Use Of Experimental Parameters Research Articles

Solvent Acidity and Basicity Scales: Analysis of Catalan’s SB and SA Scales and Gutmann’s Acceptor Number and Comparison with Kamlet and Taft’s β and α Solvent Scales, Gutmann’s Donor Number and Abraham’s B and A Solute Scales

The use of experimental parameters to quantify solvent properties, for example in linear free energy relationships, is well established and several scales of solvent acidity, basicity and polarity/polarizability have been developed. The success of this approach raises questions of which molecular properties contribute to particular solvent parameters and whether these contributions are found in all parameters representing a particular solvent property. In the present study, Catalan’s hydrogen bond basicity and acidity parameters, SB and SA, and Gutmann’s acceptor number, AN, a measure of a solvent’s Lewis acidity, are correlated with molecular properties derived from computational chemistry. The results are compared with the results of similar correlations with Kamlet and Taft’s β and α Solvent Scales, Gutmann’s donor number DN) and Abraham’s B and A solute scales. The results show that measures of solvent basicity, SB, β and DN all correlate strongly with the partial charge on the most negative atom in the solvent molecule and the energy of the donor orbital and, in all cases, the parameter values for hydrogen-bonded solvents are anomalous. Abraham’s B, a measure of solute hydrogen basicity, depends only on the partial charge on the most negative atom and there is no anomaly in the values for solutes that, in the pure state, form hydrogen-bonded liquids. Similarly, all measures of solvent acidity, SA, α and AN, and Abraham’s A, a measure of solute hydrogen bond acidity, depend on the partial charge on the most positive hydrogen on the molecule.

Aspen Plus Simulation Strategies Applied to the Study of Chitin Bioextraction from Shrimp Waste.

SUMMARYChitin is an aminopolysaccharide of industrial interest commonly obtained from shrimp processing waste through chemical or biotechnological means. Current environmental concerns offer a stimulating perspective for chitin bioextraction with lactic acid bacteria since a considerable reduction in the use of corrosive and pollutant products is possible. Nevertheless, the efficiency of this bioprocess is still a matter of discussion. In this work, the experimental studies of chitin bioextraction from Pacific white shrimp (Litopenaeus vannamei) waste with a mixed culture of Lactobacillus plantarum, Lactobacillus bulgaricus and Streptococcus thermophilus are used in process simulation using Aspen Plus software for the analysis of the potential application of a bioprocess on plant scale. The experimental results of characterization in shake flasks and 1-litre bioreactor indicated that 50 h of fermentation with the mixed culture of lactic acid bacteria was enough to extract more than 90% of minerals and proteins from the shrimp waste. The use of experimental parameters in the simulation allowed a reliable representation of the bioprocess yielding normalized root mean square values below 10%. Simulation was used for the assessment of the impact of the raw material variability on the production costs and gross margin. In this regard, the gross margin of the operation ranged from 42 to 52% depending on the raw material composition and product yield.

Modulation of cyanobacterial photosystem I deposition properties on alkanethiolate Au substrate by various experimental conditions

We present results from atomic force microscopy (AFM) images indicating various experimental conditions, which alter the morphological characteristics of self-assembled cyanobacterial PS I on hydroxyl-terminated self-assembled alkanethiolate monolayers (SAM/Au) substrates. AFM topographical images of SAM/Au substrates incubated in solutions containing different PS I concentrations solubilized with Triton X-100 as the detergent reveal large columnar aggregates (∼100 nm and hence, much taller than a single PS I trimer) at high PS I concentrations. Depositions from dilute PS I suspensions reveal fewer aggregates and relatively uniform surface topography (∼10 nm). Confocal fluorescence microscopy analysis of fluorescently tagged PS I deposited on to SAM/Au substrates using electric field and gravity driven techniques reveal preliminary indications of directionally aligned PS I attachments, besides corroborating a uniform monolayer formation, for the former deposition method. The complex attachment dynamics of PS I onto SAM substrates are further investigated from the AFM images of PS I/SAM/Au substrates prepared under different experimental conditions using: 1) PS I isolated as monomers and trimers 2) adsorption at elevated temperatures, and 3) different detergents with varying pH values. In each of the cases, the surface topology indicated distinct yet complex morphological and phase characteristics. These observations provide useful insight into the use of experimental parameters to alter the morphological assembly of PS I on to SAM substrates en route to successful fabrication of PS I based biohybrid photoelectrochemical devices.

Standard intracranial in vivo animal models of delayed cerebral vasospasm

Object. Animal models provide a basis for clarifying the complex pathogenesis of delayed cerebral vasospasm (DCVS) and for screening of potential therapeutic approaches. Arbitrary use of experimental parameters in current models can lead to results of uncertain relevance. The aim of this work was to identify and analyze the most consistent and feasible models and their parameters for each animal.Methods. An online search of the MEDLINE PubMed and EMBASE medical databases (1969 to week 21 of 2007) was performed using the key words “canine”, “mice”, “rabbit”, “pig”, “rat”, “cat”, and “primate” in combination with “subarachnoid hemorrhage”, “model”, and “vasospasm”. Cross references of each model were checked. Analysis of identified publications was considered in accordance with predetermined eligibility criteria.Results. 1254 abstracts were reviewed and 516 studies were included in the analysis. Then, 66 models in 7 animals were identified. Most often used blood amounts (ml) lead to degree (% vessel narrowing) and peak onset (day) of DCVS within animal models as follows: mice endovascular puncture (various, day 3, 20–62%); rat single injection (0.3 ml, day 2, 19–29%); rat double injection (2x0.3 ml, day 7, 28–47%); rabbit single injection (3 ml, day 3, 19–55%); rabbit double injection (not established, day 5, not established); dog double injection (2x4–5 ml, day 7, 45–66%); primate clot placement (5 ml, day 7, 32–52%).Conclusions. Among the great number of experimental SAH methods and associated parameters only a fistful reliable and consistent models can be identified and recommended. Implementation of more standardized experimental techniques could increase the relevance of future experimental studies.

Convection in relatively thin layers of nematic liquid crystals

Laser-induced convective motion in thin layers (less than a millimeter) of nematic liquid crystals is investigated experimentally. It is shown that convection arising in the presence of the vertical gradient of temperature is toroidal. Velocities of convective motions in the liquid crystal are measured for two different diameters of the incident laser beam. Comparison is made of the threshold of the temperature gradient of convective motions obtained by theoretical estimations and with use of experimental parameters.