Studies on [3]pseudorotaxane formation from a bis-azacrown derivative as host and imidazolium ion-derivatives as guest

A new host molecule, having two azacrown derivatives bridged by luminescent naphthalene diimide functionality, is found to form a [3]pseudorotaxane derivative with imidazolim ion-based guest molecules in non-polar solvents through hydrogen-bonded adduct formation. Depending upon the length of the covalent linker that links the imidazolium ion and the luminescent naphthalene fragment in the guests, the [3]pseudorotaxane adducts adopt different conformation or orientation with varying π-π/donor-acceptor interaction. The mechanism for the naphthalene-based luminescence quenching by NDI fragment on adduct formation was found to be a combination of static, as well as dynamic with static quenching as the dominant one.     

Enantioselective organocatalytic Biginelli reaction: dependence of the catalyst on sterics, hydrogen bonding, and reinforced chirality

From a systematic investigation involving the synthesis of a series of catalysts and screening studies, the organocatalyst 16, which is sterically hindered, contains a strong hydrogen-bonding site, and is endowed with reinforced chirality, is shown to promote the Biginelli cyclocondensation of aromatic as well as aliphatic aldehydes with ethyl acetoacetate and urea in a remarkably high enantioselectivity (ee ca. 94-99%).     

CdTe@Cu(OH)2 nanocomposite: Aqueous synthesis and characterization

CdTe@Cu(OH)₂ nanocomposites were synthesized in aqueous solution by a seed-mediated growth approach. The effect of refluxing time and the concentration of Cu²⁺ on the preparation of these samples were measured using UV-visible absorption and photoluminescence analysis. The emission peak of the synthesized nanocomposites (CdTe@Cu(OH)₂) was shifted from 605 (CdTe seed) to 621 nm. The size of CdTe nanoparticles were averaged about 3.22 nm, and the CdTe@Cu(OH)₂ nanocomposites were averaged as 5.19 nm. The synthesized CdTe@Cu(OH)₂ nanocomposite were characterized with XRD, EDAX, TEM, FT-IR, EPR, and thermal analysis (TG/DTG curves). The results indicate that as-prepared nanoparticles with core/shell structure exhibit interesting optical properties.     

Twist does a twist to the reactivity: stoichiometric and catalytic oxidations with twisted tetramethyl-IBX

The methyl groups in TetMe-IBX lower the activation energy corresponding to the rate-determining hypervalent twisting (theoretical calculations), and the steric relay between successive methyl groups twists the structure, which manifests in significant solubility in common organic solvents. Consequently, oxidations of alcohols and sulfides occur at room temperature in common organic solvents. In situ generation of the reactive TetMe-IBX from its precursor iodo-acid, i.e., 3,4,5,6-tetramethyl-2-iodobenzoic acid, in the presence of oxone as a co-oxidant facilitates the oxidation of diverse alcohols at room temperature.     

Heterogeneous catalyst SiO2–LaCl3·7H2O: characterization and microwave-assisted green synthesis of α-aminophosphonates and their antimicrobial activity

Molecular Diversity - Silica-supported lanthanum (III) chloride (SiO2–LaCl3·7H2O) was prepared and characterized by infrared spectroscopy, X-ray diffraction analysis, scanning electron...     

Porous Coordination Polymers of Diverse Topologies Based on a Twisted Tetrapyridylbiaryl: Application as Nucleophilic Catalysts for Acetylation of Phenols

Porous coordination polymers (CPs) with partially uncoordinated pyridyl rings based on rationally designed polypyridyl linkers are appealing from the point of view of their application as nucleophilic catalysts. A D_2d‐symmetric tetradentate organic linker L , that is, 2,2′,6,6′‐tetramethoxy‐3,3′,5,5′‐tetrakis(4‐pyridyl)biphenyl, was designed and synthesized for metal‐assisted self‐assembly aimed at porous CPs. Depending on the nature of the metal ion and the counter anion, the ligand L is found to function as a 3‐ or 4‐connecting building block leading to porous CPs of diverse topologies. The reaction of L with Zn(NO₃)₂ and Cd(NO₃)₂ yields porous 2 D CPs of “ fes ” topology, in which the tetrapyridyl linker L serves as a 3‐connecting unit with its free pyridyl rings well exposed into the pores. The functional utility of these porous CPs containing uncoordinated pyridyl rings is demonstrated by employing them as efficient heterogeneous nucleophilic catalysts for acetylation of a number of phenols with varying electronic properties and reactivities.     

An improved ultra‐high‐performance liquid chromatography–tandem mass spectrometric method for the quantitation of dexmedetomidine in small volume of pediatric plasma

Dexmedetomidine (Dex), a highly selective α₂‐adrenergic agonist, is used primarily for the sedation and anxiolysis of adults and children in the intensive care setting. A sensitive and selective assay for Dex in pediatric plasma was developed by employing ultra‐high‐performance liquid chromatography–tandem mass spectrometry with d4‐Dex as an internal standard. Dex was extracted from 0.1 mL of plasma by micro‐elution solid‐phase extraction. Separation was achieved with a Waters XBridge C₁₈ column with a flow rate of 0.3 mL/min using a mobile phase comprising 5 mm ammonium acetate buffer with 0.03% formic acid in water and methanol–acetonitrile (50:50, v/v). The intra‐day precision (coefficient of variation) and accuracy for quality control samples ranged from 1.32 to 8.91% and from 92.8 to 108%, respectively. The inter‐day precision and accuracy ranged from 2.13 to 8.45% and from 97.0 to 104%, respectively. The analytical method showed excellent sensitivity using a small sample volume (0.1 mL) with a lower limit of quantitation of 5 pg/mL. This method is robust and has been successfully employed in a pharmacokinetic study of Dex in neonates and infants postoperative from cardiac surgery.     

Growth and characterization of Ytterbium doped KGd(WO4)2 single crystal

Single crystals of Ytterbium doped KGd(WO₄)₂ were grown by Top Seeded Solution Growth technique using K₂WO₄ as flux system. The growth parameters were optimised to get optically transparent crystals. Variation in the lattice parameters were observed in comparison to the pure KGd(WO₄)₂ crystals. The absorption spectra recorded for the Yb:KGW confirms the material suitability for diode pumped solid state lasers. The vibrational studies carried out using spontaneous Raman spectra indicate the strong anionic vibration of the material. PL spectra show the lasing channel of the laser active ions present. Stimulated Raman scattering analysis confirms the material as an efficient Raman laser material. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

First sonochemical,simple and solvent-free synthesis of chiral tert-butanesulfinimines using silica supported p-toluenesulfonic acid

A solvent-free, versatile procedure has been developed for the effective synthesis of tert-butanesulfinylimines of a variety of aldehydes using chiral tert-butanesulfinamides under green, sonochemical conditions. This method utilizes silica supported p-toluenesulfonic acid (pTSA·SiO₂) as an efficient, safer and inexpensive catalyst under aerobic conditions. The practicable simplicity, easy preparation of the catalyst from readily available substances, high substrate scope, excellent yields of products in short reaction times and environmentally benign (solvent-free sonochemical) conditions are the exceptional assets of this finding.     

Spectral analysis of uranium glasses

A Taylor-series expansion of the intermediate coupling energy levels for the U⁴⁺(5f²) has been developed for the first time by using the mathematical procedures of Racah. The partial derivatives, eigenvalues and eigenfunctions reported in this paper will be of great use in analysing the optical spectral properties of the tetravalent uranium doped crystalline or non-crystalline materials. The usefulness of the Taylor serier expansion has been verified by examining the optical absorption results of the U⁴⁺ doped fluoride glasses. The physical properties, namely the refractive index and density, were also determined.Our thanks are due to Prof. S. V. J. Lakshman for his kind cooperation and support in the present work. We are also thankful to the technical staff of the Hull University, Physics Department, UK in the preparation and measurement of various physical properties of the U⁴⁺ doped alkali mixed heavy metal based fluoride glass systems.