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1.
Chem Soc Rev ; 52(18): 6417-6446, 2023 Sep 18.
Artigo em Inglês | MEDLINE | ID: mdl-37591800

RESUMO

The degree of crystallinity in cellulose significantly affects the physical, mechanical, and chemical properties of cellulosic materials, their processing, and their final application. Measuring the crystalline structures of cellulose is a challenging task due to inadequate consistency among the variety of analytical techniques available and the lack of absolute crystalline and amorphous standards. Our article reviews the primary methods for estimating the crystallinity of cellulose, namely, X-ray diffraction (XRD), nuclear magnetic resonance (NMR), Raman and Fourier-transform infrared (FTIR) spectroscopy, sum-frequency generation vibrational spectroscopy (SFG), as well as differential scanning calorimetry (DSC), and evolving biochemical methods using cellulose binding molecules (CBMs). The techniques are compared to better interrogate not only the requirements of each method, but also their differences, synergies, and limitations. The article highlights fundamental principles to guide the general community to initiate studies of the crystallinity of cellulosic materials.

2.
Int J Mol Sci ; 23(6)2022 Mar 13.
Artigo em Inglês | MEDLINE | ID: mdl-35328520

RESUMO

Peptide-cellulose conjugates designed for use as optical protease sensors have gained interest for point-of-care (POC) detection. Elevated serine protease levels are often found in patients with chronic illnesses, necessitating optimal biosensor design for POC assessment. Nanocellulose provides a platform for protease sensors as a transducer surface, and the employment of nanocellulose in this capacity combines its biocompatibility and high specific surface area properties to confer sensitive detection of dilute biomarkers. However, a basic understanding of the spatiotemporal relationships of the transducer surface and sensor disposition is needed to improve protease sensor design and development. Here, we examine a tripeptide, fluorogenic elastase biosensor attached to TEMPO-oxidized nanofibrillated cellulose via a polyethylene glycol linker. The synthetic conjugate was found to be active in the presence of human neutrophil elastase at levels comparable to other cellulose-based biosensors. Computational models examined the relationship of the sensor molecule to the transducer surface. The results illustrate differences in two crystallite transducer surfaces ((110) vs. (1-10)) and reveal preferred orientations of the sensor. Finally, a determination of the relative (110) vs. (1-10) orientations of crystals extracted from cotton demonstrates a preference for the (1-10) conformer. This model study potentiates the HNE sensor results for enhanced sensor activity design.


Assuntos
Celulose Oxidada , Elastase de Leucócito , Celulose/química , Corantes , Óxidos N-Cíclicos , Humanos , Elastase de Leucócito/química , Peptídeo Hidrolases , Peptídeos/química
3.
Molecules ; 27(7)2022 Mar 23.
Artigo em Inglês | MEDLINE | ID: mdl-35408469

RESUMO

The global burden of the SARS-CoV-2 pandemic is thought to result from a high viral transmission rate. Here, we consider mechanisms that influence host cell-virus binding between the SARS-CoV-2 spike glycoprotein (SPG) and the human angiotensin-converting enzyme 2 (ACE2) with a series of peptides designed to mimic key ACE2 hot spots through adopting a helical conformation analogous to the N-terminal α1 helix of ACE2, the region experimentally shown to bind to the SARS-CoV-2 receptor-binding domain (RBD). The approach examines putative structure/function relations by assessing SPG binding affinity with surface plasmon resonance (SPR). A cyclic peptide (c[KFNHEAEDLFEKLM]) was characterized in an α-helical conformation with micromolar affinity (KD = 500 µM) to the SPG. Thus, stabilizing the helical structure of the 14-mer through cyclization improves binding to SPG by an order of magnitude. In addition, end-group peptide analog modifications and residue substitutions mediate SPG binding, with net charge playing an apparent role. Therefore, we surveyed reported viral variants, and a correlation of increased positive charge with increased virulence lends support to the hypothesis that charge is relevant to enhanced viral fusion. Overall, the structure/function relationship informs the importance of conformation and charge for virus-binding analog design.


Assuntos
Enzima de Conversão de Angiotensina 2 , Glicoproteína da Espícula de Coronavírus , Enzima de Conversão de Angiotensina 2/metabolismo , Sítios de Ligação , COVID-19 , Humanos , Peptídeos/química , Ligação Proteica , Domínios Proteicos , SARS-CoV-2 , Glicoproteína da Espícula de Coronavírus/metabolismo
4.
Cellulose (Lond) ; 26(1): 329-339, 2019 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31289425

RESUMO

The insufficient resolution of conventional methods has long limited the structural elucidation of cellulose and its derivatives, especially for those with relatively low crystallinities or in native cell walls. Recent 2D/3D solid-state NMR studies of 13C uniformly labeled plant biomaterials have initiated a re-investigation of our existing knowledge in cellulose structure and its interactions with matrix polymers but for unlabeled materials, this spectroscopic method becomes impractical due to limitations in sensitivity. Here, we investigate the molecular structure of unlabeled cotton cellulose by combining natural abundance 13C-13C 2D correlation solid-state NMR spectroscopy, as enabled by the sensitivity-enhancing technique of dynamic nuclear polarization (DNP), with statistical analysis of the observed and literature-reported chemical shifts. The atomic resolution allows us to monitor the loss of Iα and Iß allomorphs and the generation of a novel structure during ball-milling, which reveals the importance of large crystallite size for maintaining the Iα and Iß model structures. Partial order has been identified in the "disordered" domains, as evidenced by a discrete distribution of well-resolved peaks. This study not only provides heretofore unavailable high-resolution insights into cotton cellulose but also presents a widely applicable strategy for analyzing the structure of cellulose-rich materials without isotope-labeling. This work was part of a multi-technique study of ball-milled cotton described in the previous article in the same issue.

5.
Int J Mol Sci ; 19(3)2018 Mar 13.
Artigo em Inglês | MEDLINE | ID: mdl-29534033

RESUMO

Nanocellulose has high specific surface area, hydration properties, and ease of derivatization to prepare protease sensors. A Human Neutrophil Elastase sensor designed with a nanocellulose aerogel transducer surface derived from cotton is compared with cotton filter paper, and nanocrystalline cellulose versions of the sensor. X-ray crystallography was employed along with Michaelis-Menten enzyme kinetics, and circular dichroism to contrast the structure/function relations of the peptide-cellulose conjugate conformation to enzyme/substrate binding and turnover rates. The nanocellulosic aerogel was found to have a cellulose II structure. The spatiotemporal relation of crystallite surface to peptide-cellulose conformation is discussed in light of observed enzyme kinetics. A higher substrate binding affinity (Km) of elastase was observed with the nanocellulose aerogel and nanocrystalline peptide-cellulose conjugates than with the solution-based elastase substrate. An increased Km observed for the nanocellulosic aerogel sensor yields a higher enzyme efficiency (kcat/Km), attributable to binding of the serine protease to the negatively charged cellulose surface. The effect of crystallite size and ß-turn peptide conformation are related to the peptide-cellulose kinetics. Models demonstrating the orientation of cellulose to peptide O6-hydroxymethyl rotamers of the conjugates at the surface of the cellulose crystal suggest the relative accessibility of the peptide-cellulose conjugates for enzyme active site binding.


Assuntos
Técnicas Biossensoriais/métodos , Celulose/análogos & derivados , Elastase de Leucócito/química , Nanopartículas/química , Biocatálise , Géis/química , Gossypium/química , Humanos , Elastase de Leucócito/metabolismo , Peptídeos/química , Ligação Proteica , Relação Estrutura-Atividade
6.
Molecules ; 20(2): 2892-902, 2015 Feb 11.
Artigo em Inglês | MEDLINE | ID: mdl-25679049

RESUMO

The trimethylsilyl trifluoromethanesulfonate (TMSOTf)-catalyzed reaction of methyl 6-hydroxyhexanoate with 3-O-benzyl-4-(2,4-di-O-acetyl-3-deoxy-L-glycero-tetronamido)-4,6-dideoxy-2-O-levulinoyl-α-d-mannopyranosyl trichloroacetimidate followed by a two-step deprotection (hydrogenolysis over Pd/C catalyst and Zemplén deacylation, to simultaneously remove the acetyl and levulinoyl groups) gave 5-(methoxycarbonyl)pentyl 4-(3-deoxy-L-glycero-tetronamido)-4,6-dideoxy-α-D-mannopyranoside. The structure of the latter, for which crystals were obtained in the analytically pure state for the first time, followed from its NMR and high-resolution mass spectra and was confirmed by X-ray crystallography. The molecule has two approximately linear components; a line through the aglycon intersects a line through the mannosyl and tetronylamido groups at 120°. The crystal packing separates the aglycon groups from the tetronylamido and mannosyl groups, with only C-H...O hydrogen bonding among the aglycon groups and N-H...O, O-H...O and C-H...O links among the tetronylamido and mannosyl groups. A carbonyl oxygen atom accepts the strongest O-H...O hydrogen bond and two strong C-H...O hydrogen bonds. The geometric properties were compared with those of related molecules.


Assuntos
Manosídeos/síntese química , Antígenos O/química , Vibrio cholerae O1/metabolismo , Sequência de Carboidratos , Cristalografia por Raios X , Ligação de Hidrogênio , Espectroscopia de Ressonância Magnética , Manosídeos/química , Vibrio cholerae O1/química
7.
Cellulose (Lond) ; 21(2): 879-884, 2014 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-24729665

RESUMO

Previous studies of calculated diffraction patterns for cellulose crystallites suggest that distortions that arise once models have been subjected to MD simulation are the result of both microfibril twisting and changes in unit cell dimensions induced by the empirical force field; to date, it has not been possible to separate the individual contributions of these effects. To provide a better understanding of how twisting manifests in diffraction data, the present study demonstrates a method for generating twisted and linear cellulose structures that can be compared without the bias of dimensional changes, allowing assessment of the impact of twisting alone. Analysis of unit cell dimensions, microfibril volume, hydrogen bond patterns, glycosidic torsion angles, and hydroxymethyl group orientations confirmed that the twisted and linear structures collected with this method were internally consistent, and theoretical powder diffraction patterns for the two were shown to be effectively indistinguishable. These results indicate that differences between calculated patterns for the crystal coordinates and twisted structures from MD simulation can result entirely from changes in unit cell dimensions, and not from microfibril twisting alone. Although powder diffraction patterns for models in the 81-chain size regime were shown to be unaffected by twisting, suggesting that a modest degree of twist is not inconsistent with experimental data, it may be that other diffraction techniques are capable of detecting this structural difference. Until such time as definitive experimental evidence comes to light, the results of this study suggest that both twisted and linear microfibrils may represent an appropriate model for cellulose Iß.

8.
Biopolymers ; 99(10): 746-56, 2013 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-23681971

RESUMO

Molecular dynamics (MD) simulations of cellulose microfibrils are pertinent to the paper, textile, and biofuels industries for their unique capacity to characterize dynamic behavior and atomic-level interactions with solvent molecules and cellulase enzymes. While high-resolution crystallographic data have established a solid basis for computational analysis of cellulose, previous work has demonstrated a tendency for modeled microfibrils to diverge from the linear experimental structure and adopt a twisted conformation. Here, we investigate the dependence of this twisting behavior on computational approximations and establish the theoretical basis for its occurrence. We examine the role of solvent, the effect of nonbonded force field parameters [partial charges and van der Waals (vdW) contributions], and the use of explicitly modeled oxygen lone pairs in both the solute and solvent. Findings suggest that microfibril twisting is favored by vdW interactions, and counteracted by both intrachain hydrogen bonds and solvent effects at the microfibril surface.


Assuntos
Celulose , Microfibrilas , Celulose/química , Ligação de Hidrogênio , Modelos Moleculares , Conformação Molecular , Simulação de Dinâmica Molecular
9.
Adv Carbohydr Chem Biochem ; 80: 15-93, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-34872656

RESUMO

The approaches in this article seek to enhance understanding of cellulose at the molecular level, independent of the source and the particular crystalline form of cellulose. Four main areas of structure research are reviewed. Initially, the molecular shape is inferred from the crystal structures of many small molecules that have ß-(1→4) linkages. Then, conformational analyses with potential energy calculations of cellobiose are covered, followed by the use of Atoms-In-Molecules theory to learn about interactions in experimental and theoretical structures. The last section covers models of cellulose nanoparticles. Controversies addressed include the stability of twofold screw-axis conformations, the influence of different computational methods, the predictability of crystalline conformations by studies of isolated molecules, and the twisting of model cellulose crystals.


Assuntos
Celulose , Química Computacional , Cristalografia por Raios X , Ligação de Hidrogênio , Modelos Moleculares
10.
Carbohydr Polym ; 257: 117620, 2021 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-33541648

RESUMO

Professor Dexter French (1918-1981) was an American chemist and biochemist at Iowa State College (University in 1959). He devoted his career to advance knowledge of polysaccharides and oligosaccharides, in particular starch, cyclodextrins, and enzymes. Cyclodextrins are oligosaccharides obtained from starch and are typically cage molecules with a hydrophobic cavity that can encapsulate other compounds nowadays the basis for many industrial applications. Since the 1960s, he has been recognized as an outstanding authority in the field of starches and cyclodextrins and has inspired researchers in laboratories around the world. This review, on the fortieth anniversary of his death, commemorates his remarkable contribution to starch and cyclodextrin chemistry. Firstly, we give an overview of his personal life and career. Secondly, we highlight some of the results on starch and cyclodextrins from Professor French and his group. A third part discusses his impact on the modern chemistry of cyclodextrins and starch.

11.
Carbohydr Polym ; 264: 118004, 2021 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-33910736

RESUMO

Shapes (conformations) of cellulose molecules are described by their glycosidic linkage torsion angles ϕ and ψ. Although the torsions are known for cellulose in crystals, amorphous shapes are also interesting for understanding reactivity and physical properties. ϕ and ψ determination for unorganized matter is difficult; one approach is to study their range in many related molecules. For example, linkage torsions of cellulose should be similar to those in cellobiose. Herein, torsions were measured for cellooligosaccharides and lactose moieties complexed with proteins in the Protein Data Bank (PDB). These torsions were compared with ϕ/ψ maps based on quantum mechanics energies for solvated cellobiose and analogs lacking hydroxyl groups. Most PDB conformations corresponded to low map energies. Amorphous cellulose should be generally extended with individual linkages that would give 2- to 3-fold helices. The map for an analog lacking hydrogen bonding ability was more predictive for PDB linkages than the cellobiose map.


Assuntos
Celobiose/química , Celulose/química , Oligossacarídeos/química , Proteínas/química , Configuração de Carboidratos , Ligação de Hidrogênio , Lactose/química , Modelos Moleculares , Conformação Molecular , Fenômenos Físicos , Teoria Quântica
12.
Methods Mol Biol ; 2149: 513-539, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32617954

RESUMO

Computerized molecular modeling continues to increase in capability and applicability to carbohydrates. This chapter covers nomenclature and conformational aspects of carbohydrates, perhaps of greater use to computational chemists who do not have a strong background in carbohydrates, and its comments on various methods and studies might be of more use to carbohydrate chemists who are inexperienced with computation. Work on the intrinsic variability of glucose, an overall theme, is described. Other areas of the authors' emphasis, including evaluation of hydrogen bonding by the atoms-in-molecules approach, and validation of modeling methods with crystallographic results are also presented.


Assuntos
Carboidratos/química , Simulação por Computador , Configuração de Carboidratos , Parede Celular/química , Cristalografia , Glucose/química , Ligação de Hidrogênio , Modelos Químicos , Simulação de Dinâmica Molecular , Plantas/química , Teoria Quântica , Software , Termodinâmica
13.
J Am Chem Soc ; 131(41): 14786-94, 2009 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-19824731

RESUMO

Structures, dynamics, and stabilities of different sized cellulosic oligomers need to be considered when designing enzymatic cocktails for the conversion of biomass to biofuels since they can be both productive substrates and inhibitors of the overall process. In the present work, the conformational variability, hydrogen bonding, and mechanical properties of short, soluble cellulose chains are investigated as a function of chain length. Cellulose oligomers consisting 2, 4, and 6 beta-d-glucose units are examined in explicit solvent using replica exchange molecular dynamics (REMD) which provides a rigorous evaluation of the relative stabilities of different conformations and their temperature dependencies. This application of REMD to oligosaccharides in solution also allows evaluation of the quality of the force-field and its suitability for sampling carbohydrates efficiently. Simulation results are analyzed in synergy with polymer theory and compared to known measurements of oligomers and crystals. As the chain length is increased, the conformations of the oligomers become more rigid and likely to form intrachain hydrogen bonds, like those found in crystals. Several other conformations and hydrogen bonding patterns distinguish these short cellulose chains from those in cellulose crystals. These studies have also addressed the key role played by solvent on shifting the conformational preferences of the oligosaccharides with respect to vacuum and crystals. Correlation between pyranose ring flipping and the conformation of the 1,4-glycosidic bond was observed.


Assuntos
Celulose/química , Simulação de Dinâmica Molecular , Temperatura , Configuração de Carboidratos , Rotação , Solubilidade , Fatores de Tempo , Água/química
14.
Carbohydr Polym ; 216: 360-368, 2019 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-31047078

RESUMO

Nanocellulose has functionalities suitable for efficient sensor transducer surface design including crystallinity, biocompatible and high specific surface area. Here we explore two forms of nanocellulose as transducer surfaces to enable colorimetric detection of human neutrophil elastase (HNE), and a wide range of inflammatory diseases. A deep eutectic solvent (DES) was utilized to mediate formation of cotton cellulose nanocrystals (DCNCs) employed to prepare a peptide-cellulose conjugate as a protease sensor of HNE. The tetrapeptide-cellulose analog on DCNC is contrasted with an analogous derivative of TEMPO-oxidized wood cellulose nanofibrils (WCNFs). DCNCs showed greater degree of substitution of HNE tetrapeptide and sensitivity to the elastase than WCNFs, despite the smaller surface area and pore sizes. XRD models revealed the higher crystallinity and larger crystallite sizes of DCNCs, indicating the well-arranged cellulose chains for immobilization of the tetrapeptide on (110) lattice reflections of cellulose crystals. The sensitivity of DCNCs-based colorimetric sensor was less than 0.005 U/mL, which would provide a convenient, sensitive sensor applicable for improved colorimetric point of care protease biomarker detection.


Assuntos
Celulose/química , Elastase de Leucócito/análise , Nanopartículas/química , Compostos de Anilina/química , Técnicas Biossensoriais/métodos , Colorimetria/métodos , Gossypium/química , Humanos , Proteínas Imobilizadas/química , Indicadores e Reagentes/química , Modelos Moleculares , Oligopeptídeos/química , Porosidade , Proteólise , Propriedades de Superfície
15.
Biomacromolecules ; 9(11): 3133-40, 2008 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-18855441

RESUMO

In the crystal structure of cellulose I beta, disordered hydrogen bonding can be represented by the average of two mutually exclusive hydrogen bonding schemes that have been designated A and B. An unanswered question is whether A and B interconvert dynamically, or whether they are static but present in different regions of the microfibril (giving temporally or a spatially averaged structures, respectively). We have used neutron crystallographic techniques to determine the occupancies of A and B at 295 and 15 K, quantum mechanical calculations to compare the energies of A and B, and molecular dynamics calculations to look at the stability of A. Microfibrils are found to have most chains arranged in a crystalline I beta structure with hydrogen bonding scheme A. Smaller regions of static disorder exist, perhaps at defects within or between crystalline domains in which the hydrogen bonding is complex but with certain features that are found in B.


Assuntos
Celulose/química , Ligação de Hidrogênio , Difração de Nêutrons , Estrutura Molecular , Movimento (Física) , Teoria Quântica , Temperatura
16.
Carbohydr Res ; 342(9): 1223-37, 2007 Jul 02.
Artigo em Inglês | MEDLINE | ID: mdl-17382309

RESUMO

Acylated beta-cyclodextrins (beta-CDs) were studied to gain perspective on maltose octapropanoate, the crystal structure of which was reported in the preceding paper in this issue. Acylated beta-CDs are distorted so we looked at other CDs and gained increased understanding of distortion in CDs and possibly, shapes in starch. Classic CDs have six to eight glucose residues in a doughnut shape that is stabilized by a ring of inter-residue O3,,,O2' hydrogen bonds. On a phi,psi energy map for a maltose analog that does not form hydrogen bonds, classic CD linkages have higher energies than structures that are stabilized by the exo-anomeric effect. In distorted beta-CDs, which lack hydrogen bonding, some linkages attain low-energies from the exo-anomeric effect and acyl stacking. Those linkages result in left-handed helical geometry so other linkages are forced by the CD macrocycle to have counter-balancing right-handed character. Permethylated gamma-CDs have two 'flipping' linkages as do some larger native CDs. Flipping linkages allow two left-handed segments to join into a macrocycle, thus avoiding the higher-energy, right-handed forms. Some glucose rings in derivatized beta-CDs have substantial positive twists of the pseudo torsion angle O1-C1...C4-O4, adding right-handed character to balance the left-handed linkages. In substituted gamma-CD, all residues have negative twists, giving extra left-handed character to the short, pseudo-helical segments. In non-macrocyclic molecules the twists ranged from -14 degrees to +2 degrees , averaging -6.1 degrees. In these beta- and gamma-CDs, the twists ranged from -22 degrees to +16 degrees for (4)C(1) rings, and the (O)S(2) ring in acetylated beta-CD has a twist of +34 degrees . Glucose residues in other CDs were less twisted.


Assuntos
Ciclodextrinas/química , beta-Ciclodextrinas/química , Configuração de Carboidratos , Ligação de Hidrogênio , Modelos Moleculares , Termodinâmica
17.
Carbohydr Res ; 342(9): 1210-22, 2007 Jul 02.
Artigo em Inglês | MEDLINE | ID: mdl-17383618

RESUMO

The crystal structure of beta-maltose octapropanoate (1) was solved to improve understanding of di-, oligo-, and polysaccharide conformations. The O6 and O6' atoms are in gg and gt orientations, respectively. Extrapolation of the coordinates of the non-reducing residue and observed linkage bond and torsion angles of 1 [Formula: see text] yields a left-handed helix similar to amylose triacetate I. The phi and psi values of 1 are also similar to those of other crystalline, acylated maltose compounds as well as some hydroxyl-bearing molecules. Acylated maltose moieties are often stabilized by stacking of the carbonyl groups and alpha-carbons on O3 and O2' as well as by the exo-anomeric effect. The conformation of 1 is within the 1-kcal/mol contour on a hybrid energy map built with a dielectric constant of 7.5, but corresponds to higher energies on maps made with lower dielectric constants. In one region of phi,psi space, both hydroxyl-bearing and derivatized maltose moieties are found but no inter-residue, intramolecular hydrogen-bonding occurs. In another region, only hydroxyl-bearing molecules crystallize and O2'...O3 hydrogen bonds are always found. In agreement with the energy surfaces, amylose helices extrapolated from available linkage geometries were almost all left-handed.


Assuntos
Cristalografia por Raios X/métodos , Maltose/química , Configuração de Carboidratos , Cristalização , Ligação de Hidrogênio , Maltose/análogos & derivados , Modelos Moleculares , Estrutura Molecular
18.
Carbohydr Res ; 443-444: 87-94, 2017 Apr 18.
Artigo em Inglês | MEDLINE | ID: mdl-28411418

RESUMO

The interaction of two methanol molecules, simplified models of carbohydrates and cellulose, was examined using a variety of quantum mechanics (QM) levels of theory. Energy plots for hydrogen bonding distance (H⋯O) and angle (OH⋯O) were constructed. All but two experimental structures were located in stabilized areas on the vacuum phase energy plots. Each of the 399 models was analyzed with Bader's atoms-in-molecules (AIM) theory, which showed a widespread ability by the dimer models to form OH⋯O hydrogen bonds that have bond paths and Bond Critical Points. Continuum solvation calculations suggest that a portion of the energy-stabilized structures could occur in the presence of water. A survey of the Cambridge Structural Database (CSD) for all donor-acceptor interactions in ß-D-glucose moieties examined the similarities and differences among the hydroxyl groups and acetal oxygen atoms that participate in hydrogen bonds. Comparable behavior was observed for the O2H, O3H, O4H, and O6H hydroxyls, acting either as acceptors or donors. Ring O atoms showed distinct hydrogen bonding behavior that favored mid-length hydrogen bonds.


Assuntos
Dimerização , Glucose/química , Metanol/química , Modelos Moleculares , Teoria Quântica , Cristalografia por Raios X , Ligação de Hidrogênio , Conformação Molecular , Termodinâmica
19.
Carbohydr Polym ; 135: 1-9, 2016 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-26453844

RESUMO

The Segal method estimates the amorphous fraction of cellulose Iß materials simply based on intensity at 18° 2θ in an X-ray diffraction pattern and was extended to cellulose II using 16° 2θ intensity. To address the dependency of Segal amorphous intensity on crystal size, cellulose polymorph, and the degree of polymorphic conversion, we simulated the diffraction patterns of cotton celluloses (Iß and II) and compared the simulated amorphous fractions with the Segal values. The diffraction patterns of control and mercerized cottons, respectively, were simulated with perfect crystals of cellulose Iß (1.54° FWHM) and cellulose II (2.30° FWHM) as well as 10% and 35% amorphous celluloses. Their Segal amorphous fractions were 15% and 31%, respectively. The higher Segal amorphous fraction for control cotton was attributed to the peak overlap. Although the amorphous fraction was set in the simulation, the peak overlap induced by the increase of FWHM further enhanced the Segal amorphous intensity of cellulose Iß. For cellulose II, the effect of peak overlap was smaller; however the lower reflection of the amorphous cellulose scattering in its Segal amorphous location resulted in smaller Segal amorphous fractions. Despite this underestimation, the relatively good agreement of the Segal method with the simulation for mercerized cotton was attributed to the incomplete conversion to cellulose II. The (1-10) and (110) peaks of cellulose Iß remained near the Segal amorphous location of cellulose II for blends of control and mercerized cotton fibers.


Assuntos
Celulose/química , Fibra de Algodão , Cristalização , Difração de Raios X
20.
Carbohydr Polym ; 147: 155-164, 2016 08 20.
Artigo em Inglês | MEDLINE | ID: mdl-27178920

RESUMO

Core-shell structured hydrogels consisting of a flexible interpenetrating polymer network (IPN) core and a rigid semi-IPN shell were prepared through chemical crosslinking of polyvinyl alcohol (PVA) and sodium alginate (SA) with Ca(2+) and glutaraldehyde. Short cellulose nanofibers (CNFs) extracted from energycane bagasse were incorporated in the hydrogel. The shell was micro-porous and the core was macro-porous. The hydrogels could be used in multiple adsorption-desorption cycles for dyes, and the maximum methyl blue adsorption capacity had a 10% increase after incorporating CNFs. The homogeneous distribution of CNFs in PVA-SA matrix generated additional hydrogen bonds among the polymer molecular chains, resulting in enhanced density, viscoelasticity, and mechanical strength for the hydrogel. Specifically, the compressive strength of the hydrogel reached 79.5kPa, 3.2 times higher than that of the neat hydrogel.


Assuntos
Alginatos/química , Celulose/química , Nanofibras/química , Álcool de Polivinil/química , Ácido Glucurônico/química , Ácidos Hexurônicos/química
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