Dye-sensitized Photooxidation Research Articles

BODIPY-Helicene Based Heavy-Atom-Free Photocatalyst for Oxidative Coupling of Amines and Photooxidation of Sulfides.

To develop heavy-atom-free triplet photosensitizers (PSs) based photocatalysts, we designed and synthesized two BODIPY-helicene dyes by fusing the BODIPY core and modified [5]helicene structures. These BODIPY-helicenes structures are twisted and their twisting angles are increased by the developed synthetic method. The BODIPY-helicenes have broad absorption bands over UV-visible region with high triplet conversions and long triplet lifetimes as compared to planar BODIPY dye, PM567. Consequently, these dyes are also highly efficient in generating 1O2 by transferring their triplet energy to 3O2. All these are confirmed by dye-sensitised photooxidation reaction, nanosecond transient absorption spectroscopy study, phosphorescence measurement and DFT calculations. Finally, photocatalytic activity of the highest 1O2 generating BODIPY-helicene (4 b) was checked. 4 b is highly efficient in photocatalytic oxidative coupling of differently substituted amines through aerobatic oxidation using 1O2 generated by its photosensitization. It is also highly efficient photocatalyst for aerobatic oxidation of sulfides to sulfoxides. Importantly, the photocatalyst could be quantitatively recovered and reused for several cycles. All these results confirmed the potential use of the BODIPY-helicenes as PSs for photocatalytic organic reactions and the design strategy will be useful for the future development of heavy-atom-free photocatalyst.

Concise Total Synthesis of (+)-Lanceolactone A: Revision of Absolute Stereochemistry.

A chiral-pool protecting-group-free five-step total synthesis of tetranorsesquiterpenoide (+)-lanceolactone A and all of its four stereoisomers using (S)-(+)-, and (R)-(-)-linalool (coriandrol) as building blocks is disclosed. The key steps involved in this synthetic route are regioselective ozonolysis, Au(I)-catalyzed cycloisomerization-induced construction of furan from alleneone, and dye-sensitized photo-oxidation (through 1O2; singlet oxygen) of hydroxyalkyl-tethered furan to access oxaspirolactone. After a thorough evaluation of electronic circular dichroism (ECD) and optical rotation data of all possible stereoisomers, the absolute configuration of natural lanceolactone A at the C4 and C7 positions has been assigned as (+)-(4S,7S), which is an enantiomer to the initially proposed structure (+)-(4R,7R). Further, these investigations led us to extend Feringa and Gawronski's CD correlation method to [5,5]- and [6,5]-oxaspirolactones.

The Use of Some Non-conventional Methods in Chemistry of Bicyclohomofarnesenic Methyl Esters

The present paper reports the results of microwave irradiation assisted method for the preparation of bicyclohomofarnesenic methyl esters versus classical Stoll and Hinder method. Moreover, the chemical transformations of bicyclohomofarnesenic methyl esters via anodic electrooxidation and dye-sensitized photooxidation were performed. A new method for the preparation of methyl 7-oxo-13,14,15,16-tetranorlabd-6,8(8)-dien-12-oate and the mechanism of electrochemical products formation are presented. The structure of all synthesized compounds was fully confirmed by spectral methods.

Total Synthesis of Beshanzuenone D and Its Epimers and Abiespiroside A.

A unified and protecting-group-free six-step total synthesis of bisabolane-type sesquiterpenoid beshanzuenone D and its stereoisomers and abiespiroside A using S-(+)-carvone as a common chiral-pool building block is disclosed. This synthetic route features chemoselective allylic chlorination of carvone, Au(I)-catalyzed cycloisomerization induced construction of furan from homopropargylic diol, substrate-controlled selective hydroxylation using Davis-oxaziridine, and dye-sensitized photo-oxidation (through 1O2) of hydroxyalkyl tethered furan to access oxaspirolactone as key transformations. A comprehensive set of NMR data along with DFT calculations, ECD spectra, and optical rotation measurements of the synthesized beshanzuenone D and its epimers were obtained to confirm absolute configurations.

Practical Evaluation of Compact Fluorescent Lamps for Dye-Sensitized Photooxidation Reactions

Energy-efficient compact fluorescent lamps (CFL) have been evaluated as a light source for the sensitized generation of singlet oxygen used in the oxidation of 1,3-butadienes and furfural derivatives using a range of dyes including rose bengal, methylene blue, and tetraphenylporphyrin. An ambient temperature water jacket was sufficient to cool reaction mixtures due to the low heat output of lamps and the reaction rates using 110 W of CFL were slower but comparable to those obtained using a 500 W tungsten halogen lamp. The conditions were applied to the photooxidation of a series of furan aldehydes and 1,3-butadienes to give products in good yield in 4–96 hours.

Benzochloroporphyrin Derivative Induced Cytotoxicity and Inhibition of Tumor Recurrence During Photodynamic Therapy for Osteosarcoma

Photodynamic therapy (PDT) is a promising cancer treatment modality that uses dye-sensitized photooxidation of biologic matter in target tissue. This study explored effects of the photosensitizer BCPD-17 during PDT for osteosarcoma. LM-8 osteosarcoma cells were treated with BCPD-17 and cell viability after laser irradiation was assessed in vitro with the 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay. The effects of BCPD-17 during PDT recurrence were then examined on tumor-bearing mice in vivo. BCPD-17 had dose- dependent cytotoxic effects on LM-8 osteosarcoma cells after laser irradiation which also had energy-dependent effects on the cells. The rate of local recurrence was reduced when marginal resection of mice tumors was followed by BCPD-17-mediated PDT. Our results indicated BCPD-17-mediated PDT in combination with marginal resection of tumors is a potentially new effective treatment for osteosarcoma.

ChemInform Abstract: Reaction of Singlet Oxygen with Enolic Tautomers of β-Dicarbonyls. α-Hydroxylation of 2-Acyl- and 2-Carboalkoxy-3,4- dihydronaphthalen-1(2H)-ones.

Abstract Dye-sensitized photooxidation of enolic tautomers of naphthalenones (5) gave hydroperoxynaphthalenones (6) and naphthols (7). Deoxygenation of 6 by triphenylphosphine gave hydroxynaphthalenones (8).

Antibacterial Compounds from Rose Bengal‐Sensitized Photooxidation of β‐Caryophyllene

The bactericidal activity of beta-caryophyllene photooxidized in acetonitrile was examined for 5 Gram-positive and 4 Gram-negative foodborne bacteria. The beta-caryophyllene (5 x 10(-3) M) was photooxidized in acetonitrile containing Rose Bengal (6.25 x 10(-4) M) for 24 h under fluorescent light. The antimicrobial activities of samples were determined by the agar-disc diffusion method. Active compounds from the photooxidized beta-caryophyllene were isolated by silica gel open-column chromatography in conjunction with recyclic high-performance liquid chromatography (HPLC), and were identified by infrared spectroscopy, mass spectrometry, and nuclear magnetic resonance spectroscopy. The antimicrobial activity of the photooxidized beta-caryophyllene was strongly enhanced against Streptococcus aureus and Vibrio parahaemolyticus, relative to that of beta-caryophyllene, but was weakly enhanced against other tested bacteria. The photooxidized beta-caryophyllene contained 3 active compounds specific for these 2 bacteria, and the compounds were identified as 5-alpha-hydroxycaryophylla-4(12),8(13)-diene, 5-alpha-hydroxycaryophylla-3(4),8(13)-diene, and 5-beta-hydroxycaryophylla-3(4),8(13)-diene. The efficacies of these compounds were similar, but the efficacy of 5-beta-hydroxycaryophylla-3(4),8(13)-diene was slightly higher than that of the other 2 compounds. The results suggest that the antibacterial activities of beta-caryophyllene for S. aureus and V. parahaemolyticus could be enhanced by dye-sensitized photooxidation, and the photooxidized beta-caryophyllene and the isolated individual compounds could be useful antimicrobial agents to control the growth of S. aureus and V. parahaemolyticus in certain food systems.

Synthesis and photodynamic potential of tetra- and octa-triethyleneoxysulfonyl substituted zinc phthalocyanines

Synthesis of the water soluble zinc phthalocyanines ( 3, 4) obtained from the phthalonitriles substituted with oligo(ethyleneoxy)thia groups are described. The new compounds have been characterized by elemental analysis, IR, 1H and 13C NMR spectroscopy, including HSQC, HMBC and COSY bidimensional correlation techniques, electronic spectroscopy and mass spectra. The aggregation behaviour of the phthalocyanine compounds ( 3, 4) was investigated using UV–vis spectroscopy in dimethylsulphoxide. Photochemical and photophysical measurements were conducted on oligo(ethyleneoxy)thia appended zinc phthalocyanines. General trends are described for quantum yields of photodegredation, fluorescence yields, triplet lifetimes and triplet quantum yields as well as singlet oxygen quantum yields of these compounds. The phototoxicity against cancer cells of the new compounds was investigated during several in vitro experiments. The dye-sensitized photooxidation of 1,3-diphenylisobenzofurane via 1O 2 was studied in dimethylsulphoxide.

Christopher Foote's Discovery of the Role of Singlet Oxygen [1O2 (1Δg)] in Photosensitized Oxidation Reactions

The chemistry of singlet molecular oxygen [1O2 (1Delta g)], its importance in atmospheric, biological, and therapeutic processes, and its use as a reagent in organic synthesis have been of considerable interest. Many aspects of singlet oxygen chemistry have emanated from the work of Christopher S. Foote and co-workers. Singlet oxygen is a historically interesting molecule with an unusual story connected with its discovery. Foote and Wexler conducted experiments in the 1960s where evidence was obtained supporting 1O2 generation via two independent routes: (1) a photochemical reaction (dye-sensitized photooxidation) and (2) a chemical reaction (NaOCl with H2O2). An important factor in the discovery of 1O2 as the critical reaction intermediate in dye-sensitized photooxygenations was Foote's reassessment of the chemical literature of the 1930s, when 1O2 was suggested to be a viable intermediate in dye-sensitized photooxidation reactions. Experiments that used silica gel beads provided evidence for a volatile diffusible oxidant such as 1O2. However, a contemporaneous quarrel surrounded this early work, and the possible existence of solution-phase 1O2 was ignored for over 2 decades. Not long after Foote's initial studies were published in 1964, the idea of singlet oxygen as an intermediate in photooxidation chemistry gained increasing recognition and verification in organic, gas phase, and biological processes. There are many documented impacts that 1O2 has had and continues to have on biology and medicine, for example, photodynamic therapy and plant defenses.

Synthesis and singlet oxygen production of azaphthalocyanines bearing functional derivatives of carboxylic acid

New metal-free, magnesium and zinc azaphthalocyanines ( AzaPc ) were prepared from 6-(3-tert-butylsulfany1-5,6-dicyanopyrazine-2-ylamino)hexanoic acid and its butylester and N,N-diethylamide. Their singlet oxygen production was measured by a dye-sensitized photooxidation of 1,3-diphenylisobenzofuran ( DPBF ) and ΦΔ values were calculated. It was found that the presence of carboxylic acid in the structure of AzaPc decreases their singlet oxygen production. Singlet oxygen activity of the newly prepared compounds (containing mixed alkylamino and alkylsulfanyl peripheral substituents) lies between purely alkylsulfanyl and alkylamino derivatives of AzaPc . This fact further supports previously proposed structure-activity relationships, where alkylsulfanyl derivatives belong to the best singlet oxygen producers while the presence of alkylamino substituents in the structure rapidly decreases their photodynamic properties.

Unexpected Formation of 1-Diethylaminobutadiene in Photosensitized Oxidation of Triethylamine Induced by 2,3-Dihydro-oxoisoaporphine Dyes. A 1H NMR and Isotopic Exchange Study

[reaction: see text] Photoreduction of oxoisoaporphine dyes occurs via a stepwise mechanism of electron-proton-electron transfer that leads to the N-hydrogen oxoisoaporphine anion. When triethylamine, TEA, was used as the electron donor in anaerobic conditions, 1-diethylaminobutadiene, DEAB, was one of the oxidation products of TEA, among diethylamine and acetaldehyde. DEAB was identified by (1)H NMR and GC-MS experiments by comparison with the authentic 1-diethylaminobutadiene. This is the first report of a butadienyl derivative formed in the dye-sensitized photooxidation of TEA. In addition, isotopic exchange experiments with TEA-d(15) and D(2)O show that the hydrogens at carbon-2 and carbon-4 of the butadienyl moiety are exchangeable. The observed isotopic exchange pattern could be explained by the head-to-tail coupling of an N,N-diethylvinylamine intermediate that exchanges hydrogens at the C-beta via the enammonium ion.

Comparison of aggregation properties and photodynamic activity of phthalocyanines and azaphthalocyanines

Phthalocyanines (Pc) and their aza-analogues azaphthalocyanines (AzaPc) (tetrapyrazinoporphyrazines) with eight n-octylsulfanyl or tert-butylsulfanyl peripheral substituents and different central metals (Mg, Zn, metal-free) were synthesized. Dimerization constants K d and absorption spectra of pure monomeric and dimeric magnesium complexes in toluene were calculated using series of absorbances at different concentrations. The bulky tert-butylsulfanyl substituents were found to be much better inhibitors of aggregation than long alkyl chains. Also Pc are less aggregated in organic solvents then AzaPc, short explanation is given. Singlet oxygen production of Pc and AzaPc was compared using dye-sensitized photooxidation of 1,3-diphenylisobenzofuran in pyridine. Both Pc and AzaPc showed similar activity not dependent on type of peripheral substitution. Zinc complexes of both Pc and AzaPc exceeded the magnesium ones and metal-free dyes in singlet oxygen production approximately twice.

Synthesis and comparison of photodynamic activity of alkylheteroatom substituted azaphthalocyanines

Optimal reaction conditions were developed for synthesis of octakis(butylamino), octakis(butylsulfanyl) and octakis(butoxy) azaphthalocyanines (AzaPc’s) with central metal Mg, Zn and metal-free. Their photodynamic activity was measured and compared as a dye-sensitised photooxidation of 1,3-diphenylisobenzofurane (DPBF). Compounds with alkylamino substituent are very poor producers of the singlet oxygen and therefore not suitable as sensitizers for photodynamic therapy (PDT). On the other hand, compounds with alkylsulfanyl and alkoxy substituents possess very good photodynamic activity and are suitable for PDT.

Synthesis and studies on photodynamic activity of new water-soluble azaphthalocyanines

Aza analogues of phthalocyanines (AzaPc’s) bearing four long chains with carboxy groups at the end and four “bulky” diethylamino groups on periphery were synthesised and characterised. Their sodium salts are very soluble in water. The first studies on photodynamic activity of this tetrapyrazinoporphyrazines (a type of AzaPc) are presented. The dye-sensitised photooxidation of 1,3-diphenylisobenzofurane via 1 O 2 was studied in pyridine. Their photodynamic activity in vitro was not detected due to the aggregation behaviour of these compounds in water.

Kinetics of the dye-sensitized photooxidation of trihydroxybenzenes

The kinetics of the singlet molecular oxygen [O2(1Δg)]-mediated photooxidation of the three isomeric trihydroxybenzenes (THBs), compounds of potential environmental significance as aquatic contaminants, has been studied in water solution as a function of pH and ionic strength, as well as in benzene and acetonitrile. Rate constants for chemical and overall interactions with O2(1Δg), determined by time-resolved IR phosphorescence detection and polarographic methods, are in the range 0.05×107–24.0×107M−1s−1, depending on the medium and the particular compound. In water at pH 2, the photooxidation quantum efficiencies of 1,2,3-THB, 1,2,4-THB and 1,3,5-THB are 0.07, 0.07 and 0.19, respectively. The photooxidative processes are highly favored by the ionization of the OH groups, the increase of solvent polarity, and the presence of salts in the medium, strongly suggesting the participation of a polar encounter complex of the type [THB-O2(1Δg)]. This kinetic behavior is similar to that observed in simple phenols and dihydroxybenzenes, although THBs are much easier photooxidizable, even in non-ionized form. These results possess environmental relevance, because they demonstrate that any THB in aqueous media undergoes spontaneous and fast solar-promoted photooxidation under practically any field condition.

Kinetics of the dye sensitized photooxidation of 2-amino-4-hydroxy-6-methylpyrimidine, a model compound for some fungicides

The kinetics of the dye-sensitized photooxidation of 2-amino-4-hydroxy-6-methyl-pyrimidine (AHMPD), a compound with the basic molecular structure of some systemic pyrimidine fungicides, has been studied in solution in water and in the mixture acetonitrile–water 4:1 v/v. Rate constants in the range 9×10 4–2.7×10 7 M −1 s −1 for both the overall and the reactive singlet molecular oxygen [O 2( 1 Δ g )] quenching processes were determined by time-resolved O 2( 1 Δ g )-phosphorescence detection and polarographic methods. Photooxidation quantum yields were in the range 0.005–0.41, with values significantly higher in alkalinized media. On the contrary, pyrimidine, 2-aminopyrimidine, 4-hydroxypyrimidine and 6-methylpyrimidine do not react with O 2( 1 Δ g ), in neutral or alkalinized D 2O solutions. The presence of a 4-hydroxy group in pyrimidines plays a key role in the photooxidative process, because the formation of the tautomeric 4-oxo form, the predominant one in aqueous solution, diminishes or suppresses the interaction with O 2( 1 Δ g ). However, in the presence of alkali the OH-ionization greatly enhances the photooxidation. The experimental evidence suggests a charge-transfer mediated mechanism involving an initial encounter excited complex. These results also show that the sensitized photooxidation is an alternative pathway for the environmental or programmed degradation of these colorless N-heteroaromatic compounds, in special in OH-ionized form.

Photocyclization and photooxidation of 3-styrylthiophene

The photocyclization, dye-sensitized photooxidation and auto-photooxidation of 3-styrylthiophene have been examined. cis-3-Styrylthiophene undergoes photochemical cis– trans isomerization and cyclization to dihydronaphtho-[1,2- b]thiophene. The quantum efficiency for photocyclization in nonpolar solvents is greater than that in polar solvents. Dye-sensitized photooxidation of 3-styrylthiophene gives benzaldehyde and 3-thiophenecarboxaldehyde. This oxidation proceeds via a superoxide radical anion pathway rather than singlet oxygen pathway. In the presence of oxygen photoirradiation of 3-styrylthiophene solution results in photocyclization, oxidation and dimerization. The mechanism of the latter two reactions was described in terms of formation of a charge transfer complex between oxygen and the substrate.

Imaging systems by dye-sensitized photooxidation of oxazole groups attached to polymer backbones, 5. Photooxidative amplification

Imaging systems by dye-sensitized photooxidation of oxazole groups attached to polymer backbones, 5. Photooxidative amplification

Imaging systems by dye-sensitized photooxidation of oxazole groups attached to polymer backbones, 5. Photooxidative amplification

Imaging systems by dye-sensitized photooxidation of oxazole groups attached to polymer backbones, 5. Photooxidative amplification