Ionic Equilibria and pH

Ionic Equilibria and pH reviews the quantitative aspects of aqueous acid-base chemistry. Definitions and concepts are presented and appropriate worked examples illustrate calculations of concentration, pH and ionization constants. Acid-base properties of salts (salt hydrolysis) is introduced and explained along with the common-ion effect and calculation of hydrolysis constants. Equilibria of acid-base buffers with respect to buffer preparation, calculating the pH of a buffer solution and application of the Henderson-Hasselbalch equation, buffer range and buffer capacity is discussed. Determining the pH during acid-base titrations, selecting the appropriate acid-base indicators, and generating pH titration curves are explained.

Green light perception paved the way for the diversification of GAF domain photoreceptors

Photoreceptors are proteins that sense incident light and then trigger downstream signaling events. Phytochromes are linear tetrapyrrole-binding photoreceptors present in plants, algae, fungi, and various bacteria. Most phytochromes respond to red and far-red light signals. Among the phytochrome superfamily, cyanobacteria-specific cyanobacteriochromes show much more diverse optical properties covering the entire visible region. Both phytochromes and cyanobacteriochromes share the GAF domain scaffold to cradle the chromophore as the light-sensing region. It is unknown what physiological demands drove the evolution of cyanobacteriochromes in cyanobacteria. Here we utilize ancestral sequence reconstruction and report that the resurrected ancestral cyanobacteriochrome proteins reversibly respond to green and red light signals. pH titration analyses indicate that the deprotonation of the bound phycocyanobilin chromophore enables the photoreceptor to perceive green light. The ancestral cyanobacteriochromes show modest thermal reversion to the green light-absorbing form, suggesting that they evolved to sense green-rich irradiance rather than red light, which is preferentially utilized for photosynthesis. In contrast to plants and green algae, many cyanobacteria can utilize green light for photosynthesis with their special light-harvesting complexes, phycobilisomes. The evolution of green/red sensing cyanobacteriochromes may therefore have allowed ancient cyanobacteria to acclimate to different light environments by rearranging the absorption capacity of the cyanobacterial antenna complex by chromatic acclimation.Significance StatementLight serves as a crucial environmental stimulus affecting the physiology of organisms across all kingdoms of life. Photoreceptors serve as important players of light responses, absorbing light and actuating biological processes. Among a plethora of photoreceptors, cyanobacteriochromes arguably have the wealthiest palette of color sensing, largely contributing to the success of cyanobacteria in various illuminated habitats. Our ancestral sequence reconstruction and the analysis of the resurrected ancestral proteins suggest that the very first cyanobacteriochrome most probably responded to the incident green-to-red light ratio, in contrast to modern red/far-red absorbing plant phytochromes. The deprotonation of the light-absorbing pigment for green light-sensing was a crucial molecular event for the invention of the new class of photoreceptors with their huge color tuning capacity.

Single Isomer N-Heterocyclic Cyclodextrin Derivatives as Chiral Selectors in Capillary Electrophoresis

In order to better understand the chiral recognition mechanisms of positively charged cyclodextrin (CD) derivatives, the synthesis, the pKa determination by 1H nuclear magnetic resonance (NMR)-pH titration and a comparative chiral capillary electrophoretic (CE) study were performed with two series of mono-substituted cationic single isomer CDs. The first series of selectors were mono-(6-N-pyrrolidine-6-deoxy)-β-CD (PYR-β-CD), mono-(6-N-piperidine-6-deoxy)-β-CD (PIP-β-CD), mono-(6-N-morpholine-6-deoxy)-β-CD (MO-β-CD) and mono-(6-N-piperazine-6-deoxy)-β-CD (PIPA-β-CD), carrying a pH-adjustable moiety at the narrower rim of the cavity, while the second set represented by their quaternarized, permanently cationic counterparts: mono-(6-N-(N-methyl-pyrrolidine)-6-deoxy)-β-CD (MePYR-β-CD), mono-(6-N-(N-methyl-piperidine)-6-deoxy)-β-CD (MePIP-β-CD), mono-(6-N-(N-methyl-morpholine)-6-deoxy)-β-CD (MeMO-β-CD) and mono-(6-N-(4,4-N,N-dimethyl-piperazine)-β-CD (diMePIPA-β-CD). Based on pH-dependent and selector concentration-dependent comparative studies of these single isomer N-heterocyclic CDs presented herein, it can be concluded that all CDs could successfully be applied as chiral selectors for the enantiodiscrimination of several negatively charged and zwitterionic model racemates. The substituent-dependent enantiomer migration order reversal of dansylated-valine using PIP-β-CD contrary to PYP-β-CD, MO-β-CD and PIPA-β-CD was also studied by 1H- and 2D ROESY NMR experiments.

Study on Interaction of Carboxylic Acid Gemini Surfactant with Cocamidopropyl Betaine in Aqueous Solution

The interaction of carboxylic acid gemini surfactant 4,8-didodecyl-3,9-dioxo-6-hydroxy-4,8-diaza-1,11-undecanedicarboxylic acid (CGS12) with amphoteric surfactant cocamidopropyl betaine (CAPB) at 258C and pH 7.0 has been investigated using pH titration, surface tension, dynamic light scattering (DLS) and cryogenic transmission electron microscopy (Cryo-TEM) measurements. The pH titration results show that CGS12 exhibits anionic surfactant properties and CAPB exists as a zwitterionic form at pH 7.0. The surface tension results show that the critical micelle concentration (CMC) values of the CAPB/CGS12 mixture are low, and basically exhibit a decreasing trend with decreasing molar ratio of CAPB (XCAPB). The variation of the CMC of the mixture reveals that the mixing is close to ideal. The DLS results indicate that the CAPB/ CGS12 mixture mainly forms the larger aggregates with the hydrate radii approximately 70-145 nm at various XCAPB. The Cryo-TEM images further demonstrate the CAPB/CGS12 mixtures mainly form vesicles. The results indicate that the aggregate size and microstructure of the mixture change little with the variation of XCAPB.

Protein Charge Neutralization is the Proximate Driver Dynamically Tuning a Nanoscale Bragg Reflector

Reflectin is a cationic, block copolymeric protein that mediates the dynamic fine-tuning of color and brightness of light reflected from nanostructured Bragg reflectors in iridocyte skin cells of squids. In vivo, neuronally activated phosphorylation of reflectin triggers its assembly, driving osmotic dehydration of the membrane-bounded Bragg lamellae containing the protein to simultaneously shrink the lamellar thickness and spacing while increasing its refractive index contrast, thus tuning the wavelength and increasing the brightness of reflectance. In vitro, we show that reduction in repulsive net charge of the purified, recombinant reflectin – either (for the first time) by generalized anionic screening with salt, or by pH titration - drives a finely tuned, precisely calibrated increase in size of the resulting multimeric assemblies. The calculated effects of phosphorylation in vivo are consistent with these effects observed in vitro. X-ray scattering analyses confirm the sphericity, size and low polydispersity of the assemblies. Precise proportionality between assembly size and charge-neutralization is enabled by the demonstrated rapid dynamic arrest of multimer growth. The resulting stability of reflectin assemblies with time ensures reciprocally precise control of the particle number concentration, thereby encoding a precise calibration between the extent of neuronal signaling, osmotic pressure, and the resulting optical changes. The results presented here strongly suggest that it is charge neutralization, rather than any change in aromatic content, that is the proximate driver of assembly, fine-tuning a colligative property-based nanostructured biological machine. A physical mechanism is proposed.

STUDY THE SENSORY PROPERTIES OF SOME TYPES OF JUICES THAT MADE BY USING NATURAL SWEETENER POWDER (Stevia rebaudiana)

Increased diseases and obesity currently due to increased production and excessive consumption of foods manufactured from non-food sweeteners without attention to the risk of consuming those additional high calories due to consuming these refreshing products such as juices and other various drinks, especially in the summer season by most segments of Iraqi society, especially workers, children and school students the aim of this study. Therefore, the study designed to replace sucrose with 0.03, 0.04 and 0.05% of each of the white stevia crystals and milled dry stevia leaves in the laboratory manufacture of juices and its effect on the general and sensory characteristics and the extent of their acceptability among the specialized residents. In addition to the control treatment, this was manufactured according to the specifications and concentration of the ingredients of juices manufactured by one of the locally famous juices manufacturing plants (Al-Shahir Factories) as a control treatment, with an added sucrose percentage of 8%. The results showed that the addition of stevia plant at 0.03 and 0.04% was most acceptable by sensory experts. The prepared orange juice was also analyzed for pH, titration acidity, dry matter, and density. The results also showed that by increasing the concentration of sweetener with the milled stevia plant, the pH of the mixture decreased and the acidity of the juice also increased. Whereas the juices with white stevia crystals were flavored with sweetness, clearer, more firm and acceptable by panelists.

Adsorption of nitrate and phosphate in an aqueous solution on composites of PVA and chitosan prepared from a Somanniathelphusa sinensis shell

In this study, chitosan was prepared from the shell of Somanniathelphusa sinensis, which is a crab ubiquitous in Vietnam. The 3-level, 3-factor Box–Behnken design was applied to the preparation of chitosan to investigate effects of factors, such as the HCl solution concentration, protein removal time and deacetylation time, on the degree of deacetylation (%DD). Scanning electron microscopy, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy and gel permeation chromatography were employed to examine the chitosan structure, as well as pH titration and antibacterial testing of the chitosan solution. Results revealed that as-p chitosan comprises specific functional groups, with almost no impurities. Its average molecular weight was ∼225,000 g/mol, and %DD was ∼89.7%. The chitosan/PVA composite was prepared and investigated for the adsorption of nitrate and phosphate ions in water. Experimental results revealed that the adsorption capacity of a chitosan/PVA (1:2) composite is better than that of chitosan. Accordingly, the theoretical maximum adsorption capacities of nitrate and phosphate ions on chitosan were 122.0 mg/g and 344.8 mg/g, respectively. The corresponding values on the chitosan/PVA (1:2) composite were 135.1 mg/g and 384.6 mg/g. Adsorption kinetics data at 25 °C were well fitted to the pseudo-second-order model (R2 > 0.998). These results revealed that crab shell chitosan and the chitosan/PVA (1:2) composite can be used for the adsorption of nitrates and phosphates in aqueous solutions.

Lokiarchaeota archaeon schizorhodopsin-2 (LaSzR2) is an inward proton pump displaying a characteristic feature of acid-induced spectral blue-shift

The photoreactive protein rhodopsin is widespread in microorganisms and has a variety of photobiological functions. Recently, a novel phylogenetically distinctive group named ‘schizorhodopsin (SzR)’ has been identified as an inward proton pump. We performed functional and spectroscopic studies on an uncharacterised schizorhodopsin from the phylum Lokiarchaeota archaeon. The protein, LaSzR2, having an all-trans-retinal chromophore, showed inward proton pump activity with an absorption maximum at 549 nm. The pH titration experiments revealed that the protonated Schiff base of the retinal chromophore (Lys188, pKa = 12.3) is stabilised by the deprotonated counterion (presumably Asp184, pKa = 3.7). The flash-photolysis experiments revealed the presence of two photointermediates, K and M. A proton was released and uptaken from bulk solution upon the formation and decay of the M intermediate. During the M-decay, the Schiff base was reprotonated by the proton from a proton donating residue (presumably Asp172). These properties were compared with other inward (SzRs and xenorhodopsins, XeRs) and outward proton pumps. Notably, LaSzR2 showed acid-induced spectral ‘blue-shift’ due to the protonation of the counterion, whereas outward proton pumps showed opposite shifts (red-shifts). Thus, we can distinguish between inward and outward proton pumps by the direction of the acid-induced spectral shift.

Understanding the sorption behaviour of Pu/U on zirconium phosphosilicate prepared by gelation route

Zirconium phosphosilicate (ZPS) has been prepared by gelation route for its ion exchange applications. ZPS was characterised by X-ray diffraction technique (XRD), thermogravimetry (TG), scanning electron microscopy (SEM), Fourier transformed Infrared Spectrometry (FTIR) and surface area analysis. K+ ion exchange behaviour was studied by pH titration. The material was found to extract Pu selectively over U from different mineral acids. Pu sorption behaviour on ZPS packed column was also been carried out. The pore volume was evaluated as 0.1336 mL g−1. The FTIR revealed the presence of –OH and PO43− groups on the surface of the material, while the SEM image indicates the irregular morphology and size of the sorbent. Different isotherm model: Langmuir, Freundlich, Dubinin–Rodushkevich and Temkin were used to understand the nature of sorption, while Lagergren 1st order, Intraparticle diffusion and pseudo 2nd order kinetics were used for modelling sorption kinetics. Suitable elution method was used for quantitative stripping of plutonium from sorbent. The radiolytic stability of the sorbent was evaluated upto 1500 kGy. A comparative evaluation of the sorption process has also been carried out with that reported in literature.