Short Communication A novel model to characterize the electric double layer of lectins from Cratylia mollis Camaratu bean) and Canavalia ensiformis adsorbed on metallic surface S.R. Souza a,b , M.T.S. Correia c , M.M.A. Pessoa a , J.F. Kennedy d , J.L. Lima-Filho a,e , L.C.B.B. Coelho c, * a Departamento de Quõ Âmica, Universidade Federal Rural de Pernambuco UFRPE), Recife, PE Brazil b Departamento de Cie Ãncias Biolo Âgicas, Faculdade de Filoso®a do Recife FAFIRE), Av. Conde da Boa Vista, n. 100, 50.000-00, Recife, PE Brazil c Departamento de Bioquõ Âmica, Centro de Cie Ãncias Biolo Âgicas, Universidade Federal de Pernambuco UFPE), Av. Prof. Moraes Rego s/n, Cidade Universita Âria, 50.670-420, Recife, PE, Brazil d ResearchLaboratoryfortheChemistryofBioactiveCarbohydratesandProteins,SchoolofChemistry,UniversityofBirmingham,BirminghamB152TT,UK e Laborato Ârio de Imunopatologia Keizo Asami, LIKA/UFPE, Recife, PE Brazil Received 17 September 1999; revised 18 July 2000; accepted 13 September 2000 Abstract The seed lectin from Cratylia mollis Cra) is glucose/mannose speci®c, similarly to Concanavalin A, Con A, a well characterized lectin from Canavalia ensiformis. The equilibrium properties of an adsorbed layer may be examined based on the redox potentials of the constituents of this layer. The potential for Con A and Cra was obtained by potentiostatic techniques, using a saline solution as support to control the distribution of charges between saturated calomel electrode and platinum electrode as the working electrode, in aerated environment. These potentials are modelled using a Chi-square statistical distribution p , 0:05; greater stability for Con A was obtained with 1.0 mg/ml, at 108C. The positive redox potential determined for Cra 194mV)andConA188 mV) indicated a high sensitivity of our electrodes which will give information on the kinetic behaviour of the biological interface. q 2001 Elsevier Science Ltd. All rights reserved. Keywords: Cratylia mollis; Redox potential; Potentiostatic technique 1. Introduction Lectins are proteins that bind carbohydrates with high degree of speci®city and have similar or distinct structures Correia & Coelho, 1995; Sharon & Lis, 1990; Tavares et al., 1996; Seetharaman & White, 1996). The physico- chemical characterization of lectins is important to explain their behaviour in different biological properties. The Concanavalin A, Con A, obtained from Canavalia ensifor- mis seeds is the most studied glucose/mannose lectin. Molecular forms, with glucose/mannose recognition have also been puri®ed from Cratylia mollis lectin, Cra Paiva & Coelho, 1992). Structural differences and distinct biolo- gical activities have been identi®ed between Cra and Con A Tavares et al., 1996). Electrochemical techniques are able to give a direct insight into the interface containing electri- cally charged groups adsorbed to electrode surface. This adsorption determines subsequent behaviour of the inter- face, and hence the biocompatibility of the material. The kinetics behaviour and redox potential of adsorbed molecules depend on a variety of factors: the pH near the electrode, the temperature in the system and the properties of a double layer at the interface. This potential is important for the application of cyclic voltammetry techniques in the kinetics investigation of a biological interface. In this work, the change capacity in the interface electrode/solution for Con A and Cra was monitored by potentiostatic techniques, with the purpose of determining the electrochemical redox potential of the lectins. 2. Materials and methods All lectin solutions were prepared in 0.15 M NaCl. The Con A was obtained from Sigma and Cra was puri®ed on Sephadex G-75, according to Correia and Coelho 1995). 2.1. Apparatus and experimental To carry out the experiments, an electrochemical system was used with a cell containing a working and a reference Carbohydrate Polymers 46 2001) 191±193 0144-8617/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved. PII: S0144-861700)00299-X www.elsevier.com/locate/carbpol * Corresponding author.