Significant advances during

There have been significant advances during the last decade in the synthesis of high specific surface area (Sg) carbides and nitrides of transition metals.1 2 This has naturally prompted interest in the application of these materials as catalysts. Carbides of molybdenum and tungsten received the most attention because they catalyze many reactions that typically occur on noble metals. In several reactions, molybdenum carbides show catalytic activity similar to that of ruthenium and surface reactivity of tungsten carbides resembles that of platinum.3-7... 

It is now some twelve years since the first volumes of this series were published. Perhaps the most significant advances during that time, particularly for the photochemist, have been the further development of lasers and the tremendous increase in speed and complexity of electronic devices used for signal detection and processing. These have spawned a number of new techniques for the study of kinetics and drastically modified some of the traditional methods. The aim of this chapter is to show how and where some of these techniques can be applied. 

Another significant advance during this time period was the development of N-cycle models for simulating plankton dynamics that included more detail in both the P and Z compartments than previous N-cycle models (e.g., Hoffman, 1988 ... 

The TWC has undergone significant advances during the past 20 years or so, a number of which have involved major changes in the way ceria is deployed. In the early years (roughly 198 M 985), the TWC formulation was relatively simple and consisted of noble metals co-impregnated with ceria onto alumina. Even this... 

Both the understanding as well as the computing aspect have been significantly advanced during recent years by... 

Figure 1. Significant advances during the development of PAIRS.

The field of borane chemistry has seen some significant advances during 1982, and several syntheses of natural products have appeared, utilizing the new applications, mostly due to the work of Brown and co-workers. By its reaction with alkenes and subsequent reduction, t-hexylchloroborane is converted into the unstable t-hexyl(alkyl)boranes (53), which then add to 1-halogeno-l-alkynes... 

Literature reports over the last year indicate some decrease in the amount of chemical effort devoted to new analgesic structures, but a continued increase in investigation of biochemical mechanisms of analgesia and dependence. Interest in narcotic antagonists for the treatment and prevention of narcotic abuse has stimulated much current research on new compounds. In neither area was there evidence of a significant advance during the year. 

Dry Deposition. Dry deposition occurs in two steps the transport of pollutants to the earth s surface, and the physical and chemical interaction between the surface and the pollutant. The first is a fluid mechanical process (see Fluid mechanics), the second is primarily a chemical process, and neither is completely characterized at the present time. The problem is confounded by the interaction between the pollutants and biogenic surfaces where pollutant uptake is enhanced or retarded by plant activity that varies with time (47,48). It is very difficult to measure the depositional flux of pollutants from the atmosphere, though significant advances were made during the 1980s and early 1990s (49,50). 

The chapter structure remains close to that of the first edition, although significant expansion in scope has been made, reflecting the extensive progress advanced during this period. At the end of each chapter (except Chapter 1), additional, recent references are given for researchers outside study. 

During the last decade, significant advancements in biochemistry, molecular cloning, and random and site-directed mutagenesis, directed evolution of biocatalysts, metabolic engineering and fermentation technology have led us to devise methods to circumvent the disadvantages of whole-cell biotransformation discussed in Section 10.2. The applications of these methods are summarized in this section. 

The number of really new hydrogenation catalysts, following the proliferation during the 1%0 s, is relatively small. This review is not a comprehensive critical one covering the recent literature, but is an attempt to discuss what I consider to be the more significant advances in the area since 1971. However, parts of the review are more of a simple cataloging of reported systems. 

A most significant advance in the alkyne hydration area during the past decade has been the development of Ru(n) catalyst systems that have enabled the anti-Markovnikov hydration of terminal alkynes (entries 6 and 7). These reactions involve the addition of water to the a-carbon of a ruthenium vinylidene complex, followed by reductive elimination of the resulting hydridoruthenium acyl intermediate (path C).392-395 While the use of GpRuGl(dppm) in aqueous dioxane (entry 6)393-396 and an indenylruthenium catalyst in an aqueous medium including surfactants has proved to be effective (entry 7),397 an Ru(n)/P,N-ligand system (entry 8) has recently been reported that displays enzyme-like rate acceleration (>2.4 x 1011) (dppm = bis(diphenylphosphino)methane).398... 

For a variety of reasons, it is difficult to measure stability constants of metals with Hum, and the use of stability constants measured under a given set of solution conditions (so-called conditional constants ) for a different set of conditions (e.g., at a different pH or different set of metals and Hum concentrations) must be done cautiously. Significant advances were made during the past decade in ways to model metal-Hum binding, and a sufficient variety of conditional binding constants are now available at least to approximate the metal-binding behavior of natural water and soil solutions containing Hum. 

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