Experimental Challenge

FIGURE 3 Structures of candidate antirestenosis agents used in the series of experiments described herein. DEA, Diethylamine NO, nitric oxide DETA, diethylenetriamine MAHMA, methylaminohexylmethylamine. 

With this series of compounds, an easy solution was available in the form of DETA/NO (synthesized from diethylenetriamine and NO), whose half-life under these culture conditions is 20 hr. Its structure (3) is also shown in Fig. 3. In contrast to DEA/NO, DETA/NO was potently antiproliferative in this system (Mooradian et al., 1995). From the data summarized in Fig. 4B, the initial concentration of DETA/NO capable of inhibiting DNA synthesis by 50% was calculated to be 40 /x,M. Apparently, the cytostatic effect of a given molar quantity of NO is greatest when administered continu- 

FIGURE 4 Effects of candidate cytostatic agents on DNA synthesis by rat aorta smooth muscle cells in culture. (A) The diethylamine/nitric oxide adduct (DEA/NO), whose half-life for NO release is 2.1 min under the conditions used (B) The diethylenetriamine/nitric oxide adduct (DETA/NO), with a half-life of 20 hr. Cells were incubated at 37°C for 22 hr after addition of the given drug at the indicated concentrations, whereupon [ H]thymidine was added. After an additional 2-hr incubation DNA was isolated from the cells and subjected to scintillation counting to provide a quantitative measure of DNA synthesis by these cells. [Adapted from Mooradian et al. (1995) with permission.] 

To determine whether the cytostatic action of DETA/NO could be continued for substantially longer than 22 hr and, if so, whether toxic effects would appear, a somewhat different protocol was used. Several cultures of 

The next step we have planned for this line of research is to study the potential antirestenosis effect of DETA/NO in the intact rat. However, we approach this line of work with three concerns in mind. 

---

Measurement of the total Raman cross-section is an experimental challenge. More connnon are reports of the differential Raman cross-section, doj /dQ, which is proportional to the intensity of the scattered radiation that falls within the element of solid angle dQ when viewing along a direction that is to be specified [H]. Its value depends on the design of the Raman scattering experiment. 

Raman spectroscopy of graphite can be an experimental challenge, because the material is a strong blackbody absorber. Generally, low (1—10-mW) laser power is used to minimise heating, which causes the band positions to change. In addition, the expansion of the graphite causes the material to go out of the focus of the optical system, an effect which can be more pronounced in microprobe work. 

The development of a host of scanning probe devices such as the atomic force microscope (AFM) [13-17] and the surface forces apparatus (SFA) [18-22], on the other hand, enables experimentalists to study almost routinely the behavior of soft condensed matter confined by such substrates to spaces of molecular dimensions. However, under conditions of severe confinement a direct study of the relation between material properties and the microscopic structure of confined phases still remains an experimental challenge. 

Semibatch Model "GASPP". The kinetics for a semibatch reactor are the simpler to model, in spite of the experimental challenges of operating a semibatch gas phase polymerization. Monomer is added continuously as needed to maintain a constant operating pressure, but nothing is removed from the reactor. All catalyst particles have the same age. Equations 3-11 are solved algebraically to supply the variables in equation 5, at the desired operating conditions. The polymerization flux, N, is summed over three-minute intervals from the startup to the desired residence time, t, in hours ... 

By definition a minor element in seawater is one has a concentration less than Ippm(m). It is experimentally challenging to determine the total concentrations, much less their major chemical forms. Development of new analytical techniques has greatly extended our knowledge (Johnson et al, 1992). Because early data (prior to about 1975) was so erratic, the principle of oceanographic consistency was proposed as a test for the data (Boyle and Edmond, 1975). According to this principle the analyses of minor elements should ... 

Geometric structure of the bare metal clusters and the complexes formed by reaction are unknown and present a significant experimental challenge. Chemical studies are starting to imply something about the structure of the products and will be invaluable until more direct chemical physics probes are available. 

Robinson P, Okhuysen PC, Chappell CL, Lewis DE, Shahab I, Janecki A, White AC Jr Expression of tumor necrosis factor alpha and interleukin 1 beta in jejuna of volunteers after experimental challenge with Cryptosporidium parvum correlates with exposure but not with symptoms. Infect Immun 2001 69 1172-1174. 

From the above discussion, it should be possible to appreciate how extremely subtle differences in guest-host interactions in the ground and excited states of Cu and Ag atoms and dimers in both non-reactive and reactive supports can lead to dramatically distinct chemical reactivity patterns and dynamical processes. Photochemical and photophysical phenomena of this kind should provide chemists of the 21st century with a rich field for fundamental and applied research, offering considerable scope for experimental challenges and intellectual stimulation. 

McCreery RL, Bergren AJ (2009) Progress with molecular electronic junctions meeting experimental challenges in design and fabrication. Adv Mater 21 4303 -322... 

See the discussion in Stephen J. Weininger, "The Molecular Structure Conundrum Can Classical Chemistry be Reduced to Quantum Chemistry " JChem.Ed 61 (1984) 939944. Hans Primas, "Foundations of Theoretical Chemistry," 39113, in R. G. Woolley, ed., Quantum Dynamics of Molecules The New Experimental Challenge to Theorists (New York Plenum Press, 1980) quotation on 105 and Primas,... 

Our research using the CCS approach has focused on the discovery of new dielectric thin films. This example illustrates the power of this approach and key considerations in utilizing high throughput synthesis and screening approaches. A variety of other problems appear well matched to such combinatorial-style methods. A few of these are discussed briefly below, touching on both experimental challenges and research opportunities. 

Although the theory of polyelectrolyte dynamics reviewed here provides approximate crossover formulas for the experimentally measured diffusion coefficients, electrophoretic mobility, and viscosity, the validity of the formulas remains to be established. In spite of the success of one unifying conceptual framework to provide valid asymptotic results, in qualitative agreement with experimental facts, it is desirable to establish quantitative validity. This requires (a) gathering of experimental data on well-characterized polyelectrolyte solutions and (b) obtaining the relationships between the various transport coefficients. Such data are not currently available, and experiments of this type are out of fashion. In addition to these experimental challenges, there are many theoretical issues that need further elaboration. A few of these are the following ... 

Aspects related to the chemistry of the heteroatom-terminated -carbon ligands R3P C=C and C3O have also been discussed. Thus, upon coordination, the former seem to present a partial cumulenic character [M]=C=C=PR3, but little is known about the chemical behavior of this coordinated unit. In the case of the tricarbon monoxide ligand, recent theoretical calculations have shown that coordination chemistry could be an alternative to stabilize this highly unstable heterocumulene. However, the access to metal complexes containing the C3O unit represents an exciting experimental challenge for the near future. 

Excerpt 12X uses lists to delineate both the gap (the experimental challenge) and fill-the-gap statements (facing the challenge) excerpts 12Y-12AAuse narrative form. In each case, the depiction of the work following the fill-the-gap statement is brief, laying the groundwork for a more detailed description of the proposed work. 

Scientists were faced with formidable experimental challenges in trying to determine which compounds were responsible for this biological activity. Not only are they present in trace amounts and in chemically very complex mixtures of airborne POM, but in vivo animal assays for suspected new genotoxic and carcinogenic agents were then, and remain, time-consuming, labor intensive, and expensive. 

Figure 1.2. Scheele isolated a family of naturally occurring sour substances. Subsequently, the elemental composition of each substance was determined using Lavoisier s combustion method and later the different structures were proposed. Each member contains common structural element, a carboxylic acid group which gives each its sour taste. The two-dimensional representation of chemical structures as shown is convenient but can be misleading. Also shown is the structure of urea, the first naturally occurring substance to be made in the laboratory by Wohler (shown), who provided the first experimental challenge to the concept of vitalism.

For large-weight Zn + complexes with broad (50-150 kHz) second-order quadrupolar powder patterns Zn QE NMR may be an experimental challenge. In such cases the sensitivity must be enhanced by isotope enrichment combined with, e.g., cross polarization (CP) from H ", low-temperature acquisition or sampling of the free-induction decay (FID) in the presence of a train of refocusing pulses. ... 

---