Mario Blanco - Academia.edu (original) (raw)

Papers by Mario Blanco

Journal of Physical Chemistry B, 2001

A Morse-charge equilibration force field (MS-Q FF), originally developed for the bulk oxides SiO ... more A Morse-charge equilibration force field (MS-Q FF), originally developed for the bulk oxides SiO 2 and Al 2 O 3 , has been used to model kaolinite and pyrophyllite clay minerals and their interactions with representative organic molecules. The MS-Q FF reproduces the structural parameters for these clay minerals and gives accurate enthalpies of immersions in water, organic solvents, and hydrocarbons. To form a basis for improving squeeze corrosion treatment strategies, we calculate the adsorption energy of oleic imidazoline, a corrosion inhibitor oil production chemical.

Environmental Science & Technology, 2004

Ambient particulate matter contains polar multifunctional oxygenates that partition between the v... more Ambient particulate matter contains polar multifunctional oxygenates that partition between the vapor and aerosol phases. Vapor pressure predictions are required to determine the gas-particle partitioning of such organic compounds. We present here a method based on atomistic simulations combined with the Clausius-Clapeyron equation to predict the liquid vapor pressure, enthalpies of vaporization, and heats of sublimation of atmospheric organic compounds. The resulting temperature-dependent vapor pressure equation is a function of the heat of vaporization at the normal boiling point [∆H vap (T b )], normal boiling point (T b ), and the change in heat capacity (liquid to gas) of the compound upon phase change [∆C p (T b )]. We show that heats of vaporization can be estimated from calculated cohesive energy densities (CED) of the pure compound obtained from multiple sampling molecular dynamics. The simulation method (CED) uses a generic force field (Dreiding) and molecular models with atomic charges determined from quantum mechanics. The heats of vaporization of five dicarboxylic acids [malonic (C 3 ), succinic (C 4 ), glutaric (C 5 ), adipic (C 6 ), and pimelic (C 7 )] are calculated at 500 K. Results are in agreement with experimental values with an averaged error of about 4%. The corresponding heats of sublimation at 298 K are also predicted using molecular simulations. Vapor pressures of the five dicarboxylic acids are also predicted using the derived Clausius-Clapeyron equation. Predicted liquid vapor pressures agree well with available literature data with an averaged error of 29%, while the predicted solid vapor pressures at ambient temperature differ considerably from a recent study by Bilde et al. (Environ. Sci. Technol. 2003, 37, 1371-1378 (an average of 70%). The difference is attributed to the linear dependence assumption that we used in the derived Clausius-Clapeyron equation.

Journal of Physical Chemistry B, 1997

Zinc dithiophosphate (DTP) molecules have long been used as wear inhibitor oil additives for auto... more Zinc dithiophosphate (DTP) molecules have long been used as wear inhibitor oil additives for automotive engines. In order to obtain an atomistic understanding of the mechanism by which these molecules inhibit wear, we examined the geometries, energetics, and vibrations of an oxidized iron surface [(001) surface of R-Fe 2 O 3 ] using the MSX force field (FF) based on ab initio quantum chemistry (QC) calculations. The DTP molecules studied include (RO) 2 PS 2 with R ) methyl, isobutyl, isopropyl, and phenyl. The R-Fe 2 O 3 surface is described using the generalized valence bond (GVB) model of bonding. The geometries, binding energies, and vibrational frequencies from ab initio calculations on simple clusters are used with the biased Hessian method to develop the MSX FF suitable for describing the binding of DTP molecules to the surfaces. We find that the cohesive energies for the self-assembled monolayers (SAM) of the DTP molecules on the Fe 2 O 3 surface correlate with the antiwear performance observed in experimental engine tests. This suggests that the search for more effective and environmentally benign wear inhibitors can use the cohesive energies for SAM formation as a criterion in selecting and prioritizing compounds for experimental testing.

Langmuir, 1996

Some of the most effective corrosion inhibitors for oil field pipeline applications are the oleic... more Some of the most effective corrosion inhibitors for oil field pipeline applications are the oleic imidazoline (OI) class of molecules. However, the mechanism by which OIs inhibit corrosion is not known. We report atomistic simulations (quantum mechanics and molecular dynamics) designed to elucidate this mechanism. These studies lead to the self-assembled monolayer (SAM) model for corrosion inhibition, which explains the differences in corrosion inhibition efficiency for various OI molecules. The SAM model of OI inhibitors involves the following critical elements: (i) The function of the OI is to form a self-assembled monolayer on the native oxide surface of iron; this serves a protective role by forming a hydrophobic barrier preventing migration of H 2O, O2, and electrons to the Fe surface. (ii) The imidazoline head group serves as a sufficiently strong Lewis base to displace H2O from the Lewis acid sites of the iron oxide surface. (iii) These head groups self-assemble on the surface to form an ordered monolayer on the iron oxide surface. [ 3 × 3 for the (001) cleavage surface of R-Fe2O3.] (iv) The long hydrophobic tail (e.g., 2-oleic acid) tilts to form a tightly packed hydrophobic monolayer. [For R-Fe2O3(001) the tilt angle is about 72°with respect to the surface normal.] (v) This hydrocarbon tail must have a sufficient length to cover the surface. [For R-Fe2O3-(001) the chain length must be 12 or more carbon atoms.] (vi) The hydrophobic tail and the pendent group (e.g., -CH2CH2NH2) must lead to an octanol/water partition coefficient (log P) below a critical value in order to rapidly form the monolayer. This SAM model should be useful in developing both alternative environmentally benign corrosion inhibitors and higher temperature corrosion inhibitors. Osborne, C.; Webster, S.; Klenerman, D.; Joseph, M.; Ostovar, P.; Doyle, M. Corros.

Journal of Physical Chemistry B, 2004

The effect of molecular architecture of a surfactant, particularly the attachment position of ben... more The effect of molecular architecture of a surfactant, particularly the attachment position of benzene sulfonate on the hexadecane backbone, at the decane-water interface was investigated using atomistic MD simulations. We consider a series of surfactant isomers in the family of alkyl benzene sulfonates, denoted by m-C16, indicating a benzene sulfonate group attached to the mth carbon in a hexadecane backbone. The equilibrated model systems showed a well-defined interface between the decane and water phases. We find that surfactant 4-C16 has a more compact packing, in terms of the interfacial area and molecular alignment at the interface, than other surfactants simulated in this study. Furthermore, surfactant 4-C16 leads to the most stable interface by having the lowest interface formation energy. The interfacial thickness is the largest in the case of surfactant 4-C16, with the thickness decreasing when the benzene sulfonate is located farther from the attachment position of 4-C16 (the 4th carbon). The interfacial tension profile was calculated along the direction perpendicular to the interface using the Kirkwood-Buff theory. From the comparison of the interfacial tension obtained from the interfacial tension profile, we found that surfactant 4-C16 induces the lowest interfacial tension and that the interfacial tension increases with decreasing interfacial thickness as a function of the attachment position of benzene sulfonate. Such a relationship between the interfacial thickness and interfacial tension is rationalized in terms of the miscibility of the alkyl tail of surfactant m-C16 with decane by comparing the "effective" length of the alkyl tail with the average end-to-end length of decane. Among the surfactants, the effective length of the 4-C16 alkyl tail (9.53 ( 1.36 Å) was found to be closest to that of decane (9.97 ( 1.03 Å), which is consistent with the results from the density profile and the interfacial tension profile.

Computational and Theoretical Polymer Science, 2001

Advances in theory and methods are making it practical to consider fully ®rst principles (de novo... more Advances in theory and methods are making it practical to consider fully ®rst principles (de novo) predictions of structures, properties and processes for organic materials. However, despite the progress there remains an enormous challenge in bridging the vast range of distances and time scales between de novo atomistic simulations and the quantitative continuum models for the macroscopic systems essential in industrial design and operations. Recent advances relevant to such developments include: quantum chemistry including continuum solvation and force ®eld embedding, de novo force ®elds to describe phase transitions, molecular dynamics (MD) including continuum solvent, non equilibrium MD for rheology and thermal conductivity and mesoscale simulations. To provide some¯avor for the opportunities we will illustrate some of the progress and challenges by summarizing some recent developments in methods and their applications to polymers and biopolymers. Four different topics will be covered: (1) hierarchical modeling approach applied to modeling olfactory receptors, (2) stabilization of leucine zipper coils by introduction of tri¯uoroleucine, (3) modeling response of polymers sensors for electronic nose, and (4) diffusion of gases in amorphous polymers. q

Macromolecules, 2003

The well-known helical conformations of double stranded DNA and poly(alanine) are stabilized by i... more The well-known helical conformations of double stranded DNA and poly(alanine) are stabilized by inter-and intramolecular hydrogen bonds, respectively. Perfluorinated n-alkanes also exhibit stable helical conformations, with ordered chiralities at low temperatures. In the absence of hydrogen bonds, one may ask what forces stabilize perfluorinated n-alkane helices. We combine ab initio and empirical data to study the likely classical source of this helical behavior. Past studies point to bad sterics (van der Waals interactions) between neighboring fluorine atoms as the source of helicity in perfluorinated linear alkanes. In these early studies electrostatics were ignored. We undertook a detailed force field parameter optimization strategy, using experimental and ab initio data, to obtain transferable, uncorrelated estimates of the separate classical energy components. We find that the dominant energy term, the source of helicity, is electrostatics. The coulomb repulsion, from a classical fixed-charge model, reproduces reasonably well the position of the energy minima and the energy barrier between the helical and the all-trans conformations. Polarization effects, changes in atomic charges as a result of conformational changes, are not significant. Dihedral interactions and van der Waals terms adjust the exact position of the minima only slightly. In the absence of electrostatic contributions, van der Waals and dihedral interactions predict the incorrect stable conformations.

Journal of Physical Chemistry B, 2007

It is important for many industrial processes to design new materials with improved selective per... more It is important for many industrial processes to design new materials with improved selective permeability properties. Besides diffusion, the molecule's solubility contributes largely to the overall permeation process. This study presents a method to calculate solubility coefficients of gases such as O 2 , H 2 O (vapor), N 2 , and CO 2 in polymeric matrices from simulation methods (Molecular Dynamics and Monte Carlo) using first principle predictions. The generation and equilibration (annealing) of five polymer models (polypropylene, polyvinyl alcohol, polyvinyl dichloride, polyvinyl chloride-trifluoroethylene, and polyethylene terephtalate) are extensively described. For each polymer, the average density and Hansen solubilities over a set of ten samples compare well with experimental data. For polyethylene terephtalate, the average properties between a small (n ) 10) and a large (n ) 100) set are compared. Boltzmann averages and probability density distributions of binding and strain energies indicate that the smaller set is biased in sampling configurations with higher energies. However, the sample with the lowest cohesive energy density from the smaller set is representative of the average of the larger set. Density-wise, low molecular weight polymers tend to have on average lower densities. Infinite molecular weight samples do however provide a very good representation of the experimental density. Solubility constants calculated with two ensembles (grand canonical and Henry's constant) are equivalent within 20%. For each polymer sample, the solubility constant is then calculated using the faster (10×) Henry's constant ensemble (HCE) from 150 ps of NPT dynamics of the polymer matrix. The influence of various factors (bad contact fraction, number of iterations) on the accuracy of Henry's constant is discussed. To validate the calculations against experimental results, the solubilities of nitrogen and carbon dioxide in polypropylene are examined over a range of temperatures between 250 and 650 K. The magnitudes of the calculated solubilities agree well with experimental results, and the trends with temperature are predicted correctly. The HCE method is used to predict the solubility constants at 298 K of water vapor and oxygen. The water vapor solubilities follow more closely the experimental trend of permeabilities, both ranging over 4 orders of magnitude. For oxygen, the calculated values do not follow entirely the experimental trend of permeabilities, most probably because at this temperature some of the polymers are in the glassy regime and thus are diffusion dominated. Our study also concludes large confidence limits are associated with the calculated Henry's constants. By investigating several factors (terminal ends of the polymer chains, void distribution, etc.), we conclude that the large confidence limits are intimately related to the polymer's conformational changes caused by thermal fluctuations and have to be regardedsat least at microscalesas a characteristic of each polymer and the nature of its interaction with the solute. Reducing the mobility of the polymer matrix as well as controlling the distribution of the free (occupiable) volume would act as mechanisms toward lowering both the gas solubility and the diffusion coefficients.

Journal of The American Chemical Society, 2008

The development of a miniaturized sensing platform for the selective detection of chemical odoran... more The development of a miniaturized sensing platform for the selective detection of chemical odorants could stimulate exciting scientific and technological opportunities. Oligopeptides are robust substrates for the selective recognition of a variety of chemical and biological species. Likewise, semiconducting nanowires are extremely sensitive gas sensors. Here we explore the possibilities and chemistries of linking peptides to silicon nanowire sensors for the selective detection of small molecules. The silica surface of the nanowires is passivated with peptides using amide coupling chemistry. The peptide/ nanowire sensors can be designed, through the peptide sequence, to exhibit orthogonal responses to acetic acid and ammonia vapors, and can detect traces of these gases from "chemically camouflaged" mixtures. Through both theory and experiment, we find that this sensing selectivity arises from both acid/base reactivity and from molecular structure. These results provide a model platform for what can be achieved in terms of selective and sensitive "electronic noses." J. AM. CHEM. SOC. 2008, 130, 9583-9589 9 9583

Journal of Physical Chemistry A, 1997

The oleic imidazoline (OI) class of molecules is used extensively for corrosion inhibitor oil fie... more The oleic imidazoline (OI) class of molecules is used extensively for corrosion inhibitor oil field pipeline applications. However, there is no model for understanding how they work. As a first step in elucidating this mechanism we carried out quantum mechanical calculations on clusters involving Fe 3+ , H 2 O, OH, and OI. These calculations are used to determine the MS force field for molecular dynamics simulations.

Journal of The American Chemical Society, 1999

A promising cancer therapy involves the use of the macrocyclic polyaminoacetate DOTA (1,4,7,10tet... more A promising cancer therapy involves the use of the macrocyclic polyaminoacetate DOTA (1,4,7,10tetraazacyclododecane-1,4,7,10-tetraacetic acid) attached to a tumor-targeting antibody complexed with the emitter 90 Y 3+ . However, incorporation of the 90 Y into the DOTA conjugate is too slow. To identify the origins of this problem, we used ab initio quantum chemistry methods (B3LYP/LACVP* and HF/LACVP*) to predict structures and energetics. We find that the initial complex YH 2 (DOTA) + is 4-coordinate (the four equivalent carboxylate oxygens), which transforms to YH(DOTA) (5-coordinate with one ring N and four carboxylate oxygens), and finally to Y(DOTA) -, which is 8-coordinate (four oxygens and four nitrogens). The rate-determining step is the conversion of YH(DOTA) to Y(DOTA) -, which we calculate to have an activation free energy (aqueous phase) of 8.4 kcal/mol, in agreement with experimental results (8.1-9.3 kcal/mol) for various metals to DOTA [Kumar, K.; Tweedle, M. F. ]. On the basis of this mechanism we propose a modified chelate, DO3AlPr, which we calculate to have a much faster rate of incorporation.