VNUHCM Journal of Natural Sciences

Secretion systems in Gram-negative bacteria

Khoi Nguyen Hoang Le — 2025-03-31

Biotechnology’s fast development in expressing novel proteins has been substantially facilitated, particularly in the context of recombinant protein expression in bacteria. Currently, intracellular, secretory, and surface-displayed modes of protein expression are utilized in bacteria. However, the surface display of proteins in Gram-negative bacterial species is still limited by several factors. The challenges in protein expression on the surface of Gram-negative bacteria stem from the complex structure of their cell wall, which is composed of two membrane layers. Therefore, a suitable transport system is required for recombinant protein surface expression. Previous research has indicated that bacterial secretion systems are vital to their survival. In Gram-negative bacteria, secretion systems are classified into those that translocate across a single membrane and those that translocate across both membranes. While Sec and Tat are single-membrane translocation systems, the Type I secretion system (T1SS), Type II secretion system (T2SS), Type III secretion system (T3SS), Type IV secretion system (T4SS), Type V secretion system (T5SS), and Type VI secretion system (T6SS) are double-membrane translocation systems that facilitate the export of polypeptide chains synthesized within the cell to the external environment. In this overview, the distinctive features of each secretion system will be discussed, along with their potential applications for directing recombinant proteins onto the membranes using these systems.

Isolation and establishment of reference standards for resveratrol and isorhapotigenin of the linas of Gnetum montanum markgr

Truong Nhat Van Do — 2025-03-31

Gnetum montanum, commonly known as Dây gắm, belongs to the Gnetaceae family. Chemical composition studies have shown that stilbene compounds are the main constituents of this plant. Notably, resveratrol and isorhapotigenin are two significant compounds, comprising approximately 3-5% of the ethanol extract. Both compounds exhibit remarkable biological activities, including anti-inflammatory, anti-cancer, antioxidant properties, tyrosinase inhibition, Cytochrome P450 inhibition, and α-glucosidase inhibition. Resveratrol and isorhapotigenin are essential for assessing and evaluating the quality of Gnetum montanum liana and related medicinal materials within the Gnetaceae family. This study successfully established reference standards for resveratrol and isorhapotigenin, isolated from Gnetum montanum liana. The results showed high purity levels of 99.14% for resveratrol and 96.38% for isorhapotigenin. The process for determining the purity of resveratrol and isorhapotigenin in Gnetum montanum liana was successfully validated using the HPLC-DAD Agilent 1260 system. The mobile phase used in this process was a gradient of ACN and 0.5% TFA in water. The research covered system compatibility, specificity, linearity range, repeatability, and accuracy, all in accordance with ICH guidelines. Establishing these reference standards is crucial for ensuring consistency and reliability in the quality control processes of Gnetum montanum and related medicinal products. With these highly pure standards, researchers and manufacturers can accurately measure and verify the presence and concentration of resveratrol and isorhapotigenin in various samples. This contributes to the overall efficacy and safety of herbal medicines derived from Gnetum montanum. Furthermore, the validated HPLC-DAD method provides a robust and reliable analytical technique for routine quality control, supporting the standardization of herbal products and enhancing confidence in their therapeutic use. This advancement underscores the importance of rigorous scientific methods in the development and quality assurance of traditional medicinal resources.

Structural elucidation and urease inhibitory activity of four compounds isolated from the Curcuma aromatica Salisb. rhizomes

Tho Huu Le — 2025-03-31

White turmeric (Curcuma aromatica Salisb.) belonging to the ginger family (Zingiberaceae), is widely distributed in tropical and subtropical regions such as India, China, Japan, and Southeast Asian countries. In traditional Vietnamese medicine, white turmeric rhizomes are used to treat gastrointestinal disorders, skin infections, joint pain, and insect bites. This paper reports the isolation and structural elucidation of four compounds from the fraction NTC-F of the white turmeric rhizomes. The chemical structures of these compounds were elucidated by analyzing nuclear magnetic resonance (1D- and 2D-NMR) spectroscopic data, high-resolution electrospray ionization mass spectrometry (HRESI-MS) data, and comparison with references in the literature. The isolated compounds were meso-hannokinol (1), anti-3-acetoxy-5-hydroxy-1,7-bis(4-hydroxyphenyl)heptane (2), longpene A (3) and (12Z,14R)-labda-8(17),12-diene-14,15,16-triol (4). All four were evaluated for urease inhibitory activity, and compound (1) exhibited significant urease inhibitory activity with an IC50 value of 86.7 μM, compared to the positive control hydroxyurea (IC50 74.5 μM). This result could contribute the species Curcuma aromatica to the database of Vietnamese medicinal plants with the potential to treat Helicobacter pylori-induced gastric ulcers.

Optoelectronic properties of small type II CDTE-ZNSE quantum dots passivated by INF3 ligands

Minh Triet Dang — 2025-02-02

In this study, we employ first-principles methods with density functional theory including the spin-orbit coupling effect to investigate the optoelectronic properties of pristine and InF3-ligand-assisted CdTe-ZnSe type II quantum dots. We show that when attaching InF3 ligands to type II CdTe-ZnSe quantum dots, the optical absorption spectra of these dots is red-shifted towards the lower energy range with respect to that of the pristine CdTe-ZnSe quantum dots. When we actively increase or decrease the distances between the two single dots inside a type II quantum dot, their band gaps also increase or decrease accordingly. Upon attaching InF3 ligands, the band gap of this quantum dot performs a small blue shift compared to the corresponding pristine quantum dot sample. By increasing the distances between the two interior CdTe and ZnSe portions inside the CdTe-ZnSe dots, due to the charge transfer from the ligands to the interior portions, the absorption spectra exhibit a red-shift with a significant increase of the absorption intensity with respect to the case of the pristine type II quantum dots. The results demonstrate the essence of InF3 ligands to enhance the light absorption capacity resulting in improving the light-to-electricity conversion efficiency of solar panels embedding CdTe-ZnSe type II quantum dots.

STRUCTURAL ANALYSIS AND STABILITY ASSESSMENT OF SURFACE-MODIFIED BIODEGRADABLE POROUS NANO SILICA WITH POLYETHYLENE GLYCOL

Trần Hạnh Vy Nguyễn — 2025-03-31

This study details the surface modification of biodegradable porous organosilica nanomaterials (E4S) with polyethylene glycol (PEG) to enhance its stability for camptothecin (CPT) delivery. The material is synthesized by the sol-gel method from two organic silane precursors and post-synthesized functionalization with PEG. The synthesized material was characterized using N2 adsorption-desorption isotherms, thermogravimetric analysis (TGA), and zeta potential measurement. Scanning electron microscopy (SEM) images show the particle size remained relatively unchanged, around 100 nm, before and after functionalization. Elemental analysis (EA) further validated the successful modification of PEG onto E4S through changes in elemental percentages. The ability to successfully load CPT onto the materials was demonstrated through UV-vis absorption spectroscopy results and the loading capacity was calculated from UV detector high-performance liquid chromatography (HPLC) results. The CPT drug loading capacity of E4S and E4S-PEG materials is 88.83 ± 3.63 mg/g and 74.19 ± 5.09 mg/g, respectively. Furthermore, dynamic light scattering (DLS) results demonstrated that E4S-PEG exhibited improved stability and dispersion compared to E4S material through 72 hours of testing, thereby enhancing its potential in disease treatment applications.

The dependence of neutron/gamma discrimination efficiency on demenstion of EJ-301 scintilator

Hieu Phan Bao Quoc — 2025-03-31

This paper presents the results of research on the application of the Monte Carlo simulation method to investigate the dependence of neutron detection efficiency and neutron/gamma pulse discrimination capabilities on the size of a detector using the EJ-301 scintillator, supporting the design and development of neutron detectors. We constructed and evaluated eight cylindrical detector models with varying lengths and diameters using the Geant4 toolkit. The simulated detector models consist of a scintillator coupled with a light guide and a photomultiplier tube (PMT). The simulated pulse signals obtained from each model were analyzed to assess neutron/gamma discrimination using the digital charge integration (DCI) method, and neutron detection efficiency was determined at various energy thresholds. The neutron/gamma discrimination results were evaluated based on the Figure of Merit (FoM). The results showed that both neutron/gamma discrimination and neutron detection efficiency are significantly dependent on the detector size, particularly the variations in length and diameter. These findings are crucial for optimizing the design of neutron detectors using organic scintillators like EJ-301 or similar materials, aiming to enhance neutron/gamma discrimination and neutron detection efficiency.

Ag, F−doped ZnO thin films prepared by thermal shock method for photocatalytic applications

Trinh Anh Minh Nguyen — 2025-03-31

ZnO nano−thin films were successfully prepared by the sol−gel spin coating method on a galvanized copper substrate and then modified by the thermal shock method. The modification process was carried out with individual agents as NaF or AgNO3, or a combination of AgNO3 and NaF. XRD, Raman, FTIR, FESEM, EDX and UV–visible absorption spectroscopy were used to evaluate the effects of the thermal shock method and the modifying agents on samples. The degradation of methylene blue and some other dyes under UVA and visible light was applied to evaluate the photocatalytic activity. The obtained results showed that the thermal shock method, although it had almost no effect on the bulk structure, did affect the surface of the samples via the formation of a walled-chain structure that created surface defects and increased the number of hydroxyl groups on the surface. These effects, combined with suitable modifying agents, could improve the material's photocatalytic activity. Among the studied samples, ZnO nano−thin films co−modified with the two agents AgNO3 and NaF exhibited the most significant photocatalytic activity in both UVA (kapp = 0.174 h-1) and visible light (kapp = 0.0299 h-1) regions, demonstrating an interesting synergistic effect of these two modifying agents.