X-ray diffraction and Raman spectra of merrillite at high pressures

ABSTRACT

The compressibility and effect of pressure on the vibrations of merrillite, Ca₉NaMg(PO₄)₇, were studied by using diamond anvil cell at room temperature combined with in-situ synchrotron X-ray diffraction and Raman spectroscopy up to about 18 and 15?GPa, respectively. The pressure-volume data was fitted by a third-order Birch–Murnaghan equation of state to determine the isothermal bulk modulus as K₀ ?=?87.2(32) GPa with pressure derivative K₀′?=?3.2(4). If K₀′?=?4, the isothermal bulk modulus was obtained as 81.6(10) GPa. The axial compressibility was estimated and an axial elastic anisotropy exists since a-axis is less compressible than the c-axis. The Raman frequencies of all observed modes for merrillite continuously increase with pressure, and the pressure dependences of stretching modes (v ₃ and v ₁) are larger than those of the bending modes (v ₄ and v ₂) and external modes. The isothermal mode Grüneisen parameters and intrinsic anharmonicity of merrillite were also calculated.     

Recent Advances on the Electrochemical Difunctionalization of Alkenes/Alkynes

Electroorganic synthesis is an emerging area of high impact research in organic chemistry, which is considered as one of the green and efficient methods and attracts growing research attention. In this review, we summarized comprehensively the recent literature reports on the electrochemical oxidative difunctionalization of unsaturated C—C bonds. The reaction types described in this review included electrochemical intermolecular cyclization, electrochemical intramolecular cyclization, and electrochemical difunctionalization of alkenes/alkynes. This review focuses on the discussion of its synthetic generality for the preparation of functionalized compounds and the related electrochemical oxidative reaction mechanism.     

Olefin‐Directed Palladium‐Catalyzed Regio‐ and Stereoselective Oxidative Arylation of Allenes

An olefin‐directed palladium‐catalyzed oxidative regio‐ and stereoselective arylation of allenes to afford 1,3,6‐trienes has been established. A number of functionalized allenes, including 2,3‐ and 3,4‐dienoates and 3,4‐dienol derivatives, have been investigated and found to undergo the olefin‐directed allene arylation. The olefin moiety has been proven to be a crucial element for the arylating transformation.     

Rhodium(III)‐Catalyzed [3+2]/[5+2] Annulation of 4‐Aryl 1,2,3‐Triazoles with Internal Alkynes through Dual C(sp2)?H Functionalization

A rhodium(III)‐catalyzed [3+2]/[5+2] annulation of 4‐aryl 1‐tosyl‐1,2,3‐triazoles with internal alkynes is presented. This transformation provides straightforward access to indeno[1,7‐cd]azepine architectures through a sequence involving the formation of a rhodium(III) azavinyl carbene, dual C(sp²) H functionalization, and [3+2]/[5+2] annulation.     

Base‐Promoted Coupling of Carbon Dioxide,Amines, and N‐Tosylhydrazones: A Novel and Versatile Approach to Carbamates

A base‐promoted three‐component coupling of carbon dioxide, amines, and N‐tosylhydrazones has been developed. The reaction is suggested to proceed via a carbocation intermediate and constitutes an efficient and versatile approach for the synthesis of a wide range of organic carbamates. The advantages of this method include the use of readily available substrates, excellent functional group tolerance, wide substrate scope, and a facile work‐up procedure.     

Clean and Efficient Synthesis of Pyrazole Derivatives in Aqueous Media

A series of 5‐aryl‐1H‐pyrazole derivatives were synthesized via the reaction of 3‐(dimethylamino)‐1‐arylprop‐2‐en‐1‐one with hydrazine in aqueous media without using any catalyst. This method has the advantages of easier work‐up, mild reaction condition, high yields, and an environmentally benign procedure.     

Colorimetric method for determination of bisphenol A based on aptamer-mediated aggregation of positively charged gold nanoparticles

A sensitive, specific and rapid colorimetric aptasensor for the determination of the plasticizer bisphenol A (BPA) was developed. It is based on the use of gold nanoparticles (AuNPs) that are positively charged due to the modification with cysteamine which is cationic at near-neutral pH values. If aptamers are added to such AuNPs, aggregation occurs due to electrostatic interactions between the negatively-charged aptamers and the positively-charged AuNPs. This results in a color change of the AuNPs from red to blue. If a sample containing BPA is added to the anti-BPA aptamers, the anti-BPA aptamers undergo folding via an induced-fit binding mechanism. This is accompanied by a conformational change, which prevents the aptamer-induced aggregation and color change of AuNPs. The effect was exploited to design a colorimetric assay for BPA. Under optimum conditions, the absorbance ratio of A ₅₂₇/A ₆₈₀ is linearly proportional to the BPA concentration in the range from 35 to 140 ng∙mL⁻¹, with a detection limit of 0.11 ng∙mL⁻¹. The method has been successfully applied to the determination of BPA in spiked tap water and gave recoveries between 91 and 106 %. Data were in full accordance with results obtained from HPLC. This assay is selective, easily performed, and in our perception represents a promising alternative to existing methods for rapid quantification of BPA.

The negatively-charged anti-BPA aptamers can absorb onto the positively-charged cysteamine-capped AuNPs (cysteamine-AuNPs) via electrostatic interactions, which can cause the aggregation of AuNPs accompanied by a red-to-blue color change. In the presence of BPA, the specific binding of BPA to the aptamers induces the conformation changes of anti-BPA aptamers, which can release the aptamers from cysteamine-AuNPs and thus prevent the aggregation and color change of cysteamine-AuNPs.