Decrease In D-spacing Research Articles

Montmorillonite restricts free fatty acid liberation and alters self-assembled structures formed during in vitro lipid digestion

The global rise in obesity necessitates innovative weight loss strategies. Naturally occurring smectite clays, such as montmorillonite (MMT), offer promise due to their unique properties that interfere with free fatty acid (FFA) liberation, reducing systemic uptake. However, the mechanisms of MMT-FFA interactions and their implications for weight management are undefined. This study investigates these interactions by adding MMT (10 % w/w) to in vitro lipolysis media containing medium chain triglycerides (MCTs), and monitoring FFA liberation using pH-stat titration. Nanoparticle tracking analysis (NTA) and synchrotron-based small-angle X-ray scattering (sSAXS) observed time-dependent structural changes, while electron microscopy examined clay morphology during digestion. A 35 % reduction in FFA liberation occurred after 25 min of digestion with MCT + MMT, with digestion kinetics following a biphasic model driven by calcium soap formation. NTA revealed a 17-fold decrease in vesicular structures with MCT + MMT, and sSAXS highlighted a rapid lamellar phase evolution linked to calcium soap formation. This acceleration is attributed to MMT's adsorption to unionized FFAs via hydrogen bonding, supported by TEM images showing a decrease in d-spacing, indicating FFA intercalation is not the main adsorption mechanism. These findings highlight MMT's potential as a novel intervention for reducing dietary lipid absorption in obesity and metabolic diseases.

Role of Stearic Acid as the Crystal Habit Modifier in Candelilla Wax-Groundnut Oil Oleogels

This study investigated the effects of incorporating stearic acid (SAC) in candelilla wax (CW) and groundnut oil (GO) oleogel with potential health benefits as an alternative to saturated fats in processed foods. Results showed that SAC possesses crystal habit-modifying properties on the oleogels, causing its average crystallite size to increase, as observed through polarized light microscopy and XRD analysis. Additionally, SAC caused an increase in ordering within the crystallite network as a result of the decrease in d-spacing. Interestingly, the firmness of the oleogels remained unaffected, even at a higher fraction of SAC. It is believed to be due to the interference caused by the crystallization of high-melting SAC within the fine crystal network of CW-GO oleogel. However, adding 3 mg of SAC significantly increased the work of the shear of the oleogel (SAC3), which decreased the spreadability. As observed through colorimetric analysis, SAC3 showed a dense and uniform distribution of prominent bright crystals with minimal amorphous regions, leading to a high whiteness index. SAC3 also demonstrated the highest compactness and dislocation density among the oleogels, likely due to the formation of prominent crystals. However, SAC did not affect the overall oleogel crystallization rate. SAC3 had delayed secondary crystallization and thermal equilibrium by having a prolonged crystallization time of CW crystals. In the case of controlled delivery studies, the addition of SAC improved CPCR. On the other hand, CPCR decreased with the increase in SAC amount, where SAC3 showed a moderate curcumin release ability among the oleogels.

Rejection of pharmaceuticals by graphene oxide membranes: Role of crosslinker and rejection mechanism

Graphene oxide (GO)-based membranes were fabricated by first immobilizing GO nanosheet using polydopamine (PDA) on the polyvinylidene fluoride (PVDF) substrate and then tuning the interlaminar spacing and properties by the different crosslinkers (i.e., ethylenediamine (EDA) or β-cyclodextrin functionalized EDA (β-CD-EDA)) to investigate rejection performance and mechanism of three pharmaceuticals. The d-spacings of EDA crosslinked membrane (PDA-GO/EDA) and β-CD-EDA crosslinked membrane (PDA-GO/β-CD-EDA) were determined to be 1.13 and 0.97 nm, respectively, which were much higher than that of PDA coated GO membrane (PDA-GO) of 0.78 nm. The moderate and even relatively low rejection ratio of the pharmaceuticals demonstrated that molecular sieving didn't contribute significantly to the pharmaceutical rejection as expected. In addition to molecular sieving, the electrostatic and chemical interactions from the active sites GO might play the significant and noticeable role on pharmaceutical rejection. When adsorption was not much higher in some scenarios (i.e., carbamazepine at all pH, sulfadiazine @ pH = 11 and propranolol @ pH = 3), it was plausible that conformation of GO nanosheets dramatically changed, which resulted in decrease of d-spacing and thus much higher rejection ratio. In contrast, when adsorption was much higher in some scenarios (sulfadiazine @ pH = 3, 7 and propranolol @ pH = 7, 11), the solubility in the membrane matrix increased and therefore the rejection ratio decreased. The disagreement demonstrated that more attention should be paid on the interactions between pharmaceutical and GO membranes, although the stability of the membrane was enhanced by crosslinking.

New Insights on Solid-State Changes in the Levothyroxine Sodium Pentahydrate during Dehydration and its Relationship to Chemical Instability.

Levothyroxine sodium pentahydrate (LEVO) tablets have been on the US market since the mid-twentieth century and remain the most highly prescribed product. Unfortunately, levothyroxine sodium tablets have also been one of the most highly recalled products due to potency and dissolution failures on stability. In 2008, the assay limits were tightened, yet the recalls did not decline, which highlights the serious quality concerns remaining to be elucidated. The aim of the present investigation was to test the hypothesis that the solid-state physical instability of LEVO precedes the chemical instability leading to product failure. The failure mode was hypothesized to be the dehydration of the crystal hydrate, when exposed to certain humidity and temperature conditions, followed by the oxidation of the API through vacated channels. It was previously reported by the authors that LEVO degradation occurred in the presence of oxygen at a low relative humidity (RH). Furthermore, powder X-ray diffractometry shows changes in the crystal lattice of LEVO initially and through the dehydration stages. Storage of LEVO at RT and 40°C at 4-6% RH for 12days shows a decrease in d-spacing of the (00l) planes. Based on a structure solution from the powder data of the dehydrated material, the basic packing motif persists to varying degrees even when fully dehydrated along with disordering. Therefore, the crystal structure changes of LEVO depend on RH and temperature and are now explicable at the structural level for the first time. This exemplifies the dire need for "new prior knowledge" in generic product development.

In-operando observation of microstructural evolution in a solid oxide cell electrolyte operating at high polarization

In the present work a symmetric scandia yttria stabilized zirconia electrolyte based solid oxide cell is investigated in-operando by synchrotron X-ray diffraction as a function of time and position within the electrolyte while annealing at 700 °C in air and at a polarization of 2 V. In addition, scanning electron microscopy experiments are carried out on similar cells operating at temperatures of 700, 800 and 900 °C. Void formation in the grain boundaries of the electrolyte close to the anode/electrolyte interface is detected as early as 6 h. No clear trend is observed with respect to cell operation time and temperature in cells with equal grain size. However, grain boundary surface area may be inversely related to the frequency of void observations. A decrease of d-spacing in the anode interface region can be attributed to compressive stress associated with oxygen pressure build up. Decrease of d-spacing in the cathode/electrolyte region could be associated to oxide ion deficiency. Dark field X-ray microscopy is used to map for the first time the strain gradients within an electrolyte grain close to the anode region. Changes in strain domains after 10.5 h at operating conditions are assumed to be associated with early stages of void formation.

Conduction pathways in CNF/PTFE composite: Air oxidized CNFs coated with the incomplete layer of PTFE

In the present work, the conduction pathways by air oxidized carbon nanofibers (CNFs) (coated with Polytetrafluoroethylene (PTFE)) dispersed in PTFE polymer have been studied and explored with backbone and dangling ends model. The utility of critical exponents (t) explains the distribution status of CNFs and indicates the possibility of charge transport by ohmic conduction due to connected conducting channels of CNF and tunneling transmission between close CNFs. A 5 wt% sample exhibits a conductivity of 1.91 S/m. Moreover, a cost and material saving method of coating of decomposed PTFE on CNF; regardless of the coating thickness is discussed and studied in order to improve interfacial interaction and dispersion within the polymer without using sonication. Some interesting and informative evidence have also been revealed such as a decrease in d-spacing of 〈002〉 layer of CNF after heat treatment at ~800 °C in air and confirmation of Hexafluoropropylene (HFP) and Octafluoro‑1‑butene (OF1B) thermal products of PTFE on CNFs. The presence and coating of HFP and OF1B were confirmed by FTIR and TEM respectively.

Nitridated Pd/B4C multilayer mirrors for soft X-ray region: internal structure and aging effects.

Reactive sputtering with a mixture of argon and nitrogen (N2 partial pressure of 4%, 8%, and 15%) as the working gas is used to develop the high reflectance Pd/B4C multilayers for soft X-ray region application. Compared to the pure Ar fabricated sample, the interface roughness of the nitridated multilayer is slightly increased while the compressive stress is essentially relaxed from -623 MPa (pure Ar) to -85 MPa (15% N2). A maximum reflectance of 32% is measured at the wavelength of 9.5 nm for the multilayer fabricated with 15% N2. After storing the multilayers in an air environment for 6-17 months, a distinct aging effect is observed on the nitridated samples. The transmission electron microscopy results indicate that a large part of the top layers of the nitridated samples is deteriorated with severe interdiffusion, essential decrease in d-spacing, and compacted multilayer structure. The deterioration is less pronounced for the multilayers fabricated with a higher ratio of N2. Energy dispersive X-ray spectroscopy reveals that the concentration of nitrogen and boron in the degraded area is much reduced compared to the intact layers. A primitive model of upward diffusion of nitrogen and boron is proposed to explain the aging effects of the nitridated structure.

1,3-Dialkylimidazolium modified clay sorbents for perchlorate removal from water

Clay modified using the 1-hexadecyl-3-methylimidazolium cation (C16-clay) shows perchlorate adsorption of 15.6 mg g−1 accompanied by a conformational change and decrease in d-spacing.

Synthesis of ordered photoresponsive azobenzene–siloxane hybrids by self-assembly

In this study, photoresponsive azobenzene–siloxane hybrids with lamellar structures were prepared by self-assembly using two types of alkoxysilane precursors, 4-[3-(triethoxysilyl)propoxy]azobenzene (P1) and 4-[3-(diethoxymethylsilyl)propoxy]azobenzene (P2). The films H1 and H2 were prepared by spin-coating hydrolyzed solutions of P1 and P2, respectively, on a glass substrate followed by heating to induce polycondensation. X-ray diffraction patterns revealed that H1 and H2 have lamellar structures with different d-spacings (3.20 nm and 2.37 nm, respectively), suggesting that the arrangements of the azobenzene moieties are different. These samples show slight but reversible changes in the d-spacings under photo-irradiation. Under UV irradiation, H1 shows a slight decrease in d-spacing, while H2 shows a slight increase. Such changes were caused by trans–cis isomerization of a part of the azobenzene moieties in the films, as confirmed by UV-vis absorption spectroscopy. These processes were reversible, with the d-spacings recovering their original values under visible light irradiation. Furthermore, P1 and P2 were co-hydrolyzed and polycondensed with tetraethoxysilane to give lamellar films (H1′ and H2′) showing a higher degree of trans–cis photoisomerization of the azobenzene moieties. Both H1′ and H2′ show increase in the d-spacings after soaking in various organic solvents. Possible structural models have been proposed to explain these photoresponsive properties of the azobenzene–siloxane nanohybrids, which will find potential applications as smart sensors and adsorbents in future.

160 MeV Ni12+ ion irradiation effects on the dielectric properties of polyaniline nanotubes

We report on the dielectric properties and a.c. conductivity studies of CSA doped polyaniline nanotubes. Nanotubes of 47–100nm diameter, were synthesized by the self-assembly method and irradiated using Ni12+ ions of 160MeV energy with fluences of 1×1010, 5×1010, 1×1011 and 3×1011 ions/cm2. X-ray diffraction studies reveal an increase in the degree of crystallinity and consequently, the extent of order of the nanotubes with increasing fluence, but show a lower degree of crystallinity at higher fluence. The decrease in d-spacing for the (100) reflections with fluence is ascribed to the decrease in the tilt angle of the aligned polymer chains. A significant change was seen after irradiation in dielectric and electrical properties which may be correlated with the increased carrier concentration and structural modifications in the polymer films. The surface conductivity of films increases with increasing fluence, which also decreases at higher fluence. The a.c. conduction mechanism for the nanotubes could be explained in terms of correlated barrier hopping model. The existence of polarons as the major charge carriers in the present nanotube system was confirmed by the low values of polaron binding energy, found to decrease with fluence. The hopping distance increases with fluence indicating that the hopping probability increases with fluence.

Influence of types and charges of exchangeable cations on ciprofloxacin sorption by montmorillonite

As one of the most important soil components, montmorillonite plays a vital role in transport and retention of organic pollutants in soils. Ciprofloxacin (CIP), an antibiotic of fluoroquiolones, has been frequently detected in water and soil environments due to its wide use in human and veterinary medicine. In this study, the adsorption of CIP onto different homoionic montmorillonite such as Na-, Ca- and Al-MMT was investigated, and the influence of types and charges of exchangeable cations in the interlayer of montmorillonite on CIP adsorption was evaluated. The results showed that different homoionic montmorillonite exhibited different sorption capacity of CIP. At pH 3, the sorption capacity of CIP decreased in the order Na-MMT > Ca-MMT > Al-MMT, following the lyotropic series. When solution pH increased to 11, the sorption capacity of CIP followed the order Ca-MMT > Al-MMT > Na-MMT. Accompanying CIP adsorption on Ca-MMT, a certain amount of Ca2+ was released into solution. Compared to pH 3, the lower Ca concentration in solution at pH 11 indicated that the adsorption of CIP on Ca-MMT at strong alkaline pH was no longer via cation exchange, and surface complexation or cation bridging might contribute to CIP adsorption. The adsorption of CIP on Na- and Ca-MMT at pH 3 and 11 resulted in the expansion of d-spacing, indicative of intercalation of CIP into the interlayer space of the montmorillonite. However, a decrease of d-spacing was observed when CIP adsorbed on Al-MMT at pH 11, which might be attributed to the dissolution of Al-CIP complex formed between CIP and Al3+ in the interlayer of montmorillonite. The results suggest that the types and charges of exchangeable cations in the interlayer of montmorillonite play an important role in CIP adsorption on montmorillonite.

Effects of hot water extraction and fungal decay on wood crystalline cellulose structure

The effect of hot-water extraction and two types of fungal decay, brown rot and white rot, on wood crystalline cellulose structure was examined using a combination of X-ray diffraction (XRD) and 13C solid-state nuclear magnetic resonance (NMR) spectroscopy. Although having opposite effects on the overall crystallinity of the wood, the XRD results revealed that both extraction and brown-rot decay caused a significant decrease in the 200 crystal plane spacing (d-spacing) not seen for the white-rotted samples. This effect was found to be additive, as samples that were first extracted, then decayed showed a double decrease in d-spacing compared to that caused by extraction alone. This suggested that, despite having a similarly directed effect on the spacing of the crystalline planes, the two treatment methods facilitate a decrease in d-spacing in different ways. NMR results support the conclusion of differing structural effects, suggesting that the hot-water extraction procedure was causing a co-crystallization of existing crystalline domains, while the brown rot decay was depolymerizing the cellulose chains of the crystals, possibly allowing the remaining crystalline material the freedom to relax into a more energetically favorable, tightly packed state. These findings could have important implications for those seeking to understand the effects of modification treatments or biodegradation of crystalline cellulose nanostructures in their native states.

In situSAXS study on cationic and non-ionic surfactant liquid crystals using synchrotron radiation

In situ synchrotron small-angle X-ray scattering was used to investigate various surfactant/water systems with hexagonal and lamellar structures regarding their structural behaviour upon heating and cooling. Measurements of the non-ionic surfactant Triton X-45 (polyethylene glycol 4-tert-octylphenyl ether) at different surfactant concentrations show an alignment of the lamellar liquid-crystalline structure close to the wall of the glass capillaries and also a decrease in d-spacing following subsequent heating/cooling cycles. Additionally, samples were subjected to a weak magnetic field (0.3-0.7 T) during heating and cooling, but no influence of the magnetic field was observed.

Evolution of mesoporous materials during the calcination process: structural and chemical behavior

We describe herein the study of the temporal evolution of hexagonal mesophases of silica, titania and zirconia as a function of temperature. Detailed in situ X-ray diffraction (XRD) studies with a high temperature XRD chamber system have been conducted in conjunction with thermogravimetric–differential thermal analysis coupled with mass spectrometry (TG–DTA/MS) to better understand the processes related with template removal from MCM-41 type mesophases. The thermal behavior of the cationic surfactants in the mesostructured systems has been analyzed, and the processes involved have been elucidated. In the case of Si-MCM-41, an initial change occurs up to 250°C with an increase in intensity of all reflections, with the (110) and (200) reflections increasing later and at a higher rate than the (100) reflection. After 300°C, changes are less pronounced and the intensities remain unchanged while the sample is kept at 550°C. The TG–DTA/MS data show that the decomposition mechanism in air involves three steps. An initial endothermic step is assigned to Hofmann elimination of trimethylamine, leading to a hydrocarbon chain. The second step is exothermic and results from a carbon chain fragmentation. Finally, oxidation occurring at 320°C converts the remaining organic components to carbon dioxide. Template removal appears to be completely different for the transition metal based materials: a single step complete oxidation of the surfactant is observed around 300°C in TG–DTA/MS. This is accompanied with the drastic decrease in d-spacing and initial sharp increase in reflection intensity in the XRD pattern, which generally leads to the loss of the well ordered hexagonal structure.

Palygorskite Separation from Dodecylammonium-Treated Clays

AbstractThree methods were investigated to separate palygorskite from mixtures of clay minerals in soils and sediments. The methods were based on the hydrophobic properties of a dodecylammonium-smectite complex and used the <0.2-μm fractions of reference palygorskites that contained smectite and sepiolite impurities. Palygorskite was separated from dodecylammonium-clay complexes by: (1) selective dispersion of palygorskite in H2O; (2) selective extraction of palygorskite by a water:decanol phase separation; and (3) selective extraction of palygorskite by a water: nitrobenzene phase separation. Whereas all three methods resulted in palygorskite separation, selective dispersion was the simplest and employed the more desirable reagents. Small amounts of relatively pure palygorskite in the <0.2-μm fractions were concentrated from palygorskite-containing clays from Texas, Saudi Arabia, and Libya as shown by X-ray powder diffraction and transmission electron microscopy data. A sepiolite impurity in the Georgia palygorskite was concentrated with the palygorskite. Hydrolysis of the dodecylammonium-smectite complex was suggested by the decrease in d-spacing of some samples after the extensive washing necessary for dispersion. An appreciable amount of the fibrous mineral was intimately associated with layer silicates and could not be separated.