The Structure of the Cytochrome P450cam–Putidaredoxin Complex Determined by Paramagnetic NMR Spectroscopy and Crystallography

Cytochrome P450cam catalyzes the hydroxylation of camphor in a complex process involving two electron transfers (ETs) from the iron-sulfur protein putidaredoxin. The enzymatic control of the successive steps of catalysis is critical for a highly efficient reaction. The injection of the successive electrons is part of the control system. To understand the molecular interactions between putidaredoxin and cytochrome P450cam, we determined the structure of the complex both in solution and in the crystal state. Paramagnetic NMR spectroscopy using lanthanide tags yielded 446 structural restraints that were used to determine the solution structure. An ensemble of 10 structures with an RMSD of 1.3 Å was obtained. The crystal structure of the complex was solved, showing a position of putidaredoxin that is identical with the one in the solution structure. The NMR data further demonstrate the presence of a minor state or set of states of the complex in solution, which is attributed to the presence of an encounter complex. The structure of the major state shows a small binding interface and a metal-to-metal distance of 16 Å, with two pathways that provide strong electronic coupling of the redox centers. The interpretation of these results is discussed in the context of ET. The structure indicates that the ET rate can be much faster than the reported value, suggesting that the process may be gated.     

Elucidating the chemical and biochemical applications of Citrus sinensis-mediated silver nanocrystal

Abstract

Synthesis of nanoparticles using biodegradable source is safer and echo-friendly. Here, we describe the synthesis of polycrystalline silver nanocrystals using Citrus sinensis acting as both reducing and capping agents. After exposing the silver ions to orange extract, rapid reduction of silver ions led to the formation of stable silver nanocrystals due to the reducing and stabilizing properties of orange fruit juice. The synthesized silver nanocrystals were characterized using various analytical techniques like UV–vis spectroscopy, X-ray diffraction (XRD), dynamic light scattering (DLS), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The biochemical activity of the synthesized nanocrystals was studied in the light of affinity to bovine serum albumin using several biophysical methods like absorbance, fluorescence and circular dichroism spectroscopy. Cytotoxic activity of these nanocrystals was also studied against Hep-2 cell line using fluorescence microscopy. It was also found that the synthesized nanocrystals can sense mercuric ion down to 50?µM in the presence of a number of cations. Furthermore, we established that the silver nanoparticles can effectively catalyse the reduction of methylene blue by ascorbic acid. The present study will enrich our knowledge on the chemical and biochemical activities of green-synthesized silver nanocrystals.     

Manufacture of cellulose nanocrystals by cation exchange resin-catalyzed hydrolysis of cellulose

Cellulose nanocrystals (CNC) were prepared from microcrystalline cellulose (MCC) by hydrolysis with cation exchange resin (NKC-9) or 64% sulfuric acid. The cation exchange resin hydrolysis parameters were optimized by using the Box–Behnken design and response surface methodology. An optimum yield (50.04%) was achieved at a ratio of resin to MCC (w/w) of 10, a temperature of 48 °C and a reaction time of 189 min. Electron microscopy (EM) showed that the diameter of CNCs was about 10–40 nm, and the length was 100–400 nm. Regular short rod-like CNCs were obtained by sulfuric acid hydrolysis, while long and thin crystals of cellulose were obtained with the cation exchange resin. X-ray diffraction (XRD) showed that, compared with MCC, the crystallinity of H₂SO₄-CNC and resin-CNC increased from 72.25% to 77.29% and 84.26%, respectively. The research shows that cation exchange resin-catalyzed hydrolysis of cellulose could be an excellent method for manufacturing of CNC in an environmental-friendly way.     

Construction of CoP/NiCoP Nanotadpoles Heterojunction Interface for Wide pH Hydrogen Evolution Electrocatalysis and Supercapacitor

Constructing well defined nanostructures is promising but still challenging for high‐efficiency catalysts for hydrogen evolution reaction (HER) and energy storage. Herein, utilizing the differences in surface energies between (111) facets of CoP and NiCoP, a novel CoP/NiCoP heterojunction is designed and synthesized with a nanotadpoles (NTs)‐like morphology via a solid‐state phase transformation strategy. By effective interface construction, the disorder in terms of electronic structure and coordination environment at the interface in CoP/NiCoP NTs is created, which leads to dramatically elevated HER performance within a wide pH range. Theoretical calculations prove that an optimized proton chemisorption and H₂O dissociation are achieved by an optimized phosphide polymorph at the interface, accelerating the HER reaction. The CoP/NiCoP NTs are also proved to be excellent candidates for use in supercapacitors (SCs) with a high specific capacitance (1106.2 F g^?1 at 1 A g^?1) and good cycling stability (nearly 100% initial capacity retention after 1000 cycles). An asymmetric supercapacitor shows a high energy density (145 F g^?1 at 1 A g^?1) and good cycling stability (capacitance retention is 95% after 3200 cycles). This work provides new insights into the catalyst design for electrocatalytic and energy storage applications.     

Determination of chromium(III) in aqueous solution using CePO4:Tb3+ nanocrystals in a fluorescence resonance energy transfer system

Trivalent chromium is an essential element required for normal carbohydrate, lipid and protein metabolism in humans and animals. This article describes an efficient fluorescence resonance energy transfer (FRET) system between CePO₄:Tb³⁺ nanocrystals as the donor and chromium(III) as the acceptor. CePO₄:Tb³⁺ nanocrystals were synthesized in aqueous solution, and characterized by transmission electron microscopy. Under optimum conditions, a linear calibration graph was obtained (R² = 0.996). The linear range and detection limit of chromium(III) were 0.01–2.2 μM, and 9.1 nM, respectively. The proposed method had a wide linear range and proved to be very sensitive, rapid and simple. Moreover, the method was applied successfully to the determination of chromium(III) in synthetic samples and tap water. Copyright © 2013 John Wiley & Sons, Ltd.     

Microcrystallization techniques for serial femtosecond crystallography using photosystem II from Thermosynechococcus elongatus as a model system

Serial femtosecond crystallography (SFX) is a new emerging method, where X-ray diffraction data are collected from a fully hydrated stream of nano- or microcrystals of biomolecules in their mother liquor using high-energy, X-ray free-electron lasers. The success of SFX experiments strongly depends on the ability to grow large amounts of well-ordered nano/microcrystals of homogeneous size distribution. While methods to grow large single crystals have been extensively explored in the past, method developments to grow nano/microcrystals in sufficient amounts for SFX experiments are still in their infancy. Here, we describe and compare three methods (batch, free interface diffusion (FID) and FID centrifugation) for growth of nano/microcrystals for time-resolved SFX experiments using the large membrane protein complex photosystem II as a model system.     

Synthesis and luminescence properties of lanthanide complexes with a new tripodal ligand featuring N‐thenylsalicylamide arms

To explore the relationship between the structure of the ligands and the luminescent properties of the lanthanide complexes, luminescent lanthanide complexes of a new tripodal ligand, featuring N‐thenylsalicylamide arms, were synthesized and characterized by elemental analysis, IR and TGA measurements. Photophysical properties of the complexes were studied by means of UV ? visible absorption and steady‐state luminescence spectroscopy. The results of UV ? vis spectra indicate that metal binding does not disturb the electronic structure of the ligand. Excited‐state luminescence lifetimes and quantum yields of the complexes were determined. The photoluminescence analysis suggested that there is an efficient ligand ? Ln(III) energy transfer for the Tb(III) complex, and the ligand is an efficient 'antenna' for Tb(III). From a more general perspective, the results demonstrated the potential application of the lanthanide complex as luminescent materials in material chemistry. Copyright © 2012 John Wiley & Sons, Ltd.     

High performance edible nanocomposite films containing bacterial cellulose nanocrystals

Bacterial cellulose obtained from Gluconacetobacter xylinus in the form of long fibers were acid hydrolyzed under controlled conditions to obtain cellulose nanocrystals. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) confirmed the formation of rod like cellulose nanocrystals having an average diameter and length of 20 ± 5 nm and 290 ± 130 nm respectively. These nanocrystals were used to prepare gelatin nanocomposite films and characterized for elucidating its performance. The formation of percolated networks of cellulose nanocrystals within gelatin matrix resulted in improving the mechanical properties of nanocomposites. The moisture sorption and water vapor permeability (WVP) studies revealed that the addition of cellulose nanocrystals reduced the moisture affinity of gelatin, which is very favorable for edible packaging applications. Results of this study demonstrated the use of bacterial cellulose nanocrystals (BCNCs) in the fabrication of edible, biodegradable and high-performance nanocomposite films for food packaging applications at relatively low cost.     

Enantioselective cleavage of supercoiled plasmid DNA catalyzed by chiral macrocyclic lanthanide(III) complexes

The enantiomers of the Sm (III), Eu (III) and Yb (III) complexes [LnL(NO₃)₂](NO₃) of a chiral hexaazamacrocycle were tested as catalysts for the hydrolytic cleavage of supercoiled plasmid DNA. The catalytic activity was remarkably enantioselective; while the [LnL^SSSS(NO₃)₂](NO₃) enantiomers promoted the cleavage of plasmid pBR322 from the supercoiled form (SC) to the nicked form (NC), the [LnL^RRRR(NO₃)₂](NO₃) enantiomers were inactive. Kinetics of plasmid DNA hydrolysis was also investigated by agarose electrophoresis and it indicated typical single-exponential cleavage reaction. The hydrolytic mechanism of DNA cleavage was confirmed by the successful ligation of hydrolysis product by T4 ligase. The NMR study of the solutions of the complexes in various buffers indicated that the complexes exist as monomeric cationic complexes [LnL(H₂O)₃]^3 + in slightly acidic solutions and as dimeric cationic complexes [Ln₂L₂(μ-OH)₂(H₂O)₂]^4 + in slightly basic 8 mM solutions, with the latter form being a possible catalyst for hydrolysis of phosphodiester bonds.     

Nanocrystal technology, drug delivery and clinical applications

Nanotechnology will affect our lives tremendously over the next decade in very different fields, including medicine and pharmacy. Transfer of materials into the nanodimension changes their physical properties which were used in pharmaceutics to develop a new innovative formulation principle for poorly soluble drugs: the drug nanocrystals. The drug nanocrystals do not belong to the future; the first products are already on the market. The industrially relevant production technologies, pearl milling and high pressure homogenization, are reviewed. The physics behind the drug nanocrystals and changes of their physical properties are discussed. The marketed products are presented and the special physical effects ofnanocrystals explained which are utilized in each market product. Examples of products in the development pipelines (clinical phases) are presented and the benefits for in vivo administration of drug nanocrystals are summarized in an overview.