2. 1. D 0 = k B T. k B T. , r Tsinghua Tongfang Optical Disc Co., Ltd. All rights reserved.

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1 ( FENXI HUAXU E) Chinese Journal of Analytical Chemistry (, 51061),,,,,, 0. 5 mol/ L, DLVO,,,, Z P = e Hamaker = 2. 8 k B T,,, 1,,,,, p H,, ;, 2, [1 ],, Wu [2 ],,,, DLVO , [, ] D 0, D 0 D 0 = k B T 6 r k B T,, r (1) ; (No. 2002CCC00400) (No ) (No )

2 [4,, ] D = D 0 [1 + + ( 2 ) ] + ] = D 0 [ A + s + D ) + ( 2 ) + ] (2) D 0,, Virial Oseen, s, D, g ( r) [5,6 ] A = - a 0 = a 2 0 a [ ( a r ) 6 - = - s = 75 0 [ g ( r) - 1 ] r2 dr, () [ g ( r) - 1 ] rdr, (4) 4 g ( r) a ( a r ) g ( r) r2 dr, (5) r 5 dr, (6) D = 1, (7) g ( r) W ( r) [7,8 ] g ( r) = e - W ( r) / k B T (8), W ( r), g ( r), 2., 2 DLVO [9 ],,,,,, Stern, W HS ( r) =, r 2 a 0, r > 2 a r, 2 a, W disp ( r) = - Hamaker [10 ] 12 4 a 2 r 2-4 a a2 r 2 + 2ln ( r2-4 a 2 r 2 (9), r > 2 a (10) [11, ] W elec ( r) = Z2 p e 2 - ( r - 2 a) e 4 r (1 + ) 2 (11) [10 Debye2H ckel ], e,. 1 ( ), ; 50 mmol/ L, p H , , NaCl, mol/ L, 220 nm,, (10000 g) 0 min,

3 [12 ] (coherent,verdi2v10, 0. 1 %), 10 mw, 52 nm Flex99R2160B ( correlator ),272, 150 ns, [1 ], 6, 1 1 Table 1 Diffusion coefficients at different ionic strength I (mol/ L) ( 10 ) D ( 10 7 ) cm 2 / s Error I (mol/ L) ( 10 ) D ( 10 7 ) cm 2 / s Error I (ionic strength) ; (volume fraction) ; p H = 5. 4 ; T = 27, (2), D, ( = 0), D 0 = ( ) 10-7 cm 2 / s (4) nm D D 0, D/ D 0 < ( 1),,, ( I mol/ L),, ;,,, ( 2) 2 Table 2 Values of and at different ionic strength I (mol/ L) (109 m - 1 ) Z p Hamaker 1 D/ D 0 Fig. 1 At different ionic strength, normalized diffusion co2 efficient D/ D 0 as a function of volume fraction mol/ L ; mol/ L ; mol/ L ; mol/ L ; mol/ L ; mol/ L (6) (9), Z p, p H,, [14, Z p ]

4 , Z p, A H Z p,, Z p, mol/ L ( Z p, ) 2 4. Batchelor [4 ] Felderhof [15 ],, ;, 1 2 Z P Hamaker, I = mol/ L Fig. 2 Protein charge Z P versus Hamaker,, constatant DLVO (Derjaguin2Verwey2Landau2Overbeek), 2, a (the plotted curves correspond to the interaction pa2 W total = W elec + W disp rameter at different ionic strength),, I = mol/ L, ( the curves have a common locus with coordi2 nates) Z P = e, = 2. 8 k B T,,,,,,,, b,, ( mol/ L) (a) (b) 0150 mol/ L, Fig. The potential of mean force between two protein molecule as a, function of distance for I = mol/ L (a) and dependence of the po2, tential of mean force on ionic strength (b) 4 (parameters) Z P = - 9 e, / k B T = 2. 8, a =. 45 nm A. 1., (electrostatic force) ; 2. (total force) ;. (Van der Hamaker, Waals force ) ; B mol/ L ; mol/ L ; mol/ L ; mol/ L,,, mol/ L 2 a = 16,, 5,, 4 ;, Fig. 4 Interaction parameter as a function of, DLVO dimensionless parameter 2 (parameters) Z p = e, = 2. 8 k B T,

5 140 2, Z P = e = 218 k B T References 1 Vekilov P G, Feeling2Taylor A R, Petsev D N, Galkin O. Biophycial Jouranl, 2002, 8 (2) Wu J, John M. Praunitz. Fluid Phase Equilibria, 1999, Bar2Ziv R, Meller A, Tlusty T, Moses E, Stavans J, Safran S A. Phys. Rev. L ett., 1997, 78 (1) Batchelor G K. J. Fluid Mech., 1976, Pecora R. Dynamic L ight Scattering, A pplications of Photon Correlation S pect roscopy. New York and London Oxford Science Publ., Eberstein W, Georgalis Y, Saenger W. Journal of Crystal Grow th, 1994, Kirkwood J G. J. Chem. Phys., 194, Kirkwood K G. Chem. Rev., 196, Narayanan J, Liu X Y. Biophysical Journal, 200, 84 (1) Hamaker H C. Physica, 197, Petsev D M, Denkov N D, Nagayama K. Chem. Phys., 199, Li Shaoxin( ), Xing Da ( ), Tan Shici ( ). Journal of Optoelect ronics L aser ( ), 200, Koppel D. J. Chem. Phys., 1972, Kuehner D E, Ramsch C. Biophysical Journal., 1997, Felderhof B U. J. Phys. M ath. Gen., 1978, Molecular Interactions of Bovine Serum Albumin in Electrolyte Solutions Studied by Dynamic Light Scattering Li J unfeng, Xing Da, Li Shaoxin ( Institute of L aser L if e Science, South China Norm al U niversity, Guangz hou 51061) Abstract The concentration dependence of the diffusion coefficient of particles suspended in solution de2 pends primarily on t he occupied volume f raction and on repulsive and att ractive forces. This dependency is expressed by the interaction parameter. In the present work we have measured the diffusion coefficient of Bovine Serum Albumin at different ionic st rengt h and determined t he interaction parameter. The result s in2 dicate the value of is positive at low ionic strength and the interaction between proteins is repulsive ; however, with increasing ionic strength the value of becomes negative and the interaction is attractive, and when ionic strength is higher than 0. 5 mol/ L aggregation occurs. The dependence of the interaction on ionic st rengt h is interpreted using Derjaguin2verwey2landau2overbeek ( DL VO) t heory for interactions of two hard spheres with increasing ionic strength, the repulsive electrostatic interaction is screened and Van der Waals forces become dominant. According to the correlation of with ionic strength, the protein pa2 rameters are regressed the protein net charge Z P = e, Hamaker constant = 2. 8 k B T. Ex2 perimet ns work indicate t he technique of dynamic light scattering can be used effectively to st udy protein molecular interactions. Keywords Dynamic light scattering, protein interaction, diffusion coefficient, interaction parameter (Received 8 December 200 ; accepted 9 May 2004)