Investigation on molecular interactions of antibiotics in alcohols using volumetric and acoustic studies at different temperatures

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Highlights

  • Antibiotics in different alcohols are used to study their interactions in solutions.

  • Density and sound velocity for antibiotic solutions are measured at different temperatures.

  • Apparent molar volume and isentropic compressibility are used to calculate partial molar quantities.

  • Acoustical parameters are calculated and discussed in terms of solute–solute and solute–solvent interactions.

Abstract

The density and sound velocity for pure alcohols (methanol, ethanol, iso-propanol and n-butanol) and molal solutions of nitroimidazoles (metronidazole (MNZ) and dimetridazole (DMZ) have been measured at different temperatures (293.15–313.15 K). Different volumetric and acoustical parameters like apparent molar volume (Vϕ), partial molar volume (ϕ), apparent molar isentropic compressibility (Kϕ), partial molar isentropic compressibility (ϕ), hydration number (nH), acoustic impedance (Z) and intermolecular free length (Lf) of antibiotic solutions were calculated from the experimental values of density and sound velocity. The derived values have been used to explore the solute–solute and solute–solvent interactions. The Vϕ values are positive and Kϕ values are negative in both antibiotics, indicative of strong solute–solvent interactions and closely packed structure of antibiotics in alcohols. The decreasing trend of Lf with increasing antibiotic concentration shows the presence of strong intermolecular interactions in solutions.

Introduction

Solubility is a basic physico-chemical property that has significant applications to different processes i.e. biological, chemical, pharmaceutical and environmental. Careful experimentation is required for reliable solubility data and these measurements are tedious, time consuming and costly [1]. Volumetric and acoustical properties like apparent molar volume and apparent molar isentropic compressibility etc. of any solution can be evaluated using density and sound velocity values [2]. Volumetric properties of the mixtures of alcohols are of technological and theoretical interest.

Different types of interactions like ion–ion, solvent–solvent and ion–solvent interactions are present in the solution [3]. From the density (ρ), sound velocity and viscosity (η) of solutions, structural aspects and properties of the solutions can be characterized [4]. Hence volumetric properties give helpful information regarding nature of solute and solvent [5]. The partial molar and apparent molar volumes of solutes are used to distinguish solutes of different molar masses on the basis of their ion–ion and ion–solvent affinity and in assessing drug potency whereas isentropic compressibility factors reflects the compactness of the hydration layers around the core of the solutes [6]. Solubility results also serve to construct mathematical models that help to optimize solvent composition selection in pharmaceutical technology [1].

It has been noted that by the addition of solute, changes occur in the structure of solvent i.e. it may either make or break [4]. By ultrasonic velocity measurements, the molecular interactions in pure liquids, aqueous solutions and mixtures have been studied. It gives a useful and reliable tool to study the properties of solutions of amino acids, polymers etc. However, little work has been done for the solutions of drugs [7].

Chemical transformations can take place in a gas, liquid or solid phase but majority of reactions are carried out in liquid phase in the form of solutions [8]. Alcohol is a class of organic compounds described by one or more hydroxyl (–OH) groups attached to a carbon atom of hydrocarbon chain. These might be considered as organic imitative of water, in which a hydrogen atom has been changed by –CH2 group, which may be represented by ‘R’ in organic structures. For example, in ethanol the alkyl group is the ethyl group, –CH2CH3 [9].

Globally, infections in gastrointestinal track by different parasites and bacteria are responsible for major morbidity and deaths. 5-Nitroimidazoles, a set of medicines, is a well-established group of antiprotozoal and antibacterial agents that have ability to reduce the development of anaerobic bacteria and certain anaerobic protozoa. The significance of imidazole is established from the fact that large number of medicines contains this moiety and several 5-nitroimidazole derivatives such as metronidazole (MNZ), dimetridazole (DMZ), ipronidazole (IPZ) and ronidazole (RNZ) have been used since long time, for the handling of critical cases of infections caused by protozoa and anaerobic bacteria [10]. They are placed into coccidiostat substances, but it has been reported that these compounds show mutagenic, carcinogenic and toxic properties. For this reason, their use has been prohibited as additives in feed for food-producing species. Chemical nature of drugs is essential to study their behaviour in different systems.

This study is an attempt to explore the interactions of these antibiotics with solvents and solvent–solvent interactions from volumetric and acoustical properties (apparent molar volume (Vϕ), isentropic compressibility (Kϕ), partial molar volume (ϕ), partial molar compressibility (Kϕ), acoustic impedance (Z), hydration number (nh) and intermolecular free length), which were evaluated from density and sound velocity of antibiotics (DMZ and MNZ) in different alcohols at different temperatures.

Section snippets

Materials

Chemicals, MNZ, DMZ, methanol, ethanol, iso-propanol and n-butanol, were products of Sigma, and were used as received without any purification. All glassware was carefully washed with de-ionized water, cleaned and dried in oven before use. Mass fraction purity and source of chemicals used in the experiment have been given in Table 1.

Density and sound velocity measurements

Density (d) and sound velocity (u) were measured by Anton Paar DSA 5000 M with high precision vibrating tube digital density meter and ultrasound speed measuring

Density and sound velocity measurement of antibiotic solutions

Density and sound velocity of alcohols: methanol, ethanol, iso-propanol and n-butanol have been measured at different temperatures (293.15 K–313.15 K). The measured density and sound velocity values for pure alcohols have been given in Table 2. Comparison of experimental with literature values showed that measured values is in accordance with literature reported values [11], [12], [13], [14], [15], [16], [17].

Density and sound velocity for the antibiotics (DMZ and MNZ) in alcohols were measured

Conclusions

From the present study, it is concluded that the values of apparent molar volume at all concentrations of antibiotic solution at different temperatures are found positive which indicates the presence of strong solute–solvent interactions in antibiotic and alcohols. Decrease in value of Voϕ with increasing chain length of alcohols has been observed. This can be attributed to decreasing solubility of antibiotics in pure alcohols with increasing chain length. The values of the slope of the line of

Acknowledgments

We gratefully acknowledge Lahore College for Women University for providing us the required chemicals.

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