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1.
Nature ; 611(7935): 289-294, 2022 11.
Artículo en Inglés | MEDLINE | ID: mdl-36352136

RESUMEN

The discovery of a method to separate isotopologues, molecular entities that differ in only isotopic composition1, is fundamentally and technologically essential but remains challenging2,3. Water isotopologues, which are very important in biological processes, industry, medical care, etc. are among the most difficult isotopologue pairs to separate because of their very similar physicochemical properties and chemical exchange equilibrium. Herein, we report efficient separation of water isotopologues at room temperature by constructing two porous coordination polymers (PCPs, or metal-organic frameworks) in which flip-flop molecular motions within the frameworks provide diffusion-regulatory functionality. Guest traffic is regulated by the local motions of dynamic gates on contracted pore apertures, thereby amplifying the slight differences in the diffusion rates of water isotopologues. Significant temperature-responsive adsorption occurs on both PCPs: H2O vapour is preferentially adsorbed into the PCPs, with substantially increased uptake compared to that of D2O vapour, facilitating kinetics-based vapour separation of H2O/HDO/D2O ternary mixtures with high H2O separation factors of around 210 at room temperature.

2.
Angew Chem Int Ed Engl ; 63(21): e202401005, 2024 May 21.
Artículo en Inglés | MEDLINE | ID: mdl-38584128

RESUMEN

Developing highly stable porous coordination polymers (PCPs) with integrated electrical conductivity is crucial for advancing our understanding of electrocatalytic mechanisms and the structure-activity relationship of electrocatalysts. However, achieving this goal remains a formidable challenge because of the electrochemical instability observed in most PCPs. Herein, we develop a "modular design" strategy to construct electrochemically stable semiconducting PCP, namely, Fe-pyNDI, which incorporates a chain-type Fe-pyrazole metal cluster and π-stacking column with effective synergistic effects. The three-dimensional electron diffraction (3D ED) technique resolves the precise structure. Both theoretical and experimental investigation confirms that the π-stacking column in Fe-pyNDI can provide an efficient electron transport path and enhance the structural stability of the material. As a result, Fe-pyNDI can serve as an efficient model electrocatalyst for nitrate reduction reaction (NO3RR) to ammonia with a superior ammonia yield of 339.2 µmol h-1 cm-2 (14677 µg h-1 mgcat. -1) and a faradaic efficiency of 87 % at neutral electrolyte, which is comparable to state-of-the-art electrocatalysts. The in-situ X-ray absorption spectroscopy (XAS) reveals that during the reaction, the structure of Fe-pyNDI can be kept, while part of the Fe3+ in Fe-pyNDI was reduced in situ to Fe2+, which serves as the potential active species for NO3RR.

3.
J Am Chem Soc ; 145(16): 8979-8987, 2023 Apr 26.
Artículo en Inglés | MEDLINE | ID: mdl-37067179

RESUMEN

Conductive metal-organic frameworks (c-MOFs) with outstanding electrical conductivities and high charge carrier mobilities are promising candidates for electronics and optoelectronics. However, the poor solubility of planar ligands greatly hinders the synthesis and widespread applications of c-MOFs. Nonplanar ligands with excellent solubility in organic solvents are ideal alternatives to construct c-MOFs. Herein, contorted hexabenzocoronene (c-HBC) derivatives with good solubility are adopted to synthesize c-MOFs. Three c-MOFs (c-HBC-6O-Cu, c-HBC-8O-Cu, and c-HBC-12O-Cu) with substantially different geometries and packing modes have been synthesized using three multitopic catechol-based c-HBC ligands with different symmetries and coordination numbers, respectively. With more metal coordination centers and increased charge transport pathways, c-HBC-12O-Cu exhibits the highest intrinsic electrical conductivity of 3.31 S m-1. Time-resolved terahertz spectroscopy reveals high charge carrier mobilities in c-HBC-based c-MOFs, ranging from 38 to 64 cm2 V-1 s-1. This work provides a systematic and modular approach to fine-tune the structure and enrich the c-MOF family with excellent charge transport properties using nonplanar and highly soluble ligands.

4.
J Am Chem Soc ; 145(34): 19086-19097, 2023 08 30.
Artículo en Inglés | MEDLINE | ID: mdl-37596995

RESUMEN

Metal oxide nanozymes have emerged as the most efficient and promising candidates to mimic antioxidant enzymes for treatment of oxidative stress-mediated pathophysiological disorders, but the current effectiveness is unsatisfactory due to insufficient catalytic performance. Here, we report for the first time an intrinsic strain-mediated ultrathin ceria nanoantioxidant. Surface strain in ceria with variable thicknesses and coordinatively unsaturated Ce sites was investigated by theoretical calculation analysis and then was validated by preparing ∼1.2 nm ultrathin nanoplates with ∼3.0% tensile strain in plane/∼10.0% tensile strain out of plane. Compared with nanocubes, surface strain in ultrathin nanoplates could enhance the covalency of the Ce-O bond, leading to increasing superoxide dismutase (SOD)-mimetic activity by ∼2.6-fold (1533 U/mg, in close proximity to that of natural SOD) and total antioxidant activity by ∼2.5-fold. As a proof of concept, intrinsic strain-mediated ultrathin ceria nanoplates could boost antioxidation for improved ischemic stroke treatment in vivo, significantly better than edaravone, a commonly used clinical drug.


Asunto(s)
Antioxidantes , Accidente Cerebrovascular Isquémico , Humanos , Antioxidantes/farmacología , Catálisis , Óxidos , Superóxido Dismutasa
5.
Phys Chem Chem Phys ; 25(42): 28770-28783, 2023 Nov 01.
Artículo en Inglés | MEDLINE | ID: mdl-37850473

RESUMEN

UiO-66 is one of the most valuable metal-organic frameworks because of its excellent adsorption capability for gas molecules and its high stability towards water. Herein we investigated adsorption of carbon dioxide (CO2), acetone, and methanol to infinite UiO-66 using DFT calculations on an infinite system under periodic-boundary conditions and post-Hartree-Fock (SCS-MP2 and MP2.5) calculations on cluster models. Three to four molecules are adsorbed at each of four µ-OH groups bridging three Zr atoms in one unit cell (named Site I). Six molecules are adsorbed around three pillar ligands, where the molecule is loosely surrounded by three terephthalate ligands (named Site II). Also, six molecules are adsorbed around the pillar ligand in a different manner from that at Site II, where the molecule is surrounded by three terephthalate ligands (named Site III). Totally fifteen to sixteen CO2 molecules are adsorbed into one unit cell of UiO-66. The binding energy (BE) decreases in the order Site I > Site III > Site II for all three molecules studied here and in the order acetone > methanol ≫ CO2 in the three adsorption sites. At the site I, the protonic H atom of the µ-OH group interacts strongly with the negatively charged O atom of CO2, acetone and methanol, which is the origin of the largest BE value at this site. Although the DFT calculations present these decreasing orders of BE values correctly, the correction by post-Hartree-Fock calculations is not negligibly small and must be added for obtaining better BE values. We explored NMR spectra of UiO-66 with adsorbed CO2 molecules and found that the isotropic shielding constants of the 1H atom significantly differ among no CO2, one CO2 (at Sites I, II, or III), and fifteen CO2 adsorption cases (Sites I to III) but the isotropic 17O and 13C shielding constants change moderately by adsorption of fifteen CO2 molecules. Thus, 1H NMR measurement is a useful experiment for investigating CO2 adsorption.

6.
Angew Chem Int Ed Engl ; 62(41): e202306185, 2023 Oct 09.
Artículo en Inglés | MEDLINE | ID: mdl-37507837

RESUMEN

Prussian blue (PB) has emerged as a promising cathode material in aqueous batteries. It possesses two distinct redox centers, and the potassium ions (K+ ) are unevenly distributed throughout the compound, adding complexity to the interpretation of the K+ insertion/de-insertion kinetic mechanism. Traditional ensemble-averaged measurements are limited in uncovering the precise kinetic information of the PB particles, as the results are influenced by the construction of the porous composite electrode and the redox behavior from different particles. In this study, the electrochemical processes of individual PB particles were investigated using nano-impact electrochemistry. By varying the potentials, different types of transient current signals were obtained that revealed the kinetic mechanism of each oxidation/reduction reaction in combination with theoretical simulation. Additionally, a partially contradictory conclusion between single-particle analysis and the ensemble-averaged measurement was discussed. These findings contribute to a better understanding of the electrochemical processes of cathode materials with multiple redox centers, which facilitates the development of effective strategies to optimize these materials.

7.
Angew Chem Int Ed Engl ; 62(10): e202216795, 2023 Mar 01.
Artículo en Inglés | MEDLINE | ID: mdl-36627239

RESUMEN

Targeted synthesis of kagome (kgm) topologic 2D covalent organic frameworks remains challenging, presumably due to the severe dependence on building units and synthetic conditions. Herein, two isomeric "two-in-one" monomers with different lengths of substituted arms based on naphthalene core (p-Naph and m-Naph) are elaborately designed and utilized for the defined synthesis of isomeric kgm Naph-COFs. The two isomeric frameworks exhibit splendid crystallinity and showcase the same chemical composition and topologic structure with, however, different pore channels. Interestingly, C60 is able to uniformly be encapsulated into the triangle channels of m-Naph-COF via in situ incorporation method, while not the isomeric p-Naph-COF, likely due to the different pore structures of the two isomeric COFs. The resulting stable C60 @m-Naph-COF composite exhibits much higher photoconductivity than the m-Naph-COF owing to charge transfer between the conjugated skeletons and C60 guests.

8.
Angew Chem Int Ed Engl ; 62(2): e202215234, 2023 Jan 09.
Artículo en Inglés | MEDLINE | ID: mdl-36377418

RESUMEN

Exploring new porous coordination polymers (PCPs) that have tunable structure and conductivity is attractive but remains challenging. Herein, fine pore structure engineering by ligand conformation control of naphthalene diimide (NDI)-based semiconducting PCPs with π stacking-dependent conductivity tunability is achieved. The π stacking distances and ligand conformation in these isoreticular PCPs were modulated by employing metal centers with different coordination geometries. As a result, three conjugated PCPs (Co-pyNDI, Ni-pyNDI, and Zn-pyNDI) with varying pore structure and conductivity were obtained. Their crystal structures were determined by three-dimensional electron diffraction. The through-space charge transfer and tunable pore structure in these PCPs result in modulated selectivity and sensitivity in gas sensing. Zn-pyNDI can serve as a room-temperature operable chemiresistive sensor selective to acetone.

9.
Angew Chem Int Ed Engl ; 61(25): e202116170, 2022 06 20.
Artículo en Inglés | MEDLINE | ID: mdl-35238141

RESUMEN

We present a facile route towards a dual single-atom nanozyme composed of Zn and Mo, which utilizes the non-covalent nano-assembly of polyoxometalates, supramolecular coordination complexes as the metal-atom precursor, and a macroscopic amphiphilic aerogel as the supporting substrate. The dual single-atoms of Zn and Mo have a high content (1.5 and 7.3 wt%, respectively) and exhibit a synergistic effect and a peroxidase-like activity. The Zn/Mo site was identified as the main active center by X-ray absorption fine structure spectroscopy and density functional theory calculation. The detection of versatile analytes, including intracellular H2 O2 , glucose in serum, cholesterol, and ascorbic acid in commercial beverages was achieved. The nanozyme has an outstanding stability and maintained its performance after one year's storage. This study develops a new peroxidase-like nanozyme and provides a robust synthetic strategy for single-atom catalysts by utilizing an aerogel as a facile substrate that is capable of stabilizing various metal atoms.


Asunto(s)
Antioxidantes , Peroxidasa , Catálisis , Peroxidasa/química , Peroxidasas , Zinc
10.
World J Surg Oncol ; 19(1): 100, 2021 Apr 07.
Artículo en Inglés | MEDLINE | ID: mdl-33827593

RESUMEN

OBJECTIVES: Down syndrome critical region 1 (DSCR1) is associated with carcinogenesis and tumor growth in several types of malignancy. However, little is known about the role of DSCR1 in CRC progression. The present study aimed to elucidate the clinicopathological significance, prognostic, and function roles of DSCR1 in CRC. METHODS: Firstly, we analyzed DSCR1 expression in 58 paired CRC samples and Oncomine database. Then, we analyzed DSCR1 expression in two independent CRC cohorts (test cohort: n = 70; validation cohort: n = 58) and tested its overall survival (OS) by Kaplan-Meier survival analyses. Finally, we overexpressed DSCR1 in two CRC cell lines DLD1 and LoVo and analyzed its effect on cell cycle and senescence. RESULTS: DSCR1 expression was significantly decreased in CRC samples and associated with clinicopathologic features of CRC patients, such as tumor size, lymph node metastasis, and TNM stage. CRC patients with low expression of DSCR1 had shorter overall survival (OS). Kaplan-Meier survival analyses showed that the expression of DSCR1 was significant factor for OS in both cohorts. Multiple Cox regression analysis showed that DSCR1 expression was an independent prognostic marker for OS in test cohort. Overexpression of DSCR1 isoform 4 (DSCR1-4) increased p21, p16, p-NFAT1, and p-NFAT2, while decreased CDK2, CDK4, and Cyclin D1 in CRC cells. In addition, overexpression of DSCR1-4 prevented proliferation and colony formation, and induced senescence in vitro. Moreover, overexpression of DSCR1-4 inhibited tumor growth and tumor angiogenesis in vivo. CONCLUSIONS: Our study found high expression of DSCR1 contributes to favorable prognosis of CRC patients and prevents cell cycle and proliferation of CRC cells, indicating a critical tumor suppressive role in CRC progression.


Asunto(s)
Neoplasias Colorrectales , Síndrome de Down , Biomarcadores de Tumor/genética , Proliferación Celular , Neoplasias Colorrectales/genética , Regulación Neoplásica de la Expresión Génica , Humanos , Estimación de Kaplan-Meier , Pronóstico
11.
Angew Chem Int Ed Engl ; 60(21): 11688-11694, 2021 May 17.
Artículo en Inglés | MEDLINE | ID: mdl-33594724

RESUMEN

Controlling gas sorption by simple pore modification is important in molecular recognition and industrial separation processes. In particular, it is challenging to realize the inverse selectivity, which reduces the adsorption of a high-affinity gas and increases the adsorption of a low-affinity gas. Herein, an "opposite action" strategy is demonstrated for boosting CO2 /C2 H2 selectivity in porous coordination polymers (PCPs). A precise steric design of channel pores using an amino group as an additional interacting site enabled the synergetic increase in CO2 adsorption while suppressing the C2 H2 adsorption. Based on this strategy, two new ultramicroporous PCP physisorbents that are isostructural were synthesised. They exhibited the highest CO2 uptake and CO2 /C2 H2 volume uptake ratio at 298 K. Origin of this specific selectivity was verified by detailed density functional theory calculations. The breakthrough separation performances with remarkable stability and recyclability of both the PCPs render them relevant materials for C2 H2 purification from CO2 /C2 H2 mixtures.

12.
Angew Chem Int Ed Engl ; 59(36): 15517-15521, 2020 Sep 01.
Artículo en Inglés | MEDLINE | ID: mdl-32237191

RESUMEN

To achieve unique molecular-recognition patterns, a rational control of the flexibility of porous coordination polymers (PCPs) is highly sought, but it remains elusive. From a thermodynamic perspective, the competitive relationship between the structural deformation energy (Edef ) of soft PCPs and the guest interaction is key for selective a guest-triggered structural-transformation behavior. Therefore, it is vital to investigate and control Edef to regulate this competition for flexibility control. Driven by these theoretical insights, we demonstrate an Edef -modulation strategy via encoding inter-framework hydrogen bonds into a soft PCP with an interpenetrated structure. As a proof of this concept, the enhanced Edef of PCP enables a selective gate-opening behavior toward CHCl3 over CH2 Cl2 by changing the adsorption-energy landscape of the compounds. This study provides a new direction for the design of functional soft porous materials.

13.
Angew Chem Int Ed Engl ; 59(1): 172-176, 2020 Jan 02.
Artículo en Inglés | MEDLINE | ID: mdl-31595640

RESUMEN

Single-ligand-based electronically conductive porous coordination polymers/metal-organic frameworks (EC-PCPs/MOFs) fail to meet the requirements of numerous electronic applications owing to their limited tunability in terms of both conductivity and topology. In this study, a new 2D π-conjugated EC-MOF containing copper units with mixed trigonal ligands was developed: Cu3 (HHTP)(THQ) (HHTP=2,3,6,7,10,11-hexahydrotriphenylene, THQ=tetrahydroxy-1,4-quinone). The modulated conductivity (σ≈2.53×10-5  S cm-1 with an activation energy of 0.30 eV) and high porosity (ca. 441.2 m2 g-1 ) of the Cu3 (HHTP)(THQ) semiconductive nanowires provided an appropriate resistance baseline and highly accessible areas for the development of an excellent chemiresistive gas sensor.

14.
Inorg Chem ; 58(8): 4894-4906, 2019 Apr 15.
Artículo en Inglés | MEDLINE | ID: mdl-30946577

RESUMEN

The unique Rh-Al bond in recently synthesized Rh(PAlP) 1 {PAlP = pincer-type diphosphino-aluminyl ligand Al[NCH2(P iPr2)]2(C6H4)2NMe} was investigated using the DFT method. Complex 1 has four doubly occupied nonbonding d orbitals on the Rh atom and one Rh d orbital largely participating in the Rh-Al bond which exhibits considerably large bonding overlap between Rh and Al atoms like in a covalent bond. Interestingly, Rhδ--Alδ+ polarization is observed in the bonding MO of 1, which is reverse to Rhδ+-Eδ- (E = coordinating atom) polarization found in a usual coordinate bond. This unusual polarization arises from the presence of the Al valence orbital at significantly higher energy than the Rh valence orbital energy. Characteristic features of 1 are further unveiled by comparing 1 with similar Rh complexes RhL(PMe3)2 (2 for L = AlMe2, 3 for L = Al(NMe2)2, 4 for L = BMe2, 5 for L = SiMe3, 6 for L = SiH3, 7 for L = CH3, 8 for L = OMe, and 9 for L = Cl). As expected, 7, 8, and 9 exhibit usual Rhδ+-Eδ- polarization (E = coordinating atom) in the Rh-E bonding MO. On the other hand, the reverse Rhδ--Eδ+ polarization is observed in the Rh-E bonding MOs of 2-5 like in 1, while the Rh-Si bond is polarized little in 6. These results are clearly understood in terms of the valence orbital energy of the ligand. Because the LUMO of 1 mainly consists of the Rh 4dσ, 5s, and 5p orbitals and the Al 3s and 3p orbitals, both Rh and Al atoms play the role of coordinating site for a substrate bearing a lone pair orbital. For instance, NH3 and pyridine coordinate to both Al and Rh atoms with considerably large binding energy. PAlP exhibits significantly strong trans influence, which is as strong as that of SiMe3 but moderately weaker than that of BMe2. The trans influence of these ligands is mainly determined by the valence orbital energy of the ligand and the covalent bond radius of the coordinating E atom.

15.
J Am Chem Soc ; 140(42): 13958-13969, 2018 10 24.
Artículo en Inglés | MEDLINE | ID: mdl-30264569

RESUMEN

The gate-opening adsorption mechanism and sigmoidal adsorption isotherm were theoretically investigated taking CO2 adsorption into porous coordination polymers, [Fe(ppt)2] n (PCP-N, Hppt = 3-(2-pyrazinyl)-5-(4-pyridyl)-1,2,4-triazole) and [Fe(dpt)2] n (PCP-C, Hdpt = 3-(2-pyridinyl)-5-(4-pyridyl)-1,2,4-triazole) as examples, where the hybrid method consisting of dispersion-corrected DFT for infinite PCP and a post-Hartree-Fock (SCS-MP2 and CCSD(T)) method for the cluster model was employed. PCP-N has site I (one-dimensional channel), site II (small aperture to site I), and site III (small pore) useful for CO2 adsorption. CO2 adsorption at site I occurs in a one by one manner with a Langmuir adsorption isotherm. CO2 adsorption at sites II and III occurs through a gate-opening adsorption mechanism, because the crystal deformation energy ( EDEF) at these sites is induced largely by the first CO2 adsorption but induced much less by the subsequent CO2 adsorption. Interestingly, nine CO2 molecules are adsorbed simultaneously at these sites because a large EDEF cannot be overcome by adsorption of one CO2 molecule but can be by simultaneous adsorption of nine CO2 molecules. For such CO2 adsorption, the Langmuir-Freundlich sigmoidal adsorption isotherm was derived from the equilibrium equation for CO2 adsorption. A very complicated CO2 adsorption isotherm, experimentally observed, is reproduced by combination of the Langmuir and Langmuir-Freundlich adsorption isotherms. In PCP-C, CO2 adsorption occurs only at site I with the Langmuir adsorption isotherm. Sites II and III of PCP-C cannot be used for CO2 adsorption because a very large EDEF cannot be overcome by simultaneous adsorption of nine CO2 molecules. Factors necessary for gate-opening adsorption mechanism are discussed on the basis of differences between PCP-N and PCP-C.

16.
Chemistry ; 24(24): 6412-6417, 2018 Apr 25.
Artículo en Inglés | MEDLINE | ID: mdl-29419938

RESUMEN

Two porous coordination polymers (PCPs) with different topologies (NTU-19: sql and NTU-20: dia) underwent finely controlled, stepwise crystal conversions to yield a common water-stable, flexible 2D framework (NTU-22: kgm). The crystal conversions occurred directly at higher temperature via the 3D intermediate (NTU-21: nbo), which could be observed at lower temperature. The successful isolation of the intermediate product of NTU-21, characterization with in situ PXRD and UV/Vis spectra were combined with DFT calculations to allow an understanding of the dynamic processes at the atomic level. Remarkably, breakthrough experiments demonstrate NTU-22 with integral structural properties allowed significant CO2 /CH4 mixture separation.

17.
Phys Chem Chem Phys ; 20(21): 14671-14678, 2018 May 30.
Artículo en Inglés | MEDLINE | ID: mdl-29770408

RESUMEN

Recent reports pointed out that the formal La2C2n (2n = 92-106) series can exist stably as carbide cluster metallofullerenes (CCMFs) La2C2@C2n-2 with their successful crystallographic characterization. Herein, we suggest that the corresponding dimetallofullerenes (di-EMFs) La2@C2n possessing the lowest potential energies are also plausible candidates because of their favorability in statistical thermodynamics. This can be demonstrated in our present theoretical investigations on La2C94 and previously reported other La2C2n (2n = 92, 96-100) series by density functional theory calculations and statistical mechanics analyses. Nevertheless, it was noted that these thermodynamically favorable La2@C2n isomers turned out to be kinetically unstable radicals due to the presence of one unpaired electron on the carbon cage, making them missing fullerenes and difficult to be captured in their pristine forms, except for the experimentally obtained La2@D5(450)-C100 that has no unpaired electron. Such kinetic instability could be modified by electron reduction (the products were denoted as [La2@C2n]-) or other similar exterior functionalization with ˙CF3 and benzyl radicals, resulting in La-La bonded and paramagnetic species capable of being captured. On the basis of these approaches, carbon cages D3(85)-C92, Cs(120)-C94, D2(186)-C96, and C2(157)-C96 are predicted to be feasibly captured as both pristine CCMF species and electron reduced di-EMF derivatives.

18.
J Am Chem Soc ; 139(50): 18313-18321, 2017 12 20.
Artículo en Inglés | MEDLINE | ID: mdl-29131950

RESUMEN

Here we report a soft porous crystal possessing hemilabile cross-links in its framework that exhibits exclusive gate opening for ethylene, enabling the discriminatory adsorption of ethylene over ethane. A Co-based porous coordination polymer (PCP) bearing vinylogous tetrathiafulvalene (VTTF) ligands, [Co(VTTF)], forms Co-S bonds as intermolecular cross-links in its framework in the evacuated closed state. The PCP recognizes ethylene via d-π complexation on the accessible metal site that displaces and cleaves the Co-S bond to "unlock" the closed structure. This ethylene-triggered unlocking event facilitates remarkable nonporous-to-porous transformations that open up accessible void space. This structural transformation follows a two-step gate-opening process. Each phase, including the intermediate structure, was successfully characterized by single-crystal X-ray diffraction analysis, which revealed an intriguing "half-open" structure suggestive of a disproportionate gate-opening phenomenon. The gate-opening mechanism was also investigated theoretically; density functional theory and Monte Carlo calculations revealed that the unique "half-open" phase corresponds to a substantially stable intermediate over the possible transformation trajectories. While ethylene opens the gate, ethane does not because it is unable to coordinate to the Co center. This feature is maintained even at pressures above 1 MPa and at a temperature of 303 K, demonstrating the potential of the "gate-locking/unlocking" mechanism that exploits the hemilabile cross-linking in soft porous crystals.

19.
J Comput Chem ; 38(26): 2241-2247, 2017 10 05.
Artículo en Inglés | MEDLINE | ID: mdl-28718989

RESUMEN

Although the existence of Stone-Wales (5-7) defect at graphene edge has been clarified experimentally, theoretical study on the formation mechanism is still imperfect. In particular, the regioselectivity of multistep reactions at edge (self-reconstruction and growth with foreign carbon feedstock) is essential to understand the kinetic behavior of reactive boundaries but investigations are still lacking. Herein, by using finite-sized models, multistep reconstructions and carbon dimer additions of a bared zigzag edge are introduced using density functional theory calculations. The zigzag to 5-7 transformation is proved as a site-selective process to generate alternating 5-7 pairs sequentially and the first step with largest barrier is suggested as the rate-determining step. Conversely, successive C2 insertions on the active edge are calculated to elucidate the formation of 5-7 edge during graphene growth. A metastable intermediate with a triple sequentially fused pentagon fragment is proved as the key structure for 5-7 edge formation. © 2017 Wiley Periodicals, Inc.

20.
J Comput Chem ; 38(10): 730-739, 2017 04 15.
Artículo en Inglés | MEDLINE | ID: mdl-28164347

RESUMEN

Noncovalent interactions involving aromatic rings, such as π···π stacking, CH···π are very essential for supramolecular carbon nanostructures. Graphite is a typical homogenous carbon matter based on π···π stacking of graphene sheets. Even in systems not involving aromatic groups, the stability of diamondoid dimer and layer-layer graphane dimer originates from C - H···H - C noncovalent interaction. In this article, the structures and properties of novel heterogeneous layer-layer carbon-nanostructures involving π···H-C-C-H···π···H-C-C-H stacking based on [n]-graphane and [n]-graphene and their derivatives are theoretically investigated for n = 16-54 using dispersion corrected density functional theory B3LYP-D3 method. Energy decomposition analysis shows that dispersion interaction is the most important for the stabilization of both double- and multi-layer-layer [n]-graphane@graphene. Binding energy between graphane and graphene sheets shows that there is a distinct additive nature of CH···π interaction. For comparison and simplicity, the concept of H-H bond energy equivalent number of carbon atoms (noted as NHEQ), is used to describe the strength of these noncovalent interactions. The NHEQ of the graphene dimers, graphane dimers, and double-layered graphane@graphene are 103, 143, and 110, indicating that the strength of C-H···π interaction is close to that of π···π and much stronger than that of C-H···H-C in large size systems. Additionally, frontier molecular orbital, electron density difference and visualized noncovalent interaction regions are discussed for deeply understanding the nature of the C-H···π stacking interaction in construction of heterogeneous layer-layer graphane@graphene structures. We hope that the present study would be helpful for creations of new functional supramolecular materials based on graphane and graphene carbon nano-structures. © 2017 Wiley Periodicals, Inc.

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