Physico‐Mechanical Properties of Biodegradable Starch Nanocomposites

Nanocomposites of cassava starch reinforced with waxy starch nanocrystals were prepared. They showed a 380% increase of the rubbery storage modulus (at 50 °C) and a 40% decrease in the water vapor permeability. X‐ray spectra show that the composite was more amorphous than the neat matrix, which was attributed to higher equilibrium water content in the composites. TGA confirmed this result and its thermal derivative suggested the formation of hydrogen bonding between glycerol and the nanocrystals. The reinforcing effect of starch nanocrystals was attributed to strong filler/matrix interactions due to the hydrogen bonding. The decrease of the permeability suggests that the nanocrystals were well dispersed, with few filler/filler interactions.

     

UV‐Cured Polysiloxane Epoxy Coatings Containing Titanium Dioxide as Photosensitive Semiconductor

UV‐cured polysiloxane epoxy coatings containing titanium dioxide were prepared by means of a cationic photopolymerization process. A good distribution of the inorganic filler was achieved within the polymeric network with an average size dimension of around 500 nm. UV‐vis analysis performed on organic dye (methylene blue) stained coatings showed a high efficiency of the titania photocatalytic activity: a complete degradation of the dye on the coating surface is reached after 60 min of UV irradiation without affecting the matrix photo‐degradation.

     

Microbiological evaluation of ready-to-eat foods manufactured by small Costa Rican industries

Ready-to-eat (RTE) foods are processed foodstuffs which have gained popularity in recent times because they can be ingested without further thermic treatments. In this work, the microbiological quality and safety of 90 samples of RTE foods manufactured by small Costa Rican industries was determined to evaluate whether they represent a Public Health risk. Twenty-six samples of pickled vegetables, 18 dips, 18 salads, and 12 sweet treats were studied. Each sample was analyzed with regard to its pH, the presence of culturable microbiological quality indicators and recognized foodborne pathogens (Salmonella, Listeria monocytogenes. Clostridium perfringens, C. botulinum, and Bacillus cereus) Selected genes encoding toxins of C. botulinum and C. perfringens were screened by PCR. Thirty-seven percent of the samples had a level of acidity that could allow the growth and proliferation of bacterial pathogens (pH > or = 4.5). The shelf-life indicators were acceptable but only if the RTE foods are kept at adequate conditions of temperature and humidity. Sixty-four percent of the RTE foods had total coliforms values that evidence inadequate hygiene practices during its elaboration (MPN/g >1000). This result was confirmed by the finding of fecal coliforms in 56% of the samples, which, by the way, are inacceptable for human consumption. All cultures for pathogens were negative, except for 4 samples that contained B. cereus. Toxins of C. botulinum were not detected and one single sample was positive for the PCR for C. perfringens. The elevated degree of fecal contamination detected in the RTE could be prevented by means of good manufacturing practices, better hygiene measures and a deeper attention to critical control points.     

Biofilm formation capacity of Listeria monocytogens strains isolated from soft cheese from Costa Rica

Listeria monocytogenes is a bacteria associated with the production of severe infectious disease in human being, but also with the formation of biofilms in different surfaces related to the food production environment. Biofilm represents a serious problem in food industry, since it is a constant and important contamination source and also, bacteria present in it have an increased resistance towards physical and chemical agents of common use. The capacity of biofilm formation of L. monocytogenes strains previously isolated from soft cheese samples from Costa Rica was studied under different temperature and culture conditions. The microplate technique was performed using different culture media (BHIB, TSB 1:20 and cheese serum) and at different incubation temperatures (refrigeration, environmental and 35 degrees C). Biofilm formation capacity was classified according to the optical density obtained at 620 nm. None of the strains evaluated was classified as strong biofilm former under any of the variables studied, nevertheless, weak and moderate formers were detected. The results obtained show the influence of the nutrient content of the culture media used over biofilm formation; BHIB was the only culture media that allowed the expression of moderate biofilm forms, contrary to cheese serum that did not promote biofilm production. Biofilm formation is a multifactorial process, where adsorption level depends on several variables and its study must be promoted in order to develop methodologies that allow its reduction or elimination, so food industries may offer safe food products to consumers.     

Oxidative Stress and Respiratory Diseases in Preterm Newborns

Premature infants are exposed to increased generation of reactive oxygen species, and on the other hand, they have a deficient antioxidant defense system. Oxidative insult is a salient part of lung injury that begins as acute inflammatory injury in respiratory distress disease and then evolves into chronic and structural scarring leading to bronchopulmonary dysplasia. Oxidative stress is also involved in the pathogenesis of pulmonary hypertension in newborns through the modulation of the vascular tone and the response to pulmonary vasodilators, with consequent decrease in the density of the pulmonary vessels and thickening of the pulmonary arteriolar walls. Oxidative stress has been recognized as both a trigger and an endpoint for several events, including inflammation, hypoxia, hyperoxia, drugs, transfusions, and mechanical ventilation, with impairment of pulmonary function and prolonged lung damage. Redoxomics is the most fascinating new measure to address lung damage due to oxidative stress. The new challenge is to use omics data to discover a set of biomarkers useful in diagnosis, prognosis, and formulating optimal and individualized neonatal care. The aim of this review was to examine the most recent evidence on the relationship between oxidative stress and lung diseases in preterm newborns. What is currently known regarding oxidative stress-related lung injury pathogenesis and the available preventive and therapeutic strategies are also discussed.     

Lytic Polysaccharide Monooxygenase from Talaromyces amestolkiae with an Enigmatic Linker-like Region: The Role of This Enzyme on Cellulose Saccharification

The first lytic polysaccharide monooxygenase (LPMO) detected in the genome of the widespread ascomycete Talaromyces amestolkiae (TamAA9A) has been successfully expressed in Pichia pastoris and characterized. Molecular modeling of TamAA9A showed a structure similar to those from other AA9 LPMOs. Although fungal LPMOs belonging to the genera Penicillium or Talaromyces have not been analyzed in terms of regioselectivity, phylogenetic analyses suggested C1/C4 oxidation which was confirmed by HPAEC. To ascertain the function of a C-terminal linker-like region present in the wild-type sequence of the LPMO, two variants of the wild-type enzyme, one without this sequence and one with an additional C-terminal carbohydrate binding domain (CBM), were designed. The three enzymes (native, without linker and chimeric variant with a CBM) were purified in two chromatographic steps and were thermostable and active in the presence of H₂O₂. The transition midpoint temperature of the wild-type LPMO (Tm = 67.7 °C) and its variant with only the catalytic domain (Tm = 67.6 °C) showed the highest thermostability, whereas the presence of a CBM reduced it (Tm = 57.8 °C) and indicates an adverse effect on the enzyme structure. Besides, the potential of the different T. amestolkiae LPMO variants for their application in the saccharification of cellulosic and lignocellulosic materials was corroborated.     

Synthesis and Properties of Novel Antifungal Gemini Compounds Derived from <Emphasis Type="Italic">N</Emphasis>-Acetyl Diethanolamines

A series of new N-acetylated non-ionic and cationic gemini surfactants (3a–f) having dimeric structures derived from primary and tertiary amines with variably long tails (C₈–C₁₂–C₁₈) were synthesized. In addition, N-acetylated monomeric analogues 6a and 6b were prepared and their antifungal potency and surface properties were also determined. Critical micelle concentration (CMC), effectiveness of surface tension reduction (γ_CMC), surface excess concentration (Γ), and area per molecule at the interface (A) were also determined and the resulting values indicate that the cationic series is characterized by good surface-active and self-aggregation properties. For the first time, all surfactants were tested to evaluate their antifungal properties using the method for the broth macrodilution test (M27-A2, NCCLS). Four microbial strains were used to perform the study: Candida parapsilosis (ATCC 22019), C. albicans (ATCC 64548), and a wild-type strain of C. parasilosis and Saccharomyces cerevisiae (ATCC 9763). The antimicrobial activity was measured by yeast growth inhibition expressed as minimum inhibitory concentration (MIC) values. Results were compared to those obtained for their monomeric analogues and for a commercially available reference compound (Fluconazole). Gemini 3b, 3e and 3f were found to be the most potent compounds. The results show S. cerevisiae as the most sensitive strain. In contrast, the wild strain of C. parapsilosis was resistant.

A potent integrin antagonist from a small library of cyclic RGD pentapeptide mimics including benzyl-substituted azabicycloalkane amino acids

A small library of cyclic RGD pentapeptide mimics, including benzyl-substituted azabicycloalkane amino acids, was synthesized with the aim of developing active and selective integrin antagonists. In vitro binding assays established one particular compound with affinity for both the alpha(v)beta(3) and the alpha(v)beta(5) integrins. The synthesis in solution and the in vitro screening of these RGD derivatives, as well as the determination of the conformational properties of the integrin ligands by spectroscopic and computational methods are described.     

Peptide-containing aggregates as selective nanocarriers for therapeutics

New nanocarriers are obtained by assembling two amphiphilic monomers: one containing the bioactive peptide CCK8 spaced, by a polydisperse poly(ethylene glycol), from two hydrophobic tails ((C18)2PEG2000CCK8), and the other containing a chelating agent able to give stable radiolabeled indium-111 complexes linked to the same hydrophobic moiety ((C18)2DTPAGlu). The size and shape of the supramolecular aggregates were structurally characterized by dynamic light scattering, small-angle neutron scattering, and cryogenic transmission electronic microscopy. Under the experimental conditions we investigated (pH 7.4 and molar ratio between monomers 30:70), there is the presence of high polydisperse aggregates: rod-like micelles with a radius of approximately 40 A and length >700 A, open bilayer fragments with thickness approximately 65 A, and probably vesicles. The presence of the bioactive peptide well exposed on the external surface of the aggregate allows selective targeting of nanocarriers towards the cholecystokinin receptors overexpressed by the cancerous cells. In vitro binding assays and in vivo biodistribution studies by nuclear medicine experiments using indium-111 are reported. Moreover, preliminary data concerning the drug loading capability of the aggregates and their drug efficiency on the target cells is reported by using the cytotoxic drug doxorubicin. Incubation of receptor-positive and control cells with peptide-containing aggregates filled with doxorubicin shows significantly lower cell survival in receptor-expressing cells relative to the control, for samples incubated in the presence of doxorubicin.     

Branched poly(arylene ether ketone)s with tailored thermal properties: Effects of AB/AB2 ratio, core (B3) percentage, and reaction temperature

A series of poly(ether ketone) copolymers were prepared by nucleophilic aromatic polymerization reactions of the AB monomer 4-fluoro-4′-hydroxybenzophenone, 1, and the AB₂ monomer bis(4-fluorophenyl)-(4-hydroxyphenyl)phosphine oxide, 2, in the presence of 3 or 5 mol% of a highly reactive core molecule, tris(3,4,5-trifluorophenyl)phosphine oxide (B₃), 4. All of the copolymers prepared in the presence of a core molecule were sufficiently soluble in N-methylpyrrolidinone, NMP, to allow the determination of their molecular weights and polydispersity indices, PDIs. Number-average molecular weights, M_ns, of 3200-6800 Da were determined and the PDI values ranged from 1.41 to 4.07. The M_n was controlled by the mol% of 4 present in the reaction mixture with higher molar percentages leading to lower M_n values. Lower reaction temperatures and lower ratios of AB/AB₂ monomers afforded copolymers with lower PDI values. As expected, the crystallinity of the samples decreased with an increasing AB₂ content or an increase in PDI. The copolymers also exhibited excellent thermo-oxidative stability with a number of samples suffering 5% weight losses at temperatures, in air, well in excess of 450 °C.