Proving the automatic benchtop electrochemical station for the development of dopamine and paracetamol sensors.

The introduced work represents an implementation of the automatic benchtop electrochemical station (BES) as an effective tool for the possibilities of high-throughput preparation of modified sensor/biosensors, speeding up the development of the analytical method, and automation of the analytical procedure for the determination of paracetamol (PAR) and dopamine (DOP) as target analytes. Within the preparation of gold nanoparticles modified screen-printed carbon electrode (AuNPs-SPCE) by electrodeposition, the deposition potential EDEP, the deposition time tDEP, and the concentration of HAuCl4 were optimized and their influence was monitored on 1 mM [Ru(NH3)6]3+/2+ redox probe and 50 µM DOP. The morphology of the AuNPs-SPCE prepared at various modification conditions was observed by SEM. The analytical performance of the AuNPs-SPCE prepared at different modification conditions was evaluated by a construction of the calibration curves of DOP and PAR. SPCE and AuNPs-SPCE at modification condition providing the best sensitivity to PAR and DOP, were successfully used to determine PAR and DOP in tap water by "spike-recovery" approach. The BES yields better reproducibility of the preparation of AuNPs-SPCE (RSD = 3.0%) in comparison with the case when AuNPs-SPCE was prepared manually by highly skilled laboratory operator (RSD = 7.0%).

Design of titanium nitride- and wolfram carbide-doped RGO/GC electrodes for determination of gallic acid.

In the present paper, the electrochemical behavior and the properties of two modified glassy carbon (GC) electrodes used for quantification of gallic acid in sweet wines were compared. A comparative study was conducted between titanium nitride- or wolfram carbide-doped reduced graphene oxide, labeled as TNrGO and WCrGO, respectively, modified GC electrodes, which are promising composite nanomaterials for electroanalytical applications. For the first time, WCrGO was synthesized and its electroanalytical properties compared with those of TNrGO. Results showed that the proposed materials exhibited enhanced characteristics, e.g., low limits of detection (1.1 µM and 3.1 µM for TNrGO and WCrGO, respectively), wide linear ranges (for TNrGO 4.5-76 µM and for WCrGO 10-100 µM), low adsorption, and low background current, which make them promising candidates for electrochemical sensing applications.

Novel quercetin derivatives in treatment of peroxynitrite-oxidized SERCA1.

Sarco/endoplasmic reticulum calcium ATP-ase (SERCA) is regulated by low concentrations of peroxynitrite and inhibited by high levels, as indicated in human diseases. We studied quercetin (Q) and its novel derivatives monochloropivaloylquercetin (MPQ) and chloronaphthoquinonequercetin (CHQ) as agents with expected preventive properties against peroxynitrite-induced SERCA impairment. Q and MPQ protected the SERCA1 against peroxynitrite induced activity decrease, while CHQ potentiated the inhibitory effect of peroxynitrite. Quercetin derivatives were found to be weaker antioxidants compared with Q, as indicated by their ability to scavenge peroxynitrite and prevent of SERCA1 carbonylation, both decreasing in the order (Q > MPQ > CHQ). Quantum-chemical values of theoretical parameter E HOMO also indicated lower antioxidant capacities for MPQ and CHQ. Prooxidant properties estimated by calculations of frontier molecular orbitals (E LUMO) correlated with experimentally determined SH-group decrease induced by the compounds studied. Both methods showed a decrease of prooxidant properties as follows: CHQ > MPQ > Q. In addition, experimentally measured half-wave potentials indicated stronger prooxidant properties of quercetin derivatives as compared to Q. More expressive alterations of conformation in the transmembrane region of SERCA1 induced by quercetin derivatives, as compared with Q, may at least partially correlate with their higher lipophilicities. The protective effects of Q and MPQ on different isoforms of SERCA activity may be useful in prevention and treatment of inflammation or muscle diseases. The inhibitory effect of CHQ on SERCA isoforms may be beneficial in therapeutic approaches aimed at anti-tumor treatment.

Synthesis, physicochemical properties and antimicrobial activity of mono-/dinitroxyl amides.

Two comparative sets of mono-/dinitroxyl amides were designed and prepared. The novel TEMPO and/or PROXYL derivatives were fully characterised and their spin, redox and antimicrobial properties were determined. Cyclic voltammetry revealed (quasi)reversible redox behavior for most of the studied radicals. Moreover, the electron-withdrawing substituents increased the oxidation potential of nitroxides in comparison to electron-donating groups. While EPR spectra of monoradicals featured the typical three-line signal, the spectra of biradicals showed more complex splitting patterns. The in vitro biological assay revealed that unlike pyrrolidinyl derivatives, the piperidinyl nitroxides significantly inhibited the growth of Staphylococcus sp.

Preparation and spectroscopic, magnetic, and electrochemical studies of mono-/biradical TEMPO derivatives.

A comparison set of mono-/biradical TEMPO derivatives was prepared, novel compounds were fully characterized, and their physicochemical properties were determined. Cyclic voltammetry revealed reversible redox behavior for all studied nitroxides. Moreover, the electron-withdrawing substituents increased the oxidation potential of the respective nitroxides in comparison to electron-donating groups. While EPR spectra of monoradicals in dichloromethane at 295 K reveal the expected three-line signal, spectra of biradicals show more complex features. DFT and MP2 calculations indicate that the EPR splitting pattern of dinitroxide 7 could be explained by its interactions with solvent molecules. In the solid state, mononitroxides 4 and 5 behave as a Heisenberg antiferromagnetic chain, whereas dinitroxides 6-8 are almost isolated paramagnetic diradicals coupled in an antiferromagnetic manner.

Induction of resistance in Mycobacterium smegmatis.

In this work, we assayed the ability of newly prepared indolizine derivates (epimers) 6C and 6A to inhibit the growth of Mycobacterium smegmatis and used them for resistance induction. 6A inhibited the growth of M. smegmatis at a concentration of 100 µg/mL. No inhibitory effect was observed in the presence of 6C. By incubating the bacteria with 6C and 6A, colonies resistant to 6A were observed. Finally, 37 stable resistant strains were isolated. These resistant strains were able to grow on a 5-fold higher concentration of 6A (500 µg/mL) than the minimal inhibitory concentration of the wild type (100 µg/mL), with no growth inhibition. Resistant strains were then tested for cross-resistance to other antibiotics: ampicillin, tetracycline, ciprofloxacin, chloramphenicol, gentamicin, and streptomycin. Determinations of resistance patterns to 6 antibiotics revealed 36 strains that were resistant to at least one drug.

Electrochemical flow injection approach for routine screening of lipase activity in pancreatic preparations.

A state-of-the-art strategy for the determination of lipase activity in pancreatic preparations using flow injection analysis (FIA) with electrochemical detection (FIA-ED) is described. The procedure is based on the enzymatic reaction of a specific substrate (1,3-dilinoleoyl-glycerol) with lipase from porcine pancreas and determination of enzymatically formed linoleic acid (LA) at +0.4 V by applying a cobalt (II) phthalocyanine-multiwalled carbon-nanotubes modified carbon paste electrode (Co(II)PC/MWCNT/CPE). In order to get a high-performance analytical method, sample preparation, flow system, and electrochemical conditions were optimized. Under optimized conditions the lipase activity of porcine pancreatic lipase was calculated to be 0.47 units per mg lipase protein based on the definition that 1 unit hydrolyses 1 microequivalent linoleic acid from 1,3-dilinoleoyl-glycerol per 1 min at pH 9 and 20 °C (kinetic measurement: 0-25 min). Moreover, the developed procedure was shown to be easily adaptable for the fixed-time assay (incubation time 25 min) as well. In this case, linear correlation between flow signal and lipase activity was found in the range from 0.8 to 18 U L-1. LOD and LOQ were determined to be 0.3 U L-1 and 1 U L-1, respectively. The kinetic assay was further preferred for the determination of lipase activity in commercially available pancreatic preparations. The lipase activities of all preparations obtained by the present method were found to be in good correlation with those obtained by the titrimetric method and declared by manufacturers.

(6S,7S,8S,8aS)-6-Ethyl-3-oxo-1,2,3,5,6,7,8,8a-octa-hydro-indolizine-7,8-diyl diacetate.

In the mol-ecular structure of the title compound, C(14)H(21)NO(5), the six-membered ring of the indolizine moiety adopts a chair conformation. There are two independent mol-ecules in the asymmetric unit. The oxopyrrolidine ring attached to the indolizine ring system is nearly planar, with mean deviations of 0.018 (3) and 0.010 (3) Šfor the two mol-ecules. The absolute configuration of the title compound was assigned from the synthesis.

(5S,11aS)-5-Hydro-per-oxy-1,5,11,11a-tetra-hydro-[1]benzothieno[3,2-f]indol-izin-3(2H)-one.

The absolute configuration of the title compound, C14H13NO3S, was assigned from the synthesis and confirmed by the structure determination. The central six-membered ring of the indolizine moiety adopts an envelope conformation, with the greatest deviation from the mean plane of the ring being 0.661 (2) Šfor the bridgehead C atom. The benzothiene ring attached to the indolizine ring system is planar to within 0.008 (2) Å. In the crystal, mol-ecules form chains parallel to the b axis via O-H⋯O hydrogen bonds.

(8aR,9R)-9-Hy-droxy-7,8,8a,9-tetra-hydro-furo[3,2-f]indolizin-6(4H)-one.

The title compound, C(10)H(11)NO(3), crystallizes with four independent mol-ecules in the asymmetric unit. Their geometries are very similar and corresponding bond distances are almost identical. The central six-membered ring of the indolizine moiety adopts a envelope conformation [the displacement of the flap atom (the C atom opposite the N atom) being 0.539 (2), 0.548 (3), 0.509 (3) and 0.544 (3) Šin the four molecules], while the conformation of the oxopyrrolidine ring is close to that of a flat envelope. The displacements of the non-fused C atom opposite the C=O group of the pyrrolidine ring of the four mol-ecules are 0.366 (3), 0.335 (3), 0.173 (3) and -0.310 (3) Å. In the crystal, O-H⋯O hydrogen bonds link the mol-ecules into chains, which run parallel to the c axis. The absolute configuration was assigned from the synthesis.

Batch injection analysis in tandem with electrochemical detection: the recent trends and an overview of the latest applications (2015-2020).

The purpose of the proposed review is to refer the contemporary capability of automated analytical systems, in particular batch injection analysis (BIA) in connection with electrochemical detection, for widespread applications in analytical chemistry. This combination recently represents an efficient tool for improvement of method parameters, such as speed, selectivity, and sampling rate for sensing of miscellaneous organic and inorganic substances. The review is focused on conception and usage of BIA in tandem with electrochemical detection utilizing various techniques, namely amperometry, voltammetry, and multiple pulse amperometry, as well as design of electrochemical cells constructed for BIA systems is discussed. Finally, this paper also summarizes the comprehensive overview of works published from 2015 to 2020 dealing with the electrochemical determination of different analytes by BIA in various matrices.

A Review on Recent Advances in the Applications of Boron-Doped Diamond Electrochemical Sensors in Food Analysis.

The usage of boron-doped diamond (BDD) material has found to be very attractive in modern electroanalytical methods and received massive consideration as perspective electrochemical sensor due to its outstanding (electro)chemical properties. These generally known facilities include large potential window, low background currents, ability to withstand extreme potentials and strong tendency to resist fouling compared to conventional carbon-based electrodes. As evidence of superiority of this material, couple of reviews describing the overview of various applications of BDD electrodes in the field of analytical and material chemistry has been reported in scientific literature during last decade. However, herein proposed review predominantly focuses on the most recent developments (from 2009 to 2020) dealing with the application of BDD as an advanced and environmental-friendly sensor platform in food analysis. The main method characteristics of analysis of various organic food components with different chemical properties, including additives, flavor and aroma components, phenolic compounds, flavonoids and pesticides in food matrices are described in more details. The importance of BDD surface termination, presence of sp2 content and boron doping level on electrochemical sensing is discussed. Apart from this, a special attention is paid to the evaluation of main analytical characteristics of the BDD electrochemical sensor in single- and multi-analyte detection mode in food analysis. The recent achievements in the utilizing of BDD electrodes in amperometric detection coupled to flow injection analysis, batch injection analysis, and high-performance liquid chromatography are also commented. Moreover, actual trends in sample preparation techniques prior to electrochemical sensing in food analysis are referred.

In vitro biological activity of copper(II) complexes with NSAIDs and nicotinamide: Characterization, DNA- and BSA-interaction study and anticancer activity.

Through the reaction of copper(II) acetate with nicotinamide (pyridine-3-carboxylic acid amide, niacinamide) and some derivatives of N-phenylanthranilic acid (fenamates), seven new mixed-ligand copper(II) compounds were isolated: [Cu(tolf-O)(tolf-O,O')nia-N)2(EtOH)] (1), [Cu(tolf-O)(tolf-O,O')(nia-N)2(MeOH)] (2), [Cu(meclf-O)(meclf-O,O')(nia-N)2(EtOH)] (3), [Cu(meclf-O)(meclf-O,O')(nia-N)2(MeOH)] (4), [Cu(meclf-O)(meclf-O,O')(nia-N)2(ACN)] (5), [Cu(mef-O)(mef-O,O')(nia-N)2(EtOH)] (6) and [Cu(mef-O)(mef-O,O')(nia-N)2(ACN)] (7) containing a molecule of relevant solvent as ligand in their primary crystal structure (tolf = tolfenamate, meclf = meclofenamate, mef = mefenamate, nia = nicotinamide, EtOH = ethanol, MeOH = methanol, ACN = acetonitrile). The structures of the complexes were determined by single-crystal X-ray analysis. The intermolecular interactions were studied by Hirshfeld surface analysis. The complexes were characterized by IR, UV-vis and EPR spectroscopy and their redox properties were determined by cyclic voltammetry. The interaction of the complexes with bovine serum albumin was studied by fluorescence emission spectroscopy and the albumin-binding constants of the compounds were calculated. The interaction of the complexes with calf-thymus DNA was monitored by diverse techniques (UV-vis spectroscopy, cyclic voltammetry, viscosity measurements) suggesting intercalation as the most possible mode of binding. DNA-competitive studies of the complexes with ethidium bromide were monitored by fluorescence emission spectroscopy. The cytotoxic effects of copper(II) complexes on lung carcinoma cells and healthy cells were determined by the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] colorimetric technique.

(8aRS)-8,8a-Dihydro-furo[3,2-f]indolizine-6,9(4H,7H)-dione.

The title compound, C(10)H(9)NO(3), is a chiral mol-ecule with one stereogenic carbon atom, but which crystallizes as a racemate in the centrosymmetric space group P2(1)/n. The central six-membered ring of the indolizine moiety adopts a definite envelope conformation, while the conformation of the oxopyrrolidine ring is close to that of a flat-envelope with a maximum deviation of 0.352 (1) Šfor the flap atom.

(4R,6S,7S,8S,8aS)-6-Ethyl-7,8-dihy-droxy-4-methyl-1,2,3,5,6,7,8,8a-octa-hydro-indolizin-4-ium iodide.

The title compound, C(11)H(22)NO(2) (+)·I(-), is a chiral mol-ecule with five stereogenic centres. The absolute configuration was assigned from the synthesis and confirmed by the structure determination. The central six-membered ring of the indolizine system adopts a chair conformation, with two atoms displaced by -0.690 (2) and 0.550 (2) Šfrom the plane of the other four atoms. The conformation of the pyrrolidine ring is close to that of an envelope, with the flap atom displaced by 0.563 (2) Šfrom the plane of the remaining four atoms. In the crystal, there are two O-H⋯I hydrogen bonds.

Polyradical PROXYL/TEMPO Conjugates Connected by Ester/Amide Bridges: Synthesis, Physicochemical Studies, and DFT Calculations.

A series of di-/trinitroxide esters and amides featuring PROXYL and/or TEMPO radicals connected with alicyclic bridges were prepared in 61-92 % yields and their properties were analysed by using multiple experimental techniques. The examination of EPR spectra of radicals in organic solvents augmented with DFT calculations brought valuable information on the conformational dynamics and spin exchange mechanisms. Cyclic voltammetry investigations revealed (quasi)reversible electrochemical behaviour of studied nitroxides with their half-wave potentials ranging from -51 to -17 mV. SQUID measurements of selected radicals revealed that the magnetism of di- and trinitroxides is significantly different, since antiferromagnetic coupling in biradicals is notably larger than in triradicals. The single-crystal X-ray analysis of selected biradicals revealed the existence of 3D supramolecular networks of molecules linked through hydrogen-bonding interactions. These polynitroxide radicals can serve as promising bridging or chelating ligands in the synthesis of transition-metal-based molecular magnets.

(6S,7S,8S,8aS)-6-Ethyl-7,8-dihy-droxy-1,5,6,7,8,8a-hexa-hydro-indolizin-3(2H)-one monohydrate.

The absolute configuration of the title compound, C(10)H(17)NO(3)·H(2)O, was assigned from the synthesis. In the mol-ecular structure, the central six-membered ring of the indolizine moiety adopts a chair conformation, with two atoms displaced by -0.578 (2) and 0.651 (1) Šfrom the plane of the other four atoms [maximum deviation 0.019 (2) Å] The conformation of the fused oxopyrrolidine ring is close to that of a flat envelope, with the flap atom displaced by 0.294 (1) Šfrom the plane through the remaining four atoms. In the crystal, one of the hy-droxy groups is hydrogen-bonded to two water mol-ecules, while the other hy-droxy group exhibits an inter-molecular hydrogen bond to the carbonyl O atom, resulting in a chain parallel to the b axis.

(6S,7S,8R,8aS)-6-Ethyl-perhydro-indolizine-7,8-diol.

In the title compound, C(10)H(19)NO(2), the piperidine and pyrrolidine rings of the perhydro-indolizine ring system adopt chair and envelope conformations, respectively. In the crystal structure, inter-molecular O-H⋯N and O-H⋯O hydrogen bonds link the mol-ecules into a chain running along the a axis.

(8aS)-7,8,8a,9-Tetra-hydro-thieno[3,2-f]indolizin-6(4H)-one.

In the mol-ecular structure of the title compound, C(10)H(11)NOS, the central six-membered ring of the indolizine unit adopts an envelope conformation, the maximum deviations from the mean plane of the ring being 0.533 (2) Å. The fused thieno ring is nearly coplanar [mean deviation = 0.007 (2) Å]. The conformation of the fused oxopyrrolidine ring is close to that of a flat-envelope, with a maximum deviation of 0.339 (3) Å. The crystal structure is stabilized by C-H⋯O hydrogen bonds.

(7R,8R,8aS)-8-Hydr-oxy-7-phenyl-per-hydro-indolizin-3-one.

The absolute configuration of the title compound, C(14)H(17)NO(2), was assigned from the synthesis. There are two mol-ecules in the asymmetric unit. Their geometries are very similar and corresponding bond lengths are almost identical [mean deviation for all non-H atoms = 0.015 (2) Å]. The six-membered ring of the indolizine system adopts a chair conformation. In the crystal structure, mol-ecules form chains parallel to the a axis via inter-molecular O-H⋯O hydrogen bonds, which help to stabilize the crystal structure.