Voltammetric detection of sulfonamides at a poly(3-methylthiophene) electrode

Detection of sulfonamide compounds in a mixture of standards at a poly(3-methylthiophene) coated on glassy carbon (GC) electrode is reported. The polymer, poly(3-methylthiophene), was electrochemically synthesized at a GC rotating disk-working electrode versus Ag/AgCl using cyclic voltammetry (+0.5 to +2.0 V). Square wave voltammetry (SQWV) with cathodic reduction (0 to -4.0 V) was used for the detection of seven sulfonamide compounds in a mixture. The working concentration ranges (curvilinear) established for different compounds in Britton-Robinson (BR) buffer (pH 6.26), were: 5.0x10(-6)-3.2x10(-3) M sulfamerazine, 5.0x10(-6)-3.2x10(-3) M sulfadiazine, 7.5x10(-7)-3.2x10(-4) M sulfasalazine, 9.0x10(-7)-5.0x10(-4) M sulfamethazine, 6.5x10(-8)-3.5.0x10(-5) M sulfamethoxazole, 9.7x10(-8)-5.0x10(-5) M sulfathiazole, and 9.0x10(-8)-3.2x10(-5) M 5-sulfaminouracil. Detection limits were calculated as: 3.9x10(-6) M for sulfamerazine; 4.0x10(-6) M sulfadiazine; 2.5x10(-7) M sulfasalazine; 3.7x10(-7) M sulfamethazine; 4.0x10(-8) M sulfamethoxazole; 6.4x10(-8) M sulfathiazole and 6.0x10(-9) M 5-sulfaminouracil. The data suggests a potential application of the poly(3-methylthiophene) (P3MT) electrode for determination of sulfonamides in veterinary and other applications.     

Simultaneous determination of phenylglycidol enantiomers and cinnamyl alcohol in asymmetric epoxidation processes by chiral liquid chromatography

A high-performance liquid chromatographic method has been developed for the simultaneous determination of phenylglycidol enantiomers and cinnamyl alcohol (CA). Separations were achieved on an amylose tris(3, 5-dymethylphenylcarbamate) chiral stationary phase (Chiralpak AD). The effect of concentration of organic modifier (2-propanol and ethanol) in the mobile phase and flow-rate was studied. The mobile phase selected consisted of a mixture of n-hexane-ethanol (85:15, v/v) with a flow-rate of 1.2 ml/min. The UV-vis detector was set at 254 nm. Resolution for the phenylglycidol enantiomers in the suitable chromatographic conditions was 2.4 with an analysis time of 12 min. The method developed was validated and was found to be linear in the range from 5 x 10(-4) to 3 x 10(-2) M, for phenylglycidol enantiomers and in the range from 5 x 10(-5) to 1 x 10(-3) M, for CA (r > 0.999 for the three compounds). Repeatability and intermediate precision for the three analytes at three different concentrations were below 3.6 and 2.8% R.S.D., respectively. This method has been applied to study the asymmetric epoxidation of CA with titanium(IV) alkoxide compounds as catalysts in order to evaluate their catalytic activity and stereoselectivity of the epoxidation processes.     

New renin inhibitors containing pseudodipeptidic units in P3-P2 and P1-P1' positions

A series of four non-peptidic renin inhibitors have been designed and synthesized. All of them contain in their molecule (3S,4S)-4-amino-5-cyclohexyl-3-hydroxypentanoic acid (ACHPA), a hydrophobic portion at the C-terminus and a second dipeptide-like transition state analog or unnatural dipeptidic fragment at the N-terminus. Inhibitory activity of the compounds was measured in vitro by high performance liquid chromatography (HPLC). Their IC50 (M/l) values were: <10(-3) (12), 1.0 x 10(-6) (19), 4.0 x 10(-4) (23) and 1.0 x 10(-6) (29), respectively. All the compounds are stable against chymotrypsin.     

Unusual syntheses, structures, and electronic properties of compounds containing ternary, T3-type supertetrahedral M/Sn/S anions [M5Sn(mu3-S)4(SnS4)4](10- (M = Zn, Co)

A recently discovered series of quaternary compounds of the general type [K(m)(ROH)(n)()][M(x)Sn(y)()Se(z)] (R = H, Me), containing ternary anions with [SnSe(4)](4-)-coordinated transition metal centers (M = Co, Mn, Zn, Cd, Hg) has now been extended by the synthesis and characterization of the two ortho-thiostannate-coordinated species, [Na(10)(H(2)O)(32)][M(5)Sn(mu(3)-S)(4)(SnS(4))(4)].2H(2)O (M = Zn (1), Co (2)). The central structural motifs of compounds 1 and 2 are highly charged [M(5)Sn(mu(3)-S)(4)(SnS(4))(4)](10-) anions, being the first T3-type supertetrahedral ternary anions reported to date. The exposure of single crystals of 2 to a dynamic vacuum for several hours resulted in the reversible formation of a partially dehydrated, but still monocrystalline material of the composition [Na(10)(H(2)O)(6)][Co(5)Sn(mu(3)-S)(4)(SnS(4))(4)] (3). The loss of 28 of the 34 water molecules only slightly affects the internal structure of the ternary anion in 3 and leads to a significant compacting of the crystal structure with closer linkage of the [Co(5)Sn(5)S(20)](10-) cluster units via the Na(+) cations. Magnetic measurements on 3 show that the ground state of the Co/Sn/S cluster is S = 1/2, indicating a significant antiferromagnetic coupling between the Co centers, which has also been rationalized by DFT investigations of the electronic situation in the ternary subunits of 1-3.     

High-performance liquid chromatographic method for the assay of dexamethasone and xylometazoline in nasal drops containing methyl p-hydroxybenzoate

A rapid and sensitive high-performance liquid chromatographic method has been developed for the determination of dexamethasone sodium phosphate (DSP), xylometazoline hydrochloride (XMC) and methyl p-hydroxybenzoate (MHB). An assay of the compounds has been performed on a HPLC system GBC 1210, at controlled room temperature, on a Nucleosil C8 column (250x3 mm, 5 microm). The mobile phase was acetonitrile-water (35:65, v/v), at a flow-rate of 1 ml min(-1). The parameters for validation such as linearity (r>0.9996), precision (RSD: 0.51-(1.93%), limit of detection and quantification (2.032 x 10(-4) and 4.063 x 10(-4) mg ml(-1) for DSP, 9.7 x 10(-5) and 1.953 x 10(-4) mg ml(-1) for XMC, 1.953 x 10(-4) and 3.096 x 10(-4) mg ml(-1) for MHB) have also been reported. The method was applied to the determination of DSP, XMC and MHB in nasal drops. The statistical parameters were found to be satisfactory, with recovery values ranging from 98.69 to 101.60% (RSD: 0.32-1.03%). The method is simple and accurate and therefore suitable for the simultaneous determination of these compounds in dosage form.     

A family of Group 4 metal alkoxo complexes with an M3(mu3-O) core relevant to Ziegler-Natta catalyst intermediates

Reactions of [Mg(thffo)(2)] (1) or [Ca(thffo)(2)] (2) with ZrCl(4) or HfCl(4) in a CH(2)Cl(2)/THF/CH(3)CN mixture give thermally stable neutral heterobimetallic tetranuclear complexes [M(3)M'(mu(x)-O)(mu,eta(2)-thffo)(6)(Cl)(6)] (thffo=tetrahydrofurfuroxide; M/M'/x: 3, Zr/Mg/3; 4, Hf/Mg/3; 5, Zr/Ca/4; 6, Hf/Ca/4) as colorless crystals in 75-82 % yield. X-ray diffraction studies show complexes 3-5 to contain oxo-bridged M(3) triangles that are capped by an alkaline earth metal-containing moiety to form species of C(3) symmetry. Reactions of ZrCl(4) and HfCl(4) with pure tetrahydrofurfuryl alcohol in EtOH and MeOH provide ionic complexes [M(3)(mu(3)-O)(mu,eta(2)-thffo)(3)(L)(3)(Cl)(6)]Cl (M/L: 8, Zr/EtOH; 9, Hf/EtOH; 10, Zr/MeOH) in 66-79 % yield. Complexes 8-10 consist of M(3) triangles that are analogous to those in 3-6 and possess similar overall symmetry, as shown by X-ray crystallography. Changes in the reaction conditions afforded the asymmetric neutral dimer [Zr(2)(mu-thffo)(2)(thffoH)(Cl)(6)] (7) and the homometallic [Zr(3)(mu(3)-O)(mu,eta(2)-thp)(3)(thf)(2)(Cl)(7)] (11).     

Extraction of manganese(II) with dithizone and potassium thiocyanate on foam sorbents for spectrophotometric determination in silicates

A method for selective extraction of Mn(II) with dithizone and potassium thiocyanate has been described. The method involves formation of a Mn(II)-thiocyanate-dithizone complex in a hexamine medium containing potassium thiocyanate (2.8M), dithizone (5.5-6.5 x 10(-5)M) and hydroxylamine hydrochloride (0.25%) at pH approximately 6 followed by extraction of the complex on polyurethane foam using batch squeezing mode within 1 hr. The sorbed Mn-thiocyanate-dithizone complex is eluted with acetone and made alkaline with 0.5 ml of a stabilizer solution (19 ml 2M NH(3) solution + 1 ml 5% hydroxylamine hydrochloride). The absorbance of the solution is measured at 506 nm. The adverse effect due to Pb may be obviated by separating the Pb as the sulphate during decomposition of sample and that due to iron may be removed before extraction of Mn by any suitable method. The other interfering elements (Cd, Zn, Ni, Co, Cu, etc.) are masked with KCN (6 x 10(-3)M optimum) solution. The method obeys Beer's Law from 0.1 to 2.0 mug Mn/ml. The method has been applied to various silicates, carbonates and glasses.     

Determination of trace amounts of thorium by electroanalytical techniques

Trace amounts of thorium have been determined in the presence of uranyl nitrate and ammonium diuranate (as interferents) by cyclic voltammetry, differential-pulse polarography, differential-pulse voltammetry, square-wave voltammetry and anodic-stripping voltammetry. The determination is based on the substitution of thorium for copper, lead and cadmium in their EDTA complexes and voltammetric measurement of the displaced metal ion. The detection limits ranged between 2 x 10(-7) and 1 x 10(-6)M (r.s.d. 2-7%) for solutions free from the uranium compounds, and between 8 x 10(-7) and 5 x 10(-6)M (r.s.d. 3-5%) in the presence of the uranium compounds at concentrations up to about 1000 times that of thorium. The detection limits depend on both the particular technique and the EDTA complex employed. Anodic-stripping voltammetry gave detection limits of 8 x 10(-8) and 10(-7)M in the absence and presence of uranium respectively.     

Lanthanide coordination with alpha-amino acids under near physiological pH conditions: polymetallic complexes containing the cubane-like [Ln4(mu3-OH)4]8+ cluster core

Tetranuclear lanthanide-hydroxo complexes of the general formula [Ln(4)(mu(3)-OH)(4)(AA)(x)(H(2)O)(y)](8+) (1, Ln = Sm, AA = Gly, x = 5, y = 11; 2, Ln = Nd, AA = Ala, x = 6, y = 10; 3, Ln = Er, AA = Val, x = 5, y = 10) have been prepared by alpha-amino acid controlled hydrolysis of lanthanide ions under near physiological pH conditions (pH 6-7). The core component of these compounds is a cationic cluster [Ln(4)(mu(3)-OH)(4)](8+) whose constituent lanthanide ions and triply bridging hydroxo groups occupy the alternate vertexes of a distorted cube. The amino acid ligands coordinate the lanthanide ions via bridging carboxylate groups. Utilizing L-glutamic acid as the supporting ligand, a cationic cluster complex (4) formulated as [Er(4)(mu(3)-OH)(4)(Glu)(3)(H(2)O)(8)](5+) has been obtained. Its extended solid-state structure is composed of the cubane-like [Er(4)(mu(3)-OH)(4)](8+) cluster building units interlinked by the carboxylate groups of the glutamate ligands. All compounds are characterized by using a combination of spectroscopic techniques and microanalysis (CHN and metal). Infrared spectra of the complexes suggest the coordinated amino acids to be zwitterionic. The presence of mass (MALDI-TOF) envelopes corresponding to the [Ln(4)(mu(3)-OH)(4)](8+) (Ln = trivalent Sm, Nd, or Er) core containing fragments manifests the integrity of the cubane-like cluster unit. Magnetic studies using Evans' method suggest that exchange interactions between the lanthanide ions are insignificant at ambient temperature. The structural identities of all four compounds have been established crystallographically. The tetranuclear cluster core has been demonstrated to be a common structural motif in these complexes. A mechanism responsible for its self-assembly is postulated.     

Synthesis, structure, and magnetic properties of (6-9)-nuclear Ni(II) trimethylacetates and their heterospin complexes with nitroxides

New polynuclear nickel trimethylacetates [Ni6(OH)4(C5H9O2)8(C5H10O2)4] (6), [Ni7(OH)7(C5H9O2)7(C5H10O2)6(H2O)] x 0.5 C6H14 x 0.5 H2O (7), [Ni8(OH)4(H2O)2(C5H9O2)12] (8), and [Ni9(OH)6(C5H9O2)12(C5H10O2)4] x C5H10O2 x 3 H2O (9), where C5H9O2 is trimethylacetate and C5H10O2 is trimethylacetic acid, have been found. Their structures were determined by X-ray crystallography. Because of their high solubility in low-polarity organic solvents, compounds 6-9 reacted with stable organic radicals to form the first heterospin compounds based on polynuclear Ni(II) trimethylacetate and nitronyl nitroxides containing pyrazole (L(1)-L(3)), methyl (L(4)), or imidazole (L(5)) substituent groups, respectively, in side chain [Ni7(OH)5(C5H9O2)9(C5H10O2)2(L(1))2(H2O)] x 0.5 C6H14 x H2O (6+1a), [Ni7(OH)5(C5H9O2)9(C5H10O2)2(L2)2(H2O)] x H2O (6+1b), [Ni7(OH)5(C5H9O2)9(C5H10O2)2(L(3))2(H2O)] x H2O (6+1c), [Ni6(OH)3(C5H9O2)9(C5H10O2)4(L(4))] x 1.5 C6H14 (6'), and [Ni4OH)3(C5H9O2)5(C5H10O2)4(L(5))] x 1.5 C7H8 (4). Their structures were also determined by X-ray crystallography. Although Ni(II) trimethylacetates may have varying nuclearity and can change their nuclearity during recrystallization or interactions with nitroxides, this family of compounds is easy to study because of its topological relationship. For any of these complexes, the polynuclear framework may be derived from the [Ni6] polynuclear fragment {Ni6(mu4-OH)2(mu3-OH)2(mu2-C5H9O2-O,O')6(mu2-C5H9O2-O,O)(mu4-C5H9O2-O,O,O',O')(C5H10O2)4}, which is shaped like an open book. On the basis of this fragment, the structure of 7-nuclear compounds (7 and 6+1a-c) is conveniently represented as the result of symmetric addition of other mononuclear fragments to the four Ni(II) ions lying at the vertexes of the [Ni6] open book. The 9-nuclear complex is formed by the addition of trinuclear fragments to two Ni(II) ions lying on one of the lateral edges of the [Ni6] open book. This wing of the 9-nuclear complex preserves its structure in another type of 6-nuclear complex (6') with the boat configuration. If, however, two edge-sharing Ni(II) ions are removed from [Ni6] (one of these lies at a vertex of the open book and the other, on the book-cover line), we obtain a 4-nuclear fragment recorded in the molecular structure of 4. Twinning of this 4-nuclear fragment forms highly symmetric molecule 8, which is a new chemical version of cubane.     

Rhodium/iridium-titanium azaheterometallocubanes

Treatment of [[Ti(eta5-C5Me5)(mu-NH)]3(mu3-N)] (1) with the diolefin complexes [[MCl(cod)]2] (M = Rh, Ir; cod = 1,5-cyclooctadiene) in toluene afforded the ionic complexes [M-(cod)(mu3-NH)3Ti3(eta5-C5Me5)3(mu3-N)]Cl [M = Rh (2), Ir (3)]. Reaction of complexes 2 and 3 with [Ag(BPh4)] in dichloromethane leads to anion metathesis and formation of the analogous ionic derivatives [M(cod)(mu3-NH)3Ti3-(eta5-C5Me5)3(mu3-N)][BPh4] [M = Rh (4), Ir (5)]. An X-ray crystal structure determination for 5 reveals a cube-type core [IrTi3N4] for the cationic fragment, in which 1 coordinates in a tripodal fashion to the iridium atom. Reaction of the diolefin complexes [[MCl(cod))2] (M = Rh, Ir) and [[RhCl(C2H4)2]2] with the lithium derivative [[Li(mu3-NH)2(mu3-N)-Ti3(eta5-C5Me5)3(mu3-N)]2] x C7H8 (6 C7H8) in toluene gave the neutral cube-type complexes [M(cod)(mu-NH)2(mu3-N)Ti3-(eta5-C5Me5)3(mu3-N)] [M = Rh (7), Ir (8)] and [Rh(C2H4)2(mu3-NH)2(mu3-N)Ti3(eta5-C5Me5)3(mu3-N)] (9), respectively. Density functional theory calculations have been carried out on the ionic and neutral azaheterometallocubane complexes to understand their electronic structures.     

Complexes of aminosquarate ligands with first-row transition metals and lanthanides: new insights into their hydrolysis

Attempts at synthesizing first-row transition-metal complexes of the 3-hydroxy-4-[(1'S,2'R)-(2-hydroxy-1',2'-diphenylethyl)amino]-3-cyclobutene-1,2-dione ligand in alcoholic solutions resulted in the formation of the monomers [M(NH(2)C(4)O(3))(2)(H(2)O)(4)] [M = Mn (1), Co (2), Ni (3), Cu (4), Zn (5)] instead, as a result of the hydrolysis of the ligand. 1, 2, and 3 are isomorphous (C2/c), with the metal atoms octahedrally coordinated to four aqua and two cis aminosquarate ligands. The copper and zinc complexes (4 and 5) have the same molecular formula as 1-3 but belong to the C2/m and P2(1)/c space groups respectively. 4 has square-pyramidal geometry with trans-oriented aminosquarate ligands in the basal plane; aqua ligands complete the coordination sphere. 5 has octahedral geometry, with four aqua and two trans-oriented aminosquarate ligands. Reaction of aqueous solutions of the anilinosquarate ligand with Ln(NO(3))(3) x xH(2)O produced the eight-coordinate complexes {Sm(mu-C(6)H(5)NHC(4)O(3))(3)(H(2)O)(4) x 3H(2)O}n (6), {[M(mu(2)-C(4)O(4))(H(2)O)(6)][C(6)H(5)NHC(4)O(3)] x 4H(2)O}n [M = Er (7), Yb (8)], {Sm(C(6)H(5)NHC(4)O(3)) (mu(3)-C(4)O(4))(H(2)O)(4) x H(2)O}(n) (9), and {[{(C(6)H(5)NHC(4)O(3))(2)(H(2)O)(5)Yb}(2)(mu-C(4)O(4))] x 4H(2)O}n (10). 7 and 8 are isomorphous with the previously reported analogues Eu, Gd, and Tb ionic polymers. The presence of the squarate ligand in 7-10 is indicative of some form of hydrolysis of the anilinosquarate ligand during their syntheses. However, hydrolysis was not evident in the synthesis of 6. The mechanism for the hydrolysis in the syntheses of 1-5 is apparently different from that for 7-10.     

Phenolic constituents of licorice. III. Structures of glicoricone and licofuranone, and inhibitory effects of licorice constituents on monoamine oxidase

Two new phenolic compounds, glicoricone (3) and licofuranone (4), were isolated from a species of licorice brought from the northwestern region of China, and their structures were assigned. Among the twelve licorice constituents examined for the inhibition of monoamine oxidase (MAO), six compounds, 3, 4, genistein (6), licopyranocoumarin (7), licocoumarone (14) and glycyrrhisoflavone (15), inhibited the enzyme with the IC50 (concentration required for 50% inhibition of the enzyme activity) values of 6.0 x 10(-5)-1.4 x 10(-4) M. Glycyrrhizin (1) also inhibited MAO with the IC50 value of 1.6 x 10(-4) M.     

Ortho-chalcogenostannates as ligands: syntheses, crystal structures, electronic properties, and magnetism of novel compounds containing ternary anionic substructures [M4(mu4-Se)(SnSe4)4]10- (M=Mn, Zn, Cd, Hg), 3(infinity)[[Hg4(mu4-Se)(SnSe4)3]6-], or 1(infinity)[[HgSnSe4]2-

By reaction of K4[SnSe4].1.5 MeOH with CdCl2 or Hg(OAc)2 in water/methanol it was possible to prepare single crystals of four novel compounds that contain ternary anionic coordination oligomers and polymers: [K10(H2O)16(MeOH)(0.5)][M4(mu4-Se)(SnSe4)4] (4: M=Cd, 5: M=Hg), [K6(H2O)3][Hg4(mu4-Se)(SnSe4)3].MeOH (6), and K2[HgSnSe4] (7), which were structurally characterized by single-crystal X-ray diffraction. The optical absorption properties of the isostructural compounds 4 and 5, as well as those of the recently reported Zn (2) and Mn (3) analogues, were studied by UV-visible spectroscopy. These investigations showed the quaternary phases to have relatively small optical gaps for their molecular size (2.2-2.6 eV), which are similar to the excitation energies that were observed for mesostructured solids of the respective combination of elements. According to DFT investigations on the ternary anions, an experimentally observed difference between the absorption behavior of the d10 compounds 2, 4, and 5 and the open-shell d(5) compound 3 is in line with different characters of the frontier orbitals in the two cases. Both the calculations and a magnetic measurement on 3 demonstrated antiferromagnetic coupling between the mu(4)-Se-bridged Mn centers.     

Catalysis of the beta-elimination of HF from isomeric 2-fluoroethylpyridines and 1-methyl-2-fluoroethylpyridinium salts. Proton-activating factors and methyl-activating factors as a mechanistic test to distinguish between concerted E2 and E1cb irreversible mechanisms

Second-order rate constants, k(OH)(N), M(-)(1) s(-)(1), for the beta-elimination reactions of HF with 2-(2-fluoroethyl)pyridine (2), 3-(2-fluoroethyl)pyridine (3), and 4-(2-fluoroethyl)pyridine (4) in OH(-)/H(2)O, at 50 degrees C and mu = 1 M KCl, are = 0.646 x 10(-)(4) M(-)(1) s(-)(1), = 2.97 x 10(-)(6) M(-)(1) s(-)(1), and = 5.28 x 10(-)(4) M(-)(1) s(-)(1), respectively. When compared with the second-order rate constants for the same processes with the nitrogen-methylated substrates 1-methyl-2-(2-fluoroethyl)pyridinium iodide (5), 1-methyl-3-(2-fluoroethyl)pyridinium iodide (6), and 1-methyl-4-(2-fluoroethyl)pyridinium iodide (7), the methyl-activating factor (MethylAF) can be calculated from the ratio k(OH)(NCH)3/, and a value of 8.7 x 10(5) is obtained with substrates 5/2, a value of 1.6 x 10(3) with 6/3, and a value of 2.1 x 10(4) with 7/4. The high values of MethylAF are in agreement with an irreversible E1cb mechanism (A(N)D(E) + D(N)) for substrates 5 and 7 and with the high stability of the intermediate carbanion related to its enamine-type structure. In acetohydroxamate/acetohydroxamic acid buffers (pH 8.45-9.42) and acetate/acetic acid buffers (pH 4.13-5.13), the beta-elimination reactions of HF, with substrates 2 and 4, occur at NH(+), the substrates protonated at the nitrogen atom of the pyridine ring, even when the [NH(+)] is much lower than the [N], the unprotonated substrate, due to the high proton-activating factor (PAF) value observed: 3.6 x 10(5) for 2 and 6.5 x 10(4) for 4 with acetohydroxamate base. These high PAF values are indicative of an irreversible E1cb mechanism rather than a concerted E2 (A(N)D(E)D(N)) mechanism. Finally, the rate constant for carbanion formation from NH(+) with 2 is k(B)(NH)+ = 0.35 M(-)(1) s(-)(1), which is lower than when chlorine is the leaving group ( = 1.05 M(-)(1) s(-)(1); Alunni, S.; Busti, A. J. Chem. Soc., Perkin Trans. 2 2001, 778). This is direct experimental evidence that some lengthening of the carbon-leaving group bond can occur in the intermediate carbanion. This is a point of interest for interpreting a heavy-atom isotope effect.     

Optical detection of phenolic compounds based on the surface plasmon resonance band of Au nanoparticles

An indirect colorimetric method is presented for detection of trace amounts of hydroquinone (1), catechol (2) and pyrogallol (3). The reduction of AuCl4(-) to Gold nanoparticles (Au-NPs) by these phenolic compounds in the presence of cetyltrimethylammonium chloride (CTAC) produced very intense surface plasmon resonance peak of Au-NPs. The plasmon absorbance of Au-NPs allows the quantitative colorimetric detection of the phenolic compounds. The calibration curves derived from the changes in absorbance at lambda = 568 nm were linear with concentration of hydroquinone, catechol and pyrogallol in the range of 7.0 x 10(-7) to 1.0 x 10(-4)M, 6.0 x 10(-6) to 2.0 x 10(-4)M and 6.0 x 10(-7) to 1.0 x 10(-4)M, respectively. The detection limits were 5.3 x 10(-7), 2.5 x 10(-6) and 3.2 x 10(-7)M for the hydroquinone, catechol and pyrogallol, respectively. The method was applied satisfactorily to the determination of phenolic compounds in water samples and pharmaceutical formulations.     

Fabrication of herbicide biosensors based on the inhibition of enzyme activity that catalyzes the scavenging of hydrogen peroxide in a thylakoid membrane.

A novel herbicide biosensor with a thylakoid modified membrane electrode is presented. Thylakoid, isolated from spinach leaves, was entrapped in a membrane of poly (vinylalcohol) with the styrylpyridinium group (PVA-SbQ). The thylakoid membrane was fixed on the surface of a platinum electrode. It was found that the enzymes in thylakoid kept their activity for several months in the membrane. The oxidative current of hydrogen peroxide in a Tris-HCl buffer solution (pH 7.4) was detected at the modified electrode by a differential pulse voltammetric method. In the presence of herbicides, the oxidation current from the hydrogen peroxide decreased due to an inhibitor effect on the enzymes in thylakoid compared with that in the absence of the herbicides. The changes in the oxidation current at the electrode were proportional to the herbicide concentrations. The sensor could be used to detect herbicides in concentration ranges of 3 x 10(-9) - 1.5 x 10(-7) M for paraquat, 1 x 10(-8) - 3 x 10(-7) M for diuron, 4 x 10(-8) - 3 x 10(-6) M for prometryn, 5 x 10(-8) - 5 x 10(-6) M for atrazine and 1 x 10(-7) - 5 x 10(-6) M for ametryn, respectively. The enzyme activity on scavenging hydrogen peroxide in the modified PVA-SbQ membrane was examined.     

Phytogrowth-inhibitory and antibacterial activities of 2,5-dihydroxy-1,4-dithiane and its derivatives

2,5-Dihydroxy-1,4-dithiane (I) and its derivatives (II-IV) showed rather marked inhibitory activities on the growth of the roots of two plant species. All compounds tested had phytogrowth-inhibitory activities. These compounds markedly inhibited the growth of the two plant species at the concentration of 1.0 x 10(-3) M. Seeds of Brassica rapa treated with 2,5-dihydroxy-2,5-dimethyl-1,4-dithiane (III) and its diacetate (IV) at the same concentration failed to germinate. Among these compounds, IV showed the most potent inhibitory activity on the two plant species. The radicles of both plant species treated with these compounds at concentrations higher than 1.0 x 10(-4) M showed negative geotropism, even though germination occurred. The compounds except for 2,5-diacetoxy-1,4-dithiane (II) also had antibacterial activities. In particular, III had rather marked antibacterial activity and its minimal inhibitory concentration (MIC) for Staphylococcus aureus IFO-3060 and Escherichia coli IFO-12734 was 4.0 micrograms/ml.     

A PVC-coated carbon rod ion-selective electrode for thallium and its application to the analysis of rocks and minerals

A new Tl(III) ion-selective electrode prepared by coating a graphite rod with a PVC membrane has been made and investigated. The optimum membrane composition is Butylrhodamine B-TlCl(-)(4) 5 mg, chlorobenzene 0.1 ml, dioctyl phthalate 0.4 ml, PVC 0.17 g. The electrode exhibits Nernstian response to Tl(III) over the concentration range 6.5 x 10(-7)-2.5 x 10(-3)M. The detection limit is 3.5 x 10(-7)M and the slope of the electrode response is 53 +/- 1 mV per decade. The electrode shows high stability and selectivity. The electrode is easy to make and store, and inexpensive.     

Determination of copper with neocuproine by thermal-lens spectrometry

Conditions for the spectrophotometric determination of copper with 2,9-dimethyl-l,10-phenan-throline (neocuproine) in the presence of ascorbic acid in a water-ethanol solution (9 : 1) at pH 4.5–5.0 have been found. The detection limit is 3 x 10^-6 M. The concentration range is from 4.4 x 10^-6 to 3 x 10^-4 M. Conditions for the determination of copper(I) with neocuproine by thermal lens spectrometry have been proposed. The detection limit is 4 x 10^-7 M. The concentration range is from 7 x 10^-7 to 6 x 10^-5 M. Iron(II) at concentrations as high asn x 10^-4 M does not interfere with the determination of copper. Changes in the conditions for the photometric reaction associated with passing from spectrophotometric measurements to thermal lensing are discussed.