Synthesis, Structure and (Photo)Catalytic Behavior of Ce-MOFs Containing Perfluoroalkylcarboxylate Linkers: Experimental and Theoretical Insights.

Cerium-based Metal-Organic frameworks (Ce-MOFs) are attracting increasing interest due to their similar structural features to zirconium MOFs. The redox behavior of Ce(III/IV) adds a range of properties to the compounds. Recently, perfluorinated linkers have been used in the synthesis of MOFs to introduce new characteristic into the structure.

Competition Between C -S and C -C Bond Cleavage in β-Hydroxysulfoxides Cation Radicals Generated by Photoinduced Electron Transfer.

A kinetic and product study of the 3-cyano-N-methyl-quinolinium photoinduced monoelectronic oxidation of a series of β-hydroxysulfoxides has been carried out to investigate the competition between C -S and C -C bond cleavage within the corresponding cation radicals. Laser flash photolysis experiments unequivocally established the formation of sulfoxide cation radicals showing their absorption band (λ ≈ 520 nm) and that of 3-CN-NMQ (λ ≈ 390 nm). Steady-state photolysis experiments suggest that, in contrast to what previously observed for alkyl phenyl sulfoxide cation radicals that exclusively undergo C -S bond cleavage, the presence of a β-hydroxy group makes, in some cases, the C -C scission competitive.

Solvent-Free Synthetic Route for Cerium(IV) Metal-Organic Frameworks with UiO-66 Architecture and Their Photocatalytic Applications.

A near solvent-free synthetic route for Ce-UiO-66 metal-organic frameworks (MOFs) is presented. The MOFs are obtained by energetically grinding the reagents, cerium ammonium nitrate (CAN) and the carboxylic linkers, in a mortar for a few minutes with the addition of a small amount of acetic acid (AcOH) as a modulator (8.75 equiv, 0.

Effect of Surfactant Structure on the Superactivity of Candida rugosa Lipase.

In this work, we present the effects of ionic and zwitterionic surfactants on the hydrolytic activity of Candida rugosa lipase (CRL), one of the most important and widely used microbial lipases. A series of amine N-oxide surfactants was studied to explore the relationship between their molecular structures and their effect on catalytic properties of CRL. These zwitterionic amphiphiles are known for their ability to form aggregates that can increase their size, thanks to a sphere-rod transition, without any additive.

Trifluoroacetylated tyrosine-rich D-tetrapeptides have potent antioxidant activity.

The term "oxidative stress" indicates a set of chemical reactions unleashed by a disparate number of events inducing DNA damage, lipid peroxidation, protein modification and other effects, which are responsible of altering the physiological status of cells or tissues. Excessive Reactive Oxygen Species (ROS) levels may accelerate ageing of tissues or induce damage of biomolecules thus promoting cell death or proliferation in dependence of cell status and of targeted molecules. In this context, new antioxidants preventing such effects may have a relevant role as modulators of cell homeostasis and as therapeutic agents.

Electron Transfer Mechanism in the Oxidation of Aryl 1-Methyl-1-phenylethyl Sulfides Promoted by Nonheme Iron(IV)-Oxo Complexes: The Rate of the Oxygen Rebound Process.

The oxidation of aryl 1-methyl-1-phenylethyl sulfides promoted by the nonheme iron(IV)-oxo complexes [(N4Py)Fe═O] and [(Bn-TPEN)Fe═O] occurs by an electron transfer-oxygen rebound (ET-OT) mechanism leading to aryl 1-methyl-1-phenylethyl sulfoxides accompanied by products derived from C-S fragmentation of sulfide radical cations (2-phenyl-2-propanol and diaryl disulfides). For the first time, the rate constants for the oxygen rebound process (k), which are in the range of <0.8 × 10 to 3.

Oxidation of Aryl Diphenylmethyl Sulfides Promoted by a Nonheme Iron(IV)-Oxo Complex: Evidence for an Electron Transfer-Oxygen Transfer Mechanism.

The oxidation of a series of aryl diphenylmethyl sulfides (4-X-C6H4SCH(C6H5)2, where X = OCH3 (1), X = CH3 (2), X = H (3), and X = CF3 (4)) promoted by the nonheme iron(IV)-oxo complex [(N4Py)Fe(IV)═O](2+) occurs by an electron transfer-oxygen transfer (ET-OT) mechanism as supported by the observation of products (diphenylmethanol, benzophenone, and diaryl disulfides) deriving from α-C-S and α-C-H fragmentation of radical cations 1(+•)-4(+•), formed besides the S-oxidation products (aryl diphenylmethyl sulfoxides). The fragmentation/S-oxidation product ratios regularly increase through a decrease in the electron-donating power of the aryl substituents, that is, by increasing the fragmentation rate constants of the radical cations as indicated by a laser flash photolysis (LFP) study of the photochemical oxidation of 1-4 carried out in the presence of N-methoxyphenanthridinium hexafluorophosphate (MeOP(+)PF6(-)).

Photoinduced One-Electron Oxidation of Benzyl Methyl Sulfides in Acetonitrile: Time-Resolved Spectroscopic Evidence for a Thionium Ion Intermediate.

The photo-oxidation of 4-methoxybenzyl methyl sulfide (1a), benzyl methyl sulfide (1b), and 4-cyanobenzyl methyl sulfide (1c) has been investigated in the presence of N-methoxy phenanthridinium hexafluorophosphate (MeOP(+)PF6(-)) under nitrogen in CH3CN. The steady-state photolysis experiments showed for the investigated sulfides exclusively the formation of the corresponding benzaldehyde as the oxidation product, reasonably due to a deprotonation of the sulfide radical cations. Photo-oxidation of 1a-1c occurs through an electron transfer process.

Inclusion of two push-pull N-methylpyridinium salts in anionic surfactant solutions: a comprehensive photophysical investigation.

Two N-methylpyridinium salts with push-pull properties have been investigated in the aqueous solution of anionic micelles of sodium dodecyl sulfate (SDS) and potassium p-(octyloxy)benzenesulfonate (pOoBSK) surfactants. These molecules are known to be extremely sensitive to the local environment, with their absorption spectrum being subjected to a net negative solvatochromism. These compounds are also characterized by an excited state deactivation strictly dependent on the physical properties of the chemical surrounding, with the formation of intramolecular charge-transfer (ICT) states accordingly stabilized.

Photosensitized oxidation of aryl benzyl sulfoxides. Evidence for nucleophilic assistance to the C-s bond cleavage of aryl benzyl sulfoxide radical cations.

The radical cations of a series of aryl benzyl sulfoxides (4-X-C6H4CH2SOC6H4Y(+•)) have been generated by photochemical oxidation of the parent sulfoxides sensitized by 3-cyano-N-methylquinolinium perchlorate (3-CN-NMQ(+)ClO4(-)). Steady-state photolysis experiments showed the prevailing formation of benzylic products deriving from the C-S fragmentation in the radical cations, together with sulfur-containing products. Formation of sulfoxide radical cations was unequivocally established by laser flash photolysis experiments showing the absorption bands of 3-CN-NMQ(•) (λmax = 390 nm) and of the radical cations (λmax = 500-620 nm).

An acridinium-based sensor as a fluorescent photoinduced electron transfer probe for proton detection modulated by anionic micelles.

A water-soluble fluorescent pH sensor of 9-amino-10-methylacridinium chromophore with the 2-(diethylamine)ethyl chain as a receptor shows an "off-on" response going from basic to acidic solution. Photoinduced electron transfer has been directly demonstrated to be the quenching mechanism by the observation of the long-lived acridinyl radical. The interaction of the protonated sensor with anionic micelles causes a significant increase in the detection sensitivity of pH.

Structural effects on the C-S bond cleavage in aryl tert-butyl sulfoxide radical cations.

The oxidation of a series of aryl tert-butyl sulfoxides (4-X-C6H4SOC(CH3)3: 1, X = OCH3; 2, X = CH3; 3, X = H; 4, X = Br) photosensitized by 3-cyano-N-methylquinolinium perchlorate (3-CN-NMQ(+)) has been investigated by steady-state irradiation and nanosecond laser flash photolysis (LFP) under nitrogen in MeCN. Products deriving from the C-S bond cleavage in the radical cations 1(+•)-4(+•) have been observed in the steady-state photolysis experiments. By laser irradiation, the formation of 3-CN-NMQ(•) (λ(max) = 390 nm) and 1(+•)-4(+•) (λ(max) = 500-620 nm) was observed.

Competition of C-H and C-O fragmentation in substituted p-methoxybenzyl ether radical cations generated by photosensitized oxidation.

Laser and steady-state photolysis, sensitized by 2,4,6-triphenylpyrylium tetrafluoroborate (TPP(+)BF(4)(-)), of 4-methoxybenzyl ethers [4-CH(3)O-C(6)H(4)CH(OR(1))R, 1a: R = H, R(1) = CH(3); 1b: R = H, R(1) = C(CH(3))(3); 1c: R = CH(3), R(1) = C(CH(3))(3); 1d: R = 4-CH(3)O-C(6)H(4), R(1) = CH(3)] was carried out in CH(3)CN in the presence of oxygen. In particular, steady-state irradiation of 1a, b and d produced benzylic alcohols (together with a small amount of acetamide for 1a and 1b) and the oxidation carbonyl compounds (esters and ketones); 4-methoxy-α-methylbenzyl alcohol was the only product observed with 1c. Time-resolved investigations of 1c and 1d gave evidence of the intermediate benzylic carbocation, coming from the ether radical cation formed within the laser pulse by an electron transfer process from the ether to the TPP(+) excited state.

Structural and solvent effects on the C-S bond cleavage in aryl triphenylmethyl sulfide radical cations.

Steady-state and laser flash photolysis (LFP) studies of a series of aryl triphenylmethyl sulfides [1, 3,4-(CH(3)O)(2)-C(6)H(3)SC(C(6)H(5))(3); 2, 4-CH(3)O-C(6)H(4)SC(C(6)H(5))(3); 3, 4-CH(3)-C(6)H(4)SC(C(6)H(5))(3); 4, C(6)H(5)SC(C(6)H(5))(3); and 5, 4-Br-C(6)H(4)SC(C(6)H(5))(3)] has been carried out in the presence of N-methoxyphenanthridinium hexafluorophosphate in CH(3)CN, CH(2)Cl(2), CH(2)Cl(2)/CH(3)CN, and CH(2)Cl(2)/CH(3)OH mixtures. Products deriving from the C-S bond cleavage in the radical cations 1(•+)-5(•+) have been observed in the steady-state photolysis experiments. Time-resolved LFP showed first-order decay of the radical cations accompanied by formation of the triphenylmethyl cation.

Structure and C-S bond cleavage in aryl 1-methyl-1-arylethyl sulfide radical cations.

Steady state and laser flash photolysis (LFP) of a series of p-X-cumyl phenyl sulfides (4-X-C(6)H(4)C(CH(3))(2)SC(6)H(5): 1, X = Br; 2, X = H; 3, X = CH(3); 4, X = OCH(3)) and p-X-cumyl p-methoxyphenyl sulfides (4-X-C(6)H(4)C(CH(3))(2)SC(6)H(4)OCH(3): 5, X = H; 6, X = CH(3); 7, X = OCH(3)) has been carried out in the presence of N-methoxy phenanthridinium hexafluorophosphate (MeOP(+)PF(6)(-)) under nitrogen in MeCN. Steady state photolysis showed the formation of products deriving from the C-S bond cleavage in the radical cations 1(+•)-7(+•) (2-aryl-2-propanols and diaryl disulfides). Formation of 1(+•)-7(+•) was also demonstrated by LFP experiments evidencing the absorption bands of the radical cations 1(+•)-3(+•) (λ(max) = 530 nm) and 5(+•)-7(+•) (λ(max) = 570 nm) mainly localized in the arylsulfenyl group and radical cation 4(+•) (λ(max) = 410, 700 nm) probably mainly localized in the cumyl ring.

Steady-state and time-resolved investigations of a crown thioether conjugated with methylacridinium and its complexes with metal ions.

The crown thioether 9-[4-(4,7,10,13-tetrathia-1-azacyclopentadecyl]phenyl-N-methylacridinium perchlorate (TCMA) was synthesized and characterized with the aim to verify its ability to interact selectively with metal ions and substantiate the possibility to detect easily the presence of heavy metals in fluid samples. The spectroscopic properties of TCMA, alone and in the presence of metal ions, were therefore studied in polar solvents (MeCN and H(2)O); in particular, steady-state UV-Vis spectrophotometric and fluorimetric techniques were used together with transient absorption spectroscopy with fs time resolution to investigate the spectral and dynamic properties of the lowest excited singlet state of TCMA and of TCMA/metal ion complexes. The absorption in the Vis region is characterized by a charge-transfer nature with the methylacridinium moiety acting as the electron-acceptor and the anilic group as the electron-donor.

Photophysics of aromatic thiourea derivatives and their complexes with anions. Fast and ultrafast spectroscopic investigations.

In order to collect detailed information on the interaction mechanism between fluorescent thiourea derivatives and anions, 9-[4-(trifluoromethyl)phenylthioureidomethyl]anthracene (1) and the corresponding 10-cyanoanthracene derivative (2) were synthesized and investigated in DMSO and MeCN by using absorption and emission steady state techniques, both in the absence and in the presence of different anions (AcO(-), H(2)PO(4)(-), HSO(4)(-), and Br(-)). A wide examination of the mechanism of anion recognition was also performed by time-resolved transient absorption spectroscopy, with nano- and femto-second time resolution. A complete picture of the excited state deactivation pathways of 1 and 2, where the main operative processes were fluorescence, intersystem crossing and internal conversion, was obtained.

Evidences in favour of a single electron transfer (SET) mechanism in the TiO2 sensitized photo-oxidation of α-hydroxy- and α,β-dihydroxybenzyl derivatives in water.

The TiO(2) photosensitized oxidation in water of a series of X-ring substituted benzyl alcohols gives the corresponding benzaldehyde. Kinetic evidence (from competitive experiments) suggests a single electron transfer (SET) mechanism with a changeover of the electron abstraction site from the aromatic moiety (X=4-OCH(3), 4-CH(3), H and 3-Cl) to the hydroxylic group (X=3-CF(3) and 4-CF(3)), probably due to the preferential adsorption of the above OH group on the TiO(2) surface. The same photo-oxidation of a series of 1-(X-phenyl)-1,2-ethanediols and of 2-(X-phenyl)-1,2-propanediols gives the corresponding benzaldehyde and acetophenone, respectively, accompanied by formaldehyde, whereas a series of symmetrically X-ring-substituted 1,2-diphenyl-1,2-ethanediols yields the corresponding benzaldehyde (substrate/product molar ratio=0.

Reaction of singlet oxygen with thioanisole in ionic liquids: a solvent induced mechanistic dichotomy.

A study of the reaction of thioanisole with singlet oxygen in pyrrolidinium- and imidazolium-based ionic liquids has been carried out. In these solvents, thioanisole shows a strongly enhanced reactivity with respect to molecular aprotic solvents, probably due to a stabilization of the persulfoxide intermediate in the ionic medium. Product isotope effects suggest a mechanistic change ongoing from pyrrolidinium to imidazolium solvents.

Photosensitized oxidation of alkyl phenyl sulfoxides. C-S bond cleavage in alkyl phenyl sulfoxide radical cations.

The 3-cyano-N-methylquinolinium perchlorate (3-CN-NMQ(+)ClO4(-))-photosensitized oxidation of phenyl alkyl sulfoxides (PhSOCR1R2R3, 1, R1 = R2 = H, R3 = Ph; 2, R1 = H, R2 = Me, R3 = Ph; 3, R1 = R2 = Ph, R3 = H; 4, R1 = R2 = Me, R3 = Ph; 5, R1 = R2 = R3 = Me) has been investigated by steady-state irradiation and nanosecond laser flash photolysis (LFP) under nitrogen in MeCN. Steady-state photolysis showed the formation of products deriving from the heterolytic C-S bond cleavage in the sulfoxide radical cations (alcohols, R1R2R3COH, and acetamides, R1R2R3CNHCOCH3) accompanied by sulfur-containing products (phenyl benzenethiosulfinate, diphenyl disulfide, and phenyl benzenethiosulfonate). By laser irradiation, the formation of 3-CN-NMQ(*) (lambda(max) = 390 nm) and sulfoxide radical cations 1(*+) , 2(*+), and 5(*+) (lambda(max) = 550 nm) was observed within the laser pulse.

Anomalous reactivity of radical cations produced by photosensitized oxidation of 4-methoxybenzyl alcohol derivatives: role of the sensitizer.

Steady-state and nanosecond laser flash photolysis measurements of 4-methoxybenzyl alcohol (1a), 4-methoxy-alpha-methylbenzyl alcohol (1b), 4,4'-dimethoxydiphenylmethanol (1c) and 4-methoxy-alpha,alpha'-dimethylbenzyl alcohol (1d) were carried out in air-equilibrated CH(2)Cl(2) and CH(3)CN solutions, in the presence of 9,10-dicyanoanthracene (DCA) and N-methylquinolinium tetrafluoroborate (NMQ(+)BF(4)(-)) as sensitizers. In particular, steady-state irradiation with DCA produced carbonyl compounds and, with NMQ(+)BF(4)(-), carbonyl compounds, ethers (substrates 1a-c ) and styrene (substrate 1d ) while time-resolved investigations gave evidence of charged species produced upon irradiation. The effect of solvent polarity on the reactivity was investigated; in the case of DCA, the reactivity increased with the solvent polarity, while the opposite was obtained when NMQ(+)BF(4)(-) was used.

Singlet oxygen promoted carbon-heteroatom bond cleavage in dibenzyl sulfides and tertiary dibenzylamines. Structural effects and the role of exciplexes.

The C-heteroatom cleavage reactions of substituted dibenzyl sulfides and substituted dibenzylcyclohexylamines promoted by singlet oxygen in MeCN have been investigated. In both systems, the cleavage reactions (leading to benzaldehyde and substituted benzaldehyde) were slightly favored by electron-withdrawing substituents with rho values of +0.47 (sulfides) and +0.

The singlet oxygen oxidation of chlorpromazine and some phenothiazine derivatives. Products and reaction mechanisms.

A kinetic and product study of the reactions of chlorpromazine 1, N-methylphenothiazine 2, and N-ethylphenothiazine 3 with singlet oxygen was carried out in MeOH and MeCN. 1 undergoes exclusive side-chain cleavage, whereas the reactions of 2 and 3, in MeOH, afforded only the corresponding sulfoxides. A mechanism for the reaction of 1 is proposed where the first step involves an interaction between singlet oxygen and the side-chain dimethylamino nitrogen.

Aryl sulfoxide radical cations. Generation, spectral properties, and theoretical calculations.

Aromatic sulfoxide radical cations have been generated by pulse radiolysis and laser flash photolysis techniques. In water (pulse radiolysis) the radical cations showed an intense absorption band in the UV region (ca. 300 nm) and a broad less intense band in the visible region (from 500 to 1000 nm) whose position depends on the nature of the ring substituent.