Volume 74, Issue 11

In Nature, a wide variety of complex tasks (e.g., catalysis, transport, and information storage) is performed by biomacromolecules with precise composition, dimensions, and architecture. To achieve the precise organization required for efficient function, structural information is built into the smallest building blocks of biomacromolecules (i.e., amino and nucleic acids) and subsequently transferred in a hierarchical fashion to form larger quaternary structures. These construction principles have been an inspiration for synthetic and supramolecular chemists alike, and a number of synthetic biomimetic helical macromolecules have been reported in the recent literature. Here, some recent developments in the field of helical polyisocyanides will be reviewed in combination with new prospects on the self-organization of protein/polymer hybrid architectures.

Conjugated polymers are emerging materials for electronic applications due to the tunability of their properties through variation of their chemical structure. Their applications, which currently include light-emitting diodes (LEDs), field effect transistors (FETs), plastic lasers, batteries, and sensors, are expanding to many new areas. The two critical parameters that determine the function of conjugated polymer-based devices are chemical structure and nanostructure of a conjugated polymer in the solid state. While the physical properties of isolated polymers are primarily controlled by their chemical structure, these properties are drastically altered in the solid state due to electronic coupling between polymer chains as determined by their interpolymer packing and conformation. However, the development of effective and precise methods for controlling the nanostructure of polymers in the solid state has been limited because polymers often fail to assemble into organized structures due to their amorphous character and large molecular weight. In this review, recent developments of organizing methods of conjugated polymers and the conformation and interpolymer interaction effects on the photophysical properties of conjugated polymers are summarized.

Porphyrins are the most widespread of all prosthetic groups found in Nature. The ubiquity of their functions in Nature led researchers around the globe to focus their attention on these highly colored macrocycles. The interdisciplinary interest generated by porphyrins resulted in the syntheses of modified porphyrins, which can be put to a variety of uses in medicine and industry. A brief overview of the synthetic methodologies resulting in the formation of aromatic meso -aryl-substituted core-modified aromatic heterocyclic ring-inserted expanded porphyrinoids like sapphyrins, smaragdyrins, rubyrins, hexaphyrins, heptaphyrins, and octaphyrins reported to date are discussed in this article.

ATP-binding cassette (ABC) proteins form one of the largest known protein families and have been found in all known organisms. Most members of the human ABC protein family are membrane-spanning transporters that use energy derived from the hydrolysis of ATP to transport specific substrates across cell membranes. Mutations in certain human ABC transporters of the subfamilies A, B, C, and D have been shown to cause a wide variety of inherited diseases such as the lung condition cystic fibrosis, the nervous degenerative condition adrenoleukodystrophy (of Lorenzo’s Oil fame), hereditary macular degeneration of the eye (Stargardt’s disease), and inherited deficiency of circulating high-density lipoproteins (Tangier disease or familial hypoalphalipoproteinemia). Very recent studies showed that mutations in two members of the subfamily G of human ABC transporters (ABCG5 and ABCG8) cause a condition called sitosterolemia in which plant sterols accumulate in the body and may be responsible for influencing total body sterol homeostasis. In addition, other members of the subfamily G, namely ABCG1 and ABCG4, have also been shown to be involved in cellular lipid trafficking and are thought to play important roles during foam cell formation of human macrophages. By contrast, ABCG2 is a multidrug resistance transporter. In this review, we focus on the current knowledge and physiological background of the members of the subfamily G. We also present new insights on the evolutionary relationship of human and nonhuman ABCG proteins.

The use of thick films becomes more and more important in particular for electronic and microelectronic applications. The term “thick film ” does not relate so much to the thickness of the film but more to the kind of deposition. Thick films are made by low-priced processes such as doctor (dr) blading, screen-printing, or spraying methods, etc. The preparation of thick films of ceramic material by these methods generally implies a processing sequence of the following steps: preparation of the oxide powders; preparation of pastes and slurries; painting/printing, etc.of the pastes onto a suitable substrate; drying at low temperature; and sintering at high temperature to get a consolidated layer. These technologies and the fabricated thick films of thermoresistive and superconducting materials will be discussed.

The application of the density functional techniques to processes of the conversion of hydrocarbons in zeolites has been reviewed. The conversion of hydrocarbons over zeolites is an important industrial process. The microscopic steps of the conversion, however, are still not satisfactorily understood. In order to examine reaction pathways, both static and molecular dynamics density functional theory (DFT) calculations have been performed. Simulated structural and spectral properties compare reasonably with experimental data. Comparison of energies of physisorption and chemisorption indicates possible reaction channel of the conversion through the chemisorption at the specific O-sites of the zeolite.

The widespread use of vacuum-based techniques for the deposition of ceramic coatings with specific electric, magnetic, optical, and mechanical properties is well established in the research environment, and some of them have been implemented in a variety of industrial processes. However, obtaining uninterrupted deposition at high speed, increasing flexibility in composition and in film thickness, and attaining independence of geometric constraints are areas in which many vacuum techniques will need sustained development in order to answer industrial demands. The development of the next generation of deposition methods, which could alleviate some of these shortcomings and which are based on deposition under atmospheric environment and from aqueous precursor materials, is a real challenge for the community of solid-state chemists and delineates the subject of this overview.

A hyperbranched polycarbosilane of the type [R 3 SiCH 2 −] x [−SiR 2 CH 2 −] y [−SiR(CH 2 −) 1.5 ] z [−Si(CH 2 −) 2 ] l (R = H, –CH 2 CH=CH 2 , or OR) has been prepared, which was used as a source of inorganic/organic hybrid materials and, through pyrolysis, as a precursor to inorganic solids with unusual microstructures and properties. A partially allyl-substituted derivative “AHPCS”, nominally ['Si(allyl) 0.1 H 0.9 CH 2 '] n , has been extensively studied as a precursor to silicon carbide (SiC) and is now used commercially as a SiC matrix source for C- and SiC-fiber-reinforced composites and binder for particulate ceramics. The alkoxy derivatives, ['Si(OR) 2 CH 2 '], (R = Me, Et) yield, after hydrolysis and condensation, carbosilane/siloxane gels with unusually high surface areas (700–900 m 2 /g) and microporosity that is retained in the resultant SiO x C y ceramics formed after pyrolysis to 1000 °C. The fully condensed ['Si(O)CH 2 '] gel in the latter case was obtained as thin, adherent films on Si surfaces by spin coating and was found to exhibit dielectric constants as low as 2.0 after heating to 400 °C. The SiC precursor, AHPCS, has also been used recently, along with other polymeric precursors, to make two-phase (SiC/C and SiC/BN) amorphous ceramics that exhibit unusual microstructures and thermal/mechanical properties. These microstructures are formed during the mixing and thermosetting of the constituent polymers, which undergo phase separation due to their immiscibility. Certain of the SiC/C composites, which have the C phase uniformly distributed as ca.1-µm droplets in a SiC x matrix, exhibit high oxidation resistance, and microindentation tests on the SiC/BN system suggest unusual toughness.

Improved glass-melting technology, intelligent process control, glass quality control, and establishing novel melting conditions, are realized by different kinds of physicochemical models. The model application is preceded by the analysis of homogenization processes, i.e., heating, dissolution, or vitrification and refining. The energy consumption of the process, the pull rate and size of the melting space, and glass quality are the main technological factors taken into account. In the following step, the optimum conditions are applied to simplified and complex models or processes. The mentioned models are mostly represented by systems containing melt and numerous inhomogeneities (solid particles, bubbles).

Hydrothermally cured or autoclaved cement-based building products have provided many challenges to researchers, manufacturers, and users since their inception nearly 100 years ago. The advantages, including the development of high strength within a few hours and a reduction of drying shrinkage, of the hydrothermal curing process have resulted in a variety of building products; inevitably, the technology of their production has undergone many stages of refinement. With the advent of nonconventional starting materials for the production of modern cements, and the push to utilize renewable resources to form blended cements, the chemical and physical make-up of hydrothermally cured building materials have changed considerably in recent years and will continue to change. It is, therefore, important to understand the chemical reactions taking place in an autoclave, and the consequent phase developments, if building materials produced by this process continue to be successful in the long term. A wide range of analytical techniques exists for characterizing the phase development in cement-based materials. The purpose of this paper is to illustrate the strength of thermal methods, especially when used in combination with other analytical techniques, in the understanding of hydrothermal reactions.

This paper deals with the role of chemistry in the design of high-tech ceramic materials. Grain boundary composition of polycrystalline ceramics dictates the hardness fracture toughness and creep resistance of liquid-phase sintered silicon nitride and silicon carbide materials.

The oxidation state of iron (Fe) in the crystal structure of smectite clay minerals profoundly alters their physical-chemical properties. Among the properties affected are layer charge, cation exchange and fixation capacity, swelling in water, particle size, specific surface area, layer stacking order, magnetic exchange interactions, octahedral site occupancy, surface acidity, and reduction potential. Also affected is the surface chemistry of the clay, which alters clay–water and clay–organic interaction mechanisms. Rates and extents of degradation of pesticides are increased in the presence of reduced smectites compared to oxidized and reduced-reoxidized counterparts. A hypothesis regarding the mechanism for Fe reduction in clay minerals was first developed in 1963, and subsequent modifications have been proposed periodically through the present time. Recent studies clearly reveal that the process of Fe reduction involves more than the mere transfer of an electron to octahedral Fe(III) in the clay crystal. Ancillary reactions occur that produce significant structural modifications, some of which are reversible and others of which are not. Such changes in the crystal-chemical environment of structural Fe are thought to play a dominant role in altering the clay surface chemistry.

We describe various molecular switching processes occurring in several types of inorganic solids: spin cross-over (SC) compounds, photomagnetic Prussian blue analogs (PBAs), and valence-tautomeric system. Their thermo-, photo-, piezo-, and magneto-chromic properties are illustrated by recent examples. A common description of their static properties by a two-level model is given.

The definition of a “primary method of measurement ” has permitted a full consideration of the definition of primary standards for pH, determined by a primary method (cell without transference, Harned cell), of the definition of secondary standards by secondary methods, and of the question whether pH, as a conventional quantity, can be incorporated within the internationally accepted system of measurement, the International System of Units (SI, Système International d’ Unités). This approach has enabled resolution of the previous compromise IUPAC 1985 Recommendations [ Pure Appl. Chem. 57 , 531 (1985)]. Furthermore, incorporation of the uncertainties for the primary method, and for all subsequent measurements, permits the uncertainties for all procedures to be linked to the primary standards by an unbroken chain of comparisons. Thus, a rational choice can be made by the analyst of the appropriate procedure to achieve the target uncertainty of sample pH. Accordingly, this document explains IUPAC recommended definitions, procedures, and terminology relating to pH measurements in dilute aqueous solutions in the temperature range 5-50 °C. Details are given of the primary and secondary methods for measuring pH and the rationale for the assignment of pH values with appropriate uncertainties to selected primary and secondary substances.

The terms recovery and apparent recovery are recommended to avoid confusion caused by the use of the term recovery to cover two distinct situations. These situations deal with: (a) the yield of a preconcentration or extraction stage of an analytical process (where recovery is recommended) and (b) the quantity observed value/reference value , obtained using an analytical procedure that involves a calibration graph (where apparent recovery is recommended).

Four stereochemical series of diastereomeric polyhalogenated chamigrane sesquiterpenes -headed by obtusol, isoobtusol, rogiolol, and cartilagineol- suggest the existence of four lineages of red seaweeds in the genus Laurencia.On another front, concerning marine ciliates, euplotane sesquiterpenes characterize worldwide the morphospecies Euplotes crassus, well differentiated from Euplotes raikov, Euplotes rariseta, and Euplotes vannus, which furnish different-skeleton sesquiterpenoids, and the latter also C 30 -backbone isoprenoids. The latter three morphospecies, however, show polymorphism in the variability of their isoprenoids.

The following reference citations were incorrect: Page 1643: replace 93SC with 93SK Page 1657: replace H + : 98KK with H + : 98KA Page 1657: replace Cu 2+ : 98KK with Cu 2+ : 98KA Page 1668: replace 90S with 90SW Page 1673: replace 68BE with 67BE Page 1666: replace 95WJ J.M. Wagener and N.V. Jarvis. S. Afr. J. Chem. 28, 85 (1995) with 95WJ J.M. Wagener and N.V. Jarvis. S. Afr. J. Chem. 48, 85 (1995) Page 1666: replace 95I with 95IU Page 1668: replace 90K A T. Kiss with 90KA T. Kiss