Spectroscopic and computational studies on the adenosylcobalamin-dependent methylmalonyl-CoA mutase: evaluation of enzymatic contributions to Co-C bond activation in the Co3+ ground state

Methylmalonyl-CoA mutase (MMCM) is an enzyme that utilizes the adenosylcobalamin (AdoCbl) cofactor to catalyze the rearrangement of methylmalonyl-CoA to succinyl-CoA. Despite many years of dedicated research, the mechanism by which MMCM and related AdoCbl-dependent enzymes accelerate the rate for homolytic cleavage of the cofactor's Co-C bond by approximately 12 orders of magnitude while avoiding potentially harmful side reactions remains one of the greatest subjects of debate among B(12) researchers. In this study, we have employed electronic absorption (Abs) and magnetic circular dichroism (MCD) spectroscopic techniques to probe cofactor/enzyme active site interactions in the Co(3+)Cbl "ground" state for MMCM reconstituted with both the native cofactor AdoCbl and its derivative methylcobalamin (MeCbl). In both cases, Abs and MCD spectra of the free and enzyme-bound cofactor are very similar, indicating that replacement of the intramolecular base 5,6-dimethylbenzimidazole (DMB) by a histidine residue from the enzyme active site has insignificant effects on the cofactor's electronic properties. Likewise, spectral perturbations associated with substrate (analogue) binding to holo-MMCM are minor, arguing against substrate-induced enzymatic Co-C bond activation. As compared to the AdoCbl data, however, Abs and MCD spectral changes for the sterically less constrained MeCbl cofactor upon binding to MMCM and treatment of holoenzyme with substrate (analogues) are much more substantial. Analysis of these changes within the framework of time-dependent density functional theory calculations provides uniquely detailed insight into the structural distortions imposed on the cofactor as the enzyme progresses through the reaction cycle. Together, our results indicate that, although the enzyme may serve to activate the cofactor in its Co(3+)Cbl ground state to a small degree, the dominant contribution to the enzymatic Co-C bond activation presumably comes through stabilization of the Co(2+)Cbl/Ado. post-homolysis products.     

Preparative access to medicinal chemistry related chiral alcohols using carbonyl reductase technology

Libraries of highly enantioenriched secondary alcohols in both enantiomeric forms were synthesised by enzymatic reduction of their parent ketones using selectAZyme? carbonyl reductase (CRED) technology. Commercially available CREDs were able to reduce a range of substrate classes efficiently and with very high enantioselectivity. Matching substrate classes to small subsets of CREDs enabled the fast development of preparative bioreductions and the rapid generation of 100–1500 mg samples of chiral alcohols in typically >95% ee and the majority in ?99.0% ee. The conditions for small scale synthesis were then scaled up to 0.5 kg to deliver one of the chiral alcohols, (S)-1-(4-bromophenyl)-2-chloroethanol, in 99.8% ee and 91% isolated yield.     

Microrheology and particle tracking in food gels and emulsions

Particle tracking microrheology, an emerging experimental technique, which utilizes the Brownian motion of embedded particles to probe local dynamics of soft materials, is presented. Particle tracking microrheology is a powerful technique that enables the measurement of viscoelastic responses in small sample volumes, which are inaccessible to macrorheology and to spatially map structural heterogeneities at a microlevel. Therefore, particle tracking microrheology has considerable potential in food emulsions and gels, since these systems are commonly inhomogeneous. Recent advances and achievements are discussed, including the basic principles, operating regimes and limitations of the technique. The application of the technique in the field of food gels and emulsions to study the evolving dynamics of inhomogeneous at microscale length systems and during sol–gel transition is highlighted.     

Lipases,liposomes and lipid-prodrugs

Colloidal and interfacial phenomena lie at the core of drug formulation, drug delivery, as well as drug binding and action at diseased sites, e.g., in cancer therapy. We review a class of liposome-based drug-delivery systems whose design and functional properties are intimately controlled by the stability of sub-micron structures, lipid-bilayer interfaces, and interfacially activated enzymes that can be exploited to target and deliver drugs. Moreover these drugs can themselves be special lipid molecules in the form of lipid prodrugs that both form the liposomal carrier as well as the substrate for endogenously upregulated lipases that turn the prodrugs into potent drugs precisely at the diseased site.     

Synthesis and fluorescence properties of DMCX+—a stable oxygen-bridged [4]helicenium dye

A one-step synthesis of the stable [4]helicenium dye, 1,13-dimethoxy-chromeno[2,3,4-kl]xanthenium hexafluorophosphate (DMCX⁺) from the readily available tris(2,6-dimethoxyphenyl)carbenium ion is reported. The crystal structure, the chemical stability, and dye properties of the DMCX⁺ helicenium system are described.     

Oxidation of an organic adlayer: a bird's eye view

The reaction of O(2) with an adlayer of the oligopyridine 2-phenyl-4,6-bis(6-(pyridine-2-yl)-4-(pyridine-4-yl)-pyridine-2-yl)pyrimidine (2,4'-BTP), adsorbed on the (111) surfaces of silver and gold and on HOPG--which can be considered as a model system for inorganic|organic contacts--was investigated by fast scanning tunneling microscopy (video STM) and dispersion corrected density functional theory (DFT-D) calculations. Only on Ag(111), oxidation of the 2,4'-BTP adlayer was observed, which is related to the fact that under the experimental conditions O(2) adsorbs dissociatively on this surface leading to reactive O adatoms, but not on Au(111) or HOPG . There is a distinct regiospecifity of the oxidation reaction caused by intermolecular interactions. In addition, the oxidation leads to a chiral ordering. The relevance of these findings for reactions involving organic monolayers is discussed.     

Palladium-catalyzed cross-coupling: a historical contextual perspective to the 2010 Nobel Prize

In 2010, Richard Heck, Ei-ichi Negishi, and Akira Suzuki joined the prestigious circle of Nobel Laureate chemists for their roles in discovering and developing highly practical methodologies for C-C bond construction. From their original contributions in the early 1970s the landscape of the strategies and methods of organic synthesis irreversibly changed for the modern chemist, both in academia and in industry. In this Review, we attempt to trace the historical origin of these powerful reactions, and outline the developments from the seminal discoveries leading to their eminent position as appreciated and applied today.     

Microtermolides A and B from termite-associated Streptomyces sp. and structural revision of vinylamycin

Microtermolides A (1) and B (2) were isolated from a Streptomyces sp. strain associated with fungus-growing termites. The structures of 1 and 2 were determined by 1D- and 2D-NMR spectroscopy and high-resolution mass spectrometry. Structural elucidation of 1 led to the re-examination of the structure originally proposed for vinylamycin (3). Based on a comparison of predicted and experimental (1)H and (13)C NMR chemical shifts, we propose that vinylamycin's structure be revised from 3 to 4.     

Make conjugation simple: a facile approach to integrated nanostructures

We report a facile approach to the conjugation of protein-encapsulated gold fluorescent nanoclusters to the iron oxide nanoparticles through catechol reaction. This method eliminates the use of chemical linkers and can be readily extended to the conjugation of biological molecules and other nanomaterials onto nanoparticle surfaces. The key to the success was producing water-soluble iron oxide nanoparticles with active catechol groups. Further, advanced electron microscopy analysis of the integrated gold nanoclusters and iron oxide nanoparticles provided direct evidence of the presence of a single fluorescent nanocluster per protein template. Interestingly, the integrated nanoparticles exhibited enhanced fluorescent emission in biological media. These studies will provide significantly practical value in chemical conjugation, the development of multifunctional nanostructures, and exploration of multifunctional nanoparticles for biological applications.     

Application of the lithiation-borylation reaction to the rapid and enantioselective synthesis of the bisabolane family of sesquiterpenes

The expedient enantioselective synthesis of 5 bisabolane sesquiterpenes has been achieved using a common, one-pot lithiation-borylation reaction of secondary benzylic carbamates and either protodeboronation or oxidation to give the natural products in fewer than 5 steps, with high yield and >94?:?6 er.