Presence Of Rose Bengal Research Articles

Mapping of oxidative modifications on the alpha-keto glutarate dehydrogenase complex induced by singlet oxygen: Effects on structure and activity

The large multi-subunit mitochondrial alpha-keto glutarate dehydrogenase (KGDH) complex plays a key, rate-determining, role in the tricarboxylic acid (Krebs) cycle, catalyzing the conversion of alpha-keto glutarate to succinyl-CoA. This complex is both a source and target of oxidants, but the sites of modification and association with structural changes and activity loss are poorly understood. We report here oxidative modifications induced by Rose Bengal (RB) in the presence of O2, a source of singlet oxygen (1O2). A rapid loss of activity was detected, with this being dependent on light exposure, illumination time, and the presence of RB and O2. Activity loss was enhanced by D2O (consistent with 1O2 involvement), but diminished by both pre- and (to a lesser extent) post-illumination addition of lipoic acid and lipoamide. Aggregates containing all three KGDH subunits were detected on photooxidation. LC-MS experiments provided evidence for oxidation at 45 sites, including specific Met, His, Trp, Tyr residues and the lipoyllysine active-site cofactor. Products include mono- and di-oxygenated species, and kynurenine from Trp. Mapping of the modifications to the 3-D structure showed that these are localized to both the inner channel and the external surface, consistent with reactions of free 1O2, however the sites and extent of modification do not correlate with their solvent accessibility. These products are generated concurrently with loss of activity, indicative of strong links between these events. These data provide evidence for the impairment of KGDH activity by 1O2 via the oxidation of specific residues on the protein subunits of the complex.

Organophotoredox-Catalyzed C-H Functionalizations of Benzophospholes.

An organophotoredox-catalyzed oxidative C-H functionalization of benzophospholes has been developed. The C-H alkoxycarbonylation with methyl carbazate occurs in the presence of Rose bengal, whereas Eosin Y enables the dehydrogenative coupling with secondary phosphine oxides and ethers, delivering the C-H phosphinylated and alkylated products. The scope of coupling partners is complementary to that of conventional metal-promoted C-H activation, thus successfully expanding the chemical space of substituted phospholes accessed by C-H functionalization protocols.

Organophotoredox-catalyzed stereoselective reductive dimerization of chromone-2-carboxylic esters

The photodimerization of chromone-2-carboxylic esters in the presence of Rose Bengal and triethanolamine (TEOA) gives access to various alkyl substituted 2,2′-bichromanones.

Priming effect with photoinactivation against extensively drug-resistant Enterobacter cloacae and Klebsiella pneumoniae.

In this study, we present antimicrobial blue light (aBL) and antimicrobial photoinactivation with green light in the presence of Rose Bengal (aPDI) to modulate the susceptibility of extensively drug-resistant (XDR) Enterobacter cloacae and Klebsiella pneumoniae clinical isolates to antimicrobials. This process can be considered a photodynamic priming tool that influences other therapeutic options, such as antibiotics. The current study evaluated the different environments to estimate the most effective priming conditions by testing a broad spectrum of antimicrobials (including antimicrobials with different targets and mechanisms of action). The susceptibility of the E. cloacae and K. pneumoniae clinical isolates to various antibiotics after aBL and green light (with rose bengal) as aPDI treatment was examined with multiple methods of synergy testing (e.g., diffusion methods, checkerboard assay, postantibiotic effect), and most effective photoinactivation conditions were implemented for each environment. When Enterobacteriaceae were exposed to aBL, the most efficient reduction in survival rate under TSB conditions was observed. Similar results were observed when rose bengal, as a photosensitizer, was present during the exposure to green light in PBS. aBL and aPDI led to an increased susceptibility of K. pneumoniae and E. cloacae isolates to chloramphenicol and colistin or fosfomycin and colistin antibiotics, respectively. However, among the 4 tested isolates, we observed synergies between different antimicrobial agents and photoinactivation conditions. Thus, it may suggest that the sensitization process may be considered a strain dependent priming tool.

Modelling approaches to predict light absorption in gas-liquid flow photosensitized oxidations

The photosensitized production of singlet oxygen is a benchmark reaction for characterizing flow photoreactors. Light absorption is the driving force of the photooxidation reaction and modelling represents a fast and cost-efficient method for its prediction and optimization. In this study, we report two models of photon absorption in single- and two-phase flow. Firstly, a three-dimensional ray tracing model was developed and validated by experimental 9,10-dimethylanthracene (DMA) photooxidation in presence of Rose Bengal. By comparing the simulated and experimental DMA conversion, the flow and illumination conditions affected by mass transfer limitations in liquid and gas–liquid Taylor flows were identified. Furthermore, the ray tracing model was used to compare the light absorption in Taylor, annular, and two bubbly flow configurations. At a low attenuation coefficient of 2.3 cm−1 a minor difference between flow patterns was observed irrespective of liquid hold-up. At the same liquid hold-up and between 26 cm−1 and 200 cm−1, the relative volumetric absorbed photon flux strongly depends on the flow pattern. Secondly, the ray tracing model was used as reference to develop a simplified absorption model which only requires the geometry and optical properties of the multiphase flow. The novel predictive method is based on the geometrical approximation of the optical pathlength in the liquid slugs, the liquid film and the liquid volume next to the bubble caps. As it requires minimum computational power and provides good accuracy, the geometry-based model has the potential to assist future automated optimization of gas–liquid photooxidations.

Visible Light-Mediated C(sp2)-H Selenylation of Amino Pyrazole and Amino Uracils in the Presence of Rose Bengal as an Organophotocatalyst.

Herein, we report an efficient methodology for the synthesis of alkyl, benzyl, and phenyl selenoethers of aminopyrazoles and aminouracils by C(sp2)-H functionalization in the presence of visible light and Rose Bengal as an organophotocatalyst. The reaction of amino pyrazole/iosothiazole/isoxazole or amino uracils with 0.5 equivalent of diphenyl/dibenzyl/diethyl diselenides in the presence of visible light in acetonitrile medium and a catalytic amount of Rose Bengal provided the corresponding phenyl, benzyl, or ethyl selenoethers in good to very good yields. We have also utilized some of the selenylated aminopyrazoles for the preparation of pyrazole-fused dihydropyrimidines tethered with arylselenoethers by a catalyst-free one-pot three-component reaction. The notable features of this methodology are metal-free reaction conditions, good to very good yields, use of an organic photocatalyst, and wide substrate scope; it is also applicable to gram-scale synthesis and provides selenoethers of medicinally important heterocycles such amio-pyrazole, isoxazole, isothiazole, and uracils.

Visible light-induced cross-linking of porcine pericardium for the improvement of endothelialization, anti-tearing, and anticalcification properties.

Population aging and the development of transcatheter aortic valve replacement boost the implantation of bioprosthetic heart valves (BHVs) in patients worldwide. However, the traditional glutaraldehyde cross-linked BHVs fail within 12-15 years mainly due to leaflet tear and calcification defects. In this study, a novel visible light-induced cross-linking of the porcine pericardium (PP) was realized by the photo-oxidation of the furfuryl-modified PP in the presence of Rose Bengal. The resulting material showed comparable collagen stability with the glutaraldehyde cross-linked PP and appropriate biomechanical properties such as tensile strength, modulus, and elongation, suggesting that this material could meet the general requirement for BHVs. Besides, this cross-linked PP showed significantly improved cytocompatibility compared with the Glut-cross-linked PP, with no cytotoxicity to L929 cells and the ability to support HUVECgrowth. Meanwhile, this material showed superior anti-tearing performance and much less calcification than the Glut-cross-linked PP in hope of reducing the risk of BHV failure. Considering these results, the visible light-induced cross-linking method proposed in this study could provide a promising way to construct a biocompatible and robust biomaterial for the fabrication of the BHV.

Visible Light-Induced Thiocyanation of Enaminone C-H Bond to Access Polyfunctionalized Alkenes and Thiocyano Chromones.

The visible light induced C-H bond thiocyanation on the α-site of tertiary enaminones has been realized under metal-free, photocatalytic conditions in the presence of Rose Bengal, which enables the synthesis of thiocyanated alkene derivatives and chromones using NH4SCN as the thiocyano source under an aerobic atmosphere. In addition, employing Ru(bpy)3Cl2·6H2O as the photocatalyst switches the reaction pathway to provide NH2-functionalized thiocyanated enamines via the difunctionalization process consisting of C-H bond thiocyanation and vinyl C-N bond transamination.

Wound healing effect of visible light-curable chitosan with encapsulated EGF

Low molecular O-carboxymethyl chitosan, a derivative of chitosan, was conjugated with a hydrophilic carboxymethyl group, following which the conjugate was modified with a furfuryl group. The chitosan derivative was cross-linked to encapsulate a model protein, bovine serum albumin (BSA), in the presence of Rose Bengal under visible light irradiation. The encapsulated BSA was slowly released from the matrix over 2 weeks. The modified chitosan exhibited antimicrobial activity and was non-cytotoxic to NIH3T3 fibroblasts. The wound healing effect of the cross-linked chitosan derivative was examined in Sprague-Dawley rats at 3, 7, and 14 days post-wounding. Cross-linked and murine epidermal growth factor (mEGF)-encapsulated chitosan derivatives healed wounds more rapidly in rats than non-encapsulated mEGF or chitosan derivative alone. Thus, visible light-curable chitosan has good potential for application as wound-healing matrix.

Galvanic synthesis of Cu2−XSe thin films and their photocatalytic and thermoelectric properties

Cu2−XSe thin film with cubic berzelianite phase was prepared by a simple, low-cost two electrode electrochemical technique and the photocatalytic and thermoelectric properties of the thin films were investigated. The results showed that Cu2−XSe crystallized in the cubic berzelianite phase and found to possess both direct and indirect band gaps of 2.9 and 1.05eV respectively, covering almost the entire range of solar-spectrum. The photocatalytic discoloration of aqueous methylene blue (MB) and rose-bengal (RB) dyes over Cu2−XSe thin films were investigated under visible light irradiation. Cu2−XSe thin films showed higher catalytic activity for MB compared to RB in presence of H2O2. The photocatalytic discoloration followed first-order reaction kinetics. Complete removal of aqueous MB was realized after visible light irradiation for 150min with Cu2−XSe thin film catalyst in presence of H2O2. Thermoelectric performances through power factor and figure of merit have been evaluated. Carrier concentration obtained from thermoelectric power was used to evaluate the mobility of carriers from electrical conductivity measurement.

Visible‐Light‐Induced CC Bond Cleavage of Enaminones for the Synthesis of 1,2‐Diketones and Quinoxalines in Sustainable Medium

AbstractThe CC double bond cleavage of enaminones has been realized under ambient conditions through visible‐light catalysis in the presence of Rose Bengal, which leads to the synthesis of a class of 1,2‐diketones without using any metal catalyst. In addition, the one‐pot synthesis of quinoxalines has also been achieved under identical photocatalytic conditions by making use of the in situ generated 1,2‐diketones as intermediates.

Fluorescence characteristics of sodium fluorescein-rose bengal ophthalmic solution mixtures.

To assess fluorescence emission properties of sodium fluorescein-rose bengal mixtures in buffered aqueous solution. Solutions of sodium fluorescein (NaFl) or rose bengal (RB) or mixtures of these two chemicals were prepared over a range of dilutions in 1% NaCl with 10mM phosphate buffer to give a pH of 7.5 at room temperature. Absorbance and fluorescence spectra were recorded in 10mm path length cuvettes. The fluorescence emission from NaFl extends between 480 and nearly 600nm, a spectral range that is also covered by the absorbance of RB (between 500 and 580nm). With very dilute solutions of NaFl (less than 0.002%), an apparent total quenching of its fluorescence can occur in the presence of 0.01% RB, with a proportionate decrease at lower concentrations of RB. The presence of RB in an aqueous solution of NaFl at physiological pH appears to act in a similar way to a barrier filter, resulting in the quenching of the measurable fluorescence from NaFl. It remains to be established how substantial or significant such an effect might be if a mixture of NaFl and RB as used as part of the examination of the external eye.

Effects of rose bengal on cavitation generation in gel phantom investigated using high-speed camera

Acoustic cavitation bubbles are microbubbles generated by the highly negative pressure of ultrasound. They are known to enhance the thermal bioeffect of high-intensity focused ultrasound (HIFU) treatment. Other than the use of the thermal bioeffect, sonodynamic treatment using the sonochemical bioeffect of ultrasound has been proposed. In sonodynamic treatment, a sonosensitizer is activated through the collapse of cavitation bubbles to induce a therapeutic effect sonochemically. Rose Bengal (RB) has the potential to be such a sonosensitizer. Highly efficient as well as controlled generation of cavitation bubbles is crucial for realizing effective as well as safe sonodynamic treatment. The effect of RB on cavitation generation was investigated to achieve such controlled generation. The amount and behavior of the cavitation bubbles generated by a triggered HIFU sequence in the presence of RB were observed using a high-speed camera for estimating the effect of RB. Results showed that RB increased the area of the cavitation cloud and the lifetime of sustained cavitation bubbles.

Protein oxidation: identification and utilisation of molecular markers to differentiate singlet oxygen and hydroxyl radical-mediated oxidative pathways

The effect of reactive oxidation species (ROS) on tryptophan or tyrosine was investigated by qualitatively determining the major detectable oxidation products generated by hydroxyl radicals, produced by the Fenton process, or singlet oxygen, generated by exposure to green light in the presence of Rose Bengal, on these photosensitive amino acids in synthetic pentapeptides. Based on mass spectrometric analysis it would appear that the hydroxyl radical favours a pathway leading to the formation of tryptophandione-based products from tryptophan. In contrast singlet oxygen attack appears to favour the formation of kynurenine-type products from tryptophan. Specific oxidative products observed proteomically are therefore potentially able to discriminate between predominant ROS-mediated pathways. To validate these findings, a keratin-enriched extract was exposed to UVB light under aqueous conditions. The observation of the conversion of tryptophan to hydroxytryptophan in marker peptides, and the absence of singlet-oxygen specific modifications, suggested that under these conditions oxidative degradation occurred primarily via hydroxyl radical attack. These observations provide the first direct proteomic evidence of the dominant photodegradation pathways in wet wool.

Single-source precursor approach for the preparation of CdS nanoparticles and their photocatalytic and intrinsic peroxidase like activity

CdS nanoparticles (NPs) with different shapes and sizes (rods and spheres) have been synthesized through decomposition of a newly synthesized precursor complex [Cd(SOCPh)2Lut2] using structure-directing solvents such as ethylenediamine (EN), dimethylsulfoxide (DMSO) and ammonia (NH3). In addition, CdS NPs is also prepared by thermal decomposition of the precursor complex under N2 atmosphere. The precursor complex is characterized by elemental analyses, TGA, FTIR, UV–vis spectroscopy and single crystal X-ray diffraction. The distorted tetrahedron geometry of the precursor complex has been determined by X-ray diffraction, which crystallizes in monoclinic crystal system of P2(1)/n space group with a=11.0487(17)Å, b=16.396(3), c=15.413(2)Å, α=90.00°, β=109.708(4)°, γ=90.00° and Z=4. The CdS NPs are characterized using powder X-ray diffraction, transmission electron microscopy, BET analyses, UV–vis absorption and photoluminescence spectroscopy. The photo-catalytic activity of CdS NPs is studied by the degradation of Rose Bengal (RB) dye, indicating an excellent photocatalytic activity compared to that of commercial TiO2. The mechanism behind photocatalytic degradation of RB in presence of CdS NPs is elucidated using terephthalic acid photoluminescence probing technique and evidence have shown that the photogenerated holes to be the predominant active species. This paper also demonstrates the intrinsic peroxidase like activity of CdS NPs toward peroxidase substrates 3,3′,5,5′-tetramethyl benzidine (TMB) and hydrogen peroxide. Kinetic analysis indicates that the catalysis by CdS NPs show typical Michaelis–Menten kinetics. Moreover, our synthesized CdS NPs show higher catalytic performances with a higher binding affinity for the substrate TMB than horseradish peroxidase (HRP) and other recently reported nano-mimitics.

Molecular mechanisms involved in the antithrombotic activity of aegyptin, a novel mosquito‐derived collagen‐binding protein

Aegyptin is a 30‐kDa mosquito salivary gland protein that binds to collagen with high affinity (Kd=6 nM) and inhibits platelet aggregation. It recognizes the von Willebrand factor binding‐site in collagen which could partially explain its biological activity. Herein we evaluated: 1. whether this protein could prevent in vitro collagen‐induced plasma clotting; 2. the in vivo antithrombotic activity of aegyptin. Aegyptin does not affect collagen‐mediated acceleration of plasma clotting. In accordance with this observation, aegyptin has no effect on collagen‐induced FXII activation, as indirectly determined by measurement of kallikrein formation in plasma. Aegyptin has no antithrombotic activity in vivo by employing an arteriovenous shunt model in rats. This model is independent of collagen‐exposure since presents no vascular surface for thrombus formation. On the other hand, aegyptin delays laser‐induced carotid thrombus formation in the presence of Rose Bengal, a model based on vessel injury. Our results demonstrate that aegyptin is an effective antithrombotic agent in vivo and might be regard as an important tool to dissect the hemostatic role of collagen in vivo.

Topical delivery and photodynamic evaluation of a multivesicular liposomal Rose Bengal

We investigated the pharmaceutical and physicochemical properties of different multivesicular liposome (MVL) formulations for the delivery of Rose Bengal (RB) into skin layers for topical photodynamic therapy. The drug content, uniformity, spreadability and release kinetics of the optimum hydrogel formulation were studied. Skin penetration of the prepared gels was studied in albino mice using fluorescence microscopy and the photodynamic properties were evaluated. The loading efficiency of MVL ranged from 56% to 79%. In vitro RB release from MVL followed Higuchi's diffusion mechanism and the amount of RB released after 2 h from the optimum MVL (comprising D,L-dipalmitoylphosphatidyl choline, cholesterol and tripalmitin at a molar ratio of 1:0.7:0.1, respectively) was 2.5-fold higher than from the other MVL formulations. The type and concentration of phospholipids did not significantly (p > 0.05) affect vesicle size but significantly (p < 0.05) increased the encapsulation capacity and thermal properties. RB in hydrogel was spreadable and uniformly distributed. Fluorescence microscopy 30 min after topical application to the skin of mice showed that RB loaded into MVL was significantly (p < 0.05) more distributed into the dermal layers than free RB which accumulated in the epidermis. This finding was confirmed by the presence of superficial necrotic cells in histological sections of skin treated with free RB and the presence of RB in the deep dermal layers of sections of skin treated with the MVL-RB formulation and irradiated for 10 min with light of wavelength 550 nm from a light emitting diode at 80 mW. MVL hydrogel is a promising topical delivery system which allows successful delivery of RB into skin layers for different photodynamic therapies in dermatology.

Aegyptin displays high‐affinity for the von Willebrand factor binding site (RGQOGVMGF) in collagen and inhibits carotid thrombus formation in vivo

Aegyptin is a 30 kDa mosquito salivary gland protein that binds to collagen and inhibits platelet aggregation. We have studied the biophysical properties of aegyptin and its mechanism of action. Light-scattering plot showed that aegyptin has an elongated monomeric form, which explains the apparent molecular mass of 110 kDa estimated by gel-filtration chromatography. Surface plasmon resonance identified the sequence RGQOGVMGF (where O is hydroxyproline) that mediates collagen interaction with von Willebrand factor (vWF) as a high-affinity binding site for aegyptin, with a K(D) of approximately 5 nM. Additionally, aegyptin interacts with the linear peptide RGQPGVMGF and heat-denatured collagen, indicating that the triple helix and hydroxyproline are not a prerequisite for binding. However, aegyptin does not interact with scrambled RGQPGVMGF peptide. Aegyptin also recognizes the peptides (GPO)(10) and GFOGER with low affinity (microM range), which respectively represent glycoprotein VI and integrin alpha2beta1 binding sites in collagen. Truncated forms of aegyptin were engineered, and the C-terminus fragment was shown to interact with collagen and to attenuate platelet aggregation. In addition, aegyptin prevents laser-induced carotid thrombus formation in the presence of Rose Bengal in vivo, without significant bleeding in rats. In conclusion, aegyptin interacts with distinct binding sites in collagen, and is useful tool to inhibit platelet-collagen interaction in vitro and in vivo.

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.

Dye-sensitized photodegradation of the fungicide carbendazim and related benzimidazoles

The present work studies the visible-light-promoted photodegradation of the colorless fungicide carbendazim (methyl 2-benzimidazolecarbamate) and several 2-substituted benzimidazoles (SBZ’s), in water or water–methanol solution, in the presence of air and, as a photosensitizer, the synthetic xanthene dye Rose Bengal (RB) or the natural pigment riboflavin (Rf). The results indicate that the degradation of each particular SBZ depends on its chemical structure and on the sensitizer employed. In the presence of RB, the degradation always operates via a singlet molecular oxygen (O 2( 1Δ g))-mediated mechanism, through a highly efficient process, as deduced from the comparison of the rate constants for physical and chemical quenching of O 2( 1Δ g). In the presence of Rf, the visible-light irradiation of any of the studied SBZ’s produces a series of competitive processes that depend on the relative concentrations of Rf and SBZ. These processes include the quenching of excited singlet and triplet Rf states by the SBZ and the generation of both O 2( 1Δ g) and superoxide radical anion ( O 2 - ) , the latter generated by electron transfer from excited Rf species to the dissolved oxygen. The overall result is the photodegradation of the SBZ and the photoprotection of the sensitizer.