Behavior of Binary Guests in a Porous Coordination Polymer

Controlling the condensed state of multiple guests in nanoporous media is critical to many applications, but an understanding of this phenomenon in pores smaller than a few nanometers is still unavailable. In this work, we investigate the aggregation state of binary guests, poly­(ethylene glycol) (PEG), and long-chain normal alkanes, in subnanometer channels of a porous coordination polymer (PCP) by monitoring their thermal transition behaviors. PEG and alkanes are immiscible in the bulk and their melting transitions are not affected by each other. Meanwhile, in the PCP nanochannels, the transition temperature and the heat of the binary–guest system were significantly different from when PEG or an alkane was individually included. This suggests the formation of microscopically segregated domain structures of PEG and alkane in the host crystal. The transition behaviors gradually varied by changing the introduction ratio between PEG and alkane, and thus the aggregation states of the two guests were successfully controlled by the simple variation of relative amounts. This methodology offers a promising route to control spatial configurations of multiple guest molecules in nanoporous matrices for advanced applications

Radical Copolymerization Mediated by Unsaturated Metal Sites in Coordination Nanochannels

Radical copolymerization of methyl methacrylate (MMA) and styrene was performed in [Tb­(1,3,5-benzenetrisbenzoate)]_<i>n</i> with coordinatively unsaturated metal sites (UMS) immobilized along the one-dimensional nanochannels. A drastic increase in the proportion of MMA units in the resulting copolymers was obtained compared with that obtained from the corresponding solution polymerization systems. Simultaneous coordination of MMA to the UMS is the key to increasing the MMA proportion during the copolymerization in the nanochannels, which was demonstrated by variable temperature IR measurements and several controlled experiments

Controlled Synthesis of Anisotropic Polymer Particles Templated by Porous Coordination Polymers

Nonspherical polymer particles have been efficiently prepared in different morphological crystals of porous coordination polymers (PCPs) by in situ radical polymerization of styrene and methylmethacrylate, followed by removal of the host PCP frameworks in aqueous tetrasodium ethylenediaminetetraacetate (Na-EDTA) solution. In this replication process, the isolated vinyl polymer particles retained the size and morphologies of the original PCP particles, although the polymer chains were not stabilized by cross-linking. This morphological retention of vinyl polymers after the isolation from the PCP matrixes was ensured by the rigidity and porosity of the polymers, which was confirmed by DSC and adsorption measurements. The unconventional assembly of polymer chains in the particles is of interest from the viewpoints of functional properties of the polymer particles

Opening of an Accessible Microporosity in an Otherwise Nonporous Metal–Organic Framework by Polymeric Guests

The development of highly porous metal–organic frameworks (MOFs) is greatly sought after, due to their wide range of applications. As an alternative to the development of new structures, we propose to obtain new stable configurations for flexible MOFs by insertion of polymeric guests. The guests prevent the otherwise spontaneous closing of the host frameworks and result in stable opened forms. Introduced at a fraction of the maximal capacity, polymer chains cause an opening of the occupied nanochannels, and because of the MOF reticular stiffness, this opening is propagated to the neighboring nanochannels that become accessible for adsorption. Composites were obtained by in situ polymerization of vinyl monomers in the nanochannels of an otherwise nonporous MOF, resulting in homogeneously loaded materials with a significant increase of porosity (<i>S</i>_BET = 920 m²/g). In addition, by limiting the accessible configurations for the framework and forbidding the formation of a reactive intermediate, the polymeric guest prevented the thermal degradation of the host MOF even at very low loading (as low as 3 wt %) and increased its stability domain by more than 200 °C

Preparation of Porous Polysaccharides Templated by Coordination Polymer with Three-Dimensional Nanochannels

Polymerization of monosaccharide monomers usually suffers from the production of polysaccharides with ill-defined structures because of the uncontrolled random reactions among many reactive hydroxyl groups on saccharide monomers. In particular, rational synthesis of polysaccharides with porosity approximating molecular dimensions is still in its infancy, despite their usefulness as drug carriers. Here, we disclose an efficient synthetic methodology for the preparation of polysaccharides with controllable mesoporosity in the structure, utilizing [Cu₃(benzene-1,3,5-tricarboxylate)]_<i>n</i> (HKUST-1; <b>1</b>) as templates. Cationic ring-opening polymerization of 1,6-anhydro glucose was performed in nanochannels of <b>1</b>, followed by removal of the host frameworks, giving polysaccharide particles as replicas of the original molds. Nitrogen adsorption measurement revealed that the obtained polysaccharide particles contained high mesoporosity in the structure, which could be controlled systematically depending on the polymerization conditions. Because of the large specific surface area, tunable porosity and particle size, we could also demonstrate the capabilities of our polysaccharides for loading and releasing of a drug molecule and protein

Controlled Cyclopolymerization of Difunctional Vinyl Monomers in Coordination Nanochannels

Radical cyclopolymerization of difunctional monomers based on 1,6-diene components was performed in one-dimensional channels of porous coordination polymers (PCPs). Although bulk or solution polymerization of the monomers usually gives cross-linked insoluble polymers, the unfavorable interpolymer reactions were effectively suppressed in the narrow nanochannels of PCPs to provide soluble linear polymers. The pore matrices and functionality of PCPs can be readily designed by changing the organic ligands, so that polymerization of the diene monomers in different sized pores was examined. The primary structures of the resulting polymers, such as branching, cyclic structure, and stereoregularity, were changed, depending on the pore characteristics of the PCPs

Nanostructuration of PEDOT in Porous Coordination Polymers for Tunable Porosity and Conductivity

A series of conductive porous composites were obtained by the polymerization of 3,4-ethylenedioxythiophene (EDOT) in the cavities of MIL–101­(Cr). By controlling the amount of EDOT loaded into the host framework, it was possible to modulate the conductivity as well as the porosity of the composite. This approach yields materials with a reasonable electronic conductivity (1.1 × 10⁻³ S·cm^–1) while maintaining high porosity (<i>S</i>_BET = 803 m²/g). This serves as a promising strategy for obtaining highly nanotextured conductive polymers with very high accessibility for small gas molecules, which are beneficial to the fabrication of a chemiresistive sensor for the detection of NO₂

Confinement of Single Polysilane Chains in Coordination Nanospaces

Understanding the intrinsic properties of single conducting polymer chains is of interest, largely for their applications in molecular devices. In this study, we report the accommodation of single polysilane chains with hole-transporting ability in porous coordination polymers (PCPs), [Al­(OH)­(L)]_<i>n</i> (<b>1a</b>; L = 2,6-naphthalenedicarboxylate, channel size = 8.5 × 8.5 Ų, <b>1b</b>; L = 4,4′-biphenyldicarboxylate, channel size = 11.1 × 11.1 Ų). Interestingly, the isolation of single polysilane chains increased the values of carrier mobility in comparison with that in the bulk state due to the elimination of the slow interchain hole hopping. Moreover, even when the chains are isolated one another, the main chain conformation of polysilane could be controlled by changing the pore environment of PCPs, as evidenced by Raman spectroscopy, solid-state NMR measurements, and molecular dynamics simulation. Hence, we succeeded in varying the conducting property of single polysilane chains. Additionally, polysilanes have a drawback, photodegradation under ultraviolet light, which should be overcome for the application of polysilanes. It is noteworthy that the accommodation of polysilane in the nanopores did not exhibit photodegradation. These results highlight that PCP–polysilane hybrids are promising candidates for further use in the field of molecular electronics

Peptide–Metal Organic Framework Swimmers that Direct the Motion toward Chemical Targets

Highly efficient and robust chemical motors are expected for the application in microbots that can selectively swim toward targets and accomplish their tasks in sensing, labeling, and delivering. However, one of major issues for such development is that current artificial swimmers have difficulty controlling their directional motion toward targets like bacterial chemotaxis. To program synthetic motors with sensing capability for the target-directed motion, we need to develop swimmers whose motions are sensitive to chemical gradients in environments. Here we create a new intelligent biochemical swimmer by integrating metal organic frameworks (MOFs) and peptides that can sense toxic heavy metals in solution and swim toward the targets. With the aid of Pb-binding enzymes, the peptide-MOF motor can directionally swim toward PbSe quantum dots (QD) by sensing pH gradient and eventually complete the motion as the swimmer reaches the highest gradient point at the target position in solution. This type of technology could be evolved to miniaturize chemical robotic systems that sense target chemicals and swim toward target locations

Peptide–Metal Organic Framework Swimmers that Direct the Motion toward Chemical Targets

Highly efficient and robust chemical motors are expected for the application in microbots that can selectively swim toward targets and accomplish their tasks in sensing, labeling, and delivering. However, one of major issues for such development is that current artificial swimmers have difficulty controlling their directional motion toward targets like bacterial chemotaxis. To program synthetic motors with sensing capability for the target-directed motion, we need to develop swimmers whose motions are sensitive to chemical gradients in environments. Here we create a new intelligent biochemical swimmer by integrating metal organic frameworks (MOFs) and peptides that can sense toxic heavy metals in solution and swim toward the targets. With the aid of Pb-binding enzymes, the peptide-MOF motor can directionally swim toward PbSe quantum dots (QD) by sensing pH gradient and eventually complete the motion as the swimmer reaches the highest gradient point at the target position in solution. This type of technology could be evolved to miniaturize chemical robotic systems that sense target chemicals and swim toward target locations