Approaches in biotechnological applications of natural polymers

Natural polymers, such as gums and mucilage, are biocompatible, cheap, easily available and non-toxic materials of native origin. These polymers are increasingly preferred over synthetic materials for industrial applications due to their intrinsic properties, as well as they are considered alternative sources of raw materials since they present characteristics of sustainability, biodegradability and biosafety. As definition, gums and mucilages are polysaccharides or complex carbohydrates consisting of one or more monosaccharides or their derivatives linked in bewildering variety of linkages and structures. Natural gums are considered polysaccharides naturally occurring in varieties of plant seeds and exudates, tree or shrub exudates, seaweed extracts, fungi, bacteria, and animal sources. Water-soluble gums, also known as hydrocolloids, are considered exudates and are pathological products; therefore, they do not form a part of cell wall. On the other hand, mucilages are part of cell and physiological products. It is important to highlight that gums represent the largest amounts of polymer materials derived from plants. Gums have enormously large and broad applications in both food and non-food industries, being commonly used as thickening, binding, emulsifying, suspending, stabilizing agents and matrices for drug release in pharmaceutical and cosmetic industries. In the food industry, their gelling properties and the ability to mold edible films and coatings are extensively studied. The use of gums depends on the intrinsic properties that they provide, often at costs below those of synthetic polymers. For upgrading the value of gums, they are being processed into various forms, including the most recent nanomaterials, for various biotechnological applications. Thus, the main natural polymers including galactomannans, cellulose, chitin, agar, carrageenan, alginate, cashew gum, pectin and starch, in addition to the current researches about them are reviewed in this article.. }To the Conselho Nacional de Desenvolvimento Cientfíico e Tecnológico (CNPq) for fellowships (LCBBC and MGCC) and the Coordenação de Aperfeiçoamento de Pessoal de Nvíel Superior (CAPES) (PBSA). This study was supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UID/BIO/04469/2013 unit, the Project RECI/BBB-EBI/0179/2012 (FCOMP-01-0124-FEDER-027462) and COMPETE 2020 (POCI-01-0145-FEDER-006684) (JAT)

THE CH STRETCHING SPECTRUM OF GASEOUS CYCLOPENTANE-D9: COUPLING OF STRETCHING AND PSEUDOROTATION

$^{1}$ S. Lifson and P. Stern, J. Chem. Phys. 77, 4542 (1982).Author Institution: Department of Chemistry, Duke UniversityIt is well known that the lowest frequency vibration in cyclopentane corresponds to pseudorotation, a rapid puckering motion along a nearly barrierless phase-angle coordinate $\phi$. This pseudorotational motion couples to the CH stretching vibrations and leads to pseudorotational structure in the CH stretching spectrum. We have obtained isotropic Raman spectra of gaseous $C_{5}D_{9}H$ which show this structure very clearly. Most of the stretch-pseudorotation coupling can be accounted for by the adiabatic variation in the CH stretching frequency with $\phi$. This frequency variation can then be used in an adiabatic approximation to simulate the CH stretching spectrum. We have calculated the frequency variation with $\phi$ by two methods, one using ab initio CH bondlengths and the other with a modified form of the Lifson-Stern empirical potential[1]. While both of these methods give simulated pseudorotational structure that is in qualitative agreement with the observed spectrum, the ab initio approach is significantly better at reproducing the spectral details. The effects of other perturbations on the spectrum have also been considered, including thermally excited radial levels and the variation of the zero point energy and reduced mass with $\phi$