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1.
Chemosphere ; 238: 124617, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31450108

RESUMO

Perfluorooctanoic acid (PFOA) in environmental media contains numerous isomers/enantiomers because of the PFOA manufacturing process and biological degradation of PFOA precursors. Few methods for analyzing PFOA enantiomers have been described. A simple derivatization method using (S)-1-phenethyl chloride that was developed to allow PFOA isomers/enantiomers to be separated by gas chromatography and analyzed by electron-capture negative ionization mass spectrometry is described here. PFOA standards were analyzed, and enantiomers of the chiral isomers perfluoro-3-methyl-heptanoic acid, perfluoro-4-methyl-heptanoic acid, and perfluoro-3,5-dimethyl-hexanoic acid were separated using an HP-5MS column. Linear PFOA and perfluoro-6-methyl-heptanoic acid were chromatographically separated from these enantiomers. The linear ranges (giving correlation coefficients r > 0.997) of the calibration curves for the isomers were 0.010-3.00 ng/mL. PFOA isomer/enantiomer concentrations in river water were determined using the method. The method separated the enantiomers of perfluoro-3-methyl-heptanoic acid and perfluoro-4-methyl-heptanoic acid, the isomers of perfluoro-6-methyl-heptanoic acid, and linear PFOA in river water. No significant differences were found between the PFOA enantiomer/isomer compositions of the sample and technical PFOA. Enantiomer ratios can provide information about the sources and transport of pollutant isomers/enantiomers in the environment. Enantiomeric separation requires effective separation techniques. Our method achieved chiral separation using a non-chiral GC column that is often used in general analytical laboratories. The method could be used to investigate the sources and fates of PFOA and the isomers/enantiomers of other potentially toxic persistent pollutants in the environment and the risks posed to humans.


Assuntos
Caprilatos/química , Fluorcarbonetos/química , Cromatografia Gasosa-Espectrometria de Massas/métodos , Rios/química , Poluentes Químicos da Água/química , Caprilatos/análise , Caprilatos/isolamento & purificação , Fluorcarbonetos/análise , Fluorcarbonetos/isolamento & purificação , Humanos , Estereoisomerismo , Poluentes Químicos da Água/análise , Poluentes Químicos da Água/isolamento & purificação
2.
Bioelectrochemistry ; 131: 107396, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31704455

RESUMO

We report a novel chiral interface based on polysaccharides that was integrated via an amidation reaction between the COOH of sodium alginate and the NH2 of chitosan to form a chiral selector (SA-CS) with three dimensional N-doped graphene-CNT (NGC) as the substrate material. This interface was used for chiral discrimination of tryptophan (Trp) enantiomers via electrochemical measurements. The FT-IR, SEM, TEM and XPS characterization showed that the chiral selector and substrate materials were prepared successfully. Compared with individual SA-CS and NGC, the integrated polysaccharides/3D NGC showed higher enantioselectivity for L-Trp than D-Trp due to the smaller steric hindrance for D-Trp during the formation of three-point interactions between the two diastereoisomeric enantiomer-selector complexes, which allowed L-Trp to more easily detach from the electrode modification layer and approach the electrode surface, facilitating its approach and confirming that SA-CS had a higher constant for L-Trp when applied to real samples.


Assuntos
Técnicas Eletroquímicas/métodos , Grafite/química , Nitrogênio/química , Polissacarídeos/química , Estereoisomerismo , Termodinâmica
3.
Food Chem ; 305: 125486, 2020 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-31520920

RESUMO

The formation of 3-methyl-2,4-nonanedione (MND) during red wine aging can contribute to the premature evolution of aroma, characterized by the loss of fresh fruit and development of dried fruit flavors. The identification of two new hydroxy ketones, 2-hydroxy-3-methylnonan-4-one (syn- and anti-ketol diastereoisomers) and 3-hydroxy-3-methyl-2,4-nonanedione (HMND), prompted the investigation of the precursors and pathways through which MND is produced and evolves. An HS-SPME-GC-MS method was optimized for their quantitation in numerous must and wine samples, providing insight into the evolution of MND, HMND, and ketols through alcoholic fermentation and wine aging. Alcoholic fermentation resulted in a significant decrease in MND and HMND and the simultaneous appearance of ketol diastereoisomers. The analysis of 167 dry red wines revealed significant increases in MND and anti-ketol contents through aging and a significant positive correlation between MND and anti-ketols. Additional experiments demonstrated that ketols are precursors to MND during red wine oxidation.


Assuntos
Alcanos/química , Diacetil/análogos & derivados , Sucos de Frutas e Vegetais/análise , Cetonas/análise , Vinho/análise , Alcanos/metabolismo , Diacetil/química , Diacetil/metabolismo , Etanol/química , Cromatografia Gasosa-Espectrometria de Massas , Humanos , Concentração de Íons de Hidrogênio , Cetonas/isolamento & purificação , Limite de Detecção , Microextração em Fase Sólida , Estereoisomerismo , Fatores de Tempo
4.
J Environ Sci (China) ; 87: 163-172, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31791489

RESUMO

The effects of biosolids, ZnO, and ZnO/biosolids on soil microorganism and the environmental fate of coexisting racemic-quizalofop-ethyl (rac-QE) were investigated. Microbial biomass carbon in native soil, soil/biosolids decreased by 62% and 52% in the presence of ZnO (2‰, weight ratio). The soil bacterial community structure differed significantly among native soil, soil/biosolids, soil/ZnO, and soil/biosolids/ZnO based on a principal co-ordinate analysis (PCoA) of OTUs and one-way ANOVA test of bacterial genera. Chemical transformation caused by ZnO only contributed 4% and 3% of the overall transformation of R-quizalofop-ethyl (R-QE) and S-quizalofop-ethyl (S-QE) in soil/ZnO. The inhibition effect of ZnO on the initial transformation rate of R-QE (rR-QE) and S-QE (rR-QE) in soil only observed when enantiomer concentration was larger than 10 mg/kg. Biosolids embedded with ZnO (biosolids/ZnO) caused a 17%-42% and 22%-38% decrease of rR-QE and rS-QE, although rR-QE and rS-QE increased by 0%-17% and 22%-58% by the addition of biosolids. The results also demonstrated that the effects of biosolids on agricultural soil microorganism and enantioselective transformation of chiral pesticide was altered by the embedded nanoparticles.


Assuntos
Propionatos/toxicidade , Quinoxalinas/toxicidade , Microbiologia do Solo , Poluentes do Solo/toxicidade , Herbicidas/metabolismo , Propionatos/metabolismo , Quinoxalinas/metabolismo , Solo/química , Poluentes do Solo/metabolismo , Estereoisomerismo , Óxido de Zinco
5.
Top Curr Chem (Cham) ; 378(1): 9, 2019 Dec 27.
Artigo em Inglês | MEDLINE | ID: mdl-31879793

RESUMO

Asymmetric metal/organo relay catalysis, utilizing a metal complex and a chiral organocatalyst in a one-pot cascade reaction, is aimed to sequentially impart activation on multiple steps by distinct catalysts. Such a catalysis merges the advantages of both metal catalysis and organocatalysis, providing step-economy, and, more importantly, the potential to achieve inaccessible reactivity by a single catalyst. Chiral phosphoric acids are among the most robust organocatalysts, rendering a broad range of enantioselective bond-forming reactions. The combination of metal complexes and chiral phosphoric acids in a single vessel has been well documented. In particular, the asymmetric relay catalysis of metal complex with chiral phosphoric acid has grown rapidly since 2008. Several excellent reviews have been published to cover almost all examples in this area from 2008 to early 2014; therefore, in this chapter, we will mainly highlight progress from 2014 to mid-2019.


Assuntos
Complexos de Coordenação/química , Ácidos Fosfóricos/química , Catálise , Estrutura Molecular , Estereoisomerismo
6.
Top Curr Chem (Cham) ; 377(6): 37, 2019 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-31728771

RESUMO

Over the past decade, the combination of visible light photocatalysis and organocatalysis has made remarkable progress in modern chemical synthesis. In these dual catalysis system, photocatalysts or photosensitizers absorb visible light to induce their photoexcited states which can activate unreactive substrates via electron or energy transfer mechanisms, and organocatalysts are usually employed to regulate the chemical reactivity of the other substrates. By doing so, two reactive species react with each in a selective-especially enantioselective-way, to provide the final products. This article summarizes the recent development of cooperative catalysis by the combination of organocatalysis and photocatalysis in asymmetric organic synthesis. These reactions are classified according to the manner of activation of the organocatalysts. Enamine/iminium catalysts are used to activate unreactive carbonyl molecules. Nucleophilic catalysts including nitrogen heterocycle carbene catalysts and tertiary amine catalysts are employed to reverse the reactivity of electrodeficient substrates including aldehydes and enals. Chiral Brønsted acid catalysts are used to activate substrates by forming key H-bonding complexes between substrates and catalysts.


Assuntos
Aminas/química , Iminas/química , Luz , Aldeídos/química , Alcenos/química , Catálise , Metano/análogos & derivados , Metano/química , Estereoisomerismo
7.
Top Curr Chem (Cham) ; 377(6): 38, 2019 Nov 16.
Artigo em Inglês | MEDLINE | ID: mdl-31732819

RESUMO

The concept of merging enamine activation catalysis with transition metal catalysis is an important strategy, which allows for selective chemical transformations not accessible without this combination. The amine catalyst activates the carbonyl compounds through the formation of a reactive nucleophilic enamine intermediate and, in parallel, the transition metal activates a wide range of functionalities such as allylic substrates through the formation of reactive electrophilic π-allyl-metal complex. Since the first report of this strategy in 2006, considerable effort has been devoted to the successful advancement of this technology. In this chapter, these findings are highlighted and discussed.


Assuntos
Aminas/química , Elementos de Transição/química , Alquilação , Alquinos/química , Catálise , Complexos de Coordenação/química , Ciclização , Cetonas/química , Estereoisomerismo
8.
Top Curr Chem (Cham) ; 378(1): 1, 2019 Nov 25.
Artigo em Inglês | MEDLINE | ID: mdl-31761979

RESUMO

Organocatalysis-the branch of catalysis featuring small organic molecules as the catalysts-has, in the last decade, become of central importance in the field of asymmetric catalysis, so much that it is now comparable to metal catalysis and biocatalysis. Organocatalysis is rationalized and classified by a number of so-called activation modes, based on the formation of a covalent or not-covalent intermediate between the organocatalyst and the organic substrate. Among all the organocatalytic activation modes, enamine and iminium catalysis are widely used for the practical preparation of valuable products and intermediates, both in academic and industrial contexts. In both cases, chiral amines are employed as catalysts. Enamine activation mode is generally employed in the reaction with electrophiles, while nucleophiles require the iminium activation mode. Commonly, in both modes, the reaction occurs through well-organized transitions states. A large variety of partners can react with enamines and iminium ions, due to their sufficient nucleophilicity and electrophilicity, respectively. However, despite the success, organocatalysis still suffers from narrow scopes and applications. Multicatalysis is a possible solution for these drawbacks because the two different catalysts can synergistically activate the substrates, with a simultaneous activation of the two different reaction partners. In particular, in this review we will summarize the reported processes featuring Lewis acid catalysis and organocatalytic activation modes synergically acting and not interfering with each other. We will focus our attention on the description of processes in which good results cannot be achieved independently by organocatalysis or Lewis acid catalysis. In these examples of cooperative dual catalysis, a number of new organic transformations have been developed. The review will focus on the possible strategies, the choice of the Lewis acid and the catalytic cycles involved in the effective reported combination. Additionally, some important key points regarding the rationale for the effective combinations will be also included. π-Activation of organic substrates by Lewis acids, via formation of electrophilic intermediates, and their reaction with enamines will be also discussed in this review.


Assuntos
Aminoácidos/química , Ácidos de Lewis/química , Catálise , Estrutura Molecular , Estereoisomerismo
9.
Top Curr Chem (Cham) ; 377(6): 35, 2019 Nov 13.
Artigo em Inglês | MEDLINE | ID: mdl-31720874

RESUMO

N-Heterocyclic carbene (NHC) catalysis can access umpolung reactivity of carbonyl compounds as acyl anions, enolates and homoenolates. Considerable progress has been made in asymmetric transformation by the introduction of chirality to the NHC scaffold. However, the single catalyst system has limitations in chemo-, regio- and stereoselectivity. A solution to these problems has recently emerged with the synergistic combination of NHC catalysis and metal catalysis. A number of NHC/metal combinations have been found not only to improve reactivity and stereoselectivity, but also to enable access to unprecedented transformations. This paper highlights examples of successful asymmetric NHC/metal cooperative catalysis.


Assuntos
Metais/química , Metano/análogos & derivados , Catálise , Complexos de Coordenação/química , Compostos Heterocíclicos/química , Ácidos de Lewis/química , Metano/química , Estereoisomerismo
10.
Chem Commun (Camb) ; 55(86): 12916-12919, 2019 Oct 24.
Artigo em Inglês | MEDLINE | ID: mdl-31603445

RESUMO

An enantioselective aerobic decarboxylative Povarov reaction of N-aryl α-amino acids with methylenephthalimidines through cooperative photoredox and chiral Brønsted acid catalysis is reported. With a transition metal-free dual catalytic system including a chiral phosphoric acid and DPZ as a photosensitizer mediated by visible light, the transformations provided a series of valuable chiral isoindolin-1-ones containing a 3,3-spiro-tetrahydroquinoline-based stereocenter in high yields (up to 83%) with good to excellent enantioselectivities (up to 98% ee) and excellent diastereoselectivity (>20 : 1 dr).


Assuntos
Aminoácidos/química , Luz , Ácidos Fosfóricos/química , Ftalimidas/química , Catálise , Oxirredução , Compostos de Espiro/química , Estereoisomerismo
11.
Chemistry ; 25(63): 14267-14272, 2019 Nov 13.
Artigo em Inglês | MEDLINE | ID: mdl-31603595

RESUMO

Bioinspired complexes employing the ligands 6-tert-butylpyridazine-3-thione (SPn) and pyridine-2-thione (SPy) were synthesized and fully characterized to mimic the tungstoenzyme acetylene hydratase (AH). The complexes [W(CO)(C2 H2 )(CHCH-SPy)(SPy)] (4) and [W(CO)(C2 H2 )(CHCH-SPn)(SPn)] (5) were formed by intramolecular nucleophilic attack of the nitrogen donors of the ligand on the coordinated C2 H2 molecule. Labelling experiments using C2 D2 with the SPy system revealed the insertion reaction proceeding via a bis-acetylene intermediate. The starting complex [W(CO)(C2 H2 )(SPy)2 ] (6) for these studies was accessed by the new acetylene precursor mixture [W(CO)(C2 H2 )n (MeCN)3-n Br2 ] (n=1 and 2; 7). All complexes represent rare examples in the field of W-C2 H2 chemistry with 4 and 5 being the first of their kind. In the ongoing debate on the enzymatic mechanism, the findings support activation of acetylene by the tungsten center.


Assuntos
Materiais Biomiméticos/química , Complexos de Coordenação/química , Tungstênio/química , Acetileno/química , Acetileno/metabolismo , Materiais Biomiméticos/metabolismo , Complexos de Coordenação/síntese química , Medição da Troca de Deutério , Hidroliases/química , Hidroliases/metabolismo , Espectroscopia de Ressonância Magnética , Conformação Molecular , Estereoisomerismo
12.
Chem Commun (Camb) ; 55(83): 12487-12490, 2019 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-31566647

RESUMO

CF2H-Pseudoprolines obtained from difluoroacetaldehyde hemiacetal and serine are stable proline surrogates. The consequence of the incorporation of the CF2H group is an important decrease of the trans to cis amide bond isomerization energy and a remarkable stabilisation of the cis conformer by an hydrogen bond.


Assuntos
Peptídeos/química , Prolina/análogos & derivados , Tiazóis/química , Tolueno/análogos & derivados , Ligações de Hidrogênio , Metilação , Conformação Molecular , Prolina/química , Estereoisomerismo , Tolueno/química
13.
J Agric Food Chem ; 67(45): 12558-12564, 2019 Nov 13.
Artigo em Inglês | MEDLINE | ID: mdl-31609622

RESUMO

All four stereoisomers of naturally occurring 6-(2-hydroxy-6-phenylhex-1-yl)-5,6-dihydro-2H-pyran-2-one (1) were synthesized by employing yeast-reduction products with high optical purity [from 95% enantiomeric excess (ee) to more than 99% ee], and then their phytotoxicities against lettuce and Italian ryegrass were evaluated. In the Italian ryegrass seedlings test, (6S,2'R)-1 showed the most potent and stereospecific activity against the shoots (IC50 = 260 µM) and roots (IC50 = 43.2 µM), with a significant difference from other stereoisomers. The highest seed germination inhibitory activity against Italian ryegrass seed was also observed in (6S,2'R)-1, showing a 53% germination ratio from the control at 1000 µM. This advantageous (6S,2'R) stereochemistry was employed in the syntheses of α,ß-dihydro, 2'-dehydroxy, and 2'-methoxy derivatives 13-15. By the test using these derivatives, the importance of the α,ß-unsaturated double bond and hydroxy group bonding to a chiral center on the 6-alkyl chain of 5,6-dihydro-α-pyrone for phytotoxicity was determined. In the test against lettuce, the 6S configuration and (6S,2'S) configuration were necessary for growth inhibition (IC50 = ca. 60 µM) and germination inhibition (63% germination ratio at 1000 µM), respectively.


Assuntos
Carbono/química , Herbicidas/farmacologia , Piranos/química , Carbono/farmacologia , Germinação/efeitos dos fármacos , Herbicidas/síntese química , Herbicidas/química , Alface/efeitos dos fármacos , Alface/crescimento & desenvolvimento , Lolium/efeitos dos fármacos , Lolium/crescimento & desenvolvimento , Estrutura Molecular , Piranos/farmacologia , Estereoisomerismo , Relação Estrutura-Atividade
14.
Chem Commun (Camb) ; 55(91): 13725-13728, 2019 Nov 12.
Artigo em Inglês | MEDLINE | ID: mdl-31660558

RESUMO

In this communication, the mechanism of how surface chirality affects amyloid-ß (Aß) fibrillation was firstly unravelled at the molecular level: a chiral surface serves to control the 2D-diffusion and surface residence time of Aß molecules via the chiral recognition with Aß to allow precursor Aß to laterally diffuse and collide with each other for oligomerization and fibrillation. Surface chirality that shortens the surface residence time of Aß, for example, R-cysteine modification with carboxylic, secondary amine and thiol groups surrounding the chiral center, can retard Aß oligomerization and fibrillation. This work is essential to a deeper fundamental understanding of the effects of surface chirality on amyloidosis processes as well as the development of chiral materials to inhibit Aß fibrillation.


Assuntos
Peptídeos beta-Amiloides/metabolismo , Amiloide/metabolismo , Fragmentos de Peptídeos/metabolismo , Amiloide/química , Peptídeos beta-Amiloides/química , Cisteína/química , Ligações de Hidrogênio , Microscopia de Força Atômica , Fragmentos de Peptídeos/química , Dióxido de Silício/química , Estereoisomerismo
15.
Phys Chem Chem Phys ; 21(42): 23408-23417, 2019 Nov 14.
Artigo em Inglês | MEDLINE | ID: mdl-31625550

RESUMO

In the field of artificial metalloenzyme (ArM) catalysis, how to identify the critical factors affecting the catalytic activity and enantioselectivity remains a challenge. In this work, the mechanism of enantioselective reduction of imine catalyzed by using [Rh(Me4Cpbiot)Cl2]·S112H Sav (denoted as S112H) and [Rh(Me4Cpbiot)Cl2]·K121H Sav (denoted as K121H) was studied by using molecular dynamics (MD) simulations combined with density functional theory (DFT) calculations. Four binding modes of imine, two proton sources (hydronium ion and lysine) and eight proposed reaction pathways were systematically discussed. The results showed that due to the anchoring effect of the mutation site of ArMs, the rhodium complex which oscillated like a pendulum was bound to a specific conformation, which further determined the chirality of the reduced product. C-Hπ, cation-π and ππ weak interactions played an important role in imine binding, and the favorable binding mode of imine was catalyzed by S112H in landscape orientation and catalyzed by K121H in portrait orientation, respectively. LYS121 is the most possible proton source in the S112H catalytic process while the proton source in the K121H catalytic process is the hydronium ion of the active sites. Furthermore, based on the reaction mechanism, modification of Rh(Me4Cpbiot)Cl2 was carried out in S112H and K121H, and the results suggested that the reaction barrier could be effectively reduced by replacing the methyl groups on Cp* with an amino group. This work gives a fundamental understanding of the mechanism of ArMs toward the imine reduction reaction, in the hope of providing a strategy for reasonable designs of ArMs with high enantioselectivity.


Assuntos
Complexos de Coordenação/química , Iminas/química , Sítios de Ligação , Catálise , Domínio Catalítico , Complexos de Coordenação/metabolismo , Teoria da Densidade Funcional , Metaloproteínas/química , Metaloproteínas/metabolismo , Simulação de Dinâmica Molecular , Oxirredução , Ródio/química , Estereoisomerismo , Termodinâmica
16.
Photochem Photobiol Sci ; 18(11): 2792-2803, 2019 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-31626259

RESUMO

We report the first exocyclically metallated tetrapyridinoporphyrazine, [tetrakis-(trans-Pt(NH3)2Cl)-tetra(3,4-pyrido)porphyrazine-zinc(ii)](NO3)4 (4), synthesized in a multistep synthesis starting from 3,4-pyridinedicarbonitrile (1). The synthetic procedure involved a platination reaction of the intermediate tetra(3,4-pyrido)porphyrazine-zinc(ii) (2), whereby the zinc(ii) enhanced the solubility of the intermediate enabling the platination reaction. A similar approach to synthesize [tetrakis-(trans-Pt(NH3)2Cl)-tetra(3,4-pyrido)porphyrazine](NO3)4 (5) failed due to the unsuitable solubility properties of the intermediate tetra(3,4-pyrido)porphyrazine (3). The final product 4 and the intermediates were characterized, the photochemical and photophysical properties were determined and the photocytotoxicities were investigated. We demonstrate that the platinated tetra-pyridinoporphyrazine 4 is a potential photosensitizer for photodynamic therapy (PDT).


Assuntos
Fármacos Fotossensibilizantes/química , Porfirinas/química , Zinco/química , Linhagem Celular Tumoral , Sobrevivência Celular/efeitos dos fármacos , Humanos , Luz , Neoplasias/tratamento farmacológico , Neoplasias/patologia , Fotoquimioterapia , Fármacos Fotossensibilizantes/síntese química , Fármacos Fotossensibilizantes/farmacologia , Porfirinas/síntese química , Porfirinas/farmacologia , Espécies Reativas de Oxigênio/metabolismo , Espectrometria de Fluorescência , Estereoisomerismo
17.
Chem Commun (Camb) ; 55(89): 13362-13365, 2019 Nov 18.
Artigo em Inglês | MEDLINE | ID: mdl-31631195

RESUMO

Rule-of-five parameters and membrane permeabilities have been routinely used to guide development of orally bioavailabile drugs. Here we compare enantiomeric pairs of cyclic hexapeptides with identical rule-of-five parameters and membrane permeabilities. For each enantiomeric pair, the isomer with more l- than d-amino acids is much more orally bioavailable in rats, more metabolically stable to rat liver microsomes, and cleared more slowly in vivo.


Assuntos
Peptídeos Cíclicos/metabolismo , Peptídeos Cíclicos/farmacocinética , Administração Oral , Animais , Disponibilidade Biológica , Microssomos Hepáticos/química , Microssomos Hepáticos/metabolismo , Conformação Molecular , Peptídeos Cíclicos/administração & dosagem , Ratos , Estereoisomerismo
18.
Top Curr Chem (Cham) ; 377(6): 31, 2019 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-31654245

RESUMO

Cooperative dual catalysis and bifunctional catalysis have emerged as reliable strategies for the development of hitherto difficult asymmetric transformations because they could deliver new reactivity and selectivity, and allow for the employment of substrates not amenable to reaction systems relying on a single, monofunctional catalysts. Furthermore, these modes of catalysis often improve yields and stereoselectivities via the precise recognition and simultaneous activation of nucleophiles and electrophiles. Efforts towards utilizing chiral cationic organic catalysts for asymmetric cooperative catalysis with metal complexes have provided a unique platform to address the challenging issues associated with reaction development. Chiral onium ions, such as tetraalkylammonium, guanidinium, and azolium ions, are employed mainly to control the reactivity and stereochemistry of anionic intermediates through electrostatic and hydrogen-bonding interactions. Metal complexes complement the synergy of the catalysis by activating the substrates via the formation of electrophilic π-allyl complexes, Lewis acid-base adducts, nucleophilic ate complexes, etc. The electrostatic interactions between cations and anions also offer a means to construct complex molecular assemblies, and, thus, onium ions are useful not only for controlling pairing with anionic species, but also for the design of supramolecular catalysts. The combination of onium ions and metal complexes leads to the introduction of novel concepts and powerful strategies for the development of catalysts and chemical transformations.


Assuntos
Ligantes , Metais/química , Carbono/química , Catálise , Cátions/química , Complexos de Coordenação/química , Ácidos de Lewis/química , Bases de Schiff/química , Estereoisomerismo
19.
J Phys Chem Lett ; 10(20): 6105-6111, 2019 Oct 17.
Artigo em Inglês | MEDLINE | ID: mdl-31549842

RESUMO

Protein-protein interactions (PPIs) play a pivotal role in many biological processes. Discriminating functionally important well-defined protein-protein complexes formed by specific interactions from random aggregates produced by nonspecific interactions is therefore a critical capability. While there are many techniques which enable rapid screening of binding affinities in PPIs, there is no generic spectroscopic phenomenon which provides rapid characterization of the structure of protein-protein complexes. In this study we show that chiral plasmonic fields probe the structural order and hence the level of PPI specificity in a model antibody-antigen system. Using surface-immobilized Fab' fragments of polyclonal rabbit IgG antibodies with high specificity for bovine serum albumin (BSA), we show that chiral plasmonic fields can discriminate between a structurally anisotropic ensemble of BSA-Fab' complexes and random ovalbumin (OVA)-Fab' aggregates, demonstrating their potential as the basis of a useful proteomic technology for the initial rapid high-throughput screening of PPIs.


Assuntos
Fragmentos Fab das Imunoglobulinas/metabolismo , Imunoglobulina G/metabolismo , Nanoestruturas/química , Cimento de Policarboxilato/química , Soroalbumina Bovina/metabolismo , Animais , Anisotropia , Bovinos , Ouro/química , Fragmentos Fab das Imunoglobulinas/imunologia , Imunoglobulina G/imunologia , Ovalbumina/imunologia , Ovalbumina/metabolismo , Ligação Proteica , Coelhos , Soroalbumina Bovina/imunologia , Análise Espectral/métodos , Estereoisomerismo
20.
J Agric Food Chem ; 67(42): 11650-11656, 2019 Oct 23.
Artigo em Inglês | MEDLINE | ID: mdl-31554401

RESUMO

Occurring in hops (Humulus lupulus) and beer as a racemic mixture, (2R,2S)-8-prenylnaringenin (8-PN) is a potent phytoestrogen in hop dietary supplements used by women as alternatives to conventional hormone therapy. With a half-life exceeding 20 h, 8-PN is excreted primarily as 8-PN-7-O-glucuronide or 8-PN-4'-O-glucuronide. Human liver microsomes and 11 recombinant human UDP-glucuronosyltransferases (UGTs) were used to catalyze the formation of the two oxygen-linked glucuronides of purified (2R)-8-PN and (2S)-8-PN, which were subsequently identified using mass spectrometry and nuclear magnetic resonance spectroscopy. Formation of (2R)- and (2S)-8-PN-7-O-glucuronides predominated over the 8-PN-4'-O-glucuronides except for intestinal UGT1A10, which formed more (2S)-8-PN-4'-O-glucuronide. (2R)-8-PN was a better substrate for all 11 UGTs except for UGT1A1, which formed more of both (2S)-8-PN glucuronides than (2R)-8-PN glucuronides. Although several UGTs conjugated both enantiomers of 8-PN, some conjugated just one enantiomer, suggesting that human phenotypic variation might affect the routes of metabolism of this chiral estrogenic constituent of hops.


Assuntos
Flavanonas/química , Glucuronídeos/química , Glucuronosiltransferase/química , Extratos Vegetais/química , Biocatálise , Flavanonas/metabolismo , Glucuronídeos/metabolismo , Glucuronosiltransferase/metabolismo , Humanos , Humulus/química , Humulus/metabolismo , Espectrometria de Massas , Microssomos Hepáticos/química , Microssomos Hepáticos/metabolismo , Extratos Vegetais/metabolismo , Estereoisomerismo
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