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1 9th June 08:53
pureheart
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Default Long-range and short-range mechanisms of hydrophobic attraction and hydrophilic repulsion in specific and aspecific interactions (in vitro)


Research Article

Long-range and short-range mechanisms of hydrophobic attraction and
hydrophilic repulsion in specific and aspecific interactions

Carel Jan van Oss *
Department of Microbiology,
Department of Chemical Engineering and Department of Geology,
State University of New York at Buffalo,
Buffalo, NY 14214-3000,
USA
email: Carel Jan van Oss (cjvanoss@buffalo.edu)


*Correspondence to Carel Jan van Oss, Department of Microbiology,
School of Medicine and Biomedical Sciences, South Campus, State
University of New York at Buffalo, Buffalo, NY 14214-3000, USA

Abstract

Among the three different non-covalent forces acting in aqueous media,
i.e. Lifshitz-van der Waals (LW), Lewis acid-base (AB) and electrical
double layer (EL) forces, the AB forces or
electron-acceptor/electron-donor interactions are quantitatively by
far the predominant ones. A subset of the AB forces acting in water
causes the hydrophobic effect, which is the attraction caused by the
hydrogen-bonding (AB) free energy of cohesion between the water
molecules which surround all apolar as well as polar molecules and
particles when they are immersed in water. As the polar energy of
cohesion among water molecules is an innate property of water, the
hydrophobic attraction (due to the hydrophobic effect) is unavoidably
always present in aqueous media and has a value of Ghydrophobic =
-102 mJ/m2, at 20 C, being equal to the AB free energy of cohesion
between the water molecules at that temperature. The strong underlying
hydrophobic attraction due to this effect can, however, be surmounted
by very hydrophilic molecules and particles that attract water
molecules more strongly than the free energy of attraction of these
molecules or particles for one another, plus the hydrogen-bonding
free energy of cohesion between the water molecules, thus resulting in
a net non-electrical double layer repulsion. Each of the three
non-covalent forces, LW, AB or EL, any of which can be independently
attractive or repulsive, decays, dependent on the cir***stances, as a
function of distance according to different rules. These rules,
following an extended DLVO (XDLVO) approach, are given, as well as
the measurement methods for the LW, AB and EL surface thermodynamic
properties, determined at contact. The implications of the resulting
hydrophobic attractive and hydrophilic repulsive free energies, as a
function of distance, are discussed with respect to specific and
aspecific interactions in biological systems. The discussion furnishes
a description of the manner by which shorter-range specific
attractions can surmount the usually much stronger long-range
aspecific repulsion, and ends with examples of in vitro and in vivo
effects of hydrophilization of biopolymers, particles or surfaces by
linkage with polyethylene oxide (PEO; also called polyethylene
glycol, PEG). Copyright 2003 John Wiley & Sons, Ltd.


Received: 12 November 2002; Revised: 5 March 2003; Accepted: 5 March
2003

http://www3.interscience.wiley.com/cgi-bin/abstract/104547425/START
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