Remaining Challenges

Although the feasibility of the proteomics or bioinformatics approach has been demonstrated, considerable room remains for improved methods for selective solublization of protein biomarkers and for rapid cleavage to produce peptides. There is also demand for advanced instrumentation to collect, process, and analyze microorganisms. 

Both absolute quantitation and relative quantitation of species in mixtures is of interest in some circumstances. Quantitation in a 5-minute analysis can be achieved by addition of an internal standard, ideally the target microorganism grown in special media to incorporate heavy isotopes92-95 and determination of the relative peak heights of pairs of proteins from the analyte and the standard. Isotope-labeled proteins or peptides, selected to match proteins or peptides characteristic of target microorganisms, can also serve as internal standards for isotope ratio measurement. The addition of unmatched proteins or peptides is less reliable for either ESI or MALDI measurements because of unpredictable suppression in the variable mixture. 

The analysis of microorganisms in mixtures provides a continuing analytical challenge, for which a number of solutions have been proposed  

A final problem for bioinformatics and bioanalytical scientists is the characterization of engineered microorganisms. Whole-cell analysis by mass spectrometry has been used to confirm the introduction of therapeutic genes into adenovirus vectors,100 to confirm the expression of recombinant proteins in bacteria,101,102 and also in vaccinology.103 In the broader case, identification of 

The authors thank the Defense Advanced Research Projects Agency for support. 

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Another principal difficulty is that the precise effect of local dynamics on the NOE intensity cannot be determined from the data. The dynamic correction factor [85] describes the ratio of the effects of distance and angular fluctuations. Theoretical studies based on NOE intensities extracted from molecular dynamics trajectories [86,87] are helpful to understand the detailed relationship between NMR parameters and local dynamics and may lead to structure-dependent corrections. In an implicit way, an estimate of the dynamic correction factor has been used in an ensemble relaxation matrix refinement by including order parameters for proton-proton vectors derived from molecular dynamics calculations [72]. One remaining challenge is to incorporate data describing the local dynamics of the molecule directly into the refinement, in such a way that an order parameter calculated from the calculated ensemble is similar to the measured order parameter. 

Until this work, the reactions between the benzyl sulfonium ylide and ketones to give trisubstituted epoxides had not previously been used in asymmetric sulfur ylide-mediated epoxidation. It was found that good selectivities were obtained with cyclic ketones (Entry 6), but lower diastereo- and enantioselectivities resulted with acyclic ketones (Entries 7 and 8), which still remain challenging substrates for sulfur ylide-mediated epoxidation. In addition they showed that aryl-vinyl epoxides could also be synthesized with the aid of a,P-unsaturated sulfonium salts lOa-b (Scheme 1.4). 

In order to design a zeoHte membrane-based process a good model description of the multicomponent mass transport properties is required. Moreover, this will reduce the amount of practical work required in the development of zeolite membranes and MRs. Concerning intracrystaUine mass transport, a decent continuum approach is available within a Maxwell-Stefan framework for mass transport [98-100]. The well-defined geometry of zeoHtes, however, gives rise to microscopic effects, like specific adsorption sites and nonisotropic diffusion, which become manifested at the macroscale. It remains challenging to incorporate these microscopic effects into a generalized model and to obtain an accurate multicomponent prediction of a real membrane. 

In the light of possible concern over the introduction of phenol into aquifers, mutant strains of Burkholderia (Pseudomonas) cepacia strain G4 in which toluene 2-monooxygenase is constitutive have been examined in microcosm experiments. Effective removal of TCE could be demonstrated (Krumme et al. 1993 Munakata-Marr et al. 1996), although in the first experiment serious loss in the viability of the cells occurred during the 10-week incubation. This aspect therefore presents a remaining challenge. 

Kane JS (1991) Review of geochemical reference sample programs since G-i and W-i progress to date and remaining challenges. Spectrochim Acta 463 1623-1638. 

UNSOLVED PROBLEMS IN BORON-CARBON MULTIPLE BONDING AND REMAINING CHALLENGES... 

Carbohydrates and especially oligosaccharides represent a special category for NMR spectroscopists. The structural characterization of oligosaccharides by NMR spectroscopy has remained challenging because of the lack of experimental parameters and the intrinsic high mobility in solution. For instance, the conformation around the exocyclic glycosidic bonds cannot unambiguously be determined from measurement of interresidue 1H-1H NOE measurements. 

There remain challenges to overcome in the use of FLIM and FRET in the general laboratory environment. A clear understanding of the nature of fluorescence decay is necessary for the correct interpretation of FLIM data and care must be taken to use negative controls appropriately. The contamination of lifetime data by... 

The remaining challenge is then to formulate and solve transport equations for the mapping functions g(z x, 0 (Gao and O Brien 1991 Pope 1991b). Note that if g(z x, 0 is known, then the FP model can be used to describe Z(0, and 0(0 will follow from (6.121). Since the PDF of Z is stationary and homogeneous, the FP model needed to describe it will be particularly simple. With the mapping closure, the difficulties associated with the chemical source terms are thus shifted to the model for g(z x, 0. 

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