Glycine Solution Research Articles

Study of the electrochemical behavior of printed circuit boards (PCBs) leaching solutions using glycine and copper recovery by electrodeposition from leachate solutions

The present work focuses on the study of the electrochemical behavior of printed circuit boards (PCBs) leaching solutions using glycine and copper recovery by electrodeposition from leachate solutions. The recovery is done in a minimum number of steps and under ambient conditions of temperature and pressure. Printed circuits boards (PCBs) were pulverized and sieved, which allowed to obtain a PCBs powder of particle size fraction ≤ 1 mm. X-ray fluorescence spectroscopy analysis was used for PCBs powder characterization before and after leaching. The copper leaching has been carried out from PCBs powder in the open air, under ambient conditions of temperature and pressure using a buffer solution of glycine. UV–Vis spectrophotometry and atomic absorption spectrophotometry were utilized to determine the efficiency of copper leaching. Cyclic sweep voltammetry and chronoamperometry were employed to obtain informations on the electrochemical behavior of metals in the leaching solutions and then compared to that of synthetic solutions containing Cu (II) ions. UV–Visible spectrophotometry was used to determine the nature of the formed complex. Electrodeposition technique was applied in order to recover copper in powder form. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were employed to examine the surface morphology and chemical composition of electrodeposited copper. The leaching solutions show exactly the same electrochemical behavior as the synthetic cupric solutions with two reduction peaks and a single oxidation peak, which demonstrates the high selectivity of glycine for copper. The chronoamperometric results confirm those obtained by voltammetry. UV–Visible spectrophotometry showed that the complex formed is [Cu(Gly)2] for the synthetic solutions as well as for the leachate solutions. Selective copper leaching was achieved with an efficiency of 92.5%. The resulting leachate solution was used directly for copper electrodeposition allowing the recovery of metallic copper as a pure product.

Formaldehyde preservation for deferred measurements of alkaline phosphatase activities in marine samples

Alkaline phosphatases are the main enzymes required by microorganisms to hydrolyse organic phosphorus into available phosphate in aquatic environments. The investigations of alkaline phosphatase activity (APA) usually generate numerous samples (size fractionation, Michaelis-Menten kinetics). Therefore, convenient and reliable preservation of incubated samples for a deferred analysis would be very useful when measurements cannot be performed right away. The APA of marine pond waters was measured using 4-Methylumbelliferyl phosphate (MUF-P) as the fluorogenic substrate modelling natural organic phosphorus compounds. Where typical inhibitors of other enzymatic activities, such as 1% sodium dodecyl sulfate, mercuric chloride, or buffered solutions of ammonium and glycine, failed to stop APA, the addition of formaldehyde efficiently inhibited APA. The effect of formaldehyde was the strongest with the highest concentration tested (4% final concentration) and in buffered (pH 8) solutions. Since a slow and gradual increase in APA may persist with time, the combination of the addition of 4% buffered formaldehyde with immediate freezing is the best method to entirely inhibit APA. The maximal rate of hydrolysis (Vmax) and the Michaelis constant (Km) of formaldehyde (4%)-inhibited samples did not significantly change during storage at -20 °C for 11 days. The method was successfully tested on samples with extremely high values of APA (15000–40000 nM h−1) that were preserved for 1 month at -20 °C (98% inhibition). This method is a reliable and useful means of preserving incubated samples, and it provides convenient controls for background fluorescence of water and substrate, without provoking abiotic hydrolysis of the substrate.

Development of a Maillard Reaction–Based Time-Temperature Integrator/indicator (TTI) for Visual Monitoring of Chilled Beef During Long-term Storage and Distribution

Time-temperature integrator/indicator (TTI) is a temperature monitoring tool that visually presents the temperature history of foods to easily and cost-effectively manage the temperature of food products in cold chain system. However, few TTIs exhibit suitable performance under chilled conditions over a long period, such as beyond 100 days, as in the storage and distribution of chilled beef across the world. This study aimed to visualize the temperature history of chilled vacuum-packed beef, during international distribution, using Maillard reaction–based TTIs to record the accumulated temperature under chilled conditions, for more than 100 days. The developed Maillard reaction–based TTI comprised of double-sealed large and small plastic pouches. While the small pouch contained 500 μL D-xylose solution, the large pouch contained 1000 μL glycine solution with disodium hydrogen phosphate solution. Both the solutions were mixed by breaking the small pouch into the large pouch, following which the Maillard reaction started, depending on the ambient temperature. We examined two different combinations of the solution concentrations of TTI that turned brown and yellow at − 0.5 °C after approximately 77 days and 100 days, respectively. The developed TTIs, along with Tasmanian chilled beef, were transported from Australia to Japan through commercial supply chains and stored at a constant temperature of − 0.5 °C. One of the TTIs (TTI-brown) turned pale brown after 77 days which is the current shelf life of Australian chilled beef in Japan. The color of TTI-yellow changed to clear yellow after 150 days, when the chilled beef developed an off-odor, as judged by sensory evaluation. The TTI-brown was functional until day 77 which is the current shelf life of Australian beef in Japan, while the TTI-yellow was functional until day 150 to indicate remaining shelf life of beef. The results collectively indicated the Maillard reaction–based TTIs to realize visualization of temperature history during long-term storage and distribution of chilled beef.

Investigation of hydrogen generation from sodium borohydride using different cobalt catalysts

Effective Co/Cu, CoB/Cu, and CoBM (M = Mo,Zn,Fe)/Cu catalysts were prepared on the copper surface by a simple electroless deposition method using a morpholine borane as a reducing agent in the glycine solution. The activity of the deposited catalysts was investigated for hydrogen generation from an alkaline sodium borohydride solution. It was determined that these synthesized catalysts demonstrated the catalytic activity for the hydrolysis reaction of NaBH4. The lowest obtained activation energy (EA) of the hydrolysis reaction of NaBH4was 27 kJ mol−1 for the CoBMo/Cu catalyst. The hydrogen generation rate of 15.30 ml min−1 was achieved using CoBMo/Cu catalysts at 313 K and it increased ~3.5 times with the increase of temperature to 343 K. The highest hydrogen generation rate obtained by CoBMo/Cu films may be related to the hierarchical cauliflower-shaped 3D structures and the high roughness surface area. Moreover, the CoBMo/Cu catalyst showed an excellent reusability.

Investigation into the effect of mechanical activation on the leaching of chalcopyrite in a glycine medium

The effect of mechanical activation on the leaching and electrochemistry of chalcopyrite was investigated in a glycine medium. Leaching experiments were conducted to evaluate the effect of particle size (with re-ground sample in ball mill) and mechanical activation (with re-ground sample in planetary mill for 4 h) on chalcopyrite dissolution in a stirred tank reactor. Results show that a maximum copper extraction (95.1%) was obtained for mechanically activated chalcopyrite after 12 h leaching in a 0.4 M glycine solution at 60 °C, 2% (w/v) pulp density and an initial solution pH of 10.5. Under these same leaching conditions, a decrease in particle size for conventionally ground chalcopyrite from 106 to 125 μm to <20 μm, led to a substantial increase in the level of copper extraction - from 0.6% to 33.8%. Analysis of solid residue by XRD showed that iron could be precipitated as maghemite and a part of dissolved copper could be removed from the solution as copper glycinate crystals and covellite. Result of the electrochemical analysis showed that the anodic current of the chalcopyrite‑carbon paste electrode was significantly increased for the mechanically activated sample. Nevertheless, anodic current densities were observed to reduce during subsequent voltammetry cycles as a consequence of passivating the surface of chalcopyrite electrode by reaction products and decreasing electroactive cites the electrode surface. A new 2-stage leaching flowsheet was proposed to extract copper from chalcopyrite concentrates in glycine media. Glycine leaching with mechanical activated pretreatment could be a promising method for treating low-grade chalcopyrite concentrates.

Ethanol-free antisolvent crystallization of glycine by liquefied dimethyl ether

Liquefied dimethyl ether (DME) was employed as an antisolvent to crystallize glycine from its aqueous solution. The proposed method can be performed at 20–25 °C and has the potential to reduce the energy consumption of drying or crystallizing using ethanol. α-Glycine crystals were successfully obtained from glycine aqueous solutions by mixing in liquefied DME, which was easily removed from the crystals by decompression. Contact with a liquefied DME/water mixture and small γ-glycine crystals resulted in the α-glycine converting to γ-glycine. This was only observed for saturated glycine solutions. We speculated that this conversion occurs via a solution-mediated transition. Pure liquefied DME is not capable of promoting solvent-mediated transitions, so saturated glycine solutions treated with the pure antisolvent can give α-glycine as the sole product.

Relation between biomolecular dissociation and energy of secondary electrons generated in liquid water by fast heavy ions

In this work, we measured and simulated the dissociation of biomolecules in liquid water induced by secondary electrons ejected from water molecules during fast heavy-ion irradiation. We calculated the energy spectra of secondary electrons generated along carbon ion tracks in liquid water in the Bragg peak region. The calculation was done using the Particle and Heavy Ion Transport code System (PHITS) in carbon track structure mode. This mode enables simulation of inelastic collisions along a carbon ion track based on the cross sections considered in the Monte Carlo code KURBUC. To understand the biomolecular dissociation processes in our previous MeV-SIMS experiments with microdroplet targets of glycine solution, we calculated the collision spectra of secondary electrons produced near liquid surfaces using PHITS. Furthermore, we examined the relationship between the secondary electron energy and formation of positive and negative glycine fragments. The results showed that the formation of methylene amine cations is caused by secondary electrons with energies of 13–100 eV. The formation of glycine-related negative ions such as cyanide anion, formate anion, and deprotonated glycine was found to be caused by low-energy (less than 13 eV) secondary electrons. These ions are known products of dissociative electron attachment.

Behavior of ZnO nanoparticles in glycine solution: pH and size effect on aggregation and adsorption

Growing interest in nanoparticles' (NPs) behavior in the environment needs deeper purport of interactions between NPs and amino acids. In this work, we evaluated particle size distribution, aggregation degree, zeta potential, adsorption efficiency, and specific adsorption of three ZnO NPs with average sizes 30, 135, and 210 nm in 1 M glycine solution at different pH. The interaction of ZnO NPs and glycine is stimulated by the pH growth from 4 to 8 (an increase of glycine adsorption and decrease of particle aggregation), whereas at рН > 8 colloidal and adsorption properties are weakly affected by pH change. The addition of glycine to water promotes the aggregation of 30 nm NPs, while the aggregation of bigger NPs is weakened. For smaller particles aggregation and adsorption efficiency are higher, and specific adsorption is lower, meanwhile, the size effect is stronger in aggressive medium: alkaline – in water, and acid – in glycine.

Microfluidic Laser-Induced Nucleation of Supersaturated Aqueous Glycine Solutions

A microfluidic device was designed and fabricated for non-photochemical laser-induced nucleation (NPLIN) in continuous laminar flow, which enabled real-time in situ characterization of crystal size...

Cellulose assisted combustion synthesis of high surface area Ni-MgO catalysts: Mechanistic studies

The objective of this study was to determine the combustion mechanism of cellulose paper impregnated with Mg(NO3)2, Ni(NO3)2, glycine solutions, and their different combinations. It was established that the combustion mechanism changes as a function of the impregnated media composition. In the Mg(NO3)2-cellulose system, Mg2+ ions strongly catalyze cellulose pyrolysis; hence no atmospheric oxygen is needed for the self-sustained combustion reaction. In the Ni(NO3)2-cellulose system, Ni2+ ions catalyze pyrolysis at a lower rate, and atmospheric oxygen assists the combustion wave propagation. In glycine containing systems, glycine blocks the ability of metal cations to catalyze the early cellulose pyrolysis, and the combustion front propagates due to the exothermic reactions between metal nitrates and glycine. The above mechanisms influence the microstructure of the combustion products. Due to the near-complete degradation of cellulose fibers during the Mg2+ catalyzed pyrolytic combustion, the resulting materials had a highly porous, sponge-like microstructure with a BET surface area of up to 152 m2/g. After the reduction in hydrogen, Ni segregates to the surface of NiO-MgO solid solution, and the resulting catalysts exhibited near-equilibrium methane conversion during the dry reforming of methane reaction at 600°C with low carbon formation and no deactivation for 24 h of time on stream.

Tautomeric Equilibrium in Condensed Phases.

We present an ab initio molecular dynamics (MD) investigation of the tautomeric equilibrium for the aqueous solutions of glycine and acetone under realistic experimental conditions. Metadynamics is used to accelerate proton migration among tautomeric centers. Due to the formation of complex water-ion structures involved in the proton dynamics in the aqueous environment, standard enhanced sampling approaches may face severe limitations in providing a general description of the phenomenon. Recently, we have developed a set of collective variables (CVs) designed to study protons transfer reactions in complex condensed systems [Grifoni, E. Proc. Natl. Acad. Sci. U.S.A. 2019, 116, 4054 4057]. In this work, we applied this approach to study proton dissociation dynamics leading to tautomeric interconversion of biologically and chemically relevant prototypical systems, namely, glycine and acetone in water. Although relatively simple from a chemical point of view, the results show that even for these small systems, complex reaction pathways and nontrivial conversion dynamics are observed. The generality of our method allows obtaining these results without providing any prior information on the dissociation dynamics but only the atomic species that can exchange protons in the process. Our results agree with literature estimates and demonstrate the general applicability of this method in the study of tautomeric reactions.

Gold recovery from cyanide-starved glycine solutions in the presence of Cu using a molecularly imprinted resin (IXOS-AuC)

The synergistic leaching system using glycine as the main lixiviant with low levels of cyanide as a catalyst has been shown to be an effective approach to leach gold‑copper ores and concentrates, allowing the consumption of cyanide to be remarkably reduced. The recovery of gold from the synthetic cyanide-starved glycine leachate in the presence of copper has been investigated using. It was found that the adsorbed copper was mostly cuprous cyanide. The effects of [CN−]:[CuT] and [Gly]: [CuT] molar ratios were not significant on the adsorption of gold and copper using IXOS-AuC resin. The gold recovery increased, while the copper recovery decreased with the increasing initial gold concentration. The equilibrium and kinetics studies were undertaken, and the experimental adsorption equilibrium and rate data showed an excellent fit using the Freundlich isotherm and pseudo-second-order models respectively. Elution tests showed that the loaded copper can be selectively pre-eluted over gold by 0.4 M NaCN at pH 11.5. Gold can be effectively eluted by either acidic thiourea or alkaline thiocyanate. The multi-cycle adsorption/elution tests showed that the resin can be effectively regenerated by both acidic thiourea and alkaline thiocyanate, with an insignificant decrease in adsorption and elution efficiency over 3 adsorption/elution cycles. From SEM analysis, the change of surface morphology of the resin was not significant after adsorption and the adsorption/elution cycles.

Interaction of Metal(II) Ion–Ciprofloxacin–Glycine in Solution

The aim of this work is to study the metal–drug–amino acid ternary complex formation kinetically, thermodynamically and computationally and explore the possibility of developing some potent new drugs for biological applications. Metal(II)–ciprofloxacin–glycine ternary complexes (metal = MnII, CuII, ZnII) were synthesized. The slow kinetics and thermodynamics of imine formation were investigated spectrophotometrically. The geometry optimizations of ternary complexes were studied by the density functional theory (DFT) using TURBOMOL 6.5 software. The in vitro antibacterial activities of the ternary complexes against gram-positive and gram-negative bacteria were evaluated by disc diffusion method. It turns out that Cu(II) is the most and Mn(II) is the least efficient in terms of thermodynamics control, while Zn(II) is the most active and Cu(II) is the least active in terms of kinetic control of the ternary imine complex formation, a consequence of kinetic–coordination–template process. The biological screening showed that the ternary metal complexes are as active as the parent drug (cf). However, the uncharged ternary complex may be better career of the drug to the active site due to the presence of metal ion, entailing further detailed investigation. Kinetics, thermodynamic and in vitro antibacterial activities of metal complexes were investigated. Metal complexes show similar activity towards bacteria as free drug, but they have several advantages over the neat drug (cf), such that increase in lipophilicity of the ternary complex enhances the passage into the cell wall of the microorganism more efficiently than the free drug and blocks the growth of organism; increases the time of post-bacterial activity; and meets the deficiency of metals Cu, Zn, Mn and glycine (gly) which are essential for different metabolisms in biological domain.

Sugar replacement with zwitterionic plasticizers like amino acids

In this paper, we investigate the potential of zwitterions like amino acids as alternative (bulking) sugar replacers. Commonly, polyols or oligosaccharides are taken as sugar placers, but they are perceived as less attractive due to laxative problems. The choice of amino acids as alternative sugar replacers is inspired by their presence in Natural Deep Eutectic Solvents (NADES) and compatible solutes, next to carbohydrates. In these compounds, hydrogen bonding plays an essential role similar to sugar (replacers) in food. Because of the novelty of the topic, we first discuss at length NADES as a potential source of alternative plasticizers/sugar replacers. Subsequently, we perform a detailed analysis of their thermodynamic properties, to investigate whether amino acids and related zwitterions indeed have the appropriate properties for sugar replacement.Our analysis shows that several zwitterions indeed have proper thermodynamic properties, which can make them good plasticizers and humectants. However, the use of several zwitterions can be restricted by their poor solubility, except for L-proline. Solubility problems can be circumvented by their use in mixtures of several sugar replacers, which enhances their solubility. The poor solubility makes it also difficult to characterize the glass transition temperatures of the pure solute Tg,g. Consequently, we have estimated them via extrapolation of the viscosity curves, which is shown to scale with Tg∕T. We have taken Tg of the plasticizer solution as a measure of the hydrogen bond density, nOH,eff.That measure is shown to explain the melting behaviour of biopolymers like egg white and starch in glycine and L-proline solutions, similar to sugar (replacers). However, our measurements of the biopolymer melting show indications of phase separation at high moisture contents for both amino acid solutions as for carbohydrate solutions. Overall, the amino acids and other compatible zwitterions have very similar thermodynamic behaviour as sugars and their carbohydrate-based replacers. In proper combinations with alternative plasticizers, the zwitterionic compatible solutes can well be used in sugar replacement strategies for foods.

Nano-Cu Modified Cu and Nano-Cu Modified Graphite Electrodes for Chemical Oxygen Demand Sensors.

Nano-Cu modified Cu (nano-Cu/Cu) and nano-Cu modified graphite (nano-Cu/C) electrodes were prepared by depositing a thin layer of copper nanoparticles on a Cu wire or graphite electrode. Chronoamperometric and cyclic voltammetry techniques were applied to deposit the nanoparticles. The effects of Cu2+ concentration, deposition time, number of scan cycles, and scan rate were studied to determine the optimum conditions of the experiment. The applications of both electrodes in the COD analysis were performed using glucose and glycine as the models. The voltammetry of a mixture solution of glucose (mg/L) and glycine (mg/L) in 0.075 M NaOH solution showed an oxidation peak at +0.68 V vs. Ag/AgCl. Good stability of this peak current was shown with relative standard deviations lower than 3% for 10 measurements. Amperometric determination of COD at this potential showed excellent linearities at both nano-Cu/Cu and nano-Cu/C electrodes (R2 = 0.997) as well as good precision and accuracy with estimated detection limits of around ∼9 mgO/L for both the developed electrodes. Validation using the conventional COD measurements showed that the measurements achieved the average values of 92.58 and 87.86%, respectively, for nano-Cu/Cu and nano-Cu/C electrodes. Furthermore, comparison with the theoretical COD value achieved 94.90 and 89.87%, respectively, for nano-Cu/Cu and nano-Cu/C electrodes. The results indicated that both electrodes are suitable for practical application in COD determination.

Mechanistic analysis of anodic dissolution of cobalt in alkaline glycine solution

The kinetics of dissolution of Co in alkaline glycine solution under anodic conditions was investigated. Potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) data of Co dissolving in 0.1 M glycine solution at pH 10 were acquired. At low overpotentials, in the active region, the polarization current increases with potential, whereas at high overpotentials, in the passive region, it decreases with potential. Co surface exposed to the alkaline glycine solution was characterized using scanning electron microscopy and x-ray photoelectron spectroscopy, and based on the binding energies of the deconvoluted peaks, oxides, hydroxides, and Co-glycine complexes were identified as the likely species present on the surface. Impedance data was subjected to electrical equivalent circuit analysis, and a circuit with three Maxwell elements was found to model the faradaic impedance. Polarization and EIS data were also analyzed in the framework of mechanistic analysis, and a mechanism with four adsorbed intermediates is proposed. The proposed model captures the salient features of the polarization and EIS results.

Impedance of copper electrode in slightly acid Cu(II)-glycine solutions

Electrochemical impedance spectroscopy was used to study the kinetics of reduction of Cu (II) in weakly acidic (pH 4 and 5) solutions of Cu (II) containing glycine (0.04 or 0.1 M) as a complexing agent. A rather slow equilibration was observed at pH 4 and glycine concentration cL = 0.04 M. With increasing pH or cL, the total concentration of intermediate Cu(I) decreases. At the same time, impedance increases over the entire range of frequencies applied. An equivalent circuit with two parallel sub-circuits, each containing the charge transfer resistance and Warburg impedance in series, was used to quantify the impedance spectra. The exchange current densities of two consecutive one-electron transfers were estimated. Their average values are ~1 µA cm–2 and ~0.1 mA cm–2.

Selective separation of Cd from spent Ni-Cd battery using glycine as an eco-friendly leachant and its recovery as CdS nanoparticles

Herein, an environmentally friendly and selective leaching process of Cd, from spent Ni-Cd battery, is reported by the use of alkaline glycine solution. The pertinent parameters affecting Cd leaching levels, including the concentration of glycine (0.5–1.5 mol/L), pH (8–11), temperature (25–75 °C), and time (30–150 min) were statistically investigated via response surface methodology coupled with central composite design. The results showed that the level of Ni in the leaching solution is negligible, especially at the leaching time shorter than 150 min, while Cd leaching percentage can reach higher than 80%, confirming the selectivity of the process. In addition, glycine concentration and time are the most significant parameters, and for achieving a Cd leaching percentage higher than 80%, the level of glycine should be at least 1 mol/L. It was attempted to understand the statistically significant interactions among the factors affecting the Cd leaching process based on a comprehensive thermodynamic discussion. Finally, Cd was successfully precipitated in the form of CdS nanoparticles (~20 nm) by the addition of Na2S solution into the obtained leaching solution.

Electrochemical Evaluation of the Total Antioxidant Capacity of Yam Food Samples on a Polyglycine-Glassy Carbon Modified Electrode

Background:The total antioxidant capacity of yam food grown in southern African regions was investigated by a polyglycine-glassy carbon modified electrode. The modified electrode was fabricated using glycine solution on glassy carbon electrode by electrodeposition method. The proposed modified electrode is found to be nearly 3.15-fold more sensitive than the bare electrode. For the measurement of the total antioxidants of yam, differential pulse stripping voltammetry (DPSV) was employed with standard quercetin compound.Methods:The total antioxidant capacity of yam was deduced by DPSV and cyclic voltammetry (CV) methods. The basic parameters for the stripping technique such as pH, accumulation time and accumulation potential were optimized as 20 s, 200 mV and a pH of 3 Britton-Robinson (B-R) buffer solutions in 0.5 mg quercetin/L, respectively.Results:In the optimization condition, the linear working range was determined between 5.0 μg/L and 80.0 µg/L for the quercetin. The detection (LOD) and quantification (LOQ) limits of quercetin were found to be 0.39 µg/L and 1.39 µg/L on the modified electrode by DPSV, respectively. The procedure was also applied to natural yam samples and total antioxidant capacity of 0.1 kg of yam was determined as 96.15 ± 0.85 µg/L of equivalent quercetin at 95% confidence level with the relative standard deviations of 0.88%.Conclusion:Sensitive and selective voltammetric method was developed for the determination of total antioxidant capacity in yam. Moreover, the modified polyglycine-glassy carbon electrode was constructed more selectively for quercetin. As a result, a simple, sensitive and rapid new voltammetric method for the determination of antioxidants has been developed using the modified electrode.

Aspect Ratio Control of Layered Double Hydroxide Nanosheets and Their Application for High Oxygen Barrier Coating in Flexible Food Packaging.

We report a method to rationally control the aspect ratio of layered double hydroxide for use as a barrier coating for food packaging films. The reconstruction of a Mg2Al-layered double oxide (LDO) in concentrated aqueous glycine solutions produces dispersions of Mg2Al-LDH nanosheets. The nanosheet thickness decreases and diameter increases with increasing reconstruction time from 16 to 96 h. We observe a limiting nanosheet aspect ratio of ca. 336 ± 170. These Mg2Al-LDH nanosheets can be dispersed in PVA to give a water-based dispersion that can be used to coat flexible polymeric films. Oxygen transmission rate (OTR) of a PET film decreases when the thickness of the dried coated layer increases, an OTR of <0.005 mL·m-2·day-1 is observed for a coating with thickness of 1175 ± 101 nm.