Olivieri A.C.,National University of Rosario
Analytica Chimica Acta | Year: 2015
Practical guidelines for reporting analytical calibration results are provided. General topics, such as the number of reported significant figures and the optimization of analytical procedures, affect all calibration scenarios. In the specific case of single-component or univariate calibration, relevant issues discussed in the present Tutorial include: (1) how linearity can be assessed, (2) how to correctly estimate the limits of detection and quantitation, (2) when and how standard addition should be employed, (3) how to apply recovery studies for evaluating accuracy and precision, and (4) how average prediction errors can be compared for different analytical methodologies. For multi-component calibration procedures based on multivariate data, pertinent subjects here included are the choice of algorithms, the estimation of analytical figures of merit (detection capabilities, sensitivity, selectivity), the use of non-linear models, the consideration of the model regression coefficients for variable selection, and the application of certain mathematical pre-processing procedures such as smoothing. © 2015 Elsevier B.V.
Olivieri A.C.,National University of Rosario
Chemical Reviews | Year: 2014
The search for new ways to improve analytical figures of merit is an important driving force in modern analytical chemistry research, with the sensitivity occupying one of the prominent places among these figures. Whether the purpose is the comparison of the performance of different experimental procedures or the optimization of a given methodology under various experimental conditions, a consistent numerical sensitivity parameter is required in order to judge about the real improvement obtained from various experimental strategies. Analytical figures of merit are an integral part of official protocols of analysis, as documented in international standards. The International Union of Pure and Applied Chemistry (IUPAC) has set sensitivity definitions for various calibration scenarios. What is even more worrying, the plainly extrapolated expressions to data arrays with higher number of modes appeared to lead to a serious underestimation of true sensitivities.
Sarotti A.M.,National University of Rosario
Organic and Biomolecular Chemistry | Year: 2014
The reaction energetics of 280 polar Diels-Alder (DA) reactions between 70 dienophiles and 4 dienes have been studied in detail using the B3LYP/6-31G* level of theory, combining conceptual density functional theory (DFT) analysis and the distortion/interaction model. The barrier heights are governed by a fine balance between the energy required to distort the reactants from their initial to their transition state geometries (ΔE‡d) and the binding energy between the deformed reactants in the TS (ΔE‡i). The ΔE‡i values strongly correlate with the electrophilicity index, ω, which measures the stabilization energy when the system acquires an additional electronic charge from the environment, whereas the ΔE‡d was found to depend mainly on the nature of the diene, structural parameters of the dienophile (degree of substitution and ring size) and the asynchronicity of the TS. A detailed analysis to account for the geometrical parameters of the strained diene and dienophile moieties that influence the energy strain of the distorted fragments is also reported. This journal is © The Royal Society of Chemistry.
Mendoza D.D.,National University of Rosario
Annual Review of Microbiology | Year: 2014
Bacteria remodel the fluidity of their membrane bilayer precisely via the incorporation of proportionally more unsaturated fatty acids (or fatty acids with analogous properties) as growth temperature decreases. This process, termed homoviscous adaptation, is suited to disrupt the order of the lipid bilayer and optimizes the performance of a large array of cellular physiological processes at the new temperature. As such, microbes have developed molecular strategies to sense changes in membrane fluidity, provoked by a decrease in environmental temperature, and initiate cellular responses that upregulate the biosynthesis of unsaturated fatty acids. This review focuses on the architecture of a membrane fluidity communication network; how thermal information is integrated, processed, and transduced to control gene expression; how membrane-mediated structural changes of a cold sensor are accomplished; and the intriguing possibility that temperature-induced deformations of the cell membrane act as allosteric regulators of protein function. Copyright © 2014 by Annual Reviews. All rights reserved.
Menzella H.G.,National University of Rosario
Microbial Cell Factories | Year: 2011
Background: Variations in codon usage between species are one of the major causes affecting recombinant protein expression levels, with a significant impact on the economy of industrial enzyme production processes. The use of codon-optimized genes may overcome this problem. However, designing a gene for optimal expression requires choosing from a vast number of possible DNA sequences and different codon optimization methods have been used in the past decade. Here, a comparative study of the two most common methods is presented using calf prochymosin as a model.Results: Seven sequences encoding calf prochymosin have been designed, two using the "one amino acid-one codon" method and five using a "codon randomization" strategy. When expressed in Escherichia coli, the variants optimized by the codon randomization approach produced significantly more proteins than the native sequence including one gene that produced an increase of 70% in the amount of prochymosin accumulated. On the other hand, no significant improvement in protein expression was observed for the variants designed with the one amino acid-one codon method. The use of codon-optimized sequences did not affect the quality of the recovered inclusion bodies.Conclusions: The results obtained in this study indicate that the codon randomization method is a superior strategy for codon optimization. A significant improvement in protein expression was obtained for the largely established process of chymosin production, showing the power of this strategy to reduce production costs of industrial enzymes in microbial hosts. © 2011 Menzella; licensee BioMed Central Ltd.