Mixed-Monolayer-Protected Au 25

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Measuring H-Bonding in Supramolecular Complexes by Gas Phase Ion-Molecule Reactions

H/D and guest-exchange ion-molecule reactions have been used as a new tool to elucidate the operation of multiple hydrogen bonding in gas-phase complexes formed between phosphonate cavitands and ethyl-substituted ammonium ions

Noncovalent Complexation of Monoamine Neurotransmitters and Related Ammonium Ions by Tetramethoxy-Tetraglucosylcalix[4]arene

The noncovalent complexation of monoamine neurotransmitters and related ammonium and quaternary ammonium ions by a conformationally flexible tetramethoxy glucosylcalix[4]arene was studied by electrospray ionization Fourier transform ion cyclotron resonance (ESI-FTICR) mass spectrometry. The glucosylcalixarene exhibited highest binding affinity towards serotonin, norepinephrine, epinephrine, and dopamine. Structural properties of the guests, such as the number, location, and type of hydrogen bonding groups, length of the alkyl spacer between the ammonium head-group and the aromatic ring structure, and the degree of nitrogen substitution affected the complexation. Competition experiments and guest-exchange reactions indicated that the hydroxyl groups of guests participate in intermolecular hydrogen bonding with the glucocalixarene

Noncovalent complexation of glucosylthioureidocalix[4]arenes with carboxylates and their gas-phase characteristics – An ESI-FTICR mass spectrometric study

The noncovalent complexation of three glucosylcalix[4]arenes (1-3) towards 23 mono- and dicarboxylic acid anions were studied by ESI-FTICR mass spectrometry. Competitive complexation, collision-induced dissociation and gas-phase H/D-exchange experiments were performed to obtain information on selectivity of calixarenes towards carboxylates and characteristics of their complexes. The flexibility and number of glucose units of the host and the spatial disposition of the hydrogen bonding groups on the carboxylate guests were found to affect the selectivity of complexation strongly. The glucosylcalixarenes exhibited particular selectivity for dicarboxylic acid anions incorporating π-systems, and clear isomeric selectivity was observed for isophthalic among phthalic acid anions and for fumaric acid over maleic acid anio

Hydrogen Bonding in Phosphonate Cavitands: Investigation of Host-Guest Complexes with Ammonium Salts

The H-bonding in alkylammonium complexes of phosphonate cavitands were studied by mass spectrometric methods and theoretical calculations. The alkylammonium ions included primary, secondary, and tertiary methyl- and ethylammonium ions. Their complexation with mono-, tetra-, and two di-phosphonate cavitands, which differ according to the number and position of H-bond acceptor P = O groups, was evaluated by using different competition experiments, energy-resolved CID, gas-phase H/D-exchange, and ligand-exchange reactions, together with ab initio theoretical optimization of the complexes. The phosphonate cavitands with two or more adjacent P = O groups were found to be selective towards secondary alkylammonium ions, due to simultaneous formation of two stable hydrogen bonds. In the ion-molecule reactions (both H/D- and ligand-exchange), the formation of two stable hydrogen bonds was observed either to slow down the reaction or to completely prevent it. This was, however, limited to situations where two hydrogen bonds are formed between the H-bond donor sites of the alkyl ammonium ion and the vicinal H-bond acceptor sites of the cavitand

Large glucosylthioureidocalixarenes: selective hosts for mono- and bisphosphonates

Non-covalent complexation of mono- and bisphosphonates by hexaglucosylthioureidocalix[6]arene and octaglucosylthioureidocalix[ 8]arene was studied by electrospray ionisation Fourier transform ion cyclotron resonance mass spectrometry. Glucosylthioureidocalix[8]arene formed 1:1 and 1:2 complexes with bisphosphonates, with a marked preference towards risedronate, clodronate, zoledronate and etidronate. In contrast, up to four guest molecules were bound in the case of monophosphonates, suggesting a different type of binding in comparison to bisphosphonates. Hexaglucosylthioureidocalix[ 6]arene also formed complexes with phosphonates with a somewhat similar binding selectivity. Interestingly, the addition of calcium ions into the sample of etidronate–glucosylthioureidocalix[8]arene complex resulted in a complete release of the guest due to the very high affinity between calcium and bisphosphonate. In the gas-phase hydrogen/deuterium exchange reactions, glucosylthioureidocalix[8]arene exhibited a number of exchangeable hydrogens and a bimodal exchange distribution was observed, suggesting a presence of multiple gas-phase conformations. Surprisingly, no exchange or very slow exchange for the complexes of glucosylthioureidocalix[8]arene was observed

Glucosylthioureidocalix[4]arenes: synthesis, conformations and gas-phase recognition of amino acids

The gas-phase recognition of native amino acids and the conformational properties of three glucosylthioureidocalix[4]arenes (1-3) were studied theoretically and experimentally using ab initio calculations, ESI-FTICR, 1H and 13C NMR MS. The conformational and complexation properties of the glucocalixarenes were dependent on the number of glucose units at the upper rim and the length of the alkyl chains at the lower rim of the calixarene skeleton. ESI-MS experiments showed the compounds to form 1:1 complexes with the amino acids, with a marked preference for amino acids containing an aromatic nucleus and an additional H-bonding group in their side chain (Trp, Tyr, Phe ≫ Ser, Leu and Asp). The experimental data were rationalized by the results of ab initio calculations. ESI-MS competitions carried out with enantiomeric-labelled (EL) amino acids showed enantiomeric selectivities ranging from 0.61 (Phe(D)/Phe(L) with ligand 3) to 2.58 (Tyr(D)/Tyr(L) with ligand 2). In gas-phase hydrogen-deuterium (H/D) exchange reactions, diglucosylcalix[4]arene 2 exhibited extremely slow exchange rates, which were attributed to the close proximity and strong hydrogen bonding between the facing glucosylthioureido groups. H/D exchange rates were much higher for the tetraglucosylcalix[4]arenes 1 and 3 and their amino acid complexes, and the more rigid tetrapropoxy derivative 3 showed more selective H/D exchange reactions than the calixarene 1. Bi- or trimodal H/D exchange distribution was observed for the tetraglucosyl derivatives indicating that these ligands exist in multiple isomeric forms in gas phase

Supramolecular Sensing with Phosphonate Cavitands

Phosphonate cavitands are an emerging class of synthetic receptors for supramolecular sensing. The molecular recognition properties of the third-generation tetraphosphonate cavitands toward alcohols and water at the gas–solid interface have been evaluated by means of three complementary techniques and compared to those of the parent mono- and diphosphonate cavitands. The combined use of ESI-MS and X-ray crystallography defined precisely the host–guest association at the interface in terms of type, number, strength, and geometry of interactions. Quartz crystal microbalance (QCM) measurements then validated the predictive value of such information for sensing applications. The importance of energetically equivalent multiple interactions on sensor selectivity and sensitivity has been demonstrated by comparing the molecular recognition properties of tetraphosphonate cavitands with those of their mono- and diphosphonate counterparts

Selective gas adsorption by calixarene-based porous octahedral M32 coordination cages

Giant octahedral M32 coordination cages were prepared via self-assembly of sulfonylcalix[4]arene-supported tetranuclear M(II) clusters (M = Co, Ni) with hybrid linker based on tris(dipyrrinato)cobalt(III) complexes appended with peripherical carboxylic groups. Due to intrinsic and extrinsic porosity, the obtained solid-state supramolecular architectures demonstrated good performance as adsorbents for the separation of industrially important gases mixtures.peerReviewe