RESUMO
According to literature reports and our own findings, the binding of new Ni(2+)-preloaded bis(nitrilotriacetic acid) (NTA) ligands with polyhistidine-tagged proteins has been found to be accompanied by a one- to two-order-of-magnitude increase in affinity, compared to the binding of a single Ni(2+)-preloaded NTA moiety. In spite of the introduction of a second NTA chelating group, a cooperative effect that is less than the theoretical maximum has been observed. Herein, we present a rational explanation for the observed stability of the ternary complex involving the postulated bis-NTA-(Ni(2+))(2) species and multivalent polyhistidine tags. We have found that prior to the formation of the ternary complex, the Ni(2+)-preloading step of bis-NTA ligands does not form the expected bis-NTA-(Ni(2+))(2) exclusively. Instead of the major formation of bis-NTA-(Ni(2+))(2) species, it appears that cyclic discrete 1:1 and 2:2 entities are predominantly formed. It is proposed that these species interact upon ring-opening with multivalent histidine tags. The occurrence of this phenomena accounts for the overall one- to two-order-of-magnitude increase in affinity of ternary complexes involving bis-NTA ligands.
Assuntos
Histidina/metabolismo , Níquel/química , Ácido Nitrilotriacético/química , Compostos Organometálicos/química , Compostos Organometálicos/metabolismo , Proteínas/metabolismo , Calorimetria , Polarização de Fluorescência , Ligantes , Coloração e RotulagemRESUMO
Single-walled carbon nanotubes (NT) were covalently functionalized with either 9-phenyl acridine (PhA) or 10-methyl-9-phenyl acridinium (PhMeA(+)). Absorption and fluorescence properties of acridine derivatives tethered to the nanotubes were studied in homogeneous dispersions. Exciplex emission was observed for NT functionalized with 9-phenylacridine. This phenomenon was attributed to an "intramolecular" interaction between excited phenyl acridine and carbon nanotubes. Interestingly, reverse photoinduced electron transfer from the nanotube to 10-methyl-9-phenylacridinium was detected for the NT-PhMeA(+) nanohybrid. This electron transfer led to a strong quenching of the acridinium fluorescence and to the formation of a metastable acridine radical. Evidence for the formation of this radical was obtained by ESR studies.
Assuntos
Acridinas/química , Elétrons , Nanotubos de Carbono/química , Processos Fotoquímicos , Estrutura Molecular , EspectrofotometriaRESUMO
Syntheses of chiral 6,15-dihydronaphtho[2,3-c]pentaphene derivatives of opposite configurations are reported. Starting from anthracene, the strategy involves two key steps: a Diels-Alder reaction on a prochiral dianthraquinone, and an enantiomeric resolution using (-)-menthol. The final molecules exhibit very strong optical activity, as shown by their circular dichroism spectra, and are examples of chiral facial amphiphiles. Their adsorption at the surface of single-walled carbon nanotubes (SWNTs) has also been studied, and has been found to occur preferentially on 0.8-1.0 nm diameter nanotubes among the population of a high-pressure CO conversion (HiPco) SWNT sample (0.8-1.2 nm). The synthesised facial amphiphiles act as nano-tweezers for the diameter-selective solubilisation of SWNTs in water. The expected optical activities of the SWNT samples solubilised by each of the chiral amphiphiles have been studied by circular dichroism spectroscopy, but the results are not yet conclusive.
Assuntos
Antracenos/química , Nanotubos de Carbono/química , Dicroísmo Circular , EstereoisomerismoRESUMO
The expedient synthesis of a novel chiral (1S,2S)-N-[(2-isothiocyanato)cyclohexyl] trifluoromethanesulfonamide and its use as a derivatizing auxiliary for the straightforward determination of optical purity of chiral amines are reported.
Assuntos
Aminas/química , Isotiocianatos/química , Mesilatos/química , Isotiocianatos/síntese química , Espectroscopia de Ressonância Magnética , Mesilatos/síntese química , Sensibilidade e Especificidade , EstereoisomerismoRESUMO
Remarkably stable, water-soluble glyconanoring-coated SWCNTs were prepared by self organization and photopolymerization of neutral diacetylene-based glycolipids on the nanotube surface; the nanoconstructs are able to engage in specific ligand-lectin interactions in a similar way to glycoconjugates on cell membranes.
Assuntos
Materiais Biocompatíveis/síntese química , Glicolipídeos/química , Lectinas/química , Nanotecnologia/métodos , Nanotubos de Carbono/química , Polímeros/química , Poli-Inos/química , Materiais Biocompatíveis/química , Microscopia Eletrônica de Transmissão , Aglutinina de Amendoim/química , Polímero Poliacetilênico , Solubilidade , Propriedades de SuperfícieRESUMO
3-Aryltetronic acids were prepared in one step by treatment of a mixture of methyl arylacetates and methyl hydroxyacetates with potassium tert-butoxide, via tandem transesterification/Dieckmann condensation. Several mushroom or lichen pigments, vulpinic acids, were synthesized from 3-(4-methoxyphenyl)tetronic acid in three steps involving the reaction of the corresponding dianion with an alpha-ketoester and the dehydration of the tertiary alcohols obtained into mixtures of (E)- and (Z)-alkenes, which were converted under UV irradiation at 254 nm to natural (E)-isomers. Syntheses of pinastric acid, 4,4'-dimethoxyvulpinic acid, and the first synthesis of recently isolated methyl 3',5'-dichloro-4,4'-di-O-methylatromentate were hence achieved in an efficient manner.
Assuntos
Furanos/síntese química , Fenilacetatos/síntese química , Acetatos/química , Butanóis/química , Furanos/química , Fenilacetatos/químicaRESUMO
Functionalized (Z,E)-1-halo-1,3-dienol esters are synthesized in a highly stereoselective manner via CrCl2-mediated rearrangement of allylic trihalomethylcarbinol esters induced by microwave irradiation.
Assuntos
Cloretos/química , Compostos de Cromo/química , Ésteres/síntese química , Metano/análogos & derivados , Micro-Ondas , Ésteres/química , Metano/química , Estrutura Molecular , EstereoisomerismoRESUMO
Norbadione A (NBA) is a pigment present in edible mushrooms which is presumed to selectively complex Cs(+) cations. Due to a very uncommon complexation mechanism, we used a combination of several experimental techniques, including (1)H-NMR, (133)Cs-NMR, isothermal calorimetric, potentiometric titrations and molecular dynamics MD simulations to determine the nature of the complexed species, as well as their stability constants for the NBA-M(+) systems (M(+) = Cs(+), K(+), Na(+)) in methanol:water 80:20 solutions at 25.0 degrees C. We show that almost no complexation occurs below pH 7.5, as long as a proton, involved in a strong hydrogen bond, bridges both carboxylic and enolic groups of each pulvinic moiety of NBA. Thus, neutralization of that proton is necessary to both set free potential coordination sites and to trigger a conformational change, two conditions needed to bind successively a first, then a second metallic cation. The stability constants determined in this study are in good agreement with each other, leading to the stability order Cs(+) > K(+) > Na(+) for both mono- and bimetallic complexes, which is the reversed order to the one generally observed for low molecular weight carboxylic ligands in water. According to MD simulations in solution, complexation involves a mixture of Z/E isomers and conformers of NBA with a broad diversity of binding modes. Some pH and environment dependent aggregation phenomena are considered to also contribute to the binding process, and to possibly explain the accumulation of radionuclides in mushrooms.
Assuntos
4-Butirolactona/análogos & derivados , Césio/química , Ligação de Hidrogênio , Fenilacetatos/química , Potássio/química , Sódio/química , 4-Butirolactona/química , Calorimetria , Concentração de Íons de Hidrogênio , Espectroscopia de Ressonância Magnética , Espectrofotometria UltravioletaRESUMO
The bundling state of several dry single-walled carbon nanotube (SWNT) samples is compared using isothermal microcalorimetry (IMC). So as to get different dry samples with various bundling states, the pristine SWNTs were pretreated with a solution of an aromatic amphiphile with or without sonication, washed and dried before being studied by IMC. The bundling state of the different SWNT samples, which was first analyzed by TEM, was then correlated to the obtained IMC data thanks to the interpretation of the observed energy transfer phenomena. From our results, IMC appears to be an interesting technique for the surface probing of dry SWNT samples, and herein for the evaluation of the bundling state.
RESUMO
A short and straightforward synthesis of the antihistaminic drug mequitazine is reported, based on an efficient palladium catalyzed allylic alkylation of 1-aza-bicyclo[2.2.2]oct-2-en-3-ylmethyl acetate using sodium phenothiazinate in mild conditions.
Assuntos
Compostos Bicíclicos Heterocíclicos com Pontes/química , Antagonistas dos Receptores Histamínicos H1/síntese química , Compostos Organometálicos/química , Paládio/química , Fenotiazinas/síntese química , Tiazinas/química , Alquilação , Catálise , Antagonistas dos Receptores Histamínicos H1/química , Estrutura Molecular , Fenotiazinas/química , EstereoisomerismoRESUMO
Smart nanohybrids were prepared by conjugation of CrAsH to hydrosoluble and biocompatible quantum dots (QDs). The resulting probes were shown to bind efficiently and selectively to Cys-tagged proteins. The interaction with the protein was detected by an increase of the fluorescence emission of CrAsH. While the latter faded rapidly under continuous excitation, emission of the QD remained unaffected. The persistent fluorescence of the QD should thus allow extended monitoring of the target protein.
Assuntos
Materiais Biocompatíveis/química , Corantes Fluorescentes/química , Compostos Organometálicos/química , Pontos Quânticos , Proteínas Recombinantes/química , Cisteína/química , Fluoresceínas/química , Corantes Fluorescentes/síntese química , Fosfolipídeos/químicaRESUMO
Homogeneous coating of carbon nanotubes with metallic nanoparticles was achieved using supramolecular auto-organization of amphiphilic molecules as template. The resulting Pd nanoparticles/carbon nanotube nanohybrids were then evaluated in electrocatalysis experiments, showing superior activity in ethanol oxidation compared to analogous systems.
RESUMO
The synthesis of the monoaromatic pulvinic dilactone 1 from a tetronic acid derivative is reported. The reaction of 1 with various amines was found to provide the two pulvinamides regioisomers 2a and 2b. Using tetrabutylammonium fluoride (TBAF) as an activator, pulvinamides 2a could be obtained with excellent regioselectivities and good yields. Additions of alcohols to 1 are also studied, leading to similar observations.
Assuntos
Aminas/química , Ácidos Carboxílicos/química , Química Orgânica/métodos , Furanos/química , Lactonas/química , Compostos de Amônio Quaternário/química , Álcoois/química , Amidas/química , Antioxidantes/química , Ácidos Carboxílicos/síntese química , Hidrólise , Lactonas/síntese química , Espectroscopia de Ressonância Magnética , Modelos Químicos , Solventes/química , TemperaturaRESUMO
The first example of a non-enzymatic C-2 epimerization of aldonolactones is reported. The reaction of 2,3,4,6-tetra-O-benzyl-d-gluconolactone or 2,3,4,6-tetra-O-benzyl-d-mannonolactone with MgI(2) in EtOH afforded their respective C-2 epimer. Studies conducted in EtOD showing the incorporation of a deuterium atom only at the C-2 position of the epimerized product reveal an epimerization rather than a racemization reaction. A mechanism involving a chelation with a magnesium species is proposed to explain this C-2 inversion reaction.
Assuntos
Iodetos/química , Lactonas/química , Compostos de Magnésio/química , Isomerismo , MonossacarídeosRESUMO
[Structure: see text] A polyionic gel-soaked Rh catalyst allows the formation of synthetically useful diphenylsilyl (DPS) enols under mild conditions. The reaction proceeds through dehydrogenative silylation of ketones, affording the kinetic silyl enol ether in good to excellent yields. The in situ formed DPS enols were directly involved, without purification, in one-pot aldol and Mannich condensations.
RESUMO
[reaction: see text] The combination of CrCl(2) and silyl chlorides converts aryl and conjugated aldehydes into olefinic adducts in good to excellent yields. When constrained by structural features, the intermediate vic-diol can be isolated. Available data are consistent with a novel chromium Brook rearrangement.
Assuntos
Aldeídos/química , Alcenos/síntese química , Cromo/química , Compostos Organometálicos/síntese química , Silanos/química , Alcenos/química , Catálise , Estrutura Molecular , Compostos Organometálicos/químicaRESUMO
Treatment of cyclic tert-trihalomethylcarbinols with CrCl(2) in THF/HMPA in the presence of aryl or aliphatic aldehydes initiates a cascade sequence of one carbon ring expansion-olefination affording conjugated exocyclic ketones. Acyclic tert-trihalomethylcarbinols undergo a comparable cascade of one carbon homologation-olefination.
Assuntos
Aldeídos/química , Metanol/química , CiclizaçãoRESUMO
New oligomers or polymers are prepared by polymerization of arsonium ylides in the presence of boron compounds.
Assuntos
Compostos Alílicos/química , Arsênio/química , Boro/química , Compostos Organofosforados/química , Polímeros/química , Sais/química , Espectroscopia de Ressonância Magnética , Modelos QuímicosRESUMO
Primary, secondary, and tertiary alcohols as well as phenols and carbohydrates are efficiently transformed into the corresponding 2-tetrahydrofuranyl ethers by a combination of Mn(0) powder and CCl(4) in tetrahydrofuran.