Map of 20 reactions that take place during vapor–solid phase photocatalytic dehydrogenation of ethanol on metal‐loaded TiO2

KOIRALA AGNI RAJ,Thanh Nguyen Huu,Shaariikhuu Erdenechimeg,Nguyen Thi Xuyen,Hossain Muhammad Sarwar,윤경병 대한화학회 2023 Bulletin of the Korean Chemical Society Vol.44 No.4

We report the map of 20 reactions that take place during vapor-phase photo- chemical dehydrogenation of ethanol on four metal-doped TiO2 (Mn/TiO2, Mn = nanoparticles of Pd, Pt, Au, and Cu) under solar simulated light. The reac- tions are sensitively affected by the moisture amount and the nature of the car- rier gas. To construct the above map, we also used CH3CHO, CH3CO2H, (C2H5O)2CHCH3, and CH3CO2C2H5, respectively, as an independent starting reagent. Amazingly, Mn/TiO2 not only serves as photocatalysts but also as ther- mocatalysts for various reactions that appear in the above map. The reaction is proposed to proceed by a radical mechanism in which photoinduced electron transfer from the valence band to the conduction band of TiO2 is the initial step and the subsequent electron injection from organic reactants to the hole in the TiO2 valence band. This report also features highly valuable unprece- dented reactions, which bear great potential to be commercialized.

Methylation and subsequent glycosylation of 7,8-dihydroxyflavone

Koirala, N.,Pandey, R.P.,Parajuli, P.,Jung, H.J.,Sohng, J.K. Elsevier Science Publishers 2014 Journal of biotechnology Vol.184 No.-

An O-methyltransferase SpOMT2884, originating from Streptomyces peucetius ATCC 27952, was cloned, expressed, and applied for the production of target metabolite from Escherichia coli. Biochemical characterization of the 25kDa recombinant protein by in vitro and in vivo experiments showed that SpOMT2884 was an S-adenosyl-l-methionine-dependent O-methyltransferase. SpOMT2884 catalyzed O-methylation of different classes of flavonoids such as flavones (7,8-dihydroxyflavone (7,8-DHF), luteolin), flavonols (quercetin, rutin), flavanone (naringenin), and isoflavonoids (daidzein, formononetin). Biotransformation of 7,8-DHF, a preferred substrate of SpOMT2884, in a grown-induced culture of E. coli BL21 (DE3) harboring the recombinant pET-28a-SpOMT2884 stoichiometrically converted 7,8-DHF into 7-hydroxy-8-methoxyflavone, which was confirmed by liquid chromatography, mass spectrometry and various nuclear magnetic resonance (NMR) spectroscopy analyses. In order to improve the biotransformation substrate, time and media parameters were optimized and the production was scaled up using a 3-L fermentor. The maximum yield of 7-hydroxy-8-methoxyflavone was 192μM (52.57mg/L), representing almost 96% bioconversion within 12h, when 200μM of 7,8-DHF was supplemented in the culture. Further, the 7-hydroxy-8-methoxyflavone was purified in large scale and was used as a substrate separately for in vitro glycosylation to produce glucose, galactose and 2-deoxyglucose conjugated at 7th hydroxyl position of 7-hydroxy-8-methoxyflavone. Biological activity showed that 7-hydroxy-8-methoxyflavone had long term cytoprotective and antioxidant effects compared to 7,8-DHF suggesting that methylation enhances the stability of substrate and glycosylation has proved to increase the water solubility.

Glycosylation and subsequent malonylation of isoflavonoids in E. coli: strain development, production and insights into future metabolic perspectives.

Koirala, Niranjan,Pandey, Ramesh Prasad,Thang, Duong Van,Jung, Hye Jin,Sohng, Jae Kyung Published by Stockton Press on behalf of the Socie 2014 Journal of industrial microbiology & biotechnology Vol.41 No.11

<P>Genistin and daidzein exhibit a protective effect on DNA damage and inhibit cell proliferation. Glycosylation and malonylation of the compounds increase water solubility and stability. Constructed pET15b-GmIF7GT and pET28a-GmIF7MAT were used for the transformation of Escherichia coli and bioconversion of genistein and daidzein. To increase the availability of malonyl-CoA, a critical precursor of GmIF7MAT, genes for the acyl-CoA carboxylase α and β subunits (nfa9890 and nfa9940), biotin ligase (nfa9950), and acetyl-CoA synthetase (nfa3550) from Nocardia farcinia were also introduced. Thus, the isoflavonoids were glycosylated at position 7 by 7-O-glycosyltranferase and were further malonylated at position 6() of glucose by malonyl-CoA: isoflavone 7-O-glucoside-6()-O-malonyltransferase both from Glycine max. Engineered E. coli produced 175.7 ?M (75.90 mg/L) of genistin and 14.2 ?M (7.37 mg/L) genistin 6''-O-malonate. Similar conditions produced 162.2 ?M (67.65 mg/L) daidzin and 12.4 ?M (6.23 mg/L) daidzin 6''-O-malonate when 200 ?M of each substrate was supplemented in the culture. Based on our findings, we speculate that isoflavonoids and their glycosides may prove useful as anticancer drugs with added advantage of increased solubility, stability and bioavailability.</P>

Fate of methanol under one-pot artificial photosynthesis condition with metal-loaded TiO₂ as photocatalysts

Koirala, Agni Raj,Docao, Son,Lee, Seong Beom,Yoon, Kyung Byung Elsevier 2015 CATALYSIS TODAY - Vol.243 No.-

<P><B>Abstract</B></P> <P>The experimental artificial photosynthesis (AP) systems, which have attempted AP by photo-irradiation of single-chamber reactors containing CO<SUB>2</SUB>, H<SUB>2</SUB>O, and metal-loaded TiO<SUB>2</SUB>, have received great attention during the last three decades. Such one-pot AP systems cannot be efficient because the catalysts have water oxidation sites which can oxidize the carbon-containing organic fuels more readily than water. Despite this, methanol has been the most desired product from such AP systems due to its many merits. However, CH<SUB>4</SUB> and CO have been produced as major products under normal conditions (1bar of CO<SUB>2</SUB>, 1sun, neutral condition, and irradiation wavelength>350nm). From a systematic study aimed to elucidate the fate of methanol in such one-pot AP systems with novel metal nanoparticle loaded TiO<SUB>2</SUB> (M<SUB> <I>n</I> </SUB>–TiO<SUB>2</SUB>, M=Pd, Pt, Cu and Au) as the catalyst we found that methanol and its related products formaldehyde and formic acid are not produced from such one-pot AP systems, indicating that the gaseous products should be produced from the pathways which do not involve methanol and the less-reduced products as intermediates or side products. We also elucidated that when methanol is added into the AP system, as many as fifteen different reactions take place as shown in Scheme 1. The reaction is initiated by photoinduced excitation of the charge-transfer (CT) band from methanol to TiO<SUB>2</SUB> surface, which appears in the UV region, by the UV part of the solar light. These reactions bear the potential to be used for production of various compounds.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Photocatalytic reaction of methanol and water vapors on M–TiO<SUB>2</SUB> was studied. </LI> <LI> Fifteen different reactions simultaneously take place during this reaction. </LI> <LI> One-pot photoreaction of CO<SUB>2</SUB> and H<SUB>2</SUB>O on M–TiO<SUB>2</SUB> has been studied for long time. </LI> <LI> Explains why CH<SUB>4</SUB> and CO are the major products from the above one-pot reaction. </LI> <LI> Explains why CH<SUB>3</SUB>OH, HCOH, and HCOOH cannot be intermediates in the above reaction. </LI> </UL> </P>

Time Slot Exchange Protocol in a Reservation Based MAC for MANET

Koirala, Mamata,Ji, Qi,Choi, Jae-Ho The Korea Institute of Convergence Signal Processi 2009 융합신호처리학회 논문지 (JISPS) Vol.10 No.3

Recently, much attention to a self-organizing mobile ad-hoc network is escalating along with progressive deployment of wireless networks in our everyday life. Being readily deployable, the MANET (mobile ad hoc network) can find its applications to emergency medical service, customized calling service, group-based communications, and military purposes. In this paper we investigate a time slot exchange problem found in the time slot based MAC, that is designed for IEEE 802.11b interfaces composing a MANET. The paper provides a method to maintain the quality of voice call by providing a new time slot when the channel assigned for that time slot gets noisy with interferences induced from other nodes, which belong to the same and/or other subgroups. In order to assess the performance of the proposed algorithm, a set of simulations using the OPNET modeler has been performed assuming that the IEEE 802.11b interfaces are operating under a modified MAC, which is a time slot based reservation MAC implemented in the PCF part of the superframe. In a real-time voice call service over a MANET of a size 500 ${\times}$ 500 meter squares with the number of nodes up to 100, the simulation results are collected and analyzed with respect to the packet loss rate and packet delay. The results show us that the proposed time slot exchange protocol improves the quality of voice call over that of plain DCF.

Computational Design of Bifurcation: A Case Study of Darundi Khola Hydropower Project

Koirala, Ravi,Chitrakar, Sailesh,Neopane, Hari Prasad,Chhetri, Balendra,Thapa, Bhola Korean Society for Fluid machinery 2017 International journal of fluid machinery and syste Vol.10 No.1

Bifurcation refers to wye division of penstock to divide the flow symmetrically or unsymmetrically into two units of turbine for maintaining economical, technical and geological substrates. Particularly, water shows irrelevant behavior when there is a sudden change in flow direction, which results into the transition of the static and dynamic behavior of the flow. Hence, special care and design considerations are required both hydraulically and structurally. The transition induced losses and extra stresses are major features to be examined. The research on design and analysis of bifurcation is one of the oldest topics related to R&D of hydro-mechanical components for hydropower plants. As far as the earlier approaches are concerned, the hydraulic designs were performed based on graphical data sheet, head loss considerations and the mechanical analysis through simplified beam approach. In this paper, the multi prospect approach for design of Bifurcation, incorporating the modern day's tools and technology is identified. The hydraulic design of bifurcation is a major function of dynamic characteristics of the flow, which is performed with CFD analysis for minimum losses and better hydraulic performances. Additionally, for the mechanical design, a simplified conventional design method as pre-estimation and Finite Element Method for a relevant result projections were used.

Epidemiological Study of Laryngeal Carcinoma in Western Nepal

Koirala, Krishna Asian Pacific Journal of Cancer Prevention 2015 Asian Pacific journal of cancer prevention Vol.16 No.15

Background: Laryngeal malignancy is a common malignancy of the head and neck region. Affected patients usually present with features that are characteristic of certain subsites. The larynx is oncologically divided into three: supraglottis, glottis and subglottis. Studies from Western countries have shown that the glottis is the commonest subsite to harbour laryngeal malignancy. However, the supraglottis has been reported to be the commonest subsite in developing countries, including examples in the Indian subcontinent. To our knowledge, no study has been carried out in western Nepal about the epidemiology of laryngeal cancer to date. The purpose of this study was to analyse the epidemiology of laryngeal cancer in relation to its risk factors, age distribution,and preferred subsites and to see if there is any recent change in the subsite wise distribution of laryngeal malignancy in western Nepal. Materials and Methods: Patients of all ages and both sexes with suspected laryngeal malignancy were enrolled in the initial study. Detailed history taking and clinical examination was performed to find out the involved subsite in relation to the clinical features. Direct laryngoscopy was performed to further confirm the subsite and to take biopsy from the growth under general anesthesia. After confirmation of malignancy from the biopsy report, patients were finally included in the study. Data were analysed and observations were made to find out the distribution of laryngeal malignancy in different subsites. Results: The supraglottic larynx was the commonest subsite to harbor laryngeal malignancy. Smoking and alcohol were found to be the common risk factors. The mean age of the patients was in their sixties. Conclusions: Laryngeal malignancy is common in elderly individuals. Supraglottic laryngeal malignancy is the commonest laryngeal malignancy in people who smoke and drink alcohol in Nepal. Avoidance of alcohol use and smoking will be a milestone to reduce the incidence of laryngeal cancers and associated mortality.

Altered brain functional connectivity induced by physical exercise may improve neuropsychological functions in patients with benign epilepsy

Koirala, Gyan Raj,Lee, Dongpyo,Eom, Soyong,Kim, Nam-Young,Kim, Heung Dong Elsevier 2017 Epilepsy & behavior Vol.76 No.-

<P><B>Abstract</B></P> <P><B>Objective</B></P> <P>The objective of this study was to elucidate alteration in functional connectivity (FC) in patients with benign epilepsy with centrotemporal spikes (BECTS) as induced by physical exercise therapy and their correlation to the neuropsychological (NP) functions.</P> <P><B>Methods</B></P> <P>We analyzed 115 artifact- and spike-free 2-second epochs extracted from resting state EEG recordings before and after 5weeks of physical exercise in eight patients with BECTS. The exact Low Resolution Electromagnetic Tomography (eLORETA) was used for source reconstruction. We evaluated the cortical current source density (CSD) power across five different frequency bands (delta, theta, alpha, beta, and gamma). Altered FC between 34 regions of interests (ROIs) was then examined using lagged phase synchronization (LPS) method. We further investigated the correlation between the altered FC measures and the changes in NP test scores.</P> <P><B>Results</B></P> <P>We observed changes in CSD power following the exercise for all frequency bands and statistically significant increases in the right temporal region for the alpha band. There were a number of altered FC between the cortical ROIs in all frequency bands of interest. Furthermore, significant correlations were observed between FC measures and NP test scores at theta and alpha bands.</P> <P><B>Conclusion</B></P> <P>The increased localization power at alpha band may be an indication of the positive impact of exercise in patients with BECTS. Frequency band-specific alterations in FC among cortical regions were associated with the modulation of cognitive and NP functions. The significant correlation between FC and NP tests suggests that physical exercise may mitigate the severity of BECTS, thereby enhancing NP function.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The altered brain functional connectivity was associated with the positive impact on neuropsychological function. </LI> <LI> Correlation between altered functional connectivity and neuropsychological test scores at alpha and theta bands. </LI> <LI> Significant increase in cortical current source density power in the right temporal region following exercise. </LI> </UL> </P>

Methylation of flavonoids: Chemical structures, bioactivities, progress and perspectives for biotechnological production

Koirala, N.,Thuan, N.H.,Ghimire, G.P.,Thang, D.V.,Sohng, J.K. IPC Science and Technology Press ; Elsevier Scienc 2016 Enzyme and microbial technology Vol.86 No.-

<P>Among the natural products, flavonoids have been particularly attractive, highly studied and become one of the most important promising agent to treat cancer, oxidant stress, pathogenic bacteria, inflammations, cardio-vascular dysfunctions, etc. Despite many promising roles of flavonoids, expectations have not been fulfilled when studies were extended to the in vivo condition, particularly in humans. Instability and very low oral bioavailability of dietary flavonoids are the reasons behind this. Researches have demonstrated that the methylation of these flavonoids could increase their promise as pharmaceutical agents leading to novel applications. Methylation of the flavonoids via theirs free hydroxyl groups or C atom dramatically increases their metabolic stability and enhances the membrane transport, leading to facilitated absorption and highly increased oral bioavailability. In this paper, we concentrated on analysis of flavonoid methoxides including O- and C-methoxide derivatives in aspect of structure, bioactivities and description of almost all up-to-date O- and C-methyltransferases' enzymatic characteristics. Furthermore, modern biological approaches for synthesis and production of flavonoid methoxides using metabolic engineering and synthetic biology have been focused and updated up to 2015. This review will give a handful information regarding the methylation of flavonoids, methyltransferases and biotechnological synthesis of the same. (C) 2016 Elsevier Inc. All rights reserved.</P>

Highly transmissive subtractive color filters based on an all-dielectric metasurface incorporating TiO₂ nanopillars

Koirala, Ishwor,Lee, Sang-Shin,Choi, Duk-Yong The Optical Society 2018 Optics express Vol.26 No.14