Myristic Acid Molecules Research Articles

Different starch varieties influence the complexing state and digestibility of the resulting starch-lipid complexes

In this study, we investigated the complexing state and digestibility of complexes formed between myristic acid (MA) and several varieties of starch (maize starch, MS; waxy maize starch, WS; high amylose maize starch, HMS; rice starch, RiS; cassava starch, CS; potato starch, PS). The resistant starch (RS) content, complexing index, and degree of the structural order of HMS-MA and MS-MA complexes were significantly higher (p < 0.05) than those of the other complexes. Notably, the RS increments of MS-MA complexes were the highest (14.10%). CS-MA, MS-MA and RiS-MA complexes showed better thermal stability of starch than the other complexes. The MA molecules were primarily physically embedded outside the helical structure of starch in WS-MA and PS-MA complexes. Additionally, CS-MA complexes possessed the highest relative number of physically embedded MA molecules. Moreover, the distribution of physically embedded MA molecules in WS-MA, CS-MA, and PS-MA complexes was more homogeneous than that in the other complexes. The weight-average molecular weight of amylose, average chain length of amylopectin side chains, and the proportion of chains with a degree of polymerization of 6–12 and 25–36 greatly affected their interactions with MA molecules. These results indicated that starch types substantially influenced the digestibility of the complexes, which was closely related to their complexing state and structural order.

Phase transformation in the C form of myristic-acid crystals and DFT calculations.

In this study, the vibrational frequencies of myristic acid (CH3(CH2)12COOH) were obtained using density functional theory calculations, and the results were compared with experimental Raman and infrared data. Additionally, Raman spectra of crystalline myristic acid were recorded in the 300-20 K range. Raman spectroscopy gives important insights into the effect of low temperatures on its monoclinic phase. X-ray diffraction was performed from 298 to 133 K to provide additional information about the cryogenic behavior of the crystals. These undergo a phase transformation, which was confirmed by differential scanning calorimetry through an enthalpy anomaly observed at low temperatures. Raman spectra and X-ray diffraction refinement of the cell parameters in combination with differential scanning calorimetry at low temperatures revealed slight modifications, confirming a conformational change in the myristic acid molecules involving rearrangement of dimers within the unit cell.

Controlling Foam Stability with the Ratio of Myristic Acid to Choline Hydroxide.

The interfacial and foam properties of a model system based on the mixture between myristic acid and choline hydroxide have been investigated as a function of the molar ratio ( R) between these two components and temperature. The aim of this study was to obtain insight on the links between the self-assemblies in bulk and in the foam liquid channels, the surfactant packing at the interface, and the resulting foam properties and stability. A multiscale approach was used combining small angle neutron scattering, specular neutron reflectivity, surface tension measurements, and photography. We highlighted three regimes of foam stability in this system by modifying R: high foam stability for R < 1, intermediate at R ∼ 1, and low for R > 1. The different regimes come from the pH variations in bulk linked to R. The pH plays a crucial role at the molecular scale by setting the ionization state of the myristic acid molecules adsorbed at the gas-liquid interface, which in turn controls both the properties of the monolayer and the stability of the films separating the bubbles. The main requirement to obtain stable foams is to set the pH close to the p Ka in order to have a mixture of protonated and ionized molecules giving rise to intermolecular hydrogen bonds. As a result, a dense monolayer is formed at the interface with a low surface tension. R also modifies the structure of self-assembly in bulk and therefore within the foam, but such a morphological change has only a minor effect on the foam stability. This study confirms that foam stability in surfactant systems having a carboxylic acid as polar headgroup is mainly linked to the ionization state of the molecules at the interface.

Mesoporous silica nanoparticles with wrinkled structure as the matrix of myristic acid for the preparation of a promising new shape-stabilized phase change material via simple method.

Wrinkled mesoporous silica nanoparticle (WMSN), with a special and highly uniform morphology, large specific surface area and pore volume, high porosity and radial-like wrinkled channels, was successfully prepared by a simple and easy synthetic method. WMSN was used as the matrix of myristic acid (MA) to prepare a new attractive shape-stabilized PCM (MA/WMSN), and the wrinkled channels of WMSN are useful to prevent the leakage of PCM, and increase the thermal stability and phase change enthalpy of shape-stabilized PCM. Characterizations of MA/WMSN, such as structure, crystallization properties, chemical properties and thermal properties were studied, and the interaction mechanism between the WMSN and MA molecules was elucidated. TGA results suggested that MA/WMSN had excellent thermal stability. When the loading of MA in MA/WMSN was 65%, the melting and crystallizing enthalpies of MA/WSSN were 92.0 J g−1 and 86.0 J g−1, respectively. Additionally, the thermal conductivity of MA/WMSN was 0.37 W mK−1, which was about 1.37 times higher than that of the pure MA. All of the study results demonstrated that MA/WMSN possessed of favourable thermal conductivity, high latent heats and excellent thermal stability, and therefore it could be a suitable thermal energy storage material for practical applications.

Supramolecular hydrogel based on cyclodextrin modified GO as a potent natural organic matter absorbent

New nanocomposite hydrogel was synthesized using biocompatible and biodegradable material. Firstly α-cyclodextrin functionalized with mercaptoacetic acid (MAA) and then attached to the surface of graphene oxide (GO) by ene-click reaction. Also starch (St) functionalized with myristic acid (MA) by esterification reaction. In the next step host-guest interactions formed between α-CD cavities and MA molecules. Due to this interaction graphene oxide nanosheets crosslinked to each other and a stable nanocomposite hydrogel formed successfully. These new synthesized nanomaterials were characterized by spectroscopic methods such as IR spectroscopy, UV–vis spectroscopy, X-ray diffraction (XRD) technique, scanning electron microscopy, thermogravimetric analysis (TGA) and Raman spectroscopy. FE-SEM analysis confirmed that prepared nanocomposite hydrogel has a well-defined and interconnected 3D porous network with pore sizes in the range of submicrometer to several micrometers. This nanocomposite hydrogel has beneficial application in different fields such as water purification. This newly synthesized nanomaterial is sensitive to external stimuli. We illustrated that addition of adamantane to the system as an external stimulus, result in destroying host-guest interactions between α-CD and St-MA because adamantane is a strong competitor for α-CD cavity in comparison with MA molecule. This also confirms that host-guest complex formation between α-CD and MA is the driving force for hydrogel formation. The obtained supramolecular hydrogel was used for water purification and the results showed that this product has a good ability for removal of organic materials such as humic acid (HA) from contaminated water.

Self-assembly of myristic acid in the presence of choline hydroxide: Effect of molar ratio and temperature

Salt-free catanionic systems based on fatty acids exhibit a broad polymorphism by simply tuning the molar ratio between the two components. For fatty acid combined with organic amino counter-ions, very few data are available on the phase behavior obtained as a function of the molar ratio between the counter-ion and the fatty acid. We investigated the choline hydroxide/myristic acid system by varying the molar ratio, R=ncholine hydroxide/nmyristic acid, and the temperature. Myristic acid ionization state was determined by coupling pH, conductivity and infra-red spectroscopy measurements. Self-assemblies were characterized by small angle neutron scattering and microscopy experiments. Self-assembly thermal behavior was investigated by differential scanning calorimetry, wide angle X-ray scattering and nuclear magnetic resonance. For R<1, ionized and protonated myristic acid molecules coexisted leading to the formation of facetted self-assemblies and lamellar phases. The melting process between the gel and the fluid state of these bilayers induced a structural change from facetted or lamellar objects to spherical vesicles. For R>1, myristic acid molecules were ionized and formed spherical micelles. Our study highlights that both R and temperature are two key parameters to finely control the self-assembly structure formed by myristic acid in the presence of choline hydroxide.

Probing the binding site characteristics of HSA: A combined molecular dynamics and cheminformatics investigation

Human serum albumin is a remarkable protein found in high concentrations in the body. It contains at least seven distinct fatty acid binding sites and two principle sites for drugs. Its primary function is to act as a fatty acid transport system, but it also shows the capacity to bind a diverse range of acidic, neutral and zwitterionic drug molecules. In this paper we investigate the ligand binding selectivity of HSA using cheminformatics analyses and molecular dynamics simulations. We compare and contrast the known ligand binding specificities as obtained from X-ray structural data using PCA, with additional direct analyses of the seven key binding pockets using analyses derived from molecular simulations. We assess both the fatted and defatted states of HSA using 100ns simulations of the APO and HOLO forms, as well as structures containing one, three and seven myristic acid molecules. We find that differences in fatty acid binding can have a dramatic effect on the flexibility of the protein and also the pocket characteristics. We discuss how the remarkable selectivity of the HSA pockets towards both endogenous fatty acids and exogenous drug molecules is not simply controlled by bulk property effects such as ionization state and lipophilicity.

Dynamic analysis of the atomic vibrations of proteins, as exemplified by the binding of myristic acid to human serum albumin

Prediction of the biological function of a protein from its three-dimensional structure is an important, still unsolved problem. A new approach to this objective, tried here, is use of crystallographic temperature factors, which contain the same information as IR and Raman spectra but lack their overlap problems. The hypothesis that atomic vibrations are evolutionally optimized for a particular function by adoption of collective modes governed by an attractor has been tested on 19 proteins with the result that strong correlation (r = 0.98) was found between the dimension of the attractor and the number of vectors needed to describe the function. The binding of five molecules of myristic acid (MA) to human serum albumin (HSA) at two sites accommodating two or three MA molecules, respectively, gave rise to four conformational changes in distinct regions. Two of these were located at the binding sites but the others occurred in segments far removed from the ligands both in the sequence and spatially. According to the statistical criteria employed, the conformational changes at the ligand-binding sites were not necessarily controlled by an attractor of low order, but the others were governed by one of dimension of 2-3. This was ascribed to entropic compensation. The results were tested using another ligand, an inhibitor of the BCL-2 family of proteins. The HSA underwent the same conformational changes with this ligand as with MA.

Interaction of bovine (BSA) and human (HSA) serum albumins with ionic surfactants: spectroscopy and modelling

The binding of several different categories of small molecules to bovine (BSA) and human (HSA) serum albumins has been studied for many years through different spectroscopic techniques to elucidate details of the protein structure and binding mechanism. In this work we present the results of the study of the interactions of BSA and HSA with the anionic sodium dodecyl sulfate (SDS), cationic cethyltrimethylammonium chloride (CTAC) and zwitterionic N-hexadecyl- N, N-dimethyl-3-ammonium-1-propanesulfonate (HPS) monitored by fluorescence spectroscopy of the intrinsic tryptophans at pH 5.0. Similarly to pH 7.0 and 9.0, at low concentrations, the interaction of BSA with these surfactants shows a quenching of fluorescence with Stern–Volmer quenching constants of (1.1±0.1)×10 4 M −1, (3.2±0.1)×10 3 M −1 and (2.1±0.1)×10 3 M −1 for SDS, HPS and CTAC, respectively, which are associated to the ‘effective’ association constants to the protein. On the interaction of these surfactants with HSA, an opposite effect was observed as compared to BSA, i.e., an enhancement of fluorescence takes place. For both proteins, at low surfactant concentrations, a positive cooperativity was observed and the Hill plot model was used to estimate the number of surfactant binding sites, as well as the association constants of the surfactants to the proteins. It is worthy of notice that the binding constants for the surfactants at pH 5.0 are lower as compared to pH 7.0 and 9.0. This is probably due to fact that the protein at this acid pH is quite compact reducing the accessibility of the surfactants to the hydrophobic cavities in the binding sites. The interaction of myristic acid with both proteins shows a similar fluorescence behaviour, suggesting that the mechanism of the interaction is the same. Recently published crystallographic studies of HSA–myristate complex were used to perform a modelling study with the aim to explain the fluorescence results. The crystallographic structure reveals that a total of five myristic acid molecules are asymmetrically bound in the macromolecule. Three of these sites correspond to higher affinity ones and correlate with high association constants described in the literature. Our models for BSA and HSA with bound SDS suggest that the surfactant could be bound at the same sites as those reported in the crystal structure for the fatty acid. The differences in tryptophan vicinity upon surfactant binding are explored in the models in order to explain the observed spectroscopic changes. For BSA the quenching is due to a direct contact of a surfactant molecule with the indole of W 131 residue. It is clear that the binding site in BSA which is very close, in contact with tryptophan W 131, corresponds to a lower affinity site, explaining the lower binding constants obtained from fluorescence studies. In the case of HSA the enhancement of fluorescence is due to the removal of static quenching of W 214 residue in the intact protein caused by nearby residues in the vicinity of this tryptophan.

Interlayer Dynamics of a Fatty Acid Exchanged Lithium Aluminum Layered Double Hydroxide Monitored by Infrared Spectroscopy and Pyrene Fluorescence

The interlayers of layered metal double hydroxides provide a novel environment for arrangement of molecular species as well as their reactions. In this study, we report on a system which has a dense packing of myristic acid molecules (CH[sub 3](CH[sub 2])[sub 12]COOH) in a Li-Al layered double hydroxide (LiAl[sub 2](OH)[sub 6][sup +]), the acid chains being aligned perpendicular to the metal hydroxide layer. This hydrophobic interlayer space acts as a partition medium for molecules like pyrene, which retain enough mobility to form excimers. The interlayer space is also solvated with ethanol. Upon heating the myristic acid exchanged sample, the interlayers separate making room for the solvent to escape. This leads to realignment of the myristic acid chains. The chains become considerably more rigid in the absence of ethanol and this leads to the stabilization of the expanded interlayer. Resolvation makes the chains mobile and leads rapidly to recovery of the properties of the as-synthesized material. 31 refs., 11 figs.

Surface radioactivity measurements of monomolecular films

In the last several years there has been a resurgence of interest in surface films at the air/water interface. The use of radioactive tracers in interfacial studies is attractive due to the sensitivity to detect small quantities of matter. The radiotracer method, therefore, has been utilized in various surface studies at the air/water interface including adsorption from solution [ 1,2], surface chemical reactions [ 31, monolayer desorption [ 4,5], surface diffusion [ 4-81, and surface concentration of insoluble monolayers [ 91. In this communication, we report simultaneous measurements of film loss from a sparingly soluble monolayer by radiotracer and Wilhelmy plate methods. Our findings indicate that greater caution should be exercised in the interpretation of surface radiotracer measurements of monomolecular films because of a previously unrecognized mass transport process, when a Geiger-Miiller (G-M) tube is employed, due to a possible electric field effect. Myristic [ l-‘*Cl acid (Rosechem Products, 59 mCi mmol-l) was deposited from a purified n-hexane spreading solution onto a 0.01 N HCl solution at 20-21 ‘C. The experimental apparatus is described in detail elsewhere [ 81. Compression barriers were not used in order to eliminate any possible film leakage past barriers. The monolayer was spread to an initial surface pressure of 5.5 mN m-‘, and then the surface pressure was measured as a function of time at constant area by the Wilhelmy plate method. Experimentally measured surface pressure-specific surface area (l7-A ) isotherms were then used to obtain the surface concentration dependence with time. The results were evaluated by plotting the ratio r/r, versus &, where r is the surface concentration of the myristic acid molecules, r,, is the initial surface concentration, and t is time. Simultaneously, the beta radiation emanating from the radioactive monolayer was measured by an end-window G-M tube ( Amperex 18526) and decade scaler, and the ratio of the surface concentrations, r/r,, is equal to the ratio of the monolayer activities after subtraction of the background count. Figure 1 shows the film loss measurements using the Wilhelmy plate and