Clathrate Hydrates as a Kind of Promising Ice Nanoreactors.

Since their discovery, clathrate hydrates (CHs) have received great attention both from theoretical and experimental aspects due to their great potential for gas storage and prospective applications as icy crystal materials. However, there has been limited research on the decomposition, reduction or other reactions of gases enclosed in CHs. Thanks to their unique hydrogen bonding network and cavity structures, CHs can serve as the promising nanoreactors to achieve chemical conversions, e.g. reducing greenhouse gases. In this review-type article, we characterize the potential performance of such CHs nanoreactors by discussing their multiple functions including important roles of hydrogen bonds in CHs, e.g. the confinement effect and proton source, and then discuss the enhanced electron-binding ability of guest molecules and the structures and properties of trapped electrons in the stacked nanocages, which contribute to our understanding of chemical reactions occurring in CHs. Finally, we provide detailed analyses of representative reaction mechanisms underwent in CH nanoreactors and effective investigation methods. This review-type article aims to provide a detailed summary about the functional characteristics of CHs and reactivity in CHs, which make CHs a kind of promising icy nanoreactors.

Multifunctional Roles of Clathrate Hydrate Nanoreactors for CO2 Reduction.

In this study, we explore a possible platform for the CO2 reduction (CO2 R) in one of water's solid phases, namely clathrate hydrates (CHs), by ab initio molecular dynamics and well-tempered metadynamics simulations with periodic boundary conditions. We found that the stacked H2 O nanocages in CHs help to initialize CO2 R by increasing the electron-binding ability of CO2 . The substantial CO2 R processes are further influenced by the hydrogen bond networks in CHs. The first intermediate CO2 - in this process can be stabilized through cage structure reorganization into the H-bonded [CO2 - ⋅⋅⋅H-OHcage ] complex. Further cooperative structural dynamics enables the complex to convert into a vital transient [CO2 2- ⋅⋅⋅H-OHcage ] intermediate in a low-barrier disproportionation-like process. Such a highly reactive intermediate spontaneously triggers subsequent double proton transfer along its tethering H-bonds, finally converting it into HCOOH. These hydrogen-bonded nanoreactors feature multiple functions in facilitating CO2 R such as confining, tethering, H-bond catalyzing and proton pumping. Our findings have a general interest and extend the knowledge of CO2 R into porous aqueous systems.

Ab Initio Metadynamics Simulations of Hexafluoroisopropanol Solvent Effects: Synergistic Role of Solvent H-Bonding Networks and Solvent-Solute C-H/π Interactions.

The solvent effects in Friedel-Crafts cycloalkylation of epoxides and Cope rearrangement of aldimines were investigated by using ab initio molecular dynamics simulations. Explicit molecular treatments were applied for both reactants and solvents. The reaction mechanisms were elucidated via free energy calculations based on metadynamics simulations. The results reveal that both reactions proceed in a concerted fashion. Key solvent-substrate interactions are identified from the structures of transition states with explicit solvent molecules. The remarkable promotion effect of hexafluoroisopropanol solvent is ascribed to the synergistic effect of H-bonding networks and C-H/π interactions with substrates.

Indirect Nuclear Spin-Spin Exchange Coupling through Solvated Electron in Small Sizes of Cyclic and Cage-Shaped Perfluoroalkanes.

Small perfluorocycloalkanes (hexafluorocyclopropane (c-C3 F6 ), octafluorocyclobutane (c-C4 F8 ) and decafluorocyclopentane (c-C5 F10 ) and cage-shaped perfluoroalkanes (perfluoro tetrahedral alkane (C4 F4 ), perfluoro prismane (C6 F6 ) and perfluoro cubane (C8 F8 )) are better electron scavengers. The captured excess electrons are weakly bound inside their backbone voids or over their backbones, forming the solvated electron ( e sol - ${{\rm{e}}_{{\rm{sol}}}^- }$ ) systems (e@c-Cn F2n s (n=3, 4, 5) and e@Cn Fn (n=4, 6, 8)). There have been many studies on the structures and properties of such e sol - ${{\rm{e}}_{{\rm{sol}}}^- }$ systems. However, the effect of e sol - ${{\rm{e}}_{{\rm{sol}}}^- }$ on the indirect nuclear spin-spin coupling (J-coupling) is unknown. In this work, we explore how e sol - ${{\rm{e}}_{{\rm{sol}}}^- }$ affects Ne J-coupling between two coupled F nuclei (Ne JFF -coupling) in perfluoroalkane e sol - ${{\rm{e}}_{{\rm{sol}}}^- }$ systems through density functional theory calculations. We find unusual trans-Ne JFF -couplings (two coupled F nuclei in trans-position) in e@c-Cn F2n (n=3, 4, 5) and Ne JFF -couplings in e@Cn Fn (n=4, 6, 8). One excess electron not only changes the molecular structures, but also enforces unique distributions and properties, depending on the structural characteristics. We also confirm that such unusual Ne JFF -couplings are realized by through- e sol - ${{\rm{e}}_{{\rm{sol}}}^- }$ (T-SE) transmission mechanism, rather than the conventional through-bonds (T-B)/through-space (T-S) ones. The novel transmission mechanism consists of the T-SE coupling path (path 1) and e sol - ${{\rm{e}}_{{\rm{sol}}}^- }$ -enhanced T-B ⊕ ${ \oplus }$ T-S coupling path (path 2), and the two paths jointly control Ne JFF through cooperation and competition. Interestingly, the former plays a dominant role for long-range Ne JFF -coupling (N=5), while the latter plays a role in the short-range Ne JFF -coupling (N=3, 4). Path bending angle mainly influences path 1, while path 2 is mainly influenced by the path length. This work not only provides novel insights into the mediating role of e sol - ${{\rm{e}}_{{\rm{sol}}}^- }$ in the coupling information exchange, but also proposes a new e sol - ${{\rm{e}}_{{\rm{sol}}}^- }$ -based coupling mechanism, possibly opening up potential applications for the e sol - ${{\rm{e}}_{{\rm{sol}}}^- }$ -based indirect nuclear spin couplings.

Magnetic coupling modulation in meta-nitroxide-functionalized isoalloxazine magnets with redox-active units as efficient side-modulators.

Magnetic conversion can be accomplished in a variety of ways, as organic molecules with switchable magnetic characteristics offer numerous technological applications. It is crucial to find magnetism-switchable systems because, in the field of organic magnetic materials, the redox-induced magnetic reversal is very simple to achieve and shows significant applications. Herein, we computationally design isoalloxazine-based diradicals through oxidizing N10 and adding a nitroxide to C8 as the spin source (i.e. 8-nitroxide-isoalloxazine 10-oxide, an m-phenylene-like nitroxide diradical expanded with a redox unit as a side-modulator) and its N1/N5-hydrogenated/protonated diradical derivatives and introducing substituents (-OH, -NH2, and -NO2) to C6. We demonstrate that the basically modified structure exhibits ferromagnetic (FM) characteristics with a magnetic coupling constant (J) of 561.3 cm-1 calculated at the B3LYP/6-311+G(d,p) level, obeying the meta-phenylene-mediated diradical character, and dihydrogenation can lead to an AFM diradical with considerably large J (-976.1 cm-1). Surprisingly, protonation at N1 or N5 can lead to distinctly different magnetic variations (561.3 → -1602.9 cm-1 at N1 versus 561.3 → 379.1 cm-1 at N5). Analyses indicate that small singlet-triplet energy gaps and small energy gaps between the highest occupied and lowest unoccupied molecular orbitals (HOMO, LUMO) of the closed shell singlet state are the key features of these isoalloxazine diradicals, and aromaticity variations, significant spin delocalization from the π-conjugated structure and spin polarization from the non-Kekule structure induced by modification are responsible for the magnetic conversion. Furthermore, the spin alternation rule, the singly occupied molecular orbital (SOMO) effect, and the SOMO-SOMO energy splitting of the triplet state are used to analyze these distinct variations. This work provides a novel understanding of the structures and characteristics of modified isoalloxazine diradicals, as well as essential details for the intricate design and characterization of new isoalloxazine-based potential organic magnetic switches.

How hexafluoroisopropanol solvent promotes Diels-Alder cycloadditions: ab initio metadynamics simulations.

The solvent effects in Diels-Alder cycloadditions were studied by using ab initio molecular dynamics simulations with explicit molecular treatments for both substrates and solvents. Energy decomposition analysis was used to investigate the role of H-bonding networks of hexafluoroisopropanol solvent in promoting both reactivity and regioselectivity.

Hydrogen-migration governed dynamic magnetic coupling characteristics in nitrogen-vacancy-hydrogen nanodiamonds.

The nitrogen-vacancy center doped with hydrogen (NVH) is one of the most common defects in diamonds, and the doping of hydrogen is known to enable mobility among three equivalent C-radicals in the defect, which noticeably affects the spin coupling among the radicals. Here, we for the first time uncover the dynamic nature of magnetic coupling induced by H-migration in the NVH center of nanodiamonds, using spin-polarized density functional theory calculations and enhanced sampling metadynamics simulations. The mobility of doping H enables the interior NVH region to become a variable magnetic space (antiferromagnetic/AFM versus ferromagnetic/FM). That is, the dynamic H has three frequently reachable binding C sites where H enables the center to exhibit variable AFM coupling (high up to J = -1282 cm-1) and that in other H-reachable regions including N sites, it enables the center to exhibit FM coupling (high up to J = 598 cm-1). The magnetic switching (AFM ↔ FM) and strength fluctuation strongly depend on the H-position which can adjust the ratio of the C radical orbitals in their mixing orbitals for a special three-electron three-center covalent C⋯H⋯C H-bonding and radical orbital distributions. Clearly, this work provides insights into the dynamic switching of magnetic coupling in such multi-radical centers of defect nanodiamonds.

Enhanced J-Couplings through Specially Solvated Electron in Perfluoro-[n]Prismanes and [n]Asteranes.

Perfluoro-[n]prismanes ((C2F2)n, n = 3-8) and [n]asteranes ((C3F4)n, n = 3-5) exhibit a strong perfluoro cage effect that can stably encapsulate an additional electron inside the cage. The 2s-like distribution of solvated electron (esol-) not only changes the molecular structure but also affects the nuclear spin properties. In this work, we reveal how the esol- enhances and regulates indirect nuclear spin-spin coupling between two coupled F nuclei (JFF-coupling). Results show that esol- is mainly distributed in the central cavity, and a part of it penetrates into the C-shell and C-F bond regions due to the unique polyhedral C-shell structure. Such a 2s-like esol- creates a novel esol- based coupling mechanism, including the newly generated through-esol- (TSE) and esol--enhanced traditional through-bonds and through-space (esol--enhanced TB+TS) pathways, enhancing and regulating N(e)JFF-coupling, which crosses N bonds in the shortest TB pathway and is affected by esol-. The contribution of the TSE (JTSE) is positive and increases with the increase of the central angle between two coupled F nuclei (∠F⊗F), and the contribution of the esol--enhanced TB+TS (JTB+TS) is negative and |JTB+TS| decreases with the increase of N and straight linear distance between two coupled F nuclei (dFF). Interestingly, N(e)JFF exhibits a special dependence on N/dFF and ∠F⊗F due to the cooperation and competition between JTSE and JTB+TS. When ∠F⊗F < 70°, the esol--enhanced TB+TS can play a role; JTB+TS determines sign and magnitude of N(e)JFF. When ∠F⊗F > 70°, the TSE dominates, and JTSE determines sign and magnitude of N(e)JFF. This work not only further enriches information on the states, distributions, and properties of esol- but also provides insights into the nuclei spin properties in perfluorinated polyhedrons triggered by esol-.

Hydrogen-Bonding-Assisted Substituent Engineering for Modulating Magnetic Spin Couplings and Switching in m-Phenylene Nitroxide Diradicals.

Rational modification of the coupler for the theoretical design of molecular magnets has attracted extensive interest. Substituent insertion is a widely used strategy for adjusting molecular properties, but its effect and modulation on magnetic spin couplings have been less investigated. In this work, we predict the magnetic properties of the design m-phenylene nitroxide (NO) diradicals regulated by introducing substituents. The calculated results for those two pairs of diradicals indicate that the signs of their magnetic coupling constants J do not change, but the magnitudes remarkably change after substituent regulation in the range from 253 to 730 cm-1. Such noticeable magnetic changes induced by introducing subsituents are mainly attributed to different electronic effects of substituents, assisted by the proximity of two NO groups, good planarity, conjugation, and an intramolecular hydrogen bond. In particular, the insertion of intramolecular H-bonds not only indicates an electronic effect but also has greatly changed the spin density distribution. Further aromaticity of the coupler ring, spin densities, and molecular orbitals and energetics was evaluated to gain a better understanding of magnetic regulation. Interestingly, further protonation of some substituents (e.g., -NO2 and -CO2) can noticeably turn the spin coupling from ferromagnetic to antiferromagnetic, showing manipulable magnetic switching. This work provides a promising strategy based on substituent engineering for magnetic spin coupling modulation, not only turning the coupling magnitude but also enabling the magnetic switching, thus providing insights into molecular magnetic manipulation for spintronics applications.

Electron Presolvation in Tetrahydrofuran-Incorporated Supramolecular Sodium Entities.

Alkali metal atoms can repopulate their valence electrons toward solvation due to impact from solvents or microsurroundings and provide the remaining alkali metal cations for coordinating with a variety of specific solvents, forming various electron-expanded complexes or solvated ionic pairs with special interactions. Such special solute-solvent interactions not only affect their electronic structures but also enable the formation of entirely new species. Taking Na(THF)n (n = 1-6, THF = tetrahydrofuran) and Na2@THF complexes as typical representatives, density functional theory calculations are carried out to explore the solvation of a sodium atom and its dimer in THF and characterize their complexes as solvent-incorporated supramolecular entities and particularly valence electron presolvation due to their interaction with solvent THF. Electron presolvation is caused by the Pauli repulsion between THF containing a coordinating O atom with a lone pair of electrons and the alkali metal Na or Na2 containing valence electrons, and THF coordination to them forces their valence electrons to redistribute, which can be easily realized in such solvents. Compared with strongly bound valance electrons of alkali metal atoms, THF coordination enables Na or Na2 electrons to exhibit much more active states (i.e., the presolvated states) featuring small vertical detachment energies of electrons and distorted diffuse distributions in the frames of the generally structured metal cation complexes, acting as the electron-expanded chemical entities. Furthermore, the degree of electron diffusion and the polarity of the Na-Na bond are proportional to the coordination number (n) and the coordination number difference (Δn) between two Na centers in Na2@THF. The unique properties of such entities are also discussed. This work offers a theoretical support to the supramolecular entities formed by alkali-metal atoms or their dimers with ligands containing O or N and uncovers the unique electron presolvation phenomena and also enriches our understanding of the novel metal atom complexes.

Hydrated electrons as nodes in porous clathrate hydrates.

We investigate the structures of hydrated electrons (e- aq) in one of water's solid phases, namely, clathrate hydrates (CHs). Using density functional theory (DFT) calculations, DFT-based ab initio molecular dynamics (AIMD), and path-integral AIMD simulations with periodic boundary conditions, we find that the structure of the e- aq@node model is in good agreement with the experiment, suggesting that an e- aq could form a node in CHs. The node is a H2O defect in CHs that is supposed to be composed of four unsaturated hydrogen bonds. Since CHs are porous crystals that possess cavities that can accommodate small guest molecules, we expect that these guest molecules can be used to tailor the electronic structure of the e- aq@node, and it leads to experimentally observed optical absorption spectra of CHs. Our findings have a general interest and extend the knowledge of e- aq into porous aqueous systems.

Redox-Regulated Magnetic Conversions between Ferro- and Antiferromagnetism in Organic Nitroxide Diradicals.

Redox-induced magnetic transformation in organic diradicals is an appealing phenomenon. In this study, we theoretically designed twelve couples of diradicals in which two nitroxide (NO) radical groups are connected to the redox-active couplers including p-benzoquinonyl, 1,4-naphthoquinyl, 9,10-anthraquinonyl, naphthacene-5,12-dione, pentacene-6,13-dione, hexacene-6,15-dione, pyrazinyl, quinoxalinyl, phenazinyl, 5,12-diazanaphthacene, 6,13-diazapentacene, and 6,15-diazahexacene. As evidenced at both the B3LYP and M06-2X levels of theory, the calculations reveal that the magnetic reversal can take place from ferromagnetism to antiferromagnetism, or vice versa, by means of redox method in these designed organic magnetic molecules. It was observed that p-benzoquinonyl, 1,4-naphthoquinyl, 9,10-anthraquinonyl, naphthacene-5,12-dione, pentacene-6,13-dione, and hexacene-6,15-dione-bridged NO diradicals produce antiferromagnetism while their dihydrogenated counterparts exhibit ferromagnetism. Similarly, pyrazinyl, quinoxalinyl, phenazinyl, 5,12-diazanaphthacene, 6,13-diazapentacene, and 6,15-diazahexacene-bridged NO diradicals present ferromagnetism while their dihydrogenated counterparts show antiferromagnetism. The differences in the magnetic behaviors and magnetic magnitudes of each of the twelve couples of diradicals could be attributed to their distinctly different spin-interacting pathways. It was found that the nature of the coupler and the length of the coupling path are important factors in controlling the magnitude of the magnetic exchange coupling constant J. Specifically, smaller HOMO-LUMO (HOMO: highest occupied molecular orbital, LUMO: lowest unoccupied molecular orbital) gaps of the couplers and shorter coupler lengths, as well as shorter linking bond lengths, can attain stronger magnetic interactions. In addition, a diradical with an extensively π-conjugated structure is beneficial to spin transport and can effectively promote magnetic coupling, yielding a large |J| accordingly. That is, a larger spin polarization can give rise to a stronger magnetic interaction. The sign of J for these studied diradicals can be predicted from the spin alternation rule, the shape of the singly occupied molecular orbitals (SOMOs), and the SOMO-SOMO energy gaps of the triplet state. This study paves the way for the rational design of magnetic molecular switches.

Intriguing strain-governed magnetic phase transitions in 2D vanadium porphyrin sheets.

The strain effect on the magnetic response of 2D materials as spintronic devices is always important in actual applications. Due to the intriguing electronic and magnetic properties of two-dimensional (2D) vanadium porphyrin (V-PP) sheets, we studied the strain-induced magnetic coupling changes in 2D V-PP sheets by using the density functional theory method and found intriguing magnetic variation characters. The calculated results indicate that biaxial strain can modulate the magnetic moments of the central transition metal vanadium atoms and more importantly can induce phase transitions among three magnetic modes with four magnetic states (ferromagnetic (FM), ferrimagnetic (FIM), and two antiferromagnetic (AFM: AFM1 featuring a parallel spin lattice versus AFM2 featuring a crossing spin lattice)) with unique conversion pathways due to their different responses to the strain. As the compressive strain increases, the magnetic characteristics of 2D-VPP transitions as FM → FIM → AFM1 with two critical points (-4.7% and -6%), while the tensile strain can induce the original FM coupling to transition to another AFM state (FM → AFM2) at 5.3%. Analyses of the density of states, spin densities, and Bader charges reveal that the rich magnetic response properties of the system originate from the electron transfer between the central V and the porphyrin ligand induced by strain. This work provides intriguing information regarding the strain-induced magnetic phase transition mechanism and also presents a viable development direction to design 2D porphyrin magnetic semiconductors and spintronic devices.

Modulation of proton-coupled electron transfer reactions in lysine-containing alpha-helixes: alpha-helixes promoting long-range electron transfer.

The proton-coupled electron transfer (PCET) reaction plays an important role in promoting many biological and chemical reactions. Usually, the rate of the PCET reaction increases with an increase in the electron transfer distance because long-range electron transfer requires more free energy barriers. Our density functional theory calculations here reveal that the mechanism of PCET occurring in lysine-containing alpha(α)-helixes changes with an increasing number of residues in the α-helical structure and the different conformations because of the modulation of the excess electron distribution by the α-helical structures. The rate constants of the corresponding PCET reactions are independent of or substantially shallower dependent on the electron transfer distances along α-helixes. This counter-intuitive behavior can be attributed to the fact that the formation of larger macro-cylindrical dipole moments in longer helixes can promote electron transfer along the α-helix with a low energy barrier. These findings may be useful to gain insights into long-range electron transfer in proteins and design α-helix-based electronics via the regulation of short-range proton transfer.

Intramolecular Proton Transfer Modulation of Magnetic Spin Coupling Interaction in Photochromic Azobenzene Derivatives with an Ortho-Site Hydroxyl as a Modulator.

Proton transfer modulation in an organic diradical is apparently the most conspicuously attractive phenomenon. In this work, we have computationally designed the trans and cis forms of photochromic azobenzene- (AB-) bridged diradicals by considering AB as coupler and two nitroxide (NO) as spin sources and a -OH attaching at the ortho site as modulator. Our object is that through intramolecular proton transfer to protonate the azo-unit (-N═N-) the magnetic coupling characteristics of the designed diradicals can be modulated in their photocontrolled trans and cis forms. The calculated results indicate that PT can significantly regulate the magnetic spin coupling constants, J = -701.3 cm-1 ↔ -286.2 cm-1 for the trans form and -544.1 cm-1 ↔ -328.1 cm-1 for the cis form. In particular, we discover that these designed magnetic molecules can undergo magnetic conversion between antiferromagnetic and ferromagnetic coupling through PT, besides there is considerable increase in the magnitude of their magnetic coupling constants J, (e.g., -59.97 to 172.4 cm-1) for the trans-mode at the m/m linking site. Moreover, we discover that the nitroxide radicals at different linking positions have a significant impact and remarkably alter the magnetic spin coupling characteristics of AB-based diradicals. Besides, various radical groups are used as spin sources which corroborated our assumptions and tended to the same conclusion. This work offers a novel understanding of the spin interaction mechanism and a viable approach for the rational design of new AB-based magnets which are beneficial for further applications in the future.

Endohedral σ-Diradical Nitrogen-Vacancy Diamond Nanoclusters with a Confined Magnetic Space and Strong Electronic Spin Couplings.

The electronic properties and their modulations for the nitrogen-vacancy (NV) centers in various nanoscale diamonds are of profound current interest because of their potential applications. However, although the NV centers as chromophores in diamond are the most widely studied, surprisingly, little is known about their magnetic spin coupling properties up to now. Here, we for the first time show, using the spin-polarized DFT calculations, that the NV centers can act as unique endohedral σ-diradical magnets in diamond nanoclusters and exhibit quite strong ferromagnetic (FM) or antiferromagnetic (AFM) spin coupling characteristics due to their unique endotetrahedral structures with favorable radical-radical contacts. Although the neutral NV center (NV0) in its doublet ground state exhibits quite strong AFM spin coupling among three radical C-sites (i.e., an AFM triradical center), interestingly, excess electron injection can convert it to a FM diradical magnet (i.e., the triplet ground state NV-) with almost unchanged J-coupling magnitude, and the J-coupling of the nanocluster can be noticeably enhanced by F-termination of the surface due to triradical spin delocalization mediated by excess electron. However, interior modification (one C in the endotetrahedron core is substituted by N or B or is hydrogenated) can assign the nanocluster perfect AFM diradical character. The spin coupling strength presents a quasilinear correlation with the distance between the two C radicals in the NV core for the same size of the clusters and a high linear correlation with the energy difference between two singly occupied molecular orbitals. Clearly, the FM and AFM couplings as well as their switching behavior in such NV defect diamond nanoclusters featuring the endohedral σ-diradicals are a novel type of promising magnetic material motifs. These findings open up promising spintronic application prospects of the NV diamonds and provide helpful information for the design of inorganic magnetic materials and logic devices.

[Automatic detection model of hypertrophic cardiomyopathy based on deep convolutional neural network].

The diagnosis of hypertrophic cardiomyopathy (HCM) is of great significance for the early risk classification of sudden cardiac death and the screening of family genetic diseases. This research proposed a HCM automatic detection method based on convolution neural network (CNN) model, using single-lead electrocardiogram (ECG) signal as the research object. Firstly, the R-wave peak locations of single-lead ECG signal were determined, followed by the ECG signal segmentation and resample in units of heart beats, then a CNN model was built to automatically extract the deep features in the ECG signal and perform automatic classification and HCM detection. The experimental data is derived from 108 ECG records extracted from three public databases provided by PhysioNet, the database established in this research consists of 14,459 heartbeats, and each heartbeat contains 128 sampling points. The results revealed that the optimized CNN model could effectively detect HCM, the accuracy, sensitivity and specificity were 95.98%, 98.03% and 95.79% respectively. In this research, the deep learning method was introduced for the analysis of single-lead ECG of HCM patients, which could not only overcome the technical limitations of conventional detection methods based on multi-lead ECG, but also has important application value for assisting doctor in fast and convenient large-scale HCM preliminary screening.

Electric field controlled uphill electron migration along α-helical oligopeptides.

A systematic study on applied electric field effects (Eapp) on electron transfer along the peptides is very important for the regulation of electron transfer behaviors so as to realize the functions of proteins. In this work, we computationally investigated the uphill migration behaviors of excess electrons along the peptide chains under Eapp using the density functional theory method. We examined the electronic property changes of the model α-helical oligopeptides, the dynamics behavior of an excess electron along the peptide chains under Eapp opposite to the internal dipole field of peptides. We found that Eapp of different intensities can effectively modulate the electron-binding abilities, Frontier molecular orbital (FMO) energies and distributions, dipole moments and other corresponding properties with different degrees. The electron-binding abilities of α-helical oligopeptides revealed by vertical electron affinity and FMO energies decrease in weak Eapp and then increase greatly in high Eapp, while the dipole moments change mildly in weak Eapp and increase significantly until a threshold and then become gentle in high Eapp. Analysis of FMO and electron distributions indicates that an excess electron can migrate uphill from the N-terminus to the C-terminus of the α-helical peptides in an irregular jump mode as Eapp linearly increases. Another interesting finding is that α-helical peptides with diverse chain lengths have different sensitivities to Eapp. The longer the peptide is, the more obvious the effects of Eapp are. Additionally, compared to the Eapp effect on linear oligopeptides, we summarized the systematic rule about the Eapp effect on excess electron migration uphill along the peptide chains. Clearly, this work not only enriches the information of the Eapp effect on electronic properties and electron transfers in the helical peptides, but also provides a new perspective for modulating electron migration behaviors in protein electronics engineering.

TD-DFT Studies on sp- and sp2-Hybridized Single Vacancy-Defected [60]Fullerene: Electronic Excitation and Nonlinear Optical Properties of C59 [9-4] and C59 [8-5] Isomers.

By removing one carbon atom from [60]Fullerene (C60), two different isomers (C59 [9-4] and C59 [8-5]) are generated for the C59 cluster. Inspired by their structural and electronic properties, we, theoretically, studied the static and frequency-dependent electronic (hyper)polarizabilities of sp- and sp2-hybridized isomers in vacuum by TD-DFT calculations. The simulated absorption spectra showed that all absorption bands of C59 [9-4] and C59 [8-5] are attributed to π → π* and n → π* transitions. Regarding their nonlinear optical properties, it is found that the frequency-dependent polarizability anisotropy αanisotropy(λ = 1064.80 nm) of C59 [8-5] is 4 times larger than the static regime, revealing a notable polarization anisotropy, due to the delocalized π electrons around the vacancy defect. By decreasing the incident wavelengths from λ = 1908 nm to λ =589.08 nm, the dispersion of optical nonlinearity of C59 [8-5] has achieved the maximum at ßxxx (λ = 1064.8 nm) = 38.150 au and (γxxxx (λ = 589.08 nm) = -9.896 × 107 au), indicating that the resonance effect of the hyperpolarizability amplified with the decrease of incident wavelengths. Hyperpolarizability density analyses in X and Z directions displayed that the conspicuous negative ρxxx(3)(r⃗) and -zρzzz(3)(r⃗) are more expanded on the C59 [8-5] cage when the main contributions stem from the π electrons instead to the sp-hybridized carbon.

General Dual-Switched Dynamic Singlet Fission Channels in Solvents Governed Jointly by Chromophore Structural Dynamics and Solvent Impact: Singlet Prefission Energetics Analyses.

The singlet fission (SF) channels in many systems are controlled by the thermodynamic driving force (Switch-1) and kinetic barrier (Switch-2), both of which could be modulated by chromophore structure dynamics and solvent properties. Using ab initio molecular dynamics (AIMD), we here simulate how the structural dynamics and solvent jointly govern singlet prefission energetics, taking a covalent BODIPY dimer (di-BODIPY) in solvents as an example. We report a general dual-switched dynamic channel for intramolecular SF in solvents and suggest an effective AIMD sampling method to characterize the joint effect of chromophore structure dynamics and the solvent impact on SFs. Results reveal that the joint effect not only provides di-BODIPY more chances for meeting the SF thermodynamic requirement (Switch-1 ON) but also tunes the charge-transfer state toward removing the kinetic barrier (Switch-2 ON). Two factors jointly govern each switch in the dual-switched SF channel, and any one does not open the channel alone. We suggest a general principle for dynamically dual-switching the SF channel in solvents by utilizing the joint effect to tune the pre-SF energetics for photoexcitation and the opening of the subsequent channel. AIMD sampling is used for the first time to discover explicit solvent-solute interaction and dynamics information and thus their effect on excitation energetics. This work also shows the statistical information for an ensemble of SF chromophores in solvents, which can undergo different photoexcitations and possible SFs. The high agreement of the findings here with the experiments justifies our AIMD sampling-based pre-SF energetic prediction as a reliable way for exploring novel SF systems and their controllability.