AC Impedance tracking of glassy carbon activation

Carbon materials, due to their physical and chemical properties, have found wide application in different electrochemical systems. They are often used as substrates for supercapacitors and different types of electrocatalysts. Upon activation, their electrochemical properties are improved. Glassy carbon can be successfully used as a model for studying the process of carbon activation. In this work, the activation of glassy carbon by electrochemical oxidation in sulfuric acid was investigated using cyclic voltammetry, electrochemical impedance spectroscopy and atomic force microscopy. Glassy carbon was oxidized during the same time at 5 different potentials. Cyclic voltammetry shows that the higher the potential the larger the increase in double layer capacitance is. Impedance measurements confirmed significant changes in capacitive response of activated glassy carbon in comparison to unoxidized state. AFM examination of treated GC surfaces revealed morphological changes and increase in roughness upon oxidation. If combined, the results of these studies show that the activation of glassy carbon proceeds through three stages: oxidation of active site, growing of graphite oxide layer and mechanical destruction of the surface.Belgrade, Serbia, June 6-10, 2010Related to the published paper in the Proceedings of the Second Regional Symposium on Electrochemistry South-East Europe, [http://cer.ihtm.bg.ac.rs/handle/123456789/3541

Waste-wood derived biochar as a support for horseradish peroxidase immobilization

In this paper, the suitability of waste-wood derived biochar particles as a support for the horseradish peroxidase (HRP) immobilization by adsorption method was investigated. The change in enzymatic activity of the immobilized enzyme at different values of pH and temperature, as well as stability over time, was measured. The results showed that HRP can efficiently bind to biochar particles by adsorption. The immobilized enzyme shows high activity (>80%) at a wide range of pH (7-9) and temperature (20-50°C). The immobilized enzyme retains 22% and 40% of its activity during storage at temperatures of 25 and 10°C after a period of 30 days, respectively

AC Impedance tracking of glassy carbon activation

Carbon materials, due to their physical and chemical properties, have found wide application in different electrochemical systems. They are often used as substrates for supercapacitors and different types of electrocatalysts. Upon activation, their electrochemical properties are improved. Glassy carbon can be successfully used as a model for studying the process of carbon activation. In this work, the activation of glassy carbon by electrochemical oxidation in sulfuric acid was investigated using cyclic voltammetry, electrochemical impedance spectroscopy and atomic force microscopy. Glassy carbon was oxidized during the same time at 5 different potentials. Cyclic voltammetry shows that the higher the potential the larger the increase in double layer capacitance is. Impedance measurements confirmed significant changes in capacitive response of activated glassy carbon in comparison to unoxidized state. AFM examination of treated GC surfaces revealed morphological changes and increase in roughness upon oxidation. If combined, the results of these studies show that the activation of glassy carbon proceeds through three stages: oxidation of active site, growing of graphite oxide layer and mechanical destruction of the surface.Belgrade, Serbia, June 6-10, 2010Related to the published paper in the Proceedings of the Second Regional Symposium on Electrochemistry South-East Europe, [http://cer.ihtm.bg.ac.rs/handle/123456789/3541

Dual responsive hybrid hydrogels for controlled release of local anesthetic

Inteligentni hidrogelovi, kao što su pH osetljivi hidrogelovi na bazi poli(metakrilne kiseline) (PMAA), imaju veliku primenu u ciljanoj dostavi lekova. Međutim, slaba mehanička svojstva često ograničavaju primenu PMAA. Kako bi se prevazišlo navedeno ograničenje, nanoceluloza (NC) je prvo ekstrakovana iz drvnog otpadnog materijala, a zatim dodata u PMAA, zato što je NC biokompatibilna, netoksična i ima odlična mehanička svojstva. Zatim je dodata karboskimetil celuloza (CMC) (celulozni derivat koji se često koristi za kontrolisano otpuštanje lekova). CMC može da stabilizuje nanočestice magnetita (MN) koje su takođe dodate. MN mogu značajno da poboljšaju mehanička svojstva hidrogelova i takođe poseduju magnetna svojstva zbog čega imaju primenu za ciljano otpuštanje lekova. Ovako dobijeni materijal bi mogao da zaštiti lek, dostavi ga do mesta delovanja, kontroliše brzinu njegovog otpuštanja i na taj način omogući efikasno dejstvo leka sa smanjenim neželjenim efektima. Lokalni anestetik – lidokain hidrohlorid (LH) se često u tretmanima injektira što može imati ozbiljne neželjene efekte. Inkapsulacijom LH u hidrogelove na bazi PMAA, NC, CMC i MN (PMNC/MN-L) rešen je navedeni problem. Karakterizacija PMNC/MN-L hidrogelova je izvedena primenom FTIR i SEM spektroskopija i kompresionim testovima, a zatim je analizirano bubrenje hidrogelova i otpuštanje LH. U ovom radu predstavljen je jedinstveni način „zelene” sinteze hibridnih hidrogelova osetljivih na spoljne stimulanse unapređenih svojstava i njihove primene za kontrolisano otpuštanje lokalnog anestetika sa smanjenim neželjnim efektima

Sustainable energy transition in Central Asia: status and challenges

Background: The paper aims at gaining insight into the implementation of the process of sustainable energy transition in the countries of Central Asia: Kazakhstan, Kyrgyz Republic, Tajikistan, Turkmenistan, and Uzbekistan. Information and scientific studies on the situation in these countries is scarce. On the other hand, these are resource-rich countries, some are exporters, and all are energy transit countries. The main aim of the paper was realized by applying the energy policies and regulatory framework analysis, defining priorities and monitoring selected indicators prescribed by the International Energy Agency. Methods: The following methods were used in the quantitative analysis: measurement of data intercorrelation; Pearson test of correlation; principal component analysis (with rotation method: Oblimin with Kaiser normalization); Kaiser–Meyer–Olkin measure of sampling adequacy, Bartlett’s test of sphericity and t-test. The period covered by the quantitative analysis: 1990–2018, provided that the available data for 2019 or 2020 were used in certain cases. Results: Sustainable energy transition is, at the analysis of policies and data, at a low level. There is no adequate regulatory framework in these countries. The energy transition takes place exclusively within the framework of providing enough energy, without regard to sustainability, while even energy exporting countries are not making efforts to achieve a sustainable energy transition. Conclusions: There are no indications that the energy transition in the countries of Central Asia will take place according to the standards of the European Union or global bodies. On the other hand, having in mind the natural resources of the mentioned countries and the specific geopolitical position, monitoring the changes is of special importance. The impact of changes on sustainability can be determined mainly ex post

Leptin and its mechanism of action

Leptin je hormon adipoznog tkiva koji svoje efekte ostvaruje delovanjem na centralni nervni sistem. Leptin se vezuje za svoje OB receptore na neuronima hipotalamusa i posledično suprimira unos hrane i povećava aktivnost simpatičkog nervnog sistema čime stimuliše proces termogeneze i potrošnje energije. Osim što suprimira apetit i stimuliše termogenu potrošnju energije, leptin ostvaruje svoje efekte i na druge organske sisteme, kao što su endokrini, vaskularni, hematopoetski, imunski i mišićnoskeletni, delujući bilo direktno na periferiji organizma, bilo posredstvom centralnog nervnog sistema. Svoje efekte leptin ostvaruje putem veoma rasprostranjene mreže leptinskih receptora, preko nekoliko različitih molekularnih signalnih puteva. Stanje gojaznosti je praćeno povećanjem nivoa leptina u cirkulaciji usled povećane količine masnog tkiva, ali i pored toga, gojazne osobe ispoljavaju rezistenciju na anoreksigenične i metaboličke efekte leptina. Izvestan broj studija je pokazao da leptin može povećati aktivnost simpatičkog nervnog sistema i u netermogenim tkivima glodara dovodeći do hipertenzije usled gojaznosti. Koncept selektivne rezistenicije na leptin predstavlja moguće objašnjenje ovog paradoksa. Još uvek su malobrojne studije u kojima je ispitivan fenomen selektivne leptinske rezistencije kod ljudi. U okviru ovog preglednog članka, dat je prikaz najnovijih saznanja o leptinu, mehanizmu njegovog delovanja kao i o ulozi leptina u patofiziološkim stanjima.Leptin is a hormone produced by the adipose tissue, which has effects on the central nervous system. Leptin is bound to its Ob receptor on hypo-thalamic neurons to inhibit feeding behavior and to increase sympathetically-mediated thermogenesis. In addition to anorexia and thermogenesis, leptin also has direct peripheral and central nervous system-mediated effects on the endocrine, vascular, hematopoietc, immune and musculoskeletal systems. Leptin accomplishes its effects using distributed network of leptin receptors and differential molecular signaling pathways. Leptinemia is increased in obesity because of increased adipocyte mass, but obese subjects exhibit resistance to the anorexic and metabolic effects of leptin. However, multiple studies have shown that leptin can increase sympathetic nerve activity to non-thermogenic tissues in rodents causing obesity-related hypertension. One potential explanation of this paradox is selective leptin resistance. Compared with large and persuasive number of studies on the sympathetic and blood pressure effects of leptin in experimental animals, relatively little attention was given to these effects of leptin in humans. This review article presents recent findings related to leptin and its mechanism of action, and also the role of leptin in patophysiological conditions

Influence of process parameters of simultaneous anodization/anaphoretic electrodeposition synthesis of hydroxyapatite/titanium oxide composite coatings on adhesion

In-situ synthesis of hydroxyapatite/titanium oxide (HAp/TiO2) coating on titanium was performed via anaphoretic deposition of hydroxyapatite (HAp) and simultaneous anodization of Ti to produce highly adherent and strengthened composite coating. The influence of electric potential, time, electrolyte concentration and pH value of the anodization process on titanium surface roughness and anodization of titanium was examined, as well as influence of same process parameters on adhesion strength and compactness of composite HAp/TiO2 coatings was investigated. Prior to novel in situ method of synthesis of hydroxyapatite/titanium oxide composite coatings by simultaneous anodization/anaphoretic electrodeposition described in this manuscript, optimization of anodization process of titanium was performed. Anodization was executed under different electric potentials and different distances of counter electrodes from working electrodes, but all anodization processes had constant quantity of electric charge. Characterization of titanium samples, prepared from grade 6 Ti, and having rectangular contact surfaces of 10×10×0.89 mm included SEM/EDS analyses, X-ray diffraction analyses, AFM surface topography, morphology and roughness analyses and linear measurements of roughness.A chemical precipitation method was used to prepare hydroxyapatite powder by the reaction of calcium oxide (obtained by calcination of CaCO3 for 5 h at 1000 °C in air) and phosphoric acid. A stoichiometric amount of the calcium oxide was stirred in distilled water and phosphoric acid was added drop wise to the suspension in order to obtain hydroxyapatite powder, Ca10(PO4)6(OH)2.Two types of HAp coatings were prepared, in order to compare the adhesion, morphology and consistency of the HAp and composite HAp/TiO2 on Ti, namely cathaphoretic and anaphoretic coatings, respectively [1,2]. The prepared coatings were characterized by field emission scanning electron microscopy, X-ray diffraction and electron dispersive spectroscopy. Adhesion was investigated by ASTM D 3359 – 97 Test method B. Uniform and adherent HAp/TiO2 composite coating on Ti was obtained. Since smaller size of HAp crystals within highly porous coating structures is of improved binding ability to various biomolecules, our coating is expected to be of excellent coverage and compactness. The obtained coating can be good candidate for bone implants due to improved adhesion