Reinaldo Ruggiero

Photocatalytic degradation of lignin and lignin models, using titanium dioxide: the role of the hydroxyl radical.

The role of hydroxyl radicals on the degradation of lignins during a cellulosic pulp bleaching process including a photocatalytic stage, was assessed using peroxyformic acid lignins EL1 and REL1 and two phenolic niphenyl lignin models 1 and 2. The irradiations were performed in the absence of photocatalyst TiO2 and H2O2 (condition a), in the presence of TiO2 (condition b) and in the presence of H2O2 (condition c). The experiments were conducted in alkaline (pH approximately 11) aqueous ethanol solutions with oxygen bubbling. The relative phenolic content of the irradiated solutions, which is indicative of the involvement of hydroxyl radicals, was determined by ionization absorption spectroscopy. The results obtained show that the catalyzed reaction involves both degradation of the phenolate groups by electron transfer and hydroxylation of the lignin aromatic structure. Benzyl alcohol structural elements in sodium borohydride reduced lignin REL1 and compound 2 were also found as good trapping agents for the hydroxyl radicals. The degradation of EL1 was studied by measuring its fluorescence emission by comparison to the fluorescence of compound 2. The emission spectra indicate that some biphenyl phenolate anions in EL1 are reacting under UV/visible irradiation and some others, probably polyphenolic chromophores emitting less fluorescence, are formed.

Adsorption of Procion Blue MX-R dye from aqueous solutions by lignin chemically modified with aluminium and manganese

A macromolecule, CML, was obtained by purifying and carboxy-methylating the lignin generated from acid hydrolysis of sugarcane bagasse during bioethanol production from biomass. The CMLs complexed with Al(3+) (CML-Al) and Mn(2+) (CML-Mn) were utilised for the removal of a textile dye, Procion Blue MX-R (PB), from aqueous solutions. CML-Al and CML-Mn were characterised using Fourier transform infrared spectroscopy (FTIR), scanning differential calorimetry (SDC), scanning electron microscopy (SEM) and pHPZC. The established optimum pH and contact time were 2.0 and 5h, respectively. The kinetic and equilibrium data fit into the general order kinetic model and Liu isotherm model, respectively. The CML-Al and CML-Mn have respective values of maximum adsorption capacities of 73.52 and 55.16mgg(-1) at 298K. Four cycles of adsorption/desorption experiments were performed attaining regenerations of up to 98.33% (CML-Al) and 98.08% (CML-Mn) from dye-loaded adsorbents, using 50% acetone+50% of 0.05molL(-1) NaOH. The CML-Al removed ca. 93.97% while CML-Mn removed ca. 75.91% of simulated dye house effluents.

Tetraciclinas e glicilciclinas: uma visão geral

Tetracyclines exhibits activity to a broad range of Gram-negative and Gram-positive bacteria and this fact allied to the low toxicity, low cost, and the advantage of administration by oral route led to their indiscriminate use, which caused the appearance of bacterial resistance to these agents, wich has restricted its clinical utility, though new applications have emerged. On the other hand, the glycylcyclines, semi-synthetic products are similar to tetracyclines, which are active against many bacteria resistant to tetracycline and other classes of antibiotics. The purpose of this paper is to give an overview of this important class of antibiotics focusing on its coordination chemistry and possible applications.

Direct amperometric determination of tert-butylhydroquinone in biodiesel

The direct amperometric determination of tert-butylhydroquinone (TBHQ) in biodiesel at an unmodified glassy carbon electrode is reported. A biodiesel aliquot was added into an electrochemical cell containing a 75% (v/v) ethanol-water solution under stirring (with final concentration of 50 mmol L(-1) HClO(4)). The amperometric method involved the continuous application of three sequential potential pulses to the working electrode (700 mV for 300 ms, 0 mV for 100 ms and -50 mV for 1s). TBHQ was continuously monitored at the first (direct oxidation) and optionally at the second (reduction) potential pulse while the third potential pulse was applied for cleaning of the electrode surface. For comparison, the samples were also analyzed by high-performance liquid-chromatography and a good agreement between the results was verified. Recovery values for spiked samples were between 90% and 95% and the reproducibility of the proposed method was around 5% (n=5). The proposed method can be easily adapted for on-site analysis.

Coordenação de metais a antibióticos como uma estratégia de combate à resistência bacteriana

Antibiotic resistance has been growing at an alarming rate and consequently the arsenal of effective antibiotics against Gram-negative and Gram-positive bacteria has dropped dramatically. In this sense there is a strong need to produce new substances that not only have good spectrum of activity, but having new mechanisms of action. In this regard, this paper emphasizes the coordination of metals to antibiotics as a strategy for reversing antibiotic resistance and production of new drugs, with a special focus on quinolones, fluoroquinolones, sulfonamides and tetracyclines.

The photodegradation of lignins in the presence of hydrogen peroxide

Abstract The photodegradation of lignins in solutions containing hydrogen peroxide was studied. At basic pH, the reaction is at least seven times more efficient than in acid solution, where only hydroxyl radicals are formed. Evolution of carbon dioxide and loss of mass can be observed in basic solution. The role of certain functional groups was determined: α-carbonyls and phenols favour decomposition, and their reduction of derivatization leads to a decrease in the photodegradation efficiency. The presence of carboxylate groups and an increase in molecular weight lead to a decrease in the reaction efficiency. Evidence for the participation of singlet oxygen as a reactive species, in the reactions of alkaline pH, generated by the decomposition of hydrogen peroxide, is presented.

Photochemical bleaching of chemical pulps catalyzed by titanium dioxide

A two-stage process for photochemical bleaching of cellulosic pulps is presented. The first, based on the generation of oxygen active species by the photocatalytic action of TiOZ, and the second on the photochemical decomposition of hydrogen peroxide. Both stages are carried out under alkaline pH and at 85°C in aqueous suspension at a consistency of 5% The experiments were performed on kraft (Eucul~prus grandis, firms pinasfer and Pica muuiana), acesolv (E. grandis) and peroxyformic acid (E. grandis) pulps. The presence of TiO, as photocatalyst showed several advantages, such as reduction of reaction time, preservation of the pulp viscosity, increase of the selectivity during the photobleaching and decrease of the consumption of the bleaching chemicals. UV/Vis and FHR spectroscopies indicate a decrease of the coniferaldehyde structures during the TiO, photocatalyzed stage, whereas quinones entities were found to remain in the residual lignin even

Photoreactivity of lignin model compounds in the photobleaching of chemical pulps 2. Study of the degradation of 4-hydroxy-3-methoxy-benzaldehyde and two lignin fragments induced by singlet oxygen

The degradation induced by singlet oxygen (sensitized by methylene blue) of 4-hydroxy-3-methoxy-benzaldehyde (vanillin) and two lignin fragments (from rice husks and Eucalyptus grandis wood) in methanol solution was investigated. For vanillin, a kinetic study was performed using three different pH values. The rate of degradation of vanillin was highly dependent on the pH due to the ionization of phenol groups. In addition, the physical quenching of singlet oxygen by vanillin was more sensitive than the chemical reaction to an increase in pH. The degradation of lignin under the influence of singlet oxygen was influenced by the existence of free phenol groups. Conjugated carbonyl groups were formed and their quantity was higher than that expected from the consumption of phenols during irradiation. This was attributed to the participation of benzylarylether structural elements in the photodegradation process.

Studies on fluorescence of cellulosics

Abstract Steady-state fluorescence emission spectra of various celluloses were measured at an excitation wavelength of 320 nm. Various spectra recorded in the solid state were compared: (1) ECF bleached papers made of hardwood, the anhydroglucose units of which were chemically modified at C1 and C6 or C2 and C3 positions with carboxylic groups; (2) microcrystalline cellulose; (3) cotton linters; and (4) delignified sisal fibers (mercerized or not). Fluorescence emission was quite independent of the carboxylic acid content and average molecular weight (determined by viscosimetry) of the cellulose polymers. Microcrystalline cellulose (Avicel), cotton linters, and mercerized delignified sisal cellulose were acetylated in homogeneous medium (DMAc/LiCl as solvent system) to obtain soluble polymers in dichloromethane for comparison of spectra recorded in the solid and liquid states. Fluorescence of cellulose acetates in solution (CH2Cl2) and in the solid state was compared under similar experimental conditions to non-esterified celluloses in the solid state. The importance of the solid state for fluorescence emission could be demonstrated. Fluorophores are present in minute amounts in the polymer and their favorable energy transfer for excitation in the solid state likely enhances fluorescence emission. Among numerous fluorophores, dityrosine appeared to be a good candidate for fluorescence because it displayed emission in the fluorescence range of cellulose. Dityrosine is an amino acid involved in the lignification of non-woody plants. Mercerized sisal impregnated with tyrosine in the presence of peroxidase and hydrogen peroxide did not show enhanced emission, in contrast to para-hydroxycinnamic acid (coumaric acid), which is also involved in the lignification process at least for non-woody plants. The origin of cellulose fluorescence remains uncertain and appears to have several origins. This study clearly underlines the importance of the solid state for enhancing fluorophore emission.

The use of fluorescent probes in the characterization of lignin: the distribution, by energy, of fluorophores in Eucalyptus grandis lignin

Four fluorescent probes (biphenyl, naphthalene, pyrene and phenanthrene) were used to map the energy distribution of the structural units present in lignin fragments from Eucalyptus grandis wood. This distribution shows that these fragments present two regions with a high concentration of chromophores, one between 418 and 385 kJ/mol, and the other below 322 kJ/mol. When this lignin was treated with NaBH4, the two more intense regions occurs between 418 and 346 kJ/mol, followed by a significant increase in the concentration of chromophores in almost all the studied energy range. Lifetime distributions present a bimodal pattern, with two typical peak lifetime values, the first of 1 :36 0:17 ns, with a relative amplitude above 80%, and the second of 8:48 2:32 ns, for both species, with some fluctuation for different em. The synchronous spectra indicates, for this lignin, at least three broad spectral envelopes, with a large superposition of the emission maxima. The results indicate the existence of at least three most representative fluorophores, most probably due to biphenyl, coniferyl alcohol and stilbene structures, with varying substituents. The majority of the fluorescence complexity of this lignin seems to be associated with the inhomogeneous emission decay kinetics associated with ground state heterogeneity, due to the complex mixture of the different fluorophores, on which are superimposed different distributions of environments.