Molecular timers

The analyte-induced aggregation of functionalized poly(thiophene) is reminiscent of colorimetric sensors that are based on the aggregation or dissociation of gold nanopartides. Gold nanoparticles display a red-shift of their plasmon band upon aggregation. This feature has been exploited extensively for (bio)analytical applications. A discussion of this work extends the scope of the present chapter and more details can be found in a number of review artides [25]. 

In the previous part of this chapter it was described that DCL sensors can be used to determine the identity and/or the quantity of analytes. A recent extension is the demonstration that DCL sensors can be used to obtain information about the history of analyte variations [26]. 

The examples described above are evidence that DCLs can be used as powerful analytical tools. Biologically interesting analytes such as peptides, nucleotides, or amines have been identified and/or quantified with sensors, which are cheap and easy to make. Furthermore, it has been shown that DCLs can be used to time molecular events. 

DCLs of colored or fluorescent compounds can be used for any analyte that results in a detectable re-equilibration of the Ubrary. It is thus sufficient if the analyte displays an unspecific interaction with some Ubrary members. This is in contrast to DCL selection experiments aimed to identify a high-affinity receptor. Here, a specific and strong interaction with a particular Ubrary member is of advantage, because it results in higher amplification factors. 

From an experimental point of view, DCL sensors have two key advantages, (i) 

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G-proteins are molecular timers that couple transmembrane receptor activation to downstream members of the pathway (Fig. 9-5). They are called G-proteins because they are intimately involved with the nucleotide, GTP. Before activation, the G-protein is hanging around in its GDP form. When the activated receptor finds its G-protein it activates it by increasing the rate of exchange between GTP and GDP. Once activated, the G-protein interacts with downstream effectors and can activate... 

These results illustrate the complexity of ligand binding in a simple two-component system. The results further indicate the time resolution of the MHQ technique. The reaction between metmyoglobin and azide is a useful molecular timer, but the kinetic s are not proportional to [N3 ] observation of the intermediate described here can be used to argue that the particular rapid-freezing instrument operates below the 100 ps time scale. 

Figure 2. Schematic of the apparatus. Key 1, He cylinder 2, O cylinder 3, CO cylinder 4, molecular sieve dryer 5, rotameter 6, fine-control needle valve 7, solenoid valve 8, pressure gauge 9, sand bath 10, preheater 11, reactor 12, IR spectrometer 13, gas bubbler and 14, automatic timer. 

Similarly, the molecular structure was determined for timer 25 +SbF6, which has the inter-ring bonds C4-C5 and C8-C9 with a little larger twisting (Figure 20) (32). 

The PGA salt of D AP has shown pharmacological results (peak timer shifted to a later time, increased Imax) corresponding to an increased contact time [12]. PGA consists of linear chains of D-galacturonic acid units (pyranose form), joined in a(l- 4)-glycosidic linkages, with a molecular weight ranging from 25 103 to 100 x 3. It formed a soluble salt or polyanionic complex with the... 

The common feature of these protein polymers is the presence of repetitive sequence motifs which form defined secondary structures. These repetitive amino acid sequences offer the possibihty to construct artificial genes by mul-timerization of small synthetic oligonucleotide sequences and thus the build up of high molecular weight proteins. The constructed artificial genes can be incorporated into an expression plasmid, which can subsequently be transferred to a bacterial host for production of the desired polypeptide (Fig. 19). The most commonly used host is E. coli. 

On-column injection is another admission mode, which prevents component discrimination due to volatility or molecular weight. The sample is applied directly into the column head. This might be seen as an ideal injection, but with a large number of samples there is the risk of severe column contamination. This is caused by non-volatile sample components which deposit inside the column and eventually clog it. Split/splitless injection ports include a liner just before the column, to act as a filter for these interfering substances. In the case of on-column injection, a pre-column, or retention gap, which is a short capillary with no timer coating, is used for this purpose. 

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