Theory of pair connectedness in templated quenched-annealed systems

Recently, several families of promising porous materials have been proposed where the porous matrix forms in the presence of additional molecules or templates. These materials find applications in separations, sensing, catalysis, and other technologies. For these systems, it is important to understand the connectedness of the matrix species and the porous space. In the first case, this would characterize the integrity of the porous material, whereas the second property is directly related to the accessibility of the interior porous space and thus to the function of the material. Here, we propose an integral equation theory which describes cluster population and percolation phenomena for matrix and template species at the stage of the templated material formation. We also extend this theory to provide structural characterization of the fluid confined in a templated structure. The predictions of the theory are tested for the case of rigid molecular species made of hard sphere interaction sites and compared with computer simulations. We discuss the effect of the system density, species structure, and other parameters on the average cluster size and percolation threshold for the components of the system.     

Electron Microscopic Study on Aerosol-Assisted Synthesis of Aluminum Organophosphonates Using Flexible Colloidal PS-b-PEO Templates

A wide variety of synthetic approaches from homogeneous precursor solutions have so far been developed for precise structural design of materials in multiscale. In organic templating approaches for porous materials design, we have recently developed a new approach to fabricate colloidal polystyrene-block-poly(oxyethylene) (PS-b-PEO) templated large pores that can be controlled in thick films of aluminum organophosphonate (AOP). In this study, we extended this approach using colloidal PS-b-PEO aggregates to aerosol-assisted synthesis for the fabrication of spherical particles. Structural variations (morphology and porous structure) depended on the synthetic conditions, which were mainly investigated by using electron microscopies (SEM and TEM). In addition to the insight on the colloidal PS-b-PEO templating of spherical pores in AOP spheres, it was found that colloidal PS-b-PEO aggregates were flexible for further design of pore shape that was strongly affected by external morphology. In this context, we proposed this method as flexible colloidal PS-b-PEO templating to fabricate unusual macroporous structures during morphological control from precursor solutions containing colloidal PS-b-PEO aggregates. The insights will be promising for precise construction of unique devices using porous materials templated by colloidal organic aggregates. In addition, we found a useful water adsorption-desorption behavior over the macroporous AOP bulky powders when the macropores were connected through large pores, which is also significant for future development of AOP-based porous materials.     

Hierarchically imprinted porous films for rapid and selective detection of explosives

On the basis of the combination of colloidal and mesophase templating, as well as molecular imprinting, a general and effective approach for the preparation of hierarchically structured trimodal porous silica films was developed. With this new methodology, controlled formation of well-defined pore structures not only on macro- and mesoscale but also on microscale can be achieved, affording a new class of hierarchical porous materials with molecular recognition capability. As a demonstration, TNT was chosen as template molecule and hierarchically imprinted porous films were successfully fabricated, which show excellent sensing properties in terms of sensitivity, selectivity, stability, and regeneracy. The pore system reported here combines the multiple benefits arising from all length scales of pore size and simultaneously possesses a series of distinct properties such as high pore volume, large surface area, molecular selectivity, and rapid mass transport. Therefore, our described strategy and the resulting pore systems should hold great promise for various applications not only in chemical sensors, but also in catalysis, separation, adsorption, or electrode materials.     

Aligned porous materials by directional freezing of solutions in liquid CO2

We report here a method for generating structures with aligned macropores by templating solidified carbon dioxide. The CO2 template phase can be removed by direct sublimation to yield a dry, solvent-free porous material that may be useful in applications such as tissue engineering and aligned cell growth.     

Sensitivity of cationic surfactant templates to specific anions in liquid interface crystallization

We investigated the specific effects of potassium salts of various anions upon the interfacially templated crystal nucleation of K(2)SO(4). Previously, we have shown that the presence of several salts at low concentrations could induce changes in important crystallization characteristics templated by 1-octadecylamine at the liquid-liquid interface, and that these changes depended greatly on the specific identity of the salt. In this work we extend our surfactant monolayers to include dimethyldioctadecylammonium bromide (DODAB) and hexadecyltrimethylammonium bromide (CTAB). Addition of 10 mM of various potassium salts results in a diminution in efficiency of the templating capability of CTAB monolayer, as evidenced by higher C(onset) values and polycrystalline habit. The ability of the anions to perturb these values varied in a manner consistent with a Hofmeister series. However, DODAB maintained its templating effectiveness regardless of the nature of the salt or concentration. DODAB and CTAB are likely to be undergoing different reordering effects in the monolayer upon binding with chaotropic anions: a combined reduction in surface charge with different monolayer ordering results in a differing template ability. These studies have provided significant insights into the understanding of the interaction of ordered surfactant arrays with salts, and provide exciting possibilities for crystal engineering and materials design.     

纳米团簇的超分子自组装

在纳米材料的应用过程中, 纳米团簇或纳米粒子的组装将是非常关键的一步。纳米团簇的超分子化学组装方法可分为两类, 即胶态晶体法和模板法。胶态晶体法是利用胶体溶液的自组装特性将纳米团簇组装成超晶格, 可得到二维或三维有序的超晶格。模板法是利用纳米团簇与组装模板间的识别作用来带动团簇的组装, 可应用的模板有固体膜、单分子膜、有机分子、生物分子等。其中, 单分子膜模板是研究最多也是最为成熟的一种; 生物分子间严密的分子识别功能使其成为非常有发展前途的组装模板, 而且用生物分子模板有可能实现不同纳米团簇间的组装。     

Vernier‐Templated Synthesis,Crystal Structure,and Supramolecular Chemistry of a 12‐Porphyrin Nanoring

Vernier templating exploits a mismatch between the number of binding sites in a template and a reactant to direct the formation of a product that is large enough to bind several template units. Here, we present a detailed study of the Vernier‐templated synthesis of a 12‐porphyrin nanoring. NMR and small‐angle X‐ray scattering (SAXS) analyses show that Vernier complexes are formed as intermediates in the cyclo‐oligomerization reaction. UV/Vis/NIR titrations show that the three‐component assembly of the 12‐porphyrin nanoring figure‐of‐eight template complex displays high allosteric cooperativity and chelate cooperativity. This nanoring–template 1:2 complex is among the largest synthetic molecules to have been characterized by single‐crystal analysis. It crystallizes as a racemate, with an angle of 27° between the planes of the two template units. The crystal structure reveals many unexpected intramolecular C?H???N contacts involving the tert‐butyl side chains. Scanning tunneling microscopy (STM) experiments show that molecules of the 12‐porphyrin template complex can remain intact on the gold surface, although the majority of the material unfolds into the free nanoring during electrospray deposition.     

Investigation of surface interactions in molecular recognition of phosphonate imprinted organosilicates and the role of water

Surface interactions in molecular recognition of phosphonate imprinted organosilicates and the role of water have been studied. NMR and calorimetry studies have shown the changing nature of the surface water structure on silicate surfaces due to template directed molecular imprinting. Results indicate the interaction of an organophosphonate compound with the functionalized silica surfaces to be through surrounding water molecules. However, with nonfunctionalized surfaces, additional higher energy interactions were possible. Further, our results support the possible templating effect of water during the imprint process.     

模板剂对全硅MCM-41介孔分子筛结构的影响

分别采用十六烷基三甲基溴化铵和十六烷基三乙基溴化铵作为模板剂,硅溶胶为硅源,用水热晶化法在碱性（NaOH）介质中合成了MCM-41介孔分子筛样品.通过XRD、N2吸附-脱附、TG-DTA、IR等测试手段对这两种样品进行了对比表征分析.考察了两种不同模板剂对其晶体结构、比表面及孔径大小的影响.实验结果表明,相对于十六烷基三甲基溴化铵做模板剂,采用大头基的十六烷基三乙基溴化铵可以合成较大孔径和孔容（分别为4.72 nm和1.14 cm3•g-1）的MCM-41介孔分子筛,而且具有较窄的孔径分布,因此对于合成大孔径的介孔分子筛MCM-41,十六烷基三乙基溴化铵是一种很好的模板剂.     

3D-ordered macroporous materials comprising DNA

Macroporous materials comprising DNA were fabricated with the colloidal crystal template. First, DNA and diazoresin (DR) molecules are fully filled into the voids of a colloidal crystal template. After thermal treatment and removal of the colloids, DNA porous materials with highly ordered structure were obtained. In the process of thermal treatment the cross-linking reaction takes place between DR and DNA, which plays an important role for sustaining the porous framework. The DNA porous materials will turn into a fluorescent DNA/dye composite after staining with Hoechst 33258 (Hoe), a characteristic fluorescent dye for DNA. This kind of composite DNA porous material may have potential applications in optical devices.     

Endo- and exotemplating to create high-surface-area inorganic materials

Porous and high-surface-area materials are of interest to many scientific communities. Templating pathways can be used to synthesize such materials with a high degree of control over their structural and textural properties. As templates molecular or supramolecular units are added to the synthesis mixture. They are occluded in the growing solid and leave a pore system after their removal. For such templates the term "endotemplate" is introduced. Alternatively, the templates can be materials with structural pores in which another solid is created, thus providing a scaffold for the synthesis. After removal of the scaffold, a porous or finely divided solid remains, depending on the connectivity of the template. Such a template is termed an "exotemplate". By judicious choice of the templating procedure, unprecedented control of the structure and texture on length scales between nanometers and micrometers has been achieved over the last few years.     

生物模板法制备纳米氧化锌及其表征

本文以油菜花粉为生物模板,硝酸锌为锌源制备了一种分级多孔结构的纳米氧化锌。采用SEM、TEM、XRD和 FTIR等技术手段对其进行了表征。实验结果表明,采用油菜花粉为生物模板制备的氧化锌纳米材料为六方纤锌矿结构,较好的复制了花粉的分级多孔结构。同时,研究了制备条件诸如煅烧温度和反应物浓度对产物结构、形貌和尺度的影响。     

A crystalline sponge based on dispersive forces suitable for X-ray structure determination of included molecular guests

A crystalline porous material showing one-dimensional (1-D) rectangular micropores (12 × 9 Ų) has been assembled from a semirigid macrocyclic tetraimine and EtOAc as the templating agent. The 1-D nature of the material is intrinsic to the conformationally rigid structure of a macrocyclic sub-unit bearing four cyclohexylidene residues. The multiple dispersive forces established among the aliphatic residues glutted the 1-D channels and provided thermal stability to the material at temperatures below 160 °C. Upon removal of the template, the structure of the empty solid exhibited permanent microporosity (S _BET = 342 m² g^–1). Being a true molecular sponge, the channel framework of this material allowed the inclusion of a variety of molecular sample guests without compromising its crystalline nature. Remarkably, this crystalline material enabled the structure determination by X-ray diffraction of the included molecules. Theoretical studies demonstrated the vital role played by the dispersive forces in the overall stabilization of the crystal packing.     

ELECT++: Faster conformational search method for docking flexible molecules using molecular similarity

We have developed a program, ELECT++ (Effective LEssening of Conformations by Template molecules in C++), to speed up the conformational search for small flexible molecules using the similar property principle. We apply this principle to molecular shape and, importantly, to molecular flexibility. After molecules in a database are clustered according to flexibility and shape (FCLUST++), additional reagents are generated to screen the conformational space of molecules in each cluster (TEMPLATE++). We call these representative reagents of each cluster template reagents. Template reagents and clustered reagents produce, after reaction, template molecules and clustered molecules, respectively (tREACT++). The conformations of a template molecule are searched in the context of a macromolecular target. Acceptable conformational choices are then applied to all molecules in its cluster, thus effectively biasing conformational space to speed up conformational searches (tSEARCH++). In our incremental search method, it is necessary to calculate the root-mean-square deviations (RMSD) matrix of distances between different conformations of the same molecule to reduce the number of conformations. Instead of calculating the RMSD matrix for all molecules in a cluster, the RMSD matrix of a template molecule is chosen as a reference and applied to all the molecules in its cluster. We demonstrate that FCLUST++ clusters the primary amine reagents from the Available Chemicals Directory (ACD) successfully. The program tSEARCH++ was applied to dihydrofolate reductase with virtual molecules generated by tREACT++ using clustered primary amine reagents. The conformational search by the program tSEARCH++ was about 4.8 times faster than by SEARCH++, with an acceptable range of errors. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1834–1852, 1998     

An interaction site model integral equation study of molecular fluids explicitly considering the molecular orientation

We implemented an interaction site model integral equation for rigid molecules based on a density-functional theory where the molecular orientation is explicitly considered. In this implementation of the integral equation, multiple integral of the degree of freedom of the molecular orientation is performed using efficient quadrature methods, so that the site-site pair correlation functions are evaluated exactly in the limit of low density. We apply this method to Cl(2), HCl, and H(2)O molecular fluids that have been investigated by several integral equation studies using various models. The site-site pair correlation functions obtained from the integral equation are in good agreement with the one from a simulation of these molecules. Rotational invariant coefficients, which characterize the microscopic structure of molecular fluids, are determined from the integral equation and the simulation in order to investigate the accuracy of the integral equation.     

Protein-templated organic/inorganic hybrid materials prepared by liquid-phase deposition

Organic/inorganic hybrid thin films for protein recognition have been prepared by the liquid-phase deposition (LPD) coupled with template synthesis, i.e., molecular imprinting, where pepsin (Pep) was used as a model protein and titanium oxide was deposited on gold substrates in the presence of Pep-poly-L-lysine (PL) complexes. The complexes remained in the templated film after the deposition, and the binding sites for Pep were constructured after Pep was removed from the film. Surface plasmon resonance signals on the deposited films were measured to examine the binding behaviors toward proteins. The binding of Pep on the templated film was reversible, and the binding isotherm of Pep depicted a saturation curve with a binding constant of 7.3 x 105 M(-1), which was 10 times higher than that of albumin. In contrast, titanium oxide films prepared without PL did not show any selectivity; therefore, the hybridization of PL as the organic binder with the inorganic material is necessary to obtain selective binding sites for Pep. It was also shown that the hybridization process should proceed without denaturing the template protein, in order to obtain selective binding sites for the template. The procedure for preparation of the films was simple to perform, and the process for hybridization of the thin films with nanometer-order thickness was easily controlled by changing the LPD reaction time period. Consequently, the proposed LPD coupled with template synthesis is among the most appropriate methods to prepare hybrid materials with protein recognition ability, which proceeds under mild conditions in aqueous solution.     

Synthesis of Microporous Transition Metal Oxide Molecular Sieves with Bifunctional Templating Molecules

Systematic tuning of the micropore size in microporous transition metal oxide molecular sieves can be achieved by varying the length of the hydrocarbon chain of the diamine molecules used as templating agents. The large bifunctional molecules self-assemble with much smaller cross-sectional micellar dimensions than their monofunctional counterparts. The resulting family of porous materials offers exciting new flexibility in designing molecular sieves targeted for size selectivity and chemical functionality.     

Towards mesostructured zinc imidazolate frameworks

The transfer of supramolecular templating to the realm of metal–organic frameworks opens up new avenues to the design of novel hierarchically structured materials. We demonstrate the first synthesis of mesostructured zinc imidazolates in the presence of the cationic surfactant cetyltrimethylammonium bromide (CTAB), which acts as a template giving rise to ordered lamellar hybrid materials. A high degree of order spanning the atomic and mesoscale was ascertained by powder X‐ray diffraction, electron diffraction, as well as solid‐state NMR and IR spectroscopy. The metrics of the unit cells obtained for the zinc methylimidazolate and imidazolate species are a=(11.43±0.45), b=(9.55±0.35), c=(27.19±0.34) Å, and a=(10.98±0.90), b=(8.95±0.95), c=(26.33±0.34) Å, respectively, assuming orthorhombic symmetry. The derived structure model is consistent with a mesolamellar structure composed of bromine‐terminated zinc (methyl)imidazolate chains interleaved with motionally rigid cationic surfactant molecules in an all‐trans conformation. The hybrid materials exhibit unusually high thermal stability up to 300 °C, at which point CTAB is lost and evidence for a thermally induced transformation into poorly crystalline mesostructures with larger feature sizes is obtained. Treatment with ethanol effects the extraction of CTAB from the material, followed by facile transformation into pure microporous ZIF‐8 nanoparticles within minutes, thus demonstrating a unique transition from a mesostructure into a microporous zinc imidazolate.     

Structure-directing role of molecules containing benzyl rings in the synthesis of a large-pore aluminophosphate molecular sieve: an experimental and computational study

We describe the synthesis of AlPO-5 and SAPO-5 materials (AFI topology) using five different tertiary amines or quaternary ammonium ions containing one or two benzyl rings as structure-directing agents (SDAs). All of the molecules successfully direct the crystallization of AlPO-5; however, only the most efficient templates are able to crystallize SAPO-5. The observed differences in template efficiency can be rationalized in terms of the interaction energy between these molecules and the AFI framework. In ranking the template molecules, we notice that a well-defined molecular shape enhances the templating ability, but molecules that are too rigid are not able to adapt to the AlPO framework, yielding an inferior templating ability. Results of atomic-level modeling show that templates with one benzyl ring self-assemble in the main AFI channel by forming dimers with the benzyl rings parallel to each other; templates with two benzyl rings assemble instead into longer chains in which the benzyl ring of one molecule faces the ring of the subsequent one. Both mono- and dibenzyl templates show a high space-filling ability in AFI. Kinetic and thermodynamic factors that might affect the structure-directing activity of the molecules are examined.