Search results for "Catalysis"
showing 10 items of 5944 documents
Sensing Chiral Drugs by Using CdSe/ZnS Nanoparticles Capped withN-Acetyl-L-Cysteine Methyl Ester
2013
Chiral quantum dots (QDs), differing in their core or shell size and, consequently, in their optical properties, were synthesized by the treatment of commercially available amine-capped quantum dots with methyl ester N-acetyl-L-cysteine (CysP). Interestingly, their colloidal methanol solutions remain stable for several months. Their NMR and IR spectra were in accordance with CysP binding to the QD surface through two anchoring groups; its thiolate (strongly bound) and the carbonyl group of its ester (weaker bound) group, whereas their circular dichroism (CD) spectra showed a new broad redshifted band, suggesting that the attachment to the QD surface modified the conformational equilibrium t…
Influencing the Self‐Sorting Behavior of [2.2]Paracyclophane‐Based Ligands by Introducing Isostructural Binding Motifs
2020
Abstract Two isostructural ligands with either nitrile (Lnit) or isonitrile (Liso) moieties directly connected to a [2.2]paracyclophane backbone with pseudo‐meta substitution pattern have been synthesized. The ligand itself (Lnit) or its precursors (Liso) were resolved by HPLC on a chiral stationary phase and the absolute configuration of the isolated enantiomers was assigned by XRD analysis and/or by comparison of quantum‐chemical simulated and experimental electronic circular dichroism (ECD) spectra. Surprisingly, the resulting metallosupramolecular aggregates formed in solution upon coordination of [(dppp)Pd(OTf)2] differ in their composition: whereas Lnit forms dinuclear complexes, Liso…
Circular dichroism of polynucleotides: Interactions of NiCl2 with poly(dA-dT).poly(dA-dT) and poly(dG-dC).poly(dG-dC) in a water-in-oil microemulsion.
2008
The thermal behavior of the synthetic, high molecular weight, double stranded polynucleotides poly(dA-dT)·poly(dA-dT) [polyAT] and poly(dG-dC)·poly(dG-dC) [polyGC] solubilized in the aqueous core of the quaternary water-in-oil cationic microemulsion CTAB|n-pentanol|n-hexane|water in the presence of increasing amounts of NiCl2 at several constant ionic strength values (NaCl) has been studied by means of circular dichroism and electronic absorption spectroscopies. In the microemulsive medium, both polynucleotides show temperature-induced modifications that markedly vary with both Ni(II) concentration and ionic strength. An increase of temperature causes denaturation of the polyAT duplex at lo…
Enantiomerically pure trinuclear helicates via diastereoselective self-assembly and characterization of their redox chemistry.
2014
A tris(bipyridine) ligand 1 with two BINOL (BINOL = 2, 2′-dihydroxy-1, 1′-binaphthyl) groups has been prepared in two enantiomerically pure forms. This ligand undergoes completely diastereoselective self-assembly into D2-symmeteric double-stranded trinuclear helicates upon coordination to copper(I) and silver(I) ions and to D3-symmetric triple-stranded trinuclear helicates upon coordination to copper(II), zinc(II), and iron(II) ions as demonstrated by mass spectrometry, NMR and CD spectroscopy in combination with quantum chemical calculations and X-ray diffraction analysis. According to the calculations, the single diastereomers that are formed during the self-assembly process are strongly …
Enantiomerically pure [M(6)L(12)] or [M(12)L(24)] polyhedra from flexible bis(pyridine) ligands.
2013
Coordination-driven self-assembly is one of the most powerful strategies to prepare nanometer-sized discrete (supra)molecular assemblies. Herein, we report on the use of two constitutionally isomeric BINOL-based bis(pyridine) ligands for this purpose. Upon coordination to Pd(II) ions these self-assemble into enantiomerically pure endo- and exo-functionalized hexa- and dodecanuclear metallosupramolecular spheres with a chiral skeleton depending on the substitution pattern of the BINOL core. These aggregates were characterized by NMR, MS, DLS, TEM, and EELS as well as ECD. Furthermore, experimental ECD data could be compared to those obtained from theoretical simulations using a simplified Ta…
Subcomponent self‐assembly of a cyclic tetranuclear Fe(II) helicate in a highly diastereoselective self‐sorting manner
2019
Abstract An enantiomerically pure diamine based on the 4,15‐difunctionalized [2.2]paracyclophane scaffold and 2‐formylpyridine self‐assemble into an optically pure cyclic metallosupramolecular Fe4L6 helicate upon mixing with iron(II) ions in a diastereoselective subcomponent self‐assembly process. The cyclic assembly results from steric strain that prevents the formation of a smaller linear dinuclear triple‐stranded helicate, and hence, leads to the larger strain‐free assembly that fulfils the maximum occupancy rule. Interestingly, use of the racemic diamine also leads to a racemic mixture of the homochiral cyclic helicates as the major product in a highly diastereoselective narcissistic ch…
Forever Young: Structural Stability of Telomeric Guanine Quadruplexes in the Presence of Oxidative DNA Lesions**
2021
International audience; Human telomeric DNA, in G-quadruplex (G4) conformation, is characterized by a remarkable structural stability that confers it the capacity to resist to oxidative stress producing one or even clustered 8-oxoguanine (8oxoG) lesions. We present a combined experimental/computational investigation, by using circular dichroism in aqueous solutions, cellular immunofluorescence assays and molecular dynamics simulations, that identifies the crucial role of the stability of G4s to oxidative lesions, related also to their biological role as inhibitors of telomerase, an enzyme overexpressed in most cancers associated to oxidative stress.
From Symmetry Breaking to Unraveling the Origin of the Chirality of Ligated Au13 Cu2 Nanoclusters
2018
A general method, using mixed ligands (here diphosphines and thiolates) is devised to turn an achiral metal cluster, Au13 Cu2 , into an enantiomeric pair by breaking (lowering) the overall molecular symmetry with the ligands. Using an achiral diphosphine, a racemic [Au13 Cu2 (DPPP)3 (SPy)6 ]+ was prepared which crystallizes in centrosymmetric space groups. Using chiral diphosphines, enantioselective synthesis of an optically pure, enantiomeric pair of [Au13 Cu2 ((2r,4r)/(2s,4s)-BDPP)3 (SPy)6 ]+ was achieved in one pot. Their circular dichroism (CD) spectra give perfect mirror images in the range of 250-500 nm with maximum anisotropy factors of 1.2×10-3 . DFT calculations provided good corre…
The Evolving Role of Fetuin-A in Nonalcoholic Fatty Liver Disease: An Overview from Liver to the Heart
2021
Nonalcoholic fatty liver disease (NAFLD) is strongly associated to the features of metabolic syndrome which can progress to cirrhosis, liver failure and hepatocellular carcinoma. However, the most common cause of mortality in people with NAFLD is not liver-related but stems from atherosclerotic cardiovascular disease (CVD). The prevalence of NAFLD is on the rise, mainly as a consequence of its close association with two major worldwide epidemics, obesity and type 2 diabetes (T2D). The exact pathogenesis of NAFLD and especially the mechanisms leading to disease progression and CVD have not been completely elucidated. Human fetuin-A (alpha-2-Heremans Schmid glycoprotein), a glycoprotein produ…
Bone-Targeted Cisplatin-Complexed Poly(γ-benzyl-L-glutamate)-Poly(glutamic acid) Block Polymer Nanoparticles: An Electrochemical Approach
2015
The voltammetric response of different osteotropic multifunctional nanoparticles based on cisplatin-complexed poly(γ-benzyl-L-glutamate)–poly(glutamic acid) block polymer (CDDP-PBLG-b-PGlu) copolymer, with or without poly(γ-benzyl-L-glutamate)–poly(ethylene glycol) block polymer (PBLG-b-PEG), and having bone-targeting properties is studied at biologically relevant pH. Significant differences in the cisplatin-centered voltammetric signals allow monitoring of the association of cisplatin to nanoparticles as well as release kinetics from them, in agreement with atomic absorption spectroscopy data. Electrochemical studies reveal that the cisplatin association is significant only if the proporti…