Does double electron capture lead to the formation of biradicals? An ECD-SORI-CID study on lacticin 481

We studied lacticin 481, a small lantibiotic with three lanthionine bridges, by electron capture dissociation (ECD) in a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. Following electron capture, very little fragmentation was observed, but species formed by nondissociative single and multiple electron capture were abundant. Ions formed by double electron capture were subjected to sustained off resonance irradiation collision induced dissociation (SORI-CID) to determine whether stable biradicals were formed. In the SORI-CID spectra of the ions formed by double electron capture, some, but minor, H* radical loss was observed, which was not observed at all for regularly protonated ions. A small part of the ions formed by double electron capture are thus long-lived biradicals. Apart from the observed H* loss, the SORI-CID spectra of ions that captured two electrons was similar to that of regularly protonated ions and quite different from the SORI-CID spectra of radical ions formed by single electron capture. This implies that recombination of the two radical sites is the dominant process in biradical lacticin 481 ions, at least on the time scale of our SORI-CID experiments.     

Why nature chose Mn for the water oxidase in Photosystem II

Nature performs a vital but uniquely energetic reaction within Photosystem II (PS II), resulting in the oxidation of two water molecules to yield O(2) and bio-energetic electrons, as reducing equivalents. Almost all life on earth ultimately depends on this chemistry, which occurs with remarkable efficiency within a tetramanganese and calcium cluster in the photosystem. The thermodynamic constraints for the operation of this water oxidising Mn(4)/Ca cluster within PS II are discussed. These are then examined in the light of the known redox chemistry of hydrated Mn-oxo systems and relevant model compounds. It is shown that the latest high resolution crystal structure of cyanobacterial PS II suggests an organization of the tetra-nuclear Mn cluster that naturally accommodates the stringent requirements for successive redox potential constancy with increasing total oxidation state, which the enzyme function imposes. This involves one region of the Mn(4)/Ca cluster being dominantly involved with substrate water binding, while a separate, single Mn is principally responsible for the redox accumulation function. Recent high level computational chemical investigations by the authors strongly support this, with a computed pattern of Mn oxidation states throughout the catalytic cycle being completely consistent with this interpretation. Strategies to design synthetic, bio-mimetic constructs utilising this approach for efficient electrolytic generation of hydrogen fuel within Artificial Photosynthesis are briefly discussed.     

Advanced Mass Calibration and Visualization for FT-ICR Mass Spectrometry Imaging

Mass spectrometry imaging by Fourier transform ion cyclotron resonance (FT-ICR) yields hundreds of unique peaks, many of which cannot be resolved by lower performance mass spectrometers. The high mass accuracy and high mass resolving power allow confident identification of small molecules and lipids directly from biological tissue sections. Here, calibration strategies for FT-ICR MS imaging were investigated. Sub-parts-per-million mass accuracy is demonstrated over an entire tissue section. Ion abundance fluctuations are corrected by addition of total and relative ion abundances for a root-mean-square error of 0.158?ppm on 16,764 peaks. A new approach for visualization of FT-ICR MS imaging data at high resolution is presented. The ??Mosaic Datacube?? provides a flexible means to visualize the entire mass range at a mass spectral bin width of 0.001?Da. The high resolution Mosaic Datacube resolves spectral features not visible at lower bin widths, while retaining the high mass accuracy from the calibration methods discussed.     

A performance study of radio-opaque personal protective fabrics for the reduction of transmittance of gamma-rays and neutrons

Commercial radio-opaque combat (CRC) fabrics, for incorporation into personal protective equipment used by first responders and armed forces, are marketed as having the ability to provide a level of protection against specific types of radiation. For a CRC material, a standard combat uniform and a multi-layered chemical, biological, radiological, nuclear (CBRN) protective material, the present work examines chemical composition and radiation protection against gamma-rays and neutron fluxes. Significant reduction in gamma-ray transmittance occurs only for the CRC fabric (46–514 keV) with gamma-ray attenuation coefficients of 3.10 to <0.10 cm² g⁻¹. Reduction in neutron transmittance, for all three fabrics, could not be assessed with certainty as the measured transmittance was obscured by large statistical uncertainties.     

An empirical model predicting the viscosity of highly concentrated, bimodal dispersions with colloidal interactions

The relationship between particle size distribution and viscosity of concentrated dispersions is of great industrial importance, since it is the key to get high solids dispersions or suspensions. The problem is treated here experimentally as well as theoretically for the special case of strongly interacting colloidal particles. An empirical model based on a generalized Quemada equation is used to describe η as a function of volume fraction for mono- as well as multimodal dispersions. The pre-factor η˜ accounts for the shear rate dependence of η and does not affect the shape of the η vs φ curves. It is shown here for the first time that colloidal interactions do not show up in the maximum packing parameter and φ_max can be calculated from the particle size distribution without further knowledge of the interactions among the suspended particles. On the other hand, the exponent ɛ is controlled by the interactions among the particles. Starting from a limiting value of 2 for non-interacting either colloidal or non-colloidal particles, ɛ generally increases strongly with decreasing particle size. For a given particle system it then can be expressed as a function of the number average particle diameter. As a consequence, the viscosity of bimodal dispersions varies not only with the size ratio of large to small particles, but also depends on the absolute particle size going through a minimum as the size ratio increases. Furthermore, the well-known viscosity minimum for bimodal dispersions with volumetric mixing ratios of around 30/70 of small to large particles is shown to vanish if colloidal interactions contribute significantly. Received: 7 June 2000/Accepted: 12 February 2001     

A peptide-derived strategy for specifically targeting the mitochondria and ER of cancer cells: a new approach in fighting cancer

An effective anti-cancer therapy should exclusively target cancer cells and trigger in them a broad spectrum of cell death pathways that will prevent avoidance. Here, we present a new approach in cancer therapy that specifically targets the mitochondria and ER of cancer cells. We developed a peptide derived from the flexible and transmembrane domains of the human protein NAF-1/CISD2. This peptide (NAF-1^44-67) specifically permeates through the plasma membranes of human epithelial breast cancer cells, abolishes their mitochondria and ER, and triggers cell death with characteristics of apoptosis, ferroptosis and necroptosis. In vivo analysis revealed that the peptide significantly decreases tumor growth in mice carrying xenograft human tumors. Computational simulations of cancer vs. normal cell membranes reveal that the specificity of the peptide to cancer cells is due to its selective recognition of their membrane composition. NAF-1^44-67 represents a promising anti-cancer lead compound that acts via a unique mechanism.

An effective anti-cancer therapy should exclusively target cancer cells and trigger in them a broad spectrum of cell death pathways that will prevent avoidance.     

Development of a 9-borabicyclo[3.3.1]nonane-mediated solid-phase Suzuki coupling for the preparation of dihydrostilbene analogs

A novel 9-borabicyclo[3.3.1]nonane-mediated solid-phase Suzuki coupling was developed to generate dihydrostilbenes (bibenzyls) and related compounds. Using optimized conditions (20 mol% PdCl₂(dppf), 10 equiv. Et₃N, and 10 equiv. olefin/9-BBN, in 9:1 DMF/H₂O, 50°C, 18 h), high conversions to desired products were generally obtained. A small combinatorial library of derivatives was successfully prepared via radiofrequency tagging and directed sorting techniques.     

利用对称位移脉冲改善分辨率-IMPRESS HMBC

众所周知异核二维实验在中、小分子的结构确定中非常重要. 例如¹H与¹³C/¹⁵N异核远程相关无疑是连接分子中孤立结构碎片及季碳的最有利的工具. 然而，在间接检测的异核二维实验中，间接检测域-异核维的太低分辨率一直是困扰着化学家的主要问题. 过去在有限的采样时间内提高分辨率的方法主要有线性预测、带选择脉冲和控制好的折叠3种方法. 文中介绍一种最新开发出的利用Hadamard激发雕刻的方法. 借助Varian核磁共振系统的高品质射频系统和灵活的软件工具, 用户可以方便的实施新的激发雕 刻方案，极大地改善gHMBC实验的F₁分辨率.