Molecular Recognition Applications Research Articles

Periodic Mesoporous Organosilicas with Domain Functionality: Synthesis and Advanced Characterization

Bifunctional periodic mesoporous organosilicas (PMOs) with —CH2—CH2—/—CH═CH— bridges have been synthesized using a salt assisted nonionic templating method. The ability to direct locations of the individual organic groups using a novel silica precursor prehydrolysis step is demonstrated. Depending on the prehydrolysis conditions the products showed either structural heterogeneities consisting of domains of the same functionality or a structurally homogeneous system, confirmed by 1H−29Si heteronuclear correlation (HETCOR) experiments. The resulting PMOs show large pore volumes (up to 1.34 cm3 g−1) and high surface areas (up to 1310 m2 g−1). The ability to form domain structures within the same mesostructure may have potential applications in molecular recognition and separation.

Synthesis of diamino-furostan sapogenins and their use as scaffolds for positioning peptides in a preorganized form

Abstract The synthesis of peptide–furostane conjugates from natural steroidal sapogenins is reported. The approach comprises the introduction of α-oriented amino groups into spirostanic sapogenins followed by reductive opening of the spiroketal chain, thus producing diamino-furostanic scaffolds suitable for further functionalization. Solid and solution-phase coupling processes were utilized for the incorporation of various α-amino acids and peptides into the furostanic skeletons. The attachment position depends on the steroidal sapogenin originally used, i.e., diosgenin or hecogenin. The resulting furostanic skeletons feature a trans A/B-ring fusion and hold the peptides in axial disposition. This characteristic ensures a preorganized alignment of the peptidic motifs, an important structural feature for future applications in molecular recognition and catalysis. A macrocyclic tripeptide–furostane conjugate was also produced by a combination of peptide coupling, Staudinger ligation, and a cyclization protocol. This work constitutes the first report on the use of furostanic sapogenins as scaffolds for positioning natural amino acids and (cyclo)peptides.

Recent Developments in Chiral Polynitrogenated Synthetic Receptors for Anions

In this mini-review, recent chiral receptors bearing polyamine and/or polyamide functional groups are reported. Two main features for their synthesis are the source of the enantiopure nitrogenated synthons and the strategy to assemble the building blocks within the receptor architecture. Combined solutions to both problems have been carried, ranging from chemoenzymatic methods to combinatorial approaches. Topics like conformational control or templation procedures are highlighted. Applications in chiral anion molecular recognition will be also discussed. Keywords: Molecular recognition, anion, chiral receptor, stereoselective, nitrogen, template

Ferrocenyl-terminated Dendrimers: Design for Applications in Molecular Electronics, Molecular Recognition and Catalysis

This micro-review shows how a simple but powerful organometallic C–H activation could be made very useful for the construction of a large variety of stars, dendritic cores, dendrons and dendrimers of variable sizes including giant dendrimers and gold-nanoparticle-cored dendrimers. The synthesis of ferrocenyl-terminated dendrimers was then achieved by reactions of chlorocarbonylferrocene with polyamino dendrimers, ferrocenylsilylation of polyolefin dendrons and dendrimers and “click” reactions of ferrocenyl acetylene with azido-terminated dendrimers. The functions of these metallodendrimers include molecular electronics (molecular batteries), molecular redox recognition and sensing and catalysis using dendritic stabilization of nanoparticle catalysts.

Interstitial Accommodation of C60 in a Surface‐Supported Supramolecular Network

Fullerene molecules have been accommodated in a supramolecular network formed by carboxyphenyl-substituted porphyrin molecules on a Au(111) surface. The adsorption of C60 leads to the opening of linear arrays of nanopores in the supramolecular network (see figure). These flexible porous supramolecular networks can selectively accommodate certain molecules and thus may have potential applications in molecular recognition and selective catalysis.

Optical enzymatic detection of glucose based on hydrogen peroxide-sensitive HiPco carbon nanotubes

We recently observed that surfactant sodium dodecyl sulfate (SDS)-encased HiPco single-walled carbon nanotubes (SWNTs) respond optically to hydrogen peroxide (H2O2) in the near-infrared region. In this report, we demonstrate that SDS-encased SWNTs immobilized with glucose oxidase (GOx) can be used to optically detect an enzymatic reaction of glucose based on their H2O2 sensitivity as well as pH sensitivity. Only the enzymatic product H2O2 induces the SWNT near-infrared spectral changes in buffer solutions (pH = 6.0), but both H2O2 and gluconic acid products do this in unbuffered solutions. The SWNT optical response to glucose possesses sensitivity and selectivity similar to an electrochemical method using carbon nanotube nanoelectrode arrays. Our results suggest possible carbon nanotube-based optical tools for molecular recognition applications.

Recoverable Solution Reaction of HiPco Carbon Nanotubes with Hydrogen Peroxide

There is increasing interest in developing single-walled carbon nanotubes (SWNTs)-based optical biosensors for remote or in vitro and in vivo sensing because the near-IR optical properties of SWNTs are very sensitive to surrounding environmental changes. Many enzyme-catalyzed reactions yield hydrogen peroxide (H(2)O(2)) as a product. To our knowledge, there is no report on the interaction of H(2)O(2) with SWNTs from the optical sensing point of view. Here, we study the reaction of H(2)O(2) with an aqueous suspension of water-soluble (ws) HiPco SWNTs encased in the surfactant sodium dodecyl sulfate (SDS). The SWNTs are optically sensitive to hydrogen peroxide in pH 6.0 buffer solutions through suppression of the near-IR absorption band intensity. Interestingly, the suppressed spectral intensity of the nanotubes recovers by increasing the pH, by decomposing the H(2)O(2) into H(2)O and O(2) with the enzyme catalase, and by dialytically removing H(2)O(2). Preliminary studies on the mechanisms suggest that H(2)O(2) withdraws electrons from the SWNT valence band by charge transfer, which suppresses the nanotube spectral intensity. The findings suggest possible enzyme-assisted molecular recognition applications by selective optical detection of biological species whose enzyme-catalyzed products include hydrogen peroxide.

De novo design of a stable N-terminal helical foldamer

A peptide NTH-18 was synthesized in which a N-terminal helix is stabilised by two crossed disulfide bonds to a C-terminal extension. The design was inspired by the structure of the neurotoxic peptide apamin, which has previously been used to stabilise helices in miniature enzymes. CD- and NMR-spectroscopy indicated that NTH-18 adopted a fold similar to that found in apamin. However, the arrangement of the elements of secondary structures was inverted relative to apamin; a N-terminal alpha-helix was connected by a reverse turn to a C-terminal extension of non-canonical secondary structure. NTH-18 displayed significant stability to heat and changes of pH. The high definition of the N-terminal end of the alpha-helix of NTH-18 should make this peptide a useful vehicle to stabilise alpha-helices in proteins with applications in protein engineering and molecular recognition.

Rapid isolation of high-affinity protein binding peptides using bacterial display

A robust bacterial display methodology was developed that allows the rapid isolation of peptides that bind to arbitrarily selected targets with high affinity. To demonstrate the utility of this approach, a large library (5 x 10(10) clones) was constructed composed of random 15-mer peptide insertions constrained within a flexible, surface exposed loop of the Escherichia coli outer membrane protein A (OmpA). The library was screened for binding to five unrelated proteins, including targets previously used in phage display selections: human serum albumin, anti-T7 epitope mAb, human C-reactive protein, HIV-1 GP120 and streptavidin. Two to four rounds of enrichment (2-4 days) were sufficient to enrich peptide ligands having high affinity for each of the target proteins. Strong amino acid consensus sequences were apparent for each of the targets tested, with up to seven consensus residues. Isolated peptide ligands remained functional when expressed as insertional fusions within a monomeric fluorescent protein. This bacterial display methodology provides an efficient process for identifying peptide affinity reagents and should be useful in a variety of molecular recognition applications.

A novel receptor based on a C3v-symmetrical PN3-calix[6]cryptand.

A C3v-symmetrical PN3-calix[6]cryptand was prepared in six steps from the known 1,3,5-tris-methylated calix[6]arene through a remarkably efficient [1 + 1] macrocyclization reaction. A 1H NMR study showed that the P,N-crypto cap rigidifies the whole edifice in a cone conformation ideal for molecular recognition applications. The ability of this new receptor to perform selective endo-complexation is illustrated with ammonium guests.

Nanolithography and Nanochemistry: Probe‐Related Patterning Techniques and Chemical Modification for Nanometer‐Sized Devices

AbstractFor Abstract see ChemInform Abstract in Full Text.

Armed Cyclen Receptors: From Three Dimensional Cation Recognition to Supramolecular Architecture.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Nanolithography and nanochemistry: probe-related patterning techniques and chemical modification for nanometer-sized devices.

The size regime for devices produced by photolithographic techniques is limited. Therefore, other patterning techniques have been intensively studied to create smaller structures. Scanning-probe-based patterning techniques, such as dip-pen lithography, local force-induced patterning, and local-probe oxidation-based techniques are highly promising because of their relative ease and widespread availability. The latter of these is especially interesting because of the possibility of producing nanopatterns for a broad range of chemical and physical modification and functionalization processes; both the production of nanometer-sized electronic devices and the formation of devices involving (bio)molecular recognition and sensor applications is possible. This Review highlights the development of various scanning probe systems and the possibilities of local oxidation methods, as well as giving an overview of state-of-the-art nanometer-sized devices, and a view of future development.

C—H Activation Approaches for the Application of Molecular Recognition to Organometallic Chemistry and Homogeneous Catalysis

AbstractFor Abstract see ChemInform Abstract in Full Text.

Steering molecular organization and host-guest interactions using two-dimensional nanoporous coordination systems.

Metal-organic coordination networks (MOCNs) have attracted wide interest because they provide a novel route towards porous materials that may find applications in molecular recognition, catalysis, gas storage and separation. The so-called rational design principle-synthesis of materials with predictable structures and properties-has been explored using appropriate organic molecular linkers connecting to metal nodes to control pore size and functionality of open coordination networks. Here we demonstrate the fabrication of surface-supported MOCNs comprising tailored pore sizes and chemical functionality by the modular assembly of polytopic organic carboxylate linker molecules and iron atoms on a Cu(100) surface under ultra-high-vacuum conditions. These arrays provide versatile templates for the handling and organization of functional species at the nanoscale, as is demonstrated by their use to accommodate C(60) guest molecules. Temperature-controlled studies reveal, at the single-molecule level, how pore size and chemical functionality determine the host-guest interactions.

Armed Cyclen Receptors: From Three Dimensional Cation Recognition to Supramolecular Architecture

Abstract The concept and examples of armed cyclens are described and some of their recent applications in molecular recognition and supramolecular chemistry are explained. Armed cyclens are characterized by a parent tetraamine ring and functionalized sidearms. They can act as three-dimensional ligands for octadentate metal complexation. They exhibit comparable logK values for Na+ complexation to bicyclic cryptands, though they have flexible, open-chained structures. Since the resulting octacoordinate metal complexes have quadruple helicated structures, they can work as unique building blocks having C4 symmetry for chiral supramolecular architecture. Cholesterol-armed cyclen typically formed a self-aggregate with the integrated chirality in aqueous solution, in which asymmetrically helicated cyclen complexes were arrayed on a supramolecular scale. The self-aggregate had asymmetrically ordered domains, in which achiral organic anions and racemic metal complexes were nicely accommodated in stereo-controlled fashions. Since the armed cyclens have broad structural variations, they are applicable as specific receptors for cation recognition at the molecular level and also as building blocks for supramolecular architecture.

Multiple hydrogen bonds tuning guest/host excited-state proton transfer reaction: its application in molecular recognition.

A molecular recognition concept exploiting multiple-hydrogen-bond fine-tuned excited-state proton-transfer (ESPT) was conveyed using 3,4,5,6-tetrahydrobis(pyrido[3,2-g]indolo)[2,3-a:3',2'-j]acridine (1a). The catalytic type 1a/carboxylic acids hydrogen-bonding (HB) complexes undergo ultrafast ESPT, resulting in an anomalously large Stokes shifted tautomer emission (lambdamax approximately 600 nm). Albeit forming a quadruple HB complex, ESPT is prohibited in the noncatalytic-type 1a/urea complexes (lambdamax approximately 430 nm). The HB configuration tuning ESPT properties lead to a feasible design for sensing multiple-HB-site analytes of biological interest.

C–H Activation approaches for the application of molecular recognition to organometallic chemistry and homogeneous catalysis

A series of metal complexes of 2-aminobenzoquinoline prepared by C–H activation show molecular recognition effects. For example, ketones bound both by N–H⋯O hydrogen bonding and by coordination to a metal show selectivity of binding and dynamic properties not found when the hydrogen bonding function is omitted. N-heterocyclic carbenes (NHCs) are prepared by C–H activation reactions of imidazolium salts with the goal of understanding and using molecular recognition effects in homogeneous catalysis. Abnormal binding via C5 is seen in some cases.

Metal oxide modification via transition metal complexes: hybrid materials characterizations and potential applications in molecular recognition

Transition metal complexes were grafted onto silicon oxide particles and fully characterized by DRIFT, XPS, SEM spectroscopies were used for two tailored purposes: (i) as modifiers of inorganic materials for molecular recognition and differentiation and (ii) as potential contrast agents for X-ray mapping in SEM to localize the variation of porosity in materials volume.

Dam-1 Molecular Sieve Forms, Fibers and Films

AbstractThe evolution of new molecular sieves and associated applications has generated a greater demand for new ways to manipulate and configure nanoporous materials. The required form of a molecular sieve may involve dramatically different length scales, ranging from shaped particles to fibers and continuous coatings. Various examples of these forms based on Dallas Amorphous Materials one (DAM-1), which was synthesized using a water soluble Vitamin E TPGS as the template, will be illustrated. In addition to potential drug delivery applications for this inorganic/organic composite, the hierarchical forms of DAM-1 may be employed in areas ranging from catalysis to sensors. The morphogenesis of DAM-1 shaped particles and its applications in molecular recognition and optical sensing will be described along with a novel process for spinning DAM-1 molecular sieve fibers. Additionally, our patented method for the fabrication of zeolite membranes, using pulsed laser deposition (PLD) will be discussed.