A Comparison of Three Different Biodegradable Aliphatic Oligoesters (PGA,PLLA, and PCL) with Similar Linear Alkyl End Groups by DSC and SAXS

The biodegradable aliphatic oligoesters polyglycolide (PGA), poly(L-lactide) (PLLA), and poly(?-caprolactone) (PCL) with similar number-average molecular weight M_n values but different linear alkyl end groups [CH₃?[CH₂?CH₂]_m?CH₂?] were compared in terms of their physical properties, parameters such as melting temperature (T_m), crystallinity (x_i), long period (L), and lamella thickness (D). They were analyzed by DSC and SAXS. The effect of a longer and nonpolar alkyl end group such as docosyl [CH₃?[CH₂?CH₂]₁₀?CH₂?] on the long period (L) was more evident for PCL because it was the most nonpolar species in the family of oligoesters analyzed.     

Cholesterol Hydroperoxides as Substrates for Cholesterol‐Metabolizing Cytochrome P450 Enzymes and Alternative Sources of 25‐Hydroxycholesterol and other Oxysterols

The interaction of the primary autoxidation products of cholesterol, namely 25‐ and 20ξ‐hydroperoxides, with the four principal cholesterol‐metabolizing cytochrome P450 enzymes is reported. Addition of cholesterol 25‐hydroperoxide to the enzymes CYP27A1 and CYP11A1 induced well‐defined spectral changes while generating 25‐hydroxycholesterol as the major product. The 20ξ‐hydroperoxides induced spectral shifts in CYP27A1 and CYP11A1 but glycol metabolites were detected only with CYP11A1. CYP7A1 and CYP46A1 failed to give metabolites with any of the hydroperoxides. A P450 hydroperoxide‐shunt reaction is proposed, where the hydroperoxides serve as both donor for reduced oxygen and substrate. CYP27A1 was shown to mediate the reduction of cholesterol 25‐hydroperoxide to 25‐hydroxycholesterol, a role of potential significance for cholesterol‐rich tissues with high oxidative stress. CYP27A1 may participate in the removal of harmful autoxidation products in these tissues, while providing a complementary source of 25‐hydroxycholesterol, a modulator of immune cell function and mediator of viral cell entry.     

Hydroxoiridium/Chiral Diene Complexes as Effective Catalysts for Asymmetric Annulation of α‐Oxo‐ and Iminocarboxamides with 1,3‐Dienes

The asymmetric [3+2] annulation of α‐oxo‐ and α‐iminocarboxamides with 1,3‐dienes catalyzed by hydroxoiridium/chiral diene complexes was realized, giving high yields of the corresponding γ‐lactams with high enantioselectivity.     

Isotactic rac‐Lactide Polymerization with Copper Complexes: The Influence of Complex Nuclearity

Diiminopyrrolide copper alkoxide complexes, LCuOR (OR¹=N,N‐dimethylamino ethoxide, OR²=2‐pyridyl methoxide), are active for the polymerization of rac‐lactide at ambient temperature in benzene to yield polymers with M_w/M_n=1.0–1.2. X‐ray diffraction studies showed bridged dinuclear complexes in the solid state for both complexes. While LCuOR¹ provided only atactic polylactide, LCuOR² produced partially isotactic polylactide (P_m=0.7). The difference in stereocontrol is attributed to a dinuclear active species for LCuOR² in contrast to a mononuclear species for LCuOR¹.     

Cooperative Bond Activation and Catalytic Reduction of Carbon Dioxide at a Group 13 Metal Center

A single‐component ambiphilic system capable of the cooperative activation of protic, hydridic and apolar H? X bonds across a Group 13 metal/activated β‐diketiminato (Nacnac) ligand framework is reported. The hydride complex derived from the activation of H₂ is shown to be a competent catalyst for the highly selective reduction of CO₂ to a methanol derivative. To our knowledge, this process represents the first example of a reduction process of this type catalyzed by a molecular gallium complex.