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Theoretical estimation of Hammett σ p constants of organic radical groups
Chen Wang,Yao Fu,Lei Liu
Chinese Science Bulletin , 2010, DOI: 10.1007/s11434-010-4015-5
Abstract: A quantum chemistry method was developed to calculate the Hammett substituent constants of various organic radicals. These newly obtained constants allow, for the first time, the quantitative analysis of the electron demand of organic radicals. Calculations reveal that the electron demand of organic radicals varies dramatically. It was demonstrated that the Hammett relationship of bond dissociation energies is determined only by the change of electron demand during the homolysis process.
An Assay Study of Molecular Recognition of Amino Acids in Water: Covalent Imprinting of Cysteine  [PDF]
Harsha Vardhan Reddy Burri, Donghong Yu
Journal of Biomedical Science and Engineering (JBiSE) , 2015, DOI: 10.4236/jbise.2015.812077
Abstract: A novel synthetic N-(9-fluorenyl methoxy carbonyl)-L-Cysteine (Fmoc-Cys(SH)-OH) receptor was pre- pared by co-polymerizing (9-fluorenyl methoxy carbonyl)-S-(1-propene-2-thiol)-L-Cysteine (Fmoc-Cys(SCH2CHCH2)-OH) and a non-imprinted polymer prepared from 1-propene-1-thiol photo-chemically 15 h at room temperature and additional 3 h thermally at 80℃. Subsequently, disulfides were reduced with lithium aluminum hydride (LiAlH4) from imprinted polymers. The imprinted polymers selectively recognized Fmoc-Cys(SH)-OH with high binding constants in aqueous and protic solvents by thiol-disulfide exchange reactions. In order to estimate the covalent rebinding, particles were further extracted and disulfides reduced were estimated with the non-covalent recognized and covalently bounded analytes. From rebinding studies that were conducted, we observed that proved polymer particles could be reproducible and contain constant binding strengths and recognition properties. Furthermore, we proved that short incubation periods resulted in fast and efficient thiol-disulfide interchange reactions.
Effect of Hetero Atom on the Hammett’s Reaction Constant ( ) from the Physical Basis of Dissociation Equilibriums of (Dithio) Benzoic Acids and (Thio) Phenols and Its Application to Solvolysis Reactions and Some Free Radical Reactions  [PDF]
Jagannadham Vandanapu,Sanjeev Rachuru
Advances in Physical Chemistry , 2012, DOI: 10.1155/2012/598243
Abstract: The emergence of putative Hammett equation in mid 1930s was a boon to physical-organic chemists to elucidate the reaction mechanisms of several organic reactions. Based on the concept of this equation several hundreds of papers have emerged in chemical literature in the last century on the effect of structure, on reactivity, and very few on thermodynamic stability and kinetic reactivity of intermediates. In this article an attempt is made to explain the effect of hetero atom on Hammett’s reaction constant (ρ) taking the dissociation equilibriums of benzoic acids, dithiobenzoic acids, phenols, and thiophenols. 1. Introduction Ever since the Hammett equation was developed [1, 2], there were several hundreds of redox, condensation, disproportionation, nucleophilic and electrophilic substitution, and addition reactions with meta- and para-substituted benzene derivatives in the literature, for which the Hammett reaction ( ) constants were reported. Inclusion of those references here is beyond the scope this article as they run into several pages. However the readers can find many articles and reviews in several standard physical-organic chemistry text books. In addition to these numerous reactions, a few reactions were reported by one of the authors (V. Jaganndham) from elsewhere [3] and from our laboratory [4, 5] on the solvolysis and reactions of intermediate carbocations with nucleophilic solvent water. An effect of α-hetero atom substitution on kinetic and thermodynamic stability of intermediate carbocations were also reported from elsewhere [6, 7] and from our laboratory [8]. But in these reactions [3–5] no attempt is made to explain the effect of α-hetero atom on the Hammett reaction constant ( ), which we tried to explain in the present work taking the title equilibriums as staple examples. 2. Results and Discussion The effect of substituent either in meta- or para-position in the benzene ring on the rate or equilibrium constant is given by Hammett [2] in the form of a formula: where is the equilibrium or rate constant of the substituted reactant, is that of unsubstituted reactant, “ ” is the free energy change for equilibrium process or rate process, “ ” is the distance between the substituent and the reaction center, “ ” is the dielectric constant of the medium, and , and are the constants. Here depends on the substituent and and depend on the nature of the reaction. Later, based on some experimental observations Hammett rearranged (1) to the form: where and , (2) is now known as famous Hammett equation. The magnitude of depends on the substituent
NMR Spectroscopy, Hammett Correlations and Biological Activity of Some Schiff Bases Derived from Piperonal
Echevarria, Aurea;Nascimento, Maria da Gra?a;Ger?nimo, Vanilde;Miller, Joseph;Giesbrecht, Astréa;
Journal of the Brazilian Chemical Society , 1999, DOI: 10.1590/S0103-50531999000100010
Abstract: a series of eleven schiff bases have been synthesized. they were obtained by condensation of piperonal (3,4-methylenedioxybenzaldehyde) with the corresponding aromatic primary amines. their 1h and 13c-nmr spectra have been obtained and the hammett correlations including chemical shifts and the subsitutent constants (sp, sr e si) were studied. linear and bilinear significant correlations were observed for iminic carbon (c-a) and c-1?, showing a more significant ressonance effect on chemical shifts. the chemical shifts for c-4? were highly affected by substituent effects, especially for halogens in the expected direction. their biological activity against microorganisms has also been measured and significant activity was showed against epidermophyton floccosum. the biological activity did not give a reasonable relationship with electronic effects.
NMR Spectroscopy, Hammett Correlations and Biological Activity of Some Schiff Bases Derived from Piperonal  [cached]
Echevarria Aurea,Nascimento Maria da Gra?a,Ger?nimo Vanilde,Miller Joseph
Journal of the Brazilian Chemical Society , 1999,
Abstract: A series of eleven Schiff Bases have been synthesized. They were obtained by condensation of piperonal (3,4-methylenedioxybenzaldehyde) with the corresponding aromatic primary amines. Their 1H and 13C-NMR spectra have been obtained and the Hammett correlations including chemical shifts and the subsitutent constants (sigmap, sigmaR e sigmaI) were studied. Linear and bilinear significant correlations were observed for iminic carbon (C-alpha) and C-1?, showing a more significant ressonance effect on chemical shifts. The chemical shifts for C-4? were highly affected by substituent effects, especially for halogens in the expected direction. Their biological activity against microorganisms has also been measured and significant activity was showed against Epidermophyton floccosum. The biological activity did not give a reasonable relationship with electronic effects.
Yield of aromatics from naphthenics upon catalytic cracking
Pujro, Richard A.;Falco, Marisa G.;Pedrosa, Anne M. Garrido;Souza, Marcelo J. B.;Morgado Jr., Edisson;Sedran, Ulises;
Journal of the Brazilian Chemical Society , 2012, DOI: 10.1590/S0103-50532012000700023
Abstract: cis- and trans-decalin were reacted over cracking catalysts to study the formation of aromatics in a particular fraction of the liquid products obtained in the fluid catalytic cracking process (fcc). a batch, fluidized bed crec riser simulator reactor was used at 673 and 723 k and contact times varied from 3 to 15 s. cis-decalin was much more reactive. despite differences induced and measured in their accessibility indices, the catalysts led to similar activity profiles, suggesting that diffusion restrictions do not prevail. products were c1-c12 hydrocarbons while coke was very low. isomerization, cracking, hydrogen transfer, ring opening, ring contraction and alkylation reactions occurred and products from the various reactions were observed at very short reaction times. bicyclic c10 naphthenics and alkyl-substituted c7-c11 aromatics or naphtheno-aromatics were the most important products. a reaction mechanism with three initial routes (isomerization, ring opening and direct hydrogen transfer reactions) was proposed.
The covalent bond in Particle Spectroscopy  [PDF]
D. V. Bugg
Physics , 2010, DOI: 10.1063/1.3483338
Abstract: It is proposed that meson resonances are linear combinations of q-qbar and meson-meson (MM); baryon resonances are combinations of qqq and meson-baryon (MB). Mixing between these combinations arises via decays of confined states to meson-meson or meson-baryon. There is a precise analogy with the covalent bond in molecular physics; it helps to visualise what is happening physically. One eigenstate is lowered by the mixing; the other moves up and normally increases in width. Cusps arise at thresholds. At sharp thresholds due to S-wave 2-particle decays, these cusps play a conspicuous role in many sets of data.
How the Substituent Effect Influences π-Electron Delocalisation in the Ring of Reactants in the Reaction Defining the Hammett Substituent Constants σm and σp  [PDF]
Tadeusz M. Krygowski,Beata T. St?pień,Micha? K. Cyrański
International Journal of Molecular Sciences , 2005, DOI: 10.3390/i6010045
Abstract: Application of the geometry (HOMA, EN, GEO) and magnetism based (NICS, NICS(1)) indices of aromaticity to optimised geometry of the ring in 12 meta – and 12 para – substituted benzoic acids and their anions by use of DFT computations at B3LYP/6-311+G(d,p) level has shown a very low substituent effect on the π-electron delocalisation. This resembles (qualitatively) the resistance of benzene (and typical aromatic systems) against reactions leading to the change of π-electron delocalisation.
Selective Covalent Conjugation of Phosphorothioate DNA Oligonucleotides with Streptavidin  [PDF]
Kersten S. Rabe,Christof M. Niemeyer
Molecules , 2011, DOI: 10.3390/molecules16086916
Abstract: Protein-DNA conjugates have found numerous applications in the field of diagnostics and nanobiotechnology, however, their intrinsic susceptibility to DNA degradation by nucleases represents a major obstacle for many applications. We here report the selective covalent conjugation of the protein streptavidin (STV) with phosphorothioate oligonucleotides (psDNA) containing a terminal alkylthiolgroup as the chemically addressable linking unit, using a heterobifunctional NHS-/maleimide crosslinker. The psDNA-STV conjugates were synthesized in about 10% isolated yields. We demonstrate that the terminal alkylthiol group selectively reacts with the maleimide while the backbone sulfur atoms are not engaged in chemical conjugation. The novel psDNA-STV conjugates retain their binding capabilities for both biotinylated macromolecules and the complementary nucleic acid. Moreover, the psDNA-STV conjugate retained its binding capacity for complementary oligomers even after a nuclease digestion step, which effectively degrades deoxyribonucleotide oligomers and thus the binding capability of regular DNA-STV conjugates. The psDNA-STV therefore hold particular promise for applications e.g. in proteome research and novel biosensing devices, where interfering endogenous nucleic acids need to be removed from analytes by nuclease digestion.
Covalent bonding and magnetism in cuprates  [PDF]
A. C. Walters,T. G. Perring,J. -S. Caux,A. T. Savici,G. D. Gu,C. -C. Lee,W. Ku,I. A. Zaliznyak
Physics , 2008, DOI: 10.1038/nphys1405
Abstract: The importance of covalent bonding for the magnetism of 3d metal complexes was first noted by Pauling in 1931. His point became moot, however, with the success of the ionic picture of Van Vleck, where ligands influence magnetic electrons of 3d ions mainly through electrostatic fields. Anderson's theory of spin superexchange later established that covalency is at the heart of cooperative magnetism in insulators, but its energy scale was believed to be small compared to other inter-ionic interactions and therefore it was considered a small perturbation of the ionic picture. This assertion fails dramatically in copper oxides, which came to prominence following the discovery of high critical temperature superconductors (HTSC). Magnetic interactions in cuprates are remarkably strong and are often considered the origin of the unusually high superconducting transition temperature, Tc. Here we report a detailed survey of magnetic excitations in the one-dimensional cuprate Sr2CuO3 using inelastic neutron scattering (INS). We show that although the experimental dynamical spin structure factor is well described by the model S=1/2 nearest-neighbour Heisenberg Hamiltonian typically used for cuprates, the magnetic intensity is modified dramatically by strong hybridization of Cu 3d states with O p states, showing that the ionic picture of localized 3d Heisenberg spin magnetism is grossly inadequate. Our findings provide a natural explanation for the puzzle of the missing INS magnetic intensity in cuprates and have profound implications for understanding current and future experimental data on these materials.
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