Fused Helicene Chains: Towards Twisted Graphene Nanoribbons.

By taking advantage of an unexpected regioselectivity of intramolecular Scholl reactions on pentaphenylene compounds that favors distorted [5]helicenes over their flat counterparts, a new synthetic approach to twisted graphene nanoribbons has been designed based on side-fused di-tert-butyl-[5]helicene fragments. Syntheses of both small monomers and dimers have been achieved and their structures have been studied. An iterative synthetic strategy has been developed for the formation of longer flexible precursors, which relies on the step-by-step elongation of mono-functionalized oligomeric chains. The flexible trimer and tetramer have, thus, been synthesized and submitted to intramolecular Scholl reactions, which revealed important purification and characterization issues.

Bottom-Up Synthesis of Twisted Porous Graphene through a Heterogeneous Scholl Reaction and Its Supercapacitor Application.

Anthracene- and pyrene-based twisted porous graphene (AN-Pyre-PG) with an ordered pore structure has been synthesized through bottom-up solution phase synthesis from a conjugated microporous polymer (AN-Pyre-CMP) via a heterogeneous Scholl cyclization reaction. The regular-ordered pores embedded within the graphene structures were analyzed through a Raman spectrum, different morphological analyses, and theoretical studies. A significant change in surface area from AN-Pyre-CMP to AN-Pyre-PG was observed, from 143 to 640 m2/g, respectively. Surface area-driven capacitive properties were also observed. Twisted-structure and ordered porous graphene shows better specific capacitance compared to CMP. AN-Pyre-PG shows a specific capacitance of 629 F g-1 at 1 A g-1, with 91% retention of capacitance after 3000 charge-discharge cycles, whereas AN-Pyre-CMP shows a maximum specific capacitance of 200 F g-1 was observed at 2 A g-1.

Twisted polycyclic arenes by intramolecular Scholl reactions of C3-symmetric precursors.

With the aim of opening an efficient access to large and sterically crowded polycyclic arenes as well as improving insight into the geometrical preferences of the Scholl reaction, a versatile synthesis strategy has been developed to form a family of flexible yet strongly crowded substrates for multiple dehydrocyclizations. Their intramolecular Scholl reactions lead with high selectivity either to considerably twisted species where the initial C3 symmetry is maintained, or to strongly rearranged products where the formation of multiple [6]helicene fragments is avoided by the formation of unusual hexa[7]circulene moieties under loss of the C3 symmetry.

Easy Access to Sauropunols A-D: Synthesis and Spectroscopy Correlation of Their Natural Methyl and Ethyl Glycosides.

3,6-Anhydro-2-deoxy-hexofuranoside, the natural product core, is present in natural sauropunols (A-D) and in their natural methyl and ethyl glycosides, now, namely, sauropunol H and sauropunol F. The easily synthesized d-glucose-derived 3,6-anhydro-1,2-O-isopropylidene-5-O-benzoyl-α-d-glucofuranose was elaborated to final targets employing the TsOH·H2O-catalyzed glycosylation reaction with seven different alcohols, subsequent radical deoxygenation, and appropriate deprotection reactions involving mild conditions with excellent functional group tolerance. A short total synthesis of sauropunols (A-D), sauropunol H, and the first total synthesis of sauropunol F are reported herein. The correlation of spectroscopy data of sauropunol H and sauropunol F has been derived through these syntheses.

Highly twisted arenes by Scholl cyclizations with unexpected regioselectivity.

Let's twist! The Scholl reaction with quinquephenyl derivatives has been shown to have an unexpectedly strong preference for forming twisted, helicene aromatic polycycles, instead of their flat counterparts. This tendency is so strong that it will overcome even severe steric hindrance, and the procedure can be used in the efficient synthesis of hexa-tert-butylhexabenzotriphenylene from a simple biaryl starting material (see scheme).

Modulation of amyloid fibrillation of bovine ß-lactoglobulin by selective methionine oxidation.

Deposition of oxidation-modified proteins during normal aging and oxidative stress are directly associated with systemic amyloidoses. Methionine (Met) is believed to be one of the most readily oxidisable amino acid residues of protein. Bovine beta-lactoglobulin (ß-lg), a model globular whey protein, has been presented as a subsequent paradigm for studies on protein aggregation and amyloid formation. Herein, we investigated the effect of t-butyl hydroperoxide (tBHP)-induced oxidation on structure, compactness and fibrillation propensity of ß-lg at physiological pH. Notably, whey protein modification, specifically Met residues, plays an important role in the dairy industry during milk processing and lowering nutritional value and ultimately affecting their technological properties. Several bio-physical studies revealed enhanced structural flexibility and aggregation propensity of oxidised ß-lg in a temperature dependent manner. A molecular docking study is used to predict possible interactions with tBHP and infers selective oxidation of methionine residues at 7, 24 and 107 positions. From our studies, it can be corroborated that specific orientations of Met residues directs the formation of a partially unfolded state susceptible to fibrillation with possible different cytotoxic effects. Our studies have greater implications in deciphering the underlying mechanism of different whey proteins encountering oxidative stress. Our findings are also important to elucidate the understanding of oxidation induced amyloid fibrillation of protein which may constitute a new route to pave the way for a modulatory role of oxidatively stressed proteins in neurological disorders.

Efficacious Electrochemical Oxygen Evolution from a Novel Co(II) Porphyrin/Pyrene-Based Conjugated Microporous Polymer.

Oxygen evolution reaction (OER) is energetically challenging from the platform of making many photovoltaic devices such as metal-air batteries and water splitting systems because of its poor kinetics even when precious metals are used. Herein, a Co(II)-porphyrin/pyrene-comprised conjugated microporous polymer Co-MPPy-1 has been developed which shows efficient OER in alkaline medium. The material was characterized by Fourier transform infrared, solid-state 13C cross-polarization magic angle spinning nuclear magnetic resonance, N2 volumetric adsorption/desorption analysis, scanning electron microscopy, ultra high resolution-transmission electron microscopy, X-ray photoelectron spectroscopy, and other physical studies. Co-MPPy-1 showed Brunauer-Emmett-Teller surface area of ∼501 m2 g-1. Co-MPPy-1 achieved a current density of 1 and 10 mA/cm-2 at 340 and 420 mV, respectively. The turnover frequency calculated for the OER is 0.43 s-1. The heterogeneity of this electrocatalyst was tested by chronoamperometric measurement and 1000 cycle recyclability test with retainment of the excellent electrochemical catalytic activity. This can be attributed to the presence of high density of Co(II) porphyrin unit and efficient charge transport in the π-conductive conjugated polymeric backbone.

A conjugated microporous polymer based visual sensing platform for aminoglycoside antibiotics in water.

A donor-acceptor based conjugated microporous polymer, PER@NiP-CMOP-1, has been synthesized which can achieve highly sensitive stereo-specific "Turn ON" biosensing of an aminoglycoside up to the ppb level. The coordination-driven inhibition of photo-induced electron transfer (d-PET) for d-electrons and the rotational freezing are the key factors for the recovery of the emission.

Electrochemical Stimuli-Driven Facile Metal-Free Hydrogen Evolution from Pyrene-Porphyrin-Based Crystalline Covalent Organic Framework.

A [2 + 2] Schiff base type condensation between 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TAP) and 1,3,6,8-tetrakis (4-formylphenyl) pyrene (TFFPy) under solvothermal condition yields a crystalline, quasi-two-dimensional covalent organic framework (SB-PORPy-COF). The porphyrin and pyrene units are alternatively occupied in the vertex of 3D triclinic crystal having permanent microporosity with moderately high surface area (∼869 m2 g-1) and promising chemical stability. The AA stacking of the monolayers give a pyrene bridged conducting channel. SB-PORPy-COF has been exploited for metal free hydrogen production to understand the electrochemical behavior using the imine based docking site in acidic media. SB-PORPy-COF has shown the onset potential of 50 mV and the Tafel slope of 116 mV dec-1. We expect that the addendum of the imine based COF would not only enrich the structural variety but also help to understand the electrochemical behavior of these class of materials.

A new strongly paramagnetic cerium-containing microporous MOF for CO2 fixation under ambient conditions.

Metal organic frameworks (MOFs) bearing multicarboxylate linkers are in great demand for designing robust heterogeneous catalysts. A new microporous Ce(iii)-based metal organic framework (Ce2NDC3) has been synthesized under solvothermal conditions, which showed strong paramagnetism and a CO2 uptake capacity of 1.64 mmol g-1 (7.23 weight%) at 273 K. The Ce2NDC3 showed high catalytic activity in CO2 fixation for the synthesis of cyclic carbonates with a maximum yield of 92% at ambient temperature and pressure. This rare earth metal-based MOF has been well characterized by single crystal X-ray diffraction, PXRD, N2 adsorption/desorption, UHR-TEM, FESEM, FTIR, 13C MAS NMR and TGA. Here, we have carried out magnetic analysis, which revealed that the Ce(iii) in this MOF exhibited 2F5/2 magnetism in the ground state. The Ce2NDC3 catalyst showed high recycling efficiency in CO2 fixation reactions, together with retention of the MOF structure after several rounds of reuse. Presumably, the presence of acidic Ce(iii) metal ions and microporosity in the coordinated polymer network is responsible for the high catalytic activity.

Smokeless tobacco consumption impedes metabolic, cellular, apoptotic and systemic stress pattern: A study on Government employees in Kolkata, India.

Smokeless tobacco (SLT) remains a threat amongst a large population across the globe and particularly in India. The oral use of tobacco has been implicated to cause physiological stress leading to extreme toxicological challenge. The study included 47 SLT-users and 44 non-users providing a spectrum of pathophysiological, clinico-biochemical, antioxidant parameters, cell cycle progression study of PBMC and morphological changes of red blood cells (RBC). The expressions of p53, p21, Bax, Bcl-2, IL-6, TNF- α, Cox-2, iNOS were analyzed from thirteen representative SLT-users and twelve non-users. Difference in CRP, random glucose, serum cholesterol, TG, HLDL-C, LDL-C, VLDL-C, neutrophil count, monocyte count, ESR, SOD (PBMC) and TBARS (RBC membrane) were found to be statistically significant (p < 0.05) between the studied groups. The current study confers crucial insight into SLT mediated effects on systemic toxicity and stress. This has challenged the metabolic condition leading to a rise in the inflammatory status, increased apoptosis and RBC membrane damage. The above findings were substantiated with metabolic, clinical and biochemical parameters. This is possibly the first ever in-depth report and remains an invaluable document on the fatal effects of SLT.

Helicenes from diarylmaleimides.

Perkin condensations of arylglyoxylic acids with arylacetic acids, followed by the addition of alkylamine, yield diarylmaleimides in a one-pot procedure. The arylglyoxylic acids are obtained by arene acylation with ClCOCO2Et and reduced with NaI and hypophosphorous acid to the arylacetic acids. With 2,7-di-tert-butyl-pyren-4-yl or chrysen-6-yl as the aryl, photocyclodehydrogenation of the diarylmaleimides yields substituted helicenes which can be reduced to stable anions. The helicenes combine bathochromically shifted absorption with hypsochromically shifted fluorescence with respect to their precursors.