Experimentally Based DFT Calculations on the Hindered Disproportionation of [Al₄Cp*₄]: Formation of Metalloid Clusters as Intermediates on the Way to Solid Al Prevents the Decomposition of a Textbook Molecule

Abstract

Lipase was covalently attached to multiwalled carbon nanotubes (MWNTs). Structural changes of the lipase upon attachment onto MWNTs were analyzed through circular dichroism and FTIR spectroscopy. The conjugate was utilized for the resolution of a model compound (R,S)‐1‐phenyl ethanol, and the reaction medium was n‐heptane. The enzymatic resolutions were carried out at temperatures from 35 to 60°C. The results show that the lipase attached onto MWNTs has significantly affected the performance of the enzyme in terms of temperature dependence and resolution efficiency. The activity of MWNT–lipase was less temperature‐dependent compared with that of the native lipase. The resolution efficiency was much improved with MWNT–lipase. MWNT–lipase retained the selectivity of the native lipase for (R)‐1‐phenyl ethanol. The consecutive use of MWNT–lipase showed that MWNT–lipase had a good stability in the resolution of (R,S)‐1‐phenyl ethanol. © 2010 American Institute of Chemical Engineers AIChE J, 2010

Structure, Thermodynamics, and Energy Content of Aluminum–Cyclopentadienyl Clusters

“…28 The remaining compounds in Table 2 are part of a reaction scheme proposed by Schn€ ockel and co-workers to explain the formation and stability of the large aluminum clusters. 21 All of our calculated values agree with available previous results to within 0.1 Å. Furthermore, the QM/MM multilayer calculation on the largest cluster does quite well in reproducing the geometry obtained using full B3LYP; the CÀC intraring distances are identical, and the AlÀX distance is within 0.06 Å.…”

“…In ref 21, these authors present an energy level diagram in which the energy change for an idealized reaction taking Al 4 Cp 4 to Al 50 Cp 12 and AlCp 3 is slightly negative, whereas the analogous reaction in the methylated system is strongly positive. There is not sufficient information to reproduce the energy calculations given in ref 21, as no details are given on the calculated structures, enthalpies of formation, or if the energies are corrected from the bare DFT SCF energy to account for thermal effects. In Table 9, we present our values for the reaction enthalpies in the proposed mechanism, along with the previous values from ref 21.…”

“…There is not sufficient information to reproduce the energy calculations given in ref 21, as no details are given on the calculated structures, enthalpies of formation, or if the energies are corrected from the bare DFT SCF energy to account for thermal effects. In Table 9, we present our values for the reaction enthalpies in the proposed mechanism, along with the previous values from ref 21. ΔH rxn 0 is defined as…”

“…The computational scheme used here shows good agreement with G2 results for smaller clusters, and we expect that the heats of Figure 11. Enthalpies of reaction in kcal/mol for the proposed 21 barrier mechanism with (a) Cp* and (b) Cp ligands.…”

“…17À20 In recent years, Huber and Schn€ ockel have performed density functional theory calculations in support of their X-ray diffraction and 27 Al NMR studies of larger aluminumÀCp-type clusters. 14,21 They proposed that the large clusters, such as Al 50 Cp 12 *, may serve as a type of barrier state that prevents the smaller compounds from spontaneously decomposing to metallic aluminum and trivalent aluminum species. Expanded computational studies of these materials are highly desirable to elucidate their reactivity, stability, and potential combustion properties.…”