On the convergence of Z-averaged perturbation theory

Very high order open-shell Z-averaged perturbation theory (ZAPT) energies, equilibrium bond lengths, and harmonic vibrational frequencies have been computed for a suite of small molecules using a determinantal algorithm. The convergence of ZAPTn energies is compared to alternative Moller-Plesset (MP) perturbation theories built on restricted open-shell Hartree-Fock (ROMP, RMP, OPT1, and OPT2) and unrestricted Hartree-Fock (UMP) reference wave functions for NH(2) at three N-H bond lengths and for CN. The ZAPTn energy series closely parallel those of RMPn and ROMPn theories for these systems. Further, we examine the convergence of ZAPTn energies, equilibrium bond lengths (r(e)), and harmonic vibrational frequencies (omega(e)) for X (2)Sigma(g)(+) CN, X (4)Sigma(g) (-) C(2)(+), and b (2)Delta(g) C(2)(+), tracking oscillations in the energy series for the challenging latter system to order 1000. Finally, we obtain r(e) and omega(e) values from explicit ZAPT2 and ZAPT4 computations with a triple-zeta plus double polarization basis set. The ensuing results are very close to those from second- and fourth-order RMP and ROMP for the NO and CN molecules but are significantly closer to experiment in the case of (3)Sigma(g)(-) O(2). The ZAPTn series exhibit all the fascinating diversity of behavior previously observed for closed-shell MPn theory. Particularly encouraging is the ability of Feenberg transformations to remove erratic, strongly oscillatory, and divergent behavior that may occur in ZAPTn series and provide systematic improvements toward the full configuration interaction limit. In light of the appealing mathematical properties of ZAPT and similarity of results to those from the oft-applied RMP theory, coupled with the reductions in computational cost inherent in the ZAPT method relative to theories requiring different orbitals for different spins, we recommend low-order ZAPT for general applications to open-shell systems, particularly in cases where spin contamination is of concern.     

Extraordinary NO2 Removal by the Metal–Organic Framework UiO‐66‐NH2

Here we discuss the removal of nitrogen dioxide, an important toxic industrial chemical and pollutant, from air using the MOF UiO‐66‐NH₂. The amine group is found to substantially aid in the removal, resulting in unprecedented removal capacities upwards of 1.4 g of NO₂ /g of MOF. Furthermore, whereas NO₂ typically generates substantial quantities of NO on sorbents, the amount generated by UiO‐66‐NH₂ is significantly reduced. Of particular significance is the formation of a diazonium ion on the aromatic ring of the MOF, and the potential reduction of NO₂ to molecular nitrogen.     

Shotgun proteomic analysis of Arabidopsis thaliana leaves

Two shotgun tandem MS proteomics approaches, multidimensional protein identification technology (MudPIT) and 1-D gel-LC-MS/MS, were used to identify Arabidopsis thaliana leaf proteins. These methods utilize different protein/peptide separation strategies. Detergents not compatible with MudPIT were used with 1-D gel-LC-MS/MS to help enrich for the detection of membrane-spanning and hydrophobic proteins. By combining the data from all MudPIT and 1-D gel-LC-MS/MS experiments, 2342 nonredundant proteins spanning a broad range of molecular weights and pI values were detected. With the exception of unknown proteins, the distribution of gene ontology (GO) classifications for the detected proteins was similar to that encoded by the genome, which shows that these extraction and separation procedures are useful for a broad proteomic survey of plant cells. Unknown proteins will likely have to be targeted by using additional methods, some of which should be compatible with separation strategies taken here.     

Borate binding to siderophores: structure and stability

Well-known as specific iron chelating agents produced by bacteria, it is shown that some, but not all, siderophore classes have an unexpected binding affinity for boron. The relevant criterium is the availability of a vicinal dianionic oxygen containing binding group (i.e., citrate or catecholate). The resulting boron complexes have been characterized by ESI-MS, multinuclear NMR, and DFT calculations. Detailed boron binding constants have been measured for vibrioferrin, rhizoferrin, and petrobactin. The observed affinity of certain siderophores for borate, a common chemical species in the marine but not the terrestrial environment, allows for small, but potentially significant, concentrations of B-siderophores to exist at oceanic pH. We hypothesize that these concentrations could be sufficient for them to function as cell signaling molecules or as mediators of biological boron uptake. In addition, binding of the tetrahedral boron to these siderophores results in a conformation that is different from either the free siderophore or its iron complex and would thus allow a distinction to be made between its iron uptake and any putative cell signaling roles.     

Model systems for probing metal cation hydration: the V+(H2O) and ArV+(H2O) complexes

In support of mass-selected infrared photodissociation (IRPD) spectroscopy experiments, coupled-cluster methods including all single and double excitations (CCSD) and a perturbative contribution from connected triple excitations [CCSD(T)] have been used to study the V+(H2O) and ArV+(H2O) complexes. Equilibrium geometries, harmonic vibrational frequencies, and dissociation energies were computed for the four lowest-lying quintet states (5A1, 5A2, 5B1, and 5B2), all of which appear within a 6 kcal mol(-1) energy range. Moreover, anharmonic vibrational analyses with complete quartic force fields were executed for the 5A1 states of V+(H2O) and ArV+(H2O). Two different basis sets were used: a Wachters+f V[8s6p4d1f] basis with triple-zeta plus polarization (TZP) for O, H, and Ar; and an Ahlrichs QZVPP V[11s6p5d3f2g] and Ar[9s6p4d2f1g] basis with aug-cc-pVQZ for O and H. The ground state is predicted to be 5A1 for V+(H2O), but argon tagging changes the lowest-lying state to 5B1 for ArV+(H2O). Our computations show an opening of 2 degrees -3 degrees in the equilibrium bond angle of H2O due to its interaction with the metal ion. Zero-point vibrational averaging increases the effective bond angle further by 2.0 degrees -2.5 degrees, mostly because of off-axis motion of the heavy vanadium atom rather than changes in the water bending potential. The total theoretical shift in the bond angle of about +4 degrees is significantly less than the widening near 9 degrees deduced from IRPD experiments. The binding energies (D0) for the successive addition of H2O and Ar to the vanadium cation are 36.2 and 9.4 kcal mol(-1), respectively.     

Rate constants for the reactions of hydroxyl radical with several fluoroethers by the relative rate method

Relative rate experiments were used to measure ratios of chemical kinetics rate constants as a function of temperature for the reactions of OH with eight fluoroethers, including CF3OCF2CHF2, CF3OCF2CHFCF3, CHF2CF2OCHF2, CF3CHFCF2OCH2CF3, (CF3)2CHOCHF2, CF2HCF2OCH2CF3, CHF2CF2OCHFCF3, and CF3CH2OCH2CF3. The temperature ranges were about 270-400 K. Each compound was measured against at least two references. Results are compared with previous data where available. An approach using model compounds for the approximate estimation of rate constants for the fluoroethers is discussed. Observed temperature dependences for fluoroethers from the present work and some literature work are shown to be accurately predictable, based on a previously determined correlation of k298K with the pre-exponential factor, A, in the Arrhenius equation k = Ae(-E/RT).     

Optimization of solvents for effective isolation of colchicines from Gloriosa superba L. seeds

To meet the strong demand of colchicine an attempt is made to optimize the solvent system for isolation of colchicine. Gloriosa superba dried seed powder was extracted by using different solvents. Maximum yield of colchicine was obtained when extracted with water and alcohol in the ratio of 50 : 50.