Cyrille Rochas

13C-n.m.r. spectroscopic investigation of methylated and charged agarose oligosaccharides and polysaccharides☆

Abstract The 13 C-n.m.r. signals of agarose oligomers with various substituted repeating units have been assigned. Enzymic hydrolysis of agaroses gave 2 1 - O -methylagarobiose, 6 2 - O -methylagarobiose, the agarobiose biological precursor, agarobiose 4 2 -sulfate, 2 1 - O -methylagarobiose 4 2 -sulfate, and pyruvylated agarobiose. The chemical shift data of the oligomers and the parent polymers were compared, and indicated the distribution of the substituents in hybrid polymers.

Oligosaccharide/Silicon-Containing Block Copolymers with 5 nm Features for Lithographic Applications

Block copolymers demonstrate potential for use in next-generation lithography due to their ability to self-assemble into well-ordered periodic arrays on the 3-100 nm length scale. The successful lithographic application of block copolymers relies on three critical conditions being met: high Flory-Huggins interaction parameters (χ), which enable formation of <10 nm features, etch selectivity between blocks for facile pattern transfer, and thin film self-assembly control. The present paper describes the synthesis and self-assembly of block copolymers composed of naturally derived oligosaccharides coupled to a silicon-containing polystyrene derivative synthesized by activators regenerated by electron transfer atom transfer radical polymerization. The block copolymers have a large χ and a low degree of polymerization (N) enabling formation of 5 nm feature diameters, incorporate silicon in one block for oxygen reactive ion etch contrast, and exhibit bulk and thin film self-assembly of hexagonally packed cylinders facilitated by a combination of spin coating and solvent annealing techniques. As observed by small angle X-ray scattering and atomic force microscopy, these materials exhibit some of the smallest block copolymer features in the bulk and in thin films reported to date.

CHEMICAL STRUCTURE AND PHYSICO-CHEMICAL PROPERTIES OF AGAR

Advances in the chemistry and physico-chemical properties of agar since the review of Araki at the Fifth International Seaweed Symposium in 1965 are discussed. These advances are essentially the result of better separation techniques of the heterogeneous family of polysaccharides known as agar, the use of nuclear magnetic resonance spectroscopy, the use of agarases and, particularly, the use of combinations of the three approaches. Although physico-chemical methods have evolved, particularly molecular-weight determinations, X-ray diffraction data and molecular modelling of agar, correlations between chemical and functional properties of agar and agarose and their gelation mechanisms remain to be studied.

Average molecular weight and molecular weight distribution of agarose and agarose-type polysaccharides

Abstract A procedure to determine the absolute weight-average molecular weight and molecular weight distribution of agarose and agarose-type polysaccharides by aqueous size-exclusion chromatography coupled with low-angle laser light scattering is described. The molecular weights of the majority of the commercial samples investigated were between 80 000 and 140 000 with a polydispersity lower than 1·7. In contrast, most of the laboratory-extracted agarose-type polysaccharides had lower molecular weights.

Role of the molecular weight on the mechanical properties of kappa carrageenan gels

Abstract Kappa carrageenans with different molecular weights were prepared by ultrasonication and preparative gel permeation chromatography; gels were prepared with different polymer and KCl concentrations. The yield stress and the elastic modulus of these gels were correlated with the molecular weight of the polymers.

Relation between the molecular structure and mechanical properties of carrageenan gels

Carrageenan extracted from Eucheuma cottonii was analyzed by enzymic hydrolysis, KCl fractionation, 13C and 1H NMR spectroscopy. 13C and 1H NMR of the enzymic resistant fraction and of the KCl-soluble fraction prove that the carrageenan extracted from Eucheuma cottonii is composed of several polysaccharides. The major component is kappa-carrageenan and the minor ones are irregular galactans partially methylated, containing a large proportion of the iota-carrageenan form.

Structure of Micelles of a Nonionic Block Copolymer Determined by SANS and SAXS

The micellar state of Pluronic P123, which is a poly(ethylene oxide)-b-poly(propylene oxide)-b- poly(ethylene oxide) block polymer (EO(20)PO(70)EO(20)), has been investigated using SANS, SAXS, and differential scanning calorimetry under the conditions utilized in the synthesis of ordered mesoporous materials, such as SBA-15. The absolute intensity measurements, both with SANS and SAXS, have provided a detailed quantitative description of the P123 micelles in the framework of a simple core-shell spherical model. The model developed has been used to establish the structure of the copolymer micelles, including their size, shape, aggregation number and detailed composition, as well as the structural changes induced by varying reaction conditions. The effects of temperature, pH, acidic source and the addition of swelling agents (toluene and TMB) are reported and discussed.

Nanostructure of calcium alginate aerogels obtained from multistep solvent exchange route

Ca-alginate materials were studied by small-angle X-ray scattering (SAXS) at different steps of conversion from gel to aerogel in order to determine the relation between the polymer organization at the nanoscale in the gels and the final dry aerogel. In all cases, i.e. before and after the different exchanges of solvents and after the formation of the aerogel, the SAXS patterns exhibit an asymptotic behavior at low q values (in the experimental q range 7x10(-3) up to 2.10(-2) A(-1)) close to I(q) approximately q(-1), indicative of randomly oriented rod-like scattering objects. The evolution of the diameter of such rod-like objects was thus deduced from the maxima observed on Kratky plots, i.e. I(q) q2 vs q. The results are in perfect agreement qualitatively (rod-like anisometry type of the scattering objects) and quantitatively (diameter of the rods) with direct SEM observations of the morphology of aerogels and with the results of N2 adsorption on the aerogel. This is evidence that in the chosen experimental processing conditions, the morphology of the aerogel depends on the morphology of pre-existing objects within the gel, i.e. that the structure of the aerogel provides a correct image of the structure of the parent gel.

Calorimetric determination of the conformational transition of kappa carrageenan

Abstract This paper deals with measurements of the heat of the helix-coil transition by microcalorimetry for kappa carrageenans; data are given in the absence of gel in various solvents (H 2 O, Me 2 SO, and formamide) with two counterions (K + , Rb + ). In water, the influence of gel formation on Δ H is pointed out and the influence of the time of ageing is demonstrated. The Δ H values measured in the absence of gel are interpreted in terms of the electrostatic model proposed by Manning; the agreement is quite good if a double helix is formed in water, but a monochain, ordered conformation is suggested for solutions in Me 2 SO and formamide.

Aqueous GPC of electrolytes and polyelectrolytes

Abstract The gel permeation chromatography (GPC) of polyelectrolytes is discussed. The electrostatic exclusion is demonstrated using simple electrolytes with different eluents. The data for aqueous free salt solutions of polyelectrolytes are interpreted. The osmotic coefficient is deduced and its dependence on molecular weight and polymer concentration reported. In salt eluents, the Donnan exclusion is discussed. The universal calibration obtained with different standards in aqueous solution is shown to be valid and identical to that obtained in an organic solvent using polystyrene standards.