Iliana Medina-Ramírez

Green synthesis and characterization of polymer-stabilized silver nanoparticles.

Silver nanoparticles (Ag-NPs) were synthesized using a facile green chemistry synthetic route. The reaction occurred at ambient temperature with four reducing agents introduced to obtain nanoscale Ag-NPs. The variables of the green synthetic route, such as acidity, concentration of starting materials, and molar ratio of reactants were optimized. Dispersing agents were employed to prevent Ag-NPs from aggregating. Advanced instrumentation techniques, such as X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible spectroscopy (UV-vis), and phase analysis light scattering technique (ZetaPALS) were applied to characterize the morphology, particle size distribution, elemental composition, and electrokinetic behavior of the Ag-NPs. UV-vis spectra detected the characteristic plasmon at approximately 395-410 nm; and XRD results were indicative of face-centered cubic phase structure of Ag. These particles were found to be monodispersed and highly crystalline, displaying near-spherical appearance, with average particle size of 10.2 nm using citrate or 13.7 nm using ascorbic acid as reductants from particle size analysis by ZetaPALS, respectively. The rapid electrokinetic behavior of the Ag was evaluated using zetapotential (from -40 to -42 mV), which was highly dependant on nanoparticle acidity and particle size. The current research opens a new avenue for the green fabrication of nanomaterials (including variables optimization and aggregation prevention), and functionalization in the field of nanocatalysis, disinfection, and electronics.

High removal of chemical and biochemical oxygen demand from tequila vinasses by using physicochemical and biological methods

The goal of this research is to find a more effective treatment for tequila vinasses (TVs) with potential industrial application in order to comply with the Mexican environmental regulations. TVs are characterized by their high content of solids, high values of biochemical oxygen demand (BOD 5), chemical oxygen demand (COD), low pH and intense colour; thus, disposal of untreated TVs severely impacts the environment. Physicochemical and biological treatments, and a combination of both, were probed on the remediation of TVs. The use of alginate for the physicochemical treatment of TVs reduced BOD 5 and COD values by 70.6% and 14.2%, respectively. Twenty white-rot fungi (WRF) strains were tested in TV-based solid media. Pleurotus ostreatus 7992 and Trametes trogii 8154 were selected due to their ability to grow on TV-based solid media. Ligninolytic enzymes’ production was observed in liquid cultures of both fungi. Using the selected WRF for TVs’ bioremediation, both COD and BOD 5 were reduced by 88.7% and 89.7%, respectively. Applying sequential physicochemical and biological treatments, BOD 5 and COD were reduced by 91.6% and 93.1%, respectively. Results showed that alginate and selected WRF have potential for the industrial treatment of TVs.

Numerical treatment of the spherically symmetric solutions of a generalized Fisher-Kolmogorov-Petrovsky-Piscounov equation

In the present work, the connection of the generalized Fisher-KPP equation to physical and biological fields is noted. Radially symmetric solutions to the generalized Fisher-KPP equation are considered, and analytical results for the positivity and asymptotic stability of solutions to the corresponding time-independent elliptic differential equation are quoted. An energy analysis of the generalized theory is carried out with further physical applications in mind, and a numerical method that consistently approximates the energy of the system and its rate of change is presented. The method is thoroughly tested against analytical and numerical results on the classical Fisher-KPP equation, the Heaviside equation, and the generalized Fisher-KPP equation with logistic nonlinearity and Heaviside initial profile, obtaining as a result that our method is highly stable and accurate, even in the presence of discontinuities. As an application, we establish numerically that, under the presence of suitable initial conditions, there exists a threshold for the relaxation time with the property that solutions to the problems considered are nonnegative if and only if the relaxation time is below a critical value. An analytical prediction is provided for the Heaviside equation, against which we verify the validity of our computational code, and numerical approximations are provided for several generalized Fisher-KPP problems.

On a fully discrete finite-difference approximation of a nonlinear diffusion–reaction model in microbial ecology

In this work, we introduce a numerical method to approximate the solutions of a multidimensional parabolic partial differential equation with nonlinear diffusion and reaction, subject to nonnegative initial data and homogeneous boundary conditions of the Neumann type. The equation considered is a model for both the growth of biological films and the propagation of mutant genes which are advantageous to a population. The initial-boundary-value problem under investigation is fully discretized temporally and spatially following a finite-difference methodology which results in a simple, linear, implicit scheme that is consistent with respect to the continuous problem. The method is a two-step technique that preserves the positivity and the boundedness of initial profiles. We provide some simulations on the growth of microbial colonies, and comparisons versus a standard approach.

Application of Nanometals Fabricated Using Green Synthesis in Cancer Diagnosis and Therapy

Iliana Medina-Ramirez1, Maribel Gonzalez-Garcia2, Srinath Palakurthi3 and Jingbo Liu4,5 1Department of Chemistry, Universidad Autonoma de Aguascalientes, Aguascalientes, 2Department of Chemistry, Texas A&M University-Kingsville, Kingsville, TX, 3Department of Pharmaceutical Sciences, Texas A&M Health Science Center, Kingssville, TX, 4Nanotech and Cleantech Group, Texas A&M University-Kingsville, TX, 5Department of Chemistry, Texas A&M University, College Station, TX, 1Mexico 2,3,4,5USA

The flavonoid quercetin protects and prevents against potassium dichromate-induced systemic peroxidation of lipids and diminution in renal clearance of para-aminohippuric acid and inulin in the rat.

It is well known that exposure to chromium (Cr) can lead to nephrotoxicity. Quercetin is a flavonoid of interest because of its proposed health-promoting effects. The aim of this work was to elucidate the role of quercetin against the nephrotoxicity caused by Cr in rats. Quercetin may have positive effects in combating, or helping to prevent, nephrotoxicity. It was observed that a single dose of potassium dichromate resulted in both an increase of systemic peroxidation of lipids and a decrease of the renal clearance of para-aminohippuric acid and inulin. Our results show that treatment with quercetin protected and prevented against these damaging effects.

An efficient nonlinear finite-difference approach in the computational modeling of the dynamics of a nonlinear diffusion-reaction equation in microbial ecology

In this manuscript, we present a computational model to approximate the solutions of a partial differential equation which describes the growth dynamics of microbial films. The numerical technique reported in this work is an explicit, nonlinear finite-difference methodology which is computationally implemented using Newtons method. Our scheme is compared numerically against an implicit, linear finite-difference discretization of the same partial differential equation, whose computer coding requires an implementation of the stabilized bi-conjugate gradient method. Our numerical results evince that the nonlinear approach results in a more efficient approximation to the solutions of the biofilm model considered, and demands less computer memory. Moreover, the positivity of initial profiles is preserved in the practice by the nonlinear scheme proposed.

Colloidal Synthesis and Nanocharacterization of Engineered Noble Metal Nanoparticles

ABSTRACT Engineered noble (silver [Ag], gold [Au], and platinum [Pt]) metallic nanoparticles (ENPs) were prepared in gum arabic solutions using a facile, economical, and nontoxic synthetic route. Advanced instrumentation techniques (ultraviolet-visible spectroscopy, X-ray powder diffraction, high-resolution transmission electron microscopy equipped with X-ray energy dispersive spectroscopy, and dynamic light scattering) were applied to characterize the morphology, particle size distribution, elemental composition, and electrokinetics behavior of the ENPs. The analytical results of morphology and elemental composition suggest a size-controlled growth mechanism that yields monodispersed metallic particles (3.5–10.2 nm in diameter), indicating that the nanostructured products were highly crystalline and monodispersed. Zeta potential data confirmed that stable ENPs can be produced using a green chemistry approach. The ENPs displayed excellent stability as measured by zeta potential from −55 to −35 mV over a 2...

Tetrakis(μ‐triisopropylsilanethiolato)‐1:2κ4S:S;2:3κ4S:S‐bis(triisopropylsilanethiolato)‐1κS,3κS‐trizinc(II)

The title compound, [Zn(3)(C(9)H(21)SiS)(6)] or [((i)Pr(3)SiS)Zn(mu-SSi(i)Pr(3))(2)Zn(mu-SSi(i)Pr(3))(2)Zn(SSi(i)Pr(3))], is the first structurally characterized homoleptic silanethiolate complex of zinc. A near-linear arrangement of three Zn(II) ions is observed, the metals at the ends being three-coordinate with one terminally bound silanethiolate ligand. The central Zn(II) ion is four-coordinate and tetrahedral, with two bridging silanethiolate ligands joining it to each of the two peripheral Zn(II) ions. The nonbonding intermetallic distances are 3.1344 (11) and 3.2288 (12) A, while the Zn...Zn...Zn angle is 172.34 (2) degrees. A trimetallic silanethiolate species of this type has not been previously identified by X-ray crystallography for any element.

A compact exponential method for the efficient numerical simulation of the dewetting process of viscous thin films

In this work, we propose a discrete mathematical system to model the evolution of the thickness of two-dimensional viscous thin films subject to a dewetting process. The continuous model under consideration is a degenerate partial differential equation that generalizes the classical thin film equation, and considers the inclusion of a singular potential. The analytical model is discretized using an exponential method that is capable of preserving the positive character of the approximations. In addition, the explicit nature of our approach results in an economic computer implementation which produces fast simulations. We provide some illustrative examples on the dynamics of the growth of thin films in the presence/absence of a dewetting process. The qualitative results exhibit the appearance of typical patterns obtained in experimental settings. The technique was validated against Bhattacharya’s method and a standard explicit discretization of the mathematical model.