The distinction of concerted proton-coupled electron transfer (CPCET) from sequential one as well as proton transfer-electron transfer (PT-ET) from electron transfer-proton transfer (ET-PT) in the O&#x2013;H bond cleavage reactions in various media has always been a difficult task. In this work, the activation barrier of the CPCET mechanism, its rate constants, and reaction free energies related to ET-PT and PT-ET involving coreactive species were presented as good parameters to attempt the problem. DFT calculations were carried out studying the described pathways subsequent to the scavenging of <svg xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg" style="vertical-align:-3.9935pt" id="M1" height="15.2434pt" version="1.1" viewBox="-0.0498162 -11.2499 24.7155 15.2434" width="24.7155pt"><g transform="matrix(.0095,0,0,-0.0095,0,-5.984)"><path id="g54-74" d="M333 262C333 337 270 397 193 397S54 337 54 262S116 127 193 127S333 187 333 262Z"/></g><g transform="matrix(.0135,0,0,-0.0135,4.163,0)"><path id="g190-80" d="M381 665C170 665 44 498 44 318C44 125 188 -15 369 -15C552 -15 703 117 703 333C703 534 550 665 381 665ZM359 629C491 629 601 517 601 306C601 114 502 21 390 21C249 21 146 158 146 346S248 629 359 629Z"/></g><g transform="matrix(.0135,0,0,-0.0135,14.161,0)"><path id="g190-73" d="M729 650H468V622C546 615 554 610 554 527V365H213V527C213 610 221 616 297 622V650H38V622C120 616 128 611 128 527V123C128 39 120 34 40 28V0H303V28C221 34 213 40 213 123V322H554V123C554 39 546 34 460 28V0H728V28C647 34 639 39 639 123V527C639 610 647 615 729 622V650Z"/></g></svg> and <svg xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg" style="vertical-align:-0.2402pt" id="M2" height="11.4901pt" version="1.1" viewBox="-0.0498162 -11.2499 29.3827 11.4901" width="29.3827pt"><g transform="matrix(.0135,0,0,-0.0135,0,0)"><use xlink:href="#g190-80"/></g><g transform="matrix(.0135,0,0,-0.0135,9.998,0)"><path id="g190-67" d="M372 352C427 368 507 407 507 502C507 548 486 592 451 616C420 638 376 650 301 650H44V622C124 616 128 610 128 527V123C128 40 122 34 36 28V0H257C336 0 402 12 453 40C512 72 548 124 548 191C548 291 471 335 372 350V352ZM213 362V558C213 591 216 602 226 608C235 614 258 618 282 618C377 618 415 558 415 490C415 406 369 362 260 362H213ZM213 328H258C380 328 450 283 450 181C450 76 377 35 296 34C231 34 213 53 213 125V328Z"/></g><g transform="matrix(.0135,0,0,-0.0135,17.856,0)"><path id="g190-115" d="M181 342V451C133 431 89 419 40 411V388C98 381 102 377 102 311V104C102 38 95 32 33 26V0H263V26C186 32 181 38 181 104V287C203 343 235 372 261 372C277 372 289 366 304 352C310 346 318 345 330 350C349 359 362 379 362 399C362 422 338 449 304 449C256 449 213 393 183 342H181Z"/></g><g transform="matrix(.0095,0,0,-0.0095,22.969,-5.984)"><path id="g54-33" d="M556 236V289H56V236H556Z"/></g></svg> by the 3,4-DHPPA in various media. The solvation was described in a hybrid manner using IEF-PCM model conjointly with a model that takes into account some solute-solvent interactions. As a result, we found that the scavenging of hydroxyl radical by 3,4-DHPPA is thermodynamically governed by a one-step hydrogen atom transfer (CPCET) from the acid to the radical in all media. In kinetic viewpoint, CPCET still dominates in the vacuum and in nonpolar solvents, but in polar solvents it could compete strongly with the ET-PT mechanism so that the latter could slightly dominate.

J. J. Fifen

Z. Dhaouadi

M. Nsangou

O. Holtomo

N. Jaidane

Proton-Coupled Electron Transfer in the Reaction of 3,4-Dihydroxyphenylpyruvic Acid with Reactive Species in Various Media

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International Journal of Chemical Physics

Table of Contents

Table of Contents: 2015

Proton-Coupled Electron Transfer in the Reaction of 3,4-Dihydroxyphenylpyruvic Acid with Reactive Species in Various Media