Untangling a Repetitive Amyloid Sequence: Correlating Biofilm‐Derived and Segmentally Labeled Curli Fimbriae by Solid‐State NMR Spectroscopy

Curli are functional bacterial amyloids produced by an intricate biogenesis machinery. Insights into their folding and regulation can advance our understanding of amyloidogenesis. However, gaining detailed structural information of amyloids, and their tendency for structural polymorphisms, remains challenging. Herein we compare high‐quality solid‐state NMR spectra from biofilm‐derived and recombinantly produced curli and provide evidence that they adopt a similar, well‐defined β‐solenoid arrangement. Curli subunits consist of five sequence repeats, resulting in severe spectral overlap. Using segmental isotope labeling, we obtained the unambiguous sequence‐specific resonance assignments and secondary structure of one repeat, and demonstrate that all repeats are most likely structurally equivalent.     

A Convenient Synthesis of Spiro[4-n] dione and 2,2-Disubstituted Cyclopentane-1,3-dione System

An efficient, one pot strategy for the synthesis of spiro [4. n]dione and 2,2-disubstituted cyclopentane-1,3-dione has been developed by using ketals and 1,2-disilyloxycyclobutene in the presence of excess BF ₃.Et₂O.     

From understanding structures in antiferro-ferri and ferroelelectric liquid crystals to an unusual electro-optic effect in a bent-core nematic; a celebration of innovative materials

ABSTRACT

The field of liquid crystals is truly multidisciplinary with numerous examples of virtuous circles of interaction between chemistry, physics, theory and engineering resulting in breakthroughs in both fundamental understanding and novel applications. This paper, written to mark John Goodby’s 65th birthday, offers a personal perspective of the synergy between chemistry and physics from a collaboration that has spanned three decades. The first part of the paper reviews some of the physics insights that resulted from chiral liquid crystals fundamental to understanding structures in ferroelectric, ferrielectric and antiferroelectric systems. The second part of the paper describes some of the remarkable consequences of the anomalous elasticity and flexoelectricity found in the nematic phases of bent-core materials. In particular, we present unusual bowing of disclination lines in the nematic phase of a bent-core material in the presence of a field. Finally, the paper summarises some future prospects relating for bent-core materials. The paper by no means captures the amazing breadth of contribution that John’s chemistry has made to the subject, but aims to exemplify how his generous collaborative approach coupled with innovative chemistry and physical insight has led to paradigm changes in our subject.     

Synthesis of novel N-hydroxy heterocycles via intramolecular reductive cyclization of diketoximes by NaBH3CN

A simple and efficient protocol for the construction of substituted piperazines, piperidines, thiomorpholines, decahydroquinolines, perhydrocyclopenta[b]pyridine, and pyrrolidines bearing N-hydroxy substituents through intramolecular reductive cyclization of diketoximes using sodium cyanoborohydride is described.     

Identification and characterization of phenolic compounds in castor seed

Phenolic compounds, polyphenols, and flavonoids occur ubiquitously in plant kingdom, because they are important in plants for normal growth development and defense against infection and injury. Currently, there are no reports available on the phenolic compounds obtained from the residues of the oil-extracting process from defatted castor seed powder. Our studies, for the first time, in methanol-ether extract showed five low-molecular weight phenolic compounds namely p-coumaric acid, ferulic acid, o-coumaric acids, syringic, and cinnamic acids, which were in the soluble ether fractions. All these compounds showed strong absorbance at 240 nm.     

Kinetics and mechanism of electron transfer reaction of single and double chain surfactant cobalt(III) complex by Fe2+ ions in liposome (dipalmitoylphosphotidylcholine) vesicles: effects of phase transition

In this study, we report the kinetics of reduction reactions of single and double chain surfactant cobalt(III) complexes of octahedral geometry, cis-[Co(en)₂(4AMP)(DA)](ClO₄)₃ and cis-[Co(dmp)₂(C₁₂H₂₅NH₂)₂](ClO₄)₃ (en = ethylenediamine, dmp = 1,3-diaminopropane, 4AMP = 4-aminopropane, C₁₂H₂₅NH₂ = dodecylamine) by Fe²⁺ ion in dipalmitoylphosphotidylcholine (DPPC) vesicles at different temperatures under pseudo first-order conditions. The kinetics of these reactions is followed by spectrophotometry method. The reactions are found to be second order and the electron transfer is postulated as outer sphere. The remarkable findings in the present investigation are that, below the phase transition temperature of DPPC, the rate decreases with an increase in the concentration of DPPC, while above the phase transition temperature the rate increases with an increase in the concentration of DPPC. The main driving force for this phenomenon is considered to be the intervesicular hydrophobic interaction between vesicles surface and hydrophobic part of the surfactant complexes. Besides, comparing the values of rate constants of these outer-sphere electron transfer reactions in the absence and in the presence of DPPC, the rate constant values in the presence of DPPC are always found to be greater than in the absence of DPPC. This is ascribed to the double hydrophobic fatty acid chain in the DPPC that gives the molecule an overall tubular shape due to the intervesicular hydrophobic interaction between vesicles surface and hydrophobic part of the surfactant complexes more suitable for vesicle aggregation which facilitates lower activation energy, and consequently higher rate is observed in the presence of DPPC. The activation parameters (ΔS^# and ΔH^#) of the reactions at different temperatures have been calculated which corroborate the kinetics of the reaction.