Assembly-disassembly

Aggregation-amplified colorimetric sensing using AuNPs has also been used for neutral molecules. One example involves the detection of thiols using 

FIGURE 7. Selective potassium-induced aggregation of AuNPs functionalized with crown ether-thiol groups through the formation of sandwich complexes. 

AuNPs have also been used for the detection of noncharged nerve agents. However, in this case the sensing protocol relies on a different concept not related to a modification of the aggregation state of the NPs but with their biocatalytic growth. The sensing ensemble uses acetylcholine esterase (AChE). This enzyme is known to hydrolyse aeetylthiocholine (ATCh) to yield the 

In contrast to metal ion sensing, QDs have been barely used for anion signaling. Toward this objective, Sanz-Medel et al. reported the functionalization of CdSe QDs with tert-butyl-A-(2-mercaptoethyl)-carbamate for the selective and sensitive detection of cyanide in methanol by analyte-induced luminescence quenching. In a further work, the authors prepared water-soluble CdSe QDs coated with 2-mercaptoethane sulfonate also for cyanide 

In a recent example, Kim et al. showed how the combination of several types of nanoparticles could also be wisely used for the design of signaling protocols. They designed a FRET-based inhibition assay to determine the avidin concentration in solution with AuNPs and QDs. The ensemble involves the use of streptavidin-conjugated QDs that interact with biotin-AuNPs through well-known streptavidin-biotin chemistry. This system was not luminescent due to FRET interaction between QDs and AuNPs. Addition of avidin to this ensemble caused the luminescence to increase gradually because the AuNPs were displaced from the streptavidin-functionalized QDs as a consequence of avidin-biotin interactions (Fig. 8). 

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Implement procedures for line breaking/cleaning Provide correct tools for assembly/disassembly... 

In the past, changes in RTj were viewed in terms of assembly/disassembly of the tight junctional complex (reviewed in 93). Recent studies in human vaginal-cervical epithelia have shown acute and reversible modulation of Rtj that are the result of conformational changes in assembled tight junctions [13], The examples presented below relate to effects of modulation of extracellular calcium level (Ca0) and treatments with ATR... 

Pantaloni et al. (1981) investigated the mechanism of initiation of tubulin assembly, and the role of MAPs in the stabilization of microtubules. For their work they used microtubule protein carried through two cycles of assembly/disassembly, followed by treatment with 1 M sodium chloride for 1 hour, and subsequent centrifugation to remove the 70,000-, 168,000-, and 210,000-molecular weight proteins commonly... 

Wegner also treated the case wherein assembly is coupled to nucleotide hydrolysis. Here, we consider a slight modification of his model to deal with the microtubule process. Normally, the concentration of GTP is maintained by use of a GTP-regenerating system (MacNeal et ai, 1977), and the system at the steady-state plateau of assembly can be described as in Scheme II. Under these conditions, the assembly-disassembly reactions are no longer reversible, and the primed rate constants are used to emphasize that we are dealing with a different case. The rate equations for the two ends are now given as ... 

Finally, the theory for the bioenergetics and kinetics of microtubule assembly and disassembly of microtubules has been extended by Hill and Kirschner (1983). They consider the coupling of nucleotide hydrolysis in terms of the energetics of the [GTP]/[GDP][PJ mass action ratio, the possible effects of force imparted by attachment of tubules to barriers on the rate constants, and other intriguing aspects of protomer-polymer exchange kinetics and thermodynamics. Unfortunately, much of their theory remains to be tested, and an evaluation of its importance in revealing the subtleties of assembly/disassembly remains for future investigations. 

MICROTUBULE ASSEMBLY/DISASSEMBLY KINETICS. Cellular microtubules must undergo turnover, and nucleotide hydrolysis appears to play a central role in priming microtubules for their eventual disassembly. Two fundamentally different assembly/disassembly mechanisms persist during what has been termed steady-state polymerization both rely on GTP hydrolysis to provide a source of Gibbs free energy to sustain the steady-state condition . ... 

Video microscopy has permitted direct observation of microtubule assembly/disassembly dynamics in vitro. Horio and HotanP first used dark-field optics to observe the growth and shrinkage phases, but so-called Allen video-enhanced contrast microscopy has become most convenient. 

Biochemical processes such as protein unfolding/refold-ing and supramolecular assembly/disassembly take place on a time scale of seconds to minutes after readjusting the temperature of a system. Most commercially available glass-jacketed cuvettes are not suitable for temperature jumps on this time scale, as a result of the slow kinetics of heat transfer across substances with characteristically high dielectric constants, and their use can convolute the time scale of the temperature change onto the time scale... 

Epothilones are naturally occurring cytotoxic macrolides, which were initially isolated from a mycobacterium. Their antitumor activity is similar to that of the clinically established taxoids (Taxol, Taxotere), by interrupting the dynamic mechanism of microtubule assembly/disassembly via microtubule stabilization. In contrast to taxoids, epothilones are remarkably efficient against multidrug resistant cells. 

Molecular Motions Driven by Transition Metal Redox Couples Ion Translocation and Assembling-Disassembling of Dinuclear Double-Strand Helicates... 

ASSEMBLING/DISASSEMBLING OF HELICATE COMPLEXES DRIVEN BY THE Cu /Cu" COUPLE... 

The occurrence of the redox-driven reversible assembling-disassembling process involving copper complexes of 16 has been verified through cyclic voltammetry experiments at a platinum electrode in a MeCN solution. Figure 2.17 shows the CV profile obtained with a solution of the double-strand helicate complex [ Cu 21 (16)212 +. 

Figure 6.2 Effect of sucrose on the self-assembly / disassembly of sodium caseinate in aqueous medium (ionic strength = 0.01 mol/diu3, 22 °C) on the basis of combined static and dynamic light scattering. Upper plots refer to pH > pI, i.e.. ( ) pH = 7.0, ( ) pH = 6.0, (A) pH = 5.5 (a) weight-average molar weight, A/w (b) structure-sensitive parameter p. Lower plots refer to pH < p/, i.e., ( ) pH = 3.9, (A) pH = 3.5 (c) weight-average molar weight, A/w (d) structure-sensitive parameter p.

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