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We have quantum chemically investigated how microsolvation affects the various E2 and SN2 pathways, their mutual competition, and the α-effect of the model reaction system HOO−(H2O)n + CH3CH2Cl, at the CCSD(T) level. Interestingly, we identify the dual nature of the α-nucleophile HOO− which, upon solvation, is in equilibrium with HO−. This solvent-induced dual appearance gives rise to a rich network of competing reaction channels. Among both nucleophiles, SN2 is always favored over E2, and this preference increases upon increasing microsolvation. Furthermore, we found a pronounced α-effect, not only for SN2 substitution but also for E2 elimination, i.e., HOO− is more reactive than HO− in both cases. Our activation strain and quantitative molecular orbital analyses reveal the physical mechanisms behind the various computed trends. In particular, we demonstrate that two recently proposed criteria, required for solvent-free nucleophiles to display the α-effect, must also be satisfied by microsolvated HOO−(H2O)n nucleophiles. [ABSTRACT FROM AUTHOR]

The Radboud University Nijmegen has embarked on an investment program for a free-electron laser radiation source and a 45 1 hybrid magnet system to enhance the capabilities of its High Field Magnet Laboratory. The new installations, together with the high-resolution and solid-state NMR,the Laser Laboratory and the NanoLab will be part of the Nijmegen Center for Advanced Spectroscopy of the Institute for Molecules and Materials (IMM-NCAS). The FEL and hybrid magnet system are planned to be operational in 2012. [ABSTRACT FROM AUTHOR]

The demand for electric vehicles with extended ranges has created a renaissance of interest in replacing the common metal-ion with higher energy-density metal-anode batteries. However, the potential battery safety issues associated with lithium metal must be addressed to enable lithium metal battery chemistries. A considerable performance gap between lithium (Li) symmetric cells and practical Li batteries motivated us to explore the correlation between the shape of voltage traces and degradation. We coupled impedance spectroscopy and operando NMR and used the new approach to show that transient (i.e., soft) shorts form in realistic conditions for battery applications; however, they are typically overlooked, as their electrochemical signatures are often not distinct. The typical rectangular-shaped voltage trace, widely considered ideal, was proven, under the conditions studied here, to be a result of soft shorts. Recoverable soft-shorted cells were demonstrated during a symmetric cell polarisation experiment, defining a new type of critical current density: the current density at which the soft shorts are not reversible. Moreover, we demonstrated that soft shorts, detected via electrochemical impedance spectroscopy (EIS) and validated via operando NMR, are predictive towards the formation of hard shorts, showing the potential use of EIS as a relatively low-cost and non-destructive method for early detection of catastrophic shorts and battery failure while demonstrating the strength of operando NMR as a research tool for metal plating in lithium batteries. [ABSTRACT FROM AUTHOR]

The group of Costa Figueiredo reported Cu-based catalysts for the electrosynthesis of ammonia from nitrate, and X-ray photoelectron spectroscopy demonstrated that Cu(0) is the active phase during catalysis. The Hamlin and Bickelhaupt group performed high level quantum chemical analysis, showing that C(spn)-halogen bonds are easier to activate by a palladium catalyst when the halogen is larger, due to a difference in activation strain and a more favorable electrostatic attraction between the palladium catalyst and the substrate. The importance of catalysis has been recognized a long time ago and the first industrial application stems from the early nineteenth century. We develop new catalytic processes based on 1) rational ligand design in transition metal catalysis 2) Supramolecular catalysis 3) Bio-inspired catalysis. [Extracted from the article]

Non‐hydrogenative Para‐Hydrogen Induced Hyperpolarization (nhPHIP) is a Nuclear Magnetic Resonance (NMR) hyperpolarization technique which has experimentally been used to analyze complex biological samples containing amino acids using the Ir‐IMes hyperpolarization transfer catalyst. A computational study based on Density Function Theory (DFT) was performed on all relevant stereoisomers of [Ir(H)2(IMes)(AA)(Py)] (with AA=glycine, alanine, valine; Py=pyridine), for which R/S chirality and orientation of the amino acid chelation (C/A) were considered. A total of 30 structures were calculated comprising of 6 stereoisomers for achiral glycine, and 12 stereoisomers for each of the chiral amino acids. The abundances derived from the DFT energies confirmed the trends observed in thermal (non‐hyperpolarized) NMR experiments. Additionally, theoretical calculations of electronic (Wiberg bond indices, Natural Bond Orders, Frontier Orbital Analysis), bond dissociation energies, transition states, and activation energies related to interconversion between binding modes, and steric factors (Solid angle) were performed to provide detailed explanations for NMR experimental observations. [ABSTRACT FROM AUTHOR]

Solid-to-solid polymorphic transitions are a common phenomenon in organic crystals. The different interactions that play a role in these transitions are however far from understood. In this computational study, we aim to quantify the interactions that play a role in these transitions using the α ↔ β phase transition of DL -methionine as a model system. DL -Methionine has a layered structure and its phase transition occurs via shifting of the bilayers parallel to the b and c lattice vectors and the rotation of the side chains, which mostly affects the layers along the c lattice vector. We obtained two "order parameters" to describe the changes along b and c, respectively and that can be used to quantify the phase transition in terms of its thermodynamic parameters. The potential energy landscape is an interplay between van der Waals energy and configurational energy, where α is stabilized by configurational energy and destabilized by van der Waals energy as compared to β. The entropic contribution to the free energy difference between α and β is found to be in good agreement with experiments and completely dominated by configurational entropy. [ABSTRACT FROM AUTHOR]

The blood coagulation cascade is a complex physiological process involving the action of multiple coupled enzymes, cofactors, and substrates, ultimately leading to clot formation. Serine proteases have a crucial role, and aberrations in their activity can lead to life‐threatening bleeding disorders and thrombosis. This review summarizes the essential proteases involved in blood coagulation and fibrinolysis, the endogenous peptide sequences they recognize and hydrolyze, and synthetic peptide probes based on these sequences to measure their activity. The information in this review can contribute to developing novel anticoagulant therapies and specific substrates for point‐of‐care diagnosis of coagulation pathologies. [ABSTRACT FROM AUTHOR]

The traditional and widespread rationale behind the stability trend of alkyl-substituted carbocations is incomplete. Through state-of-the-art quantum chemical analyses, we quantitatively established a generally overlooked driving force behind the stability of carbocations, namely, that the parent substrates are substantially destabilized by the introduction of substituents, often playing a dominant role in solution. This stems from the repulsion between the substituents and the C–X bond. [ABSTRACT FROM AUTHOR]

Hierarchical, convergent ab initio benchmark computations were performed followed by a systematic analysis of DFT performance for five pericyclic reactions comprising Diels-Alder, 1,3-dipolar cycloaddition, electrocyclic rearrangement, sigmatropic rearrangement, and double group transfer prototypes. Focal point analyses (FPA) extrapolating to the ab initio limit were executed via explicit quantum chemical computations with electron correlation treatments through CCSDT(Q) and correlation-consistent Gaussian basis sets up to aug′-cc-pV5Z. Optimized geometric structures and vibrational frequencies of all stationary points were obtained at the CCSD(T)/cc-pVTZ level of theory. The FPA reaction barriers and energies exhibit convergence to within a few tenths of a kcal mol−1. The FPA benchmarks were used to evaluate the performance of 60 density functionals (eight dispersion-corrected), covering the local-density approximation (LDA), generalized gradient approximations (GGAs), meta-GGAs, hybrids, meta-hybrids, double-hybrids, and range-separated hybrids. The meta-hybrid M06-2X functional provided the best overall performance [mean absolute error (MAE) of 1.1 kcal mol−1] followed closely by the double-hybrids B2K-PLYP, mPW2K-PLYP, and revDSD-PBEP86 [MAE of 1.4–1.5 kcal mol−1]. The regularly used GGA functional BP86 gave a higher MAE of 5.8 kcal mol−1, but it qualitatively described the trends in reaction barriers and energies. Importantly, we established that accurate yet efficient meta-hybrid or double-hybrid DFT potential energy surfaces can be acquired based on geometries from the computationally efficient and robust BP86/DZP level. [ABSTRACT FROM AUTHOR]

RNase MRP is a ribonucleoprotein complex involved in the endoribonucleolytic cleavage of different RNAs. Mutations in the RNA component of the RNP are the cause of cartilage hair hypoplasia. Patients with cartilage hair hypoplasia are characterized by skeletal dysplasia. Biochemical purification of RNase MRP is desired to be able to study its biochemical function, composition and activity in both healthy and disease situations. Due to the high similarity with RNase P, a method to specifically isolate the RNase MRP complex is currently lacking. By fusing a streptavidin-binding RNA aptamer, the S1m-aptamer, to the RNase MRP RNA we have been able to compare the relative expression levels of wildtype and mutant MRP RNAs. Moreover, we were able to isolate active RNase MRP complexes. We observed that mutant MRP RNAs are expressed at lower levels and have lower catalytic activity compared to the wildtype RNA. The observation that a single nucleotide substitution at position 40 in the P3 domain but not in other domains of RNase MRP RNA severely reduced the binding of the Rpp25 protein subunit confirmed that the P3 region harbours the main binding site for this protein. Altogether, this study shows that the RNA aptamer tagging approach can be used to identify RNase MRP substrates, but also to study the effect of mutations on MRP RNA expression levels and RNase MRP composition and endoribonuclease activity. [ABSTRACT FROM AUTHOR]

Fibrous networks of biopolymers possess unique properties: mechanical stability at low concentrations, an extremely porous architecture, and strong stiffening at small deformations. An outstanding challenge is to find methods that allow to tailor the mechanical properties of these bionetworks or their synthetic equivalents without changing the polymer concentration, which simultaneously changes all other hydrogel properties. Here, networks of dilute (0.1 wt.%) fibrous hydrogels are prepared and crosslink them with functional rod‐shaped nanoparticles. The crosslinking is observed to induce an architectural change that strongly affects the mechanical properties of the hydrogels with a 40‐fold increase in stiffness. The effect is strongest at the lowest polymer and particle concentrations (99.8% water) and is tailorable through tuning the crosslink density. Moreover, the nanoparticle components in the composite offer the opportunity to introduce additional functions; gels with magnetic and conductive properties are reported. However, through the generic crosslinking approach of a fibrous network with decorated nanoparticle crosslinkers as presented in this work, virtually any functionality may be introduced in highly responsive hydrogels, providing a guide to design next generations of multi‐functional soft materials. [ABSTRACT FROM AUTHOR]

The concept of dipolar repulsion has been widely used to explain several phenomena in organic chemistry, including the conformational preferences of carbonyl compounds. This model, in which atoms and bonds are viewed as point charges and dipole moment vectors, respectively, is however oversimplified. To provide a causal model rooted in quantitative molecular orbital theory, we have analyzed the rotational isomerism of haloacetaldehydes OHC–CH2X (X = F, Cl, Br, I), using relativistic density functional theory. We have found that the overall trend in the rotational energy profiles is set by the combined effects of Pauli repulsion (introducing a barrier around gauche that separates minima at syn and anti), orbital interactions (which can pull the anti minimum towards anticlinal to maximize hyperconjugation), and electrostatic interactions. Only for X = F, not for X = Cl–I, electrostatic interactions push the preference from syn to anti. Our bonding analyses show how this trend is related to the compact nature of F versus the more diffuse nature of the heavier halogens. [ABSTRACT FROM AUTHOR]

Chemical reactions are ubiquitous in the universe, they are at the core of life, and they are essential for industrial processes. The drive for a deep understanding of how something occurs, in this case, the mechanism of a chemical reaction and the factors controlling its reactivity, is intrinsically valuable and an innate quality of humans. The level of insight and degree of understanding afforded by computational chemistry cannot be understated. The activation strain model is one of the most powerful tools in our arsenal to obtain unparalleled insight into reactivity. The relative energy of interacting reactants is evaluated along a reaction energy profile and related to the rigidity of the reactants' molecular structure and the strength of the stabilizing interactions between the deformed reactants: ΔE(ζ) = ΔEstrain(ζ) + ΔEint(ζ). Owing to the connectedness between the activation strain model and Kohn–Sham molecular orbital theory, one is able to obtain a causal relationship between both the sterics and electronics of the reactants and their mutual reactivity. Only when this is accomplished one can eclipse the phenomenological explanations that are commonplace in the literature and textbooks and begin to rationally tune and optimize chemical transformations. We showcase how the activation strain model is the ideal tool to elucidate fundamental organic reactions, the activation of small molecules by metallylenes, and the cycloaddition reactivity of cyclic diene- and dipolarophiles. [ABSTRACT FROM AUTHOR]

A new line list for rovibrational and rotational transitions, including fine structure, within the NH X³Σ - ground state has been created. It contains line intensities in the form of Einstein A and fvalues, for all possible bands up to v' = 6, and for J up to between 25 and 44. The intensities are based on a new dipole moment function (DMF), which has been calculated using the internally contracted multi-reference configuration interaction method with an aug-cc-pV6Z basis set. The programs RKR1, LEVEL, and PGOPHER were used to calculate line positions and intensities using the most recent spectroscopic line position observations and the new DMF, including the rotational dependence on the matrix elements. The Hund's case (b) matrix elements from the LEVEL output (available as Supplement 1 of the supplementary material) have been transformed to the case (a) form required by PGOPHER. New relative intensities for the (1,0) band have been measured, and the calculated and observed Herman-Wallis effects are compared, showing good agreement. The line list (see Supplement 5 of the supplementary material) will be useful for the study of NH in astronomy, cold and ultracold molecular systems, and in the nitrogen chemistry of combustion. [ABSTRACT FROM AUTHOR]

This cartoon represents the situation of glutathione peroxidase, in which the presence of selenium rather than sulfur warrants a significantly faster hydroperoxide reduction along the same mechanistic path. Keywords: activation strain model; density functional theory; glutathione peroxidase; reaction mechanisms; selenocysteine EN activation strain model density functional theory glutathione peroxidase reaction mechanisms selenocysteine 520 520 1 04/23/21 20210401 NES 210401 B The Front Cover shows b two lorries along the road directed to "H SB 2 sb O SB 2 sb reduction" destination. Activation strain model, density functional theory, glutathione peroxidase, reaction mechanisms, selenocysteine. [Extracted from the article]

A fundamental and ubiquitous phenomenon in chemistry is the contraction of both C−H and C−C bonds as the carbon atoms involved vary, in s–p hybridization, along sp3 to sp2 to sp. Our quantum chemical bonding analyses based on Kohn–Sham molecular orbital theory show that the generally accepted rationale behind this trend is incorrect. Inspection of the molecular orbitals and their corresponding orbital overlaps reveals that the above‐mentioned shortening in C−H and C−C bonds is not determined by an increasing amount of s‐character at the carbon atom in these bonds. Instead, we establish that this structural trend is caused by a diminishing steric (Pauli) repulsion between substituents around the pertinent carbon atom, as the coordination number decreases along sp3 to sp2 to sp. [ABSTRACT FROM AUTHOR]

With the development and progress of nanotechnology, major advances have been achieved in the micro/nanoscale motors field. Compared with tubular, wire, and sphere nanomotors, magnetically driven helical micro/nanoscale motors show broad prospects of future biomedical applications, especially in targeted drug delivery, due to their excellent movement performance in low Reynolds numbers fluids. In recent years, many fabrication methods of helical micro‐nano motors have been reported. This review set out to provide a summary of the fabrication of helical micro/nanoscale motors. In addition, the design strategies and further functionalization to achieve targeted drug delivery will be introduced as well. With this, we hope to spur further development of novel helical micro/nanomotors and speed up their clinical translation. [ABSTRACT FROM AUTHOR]

A judiciously oriented external electric field (OEEF) can catalyze a wide range of reactions and can even induce endo/exo stereoselectivity of cycloaddition reactions. The Diels–Alder reaction between cyclopentadiene and maleic anhydride is studied by using quantitative activation strain and Kohn–Sham molecular orbital theory to pinpoint the origin of these catalytic and stereoselective effects. Our quantitative model reveals that an OEEF along the reaction axis induces an enhanced electrostatic and orbital interaction between the reactants, which in turn lowers the reaction barrier. The stronger electrostatic interaction originates from an increased electron density difference between the reactants at the reactive center, and the enhanced orbital interaction arises from the promoted normal electron demand donor–acceptor interaction driven by the OEEF. An OEEF perpendicular to the plane of the reaction axis solely stabilizes the exo pathway of this reaction, whereas the endo pathway remains unaltered and efficiently steers the endo/exo stereoselectivity. The influence of the OEEF on the inverse electron demand Diels–Alder reaction is also investigated; unexpectedly, it inhibits the reaction, as the electric field now suppresses the critical inverse electron demand donor–acceptor interaction. [ABSTRACT FROM AUTHOR]

The selectivity and rate enhancement of bifunctional hydrogen bond donor‐catalyzed Diels–Alder reactions between cyclopentadiene and acrolein were quantum chemically studied using density functional theory in combination with coupled‐cluster theory. (Thio)ureas render the studied Diels–Alder cycloaddition reactions exo selective and induce a significant acceleration of this process by lowering the reaction barrier by up to 7 kcal mol−1. Our activation strain and Kohn–Sham molecular orbital analyses uncover that these organocatalysts enhance the Diels–Alder reactivity by reducing the Pauli repulsion between the closed‐shell filled π‐orbitals of the diene and dienophile, by polarizing the π‐orbitals away from the reactive center and not by making the orbital interactions between the reactants stronger. In addition, we establish that the unprecedented exo selectivity of the hydrogen bond donor‐catalyzed Diels–Alder reactions is directly related to the larger degree of asynchronicity along this reaction pathway, which is manifested in a relief of destabilizing activation strain and Pauli repulsion. [ABSTRACT FROM AUTHOR]

The palladium-catalyzed oxidation of glucopyranosides has been investigated using relativistic density functional theory (DFT) at ZORA-BLYP􀀀 D3(BJ)/TZ2P. The complete Gibbs free energy profiles for the oxidation of secondary hydroxy groups at C2, C3, and C4 were computed for methyl β-glucoside and methyl carba-β-glucoside. Both computations and oxidation experiments on carba-glucosides demonstrate the crucial role of the ring oxygen in the C3 regioselectivity observed during the oxidation of glucosides. Analysis of the model systems for oxidized methyl β-glucoside shows that the C3 oxidation product is intrinsically favored in the presence of the ring oxygen. Subsequent energy decomposition analysis (EDA) and Hirschfeld charge analysis reveal the role of the ring oxygen: it positively polarizes C1/C5 by inductive effects and disfavors any subsequent buildup of positive charge at neighboring carbon atoms, rendering C3 the most favored site for the β-hydride elimination. [ABSTRACT FROM AUTHOR]

Additive manufacturing, known as 3D printing, has been widely applied in various fields owing to the development of 3D printing materials and 3D printing techniques. Compared with other fabrication approaches, 3D printing possesses the advantages of high resolution, high accuracy, unique customizability, and repeatability. Therefore, 3D printing can be widely used to fabricate various microstructures, including micromotors, which are capable of converting external energies into motion and subsequently accomplishing various functions. To date, five types of 3D printing techniques have been used to fabricate self‐propelled micromotors with different structures, ingredients, and functions. This progress report summarizes 3D printing techniques for the fabrication of micromotors and introduces the potential biomedical applications of 3D printed micromotors. The advantages and disadvantages of each typical 3D printing method are discussed as well. [ABSTRACT FROM AUTHOR]

Background Drug mass spectrometry imaging (MSI) data contain knowledge about drug and several other molecular ions present in a biological sample. However, a proper approach to fully explore the potential of such type of data is still missing. Therefore, a computational pipeline that combines different spatial and non-spatial methods is proposed to link the observed drug distribution profile with tumor heterogeneity in solid tumor. Our data analysis steps include pre-processing of MSI data, cluster analysis, drug local indicators of spatial association (LISA) map, and ions selection. Results The number of clusters identified from different tumor tissues. The spatial homogeneity of the individual cluster was measured using a modified version of our drug homogeneity method. The clustered image and drug LISA map were simultaneously analyzed to link identified clusters with observed drug distribution profile. Finally, ions selection was performed using the spatially aware method. Conclusions In this paper, we have shown an approach to correlate the drug distribution with spatial heterogeneity in untargeted MSI data. Our approach is freely available in an R package 'CorrDrugTumorMSI'. [ABSTRACT FROM AUTHOR]

The biocompatible, injectable and high water-swollen nature of hydrogels makes them a popular candidate to imitate the extracellular matrix (ECM) for tissue engineering both in vitro and in vivo. However, commonly used covalently cross-linked hydrogels, despite their stability and tunability, are elastic and deteriorate as bulk material degrades which would impair proper cell function. To improve these deficiencies, here, we present a self-recovering cross-linked hydrogel formed instantaneously with functionalized poly(ethylene glycol) as a basis. We combine covalent cross-links introduced via a strain-promoted azide–alkyne cycloaddition (SPAAC) click reaction and non-covalent links between phosphonate groups and calcium ions. By adjusting the ratios of non-covalent and covalent cross-links, we synthesized these dual cross-linked (DC) hydrogels that displayed storage moduli below ∼2000 Pa and relaxation times from seconds to minutes. The gels recovered to 41–96% of their initial mechanical properties after two subsequent strain failures. Cryo-scanning electron microscopy revealed that DC hydrogels containing approximately equal amounts of covalent and non-covalent cross-links displayed phase separation. Finally, we functionalized the DC hydrogels by incorporating an integrin binding motif, RGDS, to provide a biocompatible environment for human mesenchymal stem cells (HMSCs) by facilitating adhesion inside the gel network. Inside these DC gels HSMCs displayed a viability up to 73% after five days of cell culture. [ABSTRACT FROM AUTHOR]

Highly efficient and versatile natural motors play a pivotal role in biological processes. Inspired by these biological motors, researchers developed their synthetic counterparts that can convert various energies into locomotion. With the potential to revolutionize the biomedical treatment process, these micro/nanomotors have been attracting a booming research enthusiasm since the birth of the first micro/nanomotor 15 years ago (since 2004). First, typical motion mechanisms are elucidated and a detailed comparison is provided regarding their efficiency in a biological context. Next, cutting‐edge proof‐of‐concept biomedical applications of the motors are overviewed, including on‐demand drug dispensing, cell transporting, and precise microsurgery. Current achievements and remaining bottlenecks are discussed, to spur more collaboration among chemistry, nanoengineering, and the biomedical fields. With increasing attention and continuing innovation of the field, clinical translation of micro/nanomotors is possible in the next 15 years. [ABSTRACT FROM AUTHOR]

A correction to the article "Ab Initio Potential Energy Surfaces for NH3 - NH3 with Analytical Long Range" in the December 10, 2009 issue is presented.

Electric field-enhanced emission of electrons from a deep level defect in GaN grown by hydride vapor phase epitaxy has been studied. Using the field dependent mode of conventional deep level transient spectroscopy (DLTS), several frequency scans were performed keeping applied electric field (12.8-31.4 MV/m) and sample temperature (300-360 K) constant. Arrhenius plots of the resultant data yielded an activation energy of the electron trap E ranging from Ec-0.48±0.02 eV to Ec-0.35±0.02 eV, respectively. The extrapolation of the as-measured field dependent data (activation energy) revealed the zero-field emission energy (pure thermal activation energy) of the trap to be 0.55±0.02 eV. Various theoretical models were applied to justify the field-enhanced emission of the carriers from the trap. Eventually it was found that the Poole-Frenkel model associated with a square well potential of radius r=4.8 nm was consistent with the experimental data, and, as a result, the trap is attributed to a charged impurity. Earlier, qualitative measurements like current-voltage (I-V) and capacitance-voltage (C-V) measurements were performed, and screening parameters of the device were extracted to ascertain the reliability of DLTS data. [ABSTRACT FROM AUTHOR]

We present four-dimensional ab initio potential energy surfaces for the three different spin states of the NH(3Σ-)–NH(3Σ-) complex. The potentials are partially based on the work of Dhont et al. [J. Chem. Phys. 123, 184302 (2005)]. The surface for the quintet state is obtained at the RCCSD(T)/augmented correlation-consistent polarized valence triple-zeta (aug-cc-pVTZ) level of theory and the energy differences with the singlet and triplet states are calculated at the complete active space with nth-order perturbation theory/aug-cc-pVTZ (n=2,3) level of theory. The ab initio potentials are fitted to coupled spherical harmonics in the angular coordinates, and the long range is further expanded as a power series in 1/R. The RCCSD(T) potential is corrected for a size-consistency error of about 0.5×10-6 Eh prior to fitting. The long-range coefficients obtained from the fit are found to be in good agreement with first and second-order perturbation theory calculations. [ABSTRACT FROM AUTHOR]

In this study, we have employed infrared (IR) absorption spectroscopy, visible Raman spectroscopy, and x-ray absorption near edge structure (XANES) to quantify the hydrogen (H) content in hydrogenated amorphous carbon (a-C:H) films. a-C:H films with a hydrogen content varying from 29 to 47 at. % have been synthesized by electron cyclotron resonance chemical vapor deposition at low substrate temperatures (<120 °C) applying a wide range of bias voltage, Vb, (-300 Vb<＋100 V). With the application of high negative Vb, the a-C:H films undergo a dehydrogenation process accompanied by a sharp structural modification from polymer- to fullerenelike films. The trend in the H content derived from elastic recoil detection analysis (ERDA) is quantitatively reproduced from the intensity of the C–H bands and states in the IR and XANES spectra, respectively, as well as from the photoluminescence (PL) background drop in the Raman spectra. Using the H contents obtained by ERDA as reference data, semiquantitative expressions are inferred for the amount of bonded hydrogen as a function of the experimental spectroscopic parameters, i.e., the integrated area of the IR C–H stretching band at about 2900 cm-1, the PL background in visible Raman spectra, and the XANES intensity of the σ*-CH peak. [ABSTRACT FROM AUTHOR]

This work describes the composition and bonding structure of hydrogenated carbon nitride (a-CNx:H) films synthesized by electron cyclotron resonance chemical vapor deposition using as precursor gases argon, methane, and nitrogen. The composition of the films was derived from Rutherford backscattering and elastic recoil detection analysis and the bonding structure was examined by infrared (IR) spectroscopy and x-ray absorption near edge spectroscopy (XANES). By varying the nitrogen to methane ratio in the applied gas mixture, polymeric a-CNx:H films with N/C contents varying from 0.06 to 0.49 were obtained. Remarkably, the H content of the films (∼40 at. %) was rather unaffected by the nitrogenation process. The different bonding states as detected in the measured XANES C(1s) and N(1s) spectra have been correlated with those of a large number of reference samples. The XANES and IR spectroscopy results indicate that N atoms are efficiently incorporated into the amorphous carbon network and can be found in different bonding environments, such as pyridinelike, graphitelike, nitrilelike, and amino groups. The nitrogenation of the films results in the formation of N-H bonding environments at the cost of C-H structures. Also, the insertion of N induces a higher fraction of double bonds in the structure at the expense of the linear polymerlike chains, hence resulting in a more cross-linked solid. The formation of double bonds takes place through complex C=N structures and not by formation of graphitic aromatic rings. Also, the mechanical and tribological properties (hardness, friction, and wear) of the films have been studied as a function of the nitrogen content. Despite the major modifications in the bonding structure with nitrogen uptake, no significant changes in these properties are observed. [ABSTRACT FROM AUTHOR]

Ultraviolet photodissociation of SH (X 2Π, υ″=2–7) and SD (X 2Π, υ″=3–7) has been studied at 288 and 291 nm, using the velocity map imaging technique to probe the angular and speed distributions of the S(1D2) products. Photodissociation cross sections for the A 2Σ+←X 2Π(υ″) and 2Δ←X 2Π(υ″) transitions have been obtained by ab initio calculations at the CASSCF-MRSDCI/aug-cc-pV5Z level of theory. Both the experimental and theoretical results show that SH/SD photodissociation from X 2Π (υ″<=7) proceeds via the repulsive wall of the A 2Σ+ state. The angular distributions of S(1D2) indicate that the dissociation approaches the sudden recoil limit of the A 2Σ+ state, yielding strongly polarized fragments. The S(1D2) atoms are predominantly produced with total electronic angular momentum perpendicular to the recoil axis. [ABSTRACT FROM AUTHOR]

We present the ab initio potential-energy surfaces of the NH–NH complex that correlate with two NH molecules in their 3Σ- electronic ground state. Three distinct potential-energy surfaces, split by exchange interactions, correspond to the coupling of the SA=1 and SB=1 electronic spins of the monomers to dimer states with S=0, 1, and 2. Exploratory calculations on the quintet (S=2), triplet (S=1), and singlet (S=0) states and their exchange splittings were performed with the valence bond self-consistent-field method that explicitly accounts for the nonorthogonality of the orbitals on different monomers. The potential surface of the quintet state, which can be described by a single Slater determinant reference function, was calculated at the coupled cluster level with single and double excitations and noniterative treatment of the triples. The triplet and singlet states require multiconfiguration reference wave functions and the exchange splittings between the three potential surfaces were calculated with the complete active space self-consistent-field method supplemented with perturbative configuration interaction calculations of second and third orders. Full potential-energy surfaces were computed as a function of the four intermolecular Jacobi coordinates, with an aug-cc-pVTZ basis on the N and H atoms and bond functions at the midpoint of the intermolecular vector R. An analytical representation of these potentials was given by expanding their dependence on the molecular orientations in coupled spherical harmonics, and representing the dependence of the expansion coefficients on the intermolecular distance R by the reproducing kernel Hilbert space method. The quintet surface has a van der Waals minimum of depth De=675 cm-1 at Re=6.6a0 for a linear geometry with the two NH electric dipoles aligned. The singlet and triplet surfaces show similar, slightly deeper, van der Waals wells, but when R is decreased the weakly bound NH dimer with S=0 and S=1 converts into the chemically bound N2H2 diimide (also called diazene) molecule with only a small energy barrier to overcome. [ABSTRACT FROM AUTHOR]

Ca+HCl(υ,j) reactive collisions were studied for different rovibrational states of the HCl reactant using wave-packet calculations in reactant Jacobi coordinates. A recently proposed potential-energy surface was used with a barrier of ≈0.4 eV followed by a deep well. The possibility of an insertion mechanism due to this last well has been analyzed and it was found that once the wave packet passes over the barrier most of it goes directly to CaCl+H products, which shows that the reaction dynamics is essentially direct. It was also found that there is no significant change in the reaction efficiency as a function of the initial HCl rovibrational state, because CaHCl at the barrier has an only little elongated HCl bond. Near the threshold for reaction with HCl(υ=0), however, the reaction shows significant steric effects for j>0. In a complementary study, the infrared excitation from the Ca–HCl van der Waals well was simulated. The spectrum thus obtained shows several series of resonances which correspond to quasibound states correlating to excited HCl(υ) vibrations. The Ca–HCl binding energies of these quasibound states increase dramatically with υ, from 75 to 650 cm-1, because the wave function spreads increasingly over larger HCl bond lengths. Thus it explores the region of the barrier saddle point and the deep insertion well. Although also the charge-transfer contribution increases with υ, the reaction probability for resonances of the υ=2 manifold, which are well above the reaction threshold, is still negligible. This explains the relatively long lifetimes of these υ=2 resonances. The reaction probability becomes significant at υ=3. Our simulations have shown that an experimental study of this type will allow a gradual spectroscopic probing of the barrier for the reaction. [ABSTRACT FROM AUTHOR]

The potential-energy surface of the ground electronic state of CaHCl has been obtained from 6400 ab initio points calculated at the multireference configuration-interaction level and represented by a global analytical fit. The Ca+HCl→CaCl+H reaction is endothermic by 5100 cm-1 with a barrier of 4470 cm-1 at bent geometry, taking the zero energy in the Ca+HCl asymptote. On both sides of this barrier are potential wells at linear geometries, a shallow one due to van der Waals interactions in the entrance channel, and a deep one attributed to the H-Ca++Cl- ionic configuration. The accuracy of the van der Waals well depth, ≈200 cm-1, was checked by means of additional calculations at the coupled-cluster singles and doubles with perturbative triples level and it was concluded that previous empirical estimates are unrealistic. Also, the electric dipole function was calculated, analytically fitted in the regions of the two wells, and used to analyze the charge shifts along the reaction path. In the insertion well, 16 800 cm-1 deep, the electric dipole function confirmed the ionic structure of the HCaCl complex and served to estimate effective atomic charges. Finally, bound rovibrational levels were computed both in the van der Waals well and in the insertion well, and the infrared-absorption spectrum of the insertion complex was simulated in order to facilitate its detection. [ABSTRACT FROM AUTHOR]

Micro and nanomotors (MNMs) are micro/nanoscale devices that are able to convert chemical or external energy into mechanical motion. Based on a multitude of propulsion mechanisms, synthetic MNMs have been developed over the past decades for diverse biomedical applications, particularly drug delivery. Herein, we set out the classification of drugs delivered by MNMs, such as small molecules, nucleic acid, peptides, antibodies, and other proteins, and discuss their current limitations and possibilities in in vivo applications. Challenges and future perspectives are also discussed. With the increasing research enthusiasm in this field and the strengthening of multidisciplinary cooperation, intelligent MNMs will appear in the near future, which will have a profound impact on all related fields. [ABSTRACT FROM AUTHOR]

There are many efficient biological motors in Nature that perform complex functions by converting chemical energy into mechanical motion. Inspired by this, the development of their synthetic counterparts has aroused tremendous research interest in the past decade. Among these man‐made motor systems, the fuel‐free (or light, magnet, ultrasound, or electric field driven) motors are advantageous in terms of controllability, lifespan, and biocompatibility concerning bioapplications, when compared with their chemically powered counterparts. Therefore, this review will highlight the latest biomedical applications in the versatile field of externally propelled micro‐/nanomotors, as well as elucidating their driving mechanisms. A perspective into the future of the micro‐/nanomotors field and a discussion of the challenges we need to face along the road towards practical clinical translation of external‐field‐propelled micro‐/nanomotors will be provided. [ABSTRACT FROM AUTHOR]

Delicate molecular and biological motors are tiny machines capable of achieving numerous vital tasks in biological processes. To gain a deeper understanding of their mechanism of motion, researchers from multiple backgrounds have designed and fabricated artificial micro‐ and nanomotors. These nano‐/microscale motors can self‐propel in solution by exploiting different sources of energy; thus showing tremendous potential in widespread applications. As one of the most common motor systems, Janus motors possess unique asymmetric structures and integrate different functional materials onto two sides. This review mainly focuses on the fabrication of different types of micro‐ and nanomotors based on Janus structures. Furthermore, some challenges still exist in the implementation of Janus motors in the biomedical field. With such common goals in mind, it is expected that the elaborate and multifunctional design of Janus motors will overcome their challenges in the near future. [ABSTRACT FROM AUTHOR]

We aim at developing design principles, based on quantum chemical analyses, for a novel type of iron-based catalysts that mimic the behavior of their well-known palladium analogs in the bond activation step of cross coupling reactions. To this end, we have systematically explored C–X bond activation via oxidative addition of CH3X substrates (X = H, Cl, CH3) to model catalysts mFe(CO)4q (q = 0, −2; m = singlet, triplet) and, for comparison, Pd(PH3)2 and Pd(CO)2, using relativistic density functional theory at the ZORA-OPBE/TZ2P level. We find that the neutral singlet iron catalyst 1Fe(CO)4 activates all three C–X bonds via barriers that are lower than those for Pd(PH3)2 and Pd(CO)2. This is a direct consequence of the capability of the iron complex to engage not only in π-backdonation, but also in comparably strong σ-donation. Interestingly, whereas the palladium complexes favor C–Cl activation, 1Fe(CO)4 shows a strong preference for activating the C–H bond, with a barrier as low as 10.4 kcal mol−1. Our results suggest a high potential for iron to feature in palladium-type cross-coupling reactions. [ABSTRACT FROM AUTHOR]

This is an exploratory study aimed at translating concepts developed in the frame of commercial entrepreneurship studies to the university setting. Analogy is used in a particular manner that is to look for structural similarities between commercial entrepreneurship and the way knowledge is created and organized. The first step is to introduce the notion of academic opportunity. This becomes the basis for opening up a new perspective by introducing a new discourse in the practice of entrepreneurship, the academic discourse. The next step is to discuss the role of academic networks and their possible connections with the network approach in the business formation. The final part of the article contains three examples illustrating the notions introduced and discussed in the previous sections. [ABSTRACT FROM AUTHOR]

Chalcogen–π interactions occur between a covalently bound chalcogen atom that enters into a non-covalent interaction with an unsaturated moiety, a bonding motif found in various structures, such as, proteins. In this work, we have systematically explored and analyzed chalcogen–π interactions in model systems X2D…A (with D = O, S, Se, Te; X = halogen; A = acetylene, ethylene and 2-butyne), using relativistic density functional theory (DFT). The nature and trends in stability of the chalcogen–π bonds are analyzed and interpreted in terms of quantitative MO theory in combination with a matching canonical energy decomposition analysis (EDA) scheme. We find that chalcogen–π bonds increase in strength as the X–D electronegativity difference becomes greater. Moreover, 2-butyne was found to participate in the strongest non-covalent interaction due to enhanced orbital interactions. [ABSTRACT FROM AUTHOR]

The reactivity of diselenides and ditellurides of general formula (RX)2 (X = Se, Te; R = H, CH3, Ph) toward hydrogen peroxide was studied through a computational approach based on accurate Density Functional Theory (DFT) calculations. The aliphatic and aromatic dichalcogenides have been chosen in light of their activity in glutathione peroxidase (GPx)-like catalytic cycles and their promising features as efficient antioxidant compounds. The reaction products, the energetics and the mechanistic details of these oxidations are discussed. Analogous disulfides are included in our analysis for completeness. We find that the barrier for oxidation of dichalcogenides decreases from disulfides to diselenides to ditellurides. On the other hand, variation of the substituents at the chalcogen nucleus has relatively little effect on the reactivity. [ABSTRACT FROM AUTHOR]

Non-collinear spin states with unique rotational sense, such as chiral spin-spirals, are recently heavily investigated because of advantages for future applications in spintronics and information technology and as potential hosts for Majorana Fermions when coupled to a super-conductor. Tuning the properties of such spin states, e.g., the rotational period and sense, is a highly desirable yet difficult task. Here, we experimentally demonstrate the bottom-up assembly of a spin-spiral derived from a chain of iron atoms on a platinum substrate using the magnetic tip of a scanning tunneling microscope as a tool. We show that the spin-spiral is induced by the interplay of the Heisenberg and Dzyaloshinskii-Moriya components of the Ruderman-Kittel-Kasuya-Yosida interaction between the iron atoms. The relative strengths and signs of these two components can be adjusted by the interatomic iron distance, which enables tailoring of the rotational period and sense of the spin-spiral. [ABSTRACT FROM AUTHOR]