A perspective on functionalizing colloidal quantum dots with DNA

This perspective provides an overview of the techniques that have been developed for the conjugation of DNA to colloidal quantum dots (QDs), or semiconductor nanocrystals. Methods described include: ligand exchange at the QD surface, covalent conjugation of DNA to the QD surface ligands, and one-step DNA functionalization on core QDs or during core/shell QD synthesis in aqueous solution, with an emphasis on the most recent progress in our lab. We will also discuss emerging trends in DNA-functionalized QDs for potential applications.      

Electro-Fenton treatment of synthetic organic dyes: Influence of operational parameters and kinetic study

This work investigates oxidative decolorization of two different dyes, Methylene blue and Titan yellow in aqueous solution using an environmentally friendly advanced electro-chemical oxidation (electro-Fenton) process. The effect of operating conditions like H₂O₂ concentration, current density, initial dye concentration was studied in a batch stirred cell. Individual decolorization decay kinetics for both dyes was investigated. The second-order absolute rate constants (L mol^?1 s^?1) between hydroxyl radical and dye have been calculated from experimental data by fitting it to the decolorization model. The apparent kinetic constants, k _app (s^?1) for Methylene blue and Titan yellow dye decolorization were also determined. The experimental data showed a good fit to the theoretical model, which can predict data in a wide range of % dye decolorization. This process also reduces COD of the dye solution, and the unit energy demand (UED) in kWh/kg COD removed for different electrical current has been reported.     

Characterizing nutrient dynamics with relation to changes in partial pressure of CO2 in a tropical sewage‐fed aquaculture pond situated in a Ramsar wetland

The changes in nutrient dynamics (nitrate, ammonium, silicate, phosphate and iron concentration) vis‐à‐vis partial pressure of CO₂ in water [pCO₂(water)] from tropical sewage‐fed aquaculture ponds (East Kolkota Wetlands, India) were analysed by means of a microcosm. A significant relationship between these nutrient’s removal from the system and reduction in pCO₂(water) was observed (with few exceptions). These water bodies acted as significant sources of CO₂ in pre‐monsoon and monsoon seasons despite having substantial quantity of chlorophyll‐a to make it a net autotrophic system. The study revealed that if conditions favourable for optimum photosynthesis can be maintained in these ponds, the CO₂ source character of these ponds can be reversed. In the post‐monsoon season, when the pH of the water column was high, the system acted as sink for CO₂ which suggests the use of lime to prevent these systems from becoming hypereutrophic and carbon source at the same time.     

Coalescence of bubbles and stability of foams in aqueous solutions of Tween surfactants

Coalescence of air bubbles and stability of foams in aqueous solutions of Tween 20, 40, 60 and 80 are reported in this work. Adsorption of the surfactants at air–water interface was studied by measuring the surface tension of the surfactant solutions. The surface tension profiles were fitted using a surface equation of state derived from the Gibbs and Langmuir adsorption equations. The critical micelle concentration and surface tension at this concentration were determined. The effect of surfactant concentration on coalescence of air bubbles at flat air–water interface was studied. The role of steric force on coalescence time was investigated. The coalescence time distributions were fitted by the stochastic model. The mean values of the distributions were compared with the predictions of seven film-drainage models. Stability of foams was analyzed by the Ross–Miles test. The initial and residual foam heights were measured at different surfactant concentrations. The stability of foams was compared with the coalescence time of the bubbles.     

Revisiting the mechanism of the triosephosphate isomerase reaction: the role of the fully conserved glutamic acid 97 residue

An analysis of 503 available triosephosphate isomerase sequences revealed nine fully conserved residues. Of these, four residues—K12, H95, E97 and E165—are capable of proton transfer and are all arrayed around the dihydroxyacetone phosphate substrate in the three‐dimensional structure. Specific roles have been assigned to the residues K12, H95 and E165, but the nature of the involvement of E97 has not been established. Kinetic and structural characterization is reported for the E97Q and E97D mutants of Plasmodium falciparum triosephosphate isomerase (Pf TIM). A 4000‐fold reduction in k_cat is observed for E97Q, whereas the E97D mutant shows a 100‐fold reduction. The control mutant, E165A, which lacks the key catalytic base, shows an approximately 9000‐fold drop in activity. The integrity of the overall fold and stability of the dimeric structure have been demonstrated by biophysical studies. Crystal structures of E97Q and E97D mutants have been determined at 2.0 Å resolution. In the case of the isosteric replacement of glutamic acid by glutamine in the E97Q mutant a large conformational change for the critical K12 side chain is observed, corresponding to a trans‐to‐gauche transition about the Cγ? Cδ (χ³) bond. In the E97D mutant, the K12 side chain maintains the wild‐type orientation, but the hydrogen bond between K12 and D97 is lost. The results are interpreted as a direct role for E97 in the catalytic proton transfer cycle. The proposed mechanism eliminates the need to invoke the formation of the energetically unfavourable imidazolate anion at H95, a key feature of the classical mechanism.     

Bis-azobenzene crosslinkers for photocontrol of peptide structure

Crosslinkers that undergo large changes in length upon photoisomerization can produce large conformational changes, and thereby functional changes, in biomolecules. We have designed and synthesized extended and rigid bis‐azobenzene crosslinkers: 4,4′‐bis(4‐(2‐chloroacetamido)phenyl)diazenylbiphenyl (BPDB) and the water‐soluble sulfonated analogue 4,4′‐bis(4‐(2‐chloroacetamido)phenyl)diazenylbiphenyl‐2,2′‐disulfonate (BPDBS). These photoswitches can produce end‐to‐end distance changes of a minimum of ≈5 Å and a maximum of ≈23 Å upon trans/cis isomerization. They have high absorption coefficients (45–60 000 M ^?1 cm^?1) and can produce up to ≈80 % cis isomers under favorable conditions. The photoswitching behavior of BPDBS‐crosslinked peptides was found to be highly dependent on the crosslinker attachment site. Upon UV irradiation (365 nm), significant decreases in α‐helix content were observed for peptides that were crosslinked with BPDBS through Cys residues at i,i+19, and i,i+21 positions. In contrast, large increases in α‐helix content were exhibited by i,i+11 crosslinked peptides. BPDBS thus constitutes a particularly bright and effective photoswitch for biomolecule photocontrol.     

Fire retardant property of cotton fabric treated with herbal extract

Flame retardant functionality was imparted in cellulosic textile using spinach leaves juice (SJ), an eco-friendly natural product. The extracted juice was made alkaline and applied in fresh bleached and mercerized cotton fabrics. Flame retardant properties of the control and treated fabrics were analysed in terms of limiting oxygen index (LOI), horizontal and vertical flammability and radiant heat testing. The study showed that the treated fabrics had good flame retardant property compared to control fabrics. The LOI value was found to increase by 1.6 times after application of SJ. As a result of this, the fabric does not catch flame. In horizontal flammability, the treated fabric showed burning with afterglow (without presence of flame) with a propagation rate of 10 mm/min, which is almost nine times lower than the control fabric. The thermal degradation and pyrolysis was studied using thermogravimetric analysis. The chemical composition of the control and SJ-treated cellulosic fabric were analysed by FTIR, SEM and EDX. Durability of the flame retardant functionality to soap washing and weathering had also been studied. After application of SJ, cellulosic fabric sample produced natural green colour. There was no significant change in other physical properties.     

Application of single and mixtures of red sandalwood and other natural dyes for dyeing of jute fabric: studies on colour parameters/colour fastness and compatibility

Single and binary mixtures of aqueous extracts of red sandalwood (RSW) with aqueous extract of other natural dyes like manjistha (MJ), jackfruit wood (JFW), marigold (MG), sappan wood (SW) and babool (BL) in different proportions are applied on bleached jute fabric for its dyeing after double pre-mordanted with myrobolan and aluminium sulphate applied in sequence under optimised conditions of mordanting with effects of use of different proportions of binary mixture of selective natural dyes on colour strength and other colour. Parameters and colour fastness properties have been investigated. Compatibility of selective binary mixture of dyes was also judged by a relatively newer colour index parameter established earlier from this laboratory. Binary of mixture of RSW and MJ is found to be most compatible with rating 4 (in 0–5 scale), and mixture of RSW:MG and RSW:JFW is found to have average compatibility having rating 3. Dyed fabric samples have also been further treated with cationic dye-fixing agents namely N-cetyl-N-trimethylammonium bromide (CTAB), cetrimide and Sandofix-HCF to improve wash fastness. Treatment with 2% CTAB or Sandofix-HCF improves the wash fastness to nearly 1 unit. Treatment with 1% benztriazole improves the light fastness of natural dyed jute textiles nearly half to one unit. The possible chemistry and mechanisms for such improvement in wash fastness by CTAB and improvement of light fastness by benztriazole for jute have also been discussed to explain the observed effects.     

Wear Behavior of Cooling Slope Rheocast A356 Al Alloy

In the present study, the dry sliding wear behavior of rheocast A356 Al alloys, cast using a cooling slope, as well as gravity cast A356 Al alloy have been investigated at a low sliding speed of 1 ms^?1, against a hardened EN 31 disk at different loads. The wear mechanism involves microcutting–abrasion and adhesion at lower load for all of the alloys studied in the present work. On the other hand, at higher load, mainly adhesive wear along with oxide formation is observed for gravity cast A356 Al alloy and rheocast A356 Al alloy, cast using a 45° slope angle. Unlike other alloys, 60° slope rheocast A356 Al alloy is found to undergo mainly abrasive wear at higher load. Accordingly, the rheocast sample, cast using a 60° cooling slope, exhibits a remarkably lower wear rate at higher load compared to gravity cast and 45° slope rheocast samples. This is attributed to the dominance of abrasive wear at higher load in the case of rheocast A356 Al alloy cast using a 60° slope. The presence of finer and more spherical primary Al grain morphology is found to resist adhesive wear in case of 60° cooling slope processed rheocast alloy and thereby delay the transition of the wear regime from normal wear to severe wear.