Interactions of Li, Ca, and Al with aromatic carbon materials: an ab initio study

The interactions of benzene (C6H6), naphthalene (C10H8), and perinaphthene (C13H9) with metal atoms (Li, Ca, and Al) were studied using second-order M?ller-Plesset perturbation theory. By analyzing the frontier molecular orbitals, geometric structures, binding energies, and charge transfers, it was found that these metal atoms can bond strongly with C13H9, but can only bond weakly with C6H6 and C10H8. The bonding nature between a metal atom and C13H9 at their ground state depends significantly on the valence orbital of the metal atom and the pi-bonding distribution of the aromatic hydrocarbons. The spindly shaped 3p valence orbital of an Al atom results in the deviation of the adsorption site to the edge of C13H9, whereas the ball-shaped 2s/4s valence orbitals of a Li and a Ca atom facilitate their overlap with the second lowest unoccupied molecular orbital of C13H9. Further, Hartree-Fock and density-functional theory methods were demonstrated generally to be unreliable in describing the interactions of metal atoms with these pi systems.     

DFT study of metal cation-induced hydrogelation of cellulose nanofibrils

We report a density functional theory study of cation-induced bonding between carboxylated cellulose nanofibrils (CNFs). We describe a methodology of using cleaved cellulose crystal unit cells to develop simple surface and molecular models of charged CNFs. We compare bond lengths, binding energies, and displaced solvation volumes for interfibril models intercalated with alkali, alkaline earth, main group, or transition metal cations, surrounded by an implicit solvent. We characterize the type of bonding interactions that occur between metal cations, Mⁿ⁺ and carboxylated CNF surfaces by calculating the electronic density of states and Mayer bond orders. We find that Mⁿ⁺–O interactions for alkaline earth metal systems are predominantly electrostatic whereas transition metal cations form stronger, more covalent bonds with enhanced valence orbital overlap. Our results show that multivalent—as opposed to monovalent—ions can create CNF networks by effectively crosslinking multiple fibrils through surface carboxylate anions. Our computational results agree with empirical models of metal–carboxylate binding, while also providing a deeper understanding of the bonding mechanisms for different cations. Our findings help to explain trends in recent CNF hydrogelation experiments, and we also predict the existence of two new hydrogels—CNF-Mg²⁺ and CNF-Zr⁴⁺.     

Glucose interaction with Au,Ag, and Cu clusters: Theoretical investigation

Interactions of α‐D ‐glucose with gold, silver, and copper metal clusters are studied theoretically at the density functional theory (CAM‐B3LYP) and MP2 levels of theory, using trimer clusters as simple catalytic models for metal particles as well as investigating the effect of cluster charge by studying the interactions of cationic and anionic gold clusters with glucose. The bonding between α‐D ‐glucose and metal clusters occurs by two major bonding factors; the anchoring of M atoms (M = Cu, Ag, and Au) to the O atoms, and the unconventional M…H? O hydrogen bond. Depending on the charge of metal clusters, each of these bonds contributes significantly to the complexation. Binding energy calculations indicate that the silver cluster has the lowest and gold cluster has the highest affinity to interact with glucose. Natural bond orbital analysis is performed to calculate natural population analysis and charge transfers in the complexes. Quantum theory of atoms in molecules was also applied to interpret the nature of bonds. © 2012 Wiley Periodicals, Inc.     

Phenomenological Theory of Cluster Orbitals and Electronic Structures of Molecules

A method for calculation of the energy structures of molecules is developed. The method is based on construction of a matrix of interactions between the atoms in the molecules with allowance made for their symmetric arrangement in space. Matrices are parametrized by comparison of the matrix eigenvalues with the experimental values for reference molecules (methane, benzene, ammonia, water, etc.). Interaction matrices are given for molecules with different types of bonding. Eigenvalues of the molecular energy, eigenfunctions of all molecular orbitals, bond angles, atomic orbital charges, etc. are determined. The dependence of the energy levels of MH₂ molecules (M = O, S, Se, and Te) on the interatomic interaction parameter is given. The dependences of the molecular parameters on the nature of atom M are analyzed.     

羧酸共聚物与方解石晶体相互作用的MD模拟

用分子动力学方法, 模拟计算了丙烯酸-丙烯酸甲酯共聚物(AA-MAE)、丙烯酸-丙烯酸羟丙酯共聚物(AA-HPA)、丙烯酸-马来酸共聚物(AA-MA)及水解马来酸酐(HPMA)四种聚羧酸类阻垢剂与方解石晶体(110)晶面的相互作用. 结果表明, 聚羧酸与(110)晶面结合能的大小排序为AA-MA＞HPMA＞AA-HPA＞AA-MAE; 对体系各种相互作用以及径向分布函数的分析表明, 结合能主要由库仑作用(包括离子键)提供, 并含少量氢键成分. 与方解石晶面结合的聚合物发生扭曲变形, 但形变能远小于相应的非键作用能. 聚合物中不同位置羧基的动力学行为差别很大, 链端羧基的运动翻转比链中部羧基剧烈得多, 故后者与晶面的结合比前者更牢固而具有更强的阻垢能力.     

Reconciling Electrostatic and n→π* Orbital Contributions in Carbonyl Interactions

Interactions between carbonyl groups are prevalent in protein structures. Earlier investigations identified dominant electrostatic dipolar interactions, while others implicated lone pair n→π* orbital delocalisation. Here these observations are reconciled. A combined experimental and computational approach confirmed the dominance of electrostatic interactions in a new series of synthetic molecular balances, while also highlighting the distance‐dependent observation of inductive polarisation manifested by n→π* orbital delocalisation. Computational fiSAPT energy decomposition and natural bonding orbital analyses correlated with experimental data to reveal the contexts in which short‐range inductive polarisation augment electrostatic dipolar interactions. Thus, we provide a framework for reconciling the context dependency of the dominance of electrostatic interactions and the occurrence of n→π* orbital delocalisation in C=O???C=O interactions.     

A theoretical study of the interfaces between aluminium and poly(ethylene terephthalate), polycaprolactone,and polystyrene: Illustration of the reactivity of aluminium towards ester groups and phenyl rings

The interfaces between aluminium and poly(ethylene terephthalate), poly(ε-caprolactone), and polystyrene are investigated theoretically in order to assess the reactivity of aluminium towards the functional groups (i.e., ester functions and phenyl rings) present at the surface of the polymers. The theoretical approach consists in performing quantum-chemical calculations on small molecular model systems interacting with a few Al atoms. The geometric structures of the organometallic complexes are optimized and their stabilities and changes in charge densities due to Al bonding are evaluated. The results are compared to experimental X-ray photoelectron spectroscopy data collected during the early stages of interface formation following aluminium deposition on the polymer surfaces. In agreement with experimental data, it emerges from this study that aluminium interacts strongly wirth both polyesters by forming covalent bonds with the carbon and oxygen atoms of the ester functions. The attack of the poly(ethylene terephthalate) phenyl rings occurs only for high metal coverage and does not hamper the interaction with the ester sites. Furthermore, our theoretical investigation has confirmed, on one hand, that the aluminium/polystyrene interactions are weak, and on the other hand, the absence of strong reactions at the interfaces between aluminium and saturated hydrocarbon polymers.     

Reconciling Electrostatic and n→π* Orbital Contributions in Carbonyl Interactions

Interactions between carbonyl groups are prevalent in protein structures. Earlier investigations identified dominant electrostatic dipolar interactions, while others implicated lone pair n→π* orbital delocalisation. Here these observations are reconciled. A combined experimental and computational approach confirmed the dominance of electrostatic interactions in a new series of synthetic molecular balances, while also highlighting the distance-dependent observation of inductive polarisation manifested by n→π* orbital delocalisation. Computational fiSAPT energy decomposition and natural bonding orbital analyses correlated with experimental data to reveal the contexts in which short-range inductive polarisation augment electrostatic dipolar interactions. Thus, we provide a framework for reconciling the context dependency of the dominance of electrostatic interactions and the occurrence of n→π* orbital delocalisation in C=O⋅⋅⋅C=O interactions.     

Theoretical Study on the Hydrogen Bonding Interactions in Complexes of 5‐Hydroxytryptamine with Water

The energies, geometries and harmonic vibrational frequencies of 1:1 5‐hydroxytryptamine‐water (5‐HT‐H₂O) complexes are studied at the MP2/6‐311++G(d,p) level. Natural bond orbital (NBO), quantum theory of atoms in molecules (QTAIM) analyses and the localized molecular orbital energy decomposition analysis (LMO‐EDA) were performed to explore the nature of the hydrogen‐bonding interactions in these complexes. Various types of hydrogen bonds (H‐bonds) are formed in these 5‐HT‐H₂O complexes. The intermolecular C4H5^5‐HT···O^w H‐bond in HTW3 is strengthened due to the cooperativity, whereas no such cooperativity is found in the other 5‐HT‐H₂O complexes. H‐bond in which nitrogen atom of amino in 5‐HT acted as proton donors was stronger than other H‐bonds. Our researches show that the hydrogen bonding interaction plays a vital role on the relative stabilities of 5‐HT‐H₂O complexes.     

Evaluating the Free Energies of Solvation and Electronic Structures of Lithium‐Ion Battery Electrolytes

Adaptive biasing force molecular dynamics simulations and density functional theory calculations were performed to understand the interaction of Li⁺ with pure carbonates and ethylene carbonate (EC)‐based binary mixtures. The most favorable Li carbonate cluster configurations obtained from molecular dynamics simulations were subjected to detailed structural and thermochemistry calculations on the basis of the M06‐2X/6‐311++G(d,p) level of theory. We report the ranking of these electrolytes on the basis of the free energies of Li‐ion solvation in carbonates and EC‐based mixtures. A strong local tetrahedral order involving four carbonates around the Li⁺ was seen in the first solvation shell. Thermochemistry calculations revealed that the enthalpy of solvation and the Gibbs free energy of solvation of the Li⁺ ion with carbonates are negative and suggested the ion–carbonate complexation process to be exothermic and spontaneous. Natural bond orbital analysis indicated that Li⁺ interacts with the lone pairs of electrons on the carbonyl oxygen atom in the primary solvation sphere. These interactions lead to an increase in the carbonyl (C=O) bond lengths, as evidenced by a redshift in the vibrational frequencies [ν(C=O)] and a decrease in the electron density values at the C=O bond critical points in the primary solvation sphere. Quantum theory of atoms in molecules, localized molecular orbital energy decomposition analysis (LMO‐EDA), and noncovalent interaction plots revealed the electrostatic nature of the Li⁺ ion interactions with the carbonyl oxygen atoms in these complexes. On the basis of LMO‐EDA, the strongest attractive interaction in these complexes was found to be the electrostatic interaction followed by polarization, dispersion, and exchange interactions. Overall, our calculations predicted EC and a binary mixture of EC/dimethyl carbonate to be appropriate electrolytes for Li‐ion batteries, which complies with experiments and other theoretical results.     

Ab initio investigation of the complexes between bromobenzene and several electron donors: some insights into the magnitude and nature of halogen bonding interactions

Halogen bonding, a specific intermolecular noncovalent interaction, plays crucial roles in fields as diverse as molecular recognition, crystal engineering, and biological systems. This paper presents an ab initio investigation of a series of dimeric complexes formed between bromobenzene and several electron donors. Such small model systems are selected to mimic halogen bonding interactions found within crystal structures as well as within biological molecules. In all cases, the intermolecular distances are shown to be equal to or below sums of van der Waals radii of the atoms involved. Halogen bonding energies, calculated at the MP2/aug-cc-pVDZ level, span over a wide range, from -1.52 to -15.53 kcal/mol. The interactions become comparable to, or even prevail over, classical hydrogen bonding. For charge-assisted halogen bonds, calculations have shown that the strength decreases in the order OH- > F- > HCO2- > Cl- > Br-, while for neutral systems, their relative strengths attenuate in the order H2CS > H2CO > NH3 > H2S > H2O. These results agree with those of the quantum theory of atoms in molecules (QTAIM) since bond critical points (BCPs) are identified for these halogen bonds. The QTAIM analysis also suggests that strong halogen bonds are more covalent in nature, while weak ones are mostly electrostatic interactions. The electron densities at the BCPs are recommended as a good measure of the halogen bond strength. Finally, natural bond orbital (NBO) analysis has been applied to gain more insights into the origin of halogen bonding interactions.     

Ligand-receptor interactions between surfaces: the role of binary polymer spacers

The interactions between a receptor-modified planar surface and a surface grafted with a bimodal polymer layer, where one of the polymer species is ligand functionalized, are studied using a molecular theory. The effects of changing the binding energy of the ligand-receptor pair, the polymer surface coverage, the composition, and molecular weight of both the unfunctionalized and ligand functionalized polymers on the interactions between the surfaces are investigated. Our findings show that bridging exists between the surfaces including when the molecular weight of the ligand-bearing polymer is smaller than that of the unfunctionalized polymer, even though the ligand is initially buried within the polymer layer. The distance at which the surfaces bind depends only on the molecular weight of the ligand-modified polymer, while the strength of the interaction at a given surface separation can be tuned by changing the molecular weight of the polymers, the total polymer surface coverage, and the fraction of ligated polymers. The composition of the bimodal layer alters the structure of the polymer layer, thereby influencing the strength of the steric repulsions between the surfaces. Our theoretical results show good agreement with experimental data. The present theoretical study can be used as guidelines for the design of surfaces with tailored abilities for tunning the binding strength and surface-ligand separation distances for polymer-grafted surfaces bearing specific targeting ligands.     

Quantum cascade laser spectroscopy and photoinduced chemistry of Al-(CO)n clusters in helium nanodroplets

Helium nanodroplet isolation and a tunable quantum cascade laser are used to probe the fundamental CO stretch bands of aluminum carbonyl complexes, Al-(CO)(n) (n ≤ 5). The droplets are doped with single aluminum atoms via the resistive heating of an aluminum wetted tantalum wire. The downstream sequential pick-up of CO molecules leads to the rapid formation and cooling of Al-(CO)(n) clusters within the droplets. Near 1900 cm(-1), rotational fine structure is resolved in bands that are assigned to the CO stretch of a linear (2)Π(1/2) Al-CO species and the asymmetric and symmetric CO stretch vibrations of a planar C(2v) Al-(CO)(2) complex in a (2)B(1) electronic state. Bands corresponding to clusters with n ≥ 3 lack resolved rotational fine structure; nevertheless, the small frequency shifts from the n = 2 bands indicate that these clusters consist of an Al-(CO)(2) core with additional CO molecules attached via van der Waals interactions. A second n = 2 band is observed near the CO stretch of Al-CO, indicating a local minimum on the n = 2 potential consisting of an "unreacted" (Al-CO)-CO cluster. The line width of this band is ～0.3 cm(-1), which is about 30 times broader than the transitions within the Al-CO band. The additional broadening is consistent with a homogeneous mechanism corresponding to a rapid vibrational excitation induced reaction within the (Al-CO)-CO cluster to form the covalently bonded Al-(CO)(2) complex. Ab initio CCSD(T) calculations and natural bond orbital (NBO) analyses are carried out to investigate the nature of the bonding in the n = 1, 2 complexes. The NBO calculations show that both π-donation (from the occupied aluminum p orbital into a π* antibonding CO orbital) and σ-donation (from CO into the empty aluminum p orbitals) play a significant role in the bonding, analogous to transition-metal carbonyl complexes. The large red shift observed for the CO stretch vibrations is consistent with this bonding analysis.     

Molecular dynamics simulation on the interaction between polymer inhibitors and anhydrite surface

Investigation on the microscopic interaction between polymer inhibitors and calcium sulfate will be helpful for understanding its scale inhibition mechanism and can provide a theoretical guidance to developing new scale inhibitors. In this work, molecular dynamics simulations with COMPASS force field have been performed to simulate the interaction between hydrolyzed polymaleic anhydride (HPMA), polyaspartic acid (PASP), polyepoxysuccinic acid (PESA), polyacrylic acid (PAA) and the (001) and (020) surfaces of anhydrite (AD) crystal with and without water. The results show that the sequence of binding energies between four polymer inhibitors and AD (001) and (020) with water is PESA > PASP > HPMA > PAA. The binding energy of the same polymer inhibitor on AD (001) is smaller than that on AD (020). Water molecules weaken the deformations of HPMA and PAA but aggravate those of PASP and PESA. Natural bond orbital (NBO) charges of the repeat units of polymer inhibitors were calculated by B3LYP/6‐31G* method. The Coulomb interaction is formed between the O atoms of polymer inhibitors and the Ca atoms of AD crystal. The system of polymer–AD is mainly contributed from the non‐bonding interaction. Polymer inhibitors do not interact directly with AD crystal, but indirectly through the interactions between inhibitor–H₂O and H₂O–AD, i.e. water molecules participate in scale inhibition of polymer inhibitors to AD crystal. Water molecules cannot be ignored when the interaction models are constructed, i.e. solvent effect cannot be ignored. Copyright © 2015 John Wiley & Sons, Ltd.     

Electronic structure of the alpha and beta isomers of [Mo(8)O(26)](4-)

The structure and bonding in alpha and beta octamolybdate anions have been investigated using density functional methods. In general, good computational-experimental agreement for the geometrical parameters has been obtained. The electronic structure of the anions has been probed with molecular orbital and Mulliken-Mayer methods. All Mo-O interactions have been found to be predominantly d(Mo)-p(O) in character. Several multicentered molecular orbitals can be described as sigma or pi closed-loop structures, but the proposed connection with the stability of the polyanions is not completely supported by the calculations. Mayer indexes correspond to fractional multiple character for terminal bonds and approximately single or low-order character for bridging bonds, in accordance with structural and bond valence results. The valency analysis has yielded similar overall bonding capacity for the various oxygen atoms. A distribution of the negative charge over all types of oxygen sites and metal charges considerably smaller than the formal oxidation states have been obtained from the Mulliken analysis.     

固体NMR研究PAA/PEO共混物中氢键相互作用与结构演化

分子间相互作用是决定材料结构和性能的关键因素之一,而如何在分子水上实现对复杂相互作用分子的检测仍然是一个挑战性课题。本工作首先在不同p H值条下以聚丙烯酸/聚环氧乙烷(PAA/PEO)的混合水溶液制备了系列的固体薄膜,然后采用多种基于连续相调制多脉冲技术的一维和二维~1H多脉冲去耦(CRAMPS)固体NMR新技术,并结合高分辨~(13)C交叉极化魔角旋转(CPMAS)、~(23)Na多量子(MQ)等多核固体NMR实验,对PAA/PEO聚合物共混物的微观结构和动力学进行了原位和系统的研究。通过不同类型的~1H高分辨CRAMPS实验检测到共混物中包含多种不同类型质子:通过氢键相互作用形成二聚体的COOH基团、自由COOH基团、与水结合的COOH基团和主链基团。随着p H值的升高,除主链质子外,大部分其它区域的信号都明显降低,这是由于PAA与PEO以及水的氢键作用减弱所致。这些CRAMPS NMR技术也被用来阐明不同p H值制备的样品中不同基团的分子运动性。此外,二维~1H-~1H自旋交换NMR实验提供了关于聚合物PAA与PEO大分子链间、以及水与聚合物的相互作用。~1H自旋扩散实验表明,在这些共混物中明显存在相微观相分离的结构,并且测定的分散相区尺寸约为17 nm。~(23)Na MQMAS实验揭示了在共混物中存在两种类型~(23)Na位,一种是自由的钠离子,另一种是与大分子相互作用的Na离子。特别是通过~1H-检测的~(23)Na-~1H CPMAS实验揭示了Na~+离子的位置远离PEO而与PAA临近。上述这些SSNMR实验结果在分子水平上提供了氢键相互作用对PAA/PEO共混物微观结构和动力学影响的详细信息,可以获得不同p H值对PAA与PEO的氢键作用、相容性、微观结构、水-聚合物相互作用和不同组分分子运动性的影响。在上述核磁共振研究的基础上,我们提出了一种新的PAA/PEO共混物的结构模型,该模型首次成功地揭示了不同的p H值对PAA/PEO共混物中微观结构和动力学的影响。本工作清楚地表明,固态核磁共振是在分子水平上研究具有复杂相互作用的多相聚合物材料的有力工具。本文的研究工作对于探索检测聚合物弱相互作用的新方法和发展基于氢键相互作用的聚合物新材料的开发具有重要意义。     

Potassium carbamoyldi­cyano­methanide

The crystal structure of the title compound, K[(CN)₂CC(O)NH₂)] or K⁺·C₄H₂N₃O⁻, conventionally abbreviated as Kcdm, where cdm is carbamoyldi­cyano­methanide, is described. The bond lengths and angles of the cdm cation are comparable to those reported previously for [M(cdm)₂(H₂O)₄]·2H₂O (M = Ni, Mn and Co). The K atoms are coordinated to four nitrile N atoms and two carbonyl O atoms in a distorted trigonal prismatic fashion, with two further N atoms semicoordinated through the centers of two prism side faces. This coordination leads to the formation of mixed anion–cation sheets parallel to the ab plane, which are joined together via hydrogen‐bonding interactions. The cdm anion is potentially useful for the formation of transition metal coordination polymers, in which magnetic superexchange could occur through a bidentate cdm bridge. Kcdm provides a model compound by which the molecular geometry of the cdm anion can be analyzed.     

THEORETICAL COMPARISON OF THE BONDING OF CHALCOCARBONYL LIGANDS

Abstract

Fenske-Hall molecular orbital calculations on the complexes CpFe(CO)₂(CX)⁺ (X = O, S, Se, and Te) have been used to quantify the nature of bonding between the CX ligands and the metal atom. In addition, conclusions have been reached about the reactivity of the complexes under both nucleophilic and electrophilic attack. The previously established trend of increasing metal—ligand bond strength as X changes from O to S to Se is demonstrated by our molecular orbital calculations, and found to extend to Te. The mechanism for nucleophilic attack, variously explained in the past by either charge control or orbital control, is quantitatively ascribed to orbital control only. The nature of electrophilic attack on these complexes is also found to begin with orbital control.     

Electron density distribution of an oxamato bridged Mn(II)-Cu(II) bimetallic chain and correlation to magnetic properties

The electron density distribution of the ferrimagnetic MnCu(pba)(H2O)3.2H2O chain compound, where pba stands for 1,3-propylenebis(oxamato), has been derived from high resolution X-ray diffraction measurements at 114 K using a multipolar model. The analysis of the chemical bonding has been carried out through the "Atoms in Molecules" formalism and thoroughly interpreted with regards to the strong intrachain and weak interchain magnetic couplings. The topological properties of the electron density on the oxamato bridge indicate large electron delocalization and conjugation effects, in addition to high charge transfer from both metals to the bridge. The resulting positive charges on Mn (+1.45 e) and Cu (+1.56 e) induce charge polarization of the bridge, leading to a shift of electron density from the central C atoms to the metal coordinating O and N atoms. The Mn-bridge interactions are mainly closed-shell interactions with low electron density at the corresponding bond critical points, whereas the Cu-bridge interactions exhibit significant covalent character. The Cu-N bonds are moreover stronger than the Cu-O bonds. The 3d Cu and Mn orbital populations are consistent with pyramidal and regular octahedral environments, respectively, in agreement with the loss of degeneracy due to ligand field effects. Interchain interaction pathways are evidenced by the existence of four bond critical points in hydrogen bond regions. Finally, these intrachain and interchain bonding features are correlated to the results of experimental and theoretical spin density distributions, as well as magnetic measurements.