Showing papers in "Chemical Society Reviews in 2008"

Hybrid porous solids: past, present, future

Abstract: This critical review will be of interest to the experts in porous solids (including catalysis), but also solid state chemists and physicists. It presents the state-of-the-art on hybrid porous solids, their advantages, their new routes of synthesis, the structural concepts useful for their ‘design’, aiming at reaching very large pores. Their dynamic properties and the possibility of predicting their structure are described. The large tunability of the pore size leads to unprecedented properties and applications. They concern adsorption of species, storage and delivery and the physical properties of the dense phases. (323 references)

Applications of ionic liquids in the chemical industry

Abstract: In contrast to a recently expressed, and widely cited, view that “Ionic liquids are starting to leave academic labs and find their way into a wide variety of industrial applications”, we demonstrate in this critical review that there have been parallel and collaborative exchanges between academic research and industrial developments since the materials were first reported in 1914 (148 references)

Fluorine in medicinal chemistry.

Abstract: It has become evident that fluorinated compounds have a remarkable record in medicinal chemistry and will play a continuing role in providing lead compounds for therapeutic applications. This tutorial review provides a sampling of renowned fluorinated drugs and their mode of action with a discussion clarifying the role and impact of fluorine substitution on drug potency.

Understanding organofluorine chemistry. An introduction to the C–F bond

Abstract: Fluorine is the most electronegative element in the periodic table. When bound to carbon it forms the strongest bonds in organic chemistry and this makes fluorine substitution attractive for the development of pharmaceuticals and a wide range of speciality materials. Although highly polarised, the C–F bond gains stability from the resultant electrostatic attraction between the polarised Cδ+ and Fδ– atoms. This polarity suppresses lone pair donation from fluorine and in general fluorine is a weak coordinator. However, the C–F bond has interesting properties which can be understood either in terms of electrostatic/dipole interactions or by considering stereoelectronic interactions with neighbouring bonds or lone pairs. In this tutorial review these fundamental aspects of the C–F bond are explored to rationalise the geometry, conformation and reactivity of individual organofluorine compounds.

Shape control in gold nanoparticle synthesis

Abstract: In this tutorial review, we summarise recent research into the controlled growth of gold nanoparticles of different morphologies and discuss the various chemical mechanisms that have been proposed to explain anisotropic growth. With the overview and discussion, we intended to select those published procedures that we consider more reliable and promising for synthesis of morphologies of interest. We expect this to be interesting to researchers in the wide variety of fields that can make use of metal nanoparticles.

Supported gold nanoparticles as catalysts for organic reactions

Abstract: This critical review is intended to attract the interest of organic chemists and researchers on green and sustainable chemistry on the catalytic activity of supported gold nanoparticles in organic transformations. In the general part of this critical review, emphasis is given to the different procedures to form supported gold nanoparticles and to the importance of the support cooperating in the catalysis. Also the convergence of homogeneous and heterogeneous catalysis in the study of gold nanoparticles has been discussed. The core part of this review is constituted by sections in which the reactions catalyzed by supported gold nanoparticles are described. Special emphasis is made on the unique ability of gold catalysts to promote additions to multiple C–C bonds, benzannulations and alcohol oxidation by oxygen (282 references).

Hierarchical zeolites: enhanced utilisation of microporous crystals in catalysis by advances in materials design.

Abstract: The introduction of synthetic zeolites has led to a paradigm shift in catalysis, separations, and adsorption processes, due to their unique properties such as crystallinity, high-surface area, acidity, ion-exchange capacity, and shape-selective character. However, the sole presence of micropores in these materials often imposes intracrystalline diffusion limitations, rendering low utilisation of the zeolite active volume in catalysed reactions. This critical review examines recent advances in the rapidly evolving area of zeolites with improved accessibility and molecular transport. Strategies to enhance catalyst effectiveness essentially comprise the synthesis of zeolites with wide pores and/or with short diffusion length. Available approaches are reviewed according to the principle, versatility, effectiveness, and degree of reality for practical implementation, establishing a firm link between the properties of the resulting materials and the catalytic function. We particularly dwell on the exciting field of hierarchical zeolites, which couple in a single material the catalytic power of micropores and the facilitated access and improved transport consequence of a complementary mesopore network. The carbon templating and desilication routes as examples of bottom-up and top-down methods, respectively, are reviewed in more detail to illustrate the benefits of hierarchical zeolites. Despite encircling the zeolite field, this review stimulates intuition into the design of related porous solids (116 references).

Biological applications of gold nanoparticles

Abstract: This critical review gives a short overview of the widespread use of gold nanoparticles in biology. We have identified four classes of applications in which gold nanoparticles have been used so far: labelling, delivering, heating, and sensing. For each of these applications the underlying mechanisms and concepts, the specific features of the gold nanoparticles needed for this application, as well as several examples are described (142 references).

A new trend in rhodamine-based chemosensors: application of spirolactam ring-opening to sensing ions

Abstract: This tutorial review focuses on the recent development of rhodamine derivatives, in which the spirolactam (non-fluorescent) to ring-opened amide (fluorescent) process was utilized.

Chemoselective catalytic conversion of glycerol as a biorenewable source to valuable commodity chemicals

Abstract: New opportunities for the conversion of glycerol into value-added chemicals have emerged in recent years as a result of glycerol's unique structure, properties, bioavailability, and renewability. Glycerol is currently produced in large amounts during the transesterification of fatty acids into biodiesel and as such represents a useful by-product. This paper provides a comprehensive review and critical analysis on the different reaction pathways for catalytic conversion of glycerol into commodity chemicals, including selective oxidation, selective hydrogenolysis, selective dehydration, pyrolysis and gasification, steam reforming, thermal reduction into syngas, selective transesterification, selective etherification, oligomerization and polymerization, and conversion of glycerol into glycerol carbonate.

Injectable hydrogels as unique biomedical materials

Abstract: A concentrated fish soup could be gelled in the winter and re-solled upon heating. In contrast, some synthetic copolymers exhibit an inverse sol–gel transition with spontaneous physical gelation upon heating instead of cooling. If the transition in water takes place below the body temperature and the chemicals are biocompatible and biodegradable, such gelling behavior makes the associated physical gels injectable biomaterials with unique applications in drug delivery and tissue engineering etc. Various therapeutic agents or cells can be entrapped in situ and form a depot merely by a syringe injection of their aqueous solutions at target sites with minimal invasiveness and pain. This tutorial review summarizes and comments on this soft matter, especially thermogelling poly(ethylene glycol)–(biodegradable polyester) block copolymers. The main types of injectable hydrogels are also briefly introduced, including both physical gels and chemical gels.

Intermediate temperature solid oxide fuel cells

Abstract: High temperature solid oxide fuel cells (SOFCs), typified by developers such as Siemens Westinghouse and Rolls-Royce, operate in the temperature region of 850–1000 °C. For such systems, very high efficiencies can be achieved from integration with gas turbines for large-scale stationary applications. However, high temperature operation means that the components of the stack need to be predominantly ceramic and high temperature metal alloys are needed for many balance-of-plant components. For smaller scale applications, where integration with a heat engine is not appropriate, there is a trend to move to lower temperatures of operation, into the so-called intermediate temperature (IT) range of 500–750 °C. This expands the choice of materials and stack geometries that can be used, offering reduced system cost and, in principle, reducing the corrosion rate of stack and system components.This review introduces the IT-SOFC and explains the advantages of operation in this temperature regime. The main advances made in materials chemistry that have made IT operation possible are described and some of the engineering issues and the new opportunities that reduced temperature operation affords are discussed.This tutorial review examines the advances being made in materials and engineering that are allowing solid oxide fuel cells to operate at lower temperature. The challenges and advantages of operating in the so-called ‘intermediate temperature’ range of 500–750 °C are discussed and the opportunities for applications not traditionally associated with solid oxide fuel cells are highlighted. This article serves as an introduction for scientists and engineers interested in intermediate temperature solid oxide fuel cells and the challenges and opportunities of reduced temperature operation.

Modelling the optical response of gold nanoparticles

Abstract: This tutorial review presents an overview of theoretical methods for predicting and understanding the optical response of gold nanoparticles. A critical comparison is provided, assisting the reader in making a rational choice for each particular problem, while analytical models provide insights into the effects of retardation in large particles and non-locality in small particles. Far- and near-field spectra are discussed, and the relevance of the latter in surface-enhanced Raman spectroscopy and electron energy-loss spectroscopy is emphasized.

Single-molecule and single-nanoparticle SERS: from fundamental mechanisms to biomedical applications

Abstract: This tutorial review discusses a new class of colloidal metal nanoparticles that is able to enhance the efficiencies of surface-enhanced Raman scattering (SERS) by as much as 1014–1015 fold. This enormous enhancement allows spectroscopic detection and identification of single molecules located on the nanoparticle surface or at the junction of two particles under ambient conditions. Considerable progress has been made in understanding the enhancement mechanisms, including definitive evidence for the single-molecule origin of fluctuating SERS signals. For applications, SERS nanoparticle tags have been developed based on the use of embedded reporter molecules and a silica or polymer encapsulation layer. The SERS nanoparticle tags are capable of providing detailed spectroscopic information and are much brighter than semiconductor quantum dots in the near-infrared spectral window. These properties have raised new opportunities for multiplexed molecular diagnosis and in vivoRaman spectroscopy and imaging.

Designing peptide based nanomaterials

Abstract: This tutorial review looks at the design rules that allow peptides to be exploited as building blocks for the assembly of nanomaterials. These design rules are either derived by copying nature (α-helix, β-sheet) or may exploit entirely new designs based on peptide derivatives (peptide amphiphiles, π-stacking systems). We will examine the features that can be introduced to allow self-assembly to be controlled and directed by application of an externally applied stimulus, such as pH, light or enzyme action. Lastly the applications of designed self-assembly peptide systems in biotechnology (3D cell culture, biosensing) and technology (nanoelectronics, templating) will be examined.

Solvent resistant nanofiltration: separating on a molecular level

Abstract: Over the past decade, solvent resistant nanofiltration (SRNF) has gained a lot of attention, as it is a promising energy- and waste-efficient unit process to separate mixtures down to a molecular level This critical review focuses on all aspects related to this new burgeoning technology, occasionally also including literature obtained on aqueous applications or related membrane processes, if of relevance to understand SRNF better An overview of the different membrane materials and the methods to turn them into suitable SRNF-membranes will be given first The membrane transport mechanism and its modelling will receive attention in order to understand the process and the reported membrane performances better Finally, all SRNF-applications reported so far – in food chemistry, petrochemistry, catalysis, pharmaceutical manufacturing – will be reviewed exhaustively (324 references)

Anion-π interactions

Abstract: This tutorial review provides an overview of the theoretical and experimental investigations that resulted in the recognition of anion-π interactions, i.e., non-covalent forces between electron deficient aromatic systems and anions. Several pioneering theoretical studies revealed that these interactions are energetically favorable (∼20–50 kJ mol–1). Anion-π interactions are gaining significant recognition, and their pivotal role in many key chemical and biological processes is being increasingly appreciated. The design of highly selective anion receptors and channels represent important advances in this nascent field of supramolecular chemistry.

SERS--a single-molecule and nanoscale tool for bioanalytics.

Abstract: Surface enhanced Raman scattering (SERS) at extremely high enhancement level turns the weak inelastic scattering effect of photons on vibrational quantum states into a structurally sensitive single-molecule and nanoscale probe. The effect opens up exciting opportunities for applications of vibrational spectroscopy in biology. The concept of SERS can be extended to two-photon excitation by exploiting surface enhanced hyper-Raman scattering (SEHRS). This critical review introduces the physics behind single-molecule SERS and discusses the capabilities of the effect in bioanalytics (100 references).

Iron-catalysed carbon–heteroatom and heteroatom–heteroatom bond forming processes

Abstract: Given its ready availability, low price and environmentally friendly character, iron is an attractive and often advantageous alternative to other transition metals in the field of catalysis. This tutorial review summarises recent progress in the development of novel and practical iron-catalysed reactions with a particular focus on those which provide access to new carbon–heteroatom and heteroatom–heteroatom linkages. It shall be of interest for both the academic as well as the industrial community.

Gold catalysis in total synthesis.

Abstract: In this tutorial review directed towards chemists interested in synthesis or catalysis, the application of gold catalysis in total synthesis is summarised and the mode of activation of the substrate by the gold catalyst is discussed.

A briefing on aurophilicity.

Abstract: There is now compelling experimental evidence for the existence of specific intra- and intermolecular bonding between seemingly closed-shell gold(I) centers (5d10) which manifests itself in all areas of gold chemistry. This “aurophilic interaction”, which had not been predicted by conventional valence theory, was found to be associated with binding energies in some cases exceeding even those of strong hydrogen bonds and therefore to be highly significant in co-determining molecular structure and dynamics. In high-level theoretical treatments the attraction is rationalized as a “super van der Waals bonding” based on particularly strong relativistic, dispersion and correlation effects (critical review, 265 references).

Rationally designed nanostructures for surface-enhanced Raman spectroscopy

Abstract: Research on surface-enhanced Raman spectroscopy (SERS) is an area of intense interest because the technique allows one to probe small collections of, and in certain cases, individual molecules using relatively straightforward spectroscopic techniques and nanostructured substrates. Researchers in this area have attempted to develop many new technological innovations including high sensitivity chemical and biological detection systems, labeling schemes for authentication and tracking purposes, and dual scanning-probe/spectroscopic techniques that simultaneously provide topographical and spectroscopic information about an underlying surface or nanostructure. However, progress has been hampered by the inability of researchers to fabricate substrates with the high sensitivity, tunability, robustness, and reproducibility necessary for truly practical and successful SERS-based systems. These limitations have been due in part to a relative lack of control over the nanoscale features of Raman substrates that are responsible for the enhancement. With the advent of nanotechnology, new approaches are being developed to overcome these issues and produce substrates with higher sensitivity, stability, and reproducibility. This tutorial review focuses on recent progress in the design and fabrication of substrates for surface-enhanced Raman spectroscopy, with an emphasis on the influence of nanotechnology.

Anion receptors based on organic frameworks: highlights from 2005 and 2006

Abstract: This critical review covers advances in anion complexation chemistry related to receptors based on organic frameworks in the years 2005–2006. The review covers anion receptors that employ amides and thioamides, pyrroles and indoles, ureas and thioureas, ammonium, guanidinium, imidazolium, and receptors containing hydroxyl groups. There is a discussion of anion templated assembly, followed by a short section outlining modelling studies of these systems. (226 references.)

DNAzymes for sensing, nanobiotechnology and logic gate applications

Abstract: Catalytic nucleic acids (DNAzymes or ribozymes) are selected by the systematic evolution of ligands by exponential enrichment process (SELEX). The catalytic functions of DNAzymes or ribozymes allow their use as amplifying labels for the development of optical or electronic sensors. The use of catalytic nucleic acids for amplified biosensing was accomplished by designing aptamer–DNAzyme conjugates that combine recognition units and amplifying readout units as in integrated biosensing materials. Alternatively, “DNA machines” that activate enzyme cascades and yield DNAzymes were tailored, and the systems led to the ultrasensitive detection of DNA. DNAzymes are also used as active components for constructing nanostructures such as aggregated nanoparticles and for the activation of logic gate operations that perform computing.

In situ hydrothermal synthesis of tetrazole coordination polymers with interesting physical properties

Abstract: Tetrazole compounds have been studied for more than one hundred years and applied in various areas. Several yeas ago Sharpless and his co-workers reported an environmentally friendly process for the preparation of 5-substituted 1H-tetrazoles in water with zinc salt as catalysts. To reveal the exact role of the zinc salt in this reaction, a series of hydrothermal reactions aimed at trapping and characterizing the solid intermediates were investigated. This study allowed us to obtain a myriad interesting metal–organic coordination polymers that not only partially showed the role of the metal species in the synthesis of tetrazole compounds but also provided a class of complexes displaying interesting chemical and physical properties such as second harmonic generation (SHG), fluorescence, ferroelectric and dielectric behaviors. In this tutorial review, we will mainly focus on tetrazole coordination compounds synthesized by in situhydrothermal methods. First, we will discuss the synthesis and crystal structures of these compounds. Their various properties will be mentioned and we will show the applications of tetrazole coordination compounds in organic synthesis. Finally, we will outline some expectations in this area of chemistry. The direct coordination chemistry of tetrazoles to metal ions and in situ synthesis of tetrazole through cycloaddition between organotin azide and organic cyano group will be not discussed in this review.

The renaissance of iron-based Fischer-Tropsch synthesis: on the multifaceted catalyst deactivation behaviour.

Abstract: Iron-based Fischer–Tropsch catalysts, which are applied in the conversion of CO and H2 into longer hydrocarbon chains, are historically amongst the most intensively studied systems in heterogeneous catalysis. Despite this, fundamental understanding of the complex and dynamic chemistry of the iron–carbon–oxygen system and its implications for the rapid deactivation of the iron-based catalysts is still a developing field. Fischer–Tropsch catalysis is characterized by its multidisciplinary nature and therefore deals with a wide variety of fundamental chemical and physical problems. This critical review will summarize the current state of knowledge of the underlying mechanisms for the activation and eventual deactivation of iron-based Fischer–Tropsch catalysts and suggest systematic approaches for relating chemical identity to performance in next generation iron-based catalyst systems (210 references).

Supramolecular gelling agents: can they be designed?

Abstract: The last two decades have witnessed an upsurge of research activities in the area of supramolecular gelators, especially low molecular mass organic gelators (LMOGs), not only for academic interests but also for their potential applications in materials science. However, most of the gelators are serendipitously obtained; their rational design and synthesis is still a major challenge. Wide structural diversities of the molecules known to act as LMOGs and a dearth of molecular level understanding of gelation mechanisms make it difficult to pin-point a particular strategy to achieve rational design of gelators. Nevertheless, some efforts are being made to achieve this goal. Once a gelling agent is serendipitously obtained, new gelling agents with novel properties may be prepared by modifying the parent gelator molecule following a molecular engineering rationale; however, such approach is limited to the same class of gelling agent generated from the parent gelating scaffold. A crystal engineering approach wherein the single-crystal structure of a molecule is correlated with its gelling/nongelling behaviour (structure–property correlation) allows molecular level understandings of the self-assembly of the gelator and nongelator molecules and therefore, provides new insights into the design aspects of supramolecular gelling agents. This tutorial review aims at highlighting some of the developments covering both molecular and crystal engineering approaches in designing LMOGs.

Chemistry of naphthalene diimides.

Abstract: This tutorial review surveys recent developments in the chemistry of naphthalene diimides (NDIs) and explores their application in the fields of material and supramolecular science. It begins with a discussion of their general uses, methods of syntheses and their electronic and spectroscopic properties. Of interest to their application in the fields of conducting thin films and molecular sensors is the structure–function relationships that exist either as co-components of supramolecular ensembles as in the case of “nanotubes”, or as the sole components in molecular wires. Also discussed are advances in NDI research within the areas of energy and electron transfer (covalent and non-covalent systems) and in host–guest chemistry including foldamer, mechanically-interlocked and ligand-gated ion channel examples. Finally, we explore the developments in the recent field of core-substituted NDIs, their photophysical properties and applications in artificial photosynthesis. We conclude with our views on the prospects of NDIs for future research endeavours.

Microwave dielectric heating in synthetic organic chemistry

Abstract: First described more than two decades ago, microwave-assisted organic synthesis has matured from a laboratory curiosity to an established technique that today is heavily used in both academia and industry. One of the most valuable advantages of using controlled microwave dielectric heating for chemical synthesis is the dramatic reduction in reaction times: from days and hours to minutes and seconds. As will be explained in this tutorial review, there are many more good reasons why organic chemists are nowadays incorporating dedicated microwave reactors into their daily work routine.

Organogels as scaffolds for excitation energy transfer and light harvesting

Abstract: The elegance and efficiency by which Nature harvests solar energy has been a source of inspiration for chemists to mimic such process with synthetic molecular and supramolecular systems. The insights gained over the years from these studies have contributed immensely to the development of advanced materials useful for organic based electronic and photonic devices. Energy transfer, being a key process in many of these devices, has been extensively studied in recent years. A major requirement for efficient energy transfer process is the proper arrangement of donors and acceptors in a few nanometers in length scale. A practical approach to this is the controlled self-assembly and gelation of chromophore based molecular systems. The present tutorial review describes the recent developments in the design of chromophore based organogels and their use as supramolecular scaffolds for excitation energy transfer studies.