Antidiabetic Drug Metformin Oxidation and in situ Interaction with dsDNA Using a dsDNA‐electrochemical Biosensor

The antidiabetic drug metformin (MET) is one of a group of emerging pharmaceutical drug contaminants in the wastewater treatment plants. The electrochemical behaviour of MET?Cu(II) complex by differential pulse and square wave voltammetry, in a wide pH range, at a glassy carbon electrode modified with a carbon black dihexadecylphosphate film (CB?DHP/GCE), was investigated. The MET?Cu(II) complex oxidation showed one pH‐dependent process, which leads to the formation of an oxidation product, being oxidized at a lower potential. The electroanalytical MET?Cu(II) complex detection limit, LOD=0.63 μM, and quantification limit, LOQ=2.09 μM, were obtained, and the MET?Cu(II) complex determination in wastewater samples collected from a senior residence effluent, using the CB?DHP/GCE, was achieved. Considering MET toxicity, the electrochemical evaluation of MET?dsDNA interaction, in incubated solutions and using dsDNA‐electrochemical biosensors, following the changes in the oxidation peaks of guanosine and adenosine residues electrochemical currents, was also investigated. The MET?dsDNA interaction mechanism, for shorter times, occurs by the binding of MET molecules in the minor grooves of the dsDNA, and for long times, the stabilization of the MET?dsDNA complex, causing a local distortion and/or unwinding of dsDNA morphology, is described. However, MET did not promote DNA oxidative damage.     

聚四氨基酞菁铜微型传感器及其在一氧化氮测定中的应用

利用电化学聚合的方法制备了聚四氨基酞菁酮微型传感器，并探讨了微型传感器对一氧化氮（ＮＯ）的电化学响应。结果表明，电化学聚合Ｃｕ（ＴＡＰｃ）微型传感器对ＮＯ具有良好的催化氧化作用。     

An All‐solid‐state Polymeric Membrane Ca2+‐selective Electrode Based on Hydrophobic Alkyl‐chain‐functionalized Graphene Oxide

An all‐solid‐state polymeric membrane Ca²⁺‐selective electrode based on hydrophobic octadecylamine‐functionalized graphene oxide has been developed. The hydrophobic composite in the ion‐selective membrane not only acts as a transduction element to improve the potential stability for the all‐solid‐state Ca²⁺‐selective electrode, but also is used to immobilize Ca²⁺ ionophore with lipophilic side chains through hydrophobic interactions. The developed all‐solid‐state Ca²⁺‐selective electrode shows a stable potential response in the linear range of 3.0×10⁻⁷–1.0×10⁻³ M with a slope of 24.7±0.3 mV/dec, and the detection limit is (1.6±0.2 )×10⁻⁷ M (n =3). Additionally, due to the hydrophobicity and electrical conductivity of the composite, the proposed all‐solid‐state ion‐selective electrode exhibits an improved stability with the absence of water layer between the ion‐selective membrane and the underlying glassy carbon electrode. This work provides a simple, efficient and low‐cost methodology for developing stable and robust all‐solid‐state ion‐selective electrode with ionophore immobilization.     

All‐in‐one solid‐phase microextraction: Development of a selective solid‐phase microextraction fiber assembly for the simultaneous and efficient extraction of analytes with different polarities

In the present work, for the first time, an all‐in‐one solid‐phase microextraction technique was developed for the simultaneous and efficient extraction of analytes within a vast polarity range. A novel fiber assembly composed of two different steel components each coated with different coatings (polydimethylsiloxane and polyethylene glycol) in terms of polarity by sol–gel technology was employed for the extraction of model compounds of different polarity in a single run followed by gas chromatography with mass spectrometry. Effective parameters in the extraction step and gas chromatography with mass spectrometry analysis were optimized for all model compounds. The detection limits of the developed method for model compounds were below 0.2 ng/L. The repeatability and reproducibility of the proposed method, explained by relative standard deviation, varied between 7.22 and 9.15% and between 7.95 and 14.90 (n = 5), respectively. Results showed that, under random conditions, compared to separate extractions performed by two other differently end‐coated components that had not been assembled as the final dual fiber, as two individual fibers; simultaneous, efficient and relatively selective extraction of all model compounds was obtained in a single run by the proposed all‐in‐one technique. Finally, the optimized procedure was applied to extraction and determination of the model compounds in spiked water samples.     

Fabrication of solid‐state nanopores and its perspectives

Nanofluidics is becoming an extensively developing technique in the field of bioanalytical chemistry. Nanoscale hole embed in an insulating membrane is employed in a vast variety of sensing platforms and applications. Although, biological nanopores have several attractive characteristics, in this paper, we focused on the solid‐state nanopores due to their advantages as high stability, possibility of diameter control, and ease of surface functionalizing. A detection method, based on the translocation of analyzed molecules through nanochannels under applied voltage bias and resistive pulse sensing, is well established. Nevertheless, it seems that the new detection methods like measuring of transverse electron tunneling using nanogap electrodes or optical detection can offer significant additional advantages. The aim of this review is not to cite all related articles, but highlight the steps, which in our opinion, meant important progresses in solid‐state nanopore analysis.     

Simulation of solid‐state polycondensation of nylon‐66

A new model of solid‐state polymerization of nylon‐6,6 has been developed. The polymer crystalline fraction is assumed to consist of only repeat units, leaving end‐groups and condensate in the amorphous fraction. Many effects neglected by previous models are considered, such as variable crystallinity, initial moisture and starting molecular weight. This model is compared to experimental data with good agreements. Differential scanning calorimetry graphs show that the crystalline structure phase tends to be increasingly perfect during heat treatment, indicative of the premelting temperature drawing near the melting point up to 14 °C after solid‐state polycondensation with little change of melting point. Copyright © 2000 John Wiley & Sons, Ltd.     

Metal Enhanced Electrochemical Cyclooxygenase‐2 (COX‐2) Sensor for Biological Applications

Pain measurement is commonly required in biomedical and other emergency situations, yet there has been no pain biosensor reported in literature. Conventional approaches for pain measurement relies on Wong‐Baker face diagrams, which are grossly inadequate for situations involving children or unconscious people. We report a label‐free immunosensor for monitoring the pain biomarker cylooxygenase‐2 (COX‐2) in blood. The sensor is based on the concept of metal‐enhanced detection (MED). MED relies on the idea that the immobilization of underpotential deposition (upd) metallic films deposited either as a monolayer or electrostatically held onto a solid gold substrate could significantly amplify bimolecular recognition such as involving antigen‐antibody (Ab‐Ag) interactions. The surface bound Ab‐Ag complex insulates the electrode; causing a decrease in concentration‐dependent redox signals. A linear detection range of (3.64–3640.00)×10^?4 ng/mL was recorded with a detection limit of 0.25×10^?4 ng/mL, which was 4 orders of magnitude lower than that reported for ELISA for the same biomarker. The immunosensor exhibited selectivity of less than 6 % for potential interferents.     

Electrochemical Characteristics of 4‐oxo‐4H‐pyran‐dicarboxylic Acid (Chelidonic Acid) and some of its Metal Complexes

A few novel metal complexes of chelidonic acid (chelH₂), namely [Ca(chel)(H₂O)₃] ( 1 ), [Cu(chel)(H₂O)₅] ⋅ 2H₂O ( 2 ) and [VO(chel)(H₂O)₃] ⋅ 2H₂O ( 3 ) were prepared, identified by elemental analysis and characterized by electrochemical methods. IR‐spectra and thermal stability in solid state are discussed as well. The electrochemical characteristics of the free chelidonic acid and its complexes 1 – 3 were studied by (cyclic) square‐wave voltammetry, on static mercury drop electrode (SMDE) and paraffin‐impregnated graphite electrode (PIGE), in aqueous media over a wide pH range. The reduction of chelidonic acid on SMDE is a kinetically controlled electrode reaction, occurring with the transfer of one electron and two protons for 1<pH<6, whereas in very alkaline media the electron transfer is pH independent, i.e . the mechanism of electro‐reduction of chelH₂ is proposed. The experimental parameters of the electroanalytical procedure were optimized and the method was applied for the investigation of the metal ion coordination preferences toward chelidonic acid. For the direct determination of solid complexes 1 – 3 , SW voltammetry of microparticles was used.     

Electrochemical Determination of Sulphur‐containing Pharmaceuticals Using Boron‐doped Diamond Electrodes

N‐acetylcysteine (NAC) and gentamicin sulfate (GS) are biologically and pharmaceutically relevant thiol‐containing compounds. NAC is well known for its antioxidant properties, whereas GS is an aminoglycoside that is used as a broadband antibiotic. Both pharmaceuticals play a significant role in the treatment of bacterial infections by suppressing the formation of biofilms. According to the European Pharmacopeia protocol, GS is analyzed by high performance liquid chromatography (HPLC) using gold electrodes for electrochemical detection. Here, we report the electrochemical detection of these compounds at NH₂‐terminated boron‐doped diamond electrodes, which show significantly reduced electrode passivation, an issue commonly known for gold electrodes. Cyclic voltammetry experiments performed for a period of 70 minutes showed that the peak current decreased only by 1.6 %/7.4 % for the two peak currents recorded for GS, and 6.6 % for the oxidation peak of NAC, whereas at gold electrodes a decrease in peak current of 14.2 % was observed for GS, and of 64 %/30 % for the two peak currents of NAC. For their quantitative determination, differential pulse voltammetry was performed in a concentration range of 2–49 µg/mL of NAC with a limit of detection (LOD) of 1.527 µg/mL, and a limit of quantification (LOQ) of 3.624 µg/mL, respectively. The quantification of GS in a concentration range of 0.2–50 µg/mL resulted in a LOD of 1.714 µg/mL, and a LOQ of 6.420 µg/mL, respectively.     

Synthesis and Characterization of Bismuth-Silver Nanoparticles for Electrochemical Sensor Applications

Silver, bismuth, and bismuth-silver nanoparticles were synthesized and characterized by cyclic voltammetry, electrochemical impedance spectroscopy, ultraviolet-visible spectroscopy, infrared spectroscopy, Raman spectroscopy, and transmission electron microscopy to determine the electrochemical, optical, structural, and morphological properties of the nanomaterials. The silver, bismuth, and bismuth-silver nanoparticles were shown to have an average particle size of 10–30 nanometers by microscopy. The electrochemical results showed that the bismuth-silver nanoparticles exhibited good electrocatalytic activity that can be harnessed for sensor construction and related applications. The ultraviolet-visible, infrared, and Raman spectroscopy results confirmed the structural properties of the bismuth-silver nanoparticles. In addition, the microscopy and electron diffraction morphological characterization confirmed the nature of the bismuth-silver nanoparticles.     

A microwave‐assisted solid‐state synthesis and characterization of diheterocyclic thioureas

In this study, a number of new diheterocyclic thioureas have been synthesized under microwave irradiation coupled with solvent‐free condition, which proves to be simple and efficient. The structures of the prepared compounds are characterized by elemental analysis, IR, ¹H NMR, and ¹³C NMR spectra. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:148–151, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20193     

Comparative Electrochemical and Spectroscopic Studies of I‐Motif‐forming DNA Nonamers

The paper shows the structural diversity of cytosine (C)‐rich oligodeoxynucleotides (ODNs) arising from their detail nucleotide sequence and experimental conditions. In slightly acidic solutions, the ODN nonamers with different adenine (A) and cytosine (C) sequences can adopt non‐canonical structures involving protonated bases. A distinct secondary structure formed in (C)‐rich sequences, called i‐motif (iM), consists of hemiprotonated and intercalated cytosine base pairs (C.C⁺). Folding and unfolding of particular structures in solutions were monitored by ¹H NMR and CD spectroscopies and native polyacrylamide gel electrophoresis (PAGE), which are capable to determine their structural characteristics. Effects of sequences and their proclivity to formation of the iM on electrochemical behaviour of the ODN nonamers were studied by electrochemical methods. The LSV signals of A and C obtained from the reductive dissolution of ODN adsorption layers on a hanging mercury drop electrode were processed by elimination voltammetry with linear scan (EVLS), which revealed complex effects of the nonamer properties (namely their primary and secondary structure confirmed in solution) on their adsorption and reduction activity.     

Electrochemical and Spectroelectrochemical Analysis of 4‐(4‐(5‐Phenyl‐1,3,4‐oxadiazole‐2‐yl)phenoxy)‐Substituted Cobalt(II), Lead(II) and Metal‐Free Phthalocyanines

Electrochemical and spectroelectrochemical analyses of 4‐(4‐(5‐phenyl‐1,3,4‐oxadiazole‐2‐yl)phenoxy)‐substituted metal‐free phthalocyanine ( H₂Pc ( 1 )) and metallated phthalocyanines ( PbPc ( 2 ) and CoPc ( 3 )) were performed in solution. Voltammetric characterizations of the phthalocyanine complexes were investigated by using cyclic voltammetry and square wave voltammetry techniques. CoPc ( 3 ) gave common metal and ring based electron transfer reactions; however they split due to the aggregation. Although PbPc ( 2 ) illustrated reversible reduction processes during the voltammetric measurements, it was de‐metallized and thus turned to the metal free phthalocyanine during repetitive voltammetric cycles and in situ spectroelectrochemical measurements.     

Synthesis of Cysteine Modified MoS2 Nanocomposite: A Biocompatible Electrochemical Sensor Material and its Application to the Determination of Antidiabetic Dapagliflozin

Herein, for the first time, a new generation cysteine modified MoS₂ (Cys@MoS₂) based electrochemical sensor was reported. The electrochemical behaviour of dapagliflozin (DAP) was investigated through differential pulse voltammetry (DPV) on the developed sensor (Cys@MoS₂/GCE). The transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FTIR), x‐ray diffraction spectroscopy (XRD) and x‐ray photoelectron spectroscopy (XPS) methods were performed for structural and morphological characterizations of Cys@MoS₂ nanocomposite. On the surface of Cys@MoS₂/GCE, an irreversible anodic peak was observed at 1324 mV. Under the optimal conditions, linear calibration curve with two working ranges between 2.0–60.0 μM and 60.0–110.0 μM were obtained and limit of detection was found to be 1.6 μM. The developed sensor was successfully applied to determine the content of DAP in pharmaceutical sample with satisfying recovery results. It is concluded that Cys@MoS₂/GCE is a reliable, easy to apply and cost‐effective sensor for the routine DAP analysis in pharmaceutical samples.     

Detection of structured single‐strand DNA via solid‐state nanopore

Nanopore is a single‐molecule analysis method which also employed electrophoresis has achieved promising single‐molecule detections. In this study, we designed two kinds of confined spaces by fabricating solid‐state nanopores with desirable diameters to study the structured single‐strand DNA of C‐rich quadruplex. For the nanopore whose diameter is larger than the quadruplex size, the DNA molecule could directly translocate through the nanopore with extremely high speed. For the nanopore whose diameter is smaller than the quadruplex size, DNA molecule which is captured by nanopore could return to the solution without translocation or unzip the quadruplex structure into single‐strand and then pass the nanopore. This study certifies that choosing a suitable sensing interface is the vital importance of observing detailed single‐molecule information. The solid‐state nanopores hold the great potential to study the structural dynamics of quadruplex DNA molecule.     

Multidimensional solid‐state NMR of structure and dynamics of polymers

New developments in high‐resolution multidimensional NMR of solids are described. Special emphasis is placed on double‐quantum (DQ) methods employing fast magic angle spinning (MAS). This new technique allows structural elucidation with atomistic resolution including hydrogen positions in non‐crystalline materials and the determination of the anisotropy of chain motions by probing residual dipolar couplings between adjacent groups along a macromolecule. Specific examples include hydrogen bonded systems, columnar structures with π‐π interactions, polymer melts and block copolymers.     

The antitumour drug 7‐ethyl‐10‐hydroxycamptothecin monohydrate and its solid‐state hydrolysis mechanism on heating

7‐Ethyl‐10‐hydroxycamptothecin [systematic name: (4S)‐4,11‐diethyl‐4,9‐dihydroxy‐1H‐pyrano[3′,4′:6,7]indolizino[1,2‐b]quinoline‐3,14(4H,12H)‐dione, SN‐38] is an antitumour drug which exerts activity through the inhibition of topoisomerase I. The crystal structure of SN‐38 as the monohydrate, C₂₂H₂₀N₂O₅·H₂O, reveals that it is a monoclinic crystal, with one SN‐38 molecule and one water molecule in the asymmetric unit. When the crystal is heated to 473 K, approximately 30% of SN‐38 is hydrolyzed at its lactone ring, resulting in the formation of the inactive carboxylate form. The molecular arrangement around the water molecule and the lactone ring of SN‐38 in the crystal structure suggests that SN‐38 is hydrolyzed by the water molecule at (x, y, z) nucleophilically attacking the carbonyl C atom of the lactone ring at (x − 1, y, z − 1). Hydrogen bonding around the water molecules and the lactone ring appears to promote this hydrolysis reaction: two carbonyl O atoms, which are hydrogen bonded as hydrogen‐bond acceptors to the water molecule at (x, y, z), might enhance the nucleophilicity of this water molecule, while the water molecule at (−x, y + , −z), which is hydrogen bonded as a hydrogen‐bond donor to the carbonyl O atom at (x − 1, y, z − 1), might enhance the electrophilicity of the carbonyl C atom.     

Electrochemical Oxidation of Desipramine Drug in the Presence of 4,6‐Dimethylpyrimidine‐2‐thiol Nucleophile in Aqueous Acidic Medium

Electrochemical oxidation of desipramine (DES) has been studied in the presence of 4,6‐dimethylpyrimidine‐2‐thiol (DMPT) as nucleophile in acidic medium by means of cyclic voltammetry, controlled‐potential electrolysis and spectroscopic data, as diagnostic techniques. Voltammetric studies of electro‐oxidation of desipramine were realized in a range of pH 1.0 to 8.0 in the absence and presence of DMPT. The results indicate the participation of the product of electrochemical oxidation of desipramine in the reaction with DMPT with ECEC electrochemical mechanism. However, the voltammetry and coulometry results imply existence of a catalytic (EC′) electrochemical mechanism in parallel with ECEC electrochemical mechanism. The product has been characterized by IR, ¹H NMR, ¹³C NMR and MS methods.     

Superdrawing of polytetrafluoroethylene nascent powder by solid‐state coextrusion

A film of nascent powder of polytetrafluoroethylene (PTFE), compacted below the ambient melting temperature (T_m, 335 °C), was drawn by two‐stage draw techniques consisting of a first‐stage solid‐state coextrusion followed by a second‐stage solid‐state coextrusion or tensile draw. Although the ductility of extrudates was lost for the second‐stage tensile draw at temperatures above 150 °C due to the rapid decrease in strength, as previously reported, the ductility of extrudates increased with temperature even above 150 °C when the second‐stage draw was made by solid‐state coextrusion, reflecting the different deformation flow fields in a free space for the former and in an extrusion die for the latter. Thus, a powder film initially coextruded to a low extrusion draw ratio (EDR) of 6–20 at 325 °C was further drawn by coextrusion to EDRs up to ～?400 at 325–340 °C, near the T_m. Extremely high chain orientation (f_c = 0.998 ± 0.001), crystallinity (96.5 ± 0.5)%, and tensile modulus (115 ± 5 GPa at 24 °C, corresponding to 73% of the X‐ray crystal modulus) were achieved at high EDRs. Despite such a morphological perfection and a high modulus, the tensile strength of a superdrawn tape, 0.48 ± 0.03 GPa, was significantly low when compared with those (1.4–2.3 GPa) previously reported by tensile drawing above the T_m. Such a low strength of a superdrawn, high‐modulus PTFE tape was ascribed to the low intermolecular interaction of PTFE and the lack of intercrystalline links along the fiber axis, reflecting the initial chain‐extended morphology of the nascent powder combined with the fairly high chain mobility associated with the crystal/crystal transitions at around room temperature. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3369–3377, 2006     

Heat capacity of solid‐state biopolymers by thermal analysis

Heat capacities in the solid state of four globular proteins (bovine β‐lactoglobulin, chicken lysozyme, ovalbumine, and horse myoglobin) and of the poly(amino acid) poly(L ‐tryptophan) have been determined using the Advanced THermal Analysis System (ATHAS). The experimental measurements were performed with adiabatic and differential scanning calorimetry over wide temperature ranges. The heat capacities were linked to an approximate vibrational spectrum by making use of known group vibrations and of a set of parameters, Θ₁ and Θ₃, of the Tarasov function for the skeletal vibrations. Good agreement was found between experiments and calculations with root mean square errors mostly within ±3%. The experimental data were analyzed also with an empirical addition scheme using the known data for poly(amino acid)s measured earlier. Based on this study, vibrational heat capacities can now be predicted for all proteins with an accuracy comparable to common experiments. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2093–2102, 1999