Journal of Molecular Liquids 163 (2011) 83–88

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Journal of Molecular Liquids

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Densimetric and viscometric study of Gly–PVP interactions and EPA of water fittedwith IMMFT at 293.15, 298.15 and 303.15 K

Man Singh ⁎, Jainita S. Patel, Sachin B. Undre, R.K. Kale, Sanjay KumarSchool of Chemical Sciences, Central University of Gujarat, Gandhinagar-382030, India

⁎ Corresponding author.E-mail address: mansingh50@hotmail.com (M. Singh

0167-7322/$ – see front matter © 2011 Elsevier B.V. Aldoi:10.1016/j.molliq.2011.08.005

a b s t r a c t

a r t i c l e i n f o

Article history:Received 25 August 2007Received in revised form 1 July 2011Accepted 1 August 2011Available online 19 August 2011

Keywords:GlycinePVPFedorsIntrinsicHydrophobicViscosityInteractions

Densities (ρ±10−2 kg m−3), and viscosities (η±10−5 kg m−1 s−1 or ±10−2 mPa.s) for 0.05 to0.50 mol kg−1 glycine (Gly) at 0.05 mol kg−1 interval with 2, 4, 6, 8 and 10 mg%dL−1 aqueouspolyvinylpyrrolidine (PVP) at 293.15, 298.15 and 303.15 K are reported. Apparent molar volumes (Vϕ±10−6 m3 mol−1) were calculated from the densities. Limiting apparent (Vϕ

0) or partial [V20] molar volumes

were derived from Vϕ data for entire Gly molality. Transfer volumes [V20tr] of Gly from water to PVP mixtures

are positive. The experimental viscosities were fitted in Fedors model for intrinsic viscosity [η, dl mol−1]. Thevariations in the V2

0 and [η] data with change in PVP concentrations and temperature are explained onelectron pair acceptance (EPA) ability of water when the Gly interacts with PVP. A change in the EPA disruptedhydration cosphere formed around active sites of both the PVP and Gly with hydrogen bonding interactions.The V2

0tr is interpreted as a overlapping of hydrogen cosphere with hydrophobic–hydrophobic, hydrophobic–

hydrophilic and hydrophilic–hydrophilic interactions. A weakening in electrostriction of the Gly zwitterionswith partially polarized groups of the PVP had interacted. The PVP is a macromolecule with several interactingsites and fitted in intramolecular multiple force theory (IMMFT) for Zwitterionic interactions of the Gly.

).

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© 2011 Elsevier B.V. All rights reserved.

1. Introduction

Nonbonding interactions of amino acids with the aqueous PVPmixtures are of biomedical and biophysical interests because of boththe polarized and hydrophobic groups within a single molecule. Suchmixtures develop interesting thermodynamics with optimized mo-lecular activities suitable to biochemical processes with ΔGb0 statedue to spontaneity in interactions. Thus the study of molecularinteracting potential is of significance in case of biomolecularmixtures or blends due to interesting physicochemical properties,may be because of catalyzation by enzymatic activities.

Also the study on varieties of liquid mixtures such as ionic,molecular, semi-molecular, semi-ionic and mixtures of immisciblesolvents with the liquid–liquid interfacial tension of similar signifi-cance are reported in context of enhancing mutual solubilization [1].Since the PVP is a mildly soluble macromolecule and its solubilizationcould be enhanced with Zwitterionic molecules through molecularinteractions with specific activities. The water with H+δ\O−δ\H+δ

electrostatic structure develops stronger intermolecular forces (IMF)with the Gly and PVP because their charge centers excellentlycontribute due to μwater≠μGly≠μPVP chemical potentials in terms ofxwater, xGly and xPVP mole fractions respectively. Had these moleculesbeen ideal then the xwater=1 and xGly=1 with log xwater=0 and the

log xGly=0 would have not caused the molecular interactions. Suchideal condition is not noted in present mixtures where the variationsin physicochemical properties with their compositions inferredinteractions explained with Eq. 1.

μGly mixture = μ0Gly mixture + RT ln xwater + xGly + xPVP

� �ð1Þ

The (xwater+xGly)b0 so log (xwater+xGly)b0 or ΔGb0 whichdepict occurrence of interactions. Thus the intermolecular or ionicforces especially of molionic mixtures are significant for interactionsassisted with models such as Lennard Jone Potential, van der WaalsLondon dispersion forces, for analysis of quality of macromolecularmixtures in context of interactions. The macromolecules such as PVPhave different interacting sites with electrostatic force (ESF) andlonger polyvinyl alkyl chain with stronger covalent binding forces(CBF) due to sp3 hybridization. Both the ESF and CBF are largelydistributed within a single PVP molecule and are fitted in IMMFT [2]where Zwitterionic Gly, a dipolar structure is interestingly alignedwith hydrophilic and hydrophobic sites. Thus the intermolecularinteractions of amino acids with the PVP, a synthetic biocompatiblemacromolecule are of biomedical and biophysical interests [1–6] andpropose a new simulation of the ESF and CBF with the IMMFT [2]. Thephysicochemical properties of such mixtures elucidate the structuralalignments and disruption of hydrogen bonding. Also the study couldbe extended to other members of the PVP such as PVPP (poly-vinylpolypyrrolidone) or the PVPO (polyvinylpyrrolidone oxime) for

84 M. Singh et al. / Journal of Molecular Liquids 163 (2011) 83–88

analysis of their solubility which could be monitored with Gly typezwitterions. Thus the densities, viscosities and partial molar volumesof their mixtures retrieve and reveal peculiar insights of amino acid–PVP interactions [7–9] and a state of IMF. A wider literature surveywas made which inferred a very limited study on physicochemicaldata of such systems. However, viscosity and apparent molar volumesof few binary and ternary systems of the amino acids with severalcompounds are reported [1]. Interestingly, the aqueous Gly–PVPcombinations develop gel type mixtures which could have specificwater and heat holding capacities most suitable to be used for severalmedical purposes. For example, the aqueous PVP mixtures have highiodine adsorbing capacity where the zwitterions could still enhancethe same further for quality of medicinal molionic mixtures. RecentlyHankin et al. has illustrated a significance of partial molar volumes ofaqueous amino acids with rise in temperatures [10–13] for temper-ature dependence of their interactions. Interestingly, the Gly, aprimary unit of amino acids could be used as biosensor with PVPmixtures for an estimation of solvation or gel formation due tovariations in partial molar volume of the PVP [14–17]. Thus the waterbinding activities of the PVP could be analyzed with the amino acidswhere the water as well as the Gly are dipolar molecules and couldhave preferential affinity with PVP incorporated in IMMFT withspecific networking that assists and is suitable to trap drugs or toxicmetals or even act as biosensor. Alkyl chains of the PVP behave astentacles that influence the glycine zwitterions with certain entropicchanges that create fundamental motions noted as tentropy. Thus thestudies are of significance in context of the IMMFT to monitor additiveaccommodating capacity of the PVP mixtures [18,19] and similarothers. Notably the PVP resists a process of hydrolysis even withlactum group in its chain where its combination with Gly could havesome favorable impact. Thus the Gly interactions made with thesynthetic water soluble macromolecules are highly informatory andindustrially significant for colloidal and emulsion mixtures prepara-tion [20,21]. The molar volumes and viscosities are intimatelycorrelated to each other to infer a state of intramolecular sharedelectron pair shift responsible tomonitor quality of resultant mixturesfor industrial uses [22]. Medicochemically, the PVP–Gly–water ternarymixtures are highly biocompatible and develop the IMF that establisheslinks, shear stress and strain with other molecules. Thus our data wouldbe useful whose scientific interpretation opens new gateways formaking industrial mixtures of other similar components such aspolyvinylpolypyrrolidone (PVPP)+amino acids and dendrimers+amino acids. Such manipulations could be useful for developing uniquebiocompatible thin films for filtering nanoparticles and similar others.

2. Experimental

2.1. Material and procedure

PVP of 40,000 average molecular weight (Sigma) and Glycine(99.999%, AR, E. Merck) were used as received for solutionspreparations, w/v, with Millipore water of 5×10−7 S cm−1 conduc-tance. The chemicals were properly dried overnight in P2O5 filledvacuum dessicator and absolute dryness was checkedwith anhydrousCuSO4. Initially, an aqueous PVP stock solution of 1 mol L−1

composition was prepared w/v. The Gly solutions were freshlyprepared by dilution of the 1 mol L−1 stock solution and thenmixed with the w/w % PVP solutions. The solutions were stored atNTP for further use. The densities and viscosities were measured withbicappilary pyknometer and Borosil mansingh survismeter [7–10](calibration no. 06070582/1.01/C-0395, NPL, New Delhi), respectivelyat atmospheric pressure and fairly constant temperatureswith±0.05 °Ccontrol. The equipments were cleaned with standards methods anddried for 24 h in oven at 110 °C. The survismeter was verticallymountedon stainless steel stand at 90° angle and kept in thermostat of 20 Lcapacity water bath for equilibrium. About 15 mL sample was loaded in

Survismeter reservoir bulb [8]. Theweightsweremeasuredwith±10−5

accuracyMettler Toledo balance (MS105 B045083968) and the densitieswere measured to ±10−2 kg m−3 accuracy. The B/t kinetic energycorrection for the Survismeter was determined and found of 10−7orderwhich was incorporated in data [7–9]. Each measurement was repeatedseveral times for better accuracy, precision and reproducibility to 95.5%confidence level. Basically the survismeter is R4M4 (Reduce ReuseRecycle Redesign Multidimensional Multitasking Multitracking Multi-faceted) model equipment for viscous flow times measurementsprecisely with ±0.0001 s accuracy. The viscosities were reproducibleto±10−5 kg m−1 s−1 or±10−2 mPa.s accuracy. Theprocedural detailsof experiments with survismeter are reported elsewhere [8,9].

3. Result and discussion

The Vϕ data were calculated with Eq. 2.

Vϕ =Mρ

+1000 ρ0−ρð Þ

mρ0ρð2Þ

The M is Gly molar mass, m molality, ρ0 and ρ the densities ofsolvent and solution respectively. The m values could also be obtainedfrom molar mass (M) with Eq. 3.

m =wt:1000ρ0

M:Vρð3Þ

The is V required volume, ρmixture density, ρ0 solvent density, wtsolute weight. Dynamic viscosities (η, mPa.s) were calculated withEq. 4.

η =tt0

� �ρρ0

� �� �η0 ð4Þ

The η and η0 viscosities, t0 and t, flow times, the ρ and ρ0 aredensities of solvent and solutions respectively. Relative viscosity(ηr=η/η0) was analyzed with Fedors Eq. 5.

O η1=2r −1=1=η

h im− a−1ð Þ= 2:5 ð5Þ

The, ηr is relative viscosity, [η] intrinsic viscosity, a=1/ϕm, the ϕm

is a maximum volume fraction to which the particle could be packed.The 1/2[ηr

1/2−1]−1 data were plotted against 1/m Gly whose slopevalues had produced intrinsic viscosity [η] and an intercept gave thevalue of “a” and consequently of the ϕm. The 1/[η]m symbol depictsintrinsic viscosity of the solution of molalitym that tends to be zero onextrapolation. The densities were fitted in a linear relation withmolality m as in Eq. 5a.

ρ ¼ ρ0 + Sdm ð5aÞ

The ρ0 inferred limiting density at m=0 and Sd slope. In general,the densities are function of intermolecular forces (IMF) due to aninternal pressure in mixture. For example, the stronger is the IMF andhigher is an internal pressure with a lower volume. Fundamentally,the density ρ=mass/V, thus for lower V, the density is higher whichquantitatively predict a close relationship between structural in-teractions and intermolecular forces.

3.1. Densities

The higher ρ0 values of the Gly are higher than those of the aqua-PVP and inferred stronger interactions with the Gly. The electrostaticGly zwitterions caused stronger IMF than those of the aqua-PVP dueto higher interacting activities of −NH+

3 and −COO− ions. Theincrease in ρ0 and decrease in the Sd (Table 1a) with the PVP

Table 1bLimiting apparent molal volume (Vϕ

0, 10−6 m3 mol−1) and slope (Sv, kg m−3 mol−2).

Systems 293.15 K 298.15 K 303.15 K

Vϕ0 Sv Vϕ

0 Sv Vϕ0 Sv 2

Gly+H2O 42.55 6.31 42.78 10.24 42.96 12.36Gly+2% PVP+H2O 42.70 10.59 42.78 10.35 43.18 14.59Gly+4% PVP+H2O 42.79 11.00 43.83 10.64 43.21 14.91Gly+6% PVP+H2O 42.98 12.41 43.10 10.74 43.31 14.95Gly+8% PVP+H2O 43.12 12.52 43.23 11.74 43.39 15.48Gly+10% PVP+H2O 43.21 13.07 43.36 11.89 43.55 15.76

85M. Singh et al. / Journal of Molecular Liquids 163 (2011) 83–88

concentrations have denoted stronger Gly–PVP interactions thanthose of Gly–Gly and PVP–PVP interactions. Thus with concentrationof the PVP, a gel formation with weaker IMF must have occurred. Theρ0 values are higher for the Gly–water and the lower for the PVP–water than those of the water with stronger IMF between the Gly andwater than that of PVP and water. Thus the Zwitterionic Gly as aminoacid with electrostatic water had developed higher Columbic forcewith the stronger Gly–water interactions than those of the PVP–water. It seems that the Gly zwitterions had caused stronger ESF thanthose of the CBF and the ESF of the PVP. A bulky hydrophobic part ofthe PVP with stronger CBF than that of the ESF of the Gly caused agradient in IMF that developed such interactions. The Gly with−NH3

+

and −COO+ polar groups induced stronger interactions due toColumbic attractive forces noted as IMF in Eq. 6.

IMF ¼qNHþ

3qCOO�

4πε0r2ð6Þ

The IMF is intermolecular forces, the q depicts electrostatic dipolarattraction of NH3

+ and COO− at distance r, ε0 is medium permittivity.Hence a close proximity of opposite charge center influence their rand IMF as a whole. The hydrophobic interactions due to sp3

hybridization are dominant with the PVP and expanded its coiledstructure that attained a larger packing volume. The ρ0 values of theGly with the PVP are higher than those of the Gly–water and of PVP–water which increased with an increase in PVP concentrations. Thusthe Gly developed stronger interactionwith the NC=O of the PVP dueto stronger IMF between the Gly and PVP coil. In increment in the ρ0

values with PVP concentrations showed stronger interactions of theNC=O with −NH3

+ and −COO− of the Gly. It seems that when thePVP coils approach closely then the macromolecular chain entanglewith each other and confine in a smaller space. Such mechanism maydevelop chain segments in the PVP molecules which got fitted ininterstitial voids spaces of the Gly–water hydrosphere with weakerGly–Gly interactions. It might create a natural vacancy to generate theIMMFT which explains a mechanism of the PVP type molecular liquidmixtures and could be extended to giant or supramolecules.

3.2. Partial molal volume

The Gly Vϕ data with molalities (Table 1b) were fitted in Eq. 6 forthe V2

0 values which are independent of the Gly concentrations with anet variation with PVP and is listed in Eq. 7.

Vϕ=V0ϕþSv m ð7Þ

The Vϕ is apparent molal volume, V20 is limiting apparent molar

volume at infinite dilution m≈0, Sv is slope and m as usual. Theapparent molal volumes≠partial molal volumes but limiting appar-ent molar volume=partial molal volumes. Thus the Sv measured arate of change in the Vϕ with Gly concentration and its values have

Table 1aLimiting densities (ρ0, entry 103 kg m−3) and slope (Sd, entry 10−3 kg2 m−3 mol−1).

Systems 293.15 K 298.15 K 303.15 K

ρ0 Sd ρ0 Sd ρ0 Sd

Gly+H2O 0.99823 0.03170 0.99708 0.03109 0.99568 0.03064a PVP+H2O 0.99773 0.07396 0.99707 0.03520 0.99556 0.01067Gly+2% PVP+H2O 0.99790 0.03116 0.99714 0.03097 0.99564 0.03000Gly+4% PVP+H2O 0.99806 0.03095 0.99722 0.03089 0.99564 0.03006Gly+6% PVP+H2O 0.99823 0.03058 0.99731 0.03067 0.99567 0.02983Gly+8% PVP+H2O 0.99827 0.03043 0.99743 0.03043 0.99569 0.02970Gly+10% PVP+H2O 0.99857 0.03028 0.99751 0.03028 0.99572 0.02951

a Concentration of PVP in mg dL−1.

inferred a stabilization or destabilization of the Gly–PVP structuralconfigurations where the interactions occurred between the activesites of the Gly and PVP. The V2

0 and Sv of the Gly with the PVP arehigher than those of the Gly–water (Table 1b). These are plotted inFig. 1 and clearly depicted an impact of the temperature on the partialmolal volumes. The Gly zwitterions being smaller in size could closelyinteract with NC=O of the PVP and the latter being a macromoleculehas n number of interacting sites. For such molecular geometrieswhen dispersed in polar medium, the IMMFT interaction model isapplicable to monitor their interactions because the Gly approachesthe polar sites of the PVP and the CBF get aligned to form a cage ofstructured water around the polyvinyl chain. Thus an additionalvolume in such interactions is generated and is noted as transfervolume (Vϕ

0(tr)) of the Gly and is derived as is noted in Eq. 8.

V20trð Þ

� �= V2

0Gly+water+PVP−ðV2

0Gly+waterÞ ð8Þ

Increase in (Vϕ0(tr)) with the PVP concentrations is noted as 2%

PVPb4%PVPb6%PVPb8%PVP%b10%PVP (Table 1c). In general, avariation in the V2

0(tr) inferred an expansion or contraction in size

of hydration sphere of hydropbic (−CH2−) and hydrophilic (−NH3+,

COO−) groups of the zwitterions. Thus the Vϕ0(tr) with the PVP

concentrations weaken the IMF because the PVP with Gly developedweaker interactions. Thus the water molecules due to hydrogenbonding are fitted with relatively more electronegative oxygen of−COO− of the Gly and NC=O of the PVP via one of the two waterprotons (H\O\H….−O\C=O/O=Cb). If the −COO− of the Glyapproached to a free water proton for hydrogen bonding, a part of thenegative charge on −COO− is transferred to the water via hydrogenbonding hydration between the pertinent water and the COO−. Itinferred a reduction in positive charge on the water proton hydrogenbonded with NC=O, it is with a decrement of the water EPA. Thus thehydrogen bonding hydration of a polar group is destabilized andhydrodynamic volume of the PVP decreased. Since a negative chargedensity on NC=O of the PVP is relatively lower than of the COO− ofGly and the PVP weakened the −COO− water association resultingexpansion of hydration cosphere that led for a positive increment intheV2

0. On the other hand if the−NH3+ approached the water oxygen,

it subtracts the negative charge which enhanced the EPA. The densityof −NH3

+\O=Cbinteraction may be higher because of a lone pair ofelectrons on oxygen atom which occupied more space in comparisonto that of the bonding electron. Then hydrogen bonding hydration ofthe NC=O of the PVP is stabilized. Thus such interactions favorstronger association of the Gly within the PVP IMMFT networkingwith more contraction of the Gly–PVP environment. So an electro-striction between the−COO− and−NH3

+ of the Gly becomes weakerand the overlapping of the hydration cosphere of these groups issuppressed. Thus an overlapping of the hydrogen cosphere of −CH2

−

with−COO− and−NH3+ of the Gly increased resulting into a decrease

in V20. This decrease in volume was compensated by a larger

increment in volume due to a decrease of electrostriction or the ESFand a net result of these interactions caused a positive increment inV20(tr). This has inferred an impact of thermal energy on the ESF forces

42.49

42.57

42.65

42.73

42.81

42.89

42.97

43.05

43.13

43.21

43.29

43.37

43.45

43.53

Gly+H2O Gly+2%PVP+H2O

Gly+4%PVP+H2O

Gly+6%PVP+H2O

Gly+8%PVP+H2O

Gly+10%PVP+H2O

Part

ial m

o1a1

vol

ume

293.15 298.15 303.15 K

Fig. 1. Partial molal volumes (Vϕ0, 10−6m3mol−1) of the Gly depicted on Y-axis at three different temperatures.

86 M. Singh et al. / Journal of Molecular Liquids 163 (2011) 83–88

which weakened electrostriction resulting an expansion in volume(Fig. 1). Beside this, an indirect influence of the−NH3

+ could competewith the water in the hydrogen bonding with the NC=O of PVP. Thehydrogen bond and nitrogen atom in −N\C=O of the PVP are lesssignificant than that of the NC=O group because of a resonancestructure −N\C=O. Thus the dipole–dipole, dipole-induce-dipole,electrostatic, hydrophobic–hydrophobic, hydrophobic–hydrophilicand hydrophilic–hydrophilic interactions of the Gly–water, Gly–PVPand the Gly–PVP–water have led to these variations. For example, ahigher decrease in the V2

0(tr) value at 298.15 K and a slight increase at

303.15 K has denoted the conformational and steriosterical change inthe Gly–PVP interactions. Thus the thermal energy increased atranslational motion of the water molecules which result into arelease of some water molecules from hydration cosphere with adecrease in V2

0(tr) at 298.15 K. A slight decrease in V2

0(tr) at 303.15 K as

compared to the 298.15 K could be because of the Gly which acquired

Table 1cTransfer volume (Vϕ

0(tr)), entry 10−6 m3 mol−1 of Gly.

Systems 293.15 K 298.15 K 303.15 K

Vϕ0(tr) Vϕ

0(tr) Vϕ

0(tr)

Gly+H2O 0 0 0Gly+2% PVP+H2O 0.15 0.05 0.22Gly+4% PVP+H2O 0.24 0.24 0.25Gly+6% PVP+H2O 0.43 0.32 0.35Gly+8% PVP+H2O 0.57 0.45 0.43

a sufficient translation energy to approach the NC=O to initiate adirect hydrogen bonding interaction through NH3

+. These hydrophil-ic–hydrophilic interactions cause a positive increment in the V2

0(tr)

and the hydrophobic–hydrophilic interactions between the −CH2− of

PVP and −COO− of the Gly could result into a negative incrementwith a slight increase in V2

0(tr). The V2

0(tr) of the Glywith PVP (Tables 1b

and 1c) as compared to that of the Gly with water is higher due to acosphere overlap [23–25] and shows an increase in volume on overlapof cosphere of zwitterions. Thus the overlaps of hydrophobic–hydrophobic and hydrophilic–hydrophilic groups of amino acidssuch as Gly induced a net decrease in volume. Constitutionally, the V2

0

is composed up of four volume factors depicted in Eq. 9.

V20 = Vvw + Vf + Vs + Vh ð9Þ

The Vvw is an intrinsic or Van derWaals volume Vf , void volume Vs,contribution mainly from the Gly–water, and Gly–PVP interaction andVh is from hydrophobic hydration of Gly, with its −CH2- group. Thecombination of the Vvw+Vf is the same for the binary and ternarysystems. Thus the expected changes in the Vs+Vh values explainedtrends of the V2

0(tr). The Vs+Vh for the Gly with both the water and

PVP is given by Eqs. 10 and 11.

Vs + Vhð ÞGly + water = VGly−water + VGly−Gly + Vwater−water ð10Þ

Vs + Vhð ÞGly + water + PVP = VGly−Gly + VPVP−Gly + VPVP−PVP

+ VPVP−water + Vwater−water + VGly–water

ð11Þ

Table 2bRegression constants of Fedors relation.

Systems 293.15 K 298.15 K 303.15 K

1/[η] (a-1)/2.5 1/[η] (a-1)/2.5 1/[η] (a-1)/2.5

Gly+H2O 6.4699 0.7169 6.4697 4.8783 6.4688 16.1730PVP+H2O 0.5381 57.7892 0.5381 74.1805 0.5381 85.4397Gly+2% PVP+H2O 2.8376 7.9376 2.9166 4.2306 2.9924 1.2766Gly+4% PVP+H2O 2.6652 10.4990 2.7412 4.5629 2.9964 3.1966Gly+6% PVP+H2O 1.7265 12.0891 1.8544 8.0157 1.8966 1.4685Gly+8% PVP+H2O 1.3001 24.1738 1.4781 21.8615 1.5197 6.5952Gly+10% PVP+H2O 1.0101 41.2879 1.0790 24.1671 1.4557 8.4121

87M. Singh et al. / Journal of Molecular Liquids 163 (2011) 83–88

The contribution from the PVP interaction in form of the VPVP−PVP

is negligible, so the V20(tr) of the Gly from aqueous to the aqueous PVP

is obtained by subtracting the Eq. 10 from Eq. 11.

V20

trð Þ = VPVP−Gly + VPVP−water

= Vhydrophilic−hydrophylic−Vhydrophobic−hydrophobic−Vhydrophobic−hydrophylic

� �PVP−Gly

+ Vhydrophilic−water−Vhydrophobic−waterÞPVP−water

�ð12Þ

The overlapping of the hydrophilic–hydrophilic hydrationcosphere is decreased and the hydrophobic–hydrophilic is increaseddue to hydrophilic–hydrophilic interactions between the NC=O and−NH3

+ and−COO− respectively. The former led to a positive and thelatter to a negative contributions to the V2

0(tr). The positive V2

0(tr)

values have inferred a dominance of the hydrophilic–hydrophilicinteractions over the hydrophobic–hydrophilic. Since such interac-tions are highly sensitive of the temperature and hence differentvalues with increase are noted with PVP % (Fig. 1).

3.3. Viscosities

The dynamic viscosity was best fitted to η=η0+Svis m. The η0

depicts limiting viscosity and the Svis as slope value. Fundamentally,the viscosity is a function of the IMF which is being applied onadjacent layer of a flowing liquid in laminar fashion. In such situationa stronger interaction has inferred a stronger IMF that produced thehigher viscosities but when the interactions are weaker than theviscosities are lower. The η0 values of the PVP aqueous are higher thanthose of the Gly aqueous (Table 2a) due to stronger internal frictionalor resistive force with the PVP. Such behavior could be generated dueto an entanglement of the macromolecule such as PVP within solventphasewhere slowermoving layers exert a higher resistance and fastermoving layers do cause weaker force during a flow via a capillary offixed internal radii. The η0 data for the Gly aqueous with the PVP arehigher than those of the binary systems with a dominance of the PVP–Gly interactions over the Gly–Gly interactions due to IMMFT actionmechanism. Thus a decrease in the Svis inferred the solutesinteractions with an increasing PVP concentration (Table 2a), andweakening of the Gly–Gly interaction. The η0 decrease with anincrease in temperature, showed higher translational kinetic energythat allowed intermolecular interactions to be overcome more easily.Thus with the PVP the momentum transfer between layers occurredmainly by collisions among the molecules in adjacent layers. Howeverthere could not be an actual transfer of molecules between layers. Thevalues constants of Fedors equation noted as intrinsic viscosities [η](Tables 2b and 2c) of the PVP are higher than of the Gly aqueous. Thusthe intrinsic viscosities plotted in Fig. 2 are increased with the PVP %which inferred that an aggregation gets clustered with higher IMFwith larger sizes. However, the [η] values for the Gly with PVP arelower than those of the PVP and higher than of the Gly with strongerGly–PVP interaction. The Gly, being a smaller in comparison to thePVP, gets embedded into a randomly coiled PVP molecule and the

Table 2aLimiting viscosity (η0) and slope (Svis) of η=η+Svis m equation.

Systems 293.15 K 298.15 K 303.15 K

η0 cp Svis η0 cp Svis η0 cp Svis

Gly+H2O 1.0024 0.1406 0.8906 0.1397 0.7988 0.0932PVP+H2O 1.0046 0.5914 0.8932 0.4380 0.8003 0.3444Gly+2% PVP+H2O 1.0048 0.3395 0.8943 0.2804 0.8007 0.2669Gly+4% PVP+H2O 1.0099 0.2502 0.8965 0.2602 0.8021 0.2400Gly+6% PVP+H2O 1.0142 0.2836 0.9003 0.2949 0.8044 0.3641Gly+8% PVP+H2O 1.0179 0.1972 0.9027 0.2035 0.8072 0.3397Gly+10% PVP+H2O 1.0189 0.1331 0.9067 0.1804 0.8082 0.3256

−NH3+ interacted strongly with the NC=O through the hydrogen

bonding. Thus the Gly developed an internal force that enables thePVP contraction with a lower effective hydrodynamic volume of theGly–PVP complex that however decreased the [η] with PVP but thevalues increased with an increase in PVP concentration (Table 2c).Such valuable contributions could be attributed to an increase inNC=O/−NH3

+ ratio of partial charge on the −NH3+ which is

diminished with a weakening in forces with concentration. Thus anexpansion associated with the Gly–PVP interactions decreasedeffective hydrodynamic volume. Thermal energy increased a transla-tional kinetic motion where the larger molecules such as PVP, PVPP,proteins and others acquired sufficient energy to overcome an energybarrier which is required to initiate effective interaction [25]. Thetrends of the η0 and Svis values have inferred weakening of the Gly–Gly interaction with the PVP and its concentration that enhanced thePVP–Gly–water interactions, respectively. The polar ends of the Glydirect towards partially polarized NC=O and hydrophobic −CH2

− ofthe Gly did outward due to a repulsive interaction between thehydrophobic group of the Gly and PVP. Such molecular alignmentassociated with the hydrophobic and hydrophilic groups reducedelectrostatic forces between the hydrospheres of the PVP–Gly–water.

4. Conclusion

The [η] values of the Gly with PVP concentrations and temperaturecaused both the increment and decrement of electron pair acceptance(EPA) of water. A change in the EPA caused a stabilization anddestabilization of the hydration cosphere associated with active siteswithin the IMMFT of the PVP and Gly. The variation in V2

0(tr) of Gly are

interpreted with an overlapping of the hydrogen cosphere with vander Waal, hydrophobic–hydrophobic, hydrophobic–hydrophilic andhydrophilic–hydrophilic interactions. A decrease of electrostrictionforces of the Gly dipoles with partially polarized groups of PVP causeda net result. Also the entanglement of the solvent molecules wasexplained with IMMFT models due to ESF and CBF contributions.

Acknowledgments

Authors are thankful to the University Grant Commission, Govt. ofIndia, New Delhi, for financial support.

Table 2cIntrinsic viscosities [η] with Fedors relation.

Systems 293.15 K 298.15 K 303.15 K

[η]/kg mol−1 [η]/kg mol−1 [η]/kg mol−1

Gly+H2O 0.1546 0.1546 0.1546PVP+H2O 1.8584 1.8584 1.8584Gly+2% PVP+H2O 0.3524 0.3428 0.3342Gly+4% PVP+H2O 0.3752 0.3648 0.3337Gly+6% PVP+H2O 0.5792 0.5392 0.5272Gly+8% PVP+H2O 0.7692 0.6765 0.6580Gly+10% PVP+H2O 0.9900 0.9268 0.6869

0.10

0.21

0.32

0.43

0.54

0.65

0.76

0.87

0.98

1.09

1.20

1.31

1.42

1.53

1.64

1.75

1.86

Gly+H2O PVP+H2O Gly+2%PVP+H2O

Gly+4%PVP+H2O

Gly+6%PVP+H2O

Gly+8%PVP+H2O

Gly+10%PVP+H2O

Intr

insi

c vi

scos

ity

293.15 298.15 303.15 K

Fig. 2. Intrinsic viscosities ([η], kg mol−1) of the Gly depicted on Y-axis at three different temperatures.

88 M. Singh et al. / Journal of Molecular Liquids 163 (2011) 83–88

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