scholarly journals Multiple Substitution Strategies toward Tunable Luminescence in Lu2MgAl4SiO12:Eu2+ Phosphors

2020 ◽  
Vol 59 (2) ◽  
pp. 1405-1413 ◽  
Author(s):  
Zhiqiang Ming ◽  
Jianwei Qiao ◽  
Maxim S. Molokeev ◽  
Jing Zhao ◽  
Hendrik C. Swart ◽  
...  
Keyword(s):  
Multiple Substitution

scholarly journals Understanding the Lack of Reactivity of 2,4-Dihydroxybenzaldehyde Towards the Biginelli Adduct Using Density Functional Theory Molecular Modeling

Processes ◽  
2019 ◽  
Vol 7 (8) ◽  
pp. 521
Author(s):  
Virginia Flores-Morales ◽  
Eduardo D. Ayala-Medrano ◽  
José García-Elías ◽  
Margarita L. Martínez-Fierro ◽  
Edgar Marquez ◽  
...  
Keyword(s):  
Density Functional ◽  
Natural Bond Orbital ◽  
Activation Enthalpy ◽  
Computational Study ◽  
Theoretical Calculations ◽  
Condensation Reaction ◽  
Biginelli Reaction ◽  
Hydroxyl Group ◽  
Functional Theory ◽  
Multiple Substitution

The Biginelli reaction is a multicomponent reaction for obtaining dihydropyrimidinthiones quickly, with multiple substitution patterns. The reaction mechanism remains unclear. Three possible pathways proposed for the reaction are the iminium route, an enamine intermediate, and the Knoevenagel pathway. However, when thiourea was used, no theoretical calculations were reported. Thus, based on the literature, the iminium pathway was used to obtain evidence explaining the lack of reactivity of 2,4-dihydroxybenzaldehyde towards the Biginelli adduct, compared with 4-hydroxybenzaldehyde. This computational study, carried out using the B3LYP/6-31++G(d,p) level of theory, showed an increment of 150 kJ/mol in the activation energy of the slowest pathway, due to the presence of a hydroxyl group in position 2 (ortho) of the aromatic aldehyde, decreasing its reactivity. Natural bond orbital (NBO) calculations suggest that the determinant steps are simultaneous, i.e., the polarization of the carbonyl group and its corresponding protonation by the hydrogen of the SH fragment of the thiourea tautomer. The activation enthalpy values suggest that the nucleophile attack takes place later on the compound 2,4-dihydroxybenzaldehyde compared to 4-hydroxybenzaldehyde-TS, confirming that the OH group in position 2 hinders the condensation reaction.

scholarly journals Production of sucroesters using solvent-free reactive systems containing emulsifiers

2018 ◽  
Vol 38 (1) ◽  
pp. 16-23 ◽  
Author(s):  
Alvaro Orjuela ◽  
Maria Fernanda Gutierrez ◽  
Andrea Suaza ◽  
Jose Luis Rivera
Keyword(s):  
Fatty Acid ◽  
Process Design ◽  
Fatty Acid Methyl Esters ◽  
Methyl Esters ◽  
Reactive Systems ◽  
Reaction Times ◽  
Solvent Free ◽  
Acid Methyl ◽  
Color Degradation ◽  
Multiple Substitution

The transesterification reaction of sucrose and fatty acid methyl esters to produce sucroesters was experimentally evaluated using commercial emulsifiers as compatibility agents. Reactions were carried out at temperatures between 100 and 140°C, using emulsifier concentrations in the range of 5 to 15 %wt, and potassium carbonate as catalyst. Fatty acid methyl esters consumption and sucroesters production was monitored by HPLC analysis of samples. Methyl esters conversions around 40 % were obtained with 68 %wt monoester content in sucroesters mixture. Despite the reaction times were reduced by operating at high temperatures and high emulsifier’s concentration, multiple substitution and color degradation were observed. Higher productivities of sucroester and higher selectivity to monoesters were obtained when potassium palmitate was used as contacting agent. The lower monoester content in the final product was obtained when using a commercial sucroester emulsifier. Results of this study can be used for preliminary process design in a solvent-free production of biobased sucroesters.

A new highly sterically demanding silyl (TEDAMS) group. Synthesis by multiple substitution of tris(diphenylmethyl)silane with diarylcarbenium ions

2010 ◽  
Vol 51 (31) ◽  
pp. 4107-4109 ◽  
Author(s):  
Kimitada Terao ◽  
Takashi Watanabe ◽  
Takafumi Suehiro ◽  
Toshiki Nokami ◽  
Jun-ichi Yoshida
Keyword(s):  
Sterically Demanding ◽  
Multiple Substitution

Multiple substitution of protons by sodium ions in sodiated oligoglycines

2002 ◽  
Vol 219 (1) ◽  
pp. 89-99 ◽  
Author(s):  
R.Natasha Grewal ◽  
Houssain El Aribi ◽  
Jeffrey C Smith ◽  
Christopher F Rodriquez ◽  
Alan C Hopkinson ◽  
...  
Keyword(s):  
Sodium Ions ◽  
Multiple Substitution

scholarly journals Mutations in structural proteins of SARS-CoV-2 and potential implications for the ongoing outbreak of infection in India

2020 ◽  
Author(s):  
Rimjhim Dasgupta
Keyword(s):  
Structural Proteins ◽  
Significant Implication ◽  
Amino Acid Residues ◽  
Virus Propagation ◽  
Diagnostic Assays ◽  
Genetic Modifications ◽  
M Proteins ◽  
Substitution Mutations ◽  
The Stability ◽  
Multiple Substitution

SARS-CoV-2 has spread in India very quickly from its first reported case on 30 January 2020 in Thrissur, Kerala. With the drastic increasing number of positive cases around the world WHO raised the importance in the assessment of the risk of spread and understanding genetic modifications that could have occurred in the SARS-CoV-2. Using available genome sequence in NCBI repository from the samples of different locations in India, we identified the regions (hotspots) of the viral genome with high rates of mutation. We analysed four regions of the genome encoding structural proteins Spike (S), Nucleocapsid (N), envelop (E) and Membrane (M) proteins. Through computational biology approach, we identified multiple substitution mutations in S and N proteins whereas there is only one substitution in E protein and none in M protein.  We showed most of these amino acid residues are evolutionary conserved. The changes in the conserved residues may have significant implication on the stability of the proteins and subsequent interaction with other elements, which are essential for virus propagation. This provides a basis for a better understanding of the genetic variation in SARS-CoV-2 circulating in the India, which might provide important clues for identifying potential therapeutic targets, development of efficient vaccines, antiviral drugs and diagnostic assays for controlling COVID-19.

Fe(III)-Based Tandem Catalysis for Amidomethylative Multiple Substitution Reactions of α-Substituted Styrene Derivatives

ACS Catalysis ◽  
2020 ◽  
Vol 10 (18) ◽  
pp. 10627-10636
Author(s):  
Xiaolin Qian ◽  
Hui Zhou ◽  
Hetti Handi Chaminda Lakmal ◽  
James Lucore ◽  
Xuesong Wang ◽  
...  
Keyword(s):  
Tandem Catalysis ◽  
Substitution Reactions ◽  
Styrene Derivatives ◽  
Multiple Substitution

Regiocontrolled Synthesis of 6,7-Dihydro-4H-pyrazolo[5,1-c][1,4]oxazines

Synthesis ◽  
2019 ◽  
Vol 52 (01) ◽  
pp. 105-118
Author(s):  
Peter J. Lindsay-Scott ◽  
Eloise Rivlin-Derrick
Keyword(s):  
Building Blocks ◽  
High Yields ◽  
Multiple Substitution ◽  
Hydroxyethyl Group ◽  
Regiocontrolled Synthesis

Synthetic access to 6,7-dihydro-4H-pyrazolo[5,1-c][1,4]oxazines has been achieved in 3–4 steps from commercially available pyrazoles. Optimization of a protected hydroxyethyl group on N1 enabled the regiocontrolled construction of pyrazole-5-aldehydes in high yields; subsequent deprotection and reduction generated fused heterocyclic scaffolds bearing multiple substitution patterns. Moreover, the intermediate pyrazole lactols were shown to be versatile synthetic building blocks.

Highly Diastereoselective Functionalization of Piperidines by Photoredox Catalyzed C–H Arylation and Epimerization

2019 ◽  
Author(s):  
Morgan Walker ◽  
Brian Koronkiewicz ◽  
Shuming Chen ◽  
Kendall N Houk ◽  
James Mayer ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Transient Absorption ◽  
Transient Absorption Spectroscopy ◽  
Spectroscopic Methods ◽  
Reaction Conditions ◽  
Functional Theory ◽  
Transfer Processes ◽  
Electron Transfer Processes ◽  
Multiple Substitution

<div>We report a photoredox catalyzed α-amino C–H arylation reaction of highly substituted piperidine derivatives with electron deficient cyano(hetero)arenes. The scope and limitations of the reaction were explored, with piperidines bearing multiple substitution patterns providing the arylated products in good yields and with high diastereoselectivity. In order to probe the mechanism of the overall transformation, optical and fluorescent spectroscopic methods were used. By employing flash-quench transient absorption spectroscopy, we were able to observe electron transfer processes associated with radical formation beyond the initial excited state Ir(ppy)<sub>3</sub> oxidation. Following the rapid and unselective C–H arylation reaction, a slower epimerization occurs to provide the high diastereomer ratio observed for a large majority of the products. Several stereoisomerically pure products were re-subjected to the reaction conditions, each of which converged to the experimentally observed diastereomer ratios. The observed distribution of diastereomers corresponds to a thermodynamic ratio of isomers based upon their calculated relative energies using density functional theory (DFT).</div>

Sign in / Sign up

Export Citation Format

Share Document