Binding studies of cucurbit[7]uril with gold nanoparticles bearing different surface functionalities (original) (raw)
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A General Picture of Cucurbit[8]uril Host-Guest Binding: Recalibrating Bonded Interactions
Atomic-level understanding of the dynamical feature of host-guest interactions remains a central challenge in supramolecular chemistry. The remarkable guest binding behavior of the Cucurbiturils family of supramolecular containers makes them promising drug carriers. Among Cucurbit[n]urils, Cucurbit[8]uril (CB8) has intermediate portal size and cavity volume. It can exploit almost all host-guest recognition motifs formed by this host family. In our previous work, an extensive computational investigation of the binding of 7 commonly abused and structurally diverse drugs to the CB8 host was performed and a general dynamical binding picture of CB8-guest interactions was obtained. Further, two widely used fixed-charge models for drug-like molecules were investigated and compared in great detail, aiming at providing guidelines in choosing an appropriate charge scheme in host-guest modelling. Iterative refitting of atomic charges leads to improved binding thermodynamics and the best root-m...
The Journal of organic chemistry, 2018
We present a simple, direct method to prepare monohydroxylated-cucurbit[7]uril (CB7-OH) through the direct oxidation of its precursor host, cucurbit[7]uril (CB7). Although the conversion takes place in low yield (14%), the isolation of CB7-OH from the reaction mixture is straightforward and the unreacted CB7 can be easily recovered. ITC measurements with several selected guests confirmed that CB7-OH binds all of them in aqueous solution with similar, albeit slightly lower, binding affinities than those observed with the unmodified CB7 host. ESI mass spectrometric competition experiments are consistent with the ITC measurements. A variety of spectroscopic and voltammetric measurements also verify that the CB7-OH complexes exhibit essentially identical properties to those of the CB7 com-plexes. DFT computational data also confirm the similar thermodynamic stabilities and structures of the CB7-OH and CB7 inclusion complexes. Finally, the high thermodynamic stability of the CB7-OH compl...
Host-guest interaction of cucurbit[7]uril with para- nitrophenol: A weakly binding inclusion complex
2017
Host-guest interaction between water soluble rigid molecular container cucurbit[7]uril (CB[7]) and a water soluble organic guest para-nitrophenol (PNP) has been investigated using H NMR spectroscopy and isothermal titration calorimetry. The stoichiometry, binding constant and other thermodynamic parameters of complexation have been obtained which show the formation of weakly binding 1:1 inclusion complex resulting from enthalpyentropy compensation. Cyclic voltammetry study of PNP-CB[7] complex in acidic pH reveals a large cathodic shift in the reduction potentials of PNP, indicating either stabilization of PNP or destabilization of the electro-reduced product inside CB[7] cavity.
Acyclic Cucurbit[ n ]uril Congeners Are High Affinity Hosts
The Journal of Organic Chemistry, 2010
We present the design, synthesis via methylene bridged glycoluril tetramer building blocks, and charaterization of acyclic cucurbit [n]uril congeners that function as hosts for a wide variety of ammonium ions in water. The X-ray crystallographic characterization of the free host and its complexes with p-xylylenediamine and spermine establish the flexibility of the methylene bridged backbone of the acyclic cucurbit[n]uril congeners that allow them to adapt to the structural features of the guest. We find that the acyclic cucurbit[n]uril congeners;with their four contiguous methylene bridged glycoluril units and two aromatic o-xylylene walls bearing CO 2 H substituents;bind to ammonium ions in buffered water with values of K a ranging from ∼10 5 M -1 to greater than 10 9 M -1 . Similar to the cucurbit[n]uril family of hosts, we find that increasing the concentration of metal cations in the buffer reduces the affinity of the acyclic cucurbit[n]uril congener toward guests by competitive binding at the ureidyl CdO portals. Although the acyclic cucurbit[n]uril congeners retain the ability to bind to ammonium ions with high affinity, they do so with lower selectivity than cucurbit[n]urils presumably do to the structural flexibility of the hosts. A methylene bridged glycoluril tetramer model compound that lacks the substituted o-xylylene walls is a much lower affinity host, which establishes the importance of these rings on the overall recognition behavior of the acyclic cucurbit[n]uril congeners. Overall, the results in this paper establish that acyclic cucurbit-[n]uril receptors that contain four or more contiguous methylene bridged glycoluril units retain many of the excellent recognition properties of the cucurbit[n]uril family.
Cucurbit[7]uril-Tetramethylrhodamine Conjugate for Direct Sensing and Cellular Imaging
Journal of the American Chemical Society, 2016
This paper describes the design and synthesis of a conjugate (Q7R) comprising the synthetic host cucurbit[7]uril (Q7) linked to the fluorescent dye tetramethylrhodamine (TMR), and the characterization of its optical and guest-binding properties as well as its cellular uptake. Q7R was synthesized in two steps from monofunctionalized azidobutyl-Q7 and NHS-activated TMR. The fluorescence of Q7R is quenched upon guest binding, and this observable was used to determine equilibrium dissociation constant (Kd) values. Unexpectedly, the Kd values for guests binding to Q7R and to unmodified Q7 were essentially identical. Therefore, Q7R can directly report binding to Q7 without an energetic penalty due to the conjugated fluorophore. This result demonstrates a potentially general strategy for the design of single-component host-indicator conjugates that respond sensitively to analytes without perturbing the binding properties of the host. The unique properties of Q7R enabled measurement of Kd v...
2008
1. Experimental Section 1.1 Chemicals: 2-methyl naphthalene, N-Bromosuccinimide (NBS), 2,2’-Azobisisobutyronitrile (AIBN) and 3-Aminopropyltriethoxy-silane (APS) was purchased from Aldrich. Potassium hexacyanoferrate, ferrocene, ethanol and acetonitril were obtained from Beijing Chemicals Company. All other chemicals were obtained from local commercial sources. All the chemicals involved in our experiments were of analytical grade. CB[6] was synthesized as described by Mock. CB[7] and CB[8] were synthesized according to the procedure by Day and Kim. The synthesis of 2-(naphthalen-2-ylmethyl) malonic acid is described as below. Gold nanoparticles with a mean diameter of 20 nm were prepared following our previous work. Deionized water was further purified with RF ultrapure water system. Gold substrates were obtained by evaporating Cr and then Au on glass substrates.
Journal of Mass Spectrometry, 2006
When an intramolecular cavity exists in a molecule, it can trap another chemical species to form a host-guest complex. We examine the formation of such an inclusion complex with cucurbit[n]uril (CBn, n = 6, 7) as the host to trap alkali metal or ammonium ions as the guest, by electrospray ionization mass spectrometry (ESI-MS). The results show that the inclusion complexes are formed between the three-dimensional cylinder of CBn hosts and the guest cations. Selectivity of the complex formation is dependent both on (1) ion-dipole interactions between the cylindrical portal of the CBn hosts and the guest cations and (2) the hydrophobic interactions at the inner cavity of CBn.