Accurate calculation of the attractive interaction of two ground state helium atoms

The Many-Body Expansion for Metals: II. Nonadditive Terms in Clusters Composed of Metals with ns1, ns2, and ns2p1 Configurations

The many-body expansion (MBE) was applied to homometallic and heterometallic trimers of metals with ns1, ns2, and ns2p1 configurations to investigate its convergence, the magnitude and nature (stabilizing/destabilizing) of the individual terms and seek an understanding of their variation across the different families of clusters. In particular, we examined the series of alkali metals (Li3, Na3, K3, Li2Na, LiNa2), alkali metal borides (Li2B and LiB2), and alkaline earth metals (Be3, Be2Mg, BeMg3, and Mg3) trimers, as well as sodium clusters Nan, n = 2-5. We found that there is no uniform contribution (stabilizing or destabilizing) across the series in the different families of trimers. For instance, the 2-B term stabilizes the ground states of the Na3 (doublet), Na4 (singlet), and Na5 (doublet) clusters, and the 3-B term destabilizes them; however, the opposite holds for the quartet state of the Li3, Li2Na, LiNa2, and Na3 clusters (destabilizing 2-B, stabilizing 3-B). Substituting Li with B in the quartet state of Li3 results in a significant reduction of the 3-B term amounting to 16% (Li2B) and 5% (LiB3) of the binding energy. On the contrary, the ground states of the alkaline earth metal clusters (Be3, Be2Mg, BeMg3, and Mg3) are stabilized by the 3-B term, while the 2-B term destabilizes them. Overall, we find that the 3-B terms significantly stabilize the high-spin multiplicity states of the ns1 configurations and the low-spin states of the ns2 configurations. Finally, as the size of the metal increases, the contribution of the 3-B term to the binding energy decreases due to the longer metal-metal bond distances.

Systematic characterization of the homogeneous and heterogeneous hydrogen halide dimers

This study systematically characterizes the four homogeneous and six heterogeneous hydrogen-bonded dimers formed by hydrogen halide pairs (HX/HY where X, Y = F, Cl, Br, and I). The notation HX⋯HY indicates the direction of the hydrogen bond from the HY donor to the HX acceptor. All stationary points reported for these ten dimer systems are fully optimized utilizing the MP2 and CCSD(T) ab initio methods in conjunction with quadruple-ζ correlation-consistent basis sets augmented with diffuse functions, and their nature is verified by harmonic vibrational frequency computations. The electronic dissociation energies (De) for all ten global minima are evaluated near the CCSD(T) complete basis set (CBS) limit via extrapolation schemes. These values are 19.11, 8.32, 7.38, and 6.22 kJ mol-1 for the homogeneous dimers of HF, HCl, HBr, and HI, respectively. For the heterogeneous pairs, the lighter hydrogen halide is consistently the donor in the global minimum configuration, with De ranging from 12.23 kJ mol-1 for HCl⋯HF to 7.22 kJ mol-1 for HI⋯HBr near the CCSD(T) CBS limit. Interestingly, not all heterodimer donor/acceptor permutations correspond to minima. For example, the HCl⋯HBr configuration is identified as a local minimum at all levels of theory employed in this investigation, whereas the in-plane barrier for donor/acceptor exchange vanishes for HCl⋯HI and HBr⋯HI when larger quadruple-ζ basis sets are utilized. For the seven dimer systems containing Br and/or I, the structures, energetics, and vibrational frequencies computed using conventional valence-only electron correlation procedures are similar to those obtained using an expanded valence treatment that includes the (n - 1)d subvalence electrons associated with Br and I.

Electronic Instability and Solvation Stabilization of Oxocarbon Dianions (CnOn)2- (n = 4-6)

Oxocarbon dianions (CnOn)2- have been recently found to be promising candidates in the design of high-capacity and fast rechargeable batteries but are intrinsically unstable in the isolated form. Fundamental understandings of their electronic structures, solvent stabilization, and interactions with solvents and counterions are crucial in comprehending their electron transfer reactions occurring in batteries. In this article, we employed microsolvated dianionic clusters as models and combined negative ion photoelectron spectroscopy (NIPES) and theoretical computations to probe the electronic instability and solvation stabilization of (CnOn)2- (n = 4-6) dianions. Through the smallest observable members in each series of microhydrated dianions and their recorded adiabatic and vertical detachment energies (ADEs and VDEs), the minimum numbers of H2O molecules required to stabilize (CnOn)2- dianions are determined to be 4, 3, and 2 for n = 4, 5, and 6, respectively, while 3 and 2 water molecules can make (C4O4)2- and (C5O5)2- metastable and detectable. Using theoretical calculations, we determined the lowest energy structures of each complex. The first few H2O molecules prefer to be directly hydrogen bonded to two adjacent O atoms around the oxocarbon ring. The water binding strengths are generally comparable when each H2O molecule is bound at a separate binding pocket, but the binding strengths decrease when all binding pockets are occupied, in parallel with the observed ADE and VDE shift trends. Moreover, hydrated (C4O4)2- dianions are found to possess distinct electronic structures compared to its (C5O5)2- and (C6O6)2- analogues due to its near-degenerate HOMO and HOMO-1, while there exists a larger gap for the latter two dianions. Upon hydration, the overall electronic structure patterns are maintained without much distortion, but fine changes are noticeable, which warrant future studies.

Charge transfer between a metal-bound halide and a quinone through π-hole interactions leads to bulk conductivity

π-Hole interactions between a metal-bound halide and a quinoid ring are described in four novel isostructural co-crystals with the formula [Cu(terpy)ClX]·X'4Q (terpy = 2,2':6',2''-terpyridine; Q = quinone; X = Br, I; X' = Cl, Br). An unusually strong π-hole interaction between Cu-X and the quinoid ring is noted. Periodic DFT computations estimate the energy of the X⋯quinone interaction to be -20.79 kcal mol-1, indicating a very strong non-covalent interaction attributed to a higher degree of polarization along the bonding path. The black colour of the crystals originates from a cooperative intermolecular charge transfer between the [Cu(terpy)ClX] complex and the quinone π-system, with iodine playing a dominant role in this process by facilitating the π-hole interaction that enhances the charge transfer mechanism. All the compounds are considered to be weak semiconductors with the σDC magnitude ranging between 10-11 and 10-9 S cm-1. It is anticipated that by a smart choice of electron donors and electron acceptors, one can substantially enhance the effect and engineer more efficient conductive materials.

The Electronic Structure and Bonding in Some Small Molecules

The electronic structures of the first- and second-row homonuclear diatomics, XeF2, and the weakly bound dimers of nitric oxide and nitrogen dioxide molecules in their ground states are discussed in terms of molecular orbital (MO) theory and, where possible, valence bond theories. The current work is extended and supported by restricted and unrestricted Hartree-Fock (RHF and UHF) self-consistent field (SCF), complete active space SCF (CASSCF), multi-reference configuration interaction (MRCI), coupled cluster CCSD(T), and unrestricted Kohn-Sham (UKS) density functional calculations using a polarized triple-zeta basis. The dicarbon (C2) molecule is especially poorly described by RHF theory, and it is argued that the current MO theories taught in most undergraduate courses should be extended in recognition of the fact that the molecule requires at least a two-configuration treatment.

Thermally Activated Delayed Fluorescence in B,N-Substituted Tetracene Derivatives: A Theoretical Pathway to Enhanced OLED Materials

Polycyclic aromatic hydrocarbons (PAHs) exhibit intriguing characteristics that position them as promising candidates for advancements in organic semiconductor technologies. Notably, tetracene finds substantial utility in Electronics due to its application in organic light-emitting diodes (OLEDs) and organic field-effect transistors (OFETs). The strategic introduction of an isoelectronic boron-nitrogen (B,N) pair to replace a carbon-carbon pair in acenes introduces changes in the electronic structure, allowing for the controlled modulation of diradical characteristics. Consequently, this B,N substitution enables precise adjustments in chemical, optical, and electronic attributes. In this work, we undertook a systematic exploration of thermally activated delayed fluorescence (TADF) phenomena within a set of 77 B,N-substituted derivatives of tetracene. The primary objective was to identify and select prospective molecules for the fabrication of OLEDs. Employing multiconfigurational methods of computational quantum chemistry, we conducted an extensive investigation to unravel the potential candidates. As a result, we identified molecules that might exhibit the sought-after TADF behavior. Descriptors such as excitation energies, harmonic oscillator model of aromaticity (HOMA) and fractional occupation number weighted density (FOD) were assessed and indicated five candidates with stability comparable to that of pristine tetracene. This research not only contributes to a deeper understanding of the influence of B,N substitution on acene derivatives but also opens doors for the development of organic electronics by harnessing the properties of these selected molecules.

Carbon Nanotubes in Cement-A New Approach for Building Composites and Its Influence on Environmental Effect of Material

An addition of carbon nanostructures to cement paste is problematic due to the difficulties in obtaining homogenous mixtures. The paper reports on a more effective way of mixing carboxylated multi-walled carbon nanotubes (MWCNT-COOH) in cement pastes. The additional biological impact of the studied nanomodified cement was analyzed in the case of two moss species' vitality. The applied approach of obtaining a homogeneous mixture is based on intense mechanochemical mixing of MWCNT-COOH together with polycarboxylate superplasticizer (SP). As a result, a more homogenous suspension of MWCNT-COOH within a liquid superplasticizer, suitable for addition to hydrophilic cement paste, was obtained. FT-IR/Raman spectroscopy was used for materials' characterization. To explain the mixing process at the molecular level, systematic theoretical studies using density functional theory (DFT) were performed. The structures, interaction energies and IR/Raman vibrational spectra of model carboxylic acids, mixed with functionalized SWCNTs as simplified models of real MWCNTs, were obtained. Due to the controversial opinions on the environmental hazards of carbon nanostructures, additional in vivo studies were performed. In this case, effects of cement modified by the addition of small amounts of MWCNT-COOH with SP in comparison to the composite without carbon nanostructures and control subsoil on the vitality of mosses Polytrichum formosum and Pseudoscleropodium purum were studied.

Photodetachment photoelectron spectroscopy shows isomer-specific proton-coupled electron transfer reactions in phenolic nitrate complexes

The oxidation of phenolic compounds is one of the most important reactions prevalent in various biological processes, often explicitly coupled with proton transfers (PTs). Quantitative descriptions and molecular-level understanding of these proton-coupled electron transfer (PCET) reactions have been challenging. This work reports a direct observation of PCET in photodetachment (PD) photoelectron spectroscopy (PES) of hydrogen-bonded phenolic (ArOH) nitrate (NO3-) complexes, in which a much slower rising edge provides a spectroscopic signature to evidence PCET. Electronic structure calculations unveil the PCET processes to be isomer-specific, occurred only in those with their HOMOs localized on ArOH, leading to charge-separated transient states ArOH•+·NO3- triggered by ionizing phenols while simultaneously promoting PT from ArOH•+ to NO3-. Importantly, this study showcases that gas-phase PD-PES is a generic means enabling to identify PCET reactions with explicit structural and binding information.

Preparation and optimization of dummy molecularly imprinted polymer-based solid-phase extraction system for selective enrichment of p-toluene sulfonate esters genotoxic impurities

Sulfonate esters, one class of genotoxic impurities (GTIs), have gained significant attention in recent years due to their potential to cause genetic mutations and cancer. In the current study, we employed the dummy template molecular imprinting technology with a dummy template molecule replacing the target molecule to establish a pretreatment method for samples containing p-toluene sulfonate esters. Through computer simulation and ultraviolet-visible spectroscopy analysis, the optimal functional monomer acrylamide and polymerization solvent chloroform were selected. Subsequently, a dummy template molecularly imprinted polymer (DMIP) was prepared by the precipitation polymerization method, and the polymer was characterized in morphology, particle size, and composition. The results of the adsorption and enrichment study demonstrated that the DMIP has high adsorption capability (Q = 7.88 mg/g) and favorable imprinting effects (IF = 1.37); Further, it could simultaneously adsorb three p-toluene sulfonate esters. The optimal adsorption conditions were obtained by conditional optimization of solid-phase extraction (SPE). A pH 7 solution was selected as the loading condition, the methanol/1 % phosphoric acid solution (20:80, v/v) was selected as the washing solution, and acetonitrile containing 10 % acetic acid in 6 mL was selected as the elution solvent. Finally, we determined methyl p-toluene sulfonate alkyl esters, ethyl p-toluene sulfonate alkyl esters, and isopropyl p-toluene sulfonate alkyl esters in tosufloxacin toluene sulfonate and capecitabine at the 10 ppm level (relative to 1 mg/mL active pharmaceutical ingredient (API) samples) by using DMIP-based SPE coupled with HPLC. This approach facilitated the selective enrichment of p-toluene sulfonate esters GTIs from complex API samples.

Strategies to Obtain Reliable Energy Landscapes from Embedded Multireference Correlated Wavefunction Methods for Surface Reactions

Embedded correlated wavefunction (ECW) theory is a powerful tool for studying ground- and excited-state reaction mechanisms and associated energetics in heterogeneous catalysis. Several factors are important to obtaining reliable ECW energies, critically the construction of consistent active spaces (ASs) along reaction pathways when using a multireference correlated wavefunction (CW) method that relies on a subset of orbital spaces in the configuration interaction expansion to account for static electron correlation, e.g., complete AS self-consistent field theory, in addition to the adequate partitioning of the system into a cluster and environment, as well as the choice of a suitable basis set and number of states included in excited-state simulations. Here, we conducted a series of systematic studies to develop best-practice guidelines for ground- and excited-state ECW theory simulations, utilizing the decomposition of NH3 on Pd(111) as an example. We determine that ECW theory results are relatively insensitive to cluster size, the aug-cc-pVDZ basis set provides an adequate compromise between computational complexity and accuracy, and that a fixed-clean-surface approximation holds well for the derivation of the embedding potential. Additionally, we demonstrate that a merging approach, which involves generating ASs from the molecular fragments at each configuration, is preferable to a creeping approach, which utilizes ASs from adjacent structures as an initial guess, for the generation of consistent potential energy curves involving open-d-shell metal surfaces, and, finally, we show that it is essential to include bands of excited states in their entirety when simulating excited-state reaction pathways.

Probing the Effects of Size and Charge on the Monohydration and Dihydration of SiF5- and SiF62- via Comparisons with BF4- and PF6. J Phys Chem A 2024;128:5637-5645. [PMID: 38976798 DOI: 10.1021/acs.jpca.4c03430] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

This study systematically examines the interactions of the trigonal bipyramidal silicon pentafluoride and octahedral silicon hexafluoride anions with either one or two water molecules, (SiF5-(H2O)n and SiF62-(H2O)n, respectively, where n = 1, 2). Full geometry optimizations and subsequent harmonic vibrational frequency computations are performed using the CCSD(T) ab initio method with a triple-ζ correlation consistent basis set augmented with diffuse functions on all non-hydrogen atoms (cc-pVTZ for H and aug-cc-pVTZ for Si, O, and F; denoted as haTZ). Two monohydrate and six dihydrate minima have been identified for the SiF5-(H2O)n systems, whereas one monohydrate and five dihydrate minima have been identified for the SiF62-(H2O)n systems. Both monohydrated anions have a minimum in which the water molecule adopts a symmetric double ionic hydrogen bond (DIHB) motif with C2v symmetry. However, a second unique monohydrate minimum has been identified for SiF5- in which the water molecule adopts an asymmetric DIHB motif along the edge of the trigonal bipyramidal anion between one axial and one equatorial F atom. This Cs structure is more than 2 kcal mol-1 lower in energy than the C2v local minimum at the CCSD(T)/haTZ level of theory. While the interactions between the solvent and ionic solute are quite strong for the monohydrated anions (electronic dissociation energies of ≈12 and ≈24 kcal mol-1 for the SiF5-(H2O)1 and SiF62-(H2O)1 global minima, respectively), these values are nearly perfectly doubled for the dihydrates, with the lowest-energy SiF5-(H2O)2 and SiF62-(H2O)2 minima exhibiting dissociation energies of ≈24 and ≈47 kcal mol-1, respectively. Structures that form hydrogen bonds between the solvating water molecules also exhibit the largest shifts in the harmonic OH stretching frequencies for the waters of hydration. These shifts can exceed -100 cm-1 for the SiF5-(H2O)2 minimum and -300 cm-1 for the SiF62-(H2O)2 minimum relative to an isolated H2O molecule at the CCSD(T)/haTZ level of theory. This work also corrects the OH stretching frequency shifts for two dihydrate minima of PF6- that were previously erroneously reported ( J. Phys. Chem. A 2020, 124, 8744-8752, DOI: 10.1021/acs.jpca.0c06466).

Probing the Electronic Structure of [B10H10]2- Dianion Encapsulated by an Octamethylcalix[4]pyrrole Molecule

Despite being an important closo-borate in condensed phase boron chemistry, isolated [B10H10]2- is electronically unstable and has never been detected in the gas phase. Herein, we report a successful capture of this fleeting species through binding with an octamethylcalix[4]pyrrole (omC4P) molecule to form a stable gaseous omC4P·[B10H10]2- complex and its characterizations utilizing negative ion photoelectron spectroscopy (NIPES). The recorded NIPE spectrum, contributed by both omC4P and [B10H10]2-, is deconvoluted by subtracting the omC4P contribution to yield a [B10H10]2- spectrum. The obtained [B10H10]2- spectrum consists of four major bands spanning the electron binding energy (EBE) range from 1 to 5 eV, with the EBE gaps matching excellently with the energy intervals of computed high-lying occupied molecular orbitals of the [B10H10]2- dianion. This study showcases a generic method to utilize omC4P to capture unstable multiply charged anions in the gas phase for experimental determination of their electronic structures.

Systematic analysis of electronic barrier heights and widths for concerted proton transfer in cyclic hydrogen bonded clusters: (HF)n, (HCl)n and (H2O)n where n = 3, 4, 5

The MP2 and CCSD(T) methods are paired with correlation consistent basis sets as large as aug-cc-pVQZ to optimize the structures of the cyclic minima for (HF)n, (HCl)n and (H2O)n where n = 3-5, as well as the corresponding transition states (TSs) for concerted proton transfer (CPT). MP2 and CCSD(T) harmonic vibrational frequencies confirm the nature of each minimum and TS. Both conventional and explicitly correlated CCSD(T) computations are employed to assess the electronic dissociation energies and barrier heights for CPT near the complete basis (CBS) limit for all 9 clusters. Results for (HF)n are consistent with prior studies identifying Cnh and Dnh point group symmetry for the minima and TSs, respectively. Our computations also confirm that CPT proceeds through Cs TS structures for the C1 minima of (H2O)3 and (H2O)5, whereas the process goes through a TS with D2d symmetry for the S4 global minimum of (H2O)4. This work corroborates earlier findings that the minima for (HCl)3, (HCl)4 and (HCl)5 have C3h, S4 and C1 point group symmetry, respectively, and that the Cnh structures are not minima for n = 4 and 5. Moreover, our computations show the TSs for CPT in (HCl)3, (HCl)4 and (HCl)5 have D3h, D2d, and C2 point group symmetry, respectively. At the CCSD(T) CBS limit, (HF)4 and (HF)5 have the smallest electronic barrier heights for CPT (≈15 kcal mol-1 for both), followed by the HF trimer (≈21 kcal mol-1). The barriers are appreciably higher for the other clusters (around 27 kcal mol-1 for (H2O)4 and (HCl)3; roughly 30 kcal mol-1 for (H2O)3, (H2O)5 and (HCl)4; up to 38 kcal mol-1 for (HCl)5). At the CBS limit, MP2 significantly underestimates the CCSD(T) barrier heights (e.g., by ca. 2, 4 and 7 kcal mol-1 for the pentamers of HF, H2O and HCl, respectively), whereas CCSD overestimates these barriers by roughly the same magnitude. Scaling the barrier heights and dissociation energies by the number of fragments in the cluster reveals strong linear relationships between the two quantities and with the magnitudes of the imaginary vibrational frequency for the TSs.

A Synergistic Bimetallic Ti/Co-Catalyzed Isomerization of Epoxides to Allylic Alcohols Enabled by Two-State Reactivity

Isomerization of epoxides into versatile allylic alcohols is an atom-economical synthetic method to afford vicinal bifunctional groups. Comprehensive density functional theory (DFT) calculations were carried out to elucidate the complex mechanism of a bimetallic Ti/Co-catalyzed selective isomerization of epoxides to allyl alcohols by examining several possible pathways. Our results suggest a possible mechanism involving (1) radical-type epoxide ring opening catalyzed by Cp2Ti(III)Cl leading to a Ti(IV)-bound β-alkyl radical, (2) hydrogen-atom transfer (HAT) catalyzed by the Co(II) catalyst to form the Ti(IV)-enolate and Co(III)-H intermediate, (3) protonation to give the alcohols, and (4) proton abstraction to form the Co(I) species followed by electron transfer to regenerate the active Co(II) and Ti(III) species. Moreover, bimetallic catalysis and two-state reactivity enable the key rate-determining HAT step. Furthermore, a subtle balance between dispersion-driven bimetallic processes and entropy-driven monometallic processes determines the most favorable pathway, among which the monometallic process is energetically more favorable in all steps except the vital hydrogen-atom transfer step. Our study should provide an in-depth mechanistic understanding of bimetallic catalysis.

Organic Molecules Mimic Alkali Metals Enabling Spontaneous Harpoon Reactions with Halogens

The harpoon mechanism has been a milestone in molecular reaction dynamics. Until now, the entity from which electron harpooning occurs has been either alkali metal atoms or non-metallic analogs in their excited states. In this work, we demonstrate that a common organic molecule, octamethylcalix[4] pyrrole (omC4P), behaves just like alkali metal atoms, enabling the formation of charge-separated ionic bonding complexes with halogens omC4P+ ⋅ X- (X=F-I, SCN) via the harpoon mechanism. Their electronic structures and chemical bonding were determined by cryogenic photoelectron spectroscopy of the corresponding anions and confirmed by theoretical analyses. The omC4P+ ⋅ X- could be visualized to form from the reactants omC4P+X via electron harpooning from omC4P to X at a distance defined by the energy difference between the ionization potential of omC4P and electron affinity of X.

Basis Set Superposition Errors Are Partly Basis Set Imbalances

When calculating fragment interaction energies by electronic structure methods employing medium-sized atom-centered basis sets, it is often observed that the effect is systematically overestimated. The common interpretation is that the systematic error arises because the basis set for the complex is more complete than for the isolated fragments, and this is denoted basis set superposition errors. It has been observed, however, that the interaction energy in some cases is underestimated, which defies the interpretation in terms of basis set completeness, and instead suggests that the effect partly is due to basis set imbalance. The imbalance can be removed by explicit optimization of the basis sets for each structure, and it is shown that this to a significant extent reduces the systematic overestimation attributed to basis set superposition error.

Insight into the Binding of Argon to Cyclic Water Clusters from Symmetry-Adapted Perturbation Theory

This work systematically examines the interactions between a single argon atom and the edges and faces of cyclic H2O clusters containing three-five water molecules (Ar(H2O)n=3-5). Full geometry optimizations and subsequent harmonic vibrational frequency computations were performed using MP2 with a triple-ζ correlation consistent basis set augmented with diffuse functions on the heavy atoms (cc-pVTZ for H and aug-cc-pVTZ for O and Ar; denoted as haTZ). Optimized structures and harmonic vibrational frequencies were also obtained with the two-body-many-body (2b:Mb) and three-body-many-body (3b:Mb) techniques; here, high-level CCSD(T) computations capture up through the two-body or three-body contributions from the many-body expansion, respectively, while less demanding MP2 computations recover all higher-order contributions. Five unique stationary points have been identified in which Ar binds to the cyclic water trimer, along with four for (H2O)4 and three for (H2O)5. To the best of our knowledge, eleven of these twelve structures have been characterized here for the first time. Ar consistently binds more strongly to the faces than the edges of the cyclic (H2O)n clusters, by as much as a factor of two. The 3b:Mb electronic energies computed with the haTZ basis set indicate that Ar binds to the faces of the water clusters by at least 3 kJ mol-1 and by nearly 6 kJ mol-1 for one Ar(H2O)5 complex. An analysis of the interaction energies for the different binding motifs based on symmetry-adapted perturbation theory (SAPT) indicates that dispersion interactions are primarily responsible for the observed trends. The binding of a single Ar atom to a face of these cyclic water clusters can induce perturbations to the harmonic vibrational frequencies on the order of 5 cm-1 for some hydrogen-bonded OH stretching frequencies.

Stability improvement of UV-filter between methoxy cinnamic acid derivatives and cyclodextrins inclusion complexes based on DFT and TD-DFT investigations

Structures and UV-vis absorption spectra of the host-guest interaction of the methoxy cinnamic acid (MCA) derivatives and cyclodextrins (CDs) were performed by using the density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. All geometries of MCA derivatives (4-MCA, 245-MCA, 246-MCA), three types of CD (αCD, βCD, γCD), and five host-guest inclusion complexes between MCA and CD consisting of 4-MCA/αCD (1), 4-MCA/βCD (2), 245-MCA/βCD (3), 246-MCA/βCD (4), and 246-MCA/γCD (5) were fully optimized by using the M06-2X/6-31G (d,p) levels of theory. Two orientations (A and B) of the MCA guest molecule were considered. Upon examining the optimized geometry, five complexes of the methoxy cinnamic acid molecules are located inside the cavity of CD. Orientation B was more stable than orientation A because of the stronger intermolecular hydrogen bonds between the hydroxyl group of CD and the carboxylic group of MCA. The results indicated that the intermolecular hydrogen bond is mainly the driving force of formation between methoxy cinnamic acid and cyclodextrins. To reveal the host-guest interaction that is relevant to UV-filter compounds, the UV-vis absorption spectra were performed using TD-DFT calculations. The obtained results confirmed that orientation B is the most stable orientation and can absorb in both UVB and UVA regions which is similar to the parent MCA. Therefore, this knowledge will bring to understand the host-guest interaction between methoxy cinnamic acid and cyclodextrin complexes. The theoretical results are expected to provide valuable information for improving the stability of further UV-filter compounds.

Gas-Phase vs. Grain-Surface Formation of Interstellar Complex Organic Molecules: A Comprehensive Quantum-Chemical Study

Several organic chemical compounds (the so-called interstellar complex organic molecules, iCOMs) have been identified in the interstellar medium (ISM). Examples of iCOMs are formamide (HCONH2), acetaldehyde (CH3CHO), methyl formate (CH3OCHO), or formic acid (HCOOH). iCOMs can serve as precursors of other organic molecules of enhanced complexity, and hence they are key species in chemical evolution in the ISM. The formation of iCOMs is still a subject of a vivid debate, in which gas-phase or grain-surface syntheses have been postulated. In this study, we investigate the grain-surface-formation pathways for the four above-mentioned iCOMs by transferring their primary gas-phase synthetic routes onto water ice surfaces. Our objective is twofold: (i) to identify potential grain-surface-reaction mechanisms leading to the formation of these iCOMs, and (ii) to decipher either parallelisms or disparities between the gas-phase and the grain-surface reactions. Results obtained indicate that the presence of the icy surface modifies the energetic features of the reactions compared to the gas-phase scenario, by increasing some of the energy barriers. Therefore, the investigated gas-phase mechanisms seem unlikely to occur on the icy grains, highlighting the distinctiveness between the gas-phase and the grain-surface chemistry.

Is Enol Always the Culprit? The Curious Case of High Enantioselectivity in a Chiral Rh(II) Complex Catalyzed Carbene Insertion Reaction

The mechanism of Rh2 (S-NTTL)4 catalyzed carbene insertion into C(3)-H of indole is investigated using DFT methods. Since the commonly accepted enol mechanism cannot account for enantioinduction, a concerted oxocarbenium pathway was proposed in an earlier work using a model catalyst. However, after considering the full catalytic system, this study finds that akin to other reactions, here, too, the enol pathway is of lower energy, which now naturally raises a conundrum regarding the mode of chiral induction. Herein, a new water promoted mechanistic pathway involving a metal-associated enol intermediate hydrogen bonding and stereochemical model are proposed to solve this puzzle. It is shown how the catalyst bowl-shaped structure along with substrate-catalyst binding is crucial for achieving high levels of enantioselectivity. A stereodetermining water-assisted proton transfer is proposed and confirmed through deuterium-labeling experiments. The water molecules are held together by H-bonding interactions with the carboxylate ligands that is reminiscent of enzyme catalysis. Although several previous studies have aimed at understanding the mechanism of metal catalyzed carbene insertion reactions, the origin of high stereoinduction especially with chiral metal complexes remains unclear, and till date there is no transition state model that can explain the high enantioselectivity with such chiral Rh complexes. The metal-associated enol pathway is currently underrepresented in catalytic cycles and may play a crucial role in catalyst design. Since the enol pathway is commonly adopted in other metal-catalyzed X-H insertion reactions involving a diazoester, the presented results are not specific to the current reaction. Therefore, this study could provide the direction for achieving high levels of enantioselectivity which is otherwise difficult to achieve with a single metal catalyst.

Competition between Solvent···Solvent and Solvent···Solute Interactions in the Microhydration of the Tetrafluoroborate Anion, BF4-(H2O)n=1,2,3,4

This study systematically examines the interactions of the tetrafluoroborate anion (BF4-) with up to four water molecules (BF4-(H2O)n=1,2,3,4). Full geometry optimizations and subsequent harmonic vibrational frequency computations are performed using a variety of density functional theory (DFT) methods (B3LYP, B3LYP-D3BJ, and M06-2X) and the MP2 ab initio method with a triple-ζ correlation consistent basis set augmented with diffuse functions on all non-hydrogen atoms (cc-pVTZ for H and aug-cc-pVTZ for B, O, and F; denoted as haTZ). Optimized structures and harmonic vibrational frequencies were also obtained with the CCSD(T) ab initio method and the haTZ basis set for the mono- and dihydrate (n = 1, 2) structures. The 2-body:Many-body (2b:Mb) technique, in which CCSD(T) computations capture the 1- and 2-body contributions to the interactions and MP2 computations recover all higher-order contributions, was used to extend these demanding computations to the tri- and tetrahydrate (n = 3, 4) systems. Four, five, and eight new stationary points have been identified for the di-, tri-, and tetrahydrate systems, respectively. The global minimum of the monohydrate adopts a symmetric double ionic hydrogen bond motif with C2v symmetry and an electronic dissociation energy of 13.17 kcal mol-1 at the CCSD(T)/haTZ level of theory. This strong solvent···solute interaction, however, competes with solute···solute interactions in the lowest-energy BF4-(H2O)n=2,3,4 minima that are not seen in the other di-, tri-, or tetrahydrate minima. The latter interactions help increase the 2b:Mb dissociation energies to more than 26, 41, and 51 kcal mol-1 for n = 2, 3, and 4, respectively. Structures that form hydrogen bonds between the solvating water molecules also exhibit the largest shifts in the harmonic OH stretching frequencies for the waters of hydration. These shifts can exceed -280 cm-1 relative to an isolated H2O molecule at the 2b:Mb/haTZ level of theory.

Adsorption of HCN on cosmic silicates: a periodic quantum mechanical study

Hydrogen cyanide (HCN) represents a small but widely distributed fraction of the interstellar molecules, and it has been observed in all the environments characterizing the formation of a new planetary system. HCN can polymerize to form biomolecules, including adenine (H5C5N5), and it has drawn attention as a possible precursor of several building blocks of life due to the presence of its polymerization products in meteorites, comets and other asteroidal bodies. To elucidate the potential catalytic role that cosmic silicates have played in these processes, we have investigated, at DFT-PBE level inclusive of a posteriori dispersion correction, the energetic and spectroscopic features of the adsorption of HCN molecules on the most relevant crystalline surfaces of the mineral forsterite (Mg2SiO4), a common silicate constituent of the interstellar core grains and planetary rocky bodies. The results reveal that HCN adsorbs both in molecular and dissociative ways, within a wide range of adsorption energies (-29.4 to -466.4 kJ mol-1). Thermodynamic and kinetic results show that dissociative adsorption is dominant already at low temperatures, a fact particularly relevant at the protoplanetary conditions (i.e., the latest stages in the star system formation process). The simulated spectroscopic features of the studied adducts show a wide range of different degrees of perturbation of C-H and CN bonds. This finding agrees with previous experimental works, and our results confirm that a complex chemistry is observed when this astrochemically-relevant molecule interacts with Mg2SiO4, which may be associated with a considerable potential reactivity towards the formation of relevant prebiotic compounds.

Quantifying Intramolecular Basis Set Superposition Errors

We show that medium-sized Gaussian basis sets lead to significant intramolecular basis set superposition errors at Hartree-Fock and density functional levels of theory, with artificial stabilization of compact over extended conformations for a 186 atom deca-peptide. Errors of ∼80 and ∼10 kJ/mol are observed, with polarized double zeta and polarized triple zeta quality basis sets, respectively. Two different procedures for taking the basis set superposition error into account are tested. While both reduce the error, it appears that polarized quadruple zeta basis sets are required to reduce the error below a few kJ/mol. Alternatively, the basis set superposition error can be eliminated using multiresolution methods based on Multiwavelets.

Catalytic effect of graphene on the inversion of corannulene using a continuum approach with the Lennard-Jones potential

The catalytic effect of graphene on the corannulene bowl-to-bowl inversion is confirmed in this paper using a pair-wise dispersion interaction model. In particular, a continuum approach together with the Lennard-Jones potential are adopted to determine the interaction energy between corannulene and graphene. These results are consistent with previous quantum chemical studies, which showed that a graphene sheet reduces the barrier height for the bowl-to-bowl inversion in corannulene. However, the results presented here demonstrate, for the first time, that the catalytic activity of graphene can be reproduced using pair-wise dispersion interactions alone. This demonstrates the major role that pair-wise dispersion interactions play in the catalytic activity of graphene.

DFT Study of the Adsorption and SERS of Pyridine on M10N10 (M, N = Cu, Ag) Tetrahedral Clusters

This work presents a theoretical detailed analysis of the surface-enhanced Raman spectroscopy (SERS) of the pyridine-M10N10 (M, N = Ag, Cu) tetrahedral (Td) clusters considering two binding positions: vertex (V) and surface (S). In addition to the well-known monometallic Td structure, we added two different bimetallic Ag-Cu compositions, named Td1 and Td2 geometries. Density functional methodology with the use of BP86 and CAM-B3LYP exchange-correlation functionals (XCs) and LANL2DZ pseudopotential has been employed for analyzing the electronic structure and geometries, the chemical static (CHEM), and resonant Raman mechanisms (RR): charge transfer RR-CT and intracluster excitation RR-CR. The static CHEM mechanism shows an increase in the enhancement factors (EFs) of Py-V concerning Py-S positions, which can also be distinguished by the averaged adsorption energies and bond polarizabilities. The static SERS response for Cu-Py-V junction is from 5 to 10 times greater than Ag-Py-V EFs and up to 28 times greater than Py-S complexes. For the static Raman, we found that the analyses of ν8a and ν1 normal modes are related to the EF changes and allow us to distinguish V from S complexes. The TDDFT calculations show striking differences between BP86 and CAM-B3LYP XCs analyzed spectra, and CAM-B3LYP granted a clear distinction between V and S for the location of CT-type transitions. In addition, important differences were obtained from the analysis of the charge transfer excitations between both XCs. Resonant Raman calculations evidenced significant enhancements for RR-CT and RR-CR as compared to the static enhancements, and RR-CT can be distinguished from the RR-CR mechanism, while specific normal modes help to differentiate the vertex from the surface Py-junction. Bimetallic Ag-Cu nanostructures represent promising choices for SERS substrates, showing EFs higher than those of monometallic Ag.

A Theoretical Analysis of Interaction Energies and Intermolecular Interactions between Amphotericin B and Potential Bioconjugates Used in the Modification of Nanocarriers for Drug Delivery

Amphotericin B (AmB) is an antibiotic with a wide spectrum of action and low multidrug resistance, although it exhibits self-aggregation, low specificity, and solubility in aqueous media. An alternative for its oral administration is its encapsulation in polymers modified with bioconjugates. The aim of the present computational research is to determine the affinity between AmB and six bioconjugates to define which one could be more suitable. The CAM-B3LYP-D3/6-31+G(d,p) method was used for all computational calculations. The dimerization enthalpy of the most stable and abundant systems at pH = 7 allows obtaining this affinity order: AmB_1,2-distearoyl-sn-glycerol-3-phosphorylethanolamine (DSPE) > AmB_γ-cyclodextrin > AmB_DSPEc > AmB_retinol > AmB_cholesterol > AmB_dodecanol, where DSPEc is a DSPE analog. Quantum theory of atoms in molecules, the non-covalent interactions index, and natural bond orbital analysis revealed the highest abundance of noncovalent interactions for AmB-DSPE (51), about twice the number of interactions of the other dimers. Depending on the interactions’ strength and abundance of the AmB-DSPE dimer, these are classified as strong: O-H---O (2), N-H---O (3) and weak: C-H---O (25), H---H (18), C-H---C (3). Although the C-H---O hydrogen bond is weak, the number of interactions involved in all dimers cannot be underestimated. Thus, non-covalent interactions drive the stabilization of copolymers, and from our analysis, the most promising candidates for encapsulating are DSPE and γ-cyclodextrin.

Molecular dynamics simulation studies of 1,3-dimethyl imidazolium nitrate ionic liquid with water

The fundamental understanding of intermolecular interactions of ionic liquids (ILs) with water is essential in predicting IL-water thermodynamic properties. In this study, intermolecular or noncovalent interactions were studied for 1,3-dimethyl imidazolium [DMIM]⁺ cation and nitrate [NO₃]^- anion with water, employing quantum mechanics and molecular dynamics simulations. Molecular dynamics simulations were performed using a revised multipolar polarizable force field. The effect of water on ionic liquids was evaluated in terms of thermodynamic and dynamic properties. Thermodynamic properties included liquid densities ρ, excess molar volumes ΔV^E, and liquid structures gr. Dynamic properties included self-diffusion coefficients D of mixture constituents as a function of water concentration. The density of ionic liquid-water mixtures monotonically decrease with increasing concentration of water. A negative excess volume was obtained for low and high water concentrations, demonstrating strong intermolecular interactions of water with ionic liquid components. Liquid structures of ionic liquid-water mixtures revealed a tendency for anions to interact with cations at shorter intermolecular distances when the water concentration is increased. Diffusion rates were found to increase for all mixture components with increase in the fraction of water. A significant change in the diffusion rate was found at ∼0.3 weight fraction of water. However, the water self-diffusion coefficient was dominant at all concentrations. The ratio of water/anion and anion/cation self-diffusion coefficients was found to decrease linearly with increasing concentration of water molecules.

An Embedded Fragment Method for Molecules in Strong Magnetic Fields

An extension of the embedded fragment method for calculations on molecular clusters is presented, which includes strong external magnetic fields. The approach is flexible, allowing for calculations at the Hartree-Fock, current-density-functional theory, Møller-Plesset perturbation theory, and coupled-cluster levels using London atomic orbitals. For systems consisting of discrete molecular subunits, calculations using London atomic orbitals can be performed in a computationally tractable manner for systems beyond the reach of conventional calculations, even those accelerated by resolution-of-the-identity or Cholesky decomposition methods. To assess the applicability of the approach, applications to water clusters are presented, showing how strong magnetic fields enhance binding within the clusters. However, our calculations suggest that, contrary to previous suggestions in the literature, this enhanced binding may not be directly attributable to strengthening of hydrogen bonding. Instead, these results suggest that this arises for larger field strengths as a response of the system to the presence of the external field, which induces a charge density build up between the monomer units. The approach is embarrassingly parallel and its computational tractability is demonstrated for clusters of up to 103 water molecules in triple-ζ basis sets, which would correspond to conventional calculations with more than 12 000 basis functions.

Structural, vibrational and electronic properties of some tetrel-bonded complexes of the fluorinated methanes methyl fluoride, difluoromethane and fluoroform: an ab initio study

A search has been conducted, by means of ab initio molecular orbital theory, for potential tetrel-bonded complexes formed between the fluorinated methanes methyl fluoride, difluoromethane and fluoroform, and the related hydrides ammonia, water, hydrogen fluoride, phosphine, hydrogen sulphide and hydrogen chloride. Eleven such complexes have been identified, six containing CH₃F and five CH₂F₂. The complexes are typically less strongly bound than their hydrogen-bonded counterparts, and the interaction energies vary in a consistent way with the periodic trend of the electron donors. The intermolecular separations and changes of the relevant intramolecular bond lengths, the wavenumber shifts of the critical vibrational modes and the extents of charge transfer correlate, by and large, with the strengths of interaction.

Breaking covalent bonds in the context of the many-body expansion (MBE). I. The purported "first row anomaly" in XHn (X = C, Si, Ge, Sn; n = 1-4)

We present a new, novel implementation of the Many-Body Expansion (MBE) to account for the breaking of covalent bonds, thus extending the range of applications from its previous popular usage in the breaking of hydrogen bonds in clusters to molecules. A central concept of the new implementation is the in situ atomic electronic state of an atom in a molecule that casts the one-body term as the energy required to promote it to that state from its ground state. The rest of the terms correspond to the individual diatomic, triatomic, etc., fragments. Its application to the atomization energies of the XHn series, X = C, Si, Ge, Sn and n = 1-4, suggests that the (negative, stabilizing) 2-B is by far the largest term in the MBE with the higher order terms oscillating between positive and negative values and decreasing dramatically in size with increasing rank of the expansion. The analysis offers an alternative explanation for the purported "first row anomaly" in the incremental Hn-1X-H bond energies seen when these energies are evaluated with respect to the lowest energy among the states of the XHn molecules. Due to the "flipping" of the ground/first excited state between CH2 (3B1 ground state, 1A1 first excited state) and XH2, X = Si, Ge, Sn (1A1 ground state, 3B1 first excited state), the overall picture does not exhibit a "first row anomaly" when the incremental bond energies are evaluated with respect to the molecular states having the same in situ atomic states.

An accurate vibrational signature in halogen bonded molecular crystals

The far infrared (FIR) and Raman fingerprints of the halogen bond in two representative 1D halogen bonded networks based on the recognition of TFIB, tetrafluorodiiodobenzene, with piperazine or azopyridine, have been accurately identified. It was demonstrated that the signature of the halogen bonding in the solid state, especially the N⋯I signal can be simply and directly evidenced in the far infrared region. The DFT theoretical calculations identified the N⋯I interaction in the molecular crystals and allowed estimation of the corresponding energies and distances of the involved halogen bonds, in accordance with the cristallographic data.

Characterization of Competing Halogen- and Hydrogen-Bonding Motifs in Simple Mixed Dimers of HCN and HX (X = F, Cl, Br, and I)

This work performs the first systematic comparison of hydrogen- and halogen-bonded configurations of the HCN/HX mixed dimer, where X = F, Cl, Br, and I. Eleven different minima have been characterized for these four heterogeneous dimers near the CCSD(T) complete basis set (CBS) limit. For each complex, two different hydrogen-bonded minima were identified: the global minimum where HX acts as the hydrogen bond donor and a local minimum where HX acts as the hydrogen bond acceptor. A halogen-bonded local minimum was also identified for all but the fluorine mixed dimer. To the best of our knowledge, three of the minima are identified here for the first time. The hydrogen- and halogen-bonded local minima of each complex become more energetically competitive with the global minimum as the atomic radius of the halogen atom increases. CCSD(T) relative energies of the hydrogen-bonded local minima computed near the CBS limit decrease from 4.5 kcal mol^-1 for HCN/HF to 2.9, 2.4, and 1.2 kcal mol^-1 for X = Cl, Br, and I, respectively. Corresponding relative energies for the halogen-bonded local minima range from 4.0 kcal mol^-1 for X = Cl to 2.7 kcal mol^-1 for X = Br and to as little as 0.5 kcal mol^-1 X = I. Harmonic vibrational frequency shifts reported here suggest that it may be feasible to differentiate between the various minima for X = Cl, Br, and I via spectroscopic analysis, as was the case for the HCN/HF dimer.

Visualization and Comprehension of Electronic and Topographic Contrasts on Cooperatively Switched Diarylethene-Bridged Ditopic Ligand

Diarylethene is a prototypical molecular switch that can be reversibly photoisomerized between its open and closed forms. Ligands bpy-DAE-bpy, consisting of a phenyl-diarylethene-phenyl (DAE) central core and bipyridine (bpy) terminal substituents, are able to self-organize. They are investigated by scanning tunneling microscopy at the solid-liquid interface. Upon light irradiation, cooperative photochromic switching of the ligands is recognized down to the submolecular level. The closed isomers show different electron density of states (DOS) contrasts, attributed to the HOMO or LUMO molecular orbitals observed. More importantly, the LUMO images show remarkable differences between the open and closed isomers, attributed to combined topographic and electronic contrasts mainly on the DAE moieties. The electronic contrasts from multiple HOMO or LUMO distributions, combined with topographic distortion of the open or closed DAE, are interpreted by density functional theory (DFT) calculations.

A comprehensive multidisciplinary investigation on CO2 capture from diesel engine

Climate change and global warming are the visible consequences of the increased amount of carbon dioxide (CO₂) in the atmosphere. Among the various sources of anthropogenic CO₂ emission, the diesel engine has a significant contribution. The development of a reliable system to efficiently minimize CO₂ emissions from diesel engines to the safest level is lacking in the open literature. Therefore, a comprehensive multidisciplinary approach has been applied in this paper to investigate the efficacy of the post-combustion carbon capture (PCC) process for the diesel engine. The experiments have been performed on the exhaust of a direct injection diesel engine at five different brake powers with blends of aqueous ammonia (AQ_NH₃), monoethanolamine (MEA), N,N-dimethylethanolamine (DMEA), and 1-ethyl-3-methylimidazolium tetrafluoroborate (C₂mim BF₄) ionic liquid (IL) as an absorbent for CO₂ capture. The reaction mechanism of these absorbent with CO₂ are also studied by the geometrical, energetical, MESP, frontier molecular orbitals, and NBO analysis using the first-principles density functional theory (DFT) calculations. The maximum CO₂ absorption efficiency of almost 97% was achieved for the blend consisting of 67% of AQ_NH₃ and 33% of MEA. Moreover, AQ_MEA and blend of AQ_NH₃, DMEA, and C₂mim BF₄ ionic liquid showed 96% and 94% CO₂ absorption efficiency, respectively.

S66x8 noncovalent interactions revisited: new benchmark and performance of composite localized coupled-cluster methods

The S66x8 noncovalent interactions benchmark has been re-evaluated at the “sterling silver” level. Against this, a selection of computationally more economical alternatives has been assayed, ranging from localized CC to double hybrids and SAPT(DFT).

Isotope Effects on the Vaporization of Organic Compounds from an Aqueous Solution-Insight from Experiment and Computations

An isotope fractionation analysis of organic groundwater pollutants can assess the remediation at contaminated sites yet needs to consider physical processes as potentially confounding factors. This study explores the predictability of water–air partitioning isotope effects from experiments and computational predictions for benzene and trimethylamine (both H-bond acceptors) as well as chloroform (H-bond donor). A small, but significant, isotope fractionation of different direction and magnitude was measured with ε = −0.12‰ ± 0.07‰ (benzene), ε_C = 0.49‰ ± 0.23‰ (triethylamine), and ε_H = 1.79‰ ± 0.54‰ (chloroform) demonstrating that effects do not correlate with expected hydrogen-bond functionalities. Computations revealed that the overall isotope effect arises from contributions of different nature and extent: a weakening of intramolecular vibrations in the condensed phase plus additional vibrational modes from a complexation with surrounding water molecules. Subtle changes in benzene contrast with a stronger coupling between intra- and intermolecular modes in the chloroform–water system and a very local vibrational response with few atoms involved in a specific mode of triethylamine. An energy decomposition analysis revealed that each system was affected differently by electrostatics and dispersion, where dispersion was dominant for benzene and electrostatics dominated for chloroform and triethylamine. Interestingly, overall stabilization patterns in all studied systems originated from contributions of dispersion rather than other energy terms.

Solvation of Isoelectronic Halide and Alkali Metal Ions by Argon Atoms

This work systematically examines the interactions of alkali metal cations and their isoelectronic halide counterparts with up to six solvating Ar atoms (M⁺Ar_n and X^-Ar_n, where M = Li, Na, K, and Rb; X = H, F, Cl, and Br; and n = 1-6) via full geometry optimizations with the MP2 method and robust, correlation-consistent quadruple-ζ (QZ) basis sets. 116 unique M⁺Ar_n and X^-Ar_n stationary points have been characterized on the MP2/QZ potential energy surface. To the best of our knowledge, approximately two dozen of these stationary points have been reported here for the first time. Some of these new structures are either the lowest-energy stationary point for a particular cluster or energetically competitive with it. The CCSD(T) method was employed to perform additional single-point energy computations upon all MP2/QZ-optimized structures using the same basis set. CCSD(T)/QZ results indicate that internally solvated structures with the ion at/near the geometric center of the cluster have appreciably higher energies than those placing the ion on the periphery. While this study extends the prior investigations of M⁺Ar_n clusters found within the literature, it notably provides one of the first thorough characterizations of and comparisons to the corresponding negatively charged X^-Ar_n clusters.

Facile one-pot synthesis of CuCN by pulsed laser ablation in nitrile solvents and mechanistic studies using quantum chemical calculations

Binding energies of different nitrile solvents and their utilization for CuCN formation were investigated through quantum chemical calculations. A pulsed laser ablation in liquid (PLAL) method for CuCN synthesis was developed herein. Initially, the interaction between the pulsed laser and the Cu-target generated Cu-ions and electrons at the point of contact. The laser beam also exhibited sufficient energy to dissociate the bonds of the respective solvents. In the case of acetonitrile, the oxidized Cu-ions bonded with CN⁻ to produce CuCN with a cube-like surface structure. Other nitrile solvents generated spherically-shaped Cu@graphitic carbon (Cu@GC) nanoparticles. Thus, the production of CuCN was favorable only in acetonitrile due to the availability of the cyano group immediately after the fragmentation of acetonitrile (CH₃⁺ and CN⁻) under PLAL. Conversely, propionitrile and butyronitrile released large amounts of hydrocarbons, which deposited on Cu NPs surface to form GC layers. Following the encapsulation of Cu NPs with carbon shells, further interaction with the cyano group was not possible. Subsequently, theoretical study on the binding energies of nitrile solvents was confirmed by highly correlated basic sets of B3LYP and MP2 which results were consistent with the experimental outcomes. The findings obtained herein could be utilized for the development of novel metal–polymer materials.

London Dispersion Helps Refine Steric A-Values: The Halogens

Halogens are rarely considered as dispersion energy donors for organic reaction design. Here, we re-examine one of the textbook examples for assessing steric hindrance, the A-value, and demonstrate that even in this system, halogens cannot be treated solely as classic repulsive hard spheres. A significant part of the steric demand of the halogens is compensated by attractive London dispersion (LD) interactions, explaining the experimental lack of a clear trend when going down the halogens' row. Beyond monohalogenated cyclohexanes, dihalo- and perhalocyclohexanes also show significant LD interactions. We also explored several other small organic systems containing halogens. Our findings show that organic chemists should treat halogens as possible sources of LD interactions in reaction design, as these atoms can change the landscape of the potential energy surface and reverse trends of conformer stabilities and reaction selectivities.

Production of copper nanoparticles exhibiting various morphologies via pulsed laser ablation in different solvents and their catalytic activity for reduction of toxic nitroaromatic compounds

Comparative experiments were conducted to determine the effects of various solvents (i.e., deionized water, methanol, ethanol, 1-propanol, butanol, ethylene glycol, hexane, and acetonitrile) on the final compositions, morphologies, and catalytic activities of copper-based nanoparticles (NPs). The NPs were effectively synthesized by pulsed laser ablation (PLA) using a copper plate as the target. The obtained copper NPs were characterized utilizing various analytical techniques. It was established that the developed methodology allows for the production of NPs with different morphologies and compositions in a safe and simple manner. When laser ablation of a solid copper plate was performed in acetonitrile, the formation of copper(I) cyanide cubes was observed. On the other hand, in deionized water and methanol, spherical and rod-like particles of copper(I) and copper(II) oxide were detected, respectively. The catalytic activity of the prepared copper NPs in the reduction of aromatic nitro compounds, such as 4-nitrophenol and nitrobenzene, was also evaluated. A high k value was determined for the reduction over the copper(II) oxide NPs produced in methanol. Moreover, particles with graphitic carbon (GC) layers exhibited superior catalytic performance in the reduction of a hydrophobic substance, i.e., nitrobenzene, over the reduction of 4-nitrophenol. The enhanced catalytic activity of this catalyst may be due its unique surface morphology and the synergistic effects between the copper nanostructure and the GC layer. Lastly, a detailed reduction pathway mechanism for the catalytic reduction of 4-nitrophenol and nitrobenzene has been proposed.

Photoelectron Spectroscopy and Theoretical Study on Monosolvated Cyanate Analogue Clusters ECX-·Sol (ECX- = NCSe-, AsCSe-, and AsCS-; Sol = H2O, CH3CN)

Six monosolvated cyanate analogue clusters ECX^-·Sol (ECX^- = NCSe^-, AsCSe^-, and AsCS^-; Sol = H₂O and CH₃CN) were investigated using negative ion photoelectron spectroscopy (NIPES). NIPES experiments show that these clusters possess similar spectra overall compared to their respective isolated ECX^- anions but shift to higher electron binding energy with CH₃CN solvent, stabilizing the excess electrons slightly more than H₂O. For the ECX^-·H₂O series, vertical detachment energies and their increments relative to the bare species are measured to be 3.700/0.370, 3.085/0.415, and 3.085/0.430 eV for NCSe^-, AsCSe^- and AsCS^-, respectively, while the corresponding values in the ECX^-·CH₃CN series are 3.835/0.505, 3.145/0.475, and 3.135/0.480 eV. Ab initio electronic structure calculations indicate that the excess charges were located at the terminal N and Se atoms in NCSe^- and migrated to the central C atom in AsCSe^- and AsCS^-. For NCSe^-, the solvation is driven by the interactions with the two negatively charged terminal ends, while for AsCSe^- and AsCS^-, the solvation revolves around the interactions with the central C atom, where all the excess negative charge is concentrated. Two nearly degenerate isomers for NCSe^-·H₂O are identified, one forming a single strong N···H-O hydrogen bond (HB) and the other featuring a bidentate HB with two hydroxyl H atoms pointing to N and Se ends. In contrast, the negative central C atom in AsCSe^-/AsCS^- allows the formation of a bifurcated HB with H₂O. Similar effects are observed for the acetonitrile case, in which the three H atoms of the methyl group interact with the two negatively charged terminal ends in NCSe^-, while preferring to bind to the central negative carbon atom in AsCSe^-/AsCS^-. The different binding motifs derived in this work may suggest different solvation properties in NCSe^- versus AsCSe^-/AsCS^- with the former anion leading to asymmetric solvation at the N end of the solute, while the latter species creates more "isotropic" solvation around the central C equatorial plane.