Challenges Remaining to Be Addressed

Many challenges remain to be addressed in this field. The use of immobilized catalysts can often reduce the activity of a catalyst Reduced reaction rates due to diffusion limitations through a permeable membrane capsule and the ease or practicality of the synthesis of these catalyst scaffolds are issues that may pose problems. In some cases, these issues have been resolved, but this is often at the expense of other properties of the capsule. For example, the use of thin walls to reduce mass transfer limitations can be at the expense of nanocapsule strength and stability. 

The economic impact typology outlined in Table 1, and the preceding description of assessment methodologies, provides a general picture of the approaches currently being employed in assessment of the economic impacts of seismic events. Nevertheless, a number of key challenges remain to be addressed. 

Asymmetric Diels-Alder reaction represents one of the earliest successful organo-catalytic reactions [46, 60], Thongh extraordinary progresses have been achieved in this field, there are qnite a few challenges remained to be addressed. For example, the reactions have been limited with enals and successful examples with enones are rare the exo/endo selectivity is generally poor in many cases and a great number of a-substituted enals remain difficult substrates. Chiral primary amine such as 124 has been attempted in the Diels-Alder reactions of enals and cyclopentadiene. Though the reaction scope is quite limited, notable improvements on endo/exo ratio was obtained (Scheme 5.32) [61]. 

There are still many challenging issues that remain to be addressed in the field of synthetic polypeptides. NCA purification has been one of the bottlenecks limiting the availability and scale-up of NCA monomers. Recrystallization has long been the... 

Another important challenge that remains to be addressed is the relatively low success rate in obtaining useable and consistent high quality patch clamp data from most of these instruments. The success rate currently stands at around 40-60% for most systems [64], excluding the Ion Works Quattro that incorporates population patch clamping and claims a success rate of > 95% [53]. Some of the factors that contribute to this lack of success include stable positioning of the cells over the pore of the planar electrode, lack of adequate suction control in some cases, and the inability to achieve high resistance seals or electrical access. 

A number of major challenges for RE still remain to be addressed in the years ahead ... 

The conclusion of this section is that the introduction of P-stereogenic centres into chiral biaryl moieties is still a synthetic challenge, which remains to be addressed. 

Many questions remain to be addressed the origin of the stereoselectivity ( /Z) in MAP-type catalysts, the regioselectivity in en-yne metathesis, and the full catalytic cycle in alkane metathesis, among others. These issues are challenging. For instance, selectivity involves very small energy differences in combination with... 

The high reactivity of metaUanitrenes makes the search for an efficient catalytic intermolecular C(sp )-H amination reaction challenging. This is an issue that stiU remains to be addressed since many procedures, even now, are reported with the use of an excess of substrate to increase the possibility to intercept the unstable metallanitrene and avoid its competitive decomposition. Few methods are available to functionalize alkanes, alkenes, and... 

While during recent years important advances have been made in the field of geotechnical earthquake engineering, some challenges still remain to be addressed. 

Let us now recapitulate some of the key points made in this chapter and which will be treated in great detail in the remainder of this volume. Further, we oudine a few challenges and issues that remain to be addressed in future work. 

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