Formation of iron oxides clusters induced by resonant laser ablation/ionization

Photodynamic therapy (PDT) is a new rapidly developing method for cancer treatment, which is based on the systemic administration of a tumor-localizing photosensitizer (PS), followed by irradiation of the tumor with visible spectrally adapted light.1-3 The photochemical interaction of the PS, light and molecular oxygen results in the formation of singlet oxygen ( 1 O 2 ) and other reactive oxygen species (ROS), which are believed to be toxic species responsible for induction of tumor necrosis.2,3 5,10,15,20-m-(Tetrahydroxyphenyl)chlorin (m-THPC), one of the second generation photosensitizers, 4 has recently been proposed as a new sensitizer for future use in the PDT of cancer.5,6 m-THPC is a single compound, derived from 5,10,15,20-meso-(tetrahydroxyphenyl)porphyrin (m-THPP), 4 with a maximum absorption in the red region of visible light (! max 652 nm). The latter property favors deeper light penetration into tissue and allows the method to achieve 6-10 mm depth of necrosis in tumor-bearing mice. As is the case for the majority of photosensitive drugs, m-THPC is degraded upon light illumination. This process, usually called 'photobleaching', involves a decrease in absorbance for certain spectral bands, variations of the fluorescence intensity or the formation of new absorption and emission bands.7 The m-THPC photodegradation has been observed in aqueous 8 and organic solutions, 9 in vitro, 10 in vivo in tumor-bearing mice 11 and in clinical practice. 12Studyies of the photobleaching reaction are particularly important for two reasons: (1) Identification of photobleaching products, which can be photodynamically active, thus opening the possibility for 'extended' photodynamic therapy; (2) Measurement of the photochemical reactions that reflect the potential therapeutic effect and thus help to match the light dose. This paper describes the first results concerning the application of matrix-assisted laser desorption/ionization coupled to Fourier transform ion cyclotron resonance mass spectrometry (MALDI-FTICRMS) for the analysis of the parent m-THPC molecule and the products of photochemical m-THPC oxidation. We have studied the formation of photoproducts in organic solvents as a result of two consecutive irradiations separated by a dark storage period. The kinetics of photoproduct formation, assessed by MALDI, have been compared with that obtained by spectroscopic measurements. EXPERIMENTALReagents and standard solutions m-THPC (Fig. 1) was kindly provided by Scotia Pharmaceuticals Ltd. (Guildford, UK) as crystalline powder (specification: content of m-THPC: 98.4% w/w; water content: 0.20% w/w; residual solvents: ethanol 0.18% w/w; content of impurities: m-THPP 0.7% w/w). Unless otherwise indicated, the photosensitizer was dissolved in methanol or in ethanol (Prolabo SA, Fontenay sous bois, France), which had been distilled beforehand twice under an inert atmosphere. IlluminationIllumination was performed by exposing 3.5 mL of 7 mg/mL (10 À5 mol/L) of m-THPC in ethanol or methanol in a quartz cuvette (pathlength 1 c...

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“…23 Preliminary HPLC/ESI-MS studies confirm the present results, but need further study and will be submitted for publication in the future.…”

Section: Discussionsupporting

confidence: 74%

Matrix-assisted laser desorption/Ionization coupled to Fourier transform ion cyclotron resonance mass spectrometry: a method to characterize temoporpfin photoproducts

Angotti¹,

Maunit²,

Müller³

et al. 1999

Rapid Commun. Mass Spectrom.

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“…We have observed that large amounts of Cr + ions are produced when an oxide such as CrO 3 23 The CrO 3 sample (Fig. 4(b) 24 Thus, we have analysed a CrO 3 pellet onto which a solution of DABCO + 2,5-dihydroxybenzoic acid (2,5-DHB) had been adsorbed.…”

Section: Formation Of the Cromentioning

confidence: 99%

Studies of the chromium oxygenated cluster ions produced during the laser ablation of chromium oxides by laser ablation/ionization Fourier transform ion cyclotron resonance mass spectrometry

Aubriet¹,

Maunit²,

Courrier³

et al. 1997

Rapid Commun. Mass Spectrom.

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Trivalent and hexavalent chromium oxides have been examined by time-of-flight laser microprobe mass spectrometry and Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS). The positive-ion spectra show a strong correlation with the valency of chromium in the oxide. Thus, the positive cluster ion distribution and the presence of characteristic chromium cluster ions allow us to distinguish the two oxides. Metallic compounds present in industrial environments have been widely studied over the last ten years because of their toxicity. Among them are the chromium compounds, the toxicity of which depends on the metal oxidation state. Indeed, while chromium III is essential as a trace element for the normal functioning of living organisms (50-200 µg is necessary per day), chromium IV is known to have toxic effects on biological systems.1 In particular, it can cause DNA damage, cancer or allergic reactions. Thus, the valency determination of chromium is of first importance from a health point of view and many techniques are utilized for the determination of the stochiometry of chromium compounds. The most commonly used are UV/visible spectroscopy, 3-5 atomic absorption spectroscopy, 6 electrochemical techniques, 7,8 electrophoretic techniques 9 and ion chromatographic analysis.10 However, all these techniques use liquid samples, and oxidation or reduction reactions can occur during the dissolving of the chromium compounds.To overcome this problem, 'in situ' techniques such as Raman spectroscopy 11,12 or X-ray absorption spectroscopy 13 have been used; they require solid samples and thus give results more representative of the valency of the chromium in the original sample. Mass spectrometry coupled with the laser ablation/ionization process is another 'in situ' technique. Poitevin et al. and Hachimi et al. 14,15 have previously established a methodology to discriminate between trivalent and hexavalent chromium compounds by studying the relative intensities of negative cluster ions. Our purpose was to transpose this methodology to the study of positive cluster ions by time-of-flight laser microbe mass spectrometry (TOF-LMMS). In addition, we used the Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) technique with the aim of obtaining a similar discrimination of both oxides and getting a better understanding of the precursor ions, in particular the CrO + ion, present before the occurrence of clusters. EXPERIMENTAL SETUPTime-of-flight laser microprobe mass spectrometry TOF-LMMS experiments were performed using a LAMMA 500 instrument (Leybold-Heraeus, Germany) in a transmission arrangement. In our modified system 16,17 the second harmonic of a Nd-YAG laser (532 nm) pumps a dye laser (TDL50 D of Quantel, France) which is used for the ionization step. Harmonic frequencies of the dye laser are selected by a holographic network and can be doubled by a doubling crystal cell (DCC). The various wavelengths are separated by a quartz separation prism by adjusting its orientation. The alignment of...

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“…Abundances of oxides detected in present study could not be reduced by applying higher laser irradiances. Other laser ablation studies show as well that the formation of clusters and oxides is not avoidable and results from variety of chemical processes which can take place in plasma [41][42][43][44][45].…”

Section: Allendementioning

confidence: 99%

On Applicability of a Miniaturised Laser Ablation Time of Flight Mass Spectrometer for Trace Elements Measurements

Tulej

Riedo

Iakovleva

et al. 2012

International Journal of Spectroscopy

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We present results from mass spectrometric analysis of NIST standard materials and meteoritic samples conducted by a miniaturised laser ablation mass spectrometer designed for space research. The mass analyser supports investigation with a mass resolution (m/Δm) ≈ 500-600 and dynamic range within seven decades. Nevertheless, to maintain an optimal spectral quality laser irradiances lower than ∼1 GW/cm 2 are applied so far which results in a spread of RSC values. To achieve the quantitative performance of mass analyser, various effects influencing RSC factors have to be investigated. In this paper we investigate influence of laser irradiance, sampling procedure and plasma chemistry on the quantitative elemental and isotopic analysis. The studies indicate necessity for accurate control of laser characteristics and acquisition procedure. A relatively low irradiance applied causes a negligible sample damage and allows for accumulation of large number of waveforms from one sample location. The procedure yields statistically well averaged data and allows a sensitive in-depth analysis. The quantitative analyses of isotopic composition can be performed with accuracy and precision better as 1% and 2%, for isotopic patterns of elements and clusters, respectively. The numerical integration methods would be preferred to achieve more accurate results. The measurements of Allende sample yield detection of Pb isotopic pattern, nevertheless cluster species are readily observed in spectrum and make the elemental analysis of other trace elements difficult due to isobaric interferences. These detections are of a considerable interest because of possible application of the instrument for in situ elemental and isotopic analysis and radiometric dating of solids.

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Formation of iron oxides clusters induced by resonant laser ablation/ionization

Cited by 30 publications

References 22 publications

Matrix-assisted laser desorption/Ionization coupled to Fourier transform ion cyclotron resonance mass spectrometry: a method to characterize temoporpfin photoproducts

Matrix-assisted laser desorption/Ionization coupled to Fourier transform ion cyclotron resonance mass spectrometry: a method to characterize temoporpfin photoproducts

Studies of the chromium oxygenated cluster ions produced during the laser ablation of chromium oxides by laser ablation/ionization Fourier transform ion cyclotron resonance mass spectrometry

On Applicability of a Miniaturised Laser Ablation Time of Flight Mass Spectrometer for Trace Elements Measurements

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