Abstract
The paper deals with the calculation of molar refraction () and polarizability () of antibiotic drug ciprofloxacin hydrochloride ( = 0.001–0.029 mol·dm−3) solutions in ethanol-water mixtures of different compositions (30, 50, and 70% v/v) from measured density () and refractive index () at 30°C. The effect of drug concentration and composition of ethanol-water mixtures on density and optical properties of drug solutions has been described.
1. Introduction
The knowledge of physiochemical properties of drug solution plays an important role in understanding their physiological actions which is highly dependent upon solution behaviour. Drugs are organic molecules with both hydrophilic and hydrophobic groups due to which they show specific as well as electrostatic interactions. Physiochemical properties like and of solution are directly related to interactions in solution and are useful for recognition of substance; they confirm purity and concentration of substance. Refractive index along with density is used for investigated intermolecular interactions in solution. Molecular interactions are studied through the measurements of refractive indices of solution [1–3]. and are useful for getting the valuable information about polarizability of solution [4–8].
Ciprofloxacin is second-generation fluoroquinolone used as an antibiotic that can treat a number of bacterial infections. It is used to treat infections such as infections of bones and joints, endocarditis, gastroenteritis, malignant otitis externa, respiratory tract infections, cellulitis, and urinary tract infections. We have studied the optical properties of aqueous metoprolol succinate and duloxetine solutions [9, 10] and ciprofloxacin + aqueous-glycine solutions [11]. Here we report and of ciprofloxacin hydrochloride solutions in ethanol-water mixtures of 30, 50, and 70% v/v at 30°C. and of these solutions are calculated. Various properties are interpreted in terms of molecular interactions in solution. Present work deals with the molecular interactions and overall structural fitting in the drug in aqueous-ethanol solutions and therefore finds the applications in pharmaceutical and medical sciences. The data of thermodynamic properties is helpful for understanding the drug-water and drug-alcohol interactions.
2. Experimental
The ciprofloxacin hydrochloride monohydrate drug was received as a gift sample from Godavari Drugs Ltd., Nanded (MS), India. Ethanol-water mixtures of 30, 50, and 70% v/v were prepared and drug solutions of different concentrations were prepared in given ethanol-water mixtures. Distilled water was used for preparation of drug solutions. Weighing was done on single pan electronic balance (±0.001 g). were determined using calibrated single capillary pycnometer and were measured on thermostatically controlled Cyber LAB-Cyber Abbe Refractometer (Amkette Analytics, ±0.0002, 1.3000 to 1.7000). Averages of three readings of and are reported.
3. Results and Discussion
Experimental , , , and data of ternary ciprofloxacin hydrochloride + ethanol-water systems at 30°C are presented in Table 1.
and of solutions increased with drug concentration and decreased and increased with increase in vol % of ethanol in solution for given drug concentration (Figures 1 and 2). As drug concentration increases, due to the drug-solvent interactions, volume contraction occurs which resulted in increase in density of solution. The and changes are indicative of intermolecular interaction in solution.
Concentration dependence of is studied [12] using (1) and respective graphical parameters are reported in Table 2:where is constant which depends on chemical and physical properties of solute (dm3·mol−1), is molar concentration of drug solution (mol·dm−3), and is refractive index at infinite dilution. Relationship between and is also studied (Figure 3) and found to be linear ().
The parameters and in Table 1 are determined using the following equations [13–15] and presented in Figures 4 and 5:where is mole fractions of th component of mixture and is molecular mass of -component of mixture andwhere is Avogadro’s constant (6.023 × 1023 mol−1).
is an electronic polarizability per mole of component which includes contributions from each component. Deviation in is an indication of interactions between components [16]. It is used in QSAR studies for drug design [17]. and appear as a response to combined effects of intermolecular forces between solute and its surroundings [18]. Use of and has become increasingly important in the study of drug interaction.
increased slightly with drug concentration and largely with vol % of ethanol in solution which indicates strong drug-solvent interactions [19]. Plots of with concentration of drug for all the systems are found to be linear (). is directly proportional to [20]; hence, increases and becomes stronger with increase in amount of drug which elucidates structural cause of change in density and existence and modification of molecular interactions. Changes in and indicate tighter packing of drug molecules and strengthening of drug-solvent interactions at higher concentration. With increase in vol % of ethanol, the packing of drug becomes tighter.
is related to the intermolecular forces in the system like drug-receptor interactions [16]. It is increased with drug concentration as well as with vol % of ethanol in solution which indicates capability of electronic system of drug molecule to be distorted is increase with drug concentration and vol % of ethanol. Stronger polarizability is introduced to drug solution upon addition of drug in ethanol-water mixtures due to interactions between polar parts of the drug and solvent dipoles. Both and values of ciprofloxacin in ethanol-water are higher than in aqueous medium [11].
4. Conclusions
The values of ciprofloxacin in aqueous-ethanol mixtures show linear dependence over drug concentration and density. increases and becomes stronger with increase in amount of drug due to structural cause of change in density and existence and modification of drug-solvent interactions. Overall results indicated the strengthening of drug-solvent interactions with drug concentration. Capability of electronic system of drug to be distorted is increased with drug concentration and vol % of ethanol.
Conflict of Interests
The authors declare that there is no conflict of interests regarding the publication of this paper.
Acknowledgments
The authors are thankful to Godavari Drugs Limited, Nanded (MS), India, for generous gift of the drug and to the Director, School of Chemical Sciences, S. R. T. M. University, Nanded, for providing necessary facilities.