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A low-energy collision induced dissociation (CID) (low-energy CID) approach that can determine both activation energy and activation entropy has been used to evaluate gas-phase binding energies of host-guest (H-G) complexes of a heteroditopic hemicryptophane cage host (Zn (II)@1) with a series of biologically relevant guests. In order to use this approach, preliminary calibration of the effective temperature of ions undergoing resonance excitation is required. This was accomplished by employing blackbody infrared radiative dissociation (BIRD) which allows direct measurement of activation parameters. Activation energies and pre-exponential factors were evaluated for more than 10 H-G complexes via the use of low-energy CID. The relatively long residence time of the ions inside the linear ion trap (maximum of 60 s) allowed the study of dissociations with rates below 1 s-1. This possibility, along with the large size of the investigated ions, ensures the fulfilment of rapid energy exchange (REX) conditions and, as a consequence, accurate application of the Arrhenius equation. Compared with the BIRD technique, low-energy CID allows access to higher effective temperatures, thereby permitting one to probe more endothermic decomposition pathways. Based on the measured activation parameters, guests bearing a phosphate (-OPO32-) functional group were found to bind more strongly with the encapsulating cage than those having a sulfonate (-SO³-) group; however, the latter ones make stronger bonds than those with a carboxylate (-CO2-) group. In addition, it was observed that the presence of trimethylammonium (-N(CH3)3+) or phenyl groups in the guest's structure improves the strength of H-G interactions. The use of this technique is very straightforward, and it does not require any instrumental modifications. Thus, it can be applied to other H-G chemistry studies where comparison of bond dissociation energies is of paramount importance. [ABSTRACT FROM AUTHOR]

In a previous work, the ability of gold-carbonyl bond dissociation energies (BDEs) to describe ligand effects in gold(I) complexes was probed using collision-induced dissociation measurements. Despite the large experimental error of the technique, results agreed with theoretical description of these effects. We propose here another experimental approach to evaluate the BDEs of [LAu-CO]+ complexes, by using Blackbody Infrared Radiative Dissociation (BIRD) method which is able to provide absolute energetic measurements. To this aim, the dissociation of 8 gold-carbonyl complexes was studied with this approach to obtain their Arrhenius activation energies. Because these complexes do not reach the rapid energy exchange (REX) limit conditions, critical energies of these dissociations were then determined using the kinetic data and an Equilibrium Truncated Thermal (ETT) internal energy distribution model implemented in the RRKM-QET MassKinetics software. To validate our approach, the known critical energies of proton-bound amino acid dimers were first reinvestigated using this model. The results are in excellent agreement with those reported in the literature. This indicates that the assumptions of this simple model are reasonable and allow the determination of accurate dissociation energies. For [LAu-CO]+ complexes, even though a shift (from 0.18 to 0.26 eV) is observed between binding energies obtained and calculated values, a linear tendency between these two sets of data is still obtained. These results validate the use of BIRD in combination with equilibrium truncated thermal internal energy distributions model to obtain dissociation energies for relatively small ions. It is also shown herein that the measure of the gold-carbonyl bond dissociation energies is a good descriptor of ligand effects in gold(I) complexes that may be reliably evaluated using the BIRD technique. [Display omitted] • BDE of gold(I) carbonyl complexes are determined by BIRD and RRKM modeling. • BDE are in agreements with high-level theoretical values. • Gold(I) carbonyl complexes are formed by ion-molecule reactions. • The electronic effects of ligands on Au(I) complexes are studied. [ABSTRACT FROM AUTHOR]