Astaxanthinogenesis in the yeastPhaffia rhodozyma

Astaxanthin is a diketo-dihydroxy-carotenoid produced byPhaffia rhodozyma, a basidiomicetous yeast. A low-cost fermentation medium consisting of raw sugarcane juice and urea was developed to exploit the active sucrolytic/urelolytic enzyme apparatus inherent to the yeast. As compared to the beneficial effect of 0.1 g% urea, a ready nitrogen source, mild phosphoric pre inversion of juice sucrose to glucose and fructose, promptly fermentable carbon sources, resulted in smaller benefits. Corn steep liquor (CSL) was found to be a valuable supplement for both yeast biomass yield (9.2 g dry cells/L) and astaxanthin production (1.3 mg/g cells). Distillery effluent (vinace), despite only a slightly positive effect on yeast growth, allowed for the highest pigment productivity (1.9 mg/g cells). Trace amounts of Ni² (1 mg/L, as a cofactor for urease) resulted in controversial effects, namely, biomass decrease and astaxanthin increase, with no effect on the release (and uptake) of ammonium ion from urea. Since the synthesized astaxanthin is associated with the yeast cell and the pigment requires facilitated release for aquaculture uses (farmed fish meat staining), an investigation of the yeast cell wall was undertaken using detergent-treated cells. The composition of the rigid yeast envelope was found to be heterogeneous. Its partial acid or enzymatic depolymerization revealed glucose and xylose as common monomeric units of the cell-wall glycopolymers. Yeast cell-wall partial depolymerization with appropriate hydrolases may improve the pigment bioavailability for captive aquatic species and poultry.

     

Synthesis of a new decahydrohexapyrrin of biosynthetic interest

A new decahydrohexapyrrin containing a tert-butoxycarbonylbilane of type III was prepared applying a convergent type synthesis. The order of the side chains of the tert-butoxycarbonylbilane belonging to this oligopyrrole corresponds to that of a type HI uroporphyrinogen. A symmetric hexapyrrol dilactam was formed as a by product of the synthesis.     

Nitric oxide interaction with cytochrome c' and its relevance to guanylate cyclase. Why does the iron histidine bond break?

Soluble guanylate cyclase (sGC), the mammalian receptor for nitric oxide (NO), is a heme protein with a histidine as the proximal ligand. Formation of a five-coordinate heme-NO complex with the associated Fe-His bond cleavage is believed to trigger a conformational change that activates the enzyme and transduces the NO signal. Cytochrome c' (cyt c') is a protobacteria heme protein that has several similarities with sGC, including the ability to form a five-coordinate NO adduct and the fact that it does not bind oxygen. Recent crystallographic characterization of cyt c' from Alcaligenes xylosoxidans (AXCP) has yielded the discovery that exogenous ligands are able to bind to the Fe center from either side of the porphyrin plane. In this paper, we explore the molecular basis of the NO interaction with AXCP using hybrid quantum-classical simulation techniques. Our results suggest that Fe-His bond breaking depends not only on the iron-histidine bond strength but also on the existence of a local minimum conformation of the protein with the histidine away from the iron. We also show that AXCP is a useful paradigm for NO interaction with heme proteins, particularly regarding the activation/deactivation mechanism of sGC. The results presented here fully support a recently proposed model of sGC activation in which NO is not only the iron ligand but also catalyzes the activation step.     

Unraveling the primary mechanisms leading to synchronization response in dissimilar oscillators

We study how the phenomenon of response to synchronization arises in sets of pulse-coupled dissimilar oscillators. One of the sets is constituted by oscillators that can easily synchronize. Conversely, the oscillators of the other set do not synchronize. When the elements of the first set are not synchronized, they induce oscillation death in the constituents of the second set. By contrast, when synchronization is achieved in oscillators of the first set, those of the second set recover their oscillatory behavior and thus, responding to synchronization. Additionally, we found another interesting phenomenon in this type of systems, namely, a new control of simultaneous firings in a population of similar oscillators attained by means of the action of a dissimilar oscillator.     

Electrochemical template synthesis of adherent polyaniline thin films with tubular structure

The synthesis of nano and microstructured thin polyaniline (PANI) films by a simple and very efficient template-assisted method is presented. This work shows the synthesis and characterization of acoustically rigid thin films structured at nanotubular shape by using methyl orange (MO) as a template-assisted system. The amount of the tubes can be easily controlled by the charge passed. The morphology for different films growth was characterized by field emission scanning electron microscopy (FESEM), Atomic force microscopy (AFM), and quartz crystal microbalance with dissipation mode (QCM-D). Raman spectroscopy results show important changes in the conformational PANI chain of the tubular material compare with a non-tubular one that provokes the increase of bipolarons population. This should be responsible by some changes in the electrochemical behavior of tubular film compared with the granular material, due to the higher conductivity when the emeraldine form starts to be formed.     

Enantiomeric high‐performance liquid chromatography resolution and absolute configuration of 6β‐benzoyloxy‐3α‐tropanol

The absolute configuration of the naturally occurring isomers of 6β‐benzoyloxy‐3α‐tropanol ( 1 ) has been established by the combined use of chiral high‐performance liquid chromatography with electronic circular dichroism detection and optical rotation detection. For this purpose (±)‐ 1 , prepared in two steps from racemic 6‐hydroxytropinone ( 4 ), was subjected to chiral high‐performance liquid chromatography with electronic circular dichroism and optical rotation detection allowing the online measurement of both chiroptical properties for each enantiomer, which in turn were compared with the corresponding values obtained from density functional theory calculations. In an independent approach, preparative high‐performance liquid chromatography separation using an automatic fraction collector, yielded an enantiopure sample of _OR(+)‐ 1 whose vibrational circular dichroism spectrum allowed its absolute configuration assignment when the bands in the 1100–950 cm^‐1 region were compared with those of the enantiomers of esters derived from 3α,6β‐tropanediol. In addition, an enantiomerically enriched sample of 4 , instead of _OR(±)‐ 4 , was used for the same transformation sequence, whose high‐performance liquid chromatography follow‐up allowed their spectroscopic correlation. All evidences lead to the _OR(+)‐(1S,3R,5S,6R) and _OR(?)‐(1R,3S,5R,6S) absolute configurations, from where it follows that samples of 1 isolated from Knightia strobilina and Erythroxylum zambesiacum have the _OR(+)‐(1S,3R,5S,6R) absolute configuration, while the sample obtained from E. rotundifolium has the _OR(?)‐(1R,3S,5R,6S) absolute configuration.     

Voltammetric Determination of Cocaine Using Carbon Screen Printed Electrodes Chemically Modified with Uranyl Schiff Base Films

Chemically modified screen printed electrodes (CM‐SPE) using [UO₂(4‐MeOSalen)(H₂O)] ? H₂O films were employed in the voltammetric determination of cocaine. The chemical modification was performed by dip coating electrode surfaces (carbon, gold, and platinum) with methanolic solution containing the Schiff base complex with subsequent drying step at room temperature. The optimized amount of the chemical modifier over the working electrode was found to be 2.39 µg mm^?2 (geometric area). The voltammetric measurements were carried out in 50 : 50 v/v methanol:water solution containing 0.05 mol L^?1 KCl and 0.1 mol L^?1 LiCl as a supporting electrolyte without oxygen elimination by inert gas flow. The best results were obtained with carbon electrodes. Cocaine exhibits a well defined irreversible anodic peak current (i_pa) at a potential (E_pa) of 0.85 V vs Ag/AgCl. The current is directly proportional to the drug concentration. An optimal accumulation potential (E_prec), and time (t_prec) of ?0.80 V (vs Ag/AgCl), and 120 s, respectively, were determined. The linear dependence of i_pa with square root of scan rate (υ) indicates that the mass transport at the electrode surface is controlled by diffusion. An optimized scan rate of 100 mV s^?1 was obtained for analytical purposes. A limit of detection (LOD) and limit of quantification (LOQ) in 110 and 390 µmol L^?1, respectively, with intra and inter‐day repeatability of 2.61 % and 3.77 %, respectively, were obtained. In interference studies the proposed method demonstrated high specificity for cocaine in the presence of morphine and 3,4‐methylenedioxymethanphetamine. The above results demonstrate that this method provides a fast and low cost procedure for determination of cocaine in trace levels.     

Trapping and characterization of a reaction intermediate in carbapenem hydrolysis by B. cereus metallo-beta-lactamase

Metallo-beta-lactamases hydrolyze most beta-lactam antibiotics. The lack of a successful inhibitor for them is related to the previous failure to characterize a reaction intermediate with a clinically useful substrate. Stopped-flow experiments together with rapid freeze-quench EPR and Raman spectroscopies were used to characterize the reaction of Co(II)-BcII with imipenem. These studies show that Co(II)-BcII is able to hydrolyze imipenem in both the mono- and dinuclear forms. In contrast to the situation met for penicillin, the species that accumulates during turnover is an enzyme-intermediate adduct in which the beta-lactam bond has already been cleaved. This intermediate is a metal-bound anionic species with a novel resonant structure that is stabilized by the metal ion at the DCH or Zn2 site. This species has been characterized based on its spectroscopic features. This represents a novel, previously unforeseen intermediate that is related to the chemical nature of carbapenems, as confirmed by the finding of a similar intermediate for meropenem. Since carbapenems are the only substrates cleaved by B1, B2, and B3 lactamases, identification of this intermediate could be exploited as a first step toward the design of transition-state-based inhibitors for all three classes of metallo-beta-lactamases.     

Comparative analysis of nanocomposites based on polypropylene and different montmorillonites

Nanocomposites of polypropylene (PP) were prepared by melt mixing using maleic anhydride modified polypropylene (PPg) and different organophilic montmorillonites (OMMT). The selected organo-modified clays differ in their initial particle size, amount and type of surfactant and/or their cation-exchange capacity. All composites have 80, 15 and 5 wt% of PP, PPg and OMMT, respectively. The materials were characterized using TGA, XRD, SEM and rotational rheometry. Cloisite 15A, Cloisite 93A, Nanomer I44 and a bentonite modified with octadecylammonium (B18) display intercalation and exfoliation after mixing and annealing and produce nanocomposites with different degrees of ‘solid-like’ rheological behavior. The composites based in Cloisite 15A and Nanomer I44, which use the same intercalant, show very similar phase structure and rheological response, regardless of the origin and initial characteristics of the clays. These nanocomposites are the most affected by the thermal history during rheological characterization in the molten state. On the other hand, Cloisite 10A and Cloisite 30B display collapse of the silicate layers after compounding with no evidence of exfoliation.