Antiadhesive Copolymers at Solid/Liquid Interfaces: Complementary Characterization of Polymer Adsorption and Protein Fouling by Sum Frequency Generation Vibrational Spectroscopy and Quartz-Crystal Microbalance Measurements with Dissipation Monitoring.

Amphiphilic copolymers comprising hydrophilic segments of poly(ethylene glycol) and hydrophobic domains that are able to adhere to solid/liquid interfaces have proven to be versatile ingredients in formulated products for various types of applications. Recently, we have reported the successful synthesis of a copolymer designed for modifying the surface properties of polyesters as mimics for synthetic textiles. Using sum frequency generation (SFG) spectroscopy, it was shown that the newly developed copolymer adsorbs effectively on the targeted substrates even in the presence of surfactants as supplied by common detergents. In the present work, these studies were extended to evaluate the ability of the formed copolymer adlayers to passivate polyester surfaces against undesired deposition of bio(macro)molecules, as represented by fibrinogen as model protein foulants. In addition, SFG spectroscopy was used to elucidate the structure of fibrinogen at the interface between polyester and water. To complement the obtained data with an independent technique, analogous experiments were performed using quartz-crystal microbalance with dissipation monitoring for the detection of the relevant interfacial processes. Both methods give consistent results and deliver a holistic picture of brush copolymer adsorption on polyester surfaces and subsequent antiadhesive effects against proteins under different conditions representing the targeted application in home care products.

Probing Interfacial Behavior and Antifouling Activity of Adsorbed Copolymers at Solid/Liquid Interfaces.

Polymers containing poly(ethylene glycol) (PEG) units can exhibit excellent antifouling properties, which have been proposed/used for coating of biomedical implants, separation membranes, and structures in marine environments, as well as active ingredients in detergent formulations to avoid soil redepositioning in textile laundry. This study aimed to elucidate the molecular behavior of a copolymer poly(MMA-co-MPEGMA) containing antiadhesive PEG side chains and a backbone of poly(methyl methacrylate), at a buried polymer/solution interface. Polyethylene terephthalate (PET) was used as a substrate to model polyester textile surfaces. Sum frequency generation (SFG) vibrational spectroscopy was applied to examine the interfacial behavior of the copolymer at PET/solution interfaces in situ and in real time. Complementarily, copolymer adsorption on PET and subsequent antiadhesion against protein foulants were probed by quartz-crystal microbalance experiments with dissipation monitoring (QCM-D). Both applied techniques show that poly(MMA-co-MPEGMA) adsorbs significantly to the PET/solution interface at bulk polymer solution concentrations as low as 2 ppm, while saturation of the surface was reached at 20 ppm. The hydrophobic MMA segments provide an anchor for the copolymer to bind onto PET in an ordered way, while the pendant PEG segments are more disordered but contain ordered interfacial water. In the presence of considerable amounts of dissolved surfactants, poly(MMA-co-MPEGMA) could still effectively adsorb on the PET surface and remained stable at the surface upon washing with hot and cold water or surfactant solution. In addition, it was found that adsorbed poly(MMA-co-MPEGMA) provided the PET surface with antiadhesive properties and could prevent protein deposition, highlighting the superior surface affinity and antifouling performance of the copolymer. The results obtained in this work demonstrate that amphiphilic copolymers containing PMMA anchors and PEG side chains can be used in detergent formulations to modify polyester surfaces during laundry and reduce deposition of proteins (and likely also other soils) on the textile.

Density functional theory study of the complexation of the uranyl dication with anionic phosphate ligands with and without water molecules.

The structures, vibrational frequencies and energetics of anhydrous and hydrated complexes of UO2(2+) with the phosphate anions H2PO4(-), HPO4(2-), and PO4(3-) were predicted at the density functional theory (DFT) and MP2 molecular orbital theory levels as isolated gas phase species and in aqueous solution by using self-consistent reaction field (SCRF) calculations with different solvation models. The geometries and vibrational frequencies of the major binding modes for these complexes are compared to experiment where possible and good agreement is found. The uranyl moiety is nonlinear in many of the complexes, and the coordination number (CN) 5 in the equatorial plane is the predominant binding motif. The phosphates are found to bind in both monodentate and bidentate binding modes depending on the charge and the number of water molecules. The SCRF calculations were done with a variety of approaches, and different SCRF approaches were found to be optimal for different reaction types. The acidities of HxPO4(3-x) in HxPO4(3-x)(H2O)4, x = 0-3 complexes were calculated with different SCRF models and compared to experiment. Phosphate anions can displace water molecules from the first solvation shell at the uranyl exothermically. The addition of water molecules can cause the bonding of H2PO4(-) and HPO4(2-) to change from bidentate to monodentate exothermically while maintaining CN 5. The addition of water can generate monodentate structures capable of cross-linking to other uranyl phosphates to form the types of structures found in the solid state. [UO2(HPO4)(H2O)3] is predicted to be a strong base in the gas phase and in aqueous solution. It is predicted to be a much weaker acid than H3PO4 in the gas phase and in solution.

Amine-functionalized task-specific ionic liquids: a mechanistic explanation for the dramatic increase in viscosity upon complexation with CO2 from molecular simulation.

The capture of CO2 from fossil fuel combustion, particularly in coal-fired power plants, represents a critical component of efforts aimed at stabilizing greenhouse gas levels in the atmosphere. Alkanolamines have traditionally been used to this end; however, drawbacks such as volatility, degradation, and regeneration costs have been drivers for the development of new, superior technologies. Recently, several seminal studies with ionic liquids (ILs), both experimental and computational, have demonstrated their potential as CO2 capture agents. In traditional ILs, experimental studies with CO2 have revealed its unusually high physical solubility in these media. Complementary simulation studies have provided evidence that this is attributable to CO2 occupying void space within the liquid and favorably interacting with the anion. Recently, a series of second-generation task-specific ionic liquids (TSILs) containing amine functional groups have been synthesized and demonstrated to have much higher capacities for CO2 due to their reactivity with CO2, as well unusually high viscosities in both the neat and complexed states. The current work extends the seminal studies of CO2 capture with ILs by providing insight from simulations into the mechanism responsible for the dramatic increase in viscosity upon complexation. Simulations conclusively demonstrate that the slow translational and rotational dynamics, which are manifest in the high viscosity, may be attributable to the formation of a strong, pervasive hydrogen-bonded network. Semiquantitative estimates of the cation and anion self-diffusion coefficients and rotational time constants, as well as detailed hydrogen bond analysis, are consistent with the experimentally observed formation of glassy or gel-like materials upon contact with CO2. This has significant implications for the design of new approaches or materials involving ILs that take advantage of these preconceived limitations, in the synthesis or manipulation of new TSIL frameworks for CO2 capture, and in novel experimental studies of chemistries and dynamics in persistent heterogeneous environments.

Accurate thermochemical properties for energetic materials applications. II. Heats of formation of imidazolium-, 1,2,4-triazolium-, and tetrazolium-based energetic salts from isodesmic and lattice energy calculations.

A computational approach to the prediction of the heats of formation (DeltaH(f)degrees' s of solid-state energetic salts from electronic structure and volume-based thermodynamics (VBT) calculations is described. The method uses as its starting point reliable DeltaH(f)degrees' s for energetic precursor molecules and ions. The DeltaH(f)degrees' s of more complex energetics species such as substituted imidazole, 1,2,4-triazole, and tetrazole molecules and ions containing amino, azido, and nitro (including methyl) substituents are calculated using an isodesmic approach at the MP2/complete basis set level. On the basis of comparisons to experimental data for neutral analogues, this isodesmic approach is accurate to <3 kcal/mol for the predicted cation and anion DeltaH(f)degrees' s. The DeltaH(f)degrees' s of the energetic salts in the solid state are derived from lattice energy (U(L)) calculations using a VBT approach. Improved values for the alpha and beta parameters of 19.9 (kcal nm)/mol and 37.6 kcal/mol for the U(L) equation were obtained on the basis of comparisons to experimental U(L)' s for a series of 23 salts containing ammonium, alkylammonium, and hydrazinium cations. The total volumes are adjusted to account for differences between predicted and experimental total volumes due to different shapes of the ions (flat vs spherical). The predicted DeltaH(f)degrees' s of the energetic salts are estimated to have error bars of 6-7 kcal/mol, on the basis of comparisons to established experimental DeltaH(f)degrees' s of a subset of the salts studied. Energetic salts with the highest positive DeltaH(f)degrees' s are predicted for azido-containing cations, coupled with heterocyclic anions containing nitro substituents. The substitution of functional groups on carbon versus nitrogen atoms of the heterocyclic cations has interesting stabilization and destabilization effects, respectively.

Interactions of 1-methylimidazole with UO2(CH3CO2)2 and UO2(NO3)2: structural, spectroscopic, and theoretical evidence for imidazole binding to the uranyl ion.

The first definitive high-resolution single-crystal X-ray structure for the coordination of the 1-methylimidazole (Meimid) ligand to UO2(Ac)2 (Ac = CH3CO2) is reported. The crystal structure evidence is confirmed by IR, Raman, and UV-vis spectroscopic data. Direct participation of the nitrogen atom of the Meimid ligand in binding to the uranium center is confirmed. Structural analysis at the DFT (B3LYP) level of theory showed a conformational difference of the Meimid ligand in the free gas-phase complex versus the solid state due to small energetic differences and crystal packing effects. Energetic analysis at the MP2 level in the gas phase supported stronger Meimid binding over H2O binding to both UO2(Ac)2 and UO2(NO3)2. In addition, self-consistent reaction field COSMO calculations were used to assess the aqueous phase energetics of combination and displacement reactions involving H2O and Meimid ligands to UO2R2 (R = Ac, NO3). For both UO2(NO3)2 and UO2(Ac)2, the displacement of H2O by Meimid was predicted to be energetically favorable, consistent with experimental results that suggest Meimid may bind uranyl at physiological pH. Also, log(Knitrate/KAc) calculations supported experimental evidence that the binding stoichiometry of the Meimid ligand is dependent upon the nature of the reactant uranyl complex. These results clearly demonstrate that imidazole binds to uranyl and suggest that binding of histidine residues to uranyl could occur under normal biological conditions.

Ab initio prediction of the gas- and solution-phase acidities of strong Brønsted acids: the calculation of pKa values less than -10.

The intrinsic gas-phase acidities of a series of 21 Brønsted acids have been predicted with G3(MP2) theory. The G3(MP2) results agree with high level CCSD(T)/CBS acidities for H(2)SO(4), FSO(3)H, CH(3)SO(3)H, and CF(3)SO(3)H to within 1 kcal/mol. The G3(MP2) results are in excellent agreement with experimental gas-phase acidities in the range 342-302 kcal/mol to within <1 kcal/mol for 14 out of 15 acids. Five of the six acids in the range of 302-289 kcal/mol had an average deviation of 5.5 kcal/mol and the strongest acid, (CF(3)SO(2))(3)CH, deviated by 15.0 kcal/mol. These high-level calculations strongly suggest that the experimental acidities in this very acidic part of the scale need to be remeasured. The CCSD(T)/CBS (mixed exponential Gaussian) additive approach for CH(3)CO(2)H, HNO(3), H(2)SO(4), CH(3)SO(3)H, FSO(3)H, and CF(3)SO(3)H gives excellent agreement (+/-1 kcal/mol) with experiment for the DeltaH(f)(0)'s of non-sulfur containing species, and supports the low end of the experimental values for H(2)SO(4) and FSO(3)H. Use of a larger basis set (aug-cc-pV5Z) in the CBS extrapolation improves the agreement with experiment for both H(2)SO(4) and FSO(3)H. The G3(MP2) heats of formation for RSO(3)H molecules tend to be underestimated as compared to the CCSD(T)/CBS approach by 2.5-7.0 kcal/mol. COSMO solvation calculations were used to predict solution free energies and pK(a) values with pK(a)'s up to -17.4. Including the solvation of the proton gives good agreement with experimental pK(a) values in the very acidic regime, whereas it is less reliable for weaker acids. The use of CH(3)CO(2)H and HNO(3) as reference acids in the less acidic and more acidic regions of the scale, respectively, provided improved results to within +/-2 pK(a) units in nearly all cases (+/-3 kcal/mol accuracy).

Accurate thermochemical properties for energetic materials applications. I. Heats of formation of nitrogen-containing heterocycles and energetic precursor molecules from electronic structure theory.

The heats of formation of 1H-imidazole, 1H-1,2,4-trizazole, 1H-tetrazole, CH3NO2, CH3N3, CH3NH2, CH2CHNO2, HClO4, and phenol, as well as cations and anions derived from some of the molecules have been calculated using ab initio molecular orbital theory. These molecules are important as models for compounds used for energetic materials synthesis. The predicted heats of formation of the heterocycle-based compounds are in excellent agreement with available experimental values and those derived from proton affinities and deprotonation enthalpies to <1 kcal/mol. The predicted value for the tetrazolium cation differs substantially from the experimental value, likely due to uncertainty in the measurement. The heats of formation of the nitro and amino molecules, as well as phenol/phenolate, also are in good agreement with the experimental values (<1.5 kcal/mol). The heat of formation of CH3N3 is predicted to be 72.8 kcal/mol at 298 K with an estimated error bar of +/-1 kcal/mol on the basis of the agreement between the calculated and experimental values for DeltaH(f)(HN3). The heat of formation at 298 K of HClO4 is -0.4 kcal/mol, in very good agreement with the experimental value, as well as a W2 literature study. An extrapolation of the CCSD(T)/aug-cc-pV(Q,5) energies was required to obtain this agreement. This result suggests that very large basis sets (> or =aug-cc-pV5Z) may be needed to fully recover the valence correlation energy contribution in compounds containing elements with high formal oxidation states at the central atom. In addition tight d functions are needed for the geometry predictions. Douglas-Kroll-Hess (DKH) scalar relativistic corrections for HClO4 and ClO4- at the MP2 level with correlation-consistent DKH basis sets were predicted to be large, likely due to the high formal oxidation state at the Cl.

Predicting the energy of the water exchange reaction and free energy of solvation for the uranyl ion in aqueous solution.

The structures and vibrational frequencies of UO2(H2O)4(2+) and UO2(H2O)5(2+) have been calculated using density functional theory and are in reasonable agreement with experiment. The energies of various reactions were calculated at the density functional theory (DFT) and MP2 levels; the latter provides the best results. Self-consistent reaction field calculations in the PCM and SCIPCM approximations predicted the free energy of the water exchange reaction, UO2(H2O)4(2+) + H2O <--> UO2(H2O)5(2+). The calculated free energies of reaction are very sensitive to the choice of radii (O and H) and isodensity values in the PCM and SCIPCM models, respectively. Results consistent with the experimental HEXS value of -1.19 +/- 0.42 kcal/mol (within 1-3 kcal/mol) are obtained with small cavities. The structures and vibrational frequencies of the clusters with second solvation shell waters: UO2(H2O)4(H2O)8(2+), UO2(H2O)4(H2O)10(2+), UO2(H2O)4(H2O)11(2+), UO2(H2O)5(H2O)7(2+), and UO2(H2O)5(H2O)10(2+), were calculated and are in better agreement with experiment as compared to reactions involving only UO2(H2O)4(2+) and UO2(H2O)5(2+). The MP2 reaction energies for water exchange gave gas-phase results that agreed with experiment in the range -5.5 to +3.3 kcal/mol. The results were improved by inclusion of a standard PCM model with differences of -1.2 to +2.7 kcal/mol. Rearrangement reactions based on an intramolecular isomerization leading to a redistribution of water in the two shells provide good values in comparison to experiment with values of Delta G(exchange) from -2.2 to -0.5 kcal/mol so the inclusion of a second hydration sphere accounts for most solvation effects. Calculation of the free energy of solvation of the uranyl cation yielded an upper bound to the solvation energy of -410 +/- 5 kcal/mol, consistent with the best experimental value of -421 +/- 15 kcal/mol.

Prediction of the formation and stabilities of energetic salts and ionic liquids based on ab initio electronic structure calculations.

A computational approach to predict the thermodynamics for forming a variety of imidazolium-based salts and ionic liquids from typical starting materials is described. The gas-phase proton and methyl cation acidities of several protonating and methylating agents, as well as the proton and methyl cation affinities of many important methyl-, nitro-, and cyano-substituted imidazoles, have been calculated reliably by using the computationally feasible DFT (B3LYP) and MP2 (extrapolated to the complete basis set limit) methods. These accurately calculated proton and methyl cation affinities of neutrals and anions are used in conjunction with an empirical approach based on molecular volumes to estimate the lattice enthalpies and entropies of ionic liquids, organic solids, and organic liquids. These quantities were used to construct a thermodynamic cycle for salt formation to reliably predict the ability to synthesize a variety of salts including ones with potentially high energetic densities. An adjustment of the gas phase thermodynamic cycle to account for solid- and liquid-phase chemistries provides the best overall assessment of salt formation and stability. This has been applied to imidazoles (the cation to be formed) with alkyl, nitro, and cyano substituents. The proton and methyl cation donors studied were as follows: HCl, HBr, HI, (HO)2SO2, HSO3CF3 (TfOH), and HSO3(C6H4)CH3 (TsOH); CH3Cl, CH3Br, CH3I, (CH3O)2SO2, CH3SO3CF3 (TfOCH3), and CH3SO3(C6H4)CH3 (TsOCH3). As substitution of the cation with electron-withdrawing groups increases, the triflate reagents appear to be the best overall choice as protonating and methylating agents. Even stronger alkylating agents should be considered to enhance the chances of synthetic success. When using the enthalpies of reaction for the gas-phase reactants (eq 6) to form a salt, a cutoff value of -13 kcal mol(-1) or lower (more negative) should be used as the minimum value for predicting whether a salt can be synthesized.

Complexation of the carbonate, nitrate, and acetate anions with the uranyl dication: density functional studies with relativistic effective core potentials.

The structures and vibrational frequencies of uranyl carbonates, [UO2(CO3)n](2-2n) and [(UO2)3(CO3)6]6-, uranyl nitrates, [UO2(NO3)n](2-n), and uranyl acetates, [UO2(CH3COO)n](2-n) (n = 1,2,3) have been calculated by using local density functional theory (LDFT). Only bidentate ligand coordination modes to the uranyl dication have been modeled. The calculated structures and frequencies are compared to available experimental data, including IR, Raman, X-ray diffraction, and EXAFS solution and crystal structure data. The energetics of ligand binding have been calculated using the B3LYP hybrid functional. In general, the structural and vibrational results at the LDFT level are in good agreement with experimental results and provide realistic pictures of solution phase and solid-state behavior. For the [UO2(CO3)3]6- anion, calculations suggest that complexity in the CO3(2-) stretching signature upon complexation is due to the formation of C=O and C-O domains, the latter of which can split by as much as 300 cm(-1). Assessment of the binding energies indicate that the [UO2(CO3)2]2- anion is more stable than the [UO2(CO3)3]4- anion due to the accumulation of excess charge, whereas the tri-ligand species are the most stable in the nitrate and acetate anions.

Controlling the aqueous miscibility of ionic liquids: aqueous biphasic systems of water-miscible ionic liquids and water-structuring salts for recycle, metathesis, and separations.

Hydrophilic ionic liquids can be salted-out and concentrated from aqueous solution upon addition of kosmotropic salts forming aqueous biphasic systems as illustrated by the phase behavior of mixtures of 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) and K3PO4.