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Charge screening

Prabir Khatua, Sanjoy Bandyopadhyay
Aggregation of amyloid beta (A β ) peptides in the brain is responsible for one of the most devastating neurodegenerative diseases, namely, Alzheimer's disease. In this study, we have carried out atomistic molecular dynamics simulations to explore the effects of non-uniform structural distortions of A β 17-42 pre-fibrillar aggregates of different sizes on the microscopic structure and ordering of water molecules confined within their amphiphilic nanocores. The calculations revealed non-uniform peptide-water interactions resulting in simultaneous existence of both highly ordered and disordered water molecules within the spatially heterogeneous confined environment of the protofilament cores...
August 14, 2018: Journal of Chemical Physics
Butian Zhang, Ruiheng Chang, Kexin Wang, Jing-Tao Lu, Shun Wang
For semiconductor nanocrystals (NCs), the precise knowledge of phonons in presence of free carriers is important for understanding their electronic and photonic properties in device applications. Using Raman spectroscopy, this study investigates the effects of free charge carriers on optical phonon behaviors of NCs. The adoption of the photocharging method allows us to introduce free charge carriers into NCs without inducing other side effects. In the photocharged ZnO NCs, lower longitudinal optical (LO) phonon frequencies and weaker LO overtones relative to the fundamentals were found, which was explained by the screening and band-filling effects caused by the induced free carriers...
August 15, 2018: Journal of Physical Chemistry Letters
Hang Xu, Rajendra Bandari, Li E Lee, Ran Li, Ping Yu, Charles Jeffrey Smith, Lixin Ma
The bombesin (BBN) antagonist binds with high affinity to the gastrin releasing peptide receptor (GRPr), a receptor overexpressed on many human cancers. We present an investigation employing BBN antagonist for highly specific near-infrared fluorescence (NIRF) imaging of GRPr-positive tumors. Nine NIRF-dye labeled BBN antagonists with differing linkers and dyes were synthesized and characterized to screen for the optimal agent. Three novel agents, AF750-G-pip-Sta-BBN (1), AF750-GSG-Sta-BBN (2), and AF750-6Ahx-Sta-BBN (3), exhibited an excellent binding-specificity and affinity to human PC-3 prostate cancer cells in vitro, and a remarkable in vivo tumor-selectivity and NIRF imaging sensitivity in PC-3 tumor-bearing mice...
August 15, 2018: Journal of Medicinal Chemistry
Adelina Voukadinova, Mónika Valiskó, Dirk Gillespie
Classical density functional theory (DFT) is a useful tool to compute the structure of the electrical double layer because it includes ion-ion correlations due to excluded-volume effects (i.e., steric correlations) and ion screening effects (i.e., electrostatic correlations beyond the electrostatic mean-field potential). This paper systematically analyzes the accuracies of three different electrostatic excess free-energy functionals, as compared to Monte Carlo (MC) simulations of the planar electrical double layer, over a large parameter space...
July 2018: Physical Review. E
Guangcan Yang, Yanwei Wang
Dynamic Light Scattering ( DLS ) enables the characterization of sizes and electrokinetic properties of colloids, polymers, macromolecules. DNA is a charged semiflexible polyelectrolyte, which is condensed or compacted by counterions, proteins, and other condensing agents in processes such as chromosome compaction and gene therapeutic applications. DNA condensation is closely related to charge screening, since packaging requires effective neutralization of its surface negative charges. In this chapter, we describe in detail the protocol for DLS of DNA-ligand complexes...
2018: Methods in Molecular Biology
Sneha Munshi, Soundhararajan Gopi, Gitanjali Asampille, Sandhyaa Subramanian, Luis A Campos, Hanudatta S Atreya, Athi N Naganathan
DNA-binding protein domains (DBDs) sample diverse conformations in equilibrium facilitating the search and recognition of specific sites on DNA over millions of energetically degenerate competing sites. We hypothesize that DBDs have co-evolved to sense and exploit the strong electric potential from the array of negatively charged phosphate groups on DNA. We test our hypothesis by employing the intrinsically disordered DBD of cytidine repressor (CytR) as a model system. CytR displays a graded increase in structure, stability and folding rate on increasing the osmolarity of the solution that mimics the non-specific screening by DNA phosphates...
August 11, 2018: Nucleic Acids Research
Linkun Yin, Shuxin Wang, Siyang Zuo
BACKGROUND: Flexible endoscopes have become an important tool for the diagnosis and treatment of gastric cancer. However, there are several limitations to the use of endoscopes in rural areas, including their high cost, poor portability, and unstable platform. METHODS: This paper presents a novel low-cost outer sheath for stomach screening. The sheath uses braided shape memory polymer (SMP) tubes with a water-jet to control the stiffness and bending motion. The insertion part of the prototype is 250 mm long with a maximum outer diameter of 16 mm and incorporates an internal charge-coupled device camera...
August 14, 2018: International Journal of Medical Robotics + Computer Assisted Surgery: MRCAS
Sanyin Qu, Qin Yao, Bingxue Yu, Kaiyang Zeng, Wei Shi, Yanling Chen, Lidong Chen
Poly (3-hexylthiophene) (P3HT) films with various molecular weight (MW) were successfully prepared and both of their molecular structure and thermoelectric (TE) properties were investigated. It was found that molecular weight of P3HT can take important effect on the carrier transport properties by affecting the molecular structure and as a result, on the TE performance. The electrical conductivity of the P3HT film first increased with the increase of the molecular weight and then decreased at high molecular weight, whereas the Seebeck coefficient maintained the same level...
August 14, 2018: Chemistry, An Asian Journal
Pakhuri Mehta, Shubham Srivastava, Manish Sharma, Inderpal Singh, Ruchi Malik
Development of resistance against existing anti-epileptic drugs has alarmed the scientific innovators to find novel potential chemical starting points for the treatment of epilepsy and GABAA inhibition is a promising drug target strategy against epilepsy. The crystal structure of a subtype-selective β3-homopentameric ligand-gated ion channel of GABAA receptor has been used for the first time for screening the Asinex library for discovery of GABAA agonists as potential anti-epileptic agents. Co-crystallized ligand established the involvement of part of the β7-β8 loop (Glu155 and Tyr157) and β9-β10 loop (Phe200 and Tyr205) residues as the crucial amino acids in effective binding, an essential feature, being hydrogen bond or ionic interaction with Glu155 residue...
August 8, 2018: International Journal of Biological Macromolecules
Martijn Constantijn de Koning, Gabriele Horn, Franz Worek, Marco van Grol
Organophosphorous (OP) compounds (such as nerve agents) inhibit the enzyme acetylcholinesterase (AChE) by covalent phosphylation of a key serine residue in the active site of the enzyme resulting in severe symptoms and ultimately death. OP intoxications are currently treated by administration of certain oxime compounds. The presently fielded oximes reactivate OP-inhibited AChE by liberating the phosphylated serine. Recent research towards new reactivators was predominantly devoted to design, synthesis and evaluation of new oxime-based compounds dedicated to overcoming some of the major limitations such as their intrinsic toxicity, their permanent charge which thwarts penetration of brain tissues and their inability to effectively reactivate all types of nerve agent inhibited AChEs...
August 6, 2018: European Journal of Medicinal Chemistry
Paula M O' Connor, Eileen F O' Shea, Paul D Cotter, Colin Hill, R Paul Ross
Bactofencin A is a novel class IId bacteriocin, produced by the intestinal isolate Lactobacillus salivarius DPC6502, which has potent activity against medically significant pathogens including Staphylococcus aureus. This bacteriocin is unusual in that it has a highly cationic N terminus and a single disulfide bond between Cys7 and Cys22, resulting in a large C terminal loop. In this study, a library of synthetic bactofencin A variants were screened against the mastitis isolate, S. aureus DPC5246, to identify key residues responsible for activity...
August 7, 2018: Scientific Reports
Axel Newe, Linda Becker
BACKGROUND: The Portable Document Format (PDF) is the standard file format for the communication of biomedical information via the internet and for electronic scholarly publishing. Although PDF allows for the embedding of three-dimensional (3D) objects and although this technology has great potential for the communication of such data, it is not broadly used by the scientific community or by clinicians. OBJECTIVE: The objective of this review was to provide an overview of existing publications that apply 3D PDF technology and the protocols and tools for the creation of model files and 3D PDFs for scholarly purposes to demonstrate the possibilities and the ways to use this technology...
August 7, 2018: JMIR Medical Informatics
Shiyu Zhang, Can Chen, Xiaofei Qin, Qianchen Zhang, Jinhua Liu, Jixin Zhu, Yongqian Gao, Lin Li, Wei Huang
Trypsin, as one of important proteases, is specific for catalyzing the hydrolysis of peptide and ester bonds containing lysine and arginine residues at the C-terminus. The level of trypsin in biological fluids can serve as a reliable and specific diagnostic biomarker for pancreatic function and its pathological changes. Herein, we demonstrate the application of phosphorescent Cu NCs for trypsin detection for the first time depending on the electron transfer between Cu NCs and cyt c. Cyt c and Cu NCs were selected as the quencher and the fluorophore, respectively...
November 1, 2018: Talanta
Taraknath Mandal, Peter H Koenig, Ronald G Larson
Using coarse-grained molecular dynamics simulations and an umbrella sampling method that uses local surfactant density as a reaction coordinate, we directly calculate, for the first time, both the scission and branching free energies of a model charged micelle [cationic cetyltrimethylammonium chloride (CTAC)] in the presence of inorganic and organic salts (hydrotropes). We find that while inorganic salt only weakly affects the micelle scission energy, organic hydrotropes produce a strong, nonmonotonic dependence of both scission energy and branching on salt concentration...
July 20, 2018: Physical Review Letters
Zhaohui Ren, Mengjiao Wu, Xing Chen, Wei Li, Ming Li, Fang Wang, He Tian, Junze Chen, Yanwu Xie, Jiangquan Mai, Xiang Li, Xinhui Lu, Yunhao Lu, Hua Zhang, Gustaaf Van Tendeloo, Ze Zhang, Gaorong Han
Oxide heterostructure interfaces create a platform to induce intriguing electric and magnetic functionalities for possible future devices. A general approach to control growth and interface structure of oxide heterostructures will offer a great opportunity for understanding and manipulating the functionalities. Here, it is reported that an electrostatic force, originating from a polar ferroelectric surface, can be used to drive oxide heteroepitaxy, giving rise to an atomically sharp and coherent interface by using a low-temperature solution method...
August 6, 2018: Advanced Materials
Jesse G McDaniel, Arun Yethiraj
The liquid structure and electrical screening ability of ionic liquids are fundamentally intertwined. The molecular nature of the charge carriers means that screening distances of external fields depend sensitively on the ion packing and structure of the ionic liquid. In this work, we quantitatively illustrate how the liquid structure itself is directly modulated by electrostatic screening conditions. In particular, electronic polarization fundamentally relaxes long-range ion structuring in asymmetric ionic liquids such as [BMIM+ ][BF4 - ], with the influence propagating to short-range ion-ion correlation...
August 7, 2018: Journal of Physical Chemistry Letters
Sara Delilovic, Asli Kulane, Nina Åsbring, Anneli Marttila, Knut Lönnroth
BACKGROUND: In Sweden asylum seekers are offered a voluntary health examination, free-of-charge (HE). The HE coverage is low. The organization and implementation of the HE involves collaboration between different agencies with different roles within the provision of health information and service. This study aimed to assess their perspectives on the barriers and facilitators regarding implementation of the HE, as well as on the purpose, content and value of the HE. METHOD: Thematic analysis of focus groups, individual and group interviews conducted between 2016 and 17 with 41 participants from various authorities and healthcare professionals involved in the delivery of HE in Stockholm...
August 3, 2018: BMC Health Services Research
Gabriel Sánchez-Santolino, Nathan R Lugg, Takehito Seki, Ryo Ishikawa, Scott D Findlay, Yuji Kohno, Yuya Kanitani, Shinji Tanaka, Shigetaka Tomiya, Yuichi Ikuhara, Naoya Shibata
Probing the charge density distributions in materials at atomic scale remains an extremely demanding task, particularly in real space. However, recent advances in differential phase contrast-scanning transmission electron microscopy (DPC-STEM) bring this possibility closer by directly visualizing the atomic electric field. DPC-STEM at atomic resolutions measures how a sub-angstrom electron probe passing through a material is affected by the atomic electric field, the field between the nucleus and the surrounding electrons...
August 3, 2018: ACS Nano
Martine Beaufour, David Ginguené, Rémy Le Meur, Bertrand Castaing, Martine Cadene
Native mass spectrometry (MS) encompasses methods to keep noncovalent interactions of biomolecular complexes intact in the gas phase throughout the instrument and to measure the mass-to-charge ratios of supramolecular complexes directly in the mass spectrometer. Electrospray ionization (ESI) in nondenaturing conditions is now an established method to characterize noncovalent systems. Matrix-assisted laser desorption/ionization (MALDI), on the other hand, consumes low quantities of samples and largely tolerates contaminants, making it a priori attractive for native MS...
July 31, 2018: Journal of the American Society for Mass Spectrometry
Sabine M Neumayer, Anton V Ievlev, Liam Collins, Rama Vasudevan, Mohammad A Baghban, Olga Ovchinnikova, Stephen Jesse, Katia Gallo, Brian J Rodriguez, Sergei V Kalinin
Polarization switching in ferroelectric materials underpins a multitude of applications ranging from nonvolatile memories to data storage to ferroelectric lithography. While traditionally considered to be a functionality of the material only, basic theoretical considerations suggest that switching is expected to be intrinsically linked to changes in the electrochemical state of the surface. Hence, the properties and dynamics of the screening charges can affect or control the switching dynamics. Despite being recognized for over 50 years, analysis of these phenomena remained largely speculative...
August 14, 2018: ACS Applied Materials & Interfaces
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