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Hydroxylation is an effective approach for the synthesis of carbon-oxygen bonds and allylic ethers. The [NHC]Au(I) catalyzed intermolecular hydroalkoxylation of allene was studied at the DFT and Coupled Cluster level of theory. Using the Unified Reaction Valley Approach (URVA), we carry out a comprehensive mechanistic analysis of [NHC]Au(I)-catalyzed and noncatalyzed reactions. The URVA study of several possible reaction pathways reveal that the [NHC]Au(I) catalyst enables the hydroalkoxylation reaction to occur via a two step mechanism based upon the Au ability to switch between π- and σ-complexation. The first step of the mechanism involves the formation of a CO bond after the transition state with no energy penalty. Following the CO bond breakage, the OH bond breaks and CH bond forms during the second step of the mechanism, as the catalyst transforms into the more stable π-Au complex. The URVA results were complemented with local vibrational mode analysis to provide measures of intrinsic bond strength for Au(I)-allene interactions of all stationary points, and NBO analysis was applied in order to observe charge transfer events along the reaction pathway. Overall, the π-Au C═C interactions of the products are stronger than those of the reactants adding to their exothermicity. Our work on the hydroxylation of allene provides new insights for the design of effective reaction pathways to produce allylic ethers and also unravels new strategies to form C-O bonds by activation of C═C bonds.

We evaluate the correlation between binding energy (BE) and electron density ρ(r) at the bond critical point for 28 neutral hydrogen bonds, recently reported by Emamian and co-workers (J. Comput. Chem., 2019, 40, 2868). As an efficient tool, we use local stretching force constant kHBa derived from the local vibrational mode theory of Konkoli and Cremer. We compare the physical nature of BE versus kHBa , and provide an important explanation for cases with significant deviation in the BE- kHBa relation as well as in the BE-ρ(r) correlation. We also show that care has to be taken when different hydrogen bond strength measures are compared. The BE is a cumulative hydrogen bond strength measure while kHBa is a local measure of hydrogen bond strength covering different aspects of bonding. A simplified and unified description of hydrogen bonding is not always possible and needs an in-depth understanding of the systems involved.

A chelation-assisted selective etching (CASE) strategy is developed to construct a hierarchical polyoxometalate-based metal–organic framework (POM@MOF). The selected chelator, ethylenediaminetetraa...

A synthetic heavier p-block bismuth (Bi) complex with a rigid pincer ligand, is shown to be a Bi-based molecular electrocatalyst for proton reduction under weak acid conditions. High activity of the complex is observed in catalysis, with a icat/ip value of 95 with CH3CO2H. Experimental and theoretical studies indicate that the hydrogen evolution reaction (HER) mechanism involves generating a low-valent BiI complex and its reactivity toward acid to form a BiIII-hydride species. Subsequent protonolysis of the BiIII-hydride eliminates H2 through a heterolytic route. The HER cycling through the low-valent metal species and its hydride has been proposed previously in transition-metal (TM) centered catalysts but rarely validated in main-group catalytic systems. The finding brings insight into heavier main-group Bi-catalyzed H2 evolution and the role of low-valent main-group metal centre during catalysis.

Electrocatalytic hydrogen evolution reaction (HER) is a critical process in a sustainable energy conversion system. Many metal complexes as small-molecule catalysts for electrochemical H2 evolution have been reported over recent decades, which have made a great contribution to a detailed understanding of their catalytic mechanisms. In most reported mechanistic pathways, metal hydride species are always considered as key intermediates during H2 formation, with the metal centre at the active site docking both electrons and protons. These metal-centred HER routes need to employ metal ions with open coordination sites, which can accommodate multiple redox states to involve two-electron hydride transfer for H2 production. By comparison, an alternative approach, specifically focusing on redox-active ligand-centred electrocatalytic HER, has garnered increasing attention over the last six years. This review highlights recent progress in metal and metal-free ligand-centred homogeneous electrocatalytic HER since 2012 and discusses it according to two categories: organic ligand-centred and inorganic ligand-centred HER. In addition, some existing issues and suggestions for future directions in this catalytic area have been provided.

We introduce a new software, Efficient Detection of Hydrogen Bonds (EDHB), that systematically detects hydrogen bonds based on the nearest neighbors algorithm. EDHB classifies inter- and intramolecular hydrogen bonds as well as hydrogen bond networks. EDHB outperforms commonly used hydrogen bond detection methods in terms of speed of execution. An important additional feature of EDHB is that information from preceding quantum chemical studies (i.e., natural bond orbital analysis data and second energy derivative information) can be used to determine the electrostatic/covalent character of the hydrogen bonds and to calculate local-mode hydrogen bond force constants as a quantitative measure of their intrinsic strength. We applied EDHB to a diverse set of 163 proteins. We identified hydrogen bond networks forming intramolecular rings of different sizes as a common feature playing an important role for specific secondary structure orientations such as α-helixes and turns. However, these networks do not have a significant influence on the hydrogen bond strength. Our comprehensive local-mode analysis reveals the interesting result that the hydrogen bond angle is the governing factor determining the hydrogen bond strength in a protein. EDHB offers a broad range of application possibilities. In addition to proteins, EDHB can be generally used to detect and characterize hydrogen bonds in protein-ligand interactions, water clusters, and other systems where a hydrogen bond plays a critical role, as well as during molecular dynamics simulations. The program is freely available at https://github.com/ekraka/EDHB.

The unified reaction valley approach combined with the local vibrational mode and ring puckering analysis is applied to investigate the hydrogen evolution from water in the presence of small hydrides such as BH3, metal hydrides as AlH3, and their derivatives. We studied a series of reactions involving BH3, AlH3, B2H6, Al2H6, and AlH3BH3 with one- and two-water molecules, considering multiple reaction paths. In addition, the influence of the aqueous medium was examined. A general reaction mechanism was identified for most of the reactions. Those that deviate could be associated with unusually high reaction barriers with no hydrogen release. The charge transfer along the reaction path suggests that a viable hydrogen release is achieved when the catalyst adopts the role of a charge donor during the chemical processes. The puckering analysis showed that twistboat and boat forms are the predominant configurations in the case of an intermediate six-membered ring formation, which influences the activation barrier. The local mode analysis was used as a tool to detect the H-H bond formation as well as to probe catalyst regenerability. Based on the correlation between the activation energy and the change in the charge separation for cleaving O-H and B(Al)-H bonds, two promising subsets of reactions could be identified along with prescriptions for lowering the reaction barrier individually with electron-donating/withdrawing substituents.

Benzene and acetonitrile are two of the most commonly used solvents found in almost every chemical laboratory. Titan is one other place in the solar system that has large amounts of these compounds. On Titan, organic molecules are produced in the atmosphere and carried to the surface where they can mineralize. Here, we report the phase diagram of mixtures of acetonitrile and benzene, and provide an account of the structure and composition of the phases. To mimic the environment on Titan more accurately, we tested the stability of the structure under liquid ethane. The results provide new insights into the structure and stability of potential extraterrestrial minerals. In light of Dragonfly, NASA's upcoming mission to Titan, revisiting the fundamental chemistry of the smallest molecules with modern methods and techniques can have significant contributions to this epochal mission and can open new research directions in chemistry.

Seventeen singlet excited states of ethylene have been calculated via time-dependent density functional theory (TDDFT) with the CAM-B3LYP functional and the geometries of 11 excited states were optimized successfully. The local vibrational mode theory was employed to examine the intrinsic C=C/C&ndash, H bond strengths and their change upon excitation. The natural transition orbital (NTO) analysis was used to further analyze the C=C/C&ndash, H bond strength change in excited states versus the ground state. For the first time, three excited states including &pi, y&prime, &rarr, 3s, &pi, 3py and &pi, 3pz were identified with stronger C=C ethylene double bonds than in the ground state.

11 aryl&ndash, lone pair and three aryl&ndash, anion &pi, &ndash, hole interactions are investigated, along with the argon&ndash, benzene dimer and water dimer as reference compounds, utilizing the local vibrational mode theory, originally introduced by Konkoli and Cremer, to quantify the strength of the &pi, hole interaction in terms of a new local vibrational mode stretching force constant between the two engaged monomers, which can be conveniently used to compare different &pi, hole systems. Several factors have emerged which influence strength of the &pi, hole interactions, including aryl substituent effects, the chemical nature of atoms composing the aryl rings/ &pi, hole acceptors, and secondary bonding interactions between donors/acceptors. Substituent effects indirectly affect the &pi, hole interaction strength, where electronegative aryl-substituents moderately increase &pi, hole interaction strength. N-aryl members significantly increase &pi, hole interaction strength, and anion acceptors bind more strongly with the &pi, hole compared to charge neutral acceptors (lone&ndash, pair donors). Secondary bonding interactions between the acceptor and the atoms in the aryl ring can increase &pi, hole interaction strength, while hydrogen bonding between the &pi, hole acceptor/donor can significantly increase or decrease strength of the &pi, hole interaction depending on the directionality of hydrogen bond donation. Work is in progress expanding this research on aryl &pi, hole interactions to a large number of systems, including halides, CO, and OCH3- as acceptors, in order to derive a general design protocol for new members of this interesting class of compounds.

Visualizing vibrational motions calculated with different ab initio packages requires dedicated post-processing tools. Here, we present a PyMOL plugin called PyVibMS for visualizing the vibrational motions for both molecular and solid systems calculated by mainstream quantum chemical computer programs including Gaussian, Q-Chem, VASP, and CRYSTAL. Benefiting from the continuing development of the PyMOL platform, PyVibMS provides powerful functionalities and user-friendly interface. PyVibMS was written in Python and its open-source nature makes it flexible and sustainable. As an example, the motions of the Konkoli-Cremer local vibrational modes are shown in this work for the first time. PyVibMS is freely available at https://github.com/smutao/PyVibMS . Graphical abstract In this work, a PyMOL plugin named PyVibMS is developed to visualize molecular and lattice vibrations.

The unified reaction valley approach (URVA) differs from mainstream mechanistic studies, as it describes a chemical reaction via the reaction path and the surrounding reaction valley on the potential energy surface from the van der Waals region to the transition state and far out into the exit channel, where the products are located. The key feature of URVA is the focus on the curving of the reaction path. Moving along the reaction path, any electronic structure change of the reacting molecules is registered by a change in their normal vibrational modes and their coupling with the path, which recovers the curvature of the reaction path. This leads to a unique curvature profile for each chemical reaction with curvature minima reflecting minimal change and curvature maxima, the location of important chemical events such as bond breaking/forming, charge polarization and transfer, rehybridization, etc. A unique decomposition of the path curvature into internal coordinate components provides comprehensive insights into the origins of the chemical changes taking place. After presenting the theoretical background of URVA, we discuss its application to four diverse catalytic processes: (i) the Rh catalyzed methanol carbonylation&mdash, the Monsanto process, (ii) the Sharpless epoxidation of allylic alcohols&mdash, transition to heterogenous catalysis, (iii) Au(I) assisted [3,3]-sigmatropic rearrangement of allyl acetate, and (iv) the Bacillus subtilis chorismate mutase catalyzed Claisen rearrangement&mdash, and show how URVA leads to a new protocol for fine-tuning of existing catalysts and the design of new efficient and eco-friendly catalysts. At the end of this article the pURVA software is introduced. The overall goal of this article is to introduce to the chemical community a new protocol for fine-tuning existing catalytic reactions while aiding in the design of modern and environmentally friendly catalysts.

The conformational properties of ring compounds such as cycloalkanes determine to a large extent their stability and reactivity. Therefore, the investigation of conformational processes such as ring inversion and/or ring pseudorotation has attracted a lot of attention over the past decades. An in-depth conformational analysis of ring compounds requires mapping the relevant parts of the conformational energy surface at stationary and also at non-stationary points. However, the latter is not feasible by a description of the ring with Cartesian or internal coordinates. We provide in this work, a solution to this problem by introducing a new coordinate system based on the Cremer–Pople puckering and deformation coordinates. Furthermore, analytic first- and second-order derivatives of puckering and deformation coordinates, i.e., B-matrices and D-tensors, were developed simplifying geometry optimization and frequency calculations. The new coordinate system is applied to map the potential energy surfaces and reaction paths of cycloheptane (C7H14), cyclooctane (C8H16), and cyclo[18]carbon (C18) at the quantum chemical level and to determine for the first time all stationary points of these ring compounds in a systematic way.

The synthesis and structure of a giant 102-silver-atom nanocluster (NC) 1 is presented. X-ray structural analysis reveals that 1 features a multi-shelled metallic core of Ag6 @Ag24 @Ag60 @Ag12 . An octahedral Ag6 core is encaged by a truncated octahedral Ag24 shell. The Ag24 shell is composed of a hitherto unknown sodalite-type silver orthophosphate cluster (SOC) {(Ag3 PO4 )8 }, reminiscent of the Ag3 PO4 photocatalyst. The SOC is capped by six interstitial sulfur atoms, giving a unique anionic cluster [Ag6 @{(Ag3 PO4 )8 }S6 ]6- , which functions as an intricate polyhedral template with abundant surface O and S atoms guiding the formation of a rare rhombicosidodecahedral Ag60 shell. An array of 6 linear Ag2 staples further surround this Ag60 shell. [Ag6 @{(Ag3 PO4 )8 }S6 ]6- is an unusual Ag-based templating anion to induce the assembly of a SOC within silver NC. This finding provides molecular models for bulk Ag3 PO4 , and offers a fresh template strategy for the synthesis of silver NCs with high symmetry.

Periodic local vibrational modes were calculated with the rev-vdW-DF2 density functional to quantify the intrinsic strength of the X-I⋯OA-type halogen bonding (X = I or Cl, OA: carbonyl, ether and N-oxide groups) in 32 model systems originating from 20 molecular crystals. We found that the halogen bonding between the donor dihalogen X-I and the wide collection of acceptor molecules OA features considerable variations of the local stretching force constants (0.1&ndash, 0.8 mdyn/&Aring, ) for I⋯O halogen bonds, demonstrating its powerful tunability in bond strength. Strong correlations between bond length and local stretching force constant were observed in crystals for both the donor X-I bonds and I⋯O halogen bonds, extending for the first time the generalized Badger&rsquo, s rule to crystals. It is demonstrated that the halogen atom X controlling the electrostatic attraction between the &sigma, hole on atom I and the acceptor atom O dominates the intrinsic strength of I⋯O halogen bonds. Different oxygen-containing acceptor molecules OA and even subtle changes induced by substituents can tweak the n &rarr, &sigma, &lowast, (X-I) charge transfer character, which is the second important factor determining the I⋯O bond strength. In addition, the presence of the second halogen bond with atom X of the donor X-I bond in crystals can substantially weaken the target I⋯O halogen bond. In summary, this study performing the in situ measurement of halogen bonding strength in crystalline structures demonstrates the vast potential of the periodic local vibrational mode theory for characterizing and understanding non-covalent interactions in materials.

The Bacillus subtilis chorismate mutase catalysed Claisen rearrangement of chorismate to prephenate is one of the few pericyclic processes in biology, and as such provides a rare opportunity for un...

Using catastrophe theory and the concept of a mutation path, an algorithm is developed that leads to the direct correlation of the normal vibrational modes of two structurally related molecules. The mutation path is defined by weighted incremental changes in mass and geometry of the molecules in question, which are successively applied to mutate a molecule into a structurally related molecule and thus continuously converting their normal vibrational spectra from one into the other. Correlation diagrams are generated that accurately relate the normal vibrational modes to each other by utilizing mode-mode overlap criteria and resolving allowed and avoided crossings of vibrational eigenstates. The limitations of normal mode correlation, however, foster the correlation of local vibrational modes, which offer a novel vibrational measure of similarity. It will be shown how this will open new avenues for chemical studies. © 2017 Wiley Periodicals, Inc.

Theoretical studies of hydrogen-bonding based on cluster models tend to overlook the peripheral monomers which are influential. By revisiting thirteen hydrogen-bonded complexes of H2O, HF and NH3, the “push-pull” effect is identified as a general mechanism that strengthens a hydrogen bond. Enhanced Lp ( X ) → σ ∗ ( X ′ - H ) charge transfer is proved to be the core of the “push-pull” effect. The charge transfer can convert an electrostatic hydrogen bond into a covalent hydrogen bond.

In the modeling of spin-crossing reactions, it has become popular to directly explore the spin-adiabatic surfaces. Specifically, through constructing spin-adiabatic states from a two-state Hamiltonian (with spin-orbit coupling matrix elements) at each geometry, one can readily employ advanced geometry optimization algorithms to acquire a “transition state" structure, where the spin crossing occurs. In this work, we report the implementation of a fully variational spin-adiabatic approach based on Kohn-Sham density functional theory spin states (sharing the same set of molecular orbitals) and the Breit-Pauli one-electron spin-orbit operator. For three model spin-crossing reactions [predissociation of N2O, singlet-triplet conversion in CH2, and CO association to Fe(CO)4], the spin-crossing points were easily obtained. Our results also indicated the Breit-Pauli one-electron spin-orbit coupling can vary significantly along the reaction pathway on the spin-adiabatic energy surface. On the other hand, due to the restriction that low-spin and high-spin states share the same set of molecular orbitals, the acquired spin-adiabatic energy surface shows a cusp (i.e. a first-order discontinuity) at the crossing point, which prevents the use of standard geometry optimization algorithms to pinpoint the crossing point. An extension with this restriction removed is being developed to achieve the smoothness of spin-adiabatic surfaces.

Molecular acidity is an important physicochemical property, which is often represented by the pKa value as the measure of acidity strength. However, the accurate calculation and prediction of pKa values is still an unsolved problem for computational chemistry. In this work, we present for the first time a direct correlation between pKa values and local vibrational frequencies for 15 different groups of compounds with various substituents. This correlation was derived from a quadratic function of two selected local vibrational frequencies as independent variables used to characterize electronic structure features influencing the molecular acidity. In total, 180 molecules were investigated with this correlation model. For each group of molecules, we found a strong correlation with root mean squared errors and mean absolute errors of less than 0.11 and 0.09 pKa units, respectively. The correlation between pKa and local vibrational modes, established in this work, can be generally applied to all compounds whose pKa values are dominated by electronic substituent effects. In this regard, the new correlation model constitutes a powerful link between the well-known Hammett equation and vibrational spectroscopy. Furthermore, it allows a quick prediction of the pKa values for new group members with different substituents.

Computational prediction of Protein-Ligand Interaction (PLI) is an important step in the modern drug discovery pipeline as it mitigates the cost, time, and resources required to screen novel therapeutics. Deep Neural Networks (DNN) have recently shown excellent performance in PLI prediction. However, the performance is highly dependent on protein and ligand features utilized for the DNN model. Moreover, in current models, the deciphering of how protein features determine the underlying principles that govern PLI is not trivial. In this work, we developed a DNN framework named SSnet that utilizes secondary structure information of proteins extracted as the curvature and torsion of the protein backbone to predict PLI. We demonstrate the performance of SSnet by comparing against a variety of currently popular machine and non-machine learning models using various metrics. We visualize the intermediate layers of SSnet to show a potential latent space for proteins, in particular to extract structural elements in a protein that the model finds influential for ligand binding, which is one of the key features of SSnet. We observed in our study that SSnet learns information about locations in a protein where a ligand can bind including binding sites, allosteric sites and cryptic sites, regardless of the conformation used. We further observed that SSnet is not biased to any specific molecular interaction and extracts the protein fold information critical for PLI prediction. Our work forms an important gateway to the general exploration of secondary structure based deep learning, which is not just confined to protein-ligand interactions, and as such will have a large impact on protein research while being readily accessible for de novo drug designers as a standalone package.

The properties of liquid water are intimately related to the H-bond network among the individual water molecules. Utilizing vibrational spectroscopy and modeling water with DFT-optimized water clusters (6-mers and 50-mers), 16 out of a possible 36 different types of H-bonds are identified and ordered according to their intrinsic strength. The strongest H-bonds are obtained as a result of a concerted push–pull effect of four peripheral water molecules, which polarize the electron density in a way that supports charge transfer and partial covalent character of the targeted H-bond. For water molecules with tetra- and pentacoordinated O atoms, H-bonding is often associated with a geometrically unfavorable positioning of the acceptor lone pair and donor σ*(OH) orbitals so that electrostatic rather than covalent interactions increasingly dominate H-bonding. There is a striking linear dependence between the intrinsic strength of H-bonding as measured by the local H-bond stretching force constant and the delocali...

The local vibrational mode analysis, originally introduced by Konkoli and Cremer, provides a physically sound platform for a comprehensive analysis of calculated or measured vibrational spectra and for providing detailed insights into chemical bonding and other structural features. In this work, we summarize the essentials of the local vibrational mode theory with a focus on local vibrational force constants and their relationship with compliance and relaxed force constants. Furthermore, we discuss how local vibrational force constants can be used (i) to assess the quality of empirically derived force constants, (ii) to disclose bonding features in large molecules, and (iii) to provide metal ligand force field parameters. Future applications will be suggested.

The ambient solution reaction of silver salt (CF3COOAg) with a heterolytic thiolate gave rise to the isolation of an air-stable sub-nanometer sized hexanuclear silver(I) cluster, Ag6(dmmp)6‧6CH3OH (1, Hdmmp = 4,6-dimethyl-2-mercaptopyrimidine). X-ray single-crystal structural analysis shows that the Ag66+ core in 1 is a distorted octahedron surrounded by six depronated dmmp ligands as protecting units with each through a simple μ3-bridging coordinating motif. The shortest Ag–Ag bond distance of 2.835 A in the Ag66+ unit, suggests a closed shell d10‧‧‧d10 argentophilic interactions. DFT studies indicate that the HOMO in 1 is largely composed of d orbitals of AgI ions, while the LUMO mainly consists of s orbitals of AgI ions and p orbitals of S atoms. Hirshfeld surface analysis was also performed to analyze the nature of intermolecular interactions of 1. Complex 1 shows a yellow emission at λmax = 566 nm in the solid state upon excited at 395 nm and antibacterial activity.

In this contribution, a bisthienyl-substituted Bodipy sensitizer (B1) was synthesized and further axially anchored to one cobalt catalytic center via a pyridyl group located in the 8-position of the B1, affording a new sensitizer-catalyst supramolecular assembly (Co-B1). The supramolecular structure of Co-B1 was determined through single-crystal X-ray diffraction analysis, and showed nearly orthogonal stereochemistry between sensitizer B1 and Co catalyst. Visible light-driven H2-evolution performance of Co-B1 was investigated in aqueous solution with triethylamine (Et3N) as an electron donor, which displayed efficient H2 evolution activity and stability. DFT calculations indicated transition of HOMO → LUMO from the π-conjugated Bodipy B1 anion to the Co fragment is an intramolecular electron-transfer process. Notably, the present artificial photosynthetic system is an example of an absolutely noble-metal free supramolecular system for photochemical H2 generation from water using non-halogenated dye-catalyst assembly.

A computational study of cyclohexane autoxidation and catalytic oxidation to a cyclohexyl hydroperoxide intermediate (CyOOH), cyclohexanol, and cyclohexanone has been conducted using a hybrid density functional theory method. The activation of cyclohexane and O2 is the rate-determining step in the formation of CyOOH due to its relatively high energy barrier of 41.2 kcal/mol, and the subsequent reaction behavior of CyOOH controls whether the production of cyclohexanol or cyclohexanone is favored. Using CH3COOH or (CH3COO)2Co as a catalyst reduces the energy barriers required to activate cyclohexane and O2 by 4.1 or 7.9 kcal/mol, respectively. Employing CH3COOH improves the CyOOH intramolecular dehydration process, which favors the formation of cyclohexanone. The energy barrier to the decomposition of CyOOH to CyO·, an important precursor of cyclohexanol, decreases from 35.5 kcal/mol for autoxidation to 25.9 kcal/mol for (CH3COO)2Co catalysis. (CH3COO)2Co promotes the autoxidation process via a radical chain mechanism. The computational results agree with experimental observations quite well, revealing the underlying role of CH3COOH and Co ion in cyclohexane oxidation.

Inspired by the metal active sites of [NiFeSe]-hydrogenases, a dppf-supported nickel(II) selenolate complex (dppf=1,1'-bis(diphenylphosphino)ferrocene) shows high catalytic activity for electrochemical proton reduction with a remarkable enzyme-like H2 evolution turnover frequency (TOF) of 7838 s-1 under an Ar atmosphere, which markedly surpasses the activity of a dppf-supported nickel(II) thiolate analogue with a low TOF of 600 s-1 . A combined study of electrochemical experiments and DFT calculations shed light on the catalytic process, suggesting that selenium atom as a bio-inspired proton relay plays a key role in proton exchange and enhancing catalytic activity of H2 production. For the first time, this type of Ni selenolate-containing electrocatalyst displays a high degree of O2 and H2 tolerance. Our results should encourage the development of the design of highly efficient oxygen-tolerant Ni selenolate molecular catalysts.

Normal vibrational modes are generally delocalized over the molecular system, which makes it difficult to assign certain vibrations to specific fragments or functional groups. We introduce a new approach, the Generalized Subsystem Vibrational Analysis (GSVA), to extract the intrinsic fragmental vibrations of any fragment/subsystem from the whole system via the evaluation of the corresponding effective Hessian matrix. The retention of the curvature information with regard to the potential energy surface for the effective Hessian matrix endows our approach with a concrete physical basis and enables the normal vibrational modes of different molecular systems to be legitimately comparable. Furthermore, the intrinsic fragmental vibrations act as a new link between the Konkoli–Cremer local vibrational modes and the normal vibrational modes.

This review discusses the occurrence, impact, analysis and treatment of metformin and guanylurea in coastal aquatic environments of Canada, USA and Europe. Metformin, a biguanide in chemical classification, is widely used as one of the most effective first-line oral drugs for type 2 diabetes. It is difficult to be metabolized by the human body and exists in both urine and faeces samples in these regions. Guanylurea is metformin's biotransformation product. Consequently, significant concentrations of metformin and guanylurea have been reported in wastewater treatment plants (WWTPs) and coastal aquatic environments. The maximum concentrations of metformin and guanylurea in surface water samples were as high as 59,000 and 4502ngL-1, respectively. Metformin can be absorbed in non-target organisms by plants and in Atlantic salmon (Salmo salar). Guanylurea has a confirmed mitotic activity in plant cells. Analysis methods of metformin are currently developed based on high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS). The removal of metformin from aquatic environments in the target regions is summarized. The review helps to fill a knowledge gap and provides insights for regulatory considerations. The potential options for managing these emerging pollutants are outlined too.

Reaction of the N-heterocyclic carbene-stabilized phosphinoaminosilylene ArN(SiMe3)Si(I(i)Pr)PPh2 (Ar = 2,6-(i)Pr2C6H3, I(i)Pr = 1,3-diisopropyl-4,5-dimethyl-imidazol-2-ylidene) (2) with dioxygen resulted in the formation of the two products ArN = Si(I(i)Pr)(OSiMe3)(OPPh2) (3) and ArN = Si(I(i)Pr)(OSiMe3)PPh2 (4), and the ratios of the two products can be controlled by the reaction temperatures and dioxygen concentrations.

A novel approach is presented to assess chemical similarity based the local vibrational mode analysis developed by Konkoli and Cremer. The local mode frequency shifts are introduced as similarity descriptors that are sensitive to any electronic structure change. In this work, 59 different monosubstituted benzenes are compared. For a subset of 43 compounds, for which experimental data was available, the ortho-/para- and meta-directing effect in electrophilic aromatic substitution reactions could be correctly reproduced, proving the robustness of the new similarity index. For the remaining 16 compounds, the directing effect was predicted. The new approach is broadly applicable to all compounds for which either experimental or calculated vibrational frequency information is available.

A nickel pyridine-selenolate complex, [Ni(4,4′-dmbpy)(2-pySe)2] (1, where 4,4′-dmbpy = 4,4′-dimethyl-2,2′-bipyridine, and 2-pySe = pyridine-2-selenolate), has been synthesized, and investigated for photocatalytic production of H2 from aqueous solution. Electrochemical studies show that the nickel complex 1 can efficiently electrocatalyze H2 evolution from weakly acidic solutions. Under visible-light irradiation (λ > 420 nm), the complex 1 displays impressive H2 evolution activity with a TON of 1340 (based on a catalyst) in a noble-metal-free system, which contains fluorescein (Fl) as photosensitizer and triethylamine (TEA) as sacrificial electron donor in acetonitrile-water solution. It should be noted that complex 1 is the rare example of nickel pyridine-selenolate complex as molecular photocatalyst for water reduction.