Unexplored Areas

In the preceding sections of this article, a systematization of basic cluster reactions has been attempted based on the present status of knowledge. It can be seen that the number of reactions reported is still relatively small for certain reaction types. The organization of the material described here, which mostly follows reactivity patterns, may not be the best one when more facts are available. An alternative way of presentation is outlined below, based on a cluster-centered viewpoint. It brings out which areas might show future developments or deserve research activities. 

Reactions affecting single metal-metal bonds From the knowledge of metal - metal bond reactivity (15) several reaction types which are common for dinuclear complexes can be expected to occur for single metal-metal bonds in clusters. Some of these, such as nucleophilic opening (cf. Section 

C) or oxidative additions with metal-metal bond breaking (cf. Section 

have been observed. Others, such as thermal or photolytic bond breaking with subsequent reactions, reductive bond breaking, or insertion reactions, have yet to be developed. 

Hetero site reactivity The simplest difference between a cluster and a mononuclear complex is that the cluster can do two or more things where a mononuclear complex can do one. Simple as it is, this difference has hardly ever been verified other than in multiple ligand substitutions. One verification is hetero site reactivity, i.e., different modes of reaction at different sites on one and the same cluster. Two examples of this appear to exist. Different phosphine ligands substitute CO on different metal atoms in H2FeRu3(CO),3 depending on their size and basicity (210), and Ru2Co2 (CO), 3 reacts with H2 at the ruthenium atoms (cf. Section IV, A) and 

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The avaHabihty of photoconductive polymers opens up many areas for research, in addition to electrophotography. These are relatively unexplored areas and represent promising future directions. 

Until the 1950s this was an unexplored area of chemistry, but then two events occurred ... 

The chemistry of the p-silylene bridge is still a relatively unexplored area, which is quite in contrast to the high degree of knowledge about its carbon congener, the p-methylene bridge [117-183]. 

Another largely unexplored area is the change of dynamics due to the influence of the surface. The dynamic behavior of a latex suspension as a model system for Brownian particles is determined by photon correlation spectroscopy in evanescent wave geometry [130] and reported to differ strongly from the bulk. Little information is available on surface motion and relaxation phenomena of polymers [10, 131]. The softening at the surface of polymer thin films is measured by a mechanical nano-indentation technique [132], where the applied force and the path during the penetration of a thin needle into the surface is carefully determined. Thus the structure, conformation and dynamics of polymer molecules at the free surface is still very much unexplored and only few specific examples have been reported in the literature. 

This suggests that the g-strain in EPR spectra contains detailed geometric and energetic information on the 3-D position of ligand atoms for a given metalloprotein conformation with respect to a (virtual) cubic coordination, and therefore, of position and interconversion energy (by strain) of the 3-D position of ligand atoms in, say, two different protein conformations. This is an unexplored area of research. 

In conclusion, NMR methodologies have already proven successful within meat science with applications in many different areas. However, many unexplored areas still exist where the potential of NMR can be expected to reveal useful and valuable information. The inspiration that can be obtained from NMR studies within other disciplines, e.g., medical areas, material science, physical/chemical sciences and food science in general, should be rewarded with great attention in future in order to continue development of the use of NMR in meat science. 

Acknowledgements We thank the Codelco Exploration Division for permitting this publication and allowing the comprehensive study, for which they provided fund and logistic support to carry out the exploration in this unrecognised and unexplored area of the planet. We thank the team for all discussions and conclusions. 

One way authors stress importance as they share background information is to document widespread interest in the research area (i.e., if others studied it, it must be important). Slightly different tactics are used depending on how new the research area is. If the field is already well established, phrases such as longterm interest, renewed interest, extensively studied, or for decades, chemists have studied are commonly employed. If the field is relatively new, such phrases as emerging interest, increased attention, previously unstudied, promising new approach, unexplored area, or an area of mounting concern are more appropriate. 

The adaption of human pathogen strains to grow and persist on plants remains a relatively unexplored area. In many aspects, the adaption of human pathogens to plants would make sense given that the microbes need to survive in the environment between infecting hosts. 

The aim of this article is to focus on the diversity of aldonolactones as chiral synthons. The chemistry of aldonolactones was an almost unexplored area when, in 1979, we started our investigations on the reaction of aldonolactones with hydrogen bromide in acetic acid thereby obtaining bromodeoxyaldonolac-tones [1,2]. These compounds have over the years proven to be very versatile compounds for stereoselective synthesis, both in the carbohydrate field, giving access to otherwise less readily obtainable sugars, and as chiral, optically pure synthons in a broader sense within organic chemistry. 

Although the tt complexes have not yet found any practical uses, they have proved helpful in structural characterization, as well as providing some insight into the dynamical behavior of fullerenes. The a- complexes are a relatively unexplored area, but where they have been prepared, they are useful intermediates in the preparation of organic fullerene adducts. 

The coordination chemistry of zirconium(III) is an ill-defined and relatively unexplored area.19 Only one magnetically dilute zirconium(III) complex has been isolated, [ZrCl3(tfars)]-MeCN [tfars= 1, 2-bis(dimethylarsino)-3,3,4,4-tetrafluorocyclobutene (CFZ)2C2-(AsMe2)2]2° and the first structurally characterized zirconium(III) complex [ ZrCl3(PBu3)2 2] has just recently been reported.21 The known zirconium(III) complexes and their physical properties are listed in Table 2. Even less is known about the coordination chemistry of hafnium(III). Just one complex, HfCl3(py)4, has been reported.22... 

The oceans cover more than 70% of the earth s surface, which represents over 95% of the biosphere. The oceans are therefore an unexplored area of opportunity for the discovery of pharmacologically active compounds. Although it has been one of man s principal sources of food for thousands of years, the sea was not considered as a supply of biologically active substances until forty years ago. In the last two decades, the search for marine-derived natural products has been extended to all oceans of the world. The enormous potential of the sea as a source of energy, food and chemicals has led to its being the subject of intense research. The results of this search had been reported in numerous reviews [1-8]... 

A variety of unfunctionalized secondary alcohols, including saturated and unsaturated carbinols, are resolved by catalyst 25 with moderate to high selectivi-ties (fcrei=4 to >50, see Scheme 5) [25]. Octapeptide 25 was discovered by screening a split-pool library of peptide catalyst candidates for acylation of 1-phe-nylethanol (3), using a reactivity-based fluorescence screen [26], followed by structure optimization with directed libraries. While substrates with increased steric bulk about the alcohol are resolved with highest selectivities, even 2-butanol is resolved with modest selectivity (fcrei=4). Peptide-based catalysts have also been applied to the resolution of tertiary alcohols, a relatively unexplored area of nonenzymatic asymmetric acylation catalysis [27-29], By using a fluores-... 

Excitation of the Lnm ion by a d-transition metal ion is an alternative to chromophore-substituted ligands, and proof of principle has been demonstrated for several systems. The lack of quantitative data, however does not allow an evaluation of their real potential, except for their main advantage, which is the control of the luminescent properties of the 4f-metal ion by directional energy transfer. In this context, we note the emergence of self-assembly processes to build new edifices, particularly bi-metallic edifices, by the simultaneous recognition of two metal ions. This relatively unexplored area has already resulted in the design of edifices in which the rate of population, and therefore the apparent lifetime, of a 4f-excited state can be fine-tuned by energy transfer from a d-transition metal ion (Torelli et al., 2005). 

While pyrrole DoM chemistry is still a relatively unexplored area [25], the corresponding indoles, especially with respect to N-DMGs (Scheme 14), constitute a rich area of metalation exploitation [26]. 

Interpretation of the RC tails (diffuse scattering), which contain information on structural defects, is still an unexplored area. 

The catchword interferon sufficiently supports this statement, there is no clairvoyance needed to predict the rapid application of genetic engineering methods to other as yet unexplored areas. 

Section V describes the chemistry of 7r-allyl halocarbonyl complexes, mainly of the type [MX(CO)2(NCMe)2(i73-allyl)] and their derivatives. In 1995, Brisdon and Walton8 reviewed transition-metal complexes containing butadienyl ligands their review contains relevant material. Section VI is concerned with the relatively unexplored area of 7j4-diene halocarbonyl complexes of molybdenum(ll) and tungsten(II). 

This is a largely unexplored area of osmium chemistry (in contrast to the situation for iron). 

There is no field that will always remain the special province of metaphysics and into which scientific research can never carry any light there are no "eternally unexplorable" areas. 

In cluster chemistry a development is indicated promising much more than just a piling up of new compounds the way leads to an unexplored area in the field of chemical compounds. 

One essentially unexplored area for hair analysis is its application to the investigation of environmental toxin exposure. We received a research grant during 1979 from the National Institute of Occupational Safety and Health to explore the possibility of using hair analysis for monitoring exposure to polychlorinated biphenyl compounds (PCBs). Although the analytical chemical problems of this project were successfully solved, we were unable to mount successful field studies with human subjects. 

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