胶体光子晶体的平面介电常数缺陷

为引入特殊的光学性质,通常需要在三维光子晶体中人为可控地引入缺陷.通过改变局部结构单元的尺寸或介电常数,相应地引入给体或受体掺杂,带来不同的缺陷态.以前文献报道的向胶体光子晶体中引入缺陷,常会因为同时引入尺寸和介电常数掺杂,给掺杂性质的界定带来困难.本文中,我们结合对流自组装法和L-B膜法,在实心二氧化硅微球组成的三维光子晶体内引入尺寸相同的二氧化硅空心球(与实心球相比具有不同折光率)组成的单层平面缺陷,或者在空心球晶体内引入实心球缺陷层,构成实心-空心-实心或空心-实心-空心的三明治结构,在不破坏整体晶格的同时,在三维胶体光子晶体中引入单一的平面介电常数缺陷.     

A quantum mechanical study of the reactivity of (SiO)2-defective silica surfaces

The reactivity of the strained (SiO)(2)-four atom ring defect at the silica surfaces has been studied in a cluster approach adopting the ONIOM2[B3LYP6-31+G(d,p):MNDO] method to compute the ring opening reaction by interaction with H(2)O and NH(3). The vibrational "fingerprints" of the isolated defect are computed at 921, 930, and 934 cm(-1) in reasonable agreement with experimental evidence on amorphous silica outgassed at T>900 K. The opening of the (SiO)(2)-four-member ring by the considered molecules is exergonic and the actual value depends on the possible constraints enforced on the reaction products by the silica surrounding. The free kinetic energy barriers result from the interplay between the nucleophilic/electrophilic character of the adsorbed molecule and are 22 and 25 kcal mol(-1) for NH(3) and H(2)O, respectively. All free energy profiles envisage an activated complex in which the nucleophilic part of the molecule interacts on the coordinatively strained silicon atom of the (SiO)(2) defect followed by the proton transfer from the coordinated molecule towards the oxygen of the defective ring. Calculations show that this step can be speed up by the presence of more than one adsorbed molecule or even more (about seven orders of magnitude), by the copresence of water molecules acting as "proton transfer helpers." In these cases, the free energy barriers decrease to approximately 13 and 15 kcal mol(-1) for NH(3) and H(2)O, respectively. For the case of H(2)O adsorption, benchmark test calculations reveal that MP2, BLYP, and B3LYP energy profiles are in very good agreement with each other, whereas for PBE, both the reaction energy and the activation barrier are underestimated. Present data also show that the molecular model mimicking the (SiO)(2) defect is far less reactive than what appears to occur on the real defect at the surface of amorphous silica. So, only a combination of some further geometrical strains imparted by the solid on the (SiO)(2) defect, not accounted for by the cluster models, and higher adsorbate loadings are needed to reharmonize experiment and simulation. Notwithstanding, the vibrational features of the reaction products have been characterized and support the available experimental measurements.     

Microscopic description of elementary growth processes and classification of structural defects in pentacene thin films

Elementary growth processes such as kink initiation, adding a molecule to a kink, and adding a molecule between two neighboring kinks and between two grains are theoretically studied in pentacene films by adding one molecule at a time to a predefined aggregate. For each molecule, the potential energy surface is calculated using the MM3 molecular mechanics force field, which allowed one to identify useful parameters like the energy barrier for diffusion and the energy to create kinks, as well as defect configurations. Depending on the properties of the potential energy surface and the resulting growth-condition-dependent probabilities of initiating defect configurations in the film, three types of pentacene defects are identified: a thermally activated defect, an intrinsic defect, and a kinetic defect. Upon film growth, most defects relax into the ideal crystal configuration. Bulk defects that resist relaxation have densities lower than 10(16) defects/cm3 at typical growth conditions. Grain boundary defects, on the other hand, are very stable. Moreover, interstitial molecules at grain boundaries are identified as a source of compressive stress.     

Effect of orientation and mobility of polymer molecules at surfaces on contact angle and its hysteresis

The contact angle of a water droplet on the surface of a solid polymer or hydrogel (water-swollen three-dimensional network) depends on whether a hydrophilic moiety of the polymer molecule is oriented towards the air interface or towards the bulk of the solid, but not on the hydrophilicity of the molecule. Therefore, the short-range rotational mobility of a polymer molecule has a major influence on the apparent hydrophilicity of a polymer surface as measured by the contact angle of water. By the came principle, the abnormally large hysteresis effect observed in advancing and receding contact angles of water on some polymer surfaces can be attributed to the reorientation of hydrophilic moieties of polymer molecules at the surface. These factors are demonstrated by selected polymer surfaces with different degrees of mobility at the polymer-air interface.     

Crystal and Molecular Structure of the [6-Deoxy-6-[(2-(4-imidazolyl)ethyl)amino]- cyclomaltoheptaose]copper(II) Ternary Complex with L-Tryptophanate. Role of Weak Forces in the Chiral Recognition Process Assisted by a Metallocyclodextrin

The ternary copper(II) complex of 6-deoxy-6-[(2-(4-imidazolyl)ethyl)amino]cyclomaltoheptaose (CDhm) and L-tryptophanate (L-TrpO(-)) was characterized by ESR and X-ray diffraction. The solid state structure of [Cu(CDhm)(L-TrpO)](+) shows that the aromatic side chain of TrpO(-) is outside the cavity and that the two amino nitrogen atoms, one from the histamine molecule and one from the amino acidate, are in a cis disposition. The two amino nitrogens, the imidazole nitrogen, and the carboxylate oxygen atoms form the base of a square pyramid, which surrounds the copper(II) ion, a water molecule occupying an apical position. Atomic distances suggest for this complex that pi-pi and d-pi interactions could occur in the solid state. Morover, the [Cu(CDhm)(L-TrpO)](+) has a self-assembled structure in which a CDhm molecule behaves as host and as guest. The imidazole and the indole ring are directed into the cavity of an adjacent CDhm molecule from the wider cyclodextrin rim, thus forming a polymeric column structure. ESR spectra were run on the copper(II) ternary complexes with L- or D-tryptophanate and L- or D-alaninate in frozen aqueous solution and on the former pair of enantiomers in the solid state, as well. While in the case of the ternary complex with L- or D-alaninate no differences are observed in their frozen solution spectra, in the case of complexes with TrpO(-) subtle differences are found. These differences, which disappear when excess methanol is used, are ascribed to the presence of weak forces, such as hydrophobic or d-pi interactions.     

Ordered nano-structure of a stamped self-organized protein layer on a HOPG surface using a HFB carrier

A groundbreaking method for ordered molecular layer preparation on a solid surface employing the drop-stamp method has been developed by us taking advantage of the characteristics of the HFB molecule as a self-organizer/adsorption carrier. It is a smart method which can be used to prepare a self-organized protein layer on a solid surface without unspecific adsorption or defects. In our previous report, we clarified the self-organizing nature of HFB-tagged protein molecules on a surface of a solution droplet. In this report, a protein layer was prepared on a HOPG surface by using the drop-stamp method with a maltose binding protein (MBP)-tagged HFBII molecule. The structure of the stamped protein layer was investigated using frequency modulation atomic force microscopy (FM-AFM) in a liquid condition. The FM-AFM images show that the drop-stamp method can prepare an ordered protein layer on a solid surface smartly. The drop-stamp method using a HFB carrier is a practical method which can be used to prepare an ordered protein layer on a solid substrate surface without unspecific adsorption defects.     

Molecular dynamics investigation into the structural features and transport properties of C60 in liquid argon

Molecular dynamics (MD) simulations were performed to investigate the structural features and transport properties of C60 in liquid argon. The results reveal that an organized structure shell of liquid argon is formed close to the surface of a C60 fullerene molecule, thereby changing the solid/liquid interfacial structure. Furthermore, the simulation indicates that the C60-liquid argon fluid becomes structurally more stable as the C60 molecule volume fraction and the temperature increase. The viscosity of the fluid increases significantly as the C60 molecule loading is increased, particularly at a lower temperature. The thermal conductivity enhancement of the fluid in the present simulations is anomalously an order of magnitude higher than the theoretical predictions from either the Maxwell or the Lu and Liu models, and is found to vary approximately linearly with the C60 molecule volume fraction. The increased thermal conductivity is attributed to the nature of heat conduction in C60 molecule suspensions and an organized structure at the solid/liquid interface.     

Detection of structured single‐strand DNA via solid‐state nanopore

Nanopore is a single‐molecule analysis method which also employed electrophoresis has achieved promising single‐molecule detections. In this study, we designed two kinds of confined spaces by fabricating solid‐state nanopores with desirable diameters to study the structured single‐strand DNA of C‐rich quadruplex. For the nanopore whose diameter is larger than the quadruplex size, the DNA molecule could directly translocate through the nanopore with extremely high speed. For the nanopore whose diameter is smaller than the quadruplex size, DNA molecule which is captured by nanopore could return to the solution without translocation or unzip the quadruplex structure into single‐strand and then pass the nanopore. This study certifies that choosing a suitable sensing interface is the vital importance of observing detailed single‐molecule information. The solid‐state nanopores hold the great potential to study the structural dynamics of quadruplex DNA molecule.     

Ab initio MRD-CI calculations for breaking a chemical bond in a molecule in a crystal or other solid environment. III. Me2N?NO2 decomposition of dimethylnitramine in a large crystalline environment

Recently we extended our strategy for MRD-CI (multireference double excitation-configuration interaction) calculations, based on localized/local orbitals and an “effective” CI Hamiltonian, for molecular decompositions of large molecules to breaking a chemical bond in a molecule in a crystalline or other solid environment. Our technique begins with an explicit quantum chemical SCF calculation for a reference molecule surrounded by a number of other molecules in the multipole environment of more distant neighbors. The resulting canonical molecular orbitals are then localized, and the localized occupied and virtual orbitals in the region of interest are included explicitly in the MRD-CI with the remainder of the occupied localized orbitals being folded into an “effective” CI Hamiltonian. The MRD-CI calculations are then carried out for breaking a bond in the reference molecule. This method is completely general in that the space treated explicitly, as well as the surrounding space, may contain voids, defects, deformations, dislocations, impurities, dopants, edges and surfaces, boundaries, etc. Dimethylnitramine is the smallest prototype of the energetic R₂N—NO₂ nitramines, such as the 6-member ring RDX or the 8-member ring HMX. Decomposition of energetic compounds is initiated in the solid by a breaking of the target bond. Thus, it is crucial to know the difference in energy between breaking a bond in an isolated energetic molecule versus in the molecule in a solid. In the present study, we have carried out MRD-CI calculations for the Me₂N—NO₂ dissociation of dimethylnitramine in a dimethylnitramine crystal. The cases we investigated were one dimethylnitramine molecule (surrounded by 53 and 685 neighboring dimethylnitramine molecules represented by multipoles), three dimethylnitramine molecules, and three dimethylnitramine molecules (surrounded by 683 neighbors). All multipoles were cumulative atomic multipoles up through quadrupoles. The MRD-CI calculations on dimethylnitramine required large numbers of reference configurations from which were allowed all single and double excitations.     

Tetrathiafulvalene-Inserted Diphenoquinone: Synthesis,Structure, and Dynamic Redox Property

A new tetrathiafulvalene (TTF) derivative is synthesized, which is substituted with two phenoxy radicals on one 1,3-dithiole ring, and may have either open-shell diradical or closed-shell extended-quinoidal ground states. X-ray single crystal analysis and NMR measurements prove that this molecule has a closed-shell extended quinoidal structure both in the solid state and in solution. DFT calculations show the donor–acceptor electronic properties of this molecule with a well-separated HOMO–LUMO distribution and a small HOMO–LUMO energy gap. Because of this donor–acceptor character, this molecule gives both the dication and the dianion species by electrochemical oxidation and reduction. Furthermore, during the redox process between the neutral and dication states, this molecule exhibits unique changes in the cyclic voltammogram upon repeating the cycles or varying the scan rate. The observed electrochemical behavior is explained by the conformational changes in the electrochemically generated species, thus indicating that this molecule is classified as a dynamic redox system.     

Chemical adaptor systems

"Chemical adaptor systems" are molecules used to link different functionalities, based on unique reactivity that allows controlled fragmentation. Two different mechanistic reactivities were used to prepare chemical adaptor systems. The first is based on a spontaneous intra-cyclization reaction to form a stable ring molecule. Cleavage of the trigger generates a free nucleophile, for example, an amine group, which undergoes intra-cyclization to release the target molecule from the handle part (e.g., a targeting antibody or a solid support for synthesis). The second applied reactivity is an elimination reaction, which is usually based on a quinone-methide-type rearrangement. Similarly, cleavage of the trigger generates a free phenol functionality, which can undergo a self-elimination reaction through a quinone-methide rearrangement to release the target molecule. The adaptor molecules have been applied in the field of drug delivery to release a drug from a targeting device and in the field of solid-phase synthesis to release a synthetic molecule from the solid support. A chemical adaptor molecule has also been used as a building unit to construct dendrimers with a triggered fragmentation.     

The use of mass defect in modern mass spectrometry

Mass defect is defined as the difference between a compound's exact mass and its nominal mass. This concept has been increasingly used in mass spectrometry over the years, mainly due to the growing use of high resolution mass spectrometers capable of exact mass measurements in many application areas in analytical and bioanalytical chemistry. This article is meant as an introduction to the different uses of mass defect in applications using modern MS instrumentation. Visualizing complex mass spectra may be simplified with the concept of Kendrick mass by plotting nominal mass as a function of Kendrick mass defect, based on hydrocarbons subunits, as well as slight variations on this theme. Mass defect filtering of complex MS data has been used for selectively detecting compounds of interest, including drugs and their metabolites or endogenous compounds such as peptides and small molecule metabolites. Several strategies have been applied for labeling analytes with reagents containing unique mass defect features, thus shifting molecules into a less noisy area in the mass spectrum, thus increasing their detectability, especially in the area of proteomics. All these concepts will be covered to introduce the interested reader to the plethora of possibilities of mass defect analysis of high resolution mass spectra. Copyright © 2012 John Wiley & Sons, Ltd.     

A DFT study on the healing of N‐vacancy defects in boron nitride nanosheets and nanotubes by a methylene molecule

In the present work, density functional theory calculations are used to investigate the healing mechanism of a N‐vacancy defect in boron nitride nanosheet (BNNS) or nanotube (BNNT) with a CH₂ molecule. The healing process starts with the chemisorption of CH₂ at the defect site, followed by its dehydrogenation over the surface. Next, a H₂ molecule is produced which can be easily released from the surface due to its small adsorption energy. For the dehydrogenation of CH₂ molecule over the defective BNNS or BNNT, the first C? H bond dissociation is the rate determining step. Our results indicate that the dehydrogenation of CH₂ over BNNS is both thermodynamically and kinetically more favorable than over BNNT. Besides, this study proposes a novel method for achieving C‐doped BNNSs and BNNTs. Given that the healing process proceeds without using a metal catalyst, therefore, no any purification is needed to remove the catalyst.     

Highly Emissive Organic Single‐Molecule White Emitters by Engineering o‐Carborane‐Based Luminophores

The development of organic single‐molecule solid‐state white emitters holds a great promise for advanced lighting and display applications. Highly emissive single‐molecule white emitters were achieved by the design and synthesis of a series of o ‐carborane‐based luminophores. These luminophores are able to induce multiple emissions to directly emit high‐purity white light in solid state. By tuning both molecular and aggregate structures, a significantly improved white‐light efficiency has been realized (absolute quantum yield 67 %), which is the highest value among the known organic single‐molecule white emitters in the solid state. The fine‐tuning of the packing modes from H‐ to J‐ and cross‐stacking aggregates as well as intermolecular hydrogen bonds are successful in one molecular skeleton. These are crucial for highly emissive white‐light emission in the solid state.     

Template-controlled reactivity: Following nature's way to design and construct metal-organic polyhedra and polygons

We show how a template-controlled reaction performed in the organic solid state can be used to construct a molecule that functions as an organic building unit of both a metal-organic polyhedron and polygon. The template is a small organic molecule that organizes two olefins via hydrogen bonds for a [2+2] photodimerization. The process of utilizing a molecule to build a molecule that is subsequently used for self-assembly is inspired by the general two-step process of template-directed synthesis and self-assembly of Nature that is used to construct large, functional self-assembled structures.     

Adsorption reactions of alkali-halide nanocrystals: Identification of an important surface defect

The adsorption reactions of alkali-halide clusters have been investigated on a size-selected basis using flow-reactor methods. The reactivity of larger sodium-fluoride clusters [Na_nF_n?1]⁺ toward polar molecules NH₃ and H₂O shows a distinctive pattern as a function ofn at ambient temperature. Comparison with computed structures shows that aparticular kind of defect greatly facilitates the initial adsorption process. This defect can be formed by removal of an ion-pair from the face of an otherwise perfect nanocrystal, to create a basket-like opening for the adsorbed molecule. It is shown that this kind of defect occurs as a most stable low-temperature structure only to a certain size, after which a less reactive defect takes its place. The implications of these findings for the adsorption reactivity of the surfaces of ionic solids are briefly discussed.     

Model of a disclination core in nematics

The core structure of a disclination line of strength 1 in uniaxial nematics is determined by using a space-dependent mean-field approach somehow based on the rod-like molecular model. It is shown that, due to distortion, biaxiality arises at all points of the defect core, except at the centre line where symmetry dictates uniaxiality; the orientational distribution of the rod-like molecules is there 'oblate', however. Although, as is well known, the configuration of a 1 defect is stable only under limiting conditions (as compared with either escaping in the axial direction or splitting into two 1/2 lines), the simple example developed here is indicative of a method which can readily be extended to more realistic, if mathematically more complex, situations such as 1/2 lines, layers close to solid boundaries, etc.     

NMR Wool Tube: a novel method for NMR solution analysis of derivatized glass surfaces

Glass wool was placed within an NMR tube as a solid support for the covalent attachment of a molecule to allow for a simple one-dimensional 1H FT NMR solution analysis. This novel procedure avoids the use of expensive sample tubes or platforms, as required for magic angle or fast spinning, exotic pulse sequences, isotopic labeling or the use of a large number of scans to provide the ability to analyze the structure, mobility, ligand binding, and solvent interactions of the surface bound molecule.