Huynh Thi Phuong Loan  Hoang Van Duc  Duong Tuan Quang  Vo Thanh Cong  Pham Van Tat  Nguyen Tien Trung  Nguyen Thi Ai Nhung 《Vietnam Journal of Chemistry》2019,57(4):418-424

The structure and bonding of complexes containing subvalent group‐14 elements [E(PPh₃)₂ → SiH₂]²⁺ ( Si‐EP ) with E = C to Pb have been researched using charge‐ and EDA‐NOCV methods. The optimized equilibrium geometries for complexes have the most stable structure which has been found for carbone ligand CP as the nearly end‐on bonded form in Si‐CP . In contrast to this, the heavier ligands SiP to PbP in the heavier complexes Si‐SiP to Si‐PbP exhibit strongly side‐on manners. Bond dissociation energies, ‐D_e (kcal.mol^‐1), increase from Si‐CP to the stronger bonded complexes Si‐SiP to Si‐PbP . EDA‐NOCV calculations revealed that the donation [E(PPh₃)₂ → SiH₂]²⁺ displays the significant σ‐interactions of the ligands while the π‐electron sharing exhibits the charges transfer between E(PPh₃)₂ and SiH₂²⁺. Bonding analysis indicated that the Si‐E bond results from the decrease in the donation [E(PPh₃)₂ → SiH₂]²⁺ and electrostatic attraction. The investigated complexes possessed E(PPh₃)₂ → SiH₂²⁺ strong σ‐donors and E(PPh₃)₂ ↔ SiH₂²⁺ π‐π electrons shared between the two fragments.  相似文献   

    

Huynh Ngoc Dat  Le Hoang Thuy Tien  Nguyen Thi My Dung  Nguyen Van Kieu  Duong Thuc Huy  Nguyen Thi Anh Tuyet  Nguyen Kim Phi Phung 《Vietnam Journal of Chemistry》2019,57(2):202-207

Chemical investigation of the ethyl acetate extract of Ficus consociata leaves, collected at Bien Hoa city, Dong Nai province, led to the isolation and structural elucidation of seven compounds, including luteolin ( 1 ), cirsiliol ( 2 ), isoquercetin ( 3 ), quercetin 3‐O‐α‐L‐arabinopyranoside ( 4 ), nikotoflorin ( 5 ), hesperidin ( 6 ) and (2E,4E,1'S,2'R,4'S,6'R)‐dihydrophaseic acid ( 7 ). Their chemical structures were elucidated by a combination of electronic circular dichroism (ECD) experiments and spectroscopic data (HR‐MS, 1D, 2D NMR) analysis, and comparison with those reported in the literature. Although, these compounds were already known in other species, but this is the first report on chemical constituents of F. consociata.  相似文献   

    

Nguyen Canh Minh Thang  Lam Gia Linh  Nguyen Hoang Anh  Huynh Le Thanh Nguyen  Le Viet Hai  Nguyen Thai Hoang 《Vietnam Journal of Chemistry》2023,61(1):93-100

Gold nanoparticles (AuNPs) were synthesized via redox reaction, using EDTA as a protecting and reducing agent, with HAuCl₄ as precursor and seed solution. The appropriate reaction condition was found out, with the ratio of EDTA:HAuCl₄ = 10:1, 40 μL of seed solution and stirring time of 5 minutes. The UV-Vis spectroscopy observed that the appearance of two absorption peaks were at 574 and 755.5 nm with the average size of AuNPs was 64.5 nm, the zeta potential was positive. The synthesized AuNPs were deposited on FTO electrode by electrophoresis deposition. The results of solid UV-Vis and SEM images showed that the spherical AuNPs ranging from 40 to 60 nm were deposited onto FTO to fabricate the AuNPs/FTO electrodes. The electrochemical activity of AuNPs/FTO were investigated based on the redox reaction of hydroquinone; the CV results showed the electrode with applied potential at 20 V for 60 minutes has the superior performance. The analysis of As(III) were conducted by AS-SWV technique. The results showed that AuNPs/FTO electrode enable to detect As(III) at the concentrations higher than 5 ppb that is suitable for the WHO standard of domestic water.  相似文献   

    

Kim Huynh  Marcel Voia 《商业与工业应用随机模型》2017,33(1):81-94

This paper proposes a methodology that accounts for the selection effect due to non‐random entry in duration models using latent‐class models. A mixed proportional hazard model with continuous finite mixture unobserved heterogeneity (MPH‐CFM) is introduced to correct for the potential bias induced by the selection effect. Conditions for identification, consistency, and asymptotic normality of the MPH‐CFM are provided. The estimator is used to investigate the duration of new entrant Canadian manufacturing firms. For the current application, the MPH‐CFM is compared with alternative duration models and found to be superior. Empirically, the results indicate that there are two classes of firms. Class I starts with high hazard and decreases non‐monotonically while Class II has a negligible hazard. These empirical results can be used to understand alternative models of firm dynamics. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

    

Tony Huynh  Ringi Kim 《Journal of Graph Theory》2017,86(2):213-222

For a graph G and a tree‐decomposition of G, the chromatic number of is the maximum of , taken over all bags . The tree‐chromatic number of G is the minimum chromatic number of all tree‐decompositions of G. The path‐chromatic number of G is defined analogously. In this article, we introduce an operation that always increases the path‐chromatic number of a graph. As an easy corollary of our construction, we obtain an infinite family of graphs whose path‐chromatic number and tree‐chromatic number are different. This settles a question of Seymour (J Combin Theory Ser B 116 (2016), 229–237). Our results also imply that the path‐chromatic numbers of the Mycielski graphs are unbounded.  相似文献   

    

Nguyen Huy Tuan  Vo Au  Le Nhat Huynh  Yong Zhou 《Mathematical Methods in the Applied Sciences》2020,43(8):5450-5463

In this paper, we consider a backward problem for an inhomogeneous time-fractional wave equation in a general bounded domain. Such a backward problem is of practically great importance because we often do not know the initial density of substance, but we can observe the density at a positive moment. The existence and regularity for the backward problem are investigated. The backward problem is ill-posed, and we propose a regularizing scheme by using a modified regularization method. We also prove the convergence rate for the regularized solution by using some a priori regularization parameter choice rule.  相似文献   

    

Huynh Thi Phuong Loan  Hoang Van Duc  Phan Tu Quy  Bui Thi Phuong Thuy  Pham Van Tat  Duong Tuan Quang  Nguyen Thi Ai Nhung 《Vietnam Journal of Chemistry》2020,58(3):364-371

The structure and bonding situation in platinum complexes containing slight tetrylene ligands [{PtCl‐C₉H₆NO}‐NHE] (Pt‐NHE) with E = C, Si, Ge were examined by DFT calculations with the levels are BP86/def2‐SVP and BP86/def2‐TZVPP. The predicted equilibrium structure of the ligands NHE in Pt‐NHE are bonded in distorted end‐on way to PtCl‐8‐hydroxyquinolines fragment with the bending angle, α, exhibits the biggest value in carbenes systems then slightly decrease from Pt‐NHC to Pt‐NHGe . Bond dissociation energies (BDEs), D_e (kcal.mol^‐1), decrease from the carbene complex to the weaker bonded silylene and germylene manners. The BDE when considering dispersion correction at the BP86‐D3(BJ)/def2‐TZVPP level confirms that Pt‐E bond in Pt‐NHE belongs to the effect of the bulky group in slight tetrylene NHE and Pt(II)‐group fragment which makes the intrinsic Pt‐E bond strength decreases from carbene to germylene complexes. The hybridization of atoms E and Pt have large p characters while the hybridization of atom Pt has greater d character which lead to the Pt‐E bond possesses not only NHE→{PtCl‐C₉H₆NO} strong σ‐donation but also a significant contribution π‐donation NHE→{PtCl‐C₉H₆NO} and weak π‐backdonation metal‐ligand NHE←{PtCl‐C₉H₆NO} in complexes Pt‐NHE .  相似文献   

    

Lu Thi Mong Thy  Nguyen Huong Tra My  Huynh Huy Phuong Tuong  Chung Vi Chi  Tran Hoang Tu  Huynh Ky Phuong Ha  Hoang Minh Nam  Mai Thanh Phong  Nguyen Huu Hieu 《Vietnam Journal of Chemistry》2020,58(3):287-291

This work aims to synthesise manganese ferrite/graphene oxide (MnFe₂O₄/GO) matrrials with various MnFe₂O₄ contents from 20‐60 wt.% in material for arsenic(V) (As(V)) removal. The nanocomposites were studied by X‐ray diffraction, Fourier‐transform infrared spectroscopy, transmission electron microscopy, Brunauer‐Emmett‐Teller, and vibrating‐sample magnetometry. The suitable mass ratio of MnFe₂O₄ in nanocomposite for As(V) removal was 50 wt.% (MGO50). The adsorption process on MGO50 followed the pseudo‐second‐order kinetic and Langmuir isotherm models with the maximum adsorption amounts of 212.3 mg/g. Accordingly, MGO50 nanocomposite could be used as an effective adsorbent for removal of As(V) from water.  相似文献   

    

Vo Hoang Dat  Do Thi My Lien  Huynh Ngoc Dat  Ngo Thi Thuy Duong  Nguyen Kim Phi Phung  Nguyen Thi Hoai Thu  Nguyen Thi Anh Tuyet 《Vietnam Journal of Chemistry》2020,58(2):168-172

In the investigation of the chemical constituents of the ethyl acetate extract of Passiflora incarnata Linn., collected at Dong Hoa district, Phu Yen province, six compounds were isolated. They were one megastigmane, dehydrovomifoliol (1) , three megastigmane monoglycosides, roseoside (2) , byzantionoside B (3) and foliasalacioside L (4) , one flavone C‐monoglycoside vitexin (5) and one nucleotide glycoside uridine (6) . Their chemical structures were elucidated by means of HR‐MS, 1D and 2D‐NMR data analysis and the comparison their NMR data with those reported in the literature. Although, these compounds had already reported in the other species, they were known in Passiflora incarnata Linn. for the first time to the best of our knowledge.  相似文献   

    

Nguyen Thi Thuy Linh  Ade Danova  Tuong Lam Truong  Warinthorn Chavasiri  Nguyen Kim Phi Phung  Huynh Bui Linh Chi 《Vietnam Journal of Chemistry》2020,58(2):231-236

From the chloroform extract of the lichen Ramalina peruviana Ach. (Ramalinaceae), collected at Cau Dat farm, Lam Dong province, Vietnam, eight organic compounds had been isolated: nonadecan‐1‐ol ( 1 ); nonadecenoic acid ( 2 ); (+)‐(12R)‐usnic acid ( 3 ); three monophenolic compounds‐ rhizonic acid ( 4 ), divarinolmonomethylether ( 5 ) and divaricatinic acid ( 6 ); and two depsides‐ decarboxy‐2'‐O‐methyldivaricatic acid ( 7 ) and sekikaic acid ( 8 ). The chemical structure of these compounds was elucidated by spectroscopic analysis as well as high resolution ESI–MS analysis and comparison with those reported in the literature. Among these compounds, ( 1 ), ( 2 ), ( 4 ), ( 5 ) and ( 7 ) were the first time known in the Ramalina genus. Although compound ( 7 ) was detected in the lichen Neofuscelia depsidella by chromatographic comparisons with authentic material that was synthesized by condensation of the benzoic acid and 3‐methoxyl‐5‐propylphenol but it is isolated in the nature for the first time. The results of determining the α‐glucosidase inhibitory activity of four isolated compounds show that the α‐glucosidase inhibitory effect of ( 8 ) was the best with IC₅₀ values in 136.62 μg/mL (compared with the control acarbose IC₅₀ 93.63 μg/mL).  相似文献