Search results for "Reactivity"
showing 10 items of 880 documents
Unveiling the high reactivity of cyclohexynes in [3 + 2] cycloaddition reactions through the molecular electron density theory
2018
[3 + 2] cycloaddition (32CA) reactions of cyclohexyne, a cyclic strained acetylene, with methyl azide and methoxycarbonyl diazomethane have been studied within the Molecular Electron Density Theory (MEDT) at the MPWB1K/6-311G(d) computational level. These 32CA reactions, which take place through a one-step mechanism involving highly asynchronous transition state structures, proceed with relatively low activation enthalpies of 6.0 and 4.3 kcal mol-1, respectively, both reactions being strongly exothermic. The reactions are initiated by the creation of a pseudoradical center at one of the two acetylenic carbons of cyclohexyne with a very low energy cost, 1.0 kcal mol-1, which promotes the eas…
Photo-Chromium: Sensitizer for Visible-Light-Induced Oxidative C−H Bond Functionalization-Electron or Energy Transfer?
2017
The chromium(III) sensitizer [Cr(ddpd)2]3+ - based on an earth-abundant metal center - possesses a unique excited state potential energy landscape (ddpd = N,N'-dimethyl-N,N'-dipyridine-2-ylpyridine-2,6-diamine). The very large energy gap between the redox active and substitutionally labile 4T2 state and the long-lived low-energy 2E spin-flip state enables a selective, efficient sensitization of triplet dioxygen to give singlet dioxygen. Ultrafast intersystem crossing after the Franck Condon point from the 4T2 to the 2E excited state within 3.5 ps precludes intermolecular electron transfer pathways from the ultrashort-lived excited 4T2 state. This specific excited state reactivity enables a …
Influence of the solvent and R groups on the structure of (carboranyl)R2PI2 compounds in solution. Crystal structure of the first iodophosphonium sal…
2008
The influence of the electron-donor or electron-acceptor capacity of the R groups (R = (i)Pr, Ph, Et) and the solvent on the molecular geometry in solution of adducts of carboranylphosphanes [(carboranyl)(i)Pr2P, (carboranyl)Ph2P and (carboranyl)Et2P] with I2 in 1 : 1 ratios, has been studied in detail by 31P{1H} and 11B{1H} NMR spectroscopies. The more electron-accepting Ph groups make the (carboranyl)Ph2P less nucleophilic, thus stabilizing the I2 encapsulated neutral biscarboranylphosphane-diiodine adducts in solution, such as (carboranyl)Ph2PI-IPPh2(carboranyl), generating P---I-I---P motifs. Even in a polar solvent, such as EtOH, the arrangement is preserved. The expected basicity of t…
Asymmetric Vinylogous Mannich-Type Addition of α,α-Dicyanoalkenes to α-Fluoroalkyl Sulfinyl Imines
2018
Abstract. The asymmetric vinylogous Mannich reaction (AVMR) of alfa,alfa-dicyanoalkenes with alfa-fluoroalkyl sulfinyl imines has been successfully accomplished. This transformation is unprecedented with fluorinated imines at the same time as the use of dicyanoalkenes in AVMR has been scarcely reported. Several fluorinated sulfinyl imines are compatible with the process, which gaves access to a family of chiral fluorinated amines with excellent level of stereocontrol. Interestingly, the selectivity found in our protocol is reverse to that encountered in analogous AVMR previously reported. Additionally, the synthetic applicability of the addition products has been exemplified with several tr…
DFT Study on the Interaction of Tris(benzene-1,2-dithiolato)molybdenum Complex with Water. A Hydrolysis Mechanism Involving a Feasible Seven-Coordina…
2016
In the present work, the reactivity of the tris(benzene-1,2-dithiolato)molybdenum complex ([Mo(bdt)3]) toward water is studied by means of the density functional theory (DFT). DFT calculations were performed using the M06, B3P86, and B3PW91 hybrid functionals for comparison purposes. The M06 method was employed to elucidate the reaction pathway, relative stability of the intermediate products, nature of the Mo–S bond cleavage, and electronic structure of the involved molybdenum species. This functional was also used to study the transference of electrons from the molybdenum center toward the ligands. The reaction pathway confirms that [Mo(bdt)3] undergoes hydrolysis, yielding dihydroxo-bis(…
Reactivity of di-n-butyl-dicyclopentadienylzirconium towards amido stabilized stannylenes
2009
Abstract Reaction of Sn[(N(C 6 H 3 i Pr 2 -2,6)(SiMe 3 )] 2 and [{Sn(N(C 6 H 3 i Pr 2 -2,6)(SiMe 3 )(μ-Cl) 2 ] with di- n -butyl-dicyclopentadienylzirconium yielded the trimetallic a carbene-like complex {[(N(C 6 H 3 i Pr 2 -2,6)(SiMe 3 )]( n -Bu)Sn} 2 Cp 2 Zr. The oxidation of {[(N(C 6 H 3 i Pr 2 -2,6)(SiMe 3 )]( n -Bu)Sn} 2 Cp 2 Zr by oxygen gives the five-membered dioxadistannazirconacyclic complex {[(N(C 6 H 3 i Pr 2 -2,6)(SiMe 3 )]( n -Bu)Sn} 2 O 2 Cp 2 Zr.
Mechanism of the OH Radical Addition to Adenine from Quantum-Chemistry Determinations of Reaction Paths and Spectroscopic Tracking of the Intermediat…
2016
The OH radical is a well-known mediator in the oxidation of biological structures like DNA. Over the past decades, the precise events taking place after reaction of DNA nucleobases with OH radical have been widely investigated by the scientific community. Thirty years after the proposal of the main routes for the reaction of •OH with adenine (Vieira, A.; Steenken, S. J. Am. Chem. Soc. 1990, 112, 6986−6994), the present work demonstrates that the OH radical addition to C4 position is a minor pathway. Instead, the dehydration process is mediated by the A5OH adduct. Conclusions are based on density functional theory calculations for the ground-state reactivity and highly accurate multiconfigur…
BIOMARKERS OF CORONARY MICROVASCULAR DYSFUNCTION IN PATIENTS WITH MICROVASCULAR ANGINA: A NARRATIVE REVIEW
2021
The current gold standard for diagnosis of coronary microvascular dysfunction (CMD) in the absence of myocardial diseases, whose clinical manifestation is microvascular angina (MVA), is reactivity testing using adenosine or acetylcholine during coronary angiography. This invasive test can be difficult to perform, expensive, and harmful. The identification of easily obtainable blood biomarkers which reflect the pathophysiology of CMD, characterized by high reliability, precision, accuracy, and accessibility may reduce risks and costs related to invasive procedures and even facilitate the screening and diagnosis of CMD. In this review, we summarized the results of several studies that have i…
Are children more paternalistic than their mothers when choosing snacks?
2016
International audience; This paper focuses on an experiment in which mothers and their child separately chose between relatively healthy foods (flasks of stewed apples) and relatively unhealthy foods (candy bars). Each participant first filled up a first bag for her/himself, and then, a second one for the other person of the dyad. A simple nutritional message on vitamins and sugar contents of foods was then provided, and subsequently each participant filled up a third bag for her/himself and a fourth one for the other person of the dyad. The results show that before revealing the nutritional message, mothers are, on average, "indulgent", which means that they choose a lower number of relati…
Singlet Oxygen Attack on Guanine: Reactivity and Structural Signature within the B-DNA Helix
2016
International audience; Oxidatively generated DNA lesions are numerous and versatile, and have been the subject of intensive research since the discovery of 8-oxoguanine in 1984. Even for this prototypical lesion, the precise mechanism of formation remains elusive due to the inherent difficulties in characterizing high-energy intermediates. We have probed the stability of the guanine endoperoxide in B-DNA as a key intermediate and determined a unique activation free energy of around 6 kcal mol−1 for the formation of the first C−O covalent bond upon the attack of singlet molecular oxygen (1O2) on the central guanine of a solvated 13 base-pair poly(dG-dC), described by means of quantum mechan…