Late stages in the biosynthesis of abnormal erythrina alkaloids

The incorporation of (±)-, N-norprotosinomenine, N-nor-orientaline, N-nor-reticuline, norlaudanosoline, protosinomenine, and N-[2-(3-hydroxy-4-methoxyphenyl)ethyl]-2-(4-hydroxyphenyl) ethylamine into coccuvine has been studied, and the specific utilisation of the (±)-norprotosinomenine demonstrated. A double labelling experiment with (±)-[1-³H,4'-methoxy-¹⁴C]-N-norprotosinomenine showed that the 4'-O-Me group of the precursor is retained in the bioconversion and the erythrinan ring system is not formed by addition of secondary amino function onto an ortho-quinone system. Feeding of (±)-[1-³H, 7-methoxy-¹⁴C]norprotosinomenine established that O-demethylation is the terminal step in the biosynthesis of coccuvine. Feeding of labelled abnormal Erythrina alkaloids revealed that isococculidine is converted into coccoline via coccuvinine and isococculine into coccolinine via coccuvine.     

The biosynthesis of nornuciferine-I(2-methoxy-6aα-aporphine-1-ol)

The incorporation of (±)-norcoclaurine, (±)-coclaurine, (±)-N-methylcoclairine, (±)-N-methylnorcoclaurine into nornuciferine-I in Croton sparsiflorus morong has been studied, and the specific utilization of the (±)-N-methylcoclaurine demonstrated. The evidence supports the direct oxidative coupling of (+)-(S)-N-methylcoclaurine to give N-methylcrotsparine, which in turn is shown to be a specific precursor of nornuciferine-I. The experiments also show that N-methylcrotsparine is reduced to N-methylcrotsparinol and it is N-methylcrotsparinol-I which is preferentially dehydrated and rearranged to nornuciferine-I.     

Coordination properties of vic-isonitrosoimines in their copper (II) and palladium (II) complexes

Preparation and structural characterization of palladium (II) complexes of ligands III-V and copper (II) complexes of III are reported. The elemental analyses of the complexes show that the metal: ligand ratio is 1:2. The electrical conductance in acetone shows the non-electrolytic nature of the complexes. The diamagnetic character suggests a gross square-planar geometry for the palladium (II) complexes. Copper (II) complexes are paramagnetic with¼eff.～1·90 B.M. Spectral data suggest that in all the complexes the ligand coordinates to the metal (II) symmetrically through isonitroso-nitrogen and imine-nitrogen, forming a five membered chelate ring. Amine-exchange reactions of the complexes are discussed and compared on the basis of their structures.     

One‐Step In Situ Biosynthesis of Graphene Oxide–Bacterial Cellulose Nanocomposite Hydrogels

Graphene oxide–bacterial cellulose (GO/BC) nanocomposite hydrogels with well‐dispersed GO in the network of BC are successfully developed using a facile one‐step in situ biosynthesis by adding GO suspension into the culture medium of BC. During the biosynthesis process, the crystallinity index of BC decreases and GO is partially reduced. The experimental results indicate that GO nanosheets are uniformly dispersed and well‐bound to the BC matrix and that the 3D porous structure of BC is sustained. This is responsible for efficient load transfer between the GO reinforcement and BC matrix. Compared with the pure BC, the tensile strength and Young's modulus of the GO/BC nanocomposite hydrogel containing 0.48 wt% GO are significantly improved by about 38 and 120%, respectively. The GO/BC nanocomposite hydrogels are promising as a new material for tissue engineering scaffolds.

     

Iron nanoparticles decorated graphene-multiwalled carbon nanotubes nanocomposite-modified glassy carbon electrode for the sensitive determination of nitrite

In the present work, we described the preparation of iron nanoparticles decorated graphene-multiwalled carbon nanotubes nanocomposite (GR-MWCNTs/FeNPs) modified glassy carbon electrode (GCE) and its application for the sensitive determination of nitrite. First, GR-MWCNTs/FeNPs nanocomposite has been prepared by a simple solution-based approach via chemical reduction and then it was characterized. Afterwards, GR-MWCNTs/FeNPs/GCE was prepared and employed for the electrocatalysis of nitrite. Electrocatalytic oxidation of nitrite at the GR-MWCNTs/FeNPs/GCE has been significantly improved in terms of both reduction in overpotential and increase in peak current. Therefore, the modified electrode was employed for amperometric determination of nitrite which exhibited excellent analytical parameters with wide linear range of 1?×?10^?7 M to 1.68?×?10^?3 M and very low detection limit of 75.6 (±1.3)?nM. The proposed sensor selectively detects nitrite even in the presence of high concentration of common ions and biological interferrants. Good recoveries achieved for the determination of nitrite in various water samples reveal the promising practicality of the sensor. In addition, the sensor displays an acceptable repeatability and reproducibility along with appreciable storage and excellent operational stabilities.

Si-OSO3H catalyzed one-pot three-component synthesis of 1,3-oxazines

A simple and an efficient method for the synthesis of six membered nitrogen containing heterocyclic compounds—1,3-oxazines from diethyl acetylene dicarboxylate, substituted anilines or amines and formaldehyde is reported. A versatile, economical and eco-friendly heterogeneous reagent silica sulfuric acid (Si-OSO₃H) is used as a catalyst for this reaction.