Solid State NMR Analysis of Two Grafted Biopolymers
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Solid State NMR Analysis of Two Grafted Biopolymers Gerardo Cedillo1 and Emilio Bucio2 1
Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, México DF 04510, México. 2
Departamento de Química de Radiaciones y Radioquímica, Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, México DF 04510, México. ABSTRACT
A potential alternative to achieve smart materials for biomedical applications is the combination of natural and synthetic polymers. In order to understand the structure and properties of two γ-radiation grafted biopolymers, chitosan-g-poly(N-isopropylacrylamide) (CS/PNIPAAm) and cotton-g-2-(dimethylamino) ethyl methacrylate (CG-DMAEMA) were analyzed by solid state nuclear magnetic resonance (SSNMR) 13C-CPMAS at different contact times (tCP). The use of different tCP in this grafted biopolymers showed that chemical shifting, broadening, size and symmetry of the some signals, gives important information for structure elucidation and molecular mobility. SSNMR spectra indicate changes in the local order structure, CG suffered less modifications when it is grafted than CS. CG-g-DMAEMA spectrum is very similar to CG spectrum, in contrast with spectrum of CS-g-NIPAAm, is very different than CS. Spectra of swelling polymers in water showed more structural information about secondary structure. INTRODUCTION Characterization of biopolymers is very important because it can reveal his primary and secondary structure and dynamics. However there are several limitations for the study of this biomacromolecules, many of them are not soluble, so much information is lost in solution NMR due to time averaging and X-ray diffraction is not a good option when biopolymer is modified with synthetic polymers. SSNMR is a good alternative for study these materials, remarkable progress has been witnessed in the last 30 years [1], detailed structural information is available from parameters contained in solid state, biopolymers consisting in repeating units such as structural proteins and polysaccharides can be recorded easily because individual peaks from samples of natural abundance are well resolved and more intense due to their limited numbers of residues. Depending of the history and treatment of the sample we can assign different polymorphic structures, so a conformational characterization can be done by examination of their 13C chemical shifts with reference to displacement of its peaks. Is well known that physic chemistry properties of polysacharides and its biological response is strongly related to its secondary structure in solid, liquid and gel states, its secondary structure is generally defined by a set of torsion angles about the glycosidic
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linkages. A variety of monomers in polysaccharides and linkage positions such as 1-2, 1-3, 1-4, etc., anomeric forms such as α and β, together with a degree of branching lead to an extraordinary variety of primary structures. On the basis of the
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