74 research outputs found

    Magnetic structure and charge ordering in Fe3BO5 ludwigite

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    The crystal and magnetic structures of the three-leg ladder compound Fe3BO5 have been investigated by single crystal x-ray diffraction and neutron powder diffraction. Fe3BO5 contains two types of three-leg spin ladders. It shows a charge ordering transition at 283 K, an antiferromagnetic transition at 112 K, ferromagnetism below 70 K and a weak ferromagnetic behavior below 40K. The x-ray data reveal a smooth charge ordering and an incomplete charge localization down to 110K. Below the first magnetic transition, the first type of ladders orders as ferromagnetically coupled antiferromagnetic chains, while below 70K the second type of ladders orders as antiferromagnetically coupled ferromagnetic chains

    Wnt signaling: Moving in a new direction

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    Evidence supporting the postulated role of a Wnt ligand in the establishment of planar cell polarity has been elusive, but recent studies show that the movement of epithelial cells during vertebrate gastrulation or Drosophila dorsal closure depends on both a Wnt ligand and the planar cell polarity pathway

    Approaches to Pharmaceutical Analysis of Modern Peptide and Oligonucleotide Products as Illustrated by a Small Interfering RNA-Based Novel Therapeutic for the Treatment of Bronchial Asthma

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    Methods used to control the quality of peptide products depend on the level of development of analytical and bioorganic chemistry, and the level of instrumentation. Peptide identification is a difficult task and largely depends on the complexity of its structure. There does not exist a comprehensive and simple test, except for NMR, which, however, is rather expensive and time-consuming and involves complex data interpretations. Moreover, it does not allow for unambiguous determination of the peptide purity and formula (amino acid composition, sequence, chirality of amino acid residues). For this reason, a combination of methods is often used, including amino acid analysis, TLC/HPLC and mass spectrometry, and, less frequently, sequencing. Current international practice of peptide analysis is to use HPLC in combination with mass spectrometric, mainly tandem (HPLC-MS/MS), detection. According to literature sources the amino acid sequence of linear peptides can be analysed using various enzymes and subsequent identification of proteolysis products by mass spectrometry. This article presents approaches to the development of test methods for analysis of purity and identification testing of a small interfering RNA-based novel medicinal product, which will help standardise and control the quality of the production process

    Подходы к фармацевтическому анализу современных пептидных и олигонуклеотидных препаратов на примере инновационного препарата на основе малой интерферирующей РНК для лечения бронхиальной астмы

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    Methods used to control the quality of peptide products depend on the level of development of analytical and bioorganic chemistry, and the level of instrumentation. Peptide identification is a difficult task and largely depends on the complexity of its structure. There does not exist a comprehensive and simple test, except for NMR, which, however, is rather expensive and time-consuming and involves complex data interpretations. Moreover, it does not allow for unambiguous determination of the peptide purity and formula (amino acid composition, sequence, chirality of amino acid residues). For this reason, a combination of methods is often used, including amino acid analysis, TLC/HPLC and mass spectrometry, and, less frequently, sequencing. Current international practice of peptide analysis is to use HPLC in combination with mass spectrometric, mainly tandem (HPLC-MS/MS), detection. According to literature sources the amino acid sequence of linear peptides can be analysed using various enzymes and subsequent identification of proteolysis products by mass spectrometry. This article presents approaches to the development of test methods for analysis of purity and identification testing of a small interfering RNA-based novel medicinal product, which will help standardise and control the quality of the production process.Используемые методы для контроля качества лекарственных средств пептидной природы зависят от уровня развития аналитической и биоорганической химии и развития приборной базы. Анализ подлинности пептида представляет собой непростую задачу и во многом зависит от сложности его структуры. Не существует однозначного и достаточно простого теста, за исключением ЯМР, который, однако, является дорогостоящим и длительным методом со сложной интерпретацией данных. Причем этот метод не позволяет однозначно установить чистоту и формулу пептида (аминокислотный состав, последовательность, хиральность аминокислотных остатков). По этой причине нередко используется комбинация методов, включая аминокислотный анализ, ТСХ/ВЭЖХ и масс-спектрометрию и, более редко, секвенирование. В мировой практике для исследования пептидов наиболее распространен метод ВЭЖХ в сочетании с масс-спектрометрическим, преимущественно тандемным (ВЭЖХ-МС/МС) детектированием. Для установления аминокислотной последовательности линейных пептидов описано применение различных ферментов с последующей идентификацией продуктов протеолиза масс-спектрометрически. В данной статье представлены подходы к разработке методик определения подлинности и чистоты инновационного лекарственного препарата пептидной природы на основе малой интерферирующей РНК с целью стандартизации и контроля качества на производстве

    Comparative electronic band structure study of the intrachain ferromagnetic versus antiferromagnetic coupling in the magnetic oxides Ca3Co2O6 and Ca3FeRhO6

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    In the (MM'O6) chains of the transition-metal magnetic oxides Ca3MM'O6 the MO6 trigonal prisms alternate with the M'O6 octahedra by sharing their triangular faces. In the (Co2O6) chains of Ca3Co2O6 (M = M' = Co) the spins are coupled ferromagnetically, but in the (FeRhO6) chains of Ca3FeRhO6 (M = Fe, M' = Rh) they are coupled antiferromagnetically. The origin of this difference was probed by carrying out spin-polarized density functional theory electronic band structure calculations for ordered spin states of Ca3Co2O6 and Ca3FeRhO6. The spin state of a (MM'O6) chain determines the occurrence of direct metal-metal bonding between the adjacent trigonal prism and octahedral site transition-metal atoms. The extent of direct metal-metal bonding in the (Co2O6) chains of Ca3Co2O6 is stronger in the intrachain ferromagnetic state than in the intrachain antiferromagnetic state, so that the intrachain ferromagnetic state becomes more stable than the intrachain antiferromagnetic state. Such a metal-metal-bonding-induced ferromagnetism is expected to occur in magnetic insulators and magnetic metals of transition-metal elements in which direct metal-metal bonding can be enhanced by ferromagnetic ordering. In the (FeRhO6) chains of Ca3FeRhO6 the ferromagnetic coupling does not lead to a strong metal-metal bonding and the adjacent spins interact by the Fe-O···O-Fe super-superexchange, hence leading to an antiferromagnetic coupling

    Spin Exchanges between Transition Metal Ions Governed by the Ligand p-Orbitals in Their Magnetic Orbitals

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    In this review on spin exchanges, written to provide guidelines useful for finding the spin lattice relevant for any given magnetic solid, we discuss how the values of spin exchanges in transition metal magnetic compounds are quantitatively determined from electronic structure calculations, which electronic factors control whether a spin exchange is antiferromagnetic or ferromagnetic, and how these factors are related to the geometrical parameters of the spin exchange path. In an extended solid containing transition metal magnetic ions, each metal ion M is surrounded with main-group ligands L to form an MLn polyhedron (typically, n = 3–6), and the unpaired spins of M are represented by the singly-occupied d-states (i.e., the magnetic orbitals) of MLn. Each magnetic orbital has the metal d-orbital combined out-of-phase with the ligand p-orbitals; therefore, the spin exchanges between adjacent metal ions M lead not only to the M–L–M-type exchanges, but also to the M–L…L–M-type exchanges in which the two metal ions do not share a common ligand. The latter can be further modified by d0 cations A such as V5+ and W6+ to bridge the L…L contact generating M–L…A…L–M-type exchanges. We describe several qualitative rules for predicting whether the M–L…L–M and M–L…A…L–M-type exchanges are antiferromagnetic or ferromagnetic by analyzing how the ligand p-orbitals in their magnetic orbitals (the ligand p-orbital tails, for short) are arranged in the exchange paths. Finally, we illustrate how these rules work by analyzing the crystal structures and magnetic properties of four cuprates of current interest: α-CuV2O6, LiCuVO4, (CuCl)LaNb2O7, and Cu3(CO3)2(OH)2
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