Showing papers in "Croatica Chemica Acta in 2020"

Surface Enhanced Raman Spectroscopy for Molecular Identification- a Review on Surface Plasmon Resonance (SPR) and Localised Surface Plasmon Resonance (LSPR) in Optical Nanobiosensing

Abstract: Surface plasmon resonance (SPR) allows for real-time, label-free optical detection of many chemical and biological substances. Having emerged in the last two decades, it is a widely used technique due to its non-invasive nature, allowing for the ultra-sensitive detection of a number of analytes. This review article discusses the principles, providing examples and illustrating the utility of SPR within the frame of plasmonic nanobiosensing, while making comparisons with its successor, namely localized surface plasmon resonance (LSPR). In particular LSPR utilizes both metal nanoparticle arrays and single nanoparticles, as compared to a continuous film of gold as used in traditional SPR. LSPR, utilizes metal nanoparticle arrays or single nanoparticles that have smaller sizes than the wavelength of the incident light, measuring small changes in the wavelength of the absorbance position, rather than the angle as in SPR. We introduce LSPR nanobiosensing by describing the initial experiments performed, shift-enhancement methods, exploitation of the short electromagnetic field decay length, and single nanoparticle sensors are as pathways to further exploit the strengths of LSPR nanobiosensing. Coupling molecular identification to LSPR spectroscopy is also explored and thus examples from surface-enhanced Raman spectroscopy are provided. The unique characteristics of LSPR nanobiosensing are emphasized and the challenges using LSPR nanobiosensors for detection of biomolecules as a biomarker are discussed.

Diffusional Electrochemical Catalytic (EC’) Mechanism Featuring Chemical Reversibility of Regenerative Reaction-Theoretical Analysis in Cyclic Voltammetry

Abstract: We consider theoretically a specific electrochemical-catalytic mechanism associated with reversible regenerative chemical reaction, under conditions of cyclic staircase voltammetry (CSV). We suppose scenario in which two electrochemically inactive substrates “S” and “Y”, together with initial electrochemically active reactant Ox are present in voltammetric cell from the beginning of the experiment. Substrate “S” selectively reacts with initial electroactive reactant Ox and creates electroactive “product” Red (+ Y) in a reversible chemical fashion. The initial chemical equilibrium determines the amounts of Ox and Red available for electrode transformation at the beginning of the electrochemical experiment. Under conditions of applied potential, the electrode reaction Ox(aq) + ne– ⇋ Red(aq) occurs, producing flow of electric current. Under such circumstances, the chemical reaction coupled to the electrochemical step causes a regeneration of initial electroactive species during the time-frame of current-measuring segment in CSV. The features of cyclic voltammograms get significantly affected by the kinetics and thermodynamics of reversible regenerative reaction. We elaborate several aspects of this specific electrode mechanism, and we focus on the role of parameters related to chemical step to the features of calculated voltammograms. While we provide a specific set of results of this particular mechanism, we propose methods to get access to relevant kinetic and thermodynamic parameters relevant to regenerative chemical reaction. The results elaborated in this work can be valuable in evaluating kinetics of many drug-drug interactions, but they can be relevant to study interactions of many enzyme-substrate systems, as well.

Synthesis, Characterization and Biological Activity of Oxovanadium(IV) Complexes Containing α-Amino Acid Schiff Bases and 5,6-Dimethyl-1,10-phenanthroline Ligands

Abstract: Five oxovanadium(IV) complexes of the type [VO(L)(DPhen)], containing Schiff base derived from α-amino acid, [where L = 3-hydroxybenzaldehyde-α-alanine (hb-Ala), 3-hydroxybenzaldehyde-DL-phenylalanine (hb-Phe), 3-hydroxybenzaldehyde-leucine (hb-Leu), 3-hydroxybenzaldehyde-glycine (hb-Gly) and 3-hydroxybenzaldehyde-DL-methionine (hb-Met) & DPhen = 5,6-Dimethyl-1,10-phenanthroline] have been synthesized and characterized by some physicochemical properties, molar conductance, magnetic susceptibilities measurements, elemental analysis, UV-Visible, FT-IR and EIS-MS spectral studies. The molar conductance values evidenced the non-electrolytic nature of the complexes. The magnetic moment values of the complexes are in accordance with the d1 electronic configuration of the VIVO2+ moiety and indicates the paramagnetic behavior of the complexes. IR spectral data indicates the coordination of tridentate amino acid Schiff base ligands to the vanadyl (VO2+) ion through O, N, O-donor. ESI-MS spectral study confirmed the proposed structure of the complexes. All the analytical data suggested that all the complexes possess to have distorted octahedral geometry. The complexes were screened for their antibacterial activity against four human pathogenic bacteria; two Gram positive Escherichia coli & Pseudomonas aeruginosa and two Gram negative Staphylococcus aureus & Bacillus cereus with Kanamycin (K-30) standard. The result shows that all the complexes have moderate to strong potential antibacterial activity against all the pathogenic bacteria.

Some Observations on Triplet Ground-States in the Context of ‘Topological’ (HLPM) Ring-Currents in Conjugated Systems

Abstract: When the quasi graph-theoretical Hückel–London–Pople–McWeeny (HLPM) approach is used to calculate ‘topological’ π-electron ring-currents and bond-currents in conjugated hydrocarbons, a problem is identified that occurs whenever application of the Aufbau process gives rise to a π-electronic ground-state configuration that is a triplet. This circumstance seems to occur only occasionally and, even when it does, the generally somewhat outré molecular graphs in question appear unlikely to represent extant or viable conjugated systems. The molecular graphs of four examples are used to illustrate this ‘triplet ground-state problem’, only one of which represents a hydrocarbon that has actually been synthesised. It is pointed out that the ‘triplet ground-state problem’ does constitute an intrinsic limitation of the HLPM approach. It is, though, a limitation that is also necessarily inherent in other equivalent (though ostensibly different) methods of calculating magnetic properties due to π-electron ring-currents — methods that are likewise founded on the Hückel molecular-orbital conventions. When a triplet ground-state arises, topological ring-currents and bond-currents cannot be calculated by the HLPM method and its equivalents. Infinite paramagnetism is formally to be predicted in such situations.

A diverse view of science to catalyse change

Abstract: Valuing diversity leads to scientific excellence, the progress of science and, most importantly, it is simply the right thing to do We must value diversity not only in words, but also in actions

Catacondensed Chemical Hexagonal Complexes: A Natural Generalisation of Benzenoids

Abstract: Catacondensed benzenoids (those benzenoids having no carbon atom belonging to three hexagonal rings) form the simplest class of polycyclic aromatic hydrocarbons (PAH). They have a long history of study and are of wide chemical importance. In this paper, mathematical possibilities for natural extension of the notion of a catacondensed benzenoid are discussed, leading under plausible chemically and physically motivated restrictions to the notion of a catacondensed chemical hexagonal complex (CCHC). A general polygonal complex is a topological structure composed of polygons that are glued together along certain edges. A polygonal complex is flat if none of its edges belong to more than two polygons. A connected flat polygonal complex determines an orientable or nonorientable surface, possibly with boundary. A CCHC is then a connected flat polygonal complex all of whose polygons are hexagons and each of whose vertices belongs to at most two hexagonal faces. We prove that all CCHC are Kekulean and give formulas for counting the perfect matchings in a series of examples based on expansion of cubic graphs in which the edges are replaced by linear polyacenes of equal length. As a preliminary assessment of the likely stability of molecules with CCHC structure, all-electron quantum chemical calculations are applied to molecular structures based on several CCHC, using either linear or kinked unbranched catafused polyacenes as the expansion motif. The systems examined all have closed shells according to Huckel theory and all correspond to minima on the potential surface, thus passing the most basic test for plausibility as a chemical species.

Inhibitory effect of acacetin, apigenin, chrysin and pinocembrin on human cytochrome P450 3A4

Abstract: Cytochrome P450 3A4 is the most significant enzyme in metabolism of medications. Flavonoids are common secondary plant metabolites found in fruits and vegetables. Some flavonoids can interact with other drugs by inhibiting cytochrome P450 enzymes. Thus, the objective of this study was to determine inhibition kinetics of cytochrome P450 3A4 by flavonoids: acacetin, apigenin, chrysin and pinocembrin. For this purpose, testosterone was used as marker substrate, and generation of the 6β-hydroxy metabolite was monitored by high performance liquid chromatography coupled with diode array detector. IC50 values, inhibition constants, and rates of inhibition were determined. IC50 values ranged between 0.6 and 11.4 µM. The strongest inhibitor was chrysin (IC50 0.6 µM, inhibition constant 0.6 µM, inhibition rate constant 0.065 min–1, inhibition efficacy 0.108 min–1 µM–1). Compared to other flavonoids analyzed, chrysin’s inhibitory effect can be attributed to the hydrophobic nonsubstituted B ring, as well as rigidity of the structure. When foods rich in chrysin are consumed, e.g. honey and propolis, chrysin can cause food-drug interactions. Further in vitro studies are needed to determine the reactive intermediate responsible for inactivation of cytochrome P450 3A4 enzyme, as well as in vivo studies to determine possible clinical significance of this inhibition. This work is licensed under a Creative Commons Attribution 4.0 International License .

Convexity deficit of benzenoids

Abstract: In 2012, a family of benzenoids was introduced by Cruz, Gutman, and Rada, which they called convex benzenoids. In this paper we introduce the convexity deficit, a new topological index intended for benzenoids and, more generally, fusenes. This index measures by how much a given fusene departs from convexity. It is defined in terms of the boundary-edges code. In particular, convex benzenoids are exactly the benzenoids having convexity deficit equal to 0. Quasi-convex benzenoids form the family of non-convex benzenoids that are closest to convex, i.e., they have convexity deficit equal to 1. Finally, we investigate convexity deficit of several important families of benzenoids.

Screening of Natural Deep Eutectic Solvents for Green Synthesis of 2-methyl-3-substituted Quinazolinones and Microwave-Assisted Synthesis of 3-aryl Quinazolinones in Ethanol

Abstract: In this study, two fast and efficient protocols for green synthesis of 3-substituted quinazolinones were perfomed. A synthesis of 2-methyl-3-substituted quinazolinones was performed in natural deep eutectic solvents, while 3-aryl quinazolinones were obtained by using microwave assisted synthesis. Benzoxazinone, which was used as an intermediate in the synthesis of 2-methyl-3-substituted quinazolinones, was prepared conventionally from anthranilic acid and acetic anhydride. In order to find the most appropriate synthetic path, twenty natural deep eutectic solvents were applied as a solvent in these syntheses. Choline chloride:urea (1 : 2) was found to be the most efficient solvent and was further used in the synthesis of 2-methyl quinazolinone derivatives (2–12). 3-Aryl quinazolinones (13–17), on the other hand, were synthesized in one-pot microwave-assisted reaction of anthranilic acid, different amines and trimethyl orthoformate. All compounds were synthesized in good to excellent yields, characterized by LC-MS/MS spectrometry and 1H- and 13C-NMR spectroscopy.

Mn(III) Catalyzed Electrochemical Reduction of CO2 on Carbon Electrodes

Abstract: Though challenging, conversion of carbon dioxide (CO2) to valuable products is an emerging area of research. Electrochemical reduction (ECR) has emerged as an efficient and rapid technique to achieve this goal. Herein, 5,10,15,20-tetraphenyl-21H, 23H-porphine manganese(III) chloride [(Mn(TPP)Cl)] catalyzed CO2 reduction at vitreous carbon electrode in acetonitrile electrolyte is reported. The effect of catalyst concentration, addition of Brönsted acid (CF3CH2OH) to CO2-saturated solution have been studied and reported. Based on the results, possible mechanistic pathways have also been suggested and discussed.

Distribution of rare earth elements in citrus leaves and reference materials (NIST SRM 1515 and ERM CD281)

Abstract: The present study aims to discuss the data on levels and distribution of rare earth elements, including Y, (REYs) in leaves of three different citrus species (lemon, orange, and tangerine) and provide additional information about the major, minor and trace elements in two biological certified reference materials (CRMs), Apple leave (NIST SRM 1515) and Rye grass (ERM CD281). In all samples, element concentrations were determined by High Resolution Inductively Coupled Plasma Mass Spectrometry. The obtained data display substantial variability in the distribution of REY elements, not only between different citrus species but also between different genera of plants indicating their different uptake and accumulation abilities. Measured concentrations of REYs in citrus leaves were substantially lower compared to the literature values, although the fractionation indices were comparable. The data for CRMs provide additional information for the 14 elements in NIST SRM 1515 and the 30 elements in ERM CD281, including rare earth elements.

Benzotriazolium Ionic Liquid Immobilized on Periodic Mesoporous Organosilica as an Effective Reusable Catalyst for Chemical Fixation of CO2 into Cyclic Carbonates

Abstract: A type of dichloro(dimethoxyethane)nickel anionic benzotriazolium ionic liquid-functionalized periodic mesoporous organosilicas were synthesized and tested as effective and practical heterogeneous catalysts in the cycloaddition of CO2 with epoxides. The catalyst PMO@ILC4H10O2NiCl3(1.0) showed brilliant catalytic activity for the synthesis of cyclic carbonates with high yields and selectivities under solventand cocatalyst-free conditions. We also found that the catalytic activity could be significantly influenced by the hydroxyl groups sites of periodic mesoporous organosilica and the active sites (hydroxyl groups/ dichloro(dimethoxyethane)nickel anion) of the benzotriazoliumcation ionic liquid, probably due to an intensification of intramolecular synergistic effect. The catalytic process displayed ease of recovery, excellent stability and recyclability for at least five runs without significant loss of its catalytic activity.

Rotational Barrier and Quantification of Electron-Donating Substituent Effects: a Computational Study of para-Substituted Benzaldehydes

Abstract: The rotational barrier around the phenyl-formyl bond between the minimum and transition states of para-substituted benzaldehydes was computationally studied for 34 electron-donating substituents. The rotational barrier exhibited very good correlation with shortening of the phenyl-formyl bond, lengthening of carbonyl bond, increase of electron density at the formyl group, increase of stabilization energy, lowering of chemical shift in the 13C NMR of the formyl carbon, and with the values of empirical Hammett σp+ constants. Therefore, rotational barrier is a useful quantum mechanical parameter for quantifying the electron-donating substituent effect and π-conjugation in parasubstituted benzaldehydes. Based upon the rotational barrier a scale has been set in this work to judge the electron donating effect of substituents. Moreover, a canonical structure has been proposed for stronger electron-donating substituents. The results of this study reveal that simultaneous presence of electron acceptor formyl group and electron-donating groups is mandatory for the extension of resonance stabilization.

Model of Reactant Adsorption in dc Polarography

Abstract: An expanding plane model of polarogram influenced by the reactant adsorption is developed and applied to the Frumkin isotherm. It is shown that the polarogram may consist of the main wave and post-wave that are separated by the maximum and minimum. The origin of these extremes are investigated by the calculation of currents that flow during a single mercury drop.

Two Stability Criteria for Benzenoid Hydrocarbons and Their Relation

Abstract: A new, simple, relation is established between the total π-electron energy and the HOMO-LUMO gap, applicable to benzenoid hydrocarbons.

Surface Electrode Mechanism Associated with Preceding and Follow up Chemical Reactions – Theoretical Analysis in Square-Wave Voltammetry

Abstract: Surface electrode reaction (E), coupled with reversible preceding and reversible follow up chemical steps (C), or so-called “surface CEC mechanism” is considered theoretically under conditions of square-wave voltammetry. Large set of square-wave voltammograms of considered electrode system are calculated as a function of thermodynamics and kinetics of chemical steps involved in this complex mechanism. The surface CEC mechanism can be simplified to a surface CE, or a surface EC mechanism, if one assumes defined magnitudes of the equilibrium constants of chemical steps involved. Although the influence of the square-wave frequency to the voltammetric patterns is quite complex, a frequency analysis can reveal important aspects to recognize this mechanism. While we present important differences that can distinguish between the effect of the kinetics of both chemical steps, we also give the readers hints on how to design experiments in order to get access to all relevant kinetic constants. Theoretical results elaborated in this work are quite important, since there are important experimental systems, such as redox enzymes and metal-ligand complexes, whose voltammetric behaviour fits to this mechanism.

Is Phenalenyl Aromatic

Abstract: The rings phenalenyl are determined using some quantitative aromatic indices to have around 40 % the aromaticity of benzene. The monocation, monoanion, and monoradical of phenalenyl are found to be equally aromatic.

Photo-induced Dissociation of the N1–H Bond in the Imino Tautomers of Isocytosine in Water Medium

Abstract: The imino tautomers of isocytosine were objects of investigation at the TD-DFT level of theory TD BLYP/6-311++G(d,p). We studied the mechanisms of the H1-N detachment in these tautomers through excited-state reaction paths. It was proposed that these transformations occur through the 1πσ* excited-state reaction paths of the imino tautomers. The mechanisms involve dissociations of the N1–H bonds in the tautomers and lead to crossings between the reaction paths of 1πσ* and S0 electronic states. One can suppose that such processes would facilitate the tautomerizations of the imino tautomers if further mechanisms have been found.

Photoinduced Phenomena in 6,6’-Dibromoindigo (Tyrian Purple): a Theoretical Study

Abstract: The compound 6,6’-dibromoindigo, which is the main component of the pigment Tyrian purple, was studied theoretically at the TDDFT level of theory. We found that the absorption maximum of the compound about 600 nm underwent a red-shift when moving from the gas phase in solution. With the located two conical intersections S0 / S1 we investigated (TD-DFT) the mechanisms connecting these structures with the ground state equilibrium geometry. It was established that the conical intersections are not accessible along any of the excited-state reaction paths which implies optical deactivation of the first excited state of the compound. With respect to these mechanisms the pigment should exhibit high photostability when exposed to visible light.

Volatile Constituents of Aerial Parts of Capsella rubella Reut.

Abstract: Three different isolates from unexplored wild-growing Brassicaceae plant Capsella rubella were investigated in order to provide more complete insight of the composition and content of volatile constituents. The analysis of volatile compounds was performed by GC-FID/MS. C. rubella essential oil, that is isolate obtained by hydrodistillation, was characterized by a high percentage of 3,4-epithiobutanenitrile (67.8 %). The main volatile compounds in autolysate, i.e. isolate obtained by solvent extraction upon endogenous enzymatic hydrolysis, were 3,4epithiobutanenitrile (44.1 %) and ethyl isothiocyanate (29.4 %). Same as in autolysate, the main volatile constituents of hydrolysate, i.e. isolate obtained by solvent extraction upon exogenous enzymatic hydrolysis, were 3,4-epithiobutanenitrile and ethyl isothiocyanate, but with ethyl isothiocyanate as the dominating compound (57.8 %) followed by 3,4-epithiobutanenitrile (15.6 %). The results showed that qualitative and quantitative composition of C. rubella volatile constituents depends on the isolation method. But, regardless of the isolation method sulfurand nitrogen-containing volatile compounds were quantitatively dominating constituents in all isolates.

Determination of Au Film Thiolation and Silane Bonding Onto SiO2 Films Within the Frame of Biosensor Surface Functionalization – an Analysis of Best Practices and Techniques

Abstract: This paper reviews some of the most common surface modification approaches in biosensing based on self-assembled monolayers with a particular focus on Au film thiolation and SiO2 film silanization. Such approaches are routinely used to alter the materials’ surface properties towards a desired bioresponse. Furthermore, the most appropriate characterization methods towards ensuring successful surface modification are presented including XPS, HREELS, SPFS, Raman and FTIR spectroscopy as well as UPS with specific examples to demonstrate their importance. In addition, the mechanisms of fluorescent and non-fluorescent biotinylation of thiolated Au films and silanized SiO2 are discussed considering its importance in conjugating biomolecules such as enzymes, antibodies or chemokines onto surfaces, which carries high significance for biosensing applications. Finally, within this frame characterization routes towards ensuring effective attachment are discussed.

Chemical fingerprinting, total phenolics and antioxidant activity of some Iris taxa

Abstract: Some Iris taxa covered in this study were used or are still being used as remedies in European folk medicine. The most common indication for the decoction of Iris rhizomes is sore throat and productive cough, especially in case of the taxon I. domestica (L.) Goldblatt & Mabb., the well-known remedy in traditional Chinese medicine. The aim of this study is to chemically characterize rhizomes of seven wild and medicinal Iris taxa and to assess the antioxidant activity of the rhizome extracts. The HPTLC chromatograms and densitometric spectrum scan of the spots were used for untargeted metabolic profiling and tentative metabolite class identification of Iris taxa. Total number of found spots is 41, three major spots are found in all taxa, and 22 spots are found to be taxon specific. Two xanthones, three isoflavonoid glycosides, 18 isoflavonoid aglycons (isoflavonoids), and five acetophenones/benzophenones are tentatively identified. The taxon I. pallida Lam. contains largest amount of phenolic substances (28.5 ± 2.0 mg GAE / g dry plant material) and was the most effective ABTS scavenger (27.5 ± 2.4 mg TROLOXE / g dry plant material). The taxon I. illyrica Tomm. ex Vis. was the most effective in both DPPH and FRAP assays, 10.1 ± 1.5 and 17.3 ± 0.1 mg TROLOXE / g dry plant material, respectively. The most effective taxa in the metal chelating assay were I. croatica Horvat & M.D.Horvat (6.1 ± 0.1 mg EDTAE / g dry plant material) and I. germanica var. florentina (L.) Dykes (5.8 ± 0.1 mg EDTAE / g dry plant material). European Iris taxa have a relatively similar and partly shared chemical profile with Asian taxon I. domestica, which might be a sign of equivalence in the medicinal value. This work is licensed under a Creative Commons Attribution 4.0 International License .