Current Organic Chemistry - Volume 15, Issue 17, 2011

Many modern devices, which have surrounded people in daily life, are seen by their users as “black boxes”: they perform their task and only a few specialists understand the principles of their function. The students learn about electrochemistry, they know the terms as “battery”, “capacitor”, “electrode”, “a kitchen salt electrolysis”, “measurement of pH” etc. Some drivers know the principles of the car batteries. The same people gained (more or less deep) knowledge about organic chemistry during their studies. However, only a few of them are able to connect the utilization of electrochemistry with organic chemistry. Nevertheless, these two terms have been widely and intensively interconnected for many decades. During its development, electrochemistry has become an integral part of many branches of natural science and it is practically impossible to define (similarly as in other scientific branches) the borders between electrochemistry and fields, in which have been its “results” utilized. Only shortly for illustration: Electrochemistry has been very often applied in investigation, characterization, purification, or synthesis of organic compounds. In medicine, many laboratory results are utilized without knowing that they were obtained by application of electrochemical methods. Brdicka's reaction has been utilized in medicine, and in biochemistry in investigation of proteins, peptides, phytochelatines, metallothioneins, etc., for almost 80 years (Brdicka, R. Polarographic studies with the dropping mercury cathode. Part XXXIII. A new test for proteins in the presence of cobalt salts in solutions of ammonium chloride. Collect. Czech. Chem. Commun., 1933, 5, 112-128.). Voltammetric methods can be utilized in studies of DNA, RNA, proteins, and processes connected with metabolism of carcinogenic, mutagenic, and toxic compounds. These methods help to reveal the metabolic pathways in human body. Very famous and intensively developed are sensors and biosensors, based on electrochemical principles. The combination of powerful separation techniques such as high performance chromatography and electromigration techniques with extremely sensitive and relatively selective electrochemical detection take place in almost any laboratory. Frankly to say, it was a great challenge and commitment for me to be a guest editor of this special issue. When I started to take this task into consideration, I have had to answer some questions, e.g.: Which kind of electrochemistry would be interesting for organic chemists? How to extend their knowledge? How to attract their attention? Which information would be useful for them and for topics solved by them? There exist many possibilities how to solve such task. I consulted it with my colleagues and we decided to highlight the voltammetric techniques, to illustrate the modern trends of their applications, to judge critically the possibilities of their utilization in organic chemistry and to insinuate the further aims for cooperation among scientists of various branches. In February 2012, we commemorate 90th anniversary of the invention of the polarography by the phenomenal Czech scientist Professor Jaroslav Heyrovsk (more precisely, the birthday is February 10th, 1922, in the afternoon, when the first polarographic curves were plotted) (Heyrovsky, J. Electrolysis with dropping mercury electrode (In Czech). Chem. Listy, 1922, 16, 256-264.). Thirty seven years later, on December 10th, 1959, at 4.30 p.m. in Stockholm, Sweden, he was awarded the Nobel Prize “for the polarographic method of analysis” from the hands of King Gustav Adolph VI. (Fig. (1), Fig (2)). Professor Heyrovsk was convinced that his method was mostly suitable for application in physical chemistry. However, already during his life polarography had been used in many other branches of human activities: analytical chemistry, inorganic chemistry, biochemistry, medicine, chemical physics, etc. Further development of this technique and introduction of the solid electrodes and electrodes containing no liquid mercury (such techniques are called voltammetry) have enabled expansion of electrochemistry generally (and voltammetry especially) into many other branches, organic chemistry including (Baizer, M. M. In Organic electrochemistry, Lund, H.; Baizer, M. M., Eds. Marcel Dekker 1991; p. 1421.) (Lund, H. A century of organic electrochemistry. J. Electrochem. Soc., 2002, 149(4), S21-S33.).....

The review with 132 references is focused on the electroanalytical behavior of pesticides related to their chemical structure. Relative advantages and disadvantages of their determination on various electrodes are discussed and recent works dealing with both batch voltammetric methods and methods employing amperometric detection in flow systems are summarized.

Natural nucleobases are electrochemically active, producing analytically useful oxidation and reduction signals (usually measured at carbon or mercury-based electrodes, respectively). Electroactive indicators and labels are used in electrochemical nucleic acids sensing to improve selectivity and sensitivity of the biosensors and bioassays and to expand the palette of applicable electrode materials. Electrochemical activity of these species is conferred by either redox-active transition metals, or organic electroactive moieties. The noncovalently interacting indicators interact with DNA in a structure-selective manner, usually preferring double-stranded DNA, via groove binding or intercalation between base pairs within the DNA double helix. These indicators are used mostly in DNA hybridization sensors due to their ability to discriminate between single-stranded probes and probe•target hybrid duplexes. A variety of electroactive moieties has been attached to nucleic acids covalently to create labeled DNA targets or signaling probes. Covalent DNA labeling offers a clear discrimination between complementary strands forming the DNA double helix, which further improves selectivity of the hybridization assays. Moreover, redox coding of particular nucleobases can be utilized in electrochemical DNA sequencing and single nucleotide polymorphism typing. Besides classical synthesis of modified nucleic acids via solid phase phosphoramidite methodology, more facile and versatile approaches have been introduced, based on either chemical modification of natural DNA components (such as thymine bases with osmium tetroxide complexes), or enzymatic incorporation of modified nucleotides using deoxynucleotide triphosphate conjugates bearing electroactive labels. Examples of electroanalytical applications of labeled nucleic acids are discussed.

This review deals with the description of heterogeneous electrochemical reactions (reduction or oxidation processes) in the presence of cyclodextrin molecules with particular focus on the changes of the reaction mechanisms. Homogeneous processes, i.e. electron transfer between two reactants in solution are omitted. Generally, cyclodextrins (CDs) can serve as a source of protons or can effectively stabilize the reaction intermediates. Such stabilization alters the reaction pathways. This review separately treats the oxidation and reduction processes and each section also includes the effect of CDs on the electrocatalytic processes.

This review with 119 references describes applications of amalgam electrodes in organic electrochemistry. Possible detection arrangements and useful techniques utilizing voltammetric and amperometric methods are briefly discussed. However, main attention is paid to the description of mechanisms of electrode reactions of investigated organic compounds determined at amalgam electrodes during last ten years. Selected derivatives of aromatic hydrocarbons, azo dyes, herbicides, pharmaceuticals, vitamins and biomolecules (e.g. amino acids, peptides, nucleobases and/or nucleic acids) are discussed. The understanding of the discussed methods gives a reader an overview of application possibilities offered by modern electroanalytical methods using amalgam electrodes.

The knowledge of thermodynamic balances among metal species in environmental matrixes can help in the understanding of processes related to the environmental stress of plants and in the design of suitable phytoremediation strategy. In these processes, lowmolecular- weight organic acids (LMWOAs) play a very important role, and therefore the determination of metals species with LMWOAs is of current research interest. Electrochemical techniques available for the trace analysis of metal ions are suitable for speciation studies including the computation of stability constants and the determination of the stoichiometries from the properties of voltammograms/ polarograms (pseudopolarograms). Additionally, labile and inert (stable) complexes can be distinguished by several electrochemical methods. A new approach is the hyphenation of electrochemistry (EC) with electrospray ionization mass spectrometry (ESI-MS), which provides assistance to the description of the electrochemical behavior of the complexes as far as both thermodynamic aspects and kinetic properties of metals complexes with LMWOAs are concerned.

2,2-Dinitroethene-1,1-diamine (FOX-7) is a compound synthesized in 1998 with a simple structure but very unusual properties. One part of the molecule bears two geminal electron-withdrawing nitro groups as a strong oxidation center and the opposite part is represented by two electron-donating amino groups. This combination creates a so called push-pull effect of electrons. The electron distribution is unbalanced enabling intramolecular electron transfer reactions, what is typical for energetic material. Many studies appeared during last decade dealing with synthesis, physical properties, solubility, spectroscopic properties, acidobasic and redox properties, X-ray structure studies, reactivity, thermochemical properties, analytical reactions, quantum chemical calculations, energetic properties etc. The presented review article gives an overview of the papers devoted to the title compound.

The manuscript reviews the recent trends and advances regarding utilization of composite solid materials, above all, of their application for construction of composite solid electrodes (CSEs). These electrodes have been used in electrochemical studies and determinations of micromolar and submicromolar (in some cases even subnanomolar) concentrations of various environmentally important biologically active, mostly organic substances. They have been relatively frequently used in scientific as well as in commercial laboratories for last two decades. The review is focused predominantly on electrodes belonging to the group of composite electrodes with random ensembles of dispersed particles with final solid form. The composite electrode material contains, according to their principal definition, at least one conductor (metal - silver, gold, amalgam etc.), nonmetallic conductor (e.g., graphite powder) or their mixture and at least one insulator (a polymer or a monomer), which are mixed together. Some specific properties, required for determination of chosen analytes in specified matrices, can be reached by addition of proper modifiers into the electrode bulk and/or on the electrode surface, e.g., a catalyst or an enzyme. CSEs can be applied either in batch analyses or in flow liquid systems (especially HPLC or FIA with electrochemical detection). CSEs proved experimentally to be a suitable, reliable, and environmentally friendly substitutes for the hanging mercury drop electrode (HMDE) in electrochemical analyses. The review is focused on the organic applications of CSEs, nevertheless, their utilization in the field of inorganic analysis is mentioned too.

Boron doped diamond (BDD) has been recognized as nearly ideal electrode material for many electrochemical applications due to the low and stable background current over a wide potential range, corrosion and fouling resistance, high thermal conductivity, and high current densities. Microelectrodes and microelectrode arrays possess numerous attractive features for electrochemistry including reduced iR drop, low capacitive-charging currents, and steady-state diffusion currents. Coupling the advantages of the microelectrodes and their arrays with the usefulness of BDD is presented and discussed in this review on the examples of existing miniaturized BDD devices and their applications in organic electrochemistry. The varieties in their fabrication, construction, and applications in organic electrochemistry are presented. The latter include mainly electroanalysis, where single BDD microelectrodes have been employed as amperometric sensors in capillary electrophoretic techniques including electrophoretic microchips and other liquid flow systems, and further for in vivo/in vitro detection of biogenic compounds. Applications of BDD microelectrode arrays are rather limited, as their construction is a very challenging task and recent studies are more concerned with their fabrication and structural and electrochemical characterization. Thus, the techniques for the fabrication of such arrays and their construction are reviewed and their possibilities and limitations in organic electrochemistry based on existing results are discussed.

This review is focused on creatine (CR) (methyl guanidine acetic acid) and its application in the form of a dietary supplement. It has been especially utilized by athletes, but its pronounced therapeutic potential is also discussed in the present article. It is supposed that human body uses CR for the formation of creatine phosphate (PCr), which is necessary for muscular work as a source of energy. The effects of supplemented CR on dynamics of methionine cycle and other related metabolic pathways have not been fully explained yet. The review is focused on the description of affects caused by its application on human body and metabolism. Already the application of small amounts of CR rapidly increases levels of thiodiglycolic acid (TDGA) in urine after its supplementation, which phenomenon can serve as a sensitive marker of disturbance in metabolic pathways of 2C units and of thiolic compounds. Strong differences between initial and terminal TDGA levels in urine indicate that CR disturbed the equilibria of redox processes, catalyzed by folates and vitamin B12. Some theories for explanation of these effects are described in this manuscript. Nevertheless, similarly as in other metabolic studies, the results are significantly affected by the probands' individual responses, which reflect their individual genetic makeup. The various methods such as voltammetric (generally electrochemical), chromatographic, mass spectrometric, enzymatic etc., which have been most frequently utilized for determination of discussed compounds in common laboratories, have been reported.

In this review (with 100 refs), applicability of carbon paste electrodes (CPEs) in organic electrochemistry is of interest, when the authors cover the area in its entirety and over the whole period of the existence of carbon pastes in electrochemistry and electroanalysis. The individual periods are retrospectively summarised, when particular attention is paid to the Adams' era representing the most extensive research ever carried out with carbon paste-based electrodes and organic compounds (namely: aromatic amines, hydroquinones and catechols, aminophenols and catecholamines). The following activities are discussed and critically evaluated with the aid of table surveys or selected illustrative examples, when all the major trends and contemporary achievements are highlighted, including the recent years, the present time, and future prospects.

Electrochemical methods used for the investigation, determination and monitoring of carcinogenic nitro (NPAHs) and amino (APAHs) derivatives of polycyclic aromatic hydrocarbons are reviewed. Special emphasis is placed on the mechanisms of electrode reactions of NPAHs at traditional mercury electrodes and electrodes based on silver amalgam, and of APAHs at electrodes based on the different types of carbon materials, e.g., glassy carbon electrode, carbon paste electrode based on glassy carbon microbeads, or boron-doped diamond film electrode. Recently developed voltammetric and amperometric methods making use of electrochemical reduction or oxidation of NPAHs or APAHs for their sensitive and selective determination are discussed as well together with a brief survey of occurence and biological properties of these substance.

This review summarizes the recent advances on the redox reactions involving α-functionalized aldehydes catalyzed by N-heterocyclic carbenes. In the presence of N-heterocyclic carbene, α-functionalized aldehydes such as α-haloaldehydes, α-ring-fused aldehydes, α-aryloxyacetaldehydes and α-aroyloxyaldehydes undergo the redox reactions affording novel reaction types.

p-toluenesulfonic acid has been used in many organic preparations as a good solid catalyst. In this review, we wish to report some applications of this catalyst in organic reactions.

Approaches for the preparation of azaenamines as well as the chemical reactivity profiles and structures of these substances are reviewed. Emphasis is given to the use of these substances as C-nucleophiles in the synthesis of five- and six-membered heterocycles and fused derivatives.

A broad range of fundamental free radical reactions, including hydrogen and halogen atom transfer, radical deoxygenations, radical cyclization reactions, radical additions to C=C and C=N double bonds utilizing β-cyclodextrin-ionic liquid(mono-6-(1-methyl-3- imidazolium) - 6 - deoxy - β -cyclodextrin tosylate (MIM-β-CDOTs) based molecular reactors/alternative media at room temperature are investigated. The reactions proceeded smoothly in moderate to excellent yield at ambient temperature, with noticable improvements in enantioselectivity observed in several key transformations.