Study of fluid dynamics at the boundary wall of a microchannel by Bloch surface waves.

Understanding how a fluid flows at the boundaries when it is confined at the microscale/nanoscale is crucial for a broad range of engineering and biology applications. We propose an experimental technique based on Bloch surface waves sustained by a one-dimensional photonic crystal to evaluate the speed of the contact line, i.e., the triple junction separating three phases, in the low Reynold's number regime, and with a nanometric resolution. Here, we report on the experimental characterization of the translatory motion of the contact line that separates two water solutions with a relatively high refractive index mismatch (7.35×10-3) and its slipping over a solid surface. The advantages are the relative simplicity and economy of the experimental configuration.

Real-Time Study of the Adsorption and Grafting Process of Biomolecules by Means of Bloch Surface Wave Biosensors.

A combined label-free and fluorescence surface optical technique was used to quantify the mass deposited in binary biomolecular coatings. These coatings were constituted by fibronectin (FN), to stimulate endothelialization, and phosphorylcholine (PRC), for its hemocompatibility, which are two properties of relevance for cardiovascular applications. One-dimensional photonic crystals sustaining a Bloch surface wave were used to characterize different FN/PRC coatings deposited by a combination of adsorption and grafting processes. In particular, the label-free results permitted to quantitatively assess the mass deposited in FN adsorbed (185 ng/cm2) and grafted (160 ng/cm2). PRC binding to grafted FN coatings was also quantified, showing a coverage as low as 10 and 12 ng/cm2 for adsorbed and grafted PRC, respectively. Moreover, desorption of FN deposited by adsorption was detected and quantified upon the addition of PRC. The data obtained by the surface optical technique were complemented by water contact angle and X-ray photoelectron spectroscopy (XPS) analyses. The results were in accordance with those obtained previously by qualitative and semiquantitative techniques (XPS, time-of-flight secondary ion mass spectrometry) on several substrates (PTFE and stainless steel), confirming that grafted FN coatings show higher stability than those obtained by FN adsorption.

[Nixtamalization cooking characteristics of 11 maize varieties]. / Características de cocción por nixtamalización de once variedades de maíz.

In the present study, 11 maize varieties were analyzed for their nixtamalization cooking quality. The 11 varieties were grown in the same locality and in the same year. The samples were evaluated for their physical characteristics, such as moisture content averaging 13.3%, average 1000 kernel weight (312.5 g), grain hardness through density (1.28 g/ml) and percent floaters (9.5%). These data indicated that all maize varieties had a hard endosperm which is recommended for the nixtamalization cooking process. The 11 varieties were formed on the average by 5.7% seed coat, 11.5% germ and 82.8% endosperm. The low seed coat content suggest a low solids loss during processing. Cooking quality evaluation was done by applying a standard lime cooking procedure to all varieties. An average solid loss of 3.2% was measured, with 0.8% of seed coat still attached to the endosperm. Water absorption at the end of cooking was 40.8% without soaking and 46.9% at the end of soaking. Nixtamal moisture was 47.9% after soaking and only 41.5% at the end of cooking. Cooking time with soaking for 50% moisture in the grain varied from 69 to 122 minutes at 1500 meters over sea level. The cooked grain was dried with hot air and ground however, the particle size obtained was not as that in commercial nixtamalized maize flour. However, the cooking quality parameters to make dough and tortillas were acceptable, with a penetration index of hydrated flour of 178.6 mm, pH 7.97, water absorption index (WAI) of 3.23 g gel/g flour and 4.11% water solubility index (WSI). All flours from the 11 varieties of maize gave acceptable tortillas as evaluated by physical characteristics and sensory quality. However of the 11 varieties 7 including the control were superior for nixtamalization cooking quality.

Reactions of the oxidized organic cofactor in copper-depleted bovine serum amine oxidase.

A novel copper-depleted bovine serum amine oxidase (BSAO), in which about half the molecules contained the organic cofactor in the oxidized form, was prepared by adding a reductant in anaerobic conditions to the cyanide-reacted protein. The CuI-semiquinone formed in these conditions reoxidizes after the removal of copper. The inactive derivative was reduced by benzylamine at approx. 1/1000 the rate of BSAO. The pseudo-first-order reaction was preceded by the formation of a protein-benzylamine complex with dissociation constant, Kd, of 4.9+/-0.5 mM, similar to the Km of BSAO (2.2 mM). Also the reactions with phenylhydrazine and benzohydrazide were considerably slower than in holo-BSAO, whereas the reactions with p-pyridine-2-ylphenylacetohydrazide, containing a longer aromatic tail, and semicarbazide, lacking an aromatic moiety, were less severely affected. Removal of copper had no effect on the optical spectra of BSAO and of most adducts, containing the cofactor in quinol form, showing that copper is bound to neither the oxidized nor the reduced cofactor. Benzylhydrazine did not produce optical effects but was tightly bound, as inferred from its inhibitory effect on reaction with other molecules. Substrate and inhibitors might bind a hydrophobic pocket at some distance from the quinone, probably near the protein surface, with their affinity depending on the hydrophobic character and pKa. The binding, which is not greatly influenced by copper removal, probably induces a copper-dependent change of conformation, 'opening' a pathway to the active site buried in the protein interior.