Effects of alcohols on emission spectra of toluene-triethylamine mixtures in THF: separation into polar and hydrogen-bonding interactions

The emission spectra of toluene (T)–triethylamine (TEA) systems were measured under conditions of steady-state illumination in some protic and aprotic solvent–THF mixtures. The fluorescence spectrum of the T–TEA system in THF could be separated into three component bands (band A at 279 nm (fluorescence of T), band B at 336 nm (fluorescence of TEA) and band C at 373 nm (emission from an intermolecular exciplex)). The intensities of bands B and C decreased with increasing solvent polarity. The decrease in the intensities of bands B and C is considered to be caused by the enhanced conversion of the exciplex to an ion-pair with increase in solvent polarity. The intensities of bands B and C also decreased owing to the hydrogen-bonding interaction between TEA and protic solvents, but in this case the intensity of band A increased. Acetonitrile only has a polar effect and trichloroacetic acid only has a hydrogen-bonding (or protonation) effect, while alcohols have both effects. The equilibrium constants for the formation of intermolecular hydrogen-bonded complexes of TEA with alcohols were estimated from the changes in the intensity of band A. The hydrogen-bonding and polar effects of alcohols on the intensities of bands B and C could be evaluated separately. The ratio of the hydrogen-bonding effect to the polar effect of alcohols was observed to increase with increasing vol.% of alcohol.</p

Separation into polar and hydrogen-bonding factors of the effects of alcohols on the emission spectrum of 4-phenyl-1-N,N-dimethylaminobutane in THF

The effects of the additions of protic and aprotic polar solvents on the emission spectrum of 4-phenyl-1-N,N-dimethylaminobutane (PDAB) in THF have been studied under conditions of steady-state illumination. The fluorescence spectrum of PDAB in THF was reported to consist of three component bands (band A at 285 nm (fluorescence of the phenyl group), band B at 343 nm (fluorescence of the amino group) and band C at 385 nm (emission from an intramolecular exciplex)). The intensities of bands B and C decreased with increasing solvent polarity. They also decreased owing to the hydrogen-bonding interaction between the amino group in PDAB and protic solvents, but in this case the intensity of band A was found to increase. Acetonitrile has only a polar effect and trichloroacetic acid only a hydrogen-bonding (or protonation) effect, while alcohols have both effects. The equilibrium constants for the formation of intermolecular hydrogen-bonded complexes of the amino group with alcohols were estimated from the intensity change of band A. The hydrogen-bonding and polar effects of alcohols on the intensities of bands B and C could be separately evaluated. The decrease in the intensities of bands B and C with increasing solvent polarity in THF-AN and THF-alcohol mixtures is considered to be caused by the conversion of the exciplex to an ion-pair enhanced by the increase in solvent polarity.</p

A comparative study of the antioxidant profiles of olive fruit and leaf extracts against five reactive oxygen species as measured with a multiple free‐radical scavenging method

Olive fruits and leaves are recognized to have great potential as natural sources of antioxidants. The major phenolic antioxidant component in these plant tissues is oleuropein. The antioxidant activity of olive fruits and leaves was evaluated in this study using multiple free‐radical scavenging (MULTIS) methods, wherein we determined the scavenging abilities of different extracts against five reactive oxygen species (ROS; HO·, O2−·, RO·, t‐BuOO·, and 1O2). Raw olive fruits taste bitter and are inedible without undergoing a debittering treatment. Following the NaOH‐debittering process, the radical scavenging activity of olives decreased by 90%. The MULTIS measurements indicated that oleuropein and hydroxytyrosol are responsible for the radical scavenging activity of olive fruits. Furthermore, we evaluated the radical scavenging profiles of olive leaf extracts against five ROS and found significant seasonal variations in their antioxidant activities. Leaves picked in August possessed greater radical scavenging abilities (180% to 410% for different ROS) than those picked in the cold season (December and February). In roasted olive leaves, we found marked increases (230% to 300% and 180% to 220%) in the antioxidant activities of Maillard reaction products against RO· and t‐BuOO·, respectively. This study presented a useful comparative analysis of the antioxidant capacities of food against various types of ROS

Oxygen radical absorbance capacity (ORAC) of cyclodextrin-solubilized flavonoids, resveratrol and astaxanthin as measured with the ORAC-EPR method

Recently, we proposed an oxygen radical absorbance capacity method that directly quantifies the antioxidant’s scavenging capacity against free radicals and evaluated the radical scavenging abilities for water soluble antioxidant compounds. In this study, we determined the radical scavenging abilities of lipophilic antioxidants which were solubilized by cyclodextrin in water. Commonly employed fluorescence-based method measures the antioxidant’s protection capability for the fluorescent probe, while we directly quantify free-radical level using electron paramagnetic resonance spin trapping technique. In addition, the spin trapping-based method adopted controlled UV-photolysis of azo-initiator for free radical generation, but in fluorescence-based method, thermal decomposition of azo-initiator was utilized. We determined the radical scavenging abilities of seven well-known lipophilic antioxidants (five flavonoids, resveratrol and astaxanthin), using methylated β-cyclodextrin as a solubilizer. The results indicated that the agreement between spin trapping-based and fluorescence-based values was only fair partly because of a large variation in the previous fluorescence-based data. Typical radical scavenging abilities in trolox equivalent unit are: catechin 0.96; epicatechin 0.94; epigallocatechin gallate 1.3; kaempferol 0.37; myricetin 3.2; resveratrol 0.64; and astaxanthin 0.28, indicating that myricetin possesses the highest antioxidant capacity among the compounds tested. We sorted out the possible causes of the deviation between the two methods

Analysis of bis(trifluoromethylsulfonyl)imide-doped paramagnetic graphite intercalation compound using F-19 very fast magic angle spinning nuclear magnetic resonance

F atoms bonding to paramagnetic/conductive graphene layers in accepter-type graphite intercalation compounds (GICs) are analyzed using very fast magic angle spinning nuclear magnetic resonance, which is applied for the first time on F-19 nuclei to investigate paramagnetic materials. In the bis(trifluoromethylsulfonyl)imide(TFSI)-doped GIC, C-F bonds between fluorine atoms and graphene layers conform to a weak bonding of F to the graphene sheets. TFSI anions intercalated in the GIC do not show overall molecular motion; even at room temperature only the CF3 groups rotate

Kinetic study of the reaction of leuco methylene blue with 2,6-dimethyl-p-benzoquinone in a reverse micellar system

The kinetics of the reaction of leuco methylene blue (MBH) with 2,6-dimethyl-p-benzoquinone (DMBQ) were studied in a heptane/bis(2-ethylhexyl)-sulfosuccinate (AOT)/water reverse micellar system. The pseudo-first-order rate constant (k (obsd)) obtained in the presence of excess of DMBQ was found to be proportional to the initial concentration of DMBQ for W (0)=3, 5, 10, 15 and 20 (W (0)=[H2O]/[AOT]). The second-order rate constant (k (2)=k (obsd)/[DMBQ](0)) increased with an increase in the W (0) value, but was almost independent of the concentration of the water pool. A mechanism involving the distribution of DMBQ between the reverse micellar interface and bulk organic solvent was proposed to explain these findings.</p

Polar and hydrogen-bonding effects of alcohols on the emission spectrum of styrene-triethylamine system

The emission spectra of styrene (ST)-triethylamine (TEA) systems were measured under steady-state illumination conditions in some THF-protic solvent mixtures. The fluorescence spectrum of the ST-TEA system in THF consists of two bands (band A at 304 nm (fluorescence of ST) and band B at 460 nm (emission from an exciplex)). The intensity of band A increased and that of band B decreased with increasing amounts of protic solvents in THF-protic solvent mixtures. The increase in the intensity of band A was explained by the decrease in the concentration of free amine owing to the hydrogen-bonding interaction (or protonation) between TEA and protic solvents. The decrease in the intensity of band B was considered to be caused by the decrease in the concentration of free amine on the addition of protic solvents and the enhanced conversion of the exciplex to an ion pair with increasing solvent polarity. The polar effect was expressed as a function of the relative permittivity of the solution.</p

Elucidation of the role of the complex in hydride transfer reaction between methylene blue and 1-benzyl-1,4-dihydronictinamide by effect of &#947;-cyclodextrin

The kinetics of the hydride transfer reaction between Methylene Blue (MB+) and&#12288;1-benzyl-1,4-dihydronicotinamide (BNAH) were studied in 10 % ethanol-90 % water mixed solvents containing &#946;- and &#947;-cyclodextrins (&#946;-CD and &#947;-CD). The pseudo-first order rate constant shows kinetic saturation at high initial concentration of BNAH. This indicates the formation of a complex between MB+ and BNAH. The reaction was suppressed by addition of &#946;-CD, but enhanced by addition of &#947;-CD. MB+ and BNAH were separately accommodated within the &#946;-CD cavity and the cavity walls may protect the activity site of the reactants. On the other hand, in the MB+-BNAH-&#947;-CD system, the inclusion of the complex between MB+ and BNAH with &#947;-CD occurred. This effect of &#947;-CD can distinguish between the productive and non-productive nature of the complex.</p