527 research outputs found
Catalytic enantioselective alkene epoxidation using novel spirocyclic N-carbethoxy-azabicyclo[3.2.1]octanones
Compromising Anonymous Communication Systems Using Blind Source Separation
We propose a class of anonymity attacks to both wired and wireless anonymity networks. These attacks are based on the blind source separation algorithms widely used to recover individual signals from mixtures of signals in statistical signal processing. Since the philosophy behind the design of current anonymity networks is to mix traffic or to hide in crowds, the proposed anonymity attacks are very effective. The flow separation attack proposed for wired anonymity networks can separate the traffic in a mix network. Our experiments show that this attack is effective and scalable. By combining the flow separation method with frequency spectrum matching, a passive attacker can derive the traffic map of the mix network. We use a nontrivial network to show that the combined attack works. The proposed anonymity attacks for wireless networks can identify nodes in fully anonymized wireless networks using collections of very simple sensors. Based on a time series of counts of anonymous packets provided by the sensors, we estimate the number of nodes with the use of principal component analysis. We then proceed to separate the collected packet data into traffic flows that, with help of the spatial diversity in the available sensors, can be used to estimate the location of the wireless nodes. Our simulation experiments indicate that the estimators show high accuracy and high confidence for anonymized TCP traffic. Additional experiments indicate that the estimators perform very well in anonymous wireless networks that use traffic padding
Information Leakage as a Model for Quality of Anonymity Networks
Measures for anonymity in systems must be on one hand simple and concise, and on the other hand reflect the realities of real systems. Such systems are heterogeneous, as are the ways they are used, the deployed anonymity measures, and finally the possible attack methods. Implementation quality and topologies of the anonymity measures must be considered as well. We therefore propose a new measure for the anonymity degree, that takes into account these various. We model the effectiveness of single mixes or of mix networks in terms of information leakage, and we measure it in terms of covert channel capacity. The relationship between the anonymity degree and information leakage is described, and an example is shown
Compromising Anonymous Communication Systems Using Blind Source Separation
We propose a class of anonymity attacks to both wired and wireless anonymity networks. These attacks are based on the blind source separation algorithms widely used to recover individual signals from mixtures of signals in statistical signal processing. Since the philosophy behind the design of current anonymity networks is to mix traffic or to hide in crowds, the proposed anonymity attacks are very effective. The flow separation attack proposed for wired anonymity networks can separate the traffic in a mix network. Our experiments show that this attack is effective and scalable. By combining the flow separation method with frequency spectrum matching, a passive attacker can derive the traffic map of the mix network. We use a nontrivial network to show that the combined attack works. The proposed anonymity attacks for wireless networks can identify nodes in fully anonymized wireless networks using collections of very simple sensors. Based on a time series of counts of anonymous packets provided by the sensors, we estimate the number of nodes with the use of principal component analysis. We then proceed to separate the collected packet data into traffic flows that, with help of the spatial diversity in the available sensors, can be used to estimate the location of the wireless nodes. Our simulation experiments indicate that the estimators show high accuracy and high confidence for anonymized TCP traffic. Additional experiments indicate that the estimators perform very well in anonymous wireless networks that use traffic padding
Novel Ketone Catalysts for Asymmetric Epoxidation of Alkenes
Chiral non-racemic ketones have been shown to be powerful promoters of
asymmetric induction in epoxidation reactions with alkenes in the presence of
Oxone®. However, the catalyst structural features are specific for the class of olefins
used as substrates. Up to date, excellent results have been achieved for trans- and trisubstituted
alkenes, while terminal alkenes still represent one of the most challenging
areas. Much work needs to be done in developing suitable catalysts to lead to high
enantioselectivities.
Previous work in Armstrong’s group identified ketone catalysts based on
oxabicyclo[3.2.1]octan-3-ones and on the N-carboethoxytropinone skeleton, which
performed very well in enantioselective epoxidation of trans- substituted olefins (up
to 93% ee for E-stilbene). This thesis describes the synthesis and the efficiency
towards alkene epoxidations of novel α,α-disubstituted ketones based on the Ncarboethoxytropinone
scaffold. In particular, encouraged by the positive results
achieved by Shi’s group for terminal alkenes, several spiro-motifs α to the carbonyl
have been investigated. A slight improvement was observed towards the challenging
terminal olefins compared to the monosubstituted ketone analogues, whilst very high
ee were maintained for trans- substituted alkenes. However, to our surprise, only
minor changes in enantioselectivity were observed from modifications of the steric
and electronic properties of this spiro-motif in the ketone catalyst. Further axial or
equatorial α' functionalisation was explored as a possible strategy to increase
enantioselectivity towards terminal and 1,1-disubstituted alkenes. Indeed, significant
improvements were achieved in enantioselective epoxidation of styrene (up to 50%
ee) and a-methyl styrene (up to 39% ee)
Information Leakage as a Model for Quality of Anonymity Networks
Measures for anonymity in systems must be on one hand simple and concise, and on the other hand reflect the realities of real systems. Such systems are heterogeneous, as are the ways they are used, the deployed anonymity measures, and finally the possible attack methods. Implementation quality and topologies of the anonymity measures must be considered as well. We therefore propose a new measure for the anonymity degree, that takes into account these various. We model the effectiveness of single mixes or of mix networks in terms of information leakage, and we measure it in terms of covert channel capacity. The relationship between the anonymity degree and information leakage is described, and an example is shown
Tertiary and quaternary effects in the allosteric regulation of animal hemoglobins
In the last decade, protein allostery has experienced a major resurgence, boosted by the extension of the concept to systems of increasing complexity and by its exploitation for the development of drugs. Expansion of the field into new directions has not diminished the key role of hemoglobin as a test molecule for theory and experimental validation of allosteric models. Indeed, the diffusion of hemoglobins in all kingdoms of life and the variety of functions and of quaternary assemblies based on a common tertiary fold indicate that this superfamily of proteins is ideally suited for investigating the physical and molecular basis of allostery and firmly maintains its role as a main player in the field. This review is an attempt to briefly recollect common and different strategies adopted by metazoan hemoglobins, from monomeric molecules to giant complexes, exploiting homotropic and heterotropic allostery to increase their functional dynamic range
Immobilization of allantoinase for the development of an optical biosensor of oxidative stress states
Allantoin, the natural end product of purine catabolism in mammals, is non-enzymatically produced from the scavenging of reactive oxygen species through the degradation of uric acid. Levels of allantoin in biological fluids are sensitively influenced by the presence of free radicals, making this molecule a candidate marker of acute oxidative stress in clinical analyses. With this aim, we exploited allantoinase—the enzyme responsible for allantoin hydrolization in plants and lower organisms—for the development of a biosensor exploiting a fast enzymatic-chemical assay for allantoin quantification. Recombinant allantoinase was entrapped in a wet nanoporous silica gel matrix and its structural properties, function, and stability were characterized through fluorescence spectroscopy and circular dichroism measurements, and compared to the soluble enzyme. Physical immobilization in silica gel minimally influences the structure and the catalytic efficiency of entrapped allantoinase, which can be reused several times and stored for several months with good activity retention. These results, together with the relative ease of the sol-gel preparation and handling, make the encapsulated allantoinase a good candidate for the development of an allantoin biosensor
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