Carbohydrate Research 315 (1999) 63 – 69
Hydration of glucose in the rubbery and glassy states
studied by molecular dynamics simulation
Ernesto R. Caffarena
1
, J. Raul Grigera *
Instituto de Fı ´sica de Lı ´quidos y Sistemas Biolo ´gicos (IFLYSIB)
UNLP -CONICET and Departamento de Ciencias Biolo ´gicas, Uniersidad Nacional de La Plata, c.c. 565,
1900 La Plata, Argentina
Received 10 June 1998; revised 2 November 1998; accepted 27 November 1998
Abstract
We have studied the hydration properties of an 85% (w/w) aqueous solution of glucose using molecular dynamics.
The experimental values of the relative populations of and anomers were introduced into the description of the
system. We computed the radial distribution function, hydrogen bond residence times, hydration number and mean
lifetimes, as well the mean glucose and water cluster sizes. The simulated glass transition temperature (T
g
) of the
solution was computed to evaluate the quality of the model; the computed value of 241 K was in fair agreement with
the experimental value of 232 K. It was concluded that most of the water molecules are connected to more than one
glucose molecule by hydrogen bonds. The residence time of the water molecules in hydration sites changes from one
site to another, but for the anomeric and chain-oxygen atoms, the residence time is greater than for the rest. The
average residence time goes from 2.00 ps for the rubbery state at 280 K to 5.75 ps for the glassy state at 200 K. The
mean value of the cluster size of glucose is very close to the corresponding to full connectivity and does not vary
much from the rubbery to the glassy state. © 1999 Elsevier Science Ltd. All rights reserved.
Keywords: Glass transitions in carbohydrates; Glucose hydration; Carbohydrate percolation; Molecular dynamics simulation of
hydration
1. Introduction
Glasses of various carbohydrates are found
in nature as protecting systems for biological
polymers under conditions of drought or
severe cold [1]. The practical applications of
this property are mainly associated with the
food and pharmaceutical industries [2 – 6]. To
maintain the quality and stability of products,
advantage is taken of the fact that a high
concentration of carbohydrate can prevent the
damaging effects produced by water crystalli-
sation at low temperatures [7,8]. Preservation
and encapsulation of compounds are the main
applications of this protective effect of saccha-
rides. Generally, preservation is related to the
shelf life of unstable compounds such as
medicines and enzymes, whereas encapsula-
tion usually has to do with the role of matrix
in retaining flavours in processed foods. Dis-
accharides and oligosaccarides are often used
for these purposes [9]. A possible mechanism
to explain this effect is the partial replacement
of water by carbohydrates as a solvating agent
[10]. Nowadays, the glass transition is recog-
nised as a physicochemical event (i.e., a
* Corresponding author. Tel.: +54-21-254904/233283; fax:
+54-21-257317.
E -mail address: grigera@iflysib1.unlp.edu.ar (J.R. Grigera)
1
Also at the Facultad de Ingenierı ´a, Universidad Nacional
de La Plata, La Plata, Argentina.
0008-6215/99/$ - see front matter © 1999 Elsevier Science Ltd. All rights reserved.
PII:S0008-6215(98)00316-4