Demonstration of High-Throughput Building Block and Composition Analysis of Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) are composed of inorganic metal-containing nodes and organic linker groups and are promising porous materials for a wide range of applications. More than 90 000 different MOFs have been synthesized with different inorganic nodes, organic linkers, and node-linker connectivity patterns. While databases have been created to catalog this enormous number of structures, they generally do not provide functionality to easily search, sort, and understand MOFs based on composition and building blocks.

An Allosterically Regulated, Four-State Macrocycle.

Macrocycles capable of host-guest chemistry are an important class of structures that have attracted considerable attention because of their utility in chemical separations, analyte sensing, signal amplification, and drug delivery. The deliberate design and synthesis of such structures are rate-limiting steps in utilizing them for such applications, and coordination-driven supramolecular chemistry has emerged as a promising tool for rapidly making large classes of such systems with attractive molecular recognition capabilities and, in certain cases, catalytic properties. A particularly promising subset of such systems are stimuli-responsive constructs made from hemilabile ligands via the weak-link approach (WLA) to supramolecular coordination chemistry.

Palladium(II) Weak-Link Approach Complexes Bearing Hemilabile N-Heterocyclic Carbene-Thioether Ligands.

A new class of homoligated palladium(II) weak-link approach (WLA) complexes bearing hemilabile N-heterocyclic carbene (NHC)-thioether ligands is reported that, unlike previous tweezer-like WLA complexes, expand and contract in a linear fashion when switching between configurational states. These complexes can be chemically switched between a trans open state and a trans closed state via the addition or subsequent extraction of Cl. These bis(NHC) complexes also display unusual isomerization behavior.

A concerted two-prong approach to the allosteric regulation of bifunctional catalysis.

Herein, we report the reversible "on-off" allosteric regulation of hydrogen-bond-donating (HBD)-Lewis base co-catalytic activity a concerted two-prong methodology entailing cooperative acid-base chemistry and a structurally addressable coordination complex. Specifically, a heteroligated Pt(ii) weak-link approach (WLA) tweezer complex containing both a hemilabile squaramide-piperidine-based catalytic ligand and a sodium sulfonate hydrogen-bond-accepting (HBA) ligand was synthesized. Due to the hemilabile nature of the catalyst-containing ligand, the heteroligated complex can be reversibly toggled between a flexible, semi-open state and a rigid, fully closed state upon the addition of elemental ion cues.

Reversible and Selective Encapsulation of Dextromethorphan and β-Estradiol Using an Asymmetric Molecular Capsule Assembled via the Weak-Link Approach.

An allosterically regulated, asymmetric receptor featuring a binding cavity large enough to accommodate three-dimensional pharmaceutical guest molecules as opposed to planar, rigid aromatics, was synthesized via the Weak-Link Approach. This architecture is capable of switching between an expanded, flexible "open" configuration and a collapsed, rigid "closed" one. The structure of the molecular receptor can be completely modulated in situ through the use of simple ionic effectors, which reversibly control the coordination state of the Pt(II) metal hinges to open and close the molecular receptor.

Cooperative Electronic and Structural Regulation in a Bioinspired Allosteric Photoredox Catalyst.

Herein, we report the first allosteric photoredox catalyst regulated via constructively coupled structural and electronic control. While often synergistically exploited in nature, these two types of control mechanisms have only been applied independently in the vast majority of allosteric enzyme mimics and receptors in the literature. By embedding a model of photosystem II in a supramolecular coordination complex that responds to chloride as an allosteric effector, we show that distance and electronic control of light harvesting can be married to maximize allosteric regulation of catalytic activity.

Giant conductivity switching of LaAlO3/SrTiO3 heterointerfaces governed by surface protonation.

Complex-oxide interfaces host a diversity of phenomena not present in traditional semiconductor heterostructures. Despite intense interest, many basic questions remain about the mechanisms that give rise to interfacial conductivity and the role of surface chemistry in dictating these properties. Here we demonstrate a fully reversible >4 order of magnitude conductance change at LaAlO3/SrTiO3 (LAO/STO) interfaces, regulated by LAO surface protonation.

An allosteric photoredox catalyst inspired by photosynthetic machinery.

Biological photosynthetic machinery allosterically regulate light harvesting via conformational and electronic changes at the antenna protein complexes as a response to specific chemical inputs. Fundamental limitations in current approaches to regulating inorganic light-harvesting mimics prevent their use in catalysis. Here we show that a light-harvesting antenna/reaction centre mimic can be regulated by utilizing a coordination framework incorporating antenna hemilabile ligands and assembled via a high-yielding, modular approach.

Allosteric regulation of supramolecular oligomerization and catalytic activity via coordination-based control of competitive hydrogen-bonding events.

Herein, we demonstrate that the activity of a hydrogen-bond-donating (HBD) catalyst embedded within a coordination framework can be allosterically regulated in situ by controlling oligomerization via simple changes in coordination chemistry at distal Pt(II) nodes. Using the halide-induced ligand rearrangement reaction (HILR), a heteroligated Pt(II) triple-decker complex, which contains a catalytically active diphenylene squaramide moiety and two hydrogen-bond-accepting (HBA) ester moieties, was synthesized. The HBD and HBA moieties were functionalized with hemilabile ligands of differing chelating strengths, allowing one to assemble them around Pt(II) nodes in a heteroligated fashion.

A multi-state, allosterically-regulated molecular receptor with switchable selectivity.

A biomimetic, ion-regulated molecular receptor was synthesized via the Weak-Link Approach (WLA). This structure features both a calix[4]arene moiety which serves as a molecular recognition unit and an activity regulator composed of hemilabile phosphine alkyl thioether ligands (P,S) chelated to a Pt(II) center. The host-guest properties of the ion-regulated receptor were found to be highly dependent upon the coordination of the Pt(II) center, which is controlled through the reversible coordination of small molecule effectors.

Modulation of electronics and thermal stabilities of photochromic phosphino-aminoazobenzene derivatives in weak-link approach coordination complexes.

A series of d(8) transition-metal (Pt(II) and Pd(II)) coordination complexes incorporating phosphine-functionalized aminoazobenzene derivatives as hemilabile phosphino-amine (P,N) ligands were synthesized and studied as model weak-link approach (WLA) photoresponsive constructs. The optical and photochemical properties of these complexes were found to be highly influenced by various tunable parameters in WLA systems, which include type of metal, coordination mode, type of ancillary ligand, solvent, and outer-sphere counteranions. In dichloromethane, reversible chelation and partial displacement of the P,N coordinating moieties allow for toggling between aminoazobenzene- or pseudostilbene- and azobenzene-type derivatives.

Boron-dipyrromethene-functionalized hemilabile ligands as "turn-on" fluorescent probes for coordination changes in weak-link approach complexes.

Herein we report a new class of hemilabile ligands with boron-dipyrromethene (Bodipy) fluorophores that, when complexed to Pt(II), can signal changes in coordination mode through changes in their fluorescence. The ligands consist of phosphino-amine or phosphino-thioether coordinating moieties linked to the Bodipy's meso carbon via a phenylene spacer. Interestingly, this new class of ligands can be used to signal both ligand displacement and chelation reactions in a fluorescence "turn-on" fashion through the choice of weakly binding heteroatom in the hemilabile moiety, generating up to 10-fold fluorescence intensity increases.

Locally altering the electronic properties of graphene by nanoscopically doping it with Rhodamine 6G.

We show that Rhodamine 6G (R6G), patterned by dip-pen nanolithography on graphene, can be used to locally n-dope it in a controlled fashion. In addition, we study the transport and assembly properties of R6G on graphene and show that in general the π-π stacking between the aromatic components of R6G and the underlying graphene drives the assembly of these molecules onto the underlying substrate. However, two distinct transport and assembly behaviors, dependent upon the presence or absence of R6G dimers, have been identified.