IONIC STRENGTH EFFECTS ON THE GROUND STATE COMPLEXATION and TRIPLET STATE ELECTRON TRANSFER REACTION BETWEEN ROSE BENGAL and METHYL VIOLOGEN

Abstract— The equilibrium constants, K_c, for complexation between methyl viologen dication (MV²+) and Rose Bengal, or Eosin Y, decrease with increasing ionic strength. At zero ionic strength K_c is 6500 (± 500) mol^?1 dm³ for Rose Bengal and 3200 (± 200) mol^?1 dm³ for Eosin Y, and these values decrease to 1500 (± 100) and 680 (± 40) mol^?1 dm³, respectively, at an ionic strength of 0.1 mol dm^?3. K_c is independent of pH between 4.5 and 10. ΔH is -25 (± 1) kJ mol^?1 for complexation with either dye, whereas ΔS is -15 (± 3) J K^?1 mol^?1 for Rose Bengal, and - 23 (± 3) J K^?1 mol^?1 for Eosin Y. The complexation constant for Rose Bengal and the neutral viologen, 4,4'-bipyridinium-N, N'-di(propylsulphonate), (4,4'-BPS), is 420 (± 35) mol^?1 dm³, and independent of ionic strength. No complexation could be observed for either Rose Bengal or Eosin with another neutral viologen, 2,2'-bipyridinium-N,N'-di(propylsulphonate), (2,2'-BPS). MV²+ quenches the triplet state of Rose Bengal with a rate constant of 7 × 10⁹ mol^?1 dm³ s^?1, and this rate constant decreases slightly as ionic strength increases. The cage escape yield following quenching, Φ_cc is very low (Φ_cc= 0.02 (± 0.005), and independent of ionic strength. 4,4'-BPS quenches the triplet state of Rose Bengal with a rate constant of 2.2 (± 0.1) × 10⁹ mol^?1 dm³ s^?1, and gives a cage escape yield of 0.033 (± 0.006). 2,2'-BPS quenches the Rose Bengal triplet with a rate constant of 6 (± 1) × 10⁸ mol^?1 dm³ s^?1 and gives a cage escape yield of 0.07 (± 0.01). Conductivity measurements indicate that MV²+(Cl^?)₂ is completely dissociated at concentrations below 2 × 10^?2 mol dm^?3.     

An Iridium Complex as an AIE-active Photosensitizer for Image-guided Photodynamic Therapy

Image-guided photodynamic therapy (PDT) has received growing attention due to its non-invasiveness and precise controllability. However, the PDT efficiency of most photosensitizers are decreased in living system due to the aggregation-caused singlet oxygen (¹O₂) generation decreasing. Herein, we present an Iridium (III) pyridylpyrrole complex (Ir-1) featuring of aggregation-induced emission (AIE) and ¹O₂ generation characteristics for image-guided PDT of cancer. Ir-1 aqueous solution exhibits bright red phosphorescence peaked at 630 nm, large Stokes shift of 227 nm, and good ¹O₂ generation ability. The ¹O₂ generating rate of Ir-1 in EtOH/water mixture solution is 2.3 times higher than that of Rose Bengal. In vitro experimental results revealed that Ir-1 has better biocompatibility and higher phototoxicity compared with clinically used photosensitizers (Rose Bengal and Ce6), suggesting that Ir-1 can serve as a photosensitizer for image-guided PDT of cancer.     

THE REACTIVITY OF CITRONELLOL and α-THUJENE WITH SINGLET OXYGEN. RATE CONSTANTS OF CHEMICAL REACTION and PHYSICAL QUENCHING*

The quantum yields of Rose Bengal sensitized photooxidation of citronellol and α-thujene have been determined as a function of added acceptor and compared with those of furfuryl alcohol as a standard. The results permitted the calculation of the corresponding rate constants of chemical reaction (k_T) and physical quenching (K_q) of singlet oxygen. The sum (k_T+ k_q) has been verified independently by a Stern-Volmer analysis of the singlet oxygen luminescence quenching. α-Thujene reacts faster with singlet oxygen than citronellol, physical quenching being negligible in both cases.     

THE PHOTO-OXIDATION OF N, N-DIETHYLHYDROXYLAMINE BY ROSE BENGAL IN ACETONITRILE AND WATER

The Rose Bengal photosensitized oxidation of N,N-diethylhydroxylamine has been investigated in water and acetonitrile using the techniques of oxygen uptake, singlet oxygen phosphorescence and electron spin resonance. In both solvents H₂O₂ is the major oxidation product and diethylnitroxide is an intermediate. In water, superoxide dismutase decreases oxygen uptake suggesting involvement of superoxide anions in the oxidation process. Results indicate that in water the photo-oxidation proceeds mainly by a Type I(electron transfer) mechanism, while in acetonitrile a Type II(energy transfer) mechanism has been confirmed (Encinas et al., 1987, J. Chem. Soc. Perkin Trans. II,1125–1127).     

Novel PEGylated calix[5]arenes as carriers for Rose Bengal

Amphiphilic PEGylated calix[5]arenes 1 and 2 were obtained in one step from the parent p-tert-butylcalix[5]arene and p-methylcalix[5]arene. Very low critical micellar concentrations (0.5 and 4.5 μM for 1 and 2 respectively) were determined by the Rose Bengal micellization method. Aggregation features were studied by means of ¹H and DOSY NMR as well as by AFM. Release of Rose Bengal from the micellar environment was accomplished by increasing the temperature.     

Supramolecular system composed of B12 model complex and organic photosensitizer: impact of the corrin framework of B12 on the visible-light-driven dechlorination without the use of noble metals

The visible-light-driven dechlorination system without the use of a noble metal has been developed. We screened the combination of cobalt catalysts having square-planar monoanionic ligands (hydrophobic B₁₂ model complex 1/imine-oxime type complex 2) and typical red dyes (Rose Bengal 3/Rhodamine B 4/Nile Red 5) for the construction of a dehalogenation system via a noble-metal-free and visible-light-driven process. The combination of the hydrophobic B₁₂ model complex 1 and Rose Bengal 3 exhibited the highest catalytic activity to 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (DDT) to form the monodechlorinated compound, 1,1-bis(4-chlorophenyl)-2,2-dichloroethane, as the major product. The prolonged photocatalysis of DDT by the B₁₂–Rose Bengal system afforded the tri-dechlorinated compound, trans-4,4′-dichlorostilbene, as the major product. Furthermore, we investigated the mechanism of the dehalogenation cycle using various methods such as UV–vis spectroscopy and laser flash photolysis. Finally, we clarified the advantage of using the hydrophobic B₁₂ model complex 1 as an electron acceptor as well as a cobalt catalyst in the organic dye-involved photocatalysis.     

Multiarm star nanocarriers containing a poly(ethylene imine) core and polylactide arms

Star polymers (SPs) containing a hyperbranched poly(ethylene imine) (PEI; number‐average molecular weight = 10,000) core and polylactide arms were synthesized via the ring‐opening polymerization of lactide. PEI was used as a multifunctional macroinitiator for the ring‐opening polymerization of lactide. Different lactide monomer/amino‐functional group (LA/NH_n; n = 1 or 2) ratios were used for preparing SPs with different molecular weights. SPs were able to encapsulate small guest molecules such as Rose Bengal; they also transported small, hydrophilic molecules from water to the organic phase. The transport capacity of all the nanocarriers depended on the LA/NH_n ratio used for synthesizing the SPs. Nanocarriers with a higher LA/NH_n ratio had higher transport capacities. The size of all the nanocarriers depended on the type of solvent. In chloroform, these nanoparticles had several sizes that were related to the self‐assembly of these nanocarriers, but in acetone, they were monodisperse, and their size was smaller than that in chloroform. Also, the transport of polar dyes from water to the chloroform phase was possible. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5740–5749, 2006     

A Kinetic Study of the Photodynamic Effect on Tryptophan Methyl Ester and Tryptophan Octyl Ester in DOPC Vesicles

The photodynamic effect on tryptophan methyl ester (trpME) and tryptophan octyl ester (trpOE), using the O ₂ ( ¹ Δ _g )-photosensitizers Rose Bengal (RB) and Perinaphthenone (PN) has been studied in large unilamellar vesicles (LUVs) of the phospholipid 1,2-di-oleoyl-sn-glycero-3-phosphatidylcholine (DOPC) by stationary photolysis and time-resolved methods. This work reports on the influence of both the site (O ₂ ( ¹ Δ _g )) generation and the location of the tryptophan derivatives (trpD), on the photo-oxidation process in a compartmentalized system. The apparent rate constant values for chemical quenching of O ₂ ( ¹ Δ _g ) by trpOE (k _r,app ), was higher in vesicles than in water. Also, the ratio between apparent reactive and overall rate constant values for the deactivation of O ₂ ( ¹ Δ _g ) (k _r,app /k _t,app ), increases in vesicles as compared with water, when the oxidative species is generated in the lipidic region or at the interface. Nevertheless, this quotient is lower than the corresponding value in water when O ₂ ( ¹ Δ _g ) is generated in the aqueous pseudophase. For trpME, the k _r,app /k _t,app values in vesicles and in water are quite similar, confirming the fact that trpME is located in the water pseudophase. Results are discussed in terms of relative protection against O ₂ ( ¹ Δ _g ) attack in a microheterogeneous medium as compared with water.     

Enhancement of the Efficacy of Photodynamic Inactivation of Candida albicans with the Use of Biogenic Gold Nanoparticles

This study reports on successful photodynamic inactivation of planktonic and biofilm cells of Candida albicans using Rose Bengal (RB) in combination with biogenic gold nanoparticles synthesized by the cell‐free filtrate of Penicillium funiculosum BL1 strain. Monodispersed colloidal gold nanoparticles coated with proteins were characterized by a number of techniques including SEM–EDS, TEM, UV–Vis absorption and fluorescence spectroscopy, as well as Fourier transform infrared spectroscopy to be 24 ± 3 nm spheres. A Xe lamp (output power of 20mW, delivering intensity of 53 mW cm^?2) was used as a light source to study the effects of RB alone, the gold nanoparticles alone and the RB‐gold nanoparticle mixture on the viability of C. albicans cells. The most effective reduction in the number of planktonic cells was found after 30 min of Xe lamp light irradiation (95.4 J cm^?2) and was 4.89 log₁₀ that is 99.99% kill for the mixture of RB with gold nanoparticles compared with 2.19 log₁₀ or 99.37% for RB alone. The biofilm cells were more resistant to photodynamic inactivation, and the highest effective reduction in the number of cells was found after 30 min of irradiation in the presence of the RB–gold nanoparticles mixture and was 1.53 log₁₀, that is 97.04% kill compared with 0.6 log₁₀ or 74.73% for RB. The probable mechanism of enhancement of RB‐mediated photodynamic fungicidal efficacy against C. albicans in the presence of biogenic gold nanoparticles is discussed leading to the conclusion that this process may have a multifaceted character.     

The new ether derivative of phenylpropanoid and bioactivity was investigated from the leaves of Piper betle L.

Abstract

A new ether derivative of phenylpropanoid compound, γ-(γ′-isohydroxychavicol)-chavicol octanyl ether (K1) along with one known phenylpropanoid named allyl-pyrocatechol or hydroxychavicol (2) were isolated from Piper betle var. kali collected from Tumluk district, West Bengal India. We first report the presence of compound K1 in the genus Piper. Their structures were established on the basis of various spectroscopic analyses. Compounds K1 and 2 showed excellent antioxidant DPPH free radical scavenging activity with IC₅₀ values of 4.61 and 4.12?µg/mL compared to ascorbic acid as a standard antioxidant drug with IC₅₀ value of 3.42?µg/mL, respectively. Evaluation of in vitro cytotoxic activities of compounds K1 and 2 showed significant effects against human oral cancer cell lines (AW13516 and AW8507), human hepatoma cell lines (HEPG2 and PLC-PRF-5) and a human pancreatic cell line (MIA-PA-CA-2), compared to Doxorubicin^® as a standard cytotoxic drug with GI₅₀ values of <10 and 18.18?µg/mL.     

Why is Rose Bengal More Phototoxic to Fibroblasts In Vitro Than In Vivo?

Photosensitized protein cross‐linking has been recently developed to seal wounds and strengthen tissue. Although the photosensitizing dye, Rose Bengal (RB), is phototoxic to cultured cells, cytotoxicity does not accompany RB‐photosensitized tissue repair in vivo. We investigated whether the environment surrounding cells in tissue or the high irradiances used for photo–cross‐linking inhibited RB phototoxicity. Fibroblasts (FB) grown within collagen gels to mimic a tissue environment and monolayer cultured FB were treated with RB (0.01–1 mm ) and the high 532 nm laser irradiances used in vivo for tissue repair (0.10–0.50 W cm^?2). Monolayer FB were substantially more sensitive to RB photosensitization: the LD₅₀ was >200‐fold lower than that in collagen gels. Collagen gel protection was associated with increased Akt phosphorylation, a prosurvival pathway. RB phototoxicity in collagen gels was 25‐fold greater at low (0.030 W cm^?2) that at high (0.50 W cm^?2) irradiances. Oxygen depletion at high irradiance only partially accounted for the irradiance dependence of phototoxicity as replacing air with nitrogen only increased the LD₅₀ by four‐fold in monolayers. These results indicate that the lack of RB phototoxicity during in vivo tissue repair results from upregulation of prosurvival pathways in tissue cells, oxygen depletion and irradiance‐dependent RB photochemistry.     

Rose Bengal‐Sensitized Photooxidation of the Dipeptides l‐Tryptophyl‐l‐Phenylalanine,l‐Tryptophyl‐l‐Tyrosine and l‐Tryptophyl‐l‐Tryptophan: Kinetics,Mechanism and Photoproducts¶

The Rose Bengal‐sensitized photooxidations of the dipeptides l ‐tryptophyl‐l ‐phenylalanine (Trp‐Phe), l ‐tryptophyl‐l ‐tyrosine (Trp‐Tyr) and l ‐tryptophyl‐l ‐tryptophan (Trp‐Trp) have been studied in pH 7 water solution using static photolysis and time‐resolved methods. Kinetic results indicate that the tryptophan (Trp) moiety interacts with singlet molecular oxygen (O₂(¹Δ_g)) both through chemical reaction and through physical quenching, and that the photooxidations can be compared with those of equimolecular mixtures of the corresponding free amino acids, with minimum, if any, influence of the peptide bond on the chemical reaction. This is not a common behavior in other di‐ and polypeptides of photooxidizable amino acids. The ratio between chemical (k_r) and overall (k_t) rate constants for the interaction O₂(¹Δ_g)‐dipeptide indicates that Trp‐Phe and Trp‐Trp are good candidates to suffer photodynamic action, with k_rlk_t values of 0.72 and 0.60, respectively (0.65 for free Trp). In the case of Trp‐Tyr, a lower k_rlk_t value (0.18) has been found, likely as a result of the high component of physical deactivation of O₂(¹Δ_g) by the tyrosine moiety. The analysis of the photooxidation products shows that the main target for O₂(¹Δ_g) attack is the Trp group and suggests a much lower accumulation of kynurenine‐type products, as compared with free Trp. This is possibly because of the occurrence of another accepted alternative pathway of oxidation that gives rise to 3a‐oxidized hydrogenated pyrrolo[2,3‐b]indoles.     

Unusually highly efficient,singlet state,visible light photoinitiators based on styrylbenzimidazolium phenyltributylborate photoredox pairs for vinyl monomers free radical polymerization

In this article, hemicyanine dye–borate complexes, for example, 1,3‐dimethyl‐2‐[4‐(N,N‐dialkylamino)styryl]benzimidazolium phenyl‐tri‐n‐butylborates, were employed as the novel, very effective photoinitiators operating in the visible light region. The influence of the sensitizers and electron donor structure on the photopolymerization kinetics of multiacrylate monomer was investigated by photo‐DSC. The maximum photopolymerization quantum yield measured for 2‐ethyl‐2‐(hydroxymethyl)‐1,3‐propanediol triacrylate (TMPTA) was about 67 for sample of thickness of about 1 mm under 100 mW/cm² laser irradiation. It was found that the polymerization rate and the final conversion degree were depended on the dye structure. Moreover, the photoinitiating systems described gave a double bond conversion higher than the photoinitiator possessing as chromophore RBAX (Rose Bengal derivative), the common triplet state initiator. Additionally, the rate of photopolymerization depends on ΔG_el of electron transfer between borate anion and styrylbenzimidazolium cation. This latter value was estimated for a series of styrylbenzimidazolium borate salts. The relationship between the rate of polymerization and the free energy of activation for electron transfer reaction gives the dependence predicted by the classical theory of electron transfer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4119–4129, 2009     

Photo‐oxidative Stress Impacts the Expression of Genes Encoding Iron Metabolism Components in Chlamydomonas†

Chlamydomonas, like other organisms, regulates iron assimilation very tightly through differential expression of iron assimilation components. Nevertheless, in the presence of excess iron, cells do overaccumulate iron but without an evident phenotype. As iron toxicity is attributed to reactive oxygen species, we tested the impact of photon flux density (PFD) on cells with increased iron content. We noted that growth at >500 μmol m^?2 s^?1 is inhibited as iron content of the medium is increased, suggesting that high light exacerbates the systems of iron toxicity and vice versa. Cells grown in high light selectively down‐regulate the abundance of iron assimilation components, ferroxidase and FEA1, and storage protein ferritin1. At the RNA level, the abundance of ferroxidase (FOX1), iron reductase (FRE1), iron assimilatory protein (FEA1) and ferritin (FER1) mRNAs is also decreased. The time course of the response to high light compared to the response to Rose Bengal and H₂O₂ treatments suggests that both singlet oxygen and H₂O₂ may be implicated in the high light response. This hypothesis is supported by the recapitulation of some but not all of the high light responses in the carotenoid‐deficient, high light–sensitive npq1lor1 strain. We conclude that responses to iron nutrition and PFD are connected, and the determination of an optimum for photosynthetic growth for each is dependent on the other. This work defines a fourth stage of iron nutrition in Chlamydomonas, the iron excess situation, which can be molecularly and physiologically distinguished from the iron‐limited, iron‐deficient and iron‐replete stages, described previously.     

Oxidation reactions of some natural volatile aromatic compounds: anethole and eugenol

trans-Anethole [1-methoxy-4-(trans-prop-1-en-1-yl)benzene] was isolated from anise seed oil (Pimpinella anisum). Its photochemical oxidation with hydrogen peroxide gave the corresponding epoxy derivative together with 4-methoxybenzaldehyde. The thermal oxidation of trans-anethole with 3-chloroperoxybenzoic acid at room temperature resulted in the formation of dimeric epoxide, 2,5-bis(4-methoxyphenyl)-3,6-dimethyl-1,4-dioxane, as the only product. Photochemical oxygenation of trans-anethole in the presence of tetraphenylporphyrin, Rose Bengal, or chlorophyll as sensitizer led to a mixture of 1-(4-methoxyphenyl)prop-2-en-1-yl hydroperoxide and 4-methoxybenzaldehyde. Eugenol was isolated from clove oil [Eugenia caryophyllus (Spreng.)]. It was converted into 2-methoxy-4-(prop-2-en-1-yl)phenyl hydroperoxide by oxidation with hydrogen peroxide under irradiation. Thermal oxidation of eugenol with 3-chloroperoxypenzoic acid at room temperature produced 2-methoxy-4-(oxiran-2-ylmethyl)phenol, while sensitized photochemical oxygenation (in the presence of Rose Bengal or chlorophyll) gave 4-hydroperoxy-2-methoxy-4-(prop-2-en-1-yl)cyclohexa-2,5-dien-1-one. Published in Russian in Zhurnal Organicheskoi Khimii, 2008, Vol. 44, No. 6, pp. 834–841. The text was submitted by the authors in English.     

ENHANCEMENT OF THE SENSITIVITY OF RADIATIVE and NON-RADIATIVE DETECTION TECHNIQUES IN THE STUDY OF PHOTOSENSITIZATION BY WATER SOLUBLE SENSITIZERS USING A REVERSE MICELLE SYSTEMS*,†

The study of photosensitization processes in aqueous solution is complicated by the unsuit-ability of water as solvent for the commonly used techniques for monitoring radiative and non-radiative relaxation processes. The infrared luminescence method is hampered by the relatively weak intensity of emission and short lifetime of singlet molecular oxygen, O₂(¹Δ_g), in water. Photoacoustic and photothermal detection of the dominant non-radiative relaxation process for O₂(¹Δ_g) is also inhibited by the unfavorable physico-chemical properties of water which reduce the sensitivities of these techniques for the study of sensitizers in aqueous with respect to non-aqueous media. Such problems have been alleviated by incorporating the sensitizer in the aqueous core of aerosol OT reverse micelles. It is demonstrated that the sensitivity of both radiative and non-radiative detection depends not on the local environment of the sensitizer but on the overall composition of the medium, which, in the case of reverse micelle solutions, is predominantly hydrocarbon. This produces a 4.5 and 6-fold enhancement of the sensitivity of luminescence and optoacoustic detection, respectively, in comparison to purely aqueous solution. The utility of the method is demonstrated for Rose Bengal, where quantum yields of intersystem crossing (φ_isc) of 0.78 (LIOAC) and singlet oxygen generation (φ_δ) of 0.81 (LIOAC) and 0.80 (TRLD) were measured. Phenazine was also studied for comparative purposes and to corroborate values obtained for Rose Bengal.     

The Employment of a Removable Chitosan‐Derivatized Polymeric Sensitizer in the Photooxidation of Polyhydroxylated Water‐Pollutants

The known O₂(¹?_g)‐sensitizer system Chitosan bounded Rose Bengal (CH‐RB), with Rose Bengal (RB) immobilized by irreversible covalent bonding to the polymer Chitosan (CH), soluble in aquous acidic medium, was employed in the photodegradation of three tri‐hydroxy benzene water‐contaminants (THBs). The system sensitizes the O₂(¹?_g)‐mediated photodegradation of THBs by a process kinetically favored, as compared to that employing free RB dissolved in the same solvent. Additionally the free xanthene dye, degradable by O₂(¹?_g) through self‐sensitization upon prolonged light‐exposure, is considerably protected when bonded to CH‐polymer. The polymeric sensitizer, totally insoluble in neutral medium, can be removed from the solution after the photodegradative cycle by precipitation through a simple pH change. This fact constitutes an interesting aspect in the context of photoremediation of confined polluted waters. In other words, the sensitizing system could be useful for avoiding to dissolve dyestuffs in the polluted waters, in order to act as conventional sunlight‐absorbing dye‐sensitizers. In parallel the interaction CH ‐ O₂(¹?_g) in acidic solution was evaluated. The polymer quenches the oxidative species with a rate constant 2.4 × 10⁸ M^?1 s^?1 being the process mostly attributable to a physical interaction. This fact promotes the photoprotection of the bonded dye in the CH‐RB polymer.     

Immobilized Rose Bengal as Photocatalyst for Metal-Free Thiocyanation of Azaheterocycles under Continuous Flow Conditions

The immobilization of Rose Bengal onto Merrifield resin and its application in the light-driven metal-free thiocyanation of azaheterocycles in continuo were investigated. The supported photocatalyst was used in batch reactions under heterogeneous conditions, with different azaheterocycles, and proved to efficiently promote the reaction. Its recovery and recycle were also demonstrated for up to four times. The resin-supported Rose Bengal was then employed under continuous flow conditions, affording thiocyanate functionalized azaheterocycles with higher space-time-yields than the in-batch transformations, and in a shorter reaction time. The easily modification of the SCN groups was also demonstrated by synthetizing trifluoromethyl thioethers and sulfenyl tetrazoles derivates in high yields.     

Preservation strategies for inorganic arsenic species in high iron,low-<Emphasis Type="Italic">Eh</Emphasis> groundwater from West Bengal,India

Despite the importance of accurately determining inorganic arsenic speciation in natural waters to predicting bioavailability and environmental and health impacts, there remains considerable debate about the most appropriate species preservation strategies to adopt. In particular, the high-iron, low-Eh (redox potential) shallow groundwaters in West Bengal, Bangladesh and SE Asia, the use of which for drinking and irrigation purposes has led to massive international concerns for human health, are particularly prone to changes in arsenic speciation after sampling. The effectiveness of HCl and EDTA preservation strategies has been compared and used on variably arsenic-rich West Bengali groundwater samples, analysed by ion chromatography–inductively coupled plasma–mass spectrometry (IC–ICP–MS). Immediate filtration and acidification with HCl followed by refrigerated storage was found to be the most effective strategy for minimizing the oxidation of inorganic As(III) during storage. The use of a PRP-X100 (Hamilton) column with a 20 mmol L^–1 NH₄H₂PO₄ as mobile phase enabled the separation of Cl^– from As(III), monomethylarsonic acid, dimethylarsinic acid and As(V), thereby eliminating any isobaric interference between ⁴⁰Ar³⁵Cl⁺ and ⁷⁵As⁺. The use of EDTA as a preservative, whose action is impaired by the high calcium concentrations typical of these types of groundwater, resulted in marked oxidation during storage. The use of HCl is therefore indicated for analytical methods in which chloride-rich matrices are not problematical. The groundwaters analysed by IC–ICP–MS were found to contain between 5 and 770 ng As mL^–1 exclusively as inorganic arsenic species. As(III)/total-As varied between 0 and 0.94.     

Photooxygenation of Pregnanes

The course of the singlet‐oxygen reaction with pregn‐17(20)‐enes and pregn‐5,17(20)‐dienes was studied to compare the reactivity of the two alkene moieties present in some steroid families. Thus, from commercially available (3β,5α)‐hydroxy‐androstan‐17‐one and (3β)‐3‐hydroxyandrost‐5‐en‐17‐one, the following 3‐{[(tert‐butyl)dimethylsilyl]oxy}‐substituted, 17(20)‐unsaturated pregnanes were prepared (see Fig. 1): (3β,5α)‐21‐norpregn‐17(20)‐ene 1 ; (3β,5α,17Z)‐pregn‐17(20)‐ene 2 , (3β,5α,16α,17E)‐pregn‐17(20)‐en‐16‐ol 3 , (16β,5α,17E)‐pregn‐17(20)‐en‐16‐ol 4 , (3β,5α,16β,17E)‐pregn‐17(20)‐en‐16‐ol acetate 5 , (3β,16α)‐21‐norpregna‐5,17(20)‐dien‐16‐ol 6 , (3β,16α,17E)‐pregna‐5,17(20)‐dien‐16‐ol 7 , (3β,17Z)‐pregna‐5,17(20)‐diene 8 , (3β,17E)‐pregna‐5,17(20)‐dien‐21‐ol 9 and (3β,17E)‐5,17(20)‐dien‐21‐ol acetate 10 . The oxygenated products (see Fig. 2) obtained from 1 – 10 and ¹O₂, generated by irradiation of Rose Bengal in ³O₂‐saturated pyridine solution, were characterized by ¹H‐, ¹³C‐NMR, and MS (EI, FAB, HR‐EI, ESI‐ and UV‐MALDI‐TOF) data. Major products were those formed by the ene reaction involving as intermediates the corresponding hydroperoxides and the cyclic tautomers of the allylic hydroperoxides, i.e., the corresponding oxiranium oxide‐like intermediate (Scheme 5).