The synthesis of benzaldehyde derivatives by oxygenation of methylarenes is of significant conceptual and practical interest because these compounds are important chemical intermediates whose synthesis is still carried out by nonsustainable methods with very low atom economy and formation of copious amounts of waste. Now an oxygenation reaction with a 100% theoretical atom economy using a polyoxometalate oxygen donor has been found. The product yield is typically above 95% with no “overoxidation” to benzoic acids; H2 is released by electrolysis, enabling additional reaction cycles. An electrocatalytic cycle is also feasible. This reaction is possible through the use of an aqueous sulfuric acid solvent, in an aqueous biphasic reaction mode that also allows simple catalyst recycling and recovery. The solvent plays a key role in the reaction mechanism by protonating the polyoxometalate thereby enabling the activation of the methylarenes by an electron transfer process. After additional proton transfer and oxygen transfer steps, benzylic alcohols are formed that further react by an electron transfer–proton transfer sequence forming benzaldehyde derivatives.
An investigation of hydrogen production with a series of Au/TiO2 photocatalysts reveals that the Au nanoparticles play different roles depending on the wavelength of the light irradiation. Under visible-light irradiation, the photoactivity is primarily controlled by the intensity of the Au surface plasmon band, whereas under UV irradiation the Au nanoparticles act as co-catalysts with TiO2.
Serra, M., Albero, J. and García, H. (2015), Photocatalytic Activity of Au/TiO2 Photocatalysts for H2Evolution: Role of the Au Nanoparticles as a Function of the Irradiation Wavelength. ChemPhysChem. doi: 10.1002/cphc.201500141
Powders of zinc oxide nanoparticles with individual particle sizes below 10 nm in diameter are readily produced in base-induced sol–gel processes from ethanolic solutions of zinc acetate dihydrate. These particles are covered with acetate molecules and without further stabilization, they grow when stored as a powder. Here, we present three organic ligands, which reproducibly stabilize individual particle sizes <5 nm within the agglomerated powders for extended periods of time, up to months. Citric acid and 1,5-diphenyl-1,3,5-pentanetrione result in average diameters of 3 nm, whereas dimethyl-L-tartrate stabilizes 2.1 nm. X-ray diffraction and pair distribution function analysis were used to investigate the structural properties of the particles. TEM data confirm the individual particle size and crystallinity and show that the particles are agglomerated without structural coherence. Besides the introduction of these novel ligands for ZnO nanoparticles, we investigated, in particular, the influence of each synthesis step onto the final nanoparticle size in the powder. Previous studies often reported the employed synthesis parameters, but did not motivate the reasoning for their choice based on detailed experimental observations. Herein, we regard separately the steps of (i) the synthesis of the colloids, (ii) their precipitation, and (iii) the drying of the resulting gel to understand the role of the ligands therein. ZnO particles only covered with acetate grow to 5 nm during the drying process, whereas particles with any of the additional ligands retain their colloidal size of 2–3 nm. This clearly shows the efficient binding and effect of the presented ligands.
Organic ligand–inorganic nanoparticle (NP) interactions are crucial in both natural and engineering conditions. This paper reports a rich energetics of organic–NP binding as a function of molecular coverage for ethanol–nanocalcite system. A stepwise, yet gradually and continuously evolved energetics from weak associating to strong bonding to classical capping is revealed. Such information may reinforce our understanding of complex phenomena at organic–NP interfaces, and may also aid exploratory material scientists by providing solid, fundamental thermodynamic insights.
Energy Level Alignment at Titanium Oxide–Dye Interfaces: Implications for Electron Injection and Light Harvesting by Laurent Lasser, Enrico Ronca, Mariachiara Pastore, Filippo De Angelis, Jérôme Cornil, Roberto Lazzaroni and David Beljonne via The Journal of Physical Chemistry C: Latest Articles (ACS Publications) http://ift.tt/1JON9FP http://pubs.acs.org
Self-assembly of rigid building blocks with explicit shape and symmetry
is substantially influenced by the geometric factors and remains largely
unexplored. We report the selective assembly behaviors of a class of
precisely defined, nanosized giant tetrahedra constructed by placing
different polyhedral oligomeric silsesquioxane (POSS) molecular
nanoparticles at the vertices of a rigid tetrahedral framework. Designed
symmetry breaking of these giant tetrahedra introduces precise
positional interactions and results in diverse selectively assembled,
highly ordered supramolecular lattices including a Frank-Kasper A15
phase, which resembles the essential structural features of certain
metal alloys but at a larger length scale. These results demonstrate the
power of persistent molecular geometry with balanced enthalpy and
entropy in creating thermodynamically stable supramolecular lattices
with properties distinct from those of other self-assembling soft
Rising global demand for fossil resources has prompted a renewed
interest in catalyst technologies that increase the efficiency of
conversion of hydrocarbons from petroleum and natural gas to
higher-value materials. Styrene is currently produced from benzene and
ethylene through the intermediacy of ethylbenzene, which must be
dehydrogenated in a separate step. The direct oxidative conversion of
benzene and ethylene to styrene could provide a more efficient route,
but achieving high selectivity and yield for this reaction has been
challenging. Here, we report that the Rh catalyst (FlDAB)Rh(TFA)(η2–C2H4) [FlDAB is N,N′-bis(pentafluorophenyl)-2,3-dimethyl-1,4-diaza-1,3-butadiene;
TFA is trifluoroacetate] converts benzene, ethylene, and Cu(II) acetate
to styrene, Cu(I) acetate, and acetic acid with 100% selectivity and
yields ≥95%. Turnover numbers >800 have been demonstrated, with
catalyst stability up to 96 hours.
present a first-principle computational modeling investigation, based
on density functional theory (DFT) and time-dependent DFT, on the
structural, electronic, optical, and charge generation properties of the
semiconductor/dye/catalyst heterointerfaces in a prototypical
dye-sensitized photoanode for water oxidation. The investigated
architecture comprises a Ru(II) dye-sensitized TiO2 substrate tethered to an IrO2
nanoparticle catalyst. Our realistic modeling strategy and quantitative
analysis of the relevant interfacial hole/electron transfer reactions
indicates the slow hole injection into IrO2 and the fast dye excited-state quenching to IrO2
as the primary sources of the relatively poor cell efficiency
experimentally observed. On the basis of this atomistic and electronic
structure information, we propose and computationally test, against a
prototype dye, a new class of Ru(II) sensitizers, which show potentially
improved photoelectrochemical performances. This study constitutes a
first step toward the computer-assisted design of new and more efficient
materials for solar fuels production through dye-sensitized
A. Sigala, Eliza A. Ruben, Corey W. Liu, Paula M. B. Piccoli, Edward G.
Hohenstein, Todd J. Martínez, Arthur J. Schultz, and Daniel Herschlag
Publication Date (Web): April 14, 2015 (Article)
bonds profoundly influence the architecture and activity of biological
macromolecules. Deep appreciation of hydrogen bond contributions to
biomolecular function thus requires a detailed understanding of hydrogen
bond structure and energetics and the relationship between these
properties. Hydrogen bond formation energies (ΔGf)
are enormously more favorable in aprotic solvents than in water, and
two classes of contributing factors have been proposed to explain this
energetic difference, focusing respectively on the isolated and
hydrogen-bonded species: (I) water stabilizes the dissociated donor and
acceptor groups much better than aprotic solvents, thereby reducing the
driving force for hydrogen bond formation; and (II) water lengthens
hydrogen bonds compared to aprotic environments, thereby decreasing the
potential energy within the hydrogen bond. Each model has been proposed
to provide a dominant contribution to ΔGf, but
incisive tests that distinguish the importance of these contributions
are lacking. Here we directly test the structural basis of model II.
Neutron crystallography, NMR spectroscopy, and quantum mechanical
calculations demonstrate that O–H···O hydrogen bonds in crystals,
chloroform, acetone, and water have nearly identical lengths and very
similar potential energy surfaces despite ΔGf
differences >8 kcal/mol across these solvents. These results rule out
a substantial contribution from solvent-dependent differences in
hydrogen bond structure and potential energy after association (model
II) and thus support the conclusion that differences in hydrogen bond ΔGf
are predominantly determined by solvent interactions with the
dissociated groups (model I). These findings advance our understanding
of universal hydrogen-bonding interactions and have important
implications for biology and engineering.
Hui Zhu, Monika Sommerhalter, Andy K. L. Nguy, and Judith P. Klinman
Publication Date (Web): April 28, 2015 (Article)
β-monooxygenase (TβM) belongs to a family of physiologically important
dinuclear copper monooxygenases that function with a solvent-exposed
active site. To accomplish each enzymatic turnover, an electron transfer
(ET) must occur between two solvent-separated copper centers. In
wild-type TβM, this event is too fast to be rate limiting. However, we
have recently shown [Osborne, R. L.; et al. Biochemistry2013, 52,
1179] that the Tyr216Ala variant of TβM leads to rate-limiting ET. In
this study, we present a pH–rate profile study of Tyr216Ala, together
with deuterium oxide solvent kinetic isotope effects (KIEs). A solvent
KIE of 2 on kcat is found in a region where kcat
is pH/pD independent. As a control, the variant Tyr216Trp, for which ET
is not rate determining, displays a solvent KIE of unity. We conclude,
therefore, that the observed solvent KIE arises from the rate-limiting
ET step in the Tyr216Ala variant, and show how small solvent KIEs (ca.
2) can be fully accommodated from equilibrium effects within the Marcus
equation. To gain insight into the role of the enzyme in the long-range
ET step, a temperature dependence study was also pursued. The small
enthalpic barrier of ET (Ea = 3.6 kcal/mol) implicates
a significant entropic barrier, which is attributed to the requirement
for extensive rearrangement of the inter-copper environment during PCET
catalyzed by the Tyr216Ala variant. The data lead to the proposal of a
distinct inter-domain pathway for PCET in the dinuclear copper
Structural Characteristics and Eutaxy in the Photo-Deposited Amorphous Iron Oxide Oxygen Evolution Catalyst by Joshua A. Kurzman, Kevan E. Dettelbach, Andrew J. Martinolich, Curtis P. Berlinguette and James R. Neilson via Chemistry of Materials: Latest Articles (ACS Publications) http://ift.tt/1GnzrMH http://pubs.acs.org
Mengjing Wang and Kristie J. Koski *
Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
ACS Nano, 2015, 9 (3), pp 3226–3233 DOI: 10.1021/acsnano.5b00336
Molybdenum trioxide (α-MoO3) is a 2D layered oxide with use in electrochromic and photochromic devices owing to its ability to reversibly change color between transparent and light blue with electrochemical or hydrogen intercalation. Despite its significant application potential, MoO3 performance is largely limited by the destructiveness of these intercalation techniques, insignificant coloration, and slow color response. We demonstrate a reversible chemochromic method, using intercalation of zerovalent metals into α-MoO3 nanoribbons (Sn, ∼2 at. %; Co, ∼4 at. %), to chemically alter MoO3 from transparent white to a deep blue indigo, resulting in enhanced coloration and chemically tunable optical properties. We present two strategies to reversibly tune the color response of MoO3 nanoribbons. Chromism can be reversed (i) by complete oxidative deintercalation with hydrogen peroxide or iodine or (ii) through a temperature-driven disorder–order phase transition of the intercalated zerovalent metal.
Antoine Roy-Gobeil , Yoichi Miyahara *, and Peter Grutter
Department of Physics, McGill University, 3600 rue University, Montreal, Quebec H3A2T8, Canada
Nano Lett., 2015, 15 (4), pp 2324–2328 DOI: 10.1021/nl504468a
We present theoretical and experimental studies of the effect of the
density of states of a quantum dot (QD) on the rate of single-electron
tunneling that can be directly measured by electrostatic force
microscopy (e-EFM) experiments. In e-EFM, the motion of a biased atomic
force microscope cantilever tip modulates the charge state of a QD in
the Coulomb blockade regime. The charge dynamics of the dot, which is
detected through its back-action on the capacitavely coupled cantilever,
depends on the tunneling rate of the QD to a back-electrode. The
density of states of the QD can therefore be measured through its effect
on the energy dependence of tunneling rate. We present experimental
data on individual 5 nm colloidal gold nanoparticles that exhibit a near
continuous density of state at 77 K. In contrast, our analysis of
already published data on self-assembled InAs QDs at 4 K clearly reveals
discrete degenerate energy levels.
Dr. Francesca M. Toma, Dr. Fausto Puntoriero, Dr. Toan V. Pho, Marcello La Rosa, Dr. Young-Si Jun, Dr. Bertrand J. Tremolet de Villers, James Pavlovich, Prof. Galen D. Stucky, Prof. Sebastiano Campagna and Prof. Fred Wudl.
Department of Chemistry and Biochemistry, Department of Materials, Center for Polymers and Organic Solids, University of California, Santa Barbara, CA.
Dipartimento di Scienze Chimiche, Università di Messina and Centro Interuniversitario per la Conversione Chimica dell'Energia Solare (SOLARCHEM, Sezione di Messina), Messina,Italy.
A high-yielding synthesis of a series of polyimide dendrimers, including decacyclene- and perylene-containing dendrimer D6, in which two types of polyimide dyes are present, is reported. In these constructs, the branching unit is represented by trisphenylamine, and the solubilizing chains by N-9-heptadecanyl-substituted perylene diimides. The photophysical properties of the dendrimers have been studied by absorption, steady-state, and time-resolved emission spectroscopy and pump–probe transient absorption spectroscopy. Photoinduced charge-separated (CS) states are formed on the femtosecond timescale upon visible excitation. In particular, in D6, two different CS states can be formed, involving different subunits that decays independently with different lifetimes (ca. 10–100 ps).
DOI: 10.1039/C5EE00192G Received 20 Jan 2015, Accepted 24 Feb 2015 First published online 24 Feb 2015
The establishment of an efficient electric power distribution method is the key to realising a sustainable society driven by renewable-energy-based electricity, such as solar photovoltaics, wind turbine, and wave electricity, in view of supply instability. Here, we demonstrate an electric power circulation method that does not emit CO2 and is based on the glycolic acid (GC)/oxalic acid (OX) redox couple. Direct electric power storage in GC ensures considerably high energy density storage and good transportability through OX electroreduction with significantly high selectivity (>98%) using pure anatase-type titania (TiO2) spheres under mild conditions in the potential region of −0.5 to −0.7 V vs. the RHE at 50 °C. The most desirable characteristic of this electroreduction is the suppression of hydrogen evolution even in acidic aqueous media (Faraday efficiency of 70–95%, pH 2.1). We also successfully generated power without CO2emissions via selective electrooxidation of GC with an alkaline fuel cell.
Abstract: The enzyme hydrogenase reversibly converts dihydrogen to protons and electrons at a metal catalyst1. The location of the abundant hydrogens is of key importance for understanding structure and function of the protein2, 3, 4, 5, 6.
However, in protein X-ray crystallography the detection of hydrogen
atoms is one of the major problems, since they display only weak
contributions to diffraction and the quality of the single crystals is
often insufficient to obtain sub-ångström resolution7. Here we report the crystal structure of a standard [NiFe]
hydrogenase (~91.3 kDa molecular mass) at 0.89 Å resolution. The
strictly anoxically isolated hydrogenase has been obtained in a specific
spectroscopic state, the active reduced Ni-R (subform Ni-R1) state. The
high resolution, proper refinement strategy and careful modelling allow
the positioning of a large part of the hydrogen atoms in the structure.
This has led to the direct detection of the products of the heterolytic
splitting of dihydrogen into a hydride (H−) bridging the Ni and Fe and a proton (H+) attached to the sulphur of a cysteine ligand. The Ni–H− and Fe–H− bond lengths are 1.58 Å and 1.78Å, respectively. Furthermore, we can assign the Fe–CO and Fe–CN−
ligands at the active site, and can obtain the hydrogen-bond networks
and the preferred proton transfer pathway in the hydrogenase. Our
results demonstrate the precise comprehensive information available from
ultra-high-resolution structures of proteins as an alternative to
neutron diffraction and other methods such as NMR structural analysis.
Determining the Oxidation State of Small, Hydroxylated Metal-Oxide Nanoparticles with Infrared Absorption Spectroscopy by Xing Huang and Matthew J. Beck via Chemistry of Materials: Latest Articles (ACS Publications) http://ift.tt/1cE95cx http://pubs.acs.org