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Enzyme histochemistry facilitates enzyme activity visualization in situ; however, as it is a color-based method, molecular quantification is prohibitive. This study aimed to develop a semiquantitative, mass spectrometry imaging (MSI)-based enzyme histochemistry method to determine endogenous cholinesterase (ChE) activity. Using deuterium-labeled acetylcholine (ACh-d9) as a substrate to distinguish ACh-d9 and choline-d9 from endogenous acetylcholine and choline, respectively, the heterogeneous localization of de novo ChE activity was visualized using MSI, devoid of interferences from in situ factors. Furthermore, a tissue inhibitor assay involving two ChE inhibitors in the mouse brain revealed specific ChE inhibition in the corpus callosum. To the best of our knowledge, this study is the first to report a visualization method for total ChE activity in the ganglia and abdomen in Drosophila melanogaster, indicating its applicability among different animals. The present results provide novel insights into the applicability of enzyme histochemistry via MSI to the metabolism of low-molecular-weight organic compounds (i.e., "small molecules") and semiquantitative capability, suggesting that MSI enzyme histochemistry may become a powerful tool for heterogeneous tissue studies.Protein denaturation involves a change in the protein structure with the loss of activity, which proceeds via various intermediates. The possible intermediate structures account largely for understanding the process of unfolding. Hence, considerable attention is required to characterize partially unfolded protein states and to gain more insight into the information about the sequence and steps involved in protein folding mechanisms. In this report, a stepwise unfolding of bovine serum albumin (BSA) with guanidine hydrochloride (GuHCl) has been investigated using Raman spectroscopy in the amide I and III regions. Two-dimensional (2D) correlation analysis has been applied to reveal information on the sequential order and the dynamic properties of interaction during the unfolding process. Raman spectral signatures in the amide I region revealed that there is no significant change in secondary structures up to 2 M concentration of GuHCl. However, 2D correlation analysis further supports the observation by inferring the strengthening of secondary structure at the expense of tertiary structure. At a higher concentration of GuHCl (2-4 M), there is an accumulation of random and β-sheet structures that is mediated by small connecting segments of helices. It further accelerates the unfolding of helices and a complete collapse of structure. These analyses establish the ability of Raman spectroscopy to estimate the ensemble of secondary structures present in proteins. GSK3235025 The results reveal the mechanistic details of unfolding, characterizing structure of intermediates even at high concentrations, and understanding the evolution of various secondary structures with respect to each other during unfolding. Such observations can be helpful in understanding the factors affecting the shape and size of proteins during folding/unfolding.The formation of wurtzite (WZ) phase in III-V nanowires (NWs) such as GaAs and InP is a complication hindering the growth of pure-phase NWs, but it can also be exploited to form NW homostructures consisting of alternate zincblende (ZB) and WZ segments. This leads to different forms of nanostructures, such as crystal-phase superlattices and quantum dots. Here, we investigate the electronic properties of the simplest, yet challenging, of such homostructures InP NWs with a single homojunction between pure ZB and WZ segments. Polarization-resolved microphotoluminescence (μ-PL) measurements on single NWs provide a tool to gain insights into the interplay between NW geometry and crystal phase. We also exploit this homostructure to simultaneously measure effective masses of charge carriers and excitons in ZB and WZ InP NWs, reliably. Magneto-μ-PL measurements carried out on individual NWs up to 29 T at 77 K allow us to determine the free exciton reduced masses of the ZB and WZ crystal phases, showing the heavier character of the WZ phase, and to deduce the effective mass of electrons in ZB InP NWs (me= 0.080 m0). Finally, we obtain the reduced mass of light-hole excitons in WZ InP by probing the second optically permitted transition Γ7C ↔ Γ7uV with magneto-μ-PL measurements carried out at room temperature. This information is used to extract the experimental light-hole effective mass in WZ InP, which is found to be mlh = 0.26 m0, a value much smaller than the one of the heavy hole mass. Besides being a valuable test for band structure calculations, the knowledge of carrier masses in WZ and ZB InP is important in view of the optimization of the efficiency of solar cells, which is one of the main applications of InP NWs.Nanocomposite photocatalysts offer a promising route to efficient and clean hydrogen production. However, the multistep, high-temperature, solvent-based syntheses typically utilized to prepare these photocatalysts can limit their scalability and sustainability. Biosynthetic routes to produce functional nanomaterials occur at room temperature and in aqueous conditions, but typically do not produce high-performance materials. We have developed a method to produce a highly efficient hydrogen evolution photocatalyst consisting of CdS quantum dots (QDs) supported on reduced graphene oxide (rGO) via enzyme-based syntheses combined with tuned ligand exchange-mediated self-assembly. All preparation steps are carried out in an aqueous environment at ambient temperature. Size-controlled CdS QDs and rGO are prepared through enzyme-mediated turnover of l-cysteine to HS- in aqueous solutions of Cd-acetate and graphene oxide, respectively. Exchange of cysteamine for the native l-cysteine ligand capping the CdS QDs drives self-assembly of the now positively charged cysteamine-capped CdS (CdS/CA) onto negatively charged rGO. The use of this short linker molecule additionally enables efficient charge transfer from CdS to rGO, increasing exciton lifetime and, subsequently, photocatalytic activity. The visible-light hydrogen evolution rate of the resulting CdS/CA/rGO photocatalyst is 3300 μmol h-1 g-1. This represents, to our knowledge, one of the highest reported rates for a CdS/rGO nanocomposite photocatalyst, irrespective of the synthesis method.
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