Novel highly-soluble peptide-chitosan polymers: Chemical synthesis and spectral characterization

Novel water-soluble polymers, N-(gamma-propanoyl-valin)-chitosan and N-(gamma-propanoyi-aspartic acid)-chitosan, were synthesized by reaction of low molecular weight chitosan with N-alpha-(3-bromopropanoyl)-valine and N-alpha-(3-bromopropanoyl)-aspartic acid, respectively, under mild conditions. Prior to reaction with chitosan, the peptide substituents have been prepared by standard peptide chemistry methods from 3-bromopropanoic acid and the relevant a-amino acid tert-butyl esters. The chemical structure and physical properties of the novel chitosan derivatives were characterized by H-1 NMR and IR spectroscopy. The polymers are highly soluble in a wide pH range, which opens new perspectives for the applications of chitosan-based materials

Coffee certification in Brazil: compliance with social standards and its implications for social equity

© 2018, The Author(s). This paper addresses the relationship between compliance with social performance criteria (the social outcomes that must be achieved for certification) and procedural (management) criteria and this relationship’s significance for social equity at both farm and wider landscape levels. We consider social performance compliance to be pertinent to farm-level equity, and the relative compliance of small versus large farms to be pertinent to landscape-level equity. Certification’s management requirements are often deemed disproportionately burdensome for small, resource-poor producers, and hence a barrier to landscape-level equity. There is a lack of research examining how management criteria impact the ability of different sized farms to meet certification’s social performance requirements. We analysed 435 certification audits, covering all Brazilian coffee farms that sought Rainforest Alliance certification from 2006 to 2014 inclusive: 80 individual farms and 23 groups of farms. In principle, undergoing group certification permits smallholders to benefit from economies of scale. Our analysis revealed a statistically significant, positive correlation between compliance with procedural (managing sustainability plans) and social performance criteria. This correlation was stronger for groups than individual farms. Group farms’ compliance was statistically equivalent to that of individual farms, suggesting that group certification is achieving its intended purpose of socio-economic levelling of certified farmers. Over time, certified farms’ average compliances improved. Our findings suggest that management requirements play an important role in improving smallholders’ overall social sustainability performance and that group certification may help resource-poor smallholders achieve those requirements. Further work is required to understand causal mechanisms underlying the relationships we present

Practical computational toolkits for dendrimers and dendrons structure design

Dendrimers and dendrons offer an excellent platform for developing novel drug delivery systems and medicines. The rational design and further development of these repetitively branched systems are restricted by difficulties in scalable synthesis and structural determination, which can be overcome by judicious use of molecular modelling and molecular simulations. A major difficulty to utilise in silico studies to design dendrimers lies in the laborious generation of their structures. Current modelling tools utilise automated assembly of simpler dendrimers or the inefficient manual assembly of monomer precursors to generate more complicated dendrimer structures. Herein we describe two novel graphical user interface (GUI) toolkits written in Python that provide an improved degree of automation for rapid assembly of dendrimers and generation of their 2D and 3D structures. Our first toolkit uses the RDkit library, SMILES nomenclature of monomers and SMARTS reaction nomenclature to generate SMILES and mol files of dendrimers without 3D coordinates. These files are used for simple graphical representations and storing their structures in databases. The second toolkit assembles complex topology dendrimers from monomers to construct 3D dendrimer structures to be used as starting points for simulation using existing and widely available software and force fields. Both tools were validated for ease-of-use to prototype dendrimer structure and the second toolkit was especially relevant for dendrimers of high complexity and size.Peer reviewe

Soil-induced impacts on forest structure drive coarse woody debris stocks across central Amazonia

PublishedJournal Article© 2014, © 2014 Botanical Society of Scotland and Taylor & Francis. Background: Coarse woody debris (CWD) is an essential component in tropical forest ecosystems and its quantity varies widely with forest types. Aims: Relationships among CWD, soil, forest structure and other environmental factors were analysed to understand the drivers of variation in CWD in forests on different soil types across central Amazonia. Methods: To estimate CWD stocks and density of dead wood debris, 75 permanent forest plots of 0.5 ha in size were assessed along a transect that spanned ca. 700 km in undisturbed forests from north of the Rio Negro to south of the Rio Amazonas. Soil physical properties were evaluated by digging 2-m-deep pits and by taking auger samples. Results: Soil physical properties were the best predictors of CWD stocks; 37% of its variation was explained by effective soil depth. CWD stocks had a two-fold variation across a gradient of physical soil constraints (i.e. effective soil depth, anoxia and soil structure). Average biomass per tree was related to physical soil constraints, which, in turn, had a strong relationship with local CWD stocks. Conclusions: Soil physical properties appear to control average biomass per tree (and through this affect forest structure and dynamics), which, in turn, is correlated with CWD production and stocks

Agent-based-model of students’ sociocognitive learning process in acquiring tiered knowledge

Peer reviewe

Secular evolution versus hierarchical merging: galaxy evolution along the Hubble sequence, in the field and rich environments

In the current galaxy formation scenarios, two physical phenomena are invoked to build disk galaxies: hierarchical mergers and more quiescent external gas accretion, coming from intergalactic filaments. Although both are thought to play a role, their relative importance is not known precisely. Here we consider the constraints on these scenarios brought by the observation-deduced star formation history on the one hand, and observed dynamics of galaxies on the other hand: the high frequency of bars and spirals, the high frequency of perturbations such as lopsidedness, warps, or polar rings. All these observations are not easily reproduced in simulations without important gas accretion. N-body simulations taking into account the mass exchange between stars and gas through star formation and feedback, can reproduce the data, only if galaxies double their mass in about 10 Gyr through gas accretion. Warped and polar ring systems are good tracers of this accretion, which occurs from cold gas which has not been virialised in the system's potential. The relative importance of these phenomena are compared between the field and rich clusters. The respective role of mergers and gas accretion vary considerably with environment.Comment: 18 pages, 8 figures, review paper to "Penetrating Bars through Masks of Cosmic Dust: the Hubble Tuning Fork Strikes a New Note", Pilanesberg, ed. D. Block et al., Kluwe