Attachment of ferrocene nanotubes on beta-cyclodextrin self-assembled monolayers with molecular recognitions

Self-Assembling Peptidic Bolaamphiphiles for Biomimetic Applications

Bolaamphiphile, which is a class of amphiphilic molecules, has a unique structure of two hydrophilic head groups at the ends of the hydrophobic center. Peptidic bolaamphiphiles that employ peptides or amino acids as their hydrophilic groups exhibit unique biochemical activities when they self-organize into supramolecular structures, which are not observed in a single molecule. The self-assembled peptidic bolaamphiphiles hold considerable promise for imitating proteins with biochemical activities, such as specific affinity toward heterogeneous substances, a catalytic activity similar to a metalloenzyme, physicochemical activity from harmonized amino acid segments, and the capability to encapsulate genes like a viral vector. These diverse activities give rise to large research interest in biomaterials engineering, along with the synthesis and characterization of the assembled structures. This review aims to address the recent progress in the applications of peptidic bolaamphiphile assemblies whose densely packed peptide motifs on their surface and their stacked hydrophobic centers exhibit unique protein-like activity and designer functionality, respectively.

Nanoparticles generated from a tryptophan derivative: physical characterization and anti-cancer drug delivery

Surging reports of peptide-based nanosystems and their growing potency in terms of biological utility demand for the search of newer and simpler peptide-based systems that could serve as smart templates for the development of self-assembled nanostructures. Use of simple amino acids as monomeric building blocks for synthesizing ensembles of nanostructures have gained momentum in this direction with some reports focusing on the development of nanosystems from single or modified single amino acids. In this work, we have demonstrated self-assembly and nanoparticle formation ability of a single amino acid derivative, N-alpha-(9-fluorenylmethyloxycarbonyl)-N(in)-tert-butyloxycarbonyl-L-tryptophan [Fmoc-Trp(Boc)-OH]. The nanoparticles formed by the amino acid were found to be stable to various environmental perturbations like temperature, salts and showed responsiveness to pH change. These were capable of loading and releasing different bioactive molecules and were biocompatible. These systems demonstrated high cellular uptake and doxorubicin-loaded nanoparticles were found to be more efficient in killing glioma cells as compared to the drug alone. Thus, their simple amino acid-based origin along with the ability to ferry bioactive molecules to various cells, endows them the suitability for future applications in the field of drug delivery.

A ferrocene-based multiple-stimuli responsive organometallogel

Three new ferrocene-peptide compounds were designed and prepared. We investigated their gelling abilities and found that two of them were capable of gelling various organic solvents, especially alcohols. Gels also formed in mixed alcohol-water solvents, which decreased the critical gelation concentration (CGC) of the gels. Compound 1, comprised of a dipeptide (Phe-Phe) and ferrocene, acted as a novel low-molecular-weight gelator in the formation of metallogel 1 in isopropanol-water (v/v = 1 : 1). This gelation was found to be reversible under redox stimuli; changing of the redox state of ferrocene induced a reversible gel-sol phase transition. Additionally, gel 1 responded to β-CD as a result of host-guest interactions between this compound and ferrocene. With the addition of β-CD, the gel network gradually broke down, as demonstrated by SEM.

Reversible and oriented immobilization of ferrocene-modified proteins

Adopting supramolecular chemistry for immobilization of proteins is an attractive strategy that entails reversibility and responsiveness to stimuli. The reversible and oriented immobilization and micropatterning of ferrocene-tagged yellow fluorescent proteins (Fc-YFPs) onto β-cyclodextrin (βCD) molecular printboards was characterized using surface plasmon resonance (SPR) spectroscopy and fluorescence microscopy in combination with electrochemistry. The proteins were assembled on the surface through the specific supramolecular host-guest interaction between βCD and ferrocene. Application of a dynamic covalent disulfide lock between two YFP proteins resulted in a switch from monovalent to divalent ferrocene interactions with the βCD surface, yielding a more stable protein immobilization. The SPR titration data for the protein immobilization were fitted to a 1:1 Langmuir-type model, yielding K(LM) = 2.5 × 10(5) M(-1) and K(i,s) = 1.2 × 10(3) M(-1), which compares favorably to the intrinsic binding constant presented in the literature for the monovalent interaction of ferrocene with βCD self-assembled monolayers. In addition, the SPR binding experiments were qualitatively simulated, confirming the binding of Fc-YFP in both divalent and monovalent fashion to the βCD monolayers. The Fc-YFPs could be patterned on βCD surfaces in uniform monolayers, as revealed using fluorescence microscopy and atomic force microscopy measurements. Both fluorescence microscopy imaging and SPR measurements were carried out with the in situ capability to perform cyclic voltammetry and chronoamperometry. These studies emphasize the repetitive desorption and adsorption of the ferrocene-tagged proteins from the βCD surface upon electrochemical oxidation and reduction, respectively.

Mechanism and release rates of surface confined cyclodextrin guests

The dissociation of a cobalt bisdiphenylterpyridine, [Co(biptpy)(2)](2+), guest at mixed (γ-CD-(py)(2))-alkanethiol layers (where γ-CD-(py)(2) is di-6(A), 6(B)- deoxy-6-(4-pyridylmethyl)amino- γ-cyclodextrin) formed on platinum electrodes is reported. Cyclic voltammetry (CV) shows reversible one-electron surface confined waves consistent with the Co(2/3+) couple bound at the interface. The quantity of [Co(biptpy)(2)](3+) reduced is found to be dependent on the scan rate employed, with greater amounts at higher scan rates. This behavior is in contrast to the CD guest ferrocene, which upon oxidation to the ferrocenium ion shows little charge associated with reduction even at elevated scan rates. Chronocoulometry was conducted to systematically vary the time spent oxidizing [Co(biptpy)(2)](2+) and to measure the resulting charge associated with the reduction of [Co(biptpy)(2)](3+). It is determined experimentally that as the pulse width increases, i.e. greater time spent in the oxidizing region, the amount of charge needed to reduce [Co(biptpy)(2)](3+) decreases dramatically. This decrease, along with the CV data, suggests strongly that the [Co(biptpy)(2)](3+) dissociates from the cavity. Significantly, this dissociation of the interfacial host-guest complex occurs on a much longer timescale (the order of seconds) compared to the oxidation of [Co(biptpy)(2)](2+) to [Co(biptpy)(2)](3+), which has been measured using high speed chronoamperometry to occur with a rate contant, k(0), of approximately 10(3) s(-1). The comparison of the timescale for dissociation of the interfacial complex and for electron transfer signifies that the electron transfer step occurs before dissociation, i.e. dissociation via an EC mechanism. The dissociation mechanism of [Co(biptpy)(2)](3+) is contrasted with that of the ferrocene/ferrocenium couple.

Redox strategy for reversible attachment of biomolecules using bifunctional linkers

Soft attachment of streptavidin to β-cyclodextrin-modified pegylated SAMs was efficiently performed in a reversible and repetitive way via orthogonal bifunctional linkers involving streptavidin-biotin recognition and redox-driven multivalent host-guest (β-cyclodextrin-ferrocene) interactions.

Peptide separation through a CB[8]-mediated supramolecular trap-and-release process

We demonstrate a supramolecular peptide separation approach by the selective immobilization of peptides bearing an N-terminal tryptophan onto a CB[8]-modified gold substrate, followed by electrochemical release. The CB[8]-stabilized heteroternary complexes were characterized by (1)H NMR, ESI-MS, UV/vis, and fluorescence spectroscopy and cyclic voltammetry. Micropatterned CB[8]-modified gold substrates were found to trap only the recognizable N-tryptophan-containing peptides from a peptide mixture that could be visualized as green peptide arrays under fluorescence microscopy. Subsequently, the bound peptides were released from the modified substrates by the controlled single-electron reduction of viologen. The fully reversible trap-and-release process was repeated for 13 cycles, and the cumulative release profile of the dye-peptide conjugate was monitored by fluorescence spectroscopy, indicating that no degradation occurred.

Electrochemically controlled adsorption of Fc-functionalized polymers on beta-CD-modified self-assembled monolayers

This work presents an in situ study of the adsorption/desorption behavior of ferrocene(Fc)-functionalized linear polymers on a gold surface covered with beta-cyclodextrin(beta-CD)-modified self-assembled monolayers (SAMs). The characterization of binary SAMs obtained with HS-(CH(2))(11)-EG(6)-N(3) and HS-(CH(2))(11)-EG(4)-OH (EG, ethylene glycol) was performed using a quartz crystal microbalance with dissipation monitoring (QCM-D), cyclic voltammetry, and contact angle measurements. The functionalization of SAMs with beta-CD was made via the "click" reaction between the beta-CD monoalkyne derivative and azide groups exhibited by SAMs. The formation of the host-guest complex between SAM-beta-CD and Fc-derivatized polymers (chitosan (CHI) and poly(allylamine hydrochloride) (PAH)) was studied by QCM-D. The viscoelastic model of Voinova was used to fit QCM-D curves recorded during the adsorption and electrochemically controlled desorption of CHI-Fc and PAH-Fc on SAM-beta-CD. Using QCM-D coupled to cyclic voltammetry, we demonstrated that CHI-Fc and PAH-Fc can be successfully deposited on a SAM-beta-CD-coated gold surface forming a stable multivalent inclusion complex between Fc moieties of polymer and beta-CD cavities of SAM. We also showed that all specifically attached polymer chains can be detached from the SAM-beta-CD-coated gold surface by applying an electric field.

The Supramolecular Chemistry of Organic–Inorganic Hybrid Materials

The combination of nanomaterials as solid supports and supramolecular concepts has led to the development of hybrid materials with improved functionalities. These "hetero-supramolecular" ideas provide a means of bridging the gap between molecular chemistry, materials sciences, and nanotechnology. In recent years, relevant examples have been reported on functional aspects, such as enhanced recognition and sensing by using molecules on preorganized surfaces, the reversible building of nanometer-sized networks and 3D architectures, as well as biomimetic and gated chemistry in hybrid nanomaterials for the development of advanced functional protocols in three-dimensional frameworks. This approach allows the fine-tuning of the properties of nanomaterials and offers new perspectives for the application of supramolecular concepts.