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191.
Marco Lunardon Mattia Cattelan Stefano Agnoli Gaetano Granozzi 《Current Opinion in Electrochemistry》2022
Due to their low cost and overall sustainability, transition metal dichalcogenides (TMDCs) are potential alternatives to noble metals as catalysts to produce green hydrogen. A promising route to improve their performances consists of activating their basal plane, both increasing the number of active sites or their specific activity. This can be accomplished by exploiting point defects, in-plane boundaries and strain. In particular, single atom adsorbed or incorporated into TMDCs have shown remarkable results in electrochemical half-cell tests. Topological curvature or grain boundaries (and related defects) can also be used to further boost the performances. A crucial point for the application of such strategies is related to the development of cost effective and sustainable methods for the scale-up of synthetic protocols. 相似文献
192.
Glycomimetics Targeting Glycosyltransferases: Synthetic,Computational and Structural Studies of Less‐Polar Conjugates 下载免费PDF全文
Mattia Ghirardello Matilde de las Rivas Alessandra Lacetera Dr. Ignacio Delso Dr. Erandi Lira‐Navarrete Prof. Tomás Tejero Dr. Sonsoles Martín‐Santamaría Dr. Ramón Hurtado‐Guerrero Prof. Pedro Merino 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(21):7215-7224
The Leloir donors are nucleotide sugars essential for a variety of glycosyltransferases (GTs) involved in the transfer of a carbohydrate to an acceptor substrate, typically a protein or an oligosaccharide. A series of less‐polar nucleotide sugar analogues derived from uridine have been prepared by replacing one phosphate unit with an alkyl chain. The methodology is based on the radical hydrophosphonylation of alkenes, which allows coupling of allyl glycosyl compounds with a phosphate unit suitable for conjugation to uridine. Two of these compounds, the GalNAc and galactose derivatives, were further tested on a model GT, such as GalNAc‐T2 (an important GT widely distributed in human tissues), to probe that both compounds bound in the medium–high micromolar range. The crystal structure of GalNAc‐T2 with the galactose derivative traps the enzyme in an inactive form; this suggests that compounds only containing the β‐phosphate could be efficient ligands for the enzyme. Computational studies with GalNAc‐T2 corroborate these findings and provide further insights into the mechanism of the catalytic cycle of this family of enzymes. 相似文献
193.
Mattia Ghirardello Kim Öberg Samuele Staderini Olivier Renaudet Nathalie Berthet Pascal Dumy Yvonne Hed Alberto Marra Michael Malkoch Alessandro Dondoni 《Journal of polymer science. Part A, Polymer chemistry》2014,52(17):2422-2433
Alkene and alkyne functional polyester‐based dendrimers of generation 1 to 4 have been prepared and reacted under free‐radical conditions with 2‐acetamido‐2‐deoxy‐1‐thio‐β‐D ‐glucose (GlcNAc‐SH). As the alkene‐dendrimers underwent the addition of one thiyl radical per ene group whereas each yne group of alkyne‐dendrimers was saturated by two thiyl radicals, a collection of glycodendrimers with glycan density ranging from six to ninety‐six GlcNAc per dendrimer was obtained. The recognition properties of the prepared glycodendrimers toward the wheat germ agglutinin (WGA) were evaluated by enzyme‐linked lectin assay (ELLA). The eight glycodendrimers were excellent ligands showing IC50 values in the nanomolar range and relative potencies per sugar unit up to 2.27 e6 when compared to monosaccharidic GlcNAc used as monovalent reference. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2422–2433 相似文献
194.
Mattia Riccardo Monaco Belén Poladura Dr. Miriam Diaz de Los Bernardos Markus Leutzsch Dr. Richard Goddard Prof. Dr. Benjamin List 《Angewandte Chemie (International ed. in English)》2014,53(27):7063-7067
Organocatalysis, catalysis using small organic molecules, has recently evolved into a general approach for asymmetric synthesis, complementing both metal catalysis and biocatalysis. 1 Its success relies to a large extent upon the introduction of novel and generic activation modes. 2 Remarkably though, while carboxylic acids have been used as catalyst directing groups in supramolecular transition‐metal catalysis, 3 a general and well‐defined activation mode for this useful and abundant substance class is still lacking. Herein we propose the heterodimeric association of carboxylic acids with chiral phosphoric acid catalysts as a new activation principle for organocatalysis. This self‐assembly increases both the acidity of the phosphoric acid catalyst and the reactivity of the carboxylic acid. To illustrate this principle, we apply our concept in a general and highly enantioselective catalytic aziridine‐opening reaction with carboxylic acids as nucleophiles. 相似文献
195.
Mattia Riccardo Monaco Dr. Sébastien Prévost Prof. Dr. Benjamin List 《Angewandte Chemie (International ed. in English)》2014,53(31):8142-8145
The hydrolytic ring opening of epoxides is an important biosynthetic transformation and is also applied industrially. We report the first organocatalytic variant of this reaction, exploiting our recently discovered activation of carboxylic acids with chiral phosphoric acids via heterodimerization. The methodology mimics the enzymatic mechanism, which involves an enzyme‐bound carboxylate nucleophile. A newly designed phosphoric acid catalyst displays high stereocontrol in the desymmetrization of meso‐epoxides. The methodology shows wide generality with cyclic, acylic, aromatic, and aliphatic substrates. We also apply our method in the first highly enantioselective anti‐dihydroxylation of simple olefins. 相似文献
196.
Single‐Molecule Magnetism,Enhanced Magnetocaloric Effect,and Toroidal Magnetic Moments in a Family of Ln4 Squares 下载免费PDF全文
Chinmoy Das Shefali Vaidya Tulika Gupta Jamie M. Frost Mattia Righi Prof. Dr. Euan K. Brechin Prof. Dr. Marco Affronte Prof. Dr. Gopalan Rajaraman Prof. Dr. Maheswaran Shanmugam 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(44):15639-15650
Three cationic [Ln4] squares (Ln=lanthanide) were isolated as single crystals and their structures solved as [Dy4(μ4‐OH)(HL)(H2L)3(H2O)4]Cl2?(CH3OH)4?(H2O)8 ( 1 ), [Tb4(μ4‐OH)(HL)(H2L)3(MeOH)4]Cl2?(CH3OH)4?(H2O)4 ( 2 ) and [Gd4(μ4‐OH)(HL)(H2L)3(H2O)2(MeOH)2]Br2?(CH3OH)4?(H2O)3 ( 3 ). The structures are described as hydroxo‐centered squares of lanthanide ions, with each edge of the square bridged by a doubly deprotonated H2L2? ligand. Alternating current magnetic susceptibility measurements show frequency‐dependent out‐of‐phase signals with two different thermally assisted relaxation processes for 1 , whereas no maxima in χM“ appears above 2.0 K for complex 2 . For 1 , the estimated effective energy barrier for these two relaxation processes is 29 and 100 K. Detailed ab initio studies reveal that complex 1 possesses a toroidal magnetic moment. The ab initio calculated anisotropies of the metal ions in complex 1 were employed to simulate the magnetic susceptibility by using the Lines model (POLY_ANISO) and this procedure yields J1=+0.01 and J2=?0.01 cm?1 for 1 as the two distinct exchange interactions between the DyIII ions. Similar parameters are also obtained for complex 1 (and 2 ) from specific heat measurements. A very weak antiferromagnetic super‐exchange interaction (J1=?0.043 cm?1 and g=1.99) is observed between the metal centers in 3 . The magnetocaloric effect (MCE) was estimated by using field‐dependent magnetization and temperature‐dependent heat‐capacity measurements. An excellent agreement is found for the ?ΔSm values extracted from these two measurements for all three complexes. As expected, 3 shows the largest ?ΔSm variation (23 J Kg?1 K?1) among the three complexes. The negligible magnetic anisotropy of Gd indeed ensures near degeneracy in the (2S+1) ground state microstates, and the weak super‐exchange interaction facilitates dense population of low‐lying excited states, all of which are likely to contribute to the MCE, making complex 3 an attractive candidate for cryogenic refrigeration. 相似文献
197.
Tommaso R. I. Cataldi Giuliana Bianco Salvatore Abate Daniela Mattia 《Rapid communications in mass spectrometry : RCM》2009,23(21):3465-3477
A comprehensive and highly selective method for detecting in bacterial supernatants a modified sulfur nucleoside, S‐adenosyl‐L‐methionine (SAM), and its metabolites, i.e., S‐adenosylhomocysteine (SAH), adenosine (Ado), 5′‐deoxy‐5′‐methylthioadenosine (MTA), adenine (Ade), S‐adenosyl‐methioninamine (dcSAM), homocysteine (Hcy) and methionine (Met), was developed. The method is based on reversed‐phase liquid chromatography with positive electrospray ionization (ESI+) coupled to a hybrid linear quadrupole ion trap (LTQ) and 7‐T Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS). A gradient elution was employed with a binary solvent of 0.05 M ammonium formate at pH 4 and acetonitrile. The assay involves a simultaneous cleanup of cell‐free bacterial broths by solid‐phase extraction and trace enrichment of metabolites with a 50‐fold concentration factor by using immobilized phenylboronic and anion‐exchange cartridges. While the quantitative determination of SAM was performed using stable‐isotope‐labeled SAM‐d3 as an internal standard, in the case of Met and Ade, Met‐13C and Ade‐15N2 were employed as isotope‐labeled internal standards, respectively. This method enabled the identification of SAM and its metabolites in cell‐free culture of Pseudomonas aeruginosa grown in Davis minimal broth (formulation without sulphur organic compounds), with routine sub‐ppm mass accuracies (?0.27 ± 0.68 ppm). The resulting contents of SCSS‐SAM, SS‐dcSAM, MTA, Ado and Met in the free‐cell supernatant of P. aeruginosa was 56.4 ± 2.1 nM, 32.2 ± 2.2 nM, 0.91 ± 0.10 nM, 19.6 ± 1.2 nM and 1.93 ± 0.02 µM (mean ± SD, n = 4 extractions), respectively. We report also the baseline separation (Rs ≥1.5) of both diastereoisomeric forms of SAM (SCSS and SCRS) and dcSAM (SS and RS), which can be very useful to establish the relationship between the biologically active versus the inactive species, SCSS/SCRS and SS/RS of SAM and dcSAM, respectively. An additional confirmation of SAM‐related metabolites was accomplished by a systematic study of their MS/MS spectra. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
198.
199.
Spectral estimates for unreduced symmetric KKT systems arising from Interior Point methods 下载免费PDF全文
Benedetta Morini Valeria Simoncini Mattia Tani 《Numerical Linear Algebra with Applications》2016,23(5):776-800
We consider symmetrized Karush–Kuhn–Tucker systems arising in the solution of convex quadratic programming problems in standard form by Interior Point methods. Their coefficient matrices usually have 3 × 3 block structure, and under suitable conditions on both the quadratic programming problem and the solution, they are nonsingular in the limit. We present new spectral estimates for these matrices: the new bounds are established for the unpreconditioned matrices and for the matrices preconditioned by symmetric positive definite augmented preconditioners. Some of the obtained results complete the analysis recently given by Greif, Moulding, and Orban in [SIAM J. Optim., 24 (2014), pp. 49‐83]. The sharpness of the new estimates is illustrated by numerical experiments. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
200.
Yttrium and lanthanum amido-complexes with bis(pyrazol-1-yl)acetates in their coordination spheres were studied as the catalysts in ε-caprolactone and lactide ring-opening polymerisation. A high molecular mass poly(ε-caprolactone) (PCL) was obtained in almost quantitative yield under mild conditions. rac-Lactide polymerisations were less efficient and required quite harsh experimental conditions to obtain atactic PLA samples with moderate yields. The average chain-length of PCL was dependent upon the choice of the metal centre and the presence of substituents on the pyrazole rings of the ancillary ligand. The ground-state geometries of the complexes and the first stages of ε-caprolactone polymerisation were computationally modelled by means of DFT calculations. 相似文献