Despite their atmospheric abundance, heterogeneous and multiphase reactions of carbonyl compounds are poorly understood. In this study, we investigate the surface adsorption and surface chemistry of methyl ethyl ketone (MEK), the second most abundant ketone in the atmosphere, with several mineral oxide surfaces including SiO 2 , α-Fe 2 O 3 and TiO 2 . In particular, the chemistry of MEK with these common components of mineral dust, under both dry and high relative humidity (RH%) conditions, has been investigated. Furthermore, reactions of adsorbed MEK with gas-phase NO 2 were also examined. We show that MEK molecularly and reversibly adsorbs on SiO 2 whereas irreversible adsorption occurs on both α-Fe 2 O 3 and TiO 2 surfaces, followed by the formation of higher molar mass species resulting from dimerization and oligomerization reactions. Isotope labeling experiments confirmed the incorporation of H atoms from surface hydroxyl groups and strongly adsorbed water into these oligomer products. Most interesting is that at 80% RH, oligomer formation on α-Fe 2 O 3 shifts toward a higher relative abundance of MEK tetramer relative to the dimer while on TiO 2 there was no change in product distribution. In the presence of gas-phase NO 2 , MEK undergoes degradation to formaldehyde and acetaldehyde, followed by the formation of aldol condensation products of these aldehydes on the α-Fe 2 O 3 surface. Overall, this study provides mechanistic insights on mineralogy-specific heterogeneous chemistry of a prevalent and atmospherically abundant ketone.
more »
« less
Molecular recognition and specificity of biomolecules to titanium dioxide from molecular dynamics simulations
Titania (TiO2) is used extensively in biomedical applications; efforts to boost the biocompatibility of TiO2include coating it with the titania binding hexamer, RKLPDA. To understand the binding mechanism of this peptide, we employ molecular dynamics simulations enhanced by metadynamics to study three amino acids present in the peptide—arginine (R), lysine (K), and aspartate (D), on four TiO2variants that have different degrees of surface hydroxyl groups. We find that binding is a function of both sidechain charge and structure, with R binding to all four surfaces, whereas the affinity of K and D is dependent on the distribution of hydroxyl groups. Informed by this, we study the binding of the titania binding hexamer and dodecamer (RKLPDAPGMHTW) on two of the four surfaces, and we see strong correlations between the binding free energy and the primary binding residues, in agreement with prior experiments and simulations. We propose that the discrepancies observed in prior work stem from distribution of surface hydroxyl groups that may be difficult to precisely control on the TiO2interface.
more » « less- NSF-PAR ID:
- 10154215
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- npj Computational Materials
- Volume:
- 6
- Issue:
- 1
- ISSN:
- 2057-3960
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
more » « less
Abstract Ruthenium (Ru) is the one of the most promising catalysts for polyolefin hydrogenolysis. Its performance varies widely with the support, but the reasons remain unknown. Here, we introduce a simple synthetic strategy (using ammonia as a modulator) to tune metal-support interactions and apply it to Ru deposited on titania (TiO2). We demonstrate that combining deuterium nuclear magnetic resonance spectroscopy with temperature variation and density functional theory can reveal the complex nature, binding strength, and H amount. H2activation occurs heterolytically, leading to a hydride on Ru, an H+on the nearest oxygen, and a partially positively charged Ru. This leads to partial reduction of TiO2and high coverages of H for spillover, showcasing a threefold increase in hydrogenolysis rates. This result points to the key role of the surface hydrogen coverage in improving hydrogenolysis catalyst performance.
-
more » « less
Abstract Hydrogenase enzymes produce H2gas, which can be a potential source of alternative energy. Inspired by the [NiFe] hydrogenases, we report the construction of a de novo‐designed artificial hydrogenase (ArH). The ArH is a dimeric coiled coil where two cysteine (Cys) residues are introduced at tandem
a /d positions of a heptad to create a tetrathiolato Ni binding site. Spectroscopic studies show that Ni binding significantly stabilizes the peptide producing electronic transitions characteristic of Ni‐thiolate proteins. The ArH produces H2photocatalytically, demonstrating a bell‐shaped pH‐dependence on activity. Fluorescence lifetimes and transient absorption spectroscopic studies are undertaken to elucidate the nature of pH‐dependence, and to monitor the reaction kinetics of the photochemical processes. pH titrations are employed to determine the role of protonated Cys on reactivity. Through combining these results, a fine balance is found between solution acidity and the electron transfer steps. This balance is critical to maximize the production of NiI‐peptide and protonation of the NiII−H−intermediate (Ni−R) by a Cys (pK a≈6.4) to produce H2. -
more » « less
Abstract TiO2sol–gel reaction induces nanowrinkling along the surface of electrospun poly(vinyl alcohol) (PVA) nanofibers. Nanowrinkling along nanofibers is influenced by electrospinning voltage, degree of nanofiber crosslinking, and the repetitive immersion of nanofibers in TiO2precursors. Crosslinked nanofibers are dipped in alternating solutions of titanium tetraisopropoxide (TTIP) and water for up to five cycles. Interestingly, nanowrinkles only form along nanofibers that are spun at 45 kV and treated with three or more cycles of sol–gel precursor. Spectroscopy reveals that more PVA hydroxyl groups populate the nanofiber surface when electrospinning occurs at 45 kV than at 15 kV. In turn, surface PVA hydroxyl groups appear to nucleate TiO2growth. Scanning probe phase micrographs confirm modulus differences between the attached TiO2particles and PVA's surface. Those moduli differences result in wrinkling, as TTIP‐treated nanofibers undergo repetitive cycles of water swelling and isopropanol deswelling.
-
more » « less
16‐Ferrocenylmethyl‐estra‐1,3,5(10)‐triene‐3,17β‐diol crystallizes in a triclinic unit cell and P1 space group. It contains four crystallographic independent molecules in the unit, representing four different conformers of the ferrocene–hormone conjugate. It provides evidence of a low rotational barrier around C19–C20and the existence of alpha and beta conformers. The four conformers are interconnected by hydrogen bonds through hydroxyl groups of rings A and D. Density functional theory studies show the rotational barrier energy to be 4.96 Kcal/mol and the preferred conformer has a dihedral angle φ2 (defined as C16–C19–C20–C21) of 85.79°. This angle represents the conformer with the lowest steric strains. Docking studies between the subject compound and human serum albumin (HSA) showed that the most likely binding pocket of HSA is drug‐binding site 2. Quenching fluorescence spectroscopy was used to study HSA–ferrocene conjugate interaction and results showed that the complex formation was static and dominated by van der Waals and electrostatic/hydrogen bonding interactions.
