Indi an Journal of Chemistry Vol. 43A , October 2004, pp. 2073-2080 Studies of osmotic coefficients and volumetric behaviour on aqueous solutions of ~-cyclodextrin at 298.15 K Dilip H Dagade, Rahul R Kolhapurkar & Kesharsingh J Patit* Department of Chemistry, Shivaji Universi ty, Kolh apu r 416 004, Indi a Email: patilkcsharsin [email protected] Received 31 March 2004; revised 11 August 2004 The osmotic coefficient . solute activity coefficients and apparent molar vo lume are determined for ~-c y clodc x trin (~ -CD ) using the techniques of vapor press ure osmometry and digital densitometer in aqueous solutions (0.00 164 to 0.01308 1 mol kg' ) at 298.15 K. The th ermodyn ami c data of acti vities and partial molar volumes for so lvent and solute are computed usin g appropriate methodology and equations. Theories of dilute so lutions such as McMillan-Mayer and Flory- Hu gg in s arc app li ed to es timate th e second vi rial coefficient (8*2) for ~-CD , the number of binding si tes and x12 interaction parameter. Usin g the parti al mol ar volume data at infinite dilution and 8*2 val ue, the contribution du e to solute-solvent and solute­ solute interactions in terms of attracti ve and repul sive components are estimated. The values or 8*2 and the components are compared with th e val ue s reponed for mono-saccharides. di saccharidcs an d other non-electrolytes. The results are discu ssed in terms of hydrophobic hydration and hydrophobic interaction. IPC Code: Int. Cl 7 GO IN 13/04 Thermodynamic methods are frequently employed in stabilized by weak van der Waals forces. Therefore, it the studies of the properties of natural biopolymers, was thought pertinent to obtain information about the nucleic acids and polysaccharides 111 aqueous interaction in solution phase where the solubility is so I uttons. t-3 . I n recent years a new fi1 e ld , limited. We report here the osmotic coefficient and supramolecular chemistry, has emerged in which the density measurement for aqueous ~-CD solutions at intermolecular interactions of the host-guest type are 298.15 K. The data are subjected to scrutiny by 3 14 generally studied .4. Among all potential hosts, the application of McMillan-Mayer as well as Flory­ 15 cyclodextrins are important because of their inclusion Huggins theories developed for solutions . complex forming ability which results in molecular encapsulation of the guest components. Materials and Methods A study of association between ~-CD and various ~-CD (98 % pure) procured from Merck­ 5 drugs has been made by microcalorimetric methods. Schushardt was dried at 100 oc under vacuum for Similarly, many spectroscopic methods are employed about 48 hours and used without further purification. 6 7 to determine the binding constants · . However, it is The analysis of the sample for water content was felt that no adequate attention has been given to made using Karl-Fischer titration method. It was understand the host-solvent interaction, although the found that the sample is well dried and has no disaccharides and polysaccharides interactions in measurable presence of water molecules. 13 All the 8 11 water have been understood in detail - • solutions were prepared on molality basis using Cycloamylases have hydrophobic cavities that can doubly glass distilled deionized water. NaCl salt of form inclusion complexes depending upon the AR grade (BDH) was dried under vacuum for 24 structure of guest molecules (functional group, charge hours at l20°C and used for calibration of osmometer. 12 effects etc.) and cavity diameter . Recently, we The densities were measured with the help of studied the presence of water in solid ~-CD and found Anton Paar oscillating tube digital densitometer that there are seven water molecules per ~-CD (Model DMA 60/602) at constant temperature 298. 15 molecule using Karl-Fischer and TGA-DT A ± 0.02 K. Water from Julabo F25 cryostat (having an 13 technique . It is proposed that these water molecules accuracy of ± 0.02 K) was circulated through the may be H-bonded with the etheric oxygen atoms of~­ densitometer. The densitometer was calibrated with CD or may be in the form of spiral like cluster air (the appropriate humidity and pressure corrections 2074 INDIAN J CHEM, SEC A. OCTOBER 2004 were appli ed) and water. The reproducibility of 3 3 density measurements was better than ±5x 10· kg m- . .. (2) The osmotic coefficients (<t> of B-CD solutions were determined using KNAUER K-7000 vapor pressure osmometer at 298.15 ± 0.001 K. The instrument was where n1 is number of moles of water and V1° is the kept in refrigerated thermostated house, fabricated in molar volume of water at 298.15 K. The data of ifJv, our laboratory, working between 0 and 40°C. The V , V, and densities obtained at different B-CD instrument was calibrated using aqueous NaCI 2 solutions of known osmolality for which the osmotic concentrations are collected in Table 1. coeffici ent data of NaCI was taken from literature 16 The variation of ifJv as a function of concentration of (the accuracy of <t> was found to be better than ±1 x l0·3 B-CD is depicted in Fig. 1. The calculated values of at the lowest concentration studied). V2 and V, are plotted against molality and the va lues -o -o Result and Discussion of V 2 and V, are estimated by smooth extrapolation The apparent molar val umes ( ifJ.,) of B-CD in water to infinitely dilute concentration. There is no standard were obtained from the density data in the method available for aqueous non-electrolyte concentration range 0.00164 to 0.01308 mol kg·'. The sol utions in contrast to aqueous electrolytes solutions where one can use the Debye-HUckel limiting law. 18 errors in ifJv data were estimated using Redlich and 17 However, our experimental concentration range is Bigeleisen equation very dilute and hence we are justified to obtain - - o 10008d 1000(d - d 0 )8c infinitely dilute solution value of V2 as V 2 by ---+--..:__-~- doc c -o smooth extrapolation. The V 2 value obtained (7 18.9 3 1 c m mol' ) is in reasonable agreement with the value where, d and d0 are the densities of solu tion and 3 1 19 solvent respecti vely, while 8d, 8c, are the (709 ±2 cm mol' ) reported by Hoi land et al. It is uncertainties in density and concentration (c is the felt that these authors probably have studied only one molarity of B-CD). The estimated error in the ifJ" or two concentrations and the sample may contain va lues at the lowest concentration is about ±3 cm3 some water molecul es. Also, the purity may depend mol'1 and at the hi ghest concentration studied, it is of upon the method of synthesis of B-CD. The 3 1 the ord er of ±0.4 cm rnol' . The parti al mo lar volume concentration variation of ifJ., (Fig. I) indicates further ( V2 ) of B-CD at various concentrations were the presence of solute-solute interaction as difJ,. IS dm estimated usin g Eq. (l) negative. The osmotic coefficients of aqueous B-CD -v2 =-rrr. ,. + 111 [difJ,J- ... (1) dm solutions were determined over the range 0.00164 to 0.01308 mol kg·' at 298.15 K. The data are The calculations of partial molar volumes ( V, ) of represented by Eq. (3) water at different concentrations of B-CD were made usi ng Eq. (2) <J) = 1 + 7 .1651m- 251.97 m2 +II I 14111 3 ... (3) Table !- Density, ¢v· y2. v, .water activity. osmotic coefficient. and act ivity coefficient data for aqueous 13-CD sol utions at 298. 15 K Ill d ¢,. v2 v, ¢ G w y, Y2 L'.CE 1 kg m-3 3 1 1 mol kg' cm moJ' cm3mor 1 cm3mor 1 J mor 0.00 164 997.733 7 16.9 7 15.0 18069 1.0 12 14 0.999970 I .000000 I .02208 0.001 0.003 14 998.365 7 15 3 7 12. I 18. 070 I .02044 0.999942 0'.999999 I .04208 0.003 0.00487 999.096 7 13.7 709.6 18.070 1.02972 0.9999 10 0.999997 I .06376 0.007 0.00666 999.854 7 12.4 707.9 18.070 I .03955 0.999875 0.999995 I .08621 0.0 13 0.01004 1001 .286 7 10.7 707.3 18.070 I .05828 0.999809 0.999989 12839 0.028 0.01308 1002.565 7 10. I 709.5 IS 069 I .07532 0.999747 0.999982 I. 16747 0.047 DAGADE eta!.: OSMOTIC COEFFICIENTS & DENSITIES OF 0-CYCLODEXTRIN SOLUTIONS 2075 725 1.08 720 1.06 0 5 ~8 7 15 <J ~ 1.04 710 1.02 705 1.00 IL_--------~----------~--------~ 700 L_--------~----------~--------~ 0 0.005 O.QI 0.0 15 0.000 0.005 0.0 10 0.0 15 m / molkg-1 m /mol kg·' Fig. !-Apparent molar volume (¢v) of 0-CD as a function of Fig.2-Variation of osmotic coefficient (¢) of 0-CD in water as a molality (m) of 0-CD in water at 298. I 5 K. function of molality (m) of 0-CD at 298. I 5 K. The solvent activity coefficients were calculated water activity decreases slightly as a function of mole from experimental osmotic coefficient (<I>) data fraction of B-CD. following the procedure as described earlier for 18- The activity coefficient of solute (y2) has been 20 crown-6 (18C6)-H20 system and ustng the calculated using Eq.