An Anionic Ring Locked into an Anionic Axle: A Metastable Rotaxane with Chemically Activated Electrostatic Stoppers

The use of the electrostatic stoppers concept in the field of mechanically interlocked molecules is reported; these stoppers are chemically sensitive end groups on a linear guest molecule that allows for the conversion of a pseudo-rotaxane species into a rotaxane complex by a change in the medium acidity. The chemical stimulus causes the appearance of negative charges on both ends of the linear component, passing from cationic to anionic, and causing a significant ring-to-axle electrostatic repulsion. This phenomenon has two different and simultaneous effects: 1) destabilizes the complex as a consequence of confining an anionic ring into an anionic axle, and 2) increases the dissociation energy barrier, thus impeding ring extrusion. This newly formed metastable rotaxane species is resistant to solvent and temperature effects and performs as a two-state degenerated molecular shuttle in solution.     

A Bonnet theorem for isometric immersions into products of space forms

We prove a Bonnet theorem for isometric immersions of semi-Riemannian manifolds into products of semi-Riemannian space forms. Namely, we give necessary and sufficient conditions for the existence and uniqueness (up to an isometry of the ambient space) of an isometric immersion of a semi-Riemannian manifold into a product of semi-Riemannian space forms.     

A Spectroscopy-based Methodology for Rapid Screening and Characterization of Phytochrome Photochemistry in Search of Pfr-favored Variants

Phytochromes are photosensitive proteins with a covalently bound open-chain chromophore that can switch between two principal states: red light absorbing Pr and far-red light absorbing Pfr. Our group has previously shown that the bacteriophytochrome from Xanthomonas campestris pv. campestris (XccBphP) is a bathy-like phytochrome that uses biliverdin IXα as a co-factor and is involved in bacterial virulence. To date, the XccBphP crystal structure could only be solved in the Pr state, while the structure of its Pfr state remains elusive. The aims of this work were to develop an efficient screening methodology for the rapid characterization and to identify XccBphP variants that favor the Pfr form. The screening approach developed here consists in analyzing the UV-Vis absorption behavior of clarified crude extracts containing recombinant phytochromes. This strategy has allowed us to quickly explore over a hundred XccBphP variants, characterize multiple variants and identify Pfr-favored candidates. The high-quality data obtained enabled not only a qualitative, but also a quantitative characterization of their photochemistry. This method could be easily adapted to other phytochromes or other photoreceptor families.     

Modeling the Kinetics of Complex Systems: Enzymatic Hydrolysis of Lignocellulosic Substrates

Lignocellulosic biomass is mainly composed of cellulose, hemicellulose, and lignin. Fuzzy logic, in turn, is a branch of many-valued logic based on the paradigm of inference under vagueness. This paper presents a methodology, based on computational intelligence, for modeling the kinetics of a complex reactional system. The design of a fuzzy interpolator to model cellulose hydrolysis is reported, within the perspective of applying kinetic models in bioreactor engineering. Experimental data for various types of lignocellulosic materials were used to develop the interpolator. New experimental data from the enzymatic hydrolysis of a synthetic substrate, on the other hand, were used to validate the methodology. The accuracy of the results indicates that this is a promising approach to extend the application of models fitted for specific situations to different cases, thus enhancing their generality.     

The production of hydrocarbons from photoautotrophic growth ofDunaliella salina 1650

Microalga,Dunaliella salina 1650 was selected to produce hydrocarbons that may possibly substitute for fossil fuels in the near future. It can produce 0.22 (mg/L) of hydrocarbons over 20 d batch cultivation, maintaining 1.32 (g-dry wt./L) of cell density. Its productivity was similar to that fromBotryococcus braunii, which was known to economically produce liquid fuels. Optimal growth conditions for the alga were also determined as pH 7.2, 28°C, and 0.00034 (Kcal/cm²/h) of light intensity. It was shown that the hydrocarbon production from the alga was closely related to cell growth, except for the later periods of batch cultivation. Better hydrocarbon production was observed during light periods in light/dark cycle cultivation. Under chemostat conditions, maximum steady cell concentration was maintained as 1.1 (g-dry wt./L) at 0.12 (1/d) of dilution rate. The system reached to the steady state after 30 d of the cultivation. The maximum specific hydrocarbon production rate, 0.024 (mg/cell/d) was also obtained under this condition. It proves that the hydrocarbon production fromD. salina 1650 can compete with that fromB. braunii. Index Entries: Algal hydrocarbon production; photoautotrophic growth;Dunaliella salina     

MKPLS approach: switching strategies for the non-linear multi-kernel PLSR

We present two strategies to determine the kernel switching order for the non-linear multi-kernel PLSR algorithm. The multi-kernel PLS (MKPLS) algorithm builds upon a one kernel PLSR which uses a kernel matrix to hold the inner products of the projection of the independent data set onto a feature space. After building a PLSR model, MKPLS deflates the kernel matrix so that only that part which cannot be predicted by the model remains. This remainder is projected onto a different feature space and a new PLSR model is built. The switching algorithms presented for this approach address two questions: which kernel should be used at each iteration and; how many factors should be extracted before switching to another kernel.     

On the Singularities of the Exponential Map in Infinite Dimensional Riemannian Manifolds

Using symplectic techniques and spectral analysis of smooth paths of self-adjoint operators, we characterize the set of conjugate instants along a geodesic in an infinite dimensional Riemannian Hilbert manifold.The last three authors are partially sponsored by CNPq.