The reaction of benzyl radicals with m-deuteriotoluene

Jackson, R. A.; O’Neill, David

doi:10.1039/c2969001210b

Cited by 24 publications

(32 citation statements)

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“…Thus, to address the issue raised above, the key similarity of these reagents – what makes them lie on the same Polanyi correlation line – is their self-exchange rate constant. In contrast, H-transfer from a C–H bond to a carbon radical is dramatically slower: k (PhCH 2 • + PhCH 3 ) = ~4 × 10 –5 M -1 s -1 24. This k AH/A is ~ 10 8 slower than those for the RO–H + OR reactions above 2.…”

Section: Hat Self-exchange Reactionsmentioning

confidence: 90%

Understanding Hydrogen Atom Transfer: From Bond Strengths to Marcus Theory

2010

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CONSPECTUS Hydrogen atom transfer (HAT) is one of the most fundamental chemical reactions: A–H + B → A + H–B. It is a key step in a wide range of chemical, environmental, and biological processes. Traditional HAT involves p-block radicals such as tBuO• abstracting H• from organic molecules. More recently, it has been recognized that many transition metal species undergo HAT. This has led to a broader perspective, with HAT viewed as one type of proton-coupled electron transfer (PCET). When transition metal complexes oxidize substrates by removing H• (≡ e– and H+), typically the electron transfers to the metal and the proton transfers to a ligand. Two examples are shown in the Figure: iron-imidazolinate and vanadium-oxo complexes. Although such reagents do not “look like” main group radicals, they have the same pattern of reactivity. For instance, their HAT rate constants parallel the A–H bond strengths within a series of similar reactions. Just like main group radicals, they abstract H• much faster from O–H bonds than from C–H bonds of the same strength. This shows that driving force is not the only determinant of reactivity. We have found that HAT reactivity is well described using a Marcus-theory approach. In the simplest model, the cross relation, kAH/B = (kAH/AkBH/BKeqf)½, predicts the rate constant for AH + B in terms of the self-exchange rate constants (kAH/A for AH + A) and the equilibrium constant. For a variety of transition metal oxidants, kAH/B is predicted within one or two orders of magnitude with only a few exceptions. For 36 organic reactions of oxyl radicals, kAH/B is predicted with an average deviation of a factor of 3.8, and within a factor of 5 for all but six of the reactions. These reactions involve both O–H or C–H bonds, occur either in water or organic solvents, and over a range of 1028 in Keq and 1013 in kAH/B. The treatment of organic reactions of O–H bonds includes the well-established kinetic solvent effect on HAT reactions. This is one of a number of secondary effects that the simple cross relation does not include, such as hydrogen tunneling and the involvement of precursor and successor complexes. Various case studies are described, applying the cross relation and illustrating some of these additional issues. The success of the cross relation, despite it being a quite simplified treatment, shows that the Marcus approach based on free energies and intrinsic barriers captures much of the essential chemistry of HAT reactions. Among the insights derived from the analysis is that reactions correlate with ΔG°, not with bond enthalpies as has long been assumed. Also in contrast to common intuition, the radical character or spin state of an oxidant is not found to be a primary determinant of HAT abstracting ability. The intrinsic barriers for HAT reactions can be understood, at least in part, as Marcus-type inner-sphere reorganization energies. The intrinsic barriers for cross reactions are accurately derived from the HAT self-exchange rate constants, which is a remarkable and unprecedent...

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Section: Hat Self-exchange Reactionsmentioning

confidence: 90%

Understanding Hydrogen Atom Transfer: From Bond Strengths to Marcus Theory

2010

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“…There are about 150 protein phosphatases encoded in the human genome, including pS-, pT-selective phosphatases, pY phosphatases, and dual-specificity (pS and pY) phosphatases. [88] Of these, 107 are pY protein phosphatases. [89] The much smaller number of pS/pT phosphatases is balanced by the presence of many regulatory subunits that control subcellular location and substrate recognition for the pS/pT hydrolytic enzymes.…”

Section: Reversible Versus Irreversible Posttranslational Modificationmentioning

confidence: 99%

Protein Posttranslational Modifications: The Chemistry of Proteome Diversifications

2005

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The diversity of distinct covalent forms of proteins (the proteome) greatly exceeds the number of proteins predicted by DNA coding capacities owing to directed posttranslational modifications. Enzymes dedicated to such protein modifications include 500 human protein kinases, 150 protein phosphatases, and 500 proteases. The major types of protein covalent modifications, such as phosphorylation, acetylation, glycosylation, methylation, and ubiquitylation, can be classified according to the type of amino acid side chain modified, the category of the modifying enzyme, and the extent of reversibility. Chemical events such as protein splicing, green fluorescent protein maturation, and proteasome autoactivations also represent posttranslational modifications. An understanding of the scope and pattern of the many posttranslational modifications in eukaryotic cells provides insight into the function and dynamics of proteome compositions.

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“…The complex value of a in (9) is the analytical continuation of the real part of the diagonal matrix elements of a in (8). The imaginary part is zero in the saddle point.…”

Section: The Matrix Model and Naive Replica Trickmentioning

confidence: 99%

“…However, the answer to this puzzle remains unclear. This work was motivated by a desire to shed some light on this question using the random matrix approach which received considerable interest recently [5][6][7][8][9][10][11][12]. It is based on the idea that, for the purpose of studying chiral symmetry breaking, fluctuations of the Dirac operator in the background of the gauge fields can be approximated by purely random fluctuations of its matrix elements in a suitable basis.…”

Section: Introductionmentioning

confidence: 99%

Random Matrix Model of QCD at Finite Density and the Nature of the Quenched Limit

1996

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We use a random matrix model to study chiral symmetry breaking in QCD at finite chemical potential µ. We solve the model and compute the eigenvalue density of the Dirac matrix on a complex plane. A naive "replica trick" fails for µ = 0: we find that quenched QCD is not a simple n → 0 limit of QCD with n quarks. It is the limit of a theory with 2n quarks: n quarks with original action and n quarks with conjugate action. The results agree with earlier studies of lattice QCD at µ = 0 and provide a simple analytical explanation of a long-standing puzzle. * Electronic mail address: misha@uiuc.edu.

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The reaction of benzyl radicals with m-deuteriotoluene

Cited by 24 publications

References 0 publications

Understanding Hydrogen Atom Transfer: From Bond Strengths to Marcus Theory

Understanding Hydrogen Atom Transfer: From Bond Strengths to Marcus Theory

Protein Posttranslational Modifications: The Chemistry of Proteome Diversifications

Random Matrix Model of QCD at Finite Density and the Nature of the Quenched Limit

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