Density-functional approximation for the correlation energy of the inhomogeneous electron gas

Advancing green and white assessment: DFT-assisted spectrofluorimetry for accurate favipiravir quantification in human plasma

Recently, the recognition of computational chemistry potential is growing, because of its applicability for design of substances and studying their properties using computer programs and modelling approaches that help solve various problems. Computational chemistry is involved in the design of advanced fluorescent probes which can be employed in sensing of various analytes. Favipiravir (FVR) is an antiviral drug recommended for the treatment of COVID-19, known for its broad-spectrum activity against RNA viruses by inhibiting viral RNA-dependent RNA polymerase. This study introduces the first-ever integration of computational density functional theory (DFT) and experimental spectrofluorimetric approach to design a highly sensitive spectrofluorimetric method for estimation of FVR in its bulk form and human plasma. The DFT analysis was carried out to investigate the affinity of Zirconium (Zr4+) to FVR in aqueous solution and explore the formation of FVR-Zr4+ chelate. The combuted formation energy (ΔG = -416.5 kcal/mol) of [Zr (FVR)4]4+ complex confirmed the strong of ability of Zr4+ to recognize FVR in solution and evidenced the strong nature of the Zr4+- O and N coordination bonds. The results revealed a significant enhancement in the weak native fluorescence of FVR upon formation of the complex. Various experimental parameters were examined, further the established method was validated according to ICH standards where linearity range was achieved in the range of 0.50-200.0 ng mL-1, with low detection limit reached 32.99 pg mL-1. The developed DFT-assisted spectrofluorimetric methodology was successfully employed for FVR assessment in human plasma samples with good recoveries (98.74 -100.10 %) and relative standard deviation did not exceed 1.80 %. Moreover, the proposed method's eco-friendliness and sustainability were evaluated through four metrics (Red/Green/Blue 12 Algorithm (RGB12), Green Solvent Selection Tool (GSST), Analytical Greenness Metric (AGREE), and Analytical Greenness Metric for Sample Preparation (AGREEprep)), demonstrating its superiority over the existing methods in terms of using safer solvents, reduced sample preparation procedures, and higher overall greenness. Additionally, the high sensitivity and applicability of the proposed method to the reliable analysis of both bulk drug and plasma samples make it efficient and practical for routine FVR analysis in both pharmaceutical and clinical settings. Furthermore, this study opens new avenues for extending computational and experimental approaches to analyze FVR in real samples and explore other drug-metal interactions, contributing to advancements in drug analysis and mechanistic studies.

Vibrational assignments, normal coordinates analysis, force constants, and DFT/MP2 computations of 5-Chloro-2,4,6-trifluoropyrimidine

The vibrational assignments of 5-Chloro-2,4,6-trifluoropyrimidine have been early investigated, however, the proposed fundamentals were not spanned to their appropriate species owing to neglecting the overall symmetry. Nevertheless, the lack of force constants (FCs) determination encourages us to reinvestigate the molecule. Aided by DFT (B3LYP, B3P86, B3PW91, ωBX97) and MP2 = full quantum chemical computations, we have provided a reliable vibrational analysis of all normal modes based on the C2v point group. Different methods of the currently used normal coordinate analysis were also validated. Our results are compared with available infrared and Raman spectral data, including estimated infrared intensities, Raman scattering activities, genuine FCs in internal coordinates, and potential energy distributions (PEDs). Using NCA in a well-defined internal coordinate that enables us to estimate FCs based on G.F. Wilson led to better fundamental interpretations than those obtained from atomic displacements in Cartesian coordinates, VEDA, and MOLVIB programs. The current investigation potentially offers corrected vibrational mode assignments, filling gaps in prior literature and aiding in accurately characterizing fluorinated pyrimidine derivatives.

Three-fold aromatic boranes: spherical aromaticity in borane ortho-carboranes as useful trimer nodes for cluster-based architectures

The characterized tris(ortho-carboranyl)borane (BoCb3) structure enables further understanding of building blocks in three-fold architectures as useful nodes for envisaging cluster-based materials, extending the already known linear array. Our results show the formation of shielding cones enabled in adjacent cluster units that overlap in long-range regions by different orientations of the applied field, in contrast to planar aromatic triarylborane counterparts. Thus, three spherical aromatic circuits or states are retained in the resulting molecular unit, as indicated by the isotropic and anisotropic descriptors of the magnetic behavior. In addition, the superacidic Lewis characteristics of BoCb3, in comparison to triarylboranes, are enabled by the increase in the orbital interaction towards adduct formation, highlighting the relevance of the donor-acceptor charge transfer, where the control of steric repulsion may lead to further stabilization, suggesting plausible enhanced Lewis acidic performance. These results enhance the understanding of cluster-based architectures, paving the way for explorative synthesis efforts toward the achievement of novel superacidic Lewis species by using polyhedral standing molecules.

Frozen-Pair-Type pCCD-Based Methods and Their Double Ionization Variants to Predict Properties of Prototypical BN-Doped Light Emitters

Novel, robust, computationally efficient, and reliable theoretical methods are indispensable for the large-scale modeling of desired molecular properties. One such example is the orbital optimized pair coupled-cluster doubles (oo-pCCD) ansatz and its various CC extensions, which range from closed-shell ground- and excited-state models to open-shell variants. Specifically, the ionization-potential equation-of-motion frozen-pair (IP-EOM-fp)CC methods proved to be competitive with standard CC-type methods for modeling the ionization potentials of organic electronics. In this work, we extend the existing IP-EOM-pCCD-based methods to their double ionization potential (DIP) variants, resulting in various DIP-EOM-fpCC models, including up to double excitations. These methods open the way to reach open-shell singlet, triplet, and quintet states using various pCCD reference functions. Their accuracy is tested for the singlet-triplet gaps of the ortho-, meta-, and para-benzynes. Then, the most accurate models are applied to study the effects of boron and nitrogen doping on designing prototypical naphthalene-based donors and acceptors. Our results demonstrate consistent and reliable outcomes with standard methods and available experimental data. Most importantly, fpCC-type methods show slightly better performance than DIP-EOM-CCSD for strongly-correlated cases and similar performance for systems dominated by dynamical correlation when determining singlet-triplet gaps.

Capping the Electronic Lone Pair of the As(III) Central Atom in the Keggin-Type Anion: From Experimental-Theoretical Interplay to Evidence

The stereochemistry of the polycondensation processes within the Keggin-type derivatives is mainly governed by the nature of the assembly group X, being either tetrahedral or trigonal. Commonly, the use of trigonal units {XO3} gives rise to open molecular structures resulting from connections of {XM9} subunits through metal-oxo cationic fragments. Nevertheless, we show here that condensation of the vanadate VO3- onto the B-type isomer α-[AsW9O33]9- led to the saturated mixed-metal Keggin derivative α-[AsW9V3O39]6-. Experimental evidence was provided by multinuclear nuclear magnetic resonance (NMR) characterization, including 51V, 183W, and 17O NMR, supported by XPS analysis revealing unambiguously the fingerprints of the As(III) atoms compared to those of As(V). Moreover, this unexpected structural feature is fully consistent with the versatile coordination of the V(V) atoms, which makes it possible for the μ3-O bridging oxygen of the {V3} cap to be absent in front of the electronic lone pair of the As(III) ion. In addition, DFT studies give consistency to the electronic structure of this new Keggin-type derivative. At last, structural, spectroscopic, and electrochemical properties of this new version of the Keggin structure were compared to other archetypal vanadium-containing anions and then discussed with regard to the geometry and vicinity of the vanadium atoms.

Photoelectron imaging spectroscopy of Ag3- in the S0 and S1 states

We explore laboratory-frame photoelectron angular distributions (LF-PADs) originating from the outermost two orbitals, σu [the highest occupied molecular orbital (HOMO)] and σg (HOMO-1), of the silver trimer anion (Ag3-) in the S0(1Σg+) state. The experiment was performed by our novel photoelectron imaging technique using a high-repetition-rate tunable laser [T. Horio et al., J. Chem. Phys. 162, 026101 (2025)]. The LF-PAD for σu is found to be highly energy-dependent in a photoelectron kinetic energy (PKE) range from 0 to 1.57 eV; an isotropic LF-PAD with an anisotropy parameter β ∼ 0 is observed at the detachment threshold, exemplifying the Wigner threshold law, whereas the β value decreases down to β = -0.4 at 0.46 eV, followed by an increase up to β = 0.6 at 1.57 eV, as PKE increases. A small dip discernible in the PKE range of 1.2-1.3 eV suggests an influence of the autodetachment process on the β value, which is via bound electronic state(s) embedded in the D0(2Σu+) + e- continuum. On the other hand, the LF-PAD for σg exhibits a strong anisotropy parallel to the laser polarization with β of ∼1 in 0-0.39 eV. These contrasted trends are qualitatively reproduced by theoretical modeling of LF-PAD that accounts for photoelectron partial waves allowed for each photodetachment process. Furthermore, two-photon detachment spectra via the excited S1(1Σu+) state are presented, where the relative band intensities for the two detachment channels, D0(2Σu+) + e- ← S1(1Σu+) and D1(2Σg+) + e- ← S1(1Σu+), are discussed in terms of their leading electronic configurations.

Benchmark CCSD(T) and Density Functional Theory Calculations of Biologically Relevant Catecholic Systems

Approximate complete basis set CCSD(T), MP2, and HF calculations are performed for thirty-two catechol-containing complexes. These complexes, which include metal-coordination, hydrogen-bonding, π-stacking, and other, weaker interactions, are representative of the types of noncovalent interactions that catechols undergo when binding to proteins in the body, such as in the biosynthesis of dopamine. The catechols studied include the neutral catechol and dinitrocatechol molecules, as well as the charged dopamine and DOPAC molecules. Calculations with twenty-one density functional theory methods with triple and quadruple-ζ basis sets are evaluated against the CCSD(T) benchmarks to ascertain their accuracy. It is found that MN15, M06-2X-D3, ωB97XD, ωB97M-V, and CAM-B3LYP-D3 provide good accuracy when compared with CCSD(T)/CBS calculations for these systems and may be used for the study of relevant biological systems. The local DPLNO CCSD(T) method is also evaluated against the CCSD(T)/CBS energies for a subset of the complexes and found to agree within 1-3%, with a maximum difference of 0.26 kcal/mol.

Photochemistry of Ni(II) Tolyl Chlorides Supported by Bidentate Ligand Frameworks

Herein, we investigate the photoactivity of four NiII tolyl chloride complexes supported by either the new bidentate [2.2]pyridinophane (HN2) ligand or the traditional 4,4'-di-tert-butyl-2,2'-dipyridyl (tBubpy) ligand. Despite a change in the ligand framework, we observe similar quantum yields for the photodegradation of all four NiII complexes, while noting changes in their affinity for radical side reactivity and ability to stabilize the photogenerated mononuclear NiI species. Furthermore, changing from an ortho-tolyl to a para-tolyl group affects the geometry of the complexes and makes the Ni center more susceptible to side reactivity. By leveraging the newly developed HN2 ligand, a bidentate ligand that hinders axial interactions with the Ni center, we limit the radical side reactivity. Time-dependent density functional theory (TDDFT) and complete active space self-consistent field (CASSCF) calculations predict that all four complexes have accessible MLCTs that excite an electron from a Ni-aryl bonding orbital into a Ni-aryl antibonding orbital, initiating photolysis. By decreasing this energy gap and stabilizing the tetrahedral triplet excited state, we increase quantum yields of photoexcitation. Importantly, we characterize the photogenerated mononuclear NiI chloride species using X-band EPR spectroscopy and show that the HN2-supported NiI complexes do not undergo the deleterious dimerization and tetramerization observed for the (bpy)NiICl species. Overall, this study provides valuable insight into how the steric environment around the Ni center affects its photoactivity and demonstrates that such photoactivity is not unique to bipyridyl-supported Ni compounds.

Predicting the Brain-To-Plasma Unbound Partition Coefficient of Compounds via Formula-Guided Network

Blood-brain barrier (BBB) permeability plays a crucial role in determining drug efficacy in the brain, with the brain-to-plasma unbound partition coefficient (Kp,uu) recognized as a key parameter of BBB permeability in drug development. However, Kp,uu data are scarce and mostly in-house. In predicting Kp,uu the generality and applicability of existing empirical scoring models remain underexplored. To address this, we established a public rat Kp,uu data set through data mining and developed a formula-guided deep learning model, CMD-FGKpuu, which performed well on multiple benchmark tests, marking good demonstration of the potential of deep learning for Kp,uu prediction. Additionally, the model can be fine-tuning with project-specific experimental data, thus improving its practical utility. The findings offer an effective tool for predicting BBB permeability in drug development and introduce a new perspective for applying few-shot learning in the pharmaceutical field.

Predicting σ0π2 Carbene-Mediated Hydroboration and Bis-carbene Functionalization of Dinitrogen

Although the carbene-catalyzed N2 fixation process had been investigated by scientists for decades prior to borylene species, the interest in the carbene-mediated N2 activation process has drawn less attention than that of borylene species in the past few years, especially unique σ0π2 carbenes. Herein, we demonstrate the important role of unique σ0π2 carbenes in the 1,1-hydroboration and bis-carbene functionalization of N2 using density functional theory calculations. Both being kinetically and thermodynamically favorable, the reaction barriers are as low as 13.7 and 16.6 kcal/mol, respectively. Additionally, such a σ0π2 carbene can also achieve a series of X-H insertion reactions (X = H, CH3, Bpin, or SiH2Ph), with activation energies ranging from 8.2 to 15.3 kcal/mol. Our findings highlight a strong potential of carbenes with σ0π2 electronic configuration in N2 activation and its versatile transformations, providing valuable insights into main-group-element-mediated N2 activation chemistry.

Computational design of dopant-free hole transporting materials: achieving an optimal balance between water stability and charge transport

Hole transporting materials (HTMs) play a crucial role in the performance and stability of perovskite solar cells (PSCs). The interaction of HTMs with water significantly affects the overall stability and efficiency of these devices. Hydrophilic HTMs or those lacking adequate water resistance can absorb moisture, leading to degradation of both the HTM and the perovskite layer. In this study, we employed a proof-of-principle approach to investigate the effect of various chemical modifications on a promising HTM candidate, 8,11-bis(4-(N,N-bis(4-methoxyphenyl)amino)-1-phenyl)-dithieno[1,2-b:4,3-b]phenazine (TQ4). Using molecular dynamics simulations, we examined the collective behavior of chemically modified TQ4 molecules in the presence of water at different concentrations. To ensure that enhanced water resistance did not compromise the desirable electronic properties of the HTM, we analyzed both the individual and collective electronic structures of the HTM molecule and its molecular crystal. Additionally, we calculated the charge transport rate in different directions within the HTM crystal using Marcus theory. Our findings indicate that chemical modifications at the periphery of TQ4, particularly the symmetric addition of two F-chains, result in the optimal combination of electronic, crystal structure, and water-resistant properties. HOMO shape analysis reveals that the HOMO does not extend onto the added F-chains, reducing the maximum predicted hole mobility relative to TQ4 by an order of magnitude. Despite this, a hole mobility of 2.8 × 10-4 cm2 V-1 s-1 is successfully achieved for all designed HTMs, reflecting a compromise between stability and charge transport. This atomistic insight into the collective behavior of chemically modified HTMs and its effect on hole transport pathways paves the way for designing more effective HTMs for PSC applications.

Improvement of electronic structure calculations for the interpretation of the emission spectrum for NdIII complexes

A protocol to correct ab initio calculated luminescence spectra of NdIII complexes is proposed. The emission spectrum of [NdIII(bipy)(tta)3] was measured to calibrate the optimal correction for the Racah parameters on top of a CASSCF calculation to attain the best energetic placement of the 4F3/2 → 4I13/2-9/2 emission lines. As interelectronic repulsion is the most important source of error in this calculation, this straightforward correction results in an accurate placement of transitions, allowing the assignment of a complex spectral shape in terms of its underlying transitions. Finally, the correction derived for [NdIII(bipy)(tta)3] was directly applied to a different NdIII complex, demonstrating the broad use of this approach.

The Fluoride Ion Affinity Revisited: Do We Need the Anchor-Point Approach?

A large and diverse high-level benchmark data set of computed gas-phase fluoride ion affinities (FIAs) for 71 small main-group Lewis acids is presented. It has been used to evaluate quantitatively DFT approaches with 52 functionals and 4 composite methods. Two widely used indirect anchor-point methods based on isodesmic reactions with fluorophosgene or the trimethyl silyl cation are compared to the direct computation of the FIA. It has been frequently stated that anchor-point methods are to be strongly preferred over direct FIA computations at DFT levels, as they avoid treatment of the naked fluoride ion. Here it is shown that this widespread assumption does not hold when modern functionals with low self-interaction errors and suitable basis sets with diffuse functions are used. In these cases, an anchor-point approach based onOCF 2 ${{\rm{OCF}}_2 }$ has little or no advantage, and the widely used anchor-point calculations based onMe 3 Si + ${{\rm{Me}}_3 {\rm{Si}}^+ }$ even deteriorate results in most cases. It is shown that this is due to a break-down of often prevailing error cancellations in the anchor-point approach that help to improve results when using less suitable functionals or basis sets. Overall, the direct computation of FIAs at appropriate DFT levels including diffuse basis functions is the clearly preferable route.

Impact of Terminal Halogen and CN Substitutions on Photoelectric Properties of Asymmetric Y6-Based NFA with Terminal Groups in Different Orientations: A DFT/TDDFT Study

Nonfullerene acceptors (NFAs) with an acceptor-donor-acceptor-donor-acceptor (A-DA'D-A) molecular framework have attracted much attention due to their excellent performance. However, the modifications of terminal units of asymmetric Y6-based NFA with terminal groups of different orientations are still few, and its effects on photoelectrical properties are still not clear. In this work, based on asymmetric IPC-BEH-IC2F (showing better performance than Y6 in experiment) with terminal groups in different orientations, we systematically designed six new NFAs via halogen and CN substitutions on terminal groups. The molecular planarity, dipole moments, electrostatic potential maps and their fluctuations, frontier molecular orbitals, exciton binding energy, UV-vis spectra, and energy difference between the first singlet and triplet states of these NFAs are predicted using reliable density functional theory (DFT) and time-dependent DFT (T-DFT) calculations. The results show that with respect to prototype CN-F, Br-F, CN-Br, and CN-Cl exhibit comparable energy levels of the lowest unoccupied molecular orbital (LUMO), reduced energy gap (by at least 0.026 eV), Eb (by at least 0.002 eV), and ΔEST (by at least 0.009 eV) values, red shifts (by at least 2 nm) in the wavelengths of the main absorption peaks, and enhanced absorption (by at least 0.05 in total oscillator strength) in the visible to near-infrared regions, indicating their potential as outstanding asymmetric NFAs. This study offers valuable insights into the future design and optimization of NFAs featuring asymmetric terminal groups.

Capturing electronic substituent effect with effective atomic orbitals

The occupations of the effective atomic orbitals (eff-AOs) of the carbon atoms in the aromatic ring serve as the basis for deriving accurate descriptors of the inductive (F) and resonance (R) effects exerted by substituents in substituted benzene derivatives. The eff-AOs enable a clear separation of the σ-type electron density into contributions originating from the C-H/X bonds (where X represents a substituent) and those from the C-C bonding framework. Our analysis reveals that the inductive effect of a substituent is effectively captured by the shift in the occupation of the eff-AOs associated with the C-C bonding framework at the meta position. In contrast, the resonance effect is well-described by the shifts in the occupations of the 2pz-type eff-AOs at the ortho and para positions. The two introduced descriptors for inductive and resonant effects, namely IX and RX, are also applied to predict Hammett's σm and σp in meta- and para-substituted benzoic acid derivatives. In the case of the meta-substituted derivatives, the predictions of the σm values are excellent, with a mean average error of just 0.04. This approach provides a robust and systematic framework for quantifying substituent effects in aromatic systems.

An Oxoiron(IV) Complex Supported by an N-Alkylated Cyclam Ligand System Containing a Pendant Alcohol Moiety

The effect of a pendant neutral alcohol moiety in the N-alkylated cyclam (1,4,8,11-tetraazacyclotetradecane) ligand backbone is examined for the non-heme mononuclear oxoiron(IV) unit in [FeIV(Osyn)(TMC-HOR)(NCCH3)]2+ (1-syn) (TMC-HOR=2-(4,8,11-trimethyl-1,4,8,11-tetraazacyclotetradecan1-yl)ethan-1-ol). Unlike in the related [FeIV(Oanti)(TMC-SR)]+ (3-anti) (TMC-SR=1-mercaptoethyl-4,8,11-trimethyl-1,4,8,11-tetraazacyclotetradecane) complex, bearing an axial mono-anionic thiolate ligand trans to the oxo unit, the alcohol moiety in 1-syn stays protonated and does not axially coordinate to iron. The protonation of the alcohol moiety is a prerequisite for the stabilization of the oxoiron(IV) core; it presumably serves as a hydrogen bonding donor to the oxoiron(IV) unit, which is positioned syn to the three methyl groups. Comparative reactivity studies reveal 1-syn to be a stronger hydrogen atom abstraction but weaker oxygen atom transfer agent relative to the [FeIV(Osyn)(TMC)(NCCH3)]2+ (2-syn) complex, bearing the N-tetramethylated cyclam (TMC) ligand.

Photoinduced NO production from a mononuclear {MnNO}6 complex bearing a metal-diaryldisulphide ligand

A solution of six-coordinate [Mn(PS2)2] (1) is inert towards nitric oxide (NO) at room temperature. In the presence of a proton source such as p-toluenesulfonic acid or perchloric acid, however, the treatment of 1 with NO in the dark leads to the formation of {MnNO}6 [Mn(NO)(SPS-SPS)] (2) with a metal-diaryldisulphide ligand, as confirmed by several spectroscopy investigations, including single-crystal X-ray diffraction. A possible pathway for the formation of 2 was determined through theoretical studies and involves the following: (i) the thiolato sulphur in 1 interacts with H+ to generate an intermediate [Mn(PS2)(PS2H)]+ (A) with an S⋯H interaction; (ii) the reaction of A with NO yields HNO and an Mn(IV)-bound-thiyl radical species (B); and (iii) the nucleophilicity of the thiyl radical B to an adjacent thiolato sulphur produces a five-coordinate Mn(III)-diaryldisulphide species (C), which reacts with the generated HNO to yield 2. Complex 2 is sensitive to visible light. When photolysis of 2 in solution is performed, complex 1 is regenerated and NO is released, which is related to metal-disulphide/metal-thiolate interconversion.

Anti-thermal quenching in NdIII molecular near-infrared thermometers operating at physiological temperatures

Examples of molecular complexes acting as thermometers operating at room temperature in near infrared region are scarce, therefore this work showcases the anti-thermal quenching effect on neodymium(III) molecular thermometers working in biological windows within the physiological temperature range. A mononuclear complex, [Nd(L)(NO3)3] (1Nd), where L is a macrocyclic ligand, was synthesized and used as a precursor to develop two novel species: a dinuclear, [(Nd(L)(NO3))2(µ-BDC)](NO3)2·H2O (2Nd), linked by 1,4-benzenedicarboxylate (BDC), and a hexameric, [(Nd(L))(µ-BTC)(H2O)]6·35H2O (6Nd), linked with 1,3,5-benzenetricarboxylate (BTC). Thermometric properties were studied in the physiological temperature range (292-332 K), utilizing 804 nm laser excitation (first biological window) and monitoring emissions in the second biological window (908, 1065, and 1340 nm) associated with the 4F3/2 → 4I9/2, 4I11/2, 4I13/2 transitions, respectively. Among the complexes, the hexamer 6Nd exhibited exceptional performance, with Sr of 2.4%K-1 at 293 K, when luminescence intensity ratio (LIR) of two Stark components of the 4F3/2 → 4I11/2 emission was used, positioning it as a high-performance NdIII-based thermometer. All complexes displayed anti-thermal quenching behavior, surpassing the current molecular-based thermometers in the near-infrared region. Theoretical calculations using complete active space self consistent field (CASSCF) and Boltzmann population models between Kramers doublets of the 4F3/2 level were performed to rationalize the anti-thermal behavior.

Hydride Migration within RhH2Ag19 Superatom: A Combined Neutron Diffraction and DFT Analysis

An investigation combining neutron diffraction and DFT allows determining the most likely hydride migration pathway within the icosahedral metal framework of [RhH2Ag19{S2P(OnPr)2}12] (RhH2Ag19). Starting from the experimentally derived solid-state structures, a computational analysis is able to reveal an energetically favorable migration pathway with a maximum energy barrier of 4.2 kcal mol-1. The two hydrides migrate simultaneously within the Rh@Ag12 icosahedral core, traversing several positional isomers. This study expands the understanding of hydride dynamics in nanoclusters and provides critical insights into the structural flexibility of the superatom framework. These findings have significant implications for hydrogen storage, catalysis, and the design of advanced hydride-containing materials.

Density functional benchmark for quadruple hydrogen bonds

Hydrogen bonding is an important non-covalent interaction that plays a major role in molecular self-organization and supramolecular structures. It can be described accurately with ab initio quantum chemical wave function methods, which become computationally expensive for large molecular assemblies. Density functional theory (DFT) offers a better balance between accuracy and computational cost, and can be routinely applied to large systems. A large number of density functional approximations (DFAs) has been developed, but their accuracy depend on the application, necessitating benchmark studies to guide their selection for use in applications. Some of us have recently determined highly accurate hydrogen bonding energies of 14 quadruply hydrogen-bonded dimers by extrapolating coupled-cluster energies to the complete basis set limit as well as extrapolating electron correlation contributions with a continued-fraction approach [U. Ahmed et al., Phys. Chem. Chem. Phys., 2024, 26, 24470-24476]. In this work, we study the reproduction of these bonding energies at the DFT level using 152 DFAs. The top ten density functional approximations are composed of eight variants of the Berkeley functionals both with and without dispersion corrections, and two Minnesota 2011 functionals augmented with a further dispersion correction. We find the B97M-V functional with the non-local correlation functional replaced by an empirical D3BJ dispersion correction to be the best DFA, while changes to the dispersion part in other Berkeley functionals lead to poorer performance in our study.

The density-based many-body expansion for poly-peptides and proteins

Fragmentation schemes enable the efficient quantum-chemical treatment of large biomolecular systems, and provide an ideal starting point for the development of accurate machine-learning potentials for proteins. Here, we present a fragment-based method that only uses calculations for single-amino acids and their dimers, and is able to reduce the fragmentation error in total energies to ca. 1 kJ mol-1 per amino acid for polypeptides and proteins across different structural motifs. This is achieved by combining a two-body extension of the molecular fractionation with conjugate caps (MFCC) scheme with the density-based many-body expansion (db-MBE), thus extending the applicability of the db-MBE from molecular clusters to polypeptides and proteins.

Oxidation-induced double aromaticity in periodo-polycyclic hydrocarbons

The doubly oxidized hexaiodobenzene [C6I6]2+ is a well-known example of a double aromatic molecule, exhibiting both π- and σ-aromaticity. In this study, a series of periodo-monocyclic molecules and their doubly oxidized forms were systematically investigated to explore the origin of their double aromaticity. These molecules were employed to provide insights into how the size and aromaticity of the central carbon atom ring influence the aromaticity of the resulting doubly oxidized structures. The knowledge gained in this study was subsequently applied to model periodo-derivatives of polycyclic (anti)aromatic hydrocarbons in which oxidation can induce additional σ-electron cyclic delocalization along the macrocyclic iodine ring, thus also achieving their double aromaticity.

Excited-state nonadiabatic dynamics in explicit solvent using machine learned interatomic potentials

Excited-state nonadiabatic simulations with quantum mechanics/molecular mechanics (QM/MM) are essential to understand photoinduced processes in explicit environments. However, the high computational cost of the underlying quantum chemical calculations limits its application in combination with trajectory surface hopping methods. Here, we use FieldSchNet, a machine-learned interatomic potential capable of incorporating electric field effects into the electronic states, to replace traditional QM/MM electrostatic embedding with its ML/MM counterpart for nonadiabatic excited state trajectories. The developed method is applied to furan in water, including five coupled singlet states. Our results demonstrate that with sufficiently curated training data, the ML/MM model reproduces the electronic kinetics and structural rearrangements of QM/MM surface hopping reference simulations. Furthermore, we identify performance metrics that provide robust and interpretable validation of model accuracy.

A Bimolecular Diels-Alder Reaction Mediated by Inclusion in a Polar Bis-calix[4]pyrrole Octa-Imine Cage

We describe using a dynamically self-assembled octa-imine cage as a molecular flask to accelerate a bimolecular Diels-Alder reaction. We investigate the cage's binding properties using 1H NMR spectroscopic titrations, ITC experiments, and X-ray crystallography. We detect and characterize the formation of the ternary complex (Michaelis) in solution. A detailed kinetic analysis of the reaction data supports that the cage's acceleration is provided by including the two reactants, resulting in an effective molarity (EM) of ∼40 M. Exo-selectivity and shift of the reaction's chemical equilibrium are also encountered in the cage's confined space. Our results mimic enzymes' ability to bind two substrates in a polar cavity, using directional interactions, and accelerate their stereoselective reaction, with the potential for cavity engineering to enable other reactions.

Mimicking the CuD Site of pMMO via a Copper Cage-Complex

The mechanism of action of particulate monooxygenase (pMMO) has yet to be determined. The CuD site with two histidines and an asparagine coordinating to copper has been identified as a potential active site of pMMO. Here, we present a copper cage complex, that assembles this coordination sphere, being a structural mimic of the pMMO. The cage is capable to catalyze aerobic oxidations of organic substrates such as benzylic alcohols to aldehydes and hydroquinones to quinones. This is inspired by the reactivity that is observed for enzymatic active sites possessing copper.

Theoretical Insights into the Impact of the Central Atom on the Photoluminescence Mechanisms of Ligand-Protected Cu Nanoclusters

Ligand-protected copper nanoclusters (CuNCs) have attracted considerable attention in both fundamental research and practical applications due to their easy availability, environmental friendliness, and exceptional optical properties. In this study, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were employed to investigate the photoluminescence (PL) mechanism of two-electron (2e) cluster [Au@Cu14(SCH2CH3)12(P(CH2CH3)3)6]+ (Au@Cu14) and zero-electron (0e) cluster [Cl@Cu14(SCH2CH3)12(P(CH2CH3)3)6]+ (Cl@Cu14) to explore the impact of the central atom on the PL mechanisms of CuNCs. The accuracy of various exchange-correlation (XC) functionals used for fluorescence and phosphorescence energy calculations was evaluated. The BP86 and PBE0 functionals were used to calculate the radiative and nonradiative transition processes of the two clusters. Theoretical calculations showed that enhanced spin-orbit coupling, larger transition dipole moments, more significant orbital overlap, and smaller Huang-Rhys factors and reorganization energies were the main reasons for the higher PL quantum yield (PLQY) of Au@Cu14 than Cl@Cu14. These findings provide important insights into the central atom effect of CuNCs and valuable guidance for their design and optimization in optical applications.

From Donor-Acceptor Ligands to Smart Coordination Polymers: Cyanothiazole-Cu(I) Complexes for Multifunctional Electronic Devices

Cyanothiazoles, small and quite overlooked molecules, possess remarkable optical properties that can be fine-tuned through coordination with transition metals. In this study, we investigate a promising application of cyanothiazoles, where their combination with copper(I) iodide forms a new class of complexes exhibiting outstanding optical properties. X-ray crystallography of copper(I) iodide complexes with isomeric cyanothiazoles revealed key structural features, such as π─π stacking, hydrogen bonding, and rare halogen⋅⋅⋅chalcogen I⋅⋅⋅S interactions, enhancing stability and reactivity. Advanced spectroscopy and computational modeling allowed precise identification of spectral signatures in Fourier-transform infrared (FTIR), nuclear magnetic resonance (NMR), and ultraviolet-visible (UV-Vis) spectra. Fluorescence studies, along with X-ray absorption near edge structure (XANES) synchrotron analyses, highlighted their unique thermal and electronic properties, providing a solid foundation for further research in the field.

Correction: The p-block challenge: assessing quantum chemistry methods for inorganic heterocycle dimerizations

Correction for 'The p-block challenge: assessing quantum chemistry methods for inorganic heterocycle dimerizations' by Thomas Gasevic et al., Phys. Chem. Chem. Phys., 2024, 26, 13884-13908, https://doi.org/10.1039/D3CP06217A.

Mechanisms of Electron Transfer between Metal Clusters and Molecules in Plasmonic Junctions

Surface plasmons can localize the optical field and energy at the nanoscale, significantly enhancing various light-matter interactions, such as in photocatalysis. The hot electrons generated by plasmon decay play a crucial role in driving chemical reactions. To better understand the mechanisms behind electron transfer, we have developed a polarizability bond model to visualize how the electron transfer influences bond polarization. In this study, we examine molecule-metal coupled systems, where the molecules of varying dimensions are embedded between metal clusters. Our findings show that electron transfer is significantly enhanced when the molecular component is directly excited. The efficiency of electron transfer decreases as the cavity gap widens. Distinct electron transfer behaviors are observed across different molecule-metal coupled systems with the most pronounced enhancement occurring between one-dimensional molecules and metal clusters. Further analysis reveals that the atoms in the first and second layers of the metal clusters are critical in facilitating interfacial polarization. Intramolecular bond polarization is particularly strong when electron excitation originates from the molecular component, and bonds near the cavity center or those aligned with near-field polarization are more easily polarized by plasmon excitation. This study reveals the atomic-level electron transfer mechanisms and provides a theoretical basis for optimizing plasmon-mediated catalytic reactions.

Capture of an In Situ Formed Distanna-S-heterocyclic Carbene

The planar, non-twisted distannene Sn2(TIPS)4 (1, TIPS = SiiPr3) reacts with CS2 to form a tetrathiaethylene derivative via the dimerization of two S-heterocyclic carbenes (SHCs). These intermediary-formed SHCs can be transferred to palladium as ligands or captured with B(C6F5)3 (BCF) and, furthermore, facilitate a new pathway for formation of the stannaethene SHC═Sn(TIPS)2 by the reaction of 1 with (PPh3)2Pd-CS2. In addition to the characterization of the new complexes, theoretical calculations of the frontier orbitals were performed, which indicate a high π-acceptor character of the SHC.

Revisiting the Thermal Behavior and Infrared Absorbance Bands of Anhydrous and Hydrated DL-Tartaric Acid

In this work, we studied the thermal behavior and infrared fingerprint of anhydrous and hydrated DL-tartaric acid via conventional and modulated Differential Scanning Calorimetry (DSC), Thermogravimetry (TGA), Fourier Transform Infrared Spectroscopy (FTIR), nuclear magnetic resonance (NMR), pH measurements, and ab initio density functional theory (DFT) calculations. Six samples were examined in total (raw, recrystallized from D2O solution, freeze-dried, and three heated samples). The results reveal that both forms (anhydrous and hydrated) do not exhibit melting prior to decomposition. It is also shown that the so-called DL-tartaric acid does not exist in the solid state in pure form, but it contains water and a tartaric acid oligomer, which is produced through esterification. Alteration of the chemical structure (reflected through decomposition) is initiated at quite low temperatures and is more pronounced for the hydrated form. Up to 75 °C, decomposition proceeds through esterification, while at higher temperatures it seems to be reversed due to the increase in water and decrease in COOH groups emerging through anhydride formation. Either upon heating or at sub-zero temperatures during freeze-drying, the hydrated form decomposes, and although some water is removed, new water is produced due to esterification. The conclusions are also supported by DFT calculations.

Identification of metal-centered excited states in Cr(iii) complexes with time-resolved L-edge X-ray spectroscopy

New coordination complexes of 3d metals that possess photoactive metal-centered (MC) excited states are promising targets for optical applications and photocatalysis. Ultrafast spectroscopy plays an important role in elucidating the photophysical mechanisms that underlie photochemical activity. However, it can be difficult to assign transient signals to specific electronic excited states and mechanistic information is often inferred from kinetics. Here it is demonstrated that 3d L-edge X-ray absorption spectroscopy is highly selective for MC excited states. This is accomplished by probing the 2E spin-flip excited state in Cr(acac)3 using synchrotron-based picosecond time-resolved XAS in solution. This excited state of Cr(iii) has the property that its potential is nested with the ground state, which allows for the assessment of purely electronic changes upon excited state formation. Combining the measurements with ligand field and ab initio theory shows that the observed spectral changes between the 4A2 ground state and 2E excited state are due to an intensity redistribution among the core-excited multiplets. Extrapolating these results to higher-lying MC excited states predicts that Cr L3-edge XAS can distinguish two states separated by ∼0.1 eV despite the L3-edge resolution being limited by the 0.27 eV lifetime width of the 2p core-hole. This highlights the potential of L-edge XAS as a sub-natural linewidth probe of electronic state identity.

Conformational isomerization in Co(acac)2via spin-state switch: a computational study

Conformational dynamics of ligands in transition metal complexes can give rise to interesting physical, chemical, spectroscopic, and magnetic properties of the complexes. The changing ligand environment often affects the d-orbital splitting pattern that allows multiple possible ways of electron arrangement in the frontier molecular orbitals, resulting in several closely spaced electronic states with different orbital and spin symmetries. The system can explore these states with either thermal or photophysical means. In the present work, we demonstrate the possibility of a spin transition in Co(acac)2 assisted by a conformational rearrangement of the ligand. Electronic structure calculations show that the complex adopts a square-planar and tetrahedral geometry with low-spin and high-spin electronic configurations, respectively. A spin-conserved conformational change involves a larger energy barrier in both high- and low-spin states. On the other hand, a low-lying minimum-energy-crossing point exists between the two spin-states that provides a low-energy pathway for conformational isomerization between the two isomers. While the spin-assisted isomerization from a tetrahedral to square planar form requires crossing a 10 kcal mol-1 barrier, the reverse barrier is only 2 kcal mol-1. The calculation of the magnetic properties of the complex reveals a large magnetic anisotropy barrier of 57.6 cm-1 for this complex in the high-spin state.

Hydroxyl-induced structural defects in metal-organic frameworks for improved photocatalytic decontamination: Accelerated exciton dissociation and hydrogen bonding interaction

The introduction of structural defects can improve the charge separation efficiency of metal-organic frameworks (MOFs)-based photocatalysts, which however come with suboptimal decontamination performance, due to steric hindrance and limited binding capacity of the involved modulators. In this work, hydroxyl group capturing the advantages of both worlds was utilized as new modulator to improve the photocatalytic performance of Fe-based defective MOFs. Benefited from its low steric effect and strong coordination bonding capability, hydroxyl-induced defects in Fe-MOF contributed to a nearly 8-fold increase of rate constant for the photocatalytic removal of hexavalent chromium (Cr(VI)) compared to that of pristine one, which also exceeded the defective one induced by acetic acid as modulator. A combination of characterizations and theoretical calculations suggests that hydroxyl-induced structural defects fostered faster kinetics of exciton dissociation and optimal charge separation. The higher electron utilization through hydrogen bonding interaction between these hydroxyl-induced structural defects and contaminant was further confirmed by ab initio molecular dynamics (AIMD) simulations. This work presents a simple yet robust strategy for the generation of defective MOFs, upon which efficient photoreduction systems toward Cr(VI) removal are anticipated.

Reaction of a Potassium Aluminyl with Sn[N(SiMe3)2]2 - Isolation of a Stable, Trimetallic Sn(I) Radical Anion

The reaction of the potassium aluminyl K[Al(NON)] ([NON]2-=[O(SiMe2NDipp)2]2-, Dipp=2,6-iPr2C6H3) with the stannylene Sn[N(SiMe3)2]2 in benzene afforded K3[(Sn4){Al(NON)}2{N(SiMe3)2}], containing a distorted tetrahedral Sn4-cluster. Computational analysis indicates that four of the edges in this unit are composed of Sn-Sn bonds, with the remaining two that are spanned by aluminium involved in three centre two electron (3c2e) Sn-Al-Sn bonds. The formation of Al(II) species during this reaction is indicated by the isolation of the dialuminated cyclohexadiene 1,4-[Al(NON)]2(μ-C6H6). Repeating the reaction in methylcyclohexane generated a thermally stable, trimetallic Sn(I) radical anion in K[Sn{Al(NON)}2]. Compared to all other reported Sn(I) radicals, its EPR spectrum is unique; the main turning points of its spectrum appear at g values above 2 and the Sn hyperfine coupling is substantially smaller in magnitude. These data, together with ENDOR measurements and DFT calculations show that the SOMO is entirely localised in an unhybridised 5p orbital, such that spin-orbit contributions to the g and Sn hyperfine tensors are quenched.

Magnetically induced current density from numerical curls of nucleus independent chemical shifts

Instead of computing magnetically induced current densities (MICD) via the wave function and their quantum mechanical definition, one can also use the differential form of the Ampère-Maxwell law to obtain them from curls via spatial derivatives of the induced magnetic field. In magnetic molecular response calculations, the latter can be done by taking the numerical derivative of the so-called "nucleus-independent chemical shifts" (NICS), which are implemented in many standard quantum chemical programs. The resulting numerical MICD data is in contrast to any other first-principles based numerically obtained MICDs computed via the wave function route, virtually divergence-free.

Decentralized Metal-Metal Bonding in the AuNi(CO)4- Anion Described Equally Well with Dative Bonding as with Electron-Sharing Bonding

The heterodinuclear AuNi(CO)4- complex is scrutinized in the gas phase by using mass-selected anionic photoelectron velocity-map imaging spectroscopy in conjunction with theoretical computations. The ground state of AuNi(CO)4- is characterized to have an Au-Ni bonded structure, consisting of an AuCO fragment attached to the Ni center of the Ni(CO)3 fragment. Comprehensive quantum chemical studies reveal that the AuNi(CO)4- complex at equilibrium structure features a decentralized bonding scenario, where the exotic metal-metal σ bonding may be equally well described with dative bonding as with electron-sharing bonding between two fragments.

Overcoming Challenges in Density Functional Theory-Based Calculations of Hyperfine Coupling Constants for Heavy Heteroatom Radicals

This study assesses density functional theory (DFT) methods for their accuracy in calculating hyperfine coupling constants (HFCCs) of heavy heteroatom radicals with heteroatoms including Sb, Bi, In, Tl, and Sn. Given the essential role of electron paramagnetic resonance spectroscopy in characterization of these species, it is crucial that theoretical models can predict HFCCs accurately for heavy elements. This work presents a computational approach that addresses crucial factors: selection of basis set, hybrid exchange-correlation functional, higher Hartree-Fock (HF) exchange, and the Gaussian description of nuclear charge. The relativistic effects are introduced using one-component linear response theory with the second-order Douglas-Kroll-Hess formalism and the fully relativistic four-component Dirac-Kohn-Sham method. The findings show that, while one-component DFT is accurate for the 4th-row elements, the four-component method is more precise for the 5th-row radicals and the one-component approach fails for the 6th-row congeners. Increasing HF exchange significantly improves HFCC predictions. The developed framework for accurate HFCC calculations will enhance the understanding of electronic and magnetic properties of heavy element radicals and can be used by computational chemists and experimentalists alike.

The true atomistic structure of a disordered crystal: a computational study on the photon upconverting material β-NaYF4 and its Er3+-, Tm3+-, and Yb3+-doped derivates

Hexagonal (β-) NaYF4 and LiYF4 doped with trivalent lanthanide ions (Ln3+, e.g., Er3+, Tm3+, and Yb3+) are well-known photon upconverting materials. This property is crucially determined by the precise location of the Ln3+ dopant ions and their closest neighbouring ions in the host material. However, due to the inherent disorder of the crystal structures the atomistic structure of a disordered crystal such as β-NaYF4 is not unambiguously provided by X-ray diffraction techniques. Here, theoretical estimates for the true structure of the material are obtained via periodic density functional theory (DFT) calculations of large supercells. Our results reveal that Ln3+ doping of β-NaYF4 occurs in a variety of low-symmetry sites, which are significantly altered by the occupational disorder of the crystal structure. Mainly, the distribution of Na+ and Y3+ around a doping site significantly influences the positions of the F- closest to the dopant. The results of this study are substantiated by applying the same method on the well-ordered host crystal LiYF4 and by comparison with available experimental and theoretical data. Similar results are expected for other disordered crystalline host materials such as β-NaGdF4 or cubic (α-) NaYF4. The obtained structural information is a prerequisite for future accurate simulations and prediction of key parameters for the upconversion process in bulk materials and nanoparticles.

Computational exploration of vinyl sulfoxonium ylide chemistry

This review comprehensively examines the computational techniques employed to elucidate the reactivity, selectivity, and mechanistic pathways of vinyl sulfoxonium ylides. By delving into a spectrum of reactions ranging from insertion and cycloaddition to annulation, multicomponent reactions, and carbene-mediated transformations, we demonstrate the pivotal role of computational techniques in understanding the mechanism, reactivity and selectivity. The synergy between experimental and computational approaches is emphasized as a driving force for future breakthroughs and the continuous evolution of this dynamic and emerging field.

Hydrogen Oxidation by Bioinspired Models of [FeFe]-Hydrogenase

Synthetic azadithiolate-bridged diiron clusters serve as structural analogues of the active site of [FeFe]-hydrogenases. Recently, an o-alkyl substitution of aniline-based azadithiolate bridge allowed these synthetic models to both oxidize H2 and reduce H+, i.e., bidirectional catalysis. Hydrogen oxidation by synthetic analogues of hydrogenases is rare, and even rarer is the ability of diiron hexacarbonyls to oxidize H2. A series of synthetic azadithiolate-bridged biomimetic diiron hexacarbonyl complexes are synthesized where the substitution in the para position of the ortho-methyl aniline in the azadithiolate bridge is systematically varied between electron-withdrawing and electron-donating groups to understand factors that control H2 oxidation by diiron hexacarbonyl analogues of [FeFe]-hydrogenases. The results show that the substituents in the para position of the ortho-ethyl aniline affect the electronic structure of the azadithiolate bridge as well as that of the diiron cluster. The electron-withdrawing -NO2 substituent results in faster H2 oxidation relative to that of a -OCH3 substituent.

Highly increasing solubility of clofazimine, an extremely water-insoluble basic drug, in lipid-based SEDDS using digestion products of long-chain lipids

Clofazimine (CFZ) is a highly effective antibiotic against leprosy and drug-resistant tuberculosis and is on the WHO List of Essential Drugs. However, no CFZ product with optimal bioavailability is available worldwide. The manufacturer withdrew its only marketed product, presumably due to poor and erratic bioavailability because of extremely low aqueous solubility in the gastrointestinal pH range. We developed a self-emulsifying drug delivery system (SEDDS) using a lipid digestion product (LDP) containing glyceryl monooleate and oleic acid at ∼1:2 molar ratio to increase drug solubility and ensure rapid dispersion into microemulsion. While solubilities of CFZ in glyceryl monooleate, glyceryl trioleate, and two common surfactants (Tween 80 and Kolliphor EL) were comparatively low (<15 mg/g), oleic acid provided a very high solubility of ∼500 mg/g. Because of the presence of oleic acid, the clofazimine solubility in SEDDS containing a 50:50 w/w mixture of LDP and surfactants increased to 130 mg/g. Two formulations having 50 or 100 mg CFZ in one gram of SEDDS were developed. They dispersed rapidly and almost completely in simulated intestinal fluid and in the USP pH 6.8 phosphate buffer containing 3 mM sodium taurocholate. There was some precipitation of CFZ as the HCl salt at low gastric pH during dispersion testing, but the effect could be avoided using enteric-coated capsules. Thus, an enteric-coated lipid-based formulation for CFZ with as high as 100 mg/g drug loading was developed, providing complete drug release and producing microemulsions under intestinal pH conditions.

A novel type of heteroleptic Cu(I) complexes featuring nitrogen-rich tetrazine ligands: syntheses, crystal structures, spectral properties, cyclic voltammetry, and theoretical calculations

Heteroleptic copper(I) complexes with the general formula [Cu(N^N)(P^P)]X constitute one of the most studied categories of 3d metal photosensitizers. Here, we examine using 1,2,4,5-tetrazine-based ligands to synthesize photoactive Cu(I) complexes. The newly prepared complexes were characterized by single-crystal X-ray analysis, which revealed the formation of dinuclear complexes [Cu2(μ-L1)(xantphos)2](ClO4)2 (1) and [Cu2(μ-L2)(xantphos)2](ClO4)2 (2), and mononuclear complexes [Cu(L3)(xantphos)]ClO4 (3) and [Cu(L4)(xantphos)]ClO4 (4), where L1 = 3,6-di(2'-pyridyl)-1,2,4,5-tetrazine (bptz), L2 = 3,6-bis-(3,5-dimethyl-pyrazol-1-yl)-1,2,4,5-tetrazine, L3 = 3-(2-pyridyl)-1,2,4,5-tetrazine, L4 = 3-(3,5-dimethyl-1H-pyrazol-1-yl)-1,2,4,5-tetrazine and xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene. Solution stability assays were addressed by NMR spectroscopy showing that complexes are stable in dichloromethane over several days. The electronic excited states were investigated by UV-Vis and luminiscence spectroscopy and interpreted with the help of TD-DFT calculations. In the case of all the newly prepared complexes 1-4, the absorptions in the visible region were assigned to non-emissive MLCT transitions between the Cu(I) and the respective tetrazine ligand. Redox properties were probed by cyclic voltammetry and also supplemented by DFT calculations. Interestingly, tetrazine ligands L1-L4 show a shift of reduction potential to less negative values upon the formation of Cu(I) complexes 1-4. Moreover, the two complexes 3-4 represent the first reported case of mononuclear heteroleptic Cu(I)-tetrazine complexes.

Synthesis of triple-decker sandwich compounds featuring a M-M bond through cyclo-Bi5 and cyclo-Sb5 rings

The cyclopentadienyl anion is a π-aromatic five-membered ring ligand that is widely used in organometallic chemistry. By replacing the CH groups in cyclopentadiene with isoelectronic group-15 elements, an inorganic analogue can be obtained. In this line, Pn5 (Pn = P, Sb) rings have been stabilized in a triple-decker sandwich structure, prepared via high-temperature reactions, and an example of a Bi5- ring stabilized in a cobalt-based inverse-sandwich-type complex has been reported. Here we report the synthesis and structural characterization of two complexes, [Cp-V(cyclo-Sb5)V-Cp]2- and [Cp-Nb(cyclo-Bi5)Nb-Cp]2-, which are stabilized by [K(18-crown-6)]+ or [K(2.2.2-crypt)]+ cations at room temperature under mild conditions. Our bonding analysis through various quantum-chemical methods reveals that V‒V and Nb‒Nb bonds pass through the centre of the E5 rings (E = Sb, Nb). In contrast to free cyclo-E5 (E = Sb, Bi) the cyclo-E5 moieties between Cp-E units do not possess any aromatic character because the M‒M (M = V, Nb) bond passes through the centre of the ring.

A living library concept to capture the dynamics and reactivity of mixed-metal clusters for catalysis

The exploration of ligated metal clusters' chemical space is challenging, partly owing to an insufficiently targeted access to reactive clusters. Now, dynamic mixtures of clusters, defined as living libraries, are obtained through organometallic precursor chemistry. The libraries are populated with interrelated clusters, including transient and highly reactive ones, as well as more accessible but less reactive species. Their evolutions upon perturbation with substrate molecules are monitored and chemical information is gained without separation of the clusters. Here we prepared a library of all-hydrocarbon ligated Cu/Zn clusters and developed a bias-free computational framework suited to analyse the full compositional space that yields a reliable structural model for each cluster. This methodology enables efficient searches for structure-reactivity relationships relevant for catalysis with mixed-metal clusters: when treating the library with CO2 or 3-hexyne and H2, we discovered [Cu11Zn6](Cp*)8(CO2)2(HCO2) bearing a formate species related to CO2 reduction and [Cu9Zn7](Cp*)6(Hex)3(H)3 bearing C6 species related to alkyne semi-hydrogenation.

Design of Zn-Binding Peptide(s) from Protein Fragments

We designed a minimalistic zinc(II)-binding peptide featuring the Cys2His2 zinc-finger motif. To this aim, several tens of thousands of (His/Cys)-Xn-(His/Cys) protein fragments (n=2-20) were first extracted from the 3D protein structures deposited in Protein Data Bank (PDB). Based on geometrical constraints positioning two Cys (C) and two His (H) side chains at the vertices of a tetrahedron, approximately 22 000 sequences of the (H/C)-Xi-(H/C)-Xj-(H/C)-Xk-(H/C) type, satisfying Nmetal-binding H=Nmetal-binding C=2, were processed. Several other criteria, such as the secondary structure content and predicted fold stability, were then used to select the best candidates. To prove the viability of the computational design experimentally, three peptides were synthesized and subjected to isothermal calorimetry (ITC) measurements to determine the binding constants with Zn2+, including the entropy and enthalpy terms. For the strongest Zn2+ ions binding peptide, P1, the dissociation constant was shown to be in the nanomolar range (KD=~220 nM; corresponding to ΔGbind=-9.1 kcal mol-1). In addition, ITC showed that the [P1 : Zn2+] complex forms in 1 : 1 stoichiometry and two protons are released upon binding, which suggests that the zinc coordination involves both cysteines. NMR experiments also indicated that the structure of the [P1 : Zn2+] complex might be quite similar to the computationally predicted one. In summary, our proof-of-principle study highlights the usefulness of our computational protocol for designing novel metal-binding peptides.

UV Absorption Spectra of TAMRA and TAMRA Labeled Peptides: A Combined Density Functional Theory and Classical Molecular Dynamics Study

This study explores the structural and electronic factors affecting the absorption spectra of 5-carboxy-tetramethylrhodamine (TAMRA) in water, a widely used fluorophore in imaging and molecular labeling in biophysical studies. Through molecular dynamics (MD) simulations and density functional theory (DFT) calculations, we examine TAMRA UV absorption spectra together with TAMRA-labeled peptides (Arg9, Arg4, Lys9). We found that DFT calculations with different functionals underestimate TAMRA maximum UV absorption peak by ~100 nm, resulting in the maximum at ca. 450 nm instead of the experimental value of ca. 550 nm. However, incorporating MD simulation snapshots of TAMRA in water, the UV maximum peak shifts and is in close agreement with the experimental results due to the rotation of TAMRA N(CH3)2 groups, effectively captured in MD simulations. The method is used to estimate the UV absorption spectra of TAMRA-labeled peptides, matching experimental values.

Exploring Scent Distinction with Polymer Brush Arrays

The ability to distinguish scents, volatile organic compounds (VOCs), and their mixtures is critical in agriculture, food safety, and public health. This study introduces a proof-of-concept approach for VOC and scent distinction, leveraging polymer brush arrays with diverse chemical compositions designed to interact with various VOCs and scents. When VOCs or scents are exposed to the brush array, they produce distinct mass absorption patterns for different polymer brushes, effectively creating "fingerprints". Scents can be recognized without having to know the absorption of their individual components. This allows for a scent distinction technique, mimicking scent recognition within a mammalian olfactory system. To demonstrate the scent distinction, we synthesized different polymer brushes, zwitterionic, hydrophobic, and hydrophilic, using surface-initiated photoinduced electron transfer-reversible addition-fragmentation chain-transfer polymerization with eosin Y and triethanolamine as catalysts. The polymer brushes were then exposed to vapors of different single-compound VOCs and complex scents consisting of many VOCs, such as the water-ethanol mixture, rosemary oil, lavender oil, and whiskey scents. Quartz crystal microbalance measurements with dissipation monitoring (QCM-D) show a clear difference in brush absorption for these diverse VOC vapors such that distinct fingerprints can be identified. Our proof-of-concept study aims to pave the way for universal electronic nose sensors that distinguish scents by combining mass absorption patterns from polymer brush-coated surfaces.

Excited-state structural characterization of a series of nanosecond-lived [Fe(terpy)2]2+ derivatives using x-ray solution scattering

[ F e ( t e r p y ) 2 ] 2 + (terpy = 2,2':6',2″-terpyridine) is a transition metal complex where the spin state is photoswitchable and where the properties of the metal-centered quintet excited state (5MC) can be tuned by substituting different electron withdrawing or electron donating groups on the 4' position of the terpyridine. To better understand the physics determining the photoswitching performance, a deeper insight into the positions of the relevant potential energy surfaces and the molecular structure of the 5MC state is needed. We present a structural investigation based on Time Resolved x-ray Solution Scattering (TR-XSS) by which we determine the average dFe-N bond-length elongation following population of the 5MC state as well as the lifetime of this state in a series of seven modified [Fe(terpy)2]2+ systems in aqueous solution following photo-excitation. The analysis of the TR-XSS data is supported by Density Functional Theory (DFT) and Molecular Dynamics calculations. The quintet state lifetime is determined to vary by more than a factor of 10 (from 1.5 to 16 ns) based on the electron withdrawing/donating properties of the substituting group. Both the DFT calculations and the structural analysis of the experimental data show that the main photo-induced change in metal-ligand bond lengths ΔdFe-N is ∼0.2 Å for all systems.

N-Heterocyclic Carbenes: A Benchmark Study on their Singlet-Triplet Energy Gap as a Critical Molecular Descriptor

N-heterocyclic carbenes (NHCs) are used extensively in modern chemistry and materials science. The in-depth understanding of their electronic structure and their metal complexes remains an important topic of research and of experimental and theoretical interest. Herein, the adiabatic singlet-triplet gap as a superior, quantifiable critical descriptor, sensitive to the nature and the structural diversity of the NHCs, for a successful rationalization of experimental observations and computationally extracted trends is established. The choice is supported by a benchmark study on the electronic structures of NHCs, using high-level ab initio methods, that is, complete active space self-consistent field, n-electron valence second-order perturbation theory, multireference configuration interaction + singles + doubles, and domain-based local pair natural orbital-coupled cluster method with single-, double-, and perturbative triple excitations along with density functional theory methods such as BP86, M06, and M06-L, B3LYP, PBE0, TPSSh, CAM-B3LYP, and B2PLYP. In contrast to the adiabatic singlet-triplet (S-T) gap preferred as descriptor, the highest occupied molecular orbital-lowest unoccupied molecular orbital gap or the S-T vertical gap that has been used in the past occasionally leads to controversial results; some of these are critically discussed below. Extrapolation of these ideas to a group of copper-NHC complexes is also described.