José L. F. C. Lima

Multicommutation in flow analysis: concepts, applications and trends

Multicommutation refers to flow systems designed with discrete computer-controlled commutators resulting in flow networks in which all the steps involved in sample processing can be independently implemented. The flow systems can be re-configured by the control software, presenting thus increased versatility, potential for automation and for minimization of both reagent consumption and waste generation. The main objective herein is to review the concept of multicommutation in order to permit a proper evaluation of the characteristics and potentialities of the related flow systems, to assist methodological implementation and to discuss similarities with other existing strategies. Implementation of tandem streams, controlled dilutions, wide-range determinations, sequential determinations, titrations and in-line separation/concentration are emphasized.

Multi-pumping in flow analysis: concepts, instrumentation, potentialities

Abstract A novel strategy for the implementation of flow-based analytical procedures using several micropumps is proposed. The pumps are switched individually or in combination, in order to create a pulsed flowing stream through the analytical path, and are the only active devices acting simultaneously as liquid propelling units, sample insertion ports and commuting elements. Configuration and control of the flow system are then greatly simplified. The micropumps produce distinct stroke volumes at distinct pulse frequencies with high reproducibility ensuring the attainment of very stable flow rates. This leads to an enhanced versatility that enables the utilisation of different approaches for sample management including step-wise variable sample volume, binary sampling and merging zones without reconfiguration of the system hardware. In contrast to the typical flow systems, the proposed one is characterised by a pulsed flow ensuring a fast sample/reagent mixing that contributes to improve the reaction development—thus sensitivity—even in situations of limited dispersion. The basic features and the performance of the proposed strategy are evaluated in the spectrophotometric determination of Cr(VI) in natural waters with 1,5-diphenylcarbazide.

Molecular Mechanisms of Anti-Inflammatory Activity Mediated by Flavonoids

Flavonoids (or bioflavonoids) are naturally occurring compounds, ubiquitous in all vascular plants. These compounds have been considered to possess anti-inflammatory properties, both in vitro and in vivo. Although not fully understood, these health-promoting effects have been mainly related to their interactions with several key enzymes, signaling cascades involving cytokines and regulatory transcription factors, and antioxidant systems. The biological effects of flavonoids will depend not only on these pharmacodynamic features but also on their pharmacokinetics, which are dependent on their chemical structure, administered dose schedule and route of administration. Thus, the therapeutic outcome mediated by flavonoids will result from a complex and interactive network of effects, whose prediction require a deep and integrated knowledge of those pharmacokinetic and pharmacodynamic factors. The aim of the present review is thus to provide an integrated update on the bioavailability and biotransformation of flavonoids and the mechanisms of activity at the molecular, cellular, organ and organism levels that may contribute to their anti-inflammatory effects.

Use of Fluorescence Probes for Detection of Reactive Nitrogen Species: A Review

The biological and toxicological effects that have been attributed to reactive nitrogen species (RNS) are increasingly stirring the scientific inquisitiveness about the molecular mechanisms involved. However, RNS present some characteristics that complicate their detection, namely their short lifetime and the normal presence of a variety of endogenous compounds capable of reacting with these reactive species, when the studies are performed in biological matrices. The development of methodologies capable of circumvent these difficulties is thus of fundamental importance. Fluorescence probes are particularly important due to their high sensibility and usefulness in temporal and spatial monitoring of RNS, particularly in microanalysis conditions in biological media akin to cells or tissues. In the present review is given an account of the fluorescence probes that have been used for detection of nitric oxide (⋅NO), peroxynitrite anion (ONOO−), as well as of some of its derivatives in biological and nonbiological media.

Flow-through tubular PVC matrix membrane electrode without inner reference solution for flow injection analysis

A simply constructed tubular PVC matrix membrane electrode without inner reference solution suitable for flow injection analysis is described. The nitrate-selective electrode developed allows simple replacement of an exhausted membrane, or change of function with a new sensor membrane. The compact design ensures mechanical stability and the tubular configuration minimizes distortion of the hydrodynamic flow in the detector. Nitrate can be determined in the range 10−1–10−5 M, under different flow conditions, with a sampling frequency of about 120 h−1.

Multi-pumping flow systems: an automation tool

Multi-pumping flow systems (MPFS) are one of the most recent developments in terms of the design, conception and implementation of continuous flow methodologies, for sample and reagent handling and for the automation of analytical procedures. Based on the utilisation of multiple solenoid micro-pumps they enable the configuring of fully automated and easily controlled and operated analytical systems since all the fundamental operations involved in carrying out a sample analysis, including sample insertion, reagent addition and signal measurement could be carried out by the same manifold component, reducing the number of system parts and minimising its control or the occurrence of mal-functions. On the other hand, micro-pumps actuation produce a pulsed flow characterised by a chaotic movement of the solutions, which contributes to a fast sample/reagent homogenisation with low axial dispersion yielding improved analytical signals. The combination of such advantageous features resulted in simple, compact, versatile, fast, low-cost analytical procedures, exhibiting low reagent and low sample consumption, reducing the production of undesirable wastes and minimising operator intervention.

Antioxidant profile of dihydroxy- and trihydroxyphenolic acids : A structure-activity relationship study

Eight structurally similar dihydroxy and trihydroxyphenolic acids (protocatechuic acid, 3,4-dihydroxyphenylacetic acid, hydrocaffeic acid, caffeic acid, gallic acid, 3,4,5-trihydroxyphenylacetic acid, 3-(3,4,5-trihydroxyphenyl)propanoic acid and 3-(3,4,5-trihydroxyphenyl)propenoic acid) were examined for their total antioxidant capacity (TAC). Furthermore, their ability to scavenge peroxyl radicals, generated by AAPH in liposomes, was determined. The antioxidant/pro-oxidant activity of the compounds was screened using the 2′-deoxyguanosine assay. All compounds behave as radical scavengers, with 3,4,5-trihydroxyphenylacetic acid being the most potent. Nevertheless, in the lipid peroxidation assay an inverse ranking order was observed, 3,4-dihydroxyphenylacetic acid being the most effective compound. All the dihydroxylated compounds showed a pro-oxidant behaviour leading to an increase of 50% in 8-OH-dG induction. From the structure–antioxidant activity relationship studies performed it may be concluded that the number of phenolic groups and the type of the alkyl spacer between the carboxylic acid and the aromatic ring strongly influence the antioxidant activity.

Liquid–liquid extraction in flow analysis: A critical review

Liquid-liquid extractions (LLE) are a common sample pre-treatment in many analytical applications. This review aims at providing a critical overview of the distinct automated continuous flow-based approaches that were developed for liquid-liquid extraction with the purpose of pre-concentration and/or separation of multiple analytes, such as ultra-trace metal and metalloid species, phenolic compounds, surfactants, pharmaceuticals, etc., hyphenated with many detection technique such as UV/vis spectrophotometry, atomic spectrometric detection systems and luminescent detectors, including distinct extraction strategies and applications like single and multiple extraction schemes, wetting film extraction, supported liquid membrane extraction, back extraction, closed-loop systems and the utilisation of zone sampling, chromatomembranes and iterative reversal techniques. The analytical performance of the developed flow-based LLE methods and the influence of flow manifold components such as the segmenter, extraction coil and phase separator, is emphasised and object of discussion. An overall presentation of each system components, selectivity, advantages and shortcomings is carried out and exemplified with selected applications.

Isolation and activation of human neutrophils in vitro. The importance of the anticoagulant used during blood collection

OBJECTIVES To assess the effect of different anticoagulants (EDTA, citrate and heparin) on the isolation procedure of human neutrophils and in the subsequent alterations of calcium levels and respiratory burst induced by phorbol myristate acetate (PMA). DESIGN AND METHODS Isolation of human neutrophils from whole blood was performed by the gradient density centrifugation method. PMA-induced neutrophil burst was measured by chemiluminescence. Intracellular calcium ([Ca(2+)](i)) was measured using Fluo-3 AM, a calcium-sensitive dye. RESULTS EDTA provided the highest number of isolated neutrophils/mL of blood (1.7x10(6)+/-1.5x10(5)) when compared with citrate (0.46x10(6)+/-0.95x10(5)) and heparin (0.66x10(6)+/-0.15x10(5)). EDTA originated less degree of PMA-induced activation (370+/-30%) relatively to citrate (830+/-98%) and heparin (827+/-77%). [Ca(2+)](i) was lower with EDTA (122+/-11 nM) when compared with citrate and heparin (150+/-13 and 230+/-30 nM). CONCLUSION The anticoagulant used during blood collection interfered differently with the yield of isolated neutrophils as well as on their calcium levels and reactivity to PMA.

Drug-membrane interactions: significance for medicinal chemistry.

Generally drugs can act on the level of different biological membranes as well as inside the cells that are limited by membranes. Even in the latter situation, drugs must still interact with the membrane in order to cross it and reach their targets. For this reason, the efficiency of drugs to interact with the membranes constitutes one of the most important pharmacological features playing an essential role in their biological activity. Membranes are the gathering place of many proteins and lipids, and are the structures where most cellular activities occur. Although drugs bind to proteins and regulate their activity, the membrane lipid phase is no less important. Great part of compounds studied induces structural changes in the lipid phase resulting structural defects, which in turn disturb membrane function and indirectly modulate membrane proteins. This paper reviews the clinical significance of drug-membrane interaction studies with a special focus in the lipidic components of the membrane and reinforcing the importance of these studies in the field of medicinal chemistry since they constitute stimulating opportunities for understanding drugs mode of action and toxic effects and cannot be overlooked during drug design and synthesis.