14,149 research outputs found
Metastability and nucleation in the dilute fluid phase of a simple model of globular proteins
The dilute fluid phase of model globular proteins is studied. The model
possesses a fluid-fluid transition buried within the fluid-crystal coexistence
region, as do some globular proteins. If this fluid-fluid transition is not
buried deep inside the fluid-crystal coexistence region the crystalline phase
does not nucleate within the dilute fluid. We link this lack of nucleation of
the crystal to the interactions in our model and speculate that similar
interactions between globular proteins are responsible for the difficulty found
in crystallising many globular proteins.Comment: 11 pages, 4 figure
Phase behaviour of a simple model of globular proteins
A simple model of globular proteins which incorporates anisotropic
attractions is proposed. It is closely related to models used to model simple
hydrogen-bonding molecules such as water. Theories for both the fluid and solid
phases are presented, and phase diagrams calculated. The model protein exhibits
a fluid-fluid transition which is metastable with respect to the fluid-solid
transition for most values of the model parameters. This is behaviour often
observed for globular proteins. The model offers an explanation of the
difficulty observed in crystallising some globular proteins and suggests that
some proteins may not have a solid phase at all under all but extreme
conditions.Comment: 12 pages including 5 figures Error in B2 of vdW fluid correcte
The role of long-range forces in the phase behavior of colloids and proteins
The phase behavior of colloid-polymer mixtures, and of solutions of globular
proteins, is often interpreted in terms of a simple model of hard spheres with
short-ranged attraction. While such a model yields a qualitative understanding
of the generic phase diagrams of both colloids and proteins, it fails to
capture one important difference: the model predicts fluid-fluid phase
separation in the metastable regime below the freezing curve. Such demixing has
been observed for globular proteins, but for colloids it appears to be
pre-empted by the appearance of a gel. In this paper, we study the effect of
additional long-range attractions on the phase behavior of spheres with
short-ranged attraction. We find that such attractions can shift the
(metastable) fluid-fluid critical point out of the gel region. As this
metastable critical point may be important for crystal nucleation, our results
suggest that long-ranged attractive forces may play an important role in the
crystallization of globular proteins. However, in colloids, where refractive
index matching is often used to switch off long-ranged dispersion forces,
gelation is likely to inhibit phase separation.Comment: EURO-LATEX, 6 pages, 2 figure
Crystal nucleation for a model of globular proteins
A continuum model of globular proteins proposed by Talanquer and Oxtoby (J.
Chem. Phys. vol. 109, p. 223 (1998)) is investigated numerically, with
particular emphasis on the region near the metastable fluid-fluid coexistence
curve. Classical nucleation theory is shown to be invalid not only in the
vicinity of the metastable critical point but also close to the liquidus line.
An approximate analytic solution is also presented for the shape and properties
of the nucleating crystal droplet.Comment: 15 pages, 16 figure
A Model for the Thermodynamics of Globular Proteins
Comments: 6 pages RevTeX, 6 Postscript figures. We review a statistical
mechanics treatment of the stability of globular proteins based on a simple
model Hamiltonian taking into account protein self interactions and
protein-water interactions. The model contains both hot and cold folding
transitions. In addition it predicts a critical point at a given temperature
and chemical potential of the surrounding water. The universality class of this
critical point is new
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