Modes of Micromolar Host-Guest Binding of ß-Cyclodextrin Complexes Revealed by NMR Spectroscopy in Salt Water.

Multitopic supramolecular guests with finely tuned affinities toward widely explored cucurbit[n]urils (CBs) and cyclodextrins (CDs) have been recently designed and tested as functional components of advanced supramolecular systems. We employed various spacers between the adamantane cage and a cationic moiety as a tool for tuning the binding strength toward CB7 to prepare a set of model guests with KCB7 and Kß-CD values of (0.6-5.0) × 1010 M-1 and (0.6-2.6) × 106 M-1, respectively. These accessible adamantylphenyl-based binding motifs open a way toward supramolecular components with an outstanding affinity toward ß-cyclodextrin. 1H NMR experiments performed in 30% CaCl2/D2O at 273 K along with molecular dynamics simulations allowed us to identify two arrangements of the guest@ß-CD complexes. The approach, joining experimental and theoretical methods, provided a better understanding of the structure of cyclodextrin complexes and related molecular recognition, which is highly important for the rational design of drug delivery systems, molecular sensors and switches.

Gas-phase fragmentation of 1-adamantylbisimidazolium salts and their complexes with cucurbit[7]uril studied using selectively 2 H-labeled guest molecules.

RATIONALE: Bisimidazolium salts (BIMs) represent an interesting family of ditopic ligands that are used in the construction of supramolecular systems with hosts based on cyclodextrins or cucurbit[n]urils. Understanding the fragmentation mechanism of individual BIMs and how this mechanism changes after complexation with cucurbit[n]urils can bring new insight into the intrinsic host-guest relationship, thereby allowing utilization of mass spectrometry to describe binding behavior. METHODS: Selectively 2 H-labeled bisimidazolium salts were prepared and fully characterized by spectroscopic methods. All MSn experiments were conducted in the positive-ion mode using an electrospray ionization (ESI) ion-trap mass spectrometer. The structures of the proposed fragments were supported by theoretical optimizations performed at the B3LYP/6-31G(d) level of density functional theory (DFT) using the Spartan'14 program. RESULTS: Using selectively deuterium-labeled isotopologues of two adamantylated bisimidazolium salts and DFT calculations, we describe the fragmentation pathways of bisimidazolium salts. The release of two important adamantane moieties, [C11 H17 ]+ and C11 H16 , from M2+ was determined, although the former was strongly preferred. In contrast, when M2+ was complexed with CB7, the neutral loss of the C11 H16 fragment was favored. The fragmentation pattern strongly depended on the steric hindrance of the M2+ guest against slippage of the CB7 unit over the guest molecular axle. CONCLUSIONS: The structures of two adamantane-based fragments and the mechanisms of their formation were rationalized. Two distinct geometric arrangements for the adamantane cage inside the CB7 cavity were hypothesized to explain the differences in the fragmentation patterns for guests with minimal, moderate, and high steric hindrance. This finding brings new insight into the understanding of intrinsic behavior of the adamantane-based guests inside the CB7 cavity.

1-(Bromo-meth-yl)adamantane.

The title compound, C(11)H(17)Br, has crystallographically imposed mirror symmetry in the solid state with mol-ecules bis-ected by mirror planes parallel to the crystallographic ac plane (five C atoms, three H atoms and the Br atom lie on the mirror plane). The asymmetric unit contains one half-mol-ecule. The crystal packing is stabilized only via weak non-specific van der Waals inter-actions.

The effect of ripening and storage conditions on the distribution of tyramine, putrescine and cadaverine in Edam-cheese.

The aim of the work was to describe the development of selected biogenic amines (histamine, tyramine, putrescine and cadaverine) in 4 layers of Dutch-type cheese (Edam-cheese) depending on 3 ripening/storage regimes during a 98-day period. Biogenic amines were analysed by means of ion-exchange chromatography. A further goal was to identify microbial sources of biogenic amines in the material analysed. Phenotype characterization and repetitive sequence-based PCR fingerprinting were used to identify the isolated bacteria. The highest content of tyramine, putrescine and cadaverine was determined in cheeses stored in a ripening cellar at a temperature of 10 degrees C during the whole observation period. Lower biogenic amines content was determined in samples which were moved into a cold storage device (5 degrees C) after 38 days of storage in a ripening cellar (10 degrees C). The lowest concentrations of biogenic amines were detected in cheeses which were moved into a cold storage device (5 degrees C) after 23 days of storage in a ripening cellar (10 degrees C). During the 98-day period, histamine was not detected in any of the regimes. Within the cheeses analysed, non-starter lactic acid bacteria Lactobacillus curvatus, Lactobacillus casei/paracasei and Lactobacillus plantarum were detected as the main producers of the biogenic amines tested. In starter bacteria Lactococcus lactis subsp. lactis and Lactococcus lactis subsp. cremoris the decarboxylase activity tested was not detected.