SCIENCE LETTERS 2013 | Volume 1 | Issue 1 | 13007e 1 Surface and micellar properties of Clindamycine Phosphate in aqueous solution Muhammad Usman 1, 4 , Zahoor Hussain Farooqi 2,4 , Abbas Khan 3,4 , Mohammad Siddiq 4,* Muhammad Yameen 5 1 Department of Chemistry, Government College University, Faisalabad, Pakistan 2 Institute of Chemistry, University of the Punjab, Lahore, Pakistan 3 Department of Chemistry, Abdul Wali Khan University, Mardan, Pakistan 4 Department of Chemistry, Quaid-i-Azam University, Islamabad 5 Department of Applied Chemistry & Biochemistry, Government College University, Faisalabad, Pakistan Abstract This manuscript reports the solution and micellar behaviour of an antibiotic drug Clindamycine Phosphate (CLN) in aqueous media. Surface tension and specific conductivity were used to find the critical micelle concentration (CMC) and in this way its surface and thermodynamic parameters were calculated. The electrical conductivity was measured as a function of concentration at various temperatures and CMC was calculated in the temperature range of 20-50°C. Thermodynamic parameters i.e. standard free energy of micellization, o m G  standard enthalpy of micellization, o m H  and standard entropy of micellization, o m S  were calculated from CMC value using closed association model. Keywords: Micellization, drug, surface tension, entropy, conductivity, free energy, enthalp. Received May 25, 2013; Revised July 22, 2013; Accepted August 14, 2013 * Corresponding author: Mohammad Siddiq; Email: m_sidiq12@yahoo.com Introduction The solution, thermodynamics and colloidal behavior of amphiphilic drugs largely depends on the nature of the aromatic ring system of their hydrophobic part, and they help to probe the relationship between molecular architecture and physicochemical properties. It is done by conducting study about the thermodynamics of their aggregation and the factors governing this process [1]. The objective of present study is to relate the physicochemical properties of drug with its molecular structure. The structural features of amphiphilic drugs influence their association pattern in aqueous solution. Drugs represent an interesting variety amphiphilic structure ranging from the ones which are easily recognized as typical surfactants, to more complex aromatic, heteroaromatic or fused ring structure. It is interesting to know that micellization is not only the way in which drug molecules form aggregates, albeit another one which amphiphilic molecules exhibit in solution. The typical surfactants have flexible hydrocarbon based hydrophobic group and clear separation of charges creating distinct polar and nonpolar regions. Their hydophobic parts easily intertwine to form aggregates. This type of association is called closed association or micellization. If this flexible hydrocarbon chain is replaced by rigid aromatic or heterocyclic rings, the way in which molecules are disposed within aggregates changes in such way that process of aggregation may no longer be regarded as micellization. A well-known illustration of this effect is association of cationic dyes and purines and pyramidines which associate by stacking process. Such association is generally known as continuous or open association and there is no equivalent to CMC. The amphiphilic drugs lie between these two extremes. Although their hydrophobic group is aromatic but they resemble pure surfactants because of having high degree of flexibility. The lack of flexibility of hydrophobic moiety is, although, a necessary criterion for continuous association, it is not the only structural requirement. Many drugs having rigid aromatic system show closed association or micellization because their charges are generally localized at a terminal group of relatively long side chain rather than delocalized in the ring system as is common in dyes. Drugs provide an opportunity to investigate factors which are responsible for type of association exhibited by amphiphilic molecules in solution. It is this respect of studies on colloidal properties of amphiphilic drug, Citalopram HBr, rather than any pharmacological consequence of colloidal behaviour, which are being emphasized in this paper [1-6]. We, in our previous work, have already studied solution and thermodynamic behaviour of anti allergic drug Certizine HCl [7], anti-depression drug Citalopram 2HBr [8] and antibiotic drugs Dexamethasone sodium phosphate [9], Chloroquine diphosphate [10] and Quinacrine 2HCl [11]. In this paper we have discussed how antibiotic drug Clindamycine Phosphate does behave in its aqueous solution. Fig. 1 displays structure of Clindamycine.