Combined Dynamic Model for the Kinetics of Electron Transfer from Cytochrome to a Bacteriochlorophill Dimer in Reaction Centers of Rps. Sulfoviridis

The electron transfer from the heme of cytochrome c to the bacteriochlorophill dimer in reaction centers of photosynthetic purple bacteria Rps. sulfoviridis is studied by laser flash photolysis at 40–296 K in conditions where one, two, or three cytochrome hemes are chemically reduced. In the model used for the electron transfer kinetics, the protein relaxation is described with a temperature-independent oscillatory coordinate and a temperature-dependent diffusion coordinate, with the protein dielectric relaxation times widely distributed along the diffusion coordinate. It is found that all the protein complexes can be divided into proteins with fast (k _et = 10⁷ to 10^–4 s^–1) and slow (k _et 100 s^–1) electron transfer. These populations presumably differ by the protonation state of the functional group. The contribution of the oscillatory and diffusion coordinates alters, which severely affects k _et. Parameters V _ab, G, , ₀, and for these reactions are determined.     

Directed evolution of the dioxygenase complex for the synthesis of furanone flavor compounds

Herein we report a new preparation of 4-hydroxy-2,5-dimethyl-2,3-dihydrofuran-3-one, the flavor compound strawberry furanone, based on a ‘green’ approach with a minimum number of steps. The first step is an enzymatic dioxygenation of p-xylene to form cyclohexadiene-cis-diol, followed by ring opening via ozonolysis, and ring closure to form the furanone. In efforts to improve the efficiency of the enzymatic step, a directed evolution approach was taken to increase the substrate specificity and selectivity of the toluene dioxygenase enzyme system.     

Performance of a sound card as data acquisition system and a lock-in emulated by software in capillary electrophoresis

The performance of fluorescence detectors in capillary electrophoresis is maximized when the excitation light intensity is modulated in time with optimal frequencies. This is especially true when photomultiplier tubes are used to detect the fluorescent light. The photomultiplier tube amplified raw output signal can in principle be captured directly by a personal computer sound card (PCSC) and processed by a lock-in emulated by software. This possibility is demonstrated in the present work and the performance of this new setup is compared with a traditional data acquisition system. The results obtained with this “PCSC and lock-in emulated by software” were of the same quality or even better compared to that obtained by conventional time integrators (Boxcars) and data acquisition boards. With PCSC the limits of detection (LOD) found for both naphthalene-2,3-dicarboxaldehyde-derivatized tyrosine and alanine were 3.3 and 3.5 fmol (injection of 5 nL of samples at 0.66 and 0.70 μmol/L), respectively. This is at least three times better compared to conventional systems when light emitting diodes (LEDs) are used as the excitation source in fluorescence detectors. The PCSC linear response range was also larger compared to conventional data acquisition boards. This scheme showed to be a practical and convenient alternative of data acquisition and signal processing for detection systems used in capillary electrophoresis.     

Optimization of acid hydrolysis of sugarcane bagasse and investigations on its fermentability for the production of xylitol by Candida guilliermondii

The dilute-acid hydrolysis of sugarcane bagasse was optimized using a statistical experimental design resulting in hydrolysates containing 57.25 g/L of xylose, which were fermented with a high inoculum concentration (10 g/L of the yeast Candida guilliermondii IM/UFRJ 50088). The addition of urea reduced the time of conversion (t _C) to 75 h (without nitrogen source addition t _C>127 h), and, consequently, improving the rates of xylitol bioproduction. Fermentator experiments, using the optimized conditions, resulted in enhanced conversion rates, reducing t _C to 30 h. The stability of the yeast in the hydrolysate was also verified in a 480-h cultivation.     

Antifungal activity of crown ethers

Some crown ethers were found to show significant antifungal activity against some wood-decay fungi, phytopathogenic fungi and eumycetes,Trichophytons for dermatomycosis. Their toxicity was evaluated by the paper disc method as well as by determining the values of ED₅₀, i.e., the concentration which inhibits the mycelium growth by 50%. The fungi examined areTyromyces palustris, Picnoporous coccineus, Coriolous versicolor, Pyricularia filamentosa, Fusarium sp., Trichophyton rubrum, Trichophyton sp., etc. Among the 26 crown ethers tested, 3,5-di-t-butyl-benzo-15-crown-5 showed relatively high activity, the highest ED₅₀ value of which being 8 M or 3 ppm. Other alkylbenzocrown ethers, dicyclohexyl crown ethers and Kryptofix 22DD also showed considerable activity. On the other hand, unsubstituted crown ethers, benzocrown ethers with a polar substituent, Kryptofix 222B and Kryptofix 221 were inactive.     

Synthesis of 4‐(trihalomethyl)dipyrimidin‐2‐ylamines from β‐alkoxy‐α,β‐unsaturated trihalomethyl ketones

The synthesis of a novel series of twelve 4‐(trihalomethyl)dipyrimidin‐2‐ylamines, from the cyclo‐condensation reaction of 4‐(trichloromethyl)‐2‐guanidinopyrimidine, with β‐alkoxyvinyl trihalomethyl ketones, of general formula: X₃C‐C(O)‐C(R²)=C(R¹)‐OR, where: X = F, Cl; R = Me, Et, ‐(CH₂)₂‐, ‐(CH₂)₃‐; R¹ = H, Me; R² = H, Me, ‐(CH₂)₂‐, ‐(CH₂)₃‐, is reported. The reactions were carried out in acetonitrile under reflux for 16 hours, leading to the dipyrimidin‐2‐ylamines in 65‐90% yield. Depending on the substituents of the vinyl ketone, tetrahydropyrimidines or aromatic pyrimidine rings were obtained from the cyclization reaction. When X = Cl, elimination of the trichloromethyl group was observed during the cyclization step. The structure of 4‐(trihalomethyl)dipyrimidin‐2‐ylamines was studied in detail by ¹H‐, ¹³C‐ and 2D‐nmr spectroscopy.     

Fracture mechanisms in rigid core-shell particle modified high performance epoxies

The fracture mechanisms of a high performance epoxy system modified with two types of preformed rigid core-shell particles (RCSP) were investigated. The use of the preformed RCSP anables the control of the dispersion of the toughener phase in the epoxy, which, in turn, allows the mechanical properties of the modified epoxy to be optimized. The toughening effect via the RCSP modification is found to be as good as that via the core-shell rubber modification. The moduli andT _g of these RCSP-modified epoxies are virtually unaltered via the RCSP modification, when compared with the neat epoxy resin equivalent. The toughening mechanisms in these toughened systems appear to be predominantly crack deflection, crack bifurcation, and microcracking. Approaches for effective toughening of high performance polymers via rigid polymers are discussed.     

Site-selective aqueous C–H acylation of tyrosine-containing oligopeptides with aldehydes

The development of useful synthetic tools to label amino acids within a peptide framework for the ultimate modification of proteins in a late-stage fashion is a challenging task of utmost importance within chemical biology. Herein, we report the first Pd-catalyzed C–H acylation of a collection of Tyr-containing peptides with aldehydes. This water-compatible tagging technique is distinguished by its site-specificity, scalability and full tolerance of sensitive functional groups. Remarkably, it provides straightforward access to a high number of oligopeptides with altered side-chain topology including mimetics of endomorphin-2 and neuromedin N, thus illustrating its promising perspectives toward the diversification of structurally complex peptides and chemical ligation.

A novel Pd-catalyzed C–H acylation reaction with readily available aldehydes under an aqueous environment towards the assembly of non-protegenic acylated Tyr-containing oligopeptides is presented.     

Direct detection of renal function markers using microchip CE with pulsed electrochemical detection

Creatinine, creatine, and uric acid are three important compounds that are measured in a variety of clinical assays, most notably for renal function. Traditional clinical assays for these compounds have focused on the use of enzymes or chemical reactions. Electrophoretic microchips have the potential to integrate separation power of capillary electrophoresis with devices that are small, portable, and have the speed of conventional sensors. The development of a microchip CE system for the direct detection of creatinine, creatine, and uric acid is presented. The device uses pulsed amperometric detection (PAD) to detect the nitrogen-containing compounds as well as the easily oxidizable uric acid. Baseline separation of creatinine, creatine and uric acid was achieved using 30 mM borate buffer (pH = 9.4) in less than 200 s. Linear calibration curves were obtained with limits of detection of 80 microM, 250 microM and 270 microM for creatinine, creatine and uric acid respectively. An optimization of the separation conditions and a comparison of PAD with other amperometric detection modes is also shown. Finally, analysis of a real urine sample is presented with validation of creatinine concentrations using a clinical assay kit based on the Jaffé reaction.     

AlPO4?ZrO2 catalysts, II. Synthesis, textural properties and crystal structure of systems obtained in ethylene oxide

The effects of surface dehydration on textural properties, crystallinity and the structure of AlPO₄–ZrO₂ (weight ratio AlPO₄/ZrO₂=3) systems precipitated with ethylene oxide have been studied by N₂ adsorption and XRD measurements. The increase in calcination temperature in the range 773–1273 K decreases the textural parameters as a consequence of AlPO₄ crystallization to the tridymite form.

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, AlPO₄–ZrO₂ ( AlPO₄/ZrO₂=3), , N₂ - . 773 1273 , AlPO₄ .