Some hydrodynamic aspects of 3-phase inverse fluidized bed

Hydrodynamics of 3-phase inverse fluidized bed is studied experimentally using low density particles for different liquid and gas velocities. The hydrodynamic characteristics studied include pressure drop, minimum liquid and gas fluidization velocities and phase holdups. The minimum liquid fluidization velocity determined using the bed pressure gradient, decreases with increase in gas velocity. The axial profiles of phase holdups shows that the liquid holdup increases along the bed height, whereas the solid holdup decreases down the bed. However, the gas holdup is almost uniform in the bed.     

Synthesis and Langmuir studies of bivalent and monovalent alpha-D-mannopyranosides with lectin Con A

Highly avid interaction between carbohydrate ligands and lectin receptors nominally requires the ligand presentation in a clustered form. We present herein an approach involving Langmuir monolayer formation of the sugar ligands and the assessment of their lectin binding at the air-water interface. Bivalent alpha-D-mannopyranoside containing the glycolipid ligand was used to study its binding profiles with lectin Con A, in comparison to the corresponding monovalent glycolipid. In addition to the bivalent and monovalent nature of the glycolipid ligands at the molecular level, the ligand densities at the monolayer level were varied with the aid of a nonsugar lipid molecule so as to obtain mixed monolayers with various sugar-nonsugar ratios. Lectin binding of bivalent and monovalent ligands at different ratios was monitored by differential changes in the surface area per molecule of the mixed monolayer, with and without the lectin. The present study shows that maximal binding of the lectin to the bivalent ligand occurs at lower sugar densities at the interface ( approximately 10% sugar in the mixed monolayer) than for that of the monovalent ligand ( approximately 20% sugar in the mixed monolayer). It is observed that complete coverage of the monolayer with only the sugar ligands does not allow all of the sugars to be functionally active.     

A Simple and Convenient Method for the Deprotection of Tetrahydropyranyl Ether Using Iodine in Methanol

A simple and efficient method for the -deprotection of tetrahydropyranyl and 4,4′-dimethoxytrityl ethers using iodine in methanol is described.     

Towards the design of novel boron‐ and nitrogen‐substituted ammonia‐borane and bifunctional arene ruthenium catalysts for hydrogen storage

Electronic‐structure density functional theory calculations have been performed to construct the potential energy surface for H₂ release from ammonia‐borane, with a novel bifunctional cationic ruthenium catalyst based on the sterically bulky β‐diketiminato ligand (Schreiber et al., ACS Catal. 2012, 2, 2505). The focus is on identifying both a suitable substitution pattern for ammonia‐borane optimized for chemical hydrogen storage and allowing for low‐energy dehydrogenation. The interaction of ammonia‐borane, and related substituted ammonia‐boranes, with a bifunctional η⁶‐arene ruthenium catalyst and associated variants is investigated for dehydrogenation. Interestingly, in a number of cases, hydride‐proton transfer from the substituted ammonia‐borane to the catalyst undergoes a barrier‐less process in the gas phase, with rapid formation of hydrogenated catalyst in the gas phase. Amongst the catalysts considered, N,N‐difluoro ammonia‐borane and N‐phenyl ammonia‐borane systems resulted in negative activation energy barriers. However, these types of ammonia‐boranes are inherently thermodynamically unstable and undergo barrierless decay in the gas phase. Apart from N,N‐difluoro ammonia‐borane, the interaction between different types of catalyst and ammonia borane was modeled in the solvent phase, revealing free‐energy barriers slightly higher than those in the gas phase. Amongst the various potential candidate Ru‐complexes screened, few are found to differ in terms of efficiency for the dehydrogenation (rate‐limiting) step. To model dehydrogenation more accurately, a selection of explicit protic solvent molecules was considered, with the goal of lowering energy barriers for H‐H recombination. It was found that primary (1°), 2°, and 3° alcohols are the most suitable to enhance reaction rate. © 2014 Wiley Periodicals, Inc.     

Highly Mesoporous Metal‐Organic Frameworks as Synergistic Multimodal Catalytic Platforms for Divergent Cascade Reactions

Rational engineering and assimilation of diverse chemo‐ and biocatalytic functionalities in a single nanostructure is highly desired for efficient multistep chemical reactions but has so far remained elusive. Here, we design and synthesize multimodal catalytic nanoreactors (MCNRs) based on a mesoporous metal‐organic framework (MOF). The MCNRs consist of customizable metal nanocrystals and stably anchored enzymes in the mesopores, as well as coordinatively unsaturated cationic metal MOF nodes, all within a single nanoreactor space. The highly intimate and diverse catalytic mesoporous microenvironments and facile accessibility to the active site in the MCNR enables the cooperative and synergistic participation from different chemo‐ and biocatalytic components. This was shown by one‐pot multistep cascade reactions involving a heterogeneous catalytic nitroaldol reaction followed by a [Pd/lipase]‐catalyzed chemoenzymatic dynamic kinetic resolution to yield optically pure (>99 % ee) nitroalcohol derivatives in quantitative yields.     

Nanocatalosomes as Plasmonic Bilayer Shells with Interlayer Catalytic Nanospaces for Solar‐Light‐Induced Reactions

Interest and challenges remain in designing and synthesizing catalysts with nature‐like complexity at few‐nm scale to harness unprecedented functionalities by using sustainable solar light. We introduce “nanocatalosomes”—a bio‐inspired bilayer‐vesicular design of nanoreactor with metallic bilayer shell‐in‐shell structure, having numerous controllable confined cavities within few‐nm interlayer space, customizable with different noble metals. The intershell‐confined plasmonically coupled hot‐nanospaces within the few‐nm cavities play a pivotal role in harnessing catalytic effects for various organic transformations, as demonstrated by “acceptorless dehydrogenation”, “Suzuki–Miyaura cross‐coupling” and “alkynyl annulation” affording clean conversions and turnover frequencies (TOFs) at least one order of magnitude higher than state‐of‐the‐art Au‐nanorod‐based plasmonic catalysts. This work paves the way towards next‐generation nanoreactors for chemical transformations with solar energy.     

1,3-Bis(2,4,6-trimethylphenyl)imidazolium chloride in combination with triethylamine: an improved catalytic system for hydroacylation/reduction of activated ketones

A rapid, economic, and high yielding methodology has been developed for hydroacylation/reduction of activated ketones by using 1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride as a catalyst in combination with triethylamine. The reaction proceeded at an ambient temperature via generating N-heterocyclic carbene in situ that interacted with the (hetero)aryl aldehyde employed. While the reduction of ketones takes place in MeOH, the hydroacylation process was found to be effective in THF for both electron rich and deficient aldehydes.