Showing papers in "Chemical Reviews in 2010"

Dye-Sensitized Solar Cells

Abstract: Dye-sensitized solar cells (DSCs) offer the possibilities to design solar cells with a large flexibility in shape, color, and transparency. DSC research groups have been established around the worl ...

Solar Water Splitting Cells

Abstract: Energy harvested directly from sunlight offers a desirable approach toward fulfilling, with minimal environmental impact, the need for clean energy. Solar energy is a decentralized and inexhaustible natural resource, with the magnitude of the available solar power striking the earth’s surface at any one instant equal to 130 million 500 MW power plants.1 However, several important goals need to be met to fully utilize solar energy for the global energy demand. First, the means for solar energy conversion, storage, and distribution should be environmentally benign, i.e. protecting ecosystems instead of steadily weakening them. The next important goal is to provide a stable, constant energy flux. Due to the daily and seasonal variability in renewable energy sources such as sunlight, energy harvested from the sun needs to be efficiently converted into chemical fuel that can be stored, transported, and used upon demand. The biggest challenge is whether or not these goals can be met in a costeffective way on the terawatt scale.2

Semiconductor-based Photocatalytic Hydrogen Generation

Abstract: 2.3. Evaluation of Photocatalytic Water Splitting 6507 2.3.1. Photocatalytic Activity 6507 2.3.2. Photocatalytic Stability 6507 3. UV-Active Photocatalysts for Water Splitting 6507 3.1. d0 Metal Oxide Photocatalyts 6507 3.1.1. Ti-, Zr-Based Oxides 6507 3.1.2. Nb-, Ta-Based Oxides 6514 3.1.3. W-, Mo-Based Oxides 6517 3.1.4. Other d0 Metal Oxides 6518 3.2. d10 Metal Oxide Photocatalyts 6518 3.3. f0 Metal Oxide Photocatalysts 6518 3.4. Nonoxide Photocatalysts 6518 4. Approaches to Modifying the Electronic Band Structure for Visible-Light Harvesting 6519

Palladium-Catalyzed Ligand-Directed C−H Functionalization Reactions

Abstract: 1.1 Introduction to Pd-catalyzed directed C–H functionalization The development of methods for the direct conversion of carbon–hydrogen bonds into carbon-oxygen, carbon-halogen, carbon-nitrogen, carbon-sulfur, and carbon-carbon bonds remains a critical challenge in organic chemistry. Mild and selective transformations of this type will undoubtedly find widespread application across the chemical field, including in the synthesis of pharmaceuticals, natural products, agrochemicals, polymers, and feedstock commodity chemicals. Traditional approaches for the formation of such functional groups rely on pre-functionalized starting materials for both reactivity and selectivity. However, the requirement for installing a functional group prior to the desired C–O, C–X, C–N, C–S, or C–C bond adds costly chemical steps to the overall construction of a molecule. As such, circumventing this issue will not only improve atom economy but also increase the overall efficiency of multi-step synthetic sequences. Direct C–H bond functionalization reactions are limited by two fundamental challenges: (i) the inert nature of most carbon-hydrogen bonds and (ii) the requirement to control site selectivity in molecules that contain diverse C–H groups. A multitude of studies have addressed the first challenge by demonstrating that transition metals can react with C–H bonds to produce C–M bonds in a process known as “C–H activation”.1 The resulting C–M bonds are far more reactive than their C–H counterparts, and in many cases they can be converted to new functional groups under mild conditions. The second major challenge is achieving selective functionalization of a single C–H bond within a complex molecule. While several different strategies have been employed to address this issue, the most common (and the subject of the current review) involves the use of substrates that contain coordinating ligands. These ligands (often termed “directing groups”) bind to the metal center and selectively deliver the catalyst to a proximal C–H bond. Many different transition metals, including Ru, Rh, Pt, and Pd, undergo stoichiometric ligand-directed C–H activation reactions (also known as cyclometalation).2,3 Furthermore, over the past 15 years, a variety of catalytic carbon-carbon bond-forming processes have been developed that involve cyclometalation as a key step.1b–d,4 The current review will focus specifically on ligand-directed C–H functionalization reactions catalyzed by palladium. Palladium complexes are particularly attractive catalysts for such transformations for several reasons. First, ligand-directed C–H functionalization at Pd centers can be used to install many different types of bonds, including carbon-oxygen, carbon-halogen, carbon-nitrogen, carbon-sulfur, and carbon-carbon linkages. Few other catalysts allow such diverse bond constructions,5,6,7 and this versatility is predominantly the result of two key features: (i) the compatibility of many PdII catalysts with oxidants and (ii) the ability to selectively functionalize cyclopalladated intermediates. Second, palladium participates in cyclometalation with a wide variety of directing groups, and, unlike many other transition metals, promotes C–H activation at both sp2 and sp3 C–H sites. Finally, the vast majority of Pd-catalyzed directed C–H functionalization reactions can be performed in the presence of ambient air and moisture, making them exceptionally practical for applications in organic synthesis. While several accounts have described recent advances, this is the first comprehensive review encompassing the large body of work in this field over the past 5 years (2004–2009). Both synthetic applications and mechanistic aspects of these transformations are discussed where appropriate, and the review is organized on the basis of the type of bond being formed.

Cellulose nanocrystals: chemistry, self-assembly, and applications.

Abstract: Cellulose constitutes the most abundant renewable polymer resource available today. As a chemical raw material, it is generally well-known that it has been used in the form of fibers or derivatives for nearly 150 years for a wide spectrum of products and materials in daily life. What has not been known until relatively recently is that when cellulose fibers are subjected to acid hydrolysis, the fibers yield defect-free, rod-like crystalline residues. Cellulose nanocrystals (CNs) have garnered in the materials community a tremendous level of attention that does not appear to be relenting. These biopolymeric assemblies warrant such attention not only because of their unsurpassed quintessential physical and chemical properties (as will become evident in the review) but also because of their inherent renewability and sustainability in addition to their abundance. They have been the subject of a wide array of research efforts as reinforcing agents in nanocomposites due to their low cost, availability, renewability, light weight, nanoscale dimension, and unique morphology. Indeed, CNs are the fundamental constitutive polymeric motifs of macroscopic cellulosic-based fibers whose sheer volume dwarfs any known natural or synthetic biomaterial. Biopolymers such as cellulose and lignin and † North Carolina State University. ‡ Helsinki University of Technology. Dr. Youssef Habibi is a research assistant professor at the Department of Forest Biomaterials at North Carolina State University. He received his Ph.D. in 2004 in organic chemistry from Joseph Fourier University (Grenoble, France) jointly with CERMAV (Centre de Recherche sur les Macromolecules Vegetales) and Cadi Ayyad University (Marrakesh, Morocco). During his Ph.D., he worked on the structural characterization of cell wall polysaccharides and also performed surface chemical modification, mainly TEMPO-mediated oxidation, of crystalline polysaccharides, as well as their nanocrystals. Prior to joining NCSU, he worked as assistant professor at the French Engineering School of Paper, Printing and Biomaterials (PAGORA, Grenoble Institute of Technology, France) on the development of biodegradable nanocomposites based on nanocrystalline polysaccharides. He also spent two years as postdoctoral fellow at the French Institute for Agricultural Research, INRA, where he developed new nanostructured thin films based on cellulose nanowiskers. Dr. Habibi’s research interests include the sustainable production of materials from biomass, development of high performance nanocomposites from lignocellulosic materials, biomass conversion technologies, and the application of novel analytical tools in biomass research. Chem. Rev. 2010, 110, 3479–3500 3479

Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications

Abstract: Nanocrystals (NCs) discussed in this Review are tiny crystals of metals, semiconductors, and magnetic material consisting of hundreds to a few thousand atoms each. Their size ranges from 2-3 to about 20 nm. What is special about this size regime that placed NCs among the hottest research topics of the last decades? The quantum mechanical coupling * To whom correspondence should be addressed. E-mail: dvtalapin@uchicago.edu. † The University of Chicago. ‡ Argonne National Lab. Chem. Rev. 2010, 110, 389–458 389

The Catalytic Valorization of Lignin for the Production of Renewable Chemicals

Abstract: Biomass is an important feedstock for the renewable production of fuels, chemicals, and energy. As of 2005, over 3% of the total energy consumption in the United States was supplied by biomass, and it recently surpassed hydroelectric energy as the largest domestic source of renewable energy. Similarly, the European Union received 66.1% of its renewable energy from biomass, which thus surpassed the total combined contribution from hydropower, wind power, geothermal energy, and solar power. In addition to energy, the production of chemicals from biomass is also essential; indeed, the only renewable source of liquid transportation fuels is currently obtained from biomass.

Rhodium-Catalyzed C-C Bond Formation via Heteroatom-Directed C-H Bond Activation

Abstract: Once considered the 'holy grail' of organometallic chemistry, synthetically useful reactions employing C-H bond activation have increasingly been developed and applied to natural product and drug synthesis over the past decade. The ubiquity and relative low cost of hydrocarbons makes C-H bond functionalization an attractive alternative to classical C-C bond forming reactions such as cross-coupling, which require organohalides and organometallic reagents. In addition to providing an atom economical alternative to standard cross - coupling strategies, C-H bond functionalization also reduces the production of toxic by-products, thereby contributing to the growing field of reactions with decreased environmental impact. In the area of C-C bond forming reactions that proceed via a C-H activation mechanism, rhodium catalysts stand out for their functional group tolerance and wide range of synthetic utility. Over the course of the last decade, many Rh-catalyzed methods for heteroatom-directed C-H bond functionalization have been reported and will be the focus of this review. Material appearing in the literature prior to 2001 has been reviewed previously and will only be introduced as background when necessary. The synthesis of complex molecules from relatively simple precursors has long been a goal for many organic chemists. The ability to selectively functionalize a molecule with minimal pre-activation can streamline syntheses and expand the opportunities to explore the utility of complex molecules in areas ranging from the pharmaceutical industry to materials science. Indeed, the issue of selectivity is paramount in the development of all C-H bond functionalization methods. Several groups have developed elegant approaches towards achieving selectivity in molecules that possess many sterically and electronically similar C-H bonds. Many of these approaches are discussed in detail in the accompanying articles in this special issue of Chemical Reviews. One approach that has seen widespread success involves the use of a proximal heteroatom that serves as a directing group for the selective functionalization of a specific C-H bond. In a survey of examples of heteroatom-directed Rh catalysis, two mechanistically distinct reaction pathways are revealed. In one case, the heteroatom acts as a chelator to bind the Rh catalyst, facilitating reactivity at a proximal site. In this case, the formation of a five-membered metallacycle provides a favorable driving force in inducing reactivity at the desired location. In the other case, the heteroatom initially coordinates the Rh catalyst and then acts to stabilize the formation of a metal-carbon bond at a proximal site. A true test of the utility of a synthetic method is in its application to the synthesis of natural products or complex molecules. Several groups have demonstrated the applicability of C-H bond functionalization reactions towards complex molecule synthesis. Target-oriented synthesis provides a platform to test the effectiveness of a method in unique chemical and steric environments. In this respect, Rh-catalyzed methods for C-H bond functionalization stand out, with several syntheses being described in the literature that utilize C-H bond functionalization in a key step. These syntheses are highlighted following the discussion of the method they employ.

Engineering Metal Organic Frameworks for Heterogeneous Catalysis

Abstract: 2.2. MOFs with Metal Active Sites 4614 2.2.1. Early Studies 4614 2.2.2. Hydrogenation Reactions 4618 2.2.3. Oxidation of Organic Substrates 4620 2.2.4. CO Oxidation to CO2 4626 2.2.5. Phototocatalysis by MOFs 4627 2.2.6. Carbonyl Cyanosilylation 4630 2.2.7. Hydrodesulfurization 4631 2.2.8. Other Reactions 4632 2.3. MOFs with Reactive Functional Groups 4634 2.4. MOFs as Host Matrices or Nanometric Reaction Cavities 4636

Solar Energy Supply and Storage for the Legacy and Nonlegacy Worlds

Abstract: 1. Setting the Scope of the Challenge 6474 1.1. The Need for Solar Energy Supply and Storage 6474 1.2. An Imperative for Discovery Research 6477 1.3. Scope of Review 6478 2. Large-Scale Centralized Energy Storage 6478 2.1. Pumped Hydroelectric Energy Storage (PHES) 6479 2.2. Compressed Air Energy Storage (CAES) 6480 3. Smaller Scale Grid and Distributed Energy Storage 6481 3.1. Flywheel Energy Storage (FES) 6481 3.2. Superconducting Magnetic Energy Storage 6482 4. Chemical Energy Storage: Electrochemical 6482 4.1. Batteries 6482 4.1.1. Lead-Acid Batteries 6483 4.1.2. Alkaline Batteries 6484 4.1.3. Lithium-Ion Batteries 6484 4.1.4. High-Temperature Sodium Batteries 6484 4.1.5. Liquid Flow Batteries 6485 4.1.6. Metal-Air Batteries 6485 4.2. Capacitors 6485 5. Chemical Energy Storage: Solar Fuels 6486 5.1. Solar Fuels in Nature 6486 5.2. Artificial Photosynthesis and General Considerations of Water Splitting 6486

Lanthanide Luminescence for Biomedical Analyses and Imaging

Abstract: Keywords: Time-Resolved Fluorescence ; Resonance Energy-Transfer ; Near-Infrared Luminescence ; Double-Stranded Dna ; Prostate-Specific Antigen ; Photoinduced Electron-Transfer ; Europium-Tetracycline Complex ; Sybr-Green-I ; Terbium Complexes ; Optical Probes Reference EPFL-ARTICLE-149396doi:10.1021/cr900362eView record in Web of Science Record created on 2010-06-17, modified on 2017-05-12

C−H Activation for the Construction of C−B Bonds

Abstract: A number of studies were conducted to demonstrate C-H activation for the construction of C-B bonds. Investigations revealed that the conversion of C-H bonds to C-B bonds was both thermodynamically and kinetically favorable. The reaction at a primary C-H bond of methane or a higher alkene B 2(OR)4 formed an alkylboronate ester R' -B(OR)2 and the accompanying borane H-B(OR2. The ester and the borane were formed on the basis of calculated bond energies for methylboronates and dioaborolanes. The rates of key steps along the reaction pathway for the conversion of a C-H bond in an alkane or arene to the C-B bond in an alkyl or arylboronate ester were favorable. These studies also highlighted the accessible barriers for C-H bond cleavage and B-C bond formation during the borylation of alkanes and arenes.

Charge Photogeneration in Organic Solar Cells

Abstract: In recent years, organic solar cells utilizing π-conjugated polymers have attracted widespread interest in both the academic and, increasingly, the commercial communities. These polymers are promising in terms of their electronic properties, low cost, versatility of functionalization, thin film flexibility, and ease of processing. These factors indicate that organic solar cells, although currently producing relatively low power conversion efficiencies (∼5-7%),1–3 compared to inorganic solar cells, have the potential to compete effectively with alternative solar cell technologies. However, in order for this to be feasible, the efficiencies of organic solar cells need further improvement. This is the focus of extensive studies worldwide. The backbone of a π-conjugated polymer is comprised of a linear series of overlapping pz orbitals that have formed via sp2 hybridization, thereby creating a conjugated chain of delocalized electron density. It is the interaction of these π electrons that dictates the electronic characteristics of the polymer. The energy levels become closely spaced as the delocalization length increases, resulting in a ‘band’ structure somewhat similar to that observed in inorganic solid-state semiconductors. In contrast to the latter, however, the primary photoexcitations in conjugated polymers are bound electron-hole pairs (excitons) rather than free charge carriers; this is largely due to their low dielectric constant and the presence of significant electron-lattice interactions and electron correlation effects.4 In the absence of a mechanism to dissociate the excitons into free charge carriers, the exciton will undergo radiative and nonradiative decay, with a typical exciton lifetime in the range from 100 ps to 1 ns. Achieving efficient charge photogeneration has long been recognized as a vital challenge for molecular-based solar cells. For example, the first organic solar cells were simple single-layer devices based on the pristine polymer and two electrodes of different work function. These devices, based on a Schottky diode structure, resulted in poor photocurrent efficiency.5–7 Relatively efficient photocurrent generation in an organic device was first reported by Tang in 1986,8 employing a vacuum-deposited CuPc/ perylene derivative donor/acceptor bilayer device. The differing electron affinities (and/or ionization potentials) between these two materials created an energy offset at their interface, thereby driving exciton dissociation. However, the efficiency of such bilayer devices is limited by the requirement of exciton diffusion to the donor/acceptor interface, typically requiring film thicknesses less than the optical absorption depth. Organic materials usually exhibit exciton diffusion lengths of ∼10 nm and optical absorption depths of 100 nm, although we note significant progress is now being made with organic materials with exciton diffusion lengths comparable to or exceeding their optical absorption depth.9–12 The observation of ultrafast photoinduced electron transfer13,14 from a conjugated polymer to C60 and the * To whom correspondence should be addressed. E-mail: j.durrant@ imperial.ac.uk. Chem. Rev. 2010, 110, 6736–6767 6736

Imaging and photodynamic therapy: mechanisms, monitoring, and optimization.

Abstract: 1.1 Photodynamic Therapy and Imaging The purpose of this review is to present the current state of the role of imaging in photodynamic therapy (PDT). In order for the reader to fully appreciate the context of the discussions embodied in this article we begin with an overview of the PDT process, starting with a brief historical perspective followed by detailed discussions of specific applications of imaging in PDT. Each section starts with an overview of the specific topic and, where appropriate, ends with summary and future directions. The review closes with the authors’ perspective of the areas of future emphasis and promise. The basic premise of this review is that a combination of imaging and PDT will provide improved research and therapeutic strategies. PDT is a photochemistry-based approach that uses a light-activatable chemical, termed a photosensitizer (PS), and light of an appropriate wavelength, to impart cytotoxicity via the generation of reactive molecular species (Figure 1a). In clinical settings, the PS is typically administered intravenously or topically, followed by illumination using a light delivery system suitable for the anatomical site being treated (Figure 1b). The time delay, often referred to as drug-light interval, between PS administration and the start of illumination with currently used PSs varies from 5 minutes to 24 hours or more depending on the specific PS and the target disease. Strictly speaking, this should be referred to as the PS-light interval, as at the concentrations typically used the PS is not a drug, but the drug-light interval terminology seems to be used fairly frequently. Typically, the useful range of wavelengths for therapeutic activation of the PS is 600 to 800 nm, to avoid interference by endogenous chromophores within the body, and yet maintain the energetics necessary for the generation of cytotoxic species (as discussed below) such as singlet oxygen (1O2). However, it is important to note that photosensitizers can also serve as fluorescence imaging agents for which activation with light in the 400nm range is often used and has been extremely useful in diagnostic imaging applications as described extensively in Section 2 of this review. The obvious limitation of short wavelength excitation is the lack of tissue penetration so that the volumes that are probed under these conditions are relatively shallow. Open in a separate window Figure 1 (A) A schematic representation of PDT where PS is a photoactivatable multifunctional agent, which, upon light activation can serve as both an imaging agent and a therapeutic agent. (B) A schematic representation of the sequence of administration, localization and light activation of the PS for PDT or fluorescence imaging. Typically the PS is delivered systemically and allowed to circulate for an appropriate time interval (the “drug-light interval”), during which the PS accumulates preferentially in the target lesion(s) prior to light activation. In the idealized depiction here the PS is accumulation is shown to be entirely in the target tissue, however, even if this is not the case, light delivery confers a second layer of selectivity so that the cytotoxic effect will be generated only in regions where both drug and light are present. Upon localization of the PS, light activation will result in fluorescence emission which can be implemented for imaging applications, as well as generation cytotoxic species for therapy. In the former case light activation is achieved with a low fluence rate to generate fluorescence emission with little or no cytotoxic effect, while in the latter case a high fluence rate is used to generate a sufficient concentration of cytotoxic species to achieve biological effects.

New Strategies for Fluorescent Probe Design in Medical Diagnostic Imaging

Abstract: In vivo medical imaging has made great progress due to advances in the engineering of imaging devices and developments in the chemistry of imaging probes Several modalities have been utilized for medical imaging, including X-ray radiography and computed tomography (x-ray CT), radionuclide imaging using single photons and positrons, magnetic resonance imaging (MRI), ultrasonography (US), and optical imaging In order to extract more information from imaging, “contrast agents” have been employed For example, organic iodine compounds have been used in X-ray radiography and computed tomography, superparamagnetic or paramagnetic metals have been used in MRI, and microbubbles have been used in ultrasonography Most of these, however, are non-targeted reagents Molecular imaging is widely considered the future for medical imaging Molecular imaging has been defined as the in vivo characterization and measurement of biologic process at the cellular and molecular level1, or more broadly as a technique to directly or indirectly monitor and record the spatio-temporal distribution of molecular or cellular processes for biochemical, biologic, diagnostic, or therapeutic application2 Molecular imaging is the logical next step in the evolution of medical imaging after anatomic imaging (eg x-rays) and functional imaging (eg MRI) In order to attain truly targeted imaging of specific molecules which exist in relatively low concentrations in living tissues, the imaging techniques must be highly sensitive Although MRI, US, and x-ray CT are often listed as molecular imaging modalities, in truth, radionuclide and optical imaging are the most practical modalities, for molecular imaging, because of their sensitivity and the specificity for target detection Radionuclide imaging, including gamma scintigraphy and positron emission tomography (PET), are highly sensitive, quantitative, and offer the potential for whole body scanning However, radionuclide imaging methods have the disadvantages of poor spatial and temporal resolution3 Additionally, they require radioactive compounds which have an intrinsically limited half life, and which expose the patient and practitioner to ionizing radiation and are therefore subject to a variety of stringent safety regulations which limit their repeated use4 Optical imaging, on the other hand, has comparable sensitivity to radionuclide imaging, and can be “targeted” if the emitting fluorophore is conjugated to a targeting ligand3 Optical imaging, by virtue of being “switchable”, can result in very high target to background ratios “Switchable” or activatable optical probes are unique in the field of molecular imaging since these agents can be turned on in specific environments but otherwise remain undetectable This improves the achievable target to background ratios, enabling the detection of small tumors against a dark background5,6 This advantage must be balanced against the lack of quantitation with optical imaging due to unpredictable light scattering and absorption, especially when the object of interest is deep within the tissue Visualization through the skin is limited to superficial tissues such as the breast7-9 or lymph nodes10,11 The fluorescence signal from the bright GFP-expressing tumors can be seen in the deep organ only in the nude mice 12,13 However, optical molecular imaging can also be employed during endoscopy14 or surgery 15,16

Fluorescence Lifetime Measurements and Biological Imaging

Abstract: When a molecule absorbs a photon of appropriate energy, a chain of photophysical events ensues, such as internal conversion or vibrational relaxation (loss of energy in the absence of light emission), fluorescence, intersystem crossing (from singlet state to a triplet state) and phosphorescence, as shown in the Jablonski diagram for organic molecules (Fig. 1). Each of the processes occurs with a certain probability, characterized by decay rate constants (k). It can be shown that the average length of time τ for the set of molecules to decay from one state to another is reciprocally proportional to the rate of decay: τ = 1/k. This average length of time is called the mean lifetime, or simply lifetime. It can also be shown that the lifetime of a photophysical process is the time required by a population of N electronically excited molecules to be reduced by a factor of e. Correspondingly, the fluorescence lifetime is the time required by a population of excited fluorophores to decrease exponentially to N/e via the loss of energy through fluorescence and other non-radiative processes. The lifetime of photophycal processes vary significantly from tens of femotoseconds for internal conversion1,2 to nanoseconds for fluorescence and microseconds or seconds for phosphorescence.1 Open in a separate window Figure 1 Jablonski diagram and a timescale of photophysical processes for organic molecules.

Surface Modifications for Antifouling Membranes

Abstract: Fouling is the deposition of retained particles, colloids, macromolecules, salts, etc., at the membrane surface or inside the pore at the pore wall. Fouling reduces the membrane flux either temporarily or permanently. While the initial flux can be restored by washing the membrane or by applying back-pressures to the temporarily fouled membrane, it cannot be restored when the membrane becomes permanently fouled. The main focus of this Review is on the permanent flux decline. The fouling is caused by the interaction between the membrane surface and the foulants, which include inorganic, organic, and biological substances in many different forms. The foulants not only physically interact with the membrane surface but also chemically degrade the membrane material. For example, colloidal particles, such as natural organic matter (NOM), are considered as the main reason for membrane fouling, which could be controlled by the permeation hindrance and electric double layer repulsion. The formation of biofilms with extra-cellular polymeric substances (EPSs) and microbial cells matrix is the example of biofouling.1 Biofilms are developed by the microbial cell adhesion and subsequent colonization on the membrane surfaces through EPS, which may account for 50-90% of total organic carbon. The biofouling could be minimized by periodical washing with chemicals such as sodium hypochlorite solution, but it will result in the simultaneous degradation of the membrane material’s lifetime. It is a severe problem for membranes used in pressure-driven processes such as reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF) and also for other membrane processes, seriously hampering the applications of membrane processes. Hence, membrane fouling as well as its reduction has been a subject of many academic studies and industrial research and development efforts since the early 1960s when industrial membrane separation processes emerged. Selection of an appropriate membrane, pretreatment of the process fluid, adjustment of operating design, and conditions are all known to control fouling to some extent. On the other hand, development of absolutely nonfouling membranes seems extremely difficult, if not totally impossible. This Review surveys the latest efforts in which the reduction of irreversible fouling is attempted by the modification of the membrane surface. The separation process by membrane is essentially a surface phenomenon. More specifically, the skin layer or top surface layer plays the vital role. Therefore, it is a natural consequence to modify membrane surface for reducing the fouling. It is generally accepted that an increase in hydrophilicity offers better fouling resistance because protein and many other foulants are hydrophobic in nature. Most nanofiltration membranes are electrically charged, which significantly reduces the scale-formation. During the past decade, the emergence of atomic force microscopy (AFM) enabled us to study the effect of the surface roughness in nanoscale on the membrane fouling. It is believed that the membrane fouling with particulate substance is enhanced by an increase in the surface roughness. It is shown in this Review that all of the above concepts, except for the membrane surface charge, are based on correlation of data, which are, at best, valid within a limited range of surface property parameters. * To whom correspondence should be addressed. Phone: (613) 562-5800, ext 6085. Fax: (613) 562-5172. E-mail: rana@eng.uottawa.ca. Dipak Rana is presently a Research Scientist in the Industrial Membrane Research Institute, Department of Chemical and Biological Engineering, University of Ottawa, Ottawa, Canada. Dr. Rana has been a member of various prestigious organizations, such as the Indian Chemical Society, Society for Polymer Science, India, Society of Plastics Engineers, USA, American Chemical Society, etc., for a long period. He was awarded a Ph.D. in Science from Jadavpur University, Calcutta (presently Kolkata), when he was working at the Indian Association for the Cultivation of Science, Calcutta, India. He received his Master in Chemistry with specialization in Physical Chemistry as well as his Bachelor with Honors in Chemistry from the University of Calcutta, India. Dr. Rana has published over 50 professional papers and book chapters. Chem. Rev. 2010, 110, 2448–2471 2448

Ruthenium-based heterocyclic carbene-coordinated olefin metathesis catalysts.

Abstract: The fascinating story of olefin (or alkene) metathesis (eq 1) began almost five decades ago, when Anderson and Merckling reported the first carbon-carbon double-bond rearrangement reaction in the titanium-catalyzed polymerization of norbornene. Nine years later, Banks and Bailey reported “a new disproportionation reaction . . . in which olefins are converted to homologues of shorter and longer carbon chains...”. In 1967, Calderon and co-workers named this metal-catalyzed redistribution of carbon-carbon double bonds olefin metathesis, from the Greek word “μeτάθeση”, which means change of position. These contributions have since served as the foundation for an amazing research field, and olefin metathesis currently represents a powerful transformation in chemical synthesis, attracting a vast amount of interest both in industry and academia.

Dendrimers Designed for Functions: From Physical, Photophysical, and Supramolecular Properties to Applications in Sensing, Catalysis, Molecular Electronics, Photonics, and Nanomedicine

Abstract: 3.15. Miscellaneous Photophysical Studies 1874 3.16. Dendritic Fluorescent Sensors 1875 3.17. Nonlinear Optical Properties 1875 4. Supramolecular Properties 1876 4.1. Concepts and Pioneering Studies 1876 4.2. H-Bonding 1877 4.3. Electrostatic Binding 1877 4.4. Combined H-Bonding/Ionic Bonding 1879 4.5. Coordination of Metal Ions 1880 4.6. Intradendritic π-π Interactions 1880 4.7. Encapsulation of Neutral Guest Molecules 1881 4.8. Interdendritic Supramolecular Associations 1883 4.8.1. Liquid Crystals 1883 4.8.2. Other Dendritic Self-Assemblies 1884 4.9. Supramolecular Assemblies between Dendrimers and Surfactants or Polymers 1885

Materials and applications for large area electronics: solution-based approaches.

Abstract: 2.3. Medical Devices and Sensors 9 2.4. Radio Frequency Applications 10 3. Materials 12 3.1. Organic Electronics Materials 12 3.2. Semiconducting Polymer Design 13 3.3. Poly(3-alkylthiophenes) 14 3.4. Poly(thieno(3,2-b)thiophenes 15 3.5. Benchmark Polymer Semiconductors 15 3.6. High Performance Polymer Semiconductors 15 4. Device Stability 16 4.1. Bias Stress in Organic Transistors 17 4.1.1. Bias Stress Characterization 17 4.1.2. Bias Stress Mechanism 18 4.2. Short Channel Effects in Organic Transistors 19 5. Materials Patterning and Integration 20 6. Conclusions 22 7. Acknowledgments 22 8. References 22

Hybrid Organic−Inorganic Polyoxometalate Compounds: From Structural Diversity to Applications

Abstract: Polyoxometalates (POMs) are discrete anionic metaloxygen clusters which can be regarded as soluble oxide fragments. They exhibit a great diversity of sizes, nuclearities, and shapes. They are built from the connection of {MOx} polyhedra, M being a d-block element in high oxidation state, usually VIV,V, MoVI, or WVI.1 While these species have been known for almost two centuries, they still attract much interest partly based on their large domains of applications. They play a great role in various areas ranging from catalysis,2 medicine,3 electrochemistry,4 photochromism,5 to magnetism.6 This palette of applications is intrinsically due to the combination of their added value properties (redox properties, large sizes, high negative charges, nucleophilicity...). Parallel to this domain, the organic-inorganic hybrids area has followed a similar expansion during the last 10 years. The concept of organic-inorganic hybrid materials * To whom correspondence should be addressed. E-mail: dolbecq@ chimie.uvsq.fr. Chem. Rev. 2010, 110, 6009–6048 6009

Fluorescent indicators for intracellular pH.

Abstract: 5. Cyanine-Based pHi Indicators 2717 5.1. Design of pH-Sensitive Cyanine Dyes 2717 5.2. Near-Neutral Cyanine-Based pH Indicators 2718 5.3. Acidic Cyanine-Based pH Indicators 2719 6. Miscellaneous Small Molecule pHi Indicators 2719 6.1. Various Indicators for Near-Neutral pH Values 2719 6.1.1. Europium Complex 2719 6.1.2. Fluorene Derivative 2719 6.1.3. 1,4-Dihydroxyphthalonitrile (1,4-DHPN) 2720 6.1.4. 8-Hydroxypyrene-1,3,6-trisulfonic acid (HPTS) 2720

Marine indole alkaloids: potential new drug leads for the control of depression and anxiety

Abstract: The marine environment has been explored in the search for new bioactive compounds over the last 50 years, becoming a highly important and rich source of potent molecules and drug leads reported to possess a wide scope of activities. Alkaloids constitute one of the largest classes of natural products and are synthesized by terrestrial and marine organisms on all evolutionary levels. Alkaloids are usually present in an organism as a mixture consisting of several major and a few minor compounds of the same biosynthetic origin and differing only in functional groups. This group of compounds has apparently evolved as a defense mechanism against predators and as a result alkaloids are often highly potent and toxic molecules.1 Marine invertebrates have proven to be an outstanding source of active molecules, one of the most promising being indole alkaloids. Although many of these marine alkaloids closely resemble the endogenous amines (serotonin, dopamine or histamine), their potential affinity to various neurological targets and consequential impact on animal behavior is virtually unexplored. Indole alkaloids, their activity, synthesis and potential use in medicine have been already reviewed in several articles.2 In this review we provide information on current and potential pharmaceuticals including small molecule natural indole alkaloids, their biological properties, structure-activity relationship studies, and especially their potential for the treatment of neurological disorders. 1.1. The indole moiety in drugs The indole moiety is present in a number of drugs currently on the market. Most of these belong to triptans which are used mainly in the treatment of migraine headaches (Fig. 1). All members of this group are agonists of migraine associated 5HT1B and 5HT1D serotonin receptors. Sumatriptan (Imitrex) was developed by Glaxo for the treatment of migraines and introduced into the market as the first member of the triptan family.3 Relative to the second generation triptans, sumatriptan has lower oral bioavailability and a shorter half-life. Frovatriptan (FROVA®) was developed by Vernalis for the treatment of menstruation associated headaches. Frovatriptan's affinity for migraine specific serotonin receptors 5HT1B is believed to be the highest among all triptans.4 In addition, frovatriptan binds to 5HT1D and 5HT7 receptor subtypes.5 Zolmitriptan marketed by AstraZeneca is used to treat acute migraine attacks and cluster headaches. GlaxoSmithKline's naratriptan (Amerge) is also used in the treatment of migraines and some of its side effects include dizziness, tiredness, tingling of the hands and feet and dry mouth. All available triptans are well tolerated and effective.6 The highest incidence of central nervous system (CNS) related side effects (dizziness, drowsiness) was reported for zolmitriptan (5 mg), rizatriptan (10 mg) and eletriptan (40 mg, 80 mg).7 The differences in side-effect profiles for triptans are not likely caused by their different affinity towards serotonin receptors or other neurological receptors in the CNS. There is a positive correlation between the lipophilicity coefficient and CNS side effects; these undesired effects are also dose-dependent. Figure 1 Currently available drugs from the triptan group. 1.2. Serotonin receptors – possible targets for neurologically active marine indole alkaloids Given that depression affects approximately 18 million Americans annually,8 it is crucial to develop new effective treatments for this disorder. Intensive studies are being conducted in the area of new targets for antidepressant drugs,9,10 but most antidepressant drugs still target the neurotransmitter systems, mainly serotonin, dopamine and noradrenaline. Serotonin is one of the neurotransmitters present in the central and peripheral nervous system which plays an important role in normal brain function and regulates sleep, mood, appetite, sexual function, memory, anxiety and many others.11 Serotonin exerts its effects through seven families of receptors (5-HT1 – 5-HT7) further divided into several subclasses. Except for 5-HT3 receptor which is a ligand-gated ion channel, the serotonin receptors belong to the G-protein coupled receptor family. Due to a lack of selective ligands, there is still little known about several 5-HT receptor subclasses.12 Marine monoindole alkaloids, sharing structure similarities with serotonin, are certain to become useful tools to facilitate the understanding of serotonin receptor function and generate new drug leads for the treatment of depression, anxiety, migraines and other 5HT receptor related disorders.

Activatable photosensitizers for imaging and therapy

Abstract: 2. Activatable Photosensitizer Design Considerations 2842 2.1. Activation Strategy 2842 2.2. Photosensitizer Selection 2844 2.3. Photosensitizer Conjugation 2845 3. Examples of Activatable Photosensitizers 2845 3.1. Environment-Activated Photosensitizers 2845 3.2. Enzyme-Activated Photosensitizers 2846 3.3. Nucleic Acid-Activated Photosensitizers 2852 3.4. Other Activation Mechanisms 2853 4. Conclusion and Outlook 2855 5. Abbreviations 2855 6. Acknowledgments 2855 7. References 2855

Recent Developments in the Chemistry of Cubic Polyhedral Oligosilsesquioxanes

Abstract: 3.6.3. T8R7R′ Compounds (R ) i-Bu) 2127 3.6.4. T8R7R′ Compounds (R ) Et, c-C5H9, or Cy) 2128 3.7. Mass Spectra of POSS Compounds 2128 3.8. Electronic Spectra of POSS Compounds 2130 3.9. NMR and EPR Spectroscopies 2131 3.9.1. Solution 29Si NMR Studies 2131 3.9.2. Other Heteronuclear NMR Studies 2134 3.9.3. EPR Spectra 2134 3.10. Vibrational Spectra of POSS Compounds 2136 3.11. X-ray Photoelectron Spectra of POSS Compounds 2139