Copper(II) ion sensor based on electropolymerized undoped conducting polymers

A solid state copper(II) ion sensor is reported based on the application of electropolymerized undoped (neutral) polycarbazole (PCz) and polyindole (PIn) modified electrodes. The new sensor shows high selectivity to Cu²⁺ ions with a detection limit of 10^–5 M. PCz and PIn are formed respectively by the anodic oxidation of 50 mM carbazole and 5 mM indole monomers in dichloromethane containing 0.1 M tetrabutylammonium perchlorate on a platinum electrode using a single compartment cell. Potentiostatic polymerization of both the monomers are carried out at 1.3 V and 1.0 V vs. Ag/AgCl, respectively. Perchlorate ions were electrochemically removed from the polymer films by applying – 0.2 V vs. Ag/AgCl. Polymer-coated electrodes are incubated in 1 M KCl solution for 8 h followed by incubation in distilled water for 2 h before using as a metal ion sensor. The undoped PCz and PIn electrodes were found to be highly selective and sensitive for Cu²⁺ ions with little selectivity for Pb²⁺ and negligible response towards Ag⁺, Hg²⁺, Cu⁺, Ni²⁺, Co²⁺, Fe²⁺, Fe³⁺ or Zn²⁺. Potentiometric responses for Cu²⁺ ions are recorded for both the sensor electrodes together with a double-junction Ag/AgCl reference electrode. Calibration curves for Cu²⁺ are reported for both ion sensors. The polymer-modified electrodes were found to be stable for several weeks. Electronic Publication     

Enhanced selectivity and sensitivity for inorganic anions using an ion-pairing reagent and sample stacking in capillary zone electrophoresis with direct UV detection

In this paper, the use of an ion-pairing reagent to improve the separation selectivity of inorganic anions in CZE was demonstrated by the addition of tetramethylammonium hydroxide (TMAOH) to the electrolyte. The separation of inorganic anions (Cl(-), I(-), Br(-), NO(2)(-), NO(3)(-) and SCN(-)) was performed using co-electroosmotic flow (EOF) with direct UV detection at 185 nm. The parameters affecting the mobility of the tested anions and the EOF such as the electrolyte pH and concentration of TMAOH in the electrolyte were examined to optimise the separation conditions. In addition, sample-stacking techniques were investigated to improve detection sensitivity. Detection sensitivities were improved 5-13-fold using electrokinetic sample stacking. The detection limits ranged from 1-3 micro mol L(-1). Finally, the proposed method was used for the separation of anions in groundwaters.     

Classical Dynamics of H<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> in an Intense Laser Field by Using the Symplectic Method

The classical dynamics of 1D H₂⁺ in an intense field are discussed. The initial conditions are chosen at random in the field-free case, and then the Hamiltonian canonical equations of H₂⁺ system in the intense laser field are solved numerically by mean of the symplectic method under these initial conditions. The probabilities of survival, dissociation, ionization, and Coulomb explosion of H₂⁺ system in the intense laser field are obtained for different laser intensity based on the classical theory.     

Chirality transfer from guest chiral metal complexes to inorganic framework: the role of hydrogen bonding

The structure elucidation of a new zinc phosphate [Co(II)(en)(3)][Zn(4)(H(2)PO(4))(3)(HPO(4))(2)(PO(4))(2 H(2)O)(2)] (1) reveals that the racemic cobalt complex templates the zinc phosphate framework in such a way that the local C(2) point symmetry of the structural motif of the inorganic framework conforms with that of the cobalt complex pairing with it, in essence transferring its chirality to the inorganic host. An analysis of hydrogen bonding between the guest molecules and the inorganic host framework reveals that hydrogen bonding is responsible for the stereospecific structural arrangement. Upon examining previously reported chiral metal-complex-templated structures of metal phosphates, it is revealed that such hydrogen bonding is the common origin for inducing chirality transfer in metal-phosphate frameworks templated with chiral metal complexes. Crystal data of 1: orthorhombic, Pbcn (no. 60), a=10.4787(8) A, b=20.0091(14) A, c=14.9594(10) A, and Z=2.     

Unsymmetric-1,3-disubstituted imidazolium salt for palladium-catalyzed Suzuki–Miyaura cross-coupling reactions of aryl bromides

A series of 1-(ferrocenylethyl)-3-substituted-imidazolium salts [3-substitute = 2,6-di(iso-propyl)phenyl (1a), 2,4,6-trimethylphenyl (1b), tert-butyl (1c), 1-Ad (1d), cyclohexyl (1e)] have been synthesized from a racemic ferrocenylethyl acetate and the corresponding N-substituted imidazole in high yields (70–94%). A combination of Pd(OAc)₂ and 1a–d was found to form an excellent catalyst system for the Suzuki–Miyaura cross-coupling reactions of aryl bromides with phenylboronic acid in the presence of Cs₂CO₃.     

Quantitative Determination of Three Protoberberine Alkaloids in Jin-Guo-Lan by HPLC-DAD

An accurate and simple HPLC method for the simultaneous determination of three protoberberine alkaloids (columbamine, jatrorrhizine, and palmatine) contained in Chinese medicine Jin-Guo-Lan (Tinospora sagittata Oliv. and Tinospora capillipes Gagnep) is presented in this study. The herb samples from six main origins and three herb markets were investigated. The separation was performed on a YMC-C₁₈ ODS column at 30°C with a gradient elution program. Acetonitrile and phosphate buffer (0.02 mol L⁻¹ sodium dihydrogen phosphate and 0.01 mol L⁻¹ triethylamine, pH 3) were used as mobile phases and the flow rate was set at 1 mL min⁻¹. The recovery of the method was in the range of 99.43–100.96%, and all the alkaloids showed good linearity (r ² > 0.9997) in the relatively wide concentration ranges. The developed method was applied to the determination of these alkaloids in the collected herb samples, and the results showed that the contents of these components in Jin-Guo-Lan varied greatly from habitat to habitat. It was demonstrated that the proposed method was helpful for the quality evaluation of Chinese medicine Jin-Guo-Lan.     

A Novel Simplified Column-Switching Technique for the Determination of Traces of Bromate in High Concentration Matrices

The column-switching technique has been widely used to determine trace level ions in the presence of high concentration matrix. A novel simplified column-switching method is proposed where bromate (as a model compound) was determined using this technique. The switching time window was confirmed by the retention time of determined ions. This technique can completely carry out the same function as the other column-switching technique do, but only one extra ten-way injection valve coupled to ion chromatograph was used. By using column-switching technique, it is possible to determine 0.2 μg L⁻¹ bromate in the presence of 100 mg L⁻¹ chloride by direct injection of 2000 μL without any pretreatment and the relative standard deviation (RSD) of the peak height for the eleven successive injections of 0.2 μg L⁻¹ bromate solution is 23.1%. The detection limit for bromate is 0.09 μg L⁻¹, which showed the method was very sensitive. The technique has been applied to the determination of bromate in drinking water, and the spike recovery is in the range of 96–104%.     

Application of artificial neural networks in multivariable optimization of an on-line microwave FIA system for catalytic kinetic determination of iridium(III)

A new rapid, selective and sensitive on-line microwave flow injection-kinetic method was developed for spectrophotometric determination of micro amounts of Ir(III), based on its catalytic effect on the m-acetylchlorophosphonazo (CPA-mA) and KIO(4) reaction in NaOH media. An on-line microwave oven was employed to accelerate the reaction. The reaction was followed spectrophotometrically by measuring the decrease of the absorbance of CPA-mA at 580 nm. The effect of five variables for the determination of Ir(III) was optimized by means of a multilayer artificial neural network using extended delta-bar-delta (EDBD) algorithms. Under the optimum experimental conditions, Ir(III) could be determined in the range 0.060-0.60 micro gZZZ;mL(-1) with detection limit of 0.02 micro gZZZ;mL(-1) and the sampling frequency of 34 h(-1). The proposed method was applied to the determination of micro amounts of Ir(III) in refined ore and secondary alloy with the recoveries from 91.4% to 109%.     

Inclusion of nickel(<Emphasis Type="SmallCaps">II</Emphasis>) and copper(<Emphasis Type="SmallCaps">II</Emphasis>) complexes with aliphatic polyamines in cucurbit[8]uril

The inclusion compound of macrocyclic cavitand cucurbit[8]uril (CB[8]) with the nickel(II) complex containing the tetraazamacrocyclic ligand cyclam, {[Ni(cyclam)]@CB[8]}Cl₂··16H₂O (1), and the inclusion compounds of CB[8] with the copper(II) bis-ethylene-diamine complex, {trans-[Cu(en)₂(H₂O)₂]@CB[8]}Cl₂·{CB[8]}·42H₂O (2a) and {trans-[Cu(en)₂(H₂O)₂]@CB[8]}Cl₂·17H₂O (2b), were synthesized and characterized by X-ray diffraction analysis, IR and ESR spectroscopy, and electrospray mass spectrometry. Guest—host inclusion compounds can be directly synthesized starting from a metal complex and cucurbit[8]uril, as was exemplified by the preparation of compounds 2a and 2b.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2414–2419, November, 2004.     

NMR chemical shifts in the low–pH form of a-chymotrypsin. A QM/MM and ONIOM–NMR study

 The relationship between hydrogen bonding and NMR chemical shifts in the catalytic triad of low-pH α-chymotrypsin is investigated by combined use of the effective fragment potential [(2001) J Phys Chem A 105:293] and ONIOM–NMR [(2000) Chem Phys Lett 317:589] methods. Our study shows that while the His57 N^δ1−H bond is stretched by a relatively modest amount (to about 1.060 ?) this lengthening, combined with the polarization due to the molecular environment, is sufficient to explain the experimentally observed chemical shifts of 18.2 ppm. Furthermore, the unusual down-field shift of H^ɛ1 (9.2 ppm) observed experimentally is reproduced and shown to be induced by interactions with the C=O group of Ser214 as previously postulated. The free-energy cost of moving H^δ1 from His57 to Asp102 is predicted to be 5.5 kcal/mol. Received: 26 September 2001 / Accepted: 6 September 2002 / Published online: 21 January 2003 Contribution to the Proceedings of the Symposium on Combined QM/MM Methods at the 222nd National Meeting of the American Chemical Society, 2001 Correspondence to: J. H. Jensen e-mail: jan-jensen@uiowa.edu Acknowledgements. This work was supported by a Research Innovation Award from the Research Corporation and a type G starter grant from the Petroleum Research Fund. The calculations were performed on IBM RS/6000 workstations obtained through a CRIF grant from the NSF (CHE-9974502) and on supercomputers at the National Center for Supercomputer Applications at Urbana-Champaign. The authors are indebted to Visvaldas Kairys for help with the CHARMM program, and to Daniel Quinn for many helpful discussions.