Browse
Submit Data
Databases
API
Help

Dataset Information

0 Views

0 Connections

0 Citations

0 Reanalyses

0 Downloads

Omics score: 0

Cation affinity numbers of Lewis bases.

ABSTRACT: Using selected theoretical methods the affinity of a large range of Lewis bases towards model cations has been quantified. The range of model cations includes the methyl cation as the smallest carbon-centered electrophile, the benzhydryl and trityl cations as models for electrophilic substrates encountered in Lewis base-catalyzed synthetic procedures, and the acetyl cation as a substrate model for acyl-transfer reactions. Affinities towards these cationic electrophiles are complemented by data for Lewis-base addition to Michael acceptors as prototypical neutral electrophiles.

SUBMITTER: Lindner C

PROVIDER: S-EPMC3458768 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

ACCESS DATA

Json Xml

Publications

Cation affinity numbers of Lewis bases.

Lindner Christoph C Tandon Raman R Maryasin Boris B Larionov Evgeny E Zipse Hendrik H

Beilstein journal of organic chemistry 20120831

Using selected theoretical methods the affinity of a large range of Lewis bases towards model cations has been quantified. The range of model cations includes the methyl cation as the smallest carbon-centered electrophile, the benzhydryl and trityl cations as models for electrophilic substrates encountered in Lewis base-catalyzed synthetic procedures, and the acetyl cation as a substrate model for acyl-transfer reactions. Affinities towards these cationic electrophiles are complemented by data f ...[more]

PMID: 23019478

Similar Datasets

On the Significance of Lone Pair/Lone Pair and Lone Pair/Bond Pair Repulsions in the Cation Affinity and Lewis Acid/Lewis Base Interactions.

Project description:Interaction of H2O, H2S, H2Se, NH3, PH3, and AsH3 with cations H+, CH3 +, Cu+, Al+, Li+, Na+, and K+ was studied from the energetic and structural viewpoint using B3LYP/6-311++G(d,p) method. The charge transfer from the Lewis bases to the cations reduces lone pair/lone pair (LP/LP) repulsion in H2O, H2S, and H2Se and LP/bond pair (LP/BP) repulsion in NH3, PH3, and AsH3. In parallel, changes in the H-M-H angles (M = O, S, Se, N, P, and As) are observed. The change in the H-M-H angle during the interactions was proportional to the amount of charge transferred from the bases to the cations and electron density (ρ) at the molecule/cation bond critical point. Also, the opposite trend for proton affinities of these two families, that is, NH3 > PH3 > AsH3 and H2O < H2S < H2Se, was interpreted on the basis of LP/BP repulsion in their neutral and protonated forms. Interaction of the Lewis bases with neutral Lewis acids including BeH2, BeF2, and BH3 was studied energetically and structurally. The calculated energies for interactions of H2O and NH3 with BeH2, BeF2, and BH3 are larger than the corresponding values for H2S, H2Se, PH3, and AsH3. This difference was interpreted on the basis of the lower stability of H2O and NH3 because of large LP/LP and LP/BP repulsion in H2O and LP/BP repulsion in NH3.

| S-EPMC6645108 | biostudies-literature

Lewis Acidic Boranes, Lewis Bases, and Equilibrium Constants: A Reliable Scaffold for a Quantitative Lewis Acidity/Basicity Scale.

Project description:A quantitative Lewis acidity/basicity scale toward boron-centered Lewis acids has been developed based on a set of 90 experimental equilibrium constants for the reactions of triarylboranes with various O-, N-, S-, and P-centered Lewis bases in dichloromethane at 20 °C. Analysis with the linear free energy relationship log KB =LAB +LBB allows equilibrium constants, KB , to be calculated for any type of borane/Lewis base combination through the sum of two descriptors, one for Lewis acidity (LAB ) and one for Lewis basicity (LBB ). The resulting Lewis acidity/basicity scale is independent of fixed reference acids/bases and valid for various types of trivalent boron-centered Lewis acids. It is demonstrated that the newly developed Lewis acidity/basicity scale is easily extendable through linear relationships with quantum-chemically calculated or common physical-organic descriptors and known thermodynamic data (ΔH BF3 ). Furthermore, this experimental platform can be utilized for the rational development of borane-catalyzed reactions.

| S-EPMC7985883 | biostudies-literature

Methyl groups as widespread Lewis bases in noncovalent interactions.

Project description:It is well known that, under certain conditions, C(sp3) atoms behave, via their σ-hole, as Lewis acids in tetrel bonding. Here, we show that methyl groups, when bound to atoms less electronegative than carbon, can counterintuitively participate in noncovalent interactions as electron density donors. Thousands of experimental structures are found in which methyl groups behave as Lewis bases to establish alkaline, alkaline earth, triel, tetrel, pnictogen, chalcogen and halogen bonds. Theoretical calculations confirm the high directionality and significant strength of the interactions that arise from a common pattern based on the electron density holes model. Moreover, despite the absence of lone pairs, methyl groups are able to transfer charge from σ bonding orbitals into empty orbitals of the electrophile to reinforce the attractive interaction.

| S-EPMC8376930 | biostudies-literature

Lewis Superacidic Tellurenyl Cation-Induced Electrophilic Activation of an Inert Carborane.

Project description:The aryltellurenyl cation [2-(tBuNCH)C6 H4 Te]+ , a Lewis super acid, and the weakly coordinating carborane anion [CB11 H12 ]- , an extremely weak Brønsted acid (pKa =131.0 in MeCN), form an isolable ion pair complex [2-(tBuNCH)C6 H4 Te][CB11 H12 ], in which the Brønsted acidity (pKa 7.4 in MeCN) of the formally hydridic B-H bonds is dramatically increased by more than 120 orders of magnitude. The electrophilic activation of B-H bonds in the carborane moiety gives rise to a proton transfer from boron to nitrogen at slightly elevated temperatures, as rationalized by the isolation of a mixture of the zwitterionic isomers 12- and 7-[2-(tBuN{H}CH)C6 H4 Te(CB11 H11 )] in ratios ranging from 62 : 38 to 80 : 20.

| S-EPMC8596995 | biostudies-literature

Molecular Structures of the Products of a Diphosphonate Ester Building Block with Lewis Bases.

Project description:By treating a suitable Wittig reagent under acid conditions, the phosphonate ester 1,4-bimethylenebenzene phosphonate ethyl ester (H2[BBPE], 1) was obtained. As a building block, compound 1 has been reacted with the Lewis-base N,N-dimethylpiperazine, ammonia and NaOH yielded compounds 2-4. The crystal structures show that a 1D chain forming a tubular channel is constructed through hydrogen bonds in 1; hydrogen bonds form two 1D chains with left-hand and right-hand helixes and form 3D networks in compound 2; 1D hydrogen-bond chains are further connected together to afford a 3D network architecture in compound 3; the phosphonate is coordinated by two Na atoms which present different coordination environments in compound 4. Additionally, the relationships between the structure and fluorescence of the four compounds in the solid state and in different solvents have also been studied at room temperature.

| S-EPMC6332391 | biostudies-literature

Computed ammonia affinity for evaluating Lewis acidity of organoboronates and organoboronamides.

Project description:Lewis acidity of organoboronates [B(pin), B(neop), B(cat), B(eg), B(nad)] and organoboronamides [B(dan), B(aam), B(mdan)] has been found to be unifiedly evaluated by computed ammonia affinity (AA), while other methods [LUMO energies, global electrophilicity index (GEI), fluoride ion affinity (FIA)] were only partially applicable. The relationships between the AA values and such structural characters including the B-X bond lengths, the X-B-X angles, and the changes in the B-X bond lengths in the formation of the ammonia adducts were also described.

| S-EPMC9844674 | biostudies-literature

Monovalent cation binding by curved DNA molecules containing variable numbers of a-tracts.

Project description:Monovalent cation binding by DNA A-tracts, runs of four or more contiguous adenine or thymine residues, has been determined for two curved approximately 200 basepair (bp) restriction fragments, one taken from the M13 origin of replication and the other from the VP1 gene of SV40. These two fragments have previously been shown to contain stable, centrally located bends of 44 degrees and 46 degrees , respectively, located within approximately 60 bp "curvature modules" containing four or five irregularly spaced A-tracts. Transient electric birefringence measurements of these two fragments, sequence variants containing reduced numbers of A-tracts in the SV40 curvature module or changes in the residues flanking the A-tracts in the M13 curvature module, have been combined with the free solution electrophoretic mobilities of the same fragments using known equations to estimate the effective charge of each fragment. The effective charge is reduced, on average, by one-third charge for each A-tract in the curvature module, suggesting that each A-tract binds a monovalent cation approximately one-third of the time. Monovalent cation binding to two or more A-tracts is required to observe significant curvature of the DNA helix axis.

| S-EPMC2242747 | biostudies-literature

DNA copy numbers profiles in affinity-purified ovarian clear cell carcinoma.

Project description:Advanced ovarian clear cell carcinoma (CCC) is one of the most aggressive ovarian malignancies, in part because it tends to be resistant to platinum-based chemotherapy. At present, little is known about the molecular genetic alterations in CCCs except that there are frequent activating mutations in PIK3CA. The purpose of this study is to comprehensively define the genomic changes in CCC based on DNA copy number alterations.We performed 250K high-density single nucleotide polymorphism array analysis in 12 affinity-purified CCCs and 10 CCC cell lines. Discrete regions of amplification and deletion were also analyzed in additional 21 affinity-purified CCCs using quantitative real-time PCR.The level of chromosomal instability in CCC as defined by the extent of DNA copy number changes is similar to those previously reported in low-grade ovarian serous carcinoma but much less than those in high-grade serous carcinoma. The most remarkable region with DNA copy number gain is at chr20, which harbors a potential oncogene, ZNF217. This discrete amplicon is observed in 36% of CCCs but rarely detected in serous carcinomas regardless of grade. In addition, homozygous deletions are detected at the CDKN2A/2B and LZTS1 loci. Interestingly, the DNA copy number changes observed in fresh CCC tissues are rarely detected in the established CCC cell lines.This study provides the first high resolution, genome-wide view of DNA copy number alterations in ovarian CCC. The findings provide a genomic landscape for future studies aimed at elucidating the pathogenesis and developing new target-based therapies for CCCs.

| S-EPMC2848895 | biostudies-literature

Metal-free dihydrogen oxidation by a borenium cation: a combined electrochemical/frustrated Lewis pair approach.

Project description:In order to use H2 as a clean source of electricity, prohibitively rare and expensive precious metal electrocatalysts, such as Pt, are often used to overcome the large oxidative voltage required to convert H2 into 2?H(+) and 2?e(-). Herein, we report a metal-free approach to catalyze the oxidation of H2 by combining the ability of frustrated Lewis pairs (FLPs) to heterolytically cleave H2 with the in?situ electrochemical oxidation of the resulting borohydride. The use of the NHC-stabilized borenium cation [(IiPr2)(BC8H14)](+) (IiPr2=C3H2(NiPr)2, NHC=N-heterocyclic carbene) as the Lewis acidic component of the FLP is shown to decrease the voltage required for H2 oxidation by 910?mV at inexpensive carbon electrodes, a significant energy saving equivalent to 175.6?kJ?mol(-1). The NHC-borenium Lewis acid also offers improved catalyst recyclability and chemical stability compared to B(C6F5)3, the paradigm Lewis acid originally used to pioneer our combined electrochemical/frustrated Lewis pair approach.

| S-EPMC4257500 | biostudies-literature

Bimetallic effects on ethylene polymerization in the presence of amines: inhibition of the deactivation by Lewis bases.

Project description:Dinickel complexes supported by terphenyl ligands appended with phenoxy and imine donors were synthesized. Full substitution of the central arene blocks rotation around the aryl-aryl bond and allows for the isolation of atropisomers. The reported complexes perform ethylene polymerization in the presence of amines. The inhibiting effect of polar additives is up to 250 times lower for the syn isomer than the anti isomer. Comparisons with mononuclear systems indicate that the proximity of the metal centers leads to the observed inhibitory effect on the deactivation of the catalysts.

| S-EPMC3307529 | biostudies-literature

OmicsDI is part of the ELIXIR infrastructure

OmicsDI is an Elixir interoperability service. Learn more ›

Tweets

OmicsDI Databases

PRIDE
PeptideAtlas
MassIVE
JPOST Repository
Physiome Model Repository

EGA
EVA
ENA
LINCS
PAXDB
Cell Collective

MetaboLights
Metabolomics Workbench
MetabolomeExpress
GNPS
BioModels
FAIRDOMHub

ArrayExpress
dbGaP
ExpressionAtlas
GEO
NODE

Information

Databases
Help
API
Contact us
Code on GitHub
Terms of use
Submit Data