independent of LPDE concentration, whereas k(r) displays an inverse dependence on salt concentration, indicating preferential coordination of the keto tautomer with Li(+). Although 1 exits as the enol in water only to the extent of 16%, the addition of lithium perchlorate further reduces this figure. In an aqueous 4.02 M LiClO(4) solution, acetylacetone enol accounts for only 4.6% of the total amount of 2,4-pentanedione present. It has also been found that acetylacetone itself is an excellent solvent for LiClO(4) as well as for NaClO(4) with solutions containing up to 7.5 M LiClO(4) attainable. The enol content of 1 decreases dramatically from 81% to 7.4% on going from the neat liquid to a solution of 6.39 M LiClO(4) in acetylacetone.     

Electrochemical behavior of poly(ferrocenyldimethylsilane-b-dimethylsiloxane) films

The electrochemical behavior of poly(ferrocenyldimethylsilane-b-dimethylsiloxane) (PFDMS-b-PDMS) films deposited on a glassy carbon electrode was investigated by means of cyclic voltammetry (CV). The influences of the solvent, film thickness, temperature, and PDMS block length in PFDMS-b-PDMS on the electrode process were discussed. It was found that in 0.1 M aqueous LiClO(4) the electrochemical processes of the films on a glassy carbon electrode were complex and have a low rate of electron transport and mass diffusion. The kinetic parameters obtained indicated that the electrode process was controlled by both the electrode reaction and mass diffusion.     

Electrolyte-concentration and ion-size dependence of excited-state intramolecular charge-transfer reaction in (alkylamino)benzonitriles: steady-state spectroscopic studies

Steady-state spectroscopic studies have been performed with three intramolecular charge-transfer molecules, 4-(1-azetidinyl)benzonitrile (P4C), 4-(1-pyrrolidinyl)benzonitrile (P5C), and 4-(1-piperidinyl)benzonitrile (P6C), in ethyl acetate and acetonitrile in presence of lithium perchlorate (LiClO(4)) at room temperature to investigate the effects of electrolytes on excited-state intramolecular charge-transfer reaction. Electrolyte-concentration and ion-size dependences of several spectroscopic properties such as quantum yield, absorption and emission transition moments, radiative and nonradiative rates, and changes in reaction free energies associated with LE --> CT conversion have been determined for these molecules and reported. For P4C, quantum yield decreases by a factor of approximately 7 at the highest electrolyte concentration relative to that in pure ethyl acetate whereas it is a factor of approximately 4 for both P5C and P6C. However, in acetonitrile with 1.0 M LiClO(4), quantum yield reduces to almost half of that in the pure solvent. Formation of a charge-transfer (CT) state is found to be strongly favored over the locally excited (LE) state as the electrolyte (LiClO(4)) concentration is increased, electrolyte effects being more pronounced in ethyl acetate than in acetonitrile. Relative to pure ethyl acetate, reaction free energy change (-DeltaG(r)) increases by a factor of approximately 5, approximately 4, and approximately 2 for P4C, P5C, and P6C, respectively, at 2.5 M LiClO(4) in this solvent. -DeltaG(r) for P4C exhibits a change in sign (from negative to positive) upon addition of electrolyte in ethyl acetate. In acetonitrile, however, these changes are within a few percent, except for P4C where it is about 4 times greater at 1.0 M LiClO(4) than that in pure acetonitrile. The electrolyte-induced total red shift of the CT band of these TICT molecules is 3 times higher in ethyl acetate than in acetonitrile. Although both the quantum yield and CT emission peak frequency decrease linearly with the increase in ion size, -DeltaG(r) remains largely insensitive. Further studies using a nonreactive probe (coumarin 153) in concentrated electrolyte solutions also show qualitatively similar results.     

Stability constants: comparative study of fitting methods. Determination of second-order complexation constants by (23)Na and (7)Li NMR chemical shift titration

NMR chemical shift titration has been widely used as a method for the determination of stability constants. Systems involving metal-ligand complexation have been investigated using a number of methodologies. There are significant differences in the values reported for stability constants obtained by different experimental methods, such as calorimetry and ion selective electrode (ISE) titrations; nor has NMR chemical shift titration always yielded consistent results. Different researchers have obtained different results for the same system with results differing by as much as an order of magnitude. The chemical shift data are generally plotted against the concentration ratio of the metal and ligand for a set of solutions. A nonlinear least squares fitting method using an analytical solution of the cubic equation for the equilibrium concentration of the free ligand is used in this study and compared with methods used in the literature. Second-order association constants for the LiClO(4):12-crown-4 system in acetonitrile and the NaClO(4):12-crown-4 system in methanol are reported. Formation of both 1:1 and 1:2 metal-ligand complexes are considered. The LiClO(4):12-crown-4 acetonitrile system had been investigated previously by NMR titration but only 1:1 complexation was considered in that study. This study provides convincing evidence that both 1:1 and 1:2 complexes are important, at least, in the lithium system. A Monte Carlo investigation of the propagation of errors from the chemical shifts to the stability constants shows that the choice of data analysis methods may, in part, contribute to discrepancies and that the nonlinear nature of the model can dramatically affect the error limits on the stability constants.     

Determination of the expiration date of chemical solutions

Thirty-five chemical solutions, acids, bases, complexing, argentometric, reducing, oxidising, salts and eluent mixtures, were studied continuously over a 7.5-month period. Twenty-seven remained reasonably stable and had acceptable expiration dates, which were equal to or more than 2 months longer than the established average deviation of ±2% relative to the initial value. Exceptions were made for potassium permanganate (0.1 M), perchloric acid (0.1 M) and disodium hydrogen phosphate (10%) solutions, as well as for HPLC eluent mixtures, which showed stability with expiration dates equal to stated values or shorter by 1 month. The eight chemical solutions presenting expiration dating higher than 6 months were hydrochloric acid (0.1 and 1 M), sulphuric acid (0.5 and 1.5 M), ethylenediamine tetraacetic acid (EDTA) (0.1 M), silver nitrate (0.1 M), ammonium thiocyanate (0.1 M) and iodine (0.1 M). The present data is a suitable guideline for the date of several chemical solutions routinely used in the analytical laboratories.     

高氯酸锂-乙酰胺/乙烯脲体系的二元熔盐电解质

制备了高氯酸锂与乙酰胺和乙烯脲形成的二元低温熔盐电解质，采用差示扫描量热法、交流阻抗法和循环伏安法分别对其热学、电化学性质进行了研究.测试结果表明,高氯酸锂-乙酰胺体系具有较好的热稳定性和高的电导性，配比n（LiClO4）:n（Acetamide）=1.0:5.5的样品室温（25 ℃）电导率为1.25×10－3 S•cm－1，80 ℃电导率为1.15×10－2 S•cm－1;其电化学稳定电位窗近3 V左右.     

电解质溶液对聚吡咯电聚合中过氧化行为的影响

分别以硫酸/水和高氯酸锂/乙腈为电解质溶液, 采用循环伏安法在铂基底电极上电聚合制备了聚吡咯, 研究了电解质溶液对聚吡咯电聚合过程中过氧化行为的影响. 与硫酸/水溶液相比, 在高氯酸锂/乙腈溶液中电聚合制备的聚吡咯发生过氧化的峰电位正移了0.42 V. 采用原位傅里叶变换红外(in situ FTIR)光谱技术检测, 结果表明, 电聚合制备的聚吡咯在2种电解质溶液中均发生了过氧化反应, 其β-C经氧化生成C-OH或CO. 在硫酸/水溶液中, 部分聚吡咯发生电氧化降解生成CO₂, 致使其共轭结构被破坏, 电导率迅速下降. 而在高氯酸锂/乙腈溶液中, 在更高的电位范围内, 聚吡咯并没有氧化降解成CO₂.     

高分子凝胶电解质高氯酸锂 - 碳酸乙二醇酯 - 聚甲基丙烯酸甲酯体系的研究

研究了高分子凝胶电解质高氯酸锂 碳酸乙二醇酯 聚甲基丙烯酸甲酯体系（ＬｉＣｌＯ４ ＥＣ ＰＭＭＡ）的离子导电性、热稳定性和电化学稳定性．该体系的离子电导率与温度的关系服从ＶＴＦ方程．当ＬｉＣｌＯ４的浓度ＣＬｉＣｌＯ４＝１５ｍｏｌ／Ｌ、ＰＭＭＡｗｔ％（质量百分数）＝３５时，其离子电导率达极大值δ＝１９２×１０－３Ｓ／ｃｍ，光学透明度高，在空气中的稳定性较好，且具有一定的粘附性．该体系在１０２℃以下的热稳定性较高（失重率为３２８％）；电化学稳定性窗口为４５Ｖ，可满足固态电致变色“Ｓｍａｒｔ”窗的要求．     

Solution studies on chelates of nickel, zinc and cadmium with 2-thiopicolinanilide

The protonation constants of 2-thiopicolinanilide (TPA) and the stability constants of its complexes with Ni, Zn and Cd have been determined potentiometrically in 50% w/w ethanol-water medium, at 25 degrees and 0.100M ionic strength (LiClO(4)). Co-ordination centres in TPA are suggested.     

Syntheses and Application of All-lithium Salts of Heteropolyacid as Electrolyte of Lithium-ion Battery

IntroductionThesecondarylithium ionbatterieshaverecentlybecomeoneofthechemicalenergysourceswhichhavebeenresearchedanddevelopedintheworldbecauseoftheirbiggerspecificcapacity ,lighterweight ,higheroperatingvoltage ,longercycliclifeandbettersecuri ty[1— 3] .LiClO4 ,LiAsF6 andLiPF6 aremainlyusedaselectrolytesinthecommercializedlithium ioncellsintheworldinspiteoftheirdisadvantages:LiClO4 isalittleunsafewhichwillbedetonablewhenbeingbumpedandishygroscopic ;LiAsF6 ispoisonousanditisanenvironment…     

La掺杂的TiO2纳米棒在常温常压下可促进电催化的N2转化为NH3

氨在化肥、染料、药品和炸药的制造中起着重要作用.目前,传统的Haber-Bosch工艺主要用于NH3的大规模工业化生产,在苛刻的反应条件(300～500℃,150～300 atm)下不可避免地伴随着温室气体的过量排放.因此,必须寻求一种绿色并且可持续的方法来生产NH3.电化学还原N2 (NRR)已成为在环境条件下将N2连续固定NH3的一种有吸引力的替代方法.由于稳定的N-N具有较强的偶极矩并与析氢反应存在激烈竞争,因此需要高效的NRR催化剂.TiO2是典型的n型半导体,被认为是一种很有前途的NRR电催化剂.最近的研究表明,La2O3对N2还原电催化也具有活性,然而镧金属的稀土性质限制了其大规模应用.本文研究发现镧可以作为一种有效的掺杂剂提高TiO2的NRR活性.通过水热法制备了镧掺杂的TiO2纳米棒(La-TiO2).透射电子显微镜结果表明,原始TiO2与La-TiO2在形貌上都是纳米棒,镧的引入对其形貌并没有显著影响.选区电子衍射证实了La-TiO2纳米棒的高结晶度和四边形单晶结构.电子自旋共振分析结果表明La-TiO2纳米棒中存在氧空位.La-TiO2的线性扫描伏安曲线结果表明,在N2饱和电解液中的电流密度明显大于在Ar饱和电解液中,说明NRR的发生.为了进一步证实这一假设,在五个不同电位下分别进行了一系列的计时电流测试,结果表明,连续电解2h后在-0.70 V时,NH3产率最高,达23.06 μg h-1 mgcat-1,并且法拉第效率也最大,达14.54％.此外,电解2h后,没有检测到副产物N2H4,表明La-TiO2催化剂对NH3合成具有良好的选择性.本文还比较了La-TiO2/CP,TiO2/CP和CP的NRR电催化性能,结果表明,La-TiO2/CP的NH3产率最高,说明La的引入提高了La-TiO2的NRR活性.La-TiO2/CP通过在-0.70 V下连续6次循环测试以及连续48 h电解测试证实La-TiO2对NRR电催化具有良好的电化学稳定性.通过对La-Ov构型进行密度泛函理论计算,重点研究*N2+H++e-→*NNH的反应步骤,由于*N2加氢的自由能垒较低,La-TiO2更容易激活N2分子,计算了La-TiO2和纯TiO2上*NNH中间体的电荷密度差异,*NNH与La-TiO2之间存在更多的电荷转移.采用N-N键的积分晶体轨道哈密顿布居(ICOHP)分析出La-TiO2的ICOHP负值较小(-16.67 vs.-19.93),说明N-N键的活化更多.     

Behaviour of the thiodipropionic complex of In(III) and U(VI) at the DME in aqueous and aqueous methanolic solutions

The complexation of In(III) and U(VI) with thiodipropionic acid has been investigated polarographically in water and water-methanol solutions at 30 +/- 0.1 degrees . All the chelates belong to polaro-graphically reversible systems. With indium(III), complexes with metal to ligand ratios of 1:1, 1:2, 1:3 and 1:4 are found at pH 4.8. Uranium(VI) is found to form three successive complexes with metal to ligand ratios of 1:1,1:2 and 1:3 in 0.1M HCl, with 0.1M KCl as supporting electrolyte.     

Effects of electrolyte concentration on the rotational dynamics of resorufin

We report on the rotational diffusion dynamics of the anionic chromophore resorufin in water and N-octyl-2-pyrrolidone (NOP) solutions as a function of solution electrolyte concentration. Our data show that resorufin exhibits a single exponential anisotropy decay in aqueous solutions containing up to 0.1 M lithium perchlorate (LiClO(4)). In contrast to the observed behavior of resorufin in pure NOP, where biexponential decay occurs, we also observe a single exponential anisotropy decay for resorufin in NOP with the addition of up to 0.1 M tetrabutylammonium bromide (TBAB) or tetraoctylammonium bromide (TOAB). For resorufin in NOP, the reorientation time constant increases with increasing electrolyte concentration, consistent with complexation between the resorufin anion and the electrolyte ammonium cation. We observe a qualitatively different trend in the aqueous resorufin solutions and understand these data for both solvent systems in the context of interactions between the chromophore and cationic species present.     

Films of lutetium bisphthalocyanine nanowires as electrochemical sensors

Lutetium bisphthalocyanine (LuPc(2)) nanowires have been successfully obtained by electrophoretic deposition (EPD). The influence of the deposition conditions and annealing in the structure of the films has been studied by AFM, SEM, X-ray diffraction (XRD), UV-vis absorption, and near-infrared (NIR). The electrochemical properties of the EDP films immersed in different electrolytic solutions (KCl, MgCl(2), KClO(4), HCl, and NaOH) indicate that anions diffuse inside the film to maintain the electroneutrality and the kinetics follows the Randles-Sevcik equation. The stability of the response increases strongly upon annealing due to the improvement of the adhesion of the sensitive material to the substrate. The EPD films have been successfully used to detect caffeic acid (an antioxidant of interest in the food industry). The anodic peak associated with the oxidation of caffeic acid appears at 0.54 V and is linearly dependent on the caffeic acid concentration in the 6 × 10(-5) M to 5 × 10(-4) M range with a detection limit of 3.12 × 10(-5) M. The electrochemical behavior of the annealed LuPc(2) EPD films is similar to that observed using Langmuir-Blodgett (LB) nanostructured films. However, the different molecular organization of the molecules inside the film causes differences in the shape and position of the peaks. Although LuPc(2) sensors prepared with both EPD and LB techniques provide stable and reproducible responses, the use of EPD is preferred for real sensing applications because of its lower cost, shorter preparation time, and longer lifetime.     

1-乙酰胺基丙叉-1,1-二膦酸和1-丙酰胺基乙叉-1,1-二膦酸与碱土金属离子的螯合作用

用pH电位法研究了1-乙酰胺基丙叉-1,1-二膦酸(S-186)和1-丙酰胺基乙叉-1,1-二膦酸(S-106)与碱土金属的螯合作用(30±O.1℃).当金属离子与配体的摩尔浓度比为10∶1、1∶1和1∶2时,在水溶液中形成了MHL、ML、ML_2和M_2L等几种类型的配合物.分别测定了它们的稳定常数,其中S-186配合物稍高于S-106,说明配合物稳定性与螯合剂的碱度有平行关系.值得注意的是,这两种螯合剂与Sr~(2 )形成的双核配合物的稳定性均较其它碱土金属离子的为高.     

有机溶液中添加水对聚吡咯电化学性能的影响

采用电势阶跃技术, 于Pt微盘电极上在含水体积分数分别为0, 2%, 4%, 6%和8%的0.1 mol/L Pyrrole+0.1 mol/L LiClO₄的碳酸丙烯酯(PC)溶液中合成了聚吡咯(PPy)膜. 采用循环伏安法、计时电流法考察了不同含水比例条件下聚吡咯的电化学行为, 采用扫描电镜对其表面形貌进行了观察分析. 研究结果表明, 最佳的含水体积分数为6%. 在此条件下聚合得到的PPy量大, 具有较高的电化学容量、较好的电化学反应可逆性.     

Time-scale- and temperature-dependent mechanical properties of viscoelastic poly(3,4-ethylenedioxythiophene) films

The viscoelastic properties of thin films of poly(3,4-ethylenedioxythiophene) (PEDOT) have been studied using the method of acoustic impedance. The films were deposited on the Au electrodes of 10 MHz AT-cut quartz thickness shear mode resonators and exposed to acetonitrile solutions of 0.1 M TEABF4 and LiClO4. For p-doped films, admittance spectra as a function of potential (E), temperature (T), and time scale (frequency, via harmonics, in the range 10-110 MHz) were acquired. Shear modulus components extracted from these responses surprisingly showed virtually no variation with E (and thus film solvation) or with T, but the variation with frequency was dramatic. This qualitative behavior and the numerical values of the shear moduli contrast strongly with recently reported data for the related poly(3-hexylthiophene) system, which shares the same conducting spine but differs substantially in the substitution pattern. Accordingly, the models and interpretation for PEDOT are quite different: film dynamics are determined by free-volume effects, and side-chain motion is not a significant factor. Qualitatively similar potential and time-scale effects were seen for n-doped PEDOT, but the scope of the measurements was limited by film stability.