Multivalent Cooperative Catalysts

Abstract

Multivalent systems are well known for their enhanced ability to bind multivalent counterparts. This contribution addresses the question whether they can also behave as cooperative catalysts. Analyzing examples mostly (but not only) from our own laboratory we show what conditions are required for obtaining cooperativity in catalysis. Systems considered range from simple, discrete catalysts to dendrimers and monolayer-protected gold nanoparticles. Reactions taken into considerations for our analysis are the hydrolyses of carboxylate-and phosphate esters.

Polyvalent Catalysts Operating on Polyvalent Substrates: A Model for Surface‐Controlled Reactivity

“…We describe herein the first exploration of polyvalent catalyst-substrate reactivity in which ab ond-forming event, rather than an irreversible cleavage reaction, is monitored. Like others, [11,22] we think it likely that nature takes advantage of the principle in as yet unrealized ways,since living cells are full of surfaces decorated with all manner of functionality. Figure 1A shows the overall kinetic scheme that inspired the experiments described below.T he initial formation of acatalyst-substrate complex is followed by its dissociation or by capture/conversion to form ac atalyst-product complex.…”

“…Like others, [11,22] we think it likely that nature takes advantage of the principle in as yet unrealized ways, since living cells are full of surfaces decorated with all manner of functionality. Figure 1 A shows the overall kinetic scheme that inspired the experiments described below.…”

“…In such a case, for example, a twoarmed catalytic assembly would be revealed by a constant second-order dependence of rate on the density of catalystcomponent groups on the scaffold. [11,42] Figure 5 shows a different scenario in which the magnitude of rate acceleration varies across the range of functional-group densities, thus implicating a structure-dependent phenomenon such as "rolling". A simple aggregation effect would be expected to produce a steadier drop in rate as the putative aggregates were diluted by the addition of more dendrimers bearing fewer functional groups.…”

“…[1][2][3] Polyvalencym ay be regarded as atool for the transfer of molecular information, such as by the induction of cellular signaling events to give aw ide spectrum of responses.C hemical catalysis is another mechanism by which polyvalent recognition events can be magnified in their effect. Although polyvalent catalysts have been intensively investigated for practical reasons in synthetic chemistry [4][5][6][7][8][9][10][11][12] -for example,t oi ncrease activity by virtue of high local concentration and recyclability by virtue of easier recovery-they have only rarely been tested as av ehicle for information transfer in model systems. [13] However,i nteresting and illustrative examples of "cooperative" or "interfacial" catalysis involving polyvalent substrates do exist (see the Supporting Information).…”

Catalysis of Transesterification Reactions by a Self-Assembled Nanosystem

“…This then facilitates the preparation of catalyst libraries and systems of a high complexity. Complex catalytic systems are of interest, because these may manifest features that are common to enzymes, but more difficult to observe in a synthetic system [9,10]. Such phenomena include multivalency, cooperativity and allosterism, which are often fundamental in biological regulatory pathways.…”