The important role of surface charge on a new mechanism of nitrogen reduction.

The electrocatalytic nitrogen reduction reaction (NRR) is a green and sustainable approach for producing ammonia. Low-cost carbon-based materials are promising catalysts for the electrochemical NRR. Among them, Cu-N4-graphene is a unique catalytic substrate. Its catalytic performance for the NRR has remained unclear as N2 can only be physisorbed on such a substrate. In this work, we focus on the influence of an electronic environment on the electrocatalytic NRR. DFT computations reveal that the NN bond can be effectively activated at a surface charge density of -1.88 × 1014 e cm-2 on Cu-N4-graphene and further the NRR proceeds via an alternating hydrogenation pathway. This work offers a new insight into the mechanism of the electrocatalytic NRR and emphasizes the importance of environmental charges in the electrocatalytic process of the NRR.

Study on the Assembly Mechanisms and Transport Properties of Transmembrane End-Charged Cyclic Peptide Nanotubes.

In this work, two end-charged cyclic peptide nanotubes (CPNTs) embedded in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) were designed to simulate transmembrane ion channels. Density functional theory (DFT) computations at the level of M06-2X/6-31G give different assembling modes of the negatively charged ELWL-CPNT and positively charged RLWL-CPNT as (L-L)(D-L)(D-D)(L-L)(D-D)(L-L)(D-D) and (D-D)(L-L)(D-D)(L-L)(D-D)(L-L)(D-D), respectively. Molecular dynamics (MD) simulations indicate that a charge at a CPNT end obviously affects the structure of the channel water chain and the diffusion behavior of K+. The regions with the highest probability of H-bond defects in the channel water chains are gap5 and gap2 in ELWL/POPE-CPNT and RLWL/POPE-CPNT, respectively. K+ can easily enter either CPNT by desolvation, and behaves more actively in RLWL/POPE-CPNT, shuttling rapidly and frequently between an α-plane zone and an adjacent midplane region. Results of this work reveal that a charge at the end of an ionic channel may significantly alter the transport characteristics of the channel.

MD Simulations on the Transport Behaviors of Mixed Na+ and Li+ in a Transmembrane Cyclic Peptide Nanotube under an Electric Field.

Due to its inherently stronger hydration, Li+ faces a higher dehydration energy than Na+ at the entrance of the 8×(WL)4/POPE-CPNT. Present MD simulations show that it can enter the channel from a NaCl/LiCl solution only under an electric field stronger than 0.3 V nm-1, while Na+ is easier to move into the channel, which is well elucidated by two cations' PMF profiles. The cation-Ow radial distribution functions, the electrostatic interactions with water, and the orientations of neighboring water all refer to a more compact solvation structure and stronger hydration of Li+. Regardless of whether there is an external electric field, Na+ mainly appears in an α-plane zone, while Li+ does so in a midplane region. The increase in the electric field strength significantly accelerates the cations' axial diffusions, shortening the residence times of two cations in the channel. Furthermore, it makes channel water tend to take positive dipole states.

Dynamic behavior and selective adsorption of a methanol/water mixture inside a cyclic peptide nanotube.

Present molecular dynamics simulations indicate that the methanol component in a methanol/water mixture is more likely to be trapped in a cyclic peptide nanotube (CPNT), while water molecules tend to be present at the channel mouths as transient guests. Channel water resides mainly between methanol and the CPNT wall, resulting in a distinct decrease in the H-bond number per channel methanol. Six designed CPNTs with different channel diameters and outer surface characteristics all possess distinct selectivity to methanol over water. Of these, the amphipathic 8 × (AQ)4-CPNT exhibits the best performance. Results in this study provide basic information for the application of a CPNT to enrich methanol from a methanol/water mixture. Graphical Abstract Typical overview of water and methanol molecular distribution in cyclic peptide nanotubes.

Molecular Dynamics Simulations on the Behaviors of Hydrophilic/Hydrophobic Cyclic Peptide Nanotubes at the Water/Hexane Interface.

In this work, nine kinds of amino acid residues, i.e., alanine (A), leucine (L), valine (V), isoleucine (I), tryptophan (W), glutamine (Q), threonine (T), serine (S), and cysteine (C), were selected to construct seven cyclic peptide nanotubes (CPNTs) with diverse hydrophilic/hydrophobic external surfaces, which were further separately inserted at the water/hexane interface to investigate their microstructures and interfacial properties. Molecular dynamics (MD) simulations reveal that all the CPNTs except the QT- and VL-CPNTs have different degrees of tilt, fracture, and shedding at the interface. The end-CPs are more susceptible to the effect of the surroundings than the mid-CPs. The interactions of individual CP subunits with the neighborings disclose the firmness of the mid-CPs and the dissociation of the end-CPs. The results indicate that a hydrophobic CPNT is prone to stay at the interface, while a hydrophilic CPNT easily enters the water phase, resulting in many H-bonds with water. Results in this work enrich the dynamic properties of a hydrophilic/hydrophobic CPNT at the biphase interface at the atomic level.

Different transport behaviors of NH4 (+) and NH3 in transmembrane cyclic peptide nanotubes.

Two water-filled transmembrane cyclic peptide nanotubes (CPNTs) of 8×cyclo-(WL)n=4,5/POPE were chosen to investigate the dependences of the transport properties of the positive NH4 (+) and neutral NH3 on the channel radius. Molecular dynamic simulations revealed that molecular charge, size, ability to form H-bonds and channel radius all significantly influence the behaviors of NH4 (+) and NH3 in a CPNT. Higher electrostatic interactions, more H-bonds, and water-bridges were found in the NH4 (+) system, resulting in NH4 (+) meeting higher energy barriers, while NH3 can enter, exit and permeate the channels effortlessly. This work sheds a first light on the differences between the mechanisms of NH4 (+) and NH3 moving in a CPNT at an atomic level. Graphical Abstract Snapshot of the simulation system of NH4 (+)_octa-CPNT with an NH4 (+) initially positioned at one mouth of the tube, PMF profiles for single NH4 (+) ion and NH3 molecule moving through water-filled transmembrane CPNTs of 8×cyclo-(WL)n=4,5/POPE and sketch graphs of the possible H-bond forms of NH3 and NH4 (+) with the neighboring water.

Dynamic behaviors and transport properties of ethanol molecules in transmembrane cyclic peptide nanotubes.

Classical molecular dynamics simulations have been performed to investigate the dynamic behaviors and transport properties of ethanol molecules in transmembrane cyclic peptide nanotubes (CPNTs) with various radii, i.e., 8×(WL¯)n=3,4,5/POPE. The results show that ethanol molecules spontaneously fill the octa- and deca-CPNTs, but not the hexa-CPNT. In the octa-CPNT, ethanol molecules are trapped at individual gaps with their carbon skeletons perpendicular to the tube axis and hydroxyl groups towards the tube wall, forming a broken single-file chain. As the channel radius increases, ethanol molecules inside the deca-CPNT tend to form a tubular layer and the hydroxyl groups mainly stretch towards the tube axis. Computations of diffusion coefficients indicate that ethanol molecules in the octa-CPNT nearly lost their diffusion abilities, while those in the deca-CPNT diffuse as 4.5 times as in a (8, 8) carbon nanotube with a similar tube diameter. The osmotic and diffusion permeabilities (pf and pd, respectively) of the octa- and deca-CPNTs transporting ethanol were deduced for the first time. The distributions of the gauche and trans conformers of ethanol molecules in two CPNTs are quite similar, both with approximately 57% gauche conformers. The non-bonded interactions of channel ethanol with a CPNT wall and surrounding ethanol were explored. The potential of mean force elucidates the mechanism underlying the transporting characteristics of channel ethanol in a transmembrane CPNT.

[Application of miniscrew for extraction of mesially impacted wisdom tooth adjacent to the inferior alveolar nerve canal].

PURPOSE: To study the value of miniscrew for extraction of mesially impacted wisdom tooth adjacent to the inferior alveolar nerve canal. METHODS: Fourteen mesially impacted wisdom teeth were proven to be adjacent to the inferior alveolar nerve canal by means of cone-beam CT scan. The treatment began with the miniscrew traction of the wisdom teeth. After 2-5 months, they were moved away from the canal and then extracted. RESULTS: After extraction, all 14 cases did not show any obvious side effect. CONCLUSIONS: Application of miniscrew traction is a valuable method for minimally invasive extraction of mesially impacted wisdom tooth that is adjacent to the inferior alveolar nerve canal.

Transport behavior of a single Ca(2+), K(+), and Na(+) in a water-filled transmembrane cyclic peptide nanotube.

Molecular dynamics simulations have been performed to investigate the transport properties of a single Ca(2+), K(+), and Na(+) in a water-filled transmembrane cyclic peptide nanotube (CPNT). Two transmembrane CPNTs, i.e., 8×(WL)n=4,5/POPE (with uniform lengths but various radii), were applied to clarify the dependence of ionic transport properties on the channel radius. A huge energy barrier keeps Ca(2+) out of the octa-CPNT, while Na(+) and K(+) can be trapped in two CPNTs. The dominant electrostatic interaction of a cation with water molecules leads to a high distribution of channel water around the cation and D-defects in the first and last gaps, and significantly reduces the axial diffusion of channel water. Water-bridged interactions were mostly found between the artificially introduced Ca(2+) and the framework of the octa-CPNT, and direct coordinations with the tube wall mostly occur for K(+) in the octa-CPNT. A cation may drift rapidly or behave lazily in a CPNT. K(+) behaves most actively and can visit the whole deca-CPNT quickly. The first solvation shells of Ca(2+) and Na(+) are basically saturated in two CPNTs, while the hydration of K(+) is incomplete in the octa-CPNT. The solvation structure of Ca(2+) in the octa-CPNT is most stable, while that of K(+) in the deca-CPNT is most labile. Increasing the channel radius induces numerous interchange attempts between the first-shell water molecules of a cation and the ones in the outer region, especially for the K(+) system.

Tilt behavior of an octa-peptide nanotube in POPE and affects on the transport characteristics of channel water.

MD simulations have been carried out for studying the tilt behaviors of the 8 × (WL)4-CPNT embedded in the POPE bilayer in a water environment and under an anhydrous condition, respectively. Besides, the dependences of the transport characteristics of channel water on the extent of the CPNT tilt were explored. The results indicate that the presence of water may exacerbate the CPNT tilt but plays an important role in maintaining the integrity of the CPNT by forming water bridges in the end-gaps. Cation-π interactions between the indole rings of Trp residues and lipid headgroups are the major factor causing the CPNT tilt under an anhydrous condition, while H-bonded interactions between water molecules and the indole rings are primary in a water environment. The dipole orientations of channel water molecules except those in the last end-gap are gradually oriented and eventually only take "+dipole" states under 20° of the CPNT tilt. The average residence time of channel water gradually increases with the intensifying of the CPNT tilt.

Molecular dynamics studies on the influences of a gradient electric field on the water chain in a peptide nanotube.

The structure and transportation characteristics of the water chain inside a 8×cyclo-(WL)4 peptide nanotube (PNT) were simulated under a gradient electric (GE) field. The gradient was defined by the ratio of a constant (Ea) and the z-directional length (Lz) of the simulation box. Ea varies from 0.0 to 0.9 V nm(-1). As the gradient increases, the probabilities of finding two water molecules in an α-plane zone and three in a midplane region increase. To accommodate more water molecules, the axial array of channel water molecules becomes more compact. Meanwhile, the H-bonded network between the channel water is greatly intensified when Ea increases from 0.3 to 0.9 V nm(-1). Nevertheless, the proportion of strong H-bonds does not increase significantly following the formation of a more compact axial array of water molecules. When Ea reaches 0.9 V nm(-1), the water molecule in an α-plane zone may be dragged by its neighboring water molecules into the midplane region, resulting in a significant deviation from the channel axis. With the augment of the gradient, the dipoles of channel water are gradually oriented along the tube axis in the sequence from gap 1 to 7, namely along the direction of the electric field. Nevertheless, even when E a reaches 0.9 V nm(-1), the dipole orientation of the channel water is not complete, and dipole flips still occur in gap 7. Under a GE field, the rightward and leftward hopping rates of channel water are no longer equal to each other, i.e., channel water performs an asymmetric transportation.

Exploring the dynamic behaviors and transport properties of gas molecules in a transmembrane cyclic peptide nanotube.

The dynamic behaviors and transport properties of O2, CO2, and NH3 molecules through a transmembrane cyclic peptide nanotube (CPNT) of 8×cyclo-(WL)4/POPE have been investigated by steered molecular dynamics (SMD) simulations and adaptive biasing force (ABF) samplings. Different external forces are needed for three gas molecules to enter the channel. The periodic change of the pulling force curve for a gas traveling through the channel mainly arises from the regular and periodic arrangement of the composed CP subunits of the CPNT. Radial distribution functions (RDFs) between gas and water disclose the density decrease of channel water, which strongly aggravates the discontinuity of H-bond formation between a gas molecule and the neighboring water. Compared to hardly any H-bond formation between CO2 (or O2) and the framework of the CPNT, NH3 can form abundant H-bonds with the carbonyl/amide groups of the CPNT, leading to a fierce competition to NH3-water H-bonded interactions. In addition to direct H-bonded interactions, all three gases can form water bridges with the tube. The potential profile of mean force coincides with the occurring probability of a gas molecule along the tube axis. The energy barriers at two mouths of the CPNT elucidate the phenomenon that CO2 and O2 are thoroughly confined in the narrow lumen while NH3 can easily go outside the tube. Intermolecular interactions of each gas with channel water and the CPNT framework and the formation of H-bonds and water bridges illuminate the different gas translocation behaviors. The results uncover interesting and comprehensive mechanisms underlying the permeation characteristics of three gas molecules traveling through a transmembrane CPNT.

Molecular dynamics study of Na⁺ transportation in a cyclic peptide nanotube and its influences on water behaviors in the tube.

The dynamics of Na(+) transportation in a transmembrane cyclic peptide nanotube of 8 × (WL)4/POPE has been simulated. The curve of PMF (potential of mean force) for Na(+) moving through the tube, based on ABF (adaptive biasing force) method, indicates that Na(+) possesses lower free energy in an α-plane region than in a mid-plane one. It was found that Na(+) would desorb one or two water molecules in the first solvation shell when entering the tube and later maintain in a solvation state. The average numbers of water molecules around Na(+) are 4.50, 4.09 in the first solvation shell, and 3.10, 4.08 in the second one for Na(+) locating in an α-plane zone and a mid-plane region, respectively. However, water molecules far away from Na(+) location still nearly arrange in a form of 1-2-1-2 file. The dipole orientations of water molecules in the regions of gaps 1 and 7 display "D-defects", resulted from the simultaneous electrostatic potentials generated by Na(+) and the bare carbonyls at the tube mouths. Such "D-defects" accommodate the energetically favorable water orientations thereby.

Synthesis, structures and antibacterial activities of benzoylthiourea derivatives and their complexes with cobalt.

Four new thiocarbonyl fluorobenzamides and their complexes with cobalt have been synthesized and characterized by elemental analysis, FTIR, and (1)H NMR. Five crystal structures of the thioylbenzamides complexes of Co(PTCB)(3), Co(2FPTCB)(3), Co(4FPTCB)(3), Co(2FMTCB)(2) and Co(4FMTCB)(3) have been determined by X-ray diffraction. The antibacterial properties of these compounds against the bacteria, E. coli, Staphylococcus aureus, B. subtilis, P. aeruginosa, and Shewanella sp. were investigated. The experiments showed that both compounds and the complexes had the antibacterial activities against all of the studied bacteria. The thioylbenzamides had stronger controls for the bacteria of E. coli, S. aureus, B. subtilis and P. aeruginosa than their corresponding cobalt complexes. There was the contrary result against the bacteria of Shewanella sp. The para-substitution of fluorine atom increased antibacterial activities, while fluorine atom was substituted on ortho-benzoyl, the antibacterial activity weakened. The thioylbenzamides linked to piperidine instead of a morpholine group may increase the antibacterial activities.

Dependences of water permeation through cyclic octa-peptide nanotubes on channel length and membrane thickness.

Effects of the channel length and membrane thickness on the water permeation through the transmembrane cyclic octa-peptide nanotubes (octa-PNTs) have been studied by molecular dynamics (MD) simulations. The water osmotic permeability (p(f)) through the PNTs of k × (WL)(4)/POPE (1-palmitoyl-2-oleoyl-glycerophosphoethanolamine; k = 6, 7, 8, 9, and 10) was found to decay with the channel length (L) along the axis (~L(-2.0)). Energetic analysis showed that a series of water binding sites exist in these transmembrane PNTs, with the barriers of ~3k(B)T, which elucidates the tendency of p(f) well. Water diffusion permeability (p(d)) exhibits a relationship of ~L(-1.8), which results from the novel 1-2-1-2 structure of water chain in such confined nanolumens. In the range of simulation accuracy, the ratio (p(f)/p(d)) of the water osmotic and diffusion permeability is approximately a constant. MD simulations of water permeation through the transmembrane PNTs of 8 × (WL)(4)/octane with the different octane membrane thickness revealed that the water osmotic and diffusion permeability (p(f) and p(d)) are both independent of the octane membrane thickness, confirmed by the weak and nearly same interactions between the channel water and octane membranes with the different thickness. The results may be helpful for revealing the permeation mechanisms of biological water channels and designing artificial nanochannels.

Novel quadruple fluorescence properties of two benzoylthiourea isomers.

Two benzoylthiourea isomers, N-2-flurobenzoy-N'-4- (N,N-dimethyl)amidophenylthiourea (2FBDAPT) and N-4-fluro-benzoy-N'-4- (N,N-dimethyl)amidophenylthiourea (4FBDAPT) were determined by fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR) and X-ray diffraction. It was found that intra- and intermolecular hydrogen bonds played an important role in determining their conformations. Electronic spectra of the two compounds were investigated by UV absorption and steady-state fluorescence methods. The intermolecular hydrogen bond between the title compounds and methanol molecules caused the long wavelength absorption bands in methanol to weaken and vanish indeed. Quadruple fluorescence bands in ultraviolet and visible region were observed in the studied solvents upon the variable excitation wavelength. As same as Azumaya's suggestions for benzanilide (BA), F4 fluorescence bands with the maximum wavelength (λ(max)) between 546 nm and 622 nm were characteristic of TICT fluorescence. F3 bands of λ(max) from 434 nm to 483 nm were explained by the ESIPT model of the S1 state of the thiol tautomer to the S1 state of the keto tautomer. The new proposition was that F2 bands with λ(max) at about 365 nm were attributed to ESIPT from the S1 state of the thiol tautomer to the S0 state of the enol tautomer. And F1 fluorescence emissions with λ(max) at about 310 nm originated from the local S1 transitions of the enol tautomer. All experimental results were supported by MP2, CASSCF and CASPT2 quantum chemical calculations.

Water diffusion behaviors and transportation properties in transmembrane cyclic hexa-, octa- and decapeptide nanotubes.

Molecular dynamics simulations have been performed on three transmembrane cyclic peptide nanotubes, i.e., 8 × (WL)(n=3,4,5)/POPE (with uniform lengths but various radii) to investigate the radial dependences of the water-chain structures, diffusions, and transportation properties. The diffusions of individual water molecules and collective coordinates of all the channel-water in the three systems are certified as unbiased Brownian motions. From the very good linear relationships between MSDs and time intervals, the diffusion coefficients and transportation permeabilities have been deduced efficiently. Under the hydrostatic pressure differences across the membrane, a net unidirectional water flow rose up, and the osmotic permeabilities were determined. The ratios of the osmotic and diffusion permeabilities (p(f)/p(d)) were examined for all the three channels.

Molecular dynamics simulation for the structure of the water chain in a transmembrane peptide nanotube.

The structure of the water chain in the 8 x cyclo-(WL)(4) peptide nanotube embedded in the POPE lipid bilayer is studied by molecular dynamics simulations. The distribution profiles of water molecules along the nanotube axis proposes a wavelike pattern of the water chain in the nanotube, arraying in the form of a 1-2-1-2 file, in contrast to the single file in other nanochannels studied widely. Cylindrical distribution functions of water at different zones and potential of mean force of a water molecule along the axis suggest that the primary reason for forming the water-chain pattern is steric constraints. A novel hydrogen bond network in the nanotube is present such that each water in the alpha-plane zones forms two hydrogen bonds (as a donor) with the two water molecules in the adjacent midplane zone, and each water molecule in the midplane zones forms one hydrogen bond with the water molecule in the adjacent alpha-plane zone and a poor hydrogen bond with the carbonyl groups in the nanotube. Strong orientations of the water dipoles near the two opening ends pointing to the opposite directions are found, and the potential energy of a water O or H atom along the axis is explored to explain the water dipole orientations' reversing in the nanotube. Defects of the hydrogen bond network exist in the central gaps of the cyclic peptide nanotube.

Theoretical insight into the influences of alpha-substituents in aliphatic aldehydes on the enantioselectivities of aldol reactions.

Density functional theory has been applied to study the influences of alpha-substituents in aliphatic aldehydes on the enantioselectivities of the (S)-proline-catalyzed direct aldol reactions. Reaction scenarios of three kinds of aliphatic aldehydes were investigated. Four transition states associated with the stereocontrolling step of each reaction have been obtained. They are corresponding to the syn and anti arrangements of enamine intermediates and the si and re attacks to the carbonyl group of an aldehyde. The solvent effect of DMSO was investigated using self-consistent reaction field method based on the polarizable continuum model. The computed energies of transition states explain the origin of the catalysis and enantioselectivities for these (S)-proline-catalyzed aldol reactions and reveal the influences of alpha-substituents in aliphatic aldehydes on the enantioselectivities of these reactions.