Thermodynamic properties of CO2 absorption in hydroxyl ammonium ionic liquids at pressures of (100–1600) kPa

Solubility of CO₂ in six hydroxyl ammonium ionic liquids 2-hydroxyethanaminium acetate [hea], bis(2-hydroxyethyl)ammonium acetate [bheaa], 2-hydroxy-N-(2-hydroxyethyl)-N-methylethanaminium acetate [hhemea], 2-hydroxyethanaminium lactate [hel], bis(2-hydroxyethyl)ammonium lactate [bheal], 2-hydroxy-N-(2-hydroxyethyl)-N-methylethanaminium lactate [hhemel] at temperatures (298.15, 313.15, and 328.16) K and pressures ranging from (100 to 1600) kPa was determined. From the experimental solubility data, the Henry’s constant of CO₂ for each hydroxyl ammonium ionic liquids was estimated and reported as a function of temperature. Furthermore, enthalpy and entropy of absorption were obtained from estimated Henry’s constant. The results showed that the solubility increase with increasing pressure and decrease with increasing temperature and the solubility of CO₂ in these six hydroxyl ammonium ionic liquids was in sequence: [hea] > [bheaa] > [hel] > [bheal] > [hhemel] > [hhemea].     

Composition dependence of unipolar resistance switching in TaOx thin films

Amorphous TaO_x thin films were deposited at different temperatures, and the resistance switching properties of the Pt/TaO_x/Pt structure were investigated. X‐ray photoelectron spectroscopy showed that the amount of Ta₂O₅ in the film decreased and the content of Ta suboxides increased substantially when the growth temperature was increased. Unipolar resistance switching near the anode was stable only for TaO_x film grown at room temperature. The experimental results revealed the critical effect of the film composition on the resistance switching behavior of TaO_x films. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phytochemical Profile of Antibacterial Agents from Red Betel Leaf (Piper crocatum Ruiz and Pav) against Bacteria in Dental Caries

Based on data from The Global Burden of Disease Study in 2016, dental and oral health problems, especially dental caries, are a disease experienced by almost half of the world’s population (3.58 billion people). One of the main causes of dental caries is the pathogenesis of Streptococcus mutans. Prevention can be achieved by controlling S. mutans using an antibacterial agent. The most commonly used antibacterial for the treatment of dental caries is chlorhexidine. However, long-term use of chlorhexidine has been reported to cause resistance and some side effects. Therefore, the discovery of a natural antibacterial agent is an urgent need. A natural antibacterial agent that can be used are herbal medicines derived from medicinal plants. Piper crocatum Ruiz and Pav has the potential to be used as a natural antibacterial agent for treating dental and oral health problems. Several studies reported that the leaves of P. crocatum Ruiz and Pav contain secondary metabolites such as essential oils, flavonoids, alkaloids, terpenoids, tannins, and phenolic compounds that are active against S. mutans. This review summarizes some information about P. crocatum Ruiz and Pav, various isolation methods, bioactivity, S. mutans bacteria that cause dental caries, biofilm formation mechanism, antibacterial properties, and the antibacterial mechanism of secondary metabolites in P. crocatum Ruiz and Pav.     

Effectiveness of Bioactive Compound as Antibacterial and Anti-Quorum Sensing Agent from Myrmecodia pendans: An In Silico Study

Background: antibiotic resistance encourages the development of new therapies, or the discovery of novel antibacterial agents. Previous research revealed that Myrmecodia pendans (Sarang Semut) contain potential antibacterial agents. However, specific proteins inhibited by them have not yet been identified as either proteins targeted by antibiotics or proteins that have a role in the quorum-sensing system. This study aims to investigate and predict the action mode of antibacterial compounds with specific proteins by following the molecular docking approach. Methods: butein (1), biflavonoid (2), 3″-methoxyepicatechin-3-O-epicatechin (3), 2-dodecyl-4-hydroxylbenzaldehyde (4), 2-dodecyl-4-hydroxylbenzaldehyde (5), pomolic acid (6), betulin (7), and sitosterol-(6′-O-tridecanoil)-3-O-β-D-glucopyranoside (8) from M. pendans act as the ligand. Antibiotics or substrates in each protein were used as a positive control. To screen the bioactivity of compounds, ligands were analyzed by Prediction of Activity Spectra for Substances (PASS) program. They were docked with 12 proteins by AutoDock Vina in the PyRx 0.8 software application. Those proteins are penicillin-binding protein (PBP), MurB, Sortase A (SrtA), deoxyribonucleic acid (DNA) gyrase, ribonucleic acid (RNA) polymerase, ribosomal protein, Cytolysin M (ClyM), FsrB, gelatinase binding-activating pheromone (GBAP), and PgrX retrieved from UniProt. The docking results were analyzed by the ProteinsPlus and Discovery Studio software applications. Results: most compounds have Pa value over 0.5 against proteins in the cell wall. In nearly all proteins, biflavonoid (2) has the strongest binding affinity. However, compound 2 binds only three residues, so that 2 is the non-competitive inhibitor. Conclusion: compound 2 can be a lead compound for an antibacterial agent in each pathway.     

Density and Excess Molar Volume of the Protic Ionic Liquid Bis(2-hydroxyethyl)ammonium Acetate with Alcohols

Densities were determined for binary mixtures containing the protic ionic liquid bis(2-hydroxyethyl)ammonium acetate [BHEAA] and an alcohol (methanol, ethanol, and 1-propanol) at four different temperatures (293.15, 303.15, 313.15, and 323.15) K and ambient pressure. Coefficients of thermal expansion and excess molar volumes were calculated from the experimental densities. The excess molar volumes were fitted using the Redlich-Kister polynomial equation. Negative deviations from ideal behavior of the excess molar volume were observed for all systems investigated in this study. The results were interpreted in terms of ion-dipole interactions and structural factors of the ionic liquid and alcohol. It was observed that an increase of the alcohol carbon chain length led to lower interactions on mixing.     

Controlling the Formation of Ionic‐Liquid‐based Aqueous Biphasic Systems by Changing the Hydrogen‐Bonding Ability of Polyethylene Glycol End Groups

The formation of aqueous biphasic systems (ABS) when mixing aqueous solutions of polyethylene glycol (PEG) and an ionic liquid (IL) can be controlled by modifying the hydrogen‐bond‐donating/‐accepting ability of the polymer end groups. It is shown that the miscibility/immiscibility in these systems stems from both the solvation of the ether groups in the oxygen chain and the ability of the PEG terminal groups to preferably hydrogen bond with water or the anion of the salt. The removal of even one hydrogen bond in PEG can noticeably affect the phase behavior, especially in the region of the phase diagram in which all the ethylene oxide (EO) units of the polymeric chain are completely solvated. In this region, removing or weakening the hydrogen‐bond‐donating ability of PEG results in greater immiscibility, and thus, in a higher ability to form ABS, as a result of the much weaker interactions between the IL anion and the PEG end groups.     

Total synthesis and antimicrobial evaluation of xylapeptide A

Xylapeptide A is a cyclopentapeptide, [cyclo-D-Ala-L-Val-N-Me-L-Phe-L-Pip-L-Leu], first isolated from Xylaria sp. × Sophora tonkinensis, together with its analogue, xylapeptide B, which differ by only one residue, proline in xylapeptide B is replaced by pipecolinic acid (Pip) in xylapeptide A. Both xylapeptides A and B possess antimicrobial properties against several bacteria and fungi. Herein, we describe the first total synthesis and antimicrobial evaluation of xylapeptide A containing two non-proteinogenic residues, N-Me-phenylalanine and pipecolinic acid. The synthesis of xylapeptide A was achieved by a combination of solid- and solution-phase methods that were applied for the synthesis of xylapeptide B. Interestingly, the cyclization of linear xylapeptide A was more straightforward yielding 22% compared to 8.9% for xylapeptide B, suggesting that the presence of pipecolinic acid in the linear precursor affected the cyclization process. NMR analysis of synthetic xylapeptide A revealed that the chemical shifts of all protons and carbons of xylapeptide A are highly similar to the natural product. The synthetic xylapeptide A, together with xylapeptide B, were evaluated for their antimicrobial properties, showing that synthetic xylapeptide A has moderate antimicrobial activity and better antimicrobial properties compared to synthetic xylapeptide B. The presence of pipecolinic acid in xylapeptide A is an important requirement for antimicrobial activity.     

Analytical Methods for Determination of Non-Nutritive Sweeteners in Foodstuffs

Sweeteners have been used in food for centuries to increase both taste and appearance. However, the consumption of sweeteners, mainly sugars, has an adverse effect on human health when consumed in excessive doses for a certain period, including alteration in gut microbiota, obesity, and diabetes. Therefore, the application of non-nutritive sweeteners in foodstuffs has risen dramatically in the last decade to substitute sugars. These sweeteners are commonly recognized as high-intensity sweeteners because, in a lower amount, they could achieve the same sweetness of sugar. Regulatory authorities and supervisory agencies around the globe have established the maximum amount of these high-intensity sweeteners used in food products. While the regulation is getting tighter on the market to ensure food safety, reliable analytical methods are required to assist the surveillance in monitoring the use of high-intensity sweeteners. Hence, it is also necessary to comprehend the most appropriate method for rapid and effective analyses applied for quality control in food industries, surveillance and monitoring on the market, etc. Apart from various analytical methods discussed here, extraction techniques, as an essential step of sample preparation, are also highlighted. The proper procedure, efficiency, and the use of solvents are discussed in this review to assist in selecting a suitable extraction method for a food matrix. Single- and multianalyte analyses of sweeteners are also described, employing various regular techniques, such as HPLC, and advanced techniques. Furthermore, to support on-site surveillance of sweeteners’ usage in food products on the market, non-destructive analytical methods that provide practical, fast, and relatively low-cost analysis are widely implemented.     

Physicochemical Properties of Binary Mixtures of the Protic Ionic Liquid Bis(2-hydroxyethyl)methylammonium Formate with Methanol,Ethanol, and 1-Propanol

Densities and viscosities were determined for binary mixtures containing the protic ionic liquid bis(2-hydroxyethyl)methylammonium formate [BHEMF] with methanol, ethanol, and 1-propanol at four different temperatures (293.15, 303.15, 313.15, and 323.15 K) and atmospheric pressure. Excess molar volume and viscosity deviations for the binary system were calculated. The calculated results were fitted to a Redlich-Kister equation to obtain the coefficients and estimate the standard deviations between the experimental and calculated quantities. The negative values of excess volume molar for these mixtures indicate that ion-dipole interactions and packing between ionic liquids and alcohols are present. The values of viscosity deviation are also negative over the whole composition range, and their values become less negative as the temperature increases.     

Band‐Gap Control of Zinc Sulfide: Towards an Efficient Visible‐Light‐Sensitive Photocatalyst

The electronic properties of transition‐metal‐doped zinc sulfide (ZnS) have been investigated by using first‐principles calculations. Transition‐metal doping can allow electronic transitions at energies corresponding to visible‐light wavelengths, thus potentially resulting in increased photocatalytic efficiency under sunlight. In particular, our calculations show that transition‐metal atoms that produce little lattice strain, such as Co, Ni, Mn, and Fe, can be readily incorporated in ZnS. Due to their low formation energies and appropriate band energies, we predict that Ni‐ and Co‐doped ZnS will be promising materials for photocatalytic hydrogen production.