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Exciton coupling between two or more chlorophyll (Chl) pigments is a key mechanism associated with the color tuning of photosynthetic proteins but it is difficult to disentangle this effect from shifts that are due to the protein microenvironment. Herein, we report the formation of the simplest coupled system, the Chl a dimer, tagged with a quaternary ammonium ion by electrospray ionization. Based on action spectroscopic studies in vacuo, the dimer complexes were found to absorb 50–70 meV to the red of the monomers under the same conditions. First-principles calculations predict shifts that somewhat depend on the relative orientation of the two Chl units, namely 50 and 30 meV for structures where the Chl rings are stacked and unstacked, respectively. Our work demonstrates that Chl association alone can produce a large portion of the color shift observed in photosynthetic macromolecular assemblies., B.F.M. acknowledges funding from the Portuguese Foundation for Science and Technology (CONT_DOUT/11/UC/405/10150/18/2008) and thanks the DIPC and CFM (UPV/EHU) and the Laboratory for Advanced Computation (University of Coimbra) for support. S.B.N. acknowledges support from the Danish Council for Independent Research (4181-00048B) and the Villum Foundation. A.R. acknowledges financial support from the European Research Council (ERC-2010-AdG-267374), a Spanish grant (FIS2013-46159-C3-1-P), Grupos Consolidados (IT578-13), AFOSR (FA2386-15-1-0006), AOARD (144088), the H2020-NMP-2014 project MOSTOPHOS (SEP-210187476), and COST Action (MP1306, “EUSpec”).

The MeCOCH2CMe2 ligand in X3SnCMe2CH2COMe (2; X = halide) acts as a C,O-chelating group both in the solid state and in non-coordinating solutions. The intramolecular SnO bond lengths in trigonal bipyramidal 2 (X = Cl and I), as determined by X-ray crystallography, indicate that the stronger interaction occurs in 2 X = Cl. Comparisons with the SnO bond lengths in the estertin trihalides, X3SnCH2CH2CO2R (1; R = Me), suggest that the latter form stronger chelates than do 2. In chlorocarbon solution, 2 (X = Cl, I) undergoes exchange reactions, as shown by NMR spectra, to give all possible halide derivatives, ∑(ClnI3−nSnCMe2CH2COMe) (n = 0–3). Various ab initio calculations on 2 and X3SnCH2CH2COMe (3) have been carried out. Comparisons of the theoretical and experimental structures of 2 for X = Cl or I are reported. Copyright © 2005 John Wiley & Sons, Ltd.

Sequestering sea squirts: Liquid chromatography with parallel inductively coupled plasma mass spectrometry/electrospray mass spectrometry was used to discover and identify novel lipophilic metal complexes in the solvent extract of the ascidian Eudistoma gilboviride. Using these tools it is now possible to examine whether such complexes play an integral part in an organism's physiology.

Studies on the Thz, Thn and Oxn containing cyclic peptides, lissoclinamides 9 ( 9 ) and 10 ( 10 ) isolated from the Indo-Pacific ascidian (seasquirt) Lissoclinum patella have delineated their metal binding selectivity. MS and CD competition studies show that lissoclinamide 10 ( 10 ) shows selectivity for Cu 2+ in the presence of an excess of Zn 2+ whereas lissoclinamide 9 ( 9 ) is less selective for Cu 2+ . Comparison of the solution state conformations derived from nOe restrained molecular dynamics and additional Monte–Carlo conformational searches suggested binding environments for the Cu 2+ which confirmed the MS measurements and suggested a reason for the selectivity in the case of lissoclinamides 9 and 10.