Linchpins empower promiscuous electrophiles to enable site-selective modification of histidine and aspartic acid in proteins

The conservation of chemoselectivity becomes invalid for multiple electrophilic warheads during protein bioconjugation. Consequently, it leads to unpredictable heterogeneous labeling of proteins. Here, we report that a linchpin can create a unique chemical space to enable site-selectivity for histidine and aspartic acid modifications overcoming the pre-requisite of chemoselectivity.

Linchpin-enabled promiscuous electrophile uncovers an unchartered reactivity landscape for the precision engineering of proteins.     

Enhanced field emission from LaB6 thin films with nanoprotrusions grown by pulsed laser deposition on Zr foil

Lanthanum hexaboride (LaB₆) films have been deposited on a zirconium foil by pulsed laser deposition method. The field emission studies of the LaB₆ deposited film have been performed in the planar diode configuration under ultra high vacuum conditions. The Fowler-Nordheim plots were found to be linear in accordance with the quantum mechanical tunneling phenomenon. A typical field emission current of 7.02 μA was drawn at an applied electric field of 2 V/μm. The field enhancement factor is calculated to be 8913 cm⁻¹, indicating that the field emission is from nanoscale protrusions present on the emitter surface. The atomic force microscope (AFM) investigation of the surface clearly shows the conical shaped nanoprotrusions of few hundred nanometers with asperities of 20-40 nm on its top. The emission current-time plot recorded at the pre-set value of emission current of 5 μA over a period of more than 3 h exhibits an initial increase and subsequent stabilization of the current. The results reveal that the LaB₆/Zr field emitter obtained by the pulsed laser deposition (PLD) is a promising cathode material for practical applications in field emission-based devices.     

Nickel-catalyzed C−H arylation of benzoxazoles and oxazoles: Benchmarking the influence of electronic,steric and leaving group variations in phenolic electrophiles

Electronic, steric and leaving group effects for Ni-catalyzed direct arylations using C?O electrophiles were benchmarked. The scope of arylations with pivalates was general with respect to both the electronics on the electrophile and the azoles. Furthermore, the arylation of azoles with tosylates, mesylates and carbamates with varying electronics was explored, and showed electronic trends similar to those of the pivalate reactions. Finally, the relative rate of arylation of 5-methyl benzoxazole with two electronically-similar electrophiles bearing different leaving groups was established. The results from these studies implicate the following order of relative reactivity: mesylates>pivalates>carbamates.     

Role of stimuli-sensitive polymers in protein refolding: alpha-amylase and CcdB (controller of cell division or death B) as model proteins

Alginate, a calcium-sensitive polymer, could carry out simultaneous purification and refolding of 8 M urea/100 mM dithiothreitol (DTT) denatured and thermally denatured alpha-amylase present in a commercial preparation. Activity recoveries of 80 and 70% in the former and the latter cases, respectively, were obtained. The fluorescence spectra showed refolding, and PAGE showed the absence of any aggregates in the refolded preparation. As another example, Eudragit S-100, a pH-sensitive poly(methyl methacrylate), was used to refold CcdB (controller of cell division or death B) protein. Initial experiments with wild-type (WT) CcdB showed that Eudragit bound and precipitated (upon lowering the pH to 4.0) CcdB quantitatively from the latter's aqueous solution. The bioconjugate showed DNA gyrase inhibition activity of CcdB and could be recycled. The inclusion bodies of CcdB mutant CcdB-17P were solubilized in 8 M urea/100 mM dithiothreitol. This preparation could be refolded by precipitation with Eudragit. The fluorescence and CD spectra showed that protein refolding has occurred.     

Modulations in restricted amide rotation by steric induced conformational trapping

The rotation around the amide bond in N,N-diethyl-m-toluamide (m-DEET) has been studied extensively and often used in laboratory instructions to demonstrate the phenomenon of chemical exchange. Herein, we show that a simple modification to N,N-diethyl-o-toluamide (o-DEET) significantly alters the dynamics of the restricted rotation around the amide bond due to steric interactions between the ring methyl group and the two N-ethyl groups. This alters the classic two-site exchange due to restricted rotation around the amide bond, to a three-site exchange, with the third conformation trapped at a higher-energy state compared to the other two. This often overlooked phenomenon is elucidated using variable-temperature NMR, two-dimensional exchange spectroscopy and molecular modeling studies.     

Biodecolorization of Azo Dye Remazol Orange by Pseudomonas aeruginosa BCH and Toxicity (Oxidative Stress) Reduction in Allium cepa Root Cells

In this report a textile azo dye Remazol orange was degraded and detoxified by bacterium Pseudomonas aeruginosa BCH in plain distilled water. This bacterial decolorization performance was found to be pH and temperature dependent with maximum decolorization observed at pH 8 and temperature 30 °C. Bacterium tolerated higher dye concentrations up to 400 mg?l^?1. Effect of initial cell mass showed that higher cell mass concentration can accelerate decolorization process with maximum of 92 % decolorization observed at 2.5 g?l^?1 cell mass within 6.5 h. Effect of various metal ions showed Mn has inducing effect whereas Zn strongly inhibited the decolorization process at 5 mM concentration. Analysis of biodegradation products carried out with UV–vis spectroscopy, HPTLC and FTIR confirmed the decolorization and degradation of Remazol orange. Possible route for the degradation of dye was proposed based on GC-MS analysis. During toxicological scrutiny in Allium cepa root cells, induction in the activities of superoxide dismutase (SOD), guaiacol peroxidase (GPX) and inhibition of catalase (CAT) along with raised levels of lipid peroxidation and protein oxidation in dye treated samples were detected which conclusively indicated the generation of oxidative stress. Less toxic nature of the dye degraded products was observed after bacterial treatment.     

A macrocyclic piperazine linked extremely Zn selective fluorescent chemosensor with bio-imaging and for H2PO4 sensing

A new macrocyclic fluorescent chemosensor piperazine coupled diimine phenol (PCDP) which forms extremely selective Zn(II) complex and thus builds up the platform for H₂PO₄⁻ (DHP) sensing in mixed aqueous medium, has been designed and synthesized. The binding of PCDP with Zn²⁺ and its displacement by DHP have been supported by DFT studies. The blue fluorescence in the PCDP–Zn complex is useful for bio-imaging. The fluorescence enhancement of PCDP on association with Zn²⁺ ion is quenched sharply in the presence of intracellular DHP.     

Chemoselective and Site‐Selective Lysine‐Directed Lysine Modification Enables Single‐Site Labeling of Native Proteins

The necessity for precision labeling of proteins emerged during the efforts to understand and regulate their structure and function. It demands selective attachment of tags such as affinity probes, fluorophores, and potent cytotoxins. Here, we report a method that enables single‐site labeling of a high‐frequency Lys residue in the native proteins. At first, the enabling reagent forms stabilized imines with multiple solvent‐accessible Lys residues chemoselectively. These linchpins create the opportunity to regulate the position of a second Lys‐selective electrophile connected by a spacer. Consequently, it enables the irreversible single‐site labeling of a Lys residue independent of its place in the reactivity order. The user‐friendly protocol involves a series of steps to deconvolute and address chemoselectivity, site‐selectivity, and modularity. Also, it delivers ordered immobilization and analytically pure probe‐tagged proteins. Besides, the methodology provides access to antibody‐drug conjugate (ADC), which exhibits highly selective anti‐proliferative activity towards HER‐2 expressing SKBR‐3 breast cancer cells.     

On the modified inverse spinel-LiCo(PO4) x (VO4)1?x as cathode for rechargeable lithium batteries

The structural and electrochemical behavior of a modified and unmodified inverse spinel phases with general formula, LiCo(PO₄) _x (VO₄)_1???x [with x?=?0.0 and 0.1] for the possible application as cathodes in rechargeable lithium batteries have been investigated. The modified and unmodified phases, represented as LiCoP_0.1V_0.9O₄ and LiCoVO₄ have been synthesized by an aqueous route at 700 °C. Both the phases have been shown to crystallize in a cubic inverse spinel structure with Fd-3m (Oh ⁷ ) space group symmetry as corroborated through XRD studies, with the attendant decrease in the cell parameter ??a?? value in LiCoP_0.1V_0.9O₄. Vibrational spectroscopic studies confirm the introduction of PO₄ group existing together with VO₄ framework. SEM of LiCoP_0.1V_0.9O₄ shows highly porous nature of the materials. Cyclic voltammetric studies with the modified spinel evince high lithium ion reversibility in the voltage range of 3.8?C4.3 V. Subsequent galvanostatic charge?Cdischarge studies conducted on Li//LiCoP_0.1V_0.9O₄ test cells has delivered specific discharge capacity of 118 and 96 mAhg^?1, respectively at 1st and the 15th cycle indicating the advantage of doping with phosphate in the vanadate structure.