An Autocatalytic System of Photooxidation-Driven Substitution Reactions on a Fe^II₄L₆Cage Framework

The functions of life are accomplished by systems exhibiting nonlinear kinetics: autocatalysis, in particular, is integral to the signal amplification that allows for biological information processing. Novel synthetic autocatalytic systems provide a foundation for the design of artificial chemical networks capable of carrying out complex functions. Here we report a few Feᴵᴵ₄L₆ cages containing BODIPY chromophores having tuneable photosensitizing properties. Electron-rich anilines were observed to displace electrondeficient anilines at the dynamic-covalent imine bonds of these cages. When iodoaniline residues were incorporated, heavy-atom effects led to enhanced ¹O₂ production. The incorporation of (methylthio)aniline residues into a cage allowed for the design of an autocatalytic system: oxidation of the methylthio groups into sulfoxides make them electron-deficient and allows their displacement by iodoanilines, generating a better photocatalyst and accelerating the reaction.This work was funded by the European Research Council (259352).This is the author accepted manuscript. The final version is available from Wiley via http://dx.doi.org/10.1002/ange.20150704

Temperature Controls Guest Uptake and Release from Zn4L4 Tetrahedra.

We report the preparation of triazatruxene-faced tetrahedral cage 1, which exhibits two diastereomeric configurations (T1 and T2) that differ in the handedness of the ligand faces relative to that of the octahedrally coordinated metal centers. At lower temperatures, T1 is favored, whereas T2 predominates at higher temperatures. Host-guest studies show that T1 binds small aliphatic guests, whereas T2 binds larger aromatic molecules, with these changes in binding preference resulting from differences in cavity size and degree of enclosure. Thus, by a change in temperature the cage system can be triggered to eject one bound guest and take up another.This work was supported by the European Research Council (695009) and the UK Engineering and Physical Sciences Research Council (EPSRC EP/M008258/1). The authors thank the Department of Chemistry NMR Facility at the University of Cambridge for performing some NMR experiments and the EPSRC UK National Mass Spectrometry Facility at Swansea University for carrying out high-resolution mass spectrometry. D.Z. acknowledges a Herchel Smith Research Fellowship from the University of Cambridge. J.D.T. acknowledges the Rashkind Family Endowment and the Chenery Endowment from Randolph-Macon College

Coordination Cages Selectively Transport Molecular Cargoes Across Liquid Membranes.

Chemical purifications are critical processes across many industries, requiring 10-15% of humanity's global energy budget. Coordination cages are able to catch and release guest molecules based upon their size and shape, providing a new technological basis for achieving chemical separation. Here, we show that aqueous solutions of FeII4L6 and CoII4L4 cages can be used as liquid membranes. Selective transport of complex hydrocarbons across these membranes enabled the separation of target compounds from mixtures under ambient conditions. The kinetics of cage-mediated cargo transport are governed by guest binding affinity. Using sequential transport across two consecutive membranes, target compounds were isolated from a mixture in a size-selective fashion. The selectivities of both cages thus enabled a two-stage separation process to isolate a single compound from a mixture of physicochemically similar molecules

Spreadsheet-Based Computational Predictions of Isotope Effects

The focus of this chapter is a tutorial-style implementation of a dual (H-S and B-M) spreadsheet approach to calculating IEs. After introducing the requisite equations, we outline their incorporation into a spreadsheet that analyzes an easily computed example from the literature. By working through this example, the reader will be enabled to predict IEs using this dualistic approach or, at the very least, gain a better appreciation for results produced by fully integrated programs. IE calculations are now fairly routine and accurately predict experimental observations in the vast majority of cases. To make this point, the chapter concludes with a description of several studies that have featured KIE or EIE estimations, so that the utility of these calculations can be fully appreciated.https://digitalcommons.chapman.edu/sees_books/1014/thumbnail.jp

Guest Binding Drives Host Redistribution in Libraries of CoII 4 L4 Cages.

Two CoII 4 L4 tetrahedral cages prepared from similar building blocks showed contrasting host-guest properties. One cage did not bind guests, whereas the second encapsulated a series of anions, due to electronic and geometric effects. When the building blocks of both cages were present during self-assembly, a library of five CoII LA x LB 4-x cages was formed in a statistical ratio in the absence of guests. Upon incorporation of anions able to interact preferentially with some library members, the products obtained were redistributed in favor of the best anion binders. To quantify the magnitudes of these templation effects, ESI-MS was used to gauge the effect of each template upon library redistribution

Cooperative Loading and Release Behavior of a Metal–Organic Receptor

In order to design artificial chemical systems that are capable of achieving complex functions, it is useful to design synthetic receptors that mimic their biological counterparts. Biological functions are underpinned by properties that include specific binding with high affinity and selectivity, cooperativity, and release triggered by external stimuli. Here we show that a metal–organic receptor constructed through subcomponent self-assembly can selectively and cooperatively load and release oxocarbon anions. The flexible coordination spheres of its cadmium(II) centers allow the receptor to dynamically adjust its structure upon exchanging four triflate or triflimide counterions for two oxocarbon anions, resulting in strong cooperativity and very tight binding, with an apparent association constant for C5O52– of 5 × 1010 M–1. Substituting the cadmium(II) ions for copper(I) by switching solvent prompted a structural reorganization and release of the oxocarbon anions. Its cooperative behavior allows the receptor to carry a greater payload than would be possible in a noncooperative analogue

Coordination Cages Transport Molecular Cargoes Across Liquid Membranes

Chemical purifications are critical processes across many industries, requiring 10 - 15% of humanity’s global energy budget1,2. Coordination cages are able to catch and release guest molecules based upon their size and shape3,4, providing a new technological basis for achieving chemical separation. Here we show that aqueous solutions of FeII4L6 and CoII4L4 cages can be used as liquid membranes. Selective transport of complex hydrocarbons across these membranes enabled the separation of target compounds from mixtures under ambient conditions. The kinetics of cage-mediated cargo transport are governed by guest binding affinity. Using sequential transport across two consecutive membranes, target compounds were isolated from a mixture in a size-selective fashion. The selectivities of both cages thus enabled a two-stage separation process to isolate a single compound from a mixture of physicochemically similar molecules.</p

Commodity Prices and Appropriate Technology—Some Lessons from Tin Mining

This paper looks at the economics of the choice of technique in a developing country (Malaysia) as between a labour-intensive, locally developed method of production (gravel pump tin mining) and a capitabintensive method (tin dredging) developed by foreign firms. The ‘appropriateness ‘ of each technique is evaluated by cost-benefit analysis, which finds that rankings by private and by social profitabilities are sensitive both to the discount rate (as one might expect) and (rather surprisingly) to the product price. The paper suggests these findings constitute a new argument in favour of schemes to stabilise primary commodity prices