Fred J. Rispoli

Understanding the toxicity of aggregated zero valent copper nanoparticles against Escherichia coli

Copper nanoparticles are used in wide variety of applications and in the current study we report the antimicrobial activity of these particles. Influence of pH, temperature, aeration rate, concentration of nanoparticles and concentration of bacteria on the toxicity of copper nanoparticles against Escherichia coli have been studied using a centroid mixture design of experiment. The linear and quadratic regression model shows that the toxicity of copper nanoparticles not only depends on the primary effect of the parameters tested (pH, temperature, aeration, concentration of E. coli and concentration of nanoparticles), but also on the interactive effect of these parameters.

Antibacterial activity of polymer coated cerium oxide nanoparticles.

Cerium oxide nanoparticles have found numerous applications in the biomedical industry due to their strong antioxidant properties. In the current study, we report the influence of nine different physical and chemical parameters: pH, aeration and, concentrations of MgSO4, CaCl2, KCl, natural organic matter, fructose, nanoparticles and Escherichia coli, on the antibacterial activity of dextran coated cerium oxide nanoparticles. A least-squares quadratic regression model was developed to understand the collective influence of the tested parameters on the anti-bacterial activity and subsequently a computer-based, interactive visualization tool was developed. The visualization allows us to elucidate the effect of each of the parameters in combination with other parameters, on the antibacterial activity of nanoparticles. The results indicate that the toxicity of CeO2 NPs depend on the physical and chemical environment; and in a majority of the possible combinations of the nine parameters, non-lethal to the bacteria. In fact, the cerium oxide nanoparticles can decrease the anti-bacterial activity exerted by magnesium and potassium salts.

Mixture design as a first step for optimization of fermentation medium for cutinase production from Colletotrichum lindemuthianum.

Cutinase enzymes from fungi have found diverse applications in industry. However, most of the available literature on cutinase production is related to the cultivation of genetically engineered bacteria or yeast cells. In the present study, we use mixture design experiments to evaluate the influence of six nutrient elements on production of cutinase from the fungus Colletotrichum lindemuthianum. The nutritional elements were starch, glucose, ammonium sulfate, yeast extract, magnesium sulfate, and potassium phosphate. In the experimental design, we imposed the constraints that exactly one factor must be omitted in each set of experiments and no factor can account for more than one third of the mixture. Thirty different sets of experiments were designed. Results obtained showed that while starch is found to have negative influence on the production of the enzyme, yeast extract and potassium phosphate have a strong positive influence. Magnesium sulfate, ammonium sulfate, and glucose have low positive influence on the enzyme production. Contour plots have also been created to obtain information concerning the interaction effects of the media components on enzyme production.

Signature classes of transportation polytopes

Signature algorithms solve certain classes of transportation problems in a number of steps bounded by the diameter of the dual polyhedron. The class of problems to which signature algorithms may be applied—the “signature classes” of the title—are characterized, and the monotonic Hirsch conjecture is shown to hold for them. In addition, certain more precise results are given for different cases. Finally, it is explained why a supposed proof of the Hirsch conjecture for all transportation polytopes is incomplete and apparently irremedial.

Microwave assisted lipase catalyzed solvent-free poly-ε-caprolactone synthesis

Abstract Microwave (MW) assisted enzymatic polymerizations is an area that is largely unexplored. In the current study, the effect of MW reaction parameters on poly-ε-caprolactone (PCL) properties has been investigated using a statistical design. A {3,5} modified mixture experimental design was used to identify the parameter values that gave the desired properties of PCL. The three process parameters that were tested are temperature, MW intensity, and the reaction time. Experimental results showed that in the range of values tested, temperature had the highest positive influence on the properties of PCL, whereas high MW irradiation is not desirable. A cubic regression model was developed and optimal process parameters were obtained using this model. Conducting the polymerization reaction under optimal conditions (90°C, 240 min, 50 W), PCL with M n of 20,624 and polydispersity index of 1.2 were obtained. The regression model was validated by carrying out validation experiments and by 3D visualization.

Optimization of the fermentation media for sophorolipid production from Candida bombicola ATCC 22214 using a simplex centroid design

This article describes the use of a simplex centroid mixture experimental design to optimize the fermentation medium in the production of sophorolipids (SLs) using Candida bombicola. In the first stage, 16 media ingredients were screened for the ones that have the most positive influence on the SL production. The sixteen ingredients that were chosen are five different carbohydrates (fructose, glucose, glycerol, lactose, and sucrose), five different nitrogen sources (malt extract, peptone extract, soytone, urea, and yeast extract), two lipid sources (mineral oil and oleic acid), two phosphorus sources (K2HPO4 and KH2PO4), MgSO4, and CaCl2. Multiple regression analysis and centroid effect analysis were carried out to find the sugar, lipid, nitrogen source, phosphorus source, and metals having the most positive influence. Sucrose, malt extract, oleic acid, K2HPO4, and CaCl2 were selected for the second stage of experiments. An augmented simplex centroid design for five ingredients requiring 16 experiments was used for the optimization stage. This produced a quadratic model developed to help understand the interaction amongst the ingredients and find the optimal media concentrations. In addition, the top three results from the optimization experiments were used to obtain constraints that identify an optimal region. The model together with the optimal region constraints predicts the maximum production of SLs when the fermentation media is composed of sucrose, 125 g/L; malt extract, 25 g/L; oleic acid, 166.67 g/L; K2HPO4, 1.5 g/L; and CaCl2, 2.5 g/L. The optimal media was validated experimentally and a yield of 177 g/L was obtained.

A new efficient mixture screening design for optimization of media.

Screening ingredients for the optimization of media is an important first step to reduce the many potential ingredients down to the vital few components. In this study, we propose a new method of screening for mixture experiments called the centroid screening design. Comparison of the proposed design with Plackett‐Burman, fractional factorial, simplex lattice design, and modified mixture design shows that the centroid screening design is the most efficient of all the designs in terms of the small number of experimental runs needed and for detecting high‐order interaction among ingredients.

Optimization of the Media Ingredients for Cutinase Production from Colleotrichum lindemuthianum Using Mixture Design Experiments

Optimal concentrations of yeast extract, glucose and potassium phosphate in the fermentation medium have been identified for the maximum cutinase production from the fungi Colleotrichum lindemuthianum. A simplex lattice experimental design for mixtures was used to identify concentration ranges that yield maximum production. Three sets of experiments were performed all involving three ingredients. The sets of experiments differ in the number of concentration levels considered. In the first set we consider four concentration levels (i.e., 0%, 33%, 67%, 100%), and in the second and third sets we consider five and six levels, respectively. Results showed that the interactions among the nutrient ingredients are best captured when five‐ and six‐level experiments are carried out. An algorithm has been proposed in this study to design the optimal medium. Various models were also developed to predict the enzyme production, and it is concluded that the cubic model obtained using six‐level experimental data gives the best model. The study also highlighted the synergistic interaction between yeast extract and glucose toward cutinase production.

The monotonic diameter of the perfect matching and shortest path polytopes

The monotonic diameter is determined for the perfect matching, assignment, and shortest path polytopes. These results show that the diameter of a polytope and its monotonic diameter may be different. Furthermore, the monotonic Hirsch conjecture is true for these polytopes.

The monotonic diameter of traveling salesman polytopes

The monotonic diameter of the polytopes arising in the asymmetric and the symmetric traveling salesman problem (TSP) are obtained. For the asymmetric TSP polytope associated with the complete directed graph on n nodes, the monotonic diameter is shown to be exactly @?n/3@?, for all n>=3. For the symmetric TSP polytope associated with the complete undirected graph on n nodes, the monotonic diameter is shown to be exactly @?n/2@?-1, for all n>=3, except for n=5, in which case it is @?n/2@?.