International Journal of Biological Macromolecules
Thermoreversible gelation in aqueous binary solvents of chemically modified agarose
Introduction
Due to the paucity of the X-ray diffraction pattern on dried and stretched gels of agarose, the molecular structure is still a matter of debate [1], [2]. In particular, whether double or single helices are dealt with remains controversial although recent developments have suggested that single helices could be better candidates [2], [3], [4]. Similarly, the formation of complexes between agarose and the solvent is another question of interest as it has a direct bearing upon the gelation properties of this polymer [5]. Recent results by Ramzi et al. [6] have led these authors to consider the occurrence of ternary complexes when binary solvents, wherein one solvent is water, are used. From this work, these authors conclude that the formation of complexes does not arise from hydrogen bonding but from electrostatic interactions instead. The purpose of this paper is to test further this assumption by using chemically modified agarose samples where hydrogen atoms located on OH groups are replaced by CH3 groups [7] (see Fig. 1). This modification suppresses definitely the possibility for hydrogen bonding while it promotes the polarization of the covalent bonds thus leading to the appearance of fractional electric charges on different atoms.
A deeper knowledge of the gelation of these modified polymer is also of interest for understanding the gelling properties of the agarose extracted from seaweeds of various origin [8], [9], [10]. As a matter of fact, the methyl content varies from one species to another [11], and still remains puzzling despite some thorough investigations.
As in previous studies [6], the experiments have been carried out with dimethyl sulfoxide (DMSO) and a series of formamide (FOR).
Section snippets
Materials
The three chemically modified agarose samples used in this study are of differing degrees of modification: some hydrogens of the hydroxyl groups are replaced at random by CH3 groups. The three samples were kindly provided by Hispanagar (Burgos, Spain). Their molecular weights as estimated by viscometry measurements ([η]=0.07Mv0.72, from Ref. [12]) and their water content were as follows: for M1, Mv=9.87×104 and water content=12.8%; for M2, Mv=1.03×105 and water content=8%; and for M3, Mv=1.02×10
Phase behavior
The thermal behavior has been studied in the four binary mixtures water/cosolvent mentioned above. Special attention has been paid for the system agarose/water/DMSO for which kinetic effects have been assessed. In particular, various ageing times have been investigated (24 h and 1 week) to find out whether this had any effect on the amount of gelled agarose for the sample of least gelling capability, i.e. M3. As can be seen in Fig. 2, the gel melting enthalpy is little dependent upon ageing
Concluding remarks
The results presented in this paper clearly show the role of the cosolvent in the thermoreversible gelation of chemically modified agarose. This cosolvent allows the gelation of a part of the material that could not gel in pure water. As has been discussed, this effect is not due to the special interactions that may exist between water and the cosolvent. Again, the notion of polymer–solvent complex already considered for non-modified agarose is contemplated. A possible model is drawn in Fig. 10
References (22)
- et al.
J. Mol. Biol.
(1974) - et al.
Phytochemistry
(1995) - et al.
Carbohydr. Res.
(1994) - et al.
Carbohydr. Res.
(1998) - et al.
Carbohydr. Polym.
(1989) - et al.
Biopolymers
(1989) - et al.
Macromolecules
(1994) - et al.
Biopolymers
(1998) Thermoreversible Gelation of Polymers and Biopolymers
(1992)- et al.
Macromolecules
(1996)
Carbohydr. Res.
Cited by (19)
Study of the viscoelastic properties of the agarose gel
2019, Materials Today: ProceedingsOxyalkylation modification as a promising method for preparing low-melting-point agarose
2018, International Journal of Biological MacromoleculesCitation Excerpt :Agarose, a neutral and linear polysaccharide generally extracted from red algae including Gracilaria and Gelidiella [1], is composed of repeating units consisted of alternating 1,3-linked β-d-galactose (G) and 1,4-linked α-l-3,6-anhydro-galactose (A) [2,3]. Strong hydrogen bonds, where random coils associate to form single [4,5] and double [6,7] helices, contribute to the formation of the high-mechanical-strength gel [8]. With its beneficial properities of bio-inertness, bio-compatibility, and high mechanical gel strength, agarose is widely applied in DNA electrophoresis, drug delivery, cell therapy, and molecular and tissue engineering [9,10].
Anomalous behaviour of comb-like dextran-polyacrylamide copolymers in mixed solvents
2009, European Polymer JournalNew hydrogels based on the interpenetration of physical gels of agarose and chemical gels of polyacrylamide
2009, European Polymer Journal
- 1
Permanent address: Faculté des Sciences, Université Mohamed 1er, Oujda 6000, Morocco.
- 2
Permanent address: Rhodia Recherche, 52 rue de la Haie Coq, F-93308 Aubervilliers, France.