Search results for "Proton"
showing 10 items of 5886 documents
Cation-π interactions between neutral calix[5]arene hosts and cationic organic guests
1997
Abstract The binding properties of the 1,3-bridged calix[5]crowns 1–3 towards a number of quaternary ammonium, phosphonium, and iminium ions have been investigated by 1H NMR in CDCl3 solution, where the sole driving force for association is provided by cation-π interactions. We have found that the cavity of a calix[5]arene fixed in a cone-like conformation provides a fairly efficient, but rather unselective, receptor site for quaternary salts. The conformationally mobile p-tert-butylcalix[5]arene (4) is in general a much less efficient binder than the more preorganized calixcrowns, but displays a remarkable selectivity towards N-methylquinuclidinium ion that is believed to arise from a good…
Star-Shaped Push-Pull Compounds Having 1,3,5-Triazine Cores
2006
The 1,3,5-triazines 9–11 having OPV chains in the 2-, 4- and 6-position represent star-shaped compounds which exhibit strong push-pull effects. Their long-wavelength absorption S0 S1 is characterized by an intramolecular charge transfer (ICT) from the dialkylamino group as electron donor D via the conjugated chain to the 1,3,5-triazine core as electron acceptor A. Protonation of the dialkylamino group removes the donor capability, whereas protonation of the 1,3,5-triazine ring enhances the acceptor strength. Thus, the prevailing protonation site has a crucial influence on the push-pull effect and the ICT. The transition energies ΔE (S0 S1) pass through a minimum for the second generation 10…
Asymmetrically substituted calix[4]arenes; A two-dimensional 1H NMR study of a tetraester derivative in the cone-conformation
1991
Abstract Several new chiral calix[4]arenes with three or four different substituents in the p-position have been prepared by fragment condensation. Standard derivatization procedures always led to the formation of mixtures of various conformational isomers from which the derivative in the cone-conformation could be isolated only by preparative HPLC. For a tetraester derivative it was shown by two-dimensional 1H NMR spectroscopy, that due to the different substituents the cone-conformation is strongly distorted. The sodium complex of this tetraester, however, assumes a regular cone-conformation again.
Copper(ii) and Zn(ii) coordination chemistry of tetraaza[n]cyclophanes
2003
The acid–base behaviour and Zn2+ and Cu2+ metal coordination chemistry of the novel orthocyclophane ligands 2,5,8,11-tetraaza[12]orthocyclophane (L2) and 2,5,9,12-tetraaza[13]orthocyclophane (L3) and metacyclophane 2,5,8,11-tetraaza[12]metacylophane (L1) are studied. Important differences in the chemistry of these compounds are found depending on the substitution of the aromatic ring. The ortho derivatives are much more basic in their first two protonation steps while the metacyclophane presents much larger constants in the third and fourth protonation stages. The crystal structure of the picrate salt of [H2L3]2+ shows an alternate disposition of the protons in the molecule with formation o…
Generation of [2×2] Grid Metallosupramolecular Architectures from Preformed Ditopic Bis(acylhydrazone) Ligands and through Component Self‐Assembly
2007
Ditopic bis(acylhydrazone) ligands, derived from the reactions of carbohydrazides with 2-phenylpyrimidine-4,6-dicarbaldehyde and designed for grid formation with octahedrally coordinating transition-metal ions, exhibit a varied coordination chemistry depending upon the degree of their deprotonation. The neutral acylhydrazones are relatively poor ligands and are seemingly involved in multiple, labile complexation equilibria varying with the solvent and the particular metal salt in solution; nevertheless, grid complexes of different forms can be isolated in the solid state. Although only limited study has been made of the singly deprotonated ligands, grid species appear to be much more readil…
Reactivity Towards Acidic Protic Ligands of Cyclopalladated Di‐μ‐hydroxo Complexes
2008
The dinuclear hydroxo complexes [{Pd(μ-OH)(C∧N)}2] [C∧N = 2-(2-pyridyl)phenyl (Phpy) (I), 7,8-benzoquinolyl (Bzq) (II) and 2-(2-oxazolinyl)phenyl (Phox) (III)] react in a 1:2 molar ratio with a wide variety of protic electrophiles H(L∧L) bearing different sets of donor atoms (L∧L = O∧O or O∧N) to give the mononuclear neutral palladium(II) derivatives with the general formula [Pd(L∧L)(C∧N)] [O∧O = salicylaldehydate (sal) (1), acetylacetonate (acac) (2) and benzoylacetonate (bzac) (3); O∧N = N-phenylsalicylaldiminate (N-Phsal) (4), N-p-chlorophenylsalicylaldiminate (N-pClPhsal) (5), 2-pyrrolecarbaldeydate (2-pcal) (6), 8-hydroxyquinolinate (oxin) (7)]. Structural characterisation of complexes…
Structure and Conformational Studies of Aza-Crown 8-Amino-BODIPY Derivatives: Influence of Steric Hindrance on Their Photophysical Properties
2017
Herein, we report the synthesis, X-ray crystal structure and photophysical studies of six new 8-amino-BODIPY derivatives containing crown or azo-crown ether moieties. The influence of steric hindrance, caused by the crown ether, on the planarity of the BODIPY core and its relationship with the fluorescent properties has been established. 1H NMR spectroscopic studies were undertaken to clarify the changes in fluorescence observed in the presence of ZnII.
Synthesis of N-methyl alkylaminomethane-1,1-diphosphonic acids and evaluation of their complex-formation abilities towards copper(II)
2015
Abstract A series of N -methyl alkylaminomethane-1,1-diphosphonic acids ( 3a – g ) with a common tertiary nitrogen atom (CH 3 –N–R) bearing linear or branched alkyl, cycloheptyl or phenylalkyl R substituents was synthesized in the reaction of diethylphosphonate with triethyl orthoformate and secondary amine followed by hydrolysis, and by the Eschweiler–Clarke methylation of the alkylaminomethane-1,1-diphosphonic acids with formic acid and formaldehyde. Complex-formation abilities of 3a – g towards copper(II) in solution were studied by means of pH-potentiometry, ESI-MS spectrometry, UV–Vis and EPR methods. Evaluation of stability constants for the Cu(II) complexes of 3a – g has revealed the…
A High‐Capacity Negative Electrode for Asymmetric Supercapacitors Based on a PMo 12 Coordination Polymer with Novel Water‐Assisted Proton Channels
2020
The development of a negative electrode for supercapacitors is a critical challenge for the next-generation of energy-storage devices. Herein, two new electrodes formed by the coordination polymers [Ni(itmb)4 (HPMo12 O40 )]·2H2 O (1) and [Zn(itmb)3 (H2 O)(HPMo12 O40 )]·4H2 O (2) (itmb = 1-(imidazo-1-ly)-4-(1,2,4-triazol-1-ylmethyl)benzene), synthesized by a simple hydrothermal method, are described. Compounds 1 and 2 show high capacitances of 477.9 and 890.2 F g-1 , respectively. An asymmetric supercapacitor device assembled using 2 which has novel water-assisted proton channels as negative electrode and active carbon as positive electrode shows ultrahigh energy density and power density of…
Stereocontrolled solid-phase synthesis of fluorinated partially-modified retropeptides via tandem aza-Michael/enolate-protonation
2003
N-Acylation of Wang resin-bound l-α-amino acids with 2-trifluoromethyl-propenoyl chloride, followed by asymmetric tandem aza-Michael/enolate-protonation by a series of l-α-amino esters and final release from the resin, afforded a representative library of partially-modified retropeptides incorporating a stereodefined trifluoroalanine surrogate. The stereocontrol can be dramatically improved (up to 15:1) by using apolar solvents like carbon tetrachloride and DABCO as base.