Dual Optimization in Phase Transfer Catalyzed Synthesis of Dibenzyl Sulfide using Response Surface Methodology

A new reaction protocol has been developed to prepare dibenzyl sulfide (DBS), a value-added organosulfur fine chemical, by utilizing toxic hydrogen sulfide (H₂S). H₂S absorbed in monoethanolamine (MEA) has been used as a sulfiding agent for benzyl chloride (BC) under liquid–liquid phase-transfer-catalyzed condition. Response surface methodology was used to model and optimize the process parameters for simultaneous dual-maximization of BC conversion and DBS selectivity. BC/sulfide mole ratio, MEA/sulfide mole ratio, temperature, and catalyst concentration were chosen as independent variables, and conversion of BC and selectivity of DBS were chosen as responses. A quadratic regression model was derived with satisfactory prediction. Dual optimization with desirability function predicts a maximum BC conversion of 100% and a maximum DBS selectivity of 95.2% under experimental conditions: temperature 353 K, catalyst concentration 0.14 kmol/m³, BC/sulfide mole ratio 2.83, MEA/sulfide mole ratio 3.7. The analysis of variance and regression with R² values of 0.9996 for BC conversion and 0.9833 for DBS selectivity confirm the good agreement of experimental results with predicted values and therefore, the models can be successfully used to predict the synthesis of DBS successfully

A Multipulse Time-Resolved Fluorescence Method for Probing Second-Order Recombination Dynamics in Colloidal Quantum Dots

The ability to generate and utilize multiexcited electronic states in colloidal quantum dots (QDs) is key to a growing range of QD technologies, but the factors that control their radiative and nonradiative recombination dynamics are not yet fully resolved. A significant barrier toward a greater understanding of these species is the fact that their spectroscopic signatures are energetically close to dominant exciton transitions, making it difficult to separate their decay contributions in inhomogeneously broadened ensembles. Here we describe a multipulse technique wherein a controllable number of 80 MHz laser pulses are used to generate different excited state populations, which are then monitored using time-resolved fluorescence. By changing the number of pulses and using a general data analysis method we are able to separate second-order emission generated by absorption of two or more laser pulses from first-order contributions generated by just one pulse. Furthermore, we show that it is possible to determine the nature of the multiexcited state by comparing the second-order emission intensity to models of QD decay dynamics. We find that in our sample of CdSe/CdS core/shell QDs the second-order emission is dominated by emissive trion states rather than biexcitons. Our spectroscopic technique offers a powerful new way to study multiexcited QDs, and the insights that will be gained from this and future studies could be an important step toward harnessing multiexcitons and other multiexcited states in new QD technologies

Characterization of <i>Arabidopsis</i> sterol glycosyltransferase <i>TTG15/UGT80B1</i> role during freeze and heat stress

<p>Sterol glycosyltransferases regulate the properties of sterols by catalyzing the transfer of carbohydrate molecules to the sterol moiety for the synthesis of steryl glycosides and acyl steryl glycosides. We have analyzed the functional role of <i>TTG15/UGT80B1</i> gene of <i>Arabidopsis thaliana</i> in freeze/thaw and heat shock stress using T-DNA insertional <i>sgt</i> knockout mutants. Quantitative study of spatial as well as temporal gene expression showed tissue-specific and dynamic expression patterns throughout the growth stages. Comparative responses of Col-0, <i>TTG15/UGT80B1</i> knockout mutant and <i>p</i>35<i>S</i>:<i>TTG15/UGT80B1</i> restored lines were analyzed under heat and freeze stress conditions. Heat tolerance was determined by survival of plants at 42°C for 3 h, MDA analysis and chlorophyll fluorescence image (CFI) analysis. Freezing tolerance was determined by survival of the plants at -1°C temperature in non-acclimatized (NA) and cold acclimatized (CA) conditions and also by CFI analysis, which revealed that, <i>p</i>35S:<i>TTG15/UGT80B1</i> restored plants were more adapted to freeze stress than <i>TTG15/UGT80B1</i> knockout mutant under CA condition. HPLC analysis of the plants showed reduced sterol glycoside in mutant seedlings as compared to other genotypes. Following CA condition, both β-sitosterol and sitosterol glycoside quantity was more in Col-0 and <i>p</i>35<i>S</i>:<i>TTG15/UGT80B1</i> restored lines, whereas it was significantly less in <i>TTG15/UGT80B1</i> knockout mutants. From these results, it may be concluded that due to low content of free sterols and sterol glycosides, the physiology of mutant plants was more affected during both, the chilling and heat stress.</p

Phenotypes and salt tolerance of the transgenic plants.

<p>Salt stressed 3-weeks-old soil grown plants, irrigated with the indicated NaCl solutions every second day up to 14 days. Phenotypes of plants after 14 d of treatment (<b>A</b>)<b>.</b> Dry weight of whole plants measured after 14 days of salt stress. Values are mean ± SE, n = 10, (*) for <i>P≤0.05</i>, (**) for <i>P≤0.01,</i> (***) for <i>P≤0.001</i> or <i>0.005,</i> significantly different from the control (t-test) (<b>B</b>)<b>.</b> Two-weeks-old seedlings of WT and transgenic lines were used for RNA extraction. To provide salt stress, seedlings were treated with 100 mM NaCl for 24 h before RNA isolation. The transcript level of two stress genes was determined by RT-PCR analyses. The stress genes used for the tests were late embryogenesis abundant proteins <i>LEA4-5</i> and Salt overlay sensitive gene <i>SOS3</i> (AF192886) (<b>C</b>)<b>.</b></p

Phenotypes and heat tolerance of the transgenic plants.

<p>Thermotolerant phenotypes of WT and overexpression lines of <i>A.thaliana,</i> showing heat sensitivity at 7-d-old seedlings stage. Seedlings were grown on agar plates in light for 7 d and heated at 38°C for 90 min, cooled at room temperature for 120 min, and again heated at 42°C for 180 min (acquired thermotolerance). Percentage of survival of plants in relation to WT control plants on the same plate was determined 5 d after heat stress (<b>A–B</b>). Three-weeks-old soil grown plants exposed directly to 42°C for 60 min (basal thermotolerance). Photograph was taken after 7 day survival of the plants (<b>C</b>). Heat-induced oxidative damage in WT as compared to overexpression lines with decreased thermotolerance. Plants were heat treated as described in Figure (<b>A)</b>, and after 2 days of recovery, seedlings were harvested and stored in liquid nitrogen until the assay was performed. The MDA level determined from the overexpression lines of <i>A.thaliana</i> in relation to WT control on each plate was determined. Values are expressed as mean (n = 3); errors bars show the SD for each experiment. (*) <i>P≤0.05</i> compared to WT (t-test) (<b>D</b>)<b>.</b> Two-weeks-old seedlings of WT and all transgenic lines were used for RNA extraction. For heat stress, seedlings were kept at 42°C for 4 h before RNA isolation. The transcript level of two stress genes was determined by RT-PCR analyses. The stress genes used for the tests were <i>Hsp70, Hsp90</i> (<b>E</b>).</p

Structural comparison between WsSGTL1 and AtSGT protein.

<p>Three-dimensional model of the WsSGTL1 and AtSGT protein as constructed by Phyre2 server using the backbone ‘C3hbjA’. 3D model of WsSGTL1 with sugar binding domain and sterol binding domain (<b>A</b>). 3D model of AtSGT with sugar binding domain and sterol binding domain highly similar to WsSGTL1 protein structure (<b>B</b>). Structural similarity by superimposition of WsSGTL1 and AtSGT (1.423 Å) (<b>C</b>).</p

SOD activity and measurement of relative electrical conductivity.

<p>Standard calibration curve for SOD at 595 nm <b>(A).</b> SOD activity analysis in <i>WsSGTL1</i> transgenic lines of <i>A. thaliana</i> and WT (Col-0) plants. Values are expressed as mean (n = 3); errors bars show the SD for each experiment; (*) <i>P≤0.05</i> compared to WT (t-test) (<b>B</b>)<b>.</b> REC of <i>WsSGTL1</i> transgenic lines of <i>A. thaliana</i> and WT (Col-0). Values are expressed as mean (n = 3); errors bars show SD.</p

Chlorophyll Imaging Fluorescence measurements.

<p>Fv/Fm values in WT and <i>WsSGTL1</i>transgenic lines of <i>A.thaliana</i> after normal growth condition of WT (<b>A</b>)<b>.</b> Normal growth condition of transgenic line of <i>WsSGTL1</i> (<b>B</b>)<b>.</b> Salt treatments of WT and transgenic lines of 50 mM (<b>C</b>)<b>.</b> Salt treatments of WT and Transgenic lines of 100 mM NaCl (<b>D</b>)<b>.</b> Heat treatment of (42°C) in WT (<b>E</b>)<b>.</b> Heat treatment of (42°C) in transgenic lines of <i>A. thaliana</i> (<b>F</b>)<b>.</b> Cold treatment (4°C) in WT (<b>G</b>)<b>.</b> Cold treatment of (4°C) in transgenic lines of <i>A. thaliana</i> (<b>H</b>)<b>.</b> Salt treatment started after shifting the 14 days seedling plants into the pot for three weeks and all image analysis was done after three week potted plants.</p

Molecular characterization and phenotype of <i>WsSGTL1</i> over expressing transgenic <i>Arabidopsis</i> plants.

<p>PCR analysis of three positive transgenic lines of <i>A. thaliana</i> by Gene Specific Primers in T₃ generation (amplicon size 2.1 Kb) (<b>A</b>). Three transgenic lines were confirmed by Southern analysis. From Rt to Lt, Lane 1-WT, Lane 2-L1, Lane 3-L2 and Lane 4-L3, were selected for all the experiments (The probes were 700 bp and designed from the 5′ unconserved region of the <i>WsSGTL1</i>) (<b>B</b>). Semi quantitative RT-PCR analysis of two-week-old WT and independent <i>35S-WsSGTL1</i> transgenic lines and morphological comparisons of three-week-old WT and <i>WsSGTL1</i> over-expressing lines under normal growth conditions (<b>C</b>).</p

Analysis of different cis-acting regulatory elements in the promoter of <i>WsSGTL1</i> using PLACE software.

<p>Analysis of different cis-acting regulatory elements in the promoter of <i>WsSGTL1</i> using PLACE software.</p