@article { ISI:000370464800023, title = {Complexation key to a pH locked redox reaction}, journal = {Journal of Chemical Education}, volume = {93}, number = {2}, year = {2016}, month = {FEB}, pages = {355-361}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

An unfavorable pH can block a feasible electron transfer for a pH dependent redox reaction. In this experiment, a series of potentiometric titrations demonstrate the sequential loss in feasibility of iron(II) dichromate redox reaction over a pH range of 0-4. The pH at which this reaction failed to occur was termed as a pH locked reaction. The comparative ability of 10 selected iron binding ligands with varied propensity for the redox potential modification of Fe(III)/Fe(II) redox couple to restore/unlock the pH locked redox reaction is shown using potentiometric titrations. The spectrophotometric speciation analysis of Fe(III) Tiron complexation with pH was carried out to explain the differing ability of EDTA and Tiron to unlock the reaction under different pH Conditions. The experiment illustrates how environmental, biological redox reactions avoid severe laboratory conditions to occur and can be explored in the design of novel redox systems for natural attenuation of environmental toxins to their non- or lesser-toxic forms. The experiment also demonstrates prudent laboratory practice for safe waste disposal.

}, keywords = {Analytical Chemistry, Aqueous Solution Chemistry, Coordination Compounds, Oxidation/Reduction, pH, Physical Chemistry, Potentiometry, Second-Year Undergraduate, Thermodynamics, Titration/Volumetric Analysis, Upper-Division Undergraduate}, issn = {0021-9584}, doi = {10.1021/acs.jchemed.5b00499}, author = {Rizvi, Masood Ahmad and Dangat, Yuvraj B. and Shams, Tahir and Khan, Khaliquz Zaman} } @article {44242, title = {pH dependent sophorolipid assemblies and their influence on gelation of silk fibroin protein}, journal = {Materials Chemistry and Physics}, volume = {203}, year = {2018}, month = {JAN }, pages = {9-16}, type = {Article}, abstract = {

Sophorolipid (SL), a bio-derived surfactant is an excellent gelling agent for natural fibrous protein, silk fibroin (SF) leading to potential biomedical applications. Interaction of SF with SL has been shown to accelerate the formation of hydrogel with the rate being dependent on the form of SL used. Here, we examine the effect of pH on SL-SF interaction and gel formation by employing rheology, fluorescence spectroscopy, SANS and NMR. The results indicate that the size of SL assemblies decrease as pH increases from acidic to alkaline and significantly impacts the association of SL and SF. The association of SF and SL is mainly via hydrophobic interactions, with the SL molecules forming bead like structures along the SF chain. The increased charge on the acidic form of SL at higher pH results in greater repulsion between acidic SL molecules, which are bound to the hydrophobic sites of SF, leading to rapid chain unfolding and subsequent gelation. (C) 2017 Elsevier B.V. All rights reserved.

}, keywords = {Assemblies, Nuclear magnetic resonance spectroscopy, pH, Silk fibroin, Small angle neutron scattering, Sophorolipid}, issn = {0254-0584}, doi = {10.1016/j.matchemphys.2017.09.045}, author = {Dubey, Parul and Kumar, Sugam and Ravindranathan, Sapna and Vasudevan, Sahana and Aswal, Vinod K. and Rajamohanan, Pattuparambil R. and Nisal, Anuya and Prabhune, Asmita} } @article {48064, title = {Formation of zircon-type DyCrO4 and its magnetic properties}, journal = {Ceramics International}, volume = {48}, year = {2022}, month = {SEP}, pages = {24666-24676}, type = {Article}, abstract = {

The formation mechanism of hydrolytic sol-gel synthesized DyCrO4 with a complexing agent in acidic and basic mediums is thoroughly studied. The role of complexing agents and pH on phase formation temperature is also intensively investigated. The formation temperature for DyCrO4 is similar to 500 degrees C in the absence and presence of complexing agents such as oxalic acid and ethylenediaminetetraacetic acid (EDTA) at pH 10. When critic acid is used, the DyCrO4 forms with Cr2O3 impurity. The crystallite size in the presence of a complexing agent in the basic medium is similar to 55 nm which is small as compared to only ammonia solution. The various reaction modes lead to tetragonal zircon-type DyCrO4 at similar to 500 degrees C, transforming into orthorhombic perovskite DyCrO3 at 800 degrees C. The magnetization curve shows the ferromagnetic behavior of DyCrO4 below transition temperature T-c similar to 21 K. This low T-c makes nanocrystalline DyCrO4 a potential material for cryogenic applications.

}, keywords = {Complexing agent, DyCrO4, Formation mechanism, Hydrolytic sol-gel method, pH}, issn = {0272-8842}, doi = {10.1016/j.ceramint.2022.05.113}, author = {Ughade, Supriya and Joshi, Bhavana and Poddar, Pankaj} }