Biomedical subjects

Daniel Forciniti

Publications and source records attributed to Daniel Forciniti.

10 recordsLinked to original sources

PubMed2006

On one-dimensional self-assembly of surfactant-coated nanoparticles.

Nanometer-sized metal and semiconductor particles possess novel properties. To fully realize their potential, these nanoparticles need to be fabricated into ordered arrays or predesigned structures. A promising nanoparticle fabrication method is coupled surface passivation and self-assembly of surfactant-coated nanoparticles. Due to the empirical procedure and partially satisfactory results, this method still represents a major challenge to date and its refinement can benefit from fundamental understanding. Existing evidences suggest that the self-assembly of surfactant-coated nanoparticles is induced by surfactant-modified interparticle interactions and follows an intrinsic road map such that short one-dimensional (1D) chain arrays of nanoparticles occur first as a stable intermediate before further assembly takes place to form higher dimensional close-packed superlattices. Here we report a study employing fundamental analyses and Brownian dynamics simulations to elucidate the underlying pair interaction potential that drives the nanoparticle self-assembly via 1D arrays. We find that a pair potential which has a longer-ranged repulsion and reflects the effects of surfactant chain interdigitation on the dynamics is effective in producing and stabilizing nanoparticle chain arrays. The resultant potential energy surface is isotropic for dispersed nanoparticles but becomes anisotropic to favor the growth of linear chain arrays when self-assembly starts.

Journal Article↗

PubMed2006

Effect of cosolvents on the adsorption of peptides at the solid-liquid interface.

The adsorption of a peptide at solid surfaces is the result of a complex interplay of interactions between the peptide, solvent, and surface. In this work, Monte Carlo simulations were performed to evaluate the effect of the solvent hydrogen bonding ability on the adsorption of the peptide ASP(1)-ASP(2)-ILE(3)-ILE(4)-ASP(5)-ASP(6)-ILE(7)-ILE(8) at a charged surface consisting of CH(2) atoms with a fixed lattice arrangement. Various water-alcohol mixtures were used as solvent because alcohols are known to alter the dielectric constant, hydrophobicity, and hydrogen bonding capacity of water. Solvent-solvent, solvent-surface, solvent-peptide, and peptide-surface interactions were studied independently and correlated with the observed peptide behavior at the solvent-surface interface. We concluded that the behavior (and orientation) of the peptide at the surface is directly related to changes in water-water hydrogen bonding properties in water-alcohol mixtures. In the presence of increasing concentrations of methanol, the strength of solvent-peptide and solvent-surface interactions was reduced, and as a result, a stronger interaction between the peptide and the surface was observed. Stronger solvent-peptide and solvent-surface interactions were responsible for a weaker interaction of the peptide with the surface in the presence of increasing concentrations of glycerol. These results suggest that by changing solvent conditions it is possible to finely tune the orientation of a macromolecule at solid/liquid interfaces.

Adsorption↗

PubMed2005

Surface enrichment of proteins at quartz/water interfaces: a neutron reflectivity study.

Neutron reflectivity (NR) was used to study the adsorption of human serum albumin and human fibrinogen on quartz. The proteins were individually and sequentially adsorbed from heavy water and heavy water/methanol mixtures at pH 4 and 7.0. The technique allows for the subnanometer resolution of the adsorbed layer thickness and gross morphology. Under the conditions of our measurements we found that fibrinogen formed a distinct layer that we interpret as a mat of the protein three layers thick whereas albumin formed only diffuse layers. The adsorption pattern of the two proteins changed radically when one protein was adsorbed on top of the other (previously adsorbed). In general our measurements indicate that the adsorbed protein layers on quartz are rather loosely bound and that these layers, incorporating as much as 80% water, extend further into the bulk fluid than might have been expected.

Adsorption↗

PubMed2004

Aggregation and denaturation of antibodies: a capillary electrophoresis, dynamic light scattering, and aqueous two-phase partitioning study.

Protein denaturation and aggregation are well-known problems in the pharmaceutical industry. As the protein aggregates, it loses its biological activity and creates problems in its administration to patients. In this paper, we explore the use of aqueous two-phase systems, capillary zone electrophoresis, and dynamic light scattering for the monitoring of protein denaturation and aggregation. Our studies focus on human IgG and HSA. Capillary zone electrophoresis was used to monitor changes in the charge to size ratio of the proteins upon denaturation and dynamic light scattering was used to detect the presence of any aggregates and to monitor the size of the proteins. The information obtained from aqueous two-phase partitioning is similar to that obtained from capillary zone electrophoresis. The simplicity of aqueous two-phase system and its low cost (compared to the other analytical techniques) suggest that it can be routinely used for the quality control of some pharmaceutical preparations.

Antibodies↗

PubMed2004

Decontamination of surfaces by lysozyme encapsulated in reverse micelles.

Cells and enzymes can be used to decontaminate soil, water supplies, personal equipment, weapons and hospital equipment that have been exposed to bacteria, toxins or viruses. One of the problems associated with the use of microorganisms and enzymes for decontamination purposes is that the presence of water is not acceptable for some applications such as electronic equipment. One way of circumventing this problem is to allow the enzyme to distribute between a water phase and an organic phase-containing surfactant and then use the encapsulated enzyme in reverse micelles directly into the device to be clean. Reverse micelles were used to deliver the enzyme (lysozyme) to the cell-surface interface. They serve as a way to increase the local concentration of lysozyme and decrease the amount of water delivered. Specifically, we explored the lysis by free lysozyme and lysozyme encapsulated in reverse micelles of Klebsiella pneumoniae and Staphylococcus epidermidis attached to steel, glass, and hydroxyapatite. These two bacteria have been selected because they are known to be pathogenic and because of their differences in cell wall structure. Lysozyme was added to the surfaces in either reverse micelles or as a free solution and was tested under conditions of stirring and no stirring. Stirring was implemented to study the interplay between mass transfer limitations and surface roughness. We have shown that free lysozyme or lysozyme encapsulated in reverse micelles is capable of decontaminating surfaces of different texture. Lysis of the cells is slower when the encapsulated enzyme is used but lysis is more complete.

Decontamination↗

PubMed2003

Enzymatic synthesis and characterization of l-methionine and 2-hydroxy-4-(methylthio)butanoic acid (HMB) co-oligomers.

Oligomers of l-methionine (Met) and its hydroxy analogue, 2-hydroxy-4-(methylthio)butanoic acid (d,l-HMB) were synthesized with the proteolytic enzyme papain. The Met homooligomers and HMB-Met co-oligomers obtained through the enzymatic reactions were subjected to persulfonation and separated with reverse phase liquid chromatography (RPLC). The separated oligomers were characterized with electrospray ionization-mass spectrometry (ESI-MS). The oligomers were also characterized with matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS). The results showed that co-oligomers were predominantly composed of 4-8 Met residues and one HMB residue. The data also suggest that in the co-oligomers, HMB is attached at the N-terminal end of the oligopeptide chain.

Chromatography, High Pressure Liquid↗

PubMed2002

Computer simulations and neutron reflectivity of proteins at interfaces.

Computer simulations in conjunction with neutron reflectivity is an excellent combination for the study of biological materials at solid-liquid interfaces: Both techniques have excellent resolution levels (Angströms) and they are mature. A stronger interaction between physicists and biologists will allow the use of these two approaches in topics of biological-biomedical interest.

Adsorption↗

PubMed2002

Ethylene oxide and propylene oxide random copolymer/sodium chloride aqueous two-phase systems: wetting and adsorption on dodecyl-agarose and polystyrene.

Liquid/liquid partition chromatography is a mild yet powerful separation method for a variety of biological materials. This work demonstrates that it should be feasible to immobilize an ethylene oxide-propylene oxide (EO/PO) random copolymer solution and to use a solution of NaCl equilibrated against the polymer solution as the mobile-phase (poly (EO-PO) [P(EO-PO)] and NaCl form two aqueous phases known as aqueous two-phase systems). Three random copolymers with different molecular weights and EO/PO ratios were used. Dodecyl-agarose and polystyrene were tested as possible supports. The wetting energies of the aqueous two-phase systems on these two kinds of surfaces were calculated as well as contact angles for each phase on the same surfaces. Finally, the thickness of P(EO-PO) adsorption layers on polystyrene lattices were measured by dynamic light scattering. Contact angle measurements indicate that indeed some EO/PO copolymers preferentially wet hydrophobic substrates, forming thin films.

Adsorption↗

PubMedDate not supplied

Conformational changes of peptides at solid/liquid interfaces: a Monte Carlo study.

Monte Carlo simulations were performed to study the conformational changes of negatively charged model peptides dissolved in water adsorbed onto charged surfaces. 8-, 16-, and 20-residues peptides were used, each of them consisted of repeating diblock units of aspartic acid (ASP, polar amino acid) and isoleucine (ILE, nonpolar amino acid) residues. We found that a water patch was retained at the charged surface, separating the peptide from it. We believed that these water molecules were primarily responsible for giving a particular orientation to the peptide at the surface. Water did play a role to some extent in the structural stability of the 8-residues peptide. However, for higher chain lengths (16-residues and 20-residues), the intrinsic hydrogen-bonding network (or intrinsic structural stability) showed a predominant effect over hydrophobic dehydration for the stability of the peptide at the surface.

Adsorption↗

PubMedDate not supplied

Distribution of cells between solid/liquid and liquid/liquid interfaces.

The use of aqueous two-phase systems (ATPSs) and each system's individual phase-forming species to prevent Streptococcus sanguis attachment onto hydroxyapatite discs was explored. The strategy that we followed was to attach the cells to a solid surface in the presence of an additional interface. Conditions under which, simultaneously, the phase-forming species form two phases and the cells proliferate were identified. Growth curves were constructed in the presence of various polymers and salts commonly used to prepare ATPSs. Several aqueous two-phase systems were selected such that bacterial growth was comparable to that observed in pure medium. Cells were allowed to attach to hydroxyapatite discs for 7 days in the presence of varying concentrations of media, media with polymer, media with salt, and media with ATPS. Streptococcus sanguis attachment to the disks was evaluated by scanning electron microscopy. The addition of a PEG/Na(2)SO(4) ATPS to high concentrations of yeast-tryptone (YT) media (>65%) and of a PEG/MgSO(4) ATPS to nutrient-limited media reduces surface coverage of S. sanguis to less than 10%. Comparison of the attachment levels for the systems containing PEG/Na(2)SO(4) to media containing the individual phase-forming species and to the YT reference systems indicated that nutrient availability did not affect attachment.

Bacterial Adhesion↗