The distinction between different types of cooperativity is essential for understanding the fundamentals involved. The three title cooperative effects arise from the interplay of intermolecular binding interactions, the presence of one or more intramolecular binding interactions, and, in the latter case, their possible interplay. A master equation for the stability of an assembly is outlined that takes into account all of the three possible types of cooperativit

Inherent chirality'' in molecules like calix[4]arenes, fullerenes, and uranyl-salophen complexes can be related to the presence of curvature. This observation serves as a basis for the introduction of a new chirality descriptor.

Recognition of inorganic phosphates PO(4)(3-), P(2)O(7)(4-), and P(3)O(10)(5-) and nucleotides AMP(2-), ADP(3-), and ATP(4-) by Zn(2+)-salophen complexes 1 and 2 in ethanol was investigated by different spectroscopic techniques. (31)P NMR and mass spectrometry showed that anions of both series are bound by 1 and 2, while absorption and emission studies revealed that only nucleotides produce relevant changes in the spectral properties of the two hosts. (1)H NMR studies proved that the adenine aromatic group is involved in the complexation, thus pointing out the role of supramolecular ditopic receptors played by salophen derivatives toward this class of biologically relevant substrates. The lifetime of the photogenerated triplet state of the Zn(2+)-salophen compounds was measured by nanosecond laser flash photolysis, and the observed changes upon increasing the concentration of nucleotides allowed the identification of the formation of a 1:0.5 host/guest intermediate complex additionally to the formation of a 1:1 complex.

From a kinetic analysis of the "dimer model", which is the most prominent mechanism of the Soai reaction, an equation is derived predicting the amplification of enantiomeric excess as a function of initial conditions. The role played by the enantioselectivity of the catalyst-product is also taken into account. Comparison with experimental data obtained at 0 degrees C by Soai et al. shows that the predicted enantiomeric excesses are lower than the experimental values by up to four orders of magnitude, and thus revision of the dimer model in the low-temperature regime is warranted. A kinetic analysis including the formation of tetramers is presented that fits the data at 0 degrees C and indicates that 2:2 heterochiral tetramers are more stable than homochiral and 3:1 heterochiral tetramers. A DFT study on diastereomers of barrel-like tetramers indeed shows higher stability of 2:2 heterochiral tetramers and thus lends support to the above kinetic analysis.

The Soai reaction, that is, the addition of diisopropylzinc to aromatic aldehydes (see Scheme 1 for an example), is the sole case of amplifying asymmetric autocatalysis reported to date.[1] Its behavior stands out as a paradigm for absolute asymmetric synthesis and the origin of homochirality in nature, [2] yet the underlying mechanism remains elusive, thus prompting us to investigate the reaction by computational methods. [3] The reaction is confined to the addition of [iPr 2 Zn] to aromatic aldehydes with at least one pyridinic nitrogen in the g-position, but the presence of a suitable substituent in the dposition, such as a methyl or a tert-butylethynyl group, is also important to reach the highest levels of chiral amplification. Blackmond and co-workers reported that the rate with the racemic catalyst is approximately half that with the enantiopure catalyst throughout the reaction, and ascribed this fact to the catalytic activity of homochiral dimers which are in statistical equilibrium with an inactive heterochiral dimer. [2e, 4] They also found that the reaction rate is second-order in aldehyde, first-order in the active dimers, and independent of the concentration of [iPr 2 Zn].[4c,d] The initially proposed structure for the dimers, 3, [4a] was successively refuted in favor of the structure 4, detected by NMR spectroscopy, [5] although it should be noted that a catalytic intermediate is not necessarily the most abundant species.Since all the structural features noted above are essential for the success of the reaction, a meaningful computational study does require that all of them are retained in the calculations. Owing to the large size of the systems involved, energies of both ground and transition states (TSs) were calculated at the B3LYP/6-31G(d)//HF/3-21G(d) level of theory and corrected for ZPVEs. [6] At the onset, we made the reasonable working assumption that all the association processes occurring in solution are fast and reversible whereas the transfer of the isopropyl group from zinc to aldehyde is irreversible and rate limiting. The detected rate law indicates that in the TS there are two molecules each of 1 and 2, but the assumption above implies that at least one molecule of [iPr 2 Zn] must also be present. The high level of chiral induction detected suggests the fast self-assembly of an ordered complex in which the reactants are held in close proximity before the isopropyl transfer takes place. After several unsuccessful attempts to model a meaningful assembly made of two molecules of 1, two of 2, and one of [iPr 2 Zn], we passed to examine assemblies made of two molecules each of 1, 2, and [iPr 2 Zn]. At this level of complexity, we found an appealing homochiral structure, dubbed 7-(R,anti) 2 , with two symmetrically equivalent sides. For each side, the anti notation refers to the orientation of the isopropyl group bound to the R carbon relative to the neighbouring [iPr 2 Zn], as emphasized by the bond torsion in bold in the structure Anti.The structure provides a straightforward expla...