2D Graphene Oxide Membrane Nanoreactors for Rapid Directional Flow Ring-Opening Reactions with Dominant Same-Configuration Products.

Nanoconfinement within enzymes can increase reaction rate and improve selectivity under mild conditions. However, it remains a great challenge to achieve chemical reactions imitating enzymes with directional molecular motion, short reaction time, ≈100% conversion, and chiral conversion in artificial nanoconfined systems. Here, directional flow ring-opening reactions of styrene oxide and alcohols are demonstrated with ≈100% conversion in <120 s at 22 °C using graphene oxide membrane nanoreactors. Dominant products have the same configuration as chiral styrene oxide in confined reactions, which is dramatically opposed to bulk reactions. The unique chiral conversion mechanism is caused by spatial confinement, limiting the inversion of benzylic chiral carbon. Moreover, the enantiomeric excess of same-configuration products increased with higher alkyl charge in confined reactions. This work provides a new route to achieve rapid flow ring-opening reactions with specific chiral conversion within 2D nanoconfined channels, and insights into the impact of nanoconfinement on ring-opening reaction mechanisms.

Crystalline porous organic salts.

Crystalline porous organic salts (CPOSs), formed by the self-assembly of organic acids and organic bases through ionic bonding, possess definite structures and permanent porosity and have rapidly emerged as an important class of porous organic materials in recent years. By rationally designing and controlling tectons, acidity/basicity (pKa), and topology, stable CPOSs with permanent porosity can be efficiently constructed. The characteristics of ionic bonds, charge-separated highly polar nano-confined channels, and permanent porosity endow CPOSs with unique physicochemical properties, offering extensive research opportunities for exploring their functionalities and application scenarios. In this review, we systematically summarize the latest progress in CPOS research, describe the synthetic strategies for synthesizing CPOSs, delineate their structural characteristics, and highlight the differences between CPOSs and hydrogen-bonded organic frameworks (HOFs). Furthermore, we provide an overview of the potential applications of CPOSs in areas such as negative linear compression (NLC), proton conduction, rapid transport of CO2, selective and rapid transport of K+ ions, atmospheric water harvesting (AWH), gas sorption, molecular rotors, fluorescence modulation, room-temperature phosphorescence (RTP) and catalysis. Finally, the challenges and future perspectives of CPOSs are presented.

Efficient Flow Synthesis of Aspirin within 2D Sub-Nanoconfined Laminar Annealed Graphene Oxide Membranes.

The aim of this work is to develop an environmentally friendly, safe, and simple route for realizing efficient preparation of aspirin. Here, inspired by enzyme synthesis in vivo, the aspirin synthesis has been realized by sub-nanoconfined esterification with directional flow and ≈100% conversion in an unprecedented reaction time of <6.36 s at 23 °C. Such flow esterification reaction is catalyzed by thermally transformed graphene oxide (GO) membranes with tailored physicochemical properties, which can be obtained simply through a mild annealing method. A possible mechanism is revealed by density functional theory calculation, indicating that the synergistic effect of spatial confinement and surface electronic structure can significantly improve the catalytic performance. By restricting reactants within 2D sub-nano space created by GO-based laminar flow-reactors, the present strategy provides a new route to achieve rapid flow synthesis of aspirin with nearly complete conversion.

High-Performance X-Ray Imaging using Lanthanide Metal-Organic Frameworks.

Scintillating materials that convert ionizing radiation into low-energy photons hold great potential for radiation detection, nondestructive inspection, medical radiography, and space exploration. However, organic scintillators are characterized by low radioluminescence, while bulky inorganic scintillators are not suitable for the development of flexible detectors. Here, high-resolution X-ray imaging using solution-processable lanthanide-based metal-organic frameworks as microscale scintillators is demonstrated. Mechanistic studies suggest that lanthanide ions absorb X-rays to generate high-density molecular triplet excitons, and excited linkers subsequently sensitize lanthanide ions via nonradiative resonance energy transfer. Furthermore, the crystalline nature offers a delocalized electronic feature rather than isolated subunits, which enables direct trapping of charge carriers by lanthanide emitters. By controlling the concentration ratio between Tb3+ and Eu3+ ions, efficient and color-tunable radioluminescence of lanthanide ions can be achieved. When coupled with elastic, transparent polymer matrices, these metal-organic framework-based microscintillators allow the fabrication of flexible X-ray detectors. Such detectors feature a detection limit of 23 nGy s-1 , which is 240 times lower than the typical radiation dose for medical diagnosis. X-ray imaging with resolution higher than 16.6 line pairs per millimeter is further demonstrated. These findings provide insight into the future design of hybrid scintillators for optoelectronics and X-ray sensing and imaging.

AuNP-Modulated qPCR: An Optimized System for Detecting MIR Biophotons Released in DNA Replication.

Invited for the cover of this issue are Lei Jiang and Bo Song at the University of Shanghai for Science and Technology and the Technical Institute of Physics and Chemistry (CAS), and colleagues at Fudan University and South China Normal University. The image depicts how the hydrolysis of cellular energy molecules (i.e., ATP and dNTPs) releases mid-infrared photons to efficiently drive biological processes including DNA replication. Read the full text of the article at 10.1002/chem.202203513.

AuNP-Modulated qPCR: An Optimized System for Detecting MIR Biophotons Released in DNA Replication.

Living systems can utilize energy with a high efficiency. Biophotons are proposed to modulate biological functions with such efficiency; however, the underlying mechanism remains unexplored, especially due to the challenge of ultraweak mid-infrared (MIR) light detection and the theoretical perturbation from spontaneous MIR emission. Here, we proposed an optimized system to detect MIR biophotons generated in the hydrolysis of deoxynucleotide triphosphates (dNTPs, energy-storing molecules similar to ATP). The system used a quantitative polymerase chain reaction (qPCR) that was modulated by gold nanoparticle (AuNP) concentration and thus by the inter-AuNP distance, which depends on the concentration above. The measurements indicate that 33- and 84-THz photons are released by dNTP hydrolysis, which can drive DNA replication. Our findings provide a novel chain-reaction-based method for detecting MIR photons in solution, and pave a way for photon-based insights to understand the highly efficient energy utilization of biology.

Regularized Localized Molecular Orbitals in a Divide-and-Conquer Approach for Linear Scaling Calculations.

Non-orthogonal localized molecular orbitals (NOLMOs) have been employed as building blocks for the divide-and-conquer (DC) linear scaling method. The NOLMOs are calculated from subsystems and used for constructing the density matrix (DM) of the entire system, instead of the subsystem DM in the original DC approach. Also, unlike the original DC method, the inverse electronic temperature parameter ß is not needed anymore. Furthermore, a new regularized localization approach for NOLMOs has been developed, in which the localization cost function is a sum of the spatial spread function, as in the Boys method, and the kinetic energy, as a regularization measure to limit the oscillation of the NOLMOs. The optimal weight of the kinetic energy can be determined by optimization with analytical gradients. The resulting regularized NOLMOs have enhanced smoothness and better transferability because of reduced kinetic energies. Compared with the original DC, while NOLMO-DC has a similar computational linear scaling cost, the accuracy of NOLMO-DC is better by several orders of magnitude for large conjugated systems and by about 1 order of magnitude for other systems. The NOLMO-DC method is thus a promising development of the DC approach for linear scaling calculations.

Theoretical studies on triplet-state driven dissociation of formaldehyde by quasi-classical molecular dynamics simulation on machine-learning potential energy surface.

The H-atom dissociation of formaldehyde on the lowest triplet state (T1) is studied by quasi-classical molecular dynamic simulations on the high-dimensional machine-learning potential energy surface (PES) model. An atomic-energy based deep-learning neural network (NN) is used to represent the PES function, and the weighted atom-centered symmetry functions are employed as inputs of the NN model to satisfy the translational, rotational, and permutational symmetries, and to capture the geometry features of each atom and its individual chemical environment. Several standard technical tricks are used in the construction of NN-PES, which includes the application of clustering algorithm in the formation of the training dataset, the examination of the reliability of the NN-PES model by different fitted NN models, and the detection of the out-of-confidence region by the confidence interval of the training dataset. The accuracy of the full-dimensional NN-PES model is examined by two benchmark calculations with respect to ab initio data. Both the NN and electronic-structure calculations give a similar H-atom dissociation reaction pathway on the T1 state in the intrinsic reaction coordinate analysis. The small-scaled trial dynamics simulations based on NN-PES and ab initio PES give highly consistent results. After confirming the accuracy of the NN-PES, a large number of trajectories are calculated in the quasi-classical dynamics, which allows us to get a better understanding of the T1-driven H-atom dissociation dynamics efficiently. Particularly, the dynamics simulations from different initial conditions can be easily simulated with a rather low computational cost. The influence of the mode-specific vibrational excitations on the H-atom dissociation dynamics driven by the T1 state is explored. The results show that the vibrational excitations on symmetric C-H stretching, asymmetric C-H stretching, and C=O stretching motions always enhance the H-atom dissociation probability obviously.

Nanoporous and Highly Thermal Conductive Thin Film of Single-Crystal Covalent Organic Frameworks Ribbons.

Nanoporous materials are widely explored as efficient adsorbents for the storage of gases and liquids as well as for effective low-dielectric materials in large-scale integrated circuits. These applications require fast heat transfer, while most nanoporous substances are thermal insulators. Here, the oriented growth of micrometer-sized single-crystal covalent organic frameworks (COFs) ribbons with nanoporous structures at an air-water interface is presented. The obtained COFs ribbons are interconnected into a continuous and purely crystalline thin film. Due to the robust connectivity among the COFs ribbons, the entire film can be easily transferred and reliably contacted with target supports. The measured thermal conductivity amounts to ∼5.31 ± 0.37 W m-1 K-1 at 305 K, which is so far the highest value for nanoporous materials. These findings provide a methodology to grow and assemble single-crystal COFs into large area ensembles for the exploration of functional properties and potentially lead to new devices with COFs thin films where both porosity and thermal conductivity are desired.

A Robust PtNi Nanoframe/N-Doped Graphene Aerogel Electrocatalyst with Both High Activity and Stability.

Insufficient catalytic activity and stability and high cost are the barriers for Pt-based electrocatalysts in wide practical applications. Herein, a hierarchically porous PtNi nanoframe/N-doped graphene aerogel (PtNiNF-NGA) electrocatalyst with outstanding performance toward methanol oxidation reaction (MOR) in acid electrolyte has been developed via facile tert-butanol-assisted structure reconfiguration. The ensemble of high-alloying-degree-modulated electronic structure and correspondingly the optimum MOR reaction pathway, the structure superiorities of hierarchical porosity, thin edges, Pt-rich corners, and the anchoring effect of the NGA, endow the PtNiNF-NGA with both prominent electrocatalytic activity and stability. The mass and specific activity (1647 mA mgPt -1 , 3.8 mA cm-2 ) of the PtNiNF-NGA are 5.8 and 7.8 times higher than those of commercial Pt/C. It exhibits exceptional stability under a 5-hour chronoamperometry test and 2200-cycle cyclic voltammetry scanning.

BDF: A relativistic electronic structure program package.

The BDF (Beijing Density Functional) program package is in the first place a platform for theoretical and methodological developments, standing out particularly in relativistic quantum chemical methods for chemistry and physics of atoms, molecules, and periodic solids containing heavy elements. These include the whole spectrum of relativistic Hamiltonians and their combinations with density functional theory for the electronic structure of ground states as well as time-dependent and static density functional linear response theories for electronically excited states and electric/magnetic properties. However, not to be confused by its name, BDF nowadays comprises also of standard and novel wave function-based correlation methods for the ground and excited states of strongly correlated systems of electrons [e.g., multireference configuration interaction, static-dynamic-static configuration interaction, static-dynamic-static second-order perturbation theory, n-electron valence second-order perturbation theory, iterative configuration interaction (iCI), iCI with selection plus PT2, and equation-of-motion coupled-cluster]. Additional features of BDF include a maximum occupation method for finding excited states of Hartree-Fock/Kohn-Sham (HF/KS) equations, a very efficient localization of HF/KS and complete active space self-consistent field orbitals, and a unique solver for exterior and interior roots of large matrix eigenvalue problems.

A nonlinear optical switch induced by an external electric field: inorganic alkaline-earth alkalide.

Exploring a new type of nonlinear optical switch molecule with excess electron character is extremely important for promoting the application of excess electron compounds in the nonlinear optical (NLO) field. Here, we report external electric field (EEF) induced second-order NLO switch molecules of inorganic alkaline-earth alkalides, M(NH3)6Na2 (M = Mg or Ca). The centrosymmetric structure of M(NH3)6Na2 is destroyed in the presence of an EEF, and then a long-range charge transfer process occurs. It has been found that excess electrons are gradually transferred from one Na atom to the other Na atom through the inorganic metal cluster M(NH3)6. Finally, the excess electrons are completely located on one of the two Na atoms. In particular, the electronic contribution of the static first hyperpolarizability (ß e 0) for M(NH3)6Na2 exhibits a large significant difference when the EEF is switched on. The ß e 0 value of M(NH3)6Na2 is 0 when EEF = 0, while the peak ß e 0 values are 5.95 × 106 (a.u.) for Mg(NH3)6Na2 (EEF = 58 × 10-4 (a.u.)) and 1.83 × 107 (a.u.) for Ca(NH3)6Na2 (EEF = 53 × 10-4 (a.u.)). This work demonstrates that the compounds M(NH3)6Na2 can serve as potential candidates for NLO switches.

Study on the mechanism of platinum(ii)-catalyzed asymmetric ring-opening addition of oxabicyclic alkenes with arylboronic acids.

The mechanism of an asymmetric ring-opening (ARO) addition of oxabicyclic alkenes catalyzed by a platinum(ii) catalyst was investigated by M06-2X/6-311G(d,p) using density functional theory (DFT). All the structures were optimized in the solvent model density (SMD) solvation model (solvation = the mixture of H2O/CH2Cl2 1 : 10, v/v) for consistence with experimental conditions. The overall mechanism is considered as a four-step reaction including transmetalation, carboplatinum, ß-oxygen elimination, and hydrolysis. The transmetalation and carboplatinum steps are multi-step processes, and both the regioselectivity and the enantioselectivity lie in the carboplatinum process. Based on the natural population analysis (NPA) and the orbital composition analysis of oxabicyclic alkenes, the preferable coordination site with a platinum(ii) center is considered as the bridging oxygen atom by exo-coordination because of the less steric hindrance and the stronger electronic effect. This coordination is thought of as origin of the regioselectivity and the enantioselectivity, which is different from that proposed previously. The Gibbs free energy profiles show that the rate-determining step involves the migration of an aryl group from the platinum(ii) center to one of the closer enantiotopic carbon atoms in an alkene of the oxabicyclic alkenes. The theoretically predicted enantiomeric excess (ee) value of 82% for this reaction is very close to the experimental ee value of 80%. It was found that the hydrogen bonds between the oxabicyclic alkenes and water molecules promotes the platinum(ii) catalyst leaving the reaction system effortlessly and entering the next catalysis recycle. In the overall catalytic cycle, the highest free energy barrier is 30.1 kcal mol-1 and the process releases an energy of 26.3 kcal mol-1. The results confirm that the Pt(ii)-catalyzed ARO reactions take place at mild experimental conditions, which is consistent with the experiment observations. Thus, this study is important for understanding the catalytic behavior of the transition metal platinum(ii) in an asymmetric ring-opening reaction.

Time-Dependent Coupled Perturbed Hartree-Fock and Density-Functional-Theory Approach for Calculating Frequency-Dependent (Hyper)Polarizabilities with Nonorthogonal Localized Molecular Orbitals.

The time-dependent coupled perturbed Hartree-Fock/density-functional-theory (TDHF/TDDFT) approach has been reformulated based on nonorthogonal localized molecular orbitals (NOLMOs). Based on the NOLMO Fock equation, we have derived the corresponding NOLMO-TDHF/TDDFT equations up to the third order, and the formula for the frequency-dependent (hyper)polarizabilities has been given. Our approach has been applied to calculate both static and dynamic (hyper)polarizabilities of molecules varying from small molecules to large molecules. The NOLMO-TDHF/TDDFT approach can reproduce the reference canonical molecular orbital (CMO) results for all of our testing calculations. With the help of ongoing development of optimized local virtual molecular orbitals, the NOLMO-TDHF/TDDFT approach would be a very efficient method for large system calculations and tp achieve linear scaling.

Molcas 8: New capabilities for multiconfigurational quantum chemical calculations across the periodic table.

In this report, we summarize and describe the recent unique updates and additions to the Molcas quantum chemistry program suite as contained in release version 8. These updates include natural and spin orbitals for studies of magnetic properties, local and linear scaling methods for the Douglas-Kroll-Hess transformation, the generalized active space concept in MCSCF methods, a combination of multiconfigurational wave functions with density functional theory in the MC-PDFT method, additional methods for computation of magnetic properties, methods for diabatization, analytical gradients of state average complete active space SCF in association with density fitting, methods for constrained fragment optimization, large-scale parallel multireference configuration interaction including analytic gradients via the interface to the Columbus package, and approximations of the CASPT2 method to be used for computations of large systems. In addition, the report includes the description of a computational machinery for nonlinear optical spectroscopy through an interface to the QM/MM package Cobramm. Further, a module to run molecular dynamics simulations is added, two surface hopping algorithms are included to enable nonadiabatic calculations, and the DQ method for diabatization is added. Finally, we report on the subject of improvements with respects to alternative file options and parallelization.

Theoretical study on the mechanism of stereoselective synthesis of oxazolidinones.

Oxazolidinones can be synthesized through an organocatalytic cascade reaction of stable sulfur ylides and nitro-olefins. This process, sequentially catalyzed by thiourea and N,N-dimethylaminopyridine (DMAP), is theoretically studied using density functional theory by the continuum solvation model. It is shown that the rate- and stereoselectivity-determining step is the addition reaction of sulfur ylide to the nitro-olefin with two competing reaction channels. One channel is where the nitro-cyclopropane is generated first and then converted into isoxazoline N-oxide through a DMAP-catalyzed rearrangement. The other channel is the direct generation of the isoxazoline N-oxide intermediate. DMAP plays an important role in the reaction as a nucleophilic catalyst. The mechanism for the important rearrangement reaction proposed by Xiao et al. (J. Am. Chem. Soc. 2008, 130, 6946-6948) is not appropriate as the reaction energy barrier is too high; a 10-step mechanism determined by our theoretical calculations is more feasible as the energy barrier is becoming much less than that by Xiao. It is the first time that the Hofmann rearrangement involved in the cascade organocatalysis is confirmed by theoretical calculations. Our result of the stereoselectivity for the synthesis of oxazolidinones is in good agreement with the experiment.

An efficient implementation of two-component relativistic exact-decoupling methods for large molecules.

We present an efficient algorithm for one- and two-component relativistic exact-decoupling calculations. Spin-orbit coupling is thus taken into account for the evaluation of relativistically transformed (one-electron) Hamiltonian. As the relativistic decoupling transformation has to be evaluated with primitive functions, the construction of the relativistic one-electron Hamiltonian becomes the bottleneck of the whole calculation for large molecules. For the established exact-decoupling protocols, a minimal matrix operation count is established and discussed in detail. Furthermore, we apply our recently developed local DLU scheme [D. Peng and M. Reiher, J. Chem. Phys. 136, 244108 (2012)] to accelerate this step. With our new implementation two-component relativistic density functional calculations can be performed invoking the resolution-of-identity density-fitting approximation and (Abelian as well as non-Abelian) point group symmetry to accelerate both the exact-decoupling and the two-electron part. The capability of our implementation is illustrated at the example of silver clusters with up to 309 atoms, for which the cohesive energy is calculated and extrapolated to the bulk.

Local relativistic exact decoupling.

We present a systematic hierarchy of approximations for local exact decoupling of four-component quantum chemical Hamiltonians based on the Dirac equation. Our ansatz reaches beyond the trivial local approximation that is based on a unitary transformation of only the atomic block-diagonal part of the Hamiltonian. Systematically, off-diagonal Hamiltonian matrix blocks can be subjected to a unitary transformation to yield relativistically corrected matrix elements. The full hierarchy is investigated with respect to the accuracy reached for the electronic energy and for selected molecular properties on a balanced test molecule set that comprises molecules with heavy elements in different bonding situations. Our atomic (local) assembly of the unitary exact-decoupling transformation--called local approximation to the unitary decoupling transformation (DLU)--provides an excellent local approximation for any relativistic exact-decoupling approach. Its order-N(2) scaling can be further reduced to linear scaling by employing a neighboring-atomic-blocks approximation. Therefore, DLU is an efficient relativistic method well suited for relativistic calculations on large molecules. If a large molecule contains many light atoms (typically hydrogen atoms), the computational costs can be further reduced by employing a well-defined nonrelativistic approximation for these light atoms without significant loss of accuracy. We also demonstrate that the standard and straightforward transformation of only the atomic block-diagonal entries in the Hamiltonian--denoted diagonal local approximation to the Hamiltonian (DLH) in this paper--introduces an error that is on the order of the error of second-order Douglas-Kroll-Hess (i.e., DKH2) when compared with exact-decoupling results. Hence, the local DLH approximation would be pointless in an exact-decoupling framework, but can be efficiently employed in combination with the fast to evaluate DKH2 Hamiltonian in order to speed up calculations for which ultimate accuracy is not the major concern.