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.
The tripeptide derivative Z(L)Ala(L/D)Phe(L)ValOMe was obtained in 40% yield by reacting (CH3S)2CN(L)CH[CH(CH3)2]COOCH3 with the dipeptide derivative Z(L)Ala(L)PheOH and ZnCl2 at 110°C. The product obtained by bulk condensation contained 9 %, the product obtained utilizing ethylene carbonate as solvent contained 10 % of the diastereomer Z(L)la(D)Phe(L)ValOMe. Separation of diastereomers was achieved by HPLC on a silicagel column.  相似文献   

2.
The reactions of ethyldiphenylphosphine with a number of cis-dioxomolybdenum(VI) Schiff base coordination complexes are described. These molybdenum complexes incorporate tridentate Schiff base ligands obtained from the condensation of 5-X-salicylaldehyde (X = Cl, Br, H, CH3O) with o-aminobenzenethiol. Oxomolybdenum(IV) Schiff base complexes were observed as products of the reaction of these Mo(VI) complexes with PEtPh2. The kinetics for these reactions were followed spectrophotometrically and the applicable rate law is ? d[MoO2L]/dt = k1[MoO2L][PEtPh2]. The k1's were shown to vary systematically as the X-substituent on the ligand was changed. For MoO2(5-X-SSP), the specific rate constants at 30°C span the range from 19.6 × 10?4 M?1 sec?1 (X = Br) to 8.4 × 10?4 M?1 sec?1 (X = CH3O). It was also observed that a correlation exists between the cathodic reduction potentials (Epc) and the k1's within the series. The rate of reaction of MoO2(5-X-SSP) with PEtPh2 was altered and systematically controlled through ligand design.  相似文献   

3.
《Analytical letters》2012,45(3):613-623
Abstract

Lysine can be determined by adsorptive voltammetry after derivatization with acetaldehyde in 1.3 x 10?2mol/ L borax-NaOH buffer solution (containing 4 x 10?3mol/ L of CH3CHO at pH10). The Schiff's base product of the derivation can be adsorbed on a hanging mercury electrode and reduced with peak potential of about -1.33v (vs.SCE) after 120s pre-concentration time. The derivative peak height is linearly proportional to the concentration for lysine in the range 6.0 x 10?7-1.0 x 10?5mol/ L. The detection limit is 4.0 x 10?7mol/ L. Using this method, we have directly determined lysine in nutrition samples without any pre-separation step.  相似文献   

4.
Acidic aqueous solutions containing pyrrole and alkoxysulfonated PEDOT derivative (PEDOT‐S) were found to undergo polymerization in the absence of an external oxidizing agent. The product was a nearly black‐colored conducting hydrogel that after separation could be dispersed in water or acetone. The suspensions could be used to deposit cast films on a polycrystalline gold electrode. The polymer modified electrode showed a nearly Nernstian potentiometric response to Ag+ cations in the concentration range of 10?5–10?1 M with the slope of 54 mV/decade. The response was specific to Ag+ compared to a series of alkali and transition‐metal cations (pKAg/M>3.7).  相似文献   

5.
A selective and sensitive derivative method has been proposed for the simultaneous determination of trace amounts of Co(II) and Ni(II) with morpholinedithiocarbamate (MDTC) in the presence of sodium lauryl sulphate (SLS). The molar absorption coefficients of the 1:2 complex of Co(II) and Ni(II) at 326 nm and 322 nm are 2.248 × 104 and 2.505 × 104 L mol?1 cm?1 for zero order. The analytical sensitivity for the second derivative of Co(II) and Ni(II) complexes are 0.0044 μg mL?1 and 0.0060 μg mL?1. The developed derivative procedure, using the zero‐crossing technique, has been successfully applied for the analysis of Co(II) and Ni(II) simultaneously in different alloy samples.  相似文献   

6.
The behaviour of the vanadium(V) complex with 5-Br-PADAP at a mercury electrode was investigated in HOAcNaOAc. The adsorption phenomena were observed by linear-sweep voltammetry. The mechanism of the electrode reaction was found to be the irreversible reduction of the V(V) in the complex adsorbed on the surface of the electrode to the V(IV) complex with 5-Br-PADAP. In 0.02 mol l?1 HOAc-0.012 mol l?1 NaOAc (pH 4.5) and 1 × 10?6 mol l?1 5-Br-PADAP, the detection limits of linear-sweep adsorption voltammetry and 1.5th-order derivative adsorption voltammetry are 5 × 10?10 and 2.5 × 10?11 mol l?1 , respectively. The method was applied to samples of ore (Geological Deposit).  相似文献   

7.
Synthesis and photochemistry of acridin-9-ylmethoxycarbonyl(Amoc)as a new photochemically removableprotecting group for alcohols were described.Three carbonates of alcohols 1—3 were synthesized throughcondensation of 9-hydroxymethylacridine and chloroformates of alcohols,including benzyl alcohol,phenethylalcohol and one galactose derivative.The photolysis of protected alcohols can efficiently release the correspondingalcohol in the efficiencies(Q_(u1)ε)of 100—200(quantum yield Q_(u1)=0.011—0.023,and molar absorptivity ε=9.1×10~3—9.8×10~3 mol~(-1)·L·cm~(-1))under 360 nm light.  相似文献   

8.
A highly sensitive and selective catalytic adsorptive cathodic striping procedure for the determination of trace germanium is presented. The method is based on adsorptive accumulation of the Ge(IV)‐gallic acid (GA) complex onto a hanging mercury drop electrode, followed by reduction of the adsorbed species. The reduction current is enhanced catalytically by addition of vanadium(IV)‐EDTA. The optimal experimental conditions include the use of 0.03 mol/L HClO4 (pH1.6), 6.0×10?3 mol/L GA, 3.0×10?3 mol/L V(IV), 4.0×10?3 mol/L EDTA, an accumulation potential of ?0.10 V(vs. Ag/AgCl), an accumulation time of 120 s and a differential pulse potential scan mode. The peak current is proportional to the concentration of Ge(IV) over the range of 3.0×10?11 to 1.0×10?8 mol/L and the detection limit is 2×10?11 mol/L for a 120 s adsorption time. The relative standard deviation at 5.0×10?10 mol/L level is 3.1%. No serious interferences were found. The method was applied to the determination of germanium in ore, mineral water and vegetable samples with satisfactory results.  相似文献   

9.
A novel analytical approach for quantitative measurement of butylated hydroxyanisole (BHA) is dis‐ cussed in this paper. Such a method depends on the inhibitory effect of BHA on a Briggs‐Rauscher (B‐R) oscillating reaction. Unlike the classical B‐R system which involves Mn2+ as the catalyst, such a B‐R sys‐ tem is catalyzed by a macrocyclic nickel (II) complex [NiL](ClO4)2, where L in the complex is an unsatu‐ rated ligand 5,7,7,12,14,14‐hexemethyl‐1,4,8,11‐tetraazacyclotetradeca‐4,11‐diene. By perturbation of BHA on the system, the oscillation was inhibited in the presence trace amounts of BHA and the inhibition time was found to be proportional to the concentration of BHA over the range 1.00×10?7–1.20×10?4 mol/L. Two calibration curves were obtained: the first linear regression is over the range of 1.00×10?7–2.00×10?6 mol/L, and the second linear regression is over the range between 2.00×10?6 and 1.20×10?4 mol/L, with a lowest limit of detection of 4.00×10?8 mol/L. UV spectra measurements were employed to clarify the possible perturbation mechanism caused by BHA on the B‐R oscillating reaction.  相似文献   

10.
A new thiacalix[4]arene derivative in a 1,3-alternate conformation bearing four naphthalene groups through crown-3 chains has been synthesized, which exhibits high selectivity toward Hg2+ by forming a 1:2 complex, among other metal ions ( Na+, K+, Mg2+, Ba2+, Ca2+, Sr2+, Cs+, Mn2+, Fe2+, Cd2+, Co2+, Ni2+, Cu2+, Li+, and Zn2+) with a low detection limit (3.30×10?7 M). The metal ion-binding properties were studied by fluorescence, AFM, and 1H NMR spectroscopy. The in situ prepared [Hg2++L] complex shows well recognition ability for cysteine with a low detection limit (2.23×10?7 M) through fluorescence turning on. The mechanism of fluorescence turning on is the host L releasing from [L+Hg2+] for [Cys+Hg2+] complex formed. Thus the paper reports secondary-sensor design: Hg2+ as a first sensor for [L+Hg2+] form, cysteine as a second sensor for Hg2+ releasing from the [L+Hg2+] complex after cysteine adding in.  相似文献   

11.
《Electroanalysis》2004,16(16):1336-1342
The construction, performance characteristics, and application of polymeric membrane (PME) and coated graphite (CGE) thiocyanate‐selective electrodes are reported. The electrodes were prepared by incorporating the complex [Cu(L)](NO3)2 (L=4,7‐bis(3‐aminopropyl)‐1‐thia‐4,7‐diazacyclononane) into a plasiticized poly(vinyl chloride) membrane. The influence of membrane composition, pH of test solution, and foreign ions were investigated. The electrodes reveal Nernstian behavior over a wide SCN? ion concentration range (1.0×10?6–1.0×10?1 M for PME and 5.0×10?7–1.0×10?2 M for CGE) and show fast dynamic response times of 15 s and lower. The proposed sensors show high selectivity towards thiocyanate over several common organic and inorganic anions. They were successfully applied to the direct determination of thiocyanate in urine and saliva of smokers and nonsmokers, and as an indicator electrode in titration of Ag+ ions with thiocyanate.  相似文献   

12.
The synthesis and electropolymerization of a pyrrolic concanavalin A derivative (pyrrole‐Con A) onto a multiwalled carbon nanotube (MWCNT) deposit is reported. Glucose oxidase was then immobilized onto the MWCNT‐poly(pyrrole‐Con A) coating by affinity carbohydrate interactions with the polymerized Con A protein. The resulting enzyme electrode was applied to the amperometric detection of glucose exhibiting a high sensitivity of 36 mA cm?2 mol?1 L and a maximum current density of 350 μA cm?2.  相似文献   

13.
The new analogues of nifedipine, in which 2-nitrophenyl group at position 4 is replaced by phenylisoxazolyl substituent, were synthesized. The symmetrical dialkyl 1,4-dihydro-2,6-dimethyl-4-(5-phenylisoxazol-3-yl)pyridine-3,5-dicarboxylates were prepared by classical Hantzsch condensation, and the asymmetrical analogues were synthesized using a procedure reported by Dagnino that involved the condensation of alkyl acetoacetate with alkyl 3-aminocrotonate and 5-phenylisoxazole-3-carboxaldehyde. The structure of all compounds was confirmed by IR, 1H NMR and Mass spectra. In vitro calcium channel antagonist activities were evaluated as calcium channel antagonists using the high K+ concentration of guinea-pig ileum longitudinal smooth muscle (GPILSM) assay. These compounds exhibited moderate calcium antagonist activity (IC50 = 10?7 to 10? 5 M range) relative to the reference drug nifedipine (IC50 = 1.10 ± 0.40 × 10?8 M).  相似文献   

14.
Emission quenching of [Ru(bpy)2(4, 4'-dcbpy)] (PF6)2 (1) by benzenamine,4-[2-[5-[4-[4-dimethylamino]phenyl]-4,5-di-hydro-1-phenyl-1H-pyrazol-3-yl]-ethenyl]-N,N-dimetyl (2) or 1, 5-diphenyl-3-(2-phenothiazine)-2-pyrazoline (3) was observed. Measurements of the emission decay of 1 before and after addition of 2 or 3 by single photon counting technique con-finned the observations. The emission quenching of 1 by 2 or 3 was submitted to Stern-Volmer equation. It was calculated that the quenching rate constants (kq) are 5.5 × 109(mol/L)-1s-1 for 2 and 4.0 × 109(mol/L)-1s-1 for 3, respectively. These results indicated a character of dynamic quenching process. The singlet-state of 2 or 3 was also quenched by 1. The quenching behaviors did not conform to the Stern- Volmer equation and involved both static and dynamic quenching processes. The apparent quenching rate constant (kapp) was calculated to be 3 × 109 (mol/L)-1 for the interaction of excited 2 with 1, and 1.2 × 109 (mol/L)-1 for that of excited 3 wit  相似文献   

15.
Based on their high performance in gas and liquid-phase separations, 1,2-bis(triethoxysilyl)ethane (BTESE)-derived organosilica membranes have attracted much attention. To improve performance, we focused on the acid molar ratio (AR) in sol preparation and its effect on the pore formation mechanism during sol-gel processing. BTESE-derived sols with AR?=?10?4–100 were prepared, and the effect of the AR on the gel structure was evaluated in detail via FT-IR, nuclear magnetic resonance (NMR), N2 adsorption, and positron annihilation lifetime (PAL) measurements. The chemical structure of the gels was confirmed by FT-IR and NMR and showed that sols with the largest number of silanol groups (AR?=?10?2) experienced a significant increase in condensation during the firing process. The porous structures of fired gels characterized by N2 adsorption and PAL measurement showed that the AR?=?10?2 fired gel consisted of a larger number of small pores that had formed during the firing process. Single-gas permeation experiments showed high H2 permeance (5–9?×?10?7?mol/(m2?Pa?s)) and H2/CF4 selectivity (700–20,000). The gas permselectivity (He/H2, H2/N2, and H2/CF4) was highest for the intermediate AR (=10?2), which corresponded to the greatest amount of silanol groups in unfired gels and confirmed that small pores had formed from the condensation of silanol groups during firing.  相似文献   

16.
Abstract

The emission produced by sulfite after oxidation by potassium permanganate in acidic solution in the presence of Ru(phen)3 2+ is used to determine 1.0 × 10?7 to 2.5 × 10?5 mol/L sulfite. The limit of detection is 4.5 × 10?9 mol/L and the relative standard deviation is 3.1% for a 1 × 10?5 mol/L sulfite solution (n=8). The method was also applied satisfactorily to the determination of sulfur dioxide in air by using triethanolamine (TEA) as absorbent material.  相似文献   

17.
《Electroanalysis》2003,15(10):898-902
A method based on capillary electrophoresis (CE) with electrochemical detection (ED) was developed for the determination of taurine in Lycium Barbarum L., LIPOVIYAN beverage and milk powder. The effects of some important factors such as the acidity of the running buffer, separation voltage, injection time, and applied potential to working electrode were investigated. Operated in a wall‐jet configuration, a 300 μm diameter carbon‐disk electrode was used as the working electrode, which exhibits good responses at +1.05 V (vs. SCE) for taurine. Excellent linearity was obtained in the concentration range from 5.0×10?4 mol/L to 5.0×10?6 mol/L. The detection limit (S/N=3) was 1.0×10?7 mol/L. This proposed method has been successfully applied to analyze the actual samples with satisfactory assay results.  相似文献   

18.
A second‐derivative spectrophotometric method based on zero‐crossing over technique is developed in simultaneous determination of copper(II) and nickel(II) ions. Methylthymol blue (MTB) as a chromogenic reagent and cetyltrimethylammonium bromide as a surfactant were used, and measurements were carried out in buffered solution at pH 6 and at a temperature of 25 °C. The amplitude of derivative spectra was measured at wavelengths of 631.9 and 587.7 nm for the simultaneous determination of Ni2+ and Cu2+, respectively. Linearity was obtained in the range of 0.5–5.0 μg mL?1 for both ions in the presence of 0.0–5.0 μg mL?1 of the other ion as an interfering ion. IUPAC detection limits for Cu2+ and Ni2+ ions were obtained at 0.48 and 0.43 μg mL?1, respectively. The proposed procedure has been applied successfully for the simultaneous determination of copper and nickel in synthetic binary mixtures and real samples.  相似文献   

19.
New Mn(III)‐L and Mn(IV)‐L complexes were prepared from the highly lipophilic salophen ligand (L): phenol 2,2′‐[(4,5‐dimethyl‐1,2‐phenylene)bis[(E)‐nitrilomethylidyne]]bis[4,6‐bis(1,1‐dimethylethyl). The prepared complexes were fully characterized and used for the construction of thiocyanate membrane electrodes. Optimized membrane electrodes contained 33.0 mg PVC, 66.0 mg o‐nitrophenyloctylether, 50 or 5 (mole %) tetrakis(trifluoromethyl)phenyl borate and 1 mg Mn(III)‐L (sensor 2) or Mn‐(IV)‐L (sensor 12), respectively. Such electrodes exhibited linear responses toward thiocynate in a concentration range of 10?1–10?5 M and detection limits of 8.3×10?6, 8.9×10?6 M for sensor 2 and 12, respectively. Optimized membrane electrodes exhbited high selectivty toward thiocayante compared to more lipophilic anions. The observed thiocyanate selectivity of the optimized membranes was confirmed by formation constant calculations for Mn(III)‐L and Mn(IV)‐L with SCN?, β=1014.1 and 1012.5, which was measured potentiometrically using the sandwich membrane method. Furthermore, computational study using DFT calculations was performed to at DFT/B3LYP level of theory to confirm the observed selectivity data. The response times were 3 and 0.5 min for low and high concentrations. The lifetimes of the optimized electrodes were ~4–6 weeks. The analytical utility of the optimized membrane electrodes was demonstrated by the analysis of thiocyanate level in different saliva samples.  相似文献   

20.
A sensitive fluorimetric method for the determination of 1-(3-chlorophenyl)-4-methyl-7,8-dimethoxy-5H-2,3-benzodiazepine (5 × 10?8?6 × 10?4) g ml?1) is described. The method is based on acid hydrolysis and aldol condensation in alkaline solution to give a compound which shows intense fluorescence at 440 nm.  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