A Comparison of Edge-plane and Basal-plane Pyrolytic Graphite Electrodes towards Sensitive Determination of the Fungicide Mandipropamid

A sensitive square-wave voltammetry (SWV) method based on basal-plane pyrolytic graphite electrode (BPPGE) and edge-plane pyrolytic graphite electrode (EPPGE) was developed to determine the concentration of the pesticide mandipropamid (MAN) in spiked river water and grape juice samples. Under optimal experimental conditions, the SWV response of EPPGE and BPPGE was linear over the concentration ranges of 0.7 to 9.0 μmol L⁻¹ and 0.5 to 10.0 μmol L⁻¹, respectively. The method was successfully used to determine MAN in spiked samples with good recovery. Cyclic voltammetry (CV) was conducted to understand the mechanism underlying the electrode process of MAN.     

Spectral Gap of Segments of Periodic Waveguides

The lowest spectral gap of segments of a periodic waveguide in is proportional to the square of the inverse length. Dedicated to Pavel Exner on the occasion of his 60th birthday.     

Structure design of multifunctional furoate and pyroglutamate esters of dextran by polymer-analogous reactions

Well-defined multifunctionalized dextran esters bearing photo-crosslinkable and chiral groups as well as small alkyl moieties for the adjustment of the solubility were prepared from two dextran samples with different origin and molecular weight. The examination of side structures of the starting dextran was carried out by different one- and two-dimensional NMR techniques. The main synthesis path via in situ activation of furan-2-carboxylic- and pyroglutamic acid with CDI under mild conditions gives highly functionalized dextran derivatives possessing a degree of polymerization in the range of the starting polysaccharide. The subsequent reaction with propionic anhydride leads to completely substituted, CHCl(3) soluble derivatives useful for the determination of the particular degree of substitution. By variation of the molar ratios of polymer to reagent with photo-crosslinkable- and chiral moieties during the reaction and even by subsequent peracylation, multifunctional dextran derivatives with adjustable properties like the hydrophilic/hydrophobic balance were obtained that may form biocompatible spherical nanoparticles.     

Use of multivariate statistical techniques to optimize the separation of isoflavones by liquid chromatography

The aim of this paper is to optimize and validate a high performance liquid chromatography (HPLC) method for separation and quantification of five isoflavones. A statistical central composite design was used to separate all peaks. These multivariate procedures were efficient in determining the optimal separation condition using resolution, capacity factor, asymmetry and number of theoretical plates.      

Electrochemical characterization of Prussian blue type nickel hexacyanoferrate redox mediator for potential application as charge relay in dye-sensitized solar cells

A polynuclear electronically/ionically (redox) conducting mixed-valent inorganic material such as nickel(II) hexacyanoferrate(II,III), NiHCF, was considered for potential application as a redox mediator (charge relay) in dye-sensitized solar cell (DSSC). The NiHCF redox reactions were found fast and reversible not only when the system was studied as thin film exposed to an aqueous supporting electrolyte but also as bulk material (pasted powder) in solid state, i.e., in the absence of contact with external liquid electrolyte phase. Usefulness of NiHCF material was diagnosed using conventional electroanalytical approaches, solid-state voltammetric methodology, as well as the dynamic electrochemical impedance spectroscopy technique that permitted monitoring of impedance spectra under potentiodynamic conditions. The material was utilized in a mixed-valent state, i.e., as a mixture of K₄Ni^II[Fe^II(CN)₆] and K₃Ni^II[Fe^III(CN)₆] in which iron(II) and iron(III) sites were at the 1:1 ratio. Under such conditions, dynamics of electron-hopping between mixed-valent iron sites was maximized. Our DSSC utilized cis–dithiocyanoatobis(4,4′-dicarboxylic acid-2,2′-bipyridine) ruthenium(II) dye (N3) adsorbed onto TiO₂ semiconductor and NiHCF as redox mediator. Although performance of our DSSC was not optimized in terms of the NiHCF film thickness and morphology, as well as lower photocurrents in comparison to those characteristic of the iodine/iodide based DSSC were obtained, our system yielded readily fairly high open-circuit photovoltages on the level of 800 mV. An important issue was that the formal potential of NiHCF was more positive relative to the potential of the iodide/triiodide couple while being still more negative than that equivalent to the ground state of the N3 dye. Thus, NiHCF mediator was able to regenerate the dye.

     

Kinetic studies on pH controlled partial dechelation of the trans-imidazole-[Cr(His)2]+ cation

Partial dechelation of one tridentate N,N??,O-histidine in trans-imidazole-[Cr(His)₂]⁺ (where N and N?? are amine and imidazole nitrogen atoms, respectively, and O is carboxylate oxygen) has been studied. The aquation process is both acid and base catalyzed and the product with didentate His is converted back into the substrate at pH 4?C7. Kinetics of the chelate ring opening were studied spectrophotometrically within the 0.01?C1.0?M HClO₄ and 0.1?C1.0?M NaOH ranges under first-order conditions. The following dependences of k _obs on [H⁺] and [OH^?] were determined: $$ \left( {k_{\text{obs}} } \right)_{\text{H}} = a + b\left[ {{\text{H}}^{ + } } \right] + c/\left[ {{\text{H}}^{ + } } \right] $$ $$ \left( {k_{\text{obs}} } \right)_{\text{OH}} = a^{\prime } + b^{\prime } \left[ {{\text{OH}}^{ - } } \right]. $$ Mechanisms of the chelate ring opening in acidic and alkaline media are proposed, and activation parameters for the process in acidic solution have been determined. Additionally, kinetic studies were performed on the second dechelation stage in acidic media, which is ca. 15 times slower than the first one.     

Convergence of dip-pen nanolithography and acoustic biosensors towards a rapid-analysis multi-sample microsystem

The present work demonstrates for the first time patterning of a ready-to-use biosensor with several different biomolecules using Dip-Pen Nanolithography (DPN) for the development of a procedure towards more rapid and efficient multi-sample detection. The biosensor platform used is based on a Surface Acoustic Wave (SAW) device integrated with a parallel-channel microfluidic module, termed as "microfluidics-on-SAW" ("μF-on-SAW"), for reproducible multi-sample analysis. Lipids with different functionalized head groups were patterned at distinct, microfluidic-formed rectangular domains with sharp edges all located on the same sensor surface; pattern quality was verified using a fluorescent microscope. The functionality of the head groups, the efficiency of the patterning method, and the suitability of DPN for the surface modification of the acoustic device were subsequently examined through acoustic experiments. The μF-on-SAW configuration was used to detect specific binding between the pre-patterned functionalized lipids with their corresponding biomolecules. The achievement of an improved sensitivity (5-fold compared to previous acoustic configurations) and reduced preparation time by at least 2 h clearly indicates the suitability of DPN as a direct patterning method for ready-to-use acoustic sensor devices like the μF-on-SAW towards integrated, rapid-analysis, multi-sample biosensing microsystem development.