Showing papers in "Journal of the American Chemical Society in 2007"
TL;DR: The two-photon luminescence microscopy imaging of human breast cancer cells with internalized carbon dots with pulsed laser excitation in the near-infrared is demonstrated.
Abstract: Carbon nanoparticles upon simple surface passivation exhibit bright photoluminescence. Reported here is a new finding that these carbon dots are also strongly two-photon luminescent with pulsed laser excitation in the near-infrared. The experimentally measured two-photon absorption cross-sections are comparable to those of the high-performance semiconductor quantum dots already available in the literature. The two-photon luminescence microscopy imaging of human breast cancer cells with internalized carbon dots is demonstrated.
1,902 citations
TL;DR: The air-free compound exhibits the highest gravimetric and volumetric H2 uptake capacities yet demonstrated for a cryogenic hydrogen storage material and no loss of capacity was apparent during 24 complete adsorption−desorpti...
Abstract: The prototypical metal-organic framework Zn4O(BDC)3 (MOF-5, BDC2- = 1,4-benzenedicarboxylate) decomposes gradually in humid air to form a nonporous solid. Recognizing this, improved procedures for its synthesis and handling were developed, leading to significant increases in N2 and H2 gas adsorption capacities. Nitrogen adsorption isotherms measured at 77 K reveal an enhanced maximum N2 uptake of 44.5 mmol/g and a BET surface area of 3800 m2/g, compared to the 35.8 mmol/g and 3100 m2/g obtained for a sample prepared using previous methods. High-pressure H2 adsorption isotherms show improvements from 5.0 to 7.1 excess wt % at 77 K and 40 bar. The total H2 uptake was further observed to climb to 11.5 wt % at 170 bar, corresponding to a volumetric storage density of 77 g/L. Thus, the air-free compound exhibits the highest gravimetric and volumetric H2 uptake capacities yet demonstrated for a cryogenic hydrogen storage material. Moreover, no loss of capacity was apparent during 24 complete adsorption−desorpti...
1,465 citations
TL;DR: A new synthetic route for the synthesis of nearly monodisperse gold nanocrystals in the size range from 20 to 40 nm is demonstrated by simply varying the solution pH with fixed concentrations of HAuCl4 and Na3Ct.
Abstract: Growth kinetics and temporal size/shape evolution of gold nanocrystals by citrate reduction in boiling water were studied systematically and quantitatively. Results reveal that the size variation and overall reaction mechanism were mostly determined by the solution pH that was in turn controlled by the concentration of sodium citrate (Na3Ct) in the traditional Frens's synthesis. This conclusion was further confirmed by the reactions with variable pH but fixed concentrations of the two reactants, HAuCl4 and Na3Ct. Two substantially different reaction pathways were identified, with the switching point at pH = 6.2−6.5. The first pathway is for the low pH range and consists of three overlapping steps: nucleation, random attachment to polycrystalline nanowires, and smoothing of the nanowires via intra-particle ripening to dots. The second pathway that occurred above the pH switching point is consistent with the commonly known nucleation-growth route. Using the second pathway, we demonstrated a new synthetic r...
1,141 citations
TL;DR: This work provided novel structural platforms for novel materials and device applications and the unique sphere-in-sphere chamber structure allows multiple reflections of UV light resulting in greatly enhanced photocatalytic activity.
Abstract: Urchinlike TiO2 spheres with tunable chamber structure were synthesized using a template-free solvothermal method. The unique sphere-in-sphere chamber structure allows multiple reflections of UV light resulting in greatly enhanced photocatalytic activity. This work provided novel structural platforms for novel materials and device applications.
1,112 citations
TL;DR: A new approach, ensemble optimization method (EOM), is proposed to quantitatively characterize flexible proteins in solution using small-angle X-ray scattering (SAXS), and is able to distinguish between rigid and flexible proteins and to directly assess the interdomain contacts.
Abstract: Structural analysis of flexible macromolecular systems such as intrinsically disordered or multidomain proteins with flexible linkers is a difficult task as high-resolution techniques are barely applicable. A new approach, ensemble optimization method (EOM), is proposed to quantitatively characterize flexible proteins in solution using small-angle X-ray scattering (SAXS). The flexibility is taken into account by allowing for the coexistence of different conformations of the protein contributing to the experimental scattering pattern. These conformers are selected using a genetic algorithm from a pool containing a large number of randomly generated models covering the protein configurational space. Quantitative criteria are developed to analyze the EOM selected models and to determine the optimum number of conformers in the ensemble. Simultaneous fitting of multiple scattering patterns from deletion mutants, if available, provides yet more detailed local information about the structure. The efficiency of EOM is demonstrated in model and practical examples on completely or partially unfolded proteins and on multidomain proteins interconnected by linkers. In the latter case, EOM is able to distinguish between rigid and flexible proteins and to directly assess the interdomain contacts.
1,104 citations
TL;DR: An electron-transport polymer with good solution processibility, excellent thermal stability, and high electron affinity based on alternating perylene diimide and dithienothiophene units has been synthesized.
Abstract: An electron-transport polymer with good solution processibility, excellent thermal stability, and high electron affinity based on alternating perylene diimide and dithienothiophene units has been synthesized Electron mobilities as high as 13 × 10-2 cm2 V-1 s-1 have been measured in field-effect transistor geometry The polymer shows broad absorptions throughout the visible and extending into the near-IR A power conversion efficiency of over 1%, under simulated AM 15, 100 mW/cm2, was measured for a single-layer solar cell using this polymer as an acceptor and a polythiophene derivative as a donor
1,091 citations
TL;DR: It is proposed that tetrabutyl ammonium (TBA) cations most probably intercalate into the gaps and the defects during electrochemical cycling and break the tubes near the defects.
Abstract: Blue luminescent nanocrystals (NCs) were prepared electrochemically from multiwalled carbon nanotubes (MWCNTs) for the first time. The carbon NCs were characterized by UV−vis, photoluminescence, Raman, XRD spectroscopy, and high-resolution transmission electron microscopy. The structure evolution of the MWCNTs during electrochemical treatments was monitored by SEM ex situ. Since the MWCNTs were formed with scrolled graphene layers, we propose that tetrabutyl ammonium (TBA) cations most probably intercalate into the gaps and the defects during electrochemical cycling and break the tubes near the defects.
1,055 citations
TL;DR: Analysis of the molecular geometries and energetics in these materials reveals a correlation between electron mobility and substituent-induced arylene core distortion, while Vth and I(off) are generally affected by LUMO ener getics.
Abstract: Structural and electronic criteria for ambient stability in n-type organic materials for organic field-effect transistors (OFETs) are investigated by systematically varying LUMO energetics and molecular substituents of arylene diimide-based materials Six OFETs on n+-Si/SiO2 substrates exhibit OFET response parameters as follows: N,N'-bis(n-octyl)perylene-3,4:9,10-bis(dicarboximide) (PDI-8): mu = 032 cm2 V(-1) s(-1), Vth = 55 V, I(on)/I(off) = 10(5); N,N'-bis(n-octyl)-1,7- and N,N'-bis(n-octyl)-1,6-dibromoperylene-3,4:9,10-bis(dicarboximide) (PDI-8Br2): mu = 3 x 10(-5) cm2 V(-1) s(-1), Vth = 62 V, I(on)/I(off) = 10(3); N,N'-bis(n-octyl)-1,6,7,12-tetrachloroperylene-3,4:9,10-bis(dicarboximide) (PDI-8Cl4): mu = 4 x 10(-3) cm2 V(-1) (s-1), Vth = 37 V, I(on)/I(off) = 10(4); N,N'-bis(n-octyl)-2-cyanonaphthalene-1,4,5,8-bis(dicarboximide) (NDI-8CN): mu = 47 x 10(-3) cm2 V(-1) s(-1), Vth = 28, I(on)/I(off) = 10(5); N,N'-bis(n-octyl)-1,7- and N,N'-bis(n-octyl)-1,6-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI-8CN2): mu = 013 cm2 V(-1) s(-1), Vth = -14 V, I(on)/I(off) = 10(3); and N,N'-bis(n-octyl)-2,6-dicyanonaphthalene-1,4,5,8-bis(dicarboximide) (NDI-8CN2): mu = 015 cm2 V(-1) s(-1), Vth = -37 V, I(on)/I(off) = 10(2) Analysis of the molecular geometries and energetics in these materials reveals a correlation between electron mobility and substituent-induced arylene core distortion, while Vth and I(off) are generally affected by LUMO energetics Our findings also indicate that resistance to ambient charge carrier trapping observed in films of N-(n-octyl)arylene diimides occurs at a molecular reduction potential more positive than approximately -01 V (vs SCE) OFET threshold voltage shifts between vacuum and ambient atmosphere operation suggest that, at E(red1) -01 V, the trap density increase is negligible OFETs fabricated with the present n-type materials having E(red1) > -01 V operate at conventional gate biases with minimal hysteresis in air This reduction potential corresponds to an overpotential for the reaction of the charge carriers with O2 of approximately 06 V N,N'-1H,1H-Perfluorobutyl derivatives of the perylene-based semiconductors were also synthesized and used to fabricate OFETs, resulting in air-stable devices for all fluorocarbon-substituted materials, despite generally having E(red1) < -01 V This behavior is consistent with a fluorocarbon-based O2 barrier mechanism OFET cycling measurements in air for dicyanated vs fluorinated materials demonstrate that energetic stabilization of the charge carriers results in greater device longevity in comparison to the OFET degradation observed in air-stable semiconductors with fluorocarbon barriers
976 citations
TL;DR: This comprehensive parametric study provides the groundwork for the use of anionic colloidal nanocrystals to generate magnetically induced hyperthermia in various media, including complex systems and biological materials.
Abstract: Iron oxide colloidal nanomagnets generate heat when subjected to an alternating magnetic field. Their heating power, governed by the mechanisms of magnetic energy dissipation for single-domain particles (Brown and Neel relaxations), is highly sensitive to the crystal size, the material, and the solvent properties. This study was designed to distinguish between the contributions of Neel and Brownian mechanisms to heat generation. Anionic nanocrystals of maghemite and cobalt ferrite, differing by their magnetic anisotropy, were chemically synthesized and dispersed in an aqueous suspension by electrostatic stabilization. The particles were size-sorted by successive electrostatic phase separation steps. Parameters governing the efficiency of nanomagnets as heat mediators were varied independently; these comprised the particle size (from 5 to 16.5 nm), the solvent viscosity, magnetic anisotropy, and the magnetic field frequency and amplitude. The measured specific loss powers (SLPs) were in quantitative agreement with the results of a predictive model taking into account both Neel and Brown loss processes and the whole particle size distribution. By varying the carrier fluid viscosity, we found that Brownian friction within the carrier fluid was the main contributor to the heating power of cobalt ferrite particles. In contrast, Neel internal rotation of the magnetic moment accounted for most of the loss power of maghemite particles. Specific loss powers were varied by 3 orders of magnitude with increasing maghemite crystal size (from 4 to 1650 W/g at 700 kHz and 24.8 kA/m). This comprehensive parametric study provides the groundwork for the use of anionic colloidal nanocrystals to generate magnetically induced hyperthermia in various media, including complex systems and biological materials.
927 citations
TL;DR: Flexible transparent conducting films with sodium dodecyl sulfate-dispersed singlewalled carbon nanotubes (SWCNTs) were prepared by a spray method and were further immersed in various acids to improve the cross-junction resistance between SWCNT networks and enhanced metallicity of SWC NTs.
Abstract: Flexible transparent conducting films with sodium dodecyl sulfate-dispersed singlewalled carbon nanotubes (SWCNTs) were prepared by a spray method and were further immersed in various acids. The film conductivity was enhanced by a factor of ∼4 with a negligible change in the transmittance in the visible range. This enhancement was attributed to the removal of remaining SDS and the subsequent densified film formation to improve the cross-junction resistance between SWCNT networks and enhanced metallicity of SWCNTs.
916 citations
TL;DR: The highly ordered amide groups in the channels play an important role in the interaction with the guest molecules, which was confirmed by thermogravimetric analysis, adsorption/desorption measurements, and X-ray crystallography.
Abstract: To create a functionalized porous compound, amide group is used in porous framework to produce attractive interactions with guest molecules. To avoid hydrogen-bond formation between these amide groups our strategy was to build a three-dimensional (3D) coordination network using a tridentate amide ligand as the three-connector part. From Cd(NO3)2·4H2O and a three-connector ligand with amide groups a 3D porous coordination polymer (PCP) based on octahedral Cd(II) centers, {[Cd(4-btapa)2(NO3)2]·6H2O·2DMF}n (1a), was obtained (4-btapa = 1,3,5-benzene tricarboxylic acid tris[N-(4-pyridyl)amide]). The amide groups, which act as guest interaction sites, occur on the surfaces of channels with dimensions of 4.7 × 7.3 A2. X-ray powder diffraction measurements showed that the desolvated compound (1b) selectively includes guests with a concurrent flexible structural (amorphous-to-crystalline) transformation. The highly ordered amide groups in the channels play an important role in the interaction with the guest molec...
TL;DR: Grand canonical Monte Carlo simulations were used to predict adsorption isotherms for nitrogen in a series of MOFs to test the applicability of the BET theory for obtaining surface areas of microporous MOFs, and the results provide a strong validation that the bet theory can be used to obtain surface areasof MOFs.
Abstract: The surface area is one of the most important quantities for characterizing novel porous materials. The BET analysis is the standard method for determining surface areas from nitrogen adsorption isotherms and was originally derived for multilayer gas adsorption onto flat surfaces. Metal-organic frameworks (MOFs) are a relatively new class of crystalline, porous materials that have been shown to exhibit very large BET surface areas. These materials are microporous and possess surfaces that are far from flat. In some MOFs, adsorption occurs through a pore-filling mechanism rather than by layer formation. Thus, it is unclear whether BET surface area numbers reported for these materials are truly meaningful. Given the standard practice of reporting BET surface areas for novel porous materials, a critical test of the BET method is much needed. In this work, grand canonical Monte Carlo simulations were used to predict adsorption isotherms for nitrogen in a series of MOFs. The predicted isotherms were used as pseudoexperimental data to test the applicability of the BET theory for obtaining surface areas of microporous MOFs. BET surface areas calculated from the simulated isotherms agree very well with the accessible surface areas calculated directly from the crystal structures in a geometric fashion. In addition, the surface areas agree well with experimental reports in the literature. These results provide a strong validation that the BET theory can be used to obtain surface areas of MOFs.
TL;DR: By using femtosecond transient absorption spectroscopy with visible pump and IR probe to observe generation of injected electrons, plasmon-induced electron transfer from 10 nm gold nanodots to TiO2 nanocrystalline film is observed.
Abstract: By using femtosecond transient absorption spectroscopy with visible pump and IR probe to observe generation of injected electrons, we could directly observe plasmon-induced electron transfer from 10 nm gold nanodots to TiO2 nanocrystalline film. It was revealed that the reaction time was within 240 fs and the yield was about 40%.
TL;DR: Evaluations of the devices under ambient conditions showed typical p-channel FET responses with the field-effect mobility higher than 1.0 cm2 V-1 s-1 and Ion/Ioff of approximately 10(7).
Abstract: 2,7-Dialkyl[1]benzothieno[3,2-b]benzothiophenes were tested as solution-processible molecular semiconductors. Thin films of the organic semiconductors deposited on Si/SiO2 substrates by spin coating have well-ordered structures as confirmed by XRD analysis. Evaluations of the devices under ambient conditions showed typical p-channel FET responses with the field-effect mobility higher than 1.0 cm2 V-1 s-1 and Ion/Ioff of ∼107.
TL;DR: Control on shell thickness allows the tuning of plasmonic properties of the core/shell structure to be either red-shifted (to 560 nm) or blue-sh shifted (to 501 nm) which should have great potentials for nanoparticle-based diagnostic and therapeutic applications.
Abstract: Core/shell structured Fe3O4/Au and Fe3O4/Au/Ag nanoparticles are synthesized by depositing Au and Ag on the Fe3O4 nanoparticle surface in aqueous solution at room temperature. The control on shell thickness allows the tuning of plasmonic properties of the core/shell structure to be either red-shifted (to 560 nm) or blue-shifted (to 501 nm). Such magneto-optical nanoparticles should have great potentials for nanoparticle-based diagnostic and therapeutic applications.
TL;DR: Femtosecond transient absorption studies indicate that the rate constant for electron transfer from the thermalized s-state of CdSe quantum dots increases with decreasing particle size, which can be easily modulated by controlling the particle size.
Abstract: Electron injection from excited CdSe quantum dots into TiO2 nanoparticles can be easily modulated by controlling the particle size. Femtosecond transient absorption studies indicate that the rate constant for electron transfer from the thermalized s-state of CdSe quantum dots increases with decreasing particle size. The energy difference between the conduction bands of the two semiconductor systems acts as a driving force for the electron transfer in the normal Marcus region. An increase in the interparticle electron transfer rate constant by 3 orders of magnitude (from ∼107 to 1010 s-1) has been achieved by decreasing the CdSe particle diameter from 7.5 to 2.4 nm.
TL;DR: In this article, a humidity sensor based on a single SnO2 nanowire was fabricated, which has fast and sensitive response to relative humidity (RH) in air from a wide range of atmospheres at 30 °C.
Abstract: A humidity sensor based on a single SnO2 nanowire was fabricated. This sensor has fast and sensitive response to relative humidity (RH) in air from a wide range of atmospheres at 30 °C. The response sensitivity of the sensor to RH is linear to 90%.
TL;DR: Mesoporous Au/TiO2 nanocomposites with Au nanoparticles homogeneously embedded within crystalline TiO2 framework were synthesized using a simple one-pot assembly approach and exhibit significantly enhanced photocatalytic activity.
Abstract: Mesoporous Au/TiO2 nanocomposites with Au nanoparticles homogeneously embedded within crystalline TiO2 framework were synthesized using a simple one-pot assembly approach and exhibit significantly enhanced photocatalytic activity.
TL;DR: In this article, a facile three-step synthetic procedure for highly π-extended heteroarenes, dinaphtho[2,3-b:2‘,3‘-f]thieno[3,2-b]thiophene (DNTT), and DNSS, was established, and the highest field effect mobility of DNTT-and DNSS-based OFETs is 2.9 and 1.9 cm2 V-1 s-1, respectively.
Abstract: A facile three-step synthetic procedure for highly π-extended heteroarenes, dinaphtho[2,3-b:2‘,3‘-f]thieno[3,2-b]thiophene (DNTT) and dinaphtho[2,3-b:2‘,3‘-f]selenopheno[3,2-b]selenophene (DNSS), was established. Solution UV−vis spectra and electrochemistry indicated that they have relatively low-lying HOMO levels and large HOMO−LUMO energy gaps. OFET devices fabricated with evaporated thin-films of DNTT and DNSS showed excellent FET characteristics in air, and the highest field-effect mobility of DNTT- and DNSS-based OFETs is 2.9 and 1.9 cm2 V-1 s-1, respectively.
TL;DR: In this article, a new CT contrast agent based on gold nanoparticles (GNPs) was proposed to overcome the limitations of traditional iodide-based contrast agents such as short imaging times due to rapid renal clearance, renal toxicity, and vascular permeation.
Abstract: Current computed tomography (CT) contrast agents such as iodine-based compounds have several limitations, including short imaging times due to rapid renal clearance, renal toxicity, and vascular permeation. Here, we describe a new CT contrast agent based on gold nanoparticles (GNPs) that overcomes these limitations. Because gold has a higher atomic number and X-ray absorption coefficient than iodine, we expected that GNPs can be used as CT contrast agents. We prepared uniform GNPs (∼30 nm in diameter) by general reduction of HAuCl4 by boiling with sodium citrate. The resulting GNPs were coated with polyethylene glycol (PEG) to impart antibiofouling properties, which extends their lifetime in the bloodstream. Measurement of the X-ray absorption coefficient in vitro revealed that the attenuation of PEG-coated GNPs is 5.7 times higher than that of the current iodine-based CT contrast agent, Ultravist. Furthermore, when injected intravenously into rats, the PEG-coated GNPs had a much longer blood circulation ...
TL;DR: Using a novel layer-by-layer approach, metal−organic open frameworks based on benzenetricarboxylic acid ligands and Cu(II)-ions on a COOH-terminated organic surface have the same bulk structure of HKUST-1.
Abstract: Using a novel layer-by-layer approach we have deposited metal−organic open frameworks (MOFs) based on benzenetricarboxylic acid ligands and Cu(II)-ions on a COOH-terminated organic surface. The deposited layers were characterized using a number of surface analysis techniques. XRD measurements show that the MOFs deposited using this method have the same bulk structure of HKUST-1.
TL;DR: It is discovered that the cytochrome c-encapsulated MSNs could be internalized by live human cervical cancer cells (HeLa) and the protein could be released into the cytoplasm.
Abstract: An MCM-41-type mesoporous silica nanoparticle (MSN) material with a large average pore diameter (5.4 nm) is synthesized and characterized. The in vitro uptake and release profiles of cytochrome c by the MSN were investigated. The enzymatic activity of the released protein was quantitatively analyzed and compared with that of the native cytochrome c in physiological buffer solutions. We found that the enzymes released from the MSNs are still functional and highly active in catalyzing the oxidation of 2,2‘-azino-bis(3-ethylbenzthiazoline-6-sulfonate) (ABTS) by hydrogen peroxide. In contrast to the fact that cytochrome c is a cell-membrane-impermeable protein, we discovered that the cytochrome c-encapsulated MSNs could be internalized by live human cervical cancer cells (HeLa) and the protein could be released into the cytoplasm. We envision that these MSNs with large pores could serve as a transmembrane delivery vehicle for controlled release of membrane-impermeable proteins in live cells, which may lead to...
TL;DR: This study revealed that Luminescent hybrid nanoparticles suited for dual modality imaging freely circulate in the blood vessels without undesirable accumulation in lungs and liver.
Abstract: Luminescent hybrid nanoparticles with a paramagnetic Gd2O3 core were applied as contrast agents for both in vivo fluorescence and magnetic resonance imaging. These hybrid particles were obtained by encapsulating Gd2O3 cores within a polysiloxane shell which carries organic fluorophores and carboxylated PEG covalently tethered to the inorganic network. Longitudinal proton relaxivities of these particles are higher than the positive contrast agents like Gd−DOTA which are commonly used for clinical magnetic resonance imaging. Moreover these particles can be followed up by fluorescence imaging. This study revealed that these particles suited for dual modality imaging freely circulate in the blood vessels without undesirable accumulation in lungs and liver.
TL;DR: Computations of activation barriers and reaction energies for 1,3-dipolar cycloadditions by a high-accuracy quantum mechanical method (CBS-QB3) now reveal previously unrecognized quantitative trends in activation barriers.
Abstract: Computations of activation barriers and reaction energies for 1,3-dipolar cycloadditions by a high-accuracy quantum mechanical method (CBS-QB3) now reveal previously unrecognized quantitative trends in activation barriers. The distortion/interaction theory explains why (1) there is a monotonic decrease of ∼6 kcal/mol in the barrier height along the series oxides, imine, and ylide, for each class of 1,3-dipoles; (2) the corresponding nitrilium and azomethine betaines have almost identical cycloaddition barrier heights; (3) cycloadditions of a given 1,3-dipole with ethylene and acetylene have the same activation energies, in spite of very different reaction thermodynamics and frontier orbital gaps. There is a linear correlation between distortion energies (ΔEd⧧) and the activation barrier (ΔE⧧ = 0.75ΔEd⧧ − 2.9 kcal/mol) that is general for substituted and unsubstituted 1,3-dipoles in these cycloadditions. The energy to distort the 1,3-dipole to the geometry favorable for interaction with the dipolarophile, ...
TL;DR: It is shown that dealloyed Pt−Cu electrocatalysts exhibit an extraordinary increase in intrinsic reactivity of 4−6 times as compared to pure Pt electrocatalyststs.
Abstract: We report a synthetic electrochemical strategy to deliberately modify the catalytic reactivity of Pt bimetallic surfaces. The strategy consists of voltammetric surface dealloying of the non-noble constituent from Pt-poor bimetallic precursor compounds. We exemplify this method by dealloying carbon-supported Pt25Cu75 alloy nanoparticle precursors and testing the resulting active catalyst phase for the oxygen reduction reaction (ORR). We show that dealloyed Pt−Cu electrocatalysts exhibit an extraordinary increase in intrinsic reactivity of 4−6 times as compared to pure Pt electrocatalysts. Our results indicate that electrochemical treatment of the alloy precursors selectively dissolves Cu near the particle surface. The partially dealloyed particles constitute the active catalyst phase. While Cu is retained in the core of the particles after dealloying, the essentially pure Pt surface suggests a core−shell structure of the active catalyst. Geometric effects, such as exposure of more active crystallographic f...
TL;DR: This explanation organizes hydrogen bonds (HBs) with a seemingly random relationship between the X-H bond length (and IR frequency and its intensity) to its interaction energy.
Abstract: We provide a simple explanation for X-H bond contraction and the associated blue shift and decrease of intensity in IR spectrum of the so-called improper hydrogen bonds This explanation organizes hydrogen bonds (HBs) with a seemingly random relationship between the X-H bond length (and IR frequency and its intensity) to its interaction energy The factors which affect the X-H bond in all X-H [midline ellipsis] Y HBs can be divided into two parts: (a) The electron affinity of X causes a net gain of electron density at the X-H bond region in the presence of Y and encourages an X-H bond contraction (b) The well understood attractive interaction between the positive H and electron rich Y forces an X-H bond elongation For electron rich, highly polar X-H bonds (proper HB donors) the latter almost always dominates and results in X-H bond elongation, whereas for less polar, electron poor X-H bonds (pro-improper HB donors) the effect of the former is noticeable if Y is not a very strong HB acceptor Although both the above factors increase with increasing HB acceptor ability of Y, the shortening effect dominates over a range of Ys for suitable pro-improper X-Hs resulting in a surprising trend of decreasing X-H bond length with increasing HB acceptor ability The observed frequency and intensity variations follow naturally The possibility of HBs which do not show any IR frequency change in the X-H stretching mode also directly follows from this explanation
TL;DR: The facile heterolytic cleavage of H2 is readily achieved at room temperature by the cooperative action of the Lewis acidic borane and Lewis basic phosphine, where the steric congestion precludes quenching of the acid and base via adduct formation.
Abstract: The facile heterolytic cleavage of H2 is readily achieved at room temperature by the cooperative action of the Lewis acidic borane and Lewis basic phosphine, where the steric congestion precludes quenching of the acid and base via adduct formation.
TL;DR: Three new crystalline microporous and mesoporous 2D covalent organic frameworks termed COF-6, -8, and -10 from boronic acid building blocks and 2,3,6,7,10,11-hexahydroxytriphenylene have been synthesized and structurally characterized and demonstrate the effectiveness of reticular chemistry methods toward materials design.
Abstract: Three new crystalline microporous and mesoporous 2D covalent organic frameworks termed COF-6, -8, and -10 from boronic acid building blocks and 2,3,6,7,10,11-hexahydroxytriphenylene have been synthesized and structurally characterized. These materials constructed of C2O2B rings form eclipsed layered structures with pore sizes ranging from 6.4 to 34.1 A and are found to have high thermal stability, low density, and high porosity as indicated by the surface areas of 980, 1400, and 2080 m2 g-1 for COF-6, -8, and -10, respectively. The control of pore size and structure demonstrates the effectiveness of reticular chemistry methods toward materials design.
TL;DR: The particle size dependence of insertion reactions has been investigated for lithiated anatase TiO2, revealing progressively increasing Li capacity and Li-ion solubility for decreasing particle sizes, strongly deviating from the expected Li-rich andLi-poor phase separation as occurs in the bulk material.
Abstract: Insertion reactions are of key importance for Li ion and hydrogen storage materials and energy storage devices. The particle size dependence of insertion reactions has been investigated for lithiated anatase TiO2, revealing progressively increasing Li capacity and Li-ion solubility for decreasing particle sizes, strongly deviating from the expected Li-rich and Li-poor phase separation as occurs in the bulk material. The phase diagram alters significantly, changing the materials properties already at sizes as large as 40 nm. A rationale is found in the surface strain that occurs between the different intercalated phases, which becomes energetically too costly in small particles. In particular the observed particle size-induced solid solution behavior is expected to have fundamental and practical implications for two-phase lithium or hydrogen insertion reactions.
TL;DR: Structural distortion in a [Mn6] complex switches the magnetic exchange from antiferro- to ferromagnetic, resulting in a single-molecule magnet with a record anisotropy barrier.
Abstract: Structural distortion in a [Mn6] complex switches the magnetic exchange from antiferro- to ferromagnetic, resulting in a single-molecule magnet with a record anisotropy barrier.