Volume 72, Issue 8

Quantum chemistry is the field in which solutions to the Schrödinger equation are used to predict the properties of molecules and solve chemical problems. This paper considers possible future research directions in light of the discipline's past successes. After decades of incremental development—accompanied by a healthy dose of skepticism from the experimental community—the ready availability of fast computers has ushered in a "golden age" of quantum chemistry. In this new era of acceptance, theoretical predictions often precede experiment in small molecule chemistry, and quantum chemical methods play an ever greater role in biochemical and other larger systems. Quantum chemists increasingly divide their efforts along three fronts: high-level (spectroscopic) accuracy for small molecules, characterized by such techniques as Brueckner methods, r 12 formalisms, and multireference calculations; parameterization- or extrapolation-based intermediate-level schemes (such as Gaussian-N theory) for medium molecules; and lower-level (chemical) accuracy for large molecules, characterized by density functional theory and linear scaling techniques. These tools, and quantum chemistry as a whole, are examined here from a historical perspective and with a view toward their future applications.

Of the principal classes of engineering materials, ceramics are in many ways the most interesting and challenging. Many properties, or combination, of properties, not achievable with other classes of materials give ceramics enormous technical potential. The main obstacles that prevent the wider use of ceramics include insufficient reliability, reproducibility, and high cost. The physical basis of the processing steps is well established, however, the chemical reactions which occur during the high-temperature processing frequently influence the densification process and microstructure development of ceramics in an unpredictable way. Therefore, an ability to understand and control the chemical processes that occur during ceramic processing are necessary to advance and open up new uses for technical ceramics. The aim of this present report, resulting from discussions of an ad hoc group of ceramists and chemists, is to expose the areas of chemical research that can most benefit the processing, and further the use, of ceramic materials.

Guidelines are presented to assist authors in preparing manuscripts that describe the results of semiempirical computations. These guidelines are not intended to recommend how semiempirical calculations should be done, but rather to ensure that the reader can have a clear understanding of what actually was done. They are written in a form to facilitate reprinting in original research journals and as information sheets that can be distributed to authors and reviewers.

This paper presents definitions of concepts related to speciation of elements, more particularly speciation analysis and chemical species. Fractionation is distinguished from speciation analysis, and a general outline of fractionation procedures is given. We propose a categorization of species according to isotopic composition of the element, its oxidation and electronic states, and its complex and molecular structure. Examples are given of methodological approaches used for speciation analysis. A synopsis of the methodology of dynamic speciation analysis is also presented.

Methods for assessing occupational exposure to toxic chemicals have been developed semi-independently by a number of standards organizations and regulatory authorities in Europe and beyond. Few of these have been systematically reviewed against Comité Europeán de Normalisation (CEN) criteria for accuracy and reliability. Some of these methods have been complied into indexes, either in hard copy or on the Internet, but existing indices are incomplete. There is a clear need for the harmonization and validation of these methods and for a full compendium of available methods and their validation status, while avoiding duplication of essentially equivalent procedures. Many of the methods are accessible on the Internet, so that in such instances the compendium need not contain full details of the methods themselves but can provide links to the pertinent web sites.

Theory, preparation,and applications of microelectrodes and microelectrode arrays are critically reviewed, and future trends in the field are outlined. An operational definition of a microelectrode is also recommended.

Lignans and neolignans are a large group of natural products characterized by the coupling of two C 6 C 3 units. For nomenclature purposes the C 6 C 3 unit is treated as propylbenzene and numbered from 1 to 6 in the ring, starting from the propyl group, and with the propyl group numbered from 7 to 9, starting from the benzene ring. With the second C 6 C 3 unit the numbers are primed. When the two C 6 C 3 units are linked by a bond between positions 8 and 8' the compound is referred to and named as a lignan. In the absence of the C-8 to C-8' bond, and where the two C 6 C 3 units are linked by a carbon–carbon bond it is referred to and named as a neolignan. The linkage with neolignans may include C-8 or C-8'. Where there are no direct carbon–carbon bonds between the C 6 C 3 units and they are linked by an ether oxygen atom the compound is named as an oxyneolignan. The nomenclature provides for the naming of additional rings and other modifications following standard organic nomenclature procedures for naming natural products. Provision is included to name the higher homologues. The sesquineolignans have three C 6 C 3 units, and dineolignans have four C 6 C 3 units.

Measurements of the spontaneous fission half-lives of nuclides of elements Z = 82 through 109 have been compiled (cutoff date of April 1998) and evaluated. Recommended values are tabulated along with total half-lives.

A description is given of the development by collaborative study of two standardized methods for the determination of polar compounds in oils and fats by adsorption chromatography using silica minicolumns, and for quantification of polymerized triacylglycerols, oxidized triacylglycerols, and diacylglycerols in polar compounds by high-performance size-exclusion chromatography. The first procedure is sensitive, allowing savings in time, solvents, and reagents as compared to the previous determination (Standard Method 2.507), while the second is very rapid, giving a detailed information on the main groups of compounds in fats and oils associated with hydrolysis, oxidation, and thermal polymerization. Both methods are useful for the analysis of used frying fats as well as for the analysis of virgin or refined oils.