Louis J. Kirschenbaum

Hydroxyterephthalate as a Fluorescent Probe for Hydroxyl Radicals: Application to Hair Melanin

The known photoreactions of melanin include production of melanin free radicals and oxygen consumption. While qualitative descriptions of the intermediates and products of these processes have been published, no quantitative procedures have been reported that allow the convenient measurement of the products of oxygen reduction. We have used complementary fluorescence and electron spin resonance techniques to study free radical production from extracted hair melanin irradiated at wavelengths above 320 nm. As a comparison, sepia was also studied. Irradiation of aerated suspensions of melanin in the presence of terephthalic acid dianion (TA) ‡ gives rise to the characteristic fluorescence spectrum of the 2‐hydroxyterephthalate ion (HTA, λeλ= 315 nm, λem= 425 nm). Production of HTA has been studied as a function of time (at constant light flux) and in the presence of other substrates including hydroxyl radical sources and scavengers. The use of TA as a fluorescent probe can be conveniently adapted to other systems.

PHOTOSENSITIZED FORMATION OF ASCORBATE RADICALS BY RIBOFLAVIN: AN ESR STUDY

Abstract— The riboflavin‐sensitized photooxidation of ascorbate ion (HA‐) to ascorbate radical (A‐) was followed by electron spin resonance (ESR) spectroscopy in conjunction with oxygen depletion measurements. In air‐saturated aqueous media, steady‐state amounts of A‐ are rapidly established upon irradiation. The ESR signal disappears within a few seconds after the light is extinguished–more slowly under constant irradiation as oxygen is depleted. No photooxidation was observed in deaerated media. Similar results were obtained with other flavins and when ascorbyl palmitate was substituted for HA‐. The effect of added superoxide dismutase, catalase, desferrioxamine, and singlet oxygen scavengers (NaN3 and tryptophan) was studied, as was replacement of water by D2O and saturation with O2. The results are indicative of ascorbate free radical production via direct reaction between ascorbate ion and triplet riboflavin in the presence of O2. While the presence of superoxide ion tends to reduce the steady‐state concentration of A‐, competition from the reaction of HA‐ with singlet oxygen is less apparent in this system (at HA‐≥ 1 mM) than in the previously studied aluminum phthalocyanine tetrasulfonate‐photosensitized reaction.

Detection of Explosives in Hair Using Ion Mobility Spectrometry

Abstract:  Conventional explosives 2,4,6‐trinitrotoluene (TNT), nitroglycerin (NG), and ethylene glycol dinitrate (EGDN) sorbed to hair can be directly detected by an ion mobility spectrometer (IMS) in E‐mode (for explosives). Terrorist explosive, triacetone triperoxide (TATP), difficult to detect by IMS in E‐mode, was detected in N‐mode (for narcotics). Three modes of sample introduction to IMS vapor desorption unit were used: (i) placement of hair directly into the unit, (ii) swabbing of hair and placement of swabs (i.e., paper GE‐IMS sample traps) into the unit, and (iii) acetonitrile extracts of hair positioned on sample traps and placed into the unit. TNT, NG, and EGDN were detected in E‐mode by all three sample introduction methods. TATP could only be detected by the acetonitrile extraction method after exposure of the hair to vapor for 16 days because of lower sensitivity. With standard solutions, TATP detection in E‐mode required about 10 times as much sample as EGDN (3.9 μg compared with 0.3 μg). IMS in N‐mode detected TATP from hair by all three modes of sample introduction.

Enhancement of 5-Aminolevulinic acid-induced oxidative stress on two cancer cell lines by gold nanoparticles.

Abstract 5-Aminolevulinic acid (5-ALA) and its methyl ester (5-ALA-Me) at mM concentration levels induce oxidative stress via the production of reactive oxygen species (ROS). Human cancer cell lines (MCF-7 and HepG2) incubated in the dark in the simultaneous presence of 5.0 mM or more 5-ALA or 5-ALA-Me (for MCF-7) and 7 µg/mL of 15 nm citrate capped gold nanoparticles (AuNPs) were damaged more seriously compared to those in the presence of the levulinic acid alone. Damage is visible in electron micrographs which reveal similar morphology both in the presence or absence of AuNPs. Cytotoxicity was observed irrespective of the presence of serum and medium. Production of ROS in cell free samples containing 5-ALA-Me was monitored by EPR as the DMPO-OH spin adduct and also showed a catalytic effect of AuNPs. Both SOD and CAT inhibited the production of ROS and also reduced cytotoxicity in the cell samples. These observations can be explained by initial attack on the cell membrane by ROS produced in the medium outside the cell and provide insight into possible uses of 5-ALA in cancer chemotherapy.

Phenol Nitration Induced by an {Fe(NO)2}10 Dinitrosyl Iron Complex

Cellular dinitrosyl iron complexes (DNICs) have long been considered NO carriers. Although other physiological roles of DNICs have been postulated, their chemical functionality outside of NO transfer has not been demonstrated thus far. Here we report the unprecedented dioxygen reactivity of a N-bound {Fe(NO)(2)}(10) DNIC, [Fe(TMEDA)(NO)(2)] (1). In the presence of O(2), 1 becomes a nitrating agent that converts 2,4,-di-tert-butylphenol to 2,4-di-tert-butyl-6-nitrophenol via formation of a putative iron-peroxynitrite [Fe(TMEDA)(NO)(ONOO)] (2) that is stable below -80 °C. Iron K-edge X-ray absorption spectroscopy on 2 supports a five-coordinated metal center with a bound peroxynitrite in a cyclic bidentate fashion. The peroxynitrite ligand of 2 readily decays at increased temperature or under illumination. These results suggest that DNICs could have multiple physiological or deleterious roles, including that of cellular nitrating agents.

The electrochemical oxidation of divalent nickel complexes with tetra-aza-macrocyclic ligands in aqueous solutions

Abstract The electrochemical oxidation of three divalent nickel complexes with tetra-aza-macrocyclic ligands in perchlorate- and sulphate-containing aqueous solutions is reported. The mechanism of oxidation is analysed in detail. Redox potentials, diffusion coefficients, a transfer coefficient and a heterogeneous rate constant are reported. The pH effect on the electrochemical oxidations is discussed.

Accumulation of Explosives in Hair

The sorption of explosives (TNT, RDX, PETN, TATP, EGDN) to hair during exposure to their vapors is examined. Three colors of hair were simultaneously exposed to explosive vapor. Following exposure of hair, the sorbed explosive was removed by extraction with acetonitrile and quantified. Results show that sorption of explosives, via vapor diffusion, to black hair is significantly greater than to blond, brown or bleached hair. Furthermore, the rate of sorption is directly related to the vapor density of the explosive: EGDN > TATP >>>TNT >> PETN > RDX. In some cases, the explosive-containing hair was subject to repeated washings with sodium dodecylsulfate or simply left out in an open area to determine the persistence of the explosive contamination. While explosive is removed from hair with time or washing, some persists. These results indicate that hair can be a useful indicator of explosive exposure/handling.

Kinetics of the reduction of the tetrahydroxyargentate(III) ion by sulphite in aqueous alkaline media

Abstract The reduction of Ag(OH)4− by sulphite ion to give silver(I) and sulphate in strong base has been studied by stopped-flow spectrophotometry. The reaction was found to fit a second-order rate law with a rate constant k = (9.1 ± 0.1) x 102M−1s−1 (T = 25°C, μ = 1.2 M). The estimated enthalpy and entropy of activation are 27 kJ mol−1 and − 153 J K−1 mol−1 respectively. Variation of rate with ionic strength is consistent with the interaction between mononegative Ag(OH)4− and dinegative SO32−. The redox reaction appears to proceed by a one-step oxygen atom transfer. Two kinetically indistinguishable pathways are discussed. The first involves initial attack of a sulphite oxygen at an axial silver(III) site. The second pathway involves initial interaction between sulphur(IV) and a bound hydroxyl. Sulphite oxidation by silver(III) is about 104 times faster than that of phosphite, while no reaction is observed with NO2−.

Photosensitized formation of ascorbate radicals by chloroaluminum phthalocyanine tetrasulfonate: An electron spin resonance study

The chloroaluminum phthalocyanine tetrasulfonate sensitized photooxidation of ascorbic acid to ascorbate radical (A.-) was followed by electron spin resonance (ESR) spectroscopy. In air saturated aqueous media, steady-state amounts of A.- are rapidly established upon irradiation. The ESR signal disappears within a few seconds after the light is extinguished--more slowly under constant irradiation as oxygen is depleted. No photooxidation was observed in deaerated media. The effect of added superoxide dismutase, catalase, desferrioxamine, and singlet oxygen scavengers (NaN3 and tryptophan) was studied, as was replacement of water by D2O and saturation with O2. The results are indicative of free radical production by direct reaction between ascorbate ion and sensitized phthalocyanine (a Type I mechanism) in competition with the (Type II) reaction of HA- with singlet oxygen, a reaction which does not produce ascorbate radical intermediates.

Complexes of silver(III) with oxoanions

Abstract Silver(III) has a half-life at pH 11 of several hundred seconds in aqueous solutions in the presence of 0.1–1.0 M concentrations of certain basic oxoanions (Oxo) (phosphate, carbonate, borate, pyrophosphate, and arsenate). This compares with a lifetime of a few seconds at pH 11 in the absence of these oxoanions. UV-visible spectra and kinetic data for these solutions are interpreted as evidence for the following equilibria in the pH range 9–13. Ag(OH) 4 −1 + H 2 O ⇌ Ag(OH) 3 H 2 O + OH − (1) Ag(OH) 4 −1 + Oxo ⇌ Ag(OH) 3 Oxo + OH − (2) Ag(OH) 3 Oxo + H 2 O ⇌ Ag(OH) 2 (Oxo)H 2 O + OH − (3) Values of K 3 lie in the range 10 −3 K 3 4 M for the systems studied. K 2 is estimated to be ∼10 2 for phosphate and slightly smaller for the other systems. Ag(OH) 4 − undergoes an unusual reaction with pyrophosphate at pH ∼ 8 to form a novel silver(II) complex, [Ag(P 2 O 7 ) 2 ] 6− , for which EPR and electronic absorption spectral parameters are reported.