Host-guest chemistry in the gas phase: selected fragmentations of CB[6]-peptide complexes at lysine residues and its utility to probe the structures of small proteins

The gas phase host-guest chemistry between cucurbit[6]uril (CB[6]) and peptide is investigated using electrospray ionization mass spectrometry (ESI-MS). CB[6] exhibits a high preference to interacting with a Lys residue in a peptide forming a CB[6]-peptide complex. Collisionally activated CB[6] complexes of peptides yield a common highly selective fragment product at m/z 549.2, corresponding to the doubly charged CB[6] complex of 5-iminiopentylammonium (5IPA). The process involves the formation of an internal iminium ion, which results from further fragments to an a-type ion from a y-type ion, and the resulting 5IPA ion threads through CB[6]. Numerous peptides are investigated to test the generality of the observed unique host-guest chemistry of CB[6]. Its potential utility in probing protein structures is demonstrated using CB[6] complexes of ubiquitin. Low-energy collision induced dissociation yields CB[6] complex fragments, and further MS(n) spectra reveal details of the CB[6] binding sites, which allow us to deduce the protein structure in the solution phase. The mechanisms and energetics of the observed reactions are evaluated using density functional theory calculations.     

Guest-responsive,Non-proteolytic Harvest of a Cell-sheet using Controllable Host-guest Chemistry

A new non-proteolytic method to harvest a cell-sheet was demonstrated using controllable host-guest interactions which can be dissociated by treating a strong guest on demand. Fibroblast cells (NIH3T3) were grown to confluence on a 1,6-diammoniumhexane conjugated hyaluronic acid (DAH-HA) polymer which was anchored to a cucurbit[7]uril (CB[7]) surface using the host-guest interaction between DAH and CB[7]. Treating with a strong guest allowed the cultured cells to be detached from the surface as a free standing sheet. This approach demonstrated the great potential of controllable host-guest chemistry as a novel tool for non-proteolytic harvesting of cell-sheets useful for regenerative therapy.     

Ultrastable Host–Guest Complexes and Their Applications

This review describes monovalent synthetic receptor–ligand (or host–guest) pairs with extremely high binding affinity, comparable to that of the biotin–avidin pair, and their applications. Cucurbit[7]uril (CB[7]), a member of the host family cucurbit[n]uril (CB[n], n=5–8, 10), forms ultrastable host–guest complexes with ferrocene-, adamantane- or bicyclo[2.2.2]octane-based molecules having ammonium groups properly positioned to interact with the carbonyl oxygens at the portals of CB[7]. The extremely high affinity is achieved by a large enthalpic gain arising from the near perfect size/shape complementarity between the rigid CB cavity and the rigid core of the guest molecules, with the critical assistance of the positive entropy change due to the extensive dehydration of the host and guest. The high stability of the complexes allowed us and others to explore several biological applications such as immobilization of biomolecules on a solid surface, protein isolation, triggering intracellular events, and regulating enzymatic activities. These complexes with their exceptional affinity, chemical robustness, simple preparation, biocompatibility, and easy handling may replace the biotin–(strept)avidin system in diverse areas of research, including affinity chromatography, high throughput biochemical assays, imaging, and sensor technologies.     

Flexible high mobility pentacene transistor with high-k/low-k double polymer dielectric layer operating at −5 V

We report on the fabrication of pentacene-based thin-film transistors (TFTs) with a 230 nm-thick double polymer dielectric composed of 30 nm-thin low-k poly-4-vinyphenol (PVP) and 200 nm-thick high-k poly(vinylidene fluoride/trifluoroethylene) [P(VDF–TrFE)] dielectric on polyethersulfone (PES) films. Our 230 nm-thick double (high-k/low-k) polymer showed a good dielectric strength of ～2 MV/cm, a high capacitance of 26 nF/cm² with k = ～7. Based on this double polymer dielectric, our flexible pentacene TFT displayed a high saturation mobility of 1.22 cm²/V s, a threshold voltage of ?2.5 V, and on/off ratio of 10³, stably operating under ?5 V.     

Reduction‐Sensitive,Robust Vesicles with a Non‐covalently Modifiable Surface as a Multifunctional Drug‐Delivery Platform

The design and synthesis of a novel reduction‐sensitive, robust, and biocompatible vesicle (SSCB[6]VC) are reported, which is self‐assembled from an amphiphilic cucurbit[6]uril (CB[6]) derivative that contains disulfide bonds between hexaethylene glycol units and a CB[6] core. The remarkable features of SSCB[6]VC include: 1) facile, non‐destructive, non‐covalent, and modular surface modification using exceptionally strong host–guest chemistry; 2) high structural stability; 3) facile internalization into targeted cells by receptor‐mediated endocytosis, and 4) efficient triggered release of entrapped drugs in a reducing environment such as cytoplasm. Furthermore, a significantly increased cytotoxicity of the anticancer drug doxorubicin to cancer cells is demonstrated using doxorubicin‐loaded SSCB[6]VC, the surface of which is decorated with functional moieties such as a folate–spermidine conjugate and fluorescein isothiocyanate–spermidine conjugate as targeting ligand and fluorescence imaging probe, respectively. SSCB[6]VC with such unique features can be used as a highly versatile multifunctional platform for targeted drug delivery, which may find useful applications in cancer therapy. This novel strategy based on supramolecular chemistry and the unique properties of CB[6] can be extended to design smart multifunctional materials for biomedical applications including gene delivery.     

Changes in hippocampal neural response by external reward

The hippocampus is thought to contribute largely to memory processing and spatial navigation.Various research projects have shown evidence regarding these two crucial roles.However,many unknown functions of hippocampus remain.A great deal of research on the hippocampus is ongoing,but much of this research deals with single neuron,and little research has been conducted on what happens between neurons in hippocampus as they play these roles.In this paper,we intend to examine what changes hippocampal neurons undergo in response to a stimulus.Using an imbalanced,index of timedependent Gini's coefficient,the firing balance between neurons during the moment in which a stimulus is received is examined.More importantly,the different firing balances are observed in reward situation.The result demonstrates the multineuron in hippocampus fires with balance for a while when the rat has reward.In addition,time-dependent Gini's coefficient is a feature that can verify what is not shown by using existing features.