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A photoswitchable ligand and palladium(II) ions form a dynamic mixture of self-assembled metallosupramolecular structures. The photoswitching ligand is an ortho-fluoroazobenzene with appended pyridyl groups. The E-isomer is combined with palladium(II) salts affords a double-walled triangle with composition [Pd3L6] 6+ and a distorted tetrahedron [Pd4L8] 8+ (1:2 ratio at 298 K). Irradiation with 410 nm light generates a photostationary state with ~80% of the E-isomer of the ligand which results in the selective disassembly of the tetrahedron, the more thermodynamically stable structure, and the formation of the triangle, the kinetic product. The triangle is then slowly transformed back into the tetrahedron over 2 days at 333 K. The Z-isomer of the ligand does not form any well-defined structures and has a thermal half-life of 25 days at 298K. This approach shows how a thermodynamically preferred self-assembled structure can be reversibly pumped to a kinetic trap by small perturbations of the isomer distribution using non-destructive visible light.

The a-and b-class carbonic anhydrases (CAs, EC 4.2.1.1) from the pathogenic bacterium Vibrio cholerae, VchCAa, and VchCAb, were investigated for their activation with natural and non-natural amino acids and amines. The most effective VchCAa activators were L-tyrosine, histamine, serotonin, and 4-aminoethyl-morpholine, which had K A s in the range of 8.21-12.0 mM. The most effective VchCAb activators were D-tyrosine, dopamine, serotonin, 2-pyridyl-methylamine, 2-aminoethylpyridine, and 2-aminoethylpiperazine, which had K A s in the submicromolar -low micromolar range (0.18-1.37 mM). The two bacterial enzymes had very different activation profiles with these compounds, between each other, and in comparison to the human isoforms hCA I and II. Some amines were selective activators of VchCAb, including 2-pyridylmethylamine (K A of 180 nm for VchCAb, and more than 20 mM for VchCAa and hCA I/II). The activation of CAs from bacteria, such as VchCAa/b has not been considered previously for possible biomedical applications. It would be of interest to study in more detail the extent that CA activators are implicated in the virulence and colonisation of the host by such pathogenic bacteria, which for Vibrio cholerae, is highly dependent on the bicarbonate concentration and pH in the surrounding tissue.ARTICLE HISTORY

The selective and efficient activation of strong organic bonds is one of the major goals in chemistry [1] due to the intense interest in developing more cost-effective and environmentally sustainable routes for the industrial production of chemicals. [2] Many biological enzymes containing metal-oxo active site intermediates, [2b, 3] including those that contain a non-heme high-spin (S = 2) Fe IV = O active-site intermediate, [4] can mediate reactions of relevance to organic synthesis (e.g., CÀH bond hydroxylation, alcohol oxidation, olefin epoxidation, etc.). As a result, there has been considerable interest in preparing and studying novel Fe IV =O complexes that can "mimic" these beneficial properties and provide insights into the chemistry of Fe-oxo enzyme active sites. [2b, 5] A key challenge is that high-valent Fe IV -oxo complexes in high-spin states [6] are highly reactive. For example, out of a wide range of synthetic Fe IV =O complexes that have been reported, [7] only three are high-spin (S = 2) non-heme Fe IV =O complexes, [8] and these have lifetimes that range from 7 s to 2.2 h at 25 8C. [8] Another approach for studying highly reactive complexes is to generate and investigate such species in the gas phase, where effects of solvent, counterions, and aggregation, which can all lead to degradation of reactive complexes, can either be eliminated, or carefully controlled. Such studies can potentially reveal new types of transition metal mediated reactions, which may uncover important details of reaction mechanisms and direct the development of future condensedphase catalysts. Although there have been numerous gasphase studies of Fe-oxo based ions, [9] and Fe III O + in particular, [9a,b] the chemistry of high-spin non-heme Fe IV =O complexes, of the types that have only recently been synthesized in the condensed phase, [8b,c] have not been explored in vacuo leaving a considerable gap [9c,d] between the fundamental gas-phase Fe-oxo studies and the recent advances in condensedphase high-valent non-heme Fe-oxo coordination chemistry. Herein we report the gas-phase synthesis of the high-spin complex [(bpg)Fe IV =O] + (where bpg À is N,N-bis(2-pyridinylmethyl)glycinato À ) and its reactions with methanol and ethanol. [10] Electrospray ionization (ESI) of 100 mm solutions of [(bpg)Fe(H 2 O)OFe(H 2 O)(bpg)](ClO 4 ) 2 [11] dissolved in a 10:90 acetonitrile:CH 2 Cl 2 mixture resulted in the formation of a dominant ion at m/z 320, corresponding to [(bpg)FeOFe-(bpg)] 2+ . Collision-induced dissociation (CID) of isolated [(bpg)FeOFe(bpg)] 2+ (m/z 320) leads to the formation of a population of ions at m/z 328 with a stoichiometry that corresponds to that of [(bpg)Fe IV O] + , in addition to an ion at m/z 312 corresponding to [(bpg)Fe II ] + (Figure 1 a), which is formed through charge separation of the precursor ion [Eq. (1)] in a redox disproportionation reaction. [12]Figure 1. Mass spectra obtained upon a) CID of isolated [(bpg)FeOFe-(bpg)] 2+ (30 ms activation time; 7 m/z isolation window; theoretical isotope ...