Experimental studies for electrochemical and enzymatic detection of biological active sulfur compounds Authors: Niculina Dragomir, Ligia Chelmea Coordinators: Conf. Dr. Mihaela Badea, Conf. Dr. Marius Moga Faculty of Medicine, University Transilvania from Brasov

Motivation and purpose sulfur in organic compounds  different properties, depending on the function in which it is located. The paper aims to optimize biochemical methods for detection of biologically active compounds with sulfur  spectral analysis enzymatic catalysis (in the presence of peroxidase)  electrochemical methods analysis of the different behaviour of sulfur compounds: cysteine thiourea

Cysteine In scleroproteins of animal tissues (skin, hair, nails, hooves) Food sources: pork, poultry, eggs, dairy products, peppers, garlic, onions, wheat Industrial sources : hydrolysis feathers Structure of proteins - bind metal ions: Zn, Ni, Fe, Pb, Hg, Cd Applications precursor in the food industry (food additive E920), pharmaceuticals, cosmetics cysteine ​​ derivatives, multiple protective actions against hyperlipidemia, hyperglycemia and oxidative stress - drugs

Oxidized form - cystine Biological functions - thiol Cysteine ​​ -cystine system - reversible redox system Cysteine

Thiourea composed harmful, dangerous for the environment specific biological properties of thyroid tissue - transport inhibitor organic iodine Applications Intermediate in organic synthesis and medicinal - hyperthyroidism For the production of synthetic resins Vulcanization accelerator Corrosion inhibitor

Spectral analysis of enzyme kinetics Apparatus spectrophotometer (λ= 492 nm) Reaction conditions temperature: 25 ◦ C pH = 7.4 (phosphate buffer)

Principle H 2 O 2 + 2H + + 2e - 2H 2 O peroxidase Colourless substrat Coloured product

Substrate/chromophore (reduced form) Product (oxidized) 5-aminosalicylic acidBrown o-phenylenediamineOrange 4-chloro-1-naphtholBlue o-toluidine Blue o-dianisidineYellow-orange 3,3 '-diaminobenzidine Brown Principle

Principle Variation of extinction in studies of inhibition / activation of enzyme E xtinction Time E xtinction Time C0C0 C1 C2 C 2 >C 1 Activator C1C1 C2C2 C0C0 C 2 >C 1 Inhibitory

Results The equations of the regression lines Dependencies of %EA (reaction rate) vs concentrations of analytes

double behaviour of the organic sulfur compounds in presence of enzymatic media: 3,3 '-diaminobenzidine - peroxidase - hydrogen peroxide cysteine  ​​ activator thiourea  inhibitor A laborious method, consuming enzyme (expensive, non-reusable) Partial conclusions

Electrochemical analysis Apparatus Screen-printed electrodes with cobalt phthalocyanine (as mediator) Differentiated pulse voltammetry (DPV) AUTOLAB – soft GPES 4.0 Magnetic stirrer University of Perpignan via Domitia, France

Principle redox processes  electrochemical methods

Procedure 1. Preparation of solutions: buffer system watery cysteine ​​ / thiourea 2. Testing sensors stabilitation measuring method: differential pulse voltammetry (DPV) optimum potential (mV) for detection the optimum pH for detection 3. Plotting the calibration curve

Cysteine pH = 7

Thiourea acetate buffer - pH = 5.6phosphate buffer – pH = 7 Intensity (A) Potential (mV)

Thiourea Thiourea pH = 5,6

Partial conclusions sulfur compounds / DPV signals cysteine ​​ - pH = 7 - phosphate buffer system thiourea - pH = acetate buffer system Different peaks (specific intervals)  possibility of simultaneous detection of real samples

Conclusion  studies of aqueous standard samples  subsequent analysis of real samples.  mechanisms of action in peroxidase systems: activator – inhibitor different pH  electrochemical detection methods Using screen-printedelectrodes with cobalt phthalocyanine (as mediator)  cheap and fast detection of biological active compounds with sulfur in aqueous samples.

Acknowledgements The authors thank Prof. Dr. Jean-Louis Marty (Perpignan Via Domitia University of France) for providing electrochemical transducers used in experimental studies.

References Moreno L., Merkoçi A, Alegret S, Hernández-Cassou S, Saurin J, Analysis of amino acids in complex samples by using voltammetry and multivariate calibration methods, Analytica Chimica Acta, 507 (2)(2004) 247–253 CespuglioR., In vivo measurement by differential pulse voltammetry of 5-hydroxyindole compounds, J.Histochem Cytochem, 30(1982)821 Ensafi A.A., Taei M., T. Khayamian, A. Arabzadeh, Highly selective determination of ascorbic acid, dopamine, and uric acid by differential pulse voltammetry using poly(sulfonazo III) modified glassy carbon electrode, Sensors and Actuators B: Chemical, 147(1)( 2010) 213–221 Badea M., Coman G., Biochimie.Tehnici enzimatice de analiza, Editura Universitatii Transilvania din Brasov, 2007 Coman G., Draghici C., Badea M., Bigiu N., Ciurea C., Biochimie descriptiva, Editura Universitatii Transilvania din Brasov, 2009