Thermophysical and excess properties of hydroxamic acids in DMSO
Graphical abstract
Excess molar volumes (VE) vs mole fraction (x2) of (A) N-o-tolyl-2-nitrobenzo- and (B) N-o-tolyl-4-nitrobenzo-hydroxamic acids in DMSO at different temperatures: ■, 298.15 K; , 303.15 K; , 308.15 K; , 313.15 K; and , 318.15 K.
Highlights
► ρ, n of the system hydroxamic acids in DMSO are reported. ► Apparent molar volume indicates superior solute–solvent interactions. ► Limiting apparent molar expansibility and coefficient of thermal expansion. ► Behaviour of this parameter suggest to hydroxamic acids act as structure maker. ► The excess properties have interpreted in terms of molecular interactions.
Introduction
Studies on different thermophysical (volumetric properties, refractive index) and thermodynamic properties of solution within wide ranges of concentration and temperatures are valuable sources of information that may be used to examine the relationship between the internal structure of the system, nature of intermolecular interactions and the physical properties of the solute, solvent studied [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11]. Thermodynamic properties obtained through experimentation are the fundamental basis for the development of empirical, semi-empirical or theoretical model used to represented and predict the behaviour of fluids [12]. The volumetric properties of solutions have proven to be a very useful tool in elucidating the structural interactions (i.e., solute–solvent, solute–solute, and solvent–solvent) occurring in solution, because they provide an indirect insight into the conformational feature of the components in solution. The design and operation of the industrial processes that involve nonelectrolyte solutions require knowledge of rigorous models or experimental data to represent the non-ideality of the solutions. Accurate predictions of densities and refractive indices of solutions are of great importance in design engineering processes in chemical and biological industries [13], [14], [15]. The density, refractive index and thermodynamic parameters have been extensively employed to study molecular packing, different kinds of association and nature as well as extent of molecular interactions existing in solutions. Further, these properties are also used to test the applicability of differential data and also provide information about the nature and extent of molecular interactions in solution. The parameters, apparent molar volumes and limiting apparent molar volumes of dilute solutions are useful for the development of molecular models for describing the thermodynamic behaviour of solutions. The depends upon molecular size, shape, interactions and structural interactions occurring in solution [16]. Excess properties of solutions, such as excess molar volume, VE, refractive index deviation, nE, and excess molar refraction, are applicable for the design of separation techniques and to test theories of solutions [17].
Dimethyl sulfoxide (DMSO) is an important solvent in chemistry owing to their miscibility with almost all common polar and nonpolar solvents, resulting from their wide applications in industrial and medical field. It is a versatile dipolar aprotic (having a dielectric constant ε = 46.50) self-associated solvent due to SO group with large dipole moment (μ = 3.96D at T = 298.15 K) [18]. The hydroxamic acid functionality, –C(O).N.OH, is a key structural constituent of many biomolecules, some of which are naturally occurring [19] and others such as peroxidase, matrix metalloproteinase and urease inhibitors [20], [21] are of synthetic origin. Hydroxamic acid derivatives have received increasing attention due to their biological activity especially as enzyme inhibitors [22] and metal chelators [23]. Hydroxamic acids are versatile reagents in analytical chemistry [24], [25] and are widely used in medicine as analgetics, anti-inflamatories [26], antibiotics [27], anticancer agent [28], antifungal and hypotentive [29] agent.
For the commercial application of these solutions, it is essential to establish their thermophysical properties including volumetric properties, for solution and their combination with solvent. A number of researchers have measured and reported the thermophysical properties of solute with solvents. Very recently, Ivanov et al. [30] have studied the thermodynamic interrelation between excess limiting partial molar characteristics of a liquid nonelectrolyte. Gadzuric and co-workers [31] have investigated volumetric properties of the solution of N-ethylformamide with tetrahydrofuran, 2-butanone, and ethylacetate at different temperatures. Macedo et al. [32] studied the excess properties of binary mixtures and polar organic compounds. On the other hand, Fernández et al. [33] reported experimental density and viscosity measurements. Shekaari and coworkers [34], [35] made extensive studies of the volumetric properties of different solvent. They reported the volumetric properties for aqueous solutions of 1-alkyl-3-methylimidazolium alkyl sulfate as well as for 1,3-dimethylimidazolium methyl sulfate with different molecular solvents.
Over the past decade, our research group has made some remarkable efforts to study and continue the systematic investigation of thermophysical and excess properties of biochemical processes involving solute–solvent interactions in binary and pure systems using different derivatives of hydroxamic acids in DMSO at different temperatures. The data are lacking in the literature on the densities and optical properties of N-o-tolyl-2-nitrobenzo- and N-o-tolyl-4-nitrobenzo-, hydroxamic acids in pure DMSO at different temperatures. Therefore, in the present study, we report ρ, n of solution over the wide concentration range and at temperatures, T = (298.15, 303.15, 308.15, 313.13, and 318.15) K. The results retrieved through these measurements are used for the computation of different parameters, i.e., Vϕ, , , α2, ∂2/∂T2, we also evaluate the excess properties such as VE, nE, and based on the Lorentz–Lorenz relation. The excess properties were fitted to the Redlich–Kister relations to obtain their coefficients and standard deviations. Thus, the importance of these parameters has been emphasized in order to understand molecular behaviour and the nature of solute–solvent interactions [36], [37], [38].
Section snippets
Materials
Two hydroxamic acids namely N-o-tolyl-2-nitrobenzo- and N-o-tolyl-4-nitrobenzo-, hydroxamic acids were prepared by the procedure reported in literature [39]. The hydroxamic acids were then purified by crystallizing thrice with benzene and dried over phosphorus pentoxide in vacuum for several hours. The purity of the compounds was ascertained by determining their melting points, IR spectra and elemental analyses. Melting points were determined with melting point apparatus (TEMPO) and are
Results and discussion
The ρ and n values of N-o-tolyl-2-nitrobenzo- and N-o-tolyl-4-nitrobenzo-, hydroxamic acids in DMSO at T = (298.15, 303.15, 308.15, 313.13 and 318.15) K are presented as a function of their concentrations in TABLE 3, TABLE 4. FIGURE 1, FIGURE 2 show that ρ and n increases with increase in the concentration of hydroxamic acids respectively.
Conclusions
In this paper, new values of density and refractive index of two structurally related hydroxamic acids, namely N-o-tolyl-2-nitrobenzo- and N-o-tolyl-4-nitrobenzo- were measured in DMSO over a wide concentration range within the temperature range (298.15 to 318.15) K. These parameters have been correlated to the various types of interactions taking place in the solution. Values of the are positive indicating strong solute–solvent interactions which may have implications for the permeation of
Acknowledgements
The authors are thankful to University Grants Commission, New Delhi for providing Senior Research Fellowships and financial assistance under SAP program.
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