Search

Objectives: To deal with the Covid-19 pandemic and its unpredictable variations, universities must develop many different response scenarios in which online teaching is considered a suitable, strategic, and long-term solution. Our study aims to investigate and determine the relationships between digital transformation, satisfaction, word-of-mouth communication, and students' intention to continue learning online in universities. Methods/Analysis: Our study uses Structural Equation Modeling (SEM) to measure the interaction with data processing tools such as partial least squares SEM (PLS-SEM), Cronbach's Alpha coefficient, exploratory factor analysis (EFA), confirmatory factor analysis (CFA), and PLS Bootstrapping with descriptive and inferential statistics. Findings: The results show a positive interaction between students, faculty, and schools with digital transformation; between digital transformation and student satisfaction and word of mouth communication; between satisfaction with an expression of mouth communication and the intention to continue learning online; and between oral communication and a student's intention to continue learning online. Novelty/Improvement: This is the first study to simultaneously identify, examine, and measure the impact of factors influencing digital transformation, student satisfaction, word-of-mouth communication, and the intention to continue online learning and their interrelationships.JEL Classification: A22, I20, I23 Doi: 10.28991/ESJ-2022-SIED-04 Full Text: PDF

The lichen Usnea baileyi is a fruticose lichen belonging to the Usnea genus. It is well known as a rich source of natural xanthone dimers and possesses various bioactivities. Nevertheless, the chemical investigation on this type of lichen is still rare as most of researches reported its components without structural elucidation. Herein, in the continuous study on this type of lichen, we further isolate xanthone dimers from the dichloromethane extract and explore three new xanthone dimers, eumitrins F − H (1 − 3). Their structures were elucidated unambiguously by spectroscopic analyses, including high resolution electrospray ionisation mass spectrometry (HRESIMS), 1 D and 2 D nuclear magnetic resonance spectroscopy (1 D and 2 D NMR), and DP4 probability. All compounds were evaluated for their enzyme inhibition against α-glucosidase, tyrosinase, and antibacterial activity. They revealed moderate antimicrobial and weak tyrosinase inhibition. For α-glucosidase inhibition, compound 3 displayed the most significant inhibitory against α-glucosidase possessing an IC50 value of 64.2 µM.

A new benzofuran derivative, nervione (1), was isolated from Nervilia concolor (Blume) Schltr. (Orchidaceae). Eight previously reported compounds were also isolated: 5,7-dimethoxyflavone (2), 3,5,7-trimethoxyflavone (3), 7-methoxyflavone (4), 3,7-dimethoxy-5-hydroxyflavone (5), tetramethylscutellarein (4',5,6,7-tetramethoxyflavone) (6), 5,7-dimethoxy-4'-hydroxyflavone (7), rhamnetin (8), and 5,7-dihydroxy-3’,4’-dimethoxyflavone (9). The structures were elucidated by 1D, 2D NMR, and HRESIMS spectroscopy in addition to the literature. The relative configuration of 1 was defined using DP4+ probability while its absolute configuration was defined by comparison of the ECD spectrum of 1 with those of previously reported compounds. All isolated compounds were evaluated for alpha-glucosidase inhibition, revealing weak or no activity.

O6-methylguanine DNA methyltransferase (MGMT) is one of the most premutagenic, precarcinogenic and precytotoxic DNA lesions formed by alkylating agents. Repairing DNA damage is achieved by the protein MGMT which transfers the alkyl groups from the O6-position of guanine to a cysteine residue in the active center of MGMT. The most common assays of MGMT activity are time-consuming and have to employ radioactivity. In order to avoid these shortcomings, in this study we have developed a novel biosensing strategy for measuring the activity of MGMT based on fluorescence of DNA-silver nanoclusters. The results showed that a wide range from 0.01 to 1.0 µg/mL was achieved for MGMT assay and limit of detection of 8 ng/mL. The method has high sensitivity, good reproducibility, simplicity, also it is label free, rapid and cheap. Therefore, we can conclude that the developed strategy holds a great potential for quantitative measurement of MGMT activity with desirable sensitivity and reproducibility.

Sustainable development – including tourism development – is the general trend of all economies. With the orientation to build and develop the tourism industry into a key economic sector and become a tourist center of the Southeast region, Vietnam, Ba Ria-Vung Tau Province is demanding a proper, rational, development policy, while ensuring the development and exploitation of immediate natural advantages, and ensuring long-term sustainable development. The objective of this study is to examine the factors and their trends in sustainable tourism development in Ba Ria-Vung Tau Province, Vietnam. Methods used include descriptive statistical analysis, exploratory factor analysis and regression analysis. Data was collected from the results of a survey of 550 domestic and foreign tourists visiting Ba Ria-Vung Tau. With the help of SPSS statistical software, 12 groups of factors affecting sustainable development were identified including: economy, society, environment, humanistic tourism resources, natural tourism resources, tourism human resources, tourism products and service, tourism quality, infrastructure, technical facilities, governmental management and group of criteria to evaluate sustainable tourism development. The research results show that there are four groups of factors that significantly affect sustainable tourism development in Ba Ria-Vung Tau. These are groups of factors: Society, Environment, Tourism products and service, and Technical facilities.

Phytochemical analysis of Euphorbia antiquorum stem extracts afforded two new ent-atisane compounds, ent-3α-acetoxy-16β,17,18-trihydroxyatisane (1) and ent-3α,14,16β,17-tetrahydroxyatisane (2) toge...

A new glycoside, telosmoside A21 (1) and two known compounds, telosmoside A6 (2) and telosmoside A1 (3), were isolated from the roots of Jasminanthes tuyetanhiae. The structure of compound 1 was identified from its spectroscopic data and by comparison with the literature.

Untreated or inadequately treated domestic wastewater has adversely affected the aquatic environment and public health in many cities in Vietnam. A conventional anaerobic–anoxic–oxic (AAO) process is recognized as an easy-to-handle approach that constrains chemical use during the procedure. Herein, we improve an AAO system by adding more oxic orders in association with a biological membrane in order to increase the hydraulic retention time (HRT) of the oxic zone in the system. The investigated system was applied to the treatment of real domestic wastewater during 168 days of operation. The performance of the system reached a stable state after 60 days of operation. The removal efficiency of total nitrogen (TN), total phosphorus (TP), total suspended solids (TSS), biological oxygen demand (BOD5), and chemical oxygen demand (COD) was found to be 93.6 ± 3.0%, 91.9 ± 3.5%, 88.6 ± 1.2%, 82.6 ± 1.4%, and 71.8 ± 0.7%, respectively. After the operation process, the TN, TP, and TSS contents in the wastewater effluents met the A level in accordance with the QCVN 14-MT:2015/BTNMT regulation, and the effluents of COD and BOD5 almost satisfied the requirement, with only some points being slightly higher than the limit values. The obtained data revealed that the AAO/O system was capable of treating domestic wastewater in small and medium-sized domestic wastewater treatment facilities.

A new hopan-type triterpenoic peracid, tinctoride A (1), together with three known compounds, zeorin (2), 6β,22-dihydroxyhopane (3), and ergosterol peroxide (4), was isolated from Parmotrema tinctorum (Despr. ex Nyl.) Hale. Their chemical structures were identified by extensive 1D and 2D NMR analysis and high-resolution mass spectroscopy and compared with those reported in the literature. The enzyme inhibitory potential of compounds 1–3 against α-glucosidase was investigated, exhibiting nil to weak inhibitory activity.

Background As antibiotic resistance creates a significant global health threat, we need not only to accelerate the development of novel antibiotics but also to develop better treatment strategies using existing drugs to improve their efficacy and prevent the selection of further resistance. We require new tools to rationally design dosing regimens from data collected in early phases of antibiotic and dosing development. Mathematical models such as mechanistic pharmacodynamic drug-target binding explain mechanistic details of how the given drug concentration affects its targeted bacteria. However, there are no available tools in the literature that allow non-quantitative scientists to develop computational models to simulate antibiotic-target binding and its effects on bacteria. Results In this work, we have devised an extension of a mechanistic binding-kinetic model to incorporate clinical drug concentration data. Based on the extended model, we develop a novel and interactive web-based tool that allows non-quantitative scientists to create and visualize their own computational models of bacterial antibiotic target-binding based on their considered drugs and bacteria. We also demonstrate how Rifampicin affects bacterial populations of Tuberculosis bacteria using our vCOMBAT tool. Conclusions The vCOMBAT online tool is publicly available at https://combat-bacteria.org/.

Lichens, a natural source producing a number of valuable compounds is economically not feasible and profitable due to its slow growth. Mycobiont cultures are alternative sources which have become highly attractive for chemists recently. Mycobiont of Graphis sp., a native lichens in Vietnam was separated then cultivated in test tubes. The present study aimed to identify chemical constituents of the cultured mycobiont of Graphis sp. Multiple chromatographic methods were applied to isolate three eremophilane sesquiterpenes including one new compound, graphilane (1) and two known compounds sporogen-AO-1 (2) and dihydrosporogen-AO-1 (3). Their chemical structures was elucidated by extensive 1 D and 2 D NMR analysis and high resolution mass spectroscopy as well as comparisons in literature. Compound 1 was evaluated for the cytotoxic activity against K562 cancer cell line and revealed moderate activity with IC50 value of 87.20 ± 0.76 µM.

Discovery of natural antioxidants has been carried out for decades relying mainly on experimental approaches that are commonly associated with time and cost demanding biochemical assays. The maturation of quantitative structure activity relationship (QSAR) modelling has provided an alternative approach for searching and designing antioxidant compounds with alleviated costs. As a contribution to this approach, this work aimed to establish a fragment-based 3D-QSAR procedure to discover and design potential antioxidants based on tryptophyllin L structures isolated from the red tree frog Litoria rubella. A force field and a Gaussian 3D-QSAR model were built to screen for potential antioxidants from tripeptide fragments covering all sequences of tryptophyllin L database. Among those, PWY(NH2 ) corresponding tryptophyllin L 4.1 was predicted to have the highest 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) radical cation (ABTS+ ·) scavenging capability. Two newly designed peptides PYW and PYW(NH2 ) together with PWY(NH2 ), tryptophyllin L 4.1, and the reference peptide PWY were synthesized and subjected to two antioxidant assays including ABTS scavenging and ferric reducing antioxidant power assays. Although the experimental TEAC values of the five peptides were roughly similar to those from predictions, the activity order was not in agreement with the predictions. The dissimilarities were accounted by the difference in the experimental procedures, the deviation of modelling regression, and the synergetic effect of structural and experimental features. The ABTS radical scavenging assays revealed that all the tested peptides were strong ABTS+ · scavengers with the antioxidant capabilities approximately twice as high as trolox and higher than glutathione. The ferric reducing activities of the peptides were, on the other hand, much weaker than that of trolox suggesting different antioxidant mechanisms inserted by trolox and the peptides. This work was a demonstration that 3D-QSAR methods can be employed in conjunction with experimental methods to effectively detect and design antioxidant peptides.

Plukenetia volubilis Linneo (P. volubilis), or Sacha inca, is an oleaginous plant from the Euphorbiaceae family. The presence of terpenoids, saponins, tannins, glycosides, phytosterols, and phenolic compounds in the ethanol extracts of P. volubilis L leaves has been reported, showing a range of bioactivities including antimicrobial, anti-inflammatory, antioxidant, and analgesia. However, the safety of this plant has not yet been reported explicitly. This study thus is aimed at evaluating the toxicity of the ethanol extract of P. volubilis leaves (EtPV) by acute and subchronic toxicity tests in Swiss albino mice following standard procedures set by The Organization for Economic Cooperation and Development (OECD) with slight modifications. In the acute toxicity test, the treatment groups were administered orally with the EtPV at doses of 1000, 3000, 5000, and 7000 mg/kg body weight in small fractions during 16 hours, and the mice were then observed in 14 consecutive days. In the subchronic toxicity study, the EtPV was given at doses of 100, 300, 500, and 700 mg/kg body weight for 90 days. Changes in behavior, mortality rate, and body and the weights of vital organs, hematology, clinical biochemistry, urine analysis, and histologic morphology were evaluated. The acute toxicity study showed that the EtPV causes no sign of toxicity or mortality. The hematological, biochemical and urine analyses, changes in the weight of the body and vital organs (heart, liver and kidney), and histopathological analyses of organs indicated no evidence of toxicity at any doses. It was also revealed that oral administration of EtPV is safe at the oral doses set by acute and subchronic toxicity tests, and the oral lethal dose for the EtPV is higher than 7000 mg/kg. This study is the first to confirm the safety of P. volubilis leaf ethanol extract, and as a result, encouraging further investigation to examine EtPV potential for traditional medicine.

A new norlupane triterpenoid, 29-norlupane-1β-hydroxy-3,20-dione (1), along with ten known compounds, 29-norlup-1-ene-3,20-dione (2), phyllanthol (3), phyllanthone (4), glochidone (5), lupeol (6), lupeone (7), 4-hydroxybenzoic acid (8), 4-hydroxybenzaldehyde (9), phyllane A (10) and methyl β-orsellinate (11) were isolated the twigs and leaves of Phyllanthus acidus. The structure of 1 was identified by interpretation of their spectroscopic data and comparison with those reported in the literature. In addition, all isolated compounds 1-11 were evaluated for their antioxidant activity.

A new ent-atisane diterpenoid, ent-3α-acetoxy-1β,16β,17-trihydroxyatisane (1), along with four known compounds, 3,3′,4′-tri-O-methylellagic acid (2), (R)-(+)-lasiodiplodin (3), taraxerol (4) and syringic acid (5) were isolated from the aerial parts of Euphorbia antiquorum L. The structure of compound 1 was identified by interpretation of their spectroscopic data and comparison with those reported in the literature.

A new benzofuran derivative, nervione (