Regioselectivity of the protonation of captodative enamines bearing a CF3 group

Capodative enamines bearing a CF₃ group are protonated at the N- or β-C-atom depending on the structure of the initial base and the nature of protonating reagent.     

一种新合成的八极矩发色团分子单光子和双光子吸收性质的质子化效应

利用第一性原理基础上发展的一种计算方法研究质子化效应对具有1, 3, 5-三嗪核和吡咯末端基团八极矩分子三嗪的单光子和双光子吸收性质的影响. 结果表明,当三嗪被质子化时,该分子的单、双光子吸收性质发生了很大的变化. 一是出现了更多的电荷转移态,并且吸收带发生了红移;二是双光子吸收截面得到了很大的增强. 质子化效应有利于提高分子内电荷转移的强度,定性地解释了实验工作. 并提出了一种基于化合物三嗪质子化效应的双光子吸收转换开关.     

Protonation of carbonate in aqueous tetraalkylammonium salts at 25 degrees C

Protonation constants of carbonate were determined in tetramethylammonium chloride (Me₄NCl_aq 0.1 ≤ I/mol kg⁻¹ ≤ 4) and tetraethylammonium iodide (Et₄NI_aq 0.1 ≤ I/mol kg⁻¹ ≤ 1) by potentiometric ([H⁺]-glass electrode) measurements. Dependence of protonation constants on ionic strength was taken into account by modified specific ion interaction theory (SIT) and by Pitzer models. Literature data on the protonation of carbonate in NaCl_aq (0.1 ≤ I/mol kg⁻¹ ≤ 6) were also critically analysed. Both protonation constants of carbonate follow the trend Et₄NI > Me₄NCl > NaCl. An ion pair formation model designed to take into account the different protonation behaviours of carbonate in different supporting electrolytes was also evaluated.     

The Determination of the Protonation Constants of A New Macrocyclic Dinucleating Ligand, BDBPH

One of our current interests focuses on the design and synthesis of polyaza macrocyclic ligands, the determination of their protonation constants, and the stabilities of corresponding metal complexes. Two polyazadiphenol macrocycles, R(babp)2(dfc)21 and [24]RBPyBC2, one octaazamacrocycle, BPBD3,4, and several hexaaza macrocyclic ligands, BFBD5, BMXD6, and OBISDIEN7, have been reported recently. We have also reported the synthesis of a new dinucleating 24-membered hexaazadiphenol macr…     

Imidazole containing ligands for the modulation of physical properties of metal complexes upon (de)protonation

The synthetic route towards a novel tetradentate ligand bearing two amido and imidazole rings is reported. This ligand has been designed to study the relationship between the protonic state of the ligand through the imidazole moieties towards the electronic behaviour of metal complexes.     

A personal account of some dinitrogen and organometallic chemistry research at the University of Sussex

This article reviews the development of dinitrogen chemistry and some associated organometallic chemistry at the University of Sussex with which the author was directly involved. The establishment of the basic heavy-element halide phosphine chemistry laid the ground for the discovery of dinitrogen complexes of rhenium, osmium, molybdenum and tungsten. From there, some of the first well-defined reactions of coordinated dinitrogen (especially protonation and alkylation) were discovered and the essential mechanisms of such reactions were established. This allowed the development of models for the action of nitrogenases that are still probably the best available. Later work has produced similar models in iron chemistry and a range of organometallic chemistry has been uncovered in the effort to discover parallels between the basic organometallic chemistry of substances such as metal carbonyls, dinitrogen complexes and hydrides in their interactions with acetylenes and cyclpropene.     

Synthesis of a Model for Phycocyanin with Respect to the Acid-Base Chemistry between Protein and Chromophore

Summary.  Earlier investigations have shown that the cysteine adduct of phycocyanobilin dimethylester qualifies for intramolecular protonation [1]. In this context, the -Cys-Ala-Phe-Asp-tetrapeptide adduct of phycocyanobilin dimethylester was synthesized and examined for its protonation properties with respect to the zwitterionic interaction between chromophore and protein. Received March 15, 2000. Accepted March 21, 2000     

Cardiolipin containing liposomes are fully ionized at physiological pH. An FT-IR study of phosphate group ionization

Cardiolipin containing liposomes serve as model systems for probing cytochrome c binding to the inner membrane of mitochondria. In order to interpret binding isotherms properly it is important to identify the protonation state of the two phosphate groups of this phospholipid. Thus far, the literature proposed conflicting views based on experimentally and computationally support for both the fully protonated and semi-protonated state as the physiologically dominant species. In order to clarify this issue we measured the FT-IR spectra of 100% 1,1′2,2′-tetraoleyl cardiolipin (TOCL), 20% TOCL/80% 1,2-dioleyl-sn-glycero-3-phosphocholine (DOPC) and 100% DOPC as a function of pH between 2 and 11. While the integrated intensities of all DOPC bands were found to be independent of pH within purely statistical variations, we identified specific spectral regions in the TOCL spectrum for which the intensities either decrease and or increase with decreasing pH below pH 4. It was obvious that these regions contain contributions from PO₄⁻ and PO stretching modes, respectively. We confirmed this with DFT-based normal mode calculations for a truncated TOCL head group, which revealed that the spectra regions between 1050 and 1100 cm⁻¹ as well as between 1200 and 1300 cm⁻¹ can be ascribed as a superpositions of bands mostly assignable to collective CH deformation modes and PO₄ stretching modes. Our results strongly suggest that the protonation of the phosphate groups occur in the acidic region and that they exist in their fully ionized state at physiological pH.     

Acid?Base Properties of Adenosine 5′‐Monophosphate,Guanosine 5′‐Monophosphate,and Inosine 5′‐Monophosphate in Aqueous Solutions of Methanol

The protonation constants of adenosine 5′‐monophosphate, guanosine 5′‐monophosphate, and inosine 5′‐monophosphate were determined in binary mixtures of H₂O containing 0, 10, 15, 20, 25, 30, 35, 40, 45, and 50% MeOH, using a combination of potentiometric and spectrophotometric methods at a constant temperature (25°) and constant ionic strength (0.1 mol?dm^?3 NaClO₄). The protonation constants were analyzed using the normalized polarity parameter (E ), and Kamlet, Abboud, and Taft (KAT) parameters. A linear correlation of log K vs. the normalized polarity parameter was obtained. Dual‐parameter correlation of log K vs. π* (dipolarity/polarizability) and α (H‐bond‐donor acidity), as well as π* and β (H‐bond‐acceptor basicity) also gives good results in various aqueous organic solvent mixtures. Finally, the results are discussed in terms of the effect of solvent on the protonation equilibria.     

Experimental Evidence for Unusual Protonation of Tetraethyl p-tert-Butylcalix[4]arene Tetraacetate and the Most Probable Structure of the Resulting Complex

Using ¹H and ¹³C NMR, FT IR spectroscopy together with quantum mechanical DFT calculations, we show that tetraethyl p-tert-butylcalix[4]arene tetraacetate (1) forms a stable equimolecular complex with proton in the form of hydroxonium ion in acetonitrile-d ₃. Protons for this complex were offered by hydrogen bis(1,2-dicarbollyl) cobaltate (HDCC) and converted to hydroxonium ions by traces of water. The complex 1·H₃O⁺ adopts a slightly asymmetric conformation, which is distinctly more cone-like than ligand 1. According to spectral evidence, the hydroxonium ion H₃O⁺ is bound mainly to three of the phenoxy oxygen atoms of 1 by strong hydrogen bonds leaving the ester carbonyl groups, which are the usual coordination site for metal cations, free. Theoretical DFT calculations support the bonding to phenoxy oxygen atoms but slightly prefer a structure with one of the carbonyls being involved in the coordination.