João Ribeiro

Chiral Stationary Phases for Liquid Chromatography Based on Chitin- and Chitosan-Derived Marine Polysaccharides

The development of chiral stationary phases (CSPs) for liquid chromatography (LC) revolutionized the enantioseparation and, nowadays, different types of CSPs are commercially available. Polysaccharide-based CSPs are one of the most versatile and widely used for both analytical and preparative applications and they are able to resolve several classes of racemates. Phenylcarbamates of amylose and cellulose derivatives are the most successful; however, polysaccharide-based CSPs comprising marine-derived polysaccharides are also described revealing high chiral recognition abilities and wider range of mobile phases. A literature survey covering the report on chitin and chitosan based CSPs is presented. The chemical structure of the chiral selectors, their development and applications in chiral LC are emphasized.

Marine Natural Peptides: Determination of Absolute Configuration Using Liquid Chromatography Methods and Evaluation of Bioactivities

Over the last decades, many naturally occurring peptides have attracted the attention of medicinal chemists due to their promising applicability as pharmaceuticals or as models for drugs used in therapeutics. Marine peptides are chiral molecules comprising different amino acid residues. Therefore, it is essential to establish the configuration of the stereogenic carbon of their amino acid constituents for a total characterization and further synthesis to obtain higher amount of the bioactive marine peptides or as a basis for structural modifications for more potent derivatives. Moreover, it is also a crucial issue taking into account the mechanisms of molecular recognition and the influence of molecular three-dimensionality in this process. In this review, a literature survey covering the report on the determination of absolute configuration of the amino acid residues of diverse marine peptides by chromatographic methodologies is presented. A brief summary of their biological activities was also included emphasizing to the most promising marine peptides. A case study describing an experience of our group was also included.

A hybrid method to characterise the mechanical behaviour of biological hyper-elastic tissues

The characterisation of biological tissues has become high interest area in recent years, due to the grow uses and development of artificial soft tissues implants. These tissues present a nonlinear mechanical behaviour, which highly differs from typical engineering materials. This aspect brings us an enormous difficulty in characterisation of soft tissues and thus required the development of new experimental techniques associated with new numerical algorithms. This work presents the mechanical characterisation of human vaginal mucosa based on a hybrid technique that combines the experimental measurement of displacement field, acquired during a tensile test with numerical simulation, using material constitutive laws. The digital image correlation technique was used for high spatial resolution measurement of the displacements field on the hyper-elastic biological tissues. Several numerical simulations were carryout based on finite element commercial package, Ansys®, by combining the experimental displacemen...