The Structures of Cellulose

1990 ◽  
Vol 197 ◽  
Author(s):  
Rajai H. Atalla
Keyword(s):  
Material Properties ◽  
Historical Perspective ◽  
Structural Models ◽  
Spectral Information ◽  
Major Influence ◽  
Sensitive Information ◽  
Industrial Practice ◽  
Recent Developments ◽  
C Nmr

ABSTRACTThis report presents an overview of studies on the structures of cellulose. After presenting a brief historical perspective, the report reviews diffractometrically based structural models and then describes recent developments based on models that are consistent with both diffractometric and spectroscopic observations. The primary impetus for development of these models was provided by Raman and 13C NMR (CP-MAS) spectral results that could not be rationalized on the basis of classical structural models, which are constrained by diffractometric data alone. The structures derived from integrating the spectral information into the data base, which constrain the models, represent relatively small but very significant departures from those structures derived on the basis of diffractometry alone. In addition to rationalizing all the structurally sensitive information, the new models provide a basis for complementary use of spectroscopic and diffractometric methods to monitor variations of the states of aggregation of celluloses with source and history. Thus, it is now possible to investigate the effects of different processing variables, which are important in industrial practice, on both secondary and tertiary levels of structure in celluloses. These levels of structure have a major influence on the material properties of commercial celluloses, yet adequate characterization of these levels has been quite elusive.

Neurochemistry of L-Glutamate Transport in the CNS: A Review of Thirty Years of Progress

2001 ◽  
Vol 66 (9) ◽  
pp. 1315-1340 ◽  
Author(s):  
Vladimir J. Balcar ◽  
Akiko Takamoto ◽  
Yukio Yoneda
Keyword(s):  
Molecular Biology ◽  
Glutamate Transport ◽  
Mammalian Brain ◽  
Activity Data ◽  
System A ◽  
Recent Developments ◽  
The Central Nervous System ◽  
Health And Disease ◽  
Disease Analysis

The review highlights the landmark studies leading from the discovery and initial characterization of the Na+-dependent "high affinity" uptake in the mammalian brain to the cloning of individual transporters and the subsequent expansion of the field into the realm of molecular biology. When the data and hypotheses from 1970's are confronted with the recent developments in the field, we can conclude that the suggestions made nearly thirty years ago were essentially correct: the uptake, mediated by an active transport into neurons and glial cells, serves to control the extracellular concentrations of L-glutamate and prevents the neurotoxicity. The modern techniques of molecular biology may have provided additional data on the nature and location of the transporters but the classical neurochemical approach, using structural analogues of glutamate designed as specific inhibitors or substrates for glutamate transport, has been crucial for the investigations of particular roles that glutamate transport might play in health and disease. Analysis of recent structure/activity data presented in this review has yielded a novel insight into the pharmacological characteristics of L-glutamate transport, suggesting existence of additional heterogeneity in the system, beyond that so far discovered by molecular genetics. More compounds that specifically interact with individual glutamate transporters are urgently needed for more detailed investigations of neurochemical characteristics of glutamatergic transport and its integration into the glutamatergic synapses in the central nervous system. A review with 162 references.

scholarly journals Molecular Modeling of Histamine Receptors—Recent Advances in Drug Discovery

Molecules ◽  
2021 ◽  
Vol 26 (6) ◽  
pp. 1778
Author(s):  
Pakhuri Mehta ◽  
Przemysław Miszta ◽  
Sławomir Filipek
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Molecular Modeling ◽  
Molecular Targets ◽  
Histamine Receptors ◽  
Experimental Characterization ◽  
Complex Disorders ◽  
Theoretical Investigations ◽  
Recent Developments

The recent developments of fast reliable docking, virtual screening and other algorithms gave rise to discovery of many novel ligands of histamine receptors that could be used for treatment of allergic inflammatory disorders, central nervous system pathologies, pain, cancer and obesity. Furthermore, the pharmacological profiles of ligands clearly indicate that these receptors may be considered as targets not only for selective but also for multi-target drugs that could be used for treatment of complex disorders such as Alzheimer’s disease. Therefore, analysis of protein-ligand recognition in the binding site of histamine receptors and also other molecular targets has become a valuable tool in drug design toolkit. This review covers the period 2014–2020 in the field of theoretical investigations of histamine receptors mostly based on molecular modeling as well as the experimental characterization of novel ligands of these receptors.

scholarly journals New Insights into the Crystal Chemistry of Elpidite, Na2Zr[Si6O15]·3H2O and (Na1+YCax□1−X−Y)Σ=2Zr[Si6O15]·(3−X)H2O, and Ab Initio Modeling of IR Spectra

Materials ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2160
Author(s):  
Alexander Bogdanov ◽  
Ekaterina Kaneva ◽  
Roman Shendrik
Keyword(s):  
Ir Spectra ◽  
Structural Models ◽  
Chemical Characterization ◽  
Chemical Compositions ◽  
X Ray Diffraction ◽  
Special Group ◽  
X Ray ◽  
Influence Of Water ◽  
Radioactive Species

Elpidite belongs to a special group of microporous zirconosilicates, which are of great interest due to their capability to uptake various molecules and ions, e.g., some radioactive species, in their structural voids. The results of a combined electron probe microanalysis and single-crystal X-ray diffraction study of the crystals of elpidite from Burpala (Russia) and Khan-Bogdo (Mongolia) deposits are reported. Some differences in the chemical compositions are observed and substitution at several structural positions within the structure of the compounds are noted. Based on the obtained results, a detailed crystal–chemical characterization of the elpidites under study was carried out. Three different structure models of elpidite were simulated: Na2ZrSi6O15·3H2O (related to the structure of Russian elpidite), partly Ca-replaced Na1.5Ca0.25ZrSi6O15·2.75H2O (close to elpidite from Mongolia), and a hypothetical CaZrSi6O15·2H2O. The vibration spectra of the models were obtained and compared with the experimental one, taken from the literature. The strong influence of water molecule vibrations on the shape of IR spectra of studied structural models of elpidite is discussed in the paper.

Electrochemical and binding properties of a meso-tetra(4-pyridyl)porphyrinatozinc supermolecule containing four μ3-oxo-triruthenium acetate clusters

2000 ◽  
Vol 04 (08) ◽  
pp. 727-735 ◽  
Author(s):  
SERGIO DOVIDAUSKAS ◽  
KOITI ARAKIA ◽  
HENRIQUE E. TOMA
Keyword(s):  
Equilibrium Constants ◽  
Zinc Ion ◽  
Porphyrin Ring ◽  
Electronic Density ◽  
Axial Coordination ◽  
Spectrophotometric Titrations ◽  
Regular Increase ◽  
Calculated Equilibrium ◽  
C Nmr

The synthesis and characterization of a zinc meso-tetra(4-pyridyl)porphyrin containing four coordinated μ3-oxo-triruthenium acetate cluster complexes, ZnTCP , are reported. The coordination of four ruthenium acetate clusters to the zinc porphyrin has been confirmed by 1 H and 13 C NMR spectroscopy, including COSY and HETCOR bidimensional correlation techniques. Cyclic voltammetry and spectroelectrochemistry studies have revealed the presence of seven redox processes in the −1.5 to 2.5 V range, four of them attributed to cluster-centered ( Ru IV,IV,III/ Ru IV,III,III/ Ru III,III,III/ Ru III,III,II/ Ru III,II,II) and three to porphyrin ring-centered ( ZnP +/ ZnP / ZnP .−/ ZnP 2−) redox reactions. The axial coordination reaction has been monitored by spectrophotometric titrations in dichloromethane and acetonitrile, in the 380–480 nm range, using pyridine, imidazole, water and acetonitrile as ligands. The influence of the peripheral ruthenium complexes on the electronic properties of the porphyrin ring has been assayed by measuring the axial coordination properties of the zinc ion. The calculated equilibrium constants for axial coordination of pyridine and imidazole to ZnTCP in dichloromethane are respectively one and two orders of magnitude higher than for meso-tetraphenylporphyrinatozinc, showing a regular increase as a function of the basicity of the ligands. The results have demonstrated that the Ru (III,III,III) species act as electron-withdrawing groups, decreasing significantly the electronic density on the porphyrin ring.

Les oxazolines-4 précurseurs de sels d'iminium fonctionnels. Ouverture en milieu anhydre de ces hétérocycles par des acides protoniques: obtention de sels d'iminium fonctionnels, étude de leur structure

1979 ◽  
Vol 57 (21) ◽  
pp. 2876-2884 ◽  
Author(s):  
Michel Vaultier ◽  
Gurbachan Mullick ◽  
Robert Carrié
Keyword(s):  
Hydrogen Atom ◽  
Room Temperature ◽  
Iminium Salts ◽  
C Nmr

The protonation of 4-oxazolines with protic acids in anhydrous medium, both at low or at room temperature, generally leads to acyclic functional iminium salts. In those cases where the oxazoline ring bears a hydrogen atom in the four position, two diastereoisomeric cyclic iminium salts are obtained. The conditions for preparation of these salts along with the characterization of their structures were determined by the aid of 1H and 13C nmr.

Influence of Post-Treatment with Methanol Vapor on the Properties of SF/P(LLA-CL) Nanofibrous Scaffolds

2011 ◽  
Vol 236-238 ◽  
pp. 2221-2224
Author(s):  
Kui Hua Zhang ◽  
Xiu Mei Mo
Keyword(s):  
Electrospun Nanofibers ◽  
Random Coil ◽  
Methanol Vapor ◽  
Nanofibrous Scaffolds ◽  
Nanofibrous Structure ◽  
Α Helix ◽  
Β Sheet ◽  
Ideal Method ◽  
C Nmr

In order to improve water-resistant ability silk fibroin (SF) and SF/P(LLA-CL) blended nanofibrous scaffolds for tissue engineering applications, methanol vapor were used to treat electrospun nanofibers. SEM indicated SF and SF/ P(LLA-CL) scaffolds maintained nanofibrous structure after treated with methanol vapor and possessed good water-resistant ability. Characterization of 13C NMR clarified methanol vapor induced SF conformation from random coil or α- helix to β-sheet. Moreover, treated SF/ P (LLA-CL) nanofibrous scaffolds still kept good mechanical properties. Methanol vapor could be ideal method to treat SF and SF/ P(LLA-CL) nanofibrous scaffolds for biomedical applications.

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