Rui M. Rocha

Interactions of Flavonoids with Iron and Copper Ions: A Mechanism for their Antioxidant Activity

The metal chelating properties of flavonoids suggest that they may play a role in metal-overload diseases and in all oxidative stress conditions involving a transition metal ion. A detailed study has been made of the ability of flavonoids to chelate iron (including Fe 3+ ) and copper ions and its dependence of structure and pH. The acid medium may be important in some pathological conditions. In addition, the ability of flavonoids to reduce iron and copper ions and their activity-structure relationships were also investigated. To fulfil these objectives, flavones (apigenin, luteolin, kaempferol, quercetin, myricetin and rutin), isoflavones (daidzein and genistein), flavanones (taxifolin, naringenin and naringin) and a flavanol (catechin) were investigated. All flavonoids studied show higher reducing capacity for copper ions than for iron ions. The flavonoids with better Fe 3+ reducing activity are those with a 2,3-double bond and possessing both the catechol group in the B-ring and the 3-hydroxyl group. The copper reducing activity seems to depend largely on the number of hydroxyl groups. The chelation studies were carried out by means of ultraviolet spectroscopy and electrospray ionisation mass spectrometry. Only flavones and the flavanol catechin interact with metal ions. At pH 7.4 and pH 5.5 all flavones studied appear to chelate Cu 2+ at the same site, probably between the 5-hydroxyl and the 4-oxo groups. Myricetin and quercetin, however, at pH 7.4, appear to chelate Cu 2+ additionally at the ortho -catechol group, the chelating site for catechin with Cu 2+ at pH 7.4. Chelation studies of Fe 3+ to flavonoids were investigated only at pH 5.5. Only myricetin and quercetin interact strongly with Fe 3+ , complexation probably occurring again between the 5-hydroxyl and the 4-oxo groups. Their behaviour can be explained by their ability to reduce Fe 3+ at pH 5.5, suggesting that flavonoids reduce Fe 3+ to Fe 2+ before association.

MEASUREMENT OF RELATIVE ANTIOXIDANT ACTIVITY OF COMPOUNDS : A METHODOLOGICAL NOTE

The relative activities of some hydrogen-donating antioxidants were assessed by comparing their activities with that of Trolox (Trolox equivalent antioxidant capacity, TEAC) for scavenging the ABTS radical cation (ABTS.+) generated in the aqueous phase. We have verified, however, that TEAC values may change with the concentration of compounds and with the measuring times used. Not withstanding, TEAC values do not differ significantly if the compounds have kinetic curves of ABTS.+ formation similar to that of Trolox. This is the case with ascorbic acid, whose TEAC values, determined by using five concentrations at three different measuring times, are very close. For the flavonoids studied (catechin, rutin, naringenin and silibinin) which have kinetic curves of ABTS.+ formation different from that of Trolox, the TEAC values decrease with increasing concentrations of the compounds for each measuring time, and increase with increasing measuring times for each concentration. In the present study, we conclude that, in order to evaluate relative antioxidant activities of compounds by the ABTS assay, it is essential to perform kinetic studies to assess scavenging of ABTS.+ by these compounds. Therefore, when the TEAC values of compounds are determined for more than one measuring time, we may be sure that all the antioxidant potential of compounds is being considered and whether or not it is possible to establish a hierarchy for their antioxidant activities.

Antioxidants in medicinal plant extracts. A research study of the antioxidant capacity of Crataegus, Hamamelis and Hydrastis.

The antioxidant capacity of extracts of Crataegus oxyacantha, Hamamelis virginiana, Hydrastis canadensis, plants native to Europe and North America which have long been used in herbal medicine for the treatment of cardiac and circulatory functions, has been investigated. The total antioxidant potential conferred by all hydrogen donating antioxidants present in these extracts has been assessed by the ABTS assay and the relative order of antioxidant potential has been established. Gas chromatography coupled to mass spectrometry (GC‐MS) has been used for the chemical identification of the antioxidant volatile compounds present in the extracts. The GC‐MS data were related to the results obtained using the ABTS assay. Copyright

Opportunistic data collection in sparse wireless sensor networks

Opportunistic wireless sensor networks (WSNs) have recently been proposed as solutions for many remote monitoring problems. Many such problems, including environmental monitoring, involve large deployment scenarios with lower-than-average node density, as well as a long time scale and limited budgets. Traditional approaches designed for conventional situations, and thus not optimized for these scenarios, entail unnecessary complexity and larger costs. This paper discusses the issues related with the design and test of opportunistic architectures, and presents one possible solution—CHARON (Convergent Hybrid-replication Approach to Routing in Opportunistic Networks). Both algorithm-specific and comparative simulation results are presented, as well as real-world tests using a reference implementation. A comprehensive experimental setup was also used to seek a full characterization of the devised opportunistic approach including the derivation of a simple analytical model that is able to accurately predict the opportunistic message delivery performance in the used test bed.

CHARON: Routing in low-density opportunistic wireless sensor networks

Combining wireless sensor networks (WSNs) with delay-tolerant networking (DTN) has the potential to extend their use in a multitude of previously impossible applications. However, and despite numerous proposed solutions, there is still wide debate as to how to best route messages in these networks and, more importantly, how to do it in an energy-efficient way. This paper proposes CHARON (Convergent Hybrid-replication Approach to Routing in Opportunistic Networks), an approach that focuses on maximizing efficiency in addition to delivery statistics. CHARON uses delay as a routing metric, and provides basic QoS mechanisms, with both a quasi-single-copy mode for general traffic and a multi-copy mode for urgent data. It also integrates time synchronization and radio power management mechanisms. Simulation results show that it is able to achieve good delivery statistics with lower overhead than comparable solutions.

Characterizing On-Body Wireless Sensor Networks

The main goal of this work is to characterise communications through body area networks (BANs), analysing how the human body affects wireless links qualities. 802.15.4 MICAz motes were deployed on seven on-body locations of four volunteers and a test-dummy. The quality of the communications was monitored in order to study the channel behaviour. Results show that the human body clearly modifies communication properties, introducing attenuations of up to 26 dB. Differences between male and female subjects were found to be unimportant. Body posture affects the performance, mainly because of body shadowing. LoS together with the channels dynamic nature are key issues to achieve connectivity. Power settings and the local environment also influence the BANs performance.

Practical issues in the development of a minimalistic power management solution for WSNs

A flexible Wireless Sensor Network platform for implementation of diverse applications has been developed and deployed at Instituto Superior Tecnico – Technical University of Lisbon (IST-TUL). Since its initial deployment in 2007, this testbed has grown steadily, supporting new nodes, applications and experiments. However, some initial problems, which were solved on an ad hoc basis, were becoming more serious as the network spanned throughout the campus. Major issues, like global power management, have to be tackled not only with traditional protocol level approaches but also from a systems viewpoint, providing solutions capable of guaranteeing a consistent testbed. We discuss the main issues related with the development of power management solutions, presenting our architecture, design choices and implementation, and address the lessons learnt from its integration. Experimental evaluation of our solution has shown considerable energy savings, extending network lifetime by up to nine times.

A Flexible Approach to WSN Deployment

A flexible wireless sensor network platform for easier implementation of diverse applications has been developed and deployed at the Institute Superior Tecnico - Technical University of Lisbon (IST-TUL). This test-bed integrates multiple projects into a single common network, thus creating an expandable platform that facilitates the development of future applications. To achieve this flexibility, a dedicated software framework was developed that not only provides a centralized configuration panel that is accessible over the Internet, allowing the administrator to configure common network parameters, but also supports application programmability, enabling fine-grained control of in-network sensing, processing, and actuation. On top of this platform, three initial applications have been developed and are currently coexisting within the same network, thus demonstrating the new platforms capabilities. The paper discusses the main issues related with the test-bed architecture and the development of an environmental interaction application, with an illustrative purpose, along with the deployment challenges. Results of the experimental evaluation of the test-bed are also shown, focusing on the performance of the environmental interaction applications in-network processing system. A particularly relevant result is denoted by the minimum time the network needs to complete its processing tasks (approximately 200 ms in our test topology).

Resource Description Language: A Unified Description Language for Network Embedded Resources

As machine-to-machine networks become larger and more pervasive, manual configuration and discovery of resources will become intractable. It is in this context that we propose the RDL, a Resource Description Language that represents a uniform way of describing embedded resources, allowing them to be shared and enabling a new class of resource-aware applications. The RDL can describe a wide range of resources, characterizing individual nodes or entire networks. It can contribute to overcome performance issues in dense networks or mobility-driven problems in highly dynamic machine-to-machine topologies by providing the means for self-adaptability and manageability, as well as opportunistic resource sharing in context-aware embedded applications. The main goal for the RDL is to define a reusable and extensible resource description specification, which can only be reached if the resources are described in a standardized format. To illustrate the feasibility of our approach, we have also developed a Java implementation of the RDL framework, as well as a TinyOS implementation targeting resource constrained platforms. Furthermore, we have developed Modulus, a modular middleware for the development of resource-aware distributed applications.

An architecture for community mesh networking

The advances on wireless mesh networks are shifting the communications paradigm, where users can benefit from their cooperation to exchange information and make use of the spectrum space, forming wireless neighbourhood communities where resources are shared and services are distributed. This paper presents a modular cross-layer community management architecture, which considers that communities are formed and managed at different layers, from physical to application. It focus in more depth on one of its modules, implementing a community discovery mechanism designed to work in wireless mesh networks, and able to perform community advertisement and discovery with low overhead and delay, as compared to current approaches.