Performance of Localized Coupled Cluster Methods in a Moderately Strong Correlation Regime: Hückel-Möbius Interconversions in Expanded Porphyrins.

Localized orbital coupled cluster theory has recently emerged as a nonempirical alternative to DFT for large systems. Intuitively, one might expect such methods to perform less well for highly delocalized systems. In the present work, we apply both canonical CCSD(T) approximations and a variety of localized approximations to a set of flexible expanded porphyrins-macrocycles that can switch between Hückel, figure-eight, and Möbius topologies under external stimuli. Both minima and isomerization transition states are considered. We find that Möbius(-like) structures have much stronger static correlation character than the remaining structures, and that this causes significant errors in DLPNO-CCSD(T) and even DLPNO-CCSD(T1) approaches, unless TightPNO cutoffs are employed. If sub-kcal mol-1 accuracy with respect to canonical relative energies is required even for Möbius-type systems (or other systems plagued by strong static correlation), then Nagy and Kallay's LNO-CCSD(T) method with "tight" settings is the suitable localized approach. We propose the present POLYPYR21 data set as a benchmark for localized orbital methods or, more broadly, for the ability of lower-level methods to handle energetics with strongly varying degrees of static correlation.

Equilibrium gas-phase structures of sodium fluoride, bromide, and iodide monomers and dimers.

The alkali halides sodium fluoride, sodium bromide, and sodium iodide exist in the gas phase as both monomer and dimer species. A reanalysis of gas electron diffraction (GED) data collected earlier has been undertaken for each of these molecules using the EXPRESS method to yield experimental equilibrium structures. EXPRESS allows amplitudes of vibration to be estimated and correction terms to be applied to each pair of atoms in the refinement model. These quantities are calculated from the ab initio potential-energy surfaces corresponding to the vibrational modes of the monomer and dimer. Because they include many of the effects associated with large-amplitude modes of vibration and anharmonicity, we have been able to determine highly accurate experimental structures. These results are found to be in good agreement with those from high-level core-valence ab initio calculations and are substantially more precise than those obtained in previous structural studies.

Improvements on a patient-specific dose estimation system in nuclear medicine examination.

The purpose of this paper is to develop a patient-specific dose estimation system in nuclear medicine examination. A dose deposition routine to store the deposited energy of the photons during their flights was embedded in the widely used SimSET Monte Carlo code and a user-friendly interface for reading PET and CT images was developed. Dose calculated on ORNL phantom was used to validate the accuracy of this system. The ratios of S value for (99m)Tc, (18)F and (131)I computed by this system to those obtained with OLINDA for various organs were ranged from 0.93 to 1.18, which were comparable to that obtained from MCNPX2.6 code (0.88-1.22). Our system developed provides opportunity for tumor dose estimation which cannot be known from the MIRD. The radiation dose can provide useful information in the amount of radioisotopes to be administered in radioimmunotherapy.

Halogen Bonds: Benchmarks and Theoretical Analysis.

We carried out an extensive survey of wave function and DFT methods to test their accuracy on geometries and dissociation energies of halogen bonds (XB). For that purpose, we built two benchmark sets (XB18 and XB51). Between the DFT methods, it was found that functionals with high exact exchange or long-range corrections were suitable for these dimers, especially M06-2X, ωB97XD, and double hybrids. Dispersion corrections tend to be detrimental, in spite of the fact that XB is considered a noncovalent interaction. Wave function techniques require heavy correlated methods (i.e., CCSD(T)) or parametrized ones (SCS-MP2 or SCS(MI)MP2). Heavy basis sets are needed to obtain high accuracy, such as aVQZ or aVTZ+CP, and ideally a CBS extrapolation. Relativistic ECPs are also important, even for the bromine based dimers. In addition, we explored some XB with new theoretical tools, the NCI ("Non-Covalent Interactions") method and the NOFF ("Natural Orbital Fukui Functions").

Experience with a frontal core biopsy device in soft tissue and bone lesions.

OBJECTIVE: To assess the efficacy and cost of a new frontloading biopsy system, Spirotome® (system 1), in musculoskeletal lesions, and to compare the results with those obtained with commonly used biopsy devices. METHODS: System 1 was used in all soft tissue lesions (STL) and osteolytic bone lesions (OBL) of patients who presented at our department for CT-guided biopsy between January 2009 and June 2010. Accuracy and cost were compared to those of Bonopty® (system 2) and Tru-cut (system 3) procedures. RESULTS: The efficacy of system 1 was 85% in STL and 89% in OBL. The procedure was well tolerated and caused no complications. System 3 had an efficacy of 84% in STL and OBL combined. The efficacy of system 2 in OBL was 85%. The cost of single-use system 1 and system 2 was comparable, the cost of system 3 and multiuse system 1 compared to single-use system 1 was 25 and 7%, respectively. CONCLUSIONS: The efficacy of system 1 in biopsy of STL and OBL was better than that of system 3. In OBL, the efficacy of system 1 was better than that of system 2. In STL at hazardous locations and small OBL with a thin cortical shell, system 1 offers the advantage of variable length and controlled loading. In these cases, single-use system 1 was cost-effective when compared to surgical biopsy. The cost per procedure of multiuse system 1 was lower than of system 3.

Isolation of therapeutically functional mouse bone marrow mesenchymal stem cells within 3 h by an effective single-step plastic-adherent method.

OBJECTIVES: Isolation of mouse mesenchymal stem cells (mMSCs), by the approach of plastic adherence, has been difficult due to persistent contamination by haematopoietic cells (HCs); we have observed that this contamination was due to engagement between HCs and mMSCs. The HCs can be lifted together with the mMSCs despite their insensitivity to trypsin digestion. Herein, we provide a single-step procedure to rapidly segregate mMSCs from HC contaminants using transient lower-density plastic adherence (tLDA). MATERIALS AND METHODS: The tLDA was performed by replating bone marrow adherent cells at lower density (1.25 x 10(4) cells/cm(2)) than usual, allowing for transient adherence of no more than 3 h, followed by trypsin digestion. tLDA-isolated cells were evaluated by immunophenotyping, multi-differentiation potentials, immunosuppressive properties, and therapeutic potential as demonstrated by symptoms of osteoporosis. RESULTS: The single-step tLDA method can effectively eliminate the persistent HC contaminants; tLDA-isolated cells were phenotypically equivalent to those reported as mMSCs. The isolated cells possessed classic tri-lineage differentiation potential into osteogenic, adipogenic and chondrogenic lineages and had immunosuppressive properties. After intravenous transplantation, they migrated into the allogeneic bone marrow and rescued hosts from osteoporosis symptoms, demonstrating their therapeutic potential. CONCLUSIONS: We have developed a simple and economical method that effectively isolates HC-free, therapeutically functional mMSCs from bone marrow cell adherent cultures. These cells are suitable for various mechanistic and therapeutic studies in the mouse model.

A DFT study on the mechanism of a novel, regioselective, intramolecular N-pi rearrangement of cis and trans-eta1-N-Cp*Rh-hydroxytamoxifen complexes to their eta6 derivatives; potential breast cancer pharmaceuticals, and fluorescent probes.

The previously reported reactions of cis and trans-hydroxytamoxifen drug derivatives, 1 and 2, with [Cp*Rh(L)(3)](2+) complexes (L = H(2)O, CH(3)OH), initially provided the kinetically controled eta(1)-N complexes, 4(OTf, CH(3)OH) and 5(OTf, CH(3)OH), which underwent a novel, intramolecular, regioselective N-pi rearrangement to provide the eta(6) complexes, 6 and 7. A dramatic solvent effect was also observed on the rate of this N-pi rearrangement in CH(3)OH or CH(2)Cl(2). Therefore, a DFT study was conducted that provided further mechanistic and thermodynamic data on this N-pi rearrangement. The preferred structures of both the eta(1)-N and eta(6) complexes in the two solvents were determined, and a thorough analysis of their geometries and electronic structures has been provided. The influence of the solvent on the N-pi rearrangement was studied by including the solvent both implicitly using a PCM model, and explicitly by introducing the counterion and/or the solvent molecules into the inner and outer coordination spheres of the complexes. It was shown that the triflate (OTf(-)) counterion was strongly bound in the inner coordination sphere of the eta(1)-N complexes, 4(OTf) and 5(OTf), and in the outer sphere of the coordinatively saturated eta(6) complexes, 6 and 7, especially in non-polar media. The cleavage of the ionic Cp*Rh-OTf bond was found to be the rate-limiting step in the N-pi rearrangement. The thermodynamic results suggested that the eta(6) complexes were more stable than the eta(1)-N complexes in CH(2)Cl(2) and in CH(3)OH at elevated temperatures. The opposite relationship for the stabilities of the eta(1)-N complexes was found in CH(3)OH at room temperature, thus corroborating the experimental results that the N-pi rearrangement did not occur, under these conditions. A plausible mechanistic pathway for the N-pi rearrangement was proposed from our extensive DFT studies, that included several important intermediates and transition states, and provided a unique view of this novel transformation.

Directing aryl-I versus Aryl-Br bond activation by nickel via a ring walking process.

Activation of a strong aryl-Br bond of a halogenated vinylarene by nickel(0) is demonstrated in the presence of aryl-I containing substrates. eta2-Coordination of Ni(PEt3)2 to the C=C moiety of halogenated vinylarenes is kinetically preferable and is followed by an intramolecular aryl-halide bond activation process. This "ring-walking" process is quantitative and proceeds under mild reaction conditions in solution. Mechanistic studies indicate that the metal insertion into the aryl-halide bond is not the rate-determining step. The reaction obeys first-order kinetics in the eta2-coordination complexes with almost identical activation parameters for Br and I derivatives. The ring-walking process is kinetically accessible as shown by density functional theory (DFT) calculations at the PBE0/SDB-cc-pVDZ//PBE0/SDD level of theory.

Heats of formation of beryllium, boron, aluminum, and silicon re-examined by means of W4 theory.

Benchmark total atomization energies (TAE0 values) were obtained, by means of our recent W4 theory [Karton, A.; Rabinowitz, E.; Martin, J. M. L.; Ruscic, B. J. Chem. Phys. 2006, 125, 144108], for the molecules Be2, BeF2, BeCl2, BH, BF, BH3, BHF2, B2H6, BF3, AlF, AlF3, AlCl3, SiH4, Si2H6, and SiF4. We were then able to deduce "semi-experimental" heats of formation for the elements beryllium, boron, aluminum, and silicon by combining the calculated TAE0 values with experimental heats of formation obtained from reactions that do not involve the species Be(g), B(g), Al(g), and Si(g). The elemental heats of formation are fundamental thermochemical quantities that are required whenever a molecular heat of formation has to be derived from a calculated binding energy. Our recommended DeltaH degrees f,0 [A(g)] values are Be 76.4+/-0.6 kcal/mol, B 135.1+/-0.2 kcal/mol, Al 80.2+/-0.4 kcal/mol, and Si 107.2+/-0.2 kcal/mol. (The corresponding values at 298.15 K are 77.4, 136.3, 80.8, and 108.2 kcal/mol, respectively.) The Be value is identical to the CODATA recommendation (but with half of the uncertainty), while the B, Al, and Si values represent substantial revisions from established earlier reference data. The revised B and Si values are in agreement with earlier semi-ab initio derivations but carry much smaller uncertainties.

The mechanism of aluminum-catalyzed Meerwein-Schmidt-Ponndorf-Verley reduction of carbonyls to alcohols.

The mechanistic details of the Meerwein-Schmidt-Ponndorf-Verley (MSPV) reduction of ketones to the corresponding alcohols were investigated both experimentally and computationally. Density functional theory (DFT) was used to assess the energetics of several proposed pathways (direct hydrogen transfer, hydridic, and radical). Our results demonstrate that a direct hydrogen transfer mechanism involving a concerted six-membered ring transition state is the most favorable pathway for all calculated systems starting from a small model system and concluding with the experimentally investigated BINOLate/Al/(i)PrOH/MePhC=O system. Experimental values for the activation parameters of acetophenone reduction using the BINOLate/Al/(i)PrOH system (DeltaG# = 21.8 kcal/mol, DeltaH# = 18.5 kcal/mol, DeltaS# = -11.7 au) were determined on the basis of kinetic investigation of the reaction and are in good agreement with the computational findings for this system. Calculated and experimental kinetic isotope effects support the concerted mechanism.