Volume 83, Issue 1

This issue of Pure and Applied Chemistry (PAC) is special for several reasons. It is an opportunity for IUPAC to celebrate the inauguration of the International Year of Chemistry 2011 (IYC 2011), so the content departs from the usual conference papers, technical reports, or recommendations, in favor of a collection of articles by past winners of the IUPAC Prize for Young Chemists, from inception of this annual competition in 2000 up to 2009. 1 This Prize was created “to encourage outstanding young research scientists at the beginning of their careers”, and has richly fulfilled its founding objectives to recognize young talent, with the award of no less than 46 prizes over the years and honorable mention of many competitors whose excellent contributions did not receive the highest accolade. The declared goals of IYC 2011 are to “increase public appreciation of chemistry in meeting world needs, to encourage an interest in chemistry among young people, and to generate enthusiasm for the creative future of chemistry”. By happy coincidence, 2011 is the 100th anniversary of the Nobel Prize awarded to Marie Curie, and is thus also an opportunity to celebrate the contributions of women to science, and recognize the ongoing challenge of ensuring equal opportunity for all in career development. Most importantly, Marie Curie is an inspirational role model, not only to women but to all young students, and it is altogether fitting that the coming generation of scientists should be closely identified with IYC 2011, since enthusiasm is a defining characteristic of youth. IUPAC recognizes and wholeheartedly undertakes its duty to encourage and support young scientists throughout the world. As a global, scientific, nongovernmental organization, it contributes in a variety of distinctive ways to inspiring and helping young scientists to study and embark upon careers in chemistry. The Prize for Young Chemists is merely one such regular activity which, apart from monetary reward, enables recipients to attend an IUPAC Congress and the opportunity to showcase their achievements in an annual PAC Special Topic collection of invited, peer-reviewed articles, which has generated an outstanding published record since 2002. 2 In a more recent initiative commencing 2008, IUPAC has allocated a grant to enable economically disadvantaged countries to participate in the annual International Chemistry Olympiad. More generally, IUPAC operates a Financial Support for Conferences program to promote opportunities for young scientists and advanced students, particularly from scientifically emerging regions, to attend selected international conferences. The Young Ambassadors for Chemistry program was established as a partnership between the IUPAC Committee on Chemistry Education and Science Across the World, to facilitate interaction with teachers and students to increase public appreciation for and understanding of chemistry. An important feature of ongoing IUPAC strategy is to familiarize younger scientists with Union activities, and attendant opportunities for service to the international community. The Affiliate Membership Program was established in the 1980s to encourage individuals with an interest in IUPAC activities to sustain a direct relationship with the Union. Additional incentives to developing and economically disadvantaged countries include certain numbers of free affiliate memberships for young chemists. In a complementary initiative, the Young Observers Program sponsors young scientists to attend IUPAC General Assemblies and to participate as observers in selected activities and deliberations by invitation. The passage of IYC 2011 will be marked by a rich international program of activities, in which IUPAC features prominently in three cornerstone events, namely, the formal launch and closing, and the 43rd IUPAC Congress. The latter event will take place in San Juan, Puerto Rico on 30 July to 7 August 2011, 3 and offers additional incentives for young scientists to attend and participate in a unique international celebration of chemistry. 4 The winners of the 2010 and 2011 Prize for Young Chemists will attend as active delegates, and the award ceremony will have special significance in perpetuating a tradition that recognizes the hand of youth in shaping the future of chemistry. This issue of PAC pays its own tribute to the many brilliant young scientists who have been recognized by the Prize for Young Chemists jury over the past 10 years. We are grateful to those who accepted the invitation to contribute to this special collection, fittingly subtitled “Perspectives and Challenges for the International Year of Chemistry”. It is hoped that the contents will inspire and enthuse readers with fascinating insights into new and emerging aspects of chemical sciences. I am very honored to have had the opportunity to write this Preface, and thereby to congratulate all prize winners, past and present, and wish them fulfilling and successful careers, driven by enthusiasm and belief in the great future of our discipline. Nicole Moreau IUPAC President 1 The works of the 2010 winners feature in the December 2010 issue of PAC, http://www.iupac.org/publications/pac/82/12/. 2 The full archival record of the Young Chemists’ Prize Collections can be accessed at http://www.iupac.org/publications/pac/special/. 3 Consult http://www.iupac2011.org/ for details about the 43rd IUPAC Congress. 4 Details of award programs targeted to encourage young chemist’s participation at the 43rd IUPAC Congress in Puerto Rico are available at http://www.iupac.org/web/nt/2010-11-05_43_Congress.

Semiconductor quantum dots (QDs) are inorganic nanoparticles which, because of their unique size-dependent electronic properties, are of high potential interest for the construction of functional nanodevices. Photoinduced electron transfer is a versatile mechanism used to implement light-induced functionalities in multicomponent (supra)molecular assemblies. Indeed, QDs can be employed as active components in new generations of these systems. The rational design of the latter, however, requires prior knowledge of the photo-physical properties and redox potentials of the nanocrystals. Here we discuss the results of recent systematic electrochemical investigations aimed at understanding the structural factors that regulate the redox properties of CdSe core and CdSe–ZnS core–shell QDs.

Synthetic biodegradable elastomers are an emerging class of materials with many potential clinical applications including drug delivery and tissue engineering. Biodegradable elastomers offer advantages of structure diversity, tunable properties, and a wide range of processing capabilities. This review highlights some recent developments in various aspects of biodegradable materials synthesis, characterization, and processing with a specific focus on structure-processing–property relationships. Biodegradation mechanisms and issues regarding tissue biocompatibility of these materials are discussed. Applications of synthetic biodegradable elastomers, including use as a materials platform for controlled release systems, tissue engineering scaffolds, and engineered substrates for in vitro cell–biomaterials interactions will also be presented.

One of the least understood and least exploited aspects of nanoscience is dynamic coupling between directional translation at mesoscales (lengths above ~50 nm) and changes in local chemical bonding (lengths below ~1 nm). A major cause is the traditional dominance of two distinct and seemingly incompatible models for describing dynamics at the two scales: continuum mechanics based on the balance of forces, i.e., mechanical equilibrium (lengths above ~50 nm) and activated escape from an energy well, i.e., chemical equilibrium (below ~1 nm). These models yield meaningful results within their respective dimensional limits but leave processes in between in the gray area of conceptual ambiguity and technical intractability. Such processes underlie phenomena as diverse as catastrophic failure of strained materials, operation of motor polymers, behavior of polymer flows, and mechanosensing. Chemomechanics integrates the two conventional dynamic models into a single internally consistent, scale-independent framework that is essential for a quantitative understanding and the efficient exploitation of dynamic coupling across the “formidable gap” at ~1–50 nm. Chemomechanics holds promise (1) to facilitate significantly the design of new stress-responsive and actuating polymers, including those optimized specifically for the propulsion of autonomous nanomechanical devices and for use in micro- and nanoscale stress sensors; and (2) to yield general predictive molecular relationships between chemical composition, structure, and mechanical properties of polymers both at the single-chain and bulk levels. Theoretical and experimental studies of dynamic coupling across the formidable gap have traditionally been carried out within soft-matter physics. As far as I am aware, my group was the first to approach the problem from a chemist’s perspective. Below, I summarize the state-of-the-art of chemical understanding of processes in the formidable gap from both theoretical and experimental perspectives.

Fluorescent conjugated polyelectrolytes (CPEs) have attracted considerable interest over the past decade as novel materials for developing biosensing schemes and sensing devices for biomolecules. This interest stems from the exquisite polymer sensitivity to the presence of fluorescence quenchers, enabling amplified sensing of molecules of interest. Efficient energy transport along the polymer backbone is critical to their sensing capabilities. Considerable research efforts have thus gone into understanding and controlling energy transport along the polymer backbone. In particular, it has been shown that interactions between CPEs with either surfactants or lipid molecules may significantly reduce energy transport along the polymer backbone that in turn may provide for unique biosensing opportunities. In the first half of this review, we give a historical overview on energy transport in conjugated polymers and polyelectrolytes. In the second half, we summarize the most recent work on the interaction of CPEs with surfactants with an emphasis on our own work elucidating electronic energy transport in CPEs encapsulated into lipid vesicles or embedded within the membrane of lipid vesicles.

The development of more efficient processes for CO 2 capture from the flue streams of power plants is considered a key to the reduction of greenhouse gas emissions implicated in global warming. Indeed, several U.S. and international climate change initiatives have identified the urgent need for improved materials and methods for CO 2 capture. Conventional CO 2 capture processes employed in power plants world-wide are typically postcombustion “wet scrubbing” methods involving the absorption of CO 2 by amine-containing solvents such as methanolamine (MEA). These present several disadvantages, including the considerable heat required in regeneration of the solvent and the necessary use of inhibitors for corrosion control, which lead to reduced efficiencies and increased costs for electricity production. This perspective article seeks to highlight the most recent advances in new materials for CO 2 capture from power plant flue streams, with particular emphasis on the rapidly expanding field of metal–organic frameworks. Ultimately, the development of new classes of efficient, cost-effective, and industrially viable capture materials for application in carbon capture and storage (CCS) systems offers an immense opportunity to reduce atmospheric emissions of greenhouse gases on a national and international scale.

The development of NMR techniques applied in the last 10 years to partially oriented systems, and in particular to liquid crystals (LCs), is the object of this brief perspective. The evolution of NMR methods (i.e., new NMR pulse sequences) and the improvement of both theoretical models and mathematic tools for the analysis of NMR data (specifically, for partially ordered systems) allowed scientists to extend their research to increasingly complex materials, such as dendrimers, polymers, and membranes, and to investigate unique phenomena, such as field-induced alignment and confining effects. Furthermore, the fast development of nanoscience and biomedicine is offering a rich variety of new “physical chemical” problems related to partially ordered materials. Starting from a brief perspective of recent works on thermotropic and lyotropic LCs based on different NMR methods, new challenges in this field will be drawn. Moreover, recent selected research works will be discussed in detail with particular emphasis on: (i) the effect of high magnetic fields on the supramolecular structure of chiral liquid-crystalline phases, such as the SmC*, TGBA*, and “de Vries”-type SmA* phases, by means of solid-state 2 H NMR; (ii) the slow dynamics in the isotropic phase of bent-core LCs (BLCs) and of liquid single-crystal elastomers evidenced by 2 H NMR relaxation studies; and (iii) the influence of the LC environment on the conformational properties of rod-like mesogens studied by high-resolution solid-state 13 C NMR methods. This work aims to offer an occasion of reflection on this field of physical chemistry with a glance at future trends and challenges in view of the celebration of the International Year of Chemistry, 2011.

Graphite oxide sheet, now referred to as graphene oxide (GO), is the product of chemical oxidation and exfoliation of graphite powders that was first synthesized over a century ago. Interest in this old material has resurged in recent years, especially after the discovery of graphene, as GO is considered a promising precursor for the bulk production of graphene-based materials. GO sheets are single atomic layers that can readily extend up to tens of microns in lateral dimension. Therefore, their structure bridges the typical length scales of both chemistry and materials science. GO can be viewed as an unconventional type of soft material as it carries the characteristics of polymers, colloids, membranes, and as highlighted in this review, amphiphiles. GO has long been considered hydrophilic due to its excellent water dispersity, however, our recent work revealed that GO sheets are actually amphiphilic with an edge-to-center distribution of hydrophilic and hydrophobic domains. Thus, GO can adhere to interfaces and lower interfacial energy, acting as surfactant. This new property insight helps to better understand GO’s solution properties which can inspire novel material assembly and processing methods such as for fabricating thin films with controllable microstructures and separating GO sheets of different sizes. In addition, GO can be used as a surfactant sheet to emulsify organic solvents with water and disperse insoluble materials such as graphite and carbon nanotubes (CNTs) in water, which opens up opportunities for creating functional hybrid materials of graphene and other π-conjugated systems.

Mimicking the evolution processes of Nature, the combinatorial approach to biomolecular recognition properties attracts much attention due to the potential as a generic scheme to achieving complex material structures and hierarchical assemblies with molecular precision from the bottom up. In this paper, some recent efforts in the biomimetic synthesis of inorganic materials are reviewed, with emphasis placed on in vitro material formation with the use of protein/peptide molecules found in natural organisms as well as those with specific affinities to inorganic materials selected through the molecular evolution process. The applications of material-specific peptides and proteins in sensing and guiding hierarchical material assembly are also briefly discussed at the end.

Recent design tools for tuning the properties of conjugated polymers for efficient polymer solar cells (PSCs) are briefly reviewed. Based on limitations in the solar-to-electric energy conversion process imposed by material properties, recent research has focused on lowering the highest occupied molecular orbital (HOMO) level, reducing the bandgap, and controlling the molecular conformation and donor–acceptor phase separation. Additionally, the stability of PSCs can be improved through molecular design. Finally, a few less-conventional material design strategies for device improvement through polymer–polymer blends and triplet utilization are introduced. Molecular design has been an invaluable tool in controlling these material properties.

In this short critical review, selected examples of current (within the past two years) synthetic efforts toward the construction of high-spin molecules are explored, including the use of metal complexes containing stable free radical ligands, lanthanide or actinide complexes, and other coordination clusters, or a completely different approach, taking advantage of non-Heisenberg exchange in fully delocalized mixed-valence complexes (spin-dependent delocalization, SDD, or double exchange). A description of reported work in this regard is followed by a brief general discussion that highlights what the future may hold for high-spin molecule design.

Chemistry was already pioneered by ancient Egyptians up to 4000 years ago. Despite its age, chemistry is by no means a dying scientific discipline. The different branches of study within chemistry have infiltrated all fields of life science research, and nobody can work in this area without using chemistry in the broadest sense. The present article is a personal view on how chemistry supports life science research, in particular in the field of nutrition and metabolism research. It provides insight into how chemistry, in close collaboration with life science research, helps to fill the gaps between our current fragmentary understanding and the comprehensive knowledge required for better understanding the molecular details of metabolism, health and disease, and aging. The most important contributions of the chemical disciplines to these studies with respect to a systems biological description of human nutrition and metabolism will be outlined.

As a new type of functional materials, porous metal–organic frameworks (MOFs) have experienced tremendous development in the past decade. Their amenability to design, together with the functionalizable nanospace inside their frameworks, has afforded them great potential for various applications. In this review, we provide a brief summary of the current status of porous MOFs in energy-related applications, mainly, energy gas storage, CO 2 capture, gas separation, catalysis, and fuel cells.

This critical overview proposes a new concept, a charge-by-charge assembly , which consists of alternately stacked positively and negatively charged species, by introducing examples of planar anionic structures in the solid state. The preparation of planar organic anions is not easy; however, complexation of planar anion receptor molecules with inorganic anions is found to be an efficient strategy for constructing them. As suitable motifs, dipyrrolyldiketone boron complexes exhibit various receptor–anion complexes and charge-by-charge assemblies in the solid state. The concept discussed here can be applied to useful soft materials as well as crystals by modifying the anion receptors and cations.

The search for cleaner and more abundant sources of energy is one of the major scientific challenges of the 21 st century. Owing to its privileged position as the central science, chemistry is bound to play a leading role in this quest. Within the search for new materials for organic photovoltaics, some of the work we have carried out concerning the supra-molecular chemistry of electron donor and acceptor molecules is presented.

Numerous biophysical tools based on fluorescence have been developed to advance the understanding of RNA–nucleic acid, RNA–protein, and RNA–small molecule inter-actions. In this regard, fluorescent ribonucleoside analogues that are sensitive to their local environment provide sensitive probes for investigating RNA structure, dynamics, and recognition. Most of these analogues closely resemble the native ribonucleosides with respect to their overall dimension and have the ability to form canonical Watson–Crick (WC) base pairs. Therefore, it is possible to place these probes near the point of interaction in a target nucleic acid with minimum structural perturbations and gain insight into the intricacies of conformational changes taking place in and around the interaction site. Here, we provide a concise background on the development and recent advances in the applications of base-modified fluorescent ribonucleoside analogue probes. We first present various base-modified fluorescent ribonucleoside analogues, their photophysical properties, and methods to incorporate these analogues into oligoribonucleotides. We then discuss the established spectroscopic techniques, which make use of the fluorescence properties of these emissive ribonucleoside analogues. Finally, we present the applications of base-modified fluorescent ribonucleoside analogues used as probes incorporated into oligoribonucleotides in investigating RNA structures and functions.

Gold nanorods (NRs) are promising nanomaterials for biotechnology innovations that include photoassisted drug delivery, gene therapy, noninvasive cancer detection, and ultrasensitive biodetection. Owing to their unique geometry, Au NRs exhibit surface plasmon (SP) modes in the near-infrared (IR) wavelength range—ideal for carrying out optical measurements in biological fluids and tissue. Because NR interactions highly depend on the chemical nature of their solvent-accessible interface, it is necessary to carry out specific postsynthetic chemical modifications of the Au surface to create NRs that are biocompatible and biofunctional. In this review, we discuss various NR surface chemistries that have successfully enabled the integration of Au NRs into biological environments, as well as current challenges in designing the biofunctional NR interface for in vivo applications.

This article briefly reviews the development of surface science and its close relevance to nanoscience and heterogeneous catalysis. The focus of this article is to highlight the importance of nanoscale surface science for understanding heterogeneous catalysis performing at solid–gas and solid–liquid interfaces. Surface science has built a foundation for the understanding of catalysis based on the studies of well-defined single-crystal catalysts in the past several decades. Studies of catalysis on well-defined nanoparticles (NPs) significantly promoted the understanding of catalytic mechanisms to an unprecedented level in the last decade. To understand reactions performed on catalytic active sites at nano or atomic scales and thus reach the goal of catalysis by design, studies of the surface of nanocatalysts are crucial. The challenges in such studies are discussed.