Noncovalent carbon bonding, a recently explored σ-hole interaction, was hitherto supposed to be a weak and structure-guided interaction. Here, its role in the intramolecular stabilization of the cis conformation of the amide moiety in acylhydrazones is described. The calculations reveal an electron donation from the lone pair of the nitrogen atom to the empty antibonding C-N orbital [LP(N)→BD*(C-N)] with a concomitant stabilization energy of E(2) =1.2 kcal mol-1 .
Pyridinemethanol-carboxylate esters form octahedral complexes with Zn(NO3 )2 in aqueous DMF that subsequently undergo hydrolysis at elevated temperatures to form metal-carboxylate zwitterions. In situ deprotonation of the hydroxy group leads to thermally robust, neutral MOFs. This stepwise synthesis can be controlled by temperature and is made possible by the subtle difference in reactivity of the functional groups.
This month's cover is dedicated to the golden anniversary of Singapore by the collaborating groups of Wen-Hua Zhang of the IMRE, Singapore, and T. S. Andy Hor of the NUS, Singapore, and two more groups from Monash University, Malaysia, and Soochow University, P. R. China. In the cover picture the number "50" commemorates the 50th anniversary of Singapore, the Lion City. The photo on the top-right corner shows the modern skyline of Singapore. Underneath are the structures described in this article. Read the full text of the article at 10.1002/cplu.201500134.
A novel tetranuclear copper-based water oxidation catalyst was designed and synthesized by using a new multinucleating ligand containing two proton dissociation sites, 1,3-bis(6-hydroxy-2-pyridyl)-1H-pyrazole. The copper complex showed electrocatalytic activity for water oxidation reactions under aqueous basic conditions (pH 12.5) with an overpotential of approximately 500 mV. UV/Vis absorption and energy-dispersive X-ray (EDX) spectroscopic techniques coupled with electrochemical analyses of the catalyst system strongly suggest that the tetranuclear copper complex works as a homogeneous system under the conditions used. The results described here demonstrate the utility of a discrete tetranuclear copper complex in water oxidation reactions.
The incorporation of noble metals with metal-organic frameworks (MOFs) are conducive to the simultaneous electrochemical detection of analytes owing to multiple accessible reaction sites. Herein, Au@Cu-metal organic framework (Au@Cu-MOF) is successfully synthesized and modified as a screen-printed carbon electrode (SPCE), which serves as an excellent electrocatalyst for the oxidation of dopamine (DA) and uric acid (UA). The sensor shows a linear range from 10 μM to 1000 μM, with sensitivity and detection limit of 0.231 μA μM-1 cm-2 and 3.40 μM for DA, and 0.275 μA μM-1 cm-2 and 10.36 μM for UA. Au@Cu-MOF could realize the individual and simultaneous electrochemical sensing of DA and UA, with distinguishable oxidation peak potentials. Moreover, it exhibits reproducibility, repeatability, and stability. Ultimately, the sensor provides an avenue for an ultrasensitive label-free electrochemical detection of DA and UA.
A microwave-assisted synthesis of 7-amino-1,2,4-triazolo[1,5-a][1,3,5]triazine-2-propanamides was developed using a three-component, catalyst-free reaction of cyanamide and trimethyl orthoformate with 3-(5-amino-1H-1,2,4-triazol-3-yl)propanamides (3). The reaction tolerated structurally diverse substrates and proceeded chemo- and regio-selectively, affording the target compounds in high purity in 5-10 minutes. The convenient chromatography-free isolation and purification of the products add practicality to this method. The structural features of the prepared compounds were investigated using dynamic NMR spectroscopy, X-ray crystallography and computational chemistry calculations. X-ray crystallography performed on a representative compound, 3-(7-amino-1,2,4-triazolo[1,5-a][1,3,5]triazin-2-yl)-N-(4-benzyl)propanamide (4 l), showed the overall molecular conformation to adopt the shape of the letter C. Notable localisation of π-electron density is found within the 1,2,4-triazolo[1,5-a][1,3,5]triazine system; a relatively short C-NH2 bond is consistent with restricted rotation about this bond. This study also presents a detailed analysis of the molecular interactions in 4 l using DFT and QTAIM methods with a focus on the hydrogen-bonding and π-stacking interactions that influence the molecular packing of 4 l. The findings reveal the significant roles of N-H⋅O, N-H⋅N and C-H⋅N interactions, along with electrostatically enhanced π⋅π contacts. A broad screening for insecticidal, fungicidal and herbicidal properties identified several compounds with potent herbicidal activity against Matricaria inodora.
This study focuses on the sustainable production of bio-jet fuel through the catalytic hydrodeoxygenation (HDO) of isoeugenol (IE). Properties of two spraying synthesis methods (in situ and ex situ metal doping) with different platinum (Pt) loading percentages. The catalyst was characterised using various techniques such as XAS, X-ray photoelectron spectroscopy, X-ray diffraction, high-resolution transmission electron microscopy (HRTEM), field-emission scanning electron microscopy (FESEM) and thermogravimetric analysis. The HRTEM and FESEM results show the successful preparation of a spherical nanoparticle doped over activated carbon, and Pt was dispersed on the outer shell of the particles. The catalytic HDO of IE showed a high yield and conversion as follows: IE conversion of 100%, liquid-phase mass balance of 95.92%, dihydroeugenol conversion of 99.32%, propylcyclohexane yield of 88.94% and HYD yield of 76.19%. Moreover, the catalyst exhibited high reusability with low metal leaching and high coke resistance for 10 cycles. The catalyst was evaluated in a continuous flow reactor for 100 h at different reaction temperatures, and interestingly, the catalyst showed low deactivation with a high half-time.