scholarly journals Structures of furanosides: geometrical analysis of low-temperature X-ray and neutron crystal structures of five crystalline methyl pentofuranosides

2001 ◽  
Vol 57 (2) ◽  
pp. 213-220 ◽  
Author(s):  
Artem Evdokimov ◽  
A. Joseph Gilboa ◽  
Thomas F. Koetzle ◽  
Wim T. Klooster ◽  
Arthur J. Schultz ◽  
...  
Keyword(s):  
Hydrogen Bonding ◽  
Crystal Structures ◽  
Critical Role ◽  
Chair Conformation ◽  
Geometrical Analysis ◽  
X Ray ◽  
Wide Range ◽  
First Time ◽  
Ring Conformations

Crystal structures of all five crystalline methyl D-pentofuranosides, methyl α-D-arabinofuranoside (1), methyl β-D-arabinofuranoside (2), methyl α-D-lyxofuranoside (3), methyl β-D-ribofuranoside (4) and methyl α-D-xylofuranoside (5) have been determined by means of cryogenic X-ray and neutron crystallography. The neutron diffraction experiments provide accurate, unbiased H-atom positions which are especially important because of the critical role of hydrogen bonding in these systems. This paper summarizes the geometrical and conformational parameters of the structures of all five crystalline methyl pentofuranosides, several of them reported here for the first time. The methyl pentofuranoside structures are compared with the structures of the five crystalline methyl hexopyranosides for which accurate X-ray and neutron structures have been determined. Unlike the methyl hexopyranosides, which crystallize exclusively in the C 1 chair conformation, the five crystalline methyl pentofuranosides represent a very wide range of ring conformations.

scholarly journals The molecular and crystal structures of 4-N-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-l-asparagine trihydrate and 4-N-(β-d-glucopyranosyl)-l-asparagine monohydrate. The X-ray analysis of a carbohydrate–peptide linkage

1974 ◽  
Vol 143 (1) ◽  
pp. 197-205 ◽  
Author(s):  
L. T. J. Delbaere
Keyword(s):  
Hydrogen Bonding ◽  
Crystal Structures ◽  
Torsion Angle ◽  
Chair Conformation ◽  
Amide Group ◽  
British Library ◽  
X Ray ◽  
Peptide Linkage ◽  
Lending Library ◽  
The Mean

X-ray analyses have shown that the glucopyranose rings of GlcNAc-Asn [4-N-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-l-asparagine] and Glc-Asn [4-N-(β-d-glucopyranosyl)-l-asparagine] both have the C-1 chair conformation and also that the glucose–asparagine linkage of each molecule is present in the β-anomeric configuration. The dimensions (the estimated standard deviations of the last digit are in parentheses) of the glycosidic bond in GlcNAc-Asn and Glc-Asn are, respectively, C(1)-N(1) 0.1441(6)nm, 0.146(2)nm; angle O(5)-C(1)-N(1) 106.8(3)°, 105.7(8)° angle C(2)-C(1)-N(1) 111.1(4)°, 110.4(9)° angle C(1)-N(1)-C(9) 121.4(4)°, 120.5(9)°. The glycosidic torsion angle C(9)-N(1)-C(1)-C(2) is 141.0° and 157.6° in GlcNAc-Asn and Glc-Asn respectively. Hydrogen-bonding is extensive in these two crystal structures and does affect one torsion angle in particular. Two very different values of χ1(N-Cα-Cβ-Cγ) occur for the asparagine residue of the two different molecules; the values of χ1, −69.0° in GlcNAc-Asn and 61.9° in Glc-Asn, correspond to two different staggered conformations about the Cα-Cβbond as the NH3+group is adjusted to different hydrogen-bonding patterns. The two trans-peptide groups in GlcNAc-Asn show small distortions in planarity whereas that in Glc-Asn is more non-planar. The mean plane through the atoms of the amide group at C(2) in GlcNAc-Asn is approximately perpendicular (69°) to the mean plane through the C(2), C(3), C(5) and O(5) atoms of the glucose ring and that at C(1) is less perpendicular (65°). The mean plane through the atoms of the amide group in Glc-Asn makes an angle of only 55° with the mean plane through these same four atoms of the glucose ring. The N(1)-H bond of the amide at C(1) is trans to the C(1)-H bond in these two compounds; the N(2)-H bond of the amide at C(2) is trans to the C(2)-H bond in GlcNAc-Asn. The values of the observed and final calculated structure amplitudes have been deposited as Supplementary Publication SUP 50035 (26 pages) at the British Library (Lending Division), (formerly the National Lending Library for Science and Technology), Boston Spa, Yorks. LS23 7BQ, U.K., from whom copies may be obtained on the terms given in Biochem. J. (1973) 131, 5.

scholarly journals Mechanochemical Synthesis and Structure of the Tetrahydrate and Mesoporous Anhydrous Metforminium(2+)-N,N’-1,4-Phenylenedioxalamic Acid Cocrystal Salt: The Role of Hydrogen Bonding and N→π* Charge Assisted Interactions

2020 ◽  
Author(s):  
Sayuri Chong-Canto ◽  
Efrén V. García-Báez ◽  
Francisco J. Martínez-Martínez ◽  
Ángel Ramos-Organillo ◽  
Itzia I. Padilla-Martínez
Keyword(s):  
Hydrogen Bonding ◽  
Mechanochemical Synthesis ◽  
Water Molecules ◽  
X Ray ◽  
X Ray Crystallography ◽  
Adsorption Desorption ◽  
First Time ◽  
Selective Formation ◽  
Crystallization From Solution

A new cocrystal salt of metformin, an antidiabetic drug, and N,N’-(1,4-phenylene)dioxalamic acid, was synthesized by mechanochemical synthesis, purified by crystallization from solution and characterized by single X-ray crystallography. The structure revealed a salt-type cocrystal composed of one dicationic metformin unit, two monoanionic units of the acid and four water molecules namely H2Mf(HpOXA)2∙4H2O. X-ray powder, IR, 13C-CPMAS, thermal and BET adsorption-desorption analyses were performed to elucidate the structure of the molecular and supramolecurar structure of the anhydrous microcrystalline mesoporous solid H2Mf(HpOXA)2. The results suggest that their structures, conformation and hydrogen bonding schemes are very similar between them. To the best of our knowledge, the selective formation of the monoanion HpOXA⁻, as well as its structure in the solid, is herein reported for the first time. Regular O(-)∙∙∙C(), O(-)∙∙∙N+ and bifacial O(-)∙∙∙C()∙∙∙O(-) of n→* charge-assisted interactions are herein described in H2MfA cocrystal salts which could be responsible of the interactions of metformin in biologic systems. The results, support the participation of n→* charge-assisted interactions independently, and not just as a short contact imposed by the geometric constraint due to the hydrogen bonding patterns.

scholarly journals Mechanochemical Synthesis and Structure of the Tetrahydrate and Mesoporous Anhydrous Metforminium(2+)-N,N′-1,4-Phenylenedioxalamic Acid (1:2) Salt: The Role of Hydrogen Bonding and n→π * Charge Assisted Interactions

Pharmaceutics ◽  
2020 ◽  
Vol 12 (10) ◽  
pp. 998 ◽  
Author(s):  
Sayuri Chong-Canto ◽  
Efrén V. García-Báez ◽  
Francisco J. Martínez-Martínez ◽  
Angel A. Ramos-Organillo ◽  
Itzia I. Padilla-Martínez
Keyword(s):  
Hydrogen Bonding ◽  
Organic Salt ◽  
Organic Salts ◽  
X Ray ◽  
X Ray Crystallography ◽  
Adsorption Desorption ◽  
First Time ◽  
Selective Formation ◽  
Crystallization From Solution

A new organic salt of metformin, an antidiabetic drug, and N,N′-(1,4-phenylene)dioxalamic acid, was mechanochemically synthesized, purified by crystallization from solution and characterized by single X-ray crystallography. The structure revealed a salt-type crystal hydrate composed of one dicationic metformin unit, two monoanionic units of the acid and four water molecules, namely H2Mf(HpOXA)2∙4H2O. X-ray powder, IR, 13C-CPMAS, thermal and BET adsorption–desorption analyses were performed to elucidate the structure of the molecular and supramolecular structure of the anhydrous microcrystalline mesoporous solid H2Mf(HpOXA)2. The results suggest that their structures, conformation and hydrogen bonding schemes are very similar. To the best of our knowledge, the selective formation of the monoanion HpOXA−, as well as its structure in the solid, is herein reported for the first time. Regular O(δ−)∙∙∙C(δ), O(δ−)∙∙∙N+ and bifacial O(δ−)∙∙∙C(δ)∙∙∙O(δ−) of n→π * charge-assisted interactions are herein described in H2MfA organic salts which could be responsible of the interactions of metformin in biologic systems. The results support the participation of n→π * charge-assisted interactions independently, and not just as a short contact imposed by the geometric constraint due to the hydrogen bonding patterns.

scholarly journals The crystal structures and mechanical properties of the uranyl carbonate minerals roubaultite, fontanite, sharpite, widenmannite, grimselite and čejkaite

2020 ◽  
Vol 7 (21) ◽  
pp. 4197-4221 ◽  
Author(s):  
Francisco Colmenero ◽  
Jakub Plášil ◽  
Jiří Sejkora
Keyword(s):  
Mechanical Properties ◽  
Hydrogen Bonding ◽  
Diffraction Pattern ◽  
Crystal Structures ◽  
First Principles ◽  
X Ray Diffraction ◽  
Carbonate Minerals ◽  
X Ray ◽  
Uranyl Carbonate

The structure, hydrogen bonding, X-ray diffraction pattern and mechanical properties of six important uranyl carbonate minerals, roubaultite, fontanite, sharpite, widenmannite, grimselite and čejkaite, are determined using first principles methods.

Bis(1-phenyl-1-propyne) complexes of tungsten(II): crystal structures of [WI2(CO)(NCR)(η2-MeC2Ph)2] (R = Me, Et, or Ph)

2001 ◽  
Vol 79 (3) ◽  
pp. 263-271
Author(s):  
Paul K Baker ◽  
Michael GB Drew ◽  
Deborah S Evans
Keyword(s):  
Carbon Monoxide ◽  
Solid State ◽  
Crystal Structures ◽  
Octahedral Geometry ◽  
X Ray ◽  
X Ray Crystallography ◽  
Alkyne Complexes ◽  
First Time

Reaction of [WI2(CO)3(NCMe)2] with two equivalents of 1-phenyl-1-propyne (MeC2Ph) in CH2Cl2, and in the absence of light, gave the bis(1-phenyl-1-propyne) complex [WI2(CO)(NCMe)(η2-MeC2Ph)2] (1) in 77% yield. Treatment of equimolar quantities of 1 and NCR (R = Et, i-Pr, t-Bu, Ph) in CH2Cl2 afforded the nitrile-exchanged products, [WI2(CO)(NCR)(η2-MeC2Ph)2] (2-5) (R = Et (2), i-Pr (3), t-Bu (4), Ph (5)). Complexes 1, 2, and 5 were structurally characterized by X-ray crystallography. All three structures have the same pseudo-octahedral geometry, with the equatorial sites being occupied by cis and parallel alkyne groups, which are trans to the cis-iodo groups. The trans carbon monoxide and acetonitrile ligands occupy the axial sites. In structures 1 and 2, the methyl and phenyl substituents of the 1-phenyl-1-propyne ligands are cis to each other, whereas for the bulkier NCPh complex (5), the methyl and phenyl groups are trans to one another. This is the first time that this arrangement has been observed in the solid state in bis(alkyne) complexes of this type.Key words: bis(1-phenyl-1-propyne), carbonyl, nitrile, diiodo, tungsten(II), crystal structures.

scholarly journals Development of cancer metabolism as a therapeutic target: new pathways, patient studies, stratification and combination therapy

2019 ◽  
Vol 122 (1) ◽  
pp. 1-3 ◽  
Author(s):  
Adrian L. Harris
Keyword(s):  
Metabolic Pathways ◽  
Trial Design ◽  
Cancer Metabolism ◽  
Aerobic Glycolysis ◽  
Critical Role ◽  
Therapeutic Approaches ◽  
Preclinical Models ◽  
Wide Range ◽  
Patient Studies

AbstractCancer metabolism has undergone a resurgence in the last decade, 70 years after Warburg described aerobic glycolysis as a feature of cancer cells. A wide range of techniques have elucidated the complexity and heterogeneity in preclinical models and clinical studies. What emerges are the large differences between tissues, tumour types and intratumour heterogeneity. However, synergies with inhibition of metabolic pathways have been found for many drugs and therapeutic approaches, and a critical role of window studies and translational trial design is key to success.

Wildlife management and the debate on the ethics of animal use. II. A challenge for the animal protection movement.

2012 ◽  
Vol 18 (2) ◽  
pp. 81 ◽  
Author(s):  
Daniel Lunney
Keyword(s):  
Wildlife Management ◽  
Critical Role ◽  
Animal Liberation ◽  
Ethical Imperative ◽  
Animal Protection ◽  
Wide Range ◽  
Animal Use

How people coexist and interact with animals has become an intensely debated issue in recent times, particularly with the rise of the animal protection movement following the publication of Peter Singer’s book Animal Liberation in 1975. This paper discusses some shortcomings of the philosophical positions taken in this complex debate. Singer has helped put animals on a new footing as a group that cannot morally be ignored, but his focus is mainly on individual, familiar animals that are used or abused by humans. The argument of this paper is that the ethics of managing wildlife hinges on a broader view of animals, and their contexts, than is apparent from Singer’s text. Wildlife managers aim to conserve populations of a wide range of species, and their habitats, but some mechanisms for achieving these aims, such as research and the control of invasive animals, are frequently opposed by elements of the animal protection movement. We need to adapt our attitude to animals, particularly wildlife, away from the traditional legacy of a few familiar species to embrace an ethic that is more ecological and relevant to Australian contexts. The case argued here has been to see the critical role of context — geographical, ecological, historical, relational — as a basis for a degree of reconciliation between conservation-oriented wildlife managers and the rising interest in the ethics of animal use. There is much to be gained for zoologists, wildlife managers and conservation biologists by framing key elements of their case in ethical arguments. Conversely, the challenge for those in the animal protection movement is to expand their philosophical ideas to include the ethical imperative of the conservation of populations of wildlife.

scholarly journals A Critical Role of Ser26 Hydrogen Bonding in Aβ42 Assembly and Toxicity

Biochemistry ◽  
2017 ◽  
Vol 56 (48) ◽  
pp. 6321-6324 ◽  
Author(s):  
Robin Roychaudhuri ◽  
Tien-Phat V. Huynh ◽  
Taylor R. Whitaker ◽  
Elisabeth Hodara ◽  
Margaret M. Condron ◽  
...  
Keyword(s):  
Hydrogen Bonding ◽  
Critical Role

The BaAl4 Structure and its Derivatives from the R-Zn-Ga Systems

2012 ◽  
Vol 194 ◽  
pp. 5-9 ◽  
Author(s):  
Yuriy Verbovytskyy ◽  
Antonio Pereira Gonçalves
Keyword(s):  
Crystal Structures ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Powder Diffraction Data ◽  
Space Group ◽  
X Ray ◽  
First Time

Seven new ternary RZn1+xGa3-x (R = Ce, Pr, Nd, Sm, Ho and Er) and R5Zn2Ga17 (R = Ce) phases are synthesized for the first time. Their crystal structures are solved on basis of X-ray powder diffraction data. The above mentioned compounds belong to the BaAl4 (space group I4/mmm) and Rb5Hg19 (space group I4/m) structure types. Details of the structure of the Ce5Zn2Ga17 compound and relationship with RZn2-xGa2+x (BaAl4 type) and R3Zn8-xGa3+x (La3Al11 type) are briefly discussed.

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