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1.
An improved flow-based procedure is proposed for turbidimetric sulphate determination in waters. The flow system was designed with solenoid micro-pumps in order to improve mixing conditions and minimize reagent consumption as well as waste generation. Stable baselines were observed in view of the pulsed flow characteristic of the systems designed with solenoid micro-pumps, thus making the use of washing solutions unnecessary. The nucleation process was improved by stopping the flow prior to the measurement, thus avoiding the need of sulphate addition. When a 1-cm optical path flow cell was employed, linear response was achieved within 20–200 mg L−1, described by the equation S = −0.0767 + 0.00438C (mg L−1), r = 0.999. The detection limit was estimated as 3 mg L−1 at the 99.7% confidence level and the coefficient of variation was 2.4% (n = 20). The sampling rate was estimated as 33 determinations per hour. A long pathlength (100-cm) flow cell based on a liquid core waveguide was exploited to increase sensitivity in turbidimetry. Baseline drifts were avoided by a periodical washing step with EDTA in alkaline medium. Linear response was observed within 7–16 mg L−1, described by the equation S = −0.865 + 0.132C (mg L−1), r = 0.999. The detection limit was estimated as 150 μg L−1 at the 99.7% confidence level and the coefficient of variation was 3.0% (n = 20). The sampling rate was estimated as 25 determinations per hour. The results obtained for freshwater and rain water samples were in agreement with those achieved by batch turbidimetry at the 95% confidence level. 相似文献
2.
K.S. Gavrichev M.A. Ryumin A.V. Tyurin V.M. Gurevich L.N. Komissarova 《Thermochimica Acta》2008,474(1-2):47-51
In the present work temperature dependence of heat capacity of cesium tantalum tungsten oxide has been measured first in the range from 7 to 350 K and then between 330 and 630 K, respectively, by precision adiabatic vacuum and dynamic calorimetry. The experimental data were used to calculate standard thermodynamic functions, namely the heat capacity Cp° (T), enthalpy H°(T) − H°(0), entropy S°(T) − S°(0) and Gibbs function G°(T) − H°(0), for the range from T → 0 to 630 K. The structure of CsTaWO6 is refined by the Rietveld method: space group F d3m, Z = 8, a = 10.3793(2) Å, V = 1118.14(4) Å3. The high-temperature X-ray diffraction was used for the determination of temperature of phase transition and coefficient of thermal expansion. 相似文献
3.
A coordination polymer was synthesized by the reaction of CoCl2 with 1,2,4-triazole-5-one (TO) and charaterized by means of IR and TG–DTG. Single-crystal structure analysis showed that the complex crystallized in the monoclinic space group C2/c: a = 23.105(9) Å, b = 3.5683(2) Å, c = 13.589(6) Å, = 90°, β = 124.038(4)°, γ = 90°, V = 928.4(7) Å3, Z = 4. The standard molar enthalpy of formation of the complex was determined to be (−1034.28 ± 0.95) kJ mol−1. 相似文献
4.
Carole Duboc Thida Phoeung Damien Jouvenot Allan G. Blackman Lisa F. McClintock Jacques Pcaut Marie-Noëlle Collomb Alain Deronzier 《Polyhedron》2007,26(18):5243-5249
The five-coordinate mono-halide mononuclear Zn(II) complexes [Zn(tpa)X]+ (tpa = tris(2-pyridylmethyl)amine; X = I ([Zn(tpa)I]I; 1a), Br ([Zn(tpa)Br](ZnBr4)0.5; 2a) and Cl ([Zn(tpa)Cl](ZnCl4)0.5; 3a)) and the six-coordinate mononuclear complex [Zn(tpa)(NCS)2] (4a) have been synthesized and characterized by X-ray crystallography. The [Zn(tpa)X]+ complexes doped with the corresponding [Mn(tpa)X2] complexes (X = I (1b), Br (2b) and Cl (3b)) have been synthesized and their electronic properties investigated by multifrequency high field EPR (HF-EPR) (95–285 GHz). The magnetically diluted conditions allow the determination of the hyperfine coupling constant A (A = 68.10−4 cm−1 for 1b–3b). The zero-field splitting parameters (D and E) found for 1b–3b are comparable to those found for neat samples of the [Mn(tpa)X2] complexes (1b: D = 0.635 cm−1, E/D = 0.189; 2b: D = 0.360 cm−1, E/D = 0.192; 3b: D = 0.115 cm−1, E/D = 0.200). The efficacy of using multifrequency EPR under dilute conditions to precisely determine spin Hamiltonian parameters is discussed. 相似文献
5.
Bojan Kozlev
ar Marjeta Radiek Zvonko Jagli
i Franci Merzel Lea Glaar Amalija Golobi
Primo egedin 《Polyhedron》2007,26(18):5414-5419
A novel dinuclear complex [Cu2(μ-L)4(HL)2] (1) was isolated from starting 2-pyridone (HL) via a resonance and a tautomeric transformation. Each copper centre is in a square-pyramidal coordination sphere, defined by two oxygen atoms (Cu–O4 1.978(5), Cu–O11 1.964(4) Å) and two nitrogen atoms (Cu–N2 2.003(5), Cu–N3 2.007(5) Å) of four bridging deprotonated pyridin-2-olates and an oxygen atom on the top from a neutral 2-pyridone (Cu–O2 2.227(5) Å), analogous to tetracarboxylate paddle-wheel complexes. Compound 1 was compared with mixed pyridin-2-olato/methanoato analogues [Cu2(μ-HCO2)2(μ-L)2(HL)2] · 2CH3CN (2) and [Cu2(μ-HCO2)2(μ-L)2(HL)2] (2a) (2a is an air stable form obtained from 2 outside mother-liquid). The EPR spectra of air stable 1 and 2a show three signals Hz1, H2 and Hz2, typical for the binuclear systems with spin S = 1, both revealing strong antiferromagnetism 2J = −334 (1) and −324 cm−1 (2a). Interestingly, only for 1 additional H1 signal at 100 mT is noticed (D(1) = 0.293 cm−1 < hν = 0.320 cm−1 < D(2a) = 0.347 cm−1). On the other hand, several broad signals in the 100–450 mT region, only in the high temperature spectrum for 2a are observed. These results are in agreement with the magnetic susceptibility analysis. 相似文献
6.
In the present work, CdSe/ZnS core-shell quantum dots were synthesized and conjugated with enzymes, glucose oxidase (GOD) and horseradish peroxidase (HRP). The complex of enzyme-conjugated QDs was used as QD-FRET-based probes to sense glucose. The QDs were used as an electron donor, whereas GOD and HRP were used as acceptors for the oxidation/reduction reactions involved in oxidizing glucose to gluconic acid. Electron transfer between the redox enzymes and the electrochemical reduction of H2O2 (or O2) occurred rapidly, resulting in an increase of the turnover rate of the electron exchange between the substrates (e.g. glucose, H2O2 and O2) and the enzymes (GOD, HRP), as well as between the QDs and the enzymes. The transfer of non-radiative energy from the QDs to the enzymes resulted in the fluorescence quenching of the QDs, corresponding to the increase in the concentration of glucose. The linear detection ranges of glucose concentrations were 0–5.0 g/l (R = 0.992) for the volume ratios of 10/5/5, 0.2–5.0 g/l (R = 0.985) for the volume ratios of 10/5/3 and 1.0–5.0 g/l (R = 0.982) for the volume ratios of 10/5/0. Temperature (29–37 °C), pH (6–10) and some ions (NH4+, NO3−, Na+, Cl−) had no interference effect on the glucose measurement. 相似文献
7.
Sareh M. Nasseri Nasser L. Hadipour Ali Reza Mohebbi 《Journal of Molecular Structure》2007,820(1-3):48-52
In this paper, density functional theory (DFT) was used to calculate 14N nuclear quadrupole coupling constants (NQCC), χ, and asymmetry parameters, η, for a series of imidazole derivatives: imidazole, 5-methylimidazole and histidine. These calculations were carried out with the PW91P86 method via the Gaussian 98 package. A systematic theoretical investigation of the different environmental effects on (χ, η) values of amino 14N1 and imino 14N2 of imidazole ring of these compounds, reveals that the local surrounding of nitrogen atoms play an important role in determining their χ and η values. Our calculations in solution show that adding explicit solvent molecules to the polarizable continuum model (PCM) has a strong effect on (χ, η) values, thereby indicating that for long-range effects, PCM, is not sufficient to describe the whole solvent effects. We also evaluate the influence of [Fe3+ (S = 1/2)] on the (χ, η) values of proximal and remote nitrogens of an axial ligand and compare with those of free ligands. The results show that Fe3+ has a strong effect on the (χ, η) values of proximal nitrogen unlike remote nitrogen. Finally, our results predict (χ = 1.56 MHz, η = 0.690) for proximal nitrogen and (χ = 2.75 MHz, η = 0.169) for remote nitrogen in PfHRP2–Fe3+-PPIX complex. 相似文献
8.
Measurements of Rayleigh scattering and relativistic calculations of incoherent scattering functions
Recent measurements of Rayleigh scattering employing neutron capture γ-rays are presented. Experimental conditions are achieved such that the Rayleigh contribution is dominant and much larger than the other competing coherent processes. A detailed comparison with the modified relativistic form factor (MRFF) approximation is made and it is concluded that the latter overestimates the cross-section by 3–4%. New calculations of S, the incoherent scattering function, are presented in the relativistic treatment of Ribberfors and Berggren, using multiconfiguration Dirac–Fock relativistic wavefunctions. Tables of S, for Z=1–110, are shown on a momentum transfer mesh identical to previous non-relativistic calculations. S has been calculated at a representative angle θ=60° and energies compatible with the presentation mesh. For other scattering angles, the values presented in the tables are accurate to within 1–2% for momentum transfers larger than 0.1 Å−1. In the region below 0.1 Å−1 the accuracy worsens with decreasing momentum transfer, reaching 6% at 0.01 Å−1 and 10% at 0.005 Å−1. The same multiconfiguration wave functions were used to evaluate new MRFFs. The new elastic scattering cross sections differ by 3–6% compared with calculations based on single configuration wave functions. 相似文献
9.
Gonzalo Blay Isabel Fernndez Jos R. Pedro Rafael Ruiz-García Toms Temporal-Snchez Emilio Pardo Francesc Lloret M. Carmen Muoz 《Journal of molecular catalysis. A, Chemical》2006,250(1-2):20-26
The high-valent bis(oxo)-bridged dimanganese(IV) complexes with the series of binucleating 4,5-X2-o-phenylenebis(oxamate) ligands (opbaX2; X = H, Cl, Me) (1a–c) have been synthesized and characterized structurally, spectroscopically and magnetically. Complexes 1a–c possess unique Mn2(μ-O)2 core structures with two o-phenylenediamidate type additional bridges which lead to exceptionally short Mn–Mn distances (2.63–2.65 Å) and fairly bent Mn–O–Mn angles (94.1°–94.6°). The cyclovoltammograms of 1a–c in acetonitrile (25 °C, 0.1 M Bu4NPF6) show an irreversible one-electron oxidation peak at moderately high anodic potentials (Eap = 0.50–0.85 V versus SCE), while no reductions are observed in the potential range studied (down to −2.0 V versus SCE). These dinuclear manganese oxamate complexes are excellent catalysts for the aerobic oxidation of 3,5-di-tert-butylcatechol to the corresponding o-quinone in acetonitrile at 25 °C. The order of increasing catecholase activity (kobs) with the electron donor character of the ligand substituents as 1b (X = Cl) < 1a (X = H) < 1c (X = Me) correlates with Hammett σ+ values (ρ = −0.95). A mechanism involving initial activation of the catechol substrate by coordination to the dimetal center and subsequent oxidation to quinone by O2 is proposed, which is consistent with the observed saturation kinetics. 相似文献
10.
Flow injection (FI) methodology, using diffuse reflectance in the visible region of the spectrum, for the analysis of nickel, precipitated in the form of dimethylglyoximate, is presented. A reflectance cell, constructed in polytetrafluoroethylene, using a LED (light emitting diode) as light source and a LDR (light dependent resistor) as detector, is described. The analytical signal (S) correlates with nickel concentration (C) between 1.6 × 10−4 and 6.6 × 10−4 mol L−1. This correlation is described by the equation S = −1.108 + 3.314 × 104C − 2.081 × 107C2 (r = 0.9996). The experimentally observed limit of detection is about 1.3 × 10−4 mol L−1, as in lower concentrations the formation of precipitate is not observed. The experimental quantitation limit is about 1.6 × 10−4 mol L−1. The mean R.S.D. (relative standard deviation) is about 2.7%. Samples containing nickel were analyzed and the results obtained in this method were compared with those of other methods using the statistical Student's t-test. 相似文献
11.
Xue-Chuan Lv Zhi-Cheng Tan Xiao-Han Gao Zhi-Heng Zhang Li-Ni Yang Jun-Ning Zhao Li-Xian Sun Tao Zhang 《Thermochimica Acta》2006,450(1-2):102-104
A metal-organic complex, which has the potential property of absorbing gases, [LaCu6(μ-OH)3(Gly)6im6](ClO4)6 was synthesized through the self-assembly of La3+, Cu2+, glycine (Gly) and imidazole (Im) in aqueous solution and characterized by IR, element analysis and powder XRD. The molar heat capacity, Cp,m, was measured from T = 80 to 390 K with an automated adiabatic calorimeter. The thermodynamic functions [HT − H298.15] and [ST − S298.15] were derived from the heat capacity data with temperature interval of 5 K. The thermal stability of the complex was investigated by differential scanning calorimetry (DSC). 相似文献
12.
Amberlite XAD-16 resin has been functionalized using nitrosonaphthol as a ligand and characterized employing elemental, thermogravimetric analysis and FT-IR spectroscopy. The sorption of Ni(II) and Cu(II) ions onto this functionalized resin is investigated and optimized with respect to the sorptive medium (pH), shaking speed and equilibration time between liquid and solid phases. The monitoring of the influence of diverse ions on the sorption of metal ions has revealed that phosphate, bicarbonate and citrate reduce the sorption up to 10–14%. The sorption data followed Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) isotherms. The Freundlich parameters computed are 1/n = 0.56 ± 0.03 and 0.49 ± 0.05, A = 9.54 ± 1.5 and 6.0 ± 0.5 mmol g−1 for Ni(II) and Cu(II) ions, respectively. D–R isotherm yields the values of Xm = 0.87 ± 0.07 and 0.35 ± 0.05 mmol g−1 and of E = 9.5 ± 0.23 and 12.3 ± 0.6 kJ mol−1 for Ni(II) and Cu(II) ions, respectively. Langmuir characteristic constants estimated are Q = 0.082 ± 0.005 and 0.063 ± 0.003 mmol g−1, b = (4.7 ± 0.2) × 104 and (7.31 ± 0.11) × 104 l mol−1 for Ni(II) and Cu(II) ions, respectively. The variation of sorption with temperature gives thermodynamic quantities of ΔH = −58.9 ± 0.12 and −40.38 ± 0.11 kJ mol−1, ΔS = −183 ± 10 and −130 ± 8 J mol−1 K−1 and ΔG = −4.4 ± 0.09 and −2.06 ± 0.08 kJ mol−1 at 298 K for Ni(II) and Cu(II) ions, respectively. Using kinetic equations, values of intraparticle transport and of first order rate constant have been computed for both the metal ions. The sorption procedure is utilized to preconcentrate these ions prior to their determination in tea, vegetable oil, hydrogenated oil (ghee) and palm oil by atomic absorption spectrometry using direct and standard addition methods. 相似文献
13.
Iva Diblikova Kevin M. Cooper D. Glenn Kennedy Milan Franek 《Analytica chimica acta》2005,540(2):285-292
A sensitive and specific monoclonal ELISA for the determination of tissue bound furazolidone metabolite 3-amino-2-oxazolidinone (AOZ) is described. The procedure enables the detection of AOZ in matrix supernatant after homogenisation, protease treatment, acid hydrolysis and derivatisation of AOZ released from the tissue by o-nitrobenzaldehyde. The formed p-nitrophenyl 3-amino-2-oxazolidinone (NPAOZ) is determined by ELISA calibrated with matrix-matched standards in the concentration range of 0.05–5.0 μg I−1. The assay was validated according to criteria set down by Commission Decision 2002/657/EC for the performance and validation of analytical methods for chemical residues. Detection capability, set on the basis of acceptance of no false negative results, was 0.4 μg kg−1 for shrimp, poultry, beef and pork muscle. This sensitivity approaches the established confirmatory LC–MS/MS able to quantify tissue-bound AOZ at levels as low as 0.3 μg kg−1. An excellent correlation of results obtained by ELISA and LC/MS–MS within the concentration range 0–32.1 μg kg−1 was found in the naturally contaminated shrimp samples (r = 0.999, n = 8). A similar correlation was found for the incurred poultry samples within the concentration range of 0–10.5 μg kg−1 (r = 0.99, n = 8). 相似文献
14.
Automated sequential injection (SIA) method for chemiluminescence (CL) determination of nonsteroidal anti-inflammatory drug indomethacin (I) was devised. The CL radiation was emitted in the reaction of I (dissolved in aqueous 50% v/v ethanol) with intermediate reagent tris(2,2′-bipyridyl)ruthenium(III) (Ru(bipy)33+) in the presence of acetate. The Ru(bipy)33+ was generated on-line in the SIA system by the oxidation of 0.5 mM tris(2,2′-bipyridyl)ruthenium(II) (Ru(bipy)32+) with Ce(IV) ammonium sulphate in diluted sulphuric acid. The optimum sequence, concentrations, and aspirated volumes of reactant zones were: 15 mM Ce(IV) in 50 mM sulphuric acid 41 μL, 0.5 mM Ru(bipy)32+ 30 μL, 0.4 M Na acetate 16 μL and I sample 15 μL; the flow rates were 60 μL s−1 for the aspiration into the holding coil and 100 μL s−1 for detection. Calibration curve relating the intensity of CL (peak height of the transient CL signal) to concentration of I was curvilinear (second order polynomial) for 0.1–50 μM I (r = 0.9997; n = 9) with rectilinear section in the range 0.1–10 μM I (r = 0.9995; n = 5). The limit of detection (3σ) was 0.05 μM I. Repeatability of peak heights (R.S.D., n = 10) ranged between 2.4% (0.5 μM I) and 2.0% (7 μM I). Sample throughput was 180 h−1. The method was applied to determination of 1 to 5% of I in semisolid dosage forms (gels and ointments). The results compared well with those of UV spectrophotometric method. 相似文献
15.
The low lying electronic states of the molecule MoN were investigated by performing all electron ab initio multi-configuration self-consistent-field (CASSCF) calculations. The relativistic corrections for the one electron Darwin contact term and the relativistic mass-velocity correction were determined in perturbation calculations. The electronic ground state is confirmed as being 4∑−. The chemical bond of MoN has a triple bond character because of the approximately fully occupied delocalized bonding π and σ orbitals. The spectroscopic constants for the ground state and ten excited states were derived. The excited doublet states 2∑−, 2Γ, 2Δ, and 2∑+ are found to be lower lying than the 4Π state that was investigated experimentally. Elaborate multi-configuration configuration-interaction (MRCI) calculations were carried out for the states 4∑− and 4∏ using various basis sets. The spectroscopic constants for the 4∑− ground state were determined as re=1.636 Å and ωe=1109 cm−1, and for the 4∏ state as re=1.662 Å and ωe=941 cm−1. The values for the ground state are in excellent agreement with available experimental data. The MoN molecule is polar with a charge transfer from Mo to N. The dipole moment was determined as 2.11 D in the 4∑− state and as 4.60 D in the 4∏ state. These values agree well with the revised experimental values determined from molecular Stark spectroscopic measurements. The dissociation energy, De, is determined as 5.17 eV, and D0 as 5.10 eV. 相似文献
16.
D. Husain J. Lei F. Castao M. N. Snchez Rayo 《Journal of photochemistry and photobiology. A, Chemistry》1999,120(3):151-159
The collisional behaviour of Ba[6s5d(3DJ)], 1.151 eV above the 6s2(1S0) electronic ground state, in the presence of atomic strontium, has been investigated in the ‘long-time domain' (ca. 100 μs–1 ms) following the pulsed dye-laser excitation of barium vapour at elevated temperature at λ = 553.5 nm (Ba[6s6p(1P1)] ← Ba[6s2(1S0)]. Ba(3DJ) is subsequently produced from the short-lived 1P1 state (τe = 8.37 ± 0.38 ns) by a number of radiative and collisional processes. It may then be monitored in the ‘long-time domain' by atomic spectroscopic marker methods involving either collisional activation of Ba(3DJ) by Ba(1S0) and He buffer gas to yield Ba[6s6p(3PJ)] with subsequent emission from the 3P1 state (τe = 1.2 ± 0.1 μs): Ba[6s6p(3P1)] → Ba[6s2(1S0)] + hv (λ = 791.1 nm). Alternatively, emission from Ba(1P1) may be monitored at long times following the generation of this short-lived state by energy pooling following self-annihilation of Ba(3DJ) + Ba(3DJ) from Ba[6s6p(1P1)] → Ba[6s2(1S0)] + hv (λ = 553.5 nm). The generation of Ba(3DJ) in the presence of atomic strontium yields emission in the long-time domain from Sr[5s5p(3P1)] (τe = 19.6 μs): Sr[5s5p(3P1)] → Sr[5s2(1S0)] + hv (λ = 689.3 nm). Whilst the decay profiles at short times are complex in form, at long times all these atomic profiles show first-order kinetic removal with the decay coefficients for λ = 791.1 nm, 689.3 nm and 553.5 nm emissions in the ratio 1 : 2 : 2, consistent with overall third-order activation of the form: Ba(3DJ) + Ba(3DJ) + Sr(1S0) → Sr(3PJ) + 2Ba(1S0). The mechanism is modelled in detail, including measurement of integrated emission intensities, yielding kinetic data for fundamental collisional processes. The overall rate constant for the third-order collisional activation of Sr[5s5p(3PJ])from 2Ba[6s5d(3DJ)] + Sr[5s2(1S0)] takes the upper limit of 5.8 × 10−27 cm6 atom−2 s−1 (T = 900 K). The rate constant for the two body collisional quenching of Ba[6s5d(3DJ)] by ground state atomic strontium, Sr[5s2(1S0)], is found to be (2.0 ± 0.1) × 10−12 cm3 atom−1 s−1 (T = 900 K). 相似文献
17.
A “genome order index,” defined as S = a2 + c2 + t2 + g2, where a, c, t, and g are the nucleotide frequencies of A, C, T, and G, respectively, was used to suggest that there exist genome-specific constraints on nucleotide composition. We show that the “evidence” for constraint, S < 1/3, is in fact a mathematical property that is always true regardless of data. Moreover, we show that S is strictly equivalent to and derivable from the Shannon H-function and has no advantage over it. 相似文献
18.
S.C. Nunes V. de Zea Bermudez D. Ostrovskii L.D. Carlos 《Vibrational Spectroscopy》2006,40(2):278-288
The interactions occurring in di-urea (NHC(O)NH) cross-linked poly(oxyethylene) (POE)/siloxane hybrids (di-ureasils) doped with zinc triflate (Zn(CF3SO3)2) were investigated by Fourier Transform infrared (FT-IR) and Raman (FT-Raman) spectroscopies. Bonding of the Zn2+ ions to the urea carbonyl oxygen atoms occurs in the entire range of compositions studied (∞ > n ≥ 1, where n, salt content, is the molar ratio of oxyethylene moieties per Zn2+ ion). At n > 20 the incorporation of the guest cations progressively reduces the number of free CO groups. At n = 20 the saturation of the urea cross-links is attained and the Zn2+ ions start to coordinate to the POE chains giving rise to the formation of a crystalline POE/Zn(CF3SO3)2 complex. The latter process occurs at the expense of the destruction of the hydrogen-bonded POE/urea structures of the host di-ureasil structure. New hydrogen-bonded associations, more ordered than the urea–urea aggregates present in the non-doped matrix and including Zn2+OC coordination, emerge in parallel. “Free” and weakly coordinated CF3SO3− ions, present in all the xerogels studied, appear to be the main charge carriers of the conductivity maximum of this family of ormolytes located at n = 60 at 30 °C. In materials with n ≤ 20 contact ion pairs, “cross-link separated” ions pairs and higher ionic aggregates appear. The data reported demonstrate that the behaviour of the di-ureasils doped with triflate salts depends on the type of cation. 相似文献
19.
Nagata M Kondo M Suemori Y Ochiai T Dewa T Ohtsuka T Nango M 《Colloids and surfaces. B, Biointerfaces》2008,64(1):16-21
Dialkyl disulfide-linked naphthoquinone, (NQ-Cn-S)2, and anthraquinone, (AQ-Cn-S)2, derivatives with different spacer alkyl chains (Cn: n = 2, 6, 12) were synthesized and these quinone derivatives were self-assembled on a gold electrode. The formation of self-assembled monolayers (SAMs) of these derivatives on a gold electrode was confirmed by infrared reflection-absorption spectroscopy (IR-RAS). Electron transfer between the derivatives and the gold electrode was studied by cyclic voltammetry. On the cyclic voltammogram a reversible redox reaction between quinone (Q) and hydroquinone (QH2) was clearly observed under an aqueous condition. The formal potentials for NQ and AQ derivatives were −0.48 and −0.58 V, respectively, that did not depend on the spacer length. The oxidation and reduction peak currents were strongly dependent on the spacer alkyl chain length. The redox behavior of quinone derivatives depended on the pH condition of the buffer solution. The pH dependence was in agreement with a theoretical value of E1/2 (mV) = E′ − 59pH for 2H+/2e− process in the pH range 3–11. In the range higher than pH 11, the value was estimated with E1/2 (mV) = E′ − 30pH , which may correspond to H+/2e− process. The tunneling barrier coefficients (β) for NQ and AQ SAMs were determined to be 0.12 and 0.73 per methylene group (CH2), respectively. Comparison of the structures and the alkyl chain length of quinones derivatives on these electron transfers on the electrode is made. 相似文献
20.
Yuriy L. Zub Inna V. Melnyk Nataliya V. Stolyarchuk Halyna I. Dobryanska Mariusz Barczak Andrzej Dabrowski 《Progress in Solid State Chemistry》2005,33(2-4):179-186
The structure and texture characteristics of the hybrid organic–inorganic adsorbents, which were obtained by using of two-component systems of “structure-forming agent/trifunctional silane”, are compared as follows: the first component is Si(OC2H5)4 or (C2H5O)3Si–A–Si(OC2H5)3, where A = –(CH2)2– or –C6H4–; the second one is alkoxysilane with amine (–NH2, NH, –NH(CH2)2NH2) and thiol (–SH) groups. The adsorbents, derived from TEOS, have more accessible functional groups (2.6–4.2 mmol/g) than xerogels, which are based on bis(triethoxysilanes) (1.0–2.6 mmol/g). On another hand xerogels derived from bis(triethoxysilanes) have a more extended porous structure (Ssp =516–968 m2/g, Vs = 0.418–1.490 cm3/g, d = 2.5–15.0 nm) than those that are based on TEOS (Ssp = 4–631 m2/g, Vs = 0.005–1.382 cm3/g, d = 2.3–17.7 nm). The geometric dimensions of functional groups have a more essential effect on the parameters of porous structure in the case of TEOS-derived xerogels. Using solid-state NMR spectroscopy, it has been shown that in synthesis of xerogels with the use of TEOS, the molecular frame of globules is formed by structural units Qn (n = 2,3,4), and the functional groups exist as structural units of Tn (n = 2,3). The xerogels obtained with using bis(triethoxysilanes) consist only of structural units of Tn-type (n = 1,2,3). 相似文献