Highly Sensitive Determination of Tenofovir in Pharmaceutical Formulations and Patients Urine—Comparative Electroanalytical Studies Using Different Sensing Methods

This paper discusses the electrochemical behavior of antiviral drug Tenofovir (TFV) and its possible applicability towards electroanalytical determination with diverse detection strategies using square-wave voltammetry. Namely, oxidation processes were investigated using glassy carbon electrode with graphene oxide surface modification (GO/GCE), while the reduction processes, related to the studied analyte, were analyzed at a renewable silver amalgam electrode (Hg(Ag)FE). Scanning electron microscopy imaging confirmed the successful deposition of GO at the electrode surface. Catalytic properties of graphene oxide were exposed while being compared with those of bare GCE. The resultant modification of GCE with GO enhanced the electroactive surface area by 50% in comparison to the bare one. At both electrodes, i.e., GO/GCE and Hg(Ag)FE, the TFV response was used to examine and optimize the influence of square-wave excitation parameters, i.e., square wave frequency, step potential and amplitude, and supporting electrolyte composition and its pH. Broad selectivity studies were performed with miscellaneous interfering agents influence, including ascorbic acid, selected saccharides and aminoacids, metal ions, non-opioid analgesic metamizole, non-steroidal anti-inflammatory drug omeprazole, and several drugs used along with TFV treatment. The linear concentration range for TFV determination at GO/GCE and Hg(Ag)FE was found to be 0.3–30.0 µmol L^–1 and 0.5–7.0 µmol L^–1, respectively. The lowest LOD was calculated for GO/GCE and was equal to 48.6 nmol L^–1. The developed procedure was used to detect TFV in pharmaceutical formulations and patient urine samples and has referenced utilization in HPLC studies.     

Linagliptin,a Selective Dipeptidyl Peptidase-4 Inhibitor,Reduces Physical and Behavioral Effects of Morphine Withdrawal

(1) Background: Recent data indicate that receptors for GLP-1 peptide are involved in the activity of the mesolimbic system. Thus, the purpose of the present study was to examine the effect of the selective dipeptidyl peptidase-4 (DPP-4) inhibitor, linagliptin, on morphine dependence in mice. (2) Methods: Morphine dependence in mice was obtained by administration of increasing doses of morphine for eight consecutive days, twice a day. On the 9th day of the experiment, the naloxone-induced (2 mg/kg, ip) morphine withdrawal signs (jumping) were assessed. Moreover, behavioral effects of short-term (60 h after morphine discontinuation) and long-term (14 days after morphine discontinuation) morphine withdrawal were observed. In terms of behavioral effects, the depressive effect in the forced swim test and anxiety in the elevated plus maze test were investigated. Locomotor activity of mice was also studied. (3) Results: The administration of linagliptin (10 and 20 mg/kg, ip) for 8 consecutive days before morphine injections significantly diminished the number of naloxone-induced morphine withdrawal signs (jumping) in mice. In addition, the cessation of morphine administration induced depressive behavior in mice which were observed during short- and long-term morphine withdrawal. Linagliptin administered during morphine withdrawal significantly reduced the depressive behavior in studied mice. Furthermore, the short-term morphine withdrawal evoked anxiety which also was reduced by linagliptin in mice. (4) Conclusions: The present study reveals that GLP-1 receptors are involved in morphine dependence. What is more, linagliptin might be a valuable drug in attenuating the physical symptoms of morphine dependence. It might be also a useful drug in reducing emotional disturbances which may develop during the morphine withdrawal period.     

The Impact of Crystal Packing and Aurophilic Interactions on the Luminescence Properties in Polymorphs and Solvate of Aroylacetylide–Gold(I) Complexes

The influence of the chemical substitution, crystal packing, and aurophilic interactions of the gold(I) acetylide complexes of the type (ArCOC≡C)_nAuPEt₃ (n=1,2) on their luminescent properties were examined. All described complexes undergo ligand scrambling in solution, which results in the formation of stable, easily isolated crystals that contain [ArCO(C≡C)_n]₂Au⁻(Et₃P)₂Au⁺ homoleptic species. In particular, we observed that the (benzoylacetylide)gold(I) complex yields three crystal forms with strikingly different luminescence properties. We monitored the conversion pathway for these forms: an orange luminescent form of homoleptic complex upon drying undergoes spontaneous transformation to bright green fluorescent form and finally to the weakly blue emissive one. In addition, we report a rare example of a helical arrangement of Au⋅Au⋅Au chains that are observed for the first time in acetylide gold(I) complexes in the case of heteroleptic (benzoylacetylide)gold(I) complex. This is a very rare case in which crystal structures and ensuing electronic properties of the heteroleptic and Au^I complexes could be directly compared.     

Acidic Monosaccharides become Incorporated into Calcite Single Crystals**

Carbohydrates, along with proteins and peptides, are known to represent a major class of biomacromolecules involved in calcium carbonate biomineralization. However, in spite of multiple physical and biochemical characterizations, the explicit role of saccharide macromolecules (long chains of carbohydrate molecules) in mineral deposition is not yet understood. In this study, we investigated the influence of two common acidic monosaccharides (MSs), the two simplest forms of acidic carbohydrates, namely glucuronic and galacturonic acids, on the formation of calcite crystals in vitro. We show here that the size, morphology, and microstructure of calcite crystals are altered when they are grown in the presence of these MSs. More importantly, these MSs were found to become incorporated into the calcite crystalline lattice and induce anisotropic lattice distortions, a phenomenon widely studied for other biomolecules related to CaCO₃ biomineralization, but never before reported in the case of single MSs. Changes in the calcite lattice induced by MSs incorporation were precisely determined by high-resolution synchrotron powder X-ray diffraction. We believe that the results of this research may deepen our understanding of the interaction of saccharide polymers with an inorganic host and shed light on the implications of carbohydrates for biomineralization processes.     

Functionalization of parylene during its chemical vapor deposition

Two possible mechanisms for the reaction of four halogenated (metha)acrylate‐based molecules with Parylene [poly (paraxylylene)] during its chemical vapor deposition were proposed. The chemical reactivity of acrylate double bond with the paraxylylene biradical was calculated for all four (metha)acrylate‐based molecules. These calculations allowed the evaluation of the energetically favorable mechanism and indeed a direct correlation was found between both predicted and experimental reactivities. Next, the reactivity of the (metha)acrylate‐modified Parylene films was evaluated through their reaction with different amines. The obtained amidated Parylene films were characterized with X‐ray photoelectron spectroscopy, Kaiser test for primary amines, and fluorescence microscopy. The strong reactivity of (metha)acrylate‐modified Parylene films toward nucleophilic substitution emphasizes a general method for the functionalization of self‐supported Parylene films grown on the reacting solutions using the novel solid on liquid deposition process. This paves the way to the development of multifunctional materials in a one‐step process resulting from the deposition Parylene over liquid patterns. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Star‐Shaped Conjugated Molecules with Oxa‐ or Thiadiazole Bithiophene Side Arms

Star‐shaped conjugated molecules, consisting of a benzene central unit symmetrically trisubstituted with either oxa‐ or thiadiazole bithiophene groups, were synthesized as promising molecules and building blocks for application in (opto)electronics and electrochromic devices. Their optical (E_g(opt)) as well as electrochemical (E_g(electro)) band gaps depended on the type of the side arm and the number of solubilizing alkyl substituents. Oxadiazole derivatives showed E_g(opt) slightly below 3 eV and by 0.2 eV larger than those determined for thiadiazole‐based compounds. The presence of alkyl substituents in the arms additionally lowered the band gap. The obtained compounds were efficient electroluminophores in guest/host‐type light‐emitting diodes. They also showed a strong tendency to self‐organize in monolayers deposited on graphite, as evidenced by scanning tunneling microscopy. The structural studies by X‐ray scattering revealed the formation of supramolecular columnar stacks in which the molecules were organized. Differences in macroscopic alignment in the specimen indicated variations in the self‐assembly mechanism between the molecules. The compounds as trifunctional monomers were electrochemically polymerized to yield the corresponding polymer network. As shown by UV/Vis‐NIR spectroelectrochemical studies, these networks exhibited reversible electrochromic behavior both in the oxidation and in the reduction modes.     

Effective charge propagation and storage in hybrid films of tungsten oxide and poly(3,4-ethylenedioxythiophene)

Hybrid (composite) electroactive films consisting of such an organic conducting polymer as poly(3,4-ethylenedioxythiophene), PEDOT, and such a polynuclear inorganic compound as amorphous tungsten oxide, WO₃/H _x WO₃ were fabricated on carbon electrodes through electrodeposition by voltammetric potential in acid solution containing EDOT monomer and sodium tungstate. Electrostatic interactions between the negatively charged tungstic units (existing within WO₃) and the oxidized positively charged conductive polymer (oxidized PEDOT) sites create a robust hybrid structure which cannot be considered as a simple mixture of the organic and inorganic components. It is apparent from scanning electron microscopy that hybrid structures are granular but fairly dense. Because PEDOT and mixed-valence tungsten oxides are electronically conducting, the resulting hybrid films are capable of fast propagation. The reversible and fast redox reactions of tungsten oxide component lie in the potential range where PEDOT matrix is conductive. Furthermore, the hybrid films exhibit good mediating capabilities towards electron transfers between model redox couples such as cationic iron(III,II) and anionic hexacyanoferrate(III,II). Since the films accumulate effectively charge and show high current densities at electrochemical interfaces, they could be of importance to electrocatalysis and to construction of redox capacitors.     

Voltammetric Determination of Proguanil in Malarone and Spiked Urine with a Renewable Silver Amalgam Film Electrode

Electrochemical properties of proguanil were investigated by a voltammetric method (SWV) using a renewable silver amalgam film electrode. The influence of buffer pH as well as potential amplitude, frequency, and step potential was studied. The repeatability, precision and recovery of the developed method were examined. The reduction peak current was used for proguanil voltammetric determination in the range 1×10^?7–6×10^?6 mol L^?1, LOD=2.9×10^?8 mol L^?1, LOQ=9.7×10^?8 mol L^?1. The standard addition method was used to determine proguanil in a commercial formulation (Malarone) and in spiked urine.     

Renewable Silver Amalgam Film Electrode for the Determination of Dinotefuran in Spiked Carrot Juice Samples Using SW Voltammetry

The electrochemical properties of dinotefuran (DNF) were studied by SW voltammetry over the pH range 2.0–8.0 using a silver amalgam film electrode Hg(Ag)FE. The mechanism of electroreduction was analyzed. The dependence of the peak current on pH, buffer concentration, the nature of the buffer, amplitude, frequency, step potential and scan rate were investigated. The repeatability, precision and recovery of the developed method were checked. The detection and quantification limits were found to be 2.01×10^?7 and 6.71×10^?7 mol L^?1, respectively. The standard addition method was used to determine DNF in spiked carrot juice.