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The fluorescent carbon quantum dots (CQDs) represent an emerging subset of carbonaceous nanomaterials, recently becoming a powerful tool for biosensing, bioimaging, and drug and gene delivery. In general, carbon dots are defined as zero-dimensional (0D), spherical-like nanoparticles with

Spontaneous precipitation of calcium oxalate monohydrate (COM) in additive-free systems with nearly the same initial supersaturation has been investigated. The influence of thermodynamic parameters such as: temperature (t = 25, 36.5 and 48 °C), calcium concentration range of 5 mmol dm−3 ≤ ci(Ca2+) ≤ 10 mmol dm−3 and pH (5.6, 6.5 and 7.5), on the potential changes in structure, morphology and crystal size of COM have been studied. The values of the initial parameters were varied in a wide range and included values relevant for mimicking the physiological conditions related to those in biological systems and kidney stone formation. The results contributed to the knowledge about the influence of the selected individual parameters as well as their interplay influence on in vitro precipitation of COM. The findings have indicated that COM was the only precipitated phase exhibiting predominant dendritic morphology. The effects on crystal size, structure and morphology are more pronounced at higher temperature, pH and calcium concentration. These results provide basis for future studies of overall mechanism of COM formation and the future studies of kidney stone prevention. This work is licensed under a Creative Commons Attribution 4.0 International License.

Electroactivated disposable pencil graphite electrode (ePGE) was used for hesperidin detection with cv and dpv Electroactivation efficiency of the pencil graphite electrode (PGE) was examined with EIS and SECM. Enhancement of electron transfer kinetics after electroactivation was found. Hesperidin is irreversibly oxidized on ePGE (oxidation was the most pronounced at pH = 5.0). Linear dependence between the peak current and the hesperidin concentration from 5×10‐7 M to 1×10‐5 M was obtained. Determined LOD was 2×10‐7 M. Hesperidin was quantified in pharmaceutical formulation with ePGE and the results were in a good correlation with concentrations determined with HPLC‐DAD (R2 = 0.9462).

Sr3Fe2WO9 and Ba3Fe2WO9 triple perovskites have been prepared in nanocrystalline form using a modified sol–gel route with citric acid as a chelating agent. These materials have been studied by X-ray powder diffraction (PXRD), energy-dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and unpolarized Raman spectroscopy, while their magnetic properties have been determined using SQUID measurements. At room temperature, the crystal structure of 6H-perovskite Ba3Fe2WO9 is hexagonal, space group P63/mmc, with a = 5.7577(2) and c = 14.1095(5) Å, whereas Sr3Fe2WO9 presents a tetragonal lattice, space group I4/m, with a = 5.5803(1) and c = 7.8745(3) Å. Both compounds are nanocrystalline with average crystallite sizes of 25.6(1) nm for Ba3Fe2WO9 and 35.9(1) nm for Sr3Fe2WO9 with moderate microstrain. They exhibit a disordered perovskite structure, in which Fe3+ and W6+ cations distribute randomly at the B-sites of the perovskite lattice: Sr2[Fe0.72W0.28]2a[Fe0.61W0.39]2bO6 and Ba6[Fe1.71W0.29]2a[Fe2.29W1.71]4fO18. The detected hysteresis loops with non-zero remanent magnetization and a rather large coercive field reveal ferrimagnetic ordering with ordering temperatures of 373 K for Sr3Fe2WO9 and 330 K for Ba3Fe2WO9. Magnetic measurements show the onset of ferrimagnetic ordering at relatively high temperatures of 717 and 711 K for the Sr and Ba compounds, respectively ; however the magnetization isotherms at 2 K exhibit, for H = 50 kOe, maximum magnetization values close to 0.8 μB (f.u.)−1 and 0.35 μB (f.u.)−1 for Sr and Ba compounds, respectively, although full saturation is not reached.

Ova studija prikazuje mehanokemijsku sintezu kalcijeva oksalata u planetarnom kugličnom mlinu, bez prisutnosti i uz prisutnost otapala. Dosadašnja istraživanja uglavnom su bila usmjerena na otopinsku sintezu kalcijeva oksalata. U ovom radu opisujemo drugačiji pristup, koji će donijeti nova saznanja o sintezi kristala kalcijeva oksalata, koje su uzrokovane utjecajem mehaničke energije. Cilj istraživanja je sinteza, identifikacija i karakterizacija pojedine oksalatne hidratne faze sintetizirane iz kalcijevih soli (klorida, nitrata i sulfata). Ispitivan je utjecaj brzine mljevenja i praćena je reakcija u ovisnosti o vremenu sinteze. Strukturalna i termička svojstva uzoraka ispitana su spektroskopijom FTIR i termogravimetrijskom analizom (TGA). Morfološke karakteristike kalcijeva oksalata te raspodjela veličine čestica određene su optičkom mikroskopijom i dinamičkim raspršenjem svjetlosti (DLS). Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna., In this work, mechanochemical synthesis of calcium oxalate was done in a planetary ball mill, with and without addition of water as a solvent. Previous research was primarily focused on calcium oxalate synthesis in solution. Here we report a different approach which may contribute to new findings in calcium oxalate crystal synthesis caused by an influence of mechanical energy. The aim of this study was synthesis, identification, and characterization of particular oxalate hydrate phase synthesized with calcium salts (chloride, nitrate and sulphate). The effects of grinding speed and reaction duration regarding the time of synthesis were investigated. Structural and thermal sample properties were studied by FTIR spectroscopy and thermogravimetric analysis (TGA). Morphologic characteristics of calcium oxalate and size distribution were measured by optical microscopy and dynamic light scattering (DLS). This work is licensed under a Creative Commons Attribution 4.0 International License.

This work is focused on a practical procedure by which pure and well-formed COD crystals were obtained. The effect of different type of stirring on the precipitation process and properties of COD crystals is studied. Mechanical and magnetic stirring are two common stirring types for precipitation of calcium oxalate and method using ultrasonic irradiation is newly described. The precipitation processes are systematically investigated varying solution stoichiometry (defined as a ratio of concentrations of the constituent ions in solution, (Ca+/(C2O42−) and concentration of additive (citrate). The differences of the structure, morphology and crystals properties between precipitates were investigated by SEM, FT-IR, TG and PXRD. In the ultrasonically stirred systems, COD was the only precipitated phase regardless of solution stoichiometry. Pure and well formed COD crystals with well-formed planes were obtained in the system with c(Ca2+)/c(C2O42−) = 3.86 and c(citrate) = 0.009 mol dm−3. The results demonstrate that ultrasonically assisted precipitation could be a new way in synthesis of COD crystals having different potential applications (in the fields of medicine and biotechnology).

The main goal of this study was to investigate complexation of L-carnosine and its constituent amino acids beta-alanine and L-histidine with copper (II) in a buffer at pH = 10. For this study the following methods were used: potentiometry, cyclic and differential pulse voltammetry and UV/VIS spectroscopy. The results have shown that L-histidine and L- carnosine formed a complex with copper in a 1:1 ratio, while no complexation with beta-alanine was observed.

Scanning electrochemical microscopy (SECM) in a combined amperometric/potentiometric operation was used to characterize the electrochemical activity of nitinol, before and after anodic treatment, in 0.1 M NaCl solution. The SECM operation in the feedback mode showed that the nitinol surface was homogeneously passive after surface finishing and storage under ambient conditions, while heterogeneous surface characteristics occurred after application of anodic polarization, even for a limited time. That is, the development of anodic and cathodic sites has been detected due to the onset of localized corrosion processes on the metal surface. The evolution of hydrogen gas from localized sites was monitored using SECM in the substrate generation/tip collection mode (SG/TC), while SECM operated in potentiometric mode was used to map the pH distribution in the electrolyte volume adjacent to the nitinol surface. Local acidification was observed around anodic spots associated with the Ni2+ discharge, as well as alkalinization above the cathodic zones.

Electrochemical properties of vitamin C (also known as L-ascorbic acid) have been studied by cyclic and differential pulse voltammetry in the model systems in order to develop simple and suitable method for vitamin C detection in real samples. The results indicated that vitamin C oxidation is a quasi-reversible and diffusion- controlled process, as well that the oxidation product of ascorbic acid, dehydroascorbic acid is adsorbed on the glassy carbon electrode surface. Calibration curve was constructed and the linear response was obtained in a concentration range from 0.0025 mol dm-3 to 1.0 mol dm-3. Vitamin C was successfully determined in real samples (fruit juices and food supplement) with cyclic voltammetry within concentration range from 0.034 mol dm-3 to 0.340 mol dm-3. In addition, antioxidant activity of vitamin C in real samples was determined using DPPH assay with a good linear correlation obtained between the cyclic voltammetry results and the results evaluated by DPPH assay of the samples.

In this study, glassy carbon electrode modified with nano gold-crystal violet film has been used to detect arsenite (As (III)) in a model system and in groundwater samples. The modified electrode was characterized by scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS). Using voltammetric measuring technique, linear response was obtained in a concentration range of 2.0-22.0 uM. The arsenite concentrations in groundwater samples varied between 2.4 uM to 4.8 uM. The sensitivity of the modified electrode for As (III) detection was 5.6 uA/ uM cm2 and 0.8 uM concentration was found as lower limit of detection (LOD). The accuracy of the method was checked with standard method anodic stripping voltammetry (ASV). Groundwater samples were characterized with dynamic (DLS) and electrophoretic (ELS) light scattering measurements which have shown that particles present in different samples differ in size distribution and zeta potential which did not interfere with As (III) detection.

Complex perovskites have attracted extensive attention due to their fascinating physical properties and novel features owing to the coexistence of the ferro/ferri-magnetic ground state and semiconducting behavior in the single material. Herein, the triple perovskite Sr3Co2WO9 (SCWO) has been successfully synthesized for the first time in the nanocrystalline form with an average crystallite size of 23 nm using a high yield (81 %) aqueous citrate sol-gel method. At room temperature, the crystal structure of Sr3Co2WO9 is cubic, space group Fm-3m, with lattice parameter a= 7.9073(6) Å. The formation of SCWO triple perovskite was studied in situ by X-ray diffraction and subsequently analyzed by the Rietveld analysis. The detected hysteresis loops with non-zero remanent magnetization and rather large coercive field reveal ferrimagnetic ordering with a Curie temperature of 144 K. The measured effective magnetic moment of 3 μB is close to the expected value for rarely observed intermediate spin S = 1. It is found that the compound exhibits semiconducting properties with the optical band gaps equal to 3.52 eV (indirect) and 3.76 eV (direct), respectively, further confirmed by the determination of the AC conductivity, which in the measured temperature range (25 -500 °C at 1 kHz) lies within the interval from 10−5- 10−4 Ω−1 cm−1. The Maxwell -Wagner model is employed to describe the frequency dependent dielectric constant. The frequency-dependent AC conductivity follows the universal Jonscher’s power law. Since it possesses both magnetic and semiconductor properties, this material could be a promising candidate to use in devices where its semiconducting properties would be spin-controlled.

In this study, three different precipitation systems of increasing complexities were used to study formation of calcium oxalate hydrates under hyperoxaluria conditions. For this purpose, three different precipitation systems have been studied: a) a simple system (a system containing constituent ions), b) NaCl system (a system consisted of constituent ions and 0.3 mol dm−3 NaCl), and c) artificial urine system (a system containing constituent ions that are of the type and quantity mimicking real urine) at initial pH (pHi = 6.5) value, with and without added vitamin C. The vitamin C has been extensively tested for its ability to inhibit or promote the process of calcium oxalate precipitation or the formation of specific hydrate modification. In order to determine whether calcium oxalate crystallization could be affected by the presence of vitamin C in precipitation systems with increasing complexity, different amounts of vitamin C (in the mass range from 100 mg to 1000 mg) were added to the precipitation systems.The results indicated that in all investigated simple systems, calcium oxalate monohydrate (COM) is observed to be dominant precipitated hydrate phase, while in NaCl systems precipitation of COM and calcium oxalate trihydrate (COT) mixture occurrs, except in reference NaCl system (without addition of vitamin C) where COM precipitated exclusively. In reference artificial urine system, calcium oxalate dihydrate (COD) was observed to be dominant precipitated hydrate phase, while addition of vitamin C promoted precipitation of COT. Significant differences are mainly observed in crystal morphology and the content of individual hydrate phases. Electrochemical measurements have indicated the existence of electrostatic interactions between seed crystals and ascorbic acid, even at low masses of added vitamin C.

Flavonoids represent a large group of polyphenolic compounds which are widely distributed in plants and show beneficial effects on human health. Their biological activity can be connected with structural diversity and a wide range of their derivatives. Hesperidin is a phytochemical classified as bioflavonoid and can be primarily found in citrus fruits as well as in some other fruits and vegetables. Due to suppression of pro- inflammatory cytokine production and its antioxidant defense mechanism, hesperidin shows different pharmacological activities such as cardio protective, antihypertensive, antidiabetic, anti-inflammatory and antihyperlipidemic activity [1]. Graphite can be used as electrode material since it has nonmetallic and metallic properties. The pencil graphite leads are composite materials which contain approximately 65% of graphite, approximately 30 % of clay, and around 5 % is a binder (wax, resins, or high polymer) [2]. The use of disposable pencil graphite electrode (PGE) is proven to be a simple, cheap and fast alternative with superior sensitivity and performance compared to more expensive electrodes [3]. In this study, pencil graphite electrode (PGE) and electroactivated pencil graphite electrode (ePGE) were used for voltammetric characterization of hesperidin in model system with cyclic and differential pulse voltammetry. Both electrodes were characterized with EIS and SECM and the enhancement of electron transfer kinetics was observed after electroactivation. The effect of scan rate, pH and hesperidin concentration on oxidation peak current were also studied. It was determined that oxidation peak current increases with the increase of scan rate and hesperidin concentration. The hesperidin oxidation was the most pronounced at pH = 5. The peak current and the hesperidin concentration showed linear dependence in the concentration range from 5x10-7 mol dm-3 to 1x10-5 mol dm-3. Estimated limit of detection (LOD) was 5x10-7 mol dm-3.

This work focuses on systematic research of spontaneous precipitation of calcium oxalate in model systems mimicking the chemical conditions typical for hyperoxaluria. For this purpose, model systems of three different complexities (simple, NaCl and artificial urine system) and two initial pH (pHi = 5.0 and pHi = 9.0) at 37 ºC are studied. In all investigated systems, dominant precipitation of calcium oxalate monohydrate (COM) is observed, except in artificial urine system at pHi = 9.0, ci(C2O42-) ≥ 6.0 mmol dm-3 and ci(Ca2+) ≥ 7.5 mmol dm-3 where precipitation of a mixture of calcium oxalate monohydrate and calcium oxalate dihydrate (COD) occurrs. The significant difference is mainly observed in COM crystal morphology. In a simple system, COM precipitates in a dendritic form, in NaCl system dendritic form and irregular shapes are found, while in the artificial urine, prismatic hexagonal and aggregated COM crystals precipitate.

This work combines the laboratory quantitative analysis of colored solutions and common devices for digital imaging (digital or web camera or mobile phones, i.e., smartphones). ColorX software, specially designed for this study, was used for data collection and analysis in order to calculate concentration of colored solutions from measured RGB values. Three different custom methods for determination of concentration have been developed: (i) RGB value measurement by pixel ; (ii) RGB value measurement by pixel and Gaussian blur ; and (iii) calculation of average RGB value of the selected image area. The performance of the developed software ColorX is demonstrated using different colored solutions: KMnO4 (purple) ; CoSO4 (red) ; NiSO4 (green) ; and CuSO4 (blue) solutions, as well as the Lowry protein assay (blue) to determine the concentration of an unknown sample. The most suitable and effective method for study of the mentioned solutions was calculation of average RGB value of the selected image area. ColorX software is primarily designed for accessibility and simplicity with the aim of promoting and encouraging students to explore and discover potential applications of digital imaging technology in basic analytical chemistry concepts.

Ispitivan je nastanak kompleksa L-histidina i bakra u omjeru 1 : 1 u području pH od pH = 4 do pH = 10. Istraživanja su provedena u elektrokemijskoj ćeliji, gdje je kao radna elektroda upotrijebljena elektroda od staklastog ugljika, kao referentna Ag/AgCl elektroda te kao protuelektroda platinska žica. Utvrđeno je da kompleks bakra i histidina nastaje u području od pH = 6 do pH = 10 te da se oksidacijski potencijal metalnog iona u kompleksu negativira s povećanjem pH. Struja oksidacijskog strujnog vrha raste do pH = 8 te nakon toga opada, dok se potencijal oksidacijskog strujnog vrha linearno smanjuje s povećanjem vrijednosti pH. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna., Formation of L-histidine and copper complex in 1 : 1 ratio in the pH range from pH = 4 to pH = 10 was studied. Experiments were conducted in an electrochemical cell with a working glassy carbon electrode, reference Ag/AgCl electrode and a platinum wire counter electrode. The results have shown that copper and histidine complex is formed in the range from pH = 6 to pH = 10 and that the oxidation potential of metal ion in the complex became more negative with the increase in pH. Oxidation peak current increased until pH = 8, and thereafter decreased, while oxidation peak potential linearly decreased with increase in pH value. This work is licensed under a Creative Commons Attribution 4.0 International License.

In this work oxido-reduction properties of L-histidine were studied by cyclic and differential pulse voltammetry in a pH range from pH 4–10. The results have shown that L-histidine is not electroactive in a pH range from pH 4 to pH 9, while oxidation peak of L-histidine’s imidazole ring at pH 10 was detected with differential pulse voltammetry. It has been found that the oxidation peak current of L-histidine increased with the increase of its concentration in a solution. Adsorption of oxidation product of L-histidine on a glassy carbon electrode surface was also detected. Voltammetric techniques (cyclic and differential pulse voltammetry) and UV/VIS spectroscopy were used to study formation of L-histidine complexes with transition metals. It has been found that L-histidine formed octahedral complex with metal ion (Co2+ and Ni2+) in a 1 : 1 ratio. This work is licensed under a Creative Commons Attribution 4.0 International License.

The crystallization is process of the formation a crystalline phase from a parent phase, e.g. solution. The normal (bone, teeth, shells) and pathological mineralized tissues (stones, caries, gouty arthritis, arteriosclerosis) are biominerals in human body and animals. The formation of biominerals, is the formation of sparingly soluble salts from body fluids (blood, serum, urine) within an organic macromolecular matrix. Processes involved in pathological mineralization are of special interest due to the great medical and social problems that they cause. Urolithiasis, a form of pathologic biomineralization, is a disease which causes the formation of urinary stones in different parts of kidney or bladder (1). The kidney stones formation under biological conditions can be triggered by various metabolic disorders such as: hipercalciuria, hypocitraturia, hiperoxaluria and the change in the urine acidity. The mechanisms and the conditions under which they crystallize are still not completely clarified. In this work, the crystallization from supersaturated solution in model system, calcium oxalates, calcium phosphates, magnesium phosphates, uric acid and/or salts of the uric acid, also in artificial urine were reported. The reactant solutions were mixed under controlled hydrodynamic and thermodynamic conditions ; pH, ionic strength, temperature. The influence of aditives, macromolecules on crystal growth morphology and on the composition of the crystallizing phase were determined. The crystalluria from real urine system as one indicator the formation of calculi were compared with the morphology and composition of crystals which crystalized in model systems. The changes in the composition and morphology of precipitated salts were observed by means of PXRD, light microscopy, TEM, SEM, IR and TGA.

The scientific conference The 1st Young Scientist Day – PhD Conference was held on 14th June 2018 in Osijek at Aula of Josip Juraj Strossmayer University of Osijek. Scientific lectures were held by the PhD students and postdoc fellows from Josip Juraj Strossmayer University of Osijek, Faculty of Food Technology Osijek, Faculty of Agriculture Osijek, Faculty of Medicine Osijek, Department of Chemistry and Department of Biology. The main idea was the presentation of experimental results between young scientists, PhD students and postdoc fellows of the Josip Juraj Strossmayer University of Osijek, with the aim of promoting new ideas and knowledge, sharing experiences, as well as acquiring competencies in the multidisciplinary fields of science, and with the purpose of future collaboration establishing.