Acoustic and Volumetric Properties of Digoxin and Thiabendazole in 1 , 4 Dioxane at 303 K A

Acoustical and volumetric properties have been measured for substituted heterocyclic compounds digoxin and thiabendazole in 1, 4 dioxane at 303 K. The ultrasonic velocity measurement have been performed to evaluate acoustical parameter such as adiabatic compressibility (βs), partial molal volume (φv), intermolecular free length (Lf), apparent molal compressibility (φκ), specific acoustic impedance (Z), relative association (RA), salvation number (Sn), limiting apparent molal compressibility (φκ), limiting apparent molal volume(φv) and their constant (Sk,Sv). The viscosity coefficient (A, B) was evaluated by using john–dole equation. These parameters throw the light on the solute-solvent interaction and solute-solute interaction.


Introduction
In the recent years, measurements of the ultrasonic velocity are helpful to interpreted solutesolvent, ion-solvent interaction in aqueous and non aqueous medium [1][2][3][4] .Fumio Kawaizumi 5 have been studied the acoustical properties of complex in water.Jahagirdar et al. has studied the acoustical properties of four different drugs in methanol and concluded from adiabatic compressibility.The four different drugs compress the solvent methanol to the same extent but it shows different solute-solvent interaction due to their different size, shape and structure 6 .Meshram et.al. studies the different acoustical properties of some substituted pyrazolines in binary mixture acetone-water and observed variation of ultrasonic velocity with concentration 7 .Palani have investigated the measurement of ultrasonic velocity and density of amino acid in aqueous magnesium acetate at constant temperature 8 .The ion-dipole interaction mainly depends on ion size and polarity of solvent.The strength of ion-dipole attraction is directly proportional to the size of the ions, magnitude of dipole.But inversely proportional to the distance between ion and molecules.Thirumaran e .al. 9 has been studied acoustical properties of ternary liquids of substituted benzenes with 1chlorobutane at different temperature.Syal et al. has been studied the ultrasonic velocity and viscosity of PEG-8000, PEG-study of acoustical properties, viscosity coefficient of substituted heterocyclic compounds under suitable condition 10 .

Experimental
The substituted heterocyclic compounds digoxin and thiabendazole were used in the present study.Dioxane was purified by Vogel's standard method 11 .The double distilled dioxane was used for solution preparation of different concentration of drugs.The density was determined by using specific gravity bottle by relative measurement method with accuracy ± 1x10 -5 g/cm 3 .The ultrasonic velocity was measured by using ultrasonic interferometer having frequency 2MHz (Mittal Enterprises, Model No F-81).The constant temperature was mentioned by circulating water through the double wall measuring cell made up of steel.For viscosity measurement Ostwald Viscometer was used.The flow time was measured by using digital clock (0.01 sec).
From Table 1, ultrasonic velocity decreases with increase in concentration for both systems.Variation of ultrasonic velocity in solution depends upon the increase or decrease of molecular free length after mixing the component, based on a model for sound propagation proposed by Eyring and Kincaid 12 .It was found that, intermolecular free length increases linearly on increasing the concentration of substituted heterocyclic compounds (Digoxin and Thiabenazole) in dioxane.The intermolecular free length increases due to greater force of interaction between solute and solvent by forming hydrogen bonding.Hence, decrease in ultrasonic velocity with increase in concentration of substituted heterocyclic compounds.This was happened because there is significant interaction between ions and solvent molecules suggesting a structure promoting behavior of the added electrolyte.This also may indicate that decrease in number of free ions showing the occurrence of ionic association due to weak ion-ion interaction.The value of specific acoustic impedance (Z) decreases with increase in concentration in both substituted heterocyclic compounds in dioxane.When concentration of electrolyte is increases, the thickness of oppositely charged ionic atmosphere may increases due to decrease in ionic strength.This is suggested by decrease in acoustic impedance with increase in concentration in both system investigated.The increase of adiabatic compressibility with increase of concentration of solution may be due to collection of solvent molecule around ions, 13 this supporting weak ion-solvent interaction.This indicates that there is significant solute-solvent interaction.The increase in adiabatic compressibility following a decrease in ultrasonic velocity showing there by weakening intermolecular interaction.From Table 2, it is observed that apparent molal volume increases with concentration in both system indicates the existence of strange ion-solvent interaction.The value of apparent molal compressibility is increase with increase in concentration of both system in dioxane.It shows strong electrostatic attractive force in the vicinity of ions.It can be concluded that strong molecular association is found in Digoxin than thiabendazole.The value of relative association increases with increase in concentration in both systems.It is found that there is strong interaction between solute and solvent.Table 2.The values of concentration (m), relative association (R A ), apparent molal compressibility (φ κ ), apparent molal volume (φ v ), solvation number (S n )-digoxin, thiabendazole in 1,4 dioxane at K.
The solvation number increase with increase in concentration due to strong solute-solvent interaction.There is regular increase in solvation number with increase in concentration indicates the increase in size of secondary layer of solvation.The solvation number in digoxin -1, 4 dioxane system increases with concentration indicates the solvent molecule forms strong coordination bond in primary layer.The solvation number in primary layer corresponds to coordination number and it is concentration independent.The solvation number in secondary layer is concentration dependent.The concentration increases, solvation number increases indicates the solvent molecules are also strongly attached in secondary layer.
The limiting molal compressibility is positive in digoxin indicates existence of weak solute-solvent interaction in solution.The limiting molal compressibility is negative in thiabendazole indicates existence of strong solute-solvent interaction in solution.The value of S k exhibits negative in thiabendazole.It indicates the weak existence of ion-ion or solutesolute interactions in thiabendazole system.The value of S k exhibits positive in thiabendazole  3 it is found that the value of limiting apparent molal volume is positive in both systems.It indicates that the ion-dipolar interaction in thiabendazole, digoxin and 1, 4 dioxane .The positive value of S v indicates the strong solutesolvent interaction.These value indicates induced effect of 1, 4 dioxane on solute-solvent interaction.
From Table 4 it is observed that the value of 'A' (Falkenhagen coefficient) are positive in both system studied.'A' is measure of ionic interaction.It indicates that there is a strong solute-solute interaction in solute molecules.'B' is Jones-Dole coefficient measures solutesolvent interaction.The value of 'B' coefficient is negative in both drugs.Solute with negative 'B' coefficient is characterized as 'Surface breaker' indicating weak solute-solvent interactions.

Conclusion
Acoustic and volumetric properties of digoxin and thiabendazole in 1, 4 dioxane at 303 K was studied and the experimental data was presented.From the experimental data solutesolvent interaction and ion-ion / solute-solute interaction was discussed and it's existing between drugs and 1, 4 dioxane was also explained.From experimental data it can be conclude that, there is a weak solute-solvent interaction in digoxin-1, 4 dioxane systems and strong solute solvent interaction in thiabendazole-dioxane system.
dioxane system, it indicates the existence of ion-ion or solute-solute interactions in thiabendazole system.From Table