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1.
In our previous studies of the crystal structure of native cellulose (cellulose I) by solid-state two-dimensional (2D) 13C–13C INADEQUATE, it was revealed that cellulose Iα contains two kinds of β-d-glucose residues (A and A′) in the unit cell and that cellulose Iβ contains another two kinds of residues (B and B′). In the present study, the sequence of residues A and A′ along the same chains in cellulose Iα and that of residues B and B′ in Iβ were investigated by 2D 13C–13C rotor-synchronized radiofrequency-driven recoupling (RFDR) experiments using, respectively, uniformly 13C6-labeled (U−13C6) bacterial cellulose and the same [U−13C6] cellulose sample after thermal treatment at 260 °C. The RFDR spectra recorded with a short mixing time (1.0 ms) showed dipolar-coupled 13C spin pairs of only the neighboring carbon of the both phases, while those recorded with a longer mixing time (3.0–15 ms) provided correlations between weakly coupled 13C spin pairs as well as strongly coupled 13C spin pairs such as neighboring carbon nuclei. In the RFDR spectrum of the [U−13C6] cellulose recorded with a mixing time of 15 ms, the inter-residue 13C–13C correlation between C4 of residue A and C2 of residue A′ and that between C3 of residue A and C4 of residue A′ were clearly observed. In the case of cellulose Iβ, however, inter-residue 13C–13C correlations between residues B and B′ could not be detected in the series of RFDR spectra recorded with different mixing times of annealed [U−13C6] cellulose. From these findings, that cellulose Iα was revealed to have the –A–A′– repeating units along the cellulose chain. For cellulose Iβ, it was revealed that the respective residues B and B′ are composed of independent chains (–B–B– and –B′–B′– repeating units) and that there are no –B–B′– repeating units in the chain. 相似文献
2.
ROGER H. NEWMAN 《Cellulose (London, England)》1997,4(4):269-279
Solid-state 13C NMR spectroscopy was used to characterize fibrous material cut from the midrib of a fern frond. Signals associated with
cellulose crystallites were separated from those associated with the lignin--hemicellulosic matrix by exploiting differences
in proton rotating-frame relaxation time constants. Heights of signals at 90.2 and 88.5 ppm, assigned to C-4 in cellulose
Iα and Iβ, indicated similar proportions of the two crystalline forms. This observation conflicts with a suggestion that plant celluloses
can be grouped into the two categories of Iα-rich and Iβ-rich.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
Precise determination of d-spacings and compositional ratio of cellulose Iα and Iβ in various native cellulose samples was successfully carried out by synchrotron-radiated X-ray diffraction and time-of-flight
(TOF) neutron diffraction from quasi-powder specimens. X-ray diffraction peaks were separated by the deconvolution method
using six types of profile function: Gaussian, Lorentzian, intermediate Lorentzian, modified Lorentzian, pseudo-Voigt, and
Pearson VII. In terms of R-factors, the pseudo-Voigt function gave the best fit with the observation, and was used for determination
of d-spacings. The numerical results for Valonia cellulose were: dIα (1 0 0) = 0.613 nm; dIβ (1 1 0) = 0.603 nm; dIβ (1 1 0) = 0.535 nm; dIα (0 1 0) = 0.529 nm; Iα content = 0.65. The differences determined between dIα (1 0 0) and dIβ (1 1 0) and between dIβ (1 1 0) and dIα (0 1 0) were similar to those previously reported. Comparison between unresolved peaks for the two types of cellulose samples
revealed a small but definite difference between dIα (1 1 0) and dIβ (2 0 0). The TOF neutron diffractometry using deuterated samples confirmed this difference.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
Michael Santiago Cintrón Glenn P. Johnson Alfred D. French 《Cellulose (London, England)》2011,18(3):505-516
Quantum mechanics (QM) and molecular mechanics (MM) calculations were performed to elucidate Young’s moduli for a series of
cellulose Iβ models. Computations using the second generation empirical force field MM3 with a disaccharide cellulose model, 1,4′-O-dimethyl-β-cellobioside (DMCB), and an analogue, 2,3,6,2′,3′,6′-hexadeoxy-1,4′-O-dimethyl-β-cellobioside (DODMCB), that cannot make hydrogen bonds reveal a considerable contribution of intramolecular hydrogen
bonding to the molecular stiffness of cellulose Iβ; the moduli for DMCB and DODMCB being 85.2 and 37.6 GPa, respectively. QM calculations confirm this contribution with modulus
values of 99.7 GPa for DMCB and 33.0 GPa for DODMCB. However, modulus values for DMCB were considerably lower than values
previously reported for cellulose Iβ. MM calculations with extended cellulose chains (10–40 glucose units) resulted in modulus values, 126.0–147.5 GPa, more akin
to the values reported for cellulose Iβ. Comparison of the cellodecaose model, 1,4′-O-dimethyl-β-cellodecaoside (DMCD), modulus with that of its hydrogen bonding-deficient analogue, 2,3,6,2′,3′,6′-hexadeoxy-1,4′-O-dimethyl-β-cellodecaoside (DODMCD), corroborates the observed stiffness conferred by intramolecular hydrogen bonds; the moduli
for DMCD and DODMCD being 126.0 and 63.3 GPa, respectively. Additional MM3 determinations revealed that modulus values were
not strongly affected by intermolecular hydrogen bonding, with multiple strand models providing values similar to the single
strand models; 87.5 GPa for a 7-strand DMCB model and 129.5 GPa for a 7 strand DMCD model. 相似文献
5.
Malin Bergenstr?hle-Wohlert Lars A. Berglund John W. Brady P. Tomas Larsson Per-Olof Westlund Jakob Wohlert 《Cellulose (London, England)》2012,19(1):1-12
A combined solid-state NMR and Molecular Dynamics simulation study of cellulose in urea aqueous solution and in pure water
was conducted. It was found that the local concentration of urea is significantly enhanced at the cellulose/solution interface.
There, urea molecules interact directly with the cellulose through both hydrogen bonds and favorable dispersion interactions,
which seem to be the driving force behind the aggregation. The CP/MAS 13C spectra was affected by the presence of urea at high concentrations, most notably the signal at 83.4 ppm, which has previously
been assigned to C4 atoms in cellulose chains located at surfaces parallel to the (110) crystallographic plane of the cellulose
Iβ crystal. Also dynamic properties of the cellulose surfaces, probed by spin-lattice relaxation time 13CT
1 measurements of C4 atoms, are affected by the addition of urea. Molecular Dynamics simulations reproduce the trends of the
T
1 measurements and lends new support to the assignment of signals from individual surfaces. That urea in solution is interacting
directly with cellulose may have implications on our understanding of the mechanisms behind cellulose dissolution in alkali/urea
aqueous solutions. 相似文献
6.
Alexis Morales Jochem Struppe Enrique Meléndez 《Journal of inclusion phenomena and macrocyclic chemistry》2008,60(3-4):263-270
The possible inclusion complexes of Cp2NbCl2 into α-, β-, and γ-CD hosts have been investigated. The existence of a true inclusion complex in the solid state was confirmed
by a combination of thermogravimetric analysis, FTIR, PXRD, and 13C CP-MAS NMR spectroscopies. The solid-state results demonstrated that α-cyclodextrin does not form inclusion complexes with
Cp2NbCl2 whereas β- and γ-cyclodextrins do form such complexes. PXRD, NMR, and thermal analysis showed that the organometallic molecules
of Cp2NbCl2OH are included in the cavities of β- and γ-cyclodextrins, possibly adopting a symmetrical conformation in the complex, with
each glucose unit in a similar environment. In solution, 1H NMR experiments suggest that niobocene has a shallow penetration on the β-CD leading to upfield shift on H-3 signal with
a minor perturbation on the H-5 proton while for γ-CD, both H-3 and H-5 are shifted upfield substantially. This suggests that
niobocene penetrates deeper into the γ-CD cavity than in the β-CD cavity, as a result of the cavity size.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
7.
Sandrine Bourgoin-Voillard Emilie-Laure Zins Françoise Fournier Yves Jacquot Carlos Afonso Claude Pèpe Guy Leclercq Jean-Claude Tabet 《Journal of the American Society for Mass Spectrometry》2009,20(12):2318-2333
The affinity of estradiol derivatives for the estrogen receptor (ER) depends strongly on nature and stereochemistry of substituents
in C(11) position of the 17β-estradiol (I). In this work, the stereochemistry effects of the 11α-OH-17β-estradiol (IIIα) and 11β-OH-17β-estradiol (IIIβ) were investigated using CID experiments and gas-phase acidity (ΔHacid∘) determination. The CID experiments showed that the steroids decompose via different pathways involving competitive dissociations
with rate constants depending upon the α/β C(11) stereochemistry. It was shown that the fragmentations of both deprotonated [IIIα-H]− and [IIIβ-H]− epimers were initiated by the deprotonation of the most acidic site, i.e. the phenolic hydroxyl at C(3). This view was confirmed by H/D exchange and double resonance experiments. Furthermore, the ΔHacid∘ of both epimers (IIIα and IIIβ), 17β-estradiol (I), and 17-desoxyestradiol (II) was determined using the extended Cooks’ kinetic method. The resulting values allowed us to classify steroids as a function
of their gas-phase acidity as follows: (IIIβ)≫(II)>(I)>(IIIα). Interestingly, the α/β C(11) stereochemistry appeared to influence strongly the gas-phase acidity. This phenomenon could be explained through stereospecific
proton interaction with π-orbital cloud of A ring, which was confirmed by theoretical calculation. 相似文献
8.
Cellulose was dissolved in lithium chloride/1,3-dimethyl-2-imidazolidinone (LiCl/DMI), and reacted with alkylketene dimers
(AKDs) under non-aqueous and homogeneous conditions to prepare cellulose/AKD β-ketoesters with high degrees of substitution
(DS). Six AKDs synthesized from octanoic, decanoic, dodecanoic, tetradecanoic, hexadecanoic and octadecanoic acids via their
fatty acid chlorides were used in this study. The cellulose/AKD β-ketoesters obtained were gummy solid at room temperature,
and had DS values ranging from 1.9 to 2.9. Cellulose/fatty acid esters with DS 2.5–2.9 were also prepared as references. 13C-NMR spectra of the cellulose/AKD β-ketoesters showed that cellulose carbons and substituent carbons close to cellulose chains
were restricted in motion and behaved like solid in solutions. In contrast, the cellulose/fatty acid esters did not demonstrate
such anomalous 13C-NMR spectra. The unique 13C-NMR patterns are characteristic for the cellulose/AKD β-ketoesters, which have long and branched alkyl substituents in each
anhydroglucose unit. Size-exclusion chromatography furnished with multi-angle laser light scattering (SEC-MALLS) revealed,
on the other hand, that all cellulose/AKD β-ketoesters and cellulose/fatty acid esters prepared had flexible or random-coil
conformations in tetrahydrofuran (THF). There were no clear differences in conformation or stiffness of cellulose chains between
cellulose/AKD β-ketoesters and cellulose/fatty acid esters. 相似文献
9.
Xiao-Xiang Li Jun-Wen Wang Yu-Jing Guo Ling-Hong Kong Jing-Hao Pan 《Journal of inclusion phenomena and macrocyclic chemistry》2007,58(3-4):307-315
In phosphate buffer solution of pH5.4, the interaction of meso-tetrakis(2-thienyl)porphyrin(H2TTP) and Cu-meso-tetrakis(2-thienyl)porphyrin(Cu-TTP) with α-cyclodextrin(α-CD), β-CD, γ-CD, heptakis(2,3,6-tri-O-methyl)-β-CD(TM-β-CD)
has been studied by means of UV-vis, fluorescence and 1HNMR spectroscopy, respectively. The H2TTP and Cu-TTP can form 1:2 inclusion complexes with TM-β-CD and 1:1 inclusion complexes with the other three cyclodextrins.
In this paper, the inclusion constants (K) of H2TTP and Cu-TTP for the formation of the inclusion complexes have been estimated from the changes of absorbance and fluorescence
intensity in phosphate buffer solution. The inclusive capabilities of different kinds of cyclodextrins are compared. The result
shows that the inclusion ability of α-CD with H2TTP and Cu-TTP is the strongest among the three native CDs. The inclusion ability of modified β-CD with H2TTP and Cu-TTP is stronger, compared to the native β-CD, which indicates that the capacity matching plays a crucial role in
the inclusion procedure except for the hydrophobic effect. In addition 1HNMR spectra supports the inclusion conformation of the TM-β-CD-Cu-TTP inclusion complex, indicating the interaction mechanism
of inclusion processes. 相似文献
10.
11.
KEIKO TAKAHASHI HIDEKI YOKOMIZO KATSURO ISHIYAMA MASAHIKO KITSUTA MEGUMI OHASHI 《Journal of inclusion phenomena and macrocyclic chemistry》2006,56(1-2):95-99
Asymmetric reduction of indol-3-pyruvic acid (IPA) with NaBH4 in aqueous solution in the presence of various cyclodextrins (α-, β-, γ-, mono-6-amino-6-deoxy-β- and di-6ABamino-6AB-deoxy-β-cyclodextrin) was investigated. From the NMR and circular dichroism spectral studies, the conformation of the CyD–substrate complexes is suggested; the part of carboxylic group stay in the cavity of α-CyD, whole of IPA in β-CyD, two molecules in a γ-CyD cavity, and IPA(s) is/are on the rim of the cavity of mono-6-amino-6-deoxy-β- and di-6ABamino-6AB-deoxy-β-CyD (AβCyD, DAβCyD) with electrostatic interaction between amino group and carboxylic group. This conformational difference provides in the difference in the optical selectivity of reduction. 相似文献
12.
I. I. Seifullina L. Kh. Minacheva E. A. Chebanenko E. E. Martsinko V. S. Sergienko A. V. Churakov 《Russian Journal of Inorganic Chemistry》2011,56(12):1886-1893
Bis(citrato)hydroxogermanic(IV) acid was obtained for the first time in the complex [H5O2][Ge(H2Cit)(H2.5Cit)(OH)]2 · 2CH3COOH · 2H2O (H4Cit is citric acid). The complex was characterized by chemical analysis, X-ray powder diffraction, TGA, and IR spectroscopy.
Complex I was studied by X-ray crystallography. The crystals are triclinic; a = 10.0651(4) ?, b = 10.1918(4) ?, c = 10.5838(4) ?, α = 85.0110(10)°, β = 85.2170(10)°, γ = 86.7670(10)°, V = 1076.50(7) ?3, Z = 1, space group P[`1]P\bar 1, R1 = 0.0353 for 5709 reflections with I > 2σ(I). Complex I is composed of centrosymmetric dimeric complex anions [Ge2(H2Cit)2(H2.5Cit)2(OH)2]−, dioxonium cations [H5O2]+, and acetic acid and water molecules of crystallization. The coordination polyhedron of the Ge atom is a trigonal bipyramid.
Its equatorial plane comprises two O atoms of the deprotonated alcohol groups of two ligands H2Cit (A) and H2.5Cit (B) and the O atom of the terminal OH group (Ge-O, 1.7585–1.7754 ?; OeqGe(1)Oeq, 116.26°–127.64°). The axial positions are occupied by the carboxy O atom of the deprotonated carboxylate group of the α
branch of ligand A (α-Ge-O(C)(carb), 1.8882(12) ?)) and the carbonyl O atom of the hemiprotonated acetate α branch of ligand
B (α-Ge-O(C) 1.9615(12) ?, O(1)Ge(1)O(8) 170.47(5)°). In structure I, the complex dianion, the cation, and acetic acid and water molecules are united through hydrogen bonds into a three-dimensional
framework. 相似文献
13.
Dicko MH Searle-van Leeuwen MJ Traore AS Hilhorst R Beldman G 《Applied biochemistry and biotechnology》2001,94(3):225-241
The leaves of Boscia senegalensis are traditionally used in West Africa in cereal protection against pathogens, pharmacologic applications, and food processing.
Activities of α-amylase, β-amylase, exo-(1→3, 1→4)-β-d-glucanase, and endo-(1→3)-β-d-glucanase were detected in these leaves. The endo-(1→3)-β-d-glucanase (EC3.2.1.39) was purified 203-fold with 57% yield. The purified enzyme is a nonglycosylated monomeric protein with
a molecular mass of 36 kDa and pI≥10.3. Its optimal activity occurred at pH 4.5 and 50°C. Kinetic analysis gave V
max, k
cat
, and K
m
values of 659 U/mg, 395 s−1, and 0.42 mg/mL, respectively, for laminarin as substrate. The use of matrix-assisted laser desorption ionization time-of-flight
mass spectrometry and high-performance liquid chromatography revealed that the enzyme hydrolyzes not only soluble but also
insoluble (1→3)-β-glucan chains in an endo fashion. This property is unusual for endo-acting (1→3)-β-d-glucanase from plants. The involvement of the enzyme in plant defense against pathogenic microorganisms such as fungi is
discussed. 相似文献
14.
Bicudo TC Forato LA Batista LA Colnago LA 《Analytical and bioanalytical chemistry》2005,383(2):291-296
The γ-zeins are a mixture of 16, 27, and 50-kDa polypeptides which are important in the formation and stabilization of protein
bodies (PB). These organelles are used for deposition of zeins, the water-insoluble storage proteins in maize. The nature
of the physical interaction between proteins in the assembly and stabilization of PB are fairly well known. It is suggested
the repeated hexapeptide sequence (PPPVHL)8 in the N-terminus is responsible for aggregation of the γ-zeins on the PB surface. Despite this importance, there is little
information about the native conformation of γ-zeins. In this work, we have analyzed the secondary structures of γ-zeins in
purified protein bodies from two maize cultivars, in the solid state, by FTIR and NMR spectroscopy. The results revealed that
γ-zeins in their physiological state are comprise similar proportions of α-helix and β-sheet, 33 and 31% as determined by
FTIR. It was not possible to state if the polyproline II (PPII) conformation is present in the solid-state structure of γ-zeins,
as has been demonstrated for the hexapeptide in solution. Because of the similarity of the solid-state NMR spectra of γ and
α-zeins in the α carbon region we attributed their contributions to the β-sheet structures rather than to the PPII conformation
or a mixture of these extended structures. 相似文献
15.
M. B. Izbosarov B. Kh. Abduazimov I. M. Yusupova B. Tashkhodzhaev A. D. Vdovin N. D. Abdullaev 《Chemistry of Natural Compounds》1998,34(4):456-461
A sesquiterpene lactone of the germacrane series, mucrochin, has been isolated from the epigeal part ofTanacetopsis mucronata, and its structure has been studied by IR and mass spectral methods and PMR spectroscopy. It structure has been determined
unambiguously by x-ray structural analysis as 5,6-dihydroxy-5α,6β,7α,8β(H)-germacra-1(10),4(15) 1(13)-trien-8,12-olide. A
boat-chair conformation with a configuration of the1D14
15D5 type has been established.
Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 492–498, July–August, 1998. 相似文献
16.
Effects of polymeric additives with different degrees of polymerization (DP) or substitution (DS) on the crystallization of celluloses I and I have been examined at an early stage of the incubation of Acetobactor xylinum by using newly developed FT-IR spectroscopy. It was found that the mass fraction of cellulose I is greatly decreased with increasing concentrations of carboxymethyl cellulose sodium salt (CMC) or xyloglucan (XG) in the incubation medium. Such a decrease in the mass fraction of cellulose I, which corresponds to the enhanced crystallization of cellulose I, is more prominent for CMC or XG with lower DPs, but the additives with too low DPs are not so effective probably due to higher solubility and the lower adhesion on the surface of microfibrils. Moreover, the mass fractions of celluloses I and I are highly correlated with the crystallite size of microfibrils, indicating that I is crystallized in larger-size microfibrils while I is produced in smaller-size microfibrils. On the basis of these experimental results, the mechanism of the crystallization of celluloses I and I is discussed in the Acetobactor xylinum system. 相似文献
17.
G. Sugihara A. A. Nakamura T. -H. Nakashima Y. -I. Araki T. Okano M. Fujiwara 《Colloid and polymer science》1997,275(8):790-796
For a sodium salt of α-sulfonatomyristic acid methyl ester (14SFNa), one of the α-SFMe series surfactants, the differential
conductivity (∂κ/∂C)
T
,
P
vs. square root of concentration (√C) was employed in order to determine not only CMC but also the limiting molar conductance (Λ0) and the molar conductance of micellar species (ΛM).
Based on the data of the degree of counterion binding to micelles (β) determined previously at different temperatures ranging
15–50 °C at every 5 °C, the experimental values of the degree of dissociation (ionization) of a micelle (αEX) were calculated by regarding as αEX=1−β. The ratio ΛM/Λ0 corresponding to the ratio of slopes below and above CMC in the curve of specific conductivity (κ) vs. concentration (C), which has been often assumed to be the degree of ionization of micelles (α), was compared with the present αEX. However, the ratio ΛM/Λ0 (=α) was found to have a correlationship with αEX (=1−β) as αEX≈0.40×(ΛM/Λ0), or strictly, αEX=0.40 (ΛM/Λ0)+0.08, indicating that the simple ratio of the slopes below and above CMC in κ vs. C curve is not true for αEX=1−β. On the other hand, the method proposed by Evans gave a value closer to αEX compared with the simple ratio.
Received: 17 September 1996 Accepted: 8 April 1997 相似文献
18.
G. Bruni V. Berbenni C. Milanese A. Girella P. Cofrancesco G. Bellazzi A. Marini 《Journal of Thermal Analysis and Calorimetry》2009,95(3):871-876
In this work the solid-state characterization of anhydrous D-mannitol has been performed: α and β modifications can be distinguished only by XRPD and FTIR as they show melting temperature
and enthalpy that are the same within the standard deviation. The understanding of the thermal behaviour of the δ form (obtained
by re-crystallization in acetone) has required XRPD experiments performed at variable temperature. This form during heating
undergoes a solid phase transition to α modification. By cooling a melted sample, under a wide range of experimental conditions,
a very fast crystallization occurs. Independently of the starting crystal form (β or δ form), the re-crystallization of D-mannitol from melt always leads to α form. 相似文献
19.
The cellulose acetate-grafted-poly(glycidyl methacrylate) copolymers were synthesized successfully by free radical polymerization. The resulting copolymer was characterized by proton nuclear magnetic resonance (1H-NMR), solid-state 13C-NMR, Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC). The crystallization behavior, thermal properties, specific particle surface area, moisture sorption behavior of the modified cellulose acetate were investigated by wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Brunauer-Emmett-Teller (BET) method and Dynamic Vapor Sorption (DVS) instrument. It was found that the poly(glycidyl methacrylate) (PGMA) grafting was effective in improving the water adsorption of cellulose acetate (CA) changing the specific surface area, and reducing the Tg of copolymers. 相似文献
20.
Gabriela Roa Morales Teresa Ramírez Silva Laura Galicia 《Journal of Solid State Electrochemistry》2003,7(6):355-360
Cyclic voltammetry was used in order to obtain carbon paste electrodes (CPEs) modified with α- and β-cyclodextrins (CPEα-CD, CPEβ-CD) in HClO4 media as electrolyte. The modified CPEs were obtained by applying 30 potential cycles, thus forming on the substrate a film
with electroactive characteristics; a rise in current for the anodic and cathodic peaks became apparent as the number of cycles
increased. Such behaviour confirmed the CPE modification by the species mentioned. The CPEα-CD and CPEβ-CD exhibited significant stability before various electrolytes. In order to evaluate the sort of modification attained on the
CPEs, a study was conducted, varying the potential scan rate, that confirmed the CD's presence. The modified electrodes were
used to determine Pb(II) ions in solution within the range from 1×10–5 M up to 1×10–3 M. The CPEα-CD and CPEβ-CD electrochemical response was studied by means of anodic stripping voltammetry of the Pb(II) ions, thereby giving a linear
relation between the current for the anodic peak as a function of Pb(II) concentration with r
2=0.996 for the CPEβ-CD and 0.992 for the CPEα-CD.
Electronic Publication 相似文献