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A new, simple, rapid, sensitive and selective kinetic spectrophotometric method for Pd(II) traces determination was elaborated in this paper. It is based on the catalytic effect of palladium ions upon the oxidation of methylene blue B (MBB) by (NH4)2S2O8 (APS) in citric buffer (BUF) solution. At the working temperature of 25 C and the wavelength of 662.4 nm, the optimal conditions for palladium determination were found. RSD value was found to be 2.6 to 4.9% for the investigated concentration range of Pd(II). Limit of detection (LD) was found to be 2.0 ng cm–3 Pd(II), and limit of quantification (LQ) is 6.9 ng cm–3 Pd(II). Only the presence of Pb2+, Hg2+ and Sn2+ in the reaction mixture interferes the determination of palladium by this method, while Au3+ and Ag+ have the catalytic effect upon the reaction rate. By this method, it is possible to determine the Pd(II) traces in the concentration range of 3.3x10–8 to 1.0x10–6 g cm–3. The method was confirmed by determination of Pd(II) traces in alloy PtRhG as well as in the powder of Pt. The obtained results were compared to those obtained by ICP-OES method and good agreement of results was found. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. 172051]

The examination of the aerial parts, roots, and seeds of the endemic plant Rindera umbellata is reported in this paper for the first time. Phytochemical investigation of R. umbellata led to the isolation and characterization of ten pyrrolizidine alkaloids and eleven fatty acids in the form of triglycerides. Pyrrolizidine alkaloids 1-9 were found in the aerial parts, 7 and 8 in the roots, and 6-10, together with eleven fatty acids, in the seeds of this plant species. The structures of compounds 1-10 were established based on spectroscopic studies (H-1- and C-13-NMR, 2D NMR, IR and CI-MS). After trans-esterification, methyl esters of the fatty acids were analyzed using GC-MS. The effect of lindelofine-N-oxide (7) on tubulin polymerization was determined.

This study describes the effects of the substituents on electrochemical behavior and antioxidant activity of the six tetradentate Schiff bases, containing ethane-1,2-diamine or propane-1,2-diamine as the amine part and pentane-2,4-dione and/or 1-phenylbutane-1,3-dione as beta-diketone, and corresponding copper(II) complexes. Cyclic voltammograms of these compounds were recorded in dimethylsulfoxide and 0.1 M sodium perchlorate as supporting electrolyte with glassy carbon as working electrode at different scan rates. The voltammograms of Schiff bases alone showed only one irreversible peak. Voltammograms recorded for complexes showed the presence of quasi-reversible processes taking place at the metal center and reversible process at the ligand part. Both steric and inductive effects of substituents and structure of imine bridge of Schiff base ligands as well as complexes were discussed. These effects appear relevant for the antioxidant activity. Antioxidant activity of the investigated compounds expressed as Trolox equivalent antioxidant capacity is also discussed. The electrochemical behavior showed a high correlation with the antioxidant activity for investigated compounds.

Propranolol, a widely used beta-blocker, inhibits the reaction of enzyme cholinesterase hydrolysis. Measurements of the hydrolysis rate differences between and inhibited reactions, allows the development of a kinetic method for its determination. Both systems, enzyme-substrate-chromogen and enzyme-substrate-chromogen-inhibitor, were characterized through biochemical kinetic parameters (KM = 0.326-0.330 mmol/L; Vmax = 40-42.99 ?mol/Lmin), inhibition type was recognized as competitive, and inhibition constant, Ki, was determined to be 22.60 ?mol/L. The detection and quantification limits were calculated as 0.004 and 0.0136 ?mol/L, respectively. Accuracy and precision of proposed methods were tested. Proposed method is characterized with good sensitivity, selectivity, simplicity and rapidity, thus it is convenient for clinical applications.

Proteomic approach in combination with mass spectrometry demonstrates a great potential for identification of proteinaceous materials in works of art. In this study we used a linear trap quadrupole Orbitrap (LTQ-Orbitrap), a state-of-the-art mass spectrometer for parts per million accuracy analyses of peptides behind tryptic hydrolysis. After the efficiency of the proteomic method was confirmed for reference and model samples, micro-samples from historical paintings were for the first time analysed using this technique. Superior performances of the liquid chromatography–mass spectrometry approach using a LTQ-Orbitrap mass spectrometer allowed identification of egg yolk peptides in two samples from nineteenth-century Orthodox icons, indicating egg tempera as the painting technique. Accurate precursor ion masses, in the range of ±2 ppm, and retention times of tryptic peptides strengthen protein identification. Additionally, in all historical samples the presence of animal glues suggested that the ground layer was likely bound using bovine collagen. Comparing to results acquired using matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry in our previous study, here we achieved higher ion scores and protein scores, better sequence coverage and more identified proteins. In fact, a combination of the two mass spectrometric techniques provided overlapping and complementary data, related to the detection of peptides with different physicochemical properties.

A new, simple, rapid, sensitive and selective spectrophotometric kinetic method for Ag(I) traces determination at room temperature was elaborated in this paper. It is based on catalytic effect of silver ions upon the oxidation of methylene blue B (MBB) by K2S2O8 (PPS) in citric buffer (BUF) solution. The method was confirmed by determination of Ag(I) in PbO. The obtained results were compared to those obtained by ICP-OES method and good agreement of results was found. [Projekat Ministarstva nauke Republike Srbije, br. 172051]

The present paper describes two new, simple, rapid, selective and sensitive kinetic spectrophotometric methods for Co(II) and Sn(II) determination in solution at room temperature, based on their effect on phenyl fluorone (PF) oxidation by hydrogen peroxide in ammonia buffer. The new method was elaborated for nano amounts of Co(II) determination, based on its catalytic effect on the oxidation of PF by H2O2 in the presence of citric acid (CA) as an activator. Also, the new method for micro amounts of Sn(II) determination was developed based on its inhibitory effect upon the same reaction. Comparison of the results showed that the activated catalytic reaction has better sensitivity than the inhibitory one. Methods were validated by the analyze of chemical substances and results were improved by examining the same samples by AAS method. [Projekat Ministarstva nauke Republike Srbije, br. 172051]

Aim of this work is to propose an analytical protocol for proteinaceous binder identification in paintings using tryptic peptide analysis and MALDI-TOF mass spectrometry strengthened with MALDI-TOF/TOF tandem mass spectrometry (LIFT method). Proteinaceous binders are enzymatically digested with trypsin. From each individual protein frequently occurring in binders, a specific set of peptides is releasing during enzymatic digestion giving a peptide mass fingerprint (PMF) of that particular protein. The most intensive peptide peaks in PMF were determined and annotated with their corresponding amino acid sequence by MALDI-TOF/TOF analysis and subsequent database search. Before analyzing historical painting samples, procedure was tested and optimized on several painting model samples for a reliable and efficient identification of proteinaceous materials. The method is avoiding sample manipulation as much as possible in order to reduce sample loss. Since the applied procedures led to protein identification of binding media in model samples, MALDI-TOF/TOF was for the first time applied for analysis of proteinaceous binders in old painting samples. Supplementary material: [http://cherry.chem.bg.ac.rs/handle/123456789/3500]

Natural monocrystalline pyrite and chalcopyrite were examined as new indicator electrodes for the potentiometric titration of weak acids in tert-butanol and iso-propanol. The electrodes investigated demonstrated a linear dynamic response for p-toluenesulfonic acid concentrations in the range from 0.1 to 0.001 M, with a Nernstian slope of 48 mV per decade for pyrite in tert-butanol. Sodium methylate, potassium hydroxide and tetrabutylammonium hydroxide (TBAH) proved to be suitable titrating agents. The response time was less than 12 s and the lifetime of the electrodes was higher than 1 year. The advantages of the electrodes are long-term stability, rapid response, reproducibility, easy preparation and low cost.

The present paper describes a simple, selective and sensitive kinetic method for the determination of trace amounts of Sb(III) in the presence of Sb(V) based on its inhibition effect on the redox reaction between bromate and Victoria blue 4R (V.B. 4-R) in hydrochloric acid media. The reaction was followed spectrophotometrically by measuring the decrease in the absorbance of V.B. 4-R at 596.3 nm. Optimum operating conditions regarding reagent concentrations were established. The optimized conditions yielded a theoretical detection limit of 1.30·10‒8 g cm–3 Sb(III) based on the 3S0 criterion. The method allows the determination of Sb(III) in the range of 5·10‒8 ‒ 1.1·10‒6 g cm–3. The effects of certain foreign ions the reaction rate were determined for an assessment of the selectivity of the method. The kinetic parameters of the reaction were reported, and the rate equations were suggested. The results were validated statistically and through recovery studies. The proposed method has been successfully applied to the determination of Sb(III) in various model and real samples.