Templating Ability Research Articles

Conjugated bis(enaminones) as effective templates for rotaxane assembly and their post-synthetic modifications

The development of efficient methods for the synthesis of mechanically interlocked compounds is currently considered a major challenge in supramolecular chemistry. Twofold vinylogous fumaramides, a class of conjugated bis(enaminones), successfully achieve the assembly of hydrogen-bonded amide-based rotaxanes, with a templating ability comparable to that of their parent fumaramide-based systems, showcasing full conversions and impressive yields up to 92%. Computational calculations offer a compelling explanation for the remarkable efficiency of these bis(enaminones) in driving the synthesis of unprecedented rotaxanes. The reactivity of these interlocked species was thoroughly investigated, revealing that a one-step double stopper-exchange process can be successfully performed while preserving the mechanical bond. This approach facilitates the formation of controllable rotaxanes, including a three-station molecular shuttle, whose assembly via a clipping methodology is highly unselective. The internal translational motion of this latter species has been successfully controlled in a reversible way by means of a cycloaddition/retrocycloaddition sequence.

Cobalt(III) complexes with (±)-1,3-pentanediamine-N,N,N’,N’-tetraacetate. The influence of nature of alkali and alkaline earth metal counter cations on the supramolecular association of the complex

The coordination of hexadentate (±)-1,3-pentanediamine-N,N,N’,N’-tetraacetate (1,3-pndta) ligand with Co(III) has been investigated. Four octahedral [Co(1,3-pndta)]− complexes containing different counter cations, Li[Co(1,3-pndta)]⋅4H2O (1a), Li[Co(1,3-pndta)]⋅2H2O (1b), K[Co(1,3-pndta)]⋅H2O (1c) and Ca[Co(1,3-pndta)]2⋅5H2O (1d), were synthesized and structurally characterized. Single-crystal X-ray diffraction analysis, IR, NMR (1H and 13C) and electronic absorption spectroscopy were used for characterization of 1a − d. The influence of the ethyl substituent of 1,3-propanediamine chain in 1,3-pndta and the nature of metal counter cation on the structural modalities of carboxylate bridging groups in 1a − d were established by comparing with the analogous [M(1,3-pdta)] n − (1,3-pdta = 1,3-propanediamine-N,N,N’,N’-tetraacetate) and [M(1,3-pndta)] n − complexes (M = Co(III), Cr(III) and Ni(II)). Our studies have shown that the supramolecular association of the complexes is primarily governed by the size of the alkali or alkaline earth metal counter cation and its templating ability, while ethyl substituents, in most cases, prevent the formation of 3D polymeric frameworks.

Identification of a homology-independent linchpin domain controlling mouse and bank vole prion protein conversion

Prions are unorthodox pathogens that cause fatal neurodegenerative diseases in humans and other mammals. Prion propagation occurs through the self-templating of the pathogenic conformer PrPSc, onto the cell-expressed conformer, PrPC. Here we study the conversion of PrPC to PrPSc using a recombinant mouse PrPSc conformer (mouse protein-only recPrPSc) as a unique tool that can convert bank vole but not mouse PrPC substrates in vitro. Thus, its templating ability is not dependent on sequence homology with the substrate. In the present study, we used chimeric bank vole/mouse PrPC substrates to systematically determine the domain that allows for conversion by Mo protein-only recPrPSc. Our results show that that either the presence of the bank vole amino acid residues E227 and S230 or the absence of the second N-linked glycan are sufficient to allow PrPC substrates to be converted by Mo protein-only recPrPSc and several native infectious prion strains. We propose that residues 227 and 230 and the second glycan are part of a C-terminal domain that acts as a linchpin for bank vole and mouse prion conversion.

Amyloid Signaling in Filamentous Fungi and Bacteria.

Amyloids are implicated in many protein misfolding diseases. Amyloid folds, however, also display a range of functional roles particularly in the microbial world. The templating ability of these folds endows them with specific properties allowing their self-propagation and protein-to-protein transmission in vivo. This property, the prion principle, is exploited by specific signaling pathways that use transmission of the amyloid fold as a way to convey information from a receptor to an effector protein. I describe here amyloid signaling pathways involving fungal nucleotide binding and oligomerization domain (NOD)-like receptors that were found to control nonself recognition and programmed cell death processes. Studies on these fungal amyloid signaling motifs stem from the characterization of the fungal [Het-s] prion protein and have led to the identification in fungi but also in multicellular bacteria of several distinct families of signaling motifs, one of which is related to RHIM [receptor-interacting protein (RIP) homotypic interaction motif], an amyloid motif regulating mammalian necroptosis.

Functional and Templating Ability of Fluorescent RNA Aptamers in Possible Prebiotic Conditions

RNA is believed to have been central to the origin of life and may form the basis for simple synthetic cells. Herein, we investigate the role of two possible prebiotic conditions on the functional and templating ability of fluorescent RNA aptamers. Early protocells likely consisted of RNA functioning inside vesicles made of simple lipids. However, little is known about how encapsulation would affect the activity and folding of RNA. We find that confinement of the Malachite green RNA aptamer inside fatty acid vesicles increases binding affinity and locally stabilizes the bound conformation of the RNA (1). The vesicle effectively ‘chaperones’ the aptamer, consistent with an excluded volume mechanism due to confinement. Protocellular organization thereby leads to a direct benefit for the RNA. Coupled with previously described mechanisms by which encapsulated RNA aids membrane growth, this effect illustrates how the membrane and RNA might cooperate for mutual benefit. Second, Intriguing prebiotic syntheses of ribonucleotides, amino acids, and even iron-sulfur clusters rely on reactions driven by UV radiation. We irradiated two fluorescent RNA aptamers and monitored the loss of activity, folding, and the kinetics of lesion accumulation. The loss of activity differed depending on the aptamer, with the Spinach2 aptamer retaining substantial activity after long exposure times (2). The binding pocket was particularly susceptible to damage, and melting of duplex regions increased susceptibility, consistent with the view that duplex formation is protective. At the same time, susceptibility was highly variable depending on context, emphasizing the importance of studying many different RNAs to understand UV hardiness.

In situ replacement of Cu-DEN: an approach for preparing a more noble metal nanocatalyst for catalytic use

The advantage of dendritic monodisperse macromolecules’ dual templating ability was useful in the formation of silica-supported copper nanoparticles Cun@SiO2NPs.

Direct recovery of copper nanoparticles from leach pad drainage by surfactant-assisted cementation with iron powder

Copper nanoparticles were directly recovered from a leach pad drainage by surfactant-assisted cementation with iron powder. Factorial experimental designs were implemented to assess the influence of polyvinylpyrrolidone (PVP), sodium dodecyl sulfate (SDS) and temperature on cementation kinetics and copper particle size. Analysis of variance (ANOVA) was performed to quantify the effect of the investigated factors. Copper(II) was selectively reduced to metal copper by Fe powder, while Mn, Fe, Cd and Zn ions were left in solution. The cementation proceeded under enthalpic driving force and could be described by a pseudo-second-order kinetic model. Without the surfactants, the activation energy of cementation was 22.7 kJ/mol and the cemented product aggregated into micro-clusters ranging from 1 to 15 μm in size, depending on the temperature. The cementation with PVP at above 311 K was controlled by physical adsorption of PVP on Fe powder and exhibited an activation energy of about 10 kJ/mol. The average size of copper particles obtained using 4 mM PVP at 348 K was 280 nm. Adding SDS was associated with a dramatic increase in the activation energy to about 45 kJ/mol, and with the formation of nanoparticles. Using 0.2 M SDS at 348 K enabled the recovery of Cu of about 99% purity with an average particle size less than 100 nm. All results suggested that capping by SDS and PVP inhibited the cementation kinetics but provided the templating ability required to form nanoparticles.

Systematic Disruption of the Nonpolar β‐Helix Core of Hemolysin A and its Site‐Specific Effect on Protein Structure, Function, and Secretion

Gram‐negative bacteria utilize a two‐partner secretion (TPS) pathway to export disease causing virulence factors. This pathway is a member of the Type Vb secretion systems which are thought to utilize the energy of protein folding to accomplish secretion across the outer membrane. In the TPS pathway, the secreted protein (TpsA) is produced along with a specific outer membrane protein (TpsB), which uses POTRA domains to recognize nonpolar segments on the TpsA. In our current model, this recognition leads to transport and folding of the TpsA protein via a Brownian ratchet mechanism. Utilizing this TPS pathway, Hemolysin A (HpmA), a hemolytic protein from Proteus mirabilis, is able to cross the bacterial outer membrane. A version of this protein, comprising a conserved TPS domain and truncated at position 265 (HpmA265), serves as a model for secretion and folding. HpmA265 adopts a β‐helical fold that encompasses three subdomains. Folded HpmA265 can function in trans as a template to fold and activate unfolded full‐length HpmA into its hemolytically active form (Template Assisted Hemolytic Activity – TAHA). This templating is thought to mimic the Brownian ratchet mechanism of secretion‐coupled folding of the full‐length protein. Previous work suggests that destabilization of the lowest stability subdomain enhances templating while destabilization of the second subdomain reduces templating ability. To identify the positional dependence of this effect, we have systematically replaced nonpolar amino acids with polar amino acids in the nonpolar core of the protein. Using CD spectroscopy to quantify the destabilization caused by each of the introduced variants, we have correlated the folding free energies of each variant with measured values of templating ability determined via TAHA assays. These measurements have allowed us to refine our model for how HpmA265 templates the folding of full‐length HpmA. In vivo, the nonpolar amino acids that were targeted may also play a role in the POTRA domain recognition. Previous data has shown that introduction of polar residues can increase secretion, suggesting that any destabilization of the folded form is offset by changes to POTRA domain interactions. To more fully map this effect, we have quantitatively determined the levels of secretion for each variant protein. Together, these results have allowed us to refine our model of the driving mechanisms in the TPS pathway, down to an amino acid level.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Ionothermal syntheses of transition-metal-substituted aluminophosphate molecular sieves in the presence of tetraalkylammonium hydroxides

Transition-metal-substituted aluminophosphate (MeAPO) molecular sieves with SOD and AEI framework types have been synthesized ionothermally in the ionic liquid 1-ethyl-3-methylimidazolium bromide with adding four tetraalkylammonium hydroxides, including tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide and tetrabutylammonium hydroxide. Detailed synthetic investigation shows that the nature and concentration of the tetraalkylammonium hydroxide, the Me/Al ratio in the reaction mixture and the metal sources greatly influence the phase selectivity of the reaction. The products have been characterized by PXRD, SEM, ICP, CHN, UV–Vis spectroscopy, 13C, 27Al and 31P MAS NMR, and TG. The results reveal that the tetraalkylammonium cations compete with the ionic liquid cations to act as the structure directing agent. The templating ability of the tetraalkylammonium cations and the ionic liquid cations is closely related to their charge densities.

First enzymatic hydrolysis/thio-Michael addition cascade route to synthesis of AChE inhibitors

The irreversible Michael addition of thiols to acrylamides is reported as a new tool for the kinetic target-guided synthesis. In an unprecedented enzymatic hydrolysis/thio-Michael addition procedure, potent and selective acetylcholinesterase inhibitors are assembled by the enzyme using both its esterasic and templating ability.

Ruthenium(II) Tris(2,2′-bipyridine)-Templated Zinc(II) 1,3,5-Tris(4-carboxyphenyl)benzene Metal Organic Frameworks: Structural Characterization and Photophysical Properties

The ability to confine photoactive catalysts within metal organic framework (MOF) materials affords the opportunity to expand the functional diversity of these materials into solar-based applications. Here, two new Ru(II) tris(2,2'-bipyridine) (RuBpy)-based photoactive materials derived from reactions between Zn(II) ions and 1,3,5-tris(4-carboxyphenyl)benzene and templated by the presence of RuBpy (RWLC-1 and RWLC-2) are described with regard to structure and RuBpy photophysics. RuBpy cations have been successfully encapsulated within the cavities (RWLC-1) and channels (RWLC-2) of the new negatively charged frameworks, both of which are synthesized simultaneously in a single reaction vial. Single-crystal X-ray diffraction studies allowed for determination of the RuBpy position within crystal voids. RuBpy encapsulated in each of the two new MOFs exhibits biphasic triplet metal to ligand charge transfer ((3)MLCT) emission decay lifetimes (τRWLC-1-fast = 237 ns, τRWLC-1-slow = 1.60 μs, τRWLC-2-fast = 171 ns, and τRWLC-2-slow = 797 ns at 25 °C) consistent with two populations of RuBpy complexes, one being encapsulated in highly space-restricted cavities giving rise to a longer (3)MLCT lifetime, while the second is encapsulation within a larger nonperiodic pore or defect with a coencapsulated quencher giving rise to short emission lifetimes. Taken together, these results represent examples of the templating ability of RuBpy to produce novel materials with distinct photophysical environments of the encapsulated guests.

The Paradox of Dual Roles in the RNA World: Resolving the Conflict Between Stable Folding and Templating Ability

The hypothesized dual roles of RNA as both information carrier and biocatalyst during the earliest stages of life require a combination of features: good templating ability (for replication) and stable folding (for ribozymes). However, this poses the following paradox: well-folded sequences are poor templates for copying, but poorly folded sequences are unlikely to be good ribozymes. Here, we describe a strategy to overcome this dilemma through G:U wobble pairing in RNA. Unlike Watson-Crick base pairs, wobble pairs contribute highly to the energetic stability of the folded structure of their sequence, but only slightly, if at all, to the stability of the folded reverse complement. Sequences in the RNA World might thereby combine stable folding of the ribozyme with an unstructured, reverse-complementary genome, resulting in a "division of labor" between the strands. We demonstrate this strategy using computational simulations of RNA folding and an experimental model of early replication, nonenzymatic template-directed RNA primer extension. Additional study is needed to solve other problems associated with a complete replication cycle, including separation of strands after copying. Interestingly, viroid RNA sequences, which have been suggested to be relics of an RNA World (Diener, Proc Natl Acad Sci USA 86:9370-9374, 1989), also show significant asymmetry in folding energy between the infectious (+) and template (-) strands due to G:U pairing, suggesting that this strategy may even be used by replicators in the present day.

Doped-carbon electrocatalysts with trimodal porosity from a homogeneous polypeptide gel

One of the biggest challenges for materials science is to design facile routes to structurally complex materials, which is particularly important for global applications such as fuel cells. Doped nanostructured carbons are targeted as noble metal-free electrocatalysts for this purpose. Their intended widespread use, however, necessitates simple and robust preparation methods that do not compromise on material performance. Here, we demonstrate a versatile one-pot synthesis of nitrogen-doped carbons that exploits the templating ability of biological polymers. Starting with just metal nitrates and gelatin, multiphase C/Fe3C/MgO nanomaterials are formed, which are then etched to produce active carbon electrocatalysts with accessible trimodal porosity. These show remarkable performance in the oxygen reduction reaction – a key process in proton exchange membrane fuel cells. The activity is comparable to commercial platinum catalysts and shows improved stability with reduced crossover effects. This simple method offers a new route to widely applicable porous multicomponent nanocomposites.

Heterogeneous oxidation of Fe(II) on iron oxides in aqueous systems: Identification and controls of Fe(III) product formation

The aqueous Fe(II)–oxide Fe(III) system is a reactant for many classes of redox sensitive compounds via an interfacial Fe(II) sorption and electron transfer process. The poorly soluble Fe(III) products formed as a result of contaminant reduction and Fe(II) oxidation on iron oxides may be capable of modifying iron oxide surfaces and affecting subsequent reduction rates of contaminants such as halogenated ethenes or nitroaromatic compounds. The scope of this study was to identify the secondary Fe(III) mineral phases formed after Fe(II) oxidation on common iron oxides during heterogeneous contaminant reduction by directly targeting the secondary minerals using Mössbauer-active isotopes. Fe(III) mineral characterization was performed using 57Fe-Mössbauer spectroscopy, μ-X-ray diffraction, and electron microscopy after oxidation of dissolved 57Fe(II) using nitrobenzenes as a model oxidant in pH-buffered suspensions of 56hematite, 56goethite, 56magnetite, and 56maghemite. Mössbauer spectra confirmed sorbed 57Fe(II) becomes oxidized by the parent 56Fe(III)-oxide sorbent and assimilated as the sorbent oxide prior to any nitrobenzene reduction, consistent with several reports in the literature. In addition to oxide sorbent growth, Fe(II) sorption and oxidation by nitrobenzene result also in the formation of secondary Fe(III) minerals. Goethite formed on three hematite morphologies (rhombohedra, needles, and hexagonal platelets), and acicular needle shapes typical of goethite appeared on the micron-sized hexagonal platelets, at times aligned in 60° orientations on (001) faces. The proportion of goethite formation on the three hematites was linked to number of surface sites. Only goethite was observed to form on a goethite sorbent. In contrast, lepidocrocite was observed to form on magnetite and maghemite sorbents (consistent with homogeneous Fe(II) oxidation by O2) and assumed spherulite morphologies. All secondary Fe(III) phases were confirmed within μ-X-ray diffraction patterns. On hematite, the directed formation of goethite as opposed to lepidocrocite suggests hematite may possess a templating ability for the α-FeOOH atom arrangement as opposed to γ-FeOOH. The initiation of all secondary Fe-oxide formations occurred after four to six equivalents of monolayer coverage on the supporting mineral sorbent. Overall, Fe(III) product identity formed during heterogeneous Fe(II) oxidation appears to be governed mainly by the identity of the underlying sorbent and partly by the amount of available surface sites.

Validity and reliability of preoperative templating in total hip arthroplasty using a digital templating system

To evaluate the validity, interobserver reliability, and intraobserver reproducibility of a digital templating system, the Mdesk™ in preoperative templating in cemented and reverse hybrid total hip arthroplasty (THA). Validity was evaluated by comparing the planned cup size, stem size, CCD angles, and neck length with the components used in 129 patients operated with cemented and reverse hybrid THA. The reliability was measured by comparing the templating results of two surgeons with each other (interobserver) and the results of two templatings carried out by first surgeon (intraobserver). The leg length discrepancy was measured before and after the operation to assess the templating ability to correct it. The Mdesk™ system showed good validity (kappa value ranged from 0.64 to 0.96), especially when one size over and under the planned size were included. No difference between cemented and cementless stems was found. The interobserver reliability ranged from fair (kappa 0.23) to substantial (kappa 0.61) while the intraobserver reproducibility ranged from substantial (kappa 0.70) to excellent (kappa 0.82). Templating and intraoperative measures succeeded to restore the leg length. The Mdesk™ system has comparable validity and reliability with other templating systems used in clinical practice. We recommend that the same surgeon who does the preoperative radiographic templating to also perform the operation. Further studies are required to evaluate the results of succeeded templating in the long run.

Nanoparticle Arrays: Biotemplated Magnetic Nanoparticle Arrays (Small 2/2012)

A biomineralization protein from magnetotactic bacteria (Mms6) used to control both the formation and location of magnetic nanoparticles in a patterned array. Mms6 immobilized on a patterned surface templates high-quality, crystalline magnetite particles with a narrow grainsize distribution and consistent magnetic behavior under relatively mild conditions. These particles are ferrimagnetic and may be exchange-coupled on the surface, forming multiparticle attraction/repulsion zones. The biomineralization of nanomaterials in patterned arrays on surfaces using various specific proteins and peptides with templating ability could be used as a more environmentally friendly methodology to develop micro- and nanoscale devices.

Effect of Specific Anion on Templated Crystal Nucleation at the Liquid−Liquid Interface

In this work, we have investigated the effect of potassium salts of different anions upon the crystal nucleation of K(2)SO(4) as interfacially templated by a surfactant monolayer of 1-octadecylamine (ODA), in an aqueous microdroplet system bounded by a liquid-liquid interface with 1-decanol. The salts used were K(2)HPO(4), KCl, KBr, KI, KNO(3), and KSCN, present at an initial concentration of 10 mM within an aqueous microdroplet containing K(2)SO(4) at an initial concentration of 287 mM. Supersaturation and subsequent crystallization were isothermally induced by droplet dissolution into the dehydrating decanol phase. The K(2)SO(4) solute crystallization behavior was studied by measurement of the calculated concentration of the solute in the microdroplet at the onset of crystallization, i.e., at the first perceptible microscopic appearance of a solid phase, and by crystal habit. Certain salts, e.g., K(2)HPO(4), had almost no influence on the templating ability of ODA, while the ability of ODA to template nucleation and direct the formation of regular crystal habit of K(2)SO(4) became appreciably disrupted in the presence of more chaotropic anions, such as SCN(-) or NO(3)(-). The propensity for anions to disrupt crystal templating was clearly seen to follow a Hofmeister trend. For crystallization events induced in the absence of ODA, however, these added salts had no influence on the outcome of the events. Microdroplets bounded by an ODA monolayer were also found to undergo droplet shrinkage into the surrounding dehydrating phase at a rate which generally depended upon the nature of the anion in the droplet, with chaotropic anions having an apparent effect of promoting shrinkage. Our findings suggest that the packing or ordering of an ODA monolayer at a liquid-liquid interface is strongly influenced by an interaction between anions in the aqueous phase and the surfactant monolayer at the liquid-liquid interface, which is manifested in its effect upon the crystal templating behavior. These intriguing results can have important implications for the understanding of biomineralization processes which occur in heterogeneous environments.

Inducing growth of highly ordered molybdenum oxide nanoplates under ambient conditions

Large area uniform nanoplates of molybdenum oxide (MoO3), a typical semiconductor material, have been synthesized under soft conditions by using carboxymethyl cellulose (CMC) as template. Under ambient condition, hydrolysis of ammonium molybdate into layered molybdenum oxide, and its subsequent inclusion of CMC polymers results in formation of lamellar CMC/molybdenum oxide hybrid. Calcinations of this lamellar hybrid at 500 °C lead to formation of large area uniform nanoplates of orthorhombic phase of MoO3. Scanning electron microscopy and transmission electron microscopy images show that these MoO3 nanoplates are regularly packed, about 100 nm in thickness and 10–100 μm in length. The mechanism of the hybrid reaction and the templating ability of CMC polymers have been extensively discussed. The oriented growth of short molybdenum oxide flakes into long-range ordered plates has been induced by CMC polymers because of the shrinking of CMC during the hybrid reaction. This is the first report that large area highly ordered molybdenum oxide nanometer materials have been obtained under soft reaction conditions.

Electrochromic properties of polyaniline thin film nanostructures derived from solutions of ionic liquid/polyethylene glycol

Abstract By exploiting the templating ability, wetting properties and the capability of the ionic liquid, 1-ethyl,3-methylimidazolium bromide to furnish the anionic dopant, nanostructured thin films of polyaniline (PANI) have been fabricated from an aqueous solution of the monomer encompassing this organic moiety by electropolymerization. These films have been compared to films synthesized from a medium based on a conventional polymeric surfactant, polyethylene glycol 400 (PEG). The template/dopant controls pore structure and assembly patterns as an interconnected network of nanofibrils of 50–500 nm in length and 10–40 nm in diameter constitutes the PANI films derived from the ionic liquid-based solution whereas the dominant microstructural attribute of the PANI films obtained from the PEG-containing formulation are abutting nanoparticles with elongated shapes. The effect of the different thin film nanostructures on their electrochromic properties is evident from the higher coloration efficiency, transmission modulation (in the NIR region), larger charge capacity, enhanced cycling stablity and faster color-bleach rates observed for the PANI films obtained from the ionic liquid medium as compared to that shown by the PANI films fabricated from the PEG solution. The outstanding optical and electrochemical behavior of the films, in particular, for the film derived from the ionic liquid-based solutions indicate that such recyclable and environmentally benign reaction media are most useful especially for transposing PANI films to large area substrates for electrochromic window applications.

Strong templating effect of TEAOH in the hydrothermal genesis of the AlPO 4-5 molecular sieve: Experimental and computational investigations

The hydrothermal genesis of AlPO 4-5, in the presence of four different organic templates, viz., methyldicyclohexylamine (MCHA), triethylamine (TEA), tripropylamine (TPA), and tetraethylammonium hydroxide (TEAOH), has been monitored by XRD. It is shown that TEAOH has the best templating ability to the formation of AlPO 4-5 structure under the different synthesis conditions considered in this study. Density functional calculations on periodic models of AlPO 4-5 indicate the strongest nonbonding interaction energy between the template and the framework in the case of TEAOH. Therefore, a new approach correlating the nonbonding interaction energy to the template ability to form a porous structure is proposed as a step toward a better understanding of the role of the organic template in the synthesis of porous molecular sieves.