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The S22 test set of interaction energies for small model complexes [Phys. Chem. Chem. Phys. 8, 1985 (2006)] has been very valuable for benchmarking new and existing methods for noncovalent interactions. However, the basis sets utilized to compute the CCSD(T) interaction energies for some of the dimers are insufficient to obtain converged results. Here we consistently extrapolate all CCSD(T)/complete basis set (CBS) interaction energies using larger basis sets for the CCSD(T) component of the computation. The revised values, which we designate S22A, represent the most accurate results to date for this set of dimers. The new values appear to be within a few hundredths of 1 kcal mol-1 of the true CCSD(T)/CBS limit at the given geometries, but the former S22 values are off by as much as 0.6 kcal mol-1 compared to the revised values. Because some of the most promising methods for noncovalent interactions are already achieving this level of agreement (or better) compared to the S22 data, more accurate benchmark values would clearly be helpful. The MP2, SCS-MP2, SCS-CCSD, SCS(MI)-MP2, and B2PLYP-D methods have been tested against the more accurate benchmark set. The B2PLYP-D method outperforms all other methods tested here, with a mean average deviation of only 0.12 kcal mol-1. However, the consistent, slight underestimation of the interaction energies computed by the SCS-CCSD method (an overall mean absolute deviation and mean deviation of 0.24 and -0.23 kcal mol-1, respectively) suggests that the SCS-CCSD method has the potential to become even more accurate with a reoptimization of its parameters for noncovalent interactions. [ABSTRACT FROM AUTHOR]

There has been much interest in cost-free improvements to second-order Mo\ller–Plesset perturbation theory (MP2) via scaling the same- and opposite-spin components of the correlation energy (spin-component scaled MP2). By scaling the same- and opposite-spin components of the double excitation correlation energy from the coupled-cluster of single and double excitations (CCSD) method, similar improvements can be achieved. Optimized for a set of 48 reaction energies, scaling factors were determined to be 1.13 and 1.27 for the same- and opposite-spin components, respectively. Preliminary results suggest that the spin-component scaled CCSD (SCS-CCSD) method will outperform all MP2 type methods considered for describing intermolecular interactions. Potential energy curves computed with the SCS-CCSD method for the sandwich benzene dimer and methane dimer reproduce the benchmark CCSD(T) potential curves with errors of only a few hundredths of 1 kcal mol-1 for the minima. The performance of the SCS-CCSD method suggests that it is a reliable, lower cost alternative to the CCSD(T) method. [ABSTRACT FROM AUTHOR]

Cancer cell tethering and rolling on the vascular wall is facilitated by various selectin: gly-coprotein interactions which lead to eventual extravasation and metastases.The aberrantly underglycosylated mucin MUC1 has been shown to both abundantly express selectin binding moieties (sialyl Lewis x and a) and to consistently expose its core epitope. Flow cytometry was used to determine MUC1 expression on ZR-75-1 and MCF7 cells, while immunofluorescence microscopy was used to confirm the aberrant form of MUC1 and MUC1:ICAM-1 interactions. Each cell line was then perfused through combined E-selectin and ICAM-1 coated microtubes, as a model of the microvascular endothelium. ZR-75-1 and MCF7 were found to express abundant and low levels of underglycosylated MUC1, respectively. The rolling/adhesion profiles showed that ZR-75-1 cells, when compared to MCF7 cells, interact with E-selectin more efficiently resulting in sufficiently slow rolling velocities to form MUC1:ICAM-1 interactions thereby facilitating firm adhesion. The purpose and novelty of this work is the demonstration of the synergistic adhesion capabilities of MUC1 in the metastatic adhesion cascade, where the observed differential adhesion is consistent with the relative metastatic potential of the ZR-75-1 (highly metastatic) and MCF7 (weakly metastatic) cell lines. [ABSTRACT FROM AUTHOR]

Noncovalent interactions play a significant role in determining the structures of DNA, RNA, and proteins. Among the most prevalent are pi-pi interactions, which occur as favorable forces between the aromatic subunits of biochemical molecules. The aromatic side chains of amino acids tryptophan and phenylalanine are commonly modeled with indole and benzene, respectively. We have utilized the MP2 and SCS-MP2 methods with the aug-cc-pVDZ basis set to compute several T-shaped interaction energies and parallel displaced (PD) three-dimensional potential energy surfaces (PESs) at 3.4, 3.6, and 3.8 A vertical separations. At selected minima, CCSD(T) results extrapolated to the complete-basis-set (CBS) limit were obtained. The trend of the T-shaped interactions has been rationalized by considering electrostatic potential maps and symmetry-adapted perturbation theory (SAPT) results. The global minimum has been verified to be the N-H/pi T-shaped configuration with a CCSD(T)/CBS interaction energy of -5.62 kcal mol(-1). For the PD PESs, the MP2 and SCS-MP2 methods predict different minimum configurations. The CCSD(T) method favors the SCS-MP2 PD configuration over the MP2 PD configuration by 0.18 kcal mol(-1). Among the approximate methods considered here, the SCS-CCSD method extrapolated to the CBS limit incurs only around 2% error compared to CCSD(T)/CBS results and is the most reliable for the interaction energies of the indole-benzene complex. Overall, the extension of aromaticity and the highly positive hydrogen of the N-H bond, both exhibited by indole, enhance the strength of nonbonded interactions with benzene compared to those in the benzene dimer or in the pyridine-benzene complex.

The energies and optimized geometries of the lowest lying singlet, triplet, and quintet states for the Fe(II)-, Co(III)-, Ni(IV)-, Ru(II)-, Rh(III)-, and Pd(IV)-salens have been computed with the B3LYP and BP86 density functional theory (DFT) methods, and the results are compared to more robust complete active-space self-consistent field (CASSCF) values. Density functional optimizations are performed using two different models of the salen ligand, and CASSCF relative energies at these DFT geometries show no appreciable difference whether the smaller or the larger model salen is considered. Unlike in our previous studies on the d0 and d2 metal-salens, DFT methods rarely predict the correct ordering of states compared to high-level complete active-space third-order perturbation theory (CASPT3) computations. The DFT energy gaps, moreover, are generally much smaller than those predicted by the CASPT3 method. Similarly to our previous studies, DFT optimized geometries closely match the CASSCF optimized geometries with errors mostly on the order of 0.1 A least root mean squared deviation. The electronic structure of the Co(III)- and Rh(III)-salens is particularly challenging, and significant differences between CASPT2 and CASPT3 relative energies were observed in these cases.

AlCl-salen (salen=N,N'-bis(salicylidene)ethylenediamine dianion) catalysts supported onto macrocyclic oligomeric cyclooctene through linkers of varying length and flexibility have been developed to demonstrate the importance of support architecture on catalyst activity. The role played by the support and the linkers in dictating catalyst activity was found to vary for reactions with contrasting mechanisms, such as the bimetallic cyanide and the monometallic indole addition reactions. While the flexible support significantly enhanced the cyanide addition reaction, most likely by improving salen-salen interactions in the transition state, it lowered the reaction rate for the monometallic indole reaction. For both reactions, significant increase in catalytic activity was observed for catalysts with the longest linkers. The effect of the flexible macrocyclic support on catalysis was further exemplified by the enhanced activity of the supported catalyst in comparison with its unsupported analogue for the conjugate addition of tetrazoles, which is known to be catalyzed by dimeric mu-oxo-salen catalysts. Our studies with the cyclooctene supported AlCl-salen catalysts provides significant insights for rationally designing highly efficient AlCl-salen catalysts for a diverse set of reactions.

Bisalen-very cooperative: A novel styryl-substituted, unsymmetrical bisalen is shown to be a versatile precursor to both soluble and insoluble cooperative catalysts for the hydrolytic kinetic resolution of epoxides. The unique bisalen motif ensures all catalysts derived from it have the necessary molecular-level ligand pairing needed for cooperative bimetallic catalytic reactions (see scheme).