Infrared Spectra and Hydrogen-Bond Configurations of Water Molecules at the Interface of Water-Insoluble Polymers under Humidified Conditions

Modeling of the Hydrogen Bond-Induced Frequency Shifts of the HOH and HOD Bending Modes of Water

The intramolecular bending mode of water is a possible useful probe of the hydrogen-bond situations in aqueous systems, but the behavior of its frequency and intensity should be further elucidated for better understanding on its nature and, hence, for its better utilization as a probe. Here, an analysis toward this goal is conducted by doing theoretical calculations on molecular clusters of normal isotopic and deuterated species of water and examining the correlations among the vibrational, structural, and electrostatic properties. It is shown that electrostatic interactions, particularly both of the in-plane components of the electric field along the OH bond and perpendicular to it, play a major role in controlling the hydrogen bond-induced shifts of the force constant, but additional factors, including the intermolecular structural and/or charge-transfer properties, are also important. Models of the hydrogen bond-induced shifts of the force constant are presented in a form that may be combined with classical molecular dynamics. With regard to the infrared intensity changes, it is shown on the basis of the electron density analysis that the intermolecular charge flux and polarization effect play an important role, depending on the angular characteristics of the hydrogen bond.

Enhanced Stability, Superior Anti-Corrosive, and Tribological Performance of Al2O3 Water-based Nanofluid Lubricants with Tannic Acid and Carboxymethyl Cellulose over SDBS as Surfactant

In this research work, the stability, tribological, and corrosion properties of a water-based Al2O3 nanofluid (0.5 wt%) formulated with tannin acid (TA) and carboxymethyl cellulose (CMC) as dispersants or surfactants were investigated. For comparative purposes, sodium dodecylbenzene sulfonate (SDBS) was also incorporated. The stability of the nanofluid was assessed through zeta potential measurements and photo-capturing, revealing the effectiveness of TA and CMC in preventing nanoparticle agglomeration. Tribological properties were examined using a pin-on-disk apparatus, highlighting the tribofilm of Al2O3 that enhanced lubricating properties of the nanofluid by the SEM, resulting in reduced friction and wear of the contacting surfaces. Sample with the addition of both TA and CMC exhibited the best tribological performance, with a ~ 20% reduction in the friction coefficient and a 59% improvement in wear rate compared to neat nanofluid without TA and CMC. Additionally, the corrosion resistance of the nanofluids were evaluated via weight loss and electrochemical impedance spectroscopy. The nanofluid sample containing both TA and CMC exhibited the lowest corrosion rate, with 97.6% improvement compared to sample without them. This study provides valuable insights into the potential applications of TA and CMC-based Al2O3 nanofluids as effective and environmentally friendly solutions for coolant or lubrication in cutting processes.

Kinetics of Direct Reaction of Vanadate, Chromate, and Permanganate with Graphene Nanoplatelets for Use in Water Purification

Oxometalates of vanadium(V), chromium(VI), and manganese(VII) have negative impacts on water resources due to their toxicity. To remove them, the kinetics of 0.04 mM oxometalates in natural and synthetic water were studied using graphene nanoplatelets (GNP). The GNP were dispersible in water and formed aggregates >15 µm that could be easily separated. Within 30 min, the GNP were covered with ~0.4 mg/g vanadium and ~1.0 mg/g chromium as Cr(OH)3. The reaction of 0.04 mM permanganate with 50 mg of GNP resulted in a coverage of 10 mg/g in 5 min, while the maximum value was 300 mg/g manganese as Mn2O3/MnO. TEM showed a random metal distribution on the surfaces; no clusters or nanoparticles were detected. The rate of disappearance in aerated water followed a pseudo second-order adsorption kinetics (PSO) for V(V), a pseudo second-order reaction for Cr(VI), and a pseudo first-order reaction for Mn(VII). For Cr(VI) and Mn(VII), the rate constants were found to depend on the GNP mass. Oxygen sorption occurred with PSO kinetics as a parallel slow process upon contact of GNP with air-saturated water. For thermally regenerated GNP, the rate constant decreased for V(V) but increased for Cr(VI), while no effect was observed for Mn(VII). GNP capacity was enhanced through regeneration for V(V) and Cr(VI); no effect was observed for Mn(VII). The reactions are well-suited for use in water purification processes and the reaction products, GNP, decorated with single metal atoms, are of great interest for the construction of sensors, electronic devices, and for application in single-atom catalysis (SAC).

Biodegradable AZ91 magnesium alloy/sirolimus/poly D, L-lactic-co-glycolic acid-based substrate for cardiovascular device application

Biodegradable drug-eluting stents (DESs) are gaining importance owing to their attractive features, such as complete drug release to the target site. Magnesium (Mg) alloys are promising materials for future biodegradable DESs. However, there are few explorations using biodegradable Mg for cardiovascular stent application. In this present study, sirolimus-loaded poly D, L-lactic-co-glycolic acid (PLGA)-coated/ sirolimus-fixed/AZ91 Mg alloy-based substrate was developed via a layer-by-layer approach for cardiovascular stent application. The AZ91 Mg alloy was prepared through the squeeze casting technique. The casted AZ91 Mg alloy (Mg) was alkali-treated to provide macroporous networks to hold the sirolimus and PLGA layers. The systematic characterization was investigated via electrochemical, optical, physicochemical, and in-vitro biological characteristics. The presence of the Mg17 Al12 phase in the Mg sample was found in the x-ray diffraction system (XRD) spectrum which influences the corrosion behavior of the developed substrate. The alkali treatment increases the substrate's hydrophilicity which was confirmed through static contact angle measurement. The anti-corrosion characteristic of casted-AZ91 Mg alloy (Mg) was slightly less than the sirolimus-loaded PLGA-coated alkali-treated AZ91 Mg alloy (Mg/Na/S/P) substrate. However, dissolution rates for both substrates were found to be controlled at cell culture conditions. Radiographic densities of AZ91 Mg alloy substrates (Mg, Mg/Na, and Mg/Na/S/P) were measured to be 0.795 ± 0.015, 0.742 ± 0.01, and 0.712 ± 0.017, respectively. The star-shaped structure of 12% sirolimus/PLGA ensures the bioavailability of the drugs. Sirolimus release kinetic was fitted up to 80% with the "Higuchi model" for Mg samples, whereas Mg/Na/S/P showed 45% fitting with a zero-order mechanism. The Mg/Na/S/P substrate showed a 70% antithrombotic effect compared to control. Further, alkali treatment enhances the antibacterial characteristic of AZ91 Mg alloy. Also, the alkali-treated sirolimus-loaded substrates (Mg/Na/S and Mg/Na/S/P) inhibit the valvular interstitial cell's growth significantly in in-vitro. Hence, the results imply that sirolimus-loaded PLGA-coated AZ91 Mg alloy-based substrate can be a potential candidate for cardiovascular stent application.

Phase Inversion Gelation Process and Additive Effects on Hydrogel Film Properties of Cotton Cellulose

During the preparation of cotton cellulose hydrogels using the phase inversion gelation method of N,N-dimethylacetamide/LiCl solution under ethanol vapor, acetone (AC), methyl ethyl ketone (MEK), or diethyl ketone (DEK) were added as additives, and their gelation state and the properties of the resulting hydrogels were evaluated. Adding the ketones to the cellulose solution caused an increase in the gelation time, but the solution viscosity decreased, indicating that the cellulose tended to aggregate in the solution. Among the hydrogels prepared by adding ketones, the water content was as high as 2050%, especially for AC and MEK. In these hydrogels, cellulose formed an agglomerated fibrous network of a few micron widths, forming a tuft-like entrapment space of about 10 to 100 μm size. The structure surrounded water and held it in the hydrogels. The FTIR results showed that the water, which formed hydrogen bonds, was retained within the hydrogel network. This structural configuration was determined to be conducive to maintaining the gel state against external deformation forces, especially in the case of the addition of MEK.

Optimization of stabilized anaerobic landfill leachate treatment using ozonation with metallic compound using response surface methodology

Malaysia encounters a consistent rise in the generation of solid waste and leachate on a daily basis. It should also be noted that leachate has a low degree of biodegradability (BOD5 /chemical oxygen demand [COD]), as shown by its BOD5 /COD ratio. Its high toxicity levels significantly threaten the environment, water bodies, and human well-being. High concentrations of COD, color, and ammoniacal nitrogen (NH3 -N) in leachate prevent this wastewater from being allowed to be discharged directly into the water body. Therefore, an effective process to remove the pollutant is desired. The aims of this study are to investigate the performance of ozonation with two metallic compounds, ZrCl4 and SnCl4 , and optimize their performance using response surface methodology (RSM). In this study, the performance of ozonation with ZrCl4 (O3 /ZrCl4 ) recorded better pollutant removals compared with the ozonation with tin tetrachloride (O3 /SnCl4 ), as seen in the removals of 99.8%, 93.5%, and 46.3% for color, COD, and NH3 -N, respectively. These removals were achieved by following the experimental model (optimum experiment condition) generated by RSM at O3 dosage of 31 g/m3 , COD and ZrCl4 dosage ratio (COD, mg/L/ZrCl4 , mg/L) of 1:1.35, with the pH solution of 8.78 and reaction time of 89 min. The R2 of each parameter for this model was recorded as 0.999 (COD), 0.999 (color), and 0.998 (NH3 -N), respectively. These data indicated that the model is well fitted as the predicted data by statistical calculation and in good agreement with the actual data. PRACTITIONER POINTS: The performance of O3 /ZrCl4 and O3 /SnCl4 was examined for remediate stabilized landfill leachate. The performance of O3 /ZrCl4 and O3 /SnCl4 was optimized using RSM, and a set of experimental models was generated and tested. O3 /ZrCl4 recorded the higher removal of COD, color, and NH3 -N compared with O3 /SnCl4 . At best condition, both methods recorded removal as 89% to 99.8% of pollutants in leachate and product clear effluent. This finding gives a new approach to treat landfill leachate effectively and efficiently.

Functionality and characterization of modified starch films with pineapple leaf fibers

The objective of this work was to modify banana starch with pineapple leaf fibers (PALF) and its production of biodegradable films. The reaction conditions of the starch modification were a Starch/PALF mass ratio of 50, a time of 1 h and a temperature of 140 °C, to obtain a yield of 41.18 %. Characterization by FTIR and NMR confirmed that the chemical reaction was carried out. XRD and TGA analysis showed that the crystalline zones of the starch were affected during the modification and the product obtained is thermally less stable compared to unmodified starch. The modified starch showed a lower pasting profile compared to the native starch; however, the modified starch showed the ability to form a film. The starch-PALF films were obtained by the casting method and partially characterized. These films presented better mechanical properties compared to the unmodified films. Also, these films could compete with conventional non-biodegradable plastics.

Asymmetry of the Electrostatic Environment as the Origin of the Symmetry Breaking Effect of the Nitrate Ion in Aqueous Solution

Elucidating the mechanism of how vibrational modes are affected by intermolecular interactions is important for a better understanding of the nature of the former as probes of the latter. Here, such an analysis is carried out for the N-O stretching modes of the nitrate ion interacting with water, with an emphasis on the symmetry breaking effect. On the basis of theoretical calculations on the structural, vibrational, and electrostatic properties of molecular clusters and spectral simulations for an aqueous solution, a transparent view is demonstrated on the mechanism that modulations of spatially local electrostatic environment give rise to structural and spectroscopic symmetry breaking effect. The electrostatic interaction model constructed here is a seven-parameter model; the use of a single electrostatic parameter, such as the electric field on a single atomic site, is found to be insufficient for quantitative evaluation. It is also shown that the frequency modulations of the N-O stretching modes in aqueous solution occur on a time scale much shorter than 0.1 ps.

Molecular Dynamics Studies of the Ho(III) Aqua-tris(dibenzoylmethane) Complex: Role of Water Dynamics

The seven-coordinate Ho(III) aqua-tris(dibenzoylmethane)(DBM) complex, referred to as Ho-(DBM)₃·H₂O, was first reported in the late 1960s. It has a threefold symmetric structure, with Ho at the center of three dibenzoylmethane ligands and hydrogen-bonded water to ligands. It is considered that the hydrogen bonds between the water molecule and the ligands surrounding Ho play an important role in the formation of its symmetrical structure. In this work, we developed new force-field parameters for classical molecular dynamics (CMD) simulations to theoretically elucidate the structure and dynamics of Ho-(DBM)₃·H₂O. To develop the force field, structural optimization and molecular dynamics were performed on the basis of ab initio calculations using the plane-wave pseudopotential method. The force-field parameters for CMD were then optimized to reproduce the data obtained from ab initio calculations. Validation of the developed force field showed good agreement with the experimental crystalline structure and ab initio data. The vibrational properties of water in Ho-(DBM)₃·H₂O were investigated by comparison with bulk liquid water. The vibrational motion of water was found to have a characteristic mode originating from stationary rotational motion along the c-axis of Ho(III) aqua-tris(dibenzoylmethane). Contrary to expectations, the hydrogen-bond dynamics of water in Ho-(DBM)₃·H₂O were found to be almost equivalent to those of bulk liquid water except for librational motion. This development route for force-field parameters for CMD and the establishment of water dynamics can advance the understanding of water-coordinated metal complexes with high coordination numbers such as Ho-(DBM)₃·H₂O.

Eumelanin decorated poly(lactic acid) electrospun substrates as a new strategy for spinal cord injury treatment

Spinal cord injury (SCI) is characterized by neuroinflammatory processes that are marked by an uncontrolled activation of microglia, which directly damages neurons. Natural and synthetic melanins represent an effective tool to treat neuroinflammation because they possess immunomodulatory properties. Here, the main objective was to evaluate the effect of eumelanin-coated poly(lactic acid) (EU@PLA) aligned microfibers on in vitro model of neuroinflammation related to spinal cord injury in terms of inflammatory mediators' modulation. Aligned fibers were chosen to provide physical cues to guide axonal growth in a specific direction thus restoring the synaptic connection. Eumelanin decorated PLA electrospun substrates were produced combining electrospinning, spin coating and solid-state polymerization processes (oxidative coupling under oxygen atmosphere). Biological response in terms of antioxidant and anti-inflammatory activity was analyzed on an in vitro model of neuroinflammation [microglial cells stimulated with lipopolysaccharide (LPS)]. Cell morphology and EU@PLA mechanism of action, in terms of toll-like receptor-4 (TLR-4) involvement were assessed. The results show that EU@PLA fibers were able to decrease reactive oxygen species, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-кB) expression >50 % compared to PLA + LPS and interleukin 6 (IL-6) secretion about 20 %. Finally, the mechanism of action of EU@PLA in microglia was found to be dependent on the TLR-4 signaling. Protein expression analysis revealed a decreased in TLR-4 production induced by LPS stimulation in presence of EU@PLA. Overall, our results show that EU@PLA represents an innovative and effective strategy for the control of inflammatory response in central nervous system.

Hydrogen-Bond Configurations of Hydration Water around Glycerol Investigated by HOH Bending and OH Stretching Analysis

Toward a comprehensive understanding of the mechanism of glycerol as a moisturizer, studies on the hydrogen-bond (HB) structure of hydration water, which is known to be disordered by glycerol, are insufficient. To this aim, we evaluated the HB configurations based on the HOH bending and OH stretching spectra of the hydration water from those of glycerol/water mixtures by subtracting the contributions of bulk water and glycerol using dielectric relaxation spectroscopy. Analysis of the HOH bending band showed that hydration water-donating HBs lose the intermolecular bending coupling with increasing glycerol by replacing the water-water HBs with water-glycerol HBs. The OH stretching band provided more detailed insight into the HB configuration, indicating that the double-donor double-acceptor and double-donor single-acceptor configurations in bulk water change to a predominantly double-donor single-acceptor configuration in hydration water around glycerol. The formation of more donor HBs than acceptor HBs may be due to the steric constrains by glycerol and/or differences in the partial charge on the oxygen atom between water and glycerol.