Uric Acid as a Photosensitizer in the Reaction of Deoxyribonucleosides with UV Light of Wavelength Longer than 300 nm: Identification of Products from 2'-Deoxycytidine.

DNA reacts directly with UV light with a wavelength shorter than 300 nm. Although ground surface sunlight includes little of this short-wavelength UV light due to its almost complete absorption by the atmosphere, sunlight is the primary cause of skin cancer. Photosensitization by endogenous substances must therefore be involved in skin cancer development mechanisms. Uric acid is the final metabolic product of purines in humans, and is present at relatively high concentrations in cells and fluids. When a neutral mixed solution of 2'-deoxycytidine, 2'-deoxyguanosine, thymidine, and 2'-deoxyadenosine was irradiated with UV light with a wavelength longer than 300 nm in the presence of uric acid, all the nucleosides were consumed in a uric acid dose-dependent manner. These reactions were inhibited by the addition of radical scavengers, ethanol and sodium azide. Two products from 2'-deoxycytidine were isolated and identified as N4-hydroxy-2'-deoxycytidine and N4,5-cyclic amide-2'-deoxycytidine, formed by cycloaddition of an amide group from uric acid. A 15N-labeled uric acid, uric acid-1,3-15N2, having two 14N and two 15N atoms per molecule, produced N4,5-cyclic amide-2'-deoxycytidine containing both 14N and 15N atoms from uric acid-1,3-15N2. Singlet oxygen, hydroxyl radical, peroxynitrous acid, hypochlorous acid, and hypobromous acid generated neither N4-hydroxy-2'-deoxycytidine nor N4,5-cyclic amide-2'-deoxycytidine in the presence of uric acid. These results indicate that uric acid is a photosensitizer for the reaction of nucleosides by UV light with a wavelength longer than 300 nm, and that an unidentified radical derived from uric acid with a delocalized unpaired electron may be generated.

Anchoring of triethanolamine-Cu(II) complex on magnetic carbon nanotube as a promising recyclable catalyst for the synthesis of 5-substituted 1H-tetrazoles from aldehydes.

The development of heterogenization of copper nanoparticles on conductive supports is very challenging and has received much attention. Here, we synthesize a practical, efficient, and inexpensive heterogeneous catalyst to grow stable metallic copper(II) nanoparticles on the surface of magnetic carbon nanotube (Fe3O4-CNT) catalyst support physically functionalized with triethanolamine (TEA) that acts as a low-cost and non-toxic ligand to capture the copper nanoparticles [Fe3O4-CNT-TEA-Cu(II)]. The as-prepared heterogeneous catalyst was characterized by different techniques, such as Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, thermogravimetric analysis, vibrating sample magnetometer, X-ray diffraction patterns, field-emission scanning electron microscopy, and atomic absorption spectroscopy analysis. The catalytic behavior of Fe3O4-CNT-TEA-Cu(II) was investigated in the preparation of 5-substituted 1H-tetrazole derivatives via one-pot, three-component reaction between aromatic aldehydes, hydroxylamine, and sodium azide. The low catalyst loading, wide substrate scope, use of inexpensive materials, simple separation of the catalyst from the reaction mixture by an external magnet, short reaction times, easy workup, affordability, and superb yield are some advantages of this protocol.

Synthesis and Structure-Activity Relationship Studies of Hydrazide-Hydrazones as Inhibitors of Laccase from Trametes versicolor.

A series of hydrazide-hydrazones 1-3, the imine derivatives of hydrazides and aldehydes bearing benzene rings, were screened as inhibitors of laccase from Trametes versicolor. Laccase is a copper-containing enzyme which inhibition might prevent or reduce the activity of the plant pathogens that produce it in various biochemical processes. The kinetic and molecular modeling studies were performed and for selected compounds, the docking results were discussed. Seven 4-hydroxybenzhydrazide (4-HBAH) derivatives exhibited micromolar activity Ki = 24-674 µM with the predicted and desirable competitive type of inhibition. The structure-activity relationship (SAR) analysis revealed that a slim salicylic aldehyde framework had a pivotal role in stabilization of the molecules near the substrate docking site. Furthermore, the presence of phenyl and bulky tert-butyl substituents in position 3 in salicylic aldehyde fragment favored strong interaction with the substrate-binding pocket in laccase. Both 3- and 4-HBAH derivatives containing larger 3-tert-butyl-5-methyl- or 3,5-di-tert-butyl-2-hydroxy-benzylidene unit, did not bind to the active site of laccase and, interestingly, acted as non-competitive (Ki = 32.0 µM) or uncompetitive (Ki = 17.9 µM) inhibitors, respectively. From the easily available laccase inhibitors only sodium azide, harmful to environment and non-specific, was over 6 times more active than the above compounds.

Synthesis and Spectral Study of a New Family of 2,5-Diaryltriazoles Having Restricted Rotation of the 5-Aryl Substituent.

Efficient synthesis of 2,5-diaryl substituted 4-azido-1,2,3-triazoles by the reaction of sodium azide with dichlorosubstituted diazadienes was demonstrated. The optical properties of the prepared azidotriazoles were studied to reveal a luminescence maximum in the 360-420 nm region. To improve the luminescence quantum yields a family of 4-azido-1,2,3-triazoles bearing ortho-propargyloxy substituents in the 5 position was prepared. Subsequent intramolecular thermal cyclization permits to construct additional triazole fragment and obtain unique benzoxazocine derivatives condensed with two triazole rings. This new family of condensed heterocycles has a flattened heterocyclic system structure to provide more conjugation of the 5-aryl fragment with the triazole core. As a result, a new type of UV/"blue light-emitting" materials with better photophysical properties was obtained.

Mechanistic Insight into the Photodynamic Effect Mediated by Neutral Red and a New Azine Compound in Staphylococcus aureus Cells.

The photodynamic activity of Neutral Red and the new monobrominated Neutral Red was studied in suspensions of Staphylococcus aureus. The effect of mannitol and sodium azide in the presence of 25 µm photosensitizer on lethal photosensitization were investigated. The results of the mechanistic evaluation of Neutral Red showed that both mannitol and sodium azide produced a completed protective effect after irradiation without significant differences between them. The evaluation of monobrominated Neutral Red also showed a protective effect of microorganisms with the addition of mannitol. Although sodium azide produced a protective effect of the photoinactivation, it was incomplete and less than that exhibited by mannitol. The results indicate that the starting reagent, Neutral Red, is a producer of radical species, acting through a type I mechanism, whereas the halogenated derivative of Neutral Red produced reactive oxygen species and a contribution of singlet molecular oxygen cannot be discarded in the photoinactivation of Staphylococcus aureus cells. These results, analyzed together with the previously evaluated properties of the dyes, allow us to explain the differences observed in the photoinactivation of Staphylococcus aureus mediated by both azine photosensitizers.

The Effect of UVB Irradiation and Oxidative Stress on the Skin Barrier-A New Method to Evaluate Sun Protection Factor Based on Electrical Impedance Spectroscopy.

Sunlight is vital for several biochemical processes of the skin organ. However, acute or chronic exposure to ultraviolet radiation (UVR) has several harmful effects on the skin structure and function, especially in the case of the failing function of antioxidative enzymes, which may lead to substantial tissue damage due to the increased presence of reactive oxygen species (ROS). The aim of this work was to investigate the combined effect of ultraviolet B (UVB) irradiation and oxidative stress on the skin barrier integrity. For this, we employed electrical impedance spectroscopy (EIS) to characterize changes of the electrical properties of excised pig skin membranes after various exposure conditions of UVB irradiation, oxidative stress, and the inhibition of antioxidative enzymatic processes. The oxidative stress was regulated by adding hydrogen peroxide (H2O2) as a source of ROS, while sodium azide (NaN3) was used as an inhibitor of the antioxidative enzyme catalase, which is naturally present throughout the epidermis. By screening for the combined effect of UVB and oxidative stress on the skin membrane electrical properties, we developed a new protocol for evaluating these parameters in a simple in vitro setup. Strikingly, the results show that exposure to extreme UVB irradiation does not affect the skin membrane resistance, implying that the skin barrier remains macroscopically intact. Likewise, exposure to only oxidative stress conditions, without UVB irradiation, does not affect the skin membrane resistance. In contrast to these observations, the combination of UVB irradiation and oxidative stress conditions results in a drastic decrease of the skin membrane resistance, indicating that the integrity of the skin barrier is compromised. Further, the skin membrane effective capacitance remained more or less unaffected by UVB exposure, irrespective of simultaneous exposure of oxidative stress. The EIS results were concluded to be associated with clear signs of macroscopic tissue damage of the epidermis as visualized with microscopy after exposure to UVB irradiation under oxidative stress conditions. Finally, the novel methodology was tested by performing an assessment of cosmetic sunscreen formulations with varying sun protection factor (SPF), with an overall successful outcome, showing good correlation between SPF value and protection capacity in terms of skin resistance change. The results from this study allow for the development of new skin sensors based on EIS for the detection of skin tissue damage from exposure to UVB irradiation and oxidative stress and provide a new, more comprehensive methodology, taking into account both the influence of UVB irradiation and oxidative stress, for in vitro determination of SPF in cosmetic formulations.

pH regulation in glycosomes of procyclic form Trypanosoma brucei.

Here we report the use of a fluorescein-tagged peroxisomal targeting sequence peptide (F-PTS1, acetyl-C{K(FITC)}GGAKL) for investigating pH regulation of glycosomes in live procyclic form Trypanosoma brucei When added to cells, this fluorescent peptide is internalized within vesicular structures, including glycosomes, and can be visualized after 30-60 min. Using F-PTS1 we are able to observe the pH conditions inside glycosomes in response to starvation conditions. Previous studies have shown that in the absence of glucose, the glycosome exhibits mild acidification from pH 7.4 ± 0.2 to 6.8 ± 0.2. Our results suggest that this response occurs under proline starvation as well. This pH regulation is found to be independent from cytosolic pH and requires a source of Na+ ions. Glycosomes were also observed to be more resistant to external pH changes than the cytosol; placement of cells in acidic buffers (pH 5) reduced the pH of the cytosol by 0.8 ± 0.1 pH units, whereas glycosomal pH decreases by 0.5 ± 0.1 pH units. This observation suggests that regulation of glycosomal pH is different and independent from cytosolic pH regulation. Furthermore, pH regulation is likely to work by an active process, because cells depleted of ATP with 2-deoxyglucose and sodium azide were unable to properly regulate pH. Finally, inhibitor studies with bafilomycin and EIPA suggest that both V-ATPases and Na+/H+ exchangers are required for glycosomal pH regulation.

Determining δ15N-NO3- values in soil, water, and air samples by chemical methods.

Soil, water, and air NO3- pollution is a major environmental problem worldwide. Stable isotope analysis can assess the origin of NOx because different NOx sources carry different isotope signatures. Hence, using appropriate chemical methods to determine the δ15N-NOx values in different samples is important to improve our understanding of the N-NOx pollution and take possible strategies to manage it. Two modified chemical methods, the cadmium-sodium azide method and the VCl3-sodium azide method, were used to establish a comprehensive inventory of δ15N-NOx values associated with major NOx fluxes by the conversion of NO3- into N2O. Precision and limit of detection values demonstrated the robustness of these quantitative techniques for measuring δ15N-NOx. The standard deviations of the δ15N-NO3- values were 0.35 and 0.34‰ for the cadmium-sodium azide and VCl3-sodium azide methods. The mean δ15N-NO3- values of river water, soil extracts, and summer rain were 8.9 ± 3.3, 3.5 ± 3.5, and 3.3 ± 2.1‰, respectively. The δ15N-NO3- values of low concentration samples collected from coal-fired power plants, motor vehicles, and gaseous HNO3 was 20.3 ± 4.3, 5.6 ± 2.78, and 5.7 ± 3.6‰, respectively. There was a good correlation between the δ15N-NO3- compositions of standards and samples, which demonstrates that these chemical reactions can be used successfully to assess δ15N-NO3- values in the environment.

Generation of hazardous methyl azide and its application to synthesis of a key-intermediate of picarbutrazox, a new potent pesticide in flow.

Generation and reactions of methyl azide (MeN3) were successfully performed by using a flow reactor system, demonstrating that the flow method serves as a safe method for handling hazardous explosive methyl azide. The reaction of NaN3 and Me2SO4 in a flow reactor gave a MeN3 solution, which was used for Huisgen reaction with benzoyl cyanide in a flow reactor after minimal washing. The resulting 1-methyl-5-benzoyltetrazole serves as a key intermediate of picarbutrazox (IX), a new potent pesticide.

Approaches to unravel pathways of reactive oxygen species in the photoinactivation of bacteria induced by a dicationic fulleropyrrolidinium derivative.

The photodynamic mechanism sensitized by N,N-dimethyl-2-[4-(3-N,N,N-trimethylammoniopropoxy)phenyl]fulleropyrrolidinium (DPC602+) was investigated in Staphylococcus aureus cells. Different experimental conditions were used to detect reactive oxygen species (ROS) in S. aureus cell suspensions. First, a photoinactivation of 4 log decrease of S. aureus viability was chosen using 0.5µM DPC602+ and 15min irradiation. An anoxic atmosphere indicated that oxygen was required for an effective photoinactivation. Also, photoprotection was found in the presence of sodium azide, whereas the photocytotoxicity induced by DPC602+ increased in D2O. The addition of diazabicyclo[2.2.2]octane or d-mannitol produced a reduction in the S. aureus photokilling. Moreover, singlet molecular oxygen, O2(1Δg), was detected by the reaction with 9,10-dimethylanthracene into the S. aureus cells. A decrease in the photoinactivation of S. aureus was observed in the presence of ß-nicotinamide adenine dinucleotide reduced form, which was dependent on the NADH concentration. Therefore, under aerobic condition the photocytotoxicity activity induced by DPC602+ was mediated by mainly a contribution of type II process. Moreover, photoinactivation of S. aureus was possible with DPC602+ in the presence of azide anions under anoxic condition. However, these conditions were not effective to photoinactivate Escherichia coli. On the other hand, the addition of potassium iodide produced an increase in the photokilling of bacteria, depending on the KI concentration and irradiation times. The formation of reactive iodine species may be contributing to inactivate S. aureus cells photoinduced by DPC602+.

Anti-mutagenic potential of algal extracts on chromosomal aberrations in Allium cepa L.

In the present study, sodium azide (SA) toxicity and the anti-mutagenic effects of different algal extracts at 0.1% and 0.2% concentrations were studied on the mitotic index (MI), chromosomal and nuclear aberrations using Allium cepa L. root assay. Moreover, phytochemical screening of photosynthetic pigments, antioxidants compounds, total antioxidant, DPPH scavenging activity, polysaccharides, and phenolic contents were done for two red seaweeds (Laurencia obtusa (Hudson) Lamouroux and Polysiphonia morrowii Harvey) and for one brown seaweed (Dictyopteris delicatula Lamouroux). Treatment with 300 µg/ml sodium azide (SA) induced the highest number of aberrations in A. cepa root. A highly significant decrease in the MI appeared after treatment with SA, whereas its value increased following different algal extracts treatments. The highest anti-mutagenic inhibition activity of Dictyopteris delicatula added at 0.2% concentration was 72.96%, 69.84%, 56.89% and 43.59% with the algal polyphenol, polysaccharide, aqueous and methanol extract treatments, respectively. The different algal extracts minimized the genotoxicity and exhibited anti-mutagenic potential against SA in a dose-dependent manner. Phytochemical studies showed that Dictyopteris delicatula contained the highest total phenol, chlorophyll-a and carotenoid quantity. Moreover it exhibited the highest total antioxidant and DPPH scavenging activities. Total polysaccharides and the weight percentage of sulphated polysaccharides were relatively higher in Polysiphonia morrowii followed by Laurencia obtusa. Hydroquinone and bromophenol were detected only in the studied brown and red seaweeds, respectively. Polysiphonia morrowii and Laurencia obtusa contained the highest quantity of galactose, rhmnose and xylose, while Dictyopteris delicatula contained fucose and mannitol as main monosaccharide units. In conclusion, the studied seaweeds may be considered as rich sources of natural antioxidants. Meanwhile the investigated different algal extracts can minimize the genotoxicity in a dose-dependent manner and exhibit anti-mutagenic potential against the mutagenic substance sodium azide.

Structural and Kinetic Studies of Formate Dehydrogenase from Candida boidinii.

The structure of formate dehydrogenase from Candida boidinii (CbFDH) is of both academic and practical interests. First, this enzyme represents a unique model system for studies on the role of protein dynamics in catalysis, but so far these studies have been limited by the availability of structural information. Second, CbFDH and its mutants can be used in various industrial applications (e.g., CO2 fixation or nicotinamide recycling systems), and the lack of structural information has been a limiting factor in commercial development. Here, we report the crystallization and structural determination of both holo- and apo-CbFDH. The free-energy barrier for the catalyzed reaction was computed and indicates that this structure indeed represents a catalytically competent form of the enzyme. Complementing kinetic examinations demonstrate that the recombinant CbFDH has a well-organized reactive state. Finally, a fortuitous observation has been made: the apoenzyme crystal was obtained under cocrystallization conditions with a saturating concentration of both the cofactor (NAD(+)) and inhibitor (azide), which has a nanomolar dissociation constant. It was found that the fraction of the apoenzyme present in the solution is less than 1.7 × 10(-7) (i.e., the solution is 99.9999% holoenzyme). This is an extreme case where the crystal structure represents an insignificant fraction of the enzyme in solution, and a mechanism rationalizing this phenomenon is presented.

Purification and characterization of polyphenol oxidase from corn tassel.

In this study, polyphenol oxidase (PPO) from corn tassel  was extracted and partially purified through  (NH4)2SO4 precipitation and gel filtration chromatography. Optimal temperatures for subsrates catechol and 4-methyl catechol were 40 °C and 30 °C, respectively. The optimal pH values were 8.0 for catechol and 6.0 for 4-methyl catechol. Catechol was the most suitible substrate (Km: 3.48 mM, Vmax: 1.0 Abs./ min.). The moleculer mass of PPO was determined as 158 kDa. In this work, sodium azide, ethylenediaminetetraacetic acid (EDTA) and sodium dodecyl sulfate (SDS) were found to inhibit the enzyme activity as 26.6 %,  22.2 % and 12.2 % ratio, respectively. Besides, the effects of carbohydrates such as sucrose, fructose, ribose and glucose on PPO activity were investigated. The enzyme was found to be activated 17 % by fructose and ribose, 16 % by glucose and 4 % by sucrose.

A sensitive gel-based method combining distinct cyclophellitol-based probes for the identification of acid/base residues in human retaining ß-glucosidases.

Retaining ß-exoglucosidases operate by a mechanism in which the key amino acids driving the glycosidic bond hydrolysis act as catalytic acid/base and nucleophile. Recently we designed two distinct classes of fluorescent cyclophellitol-type activity-based probes (ABPs) that exploit this mechanism to covalently modify the nucleophile of retaining ß-glucosidases. Whereas ß-epoxide ABPs require a protonated acid/base for irreversible inhibition of retaining ß-glucosidases, ß-aziridine ABPs do not. Here we describe a novel sensitive method to identify both catalytic residues of retaining ß-glucosidases by the combined use of cyclophellitol ß-epoxide- and ß-aziridine ABPs. In this approach putative catalytic residues are first substituted to noncarboxylic amino acids such as glycine or glutamine through site-directed mutagenesis. Next, the acid/base and nucleophile can be identified via classical sodium azide-mediated rescue of mutants thereof. Selective labeling with fluorescent ß-aziridine but not ß-epoxide ABPs identifies the acid/base residue in mutagenized enzyme, as only the ß-aziridine ABP can bind in its absence. The Absence of the nucleophile abolishes any ABP labeling. We validated the method by using the retaining ß-glucosidase GBA (CAZy glycosylhydrolase family GH30) and then applied it to non-homologous (putative) retaining ß-glucosidases categorized in GH1 and GH116: GBA2, GBA3, and LPH. The described method is highly sensitive, requiring only femtomoles (nanograms) of ABP-labeled enzymes.

The singlet-oxygen-sensitized delayed fluorescence in mammalian cells: a time-resolved microscopy approach.

The present work provides a proof-of-concept that the singlet oxygen-sensitized delayed fluorescence (SOSDF) can be detected from individual living mammalian cells in a time-resolved microscopy experiment. To this end, 3T3 mouse fibroblasts incubated with 100 µM TPPS4 or TMPyP were used and the microsecond kinetics of the delayed fluorescence (DF) were recorded. The analysis revealed that SOSDF is the major component of the overall DF signal. The microscopy approach enables precise control of experimental conditions - the DF kinetics are clearly influenced by the presence of the (1)O2 quencher (sodium azide), H2O/D2O exchange, and the oxygen concentration. Analysis of SOSDF kinetics, which was reconstructed as a difference DF kinetics between the unquenched and the NaN3-quenched samples, provides a cellular (1)O2 lifetime of τΔ = 1-2 µs and a TPPS4 triplet lifetime of τT = 22 ± 5 µs in agreement with previously published values. The short SOSDF acquisition times, typically in the range of tens of seconds, enable us to study the dynamic cellular processes. It is shown that SOSDF lifetimes increase during PDT-like treatment, which may provide valuable information about changes of the intracellular microenvironment. SOSDF is proposed and evaluated as an alternative tool for (1)O2 detection in biological systems.

Mn(II)- and Co(II)-Catalyzed Transformation of 2-Cyanopyrimidine to Methylimidate by Sodium Azide: Isolation, Structural Characterization, and Magnetic Studies on 2D Mn(II)- and Cu(II)-Complexes.

The Mn(II)-mediated transformation of 2-cyanopyrimidine to methylimidate in the presence of inorganic azide is proven through isolation and structural characterization of a metal complex. Though the reaction conditions are favorable for a "click" reaction leading to the formation of tetrazole, as evidenced from recent studies, we are astonished to see the formation of methylimidate in MeOH instead of tetrazole, which is supposed to form only in the presence of catalytic amount of corresponding alkoxide ion as base. The catalytic nature of this transformation reaction was confirmed by performing these experiments under catalytic conditions and analyzing the products using liquid chromatography-mass spectrometry techniques, which clearly showed ∼96% and ∼60% selectivity of methylimidate along with almost 100% conversion in the presence of Mn(II) and Co(II) as catalysts, respectively. In absence or presence of other metal ions like Cu(II), Ni(II), Fe(II), Zn(II), etc. only tetrazole formation takes place. So the present findings extended the formation of methylimidate catalyzed by metal ions in the presence of azide ion in alcoholic medium. Importantly, a probable mechanism for this unexpected transformation was framed based on the structural analysis and high-resolution mass spectrometry (electrospray ionization MS(+)) studies. The magnetic studies were also performed on complexes [Mn(L)(N3)2]n (1) and [Cu (L(2))2]n (2a), showing anti-ferromagnetic character for compound 1 and negligible coupling for the copper complex 2a.

A mild removal of Fmoc group using sodium azide.

A mild method for effectively removing the fluorenylmethoxycarbonyl (Fmoc) group using sodium azide was developed. Without base, sodium azide completely deprotected N (α)-Fmoc-amino acids in hours. The solvent-dependent conditions were carefully studied and then optimized by screening different sodium azide amounts and reaction temperatures. A variety of Fmoc-protected amino acids containing residues masked with different protecting groups were efficiently and selectively deprotected by the optimized reaction. Finally, a biologically significant hexapeptide, angiotensin IV, was successfully synthesized by solid phase peptide synthesis using the developed sodium azide method for all Fmoc removals. The base-free condition provides a complement method for Fmoc deprotection in peptide chemistry and modern organic synthesis.

Potentiation of photoinactivation of Gram-positive and Gram-negative bacteria mediated by six phenothiazinium dyes by addition of azide ion.

Antimicrobial photodynamic inactivation (APDI) using phenothiazinium dyes is mediated by reactive oxygen species consisting of a combination of singlet oxygen (quenched by azide), hydroxyl radicals and other reactive oxygen species. We recently showed that addition of sodium azide paradoxically potentiated APDI of Gram-positive and Gram-negative bacteria using methylene blue as the photosensitizer, and this was due to electron transfer to the dye triplet state from azide anion, producing azidyl radical. Here we compare this effect using six different homologous phenothiazinium dyes: methylene blue, toluidine blue O, new methylene blue, dimethylmethylene blue, azure A, and azure B. We found both significant potentiation (up to 2 logs) and also significant inhibition (>3 logs) of killing by adding 10 mM azide depending on Gram classification, washing the dye from the cells, and dye structure. Killing of E. coli was potentiated with all 6 dyes after a wash, while S. aureus killing was only potentiated by MB and TBO with a wash and DMMB with no wash. More lipophilic dyes (higher log P value, such as DMMB) were more likely to show potentiation. We conclude that the Type I photochemical mechanism (potentiation with azide) likely depends on the microenvironment, i.e. higher binding of dye to bacteria. Bacterial dye-binding is thought to be higher with Gram-negative compared to Gram-positive bacteria, when unbound dye has been washed away, and with more lipophilic dyes.

α-Haloacrylates as acceptors in the [3 + 2] cycloaddition reaction with NaN3: an expedient approach to N-unsubstituted 1,2,3-triazole-4-carboxylates.

An expedient synthesis of N-unsubstituted 1,2,3-triazole-4-carboxylates has been demonstrated through [3 + 2] cycloaddition of sodium azide with α-haloacrylates. The process is highly reliable and exhibits an unusually wide scope with respect to α-fluoro-, α-chloro-, α-bromo-, and α-iodoacrylates. The potential of selected 1,2,3-triazole-4-carboxylates in the preparation of 1,5-dihydro-4H-[1,2,3]-triazolo-[4,5-c]-quinolin-4-one has also been illustrated.

Validation of photodynamic action via photobleaching of a new curcumin-based composite with enhanced water solubility.

Motivated by the photochemical and photophysical properties of curcumin-based composites, the characteristics of a new curcumin-based water-soluble salt were investigated via absorption and fluorescence spectroscopy. Photobleaching was investigated using a set of LEDs in three different wavelengths (405 nm, 450 nm and 470 nm) to illuminate an aqueous solution of curcumin, evaluating its degradation for five different exposure times (0, 5, 15, 45 and 105 minutes). The results were compared with equivalent measurements of dark degradation and illumination in the presence of a singlet-oxygen quencher. Three solution concentrations (50, 100 and 150 µg/ml) were studied. To measure the fluorescence, it was used low power 405 nm excitation laser source. Time dependent photodegradation of curcumin was observed, as compared to the natural degradation of samples maintained on a dark environment. Two main absorption peaks were detected and their relation responded to both concentration and wavelength of the illumination source. A spectral correlation between absorption of curcumin and the emission bands of the sources showed an optimal spectral overlap for the 450 nm LED. For this source, photobleaching showed a less intense degradation on the presence of singlet oxygen quencher. This last result confirmed singlet oxygen production in vitro, indicating a strong potential of this composite to be used as a blue-light-activated photosensitizer.