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Results for “Biomimetics”

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At least 343 records · Page 19Linked to original sources

PubMed2000

Biomimetic growth of hydroxyapatite on gelatin films doped with sodium polyacrylate.

Gelatin films were used as biomimetic substrates for the nucleation of hydroxyapatite from simulated body fluid (SBF). Stretching and presence of sodium polyacrylate appear to be essential factors for the specific nucleation and growth of hydroxyapatite crystals inside the films. After soaking in 1.5SBF for periods longer than 4 days, all the films display a completely calcified surface. However, the spherical aggregates on the film surfaces do not give any X-ray diffraction effect and exhibit a low Ca/P molar ratio, typical of amorphous calcium phosphate. The ordered deposition of crystalline hydroxyapatite has been verified to take place only in stretched polyacrylate--gelatin films. The crystals grow as tablets about 2 microns thick among the gelatin layers, with their crystallographic c-axes preferentially oriented parallel to the direction of orientation of the collagen molecules, thus resembling the parallel orientation of apatitic crystals and collagen fibrils in calcified biological tissues.

Acrylic Resins↗

PubMed2001

Ultramicrostructure and microthermomechanics of biological IR detectors: materials properties from a biomimetic perspective.

Microstructural organization of the biological infrared (IR) receptors was studied to elucidate their materials properties useful for prospective biomimetic design of artificial IR sensors from organic/polymeric materials. The IR receptors in Melanophila acuminata beetles were studied with ultrahigh-resolution scanning probe microscopy (SPM) in a range of temperatures. By application of micromechanical mapping and thermal stage, we made attempts to reveal the micromechanical and thermomechanical properties of the cuticular apparatus of the IR sensillum. The main component of the cuticular apparatus is an internal endocuticular sphere with a diameter of about 15-20 microm. Highly ordered multilayered organization of the lamellated peripheral mantle of the sphere was confirmed and characterized. We observed that the interlayer spacing of this microstructure varied along the circumference and decreased to 300 nm in the vertex of the sphere. We demonstrated that the microlayered structure is composed of nanolayers with very different micromechanical properties and thermal behaviors. Thermal expansion of the outer mantle was observed, and the local thermal expansion coefficient under given preparation conditions was estimated to be below 1.5 x 10(-4) grad(-1).

Animals↗

PubMedDate not supplied

Biomimetic synthesis of a water soluble conducting molecular complex of polyaniline and lignosulfonate.

A new biomimetic route for the synthesis of a conducting molecular complex of polyaniline (Pani) and a natural polyelectrolyte, lignosulfonate (LGS) is presented. A poly(ethylene glycol) modified hematin (PEG-hematin) was used to catalyze the polymerization of aniline in the presence of LGS to form a Pani/LGS complex. UV-vis, FTIR, conductivity and TGA studies for the LGS-polyaniline complex indicate the presence of a thermally stable and electrically conductive form of polyaniline. Also the presence of LGS in this complex, an inexpensive byproduct from pulp processing, provides a unique combination of properties such as electronic conductivity, processability and biodegradability. The use of this conductive complex for corrosion protection is also proposed.

Aniline Compounds↗

PubMed2006

Dual-functional biomimetic materials: nonfouling poly(carboxybetaine) with active functional groups for protein immobilization.

We introduce a dual-functional biocompatible material based on zwitterionic poly(carboxybetaine methacrylate) (polyCBMA), which not only highly resists protein adsorption/cell adhesion, but also has abundant functional groups convenient for the immobilization of biological ligands, such as proteins. The dual-functional properties are unique to carboxybetaine moieties and are not found in other nonfouling moieties such as ethylene glycol, phosphobetaine, and sulfobetaine. The unique properties are demonstrated in this work by grafting a polyCBMA polymer onto a surface or by preparing a polyCBMA-based hydrogel. PolyCBMA brushes with a thickness of 10-15 nm were grafted on a gold surface using the surface-initiated atom transfer radical polymerization method. Protein adsorption was analyzed using a surface plasmon resonance sensor. The surface grafted with polyCBMA very largely prevented the nonspecific adsorption of three test proteins, that is, fibrinogen, lysozyme, and human chorionic gonadotropin (hCG). The immobilization of anti-hCG on the surface resulted in the specific binding of hCG while maintaining a high resistance to nonspecific protein adsorption. Transparent polyCBMA-based hydrogel disks were decorated with immobilized fibronectin. Aortic endothelial cells did not bind to the polyCBMA controls, but appeared to adhere well and spread on the fibronectin-modified surface. With their dual functionality and biomimetic nature, polyCBMA-based materials are very promising for their applications in medical diagnostics, biomaterials/tissue engineering, and drug delivery.

Adsorption↗

PubMed2002

Biomimetic studies of terminal oxidases: trisimidazole picket metalloporphyrins.

Three biomimetic models for the binuclear Fe/Cu (heme/trisimidazole) active site of terminal oxidases, such as cytochrome c oxidase and related enzymes, have been prepared. Based upon a tetrakis(aminophenyl)porphyrin core, these models possess a single covalently linked imidazole-bearing tail on one side of the porphyrin and three imidazole "pickets" on the opposite side of the porphyrin ring. Three different imidazole picket motifs are characterized in free base, Fe, Zn, Fe/Cu, and Zn/Cu forms. A combination of NMR, EPR, and IR demonstrates that, for the N-methylimidazole systems studied, the distal Cu is bound within the trisimidazole environment in the reduced (Cu(I)) and oxidized (Cu(II)) forms. The imidazole picket substitution pattern and state of metalation have significant influence on the interaction of these compounds with CO. For imidazole picket systems containing NH groups, intramolecular H bonds compete with Cu(I) coordination of the N donors.

Amines↗

PubMed2002

Protonation state of the equatorial ligands and dynamics of the OH...O units in a cobaloxime biomimetic.

The protonation state of the dimethylglyoxime ligands in the B(12) coenzyme biomimetic [Co(CCl=CHCl)(dmgH)(2)(py)].CHCl(3) was investigated by using first-principles molecular dynamics. Our simulations at 173 and 300 K reveal that one of the oxime protons remains bonded to a nitroxyl group, while the proton of the second NO...H-ON unit is essentially shared with similar probability between the two oxygen atoms. This reconciles the results of the experimental determination (Jones, P. G.; Yang, L.; Steinborn, D. Acta Cryst. 1996, C52, 2399), showing all N-O distances as equivalent, with the commonly accepted rule that the protonation state of the dimethylglyoxime ligands can be identified by the different N-O distances. Further aspects of the dynamics of the OH...O units, in relation to the occurrence of weak CH...O intermolecular interactions, are analyzed.

Journal Article↗

PubMed2001

Continuous crystalline carbonate apatite thin films. A biomimetic approach.

In contrast to extensive studies on hydroxyapatite thin films, very little has been reported on the thin films of carbonated apatite (dahllite). In this report, we describe the synthesis and characterization of a highly crystalline dahllite thin film assembled via a biomimetic pathway. A free-standing continuous precursor film of carbonated calcium phosphate in an amorphous phase was first prepared by a solution-inhibited templating method (template-inhibition) at an air-water interface. A stearic acid surface monolayer acted as the template, while a carbonate-phosphate solution composed a binary inhibition system. The precursor film formed at the air/water interface was heated at 900 degrees C and transformed into a dense crystalline film that retained the overall shape of the precursor. The crystalline phase was characterized by XRD and IR to be a single-phase carbonate apatite, with carbonate substitutions in both type A (OH-) and type B (PO4(3-)) lattice positions.

Journal Article↗

PubMed2001

Rapid colorimetric detection of antibody-epitope recognition at a biomimetic membrane interface.

Biomolecular recognition of antigens and epitopes by antibodies is a fundamental event in the initiation of immune response and plays a central role in a variety of biochemical processes. Peptide binding requires, in many cases, presentation of the peptides at interfaces, such as protein surfaces, cellular membranes, and synthetic polymer surfaces. We describe a novel molecular system in which interactions between antibodies and peptide epitopes displayed at a biomimetic membrane interface can be detected through induction of visible, rapid color transitions. The colorimetric assembly consists of a phospholipid/polydiacetylene matrix anchoring a hydrophobic peptide displaying the epitope at its N-terminus. The colorimetric transitions observed in the assembly, corresponding to perturbation of the polydiacetylene framework, are induced only upon recognition of the displayed epitope by its specific antibody present in the aqueous solution. Significantly, the color changes occur after a single mixing step, without further chemical reactions or enzymatic processing. The new molecular system could be utilized for studying antigen-antibody interactions and peptide-protein recognition, epitope mapping, and rapid screening of biological and chemical libraries.

Antibodies, Monoclonal↗

PubMed2002

Biomimetic synthesis of (-)-longithorone A.

An enantioseletive, biomimetic synthesis of (-)-longithorone A has been achieved using an intermolecular/transannular Diels-Alder sequence which provides some support for the proposed biosynthesis. The cycloaddition precursors were two [12]-paracyclophanes that were constructed with atropisomer control during ene-yne metathesis macrocyclizations.

Biological Factors↗

PubMed2002

Proposed mechanism for the reaction catalyzed by a diterpene cyclase, aphidicolan-16beta-ol synthase: experimental results on biomimetic cyclization and examination of the cyclization pathway by ab initio calculations.

To examine the mechanism of the cyclization reaction catalyzed by aphidicolan-16beta-ol synthase (ACS), which is a key enzyme in the biosynthesis of diterpene aphidicolin, a specific inhibitor of DNA polymerase alpha, skeletal rearrangement of 2a and biomimetic cyclization of 4b were employed. The structures of the reaction products, which reflect penultimate cation intermediates, allowed us to propose a detailed reaction pathway for the Lewis acid-catalyzed cyclizations and rearrangements. Isolation of these products in an aphidicolin-producing fungus led us to speculate that the mechanism of the ACS-catalyzed cyclization reaction is the same as that of a nonenzymatic reaction. Ab initio calculations of the acid-catalyzed reaction intermediates and the transition states indicate that the overall reaction catalyzed by ACS is an exothermic process though the reaction proceeds via an energetically disfavored secondary cation-like transition state. In conjunction with the solvent effect in the acid-catalyzed reactions, this indicates that the actual role of ACS is to provide a template which enforces conformations of the intermediate cations leading to the productive cyclization although it has been believed that the cation-pi interaction between cation intermediates and aromatic amino acid residues in the active site is important for the enzymatic catalysis. This study provided important information on the role of various cationic species, especially secondary cation-like structures, in both nonenzymatic and enzymatic reactions.

Acremonium↗

PubMed1999

NMR experiments of oleuropein biomimetic hydrolysis.

The oleuropein hydrolytic conversion, under biomimetic conditions, induced by the endogenous enzymatic system of the olive fruit, has been monitored by the intermediate derivative formation through (1)H and (13)C NMR spectra; the assigned molecular structures reveal the identity of new bioactive biophenolic metabolites, the hemiacetal aglycon, and the two epimeric dialdehydes, which influence the pathogen antagonism of olive fruits and the hedonistic-sensorial characteristics of olive oil.

Carbon Isotopes↗

PubMed2001

Synthesis, antimalarial activity, biomimetic iron(II) chemistry, and in vivo metabolism of novel, potent C-10-phenoxy derivatives of dihydroartemisinin.

The combination of TMSOTf and AgClO(4) promotes the efficient C-10-phenoxylation of dihydroartemisinin (3) in good chemical yield and excellent stereoselectivity. All of the new phenoxy derivatives have potent in vitro antimalarial activity. On the basis of the excellent yield and stereoselectivity obtained for the p-trifluoromethyl derivative 7b, this compound and the parent phenyl-substituted derivative 5b were selected for in vivo biological evaluation against Plasmodium berghei in the mouse model and for metabolism studies in rats. Compound 7b demonstrated excellent in vivo antimalarial potency with an ED(50) of 2.12 mg/kg (cf. artemether = 6 mg/kg) versus P. berghei. Furthermore, from preliminary metabolism studies, this compound was not metabolized to dihydroartemisinin; suggesting it should have a longer half-life and potentially lower toxicity than the first-generation derivatives artemether and arteether. From biomimetic Fe(II)-catalyzed decomposition studies and ESR spectroscopy, the mechanism of action of these new lead antimalarials is proposed to involve the formation of both primary and secondary C-centered cytotoxic radicals which presumably react with vital parasite thiol-containing cellular macromolecules.

Animals↗

PubMed1984

Biomimetic approach to potential benzodiazepine receptor agonists and antagonists.

Several beta-carbolines, isoquinolines, imidazopyridines , and canthin -6-ones prepared in biomimetic fashion were tested for their ability to bind to the benzodiazepine receptor. Methyl isoquinoline-3-carboxylate, methyl 6,7- dimethoxyisoquinoline -3-carboxylate (3b) 1-phenyl-3- carbomethoxyimidazopyridine , (6B,) and canthin -6- one ( 13a ) bound with moderate affinities, while 2- carbomethoxycanthin -6- one ( 13b ) bound to benzodiazepine receptors with an affinity comparable to several pharmacologically active benzodiazepines. The potency of 13b suggests that the benzodiazepine receptor(s) can tolerate substitution at positions 1 and 9 of a beta-carboline without loss of activity if the substituents are trigonal and maintain a planar topography. Moreover, displacement of the carbonyl group by two atoms from the aromatic ring (C) of the beta-carboline skeleton caused a marked decrease in binding to the benzodiazepine receptor. This observation supports the hypothesis that maximum binding affinity of beta-carbolines is achieved when the carbonyl group at position 3 is attached directly to the aromatic pyridine ring.

Animals↗

PubMed2001

An unusual decarboxylative Maillard reaction between L-DOPA and D-glucose under biomimetic conditions: factors governing competition with Pictet-Spengler condensation.

In 0.1 M phosphate buffer at pH 7.4 and 37 degrees C, the tyrosine metabolite L-3,4-dihydroxyphenylalanine (L-DOPA) reacts smoothly with D-glucose to afford, besides diastereoisomeric tetrahydroisoquinolines 1 and 2 by Pictet-Spengler condensation, a main product shown to be the unexpected decarboxylated Amadori compound N-(1-deoxy-D-fructos-1-yl)-dopamine (3). Under similar conditions, dopamine gave only tetrahydroisoquinoline products 4 and 5, whereas L-tyrosine gave exclusively the typical Amadori compound 6. Fe(3+) and Cu(2+) ions, which accumulate in relatively high levels in parkinsonian substantia nigra, both inhibited the formation of 3. Cu(2+) ions also inhibited the formation of 1 and 2 to a similar degree, whereas Fe(3+) ions increased the yields of 1 and 2. Apparently, the formation of 3 would not be compatible with a simple decarboxylation of the initial Schiff base adduct, but would rather involve the decarboxylative decomposition of a putative oxazolidine-5-one intermediate assisted by the catechol ring. These results report the first decarboxylative Maillard reaction between an amino acid and a carbohydrate under biomimetic conditions and highlight the critical role of transition metal ions in the competition with Pictet-Spengler condensation.

Chromatography, High Pressure Liquid↗

PubMed2002

Total synthesis of (15R)- and (15S)-F(2t)-isoprostanes by a biomimetic process using the cyclization of acyclic dihydroxylated octa-5,7-dienyl radicals.

We report a new route to F(2t)-IsoP (formerly named 8-epi-PGF(2alpha)) using a biomimetic radical cyclization of a highly functionalized C20 precursor. The strategy employed gives a beta-hydroxy free radical followed by molecular oxygen trapping, which is an unusual method for quenching carbon free radicals. We observed the formation of unique diastereoisomers (15R)- and (15S)-F(2t)-IsoP. This result is consistent with a strong stereoelectronic control associated with a steric effect initiated by the side chains alpha and omega on the cyclopentane ring.

Cyclization↗

PubMed2002

Efficient ruthenium-catalyzed aerobic oxidation of alcohols using a biomimetic coupled catalytic system.

Efficient aerobic oxidation of alcohols was developed via a biomimetic catalytic system. The principle for this aerobic oxidation is reminiscent of biological oxidation of alcohols via the respiratory chain and involves selective electron/proton transfer. A substrate-selective catalyst (ruthenium complex 1) dehydrogenates the alcohol, and the hydrogens abstracted are transferred to an electron-rich quinone (4b). The hydroquinone thus formed is continuously reoxidized by air with the aid of an oxygen-activating Co[bond]salen type complex (6). Most alcohols are oxidized to ketones in high yield and selectivity within 1-2 h, and the catalytic system tolerates a wide range of O(2) concentrations without being deactivated. Compared to other ruthenium-catalyzed aerobic oxidations this new catalytic system has high turnover frequency (TOF).

Aerobiosis↗

PubMed2002

Biomimetic synthesis of petuniasterone D via the epoxy ester[bond]ortho ester rearrangement.

The side chain of the insecticidal steroid petuniasterone D was synthesized by the biomimetic acid-catalyzed epoxy ester[bond]ortho ester rearrangement. In addition to the natural (22R,24R)-configuration of the side chain ortho ester, compounds bearing the epimeric (22R,24S)-, (22S,24R)-, and (22S,24S)- [3.2.1]-bicyclic ortho esters were also produced by stereospecific rearrangement of the corresponding isomeric epoxy esters. Functionalization of the steroid nucleus of the (22R,24R)-ortho ester completed the synthesis of the natural product.

Journal Article↗

PubMed2002

A biomimetic transformation of serratinine into serratezomine A through a modified Polonovski reaction.

Application of a modified Polonovski reaction for serratinine (1) resulted in generation of serratezomine A (2) with a novel seco-serratinine-type skeleton recently isolated from the club moss Lycopodium serratum var. serratum. This biomimetic transformation supports a biogenetic pathway proposed for serratezomine A (2). The absolute stereochemistry of serratezomine A (2) was established by an induced exciton chirality and modified Mosher methods.

Alkaloids↗