Laura Valenti - Academia.edu (original) (raw)

Papers by Laura Valenti

Colloids and Surfaces B: Biointerfaces, 2015

Silver-coated orthopedic implants and silver composite materials have been proposed to produce lo... more Silver-coated orthopedic implants and silver composite materials have been proposed to produce local biocidal activity at low dose to reduce post-surgery infection that remains one of the major contributions to the patient morbidity. This work presents the synthesis combined with the characterization, colloidal stability in biological relevant media, antimicrobial activity and handling properties of silver nanoparticles (Ag-NP) before and after freeze dry and storage. The nanomaterial was synthesized in aqueous solution with simple, reproducible and low-cost strategies using bovine serum albumin (BSA) as the stabilizing agent. Ag-NP were characterized by means of the size distribution and morphology (UV-vis spectra, dynamic light scattering measurements and TEM images), charge as a function of the pH (zeta potential measurements) and colloidal stability in biological relevant media (UV-vis spectra and dynamic light scattering measurements). Further, the interactions between the protein and Ag-NP were evaluated by surface enhanced Raman spectroscopy (SERS) and the antimicrobial activity was tested with two bacteria strains (namely Staphylococcus aureus and Staphylococcus epidermidis) mainly present in the infections caused by implants and prosthesis in orthopedic surgery. Finally, the Ag-NP dispersed in aqueous solution were dried and stored as long-lasting powders that were easily reconstituted without losing their stability and antimicrobial properties. The proposed methods to stabilize Ag-NP not only produce stable dispersions in media of biological relevance but also long-lasting powders with optimal antimicrobial activity in the nanomolar range. This level is much lower than the cytotoxicity determined in vitro on osteoblasts, osteoclasts and osteoarthritic chondrocytes. The synthesized Ag-NP can be incorporated as additive of biomaterials or pharmaceutical products to confer antimicrobial activity in a powdered form in different formulations, dispersed in aqueous and non-aqueous solutions or coated on the surface of different materials.

ACS Symposium Series, 2012

Journal of Materials Chemistry B, 2013

Key Engineering Materials, 2010

Page 1. Driving Forces and Consequences of the Adsorption of Proteins to Carbon Nanotubes María F... more Page 1. Driving Forces and Consequences of the Adsorption of Proteins to Carbon Nanotubes María F. Mora 1,a , Laura E. Valenti 2,b , Carlos D. García 1,c , Carla E. Giacomelli 2,d 1Department of Chemistry, The University of Texas at San Antonio, San Antonio, Texas 78249. ...

Journal of Inorganic Biochemistry, 2006

The aim of this work is to study the binding of nickel ions to hexahistidine (His 6 ) combining p... more The aim of this work is to study the binding of nickel ions to hexahistidine (His 6 ) combining potentiometric titrations and spectroscopic (UV-Vis and circular dichroism) determinations in order to establish the species distribution as a function of the pH, their stoichiometry, stability and geometry. For comparative purposes, the same procedure was applied to the Ni-histidine (His) system. His behaves as a tridentate ligand, coordinating the carboxyl group, the imidazole and the amino nitrogen atoms to Ni(II) ions in an octahedral coordination and a bis(histidine) complex is formed at pH higher than 5. For the Ni-His 6 system, the complex formation starts at pH 4 and five different species (Ni(His 6 )H, Ni(His 6 ), Ni n (His 6 ) n , Ni n (His 6 ) n H Àn/2 , Ni n (His 6 ) n H Àn ) are formed as a function of the pH. Ni(His 6 )H involves the coordination of the imidazole nitrogen and a deprotonated amide nitrogen (N Im , N À ) resulting in an octahedral geometry. In Ni(His 6 ), an imidazole nitrogen is deprotonated and coordinated (2N Im , N À ) to the metal ion with a square planar geometry. The aggregated forms result from the extra Ni-N Im coordination, resulting in a 4N square planar geometry that is stabilized by inter/intramolecular hydrogen bonds. This coordination mode is not altered during the deprotonation steps from Ni n (His 6 ) n .

Journal of Colloid and Interface Science, 2007

The aim of this work is to study the adsorption-desorption process of bovine serum albumin (BSA) ... more The aim of this work is to study the adsorption-desorption process of bovine serum albumin (BSA) on carbon nanotubes (CNT) by reflectometry. The effect of the surface properties was analyzed by comparing the behavior of BSA on silica. The experiments were performed by reflectometry at different BSA concentrations, at pH 3.0, 4.8, and 7.0 and at two ionic strengths. Protein desorption was induced by either dilution with buffer or the addition of SDS. The initial adsorption rate is controlled by the attachment of BSA molecules to the surface, and strongly diminishes at pH 7. Adsorption isotherms reflect the high affinity of BSA for both sorbent surfaces and reach well-defined plateau values that depend on the pH, being the highest at pH 4.8 on CNT. Experiments performed at different ionic strengths (NaCl added) showed a less pronounced effect. Dilution does not induce desorption on either surface however, the addition of SDS removes protein only from the silica surface.

Colloids and Surfaces B: Biointerfaces, 2013

In order to rationally design a bio-functional surface based on the adsorption of a His-tag antig... more In order to rationally design a bio-functional surface based on the adsorption of a His-tag antigen, three requirements have to be considered: the bio-recognition element, the driving forces for the adsorption process and the detection mode of the bio-recognition event. This work is focused on the study of the adsorption mechanism of the His-tag H49 Chagas antigen on Ni(II) modified substrates. In order to construct the bio-functional surface, the gen of the H49 Chagas antigen was modified to incorporate His6 moiety at the N-terminal (His6-H49). Then, its physical adsorption and bio-affinity interaction with the solid substrate was studied by reflectometry. Besides His-Ni(II) bio-affinity interactions, His6-H49 was also physically adsorbed on Ni(II) modified substrates, leading to randomly oriented antigens. These loosely attached bio-molecules were partially removed using conditions of electrostatic repulsion. On the other hand, bio-affinity interactions, resulting in site-oriented molecules on the substrate, were only removable by specific competitors for Ni(II) surface sites. Finally, the surface bio-activity was determined from the peak separations of voltammetry waves due to the change of the electron transfer kinetics of a redox probe through the bio-functional surface (working electrode).

Analytical Biochemistry, 2011

Synthetic peptide or protein samples are mostly unpurified with trifluoroacetic acid (TFA) used d... more Synthetic peptide or protein samples are mostly unpurified with trifluoroacetic acid (TFA) used during the synthesis procedure, which strongly interferes with structure determination by infrared (IR) spectroscopy. The aim of this work was to propose a simple strategy to remove TFA contribution from attenuated total reflection (ATR)-IR spectra of the hexahistidine peptide (His6) in aqueous solution to study the conformation of this synthetic peptide without previous purification. Such a strategy is based on the subtraction mode widely employed to remove water contribution, and it is tested with TFA unpurified histidine as a model system. The subtraction is based on eliminating the strong TFA bands at 1147 and 1200 cm À1 by applying a scaling factor (as in buffer correction). The proposed modes represent excellent strategies that do not modify spectral features, and they provide reliable routines to obtain the synthetic peptide spectrum without TFA contribution. The conformational information from the corrected spectra at different pH values is deduced from semiempirical calculated IR spectra of different His6 conformers. The spectral features and the band positions of the corrected spectrum suggest that the peptide molecules mainly adopt an intermolecular b-sheet structure.

Clays and Clay Minerals, 2001

Methylene blue (MB) was adsorbed from aqueous solutions onto a kaolinite and four soil samples to... more Methylene blue (MB) was adsorbed from aqueous solutions onto a kaolinite and four soil samples to determine the effects of MB dimerization on the measured surface area. Adsorption isotherms were prepared using four adsorbing solutions containing, respectively, 9, 46, 71, and 83% of MB molecules in the dimeric state. Langmuir-type isotherms were obtained in each case. The results indicate that equilibration occurs quickly. The aggregation state of MB molecules at the surface does not depend on the aggregation state in the initial adsorbing solutions, but on the final equilibrium concentration of MB. A comparison with the specific surface area measured by adsorption of ethylene glycol monoethyl ether indicates that MB adsorbs as a monomer, regardless of the aggregation number in solution. This result occurs owing to the strength of monomer-surface and monomer-monomer interactions. If monomer-surface interactions are favored, the MB dimer adsorbs in the monomeric form. If monomer-monomer interactions are favored, dimer adsorption may occur. The visible spectra of adsorbed molecules indicated that MB was present at the surface as a mixture of monomeric and dimeric species. These results suggest that dimers are formed in the contact region between two aggregating particles.