scholarly journals Molecular Analysis of Retrogradation of Corn Starches

Polymers ◽  
2019 ◽  
Vol 11 (11) ◽  
pp. 1764 ◽  
Author(s):  
Marek Sikora ◽  
Magdalena Krystyjan ◽  
Anna Dobosz ◽  
Piotr Tomasik ◽  
Katarzyna Walkowiak ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Correlation Time ◽  
Guar Gum ◽  
Corn Starch ◽  
Solid Phase ◽  
Amylose Content ◽  
Relaxation Times ◽  
Water Molecules ◽  
Correlation Times ◽  
Polymeric Network

Changes of the molecular dynamics of water in 5% corn starch pastes and 5% systems composed of starch and non-starchy hydrocolloid were studied during short and long term retrogradation. Low Field NMR was used to record mean correlation times (τc) of water molecules. This molecular parameter reflects the rotation of water molecules within the network of paste. Starches of different amylose and amylopectin content were selected for this study. Comparison of the changes of τc shows how particular polymers bind water molecules. During 90 days of storage, over 50% increase in mean correlation time was recorded in pastes of starches with high amylose content. This suggests that the formation of polymeric network is controlled by amylose to which water is binding. Amylopectin was found to influence the mobility of water in the pastes to a lesser extent with changes in mean correlation times of approximately 10–15% over 90 days. On retrogradation, amylopectin, Arabic and xanthan gums hindered the formation of solid phase structures. Guar gum evoked an increase in mean correlation times of approximately 40–50% during the prolonged process of changes of the molecular dynamics of water. This indicates continued expansion of the polymeric network. Mean correlation time available from spin–lattice and spin–spin relaxation times can be useful in the analysis of the rotational vibrations of the water molecules in biopolymeric structures.

scholarly journals Release of Strawberry Aroma Compounds by Different Starch-Aroma Systems

2009 ◽  
Vol 27 (Special Issue 1) ◽  
pp. S58-S61 ◽  
Author(s):  
R. Vidrih ◽  
E. Zlatić ◽  
J. Hribar
Keyword(s):  
Guar Gum ◽  
Corn Starch ◽  
Cold Water ◽  
Solid Phase ◽  
Aroma Compounds ◽  
Aroma Release ◽  
Ethyl Hexanoate ◽  
Ethyl Butanoate ◽  
Trained Panel ◽  
Modified Starches

In the food industry, the addition of flavours is used to reinforce the aroma profile of different goods. However, interactions between starch and aroma compounds can occur, and this can impact upon aroma release and perception. In the present study, we have investigated the influence of starch type on aroma release from starch-aroma systems. The food model system used was composed of an aqueous starch dispersion (1 g dry starch/100 g dispersion) and 10 aroma compounds (ethyl butanoate, ethyl 2-methylbutanoate, ethyl 3-methylbutanoate, ethyl pentanoate, methyl hexanoate, ethyl hexanoate, methyl ethyl propanoate, hexyl acetate, 3-hexenol, and phenyl methyl acetate). Different commercially available starches were used: Amilogels P, K, PDP, G, MVK, HP, OK and HPW, and carrageenan (Amilogel CAR) and guar gum (Amilogel GG). Aroma release from these starch-aroma systems into the gas phase above food (headspace) were monitored by GC-MS analysis with a solid-phase micro-extraction technique. The smell of the starch-aroma system was also evaluated sensorially by a trained panel. The release of aroma compounds from the different starch-aroma systems was statistically significant (<I>P</I> < 0.0001) for all of the aroma compounds, with the exception of ethyl pentanoate. A correlation between the concentration of individual aroma compounds in the headspace and the sensory evaluation (smell) was seen. Starch-aroma systems comprising corn starch (Amilogel G), physically modified starches that are soluble in cold water (Amilogels K, PDP), and hydroxypropyl distarch phosphate (Amilogels HP) had sensorially superior smells compared to the other types of starches tested. At the same time, the headspace GC-MS analyses showed ethyl butanoate, ethyl 2-methylbutanoate, ethyl 3-methylbutanoate and ethyl pentanoate to be at the highest concentrations, which are all typical aroma compounds of strawberry fruit, and which also have low perception thresholds. Dextrin-roasted starch, guar gum and carrageenan provided the lowest sensory scores, although in contrast, they more strongly retained these aroma compounds.

scholarly journals Comparison of the Molecular Dynamics of C70 in the Solid and Liquid Phases

2009 ◽  
Vol 2009 ◽  
pp. 1-7 ◽  
Author(s):  
R. M. Hughes ◽  
P. Mutzenhardt ◽  
A. A. Rodriguez
Keyword(s):  
Molecular Dynamics ◽  
Solid State ◽  
Liquid Phase ◽  
Lower Energy ◽  
Solid Phase ◽  
Small Step ◽  
Correlation Times ◽  
Diffusion Constants ◽  
Liquid Phases ◽  
Two Phases

A previous study of C70 in deuterated benzenes generated evidence suggesting C70 exhibited unique reorientational behavior depending on its environment. We present a comparison of the dynamic behavior of this fullerene, in the solid and solution phases, to explore any unique features between these two phases. The effective correlation times, τCeff, of C70 in the solid state are 2 to 3 times longer than in solution. In the solid state, a noticeable decrease in all the carbons' correlation times is seen between 293 K to 303 K; suggesting a transition from isotropic to anisotropic reorientational behavior at this temperature change. Although C70 in solution experiences van der Waals type interactions, these interactions are not strong enough to slow the solution-state motion below what is observed in the solid state. All observed differences in the diffusion constants, DX and DZ, in solution are smaller than in the solid state suggesting a lower energy of activation between these two modes of reorientation in the liquid phase. A small-step diffusion “like” condition appears to be thermally generated in the solid phase at 323 K.

Global and internal molecular dynamics of poly(acrylamide-co-allyl 2-acetamido-2-deoxy-D-glucopyranoside) glycopolymers from 13C NMR relaxation studies

1993 ◽  
Vol 71 (12) ◽  
pp. 1995-2006 ◽  
Author(s):  
René Roy ◽  
François D. Tropper ◽  
Antony J. Williams ◽  
Jean-Robert Brisson
Keyword(s):  
Molecular Dynamics ◽  
Spin Relaxation ◽  
Correlation Time ◽  
Relaxation Times ◽  
Nmr Relaxation ◽  
Relaxation Rates ◽  
Polymer Backbone ◽  
Model Free ◽  
Internal Motions ◽  
Poly Acrylamide

13C spin-lattice and spin–spin relaxation times and nuclear Overhauser enhancements have been used to examine the molecular dynamics of the α- (1) and β- (2) anomeric forms of poly(acrylamide-co-allyl 2-acetamido-2-deoxy-D-glucopyranoside) glycopolymers. The timescale of motions and the spatial restriction of these motions were determined by using various forms of the "model-free" approach. It is shown that the motions of the C—H vectors of the polymer backbone may be described by a scaled Lorentzian spectral density function, giving rise to an effective correlation time for overall tumbling. The temperature dependence of this correlation time suggests that the overall motion is dependent on viscosity. The overall motion of the polymer molecules is shown to be anisotropic in nature by including the spin–spin relaxation data in the analysis. The N-acetyl methyl and sugar hydroxymethyl (C6) groups exhibit internal motions. The activation energies associated with these internal motions are derived. The difference in relaxation rates between the α and β anomeric forms, though small, suggests that the motions of the sugar ring may be different for the two systems. This conclusion is supported by potential energy contour map calculations, which indicate that the β anomer (2) has almost twice the conformational flexibility of the α anomer (1).

scholarly journals The Impact of the Electric Field on Surface Condensation of Water Vapor: Insight from Molecular Dynamics Simulation

Nanomaterials ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 64 ◽  
Author(s):  
Qin Wang ◽  
Hui Xie ◽  
Zhiming Hu ◽  
Chao Liu
Keyword(s):  
Molecular Dynamics ◽  
Water Vapor ◽  
Electric Field ◽  
Intermolecular Forces ◽  
Dynamics Simulation ◽  
Water Molecules ◽  
Attraction Force ◽  
Condensation Rate ◽  
Shape Transformation ◽  
The Impact

In this study, molecular dynamics simulations were carried out to study the coupling effect of electric field strength and surface wettability on the condensation process of water vapor. Our results show that an electric field can rotate water molecules upward and restrict condensation. Formed clusters are stretched to become columns above the threshold strength of the field, causing the condensation rate to drop quickly. The enhancement of surface attraction force boosts the rearrangement of water molecules adjacent to the surface and exaggerates the threshold value for shape transformation. In addition, the contact area between clusters and the surface increases with increasing amounts of surface attraction force, which raises the condensation efficiency. Thus, the condensation rate of water vapor on a surface under an electric field is determined by competition between intermolecular forces from the electric field and the surface.

scholarly journals Electrical Breakdown Mechanism of Transformer Oil with Water Impurity: Molecular Dynamics Simulations and First-Principles Calculations

Crystals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 123
Author(s):  
Bin Cao ◽  
Ji-Wei Dong ◽  
Ming-He Chi
Keyword(s):  
Molecular Dynamics ◽  
Thermal Diffusion ◽  
First Principles ◽  
Electrical Breakdown ◽  
Transformer Oil ◽  
Water Molecules ◽  
Conducting Channel ◽  
Breakdown Mechanism ◽  
Water Impurity ◽  
Dynamics Simulations

Water impurity is the essential factor of reducing the insulation performance of transformer oil, which directly determines the operating safety and life of a transformer. Molecular dynamics simulations and first-principles electronic-structure calculations are employed to study the diffusion behavior of water molecules and the electrical breakdown mechanism of transformer oil containing water impurities. The molecular dynamics of an oil-water micro-system model demonstrates that the increase of aging acid concentration will exponentially expedite thermal diffusion of water molecules. Density of states (DOS) for a local region model of transformer oil containing water molecules indicates that water molecules can introduce unoccupied localized electron-states with energy levels close to the conduction band minimum of transformer oil, which makes water molecules capable of capturing electrons and transforming them into water ions during thermal diffusion. Subsequently, under a high electric field, water ions collide and impact on oil molecules to break the molecular chain of transformer oil, engendering carbonized components that introduce a conduction electronic-band in the band-gap of oil molecules as a manifestation of forming a conductive region in transformer oil. The conduction channel composed of carbonized components will be eventually formed, connecting two electrodes, with the carbonized components developing rapidly under the impact of water ions, based on which a large number of electron carriers will be produced similar to “avalanche” discharge, leading to an electrical breakdown of transformer oil insulation. The water impurity in oil, as the key factor for forming the carbonized conducting channel, initiates the electric breakdown process of transformer oil, which is dominated by thermal diffusion of water molecules. The increase of aging acid concentration will significantly promote the thermal diffusion of water impurities and the formation of an initial conducting channel, accounting for the degradation in dielectric strength of insulating oil containing water impurities after long-term operation of the transformer.

scholarly journals Solid-Phase “Self-Hydrolysis” of [Zn(NH3)4MoO4@2H2O] Involving Enclathrated Water—An Easy Route to a Layered Basic Ammonium Zinc Molybdate Coordination Polymer

Molecules ◽  
2021 ◽  
Vol 26 (13) ◽  
pp. 4022
Author(s):  
Kende Attila Béres ◽  
István E. Sajó ◽  
György Lendvay ◽  
László Trif ◽  
Vladimir M. Petruševski ◽  
...  
Keyword(s):  
Coordination Polymer ◽  
Solid Phase ◽  
Water Molecules ◽  
Temperature Dependent ◽  
Dynamic Interactions ◽  
Ammonia Release ◽  
Successive Substitution ◽  
Red Dye ◽  
Hydrolysis Of ◽  
Zinc Molybdate

An aerial humidity-induced solid-phase hydrolytic transformation of the [Zn(NH3)4]MoO4@2H2O (compound 1@2H2O) with the formation of [(NH4)xH(1−x)Zn(OH)(MoO4)]n (x = 0.92–0.94) coordination polymer (formally NH4Zn(OH)MoO4, compound 2) is described. Based on the isostructural relationship, the powder XRD indicates that the crystal lattice of compound 1@2H2O contains a hydrogen-bonded network of tetraamminezinc (2+) and molybdate (2−) ions, and there are cavities (O4N4(μ-H12) cube) occupied by the two water molecules, which stabilize the crystal structure. Several observations indicate that the water molecules have no fixed positions in the lattice voids; instead, the cavity provides a neighborhood similar to those in clathrates. The @ symbol in the notation is intended to emphasize that the H2O in this compound is enclathrated rather than being water of crystallization. Yet, signs of temperature-dependent dynamic interactions with the wall of the cages can be detected, and 1@2H2O easily releases its water content even on standing and yields compound 2. Surprisingly, hydrolysis products of 1 were observed even in the absence of aerial humidity, which suggests a unique solid-phase quasi-intramolecular hydrolysis. A mechanism involving successive substitution of the ammonia ligands by water molecules and ammonia release is proposed. An ESR study of the Cu-doped compound 2 (2#dotCu) showed that this complex consists of two different Cu2+(Zn2+) environments in the polymeric structure. Thermal decomposition of compounds 1 and 2 results in ZnMoO4 with similar specific surface area and morphology. The ZnMoO4 samples prepared from compounds 1 and 2 and compound 2 in itself are active photocatalysts in the degradation of Congo Red dye. IR, Raman, and UV studies on compounds 1@2H2O and 2 are discussed in detail.

scholarly journals Origin and control of ionic hydration patterns in nanopores

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Miraslau L. Barabash ◽  
William A. T. Gibby ◽  
Carlo Guardiani ◽  
Alex Smolyanitsky ◽  
Dmitry G. Luchinsky ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Distribution Functions ◽  
Water Molecules ◽  
Surrounding Water ◽  
Ionic Hydration ◽  
Hydration Shells ◽  
Water Layers ◽  
Dynamics Simulations ◽  
And Control

AbstractIn order to permeate a nanopore, an ion must overcome a dehydration energy barrier caused by the redistribution of surrounding water molecules. The redistribution is inhomogeneous, anisotropic and strongly position-dependent, resulting in complex patterns that are routinely observed in molecular dynamics simulations. Here, we study the physical origin of these patterns and of how they can be predicted and controlled. We introduce an analytic model able to predict the patterns in a graphene nanopore in terms of experimentally accessible radial distribution functions, giving results that agree well with molecular dynamics simulations. The patterns are attributable to a complex interplay of ionic hydration shells with water layers adjacent to the graphene membrane and with the hydration cloud of the nanopore rim atoms, and we discuss ways of controlling them. Our findings pave the way to designing required transport properties into nanoionic devices by optimising the structure of the hydration patterns.

Proton spin thermometry and molecular dynamics of the liquid crystal PAA in the solid phase

1974 ◽  
Vol 61 (11) ◽  
pp. 4646-4649 ◽  
Author(s):  
R. T. Thompson ◽  
D. W. Kydon ◽  
M. M. Pintar
Keyword(s):  
Molecular Dynamics ◽  
Liquid Crystal ◽  
Solid Phase ◽  
Proton Spin
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