Bienzymatic Spectrophotometric Method for Uric Acid Estimation in Human Serum and Urine

Journal of Analytical Chemistry - In this study, a novel and efficient bienzymatic method for the quantification of uric acid in serum and urine samples was developed. This method is based on the...     

Highly Conductive Graphene and Polyelectrolyte Multilayer Thin Films Produced From Aqueous Suspension

Rapid, large‐scale exfoliation of graphene in water has expanded its potential for use outside niche applications. This work focuses on utilizing aqueous graphene dispersions to form thin films using layer‐by‐layer processing, which is an effective method to produce large‐area coatings from water‐based solutions of polyelectrolytes. When layered with polyethyleneimine, graphene flakes stabilized with cholate are shown to be capable of producing films thinner than 100 nm. High surface coverage of graphene flakes results in electrical conductivity up to 5500 S m⁻¹. With the relative ease of processing, the safe, cost effective nature of the ingredients, and the scalability of the deposition method, this system should be industrially attractive for producing thin conductive films for a variety of electronic and antistatic applications.

     

Radical transfer hydroamination with aminated cyclohexadienes using polarity reversal catalysis: scope and limitations

The synthesis of various new 1-aminated-2,5-cyclohexadienes is described. These reagents can be used in radical transfer hydroaminations of unactivated and electron-rich double bonds. With thiols as polarity reversal catalysts good yields are obtained. The radical hydroamination occurs with good to excellent anti-Markovnikov selectivity. Many functional groups such as alcohols, silyl ethers, phosphonates, arylbromides, imides, amides, and also acidic protons are tolerated under the reaction conditions. DFT calculations provide insights into the aromatization of silyl, alkyl, and aminyl substituted cyclohexadienyl radicals to generate the corresponding C-, Si-, and N-centered radicals.     

Pd on surface-modified NiFe2O4 nanoparticles: a magnetically recoverable catalyst for Suzuki and Heck reactions

This communication reports on the use of NiFe2O4-DA-Pd, a complete magnetically separable catalyst for Suzuki and Heck coupling reactions of aromatic halide derivatives. The catalyst efficiency for the coupling of chloro derivatives is as good as bromo and iodo derivatives. Catalytic efficiency remains unaltered even after three repeated cycles.     

Nonlinear dynamics of functionally graded pipes conveying hot fluid

For improved stability of fluid-conveying pipes operating under the thermal environment, functionally graded materials (FGMs) are recommended in a few recent studies. Besides this advantage, the nonlinear dynamics of fluid-conveying FG pipes is an important concern for their engineering applications. The present study is carried out in this direction, where the nonlinear dynamics of a vertical FG pipe conveying hot fluid is studied thoroughly. The FG pipe is considered with pinned ends while the internal hot fluid flows with the steady or pulsatile flow velocity. Based on the Euler–Bernoulli beam theory and the plug-flow model, the nonlinear governing equation of motion of the fluid-conveying FG pipe is derived in the form of the nonlinear integro-partial-differential equation that is subsequently reduced as the nonlinear temporal differential equation using Galerkin method. The solutions in the time or frequency domain are obtained by implementing the adaptive Runge–Kutta method or harmonic balance method. First, the divergence characteristics of the FG pipe are investigated and it is found that buckling of the FG pipe arises mainly because of temperature of the internal fluid. Next, the dynamic characteristics of the FG pipe corresponding to its pre- and post-buckled equilibrium states are studied. In the pre-buckled equilibrium state, higher-order parametric resonances are observed in addition to the principal primary and secondary parametric resonances, and thus the usual shape of the parametric instability region deviates. However, in the post-buckled equilibrium state of the FG pipe, its chaotic oscillations may arise through the intermittent transition route, cyclic-fold bifurcation, period-doubling bifurcation and subcritical bifurcation. The overall study reveals complex dynamics of the FG pipe with respect to some system parameters like temperature of fluid, material properties of FGM and fluid flow velocity.     

An iron(ii)-based metalloradical system for intramolecular amination of C(sp2)–H and C(sp3)–H bonds: synthetic applications and mechanistic studies

A catalytic system for intramolecular C(sp²)–H and C(sp³)–H amination of substituted tetrazolopyridines has been successfully developed. The amination reactions are developed using an iron-porphyrin based catalytic system. It has been demonstrated that the same iron-porphyrin based catalytic system efficiently activates both the C(sp²)–H and C(sp³)–H bonds of the tetrazole as well as azide-featuring substrates with a high level of regioselectivity. The method exhibited an excellent functional group tolerance. The method affords three different classes of high-value N-heterocyclic scaffolds. A number of important late-stage C–H aminations have been performed to access important classes of molecules. Detailed studies (experimental and computational) showed that both the C(sp²)–H and C(sp³)–H amination reactions involve a metalloradical activation mechanism, which is different from the previously reported electro-cyclization mechanism. Collectively, this study reports the discovery of a new class of metalloradical activation modes using a base metal catalyst that should find wide application in the context of medicinal chemistry, drug discovery and industrial applications.

A catalytic system for intramolecular C(sp²)–H and C(sp³)–H amination of substituted tetrazolopyridines has been successfully developed.     

Study on South African Indigenous Teas—Antioxidant Potential,Nutritional Content,and Hypoxia-Induced Cyclooxygenase Inhibition on U87 MG Cell Line

Background: This study comparatively assessed seven indigenous traditional tea plants on several attributes that included antioxidant, nutritional, caffeine contents, and cyclooxygenase activity. Methodology: Nutritional content of all tea plants were determined for energy, fat, carbohydrates, total sugars, dietary fiber and amino acids. Antioxidant potential and the antioxidant potentiating secondary metabolites were also measured and compared. Further, we investigated the tea plants for any role they would have on cyclooxygenase (COX) activity on cobalt chloride (CoCl₂) induced human glioma cell lines (U87MG). Results: The tea plants were found non-cytotoxic at concentrations tested against the human Chang liver and HeK 293 kidney cells and were found to be naturally caffeine free. The lowest and highest extraction yield among the tea plants was 7.1% for B. saligna and 15.48% for L. scaberrimma respectively. On average, the flavonol content was 12 to 8 QE/g, ORAC 800 µmol TE/g, TEAC 150 µmol TE/g, FRAP 155 µmol AAE/g, polyphenols 40 mg GAE/g, flavanols 0.35 mg CE/g, flavonols 12 mg QE/g and total flavonoid content (TFC) 180 µg QE/mg. The COX activity has been found to be inhibited by a dose-dependent manner by L. scaberrimma, B. saligna and L. javanica. Conclusion: The results further support competitive value of tea plants and need for improved and further development.     

Combinatorial Ligand Assisted Simultaneous Control of Axial and Central Chirality in Highly Stereoselective C−H Allylation

The significance of stereoselective C−H bond functionalization thrives on its direct application potential to pharmaceuticals or complex chiral molecule synthesis. Complication arises when there are multiple stereogenic elements such as a center and an axis of chirality to control. Over the years cooperative assistance of multiple chiral ligands has been applied to control only chiral centers. In this work, we harness the essence of cooperative ligand approach to control two different stereogenic elements in the same molecule by atroposelective allylation to synthesize axially chiral biaryls from its racemic precursor. The crucial roles played by chiral phosphoric acid and chiral amino acid ligand in concert helped us to obtain one major stereoisomer out of four distinct possibilities.     

Transition-Metal-Free C2-Functionalization of Pyridines through Aryne Three-Component Coupling

The direct C2-functionalization of pyridines through a transition-metal-free protocol by using aryne multicomponent coupling is demonstrated. The reaction allowed a broad-scope synthesis of C2-substituted pyridine derivatives bearing the −CF₃ group in good yields with α,α,α-trifluoroacetophenones as the third component. Activated keto esters could also be employed as the third component in this formal 1,2-di(hetero)arylation of ketones. Performing the reaction under dilute conditions inhibited the competing pyridine–aryne polymerization pathway. Nucleophilic attack by the initially generated pyridylidene intermediate on the carbonyl followed by an S_NAr process resembling the Smiles rearrangement affords the desired products.