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The present study focuses on the effects of the physicochemical properties of superparamagnetic PEG-modified, positively charged, and negatively charged iron oxide nanoparticles (SPIONs) on their reactivity with hydrogen peroxide. Our hypothesis was that the reactivity of SPIONs in this reaction would depend on their surface properties. The comparative study of the nanoparticles with DLS and TEM revealed the average sizes of PEG-modified, positively charged, and negatively charged SPIONs. We observed that the reactivity of negatively charged SPIONs with hydrogen peroxide was less than that of positively charged SPIONs and that of these second nanoparticles was less than that of PEG-modified SPIONs. This difference in the reactivity of these SPIONs with hydrogen peroxide was attributed to the presence of carboxyl or amine groups on their surface. However, the values of the rate constants of the reactions of PEG-modified, positively charged, and negatively charged SPIONs with hydrogen peroxide showed that the reaction of negatively charged SPIONs with hydrogen peroxide was more rapid than that of PEG-modified SPIONs and the reaction of these second SPIONs with hydrogen peroxide was more rapid than that of positively charged SPIONs. The surface study of the SPIONs using XPS showed that the high-resolution spectra of these nanoparticles changed after reaction with hydrogen peroxide, which indicates their surface modifications. These investigations can help develop more appropriate nanoparticles with controlled physicochemical properties. Key words: superparamagnetic iron oxide nanoparticles, FTIR, DLS, SEM, XPS, oxygen uptake. La presente etude porte sur les effets des proprietes physicochimiques de nanoparticules d'oxyde de fer superparamagetique (SPION, acronyme anglais pour superparamagnetic iron oxide nanoparticles) soit modifiees par le polyethylèneglycol (PEG), chargees positivement ou chargees negativement sur leur reactivite face au peroxyde d'hydrogène. Nous avions pose l'hypothèse que la reactivite des SPIONs dans cette reaction devrait dependre de leurs proprietes de surface. L'etude comparative de ces nanoparticules par diffusion dynamique de la lumière (DDL) et microscopie electronique en transmission (MET) a permis de determiner la taille moyenne des SPIONs modifiees par le PEG, chargees positivement et chargees negativement. Nous avons observe que la reactivite des SPIONs chargees negativement à l'egard du peroxyde d'hydrogène etait moindre que celle des SPIONs chargees positivement, et que celle de ces dernières nanoparticules etait moindre que celle des SPIONs modifiees par le PEG. Nous avons attribue cette difference de reactivite entre ces SPION à l'egard du peroxyde d'hydrogène à la presence de groupes carboxyle et amine à leur surface. Cependant, les valeurs de la constante de vitesse des reactions des SPION-PEGs, des SPIONs chargees positivement et des SPIONs chargees negativement avec le peroxyde d'hydrogène ont montre que la reaction des SPIONs chargees negativement avec le peroxyde d'hydrogène etait plus rapide que celle des SPION-PEGs et que la reaction de ces dernières avec le peroxyde d'hydrogène etait plus rapide que celle des SPIONs chargees positivement. L'etude de surface des SPIONs à l'aide de la spectroscopie de photoelectrons X (XPS) a montre que les spectres à haute resolution de ces nanoparticules avaient change après la reaction avec le peroxyde d'hydrogène, ce qui est revelateur de modifications de la surface. Ces recherches pourront permettre la mise au point de nanoparticules plus appropriees aux proprietes physicochimiques modulables. [Traduit par la Redaction] Mots-cles : nanoparticules d'oxyde de fer superparamagnetique, FTIR, DDL, MEB, XPS, consommation d'oxygène., Introduction The surface modification of nanoparticles (NPs) has attracted significant interest over the last decades. NPs consist of a core and shell with dimensions of 1-100 nm that result in [...]

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Acid-catalyzed deprotection of tert-butoxycarbonyl (t-Boc) pendant groups present in a polymer film is one of the most common chemical reactions in photolithography. We present here a novel method to determine the catalytic chain length of this reaction under different development conditions. We demonstrate this in model PMMA thin films containing triphenylsulphonium triflate as a photoacid generator, acid sensor coumarin 6, t-Boa protected coumarin 4, and base 2-piperidin-l-yl-ethanol (2-PE). Deprotection of the t-Boa group, catalyzed by the photogenerated acid, during the post-exposure bake leads to formation of coumarin 4, a strongly fluorescent molecule whose concentration is monitored using fluorescence. We take advantage of the change in the emission spectra of coumarin 6 upon protonation to monitor acid formation. To quantify the amount of acid, an acid-base titration is done in the polymer film using 2-PE. Knowing the amount of deprotected probe and the amount of acid, we are able to calculate the number of moles of deprotected C4-t-Boc per mol of acid, which is the actual catalytic chain length. Key words: photolithography, chemical amplification, catalytic chain length, fluorescent sensors, photoacid generator. La deprotection acidocatalysee des groupes pendants tert-butoxycarbonyles (t-Boc) presents dans un film de polymere est une des reactions chimiques les plus communes en photolithographie. Dans ce travail, on presente une nouvelle methode pour determiner la longueur de la chaine catalytique de cette reaction dans diverses conditions de developpement. Ceci est demontre dans des films minces modeles de PMMA contenant du triflate de triphenylsulfonium comme generateur photoacide, le detecteur d'acide coumarine 6, la coumarine 4 portant un groupe protecteur t-Boc et la base 2-piperidin-l-yl-ethanol (2-PE). La deprotection du groupe t-Boc, catalysee par l'acide photogenere au cours de la cuisson suivant l'exposition, conduit a la formation de la coumarine 4, une molecule fortement fluorescente dont on peut determiner la concentration par fluorescence. On tire avantage du changement dans le spectre d'emission de la coumarine 6 lors de la protonation pour deceler la formation d'acide. Afin de quantifier la quantite d'acide, on realise un titrage acide-base dans le film de polymere a l'aide du 2-PE. Connaissant la quantite de sonde deprotonee et la quantite d'acide, il est possible de calculer le nombre de moles de C4-t-Boc deprotege par mol d'acide, ce qui correspond a la longueur de la chaine catalytique. Mots cles : photolithographie, amplification chimique, longueur d'une chaine catalytique, detecteurs fluorescents, generateur photoacide. [Traduit par la Redaction]

The photophysical and electrochemical properties for a series of BODIPY dyes with incremental 3‐ and 3,5‐vinyl conjugation, as well as incremental electron‐donating groups (anisole < triphenylamine < ferrocenyl), are presented. Insight into the influence of each vinyl‐conjugated electron‐donating group on both vis‐NIR absorption and fluorescence emission properties is provided. These trends are further corroborated by density functional theory computational analysis. Two of this series containing the 3,5‐bis(vinyltriphenylamine) and 3,5‐bis(vinylferrocenyl) substituents exhibit significant absorption cross sections in the biological transparency window justifying further investigation of their photoacoustic emission properties via both optical photoacoustic z‐scan and photoacoustic tomography experiments. Both the 3,5‐bis(vinyltriphenylamine) and 3,5‐bis(vinylferrocenyl) substituted BODIPY dyes exhibit quantitative photoacoustic quantum yields. Relative to the commercially available methylene blue and indocyanine green molecular photoacoustic contrast agents, the 3,5‐bis(vinyltriphenylamine)‐derived BODIPY exhibits the greatest photoacoustic emission and contrast upon excited‐state absorption at 685 nm excitation at a low power laser fluence (<20 mJ cm‐2). [ABSTRACT FROM AUTHOR]

The photophysical and electrochemical properties for a series of BODIPY dyes with incremental 3‐ and 3,5‐vinyl conjugation, as well as incremental electron‐donating groups (anisole < triphenylamine < ferrocenyl), are presented. Insight into the influence of each vinyl‐conjugated electron‐donating group on both vis‐NIR absorption and fluorescence emission properties is provided. These trends are further corroborated by density functional theory computational analysis. Two of this series containing the 3,5‐bis(vinyltriphenylamine) and 3,5‐bis(vinylferrocenyl) substituents exhibit significant absorption cross sections in the biological transparency window justifying further investigation of their photoacoustic emission properties via both optical photoacoustic z‐scan and photoacoustic tomography experiments. Both the 3,5‐bis(vinyltriphenylamine) and 3,5‐bis(vinylferrocenyl) substituted BODIPY dyes exhibit quantitative photoacoustic quantum yields. Relative to the commercially available methylene blue and indocyanine green molecular photoacoustic contrast agents, the 3,5‐bis(vinyltriphenylamine)‐derived BODIPY exhibits the greatest photoacoustic emission and contrast upon excited‐state absorption at 685 nm excitation at a low power laser fluence (<20 mJ cm‐2). [ABSTRACT FROM AUTHOR]

We report detailed mechanistic investigations of an iron‐based catalyst system, which allows the α‐C−H oxidation of a wide variety of amines. In contrast to other catalysts that effect α‐C−H oxidations of tertiary amines, the system under investigation exclusively employs peroxy esters as oxidants. More common oxidants (e. g. tBuOOH) previously reported to affect amine oxidations via free radical pathways do not provide amine α‐C−H oxidation products in combination with the described catalyst system. The investigations described herein employ initial rate kinetics, kinetic profiling, DFT calculations as well as Eyring, kinetic isotope effect, Hammett, ligand coordination, and EPR studies to shed light on the Fe catalyst system. The obtained data suggest that the catalytic mechanism proceeds through C−H abstraction at a coordinated substrate molecule. This rate‐determining step occurs either through an Fe(IV) oxo pathway or a 2‐electron pathway at an Fe(II) intermediate with bound oxidant. DFT calculations indicate that the Fe(IV) oxo mechanism will be the preferred route of these two possibilities. We further show via kinetic profiling and EPR studies that catalyst activation follows a radical pathway, which is initiated by hydrolysis of PhCO3tBu to tBuOOH. Overall, the obtained mechanistic data support a non‐classical, Fe catalyzed pathway that requires substrate binding, inducing selectivity for α‐C−H functionalization. [ABSTRACT FROM AUTHOR]

Evidence is provided for the formation of hydroxyl radicals during lipid peroxidation, a common process associated with oxidative stress. The [alpha]C-H hydrogen abstraction from hydroperoxides formed during lipid autooxidation has led to the formation of ketones and hydroxyl radicals.

A new class of thermally activated chain-breaking antioxidants based on a radical-dimer equilibrium is discovered. It is shown that these dimers can prevent autoxidation in model systems by trapping peroxyl radicals very efficiently, even at temperatures as low as 30 degrees Celsius.

The synthesis and characterization of a series of donor-π-acceptor-π-donor (D-A-D) curcuminoid molecules is presented herein that incorporates π-extended aryl and electron-donating amino terminal functionalization. Computational evaluation shows these molecules possess quadrupolar character with the lowest energy transitions displaying high molar extinction coefficients with broad tunability through manipulation of terminal donating groups. Consistent with their quadrupolar nature, these molecules show varying degrees of solvatochromic behavior in both their absorption and emission spectra, which has been analyzed by Lippert-Mataga and Kamlet-Taft analysis. Photophysical and photoacoustic (PA) properties of these molecules have been investigated by the optical photoacoustic z-scan (OPAZ) method. Selected curcuminoid molecules display nonlinear behavior at a high laser fluence through excited state absorption that translates to the production of an enhanced photoacoustic emission. A relative comparison of "molar PA emission" is also presented with the crystal violet linear optical absorbing/linear PA emitting system being utilized as a standard reference material for OPAZ experiments. Furthermore, PA tomography experiments are presented to illustrate the enhanced PA contrast obtainable via an excited state absorption. [ABSTRACT FROM AUTHOR]