Effect of surfactants on the voltammetric response and determination of an antihypertensive drug

The effect of adding surface-active agents to electrolytes containing terazosin, an antihypertensive drug, on the voltammetric response of glassy carbon electrode was studied. The current signal due to the oxidation process was a function of the amount of terazosin, pH of the medium, type of surfactant, and accumulation time at the electrode surface. Two surfactants were used, an anionic type, sodium dodecyl sulfate (SDS) and a cationic type, cetyl trimethyl ammonium bromide (CTAB). Addition of SDS to the terazosin-containing electrolyte was found to enhance the oxidation current signal while CTAB showed an opposite effect. Beside the interfacial interaction of the surfactant with the electrode surface in reference to the bias applied potential and the charge of surfactant, terazosin-surfactant interaction in the electrolytic solution was found to be critical to the magnitude of current signal. Addition of SDS to terazosin-containing buffer solution resulted in a decrease in the drug absorption spectrum both in the ultra-violet and visible (UV-vis) regions. Moreover, NMR measurements showed considerable chemical shifts for the aromatic protons of the quinazolinyl moiety of the terazosin in presence of SDS. The affected aromatic protons are positioned next to the interacting protonated amino-group of the terazosin with the charged sulfonate-group of SDS. On the other hand, addition of CTAB did not cause noticeable changes both to the UV-vis and NMR spectra of the drug. The use of SDS in the electrochemical determination of terazosin using linear sweep voltammetry and differential pulse voltammetry at solid glassy carbon electrode enhanced the detection limit from 6.00 × 10⁻⁷ mol L⁻¹ in absence of surfactant to 4.58 × 10⁻⁹ mol L⁻¹ when present. The validity of using this method in the determination of drug active ingredient in urine samples and tablet formulations was also demonstrated.     

Partial Least-Squares Study of the Effects of Organic Modifier and Physicochemical Properties on the Retention of Some Thiazoles

JPC – Journal of Planar Chromatography – Modern TLC - Reversed-phase (RP) HPTLC with aqueous ammonia-organic modifier (acetonitrile, dioxane, acetone) mobile phases has been used to...     

Study of the Retention Behavior of Newly Synthesized s-Triazine Derivatives in RP TLC Systems,and the Lipophilicity of the Compounds

JPC – Journal of Planar Chromatography – Modern TLC - The chromatographic behavior of nine newly synthesized s-tri-azines has been studied by thin-layer chromatography on C18/UV254...     

Electrochemical synthesis, characterization and some properties of a polymer derived from thioflavin S

Polymeric films derived from thioflavin S were electrosynthesized on mild steel and silver electrodes in sulfuric acid and lithium perchlorate-containing aqueous solutions. The introduction of thioflavin S in an acidic solution protected the surface of steel from corrosion. The electrochemical behavior of the steel coated with a layer of poly(thioflavin) was examined by electrochemical impedance spectroscopy. The films exhibited a capacitive behavior and were semi-conductive in nature. Infra red reflectance measurements of the polymer films at the steel surface showed that the polymer structure retained the aromatic structure of the benzene and thiazole rings with the distinction of a nitrogen quinone vibrational band. Surface morphology of the polymer film was examined with scanning electron microscopy. The films are yellow, compact and dense when electrochemically formed onto steel surfaces when compared to a blue rather porous when formed onto silver electrode. The mechanism of electropolymerization of thioflavin is given and found similar to that of aniline with the possibility of metal chelation with the sulfur and/or nitrogen in the thiazole ring.     

Determination of diamine oxidase by a kinetic method with 2,2''-azino-di(3-ethylbenzthiazoline-6-sulfonate)

Hydrogen peroxide, the product of diamine oxidase-catalyzed putrescine or cadaverine oxidation, formed in proportion to the enzyme activity, is measured spectrophotometrically by using the above sulfonate (ABTS) and peroxidase. Only one reagent solution containing 3 mmol of putrescine or 10 mmol of cadaverine, 4 mmol of ABTS and 3000 U of peroxidase per litre of 0.2 mol l^-1 Tris—0.1 mol l^-1 HCl buffer pH 7.5 is needed. Absorbance changes are measured at 410 nm over the first 3 min of the reaction. This initial oxidation rate of the chromogen enables diamine oxidase activity up to 230 U l^-1 to be determined.     

Thermal analysis and kinetics of the copper-lead matte roasting process

In this paper, the results of copper-lead matte investigations are presented. Investigated copper-lead matte is intermediate product of the lead production in TREPCA-Zvečan. In the first part of the paper characterization of starting material is presented, consisting of: chemical composition analysis (XRQ), scanning electron microscopy (SEM) and diffractometry (XRD). Thermal properties of investigated matte were determined using differential thermal analysis (DTA) at characteristic temperatures. Using results of induced analysis, mechanism of matte oxidation process was determined. In the second part of the paper kinetic parameters describing oxidative roasting of copper-lead matte are presented. For activation energy calculations, non-isothermal methods defined by Kissinger and Ozawa were used [1, 2]. Kinetic equation describing oxidation process was determined using Sharps method of reduced half time of reaction [3].     

Non-covalent assemblies of negatively charged boronated porphyrins with different cationic moieties

A unique approach to non-covalent electron and energy transfer is described that is based on the formation of salt bridges between oppositely charged porphyrin units. A new class of electrostatically linked dimeric and pentameric porphyrins was synthesized by interaction of novel anionic boron containing porphyrins such as 5-(benzamidodecahydro-closo-dodecaborate)-10,15,20-triphenylporphyrin (N1) and meso-tetrakis-benzamidodecahydro-closo-dodecaborate)porphyrin (N2) and a variety of cationic meso-tetraarylporphyrin units. A bipyridine linked dimer (N1 · bpy · N1) was also prepared by employing N,N′-dimethyl-4,4′-bipyridinium (bpy) as a spacer between two mono-anionic species. A quinone-porphyrin dyad was also prepared for electron or energy transfer demonstration. All the synthesized assemblies were characterized by NMR, IR, UV-Vis, and mass spectroscopy. Significant spectral changes occurred in the absorption spectra of these non-covalent porphyrin assemblies compared to those of the reference monomers, indicating the presence of electronic interaction between the adjacent porphyrin units. Resonance light scattering was also used to study the formation of these assemblies in solution.     

Synthesis and characterization of a novel functionalized azanonaborane cluster for boron neutron capture therapy

The reactivity of an azanonaborane cluster containing free amino groups {H2N(CH2)4H2NB8H11NH(CH2)4NH2} towards ketones and aldehydes is investigated. In a one step reaction, the reductive amination of some ketones and aldehydes (namely acetone, benzaldehyde, 3-hydroxybenzaldehyde, 4-hydroxybenzaldehyde, 4-nitrobenzaldehyde, 4-acetoxybenzaldehyde, and 4-acetamidobenzaldehyde) with an azanonaborane cluster in the presence of H3BNH2(CH2)4NH2 gives monoalkylamino derivatives of the azanonaborane cluster {RHN(CH2)4H2NB8H11NH(CH2)4NHR} where (R =(Me)2CH-, C6H5CH2-, 3-OHC6H4CH2-, 4-OHC6H4CH2-, 4-NO2C6H4CH2-, 4-MeOCOC6H4CH2-, or 4-NH2COC6H4CH2-). The functionalized derivatives of the {B8N} cluster can be used in boron neutron capture therapy for tumors (BNCT). Similarly, the reductive amination of 5-(4"-formylphenyl)-10,15,20-triphenylporphyrin with the {B8N} cluster gave a porphyrin bearing azanonaborane cluster, while a porphyrin dimer linked by an azanonaborane moiety was obtained following the same method, starting with a 2:1 molar ratio of porphyrin:{B8N} cluster. 5,10,15,20-Tetraformylphenylporphyrin gave the chance to increase the percentage of boron in the resulting boronated porphyrin, which is considered an important factor for a BNCT delivery agent. With these compounds, the cell toxicity using V79 cells was carried out to determine whether these compounds would have favorable biological properties.     

The chemistry of the azanonaborane cluster RNH2---B8H11NHR

The preparation and properties of the R¹R²NH---B₈H₁₁NHR cluster are described. The cluster is stable to aqueous solutions and can be made water-soluble by the introduction of a few hydrophilic groups. This makes the cluster a good candidate as the boron moiety in compounds for boron neutron capture therapy. The chemistry of the cluster preparation, the stability of the cluster, and conditions for reactions of the organic moieties are reviewed. Pyridine derivatives of the cluster show electronic interaction between the cluster and the pyridine.