Determination of Naphthalenesulfonate Isomers in Industrial Effluents and River Water by Solid‐Phase Extraction and Capillary Zone Electrophoresis

This work presents a method to separate polar naphthalenesulfonate (NS) isomers by capillary zone electrophoresis (CZE) with ultraviolet detection in industrial effluents and river water samples. The method involves extraction of samples by a polystyrene‐divinylbenzene copolymer (PS‐DVB) solid‐phase extraction (SPE) cartridge. The most effective CZE separation conditions were obtained in 20 mM borate buffer with 30% acetonitrile at pH 9.0 and 30 °C. The method proposed herein provides a high precision and sensitivity for NS isomers, to quantitation at ≤ 1.0 μg/L in 200 mL of the water samples. Recovery of the NS isomers in spiked water samples ranged from 73% to 87% while RSD ranging from 5.6 to 9.7%. The analysis of industrial effluents and river water samples was performed and naphthalene‐2‐sulfonate was found as a major pollutant. The difficulties in quantitating and identifying analytes in complex environmental samples can be resolved by using an internal standard response factor to calculate concentrations and relative migration times for peak confirmation.     

On constrained multivariate splines and their approximations

Summary The variational formulation of multivariate spline functions is generalized to include cases where the function has to satisfy inequality constraints such as positivity and convexity. Condition for existence and uniqueness of a solution is given. Approximation to the solution can be obtained by solving the variational problem in a finite dimensional subspace. Conditions for convergence and error estimates of the approximations are presented, both for interpolation problems and smoothing problems. The general theory is illustrated by specific examples including the volume-matching problem and the one-sided thin plate spline.This research is partially supported by the U.S. Army Contract No. DAAG 29-77-G-0207, and by NSF Grant No. MCS-8101836Part of this paper is based on Chapters 2 and 3 of the author's Ph. D. thesis. The author would like to express his sincere thanks to Professor Grance Wahba and to two referees for many helpful comments     

Resonant Raman spectra and first molecular hyperpolarizabilities of strongly charge-transfer molecules

The effect of vibrational structure on the frequency dependence of the first molecular hyperpolarizability of two thiophene-based charge-transfer chromophores is investigated. A time domain formulation is used to express the polarizability. The new expression includes the solvent-induced inhomogeneous distribution of electronic transition frequencies as well as the effect of the motion of solvent molecules that modulates the vibrational and electronic transition frequencies of the nonlinear optical molecule on which the first molecular hyperpolarizability depends. Resonance Raman scattering and one-photon absorption spectra of the chromophores are measured. By simultaneously fitting the experimental one-photon absorption spectrum and Raman cross sections of vibrational lines derived from resonance Raman scattering to a theoretical model, important parameters needed for the calculation of the first molecular hyperpolarizability are obtained. The first molecular hyperpolarizability is calculated as a function of frequency covering both nonresonance and two-photon resonance regions. The calculated result is compared with the measured hyperpolarizability as a function of frequency of the excitation laser. The resonance Raman-based analysis is shown to account reasonably well for the dispersion of the hyperpolarizability of the two charge transfer chromophores.     

Six-coordinate and five-coordinate Fe(II)(CN)(2)(CO)(x) thiolate complexes (x = 1, 2): synthetic advances for iron sites of [NiFe] hydrogenases

The dicyanodicarbonyliron(II) thiolate complexes trans,cis-[(CN)(2)(CO)(2)Fe(S,S-C-R)](-) (R = OEt (2), N(Et)(2) (3)) were prepared by the reaction of [Na][S-C(S)-R] and [Fe(CN)(2)(CO)(3)(Br)](-) (1). Complex 1 was obtained from oxidative addition of cyanogen bromide to [Fe(CN)(CO)(4)](-). In a similar fashion, reaction of complex 1 with [Na][S,O-C(5)H(4)N], and [Na][S,N-C(5)H(4)] produced the six-coordinate trans,cis-[(CN)(2)(CO)(2)Fe(S,O-C(5)H(4)N)](-) (6) and trans,cis-[(CN)(2)(CO)(2)Fe(S,N-C(5)H(4))](-) (7) individually. Photolysis of tetrahydrofuran (THF) solution of complexes 2, 3, and 7 under CO led to formation of the coordinatively unsaturated iron(II) dicyanocarbonyl thiolate compounds [(CN)(2)(CO)Fe(S,S-C-R)](-) (R = OEt (4), N(Et)(2) (5)) and [(CN)(2)(CO)Fe(S,N-C(5)H(4))](-) (8), respectively. The IR v(CN) stretching frequencies and patterns of complexes 4, 5, and 8 have unambiguously identified two CN(-) ligands occupying cis positions. In addition, density functional theory calculations suggest that the architecture of five-coordinate complexes 4, 5, and 8 with a vacant site trans to the CO ligand and two CN(-) ligands occupying cis positions serves as a conformational preference. Complexes 2, 3, and 7 were reobtained when the THF solution of complexes 4, 5, and 8 were exposed to CO atmosphere at 25 degrees C individually. Obviously, CO ligand can be reversibly bound to the Fe(II) site in these model compounds. Isotopic shift experiments demonstrated the lability of carbonyl ligands of complexes 2, 3, 4, 5, 7, and 8. Complexes [(CN)(2)(CO)Fe(S,S-C-R)](-) and NiA/NiC states [NiFe] hydrogenases from D. gigas exhibit a similar one-band pattern in the v(CO) region and two-band pattern in the v(CN) region individually, but in different positions, which may be accounted for by the distinct electronic effects between [S,S-C-R](-) and cysteine ligands. Also, the facile formations of five-coordinate complexes 4, 5, and 8 imply that the strong sigma-donor, weak pi-acceptor CN(-) ligands play a key role in creating/stabilizing five-coordinate iron(II) [(CN)(2)(CO)Fe(S,S-C-R)](-) complexes with a vacant coordination site trans to the CO ligand.     

Electrophoresis of a sphere at an arbitrary position in a spherical cavity filled with Carreau fluid

Boundary effects on the electrophoretic behavior of a charged entity are of both fundamental and practical significance. Here, they are examined by considering the case where a sphere is at an arbitrary position in a spherical cavity under conditions of low surface potential and weak applied electrical field. Previous analyses are extended to the case of a non-Newtonian fluid, and a Carreau model is adopted for this purpose. The effects of key parameters such as the thickness of a double layer, the relative sizes of particle and cavity, the position of a particle, and the nature of a fluid on the electrophoretic mobility of a particle are discussed. Several interesting phenomena are observed. For example, if the applied electric field points toward north, the mobility of a particle has a local maximum when it is at the center of a cavity. However, if a particle is sufficiently close to the north pole of a cavity, its mobility exhibits a local minimum as its position varies. This does not occur when the particle is close to the south pole of the cavity; instead, it may move in the direction opposite to that of the applied electric field. For a Newtonian fluid, if a particle is close to the north pole of a cavity, its upward movement yields a clockwise (counterclockwise) vortex near the north pole of the cavity and a counterclockwise (clockwise) vortex near the south pole of the cavity on its right (left)-hand side. The latter is not observed for a Carreau fluid.     

A nickel(0) catalyzed cycloaddition of alkynes and isocyanates that affords pyrimidine-diones

A Ni/N-heterocyclic carbene catalyzed cycloaddition of one alkyne and two isocyanates that affords pyrimidine-dione is described. The key to the success of this protocol is the use of unsymmetrically substituted alkynes that favors the formation of pyrimidine-diones over pyridones. A variety of pyrimidine-diones were prepared. A one-pot cycloaddition and Stille coupling were reported for tributyl(1-propynyl)tin. Competition studies also provide insights into the mechanism of the cycloaddition.     

Reduction of octacyanomolybdate(V) by thioglycolic acid in aqueous media

In aqueous media at 25 degrees C [Mo(CN)(8)](3-) is reduced by thioglycolic acid (HSCH(2)COOH, TGA), and the reaction is strongly accelerated by the presence of trace amounts of copper ions. Dipicolinic acid (dipic) is an effective inhibitor of the copper catalysis. Both with and without dipic the reaction has the stoichiometry 2[Mo(CN)(8)](3-) + 2TGA --> 2[Mo(CN)(8)](4-) + RSSR, where RSSR is the disulfide derived from formal oxidative dimerization of TGA. In the presence of dipic, PBN (N-tert-butyl-alpha-phenyl-nitrone), and with a large excess of TGA the rate law for consumption of [Mo(CN)(8)](3-) is first order in both [TGA] and [Mo(CN)(8)(3-)]. The complex pH dependence is consistent with (-)SCH(2)CO(2)(-) being highly reactive (k = 1.8 x 10(4) M(-1) s(-1)), the monoanion being less reactive, and HSCH(2)CO(2)H being unreactive. A mechanism is proposed in which the dianion undergoes electron transfer to [Mo(CN)(8)](3-), thus generating the thiyl radical. Analysis of the electron-transfer rate constant in terms of Marcus theory yields an effective self-exchange rate constant for the thiolate/thiyl redox couple that is in reasonable agreement with the value derived previously from the reaction of TGA with [IrCl(6)](2-). When copper catalysis is inhibited, the two reactions differ substantially in that the yield of (-)O(3)SCH(2)CO(2)(-) is significant for [IrCl(6)](2-) but undetectable for [Mo(CN)(8)](3-).     

Cationic polymerization of dienes VII. New electron donors in the polymerization of 1,3-pentadiene initiated by aluminum trichloride in non-polar solvent

The aim of this research was to investigate new bulky electron donors (EDs) generating hindered active species in the cationic polymerization of 1,3-pentadiene initiated by AlCl₃ in pentane, in order to avoid or strongly reduce the reaction between the active species and the double bonds of the polymer which are responsible for side reactions. At room temperature, the polymerization in the presence of new ED, such as OPh₂, N(PhBr)₃, NPh₃ and SPh₂, allowed to obtain higher conversions and lower insoluble fractions than without electron donor. The formation of a complex ED/AlCl₃ was shown for each electron donor. However, in the case of NPh₃ and SPh₂, variations of the polymer microstructure demonstrated an interaction between active species and these EDs. Similar results were obtained at lower temperature (−10 °C). The beneficial effect of the presence of electron donors such as NPh₃ and SPh₂ demonstrated the validity of the concept of sterically hindered active species, but the polymerization was still uncontrolled.     

Ruthenium complexes of 2-[(4-(arylamino)phenyl)azo]pyridine formed via regioselective phenyl ring amination of coordinated 2-(phenylazo)pyridine: isolation of products,X-ray structure,and redox and optical properties

Aromatic ring amination reactions in the ruthenium complex of 2-(phenylazo)pyridine is described. The substitutionally inert cationic brown complex [Ru(pap)(3)](ClO(4))(2) (1) (pap = 2-(phenylazo)pyridine) reacts smoothly with aromatic amines neat and in the presence of air to produce cationic and intense blue complexes [Ru(HL(2))(3)](ClO(4))(2) (2) (HL(2) = 2-[(4-(arylamino)phenyl)azo]pyridine). These were purified on a preparative TLC plate. The X-ray structure of the new and representative complex 2c has been solved to characterize them. The results are compared with those of the starting complex, [Ru(pap)(3)](ClO(4))(2) (1). The transformation 1 --> 2 involves aromatic ring amination at the para carbon (with respect to the diazo function) of the pendant phenyl rings of all three coordinated pap ligands in 1. The transformation is stereoretentive, and the amination reaction is regioselective. The extended ligand HL(2) coordinates as a bidentate ligand and chelates to ruthenium(II) through the pyridine and one of the azo nitrogens. The amine nitrogen of this bears a hydrogen atom and remains uncoordinated. Similarly, the amination reaction on the mixed-ligand complex [Ru(pap)(bpy)(2)](ClO(4))(2) produces the blue complex [Ru(HL(2))(bpy)(2)](ClO(4))(2) (3) as anticipated. The reactions of [RuCl(2)(dmso)(4)] and [Ru(S)(2)(L)(2)](2+) (dmso = dimethyl sulfoxide, S = labile coordinated solvent, L = 2,2'-bipyridine (bpy) and pap) with the preformed HL(2) ligand have been explored. The structure of the representative complex [RuCl(2)(HL(2a))(2)] (5a) is reported. It has the chlorides in trans configuration while the pyridine as well as azo nitrogens are in cis geometry. Optical spectra and redox properties of the newly synthesized complexes are reported. All the ruthenium complexes of HL(2) are characterized by their intense blue solution colors. The lowest energy transitions in these complexes appear near 600 nm, which have been attributed to intraligand charge-transfer transitions. For example, the lowest energy visible range transition in [Ru(HL(2b))(3)](2+) appears at 602 nm and its intensity is 65 510 M(-1) cm(-1). All the tris chelates show multiple-step electron-transfer processes. In [Ru(HL(2))(3)](2+), six reductions waves constitute the complete electron-transfer series. The electrons are believed to be added successively to the three azo functions. In the mixed-ligand chelates [Ru(HL(2))(pap)(2)](2+) and [Ru(HL(2))(bpy)(2)](2+) the reductions due to HL(2), pap, and bpy are observed.