Hardback : Add to Wish List. Description Subjects. Description This text details contemporary electroanalytical strategies of biomolecules and electrical phenomena in biological systems. Offline Computer — Download Bookshelf software to your desktop so you can view your eBooks with or without Internet access.
Because of their low proliferative activity and inaccessibility to blood-borne drugs, these cells represent a potential clinical problem in the chemotherapy of solid tumours. They are radioresistant and may contribute to local failure in radiotherapy. One method for overcoming this problem is the use of chemical radiosensitizers.
The hypoxic microenvironment offers an attractive target. Drugs activated only in hypoxic regions may be truly specific for solid tumours. It is well recognised that pH plays a significant regulatory role in most cellular processes. There is an increased interest in transmembrane pH gradients, particularly with respect to tumour growth and response to therapy. The same is true for electrochemical studies. Hence, in the absence of O 2 , the activated reduction product is long-lived enough to inflict macromolecular damage resulting in cytotoxicity. It has been demonstrated that agents possessing reduction potentials in the range to mV vs NHE are accessible to enzymatic reduction in vivo.
In spite of not being absolute, it appears that molecules with electron affinity less than mV but more than mV will show little activity against hypoxic cells in vivo. Molecules with low electron affinities are expected to be inadequately activated by bioreductive enzymes, while molecules with too high an electron affinity are expected to be rapidly metabolised and excreted. Two hypoxic active nitrobenzyloxycarbonyl derivatives of 1,2-bis methylsulfonyl 2-chloroethyl hydrazines 33 were studied by pulse polarography in different pH values and appear to be reduced more easily under acidic conditions than under neutral conditions Scheme Very frequently, different oxygen concentrations for activation are required.
This difference can be rationalised by the large variation in redox potential. The cytotoxic activity depends upon reduction of the nitro group, usually at low redox potentials, which are normally unattainable in well-oxygenated cells. The relative reduction rates in hypoxia or anoxia and under oxic conditions are the basis for their selective toxicity and therapeutic differential. In the presence of oxygen, this free radical is rapidly oxidized back to the parent molecule with the formation of a superoxide radical. Concluding Remarks. Electrochemical methods analytical and preparative and parameters can be widely used in Biomedical Chemistry, especially because they furnish an enormous amount of evidences regarding the mechanisms of biological electron-transfer processes.
The comparison between electrochemical and bioactive properties, based upon the general theoretical frameworks, as shown, carries a great significance, allowing the use of electrochemical parameters as direct evaluators of biological activities. As electrochemical parameters can be, generally, directly related to the effects of substituent, the benefits of QSAR studies, finding mathematical forms for the relationship, bring additional relevance to the methodology and allow prediction of biomedical properties.
One should not expect a general direct correlation between reduction potential and bioactivity. Many other important factors must be also considered in the mechanistic aspects of in vivo drug activity, e. It is more probable to find correlation in case of ET-OS. Discrepancy of results absence of correlation between electrochemical and other studies enzymatic could be explained by specific reactions catalysed by specific enzymes or by different biological pathways, not related to electron transfer.
Indeed, the number of physiologically active substances that possess E 1 7 values greater than about NHE, in the physiological active range, which can permit electron acceptance from biological donors is significant.
When the potential for a given drug is too low or two high, they can be modified in vivo to adequately potential-driven metabolites, that are the useful agents. Electrochemistry is also used to follow this chemical transformation. The versatility of the electrochemical methodology allows to mimic the multitude of biological environments: the conditions can be widely varied in the attempt to resemble them.
Different ranges of pH, oxygen content in the electrochemical cell and solvents of diverse properties can be used. However, standardization is urgently required, in terms of methods, electrodes, supporting electrolytes, etc. In electrochemistry, considerable progress has recently been made in the development of new and rather sophisticated techniques, as exemplified in the present article.
The field of Biomedical Chemistry will, naturally, take advantage of this progress. They work by interacting with cellular enzymes and therefore stopping the cell from making, for example, the extra DNA necessary for replication.
According to Molecular Orbital Theory, oxidation of a species occurs by removing one electron from the highest occupied molecular orbital HOMO and reduction by addition of an electron to the lowest unoccupied molecular orbital LUMO. Thus, if the ET reactivity ionisation potential, electron affinity, anodic and cathodic half-wave potentials, ET rate constants, etc.
Blood supply to the hypoxic region delivers less oxygen than in normal cells. Hypoxia in human tumours has also been associated with malignant progression and formation of metastases. It is the major physiological difference between tumours and normal tissues, and hence, it constitutes a very attractive target for selective therapy. It results from an inadequate and disorganized tumour vasculature, and hence an impaired oxygen delivery.
It is also the key cellular target for a number of clinically important anticancer drugs including etoposide and the anthracyclines doxorubicin and daunorubicin. They wish to thank Prof. Zani, Dr. Ricardo J. Alves, Prof. Solange Castro and Dr.
Maria A. Prado for helpful discussions, Dr. Alessandra C. Gomes for assistance in figures and graphics, Prof. Peter Kovacic and Dr. Christian Amatore for pre-prints and Dr. Josealdo Tonholo for relevant discussions. References 1. Kunz, K. Dryhurst, G. Rosenberg, B. Rajski, S. Kovacic P.
This text details contemporary electroanalytical strategies of biomolecules and electrical phenomena in biological systems. It presents significant developments . Buy Electroanalytical Methods Of Biological Materials on lirodisa.tk ✓ FREE SHIPPING on qualified orders.
Bard, A. Lunte, S. Bernd, S. Kovacic, P. Chow, C. Lown, J.
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