Regioselective addition of 1,3-dicarbonyl dianion to N-sulfonyl aldimines: an expedient route to N-sulfonyl piperidines and N-sulfonyl azetidines

A simple route for the synthesis of δ-amino-β-keto esters and δ-amino-β-diketones is reported. This involves regioselective addition of 1,3-dianions derived from ethyl acetoacetate and acetyl acetone to N-sulfonyl aldimines. The δ-amino-β-keto ester derivatives were further converted into the corresponding N-sulfonyl piperidines and N-sulfonyl azetidines.     

Site-specific Heterogeneity of Multi-domain Human Serum Albumin and its Origin: A Red Edge Excitation Shift Study†

Conformational heterogeneity is a defining characteristic of a protein and is vital in understanding its function and folding landscape. In the present work, we interrogated the presence of conformational heterogeneity in multi-domain human serum albumin in a domain-specific manner using red edge excitation shift (REES) in its native state and also monitored its variation along the unfolding transition. We also looked into the origin of such conformational heterogeneity by varying the solution viscosity. We observed (1) even in the native state, the heterogeneity and dynamics of the side chain exhibit varied behaviors depending on which domain of the multi-domain human serum albumin (HSA) is being examined. (2) When the protein is in the unfolded state, the extent of REES is rendered unimportant since there is a greater quantity of free water present, in addition to the disruption of the protein's structure. (3) While the rigid protein matrix provides the rigidity of domain-I and domain-III, the rigidity of domain-II is provided by water molecules, which indicates that the role of water molecules in providing the rigidity is significant. Overall, our results provide direct evidence of the rigidity and alternate side chain packing arrangement of protein core that varies domain-wise in multi-domain HSA.     

Versatile synthesis of 3,4-b diheteropentalenes

We describe a new route for the synthesis of thieno[3,4-b]thiophene, alkyl derivatives thereof, seleno[3,4-b]thiophene, and thieno[3,4-b]furan made from inexpensive starting materials, such as thiophene-2-carboxylic acid and furan-2-carboxylic acid. Such fused heterocycles are of great interest for low band gap organic semiconductors and applications including OLEDs, organic photovoltaic cells, and electrochromics.     

Poly[μ4‐sulfido‐tris(thiocyanato‐κN)tris(μ3‐1,2,4‐triazolato‐κ3N1:N2:N4)tetrazinc(II)]: a three‐dimensional zinc sulfide coordination polymer

The title compound, [Zn₄(C₂H₂N₃)₃(NCS)₃S]_n, is a three‐dimensional coordination polymer consisting of tetrahedral SZn₄ clusters bridged by triazole ligands. In the tetrahedral unit, three Zn atoms are connected to six bridging triazolate ligands, whereas the fourth Zn atom (site symmetry 3m) is bonded to three terminal thiocyanate anions that protrude into the void space created by the Zn–triazolate network. The network prototype is simple cubic, but a strong distortion along a body diagonal and the imposition of a polar direction by the arrangement of the molecular constituents lead to the trigonal space group R3m. This study demonstrates the use of the 3‐mercapto‐1,2,4‐triazole ligand as an effective source for sulfide ions in the synthesis of sulfide‐based coordination polymers.     

Ultrastable Imine‐Based Covalent Organic Frameworks for Sulfuric Acid Recovery: An Effect of Interlayer Hydrogen Bonding

A rapid and scalable synthesis of six new imine‐linked highly porous and crystalline COFs is presented that feature exceptionally high chemical stability in harsh environments including conc. H₂SO₄ (18 m ), conc. HCl (12 m ), and NaOH (9 m ). This is because of the presence of strong interlayer C?H???N hydrogen bonding among the individual layers, which provides significant steric hindrance and a hydrophobic environment around the imine (?C=N?) bonds, thus preventing their hydrolysis in such an abrasive environment. These COFs were further converted into porous, crystalline, self‐standing, and crack‐free COF membranes (COFMs) with extremely high chemical stability for their potential applications for sulfuric acid recovery. The as‐synthesized COFMs exhibit unprecedented permeance for acetonitrile (280 Lm^?2 h^?1 bar^?1) and acetone (260 Lm^?2 h^?1 bar^?1).     

Investigation of gas transport and other physical properties in relation to the bromination degree of polymers of intrinsic microporosity

In this work, the synthesis of novel polymers of intrinsic microporosity (PIMs) with different degrees of bromine substitution by a free-radical substitution reaction was performed. The synthesized polymers were thoroughly characterized and their bromination degree was verified via nuclear magnetic resonance. The brominated PIMs were investigated by infrared spectroscopy, X-ray diffraction, and density measurements and correlated with their gas transport properties. It was found that with an increase in the bromination degree, the synthesized PIMs exhibited a significant increase in polymer chain packing density which led to reduced fractional free volume and consequent decrease in gas diffusion and permeability coefficients. The change in permeability coefficients caused an improvement in the CO₂/N₂, CO₂/CH₄, and O₂/N₂ ideal permeability selectivities. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2752–2761     

SURFACE PROPERTIES OF SOME LOW MOLECULAR WEIGHT PROTEINS

Surface properties of four proteins having molecular weights less than 5,000 are reported at air/water and alumina/water interface at pH 7.0. Reversibility in the adsorption of these proteins at the alumina/water interface is tested. The adsorption on alumina/water interface has been found to be controlled by electrostatic interaction. Positive adsorption was obtained when protein and alumina surface had opposite charges and negative adsorption was obtained when both protein and surface had same charges. Of the four proteins reversibility in adsorption was observed with the one having the lowest molecular weight of 3100. The adsorption behavior apparently had no correlation with their surface hydrophobic!ty. Time dependent changes in air/water interfacial tension was observed for all the four proteins indicating time dependent loosening of compact protein structure and surface unfolding.     

Pristine Carbon‐Nanotube‐Included Supramolecular Hydrogels with Tunable Viscoelastic Properties

Research investigations involving pristine carbon nanotubes (CNTs) and their applications in diversified fields have been gathering enormous impetus in recent times. One such emerging domain deals with the hybridization of CNTs within hydrogels to form soft nanocomposites with superior properties. However, till now, reports on the inclusion of pristine CNTs within low‐molecular‐weight hydrogels are very scarce due to their intrinsic feature of remaining in the bundled state and strong repulsive behavior to the aqueous milieu. Herein, the synthesis of a series of amino acid/dipeptide‐based amphiphilic hydrogelators having a quaternary ammonium/imidazolium moiety at the polar head and a C16 hydrocarbon chain as the hydrophobic segment is reported. The synthesized amphiphiles exhibited excellent hydrogelation (minimum gelation concentration (MGC) ≈0.7–5 % w/v) as well as single‐walled carbon nanotube (SWNT) dispersion ability in aqueous medium. Interestingly, the dispersed SWNTs were incorporated into the supramolecular hydrogel formed by amphiphiles with an imidazolium moiety at the polar end through complementary cation–π and π–π interactions. More importantly, the newly synthesized hydrogelators were able to accommodate a significantly high amount of pristine SWNTs (2–3.5 % w/v) at their MGCs without affecting the gelating properties. This is the first time that such a huge amount of SWNTs has been successfully incorporated within hydrogels. The efficient inclusion of SWNTs to develop soft nanocomposites was thoroughly investigated by spectroscopic and microscopic methods. Remarkably, the developed nanocomposites showed manifold enhancement (≈85‐fold) in their mechanical strength compared with native hydrogel without SWNTs. The viscoelastic properties of these nanocomposites were readily tuned by varying the amount of incorporated CNTs.