Conductometric Titration of Chlorhexidine and Proguanil

Abstract

Conductometric titrations of chlorhexidine and proguanil are reported. The procedure is based on the copper-bi-guanide reaction which gives a pink solid. Studies at several pH values, and presence of NH₃ and ethanol are carried out. 3 ml of 0.2 M NH3, 9ml of 0.01 M NaOH diluted to 60 mL with 15% ethanol are added to 5ml of biguenide aqueous solution and titrated awith cooper acetate. Concentrations of Chlorhexidine in 5.9x10^?5 - 3.4x10^?4 M range are determined. Fareignspecies presence is studied too.

Biguanides are found in several pharmaceutical formulations and industrial samples.

Estimetion of chlorhexidine and proguanil salts with the standard method lacks selectivity since it is based on perchloric acid titration in acetic acid medium¹. Some recent papers about determination of chlorhexidine and proguanil have been publisghed: potentiometric titration of chlorhexidine² polarographic determinetion of praguanil and chlorhexidine^3,4 spectrophotometric assay of chlorhexidine in contact lens solutions⁵ and suppositories⁶, HPLC of proguanil in serum sam-ples⁷ and chlorhexidine in several samples ^8,9,10,10,11 or G C ^12,13 and mass fragmentography^14,15.     

Spectrophotometric Determination of Trace Amounts of Ascorbic Acid

Abstract

Colourless silver-gelatin complex is quantitatively reduced by ascorbic acid to yellow silver sol in water within the pH range 7.5–10.0 at room temperature. The determination of 1–10μg/ml of ascorbic acid is possible at 415 nm in the presence of glycine, alanine, fructose, sucrose, citric, tartaric, oxalic, malic, succinic acids and also in the presence of various reducing agents. The molar absorptivity of ascorbic acid at the δ_max is found to be 21500 lit mol^?1 cm^?1 and the Sandell sensitivity of the sol is 8.18x10^?3 μg ascorbic acid cm^?2 for 0.001 absorbance. The relative standard deviation is ±0.22% and the confidence limit (20 determinations, 95%) being 8.806±0.0093%.     

Kinetic Studies of the Fe(III)/DI-2-Pyridyl Ketone Benzoylhydrazone Complex Reduction By Sulfite

The reactions of HSO^? ₃ with Fe(III) in the presence of di-2-pyridyl ketone benzoylhydrazone (DPKBH) have been investigated at 4.2-7.2 pH. The decomposition reaction of Fe(III)/DPKBH has been studied as a function of total sulfite concentration using spectrophotometric techniques. The kinetics are controlled by the equilibrium [Fe^III(DPKBH)(H₂O)]²⁺ ? [Fe^III(DPKBH)(OH)]⁺+H⁺, for which the hydrolysis constant was potentiometrically determined as 4.3 x 10^-5M, at (25.0 ± 0.1)°C and 1.5 x 10^-3M ionic strength. Both of those species undergo sulfite substitution and the significantly more labile species is the aqua complex. The formation constants of [Fe^III(DPKBH)(SO₃)] are 1.2 x 10⁴ at pH 4.2 and 1.9 x 10²M^-1 at pH 6.2. The limiting rate constants, k, at high HSO^? ₃ concentrations are 3.5 x 10^-2s^-1 and 1.4 x 10^-2s^-1, respectively, at pH 4.2 and 6.2, I = 1.3 x 10^-2M. The results are discussed with reference to the available literature data.     

Determination of Nitrite in Aqueous Solutions using the Linear Sweep Voltammetry Technique

ABSTRACT

An electrochemical method using linear sweep voltammetry techniques was developed to determine nitrite ion in aqueous solution in the presence of nitrate. Nitrite solutions exhibited a well-defined oxidation wave at +1.0V vs SCE at vitreous carbon, while no oxidation process was observed for nitrate solutions. The pH of the nitrite solutions varied from 2.37 to 5.60 and no change was observed in the Ep values, except for the pH 5.60 solution, where little change was verified. The potential also did not vary with change in the nitrite concentration in the 5.0 x 10^?5 to 7.0 x 10^?4 mol L^?1 range. Very good straight lines for plots of current versus nitrite concentration in the 7.0 x 10^?5 to 7.0 x 10^?4 mol L^?1 range were obtained; the correlation coefficient was never worse than 0.990. The nitrite determination was also performed in the presence of 1.0 x 10^?3 mol L^?1 of NO₃ ^? ions. The addition of NO₃ ^? did not change significantly the current values even when it was added in one hundred times molar excess.     

Novel Mixed-Valence μ-Oxo-Bridged Trinuclear Manganese Complexes [Mn3O(O2CR)6L3] (R=4-Cl-C6H4OCH2, 3-Cl-C6H5, BrCH2, L=3-Methylpyridine or Water): Structures and Magnetic Properties

Preparation of three new mixed-valence oxo-centered trinuclear manganese complexes [Mn₃O(O₂CR)₆L₃] (R=4-Cl-C₆H₄OCH₂, 1, 3-Cl-C₆H₅, 2, BrCH₂, 3; L=3-methylpyridine or water), by reaction of N-n-Bu₄MnO₄ with appropriate reagents in ethanol and 3-methelpyridine is reported. The crystal structure of 1 has shown to have an oxo-centered Mn₃O unit with peripheral ligands provided by bridging carboxylate and terminal 3-methylpyridine groups, and with an approximate 3-fold symmetry axis for the whole cluster. Variable temperature magnetic susceptibilities of the complexes in the range 1.5-300 K have been measured and are interpreted in terms of the Kambe vector-coupling method and Van Vleck equation; J (cm^?1), J' (cm^?1), g, and R parameters obtained are -8.2, -10.9, 2.04, 2.15 x 10^?3 (1); -7.3, -11.1, 2.20, 3.32 x 10^?3 (2); -2.1, -4.1, 1.97, 2.34 x 10^?3 (3). There is weak antiferromagnetic exchange between manganese ions. Effects of bridging and terminal ligands on the J, J' values and spin ground state are discussed.     

Parameters Affecting the Peroxyoxalate Chemiluminescence

ABSTRACT

A careful study of the parameters affecting the chemiluminescent reaction of TCPO (bis(2,4,6-trichlorophenyl)oxalate) and 2-NPO (bis(2-nitrophenyl)oxalate) with hydrogen peroxide, in the presence of imidazole (used as buffer and catalyst) and the fluorophore 3-AFA (3-aminofluoranthene), was carried out in acetonitrile/water medium. The data are reported in terms of the time (t_Imax) required for the relative maximum chemiluminescence intensity (I_max) and the area (A) under the curve of intensity νs. time. At controlled acidity and high unprotonated imidazole concentration ([IMI] = 1x10^?2 mol.L^?1), the I_max and t_Imax values do not depend on the acetonitrile/water ratio. The CL intensity is maximum at around pH 6.0 (higher buffer capacity). For 1x10^?2 < [IMI] < 1x10^?4 mol.L^?1, the area is largest when [IMI] = 1x10^?3 mol.L^?1 and linearly dependent on the hydrogen peroxide concentration (10^?5 ? 10^?3 mol.L^?1). The area is also enhanced by increasing the fluorophore concentration. The acidity controls the unprotonated imidazole and H⁺ concentration. Several errors can arise from quantitative analyses carried out without control of the HIMI⁺ and IMI concentrations.     

Determination of Lysine in Nutrition Sample by Adsorption Voltammetry

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.     

Use of A Novel Acetone-H2O2−C10− Chemiluminescence System for the Determination of Iodide Ion

Abstract

The present paper reports a new chemiluminescence system, i.e, acetone-H₂O₂?C10^?, which can be catalyzed by iodide ion (I^?). Based on this catalysis, a new chemiluminescence method for the determination of trace iodide ion is proposed. the optimum conditions are reported in this note. the detection limit is 2 × 10^?11 g/ml I^?, the linear dynamic range is 4 × 10^?10 g/ml to 3 × 10^?7 g/ml I^?, and the variation coefficient at an iodide concentration of 5 × 10^?9 g/ml I^? (n=10) is 4.6%. the method has been satisfactorily applied to the determination of trace iodide ion in water.     

Electrocatalytical Oxidation and Determination of Dopamine at Redox Polymer/Nafion Modified Electrodes

ABSTRACT

The modified glassy carbon electrodes prepared by simultaneously covering with [Os(bpy)₂(PVP)₁₀Cl]⁺ redox polymer and Nafion film exhibited excellent electrocatalytic activity for the oxidation of dopamine (DA). Dual linear regions between 1.0x10^?8-1.8x10^?5 M and 1.8x10^?5-4.0x10^?4 M with correlation coefficients of 0.998 and 0.995, respectively, were obtained for log-log plots of catalytic current versus DA concentration. The detection limit for DA determination was ca. 5 nM with 3σ. The dual-film modified electrodes eliminated efficiently the interference from AA presence in a 1000-fold concentration ratio and showed excellent reproducibility for the determination of DA. The modified electrodes have been used to determine DA concentration with both cyclic voltammetric and chronoamperometric techniques. Electrocatalytic kinetics have been studied using a rotating disk electrode. Both the addition of Nafion film and an increase in DA concentration resulted in a decrease in the electrocatalytic rate constant. An apparent Michaelis-Menten constant of 1.3 mM and maximum catalytic current of 88μA were evaluated from the chronoamperometric measurements.     

Polymeric membrane sodium-selective electrodes based on calix[4]arene ionophores

Six kinds of tetra alkylester type calix[4]arene derivatives, (R₁=R₂=CH₃1, C₂H₅2, C₃H₇3,n-C₄H₉4,t-C₄H₉5,n-C₁₀H₂₁6), a diethyl-didecyl mixed ester type (R₁=C₂H₅, R₂ =C₁₀H₂₁7), and three kinds of lower rim bridged types (R₁=C₂H₅, R₂–R₂=(CH₂)₁₀8, (CH₂)₁₂9, (CH₂)₂(OCH₂CH₂)₃10) were characterized by electrochemical measurement to elucidate the effect of the length of the alkyl group of alkoxycarbonyl substituents on Na⁺ selectivity. To obtain excellent Na⁺ selective ionophores, introduction of short chain alkyl groups rather than long chain ones, such as a decyl group, and maintenance of sufficient solubility of the calix[4]arene derivatives in the membrane solvent are required concurrently. Among the calix[4]arenes tested, 25,26,27,28-tetrakis[(ethoxycarbonyl)methoxy]-p-tert-butylcalix[4]arene2, and the diethyl-didecyl mixed ester type derivative7 are the best ionophores for a Na⁺ selective electrode. On the other hand, sodium selectivity of the bridged type derivative9 is comparable or even superior to that of the known bis(12-crown-4).This paper is dedicated to the commemorative issue on the 50th anniversary of calixarenes.     

Rate of hydrolysis of Na4P2O7 and Na5P3O10 at 100°C and the effect of urea

³¹P NMR analysis has been used to measure the rates of hydrolysis of Na₄P₂O₇ and Na₅P₃O₁₀ at 100°; the rate constants are 6.07 x 10^?3 and 2.24 x 10^?1 hr^?1 respectively. The presence of urea has a catalytic effect on the former but an inhibiting effect on the latter. These observations are explained by the hydrogen-bonding capabilities of urea.     

REACTION DES ENOLATES MASQUES DE SILICIUM ISSUS WESTERS DE TRIMETHYLSILYLE AVEC LES DERIVES CARBONYLES α,β-INSATURES

Abstract

Bis(trimethylsilyl) ketene acetals RCH[dbnd]C[OSi(CH₃)₃]₂ 1 add to PhCH[dbnd]CH[sbnd]COR¹ 2 in the presence of catalytic amounts (10%) of TiCl₄ leading, in good to excellent yields to the corresponding β-hydroxy or δ-ketoacids. Under kinetic control, the regioselectivity of the reaction markedly depends on the nature of R and R¹. Mixtures of 1,2 and 1,4 products are formed in some of the cases; in others, solely Michael or aldol adducts are obtained. On the contrary, the stereoselectivity, which ranges from zero to moderate, is slightly influenced by R and R¹.

It is also shown that trimethylsilyl ester of α-trimethylacetic acid (CH₃)₃SiCH₂CO₂Si(CH₃)₃ 5 add to 2 in the presence of TBAF (10%) in THF.     

Determination of Pyridostigmine in Human Plasma by High-Performance Liquid Chromatography

Abstract

An easy to perform, specific, reproducible and sensitive high performance liquid chromatographic (HPLC) method to measure pyridostigmine concentration in human plasma was developed and validated. Sample clean-up consists of ion-pair extraction into dichloromethane in the presence of neostigmine as internal standard, followed by back extraction into an aqueous phase. Mean recovery of 110% (with a standard deviation of 10%) was determined for concentrations of 5 – 100 ng/ml. Chromatography on a 125·4 mm CN-propyl column using a mobile phase composed of 10% acetonitrile in 3.5×10^?4M NaH₂PO₄ and UV detection at 270 nm, yields clean chromatograms without any interferences from endogenous plasma components. Using 1 ml plasma samples the method has a limit of detection (LD) of 3 ng/ml, with %CV (precision) and bias (accuracy) ≥ 10% for concentrations in the range of 0–100 ng/ml. The method is being used in human pharmacokinetic studies of oral dosage forms of pyridostigmine.     

Interaction of Triosmium Complexes with Hydrogen Chloride: A Model for Fine-Tuning Regioselective Protonation in Metal Clusters

The reaction of Os₃(CO)₁₀(CNR)(NCMe) (1) with HCl was studied and this system was found to be a good model for observing the fine-tuning of site-selective protonation in metal complexes. Three products including the protonated species [(-H)Os₃(CO)₁₀(CNR)(NCMe)]⁺Cl^– (2), the bridging aminocarbyne complex (µ-Cl)Os₃(CO)₁₀(µ₂-C = NHR) (3), and the hydrido derivative (-H)Os₃Cl(CO)₁₀(CNR) (4) were obtained for the reaction. The site of protonation, either on the Os center or on the nitrogen atom of coordinated isocyanide, was tuned in a sensitive manner by the nature of the coordinated isocyanides, the polarity of the solvents, and the strengths of the acids, leading to different product distributions. The more electron withdrawing isocyanides (CNCH₂Ph, CNPh) favor the formation of the aminocarbyne complex 3. In a nonpolar solvent like cyclohexane the reaction afforded 3 as the main product. Furthermore, complex 2 was converted to (-H)Os₃(CO)₁₀(₂-CONHR) (5) upon hydrolysis, in which the coordinated isocyanide was transformed to a carboxamido group. This was verified by obtaining the deuterated species (-H)Os₃(CO)₁₀(₂-CONDPr) when [(-H)Os₃(CO)₁₀(CNPr)(NCMe)]⁺Cl^– (2a) was treated with D₂O in THF. The molecular structures of (µ₂-Cl)Os₃(CO)₁₀(µ₂-C = NHCH₂Ph) (3b) and (-H)Os₃Cl(CO)₁₀(CNPr) (4a) were determined by X-ray diffraction analyses. Complex 3b contains both bridging chloride and bridging aminocarbyne groups, whereas 4a contains a terminal chloride, a terminal isocyanide and a bridging hydride.     

Spectral properties and structures of supramolecular complexes of naphthylpyridine with β-cyclodextrin

The electronic absorption and fluorescence spectra of 4-(2-naphthyl)pyridine (1) and N-methyl-4-(2-naphthyl)pyridinium perchlorate (2 ⁺·ClO₄ ^–) were studied in aqueous solutions in the absence and presence of -cyclodextrin (-CD). In aqueous solutions and organic solvents in the presence of water or H⁺ ions, compound 1 exhibits intense fluorescence with a maximum at 21 270 cm^–1, and its quantum yield in an aqueous solution is 0.9±0.09. The same fluorescence spectrum was detected for an aqueous solution of 2 ⁺·ClO₄ ^–. In an aqueous solution, compound 1 and -CD form stable fluorescing supramolecular 2:2 complexes, whose structure was calculated by the quantum-chemical MNDO/PM3 method. The formation of these complexes induces a hypsochromic shift of the fluorescence maximum of 1 by 5000 cm^–1. The stability constant of the complex is 2·10³ L mol^–1. A decrease in the pH results in the formation of a protonated form of 1(1·H⁺) and destruction of the complex, thus favoring the escape of the substrate from the -CD cavity. The quantum-chemical calculations showed that the insertion of 1 into the -CD cavity is thermodynamically more favorable than hydration; on the contrary, the formation of 1·H⁺ increases dramatically the hydration energy, which promotes the escape of 1·H⁺ from the -CD cavity; cation 2 ⁺ does not form a complex with -CD; in the thermodynamically most favorable 2:2 complex, the naphthalene fragments of two molecules 1 are parallel to each other in a broad section of the -CD dimer constructed according to the head-to-head type.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2420–2425, November, 2004.     

Gas Permeability of Poly (organophosphazenes)

Abstract

The gas permeability and an oxygen to nitrogen selectivity was determined with some poly (organophosphazenes). It is found from the data that the membrance having the highest gas permeability was [NP(NHPrⁿ) (NHEt)]_n, and had 1.5x10^?6 cm^3. cm/cm³ sec.cmHg to oxgen or 2.2x10^?6cm³.cm/cm³.sec.cm.Hg to nitrogen. On the other hand, the membrance having the highest oxgen to nitrogen selectivity of about 3, had the formular of [NP(OC₆H₄Cl-p)₂]_n. Also, the selectivity does not depend on the glass transition temperature of the membrances. The membrance prepared from [NP(OC₆H₄CH₃-p)₂]_n has a negative activation energy to oxgen and nitrogen permeability.     

Europium(III)-Sensitized Chemiluminescence Determination of Ibuprofen in Pharmaceutical Preparations and Biological Fluids

Abstract

Chemiluminescence reaction of the system containing europium(III) ion, KMnO₄, Na₂SO₃, and ibuprofen was investigated for the determination of ibuprofen. The introduction of Eu(III) ion into the system of KMnO₄-Na₂SO₃-ibuprofen caused a significant increase in the chemiluminescence signal. The increment of the chemiluminescence signal is proportional to ibuprofen concentration in the range of 5.0 × 10^?8–5.0 × 10^?6 g/ml with a detection limit of 1 × 10^?8 g/ml. The relative standard deviation for 1.0 × 10^?7 g/ml ibuprofen solution was 1.7% (n = 11). The proposed method was successfully applied to determine ibuprofen in tablets and human plasma.     

Arene complexes of zirconium containing triangular cluster cations [(η6-C6H6Me3)3Zr3(μ-Cl)6]n+,n = 2,3

Ionic -mesitylene zirconium complexes (1–4) have been obtained by a reaction between ZrCl₄ and a metal reducer (Al, Zn or Mg) in the presence of AlCl₃ in mesitylene. An X-ray study has shown that in the triangular cluster cations [(-C₆H₃Me₃Zr₃(-Cl₆)]ⁿ⁺ an increase in the charge from 2+ (1,2) to 3+ (3,4) is accompanied by shortening of the Zr-Zr distances from 3.32–3.33 A to 3.27–3.28 Å. AlCl₄ ^– (1), Al₂Cl₇ ^– (1–3), and Mg[(-Cl)₂AlCl₂]₃ ^– (4), the latter found here for the first time, are present in the complexes studied as counterions.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 134–142, January, 1994.     

Copper(I) π-Complexes with Alkyne Ligands: Synthesis and Crystal Structure of M[CuCl2(HOCH2C≡CCH2OH)] (M = K+, NH+ 4)

Crystals of anionic complexes of the composition M[CuCl₂(HOCH₂CCCH₂OH)], where M = NH₄ ⁺ (I), K⁺ (II), were isolated from concentrated aqueous solutions of CuCl and MCl (M = NH₄ ⁺, K⁺) in the presence of 2-butyne-1,4-diol. Their structures were studied by X-ray diffraction analysis. Isostructural crystals I and II are orthorhombic; Z = 8, space group Ibam; a = 6.735(1) and 6.666(2) Å, b = 17.206(3) and 16.874(6) Å, c = 15.172(3) and 15.032(4) Å, V = 1758(1) and 1691(1) ų, respectively. The compounds are built of individual [CuCl₂(HOCH₂CCCH₂OH)] anions; the NH₄ ⁺ (I) or K⁺ (II) cations are arranged in the voids between the anions. The -coordinated Cu(I) atoms have trigonal-planar environment of two chlorine atoms and CC bond of the 2-butyne-1,4-diol molecule. The Cu–(CC) distances in the -core are 1.892(4) and 1.887(6) Å, CC are 1.233(5) and 1.228(5) Å in I and II, respectively. In complex I, additional hydrogen bonds Cl···H–NH₃ (Cl···H 2.43(4) Å) and O···H–NH₃ (O···H 1.97(3) Å) stabilize the structure.     

Determination of Formaldehyde in Waste Water by Lucigenin Chemilummescence

Abstract

A chemiluminescence analysis has been developed for the determination of formaldehyde based on its inhibition of the chemiluminescence reaction of lucigenin-C10^?-H₂o₂. The method is sensitive, convenient and selective with a detection limit of 0.05ng/ml. The linear dynamic range is 1.0ng/ml to 0.1 μg/ml. The variation coefficient of ten determinations for 2.Ong/ml formaldehyde is 1.2%. Applications to the trace determination of formaldehyde in industrial waste waters are discussed.