Current Organic Chemistry - Volume 15, Issue 8, 2011

Synthetic carbon allotropes have received a lot of attention from the scientific community during the last 25 years. In addition to the more explored fullerenes and carbon nanotubes, other carbon nanostructures such as graphenes, nano-onions, nanohorns and endohedral structures have attracted great interest. Concerning the chemistry aspects of carbon-based nanostructures as well as their potential applications in nanotechnology, there have been a few thematic issues in peer-reviewed journals, covering exclusively either fullerene materials (M. Prato, N. Martin, eds. J. Mater. Chem. 2002, 1931-2159) or carbon nanotubes (R. C. Haddon, ed. Acc. Chem. Res. 2002, 997-1113). In addition, during the last 5 years, there is a drastic increase of published works appearing in the related literature (about 40000 scientific papers), three quarters of them dealing about carbon nanotubes. This huge amount of work stems from the expectations that carbon-based nanostructures have potential applications in different fields ranging from materials science and molecular electronics to biological and biomedical applications. When my proposal of a special issue entitled “Chemistry of carbon-based nanostructures and applications in nanotechnology” for Current Organic Chemistry was approved by the Editor-in-Chief in mid 2009, I was very excited to organize the edition of this special issue. Finally, six (6) papers from different universities and institutes were collected for publication with respect to different themes in the chemistry and applications of carbon-based nanostructures. These groups are active in the research of carbon-based nanostructures and try to show the state of the art in specific fields of nanotechnology. The review article of Baibarac et al. (Romania - France) deals with the development of composite materials based on carbon nanotubes and conjugated polymers (contains 173 references). The different types of composites, the new protocols used in their synthesis as well as their vibrational properties (FT-IR, Raman scattering) are described in detail. The review provides also information on desirable composite properties specific to applications in the fields of energy storage, optical limiting and electron field emission devices, transistors, conducting textiles, sensors and rewritable devices. In his contribution, Campidelli (France) describes how the emerging field of “click chemistry” has the potential to provide an elegant protocol to prepare carbon nanotube-based functional materials (contains 64 references). In particular, the Huisgen 1,3-dipolar cycloaddtion catalyzed by Cu(I) is demonstrated and is shown to produce nanotube-based innovative materials. Garcia and co-workers (Spain) describe synthetic strategies to obtain covalently functionalized carbon nanotubes with photoactive functionalities (contains 61 references). The authors show that tubes can act as electron acceptor as well as electron donor subunit. These photoactive materials have a large potential in optoelectronic applications requiring nanometric components and particularly photovoltaic cells. In their contribution, Porfyrakis and co-workers (UK) review the current state-of-the-art in the synthesis and chemistry of endohedral fullerenes with particular focus on endohedral nitrogen fullerenes, such as N@C60 (contains 64 references). In the review of Spitalsky et al. (Slovakia) the chemistry of graphene is discussed in detail (contains 127 references). The covalent chemical reactions that have been performed on individual graphene sheets, the production of graphene oxide with subsequent transformation to reduced graphene, the covalent modification of graphene oxide functional groups and the surface chemistry of the aromatic rings of graphene sheets are documented in detail. The sixth review, prepared by Tagmatarchis and co-workers (Greece), presents an overview of the latest trends in microwave-assisted functionalization of carbon nanostructured materials, covering major breakthroughs achieved in the last years for this novel, intriguing and non-conventional synthetic approach (contains 87 references). I believe this issue has a comprehensive coverage concerning chemistry aspects of carbon-based nanostructures and their applications in nanotechnology. As guest editor, I would first like to acknowledge all the authors who have contributed to this special issue as well as all the referees for their precious comments on improving the quality of the manuscripts. I would like to express a special thanks to Dr. Atta-ur- Rahman, Editor-in-Chief of Current Organic Chemistry for his kind invitation and to Ms. Donia Akhter, assistant manager of the publication department at Bentham Science Publishers, for her help throughout the whole process of editing. I hope that this special issue will be appreciated by chemists who deal with the organic derivatization of nanomaterials.

This chapter reviews some of the strategies that have been used to synthesize single walled carbon nanotubes having covalently bonded photoresponsive chromophores. In the first part, the synthetic route is discussed as well as the different characterization techniques and how the information gained by each of them has to be combined to have a more detailed information on the material. Emphasis is made on commenting the advantages of using short-soluble carbon nanotubes that can be more firmly characterized (particularly the occurrence of the covalent linkage) and how the covalent attachment reinforces considerably the interaction between the nanotube walls and the chromophore. The photophysics of the entities derived from the covalent functionalization of the carbon nanotubes by photoactive units is discussed in the second part. Examples are provided to show that single wall carbon nanotubes behave as semiconductors and behave accepting or donating electrons. Thus, in contrast to fullerenes that are always strong electron acceptors, the behavior of single wall carbon nanotubes in the photoinduced charge separation event depends on the nature of the partner attached covalently.

Microwaves have proven to be a powerful ally in any synthetic effort, shortening reaction times considerably and in some cases facilitating the reaction by offering higher yields or fewer byproducts. Since the mid ‘90s microwave-assisted synthesis has found its way into carbon nanostructures, offering significant advantages towards their functionalization. In this review, an overview of the latest trends in microwave-assisted functionalization of carbon nanostructured materials is presented covering major breakthroughs achieved in the last years for this novel, intriguing and non-conventional synthetic approach.

Graphene is a new and hot research topic due to properties previously not observed on the nanoscale. These properties make graphene a promising candidate for new devices. However, graphene is not soluble, and this property limits its processability. Therefore, chemical functionalization is needed. This short review summarizes the covalent chemical reactions that have been performed on individual graphene sheets - the production of graphene oxide with subsequent transformation to graphene, the covalent modification of graphene oxide functional groups and the surface chemistry of the aromatic rings of graphene sheets.

Carbon nanotubes (CNTs) display unique structural, chemical and physical properties which make them promising materials for electronic and sensing applications, solar energy conversion, for the realization of composites and in life science. For many of these applications, nanotube functionalization needs to be controlled. So there is a real need for original chemical reactions which allow the modification of carbon nanotubes in a simple way. The emerging field of “click chemistry” has the potential to provide an elegant protocol to prepare carbon nanotube-based functional materials. In particular the Huisgen 1,3-dipolar cycloaddtion catalyzed by Cu(I) has been successfully applied to produce nanotube-based innovative materials. This review focuses on this reaction and presents the recent examples described in literature.

This review deals with recent progress on the development of composite materials based on cojugated polymers (CPs) and carbon nanotubes (CNTs), both from fundamental and applied point of view. In the first part of the manuscript, we present the different types of composites, the new protocols used in their synthesis as well as their vibrational properties reported in the last five years. A brief review of the contribution of Raman light scattering and FTIR spectroscopy to establish the type of interaction between the two constituents is discussed for different cases, i.e. bi-layers of polymers and carbon nanotubes, CPs doped with CNTs and CNTs functionalized with CPs. Recently, anti-Stokes resonant Raman studies have appeared as fruithful tools in the evaluation of functionalization process of CNTs with CPs. The review provides also information on CPs/CNTs composite properties specific to applications in the field of energy storage, optical limiting and electron field emission devices, transistors, conducting textiles, sensors, rewritable devices, biomedical and food domains as well as how these materials have been optimized to generate exploitable properties.

Endohedral fullerenes are remarkable molecules that offer a unique paradigm in the molecular world: the trapping of atom(s) or clusters in a 3-dimensional, almost perfectly symmetrical structure. The electron deficient nature of the fullerene surface makes it amenable to a range of chemical reactions. Hence the fullerene can obtain functionality and become a building block of larger molecular structures. Careful engineering of the endohedral species and of the exohedral adduct can modify the electronic, optical, as well as chemical and physical properties of the molecule. The last few years have seen an increase in the chemical functionalization of these molecules. The present article reviews the current state-of-the-art in the synthesis and chemistry of endohedral fullerenes with particular focus on endohedral nitrogen fullerenes such as N@C60.

The HPLC enantioseparation of eight racemic atropisomeric biphenyls on commercially available polymeric Chiralcel OD-H, Lux Cellulose-1, Lux Cellulose-2, Chiralcel OJ, Lux Amylose-2 and Chiralpak OT(+) and on the brush-type Whelk-O1 columns, both in normal-phase mode and in polar organic solvent mode, has been investigated. The attempts to enantioseparate the selected biphenyls on Whelk-O1 were unsuccessful. All compounds were well resolved on almost one of the polymeric columns. Lux Cellulose-2 showed to be suitable for enantioseparation of all biphenyls. The effect of mobile phase, temperature, type of chiral selector and analyte structure on enantioseparation are examined and discussed. 2-Propanol and ethanol were employed as mobile phase modifiers and their influence on the retention and enantioseparation was investigated. Also a ternary mobile phase (n-hexane/2-propanol/methanol 91:6:3) was employed to test the separation of the eight biphenyls. In same cases, the elution with pure ethanol provided good enantioseparation in shorter elution times. The experimental data evidenced the complemental chiral recognition capabilities of polysaccharide-based CSPs. Noteworthy, Lux Cellulose-1 and Chiralcel OD-H contain the same chiral selector, but the first one exhibited higher retention factors. The evaluation of chromatographic data provided information about the chiral recognition mechanisms. In this regard, we report on the effect of ortho and meta biphenyl substituents on the retention and enantioseparation. In addition, computational evaluation of electrostatic potentials of analytes furnished a very interesting piece of information about the enantioseparability as well as the chiral recognition mechanisms on the evaluated chiral selectors.

The reduction of 7-gem-dihalo-3-oxo-2-azabicyclo[4.1.0]heptanes with metallic zinc yielded stereoselective synthesis of novel heterocyclic endo-7-halo-3-oxo-2-azabicyclo[4.1.0]heptanes in good to high yields without any evidence for the formation of corresponding exo-isomers. The prepared heterocyclic compounds were characterized by various techniques and their stereochemistry was established on the basis of the values of the coupling constants for H-1, H-5, H-6 and H-7 by recording homonuclear spin-spin decoupled 1H NMR spectra. The developed protocol has many advantages such as simple reaction conditions, lower cost, high yields, and selective synthesis of novel heterocyclic cyclopropyl compounds present in a large number of biologically active natural products and pharmaceuticals compounds.

Task specific ionic liquids (TSILs) have received increased attention over the last few years as it is possible to form any specific ionic liquid composition depending upon user's need of the desired physical, chemical and biological properties. The present review gives an update of recent developments in the field of TSILs with emphasis on their applications in organic synthesis.