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Flexible energy storage devices show promising advantages in next-generation bendable, wearable, and implantable electronic systems, and therefore, they attract considerable interest for researchers to fulfill requirements of future energy storage devices. Here, we report a facile two-step strategy to construct flexible and binder-free NaTi2(PO4)3/graphene film with a sandwich structure (GN/NaTi2(PO4)3/GN). Such a design makes the resulting film with an excellent flexibility, which can be used for a binder-free anode for flexible sodium-ion batteries (SIBs). GN nanosheet supported NaTi2(PO4)3 nanocrystals (NaTi2(PO4)3/GN) are first prepared by a facile hydrothermal route. Then, the resultant NaTi2(PO4)3/GN hybrid is embedded homogeneously in interconnected GN nanosheet framework to form three-dimensional flexible GN/NaTi2(PO4)3/GN film. The flexible film exhibits excellent cycling stability (91% capacity retention over 1000 cycles at 500 mA g–1) for sodium half cells. Furthermore, it can be assembled into flexible full SIBs (Na0.44MnO2 as the cathode) for practical application. The flexible full battery shows good cycling stability both under flat and bent states, maintaining 92.9% retention after the first 30 cycles under a flat state compared to the original capacity and 86% retention after another 40 cycles under a bent state. This synthesis route offers a general method for constructing other flexible films for SIBs. [ABSTRACT FROM AUTHOR]

Future electronics will take on more important roles in people's lives. They need to allow more intimate contact with human beings to enable advanced health monitoring, disease detection, medical therapies, and human-machine interfacing. However, current electronics are rigid, nondegradable and cannot self-repair, while the human body is soft, dynamic, stretchable, biodegradable, and self-healing. Therefore, it is critical to develop a new class of electronic materials that incorporate skinlike properties, including stretchability for conformable integration, minimal discomfort and suppressed invasive reactions; self-healing for long-term durability under harsh mechanical conditions; and biodegradability for reducing environmental impact and obviating the need for secondary device removal for medical implants. These demands have fueled the development of a new generation of electronic materials, primarily composed of polymers and polymer composites with both high electrical performance and skinlike properties, and consequently led to a new paradigm of electronics, termed "skin-inspired electronics". This Account covers recent important advances in skin-inspired electronics, from basic material developments to device components and proof-of-concept demonstrations for integrated bioelectronics applications. To date, stretchability has been the most prominent focus in this field. In contrast to strain-engineering approaches that extrinsically impart stretchability into inorganic electronics, intrinsically stretchable materials provide a direct route to achieve higher mechanical robustness, higher device density, and scalable fabrication. The key is the introduction of strain-dissipation mechanisms into the material design, which has been realized through molecular engineering (e.g., soft molecular segments, dynamic bonds) and physical engineering (e.g., nanoconfinement effect, geometric design). The material design concepts have led to the successful demonstrations of stretchable conductors, semiconductors, and dielectrics without sacrificing their electrical performance. Employing such materials, innovative device design coupled with fabrication method development has enabled stretchable sensors and displays as input/output components and large-scale transistor arrays for circuits and active matrixes. Strategies to incorporate self-healing into electronic materials are the second focus of this Account. To date, dynamic intermolecular interactions have been the most effective approach for imparting self-healing properties onto polymeric electronic materials, which have been utilized to fabricate self-healing sensors and actuators. Moreover, biodegradability has emerged as an important feature in skin-inspired electronics. The incorporation of degradable moieties along the polymer backbone allows for degradable conducting polymers and the use of bioderived materials has led to the demonstration of biodegradable functional devices, such as sensors and transistors. Finally, we highlight examples of skin-inspired electronics for three major applications: prosthetic e-skins, wearable electronics, and implantable electronics. [ABSTRACT FROM AUTHOR]

Recent advances in materials chemistry establish the foundations for unusual classes of electronic systems, characterized by their ability to fully or partially dissolve, disintegrate, or otherwise physically or chemically decompose in a controlled fashion after some defined period of stable operation. Such types of "transient" technologies may enable consumer gadgets that minimize waste streams associated with disposal, implantable sensors that disappear harmlessly in the body, and hardware-secure platforms that prevent unwanted recovery of sensitive data. This second area of opportunity, sometimes referred to as bioresorbable electronics, is of particular interest due to its ability to provide diagnostic or therapeutic function in a manner that can enhance or monitor transient biological processes, such as wound healing, while bypassing risks associated with extended device load on the body or with secondary surgical procedures for removal. Early chemistry research established sets of bioresorbable materials for substrates, encapsulation layers, and dielectrics, along with several options in organic and bio-organic semiconductors. The subsequent realization that nanoscale forms of device-grade monocrystalline silicon, such as silicon nanomembranes (m-Si NMs, or Si NMs) undergo hydrolysis in biofluids to yield biocompatible byproducts over biologically relevant time scales advanced the field by providing immediate routes to high performance operation and versatile, sophisticated levels of function. When combined with bioresorbable conductors, dielectrics, substrates, and encapsulation layers, Si NMs provide the basis for a broad, general class of bioresorbable electronics. Other properties of Si, such as its piezoresistivity and photovoltaic properties, allow other types of bioresorbable devices such as solar cells, strain gauges, pH sensors, and photodetectors. The most advanced bioresorbable devices now exist as complete systems with successful demonstrations of clinically relevant modes of operation in animal models. This Account highlights the foundational materials concepts for this area of technology, starting with the dissolution chemistry and reaction kinetics associated with hydrolysis of Si NMs as a function of temperature, pH, and ion and protein concentration. A following discussion focuses on key supporting materials, including a range of dielectrics, metals, and substrates. As comparatively low performance alternatives to Si NMs, bioresorbable organic semiconductors are also presented, where interest derives from their intrinsic flexibility, low-temperature processability, and ease of chemical modification. Representative examples of encapsulation materials and strategies in passive and active control of device lifetime are then discussed, with various device illustrations. A final section outlines bioresorbable electronics for sensing of various biophysical parameters, monitoring electrophysiological activity, and delivering drugs in a programmed manner. Fundamental research in chemistry remains essential to the development of this emerging field, where continued advances will increase the range of possibilities in sensing, actuation, and power harvesting. Materials for encapsulation layers that can delay water-diffusion and dissolution of active electronics in passively or actively triggered modes are particularly important in addressing areas of opportunity in clinical medicine, and in secure systems for envisioned military and industrial uses. The deep scientific content and the broad range of application opportunities suggest that research in transient electronic materials will remain a growing area of interest to the chemistry community. [ABSTRACT FROM AUTHOR]

Using the time-dependent density functional theory, we perform quantum calculations of the electron dynamics in small charged metallic nanoparticles (clusters) of spherical geometry. We show that the excess charge is accumulated at the surface of the nanoparticle within a narrow layer given by the typical screening distance of the electronic system. As a consequence, for nanoparticles in vacuum, the dipolar plasmon mode displays only a small frequency shift upon charging. We obtain a blue shift for positively charged clusters and a red shift for negatively charged clusters, consistent with the change of the electron spill-out from the nanoparticle boundaries. For negatively charged clusters, the Fermi level is eventually promoted above the vacuum level leading to the decay of the excess charge via resonant electron transfer into the continuum. We show that, depending on the charge, the process of electron loss can be very fast, on the femtosecond time scale. Our results are of great relevance to correctly interpret the optical response of the nanoparticles obtained in electrochemistry, and demonstrate that the measured shift of the plasmon resonances upon charging of nanoparticles cannot be explained without account for the surface chemistry and the dielectric environment. [ABSTRACT FROM AUTHOR]

Laserscribing is an attractive reduced graphene oxide (rGO) growthand patterning technology because the process is low-cost, time-efficient,transfer-free, and flexible. Various laser-scribed rGO (LSG) componentssuch as capacitors, gas sensors, and strain sensors have been demonstrated.However, obstacles remain toward practical application of the technologywhere all the components of a system are fabricated using laser scribing.Memory components, if developed, will substantially broaden the applicationspace of low-cost, flexible electronic systems. For the first time,a low-cost approach to fabricate resistive random access memory (ReRAM)using laser-scribed rGO as the bottom electrode is experimentallydemonstrated. The one-step laser scribing technology allows transfer-freerGO synthesis directly on flexible substrates or non-flat substrates.Using this time-efficient laser-scribing technology, the patterningof a memory-array area up to 100 cm2can be completed in25 min. Without requiring the photoresist coating for lithography,the surface of patterned rGO remains as clean as its pristine state.Ag/HfOx/LSG ReRAM using laser-scribingtechnology is fabricated in this work. Comprehensive electrical characteristicsare presented including forming-free behavior, stable switching, reasonablereliability performance and potential for 2-bit storage per memorycell. The results suggest that laser-scribing technology can potentiallyproduce more cost-effective and time-effective rGO-based circuitsand systems for practical applications. [ABSTRACT FROM AUTHOR]

The character of the electronic transitions in the ultraviolet-visible--near infrared (UV--vis--NIR) spectra of platinum-bis(alkynyl) bridged, bis-triarylamine mixed-valence systems trans-[Pt(C = CC6H4NAr2)2 (PR3)2]n+ (R = ethyl, Ar = C6H4CH3-4 (l) or C6H4OCH3-4 (2); R = Ph, Ar = C6H4CH3-4 (3) or C6H4OCH3-4 (4), n = 0, 1, 2) has been determined from a combination of spectroscopic measurement and density functional theory calculations. The hybrid functional BLYP35 in combination with a suitable solvent model (i.e., conductor-like screening model (COSMO)) has been used to model the UV--vis--NIR and IR spectroscopic properties of [l--4]+, to confirm the description of [l--4]+ as examples of metal-bridged organic mixed-valence compounds, and to assign the principal features of the electronic spectra, including the triarylamine-based intervalence charge transfer transition located in the NIR region. The successful modeling of the charge distribution within the system demonstrates the utility of the BLYP35-COSMO protocol as a tool for use in the study of intramolecular charge transfer properties in mixed-valence complexes. [ABSTRACT FROM AUTHOR]

The structural, electronic, and electrochemical properties of a series of novel 12-membered pyridine- and pyridol-based tetra-aza transition-metal (Ni, Cu, Zn) complexes {[MII(L1)-Cl](C104), [MII(L2)Cl](ClO4), and [MII(L3)Cl](ClO4)} are described (L1 (Pyclen) - 1,4,7,10-tetra-aza-2,6-pyridinophane; L2 = 3,6,9,15-tetraazabicyclo[9.3.1]penta-deca-1(15),11,13-trien-13-ol; L3 - 3,6,9,15-tetra-azabicyclo[9.3.1]penta-deca- 1(15),11,13-trien-12-ol). The subtle variations in the chemical properties of these complexes were investigated using X-ray crystallography, UV-vis and NMR spectroscopy, and cyclic voltammetry. In the solid-state, the Ni(II) complexes adopt a unique bimetallic and cis-octahedral (μ-Cl)2 coordination sphere, and the electronic studies provide further evidence for the existence of a six-coordinate Ni(II) species in solution. The pyridol-based Cu(II) and Zn(II) complexes contain five-coordinate (N4Cl) geometries in the solid-state, in which the four N-donor atoms are not coplanar. Hydroxylation of the pyridine ring was found to increase the amount of π electronic charge density residing throughout the aromatic system of the ligand backbone, increase the strength of the M-Cl and M-N (pyridine) basal x- and y-plane interactions, and decrease the axial M-N bonding interaction. The electrochemical studies demonstrate that (i) the Lewis-acidity of the metal center systematically decreases across the series {[CuII(L3)Cl](ClO4) > [CuII(L1)Cl](C1O4) > [CuII(L2)Cl](ClO4)}, and (ii) the aromatic backbones allow access to both Cu(I) and Cu(III) species in solution. Overall, the experimental findings are consistent with the idea that p-hydroxylation enhances the Lewis-basicity of pyridine-based macrocycle and decreases the Lewis-acidity of the metalion, while m-hydroxylation decreases the electron-donating ability of the backbone and increases the metal-ion Lewis-acidity. [ABSTRACT FROM AUTHOR]

Ladder systems situated in a crossover from one dimensionality to two dimensionalities have been an attractive research target, because the physical properties, which are associated with dimensionality, are strongly dependent on the number of constituent legs. However, control of the intraladder configuration and electronic properties based on the substitution of structural components remain challenging tasks in materials science. On the other hand, structural design using coordination chemistry offers crucial advantages for architectural and electronic variations through substitutions of metal--organic building blocks. Here, we show the rational design and electronic properties of novel metal complex-based two-legged ladder compounds with several organic rung units: 4,4'-bipyridine, trans-1,4-diaminocyclohex-ane, and 4,4'-azopyridine. Single-crystal X-ray studies show that these two-legged ladder compounds are composed of halogen-bridged mixed-valence one-dimensional chains (MX chains) as their constituent legs. Depending on the molecular shape of the organic rung units, unique configurations of two-legged ladder lattices with periodic distortion of the legs are achieved. In addition, the electronic absorption spectra show that intervalence charge-transfer (IVCT) band gap of the two-legged ladder system increases with increasing degree of distortion of the leg. We have demonstrated for the first time that a two-legged ladder system shows a unique relationship between IVCT energy and the distortion parameter of the leg, as distinct from a single MX chain system. These systematic investigations, not only of configurations based on the rung variation but also of electronic states in metal--organic ladder system, provide the possibility for wide and rational tunings of physical and electronic properties of metal complex-based functional materials. [ABSTRACT FROM AUTHOR]

Lowefficiency of charge extraction (and conversely charge injection)across biotic–abiotic interfaces constitutes an obstacle tothe integration of biological and electronic systems in high-performancebioelectronic devices. Advances in the promotion of charge transportacross these typically nonconductive interfaces will have far-reachingimplications in important applications such as alternative energygeneration, bioelectrosynthesis, diagnostics, and environmental monitoring.This review highlights the use of synthetic materials to improve electricalinterfacing between biological systems and electrodes, focusing specificallyon whole cell bioelectrochemical systems. By taking advantage of arich variety of materials chemistry and synthetic methodologies, significantimprovements to the facilitation of charge transport across abiotic–bioticinterfaces have been realized. The modifications of the bioelectronicinterfaces presented herein include the use of organic small molecules,semiconducting and redox active polymers, inorganic nanoparticles,carbon nanotubes, graphene, hybrid organic–inorganic systems,and micro-/nanoelectrodes. However, design rules to guide materialselection and choices regarding device architecture remain ambiguous.Establishment of a clearer understanding of bioelectronic charge transferphenomena, their constituent pathways, and means of stimulating orselecting for different pathways is still work in progress. As such,great opportunities exist for materials scientists to contribute tothese topics through design and implementation. [ABSTRACT FROM AUTHOR]

Gas-phase conformations and electron transfer dissociations of pentapeptide ions containing the photo-Leu residue (L*) were studied. Exhaustive conformational search including molecular dynamics force-field, semi-empirical, ab initio, and density functional theory calculations established that the photo-Leu residue did not alter the gas-phase conformations of (GL*GGK + 2H) and (GL*GGK-NH + H) ions, which showed the same conformer energy ranking as the unmodified Leu-containing ions. This finding is significant in that it simplifies conformational analysis of photo-labeled peptide ions. Electron transfer dissociation mass spectra of (GL*GGK + 2H), (GL*GGK-NH + 2H),(GL*GGKK + 2H), (GL*GLK + 2H), and (GL*LGK + 2H) showed 16 %-21 % fragment ions originating by radical rearrangements and cleavages in the diazirine ring. These side-chain dissociations resulted in eliminations of NH, NH, [NH], and [NHO] neutral fragments and were particularly abundant in long-lived charge-reduced cation-radicals. Deuterium labeling established that the neutral hydrazine molecules mainly contained two exchangeable and two nonexchangeable hydrogen atoms from the peptide and underwent further H/D exchange in an ion-molecule complex. Electron structure calculations on the charge-reduced ions indicated that the unpaired electron was delocalized between the diazirine and amide π* electronic systems in the low electronic states of the cation-radicals. The diazirine moiety in GL*GGK-NHwas calculated to have an intrinsic electron affinity of 1.5 eV, which was further increased by the Coulomb effect of the peptide positive charge. Mechanisms are proposed for the unusual elimination of hydrazine from the photo-labeled peptide ions. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Strong interest in resistive switching phenomena is drivenby apossibility to develop electronic devices with novel functional propertiesnot available in conventional systems. Bistable resistive devicesare characterized by two resistance states that can be switched byan external voltage. Recently, memristorselectric circuitelements with continuously tunable resistive behaviorhaveemerged as a new paradigm for nonvolatile memories and adaptive electroniccircuit elements. Employment of memristors can radically enhance thecomputational power and energy efficiency of electronic systems. Mostof the existing memristor prototypes involve transition metal oxideresistive layers where conductive filaments formation and/or the interfacecontact resistance control the memristive behavior. In this paper,we demonstrate a new type of memristor that is based on a ferroelectrictunnel junction, where the tunneling conductance can be tuned in ananalogous manner by several orders of magnitude by both the amplitudeand the duration of the applied voltage. The ferroelectric tunnelmemristors exhibit a reversible hysteretic nonvolatile resistive switchingwith a resistance ratio of up to 105% at room temperature.The observed memristive behavior is attributed to the field-inducedcharge redistribution at the ferroelectric/electrode interface, resultingin the modulation of the interface barrier height. [ABSTRACT FROM AUTHOR]

Singlet fission, where an electronically excited singleton onechromophore converts into a doubly excited state on two, has gonefrom a curiosity in organic photophysics to a potential pathway forincreasing solar energy conversion efficiencies. Focusing on the roleof solvent-induced energy level fluctuations that would be presentin a dye-sensitized solar cell, we present a microscopic model forsinglet fission. Starting from an electronic model Hamiltonian, weconstruct diabatic states in a manifold of single and double excitationswith total singlet multiplicity and then develop a multilevel non-Markoviantheory of dynamics for electronic populations in the presence of energylevel fluctuations. Depending on the energy scales, energy gap fluctuationscan either facilitate or hinder interconversion steps that lead tosinglet fission. We critically assess the Markovian approximationthat leads to golden rule rates and study the role of intramolecularsolvation dynamics and electron transfer. [ABSTRACT FROM AUTHOR]

The demand for flexible electronic systems such as wearable computers, E-paper, and flexible displays has recently increased due to their advantages over present rigid electronic systems. Flexible memory is an essential part of electronic systems for data processing, storage, and communication and thus a key element to realize such flexible electronic systems. Although several emerging memory technologies, including resistive switching memory, have been proposed, the cell-to-cell interference issue has to be overcome for flexible and high performance nonvolatile memory applications. This paper describes the development of NOR type flexible resistive random access memory (RRAM) with a one transistor–one memristor structure (1T-1M). By integration of a high-performance single crystal silicon transistor with a titanium oxide based memristor, random access to memory cells on flexible substrates was achieved without any electrical interference from adjacent cells. The work presented here can provide a new approach to high-performance nonvolatile memory for flexible electronic applications. [ABSTRACT FROM AUTHOR]

Coherent two-dimensional electronic spectroscopy is usually employed on molecular species with fixed geometric configuration. Here we present two-dimensional Fourier-transform electronic spectra of dissolved 6,8-dinitro-1',3',3'-trimethylspiro[2H-1-benzopyran-2,2'-indoline] (6,8-dinitro-BIPS), a photochromic system present in two ring-open forms differing in the cis/trans configuration of a double bond, which both undergo a photoinduced ring closure. The two-dimensional spectra, recorded with 20 fs pump pulses centered at 605 nm and a supercontinuum probe covering the complete visible spectral range, allow for a detailed analysis of the photo-physics and photochemistry of the two isomers and directly reveal that cis/trans isomerization among them does not play a major role. This experiment demonstrates the potential of two-dimensional electronic spectroscopy for reactive processes. [ABSTRACT FROM AUTHOR]

We have computationally investigated the mechanism of the H2 activation reaction by (amino)carbenes compounds. Describing the electronic activity taking place during the reaction through the Reaction Electronic Flux, it has been possible to elucidate the mechanism of the hydrogen activation process and assign the energetic cost associated to every chemical event that drives the process along the reaction coordinate; this is crucial information to rationalize the reported experimental results. It has been observed that the substituent effect may induce early charge-transfer phenomena that increases the energy barrier and lowers the exothermicity of the reaction. Reversibility of the process is discussed in light of specific interactions defining the components of the reverse activation energy. [ABSTRACT FROM AUTHOR]

A micropump provides flow and pressure for a lab-on-chip device, just as a battery supplies current and voltage for an electronic system. Numerous micropumps have been developed, but none is as versatile as a battery. One cannot easily insert a micropump into a nonterminal position of a fluidic line without affecting the rest of the fluidic system, and one cannot simply connect several micropumps in series to enhance the pressure output, etc. In this work we develop a flow battery (or pressure power supply) to address this issue. A flow battery consists of a +EOP (in which the liquid flows in the same direction as the field gradient) and a -EOP (in which the liquid flows opposite to the electric field gradient), and the outlet of the +EOP is directly connected to the inlet of the -EOP. An external high voltage is applied to this outlet-inlet joint via a short gel-filled capillary that allows ions but not bulk liquid flow, while the +EOP's inlet and the -EOP's outlet (the flow battery's inlet and outlet) are grounded. This flow battery can be deployed anywhere in a fluidic network without electrically affecting the rest of the system. Several flow batteries can be connected in series to enhance the pressure output to drive HPLC separations. In a fluidic system powered by flow batteries, a hydraulic equivalent of Ohm's law can be applied to analyze system pressures and flow rates. [ABSTRACT FROM AUTHOR]

Silicon oxide (SiOx) has been widely used in many electronic systems as a supportive and insulating medium. Here, we demonstrate various electrical phenomena such as resistive switching and related nonlinear conduction, current hysteresis, and negative differential resistance intrinsic to a thin layer of SiOx. These behaviors can largely mimic numerous electrical phenomena observed in molecules and other nanomatenals, suggesting that substantial caution should be paid when studying conduction in electronic systems with SiOx as a component The actual electrical phenomena can be the result of conduction from SiOx at a post soft-breakdown state and not the presumed molecular or nanornaterial component. These electrical properties and the underlying mechanisms are discussed in detail. [ABSTRACT FROM AUTHOR]

A new self-assembling tricyclic module (×K1) featuring the Watson-Crick H-bonding arrays of guanine and cytosine fused to an internal pyridine ring was synthesized. When dissolved in water at room temperature, this module rapidly self-assembles into hexameric rosettes, which then stack to form J-type rosette nanotubes (RNTs) with increased inner/outer diameters and the largest molar ellipticity ever reported (4 × 106 deg·M-1·m-1). Using a combination of imaging and spectroscopic techniques we established the structure of ×K1-RNT and have shown that the extended π system of the self-assembling module resulted in a new family of J-type RNTs with enhanced intermodular electronic communication. [ABSTRACT FROM AUTHOR]

The synthesis, structural, redox, and photophysical properties of the two- and three-layered donor- acceptor (D-A) type [3.3]paracyclophanes ([3.3]PCPs) are described. The synthesis of the two- and three-layered [3.3]PCPs 1 and 2 containing 2,l,3-benzothiadiazole (BTD) as an acceptor was achieved by the (p-ethylbenzenesulfonyl)methyl isocyanide coupling method. The cyclic voltammograms of 1 and 2 along with those of respective dione precursors 5 and 7 clearly indicate that the presence of the -CH2COCH2- bridge interferes with the electronic interactions between the BTD and the benzene rings, suggesting the importance of the through-bond interaction in the ground state. In sharp contrast, the UV/vis spectra of 1 and 5 as well as those of 2 and 7 exhibit similar bands regardless of the presence of the -CH2COCH2- or -CH2CH2CH2- bridges, indicating that the charge-transfer (CT) interaction is mainly responsible for the through-space interaction. The two- layered PCPs, Sand I, show broad structureless fluorescence bands at the same position of 468 nm, while those of the three-layered PCPs, 7 and 2, appear at 501 and 496 nm, respectively, with lower quantum yields compared to those of the two-layered PCPs probably due to the stronger intramolecular CT interaction of the three-layered PCPs in the ground state. [ABSTRACT FROM AUTHOR]

Tryptophan 2,3-dioxygenase (TDO) is an essential enzyme in the pathway of NAD biosynthesis and important for all living organisms. TDO catalyzes oxidative cleavage of the indole ring of L-tryptophan (L-Trp), converting it to N-formylkynurenine (NFK). The crystal structure of TDO shows a dimer of dimer quaternary structure of the homotetrameric protein. The four catalytic sites of the protein, one per subunit, contain a heme that catalyzes the activation and insertion of dioxygen into L-Trp. Because of the a~ structure and because only one type of heme center has been identified in previous spectroscopic studies, the four hemes sites have been presumed to be equivalent. The present work demonstrates that the heme sites of TDO are not equivalent. Quantitative interpretation of EPR and Mössbauer spectroscopic data indicates the presence of two dominant inequivalent heme species in reduced and oxidized states of the enzyme, which is consistent with a dimer of dimer protein quaternary structure that now extends to the electronic properties of the hemes. The electronic properties of the hemes in the reduced state of TDO change significantly upon L-Trp addition, which is attributed to a change in the protonation state of the proximal histidine to the hemes. The binding of 02 surrogates NO or CO shows two inequivalent heme sites. The heme-NO complexes are 5- and 6-coordinate without L-Trp, and both 6-coordinate with L-Trp. NO can be selectively photodissociated from only one of the heme-NO sites and only in the presence of L-Trp. Cryoreduction of TDO produces a novel diamagnetic heme species, tentatively assigned as a reduced heme-OH complex. This work presents a new description of the heme interactions with the protein, and with the proximal His, which must be considered during the general interpretation of physical data as it relates to kinetics, mechanism, and function of TDO. [ABSTRACT FROM AUTHOR]

The electronic structures of the low and high-spin states of the cationic complex [Ni(H)(OH)]+ that was previously found to be highly reactive toward OH4 and O2 were examined. Earlier computational work suggested that the low-spin doublet state D0 of the NiIII-d7 system is significantly lower in energy than its high-spin quartet analogue Q1. Recent DFT-studies indicated, however, that Q1 is the reactive species requiring Q1 to have a sufficiently long lifetime for undergoing thermal reactions with the small molecule reactants under single collision conditions in the gas phase. These observations raise the question as to why Q1 does not spontaneously undergo intersystem crossing. Our work based on DFT, coupled-cluster and MCSCF calculations suggests that the hydroxyl ligand behaves as a redox noninnocent ligand and becomes oxidized to formally afford an electronic structure that is consistent with a NiII-(OH)• species. As a result, the doublet and quartet ground states are not related by a single electron spin flip and the intersystem crossing becomes inhibited, as indicated by unexpectedly small spin-orbit coupling constants. After extensive sampling of the potential energy surfaces, we concluded that there is no direct way of converting Q1 to the ground state doublet D0. Alternative multistep pathways for the Q1 - D0 decay involving doublet excited states were also evaluated and found to be energetically not accessible under the experimental conditions. [ABSTRACT FROM AUTHOR]

In order to understand how electronic and other structural characteristics of biphenyl phosphine ligands affect Pd-catalyzed C-N and C-C bond-forming reactions, a new ligand, 2-(dicyclohexylphosphino)-4′-(N,N-dimethylamino)-1,1′-biphenyl, was synthesized. This compound is isomeric with the commercially available 2-(dicyclohexylphosphino)-2′-(N,N-dimethylamino)-1,1′-biphenyl that has been useful in C-N bond-forming reactions of nucleosides. The new p-dimethylamino biphenyl ligand bears electronic similarities to the o-dimethylamino isomer, but it also possesses structural similarities to 2-(dicyclohexylphosphino)biphenyl, such as the unsubstituted ortho positions in the non-phosphine ring. Whereas 2-(dicyclohexylphosphino)biphenyl can support catalysts for C-C bond formation, it was not effective in promoting aryl amination of a nucleoside substrate. However, the new ligand proved to be effective in promoting both aryl amination and C-C bond-forming reactions of nucleoside substrates, with some reactions even occurring at room temperature. Thus, the composite structural elements of this new ligand are thought to be criteria for reactivity of the catalytic system derived from it. We have probed the structures of the isomeric N,N-dimethylamino biphenyl ligands by X-ray crystallographic analysis. Interactions of the two ligands with Pd(OAc)2 have been investigated by 31P NMR, and they show substantial stoichiometry-dependent differences. These results have been compared to the interactions of Pd(OAc)2 with 2-(dicyclohexylphosphino)biphenyl as well as 2-(di-tert-butylphosphino)biphenyl, and they reveal marked differences as well. In this process, three cyclopalladated biaryl derivatives have been isolated and characterized by X-ray analysis. [ABSTRACT FROM AUTHOR]

In this report, an electrical detection scheme for the quantification of DNA using a nanogap sensor array is detailed. The prime objective is to develop a novel sensing procedure, based on the electronic transduction mechanism, which would mitigate the problems intrinsic to nanostructure-based biosensing devices. Design considerations of the sensor array take into account the feasibility of mass production in a cost-effective way by using standard silicon microfabrication technologies. The sensing mechanism relies on bridging the nanogap upon hybridization of the two termini of a target DNA with two different surface-bound capture probes, followed by a simple metallization step. About 2 orders of magnitude enhancement in conductance, as referred to a clean background (<1.0 pS) observed at a control sensor, was obtained in the presence of as little as 1.0 fM target DNA. This sensitivity is comparable to the best of electrochemical/electrical biosensors. A linear relationship between the conductance and the DNA concentration was obtained from 1.0 fM to 1.0 pM with an exceptional signal intensity of 2.1 × 104% change per unit concentration. This change in conductivity is so large that it can unambiguously detect the concentration of DNA quantitatively and may obviate the need for target amplification used in current DNA tests. Moreover, the sensor array exhibited excellent single-base mismatch discrimination due to its unique vertically aligned nanostructure and the two-probe configuration. [ABSTRACT FROM AUTHOR]

We report results of first-principles total-energy calculations of structural and optical properties of the TiS2single crystals intercalated with copper. Calculations have been performed using an all-electron, full potential, linearized, augmented, plane-wave method based on density functional theory using generalized gradient approximation for the exchange correlation energy functional. To complete the fundamental characteristics of these compounds, we have calculated and analyzed their linear optical susceptibilities. We demonstrate the efficiency of using a full potential on the band structure, density of states, and the optical properties. We compare our results of the intercalated Cu in different sites and concentrations with the host TiS2compound to ascertain the effect of Cu intercalation on the electronic and optical properties. Our calculations have shown that the electronic and optical properties are influenced significantly by the location and concentration of the Cu intercalate in the host compound. The Cu-s and Cu-p bands are very broad and do not contribute much to the density of states. The density of states and the electron charge density show that all Ti−Ti and S−S bonds are basically of ionic character and that Ti−S bonds are of covalent character. No covalent electrons are found between Cu and S atoms; that is, no covalent bond exists between the Cu and S atoms. The Cu atoms are ionic in the intercalated compounds. [ABSTRACT FROM AUTHOR]

We report serial-to-parallel interfaces for rapidly and efficiently transferring samples from a single microfluidic channel to multiple parallel channels. Three designs and operation modes were evaluated to determine the most efficient transfer process. All designs employed two routing channels to direct the sample into the parallel channels and to prevent sample from leaking into adjacent channels. For two of the three designs, a tee valve and gated valve were added to the interface prior to routing the samples to assist with sample injections into the parallel channels. Injection times as short as 20 ms and injection frequencies up to 10 Hz were achieved with relative standard deviations less than 0.5% for the injected area. With an injection time of 50 ms and injection frequency of 10 Hz, up to 50% of the sample is efficiently transferred. Among the three designs, the interface with the gated valve provided the highest performance and reproducibility. [ABSTRACT FROM AUTHOR]

Our research on the triplet photochemistry of vinylcyclopropenes has dealt with a diverse series of systems, providing a series of experimental examples and mechanstic studies. It perhaps is not surprising that the reaction mechanisms have been controversial. The present study is theoretical and provides evidence for control by a critical T1 diradical intermediate which has a high spin-orbit coupling with S0 ground-state along the mechanistic pathway. The evidence now for the one pathway derives from independent generation and behavior of this diradical, prediction of the reaction regioselectivity in nine diverse examples, the S0 and T1 hypersurfaces in the reaction, and an S0-T1 degeneracy with SOC for the critical diradical. This triplet diradical when independently generated gives the same regioselectivity observed in examples starting with the vinylcyclopropene triplet itself. The overall reaction provides a useful synthesis of cyclopentadienes. [ABSTRACT FROM AUTHOR]

While N2 and CO have played central roles in developing models of electronic structure, and their interactions with transition metals have been widely investigated, the valence isoelectronic diatomic molecules EX (E = group 13 element, X = group 17 element) have yet to be isolated under ambient conditions, either as the "free" molecule or as a ligand in a simple metal complex. As part of a program designed to address this deficiency, together with wider issues of the chemistry of cationic systems [LnM(ER)]+ (E = B, Al, Ga; A = aryl, amido, halide), we have targeted complexes of the type [LnM(GaX)]+ Halide abstraction is shown to be a viable method for the generation of mononuclear cationic complexes containing gallium donor ligands. The ability to isolate tractable two-coordinate products, however, is strongly dependent on the steric and electronic properties of the metal/ligand fragment. In the case of complexes containing ancillary ar-acceptor ligands such as CO, cationic complexes can only be isolated as base-trapped adducts, even with bulky aryl substituents at gallium. Base-free gallylene species such as [Cp*Fe(CO)2(GaMes)]+ can be identified only in the vapor phase by electrospray mass spectrometry experiments. With bis(phosphine) donor sets at the metal, the more favorable steric/electronic environment allows for the isolation of two-coordinate ligand systems, even with halide substituents at gallium. Thus, [Cp*Fe(dppe)(Gal)]+iBArf4]- (9) can be synthesized and shown crystallographically to feature a terminally bound Gal ligand; 9 represents the first experimental realization of a complex containing a valence isoelectronic group 13/group 17 analogue of CO and N2. DFT calculations reveal a relatively weakly bound Gal ligand, which is confirmed experimentally by the reaction of 9 with CO to give [Cp*Fe(dppe)+ (CO)]+[BArf4]-. In the absence of such reagents, 9 is stable for weeks in fluorobenzene solution, presumably reflecting (i) effective steric shielding of the gallium center by the ancillary phosphine and Cp* ligands; (ii) a net cationic charge which retards the tendency toward dimerization found for putative charge neutral systems; and (iii) (albeit relatively minor) population of the LUMOs of the Gal molecule through π overlap with the HOMO and HOMO-2 of the [Cp*Fe(dppe)]+ fragment. [ABSTRACT FROM AUTHOR]

We recently reported that the photoisomerization of molecular motors used as chiral dopants in a cholesteric liquid crystal film induces a rotational reorganization which can be observed by optical microscopy and produces the motion of microscopic objects placed on top of the film (Feringa, B. L.; et al. Nature 2006, 440, 163; J. Am. Chem. Soc. 2006, 128, 14397). The mechanism underlying the mesoscopic manifestation of the molecular process was not fully understood, and here we present a joint theoretical and experimental investigation, which provides a detailed insight into the mechanism of texture rotation. This description allows us to identify the interplay between the chemical structure of the chiral dopant and the material properties of the liquid crystal host, and to quantify their role in the observed dynamic phenomenon. We have found that a crucial role is played by the hybrid anchoring of the liquid crystal, with the director parallel to the substrate and perpendicular to the interface with air; in this configuration an almost unperturbed cholesteric helix, with its axis normal to the substrate, is present in most of the film, with strong deformations only close to the free interface. The texture rotation observed in the experiment reflects the rotation of the director during the unwinding of the cholesteric helix, produced by the change in shape of the chiral dopant under photoisomerization. The rotational reorganization is controlled by the photochemical process, via the coupling between the chirality of the dopant and the elastic properties of the liquid crystal host. [ABSTRACT FROM AUTHOR]

The effects of structural fluctuations on charge transfer in double-stranded DNA and peptide nucleic acid (PNA) are investigated. A palindromic sequence with two guanine bases that play the roles of hole donor and acceptor, separated by a bridge of two adenine bases, was analyzed using combined molecular dynamics (MD) and quantum-chemical methods. Surprisingly, electronic structure calculations on individual MD snapshots show significant frontier orbital electronic population on the bridge in ~10% of the structures. Electron-density delocalization to the bridge is found to be gated by fluctuations of the covalent conjugated bond structure of the aromatic rings of the nucleic bases. It is concluded, therefore, that both thermal hopping and superexchange should contribute significantly to charge transfer even in short DNA! PNA fragments. PNA is found to be more flexible than DNA, and this flexibility is predicted to produce larger rates of charge transfer. [ABSTRACT FROM AUTHOR]

A study of the reactivity of [MoCp Bz(CO) 3H] (Cp Bz= pentabenzylcyclopentadienyl) as a catalyst precursor for the ionic hydrogenation of 3-pentanone is presented. The complexes [MCp Bz(CO) 3OTf] (M = Mo ( 3), W ( 4)), [MoCp Bz(CO) 3(OCEt 2)]BF 4( 9), and [MoCp Bz(CO) 3(OCMe 2)]BF 4( 12) are described. 9+and [MoCp Bz(CO) 3(OHCHEt 2)] +( 8+) were identified by NMR under catalytic conditions. The reaction of [WCp Bz(CO) 3H] with triflic acid led to [WCp Bz(CO) 3(H) 2] +( 7+), which was identified by NMR as a dihydride complex. The influence of steric and electronic effects on the catalyst activity is discussed on the basis of experimental results and a mechanism proposal resulting from DFT calculations. The proposed mechanism includes facile protonation of the acetone O atom promoted by a dihydride Mo(IV) complex, followed by slower hydride transfer from the metal center to the carbonyl C atom. The results indicate strong coordination of both the product (isopropyl alcohol) and the reactant (acetone), leading to some blocking of the catalyst active site. Regeneration of the catalyst active species is the rate-limiting step of the catalytic cycle. The steric bulk of the Cp Bzligand increases the catalyst activity. [ABSTRACT FROM AUTHOR]

The electronic and geometric structures of gallium dinitride GaN 2, and gallium tetranitride molecules, GaN 4, were systematically studied by employing density functional theory and perturbation theory (MP2, MP4) in conjunction with the aug-cc-pVTZ basis set. In addition, for the ground-state of GaN 4( 2B 1) a density functional theory study was carried out combining different functionals with different basis sets. A total of 7 minima have been identified for GaN 2, while 37 structures were identified for GaN 4corresponding to minima, transition states, and saddle points. We report geometries and dissociation energies for all the above structures as well as potential energy profiles, potential energy surfaces and bonding mechanisms for some low-lying electronic states of GaN 4. The dissociation energy of the ground-state GaN 2( X̃2Π) is 1.1 kcal/mol with respect to Ga( 2P) + N 2( X1Σ g+). The ground-state and the first two excited minima of GaN 4are of 2B 1( C2v), 2A 1( C2v, five member ring), and 4Σ g−( D ∞h) symmetry, respectively. The dissociation energy ( De) of the ground-state of GaN 4, X̃2B 1, with respect to Ga( 2P) + 2 N 2( X1Σ g+), is 2.4 kcal/mol, whereas the Deof 4Σ g−with respect to Ga( 4P) + 2 N 2( X1Σ g+) is 17.6 kcal/mol. [ABSTRACT FROM AUTHOR]

Hyperquenched glassy water (HGW) has been suggested as the best model for liquid water, to be used in low-temperature studies of indirect radiation effects on dissolved biomolecules (Bednarek et al. J. Am. Chem. Soc.1996, 118, 9387). In the present work, these effects are examined by X-band electron spin resonance spectroscopy (ESR) in γ-irradiated HGW matrix containing 2′-deoxyguanosine-5′-monophosphate. Analysis of the complex ESR spectra indicates that, in addition to OH ·and HO 2·radicals generated by water radiolysis, three species are trapped at 77 K: (i) G(C8)H ·radical, the H-adduct to the double bond at C8; (ii) G − ·radical anion, the product of electron scavenging by the aromatic ring of the base; and (iii) dR(−H) ·radicals formed by H abstraction from the sugar moiety, predominantly at the C′5 position. We discuss the yields of the radicals, their thermal stability and transformations, as well as the effect of photobleaching. This study confirms our earlier suggestion that in HGW the H atom addition/abstraction products are created at 77 K in competition with HO 2·radicals, in a concerted process following ionization of water molecule at L-type defect sites of the H-bonded matrix. The lack of OH ·reactivity toward the solute suggests that the H-bonded structure in HGW is much more effective in recombining OH ·radicals than that of aqueous glasses obtained from highly concentrated electrolyte solutions. Furthermore, complementary experiments for the neat matrix have provided evidence that HO 2·radicals are not the product of H atom reaction with molecular oxygen, possibly generated by ultrasounds used in the process of sample preparation. [ABSTRACT FROM AUTHOR]

A novel series of soluble alternating conjugated copolymers, comprised of 9,9-dihexylfluorene and cyclopentadithiophenes ( P1− P5), were synthesized via Pd-catalyzed Suzuki coupling reaction in good yields. The UV−vis absorption spectra, fluorescence spectra, fluorescence quantum yields, and cyclic voltammograms of P1− P5are also reported. The P2and P3with electron-donating non-π-substituents (ethylenedioxy and propylenedioxy bridges the 3,3-positions of the thiophene groups) display high fluorescence quantum yields and red-shifted absorption as compared with nonsubstituted P1. However, the P4and P5are weakly fluorescent and exhibit blue-shifted absorption which are due to the presence of electron-withdrawing π-substituents (carbonyl and dicyanoethenyl). The behavior of P4and P5can be attributed to the significant electronic coupling between the π-substituents and the conjugated polymer backbone that leads to a less allowed optical transition between the ground and the lowest excited state, resembling the metaconjugation effect in phenylene-derived conjugated π-systems. This argument is supported by molecular orbital distribution calculations. [ABSTRACT FROM AUTHOR]

We report on reversible metal to insulator transitions in metallic single-walled carbon nanotube devices induced by repeated electron irradiation of a nanotube segment. The transition from a low-resistive, metallic state to a high-resistive, insulating state by 3 orders of magnitude was monitored by electron transport measurements. Application of a large voltage bias leads to a transition back to the original metallic state. Both states are stable in time, and transitions are fully reversible and reproducible. The data is evidence for a local perturbation of the nanotube electronic system by removable trapped charges in the underneath substrate and excludes structural damage of the nanotube. The result has implications for using electron-beam lithography in nanotube device fabrication. [ABSTRACT FROM AUTHOR]

We demonstrate a mechanical−electrical trigger using a ZnO piezoelectric fine-wire (PFW) (microwire, nanowire). Once subjected to mechanical impact, a bent PFW creates a voltage drop across its width, with the tensile and compressive surfaces showing positive and negative voltages, respectively. The voltage and current created by the piezoelectric effect could trigger an external electronic system, thus, the impact force/pressure can be detected. The response time of the trigger/sensor is ∼10 ms. The piezoelectric potential across the PFW has a lifetime of ∼100 s, which is long enough for effectively “gating” the transport current along the wire; thus a piezoelectric field effect transistor is possible based on the piezotronic effect. [ABSTRACT FROM AUTHOR]

Vibrational circular dichroism (VCD) measurements and density functional theory (DFT) calculations were used to obtain the absolute configuration of a cryptophane molecule having C1-symmetry (labeled cryptophane-H). This molecule exhibits chiroptical properties different from those published for cryptophane-A having D3-symmetry [Brotin et al. J. Am. Chem. Soc. 2006, 128, 5533−5540]. In particular, we have shown that the conformation of the aliphatic linkers is very dependent on the solvent used and its ability to enter (CDCl 3solution) or not (C 2D 2Cl 4solution) in the cryptophane cavity. Calculations performed at the DFT (B3PW91/6-31G*) level establish, besides the absolute configuration, the preferential anti and gauche conformations of the aliphatic linkers of the chloroform@cryptophane-H complex and the empty cryptophane-H molecule, respectively. Polarimetric measurements performed in several solvents reflect also the change of conformation of the bridges upon guest encapsulation. [ABSTRACT FROM AUTHOR]

Structures, relative energies, and bonding characteristics for various conformers of 3-imino- N-(oxoboryl)prop-1-en-1-amine, HNCH−CHCH−NH−BO, and the corresponding borocycle (−HNCH−CHCH−NH−B−)O are discussed using results from second-order Møller−Plesset (MP2) perturbation theory with the Dunning−Woon correlation-consistent cc-pVDZ, aug-cc-pVDZ, and cc-pVTZ basis sets. These MP2 results are compared to those from computationally efficient density functional theory (DFT) calculations using the LDA, PBE, TPSS, BLYP, B3LYP, BVP86, OLYP, O3LYP, and PBE1PBE functionals in conjunction with the economical Pople-type 6-311++G(d,p) basis set to evaluate the suitability of these DFT/6-311++G(d,p) levels for use with larger boron-containing systems. The effects of an aqueous environment were incorporated into the calculations using COSMO methodology. The calculated boron−oxygen bond lengths, orbital compositions, and bond orders in all the (acyclic) HNCH−CHCH−NH−BO conformers were consistent with the presence of a boron−oxygen triple bond, similar to that found in H−BO and H 2N−BO. The (−HNCH−CHCH−NH−B−)O borocycle is predicted to be planar ( C2 vsymmetry), and it is ∼30 kcal/mol lower in energy than any of the (acyclic) HNCH−CHCH−NH−BO conformers; the boron−oxygen bond in this borocycle has significant double bond character, a bonding scheme for which there has been only one experimental structure reported in the literature ( Vidovic, D.; et al. J. Am. Chem. Soc.2005, 127, 4566− 4569). [ABSTRACT FROM AUTHOR]

To attempt theoretical predictions of the regioselectivity pattern in molecules with multiple reactive sites, the energies of formation of all possible isomers are usually considered. This means that the computing becomes highly demanding if high theoretical levels are used. The study objective was to predict the regioselectivity in the reaction of hydrogen addition onto azahydro[60]fullerene C 59H n+1 N ( n= 0−4) systems using a new reactivity indicator termed general-purpose reactivity indicator, Ξ Δ N≤0,α κ, proposed by Anderson et al. ( J. Chem. Theory Comput.2007, 3, 358). Because Ξ Δ N≤0,α κcombines the information from the electrostatic potential and the Fukui function, this indicator is a two-parameter model that depends on the atomic charges and Fukui values calculated. We used the gradient-corrected BLYP and BOP functionals to approximate the electronic density of the systems, and these densities were employed to determinate the parameters. In terms of regioselectivity, the preferential addition sites at every hydrogenation step on C 59H n+1 N ( n= 0−4) shows that 1,4-adducts are more stable than 1,2-adducts. However, we show that the multiple additions are only feasible up to a C 59H 5N (tetraddition) product. Consequently, the application of this indicator not only helps to avoid systematic computational studies by comparing energies of formation in several isomersmany of which are not currently supported by experimental resultsbut also provides an insight of how the pattern of addition is achieved. Comparisons with traditional indicators show that the application of Ξ Δ N≤0,α κperforms much better for predicting reactivity in the aza[60]fullerene derivatives studied. [ABSTRACT FROM AUTHOR]

Geometry structures, electronic spectra, and third-order nonlinear optical (NLO) properties of Fe(η 5-C 55X 5) 2(X = CH, N, B) have first been investigated by time-dependent density functional theory. We analyzed the intramolecular interactions between ferrocene and the C 50moiety. The calculated electronic absorption spectrum indicates that the short wavelength transitions are ascribed to the C 50moiety mixed charge transfer transition of ferrocene itself, while the low energy excitation transitions are ascribed to the unique charge transfer transition from ferrocene to C 50moiety in these systems. The third-order polarizability γ values based on sum of states (SOS) method show that this class of ferrocene/fullerene hybrid molecule possesses a remarkably large third-order NLO response, especially for Fe(η 5-C 55B 5) 2with the static third-order polarizability (γ av) computed to be −10410 × 10 −36esu and the intrinsic second hypepolarizability to be 0.250. Thus, these complexes have the potential to be used for excellent third-order nonlinear optical materials. Analysis of the major contributions to the γ avvalue suggest that the charge transfer from ferrocene to C 50moiety along the z-axis (through Fe atom and the centers of two hybrid fullerenes) play the key role in the NLO response. Furthermore, boron substitution is an effective way of enhancing the optical nonlinearity compared to CH and N substitution, owing to smaller energy gap and better conjugation through the whole molecule. [ABSTRACT FROM AUTHOR]

The structure and spectroscopic properties of B 2O 3glass are examined from a theoretical point of view by using a model of 20 B 2O 3molecules at the DFT/6-31G* level of theory and no predetermined constraints. Useful results are deduced regarding the structure, the fraction of boroxol rings, and the infrared and Raman spectra. [ABSTRACT FROM AUTHOR]

Trichloromethanesulfenyl acetate, CCl 3SOC(O)CH 3, belongs to the family of sulfenic esters. This molecule has been characterized by vibrational spectroscopy. The conformational and geometrical properties of this species have been determined by IR and Raman spectroscopy, X-ray diffraction, and quantum chemical calculations. Geometry optimizations of the most stable forms were performed with ab initio (HF, MP2) and density functional theory (B3LYP) methods. According to our data, this compound results in a gauche−syn conformer with C1symmetry (gauche orientation around the S−O bond and syn orientation of the CO double bond with respect to the S−O single bond) for the most stable geometry, and trans−syn conformer with C ssymmetry (trans orientation around the S−O bond and syn orientation of the CO double bond with respect to the S−O single bond) for the second stable conformer (1.1 and 0.53 kcal/mol higher in energy than the most stable C1form according to the matrix FTIR spectroscopy and MP2/6-31G* level of the theory, respectively). The crystalline solid (monoclinic, P2 1/ n, a= 8.0152(17) Å, b= 5.7922(13) Å, c= 17.429(4) Å, α = γ= 90°, β = 100.341(3)°) consists exclusively of the main form. The geometrical parameters (X-ray diffraction) are dC−Cl= 1.767(19) Å, dC−S= 1.797(2) Å, dS−O= 1.663(14) Å, dCO= 1.189(2) Å, dO−C= 1.389(3) Å, dC−C= 1.483(3) Å, angles Cl−C−Cl = 110.3(11)°, Cl−C−S = 111.8(12)°, C−S−O = 97.4(8)°, S−O−C = 116.7(11)°, O−CO = 122.8(19)°, OC−C = 127.1(2)°, and the main torsion angles are δ(CSOC) = 105.9(15)° and δ(SOC(O)) = 7.6(3)°. The geometrical data calculated with B3LYP/6-31G++(3df,3pd), B3LYP/6-311G++(3df,3pd), B3LYP/aug-cc-pVTZ, and MP2/6-31G* are in good agreement with diffraction data. [ABSTRACT FROM AUTHOR]

Electronic circular dichroism (ECD) is a valuable tool to explore the secondary and tertiary structure of proteins. With respect to heme proteins, the corresponding visible ECD spectra, which probe the chirality of the heme environment, have been used to explore functionally relevant structural changes in the heme vicinity. While the physical basis of the obtained ECD signal has been analyzed by Woody and co-workers in terms of multiple electronic coupling mechanism between the electronic transitions of the heme chromophore and of the protein (Hsu, M.C.; Woody, R.W. J. Am. Chem. Soc.1971, 93, 3515), a theory for a detailed quantitative analysis of ECD profiles has only recently been developed (Schweitzer-Stenner, R.; Gorden, J. P.; Hagarman, A. J. Chem. Phys.2007, 127, 135103). In the present study this theory is applied to analyze the visible ECD-spectra of both oxidation states of three cytochromes c from horse, cow and yeast. The results reveal that both B- and Q-bands are subject to band splitting, which is caused by a combination of electronic and vibronic perturbations. The B-band splittings are substantially larger than the corresponding Q-band splittings in both oxidation states. For the B-bands, the electronic contribution to the band splitting can be assigned to the internal electric field in the heme pocket, whereas the corresponding Q-band splitting is likely to reflect its gradient (Manas, E. S.; Vanderkooi, J. M.; Sharp, K. A. J. Phys. Chem. B1999, 103, 6344). We found that the electronic and vibronic splitting is substantially larger in the oxidized than in the reduced state. Moreover, these states exhibit different signs of electronic splitting. These findings suggest that the oxidation process increases the internal electric field and changes its orientation with respect to the molecular coordinate system associated with the N−Fe−N lines of the heme group. For the reduced state, we used our data to calculate electric field strengths between 27 and 31 MV/cm for the investigated cytochrome c species. The field of the oxidized state is more difficult to estimate, owing to the lack of information about its orientation in the heme plane. Based on band splitting and the wavenumber of the band position we estimated a field-strength of ca. 40 MV/cm for oxidized horse heart cytochrome c. The thus derived difference between the field strengths of the oxidized and reduced state would contribute at least −55 kJ/mol to the enthalpic stabilization of the oxidized state. Our data indicate that the corresponding stabilization energy of yeast cytochrome c is smaller. [ABSTRACT FROM AUTHOR]

We report the syntheses, structures, photophysical properties, and redox characteristics of the [2 + 2] pyromellitic diimide-based macrocycle with a linear π-electronic system 2 as well as the 3,6-bis(phenylethynyl)pyromellitic diimide derivative 3. The interesting solid state structural properties of the clathrates of 3 with π-donors are also reported. The macrocycle 2 was synthesized by the direct cyclocondensation followed by the Sonogashira coupling reaction. X-ray crystallographic studies showed that the phenylacetylene moieties in 2 formed the intramolecular benzene dimer structures, and the bis(phenylethynyl)pyromellitic diimide moieties in both 2 and 3 were stacked in a parallel and slanted arrangement. Theoretical calculations for 2′ and 3 suggested the existence of electrostatic interactions between the bis(phenylethynyl)pyromellitic diimide moieties. The UV/vis spectral measurements and TDDFT calculations of 2, 2′, and/or 3 were performed to understand their electronic transitions. The fluorescence spectral measurements showed that 2 and 3 have visible fluorescence properties and 2 displays an excimer fluorescence at ca. 590 nm. The cyclic voltammetry measurements revealed that the electrostatic repulsion between the diimide moieties in 2 is greater than that in 1 according to the extension of the π-electronic systems. X-ray crystallography of the clathrates of 3 with various π-donors demonstrated the formation of the segregated donor-acceptor structures, indicating the strong aggregation ability of the bis(phenylethynyl)pyromellitic diimide moiety. [ABSTRACT FROM AUTHOR]

Attractive interactions between molecules lead to formation of the liquid phase at sufficiently low temperatures. In the absence of external fields or containers, liquids assume the shape of spherical drops, which minimize their surface area. In systems with 3-D periodic boundary conditions (PBCs), which are routinely employed in molecular simulations, alternate configurations can be stable depending on the extent of the system. The stability of a variety of structures under 3-D PBCs originates from the underlying variation of free energy with density as shown elegantly by MacDowell and co-workers (MacDowell, L. G.; Shen, V. K.; Errington, J. R. J. Chem. Phys.2006, 125, 3.). Here we present analysis of extensive Monte Carlo and molecular dynamics simulations of Lennard-Jones and water fluids to calculate free energy and explore the phase diagram that governs formation of different liquid assemblies. We also study metastability of different shapes and their interconversions by systematically initializing simulations in various configurations. Further, We present results on the rupture of thin liquid films on solid substrates, with focus on the evolution of liquid structure and the rupture mechanism. Our estimates of important capillary wavelengths from simulations are in good agreement with theoretical predictions of Vrij and Overbeek (Vrij, A.; Overbeek, J. T. J. Am. Chem. Soc.1968, 90, 3074−3078.). Collectively, our work significantly extends the previous simulation studies of interfacial systems, and especially of thin-film structure, stability, and rupture processes in molecular simulations. [ABSTRACT FROM AUTHOR]

Electronic readout of the motions of genuinely nanoscale mechanical devices at room temperature imposes an important challenge for the integration and application of nanoelectromechanical systems (NEMS). Here, we report the first experiments on piezoresistively transduced very high frequency Si nanowire (SiNW) resonators with on-chip electronic actuation at room temperature. We have demonstrated that, for very thin (∼90 nm down to ∼30 nm) SiNWs, their time-varying strain can be exploited for self-transducing the devices’ resonant motions at frequencies as high as ∼100 MHz. The strain of wire elongation, which is only second-order in doubly clamped structures, enables efficient displacement transducer because of the enhanced piezoresistance effect in these SiNWs. This intrinsically integrated transducer is uniquely suited for a class of very thin wires and beams where metallization and multilayer complex patterning on devices become impractical. The 30 nm thin SiNW NEMS offer exceptional mass sensitivities in the subzeptogram range. This demonstration makes it promising to advance toward NEMS sensors based on ultrathin and even molecular-scale SiNWs, and their monolithic integration with microelectronics on the same chip. [ABSTRACT FROM AUTHOR]

We study the coherence quantum beats in two-dimensional (2D) electronic spectroscopy of a coupled dimer system using a theoretical method based on a time-nonlocal quantum master equation and a recently proposed scheme for the evaluation of the third-order photon echo polarization Gelin, M. F.; Egorova, D.; Domcek, W. J. Chem. Phys.2005, 123, 164112. The simulations show that the amplitude and peak shape beating in the 2D spectra is a result of the interplay between the rephasing and non-rephasing contributions to the 2D signals and can be used to elucidate the coherence dynamics in a multichromophoric system. In addition, the results suggest that the rephasing and non-rephasing 2D spectra contain complementary information, and a study of both of them could provide more dynamical information from 2D electronic spectroscopy. [ABSTRACT FROM AUTHOR]

Time-resolved electron paramagnetic resonance studies show that the primary mechanism of triplet formation following photoexcitation of julolidine-anthracene molecules linked by a single bond and having perpendicular systems is a spin−orbit, charge-transfer intersystem crossing mechanism (SOCT−ISC). This mechanism depends on the degree of charge transfer from julolidine to anthracene, the dihedral angle (1) between their systems, and the magnitude of the electronic coupling between julolidine and anthracene. We compare 4-(9-anthracenyl)-julolidine with the more sterically encumbered 4-(9-anthracenyl)-3,5-dimethyljulolidine and find that fixing 1≅ 90° serves to enhance SOCT−ISC by increasing the change in orbital angular momentum accompanying charge transfer. Given that the requirements for the SOCT−ISC mechanism are quite general, we expect it to occur in a variety of electron donor−acceptor systems. [ABSTRACT FROM AUTHOR]

The effect of delay on the stability of a coupled reactor separator system is investigated in this work, using the DDE-BIFTOOL software package. The reactor considered is a continuously stirred tank reactor (CSTR), and the separator is modeled as a flash unit operating isothermally and isobarically. A first-order isothermal irreversible reaction A → B is considered to investigate the effect of delay arising as a result of transportation lag from the CSTR to the flash. The dynamic behavior of the coupled CSTR−flash system is governed by the delay differential equations. In this work, the dynamic instability induced by delay that is crucially dependent on the flow control strategy of the system is investigated using DDE-BIFTOOL. It is shown that delay can destabilize the steady state of the coupled system when the reactor effluent flow rate Fis flow-controlled, and the molar holdup MRin the reactor is allowed to vary. When the fresh feed flow rate F0is flow-controlled, the system exhibits delay-independent stability. The critical delay and frequency of oscillation obtained using DDE-BIFTOOL show good agreement with the same obtained using the analytical expressions proposed in the literature. [ABSTRACT FROM AUTHOR]

Four poly((1,2-butadiene)- block-ethylene oxide) (PB–PEO) diblock copolymers were shown to self-assemble into micelles with PB cores and PEO coronas (including spheres, cylinders, and vesicles) in the ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]). All four systems exhibited the “micelleshuttle” (He, Y.; Lodge, T. P. J. Am. Chem. Soc.2006, 128, 12666−12667), whereby PB–PEO micelles transferred, reversibly and with preservation of micelle structure, from an aqueous phase at room temperature to a hydrophobic ionic liquid at high temperature. The micelle size (both mean and distribution) depends on whether it was initially dissolved in water or in the ionic liquid, but the initial micelle structures in the ionic liquid were shown by dynamic light scattering to be preserved during the transfer and persist essentially unchanged for months in both the ionic liquid and water. The transfer was shown to be driven by the deteriorating solvent quality of water for PEO at high temperature, while the ionic liquid remains a good solvent. The transfer temperature could be tuned by adding ionic or nonionic additives to the aqueous phase to change the solvent quality of water for PEO, and by using ionic liquids with different polarity. [ABSTRACT FROM AUTHOR]

A new mechanism of charge transmission through a metal−molecule−metal junction is suggested that is based on optical driving of electronic transitions in the neutral and singly charged molecular state. The effects of strong electron vibrational coupling, intramolecular vibrational energy redistribution, and molecular de-excitation caused by electron−hole pair formation in the leads are taken into account. It is shown that current suppression due to the Franck−Condon blockade can be overcome by opening new transmission channels via photoexcitation. [ABSTRACT FROM AUTHOR]