45866-17-9Relevant academic research and scientific papers
Excited-state proton-coupled electron transfer within ion pairs
Hammarstr?m, Leif,Meyer, Gerald J.,Swords, Wesley B.
, p. 3460 - 3473 (2020/04/17)
The use of light to drive proton-coupled electron transfer (PCET) reactions has received growing interest, with recent focus on the direct use of excited states in PCET reactions (ES-PCET). Electrostatic ion pairs provide a scaffold to reduce reaction orders and have facilitated many discoveries in electron-transfer chemistry. Their use, however, has not translated to PCET. Herein, we show that ion pairs, formed solely through electrostatic interactions, provide a general, facile means to study an ES-PCET mechanism. These ion pairs formed readily between salicylate anions and tetracationic ruthenium complexes in acetonitrile solution. Upon light excitation, quenching of the ruthenium excited state occurred through ES-PCET oxidation of salicylate within the ion pair. Transient absorption spectroscopy identified the reduced ruthenium complex and oxidized salicylate radical as the primary photoproducts of this reaction. The reduced reaction order due to ion pairing allowed the first-order PCET rate constants to be directly measured through nanosecond photoluminescence spectroscopy. These PCET rate constants saturated at larger driving forces consistent with approaching the Marcus barrierless region. Surprisingly, a proton-transfer tautomer of salicylate, with the proton localized on the carboxylate functional group, was present in acetonitrile. A pre-equilibrium model based on this tautomerization provided non-adiabatic electron-transfer rate constants that were well described by Marcus theory. Electrostatic ion pairs were critical to our ability to investigate this PCET mechanism without the need to covalently link the donor and acceptor or introduce specific hydrogen bonding sites that could compete in alternate PCET pathways.
Cationic Micellar Effect on the Kinetics of the Protolysis of Aromatic Carboxylic Acids studied by the Ultrasonic Absorption Method
Isoda, Teruyo,Yamasaki, Miyuki,Yano, Hiroshige,Sano, Takayuki,Harada, Shoji
, p. 869 - 874 (2007/10/02)
The protolysis of carboxylic acids has been kinetically studied by the ultrasonic absorption method in the presence of tetradecyltrimethylammonium bromide (TTAB) micelles in aqueous solution.The carboxylic acids studied were classified into two categories, one capable of formation of intramolecular hydrogen bond, namely the salicylic acid derivatives (SAD) and the other which cannot form the bond, namely the benzoic acid derivatives (BAD).The rate constant (γ2kf, kb), the apparent dissociation constant (Ka), and the volume change of the reaction (ΔV) were obtained.Different Ka dependences of the rate constants observed for SAD and BAD are discussed in relation to the effect of intramolecular hydrogen bond. pKa dependences were also observed for ΔV of SAD and BAD.These dependences are larger than those in aqueous solution.This result was attributed to the change of arrangement of water molecules around the solute in micellar solution and aqueous solution.
Chain Length Effects in the Cleavage of Aryl Esters by Cyclodextrins. Different Transition States for m- and p-Nitrophenyl Alkanoates
Tee, Oswald S.,Mazza, Charles,Du, Xian-xian
, p. 3603 - 3609 (2007/10/02)
The kinetics of cleavage of m- and p-nitrophenyl esters (acetate, propanoate, butanoate, pentanoate, and hexanoate) in a basic aqueous phosphate buffer containing α- or β-cyclodextrin (α- or β-CD) have been measured.For these two series of esters the m-nitro derivatives undergo more efficient cleavage than their p-nitro isomers, indicating that the former react via a transition state in which the aryloxy moiety is included in the CD cavity, even though substrate binding probably occurs through the alkyl group.For the p-nitrophenyl esters kinetic parameters vary significantly with the length of the alkanoate chain, and in a manner that suggests that substrate binding and transition-state binding both involve inclusion of the alkyl moiety.In contrast to the above, kinetic parameters for the cleavage of 2-carboxy-5(or 5)-chlorophenyl esters by α- and β-CD show little or no variation with the chain length of the alkanoate, implying that both series of esters react solely by aryloxy group inclusion.The present studies illustrate the usefulness of the pseudo constants pKTS (=-logKTS), where KTS is the apparent dissociation constant of the transition state of the CD-mediated reaction into the transition state of the normal reaction and CD.The variation of these constants with structure can be a useful probe of mechanism, particularly with regard to the mode of binding a transition state of the CD-mediated reaction.
Binary and Ternary Chelates of Scandium(III), Yttrium(III) and Lanthanum(III) with Ethyleneglycol-Bis(β-Aminoethylether)-Tetraacetic Acid as Primary and Substituted Salicylic Acids as Secondary Ligands
Pandey, Ashok Kumar,Chandra, M.,Agarwala, B. V.,Dey, A. K.
, p. 32 - 34 (2007/10/02)
Formation constants of binary and ternary complexes of the systems of the type: M-L and M-egta-L have been determined pH-metrically at 25 deg and μ=0.1 M (KNO3) in 50 percent (v/v) aqueous-ethanol medium.The order of stabilities of ternary complexes have compared with those of corresponding binary complexes, and results discussed on the basis of coulombic interactions.
