Jason K. Pearson

Can correlation bring electrons closer together

We discuss the exact Coulomb hole for the ground state of the helium atom and helium-like ions. We find that the correlated wavefunction yields a smaller probability of finding the electrons at large separations than does the Hartree–Fock wavefunction, leading to the counterintuitive conclusion that correlation brings distant electrons closer together. This effect becomes less pronounced as the nuclear charge increases.

Intracule functional models. IV. Basis set effects

We have calculated position and dot intracules for a series of atomic and molecular systems, starting from an unrestricted Hartree-Fock wave function, expanded using the STO-3G, 6-31G, 6-311G, 6-311++G, 6-311++G(d,p), 6-311++G(3d,3p), and 6-311++G(3df,3pd) basis sets as well as the nonpolarized part of Dunnings cc-pV5Z basis. We find that the basis set effects on the intracules are small and that correlation energies from the dot intracule ansatz are remarkably insensitive to the basis set quality. Mean absolute errors in correlation energies across the G1 data set agree to within 2 mE(h) for all basis sets tested.

Isolation, Biomimetic Synthesis, and Cytotoxic Activity of Bis(pseudopterane) Amines

LC-MS/MS-based screening of the dichloromethane extract of the gorgonian coral Pseudopterogorgia acerosa led to the isolation of a novel bis(pseudopterane) amine (1). The structural assignment of 1 was achieved by 1D and 2D NMR and mass spectrometry analysis. A biomimetic synthesis of 1 and the known symmetrical diterpene 2 from pseudopterolide (3) is described in this report. Bis(pseudopterane) amine showed selective growth inhibition activity against cancer cell lines with IC(50) values of 4.2 microM (HCT116) and 42 microM (HeLa).

Design of coordination polymers with 4′-substituted functionalized terpyridyls in the backbone and pendent cyclopentadienyliron moieties

The reaction of dichloro-terminated organoiron complex [Fe(1,4-C6H4Cl2)Cp]+PF6− (3) with 4-hydroxybenzoic acid resulted in the formation of dicarboxylic acid organoiron complex 4. 4′-Hexyl alcohol-2,2′:6′,2′′-terpyridine (hextpy) 2 was reacted with dicarboxylic acid organoiron complex 4 or the similar monoacid organoiron complex 5 to afford two novel organoiron complexes containing one or two terminal terpyridine moieties (complexes 6 and 7, respectively). Molecular dynamics simulations of 7 revealed that the terminal terpyridine units readily interact with one another. The metal-containing complexes [M(hextpy)2](PF6)2 {M = Fe (8), Ni (9)} were prepared from the reaction of FeCl2·4H2O or Ni(CH3COO)2·4H2O with hextpy 2. The products were fully characterized by IR, UV-visible, and NMR spectroscopies, as well as elemental analysis. The reaction of monocarboxylic acid organoiron complex 5 with bis(hextpy) complexes 8 and 9 afforded the novel chloro-terminated monomers 10 and 11 containing two different metals. The reaction of monomer 7 with iron(II) chloride or nickel(II) acetate in methanol produced iron(II)- or nickel(II)-containing polymers 12 (M = Fe) and 13 (M = Ni), respectively. The monomers containing multimetal centers were polymerized through aromatic substitution reactions with bisphenol A or hydroquinone to afford polymers 14 and 15, respectively. The thermal properties of the polymers were also investigated, providing glass transition temperatures of approximately −25 °C for the iron-chelated polymers and a stepwise degradation of the polymers, beginning with the decoordination of the pendent cationic iron moieties and ending with the loss of the bonding interaction between the iron center and the nitrogen atoms of the chelated terpyridine groups.

Isolation and Structure Elucidation of Satosporin A and B: New Polyketides from Kitasatospora griseola

Satosporins A and B, two novel glucosylated polyketides, were isolated from the actinomycete Kitasatospora griseola MF730-N6. The polyketides possess an unprecedented tricyclic ring system that was fully characterized using a combination of spectroscopic analyses and computational calculations. Satosporin A was quantitatively converted into its aglycon homologue, satosporin C, using a β-glucosidase. The determination of the absolute stereochemistry was achieved using solution TDDFT/ECD calculations and chemical derivatization methods.

New Technique for Determining the Optical Constants of Liquids

The traditional techniques of transmission and attenuated total reflectance (ATR) spectroscopy for determining the optical constants of liquids are not practical or reliable for very strong absorption bands. Specular reflectance can be used in these cases, but for volatile liquids it is impossible to separate the reflectance spectrum of the liquid from the absorption spectrum of the vapor above the liquid. Methods using special cells have been described in the literature to prevent the liquid from evaporating. In this paper, a similar technique that makes use of traditional transmission cells is presented. It is shown that this new technique generates k(ν˜) spectra for strong absorption bands that are accurate to approximately 2%.

A simultaneous probability density for the intracule and extracule coordinates

We introduce the intex density X(R,u), which combines both the intracular and extracular coordinates to yield a simultaneous probability density for the position of the center-of-mass radius (R) and relative separation (u) of electron pairs. One of the principle applications of the intex density is to investigate the origin of the recently observed secondary Coulomb hole. The Hartree-Fock (HF) intex densities for the helium atom and heliumlike ions are symmetric functions that may be used to prove the isomorphism 2I(2R)=E(R), where I(u) is the intracule density and E(R) is the extracule density. This is not true of the densities that we have constructed from explicitly correlated wave functions. The difference between these asymmetric functions and their symmetric HF counterparts produces a topologically rich intex correlation hole. From the intex hole distributions (X(exact)(R,u)-X(HF)(R,u)), we conclude that the probability of observing an electron pair with a very large interelectronic separation increases with the inclusion of correlation only when their center-of-mass radius is close to half of their separation.

Understanding the Electronic Structure, Reactivity, and Hydrogen Bonding for a 1,2-Diphosphonium Dication

The experimental charge density for hexamethyldiphosphonium ditriflate has been determined from low-temperature high-resolution X-ray diffraction data. These results have been compared with theoretically calculated values for the isolated gas-phase compound. Analysis of the topological and atomic basin properties has provided insight into the exact nature of the P-P bond in both the crystalline and the gas-phase structures. The rho(b)(r) and nabla2rho(b)(r) values highlight the covalent nature of the P-P bond, while the atomic charges indicate a localization of the positive charges on the two phosphorus atoms. This seems to indicate that a covalent bond is formed despite a strong electrostatic repulsion between these two heteroatoms. The topological properties and electrostatic potentials have also been shown to provide significant insight into the chemical reactivity of the title compound. A topological analysis of P2Me4, P2Me5(+), and P2Me6(+2) species has provided information about the progression of the P-P bond in the synthesis of the title compound. An investigation of the different hydrogen-bonding networks present in the crystalline and gas-phase structures, along with their affect on the electronic structure of the title compound has also been investigated. This has all led to significant new insight into the electronic structure, reactivity, and weak hydrogen bonding in prototypical 1,2-diphosphonium dications.

Assessment and Application of Density Functional Theory for the Prediction of Structure and Reactivity of Vanadium Complexes

We assess the performance of six density functionals, each paired with one of five basis sets (a total of 30 model chemistries) for the prediction of geometrical parameters in the coordination sphere of nine vanadium complexes (for a total of 270 structural analyses). We find that results are generally consistent over the range of functionals tested and that none fail drastically. For bond lengths, the model chemistry PBE0/QZVP performed the best overall (having a MAD of only 0.02 Å from experiment) yet PBE0/6-31G* provides nearly identical results. For bond angles, PBE0 also performed best overall and, when combined with the 6-31G* basis, produces one of the smallest error distributions of any model chemistry tested. We subsequently applied the PBE0/6-31G* model chemistry to understanding the mechanism of action of a [BIMPY]VCl3 catalyst in the polymerization of styrene (Sty) and vinyl acetate (VAc). Our results indicate that the [BIMPY]VCl3 catalyst operates through a unique, two-step reaction pathway: dehalogenation to form a reactive V(II) intermediate (a highly favorable process) followed by a potentially reversible OMRP to control the polymerization of vinyl acetate. Control over vinyl acetate is facilitated by both the higher reactivity of the radical species and the participation of the ester group in the trapping step. In both the Sty and VAc cases we predict relatively poor control of the polymerization with the vanadium catalyst, which is in good agreement with our experimental results.