Search results for "bond"
showing 10 items of 3527 documents
N-heterocyclic carbenes and parent cations: acidity, nucleophilicity, stability, and hydrogen bonding-Electrochemical Study and ab initio calculations
2016
N-Heterocyclic carbenes (NHCs) are widely used as organocatalysts. Their reactivity (and instability) is related to their basicity and nucleophilicity, which, in turn, are linked to their scaffold. NHCs can be generated by chemical deprotonation or electrochemical reduction of the parent azolium cations, NHCH+s. Cyclic voltammetry enabled the reduction potential of the NHCH+s to be determined; the reduction potential is related to the acidity of the NHCH+s and the oxidation potential of the NHCs, which is related to the nucleophilicity of the NHCs. It was thus possible to order different NHCH+s and NHCs by their acidity and nucleophilicity, respectively. A study on the stability of NHCs was…
Classical ionic fluids in the mean spherical approximation
1980
The recently obtained analytical solution of the mean spherical approximation has been used to calculate thermodynamic and structural properties of aqueous solutions of asymmetric electrolytes. The same approximation has also been used to calculate structure functions of pure and mixed molten salts. The agreement between experimental or “quasi-experimental” structure functions and those obtained within the framework of the MSA is quite good especially when the ionic radii are obtained by fitting the long wavelength limit of the structure functions to the isothermal compressibility of the system, under the condition that the diameter ratio is the same as in the crystal.
Luminescent Ionic Transition-Metal Complexes for Light-Emitting Electrochemical Cells
2012
Higher efficiency in the end-use of energy requires substantial progress in lighting concepts. All the technologies under development are based on solid-state electroluminescent materials and belong to the general area of solid-state lighting (SSL). The two main technologies being developed in SSL are light-emitting diodes (LEDs) and organic light-emitting diodes (OLEDs), but in recent years, light-emitting electrochemical cells (LECs) have emerged as an alternative option. The luminescent materials in LECs are either luminescent polymers together with ionic salts or ionic species, such as ionic transition-metal complexes (iTMCs). Cyclometalated complexes of Ir(III) are by far the most util…
Impact of Surface Charge Directionality on Membrane Potential in Multi-ionic Systems
2020
The membrane potential (Vmem), defined as the electric potential difference across a membrane flanked by two different salt solutions, is central to electrochemical energy harvesting and conversion. Also, Vmem and the ionic concentrations that establish it are important to biophysical chemistry because they regulate crucial cell processes. We study experimentally and theoretically the salt dependence of Vmem in single conical nanopores for the case of multi-ionic systems of different ionic charge numbers. The major advances of this work are (i) to measure Vmem using a series of ions (Na+, K+, Ca2+, Cl-, and SO42-) that are of interest to both energy conversion and cell biochemistry, (ii) to…
Do zwitterionic species exist in the non-enzymatic peptide bond formation?
2012
The use of proper computational methods and models has allowed answering the controversial question of whether zwitterionic species exist in the mechanism of peptide bond synthesis in aqueous solution. In fact, the different conformations of zwitterionic species open the door to different mechanistic paths.
Mass Spectrometric Investigation of Noncovalent Complexation between a Tetratosylated Resorcarene and Alkyl Ammonium Ions
2004
Noncovalent complexation between tetratosylated tetraethyl resorcarene (1) and primary, secondary, and tertiary alkyl ammonium ions (mMe, dMe, tMe, mEt, dEt, tEt, dBu, and dHex) was studied by electrospray ionization Fourier transform ion cyclotron resonance (ESI-FTICR) mass spectrometry. Interactions of the noncovalent complexes were investigated by means of competition experiments, collision-induced dissociation (CID) experiments, ion-molecule reactions with tripropylamine and gas phase H/D-exchange reactions with deuteroammonia. Gas phase ion-molecule reactions gave especially valuable information about the structure and properties of the complexes. Resorcarene 1 formed relatively stable…
Molecular “Pincer” from a Diimidazolium Salt: A Study of Binding Ability
2013
The anion recognition ability of the dicationic imidazolium salt 3,3′-di-n-octyl-1,1′- (1,3-phenylenedimethylene)diimidazolium 1,5-naphthalenedisulfonate ([m-Xyl-(oim)2][1,5-NDS]) was investigated in acetonitrile solution by means of proton NMR titrations. A wide range of anions, comprising simple inorganic ions, halides, and mono- and dicarboxylates was taken into account. The study showed that this receptor binds carboxylate anions more strongly than halides. Moreover [m- Xyl-(oim)2][1,5-NDS] displays selectivity for di- over monocarboxylate anions. The complex stability was mainly affected by the anion basicity in the presence of monocarboxylates, whereas the flexibility of the alkyl cha…
Regio- and Stereoselective Synthesis of Spiropyrrolizidines and Piperazines through Azomethine Ylide Cycloaddition Reaction.
2015
A series of original spiropyrrolizidine derivatives has been prepared by a one-pot three-component [3 + 2] cycloaddition reaction of (E)-3-arylidene-1-phenyl-pyrrolidine-2,5-diones, l-proline, and the cyclic ketones 1H-indole-2,3-dione (isatin), indenoquinoxaline-11-one and acenaphthenequinone. We disclose an unprecedented isomerization of some spiroadducts leading to a new family of spirooxindolepyrrolizidines. Furthermore, these cycloadducts underwent retro-1,3-dipolar cycloaddition yielding unexpected regioisomers. Upon treatment of the dipolarophiles with in situ generated azomethine ylides from l-proline or acenaphthenequinone, formation of spiroadducts and unusual polycyclic fused pip…
A bibliometric review of sukuk literature
2023
Abstract Sukuk (Islamic bonds) are one of the Islamic finance sectors that have experienced the fastest growth during the last decade. Using a quali-quantitative approach known as meta-literature review, the aim of this paper is to survey the sukuk literature over the period 1950–2018. In total we review and analyze 80 papers through bibliometric citation analysis (using HistCite and VOSviewer software) coupled with content analysis. We show the influential aspects of the literature, such as countries, institutions, journals, authors, articles and topics. We also present the co-authorship network and identify three research streams: (1) sukuk overview and growth, (2) sukuk and finance theor…
Synthesis and X-ray structure of amide-based macrocycles, catenanes and pretzelane
2001
The syntheses and crystal structure studies of amide-based catenanes derived from m-phenylene diacrylic acid and 5-acetoxy isophthalic acid (17% and 3% yield of 4a and 4b resp.) and octalactam macrocycles (21% yield of 3) are described. Hydrogen bonding patterns play a key role in the formation of the different conformations of octalactam 3. The crystal structures of 3 reveal a number of hydrogen-bonding interactions between the macrocycle and two different solvent molecules, which are presumably responsible for the different conformations. Furthermore, we report the X-ray structure of a catenane, which was converted into a “pretzelane” by bridging two phenolic hydroxy groups with a p-xylyl…