Photolysis of Hydrophobic Vitamin B12 Derivatives Covalently Bound to Lipid in Aqueous Media

An alkyl ligand coordinated to hydrophobic vitamin B12 derivatives covalently bound to N,N-dihexadecyl-Nα-[6-(trimethylammonio)hexanoyl]-L-aspartamide bromide underwent a novel bromination reaction along with its rearrangement in the single-walled vesicle of N,N-dihexadecyl-Nα-[6-(trimethylammonio)hexanoyl]-L-alaninamide bromide under photolysis conditions

Enantioselective Alkylation of Hydrophobic Vitamin B12 Bearing a Binaphthyl Moiety

The enantioselective alkylation of hydrophobia vitamin B12 derivatives at the β-axial site was examined in methanol with various alkyl bromides, and those B12 analogues bearing a peripheral binaphthyl moiety showed the highest S-selectivity toward enantiomeric alkyl bromides among vitamin B12 models as caused by a steric effect of the peripheral substituent

Hydrophobic Vitamin B12. XI. Preparation, Characterization, and Enantioselective Alkylation of Hydrophobic Vitamin B12 Bearing a Binaphthyl Moiety

Hydrophobic vitamin B12 derivatives bearing a chiral binaphthyl moiety, hexamethyl 71-decarboxy-71-[(R)-2′-methoxy-1,1′-binaphthyl-2-carboxymethyl]cobyrinate perchlorate [B12–BINAP(R)] and hexamethyl 71-decarboxy-71-[(S)-2′-methoxy-1,1′-binaphtyl-2-carboxymethyl]cobyrinate perchlorate [B12–BINAP(S)], were prepared from cyanocobalamin. These complexes were characterized by means of electronic and circular dichroism spectroscopy as well as by cyclic voltammetry in comparison with those data for a hydrophobic vitamin B12 without a binaphthyl moiety. The enantioselective alkylation of hydrophobic vitamin B12 derivatives at the β-axial site was examined in methanol with various 3-bromo-2-methylpropionic esters by means of 1H NMR spectroscopy. All the hydrophobic vitamin B12 derivatives used here, the one bearing methoxycarbonyl groups as peripheral substituents without a binaphthyl moiety, B12–BINAP(R), and B12-BINAP(S), were found to bind (S)-2-methylpropionates more favorably than the corresponding R-enantiomers; the highest S-selectivity was observed with the latter two derivatives, 65% e.e. The cause of such S-enantioselectivity was discussed with attention to stereochemical configurations of the peripheral substituents placed in the corrin ring

Aqua­bis­(1,1,1,5,5,5-hexa­fluoro­acetyl­acetonato)[4′-(4-pyrid­yl)-2,2′:6′,2′′-terpyridine]­ytterbium(III) chloride methanol monosolvate monohydrate

The title compound, [Yb(C5HF6O2)2(C20H14N4)(H2O)]Cl·CH3OH·H2O, adopts an eight-coordinated geometry around the YbIII atom consisting of a 4′-(4-pyrid­yl)-2,2′:6′,2′′-terpyridine (pytpy) ligand, two 1,1,1,5,5,5-hexa­fluoro­acetyl­acetonate (hfac) anions and an aqua ligand. In the solid state, the compound forms supra­molecular chains running along the b-axis via inter­molecular hydrogen bonds between the Yb—OH2 unit and the N-atom donor of the 4-pyridyl pendant of pytpy, with an O⋯N distance of 2.686 (4) Å. A chloride counter-anion and lattice methanol and water solvent mol­ecules occupy a hydro­philic columnar space along the coordination chains. O—H⋯Cl hydrogen bonds occur. The two water molecules and the four trifluoromethyl groups are disordered over two sets of sites, each with different occupancy ratios

Vapochromism of Organic Crystals Based on Macrocyclic Compounds and Inclusion Complexes

Vapochromic materials, which change color and luminescence when exposed to specific vapors and gases, have attracted considerable attention in recent years owing to their potential applications in a wide range of fields such as chemical sensors and environmental monitors. Although the mechanism of vapochromism is still unclear, several studies have elucidated it from the viewpoint of crystal engineering. In this mini-review, we investigate recent advances in the vapochromism of organic crystals. Among them, macrocyclic molecules and inclusion complexes, which have apparent host–guest interactions with analyte molecules (specific vapors and gases), are described. When the host compound is properly designed, its cavity size and symmetry change in response to guest molecules, influencing the optical properties by changing the molecular inclusion and recognition abilities. This information highlights the importance of structure–property relationships resulting from the molecular recognition at the solid–vapor interface

Analyses of the Adsorption Structures of Friction Modifiers by Means of Quantitative Structure-Property Relationship Method and Sum Frequency Generation Spectroscopy

Blending an optimum amount of friction modifiers into lubricant is one of the important measures to reduce fuel consumption induced by the frictional loss for automobiles. However, the agents containing metal or phosphorus compounds can cause catalyst poisoning and clogging in the filters of the exhaust gas refining system. Thus, development of metal-free and phosphorus-free agents with a long-term stability under real working condition is highly desirable. In the present work, the friction coefficients on the metal surface in lubricants containing different friction modifiers were investigated by the reciprocating friction test in detail. A statistical method based on the quantitative structure-property relationship (QSPR) analysis has been employed to correlate the chemical nature of additives with their effect on the friction reduction behaviors. An empirical equation relating the molecular structure and its friction reduction efficiency has been proposed as a standard for a good friction modifier. Furthermore, a surface-sensitive vibration spectroscopy, sum frequency generation (SFG) spectroscopy, has been used to analyze the molecular structures of the lubricants adsorbed on the metal surface. The SFG observation suggested that a certain relationship between the adsorption structure and friction reduction effect of these agents

Learning from B12 enzymes: biomimetic and bioinspired catalysts for eco-friendly organic synthesis

Cobalamins (B12) play various important roles in vivo. Most B12-dependent enzymes are divided into three main subfamilies: adenosylcobalamin-dependent isomerases, methylcobalamin-dependent methyltransferases, and dehalogenases. Mimicking these B12 enzyme functions under non-enzymatic conditions offers good understanding of their elaborate reaction mechanisms. Furthermore, bio-inspiration offers a new approach to catalytic design for green and eco-friendly molecular transformations. As part of a study based on vitamin B12 derivatives including heptamethyl cobyrinate perchlorate, we describe biomimetic and bioinspired catalytic reactions with B12 enzyme functions. The reactions are classified according to the corresponding three B12 enzyme subfamilies, with a focus on our recent development on electrochemical and photochemical catalytic systems. Other important reactions are also described, with a focus on radical-involved reactions in terms of organic synthesis

Redox active ionic liquid as efficient mediator and solvent for visible light-driven B12 catalytic reactions

The redox active ionic liquid, 1-ethyl-4-(methoxycarbonyl)pyridinium bis(trifluoromethanesulfonyl)amide (RIL), was synthesized from its iodide form by an anion exchange reaction of Li(NTf2) with viscos liquid (η = 122 cP at 25 °C) and characterized by NMR, IR, and elemental analysis. The compound showed reversible redox couples at −0.65 V and −1.48 V vs. Ag/AgCl and worked as an electron mediator in the B12 complex/[Ru(bpy)3]Cl2 photosensitizer catalytic system under visible light irradiation. The catalytic efficiency in the RIL was higher than those in DMF, MeOH, and the redox inactive ionic liquid, 1-butyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)amide. Keywords: Ionic liquid, Photosensitizer, Redox active, Visible light, Vitamin B1