The valence state of C atoms and the structure of molecular orbitals of the (Buckminster)Fullerene C_(60)have been demonstrated. It has been shown that when a motion-coordinate system is adopted, in which the coordina...The valence state of C atoms and the structure of molecular orbitals of the (Buckminster)Fullerene C_(60)have been demonstrated. It has been shown that when a motion-coordinate system is adopted, in which the coordinate origin is at every C atom, the z axis is in the direction of the normal and the (x,y) axes are in the direction of tangents of C_(60)'s spherical surface, 240 valence atomic orbitals of C_(60) can be divided into two groups. All (P_x, P_y)atomic orbitals named as Pt ones and all the other P_z atomic orbitals named as p. ones, That is to say that if we name the molecular orbital linearly combined of P_t atomic orbitals as σ_t and the molecular orbital linearly combined of P_n atomic orbitals as π_n, the 240 valence molecular orbitals are of the property of σ_t-π_n separability. It has also been shown that the frontier and nearby frontier molecular orbitals are π_n ones, and therefore the essential physical and chemical properties of C_(60) are determined by its π_n molecular orbitals.展开更多
This paper calculates the five most stable conformers of serine with Hartree-Fock theory, density functional theory (B3LYP), Moller-Plesset perturbation theory (MP4(SDQ)) and electron propagation theory with the...This paper calculates the five most stable conformers of serine with Hartree-Fock theory, density functional theory (B3LYP), Moller-Plesset perturbation theory (MP4(SDQ)) and electron propagation theory with the 6-311++G(2d,2p) basis set. The calculated vertical ionization energies for the valence molecular orbitals of each conformer are in agreement with the experimental data, indicating that a range of molecular conformations would coexist in an equilibrium sample. Information of the five outer valence molecular orbitals for each conformer is explored in coordinate and momentum spaces using dual space analysis to investigate the conformational processes, which are generated from the global minimum conformer Serl by rotation of C2-C3 (Ser4), C1 C2 (Ser5) and C1-O2 (Set2 and Ser3). Orbitals 28a, 27a and 26a are identified as the fingerprint orbitals for all the conformational processes.展开更多
Recently, there was a hot controversy about the concept of localized orbitals, which was triggered by Grushow's work titled "Is it time to retire the hybrid atomic orbital?" [J. Chem. Educ. 88, 860 (2011)]. To c...Recently, there was a hot controversy about the concept of localized orbitals, which was triggered by Grushow's work titled "Is it time to retire the hybrid atomic orbital?" [J. Chem. Educ. 88, 860 (2011)]. To clarify the issue, we assess the delocalized and localized molecular orbitals from an experimental view using electron momentum spectroscopy. The delocalized and localized molecular orbitals based on various theoretical models for CH4, NH3, and H20 are compared with the experimental momentum distributions. Our results show that the delocalized molecular orbitals rather than the localized ones can give a direct interpretation of the experimental (e, 2e) results.展开更多
This paper studies the molecular rotational excitation and field-free spatial alignment in a nonresonant intense laser field numerically and analytically by using the time-dependent SchrSdinger equation. The broad rot...This paper studies the molecular rotational excitation and field-free spatial alignment in a nonresonant intense laser field numerically and analytically by using the time-dependent SchrSdinger equation. The broad rotational wave packets excited by the femtosecond pulse are defined in conjugate angle space, and their coefficients are obtained by solving a set of coupled linear equations. Both single molecule orientation angles and an ensemble of O2 and CO molecule angular distributions are calculated in detail. The numerical results show that, for single molecule highest occupied molecular orbital (HOMO) symmetry σ tends to have a molecular orientation along the laser polarization direction and the permanent dipole moment diminishes the mean of the orientation angles; for an ensemble of molecules, angular distributions provide more complex and additional information at times where there are no revivals in the single molecule plot. In particular, at the revival peak instant, with the increase of temperature of the molecular ensemble, the anisotropic angular distributions with respect to the laser polarization direction of the πg orbital gradually transform to the symmetrical distributions regarding the laser polarization vector and for two HOMO configurations angular distributions of all directions are confined within a smaller angle when the temperature of the molecular ensemble is higher.展开更多
A localized INDO method was used to calculate the ion [Fe_2 (CH_3) (CO) (Ph_2PCH_2PPh_2)- Cp_2]^+. Based on the analysis of the localized molecular orbitals (LMO), bond orders and contour maps, it was pointed out that...A localized INDO method was used to calculate the ion [Fe_2 (CH_3) (CO) (Ph_2PCH_2PPh_2)- Cp_2]^+. Based on the analysis of the localized molecular orbitals (LMO), bond orders and contour maps, it was pointed out that the LMO no. 20 corresponds to the coordination of C(1)-H(I) σbond to Fe(2) atom. Non occurrence of metal-metal bond between Fe(1) and Fe(2) atoms was found and the covalence of irons was numerated, which coincides with the value in ref 17.展开更多
Understanding the influence of adsorption sites to the electronic properties of adsorbed molecules on two-dimensional(2D)ultrathin insulator is of essential importance for future organic-inorganic hybrid nanodevices.H...Understanding the influence of adsorption sites to the electronic properties of adsorbed molecules on two-dimensional(2D)ultrathin insulator is of essential importance for future organic-inorganic hybrid nanodevices.Here,the adsorption and electronic states of manganese phthalocyanine(MnPc)on a single layer of hexagonal boron nitride(h-BN)have been comprehensively studied by low-temperature scanning tunneling microscopy/spectroscopy and tight binding calculations.The frontier orbitals of the MnPc can change drastically by reversible manipulation of individual MnPc molecules onto and away from the single atomic vacancies at the h-BN surface.Particularly,the change of the molecular electronic configuration can be controlled depending on whether the atomic vacancy is below the metal center or the ligand of the MnPc.These findings give new insight into defect-engineering of the organic-inorganic hybrid nanodevices down to submolecular level.展开更多
The single ionization rate of the diatomic molecular ion H2^+ with different active orbitals in an intense field is studied by using S-matrix theory. Our results show that the orientation-dependent single ionization ...The single ionization rate of the diatomic molecular ion H2^+ with different active orbitals in an intense field is studied by using S-matrix theory. Our results show that the orientation-dependent single ionization probability of H2^+ is greatly dependent on the symmetry and the electron density distribution of its initial states, and it can be used to identify the excited state of the molecular ion in the dissociation process.展开更多
Melanins represent one of the most ancient and important group of natural macromolecular pigments.They have multiple biological roles in almost all organisms across the Phyla,examples being photoprotection,anti-oxidat...Melanins represent one of the most ancient and important group of natural macromolecular pigments.They have multiple biological roles in almost all organisms across the Phyla,examples being photoprotection,anti-oxidative action,radical scavenger activity,and heavy metal removal.From the biomedical point of view,melanocytes are involved in the origin of melanoma tumors,and the main therapeutic advances for their treatment have been revised in Part 1 of this review.The chemical structure of eumelanin is a biological concern of great importance,and therefore,exploring theoretical molecular models and synthesis mechanisms will be here described,as well as molecular orbital features and supramolecular organization,which are responsible for the key properties that make these biological pigments so important,and so fascinating.Ultimately,this updated overview is devoted to describe present structural models and physico-chemical characteristics of eumelanin,in order to explain and utilize melanin properties on which new photothermal and ultrasonic protocols for melanoma treatment can be devised and applied.展开更多
A basic calculation procedure for the MOSMO method under CNDO/2 approximation is presented in this paper,and performed by using the same parameters as those used in the ordinary CNDO/2 LCAO-MO calculation.The calculat...A basic calculation procedure for the MOSMO method under CNDO/2 approximation is presented in this paper,and performed by using the same parameters as those used in the ordinary CNDO/2 LCAO-MO calculation.The calculated results on the whole are close to those obtained by use of the ordinary CNDO/2 LCAO-MO calculation,illustrating that the presented procedure is reasonable.Due to its simplicity,the presented calculation procedure may be feasible even in very large molecular s ystems.展开更多
The concept of resonance-assisted hydrogen bonds(RAHBs)highlights the synergistic interplay between theπ-resonance and hydrogen bonding interactions.This concept has been well-accepted in academia and is widely used ...The concept of resonance-assisted hydrogen bonds(RAHBs)highlights the synergistic interplay between theπ-resonance and hydrogen bonding interactions.This concept has been well-accepted in academia and is widely used in practice.However,it has been argued that the seemingly enhanced intramolecular hydrogen bonding(IMHB)in unsaturated compounds may simply be a result of the constraints imposed by theσ-skeleton framework.Thus,it is crucial to estimate the strength of IMHBs.In this work,we used two approaches to probe the resonance effect and estimate the strength of the IMHBs in the two exemplary cases of the enol forms of acetylacetone and o-hydroxyacetophenone.One approach is the block-localized wavefunction(BLW)method,which is a variant of the ab initio valence bond(VB)theory.Using this approach,it is possible to derive the geometries and energetics with resonance shut down.The other approach is Edmiston’s truncated localized molecular orbital(TLMO)technique,which monitors the energy changes by removing the delocalization tails from localized molecular orbitals.The integrated BLW and TLMO studies confirmed that the hydrogen bonding in these two molecules is indeed enhanced byπ-resonance,and that this enhancement is not a result ofσconstraints.展开更多
The critical _d vahues ( _ ) of the γ/(γ+σ).γ/(γ+μ) and γ/(γ+γ') phase boundaries in some ternar alloy phase diagrams at various temperatures are calculated by averaging the _d values of sererai selecte...The critical _d vahues ( _ ) of the γ/(γ+σ).γ/(γ+μ) and γ/(γ+γ') phase boundaries in some ternar alloy phase diagrams at various temperatures are calculated by averaging the _d values of sererai selected characteristic points at the phase boundaries.Approxmate equations for the temperature dependence of the critical _d of γ/(γ+σ).γ/(γ+μ) and γ/(γ+γ') phase boundaries are established.The accuracy of the analysis is discussed in detail. It is found for the first time that the average value of the bond order _ at the phase boundaries ts also approximatelr a constant and therefore a critical average bond order _ like - can be introduced for the analysts of phase stability展开更多
The localized molecular orbitals for typical bowl-shaped circulenes are obtained by the use of INDO-LMO method. It is found that these bowl-shaped circulenes with strained π-electron systems are still aromatic and th...The localized molecular orbitals for typical bowl-shaped circulenes are obtained by the use of INDO-LMO method. It is found that these bowl-shaped circulenes with strained π-electron systems are still aromatic and the rim π-bonds with larger localization form reactive regions for formation of buckminsterfullerene.展开更多
The localized molecular orbitals and energy levels for [Co_6 (μ_3-S)_8 (PH_3)_6] ̄(n+)(n=0, 1) as model molecules of the electron-rich [Co_6 (μ_3-S)_8 (PPh_3)_6] ̄(n+) (n=0,1) cluster compounds have been calculated ...The localized molecular orbitals and energy levels for [Co_6 (μ_3-S)_8 (PH_3)_6] ̄(n+)(n=0, 1) as model molecules of the electron-rich [Co_6 (μ_3-S)_8 (PPh_3)_6] ̄(n+) (n=0,1) cluster compounds have been calculated by using Edmiston-Ruedenberg energy localization scheme under the spin-unrestricted CNDO/2 approximation. It is shown that the cluster skeletons of these two isostructural molecules consist of the edge-localized two-centered two-electron (Co-S) bonds plus a pair of the skeleton electrons delocalized on the whole cluster core,leading an extra stability of the cluster core.The one-electron oxidation for the neutral molecule gives rise to a one-electron σ (Co-Co) bond.which further resonates among the three diagonal lines of the {Co_6} octahedron. The comparison between [Co_6 (μ_3-S)_8(PPh_3)_6] and [Co_6(μ_3-CO)_8(CO)_6] ̄(4-) indicates that the latter possesses face-localized bridging-bonds which are further delocalized on the whole surface of the cluster octahedron by the back-donation bonds from the lone electron pairs on the Co atoms to the capping carbonyl CO ligands. The structural features of the series of the [Co6(μ_3-X)_8L_6] ̄(n+)(X =S, Se; L=PPh_3,PEt_3, CO;n=0, 1) cluster compounds are briefly rationalized on the basis of the localization description as well.展开更多
Calculation of the bonding energy of a molecular orbital for a series of small molecules has been carried out by using ab initio STO-3G method. The results obtained demonstrate that the concept of the molecular orbita...Calculation of the bonding energy of a molecular orbital for a series of small molecules has been carried out by using ab initio STO-3G method. The results obtained demonstrate that the concept of the molecular orbital bonding energy is applicable for judging whether a molecular orbital is bonding, nonbonding or antibonding besides Mulliken overlap criterion.展开更多
The highest occupied molecular orbital(HOMO) energies of fullerenes are found by quantitative first-principles calculations to be raised by negative charging, and the rising rate rank of the fullerenes is C60 >C7...The highest occupied molecular orbital(HOMO) energies of fullerenes are found by quantitative first-principles calculations to be raised by negative charging, and the rising rate rank of the fullerenes is C60 >C70 >C80 >C90>C100 >C180. Then we compare fullerenes with carbon nanotubes(CNTs) and graphene sheets(GSs) and find that the increase of the HOMO energy of a fullerene is much faster than that of CNTs and graphene sheets with the same number of C atoms. The rising rate rank is fullerene>CNT>GS, which holds no matter what the number of C atoms is or which structure the fullerene isomer is. This work paves a new path for developing all-carbon devices with low-dimensional carbon nanomaterials as different functional elements.展开更多
The title compound was synthesized and its crystal structure was determined. C_(13)H(21)NO_2·HCl, orthorhombic, space group P2_12_12_1 with dimensions:a =10. 635(2), b=26.942(6), c=6.193(2), V=1774.5(8),Z=4,Mr=31...The title compound was synthesized and its crystal structure was determined. C_(13)H(21)NO_2·HCl, orthorhombic, space group P2_12_12_1 with dimensions:a =10. 635(2), b=26.942(6), c=6.193(2), V=1774.5(8),Z=4,Mr=319. 83 and Dc=1.20g/cm ̄3. The final residual factor R=0.048, Rw=0.062. The C atoms except those in rings has a distorted tetrahedron structure.The dihedral angle between the phenyl rings in the molecule is 74. 56°. There is no bond between HCl and ester.The molecules join each other by van der Waals force. Its molecular orbital calculations were carried out by means of extended Huckel molecular orbital method.展开更多
Seven transition metal complexes of Mn<sup>2+</sup>, Ni<sup>2+</sup>, Co<sup>2+</sup>, Cu<sup>2+</sup> and Zn<sup>2+</sup> with 3-aminopyridine (3-APy) as li...Seven transition metal complexes of Mn<sup>2+</sup>, Ni<sup>2+</sup>, Co<sup>2+</sup>, Cu<sup>2+</sup> and Zn<sup>2+</sup> with 3-aminopyridine (3-APy) as ligand have been synthesized, characterized by different techniques and their antibacterial activities were studied. Molecular modeling calculations were performed using DMOL<sup>3</sup> program in materials studio package which is designed for the realization of large scale density functional theory calculation (DFT). The quantum mechanical and chemical reactivity parameters such as chemical hardness, chemical potential, electronegativity, electrophilicity index and Homo-Lumo energy gap were obtained theoretically and were used to understand the biological activity of the prepared compounds. Some complexes were tested for their in-vitro cytotoxic activity in human lung cancer cell lines (A-549 cell line), and structureactivity relationships were established. In general, the coordination to Co<sup>2+</sup> increased the cytotoxicity while the Ni<sup>2+</sup> complexes show reduced cytotoxic activity compared to the metal-free 3-aminopyridine.展开更多
The energy-localized CNDO/2 molecular orbitals have been calculated for the cluster anions of [Co_6 (CO)_(14)] ̄(4-) and [Ni_2Co_4 (CO)_(14)] ̄(2-)in order to get a deeper insight into the nature of their skeletal bon...The energy-localized CNDO/2 molecular orbitals have been calculated for the cluster anions of [Co_6 (CO)_(14)] ̄(4-) and [Ni_2Co_4 (CO)_(14)] ̄(2-)in order to get a deeper insight into the nature of their skeletal bonding. The bonding characteristics of these hexanuclear carbonyl cobaltates are described from a localization bonding viewpoint. There are two typical M-CO bondings, one of which is formed by electron donation from the terminal and capping carbonyl ligands into the vacant hybrid orbitals on the metal atoms , leading to formation ofσ(C_t→Co) and σ(C_b→{Co_3})bonds. The other typical M-CO bonding is back donation of the lone d-electron pairs on the metal atoms into the carbonyl ligands, forming π(Co→C_t) bonds, σ(Co→{C_(b2)}) bonds and π(Co→{C_(b4)} ) bonds. It is found that there are no direct metalmetal bondings in the skeletons of these two cluster anions.The delocalization situation of the skeletal bonding electrons is briefly discussed.展开更多
The stabilization energies of substituted lithium carbene cations were calculated by using ab initio molecular orbital theory, and the relationship between the stabilization energies and molecular orbitals was discuss...The stabilization energies of substituted lithium carbene cations were calculated by using ab initio molecular orbital theory, and the relationship between the stabilization energies and molecular orbitals was discussed. The substituents with pi donor engender strong stabilization to CH2Li+. The calculations show the Y-C* bond lengths of cations become shorter and H-Y bond lengths longer than those of corresponding neutral molecules.展开更多
The title compound, 1-(naphthalene-2-yl)-2-(1H-pyrazol-1-yl)ethanone O-butyl oxime, I, was synthesized. The crystal and molecular structures of I were determined by IR, 1H-NMR, mass spectrum, elemental analysis an...The title compound, 1-(naphthalene-2-yl)-2-(1H-pyrazol-1-yl)ethanone O-butyl oxime, I, was synthesized. The crystal and molecular structures of I were determined by IR, 1H-NMR, mass spectrum, elemental analysis and X-ray single crystal diffraction. Molecular geometry from X-ray experiment of I in the ground state was compared using the Density Functional Theory (DFT) with B3LYP/6-311G(d,p) basis set. In addition, DFT calculation, molecular electrostatic potentials (MEP) and frontier molecular orbitals of I were performed at the B3LYP/6-311G(d,p) level of the theory.展开更多
文摘The valence state of C atoms and the structure of molecular orbitals of the (Buckminster)Fullerene C_(60)have been demonstrated. It has been shown that when a motion-coordinate system is adopted, in which the coordinate origin is at every C atom, the z axis is in the direction of the normal and the (x,y) axes are in the direction of tangents of C_(60)'s spherical surface, 240 valence atomic orbitals of C_(60) can be divided into two groups. All (P_x, P_y)atomic orbitals named as Pt ones and all the other P_z atomic orbitals named as p. ones, That is to say that if we name the molecular orbital linearly combined of P_t atomic orbitals as σ_t and the molecular orbital linearly combined of P_n atomic orbitals as π_n, the 240 valence molecular orbitals are of the property of σ_t-π_n separability. It has also been shown that the frontier and nearby frontier molecular orbitals are π_n ones, and therefore the essential physical and chemical properties of C_(60) are determined by its π_n molecular orbitals.
基金supported by the Doctoral Research Fund of Henan Normal University,China (Grant No. 525449)
文摘This paper calculates the five most stable conformers of serine with Hartree-Fock theory, density functional theory (B3LYP), Moller-Plesset perturbation theory (MP4(SDQ)) and electron propagation theory with the 6-311++G(2d,2p) basis set. The calculated vertical ionization energies for the valence molecular orbitals of each conformer are in agreement with the experimental data, indicating that a range of molecular conformations would coexist in an equilibrium sample. Information of the five outer valence molecular orbitals for each conformer is explored in coordinate and momentum spaces using dual space analysis to investigate the conformational processes, which are generated from the global minimum conformer Serl by rotation of C2-C3 (Ser4), C1 C2 (Ser5) and C1-O2 (Set2 and Ser3). Orbitals 28a, 27a and 26a are identified as the fingerprint orbitals for all the conformational processes.
基金supported by the National Natural Science Foundation of China(Grant No.11174175)the Tsinghua University Initiative Scientific Research Program,China
文摘Recently, there was a hot controversy about the concept of localized orbitals, which was triggered by Grushow's work titled "Is it time to retire the hybrid atomic orbital?" [J. Chem. Educ. 88, 860 (2011)]. To clarify the issue, we assess the delocalized and localized molecular orbitals from an experimental view using electron momentum spectroscopy. The delocalized and localized molecular orbitals based on various theoretical models for CH4, NH3, and H20 are compared with the experimental momentum distributions. Our results show that the delocalized molecular orbitals rather than the localized ones can give a direct interpretation of the experimental (e, 2e) results.
基金supported by the Program of Excellent Team in Harbin Institute of Technologythe Program for New Century Excellent Talents in University (NCET)National Natural Science Foundation of China (Grant Nos 10774033,60878018 and 10674036)
文摘This paper studies the molecular rotational excitation and field-free spatial alignment in a nonresonant intense laser field numerically and analytically by using the time-dependent SchrSdinger equation. The broad rotational wave packets excited by the femtosecond pulse are defined in conjugate angle space, and their coefficients are obtained by solving a set of coupled linear equations. Both single molecule orientation angles and an ensemble of O2 and CO molecule angular distributions are calculated in detail. The numerical results show that, for single molecule highest occupied molecular orbital (HOMO) symmetry σ tends to have a molecular orientation along the laser polarization direction and the permanent dipole moment diminishes the mean of the orientation angles; for an ensemble of molecules, angular distributions provide more complex and additional information at times where there are no revivals in the single molecule plot. In particular, at the revival peak instant, with the increase of temperature of the molecular ensemble, the anisotropic angular distributions with respect to the laser polarization direction of the πg orbital gradually transform to the symmetrical distributions regarding the laser polarization vector and for two HOMO configurations angular distributions of all directions are confined within a smaller angle when the temperature of the molecular ensemble is higher.
文摘A localized INDO method was used to calculate the ion [Fe_2 (CH_3) (CO) (Ph_2PCH_2PPh_2)- Cp_2]^+. Based on the analysis of the localized molecular orbitals (LMO), bond orders and contour maps, it was pointed out that the LMO no. 20 corresponds to the coordination of C(1)-H(I) σbond to Fe(2) atom. Non occurrence of metal-metal bond between Fe(1) and Fe(2) atoms was found and the covalence of irons was numerated, which coincides with the value in ref 17.
基金L.W.L.,Y.L.W.and T.Z.thank the Beijing Natural Science Foundation(Nos.4192054 and Z190006)the National Natural Science Foundation of China(Nos.61971035,61901038,and 61725107)+2 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB30000000)the Beijing Institute of Technology Research Fund Program for Young Scholars(No.3050011181814)L.W.L.and O.G.would like to thank the EU-EMPA COFUND Project BONMAT and the Swiss National Science Foundation(Nos.CRSI20-122703 and 200021_149627).
文摘Understanding the influence of adsorption sites to the electronic properties of adsorbed molecules on two-dimensional(2D)ultrathin insulator is of essential importance for future organic-inorganic hybrid nanodevices.Here,the adsorption and electronic states of manganese phthalocyanine(MnPc)on a single layer of hexagonal boron nitride(h-BN)have been comprehensively studied by low-temperature scanning tunneling microscopy/spectroscopy and tight binding calculations.The frontier orbitals of the MnPc can change drastically by reversible manipulation of individual MnPc molecules onto and away from the single atomic vacancies at the h-BN surface.Particularly,the change of the molecular electronic configuration can be controlled depending on whether the atomic vacancy is below the metal center or the ligand of the MnPc.These findings give new insight into defect-engineering of the organic-inorganic hybrid nanodevices down to submolecular level.
基金Project supported by the National Natural Science Foundation of China (Grant No.10674087)the National Basic Research Program of China (Grant No.2006CB806000)+2 种基金the Hebei Provincial Natural Science Foundation (Grant No.A2008000136)the Project of National Center for Educational Techonology of the Ministry of Education of China (Grant NCET-08-0883)the Program of TYAl of Shanxi Province and China Academy of Engineering Physics Foundation (Grant No.2008B0102007)
文摘The single ionization rate of the diatomic molecular ion H2^+ with different active orbitals in an intense field is studied by using S-matrix theory. Our results show that the orientation-dependent single ionization probability of H2^+ is greatly dependent on the symmetry and the electron density distribution of its initial states, and it can be used to identify the excited state of the molecular ion in the dissociation process.
文摘Melanins represent one of the most ancient and important group of natural macromolecular pigments.They have multiple biological roles in almost all organisms across the Phyla,examples being photoprotection,anti-oxidative action,radical scavenger activity,and heavy metal removal.From the biomedical point of view,melanocytes are involved in the origin of melanoma tumors,and the main therapeutic advances for their treatment have been revised in Part 1 of this review.The chemical structure of eumelanin is a biological concern of great importance,and therefore,exploring theoretical molecular models and synthesis mechanisms will be here described,as well as molecular orbital features and supramolecular organization,which are responsible for the key properties that make these biological pigments so important,and so fascinating.Ultimately,this updated overview is devoted to describe present structural models and physico-chemical characteristics of eumelanin,in order to explain and utilize melanin properties on which new photothermal and ultrasonic protocols for melanoma treatment can be devised and applied.
文摘A basic calculation procedure for the MOSMO method under CNDO/2 approximation is presented in this paper,and performed by using the same parameters as those used in the ordinary CNDO/2 LCAO-MO calculation.The calculated results on the whole are close to those obtained by use of the ordinary CNDO/2 LCAO-MO calculation,illustrating that the presented procedure is reasonable.Due to its simplicity,the presented calculation procedure may be feasible even in very large molecular s ystems.
文摘The concept of resonance-assisted hydrogen bonds(RAHBs)highlights the synergistic interplay between theπ-resonance and hydrogen bonding interactions.This concept has been well-accepted in academia and is widely used in practice.However,it has been argued that the seemingly enhanced intramolecular hydrogen bonding(IMHB)in unsaturated compounds may simply be a result of the constraints imposed by theσ-skeleton framework.Thus,it is crucial to estimate the strength of IMHBs.In this work,we used two approaches to probe the resonance effect and estimate the strength of the IMHBs in the two exemplary cases of the enol forms of acetylacetone and o-hydroxyacetophenone.One approach is the block-localized wavefunction(BLW)method,which is a variant of the ab initio valence bond(VB)theory.Using this approach,it is possible to derive the geometries and energetics with resonance shut down.The other approach is Edmiston’s truncated localized molecular orbital(TLMO)technique,which monitors the energy changes by removing the delocalization tails from localized molecular orbitals.The integrated BLW and TLMO studies confirmed that the hydrogen bonding in these two molecules is indeed enhanced byπ-resonance,and that this enhancement is not a result ofσconstraints.
文摘The critical _d vahues ( _ ) of the γ/(γ+σ).γ/(γ+μ) and γ/(γ+γ') phase boundaries in some ternar alloy phase diagrams at various temperatures are calculated by averaging the _d values of sererai selected characteristic points at the phase boundaries.Approxmate equations for the temperature dependence of the critical _d of γ/(γ+σ).γ/(γ+μ) and γ/(γ+γ') phase boundaries are established.The accuracy of the analysis is discussed in detail. It is found for the first time that the average value of the bond order _ at the phase boundaries ts also approximatelr a constant and therefore a critical average bond order _ like - can be introduced for the analysts of phase stability
文摘The localized molecular orbitals for typical bowl-shaped circulenes are obtained by the use of INDO-LMO method. It is found that these bowl-shaped circulenes with strained π-electron systems are still aromatic and the rim π-bonds with larger localization form reactive regions for formation of buckminsterfullerene.
文摘The localized molecular orbitals and energy levels for [Co_6 (μ_3-S)_8 (PH_3)_6] ̄(n+)(n=0, 1) as model molecules of the electron-rich [Co_6 (μ_3-S)_8 (PPh_3)_6] ̄(n+) (n=0,1) cluster compounds have been calculated by using Edmiston-Ruedenberg energy localization scheme under the spin-unrestricted CNDO/2 approximation. It is shown that the cluster skeletons of these two isostructural molecules consist of the edge-localized two-centered two-electron (Co-S) bonds plus a pair of the skeleton electrons delocalized on the whole cluster core,leading an extra stability of the cluster core.The one-electron oxidation for the neutral molecule gives rise to a one-electron σ (Co-Co) bond.which further resonates among the three diagonal lines of the {Co_6} octahedron. The comparison between [Co_6 (μ_3-S)_8(PPh_3)_6] and [Co_6(μ_3-CO)_8(CO)_6] ̄(4-) indicates that the latter possesses face-localized bridging-bonds which are further delocalized on the whole surface of the cluster octahedron by the back-donation bonds from the lone electron pairs on the Co atoms to the capping carbonyl CO ligands. The structural features of the series of the [Co6(μ_3-X)_8L_6] ̄(n+)(X =S, Se; L=PPh_3,PEt_3, CO;n=0, 1) cluster compounds are briefly rationalized on the basis of the localization description as well.
文摘Calculation of the bonding energy of a molecular orbital for a series of small molecules has been carried out by using ab initio STO-3G method. The results obtained demonstrate that the concept of the molecular orbital bonding energy is applicable for judging whether a molecular orbital is bonding, nonbonding or antibonding besides Mulliken overlap criterion.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11374174,51390471,51527803,and 51701143the National Basic Research Program of China under Grant No 2015CB654902+4 种基金the National Key Research and Development Program under Grant No 2016YFB0700402the Foundation for the Author of National Excellent Doctoral Dissertation under Grant No 201141the National Program for Thousand Young Talents of China,the Tianjin Municipal Education Commissionthe Tianjin Municipal Science and Technology Commissionthe Fundamental Research Fund of Tianjin University of Technology
文摘The highest occupied molecular orbital(HOMO) energies of fullerenes are found by quantitative first-principles calculations to be raised by negative charging, and the rising rate rank of the fullerenes is C60 >C70 >C80 >C90>C100 >C180. Then we compare fullerenes with carbon nanotubes(CNTs) and graphene sheets(GSs) and find that the increase of the HOMO energy of a fullerene is much faster than that of CNTs and graphene sheets with the same number of C atoms. The rising rate rank is fullerene>CNT>GS, which holds no matter what the number of C atoms is or which structure the fullerene isomer is. This work paves a new path for developing all-carbon devices with low-dimensional carbon nanomaterials as different functional elements.
文摘The title compound was synthesized and its crystal structure was determined. C_(13)H(21)NO_2·HCl, orthorhombic, space group P2_12_12_1 with dimensions:a =10. 635(2), b=26.942(6), c=6.193(2), V=1774.5(8),Z=4,Mr=319. 83 and Dc=1.20g/cm ̄3. The final residual factor R=0.048, Rw=0.062. The C atoms except those in rings has a distorted tetrahedron structure.The dihedral angle between the phenyl rings in the molecule is 74. 56°. There is no bond between HCl and ester.The molecules join each other by van der Waals force. Its molecular orbital calculations were carried out by means of extended Huckel molecular orbital method.
文摘Seven transition metal complexes of Mn<sup>2+</sup>, Ni<sup>2+</sup>, Co<sup>2+</sup>, Cu<sup>2+</sup> and Zn<sup>2+</sup> with 3-aminopyridine (3-APy) as ligand have been synthesized, characterized by different techniques and their antibacterial activities were studied. Molecular modeling calculations were performed using DMOL<sup>3</sup> program in materials studio package which is designed for the realization of large scale density functional theory calculation (DFT). The quantum mechanical and chemical reactivity parameters such as chemical hardness, chemical potential, electronegativity, electrophilicity index and Homo-Lumo energy gap were obtained theoretically and were used to understand the biological activity of the prepared compounds. Some complexes were tested for their in-vitro cytotoxic activity in human lung cancer cell lines (A-549 cell line), and structureactivity relationships were established. In general, the coordination to Co<sup>2+</sup> increased the cytotoxicity while the Ni<sup>2+</sup> complexes show reduced cytotoxic activity compared to the metal-free 3-aminopyridine.
文摘The energy-localized CNDO/2 molecular orbitals have been calculated for the cluster anions of [Co_6 (CO)_(14)] ̄(4-) and [Ni_2Co_4 (CO)_(14)] ̄(2-)in order to get a deeper insight into the nature of their skeletal bonding. The bonding characteristics of these hexanuclear carbonyl cobaltates are described from a localization bonding viewpoint. There are two typical M-CO bondings, one of which is formed by electron donation from the terminal and capping carbonyl ligands into the vacant hybrid orbitals on the metal atoms , leading to formation ofσ(C_t→Co) and σ(C_b→{Co_3})bonds. The other typical M-CO bonding is back donation of the lone d-electron pairs on the metal atoms into the carbonyl ligands, forming π(Co→C_t) bonds, σ(Co→{C_(b2)}) bonds and π(Co→{C_(b4)} ) bonds. It is found that there are no direct metalmetal bondings in the skeletons of these two cluster anions.The delocalization situation of the skeletal bonding electrons is briefly discussed.
文摘The stabilization energies of substituted lithium carbene cations were calculated by using ab initio molecular orbital theory, and the relationship between the stabilization energies and molecular orbitals was discussed. The substituents with pi donor engender strong stabilization to CH2Li+. The calculations show the Y-C* bond lengths of cations become shorter and H-Y bond lengths longer than those of corresponding neutral molecules.
基金the Faculty of Arts and Sciences, Ondokuz Mayιs University, Turkey, for the use of the Stoe IPDSII diffractometer (purchased under grant No. F279 of the University Research Fund)
文摘The title compound, 1-(naphthalene-2-yl)-2-(1H-pyrazol-1-yl)ethanone O-butyl oxime, I, was synthesized. The crystal and molecular structures of I were determined by IR, 1H-NMR, mass spectrum, elemental analysis and X-ray single crystal diffraction. Molecular geometry from X-ray experiment of I in the ground state was compared using the Density Functional Theory (DFT) with B3LYP/6-311G(d,p) basis set. In addition, DFT calculation, molecular electrostatic potentials (MEP) and frontier molecular orbitals of I were performed at the B3LYP/6-311G(d,p) level of the theory.