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1.
Phys Chem Chem Phys ; 25(45): 31418-31430, 2023 Nov 22.
Artículo en Inglés | MEDLINE | ID: mdl-37962373

RESUMEN

Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) plays a crucial role in inflammation and cell death, so it is a promising candidate for the treatment of autoimmune, inflammatory, neurodegenerative, and ischemic diseases. So far, there are no approved RIPK1 inhibitors available. In this study, four machine learning algorithms were employed (random forest, extra trees, extreme gradient boosting and light gradient boosting machine) to predict small molecule inhibitors of RIPK1. The statistical metrics revealed similar performance and demonstrated outstanding predictive capabilities in all four models. Molecular docking and clustering analysis were employed to confirm six compounds that are structurally distinct from existing RIPK1 inhibitors. Subsequent molecular dynamics simulations were performed to evaluate the binding ability of these compounds. Utilizing the Shapley additive explanation (SHAP) method, the 1855 bit has been identified as the most significant molecular fingerprint fragment. The findings propose that these six small molecules exhibit promising potential for targeting RIPK1 in associated diseases. Notably, the identification of Cpd-1 small molecule (ZINC000085897746) from the Musa acuminate highlights its natural product origin, warranting further attention and investigation.


Asunto(s)
Aprendizaje Automático , Simulación de Dinámica Molecular , Simulación del Acoplamiento Molecular
2.
J Org Chem ; 80(9): 4672-82, 2015 May 01.
Artículo en Inglés | MEDLINE | ID: mdl-25836059

RESUMEN

Bidentate directing group (DG) strategy is a promising way to achieve sp(2) and more inert sp(3) C-H bond activations in transition metal (TM) catalysis. In this work, we systematically explored the assisting effects exerted by bidentate DGs in the C-H bond activations. Through DFT calculations and well-defined comparative analysis, we for the first time unified the rationale of the reactivity promoted by bidentate DG in sp(2) and sp(3) C-H activations, which are generally consistent with available experimental discoveries about the C-H activation reactivity up to date. In addition to the general rationale of the reactivity, the assisting effects of several typical bidentate DGs were also quantitatively evaluated and compared to reveal their relative promoting ability for C-H activation reactivity. Finally, the effect of the ligating group charge and the position of the ligating group charge in bidentate DGs were also investigated, based on which new types of DGs were designed and proposed to be potentially effective in C-H activation. The deeper understanding and new insight about the bidentate DG strategy gained in this work would help to enhance its further experimental development in sp(2) and sp(3) C-H bond activations.

3.
J Comput Chem ; 33(16): 1448-57, 2012 Jun 15.
Artículo en Inglés | MEDLINE | ID: mdl-22517297

RESUMEN

A general comparison of fundamental distinctions between the FeO(2+) and FeS(2+) complexes in an identical cyanide or isocyanide ligand environment for methane hydroxylation has been probed computationally in this work in a series of hypothetical [Fe(IV)(X)(CN)5](3-), [Fe(IV)(X)(NC)5](3-), (X = O, S) complexes. We have detailed an analysis of the geometric and electronic structures using density functional theory calculations. In addition, their σ- and π-mechanisms in C-H bond activation process have been described with the aid of the schematic molecular orbital diagram. From our theoretical results, it is shown that (a) the iron(IV)-sulfido complex apparently is able to hydroxylate C-H bond of methane as good as the iron(IV)-oxo species, (b) the O-CN, S-CN complexes have an inherent preference for the low-spin state, while for the case of O-NC and S-NC in which S = 1 and S = 2 states are relatively close in energy, (c) each of the d block electron orbital plays an important role, which is not just spectator electron, and (d) in comparison to the cyanide and isocyanide ligand environment, we can see that the FeS(2+) species prefer the cyanide ligand environment, while the FeO(2+) species favor the isocyanide ligand environment. In addition, a remarkably good correlation of the σ-/π-mechanism for hydrogen abstraction from methane with the gap between the Fe-dz2 (α) and C-H (α) pair as well as the Fe-dxz/yz (ß) and C-H (ß) pair has been found.

4.
Phys Chem Chem Phys ; 14(1): 246-56, 2012 Jan 07.
Artículo en Inglés | MEDLINE | ID: mdl-22068928

RESUMEN

The conversion of benzene to phenol by high-valent bare FeO(2+) was comprehensively explored using a density functional theory method. The conductor-like screen model (COSMO) was used to mimic the role of solvent effect with acetonitrile chosen as the solvent. Two radical mechanisms and one oxygen insertion mechanism were tested for this conversion. The first radical mechanism can also be named as the concerted mechanism in which the hydrogen-atom abstraction process is accomplished via a four-centered transition state. The second radical mechanism is initiated by a direct hydrogen-atom abstraction with a collinear C-H-O transition structure. It is actually the same as the well-accepted rebound mechanism for the C-H bond activation by heme and nonheme iron-oxo catalysts. The third is an oxygen insertion mechanism which is essentially an aromatic electrophilic attack leading to an arenium σ-complex intermediate. The formation of a precomplex with an η(4) coordinate environment in the first radical mechanism is energetically more favorable. However, the relatively lower activation energy barrier of the oxygen insertion mechanism compared to the radical ones makes it highly competitive if the Fe=O(2+) collides with benzene in the proper orientation. The detailed potential energy surfaces also indicate that the second radical mechanism, i.e., the benzene C-H bond activation through the rebound mechanism, is less favorable. This thorough theoretical study, especially the electronic structure analysis, may offer very important clues for understanding and studying C-H bond activation by iron-based catalysts and enzymatic reactions in protein active pockets.


Asunto(s)
Benceno/química , Hidroxilación , Modelos Moleculares , Catálisis , Simulación por Computador , Hierro/química , Oxígeno/química , Fenol/química , Termodinámica
5.
J Phys Chem A ; 116(5): 1475-85, 2012 Feb 09.
Artículo en Inglés | MEDLINE | ID: mdl-22239679

RESUMEN

Alkane C-H bond activation by various catalysts and enzymes has attracted considerable attention recently, but many issues are still unanswered. The conversion of ethane to ethanol and ethene by bare [Fe(III)═O](+) has been explored using density functional theory and coupled-cluster method comprehensively. Two possible reaction mechanisms are available for the entire reaction, the direct H-abstraction mechanism and the concerted mechanism. First, in the direct H-abstraction mechanism, a direct H-abstraction is encountered in the initial step, going through a collinear transition state C···H···O-Fe and then leading to the generation of an intermediate Fe-OH bound to the alkyl radical weakly. The final product of the direct H-abstraction mechanism is ethanol, which is produced by the hydroxyl group back transfer to the carbon radical. Second, in the concerted reaction mechanism, the H-abstraction process is characterized via overcoming four/five-centered transition states (6/4)TSH_c5 or (4)TSH_c4. The second step of the concerted mechanism can lead to either product ethanol or ethene. Moreover, the major product ethene can be obtained through two different pathways, the one-step pathway and the stepwise pathway. It is the first report that the former pathway starting from (6/4)IM_c to the product can be better described as a proton-coupled electron transfer (PCET). It plays an important role in the product ethene generation according to the CCSD(T) results. The spin-orbital coupling (SOC) calculations demonstrate that the title reaction should proceed via a two-state reactivity (TSR) pattern and that the spin-forbidden transition could slightly lower the rate-determining energy barrier height. This thorough theoretical study, especially the explicit electronic structure analysis, may provide important clues for understanding and studying the C-H bond activation promoted by iron-based artificial catalysts.

6.
J Comput Chem ; 32(9): 2005-11, 2011 Jul 15.
Artículo en Inglés | MEDLINE | ID: mdl-21484837

RESUMEN

Several new electride compounds M@pyrrole (M = Li, Na, and K), Li@AR (AR = indole, thiophene, and benzene), Li@tryptophan and Li@serotonin were designed and investigated, which exhibit considerably large first hyperpolarizabilities (ß(0)) (6705, 1116, 11399, 5781, 4808, 1536, 8106, and 9389 au, respectively) by comparison with their corresponding sole molecules pyrrole (ß(0) = 30 au), indole (104 au), thiophene (6 au), benzene (0 au), tryptophan (159 au) and serotonin (151 au), respectively. The computational results revealed that the interaction of the alkali metal atom with π-conjugated aromatic ring (AR) is one effectively new approach to produce diffuse excess electron to get a large ß(0) value, which is advantageous for the design of the novel high-performance NLO materials with π-conjugated AR: alkali metal atoms doped nanomaterials and biomolecules.

7.
Chemistry ; 17(8): 2414-9, 2011 Feb 18.
Artículo en Inglés | MEDLINE | ID: mdl-21319235

RESUMEN

Graphene nanoribbon (GNR) has been used, for the first time, as an excellent conjugated bridge in a donor-conjugated bridge-acceptor (D-B-A) framework to design high-performance second-order nonlinear optical materials. Owing to the unique diradical planar conjugated bridge of GNR, D(NH(2))-GNR-A(NO(2)) exhibits exceptionally large static first hyperpolarizability (ß(0)) up to 2.5×10(6) a.u. (22000×10(-30) esu) for H(2)N-(7,3)ZGNR-NO(2) (ZGNR=zigzag-edged GNR), which is about 15 times larger than the recorded value of ß(0) (1470×10(-30) esu) for the D-A polyene reported by Blanchard-Desce et al. [Chem. Eur. J. 1997, 3, 1091]. Interestingly, we have found that the size effect of GNR plays a key role in increasing ß(0) for the H(2)N-GNR-NO(2) system, in which the width effect of GNR perpendicular to the D-A direction is superior to the length effect along the D-A direction.

8.
J Phys Chem A ; 115(10): 2041-6, 2011 Mar 17.
Artículo en Inglés | MEDLINE | ID: mdl-21332234

RESUMEN

Superalkalies with low ionization potentials (IPs) can exhibit behaviors reminiscent of alkali atoms and hence be considered as potential building blocks for the assembly of novel nanostructured materials. A new series of binuclear superalkali cations M(2)Li(2k+1)(+) (M = F, O, N, C) has been studied using ab initio methods. The structural features of such cations are found to be related to the central atoms. In the preferred structures of F(2)Li(3)(+), O(2)Li(5)(+), and N(2)Li(7)(+), two central atoms are bridged by lithium atoms. While in the global minima of C(2)Li(9)(+), two central carbon atoms directly link each other and the C-C unit extends to the surface of the whole system. These M(2)Li(2k+1)(+) species exhibit very low vertical electron affinities of 2.74-4.61 eV at the OVGF/6-311+G(3df) level and hence should be classified as superalkali cations.

9.
J Phys Chem A ; 115(15): 3576-82, 2011 Apr 21.
Artículo en Inglés | MEDLINE | ID: mdl-21443216

RESUMEN

The methane (CH(4)) hydrogen abstraction reaction by linear butadiynyl radical C(4)H (CCCCH) has been investigated by direct ab initio dynamics over a wide temperature range of 100-3000 K, theoretically. The potential energy surfaces (PESs) have been constructed at the CCSD(T)/aug-cc-pVTZ//BB1K/6-311G(d,p) levels of theory. Two different hydrogen abstraction channels by C(1) and C(4) of C(4)H (C(1)C(2)C(3)C(4)H) have been considered. The results indicate that the C(1) position of C(4)H is a more reactive site. The electron transfer behaviors of two possible channels are also analyzed by quasi-restricted orbital (QRO) in detail. The rate constants calculated by canonical variational transition-state theory (CVT) with the small-curvature tunneling correction (SCT) are in excellent agreement with available experimental values. The normal and three-parameter expressions of Arrhenius rate constants are also provided within 100-3000 K. It is expected to be helpful for further studies on the reaction dynamics behaviors over a wide temperature range where no experimental data is available so far.


Asunto(s)
Metano/química , Teoría Cuántica , Radicales Libres/química , Temperatura
10.
J Phys Chem A ; 115(8): 1418-22, 2011 Mar 03.
Artículo en Inglés | MEDLINE | ID: mdl-21302909

RESUMEN

It is well-known that single H3N-HCl and H2O-HCl acid-base pairs do not react to form the ion pairs, H4N(+)Cl(-) and H3O(+)Cl(-), in isolation. On the basis of ab initio method, we propose a physical method of external electric field (Eext) to drive the proton transfer from acid (HCl) to base (NH3/H2O). Our results show that when Eext along the proton-transfer direction achieves or exceeds the critical electric field (Ec), the proton transfer occurs, such as, the Ec values of proton transfer for H3N-HCl and H2O-HCl are 54 × 10(-4) and 210 × 10(-4) au, respectively. And the degree of the proton transfer can be controlled by modulating the strength of Eext. Furthermore, we estimate the inductive strength of an excess electron (Ee) equivalent to the Eext = 125 × 10(-4) au, which is greater than the Ec (54 × 10(-4) au) of NH3-HCl but less than the Ec (210 × 10(-4) au) of H2O-HCl. This explains well the anion photoelectron spectroscopy [Eustis et al. Science 2008, 319, 936] that an excess electron can trigger the proton transfer for H3N-HCl but not for H2O-HCl. On the basis of the above estimation, we also predict that two excess electrons can induce H2O-HCl to undergo the proton transfer and form the ion pair H3O(+)Cl(-).


Asunto(s)
Amoníaco/química , Campos Electromagnéticos , Ácido Clorhídrico/química , Modelos Químicos , Protones , Agua/química , Electrones
11.
J Struct Biol ; 172(3): 284-93, 2010 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-20732428

RESUMEN

The aromatized chromophore (Chr) of C-1027 with selective DNA-cleaving ability, which is stabilized and delivered by the apoprotein (Apo) in vitro, is not released until the holoprotein (Apo+Chr) penetrates into the cultured cancer cells. As a drug delivery system, the holoprotein has gained much attention in clinical application. However, the Chr-releasing mechanism is ambiguous so far. In this paper, the releasing pathway is investigated using conventional molecular dynamics (MD), essential dynamics (ED), essential dynamics sampling and steered molecular dynamics (SMD) simulations. The results indicate that the releasing paths are related to the local motions of three loops: L3 (Val39-Gln42), L7 (Thr75-Thr79) and L9 (Asn97-Leu100). The major obstacles to Chr releasing come from steric hindrance, direct hydrogen bonds and hydrophobic interactions formed by the three loops, and Ser98 is an important residue in the releasing process. The most favorable direction of releasing is almost parallel to the connection between L7 and L3. Releasing from the direction, Chr only needs to break three hydrogen bonds from Ser98 and Pro76 and the weakest steric hindrance.


Asunto(s)
Aminoglicósidos/química , Enediinos/química , Simulación de Dinámica Molecular , Apoproteínas/química , Modelos Moleculares
12.
J Struct Biol ; 169(1): 14-24, 2010 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-19747549

RESUMEN

The enediyne ring chromophore with strong DNA cleavage activity of neocarzinostatin is labile and therefore stabilization by forming the complex (carrying protein+chromophore: holo-NCS). Holo-NCS has gained much attention in clinical use as well as for drug delivery systems, but the chromophore-releasing mechanism to trigger binding to the target DNA with high affinity and producing DNA damage remain unclear. Three possible pathways were initially determined by conventional MD, essential dynamics and essential dynamics sampling. One of the paths runs along the naphthoate moiety; another runs along the amino sugar moiety; the third along the enediyne ring. Further, calculated forces and time by FPMD (force-probe molecular dynamics) suggest that the opening of the naphthoate moiety is most favorable pathway and Leu45, Phe76 and Phe78 all are key residues for chromophore release. In addition, conformational analyses indicate that the chromophore release is only local motions for the protein.


Asunto(s)
Simulación de Dinámica Molecular , Cinostatina/química , Cinostatina/metabolismo , Estructura Secundaria de Proteína , Cinostatina/análogos & derivados
13.
J Phys Chem A ; 114(35): 9496-506, 2010 Sep 09.
Artículo en Inglés | MEDLINE | ID: mdl-20704295

RESUMEN

A detailed theoretical study is performed at the B3LYP/6-311G(d,p) and G3B3 (single-point) levels as an attempt to explore the reaction mechanism of CH with C(3)H(6). It is shown that the barrierless association of CH with C(3)H(6) forms two energy-rich isomers CH(3)-cCHCHCH(2) (1), and CH(2)CH(2)CHCH(2) (4). Isomers 1 and 4 are predicted to undergo subsequent isomerization and dissociation steps leading to ten dissociation products P(1) (CH(3)-cCHCHCH + H), P(2) (CH(3)-cCCHCH(2) + H), P(3) (cCHCHCH(2) + CH(3)), P(4) (CH(3)CHCCH(2) + H), P(5) (cis-CH(2)CHCHCH(2) + H), P(6) (trans-CH(2)CHCHCH(2) + H), P(7) (C(2)H(4) + C(2)H(3)), P(8) (CH(3)CCH + CH(3)), P(9) (CH(3)CCCH(3) + H) and P(12) (CH(2)CCH(2) + CH(3)), which are thermodynamically and kinetically possible. Among these products, P(5), P(6), and P(7) may be the most favorable products with comparable yields; P(1), P(2), and P(3) may be the much less competitive products, followed by the almost negligible P(4), P(8), P(9), and P(12). Since the isomers and transition states involved in the CH + C(3)H(6) reaction all lie lower than the reactant, the title reaction is expected to be fast, which is consistent with the measured large rate constant in experiment. The present study may lead us to a deep understanding of the CH radical chemistry.

14.
J Phys Chem A ; 114(18): 5888-93, 2010 May 13.
Artículo en Inglés | MEDLINE | ID: mdl-20405894

RESUMEN

The effects of intermolecular interaction on dipole moment (mu(z)), the mean (alpha(0)) and anisotropy (Deltaalpha) of the polarizability, and the first and second hyperpolarizabilities (beta(0) and gamma(0), respectively) for four lithium-bond dimers (LiCN...LiCN, LiNC...LiNC, H(4)C(2)...LiF, and H(3)N...LiF) have been investigated in the finite-field approach. The electric properties were obtained at the CCSD(T)/6-311++G(2df, 2p) level. For the four dimers, electron correlation contributions are very important to the total and interaction static electric properties. Different from the H bond interaction effects on hyperpolarizabilities of H-bond dimers, the Li-bond interactions significantly decrease the beta(0) values of the four Li-bond dimers (by 73.6% for LiCN...LiCN, by 204.8% for LiNC...LiNC, by 75.5% for H(4)C(2)...LiF, and by 24.0% for H(3)N...LiF), and also considerably decrease the second hyperpolarizabilities of the Li-bond dimers investigated (by 52.7% for LiCN...LiCN, by 43.7% for LiNC...LiNC, by 16.4% for H(4)C(2)...LiF, and by 62.6% for H(3)N...LiF).

15.
J Phys Chem A ; 114(8): 2874-84, 2010 Mar 04.
Artículo en Inglés | MEDLINE | ID: mdl-20146458

RESUMEN

A detailed theoretical study for the poorly understood ion-molecule reaction of CHCl(-) with CS(2) is explored at the B3LYP/6-311++G(d,p) and CCSD(T)/6-311++G(3df,2p) (single-point) levels. Various possible reaction pathways are considered. On the doublet potential energy surface, five dissociation products are both thermodynamically and kinetically possible. Among these products, P(7) (SCHCl(-) + CS) may be the most favorable product with predominant abundances, whereas P(1) (Cl(-) + SCHCS) and P(2) (Cl(-) + HCCSS) may be the second and third feasible products followed by the almost negligible P(3) (Cl(-) + HSCCS), P(4) (CClS(-) + HCS), and P(6) (S-cCCS(-) + HCl). Because the isomers and transition states involved in the most feasible pathways all lie below the reactant, the title reaction is expected to be fast, which is consistent with the measured large rate constant in recent experiment. The present paper may provide a useful guide for understanding other analogous ion-molecule reactions such as CHF(-) and CHBr(-) with CS(2), COS, and CO(2).

16.
J Comput Chem ; 30(7): 1135-45, 2009 May.
Artículo en Inglés | MEDLINE | ID: mdl-18942727

RESUMEN

Recoverin is an important neuronal calcium sensor (NCS) protein, which have been implicated in a wide range of Ca(2+) signaling events in neurons and photoreceptors. To characterize the conformational transition of recoverin from the myristoyl sequestered state to the extrusion state, a series of conventional molecular dynamics (CMD) and targeted molecular dynamics (TMD) simulations were performed. The 36.8 ns long CMD and TMD simulations on recoverin revealed a reliably conformational transition pathway, which can be viewed as a sequential two-stage process. A very important mechanistic conclusion from the present TMD simulations is that the hydrophobic and hydrophilic interactions modulate the allostery cooperatively in the conformational transition pathway. In the first stage, three salt-bridges broken between Lys-84 and Gly-124, between Lys-5 and Glu-103 and between Gly-16 and Lys-97 are major components to destabilize the structure of state T and trigger the swivel of the N- and C-terminal domains. In the second stage, the rupture of H-bond Phe-56-O(...)H(O)-Thr-21 leads to the two helices of EF-1 apart from each other, destabilizing the hydrophobic interactions of the myristoyl group with its environment, whereas the making of H-bond Leu-108-O(...)H(O)-Ser-72 helps the interfacial domain maintain its structural integrity during the course of the myristoyl extrusion. The molecular dynamics simulations results are beneficial to understanding the mechanism of how and why NCS proteins make progress in the photo-signal transduction processes. Further experimental and theoretical studies are still very desirable.


Asunto(s)
Calcio/farmacología , Simulación por Computador , Recoverina/química , Regulación Alostérica/efectos de los fármacos , Calcio/química , Enlace de Hidrógeno , Interacciones Hidrofóbicas e Hidrofílicas , Modelos Químicos , Modelos Moleculares , Conformación Proteica/efectos de los fármacos , Recoverina/metabolismo , Factores de Tiempo
17.
J Phys Chem A ; 113(24): 6800-11, 2009 Jun 18.
Artículo en Inglés | MEDLINE | ID: mdl-19514788

RESUMEN

The complex triplet potential energy surface for the reaction of ground-state carbon atom C((3)P) with trans-C(4)H(8) is theoretically investigated at the B3LYP/6-311G(d,p) and G3B3(single-point) levels. Various possible isomerization and dissociation pathways are probed. The initial association between C((3)P) and trans-C(4)H(8) is found to be the C((3)P) addition to the C=C bond of trans-C(4)H(8) to barrierlessly generate the three-membered cyclic isomer 1 CH(3)-cCHCCH-CH(3). Subsequently, 1 undergoes a ring-opening process to form the chainlike isomer 3a cis-trans-CH(3)CHCCHCH(3), which can either lead to P(6)((2)CH(3)CHCCCH(3) + (2)H) via the C-H bond cleavage or to P(7)((2)CH(3)CHCCH + (2)CH(3)) via C-C bond rupture. These two paths are the most favorable channels of the title reaction. Other channels leading to products P(1)((2)CH(3)-cCHCCH + (2)CH(3)), P(2)((2)CH(3)-cCHCC-CH(3) + (2)H), P(3)(trans-(2)CH(3)CHCH + (2)C(2)H(3)), P(4)(cis-(2)CH(3)CHCH + (2)C(2)H(3)), P(5)((3)CH(3)CH + (1)CH(3)CCH), P(8)(cis-(2)CH(3)CHCHCCH(2) + (2)H), P(9)(trans-(2)CH(3)CHCHCCH(2) + (2)H), P(10)((2)CH(3)CCCH(2) + (2)CH(3)), and P(11)((2)CH(3)CHCCHCH(2) + (2)H), however, are much less competitive due to either kinetic or thermodynamic factors. Because the intermediates and transition states involved in the C((3)P) + trans-C(4)H(8) reaction all lie below the reactant, the title reaction is expected to be rapid, as is consistent with the measured large rate constant. Our results may be helpful for future experimental investigation of the title reaction.

18.
J Phys Chem A ; 113(12): 2961-6, 2009 Mar 26.
Artículo en Inglés | MEDLINE | ID: mdl-19256524

RESUMEN

Doping Li atom into higher flexible cyclic polyamines with many amine unit petals (ethyleneimine) forms the n-petal-shaped Li-doped cyclic polyamines (n = 3-5). Three structures, referred to as three-petal-shaped Li-[9]aneN(3), four-petal-shaped Li-[12]aneN(4), and five-petal-shaped Li-[15]aneN(5), with all-real frequencies are obtained at the MP2/6-31+G(d) level. Because the chemical doping with Li and the deformation of the complexant produce more diffuse excess electron, the three molecules with the excess electrons exhibit considerably large static first hyperpolarizabilities (beta(0)) at the MP2 level. Additionally, the beta(0) value increases with increasing the petal number (n) as follows: 52282 (n = 3) < 65505 (n = 4) < 127617 au (n = 5). This shows a new complexant effect on beta(0), that is, a dependence on the petal number (n) of beta(0) owing to the flexibility of the complexants increasing with the petal number. The MP2 frequency-dependent beta values are estimated by using the multiplicative approximation. The frequency dispersion is found to be strong. For the MP2 frequency-dependent beta values, the more pronounced dependence on the petal number (n) of beta (-2omega; omega, omega) and beta (-omega; omega, 0) are shown.

19.
J Phys Chem A ; 113(39): 10577-87, 2009 Oct 01.
Artículo en Inglés | MEDLINE | ID: mdl-19731902

RESUMEN

The complex triplet potential energy surface for the reaction of ground-state atomic carbon C(3P) with propylene C3H6 is explored at the B3LYP/6-311G(d,p), QCISD/6-311G(d,p), and G3B3 (single-point) levels. Various possible reaction pathways are probed. It is shown that the reaction is initiated by the addition of C(3P) to the C=C bond of C3H6 to generate barrierlessly the three-membered ring isomer 1 CH3-cCHCCH2, followed by the ring-opening process to form 2a trans-CH3CHCCH2, which can easily interconvert to 2b cis-CH3CHCCH2. Starting from 2 (2a, 2b), the most feasible pathway is the internal C-H bond rupture of 2a leading to P4(2CH3CCCH2 + 2H), terminal C-H bond cleavage of 2 (2a,2b) to form P5(2CH3CHCCH + 2H), or direct C-C bond fission of 2b to form P7(2CH2CCH + 2CH3), all of which may have comparable contributions to the title reaction. Much less competitively, 2a takes a 1,2-H-shift to form 5a trans-cis-CH3CHCHCH, followed by a C-C bond rupture leading to P6(1C2H2 + 3CH3CH). Because the intermediates and transition states involved in the feasible pathways all lie below the reactant, the title reaction is expected to be rapid, which is consistent with the measured large rate constant. The present article may provide some useful information for future experimental investigation of the title reaction.

20.
J Chem Phys ; 131(16): 164307, 2009 Oct 28.
Artículo en Inglés | MEDLINE | ID: mdl-19894947

RESUMEN

A new type of binuclear superalkali B(2)Li(11) and its corresponding cation B(2)Li(11) (+) were theoretically predicted based on the density functional theory calculations. B(2)Li(11) was found to have six minimum energy structures corresponding to five cation states exhibiting superalkali nature. The global minima of B(2)Li(11) and B(2)Li(11) (+) are similar to each other in structure, where two central boron atoms directly link each other and the whole geometry resembles a capsule with an additional Li atom localized on its side. The vertical electron affinities for the B(2)Li(11) (+) cations at the OVGF/6-311+G(3df) level are in the range of 3.40-3.73 eV, which are lower than the ionization potential (IP) of Cs atom, and even lower than the IP=3.75 eV of the mononuclear superalkali BLi(6). Hence, the studied B(2)Li(11) (+) species should be classified as superalkali cations, and the B(2)Li(11) species can be regarded as superalkalies. Such binuclear superalkalies added candidates to the research on superatoms and offered potential building blocks for the assembly of new materials in which strong electron donors are involved. Note that the electronic shell structure of B(2)Li(11) is not consistent with the prediction of the cluster electronic shell model. It demonstrates that the doped nonmetal atoms make the molecular orbital-level distribution of heteronuclear species much more complex than that of homonuclear metal clusters.

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