A Dual-Enzyme Electrode for the Determination of Flavin Adenine Dinucleotide in the Presence of Riboflavin and Flavin Mononucleotide

Abstract

An electrode method has been developed for the determination of flavin adenine dinucleotide (FAD) using a potentiometric gas sensor and commercially available enzyme preparations. The construction of the FAD-sensitive electrode is based on immobilizing alkaline phosphatase (E.C. 3.1.3.1) and adenosine deaminase (E.C. 3.5.4.4) on the sensing tip of an ammonia gas sensor. Alkaline phosphatase enzymatically catalyzes the hydrolysis of FAD to adenosine which is subsequently converted to ammonia by adenosine deaminase. The response of the dual-enzyme electrode is linear between 8 × 10^?5 M and 4 × 10^?3 M FAD with a slope of 43 mV/decade concentration at pH 8.5 and 37[ddot]C. The optimum buffer system is 0.5 M diethanolamine, 1 × 10^?3 M Tris-HCl and 1 × 10^?3 M MgCl₂. Electrodes constructed with enzymes immobilized by cross-linking with glutaraldehyde and bovine serum albumin showed longer life times than electrodes using enzymes entrapped by a dialysis membrane. The electrode is highly selective over riboflavin and flavin mononucleotide, but it does respond to other nucleotides.     

1,4,7,10-Tetraoxacyclododecane(12-Crown-4) as Neutral Carrier for Lithium Ion in Lithium Ion Selective Electrode

Abstract

1,4,7,10-Tetraoxacyclododecane (12-crown-4) (I) and its lithium complex (II) are used as neutral carriers for lithium ion in polyvinylchloride membrane ion selective electrodes. The lithium response varies with concentration, being near Mernstian at low (10^?5-10^?4 M) concentrations and sub-Nernstian (24-28 aV) at higher concentrations (10^?3 M). The selectivity coefficients K_Li ^Pot _M for II are: Na⁺ (0.12), K⁺ (0.66), Cs⁺ (0.15), Mg²⁺ (1.6 × 10^?4), Ca²⁺ (3.1 × 10^?4), Ba²⁺ (9.5 × 10^?7), NH⁺ ₄ (9.0 × 10^?2), H⁺ (2.2).     

Use of the Rotated Ring Disc Electrode for the Analytical Determination of Dithiaalcanediols in Aquo-Alcoholic Media and Its Rate of Oxidation with Bromine

Abstract

We used bromine generated and detected on the ring-dise electrode for the titration of aquo-alcoholic solution of dithiaalcanediol. The analysis of the ring current vs disc current curve provided a means of determination of the rate constant k of the second order homogeneous and fast reaction of bromine with each of the two sulfide groups of dithiaalcanediol. A value of (3+1)× 10^?6M^?1 _s ^?1 was found for k at 25°C.     

An Organic Cation-Selective Electrode: Potentiometric Determination of Acetylcholine Activity

Abstract

The performance characteristics of the first ion-selective electrode specifically designed for the quantitation of an organic cation are described. The liquid membrane electrode exhibits rapid and near Nernstian response to acetylcholine ion activity from 10^?1 to 10^?5 M. High selectivity over Na⁺, K⁺ and NH₄ ⁺ is observed.     

Highly Selective Potassium Ion Responsive Liquid-Membrane Electrode

Abstract

The performance of a new liquid-membrane electrode using valinomycin as membrane component is described with respect to selectivity, working range, speed of response and accuracy. The electrode makes possible the measurement of potassium ion activities in the range of 10^?1 M to at least 10^?6 M in unbuffered systems with a selectivity of potassium over sodium ions of more than 4,000. The electrode was used for the direct titration of potassium ions.     

The Separation and Determination of Molybdenum by Electron Paramagnetic Resonance

Abstract

A procedure is described for the separation and quantitative determination of molybdenum by means of EPR. Molybdenum(VI) was precipitated from a hydrochloric acid solution (1.5 Molar) with α-benzoinoxime. The precipitate was separated by centrifugation and then the sample was dried in an oven at 105°C. Nitrogen was passed over the sample to complete the drying procedure. The precipitate was dissolved in acetonitrile which was 0.5 M in lithium perchlorate. Electrochemical reduction of the sample produced the molybdenum(V) species. The concentration of molybdenum(V) was determined directly from the intensity of the first derivative EPR signal. The range of linearity of the analytical curve was 1.00 × 10^?2 M to 1.00 × 10^?4 M, and a routine accuracy of less than 6% was obtained.     

Aqueous Polymerization of Methyl Methacrylate Initiated by the Potassium Bromate-Thiomalic Acid Redox System

The redox system composed of potassium bromate and thiomalic acid was used to initiate the aqueous polymerization of methyl methacrylate under nitrogen atmosphere at 35 ± 0.2°C. The initial rates of polymerization have been found to be approximately proportional to the first power of the initiator concentration in the range of 2.5 to 6.0 ± 10^?3 M and to the first power (1.15) of monomer concentration in the range of 3.72 to 11.16 ± 10^?2 M The overall rate was independent of activator concentration, approaching a maximum at 10 × 10^?3 M. The overall energy of activation was found to be 8.80 kcal/mol. The initial rate and the maximum conversion attained a maximum value at 35°C in the temperature range of 20 to 45°C.     

An Ion-Selective Electrode for Dibasic Phosphate Ion

Abstract

A phosphate-selective electrode is developed based on a silver coordination reaction. The electrode responds linearly toward HPO₄ ⁼ in the concentration range of 10^?4 to 10^?1 M (slope = 27 mV/dec.). The electrode also shows good selectivity over sulfate, nitrate, perchlorate and acetate.     

Use of Catecholoxygenase for Determination of Catechol

Abstract

A cell extract from Trichosporon cutaneum containing catechol 1,2-oxygenase catalyzes the oxidation of catechol to cis,cis-muconic acid. The absorbance of the cis,cis-muconic acid at 260 nm can be correlated with the initial catechol concentration in the range 5 × 10^?6 M to 5 × 10^?5 M in aqueous solutions. This enzymatic assay has been applied to the determination of catechol in aqueous samples derived from coal processing.     

Human Isoionic Hemoglobin: Preparation and Kinetic Properties

Abstract

Much of the data on hemoglobin-gas interactions which have accumulated in the literature is difficult to interpret because the hemoglobin preparations contained extraneous ligands and salts. In order to obtain hemoglobin which is completely free of 2, 3-DPG and other ionic substances, we have developed a method for isolating isoionic hemoglobin. These data serve as a baseline against which other data obtained with added ligands and salts can be compared.

Specifically, isoionic hemoglobin had these properties: Second-order rate constant for combination with 0₂: 2.2 × 10⁷ M^?1S^?1; p₅₀ at 20^[ddot] was 0.87mm Hg at heme concentration of 10^?4 M.     

Photoinduced Graft Copolymerization. V. Graft Copolymerization of Methyl Methacrylate onto Cellulose in the Presence of N-Bromosuccinimide as Initiator

Abstract

The photoinduced graft copolymerization of methyl methacrylate onto cellulose was studied using N-bromosuccinimide as the photoinitiator. The formation of graft copolymer increases with an increasing amount of cellulose. The graft copolymerization increases with increasing initiator concentration up to 1,25 × 10^?2 M and thereafter it decreases. The percentage of graft increases with increasing monomer concentration up to 46.9 × 10^?2 M and thereafter it decreases. The percentage graft-on increases with increasing temperature. The overall activation energy was computed to be 8.40 kcal/mol. The percentage graft was investigated using different water-miscible organic solvents. The graft copolymerization was also investigated using differently modified cellulose. A possible mechanism for the photo-graft copolymerization onto cellulose is suggested.     

Perchlorate Ion-Selective Electrodes with the Liquid Membranes of the O-Phenanthroline Chelate or its Related Compounds

Abstract

The metal chelates of o-phenanthroline, a, a′-dipyridyl or bathophenanthroline were used as the ion exchanger in the liquid membrane of the perchlorate ion-selective electrode. The electrode with a nitrobenzene membrane containing tris(bathophenanthroline)ferrous perchlorate is the highest sensitive one and gives a linear Nernstian response up to about 1 × 10 ^?5 M perchlorate. The membrane electrode having the ferrous ion-chelate of o-phenanthroline as an ion exchanger shows an excellent selectivity for perchlorate ion over nitrate or iodide Ion. The effects of the chelate concentration in the membrane and the central metal species of the chelate are examined on the electrode performance.     

Polymerization of Styrene Initiated by 1,4-Dimethyl-1,4-bis(p-anisyl)-2-tetrazene

Abstract

The polymerization of styrene (St) initiated by 1,4-dimethyl-1,4-bis(p-anisyl)-2-tetrazene (1a) was studied kinetically in benzene. The polymerization proceeds through a radical mechanism. The rate of polymerization is proportional to [1a]^0.5 and [St]^1.0. The overall activation energy for the polymerization is found to be 81.2 kJ/mol within the temperature range of 65 to 80°C. The activation parameters for the decomposition of 1a at 70°C are k_d = 1.88 × 10^?5s^?1, δH? = 133.1 kJ/mol, and δS? = 29.9 J/mol·deg.     

Novel Flow Injection/Potentiometric Measurement of Slightly Soluble Salts in Small Volumes: Determination of Solubility Product Constants of Some Silver Salts

Abstract

The flow injection technique is shown to provide fast, reliable and sensitive determination of solubility product constants of silver acetate, silver sulfate, silver oxide, silver bromate and silver chloride in microliter volume samples. Potentiometric detection using electrodes of the first kind and second kind was used for measuring silver ions and chloride ions, respectively. The solubilities were determined from measurement of the silver ion concentration in the saturated solutions. In the case of silver chloride, the solubility product constant was calculated from the concentrations corresponding to the intersection of the silver ion calibration curve and the chloride ion calibration curve, i.e., where the potentials of the two electrodes are equal. Tenth-molar sodium nitrate was used for all solutions to maintain constant ionic strength. At a concentration range of 1.00 × 10^?2 ? 1.00 × 10^?5 M silver, and 1.00 × 10^?2 ? 1.00 × 10^?4 M chloride, a Nernstian response of 60 m V per decade was obtained. At a sampling rate of 50–70 samples per hour, with 50 μl sample injections, high reproducibility of measurements was achieved, with a -pL 2% relative standard deviation in measured concentrations. The scope and applications of this system are discussed.     

Indirect Complexometric Determination of Aluminium using a Solid-Membrane Cupric Ion-Selective Electrode

Abstract

Indirect complexometric determination of 0.4–4 mg of A1 in 0.2 M solutions of NaNO₃, NH₄NO₃ and 0.01 M Mg(NO₃)₂ or 0,01 M Ca(NO₃)₂ was studied. The solid membrane cupric-ion selective electrode was used for end-point detection in back‐titration of DCTA (added in excess) with a cupric standard solution.     

Sodium Ion Selective Electrodes Based on Lipophilic 16-Crown-5 Derivatives

Abstract

Six kinds of lipopholic 16-crown-5 derivatives possessing double side-chains were synthesized. The Na⁺-selectivities were examined with poly(vinyl chloride) (PVC) matrix-membrane electrodes using these crown compounds. It is an effective way for obtaining high Na⁺-selectivity by introducing a bulky side-chain such as a benzyloxymethyl group into the 16-crown-5. The electrodes based on 16-crown-5 derivatives having both a methyl or ethyl group and a benzyloxymethyl group at the pivot carbon (C-15) (3 or 4, see Figure 1) exhibited excellent Na⁺-selectivity over K⁺ (log k _Na.x = -2.65 and -2.75 for 3 and 4, respectively).     

Poly(Vinyl Chloride) Containing Dibenzo-18-crown-6 as an Ion-Selective Membrane for Hyamine 1622

Abstract

A poly(vinyl chloride) membrane ion-selective electrode for the Hyamine 1622 cation is proposed. The active substance of the electrode was the neutral carrier dibenzo-18-crown-6 and di-iso-octylphthalate was used as plasticizer. The electrode had a Nernstian behaviour between 6.0 × 10^?6 and 1.6 × 10^?3 mol/dm³, a pH working range of 2 – 12 and high selectivity towards inorganic cations. Among the organic cations tested, only those having surfactant properties did interface. The electrode was suitable for determining the critical micelle concentration and as end-point detector in the potentiometric titration of the cationic surfactants.     

Asymmetric Synthesis of Phosphinous Tungsten Complexes

Abstract

The asymmetric synthesis of phosphinous compounds from diheterophosphacycloal kane-1,3,2 was investigated in a transition metal complex series. Complexes 1 and 2 were prepared from diaminophosphine, (?)-ephedrine and W (CO)₅ THP (1: δ³¹ P=+147,6 ppm; J_PW=313 Hz M^.+=595;2 δ³ p=+156 ppm J_PW=304 Hz M^.+=533; 90%dp) in two steps. Methyl lithium reacted with 1 to give stereospecific 3 (83%Yield) by P-O linkage (3 δ³¹ P=+64 ppm; J_PW =261 Hz; M^.+ ? 28=583). The aminophosphine complex 3 was stereochemically stable and was used for studies of synthetic applications. HCL gas reacted with 3 in CH₂Cl₂ to give the non optically active chlorophosphine complex 4 (δ³¹ P=+103,6 ppm; J_PW=290 Hz; M^.+ =482). This compound immediately gave salt 6 (δ³¹ P=+66,7 ppm; J_PW =240 Hz) by reaction with (?)-menthol and triethylamine. The acid methanolysis of 3 gave a mixture of 5 and 6 and the unchanged (?)-ephedrine salt [5:30% yield; δ³¹ P=+114 ppm; J_pw=280 Hz; [α]_D=+1,2° (CH₂Cl₂); M^.+=478; 6 : 60% yield; δ³¹p=+102,9 ppm; J_PW=264 Hz; [α]_D =+16,9° (CH₂Cl₂); M^.+=464]. Compound 6 was thus obtained with a 80% yield and a specific rotation of + 20,2° (CH₂Cl₂) in isopropanol/H₂SO₄ 5M medium. The enantiomeric excess of 6 was determined by RMN³¹P. Acid hydrolysis of 3 or the reaction with CH₃SO₃H, gave phosphinous acid complex 6 with an optical rotation of + 4,8° or ?1,8° respectively. These results provide precious informations about the stereochemistry and reactivity of the P-N linkage in this aminophosphine transition metal series, which differs notably from that of the corresponding (PO) N bond.     

Stereoselective Synthesis of 3-C-Branched-Chain Sugars by Aldol Reaction of Furanos-3-Uloses with Acetone

Abstract

Aldol reaction of 1,2-O-isopropylidene-5-O-tertbutyl-dimethylsilyl-α-D-erythro-pentofuranos-3-ulose (1) with acetone in the presence of aqueous K₂CO₃ afforded 3-C-acetonyl-1,2-O-isopropylidene-5-O-tertbutyl-dimethylsilyl-α-D-ribofuranose(2). Similar reaction of 1,2:5, 6-di-o-isopropylidene- α-D-ribo-hexofuranos-3-ulose (3) afforded 3-C-acetonyl-1,2:5, 6-di-o-isopropylidene- α-D-allofuranose (4) and (1R, 3R, 7R, 8S, 10R)-perhydro-8-hydroxy-5,5,10-trimethyl-2,4,6,11,14-pentaoxatetracyclo[8,3,1,0^1,8,0^3,7] tetradecane. The stereochemistry of the new chiral centers were determined by ¹H NOE experiments.     

High Performance Liquid Chromato-Graphic Assay For 5-Fluorouracil and 5-Fluorocytosine

Abstract

A high performance liquid chromatographic assay for separating 5-fluorouracil and 5-fluorocytosine in the presence of potential decomposition products urea, barbituric acid, uracil 6-hydroxycytosine, and cytosine was developed.

It was found that ion-pair chromatography using a reversephase C18 column, 0.46 cm i.d. by 15 cm in length, employing gradient elution was satisfactory for separating the various compounds, however, isocratic elution was more appropriate for determining the concentration of the two drugs in the presence of their actual decomposition products.

The mobile phase for isocratic elution was 85% aqueous phosphate buffer pH 2.1 and 15% methanol containing 0.0025 M pentane and heptane sulfonic acid sodium salts delivered at 1.0 mllmin. The eluent was monitored at 254 and 285 nm as all compounds do not absorb strongly at a single wavelength. A linear relationship was obtained for the peak height ratio for both 5-fluorouracil and 5-fluorocytosine against 5-methylcytosine, the internal standard over the range 0.125 to 1.000 × ? 10^?4 M ₀