Unusual catalytic effect of the two-dimensional molecular space with regular triphenylphosphine groups

A novel organic-inorganic hybrid 2D molecular space with regular triphenylphosphine groups (triphenylphosphineamidephenylsilica, PPh(3)APhS) was successfully synthesized through grafting triphenylphosphine groups in the 2D structure of layered aminophenylsilica dodecyl sulfate (APhTMS-DS), which was developed in our previous research, with regular ammonium groups. The 2D structures were kept after the grafting reaction of triphenylphosphine groups in PPh(3)APhS. The catalytic potentials of 2D molecular space with regular triphenylphosphine groups were investigated. An unusual catalytic effect was found in a carbon-phosphorus ylide reaction. The PPh(3)-catalyzed reaction of modified allylic compounds, including bromides and chlorides with tropone yielded a [3 + 6] annulation product. However, an unusual [8 + 3] cycloadduct was obtained in the reaction of modified allylic compounds, including bromides and chlorides with tropone catalyzed by PPh(3)APhS. Otherwise, the stable catalytic intermediate was successfully separated, and the reaction activity of the catalytic intermediate was confirmed in the reaction of modified allylic compounds with tropone catalyzed by PPh(3)APhS. This research is the first successful example of directly influencing catalytic reaction processes and product structures by utilizing the chemical and geometrical limits of 2D molecular spaces with regular catalyst molecules and affords a novel method for controlling catalytic reaction processes and catalyst design.     

Two-dimensional structure control by molecular width variation with metal coordination

The self-assembled monolayer of bipyridine derivative 1, which has two alkyl chains on each end, at the HOPG/1-phenyloctane interface was studied by in situ scanning tunneling microscopy (STM). The detailed mechanism of a spontaneous change in the monolayer packing pattern by Pd coordination was studied. Uncomplexed 1 existed in a bent form in the monolayer, and the alkyl chains were interdigitated, whereas Pd-complexed 1 was in a straight form and the alkyl chains were not interdigitated. An intermediate state of 1 was successfully observed during metal coordination. The structure was the bent form with noninterdigitated alkyl chains. Equilibrium intermolecular distances reported from ab initio calculations indicate that the molecular width of the central aromatic part of uncomplexed 1 (7.5 A) is substantially smaller than that of the peripheral alkyl chain part (9.2 A). The bent form was suitable for covering up the surface to maximize the packing density. However, the molecular width of the aromatic unit of Pd-complexed 1 (9.1 A) was almost identical to that of the alkyl chain unit (9.2 A). Therefore, Pd-complexed 1 took the straight form in the monolayer. The observation of surface coverage by STM suggests that the bent form increases the packing density by as much as 16% compared with that of the straight form. These results indicate that the control of molecular width can be used to design molecular templates for nanostructure formation.     

Two-dimensional molecular sieves: structure design by computer simulations

Nanoporous molecular networks formed spontaneously by organic molecules adsorbed on solid substrates are promising materials for future nanotechnological applications related to separation and catalysis. With their unique ordered structure comprising nanocavities of a regular shape planar networks can be treated as 2D analogs of bulk nanoporous materials. In this report we demonstrate how the Monte Carlo simulation method can be effectively used to predict morphology of self-assembled porous molecular architectures based on structural properties of a building block. The simulated results refer to the assemblies created by cross-shaped organic molecules which are stabilized by different intermolecular interactions, including hydrogen bonding and van der Waals interactions. It is demonstrated that tuning of size and aspect ratio of the building block enables the creation of largely diversified extended structures comprising pores of a square and rectangular shape. Our theoretical predictions can be helpful in custom design of functional adsorbed overlayers for controlled deposition, sensing and separation of guest molecules.     

二维分子晶体的研究进展

二维分子晶体具有超薄、长程有序、无晶界和缺陷密度低等优点,是构建多种高性能光电器件的理想材料.实现二维分子晶体的低成本、大面积制备是二维分子晶体走向应用的关键.目前,人们开发了多种方法,在气相和液相中实现了二维分子晶体的可控制备,并揭示了这类二维有机体系独特的光电性能.本文综述了二维分子晶体的制备方法及其在有机场效应晶...     

Two-dimensional Hückel molecular orbital theory

The simple Hückel molecular orbital theory is extended to include hydrocarbons with sp-hybridization in addition to the sp²-hybridization. Molecular orbitals are constructed as linear. combinations of 2p orbitals in two dimensions perpendicular to each other. Total π bond orders (P) are defined and cover the range up to P = 2 in the two-dimensional case. The relationship between bond orders and CC bond lengths is studied. The theory is applied to nine hydrocarbons, which include systems with conjugated and cumulated double bonds as well as triple bonds. Calculated bond lengths from the bond orders are found to agree within ±0.03 Å with experimental values.     

Two-dimensional molecular pattern in the structure of a calcium(II) complex with pyrazine-2,3-dicarboxylate and water ligands

The structure of di(aquo-O)(pyrazine-2,3-dicarboxylato-N,O; -O′,O′′) calcium(II) hydrate [Ca(2,3-PZDC)(H₂O)₂·;H₂O] contains molecular sheets in which Ca(II) ions are bridged by the carboxylate groups of the ligand molecules. Two bridging paths are evident. In the first, an N,O-bonding moiety formed by a hetero-ring nitrogen atom and the carboxylate oxygen atom nearest to it and both oxygen atoms of the second carboxylic group are active. The second path is formed by the other oxygen atom from the carboxylic group involved in the N,O-bonding moiety and an oxygen atom from the second carboxylic group. The latter atom is bidentate. A two-dimensional molecular pattern is formed. Each Ca(II) ion is also coordinated by two water oxygen atoms, making the number of coordinated atoms eight. The coordination polyhedron is a distorted pentagonal bipyramid with an oxygen atom at the apex on one side of the equatorial plane and two oxygen atoms forming the apices on the other side.     

Synthesis of molecular objects: Two-dimensional polymers

Throughout this century polymer science has studied the linear chain and its architectural derivatives which include familiar forms such as the branched chain and the three dimensional network. Other derivatives with unique properties have been investigated more recently and include macromolecular rings, dendrimers, stars, combs and ladders. The objective of this work is to depart from the focus on linear chains and explore the “bulk” synthesis and properties of polymer molecules that can be considered molecular objects. Ideal molecular objects should be macromolecules with well defined shapes that persist as systems transform reversibly from solids to melts or solutions. The limited access to conformational space which is required in order to define and maintain shape in liquid and solid states of the system is an unusual molecular characteristic in common polymers. Our ability to create such objects through bulk reactions of reasonable scale will undoubtedly extend the current boundaries of polymer science and technology. Shapes that are particularly interesting are those not common in the conformational space of linear chains, for example, two-dimensional polymers shaped as plates and macromolecular bundles shaped as cylinders or parallelepipeds. The molecular object to be discussed in this lecture is a rigid and anisotropic two-dimensional polymer with planar dimensions greater than its thickness and a shape-granting skeleton built by covalent bonds. We have so far developed three different strategies for their synthesis, all involving systems in which reactive oligomers organize spontaneously into the necessary planar assemblies to form the object. In one strategy molecular recognition driven by homochiral interactions plays a key role in the formation of two-dimensional polymers.¹ A different methodology relies on entropy-driven nanophase separation in rodcoil block molecules in which a rigid segment is covalently bonded to a flexible one sharing the same backbone. The third strategy involves the folding of oligomers into hairpin structures which self assemble into two-dimensional liquids. The lecture will also describe examples of unique properties that could be achieved in materials containing these rigid two-dimensional objects. These examples will include bulk materials with self-organized surfaces and also remarkably stable nonlinear optical properties.     

Two-dimensional hückel molecular orbital theory

The conventional Hückel molecular orbital (HMO) theory is extended to include hydrocarbons with sp-hybridized C atoms in addition to the sp²-hybridization. MOs are constructed as linear combinations of 2p-orbitals in two dimensions perpendicular to each other. The resulting two parts of the π system (viz. π′ and π″) are assumed to be independent. The total π-bond order is assumed to be obtained by the addition of contributions from π′ and π″. The two-dimensional HMO theory covers hydrocarbons with acetylenic (CC) bonds and cumulated CC bonds. The theory is applied to vinylacetylene, diacetylene, allene, butatriene and divinylacetylene. CC bond lengths calculated from the theoretical π-bond orders are compared with experimental data. Agreements between calculated and observed bond lengths within ±0.03 Å are found.     

Novel polyelectrolytes with regular structure synthesis,properties and applications

Cationic polyelectrolytes and polymeric betaines with narrow molecular weight distribution as well as block copolymers containing charged and uncharged blocks of different hydrophilicity/hydrophobicity were synthesized by different routes of radical polymerization. The cationic polyelectrolytes were characterized with respect to solution properties and electrolyte behaviour. The block copolymers serve as powerful stabilizers in precipitation and emulsion polymerization processes.     

Two-dimensional molecular profiling of mantle cell lymphoma

The present research establishes standard two-dimensional (2-D) maps for control, reactive lymph node and non-Hodgkin's lymphoma (mantle cell lymphoma, MCL). Medium sensitivity, mass spectrometry compatible colloidal Coomassie has revealed a total of ca. 750 spots in each of the maps. Comparison of 2-D maps by statistical packages, such as the PDQuest, established up- and downregulation of a total of ca. 145 spots, with positive variations of up to 10-folds and negative variations of up to 13-folds in both MCL biopsies' protein extracts. Qualitative and quantitative variations in the two lymphoma samples are consistent. More than 20 proteins have been so far identified by matrix assisted laser desorption/ionisation-time of flight (MALDI-TOF)-mass spectrometry, with an additional five spots, which gave very good spectra but could not be matched to any of the presently available databases. Some of the spots, such as the 78 kDa glucose-regulated protein precursor and the glutathione S-transferase P, appear to be in common with other tumors, such as lung adenocarcinoma. Others may simply reflect overall changes in cellular metabolism and growth rate that occur during malignancy and thus might turn out to be in common with any cell population receiving any kind of stress. Some (notably T-cell leukemia/lymphoma protein 1A, TCL1, found to be 10-fold overexpressed) appear to be specific of the non-Hodgkin's lymphoma here studied. Western blot and immunohistochemical analyses were applied to obtain further information about stathmin (Op18) and TCL1, respectively.     

Two-dimensional quantum propagation using wavelets in space and time

A recent method for solving the time-dependent Schrodinger equation has been developed using expansions in compact-support wavelet bases in both space and time [H. Wang et al., J. Chem. Phys. 121, 7647 (2004)]. This method represents an exact quantum mixed time-frequency approach, with special initial temporal wavelets used to solve the initial value problem. The present work is a first extension of the method to multiple spatial dimensions applied to a simple two-dimensional (2D) coupled anharmonic oscillator problem. A wavelet-discretized version of norm preservation for time-independent Hamiltonians discovered in the earlier one-dimensional investigation is verified to hold as well in 2D and, by implication, in higher numbers of spatial dimensions. The wavelet bases are not restricted to rectangular domains, a fact which is exploited here in a 2D adaptive version of the algorithm.     

Decoding of complex isothermal chromatograms recovered from space missions. Identification of molecular structure

A chemometric approach, based on the study of the autocovariance function, is described to study isothermal GC chromatograms of multicomponent mixtures: isothermal GC analysis is the method of choice in space missions since it is, to date, the only method compatible with flight constraints. Isothermal GC chromatograms look inhomogeneous and disordered with peak density decreasing at higher retention times: a time axis transformation is proposed to make retention an homogeneous process so that CH2 addition in terms of an homologous series yields a constant retention increment. The time axis is transformed into a new scale based on the retention times of n-alkanes, as they are the basis of the universal Kovats indices procedure. The order introduced into the chromatogram by retention time linearization can be simply singled out by the experimental autocorrelation function (EACF) plot: if constant inter-distances are repeated in different regions of the chromatogram, well-shaped peaks are evident in the EACF plot. By comparison, with a standard mixture it is possible to identify peaks diagnostic of specific molecular structures: study of the EACF plot provides information on sample chemical composition. The procedure was applied to standard mixtures containing compounds representative of the planetary atmospheres that will be investigated in the near future: in particular, those related to Titan's atmosphere (Cassini-Huygens mission) and cometary's nucleus (Rosetta mission). The employed experimental conditions simulated those applied to GC instruments installed on space probes and landers in space missions. The method was applied to two specific investigations related to space research, i.e., a comparison of retention selectivity of different GC columns and identification of the chemical composition of an unknown mixture.     

Two-dimensional dynamics of molecules and structure of fluorographite intercalated with acetone

Institute of Inorganic Chemistry, Siberian Branch, Academy of Sciences of the USSR Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 1, pp. 66–71, January–February, 1989.     

Borromean-entanglement-driven assembly of porous molecular architectures with anion-modified pore space

A series of metal-organic frameworks based on a flexible, highly charged Bpybc ligand, namely 1?Mn?OH(-), 2?Mn?SO(4)(2-), 3?Mn?bdc(2-), 4?Eu?SO(4)(2-) (H(2)BpybcCl(2) = 1,1'-bis(4-carboxybenzyl)-4,4'-bipyridinium dichloride, H(2)bdc = 1,4-benzenedicarboxylic acid) have been obtained by a self-assembly process. Single-crystal X-ray-diffraction analysis revealed that all of these compounds contained the same n-fold 2D→3D Borromean-entangled topology with irregular butterfly-like pore channels that were parallel to the Borromean sheets. These structures were highly tolerant towards various metal ions (from divalent transition metals to trivalent lanthanide ions) and anion species (from small inorganic anions to bulky organic anions), which demonstrated the superstability of these Borromean linkages. This non-interpenetrated entanglement represents a new way of increasing the stability of the porous frameworks. The introduction of bipyridinium molecules into the porous frameworks led to the formation of cationic surface, which showed high affinities to methanol and water vapor. The distinct adsorption and desorption isotherms of methanol vapor in four complexes revealed that the accommodated anion species (of different size, shape, and location) provided a unique platform to tune the environment of the pore space. Measurements of the adsorption of various organic vapors onto framework 1?Mn?OH(-) further revealed that these pores have a high adsorption selectivity towards molecules with different sizes, polarities, or π-conjugated structures.     

Two-dimensional molecular organization of pyridinecarboxylic acids adsorbed on graphite

Pyridinecarboxylic acids 3-9 are adsorbed from solution onto graphite to produce well-ordered adlayers that can be imaged by scanning tunneling microscopy. Hydrogen bonds involving the carboxyl groups and the nitrogen atom of the pyridyl ring play key roles in controlling the observed two-dimensional (2D) organization. Pyridinecarboxylic acids have a strong tendency to associate to form hydrogen-bonded chains and cyclic oligomers, which then pack to produce sheets. The preference for sheets ensures that molecular organization in 2D and 3D typically shows a significant degree of homology. Together, our observations highlight the potential of engineering similarly ordered 2D and 3D structures built from simple compounds that combine an inherent affinity for surfaces with an ability to engage in strong coplanar intermolecular interactions.     

Two-dimensional infrared spectroscopy of antiparallel beta-sheet secondary structure

We investigate the sensitivity of femtosecond Fourier transform two-dimensional infrared spectroscopy to protein secondary structure with a study of antiparallel beta-sheets. The results show that 2D IR spectroscopy is more sensitive to structural differences between proteins than traditional infrared spectroscopy, providing an observable that allows comparison to quantitative models of protein vibrational spectroscopy. 2D IR correlation spectra of the amide I region of poly-l-lysine, concanavalin A, ribonuclease A, and lysozyme show cross-peaks between the IR-active transitions that are characteristic of amide I couplings for polypeptides in antiparallel hydrogen-bonding registry. For poly-l-lysine, the 2D IR spectrum contains the eight-peak structure expected for two dominant vibrations of an extended, ordered antiparallel beta-sheet. In the proteins with antiparallel beta-sheets, interference effects between the diagonal and cross-peaks arising from the sheets, combined with diagonally elongated resonances from additional amide transitions, lead to a characteristic "Z"-shaped pattern for the amide I region in the 2D IR spectrum. We discuss in detail how the number of strands in the sheet, the local configurational disorder in the sheet, the delocalization of the vibrational excitation, and the angle between transition dipole moments affect the position, splitting, amplitude, and line shape of the cross-peaks and diagonal peaks.     

Understanding molecular structure from molecular mechanics

Molecular mechanics gives us a well known model of molecular structure. It is less widely recognized that valence bond theory gives us structures which offer a direct interpretation of molecular mechanics formulations and parameters. The electronic effects well-known in physical organic chemistry can be directly interpreted in terms of valence bond structures, and hence quantitatively calculated and understood. The basic theory is outlined in this paper, and examples of the effects, and their interpretation in illustrative examples is presented.