Spectrophotometric study of the ruthenium(III,II)–2,2′,2″- terpyridine system

Ruthenium(III) reacts with 2,2′,2″-terpyridine in aqueous solution at pH 3.0–4.5, when heated at 85 °C for 2 min, giving a green cationic complex with an absorbance maximum at 690 nm. The color is stable for at least 25 h. The system conforms to Beer's law. The optimal range for measurement (1.00-cm optical path) is 2–10 p.p.m. Ru; the molar absorptivity is 8.3 ·10³. Ruthenium(II) reacts with terpyridine at pH 5.5 to develop an amber cationic complex (absorption maximum at 475 nm) on heating at 95° C for 45 min. The color is apparently stable indefinitely. The system conforms to Beer's law; the optimal range is 1–5 p.p.m. Ru; the molar absorptivity is 1.45·10⁴ l mol^?1 cm^?1. Common anions do not interfere; separation as RuO₄ is necessary when iron and a few other transition cations are present. The green complex, a strong oxidant, is converted to the ruthenium(II) complex by oxidation of water, slowly at room temperature, or more quickly by longer heating and/or higher temperature, and by increase of pH. The Ru(II) complex can be converted to the Ru(III) complex by strong oxidants such as Ce(IV). In the amber complex, the reaction ratio is 1 Ru: 2 terpyridine, in which the ligand is tridentate, whereas in the green complex the reaction ratio is 1 Ru : 3 terpyridine, the latter acting only as a bidentate ligand. Short gentle warming of a mixture of ruthenium(III) and terpyridine first produces a transient unidentified blue-colored species (absorbance at 790 nm).     

Selective volatilisation of trace metals from refractory solids into an inductively coupled plasma

Feasibility studies have been carried out on the use of a graphite electrode assembly for the introduction of U₃O₈ solid samples into a continuously running low-powered argon inductively coupled plasma for the assay of trace metallic elements in uranium. The d.c. arc carrier distillation procedure has been adopted here for the selective volatilisation of analyte elements from the refractory matrix by injecting analyte vapours into the central zone of the plasma using Scribner-Mullin electrodes covered with a graphite lid having a central opening. The experimental parameters have been optimised for the direct determination of B, Be, Cd, Co, Cr, Cu, Fe, K, Li, Mn, Na, Ni and Pb in U₃O₈ powders. The analytical performance of the method has been checked by analysing spiked U₃O₈ samples and is seen to be comparable to or better than d.c. arc methods for these analytes. These results indicate that the carrier-distillation-ICP combination shows promise as a sensitive and precise method for analysis of trace metallic elements in a refractory matrix with a complex spectrum.     

A new sensitive method for the spectrophotometric determination of molybdenum using 3-hydroxy-2-(2'-thienyl)-4H-chromen-4-one

A spectrophotometric method has been developed for the determination of Molybdenum (VI) using 3-hydroxy-2-(2'-thienyl)-4H-chromen-4-one as a complexing agent. The complex formed was dissolved in water in the presence of Triton X-100 and exhibits an absorption maximum at 410 nm. A large number of metal ions like Co(II), Ni(II), Mn(II), Cr(III), Zn(II), Cu(II), Hg(II), Bi(III), Fe(II), Fe(III), Zr(IV), V(V) can be tolerated at an appreciable concentrations. Molar absorptivity and Sandell's sensitivity of the method is 2.80 x 10(5) l mol-1cm-1 and 3.42 x 10(-4) micrograms cm-2, respectively. Beer's law is obeyed in the concentration range of 0.01-0.4 ppm Mo(VI). Aliquots containing 0.2 ppm of Mo(VI) give a mean absorbance of 0.56 with a relative standard deviation of 1.3%.     

Convex programming with single separable constraint and bounded variables

In this paper a minimization problem with convex objective function subject to a separable convex inequality constraint “≤” and bounded variables (box constraints) is considered. We propose an iterative algorithm for solving this problem based on line search and convergence of this algorithm is proved. At each iteration, a separable convex programming problem with the same constraint set is solved using Karush-Kuhn-Tucker conditions. Convex minimization problems subject to linear equality/ linear inequality “≥” constraint and bounds on the variables are also considered. Numerical illustration is included in support of theory.     

Capacitated transportation problem with bounds on RIM conditions

Motivated by dead-mileage problem assessed in terms of running empty buses from various depots to starting points, we consider a class of the capacitated transportation problems with bounds on total availabilities at sources and total destination requirements. It is often difficult to solve such problems and the present paper establishes their equivalence with a balanced capacitated transportation problem which can be easily solved by existing methods. Sometimes, total flow in transportation problem is also specified by some external decision maker because of budget/political consideration and optimal solution of such problem is of practical interest to the decision maker and has motivated us to discuss such problem. Various situations arising in unbalanced capacitated transportation problems have been discussed in the present paper as a particular case of original problem. In addition, we have discussed paradoxical situation in a balanced capacitated transportation problem and have obtained the paradoxical solution by solving one of the unbalanced problems. Numerical illustrations are included in support of theory.     

Power penalty in multitone radio-over-fibre system employing direct and external modulation with optical amplifiers

This paper presents a multitone RoF system employing a central station and a remote antenna station to transmit modulated microwave or mm-wave signals. Two configurations of the system employing direct and external modulation are presented. First, at the central station, the modulating signal is directly and externally modulated at 1549.5 and 1550.5 nm, respectively, and the combined signal is then transmitted using wireless mode. In the second configuration, the combined signal is transmitted over 20 km to the remote antenna station using optical fibre connectivity. At the remote antenna station, both channel wavelengths are separated and amplified with an EDFA and SOA and are detected. The demonstration results show that there exists a small power penalty between the direct and the external modulation. But a large power penalty is reported depending upon the choice of optical amplifier viz. EDFA or SOA. Better performance is recorded in later case. The results also show that power is being distributed among the operating frequency and sidebands adjacent to it after transmission over a fibre link.     

Physicochemical studies of (o-vanillin thiosemicarbazonato)-nickel(ii) chelate

Summary Five- and six-membered rings result from the chelation of nickel(II) by the dibasic tridentate Schiff base ligand, o-vanillin thiosemicarbazone(o-VTSC), a new chelate prepared and characterized. The structural results are discussed in the light of spectroscopic and other data.Presented at 29th ICCC, Lausanne, Switzerland, 1992.     

Novel Oligopyrrole Carboxamide based Nickel(II) and Palladium(II) Salens,Their Targeting of Human G‐Quadruplex DNA,and Selective Cancer Cell Toxicity

DNA targeting by various metal complexes is a key strategy toward the restriction of cancer cell proliferation. Toward this end, we designed and synthesized novel salen‐based Ni^II and Pd^II metal complexes with positively charged flanking side chains comprising N‐methylpyrrole carboxamides of varying lengths. The compounds showed high specificity toward G‐quadruplex DNA over duplex DNA. Sufficient inhibition of the telomerase activity was observed, which was ascertained by the prominent restriction of cancer cell proliferation in the long‐term cell viability and telomerase inhibition assays. The compounds exhibited selective cancer cell death following an apoptotic pathway. Analysis of the binding mode showed partial stacking of the salen moiety over the G‐tetrads and association of the pendant oligopyrrole carboxamide units with the grooves. The conjugation of the tetrad‐binding metal salen core with groove‐oriented flexible oligopyrrole moieties resulted in the high selectivity and stabilization of the human G‐quadruplex DNA structures.     

Xylanase production by the thermophilic mold Humicola lanuginosa in solid-state fermentation

Among the lignocellulosic substrates tested, wheat bran supported a high xylanase (EC 3.2.1.8) secretion by Humicola lanuginosa in solid-state fermentation (SSF). Enzyme production reached a peak in 72 h followed by a decline thereafter. Enzyme production was very high (7832 U/g of dry moldy bran) when wheat bran was moistened with tap water at a substrate-to-moistening agent ratio of 1:2.5 (w/v) and an inoculum level of 3 × 10⁶ spores/10 g of wheat bran at a water activity (a _w ) of 0.95. Cultivation of the mold in large enamel trays yielded a xylanase titer comparable with that in flasks. Parametric optimization resulted in a 31% increase in enzyme production in SSF. Xylanase production was approx 23-fold higher in SSF than in submerged fermentation (SmF). A threshold constitutive level of xylanase was secreted by H. lanuginosa in a medium containing glucose as the sole carbon source. The enzyme was induced by xylose and xylan. Enzyme synthesis was repressed beyond 1.0% (w/v) xylose in SmF, whereas it was unaffected up to 3.0% (w/w) in SSF, suggesting a minimization of catabolite repression in SSF.