Functionalized Silicas for Metal‐Free and Metal‐Based Catalytic Applications: A Review in Perspective of Green Chemistry

Heterogeneous catalysis plays a key role in promoting green chemistry through many routes. The functionalizable reactive silanols highlight silica as a beguiling support for the preparation of heterogeneous catalysts. Metal active sites anchored on functionalized silica (FS) usually demonstrate the better dispersion and stability due to their firm chemical interaction with FSs. Having certain functional groups in structure, FSs can act as the useful catalysts for few organic reactions even without the need of metal active sites which are termed as the covetous reusable organocatalysts. Magnetic FSs have laid the platform where the effortless recovery of catalysts is realized just using an external magnet, resulting in the simplified reaction procedure. Using FSs of multiple functional groups, we can envisage the shortened reaction pathway and, reduced chemical uses and chemical wastes. Unstable bio‐molecules like enzymes have been stabilized when they get chemically anchored on FSs. The resultant solid bio‐catalysts exhibited very good reusability in many catalytic reactions. Getting provoked from the green chemistry aspects and benefits of FS‐based catalysts, we confer the recent literature and progress focusing on the significance of FSs in heterogeneous catalysis. This review covers the preparative methods, types and catalytic applications of FSs. A special emphasis is given to the metal‐free FS catalysts, multiple FS‐based catalysts and magnetic FSs. Through this review, we presume that the contribution of FSs to green chemistry can be well understood. The future perspective of FSs and the improvements still required for implementing FS‐based catalysts in practical applications have been narrated at the end of this review.     

An atomic gravitational wave interferometric sensor in low earth orbit (AGIS-LEO)

We propose an atom interferometer gravitational wave detector in low Earth orbit (AGIS-LEO). Gravitational waves can be observed by comparing a pair of atom interferometers separated by a 30 km baseline. In the proposed configuration, one or three of these interferometer pairs are simultaneously operated through the use of two or three satellites in formation flight. The three satellite configuration allows for the increased suppression of multiple noise sources and for the detection of stochastic gravitational wave signals. The mission will offer a strain sensitivity of ${<10^{-18}/\sqrt{{\rm Hz}}}$ in the 50mHz?C10Hz frequency range, providing access to a rich scientific region with substantial discovery potential. This band is not currently addressed with the LIGO, VIRGO, or LISA instruments. We analyze systematic backgrounds that are relevant to the mission and discuss how they can be mitigated at the required levels. Some of these effects do not appear to have been considered previously in the context of atom interferometry, and we therefore expect that our analysis will be broadly relevant to atom interferometric precision measurements. Finally, we present a brief conceptual overview of shorter-baseline $({\lesssim100\,{\rm m}})$ atom interferometer configurations that could be deployed as proof-of-principle instruments on the International Space Station (AGIS-ISS) or an independent satellite.     

Synthesis of functionalized diaryl alkanes from azines using Lewis acidic ionic liquids

Novel Lewis acidic ionic liquids containing thionyl cations and chlorozincate anions were obtained by one pot synthesis for the first time. This ionic liquid is used as catalyst for Friedel–Crafts alkylation of benzalazines and acetophenone azines for the synthesis of substituted diaryl alkanes. The products were characterized by elemental and spectral (FT-IR, 1H-NMR and 13C-NMR) analyses.     

Analytical expression of non-steady-state concentrations and current pertaining to compounds present in the enzyme membrane of biosensor

A mathematical model of trienzyme biosensor at an internal diffusion limitation for a non-steady-state condition has been developed. The model is based on diffusion equations containing a linear term related to Michaelis-Menten kinetics of the enzymatic reaction. Analytical expressions of concentrations and current of compounds in trienzyme membrane are derived. An excellent agreement with simulation data is noted. When time tends to infinity, the analytical expression of non-steady-state concentration and current approaches the steady-state value, thereby confirming the validity of the mathematical analysis. Furthermore, in this work we employ the complex inversion formula to solve the boundary value problem.     

Two-dimensional DNA origami assemblies using a four-way connector

Two-dimensional self-assembly of DNA origami structures was carried out using a connector that has connection sites at all four edges. By utilizing this four-way connector, five and eight origami monomers were assembled to form a cruciate and a hollow square structure, respectively.     

Systematic survey of positive chlorine sources in the asymmetric Appel reaction: oxalyl chloride as a new phosphine activator

A wide selection of phosphine activators has been screened to improve the selection process in the asymmetric Appel reaction. Of the activators screened, hexachloroacetone (HCA) gave the highest selectivity with excellent yield, but at least one of its by-products, pentachloroacetone (PCA), can become involved in the selection process. In addressing this, a new reaction of phosphines with oxalyl chloride was discovered that can also generate the key intermediate chlorophosphonium salt (CPS), gives better enantioselectivity and possesses significant advantages over other phosphine activators.     

Cleavage of PO in the Presence of P–N: Aminophosphine Oxide Reduction with In Situ Boronation of the PIII Product

In contrast to tertiary phosphine oxides, the deoxygenation of aminophosphine oxides is effectively impossible due to the need to break the immensely strong and inert P?O bond in the presence of a relatively weak and more reactive P? N bond. This long‐standing problem in organophosphorus synthesis is solved by use of oxalyl chloride, which chemoselectively cleaves the P?O bond forming a chlorophosphonium salt, leaving the P? N bond(s) intact. Subsequent reduction of the chlorophosphonium salt with sodium borohydride forms the P^III aminophosphine borane adduct. This simple one‐pot procedure was applied with good yields for a wide range of P? N‐containing phosphoryl compounds. The borane product can be easily deprotected to produce the free P^III aminophosphine. Along with no observed P? N bond cleavage, the use of sodium borohydride also permits the presence of ester functional groups in the substrate. The availability of this methodology opens up previously unavailable synthetic options in organophosphorus chemistry, two of which are exemplified.     

Synthesis of Selenolo(2,3-b)quinoline-2-carboxylic Ethyl Esters: Cytogenetic Studies on Human Peripheral Blood Leucocyte Cultures,and Anti-Bacterial Studies,and Anti-Fungal Studies of Their Effects

The compounds selenolo(2,3-b)quinoline-2-carboxylic ethyl esters were synthesized in good yields by the reaction of 3-(2-chloro-3-quinolyl)acrylic ethyl esters, with the nucleophilic reagent sodium diselenide in ethanol medium under a nitrogen atmosphere. Cytogenetic studies on human blood leucocytes in vitro were evaluated for some of the synthesized compounds. Most of the synthesized compounds were tested for their antibacterial and antifungal activities.     

AN EFFICIENT SYNTHESIS OF DIHYDRO SELENOLO (2,3-b)QUINOLINE-2-CARBOXYLIC ETHYL ESTERS AND 2-SELENOXO-1, 2-DIHYDRO-3-CARBETHOXY ETHYL QUINOLINES—THEIR ANTI-BACTERIAL STUDIES

The compounds dihydro selenolo(2,3-b)quinoline-2-carboxylic ethyl esters and 2-selenoxo-1, 2-dihydro-3-carbethoxy ethyl quinolines were synthesized in varying yields upon reacting 3-(2-chloro-3-quinolyl)acrylic methyl esters with the nucleophilic reagent sodium hydrogen selenide in ethanol medium under nitrogen atmosphere.     

Analytical expression of the concentration of species and effectiveness factors in porous catalysts using the Adomian decomposition method

A mathematical model by Hayes et al. [10] of porous catalysts that have non-linear reactions kinetic is discussed. The model involves the non-linear steady-state reaction-diffusion equation. The analytical solution for the concentration of species is obtained using the Adomian decomposition method. Simple and an approximate polynomial expressions for concentration and effectiveness factors are derived for general non-linear Langmiur-Hinshelwood-Haugen-Watson (LHHW) type models which has variety of real rate function. Comparison of the analytical approximation and numerical simulation is also presented. A good agreement between theoretical predictions and numerical results is observed. The concentration and the effectiveness factors are also computed for the limiting cases of LHHW type models.