pH-dependent Changes Research Articles

Cyclometalated Iridium(III) Complex with Substituted Benzimidazole: pH Directed Organelle-Specific Localization Within Lysosome.

We report the synthesis and pH dependent emission spectral behaviour of four emissive iridium(III) complexes (Ir1-Ir4) with two isomeric pairs of bis-trifluoromethyl appended benzimidazole ligands. The imidazolyl hydrogen(N-H) has been replaced by phenyl groups (N-Ph) in two ligands to understand the impact of hydrogen bonding on the photophysical properties of the complexes and it indeed plays interesting role in the charge-transfer dynamics. The pH dependent electronic spectral change is observed for two of the complexes. The enhancement of emission intensity is observed at different wavelength for pH<7 and pH>7 for Ir1 and Ir3. The emission sensing of biogenic amines with pka values ranging from 5.80-9.74 is reported along with cellular imaging. The complex Ir1 specifically localizes within lysosome (pH=4.5-5) and thus image this organelle with great precision. The detail electronic spectra and electrochemical behaviour were reported here along with TDDFT results.

Colorimetric polymerase chain reaction mediated by pH indicator: rapid detection of drug-resistant nosocomial bacteria

Polymerase chain reaction (PCR) is the gold standard for molecular diagnoses due to its high sensitivity and accuracy. However, conventional PCR exhibits limitations including extended analysis time and complicated sample treatment. To shorten the analysis time of standard three-step PCR, we employed a two-step PCR allowing for fast amplification of nucleic acid in a chip format. Moreover, to realize a fully-integrated and on-site visual discrimination of opportunistic and multidrug-resistant pathogens, namely, Enterococcus faecium and Acinetobacter baumannii. DNA was extracted using FTA card, and pH-dependent color changes of the PCR amplicons were monitored by using phenolphthalein as a pH indicator. The overall reaction took less than 35 min and exhibited high selectivity and sensitivity confirmed by the limit of detection of approximately 103 CFU/mL for E. faecium. In addition, carbapenem-resistant A. baumannii was successfully detected demonstrating the clinical applicability of the introduced technique using a thermoplastic chip. E. faecium both in bacterial cell culture solution and a contaminated surface were also successfully detected proving the feasibility of the chip-based detection system and paving the way for a facile discrimination of opportunistic pathogens prevalent in hospitals and our environment.

Investigating pH-induced conformational switch in PIM-1: An integrated multi spectroscopic and MD simulation study

PIM-1 is a Ser/Thr kinase, which has been extensively studied as a potential target for cancer therapy due to its significant roles in various cancers, including prostate and breast cancers. Given its importance in cancer, researchers are investigating the structure of PIM-1 for pharmacological inhibition to discover therapeutic intervention. This study examines structural and conformational changes in PIM-1 across different pH using various spectroscopic and computational techniques. Spectroscopic results indicate that PIM-1 maintains its secondary and tertiary structure within the pH range of 7.0–9.0. However, protein aggregation occurs in the acidic pH range of 5.0–6.0. Additionally, kinase assays suggested that PIM-1 activity is optimal within the pH range of 7.0–9.0. Subsequently, we performed a 100 ns all-atom molecular dynamics (MD) simulation to see the effect of pH on PIM-1 structural stability at the molecular level. MD simulation analysis revealed that PIM-1 retains its native conformation in alkaline conditions, with some residual fluctuations in acidic conditions as well. A strong correlation was observed between our MD simulation, spectroscopic, and enzymatic activity studies. Understanding the pH-dependent structural changes of PIM-1 can provide insights into its role in disease conditions and cellular homeostasis, particularly regarding protein function under varying pH conditions.

Blue in Food and Beverages—A Review of Socio-Cultural, Economic, and Environmental Implications

The presented review concerns the cross-disciplinary approaches to the subject of blue food and blue colourants, the socio-cultural aspects of blue food and beverage consumption, human health effects, environmental impact, and economic aspects. Blue colour in relation to food is not only about improving visual appeal, to which the addition of food colouring is usually limited when the food is coloured in some way that does not encourage eating. It is also the rich and complex sociological side related to food, that is, not only the food itself but also the background, dishware, and light, depending on whether we want to encourage—to increase consumption—or discourage—to, for example, reduce the amount of food eaten for dietary purposes. The negative side of consuming and disposing of synthetic dyes and the health-promoting aspects of natural dyes are also mentioned, with the economic and environmental aspects of sourcing natural dyes being discussed. The food industry uses blue dyes not only for consumption, but also for food quality control, taking advantage of the pH-dependent colour change properties of the compound.

Revealing the pH-dependent conformational changes in sol g 2.1 protein and potential ligands binding

Sol g 2, a major protein found in the venom of the tropical fire ant (Solenopsis geminata), is well-known for its ability to bind various hydrophobic molecules. In this study, we investigate the binding activity of recombinant Sol g 2.1 protein (rSol g 2.1) with potential molecules, including (E)-β-Farnesene, α-Caryophyllene, and 1-Octen-3-ol at different pH levels (pH 7.4 and 5.5) using fluorescence competitive binding assays (FCBA). Our results revealed that Sol g 2.1 protein has higher affinity binding with these ligands at neutral pH. Relevance to molecular docking and molecular dynamics simulations were utilized to provide insights into the stability and conformational dynamics of Sol g 2.1 and its ligand complexes. After simulation, we found that Sol g 2.1 protein has higher affinity binding with these ligands as well as high structural stability at pH 7.4 than at an acidic pH level, indicating by RMSD, RMSF, Rg, SASA, and principal component analysis (PCA). Additionally, the Sol g 2.1 protein complexes at pH 7.4 showed significantly lower binding free energy (∆Gbind) and higher total residue contributions, particularly from key non-polar amino acids such as Trp36, Met40, Cys62, and Ile104, compared to the lower pH environment. These explain why they exhibited higher binding affinity than the lower pH. Therefore, we suggested that Sol g 2.1 protein is a pH-responsive carrier protein. These findings also expand our understanding of protein–ligand interactions and offer potential avenues for the development of innovative drug delivery strategies targeting Sol g 2.1 protein.

Reorientation of interfacial water molecules during melting of brain sphingomyelin is associated with the phase transition of its C24:1 sphingomyelin lipids

Melting of brain sphingomyelin (bSM) manifests as a broad feature in the DSC curve that encompasses the temperature range of 25 – 45 °C, with two distinguished maxima originating from the phase transitions of two the most abundant components: C24:1 (Tm,1) and C18:0 (Tm,2). While C24:1/C18:0 sphingomyelin transforms from the gel/ripple phase to the fluid/fluid phase, the dynamics of water molecules in the interfacial layer remain completely unknown. Therefore, we carried out a calorimetric (DSC), spectroscopic (temperature-dependent UV-Vis and fluorescence) and MD simulation study of bSM in the absence/presence of Laurdan® (bSM ± L) suspended in Britton-Robinson buffer with three different pH values, 4 (BRB4), 7 (BRB7) and 9 (BRB9), and of comparable ionic strength (I = 100 mM). According to DSC, T̅m, 1 (≈ 34.5 °C/≈ 32.1 °C) and T̅m, 2 (≈ 38.0 °C/≈ 37.2 °C) of bSM suspended in BRB4, BRB7, and BRB9 in the absence/presence of Laurdan® are found to be practically pH-independent. Turbidity-based data (UV-Vis) detected both qualitative and quantitative differences in the response of bSM suspended in BRB4/BRB7/BRB9 (T̅m: ∼ 35 °C/32.0 ± 0.2 °C/36.4 ± 0.4), suggesting an intricate interplay of weakening of van der Waals forces between their hydrocarbon chains and of increased hydration in the polar headgroups region during melting. The temperature-dependent response of Laurdan® reported a discontinuous, pH-dependent change in the reorientation of interfacial water molecules that coincides with the melting of C24:1 lipids (on average, T̅m (LTC/HTC): ≈ 31.8 °C/30.6 °C/30.5 °C). MD simulations elucidated the impact of Laurdan® on a change in the physicochemical properties of bSM lipids and characterized the hydrogen bond network at the interface at 20 °C and 50 °C.

Mesoporous Fe3O4/SiO2/poly(2-carboxyethyl acrylate) composite polymer particles for pH-responsive loading and targeted release of bioactive molecules.

pH-responsive polymer microspheres undergoing reversible changes in their surface properties have been proved useful for drug delivery to targeted sites. This paper is aimed at preparing pH-responsive polymer-modified magnetic mesoporous SiO2 particles. First, mesoporous magnetic (Fe3O4) core-particles are prepared using a one-pot solvothermal method. Then, magnetic Fe3O4 particles are covered with a C[double bond, length as m-dash]C functional mesoporous SiO2 layer before seeded emulsion polymerization of 2-carboxyethyl acrylate (2-CEA). The composite polymer particles are named Fe3O4/SiO2/P(2-CEA). The average diameters of the Fe3O4 core and Fe3O4/SiO2/P(2-CEA) composite polymer particles are 414 and 595 nm, respectively. The mesoporous (pore diameter = 3.41 nm) structure of Fe3O4/SiO2/P(2-CEA) composite polymer particles is confirmed from Brunauer-Emmett-Teller (BET) surface analysis. The synthesized Fe3O4/SiO2/P(2-CEA) composite polymer exhibited pH-dependent changes in volume and surface charge density due to deprotonation of the carboxyl group under alkaline pH conditions. The change in the surface properties of Fe3O4/SiO2/P(2-CEA) composite polymer particles following pH change is confirmed from the pH-dependent sorption of cationic methylene blue (MB) and anionic methyl orange (MO) dye molecules. The opening of the pH-responsive P(2-CEA) gate valve at pH 10.0 allowed the release of loaded vancomycin up to 99% after 165 min and p-acetamido phenol (p-AP) up to 46% after 225 min. Comparatively, the amount of release is lower at pH 8.0 but still suitable for drug delivery applications. These results suggested that the mesoporous Fe3O4/SiO2 composite seed acted as a microcapsule, while P(2-CEA) functioned as a gate valve across the porous channel. The prepared composite polymer can therefore be useful for treating intestine/colon cancer, where the pH is comparatively alkaline.

Spectroscopically Validated pH-dependent MSOX Movies Provide Detailed Mechanism of Copper Nitrite Reductases

Copper nitrite reductases (CuNiRs) exhibit a strong pH dependence of their catalytic activity. Structural movies can be obtained by serially recording multiple structures (frames) from the same spot of a crystal using the MSOX serial crystallography approach. This method has been combined with on-line single crystal optical spectroscopy to capture the pH-dependent structural changes that accompany during turnover of CuNiRs from two Rhizobia species. The structural movies, initiated by the redox activation of a type-1 copper site (T1Cu) via X-ray generated photoelectrons, have been obtained for the substrate-free and substrate-bound states at low (high enzymatic activity) and high (low enzymatic activity) pH. At low pH, formation of the product nitric oxide (NO) is complete at the catalytic type-2 copper site (T2Cu) after a dose of 3 MGy (frame 5) with full bleaching of the T1Cu ligand-to-metal charge transfer (LMCT) 455 nm band (S(σ)Cys → T1Cu2+) which in itself indicates the electronic route of proton-coupled electron transfer (PCET) from T1Cu to T2Cu. In contrast at high pH, the changes in optical spectra are relatively small and the formation of NO is only observed in later frames (frame 15 in Br2DNiR, 10 MGy), consistent with the loss of PCET required for catalysis. This is accompanied by decarboxylation of the catalytic AspCAT residue, with CO2 trapped in the catalytic pocket.

Experimental, theoretical and numerical simulation-based investigations on the fabricated Cu2ZnSn thin-film-based Schottky diodes with enhanced electron transport for solar cell

Copper-zinc-tin Cu2ZnSn (CZT) thin films are promising materials for solar cell applications. This thin film was deposited on a fluorine-doped tin oxide (FTO) using an electrochemical deposition hierarchy. X-ray diffraction of thin-film studies confirms the variation in the structural orientation of CZT on the FTO surface. As the pH of the solution is increased, the nature of the CZT thin-film aggregate changes from a fern-like leaf CZT dendrite crystal to a disk pattern. The FE-SEM surface micrograph shows the dendrite fern leaf and sharp edge disks. The 2-D diffusion limitation aggregation under slippery conditions for ternary thin films was performed for the first time. The simulation showed that by changing the diffusing species, the sticking probability was responsible for the pH-dependent morphological change. Convincingly, diffusion-limited aggregation (DLA) simulations confirm that the initial structure of copper is responsible for the final structure of the CZT thin films. An experimental simulation with pH as a controlled parameter revealed phase transition in CZT thin films. The top and back contact of Ag-CZT thin films based on Schottky behavior give a better electronic mechanism in superstrate and substrate solar cells.

Assessing pH-Dependent Conformational Changes in the Fusion Peptide Proximal Region of the SARS-CoV-2 Spike Glycoprotein.

One of the entry mechanisms of the SARS-CoV-2 coronavirus into host cells involves endosomal acidification. It has been proposed that under acidic conditions, the fusion peptide proximal region (FPPR) of the SARS-CoV-2 spike glycoprotein acts as a pH-dependent switch, modulating immune response accessibility by influencing the positioning of the receptor binding domain (RBD). This would provide indirect coupling of RBD opening to the environmental pH. Here, we explored this possible pH-dependent conformational equilibrium of the FPPR within the SARS-CoV-2 spike glycoprotein. We analyzed hundreds of experimentally determined spike structures from the Protein Data Bank and carried out pH-replica exchange molecular dynamics to explore the extent to which the FPPR conformation depends on pH and the positioning of the RBD. A meta-analysis of experimental structures identified alternate conformations of the FPPR among structures in which this flexible regions was resolved. However, the results did not support a correlation between the FPPR conformation and either RBD position or the reported pH of the cryo-EM experiment. We calculated pKa values for titratable side chains in the FPPR region using PDB structures, but these pKa values showed large differences between alternate PDB structures that otherwise adopt the same FPPR conformation type. This hampers the comparison of pKa values in different FPPR conformations to rationalize a pH-dependent conformational change. We supplemented these PDB-based analyses with all-atom simulations and used constant-pH replica exchange molecular dynamics to estimate pKa values in the context of flexibility and explicit water. The resulting titration curves show good reproducibility between simulations, but they also suggest that the titration curves of the different FPPR conformations are the same within the error bars. In summary, we were unable to find evidence supporting the previously published hypothesis of an FPPR pH-dependent equilibrium: neither from existing experimental data nor from constant-pH MD simulations. The study underscores the complexity of the spike system and opens avenues for further exploration into the interplay between pH and SARS-CoV-2 viral entry mechanisms.

Assignment of the Lassa virus transmembrane domain in the prefusion and postfusion states in detergent micelles.

Lassa virus (LASV) is the most prevalent member of the arenavirus family and the causative agent of Lassa fever, a viral hemorrhagic fever. Although there are annual outbreaks in West Africa, and recently isolated cases worldwide, there are no current therapeutics or vaccines. As such, LASV poses a significant global public health threat. One of the key steps in LASV infection is delivering its genetic material by fusing its viral membrane with the host cell membrane. This process is facilitated by significant conformational changes within glycoprotein 2 (GP2), yielding distinct prefusion and postfusion structural states. However, structural information is missing to understand the changes that occur in the transmembrane domain (TM) during the fusion process. Previously, we showed that the TM undergoes pH-dependent structural changes that result in a helical extension. Here, we provide the 1H, 15N, and 13C assignment of the LASV TM backbone in the prefusion and postfusion states. We also provide the 1H, 15N, and 13C assignment of two mutants, G429P and D432P, which prevent this helical extension. These results will help understand the role the TM plays in membrane fusion and can lead to the design of therapeutics against LASV infection.

Soil organic matter priming: The pH effects.

Priming of soil organic matter (SOM) decomposition by microorganisms is a key phenomenon of global carbon (C) cycling. Soil pH is a main factor defining priming effects (PEs) because it (i) controls microbial community composition and activities, including enzyme activities, (ii) defines SOM stabilization and destabilization mechanisms, and (iii) regulates intensities of many biogeochemical processes. In this critical review, we focus on prerequisites and mechanisms of PE depending on pH and assess the global change consequences for PE. The highest PEs were common in soils with pH between 5.5 and 7.5, whereas low molecular weight organic compounds triggered PE mainly in slightly acidic soils. Positive PEs up to 20 times of SOM decomposition before C input were common at pH around 6.5. Negative PEs were common at soil pH below 4.5 or above 7 reflecting a suboptimal environment for microorganisms and specific SOM stabilization mechanisms at low and high pH. Short-term soil acidification (in rhizosphere, after fertilizer application) affects PE by: mineral-SOM complexation, SOM oxidation by iron reduction, enzymatic depolymerization, and pH-dependent changes in nutrient availability. Biological processes of microbial metabolism shift over the short-term, whereas long-term microbial community adaptations to slow acidification are common. The nitrogen fertilization induced soil acidification and land use intensification strongly decrease pH and thus boost the PE. Concluding, soil pH is one of the strongest but up to now disregarded factors of PE, defining SOM decomposition through short-term metabolic adaptation of microbial groups and long-term shift of microbial communities.

Folding Kinetics and Volume Variation of the β-Hairpin Peptide Chignolin upon Ultrafast pH-Jumps.

In-depth characterization of fundamental folding steps of small model peptides is crucial for a better understanding of the folding mechanisms of more complex biomacromolecules. We have previously reported on the folding/unfolding kinetics of a model α-helix. Here, we study folding transitions in chignolin (GYDPETGTWG), a short β-hairpin peptide previously used as a model to study conformational changes in β-sheet proteins. Although previously suggested, until now, the role of the Tyr2-Trp9 interaction in the folding mechanism of chignolin was not clear. In the present work, pH-dependent conformational changes of chignolin were characterized by circular dichroism (CD), nuclear magnetic resonance (NMR), ultrafast pH-jump coupled with time-resolved photoacoustic calorimetry (TR-PAC), and molecular dynamics (MD) simulations. Taken together, our results present a comprehensive view of chignolin's folding kinetics upon local pH changes and the role of the Tyr2-Trp9 interaction in the folding process. CD data show that chignolin's β-hairpin formation displays a pH-dependent skew bell-shaped curve, with a maximum close to pH 6, and a large decrease in β-sheet content at alkaline pH. The β-hairpin structure is mainly stabilized by aromatic interactions between Tyr2 and Trp9 and CH-π interactions between Tyr2 and Pro4. Unfolding of chignolin at high pH demonstrates that protonation of Tyr2 is essential for the stability of the β-hairpin. Refolding studies were triggered by laser-induced pH-jumps and detected by TR-PAC. The refolding of chignolin from high pH, mainly due to the protonation of Tyr2, is characterized by a volume expansion (10.4 mL mol-1), independent of peptide concentration, in the microsecond time range (lifetime of 1.15 μs). At high pH, the presence of the deprotonated hydroxyl (tyrosinate) hinders the formation of the aromatic interaction between Tyr2 and Trp9 resulting in a more disorganized and dynamic tridimensional structure of the peptide. This was also confirmed by comparing MD simulations of chignolin under conditions mimicking neutral and high pH.

The release of host-derived antibodies bound to the variant surface glycoprotein (VSG) of Trypanosoma brucei cannot be explained by pH-dependent conformational changes of the VSG dimer.

Trypanosoma brucei is a protozoan parasite that evades the mammalian host's adaptive immune response by antigenic variation of the highly immunogenic variant surface glycoprotein (VSG). VSGs form a dense surface coat that is constantly recycled through the endosomal system. Bound antibodies are separated in the endosome from the VSG and destroyed in the lysosome. For VSGs it has been hypothesized that pH-dependent structural changes of the VSG could occur in the more acidic environment of the endosome and hence, facilitate the separation of the antibody from the VSG. We used size exclusion chromatography, where molecules are separated according to their hydrodynamic radius to see if the VSG is present as a homodimer at both pH values. To gain information about the structural integrity of the protein we used circular dichroism spectroscopy by exposing the VSG in solution to a mixture of right- and left-circularly polarized light and analysing the absorbed UV spectra. Evaluation of protein stability and molecular dynamics simulations at different pH values was performed using different computational methods. We show, for an A2-type VSG, that the dimer size is only slightly larger at pH 5.2 than at pH 7.4. Moreover, the dimer was marginally more stable at lower pH due to the higher affinity (ΔG = 353.37 kcal/mol) between the monomers. Due to the larger size, the predicted epitopes were more exposed to the solvent at low pH. Moderate conformational changes (ΔRMSD = 0.35 nm) in VSG were detected between the dimers at pH 5.2 and pH 7.4 in molecular dynamics simulations, and no significant differences in the protein secondary structure were observed by circular dichroism spectroscopy. Thus, the dissociation of anti-VSG-antibodies in endosomes cannot be explained by changes in pH.

Colloidal interaction of fly ash and soil clay

The combustion of coal worldwide creates a large quantity of fly ash (FA), and the application of FA to agricultural soils is being encouraged as a resource utilization strategy. While most of our attention has focused on positive aspects such as nutrient supplementation and pollution mitigation, the negative impacts of FA have likely been overlooked. In this study, we examined the colloidal properties of FA and soil clay, aiming to demonstrate the ability of FA to increase the dispersibility and transportability of soil clay. Dynamic light scattering technique was coupled with the test tube method to track the kinetics and pH-dependent changes in the zeta potential, hydrodynamic size and colloidal stability of FA, soil clay and their mixtures. We found that FA occurred in solution as “negatively charged balls”, and its negative surface charges increased with increasing pH. FA itself showed a low dispersibility; however, FA became more dispersive when it was introduced to clay suspensions. The mechanism is that the introduction of FA supplied more negative charges to the clay suspension, inducing electrostatic repulsion with soil clay, from which both FA and soil clay were favoured to disperse. Therefore, it can be inferred that off-site transport of FA is possible. More importantly, excessive application of FA can inadvertently intensify clay dispersibility, eventually resulting in soil clays together with FA being more vulnerable to leaching and/or surface run-off erosion. This suggests that the application of FA needs more careful consideration, and the development of more suitable techniques for the sustainable application of FA is still needed.

PH-Induced structural changes in xylanase GH11 from Thermoanaerobacterium saccharolyticum

Background Glycosyl hydrolase 11 (GH11) xylanase is utilized in various in industrial applications such as baking, fruit juice production, pulp processing, and animal feed. Thermophilic GH11 from Thermoanaerobacterium saccharolyticum (TsaGH11) exhibits maximum activity at acid pH with high catalytic efficiency toward beechwood xylan. TsaGH11 activity is pH dependent, exhibiting relative low hydrolase activity at basic pH. However, the effect of a basic pH environment on the structure of TsaGH11 correlated with enzyme activity remains unknown. To understand pH-dependent activity changes, the crystal structure of TsaGH11 at basic pH was determined and compared with that of TsaGH11 at acid pH. Methods TsaGH11 was crystallized at basic pH of 8.5, and the crystal structure was determined at 1.95 Å resolution. The structure, flexibility, and water molecules of TsaGH11 at pH 8.5 and pH 4.3 were compared. Results The open and closed conformations of TsaGH11 at pH 8.5 are reported. Subtle movements of the side chains of amino acids involved in the substrate-binding cleft and catalytic residues were observed. The overall temperature factor of TsaGH11 at pH 8.5 was higher than that at pH 4.6. The position of water molecules near the catalytic residues in TsaGH11 exhibited variations in different pH environments. Conclusions The structural comparison of TsaGH11 at basic and acidic pH offers valuable insights into the pH-dependent functionality of TsaGH11, enhancing our understanding of these structural alterations.

Dynamic conformational changes of acid-sensing ion channels in different desensitizing conditions

Acid-sensing ion channels (ASICs) are proton-gated cation channels that contribute to fast synaptic transmission and have roles in fear conditioning and nociception. Apart from activation at low pH, ASIC1a also undergoes several types of desensitization, including acute desensitization, which terminates activation; steady-state desensitization, which occurs at sub-activating proton concentrations and limits subsequent activation; and tachyphylaxis, which results in a progressive decrease in response during a series of activations. Structural insights from a desensitized state of ASIC1 have provided great spatial detail, but dynamic insights into conformational changes in different desensitizing conditions are largely missing. Here, we use electrophysiology and voltage-clamp fluorometry to follow the functional changes of the pore along with conformational changes at several positions in the extracellular and upper transmembrane domain via cysteine-labeled fluorophores. Acute desensitization terminates activation in wild type, but introducing an N414K mutation in the β11-12 linker of mouse ASIC1a interfered with this process. The mutation also affected steady-state desensitization and led to pronounced tachyphylaxis. Although the extracellular domain of this mutant remained sensitive to pH and underwent pH-dependent conformational changes, these conformational changes did not necessarily lead to desensitization. N414K-containing channels also remained sensitive to a known peptide modulator that increases steady-state desensitization, indicating that the mutation only reduced, but not precluded, desensitization. Together, this study contributes to our understanding of the fundamental properties of ASIC1a desensitization, emphasizing the complex interplay between the conformational changes of the extracellular domain and the pore during channel activation and desensitization.

Piperazine based pH-responsive cyanine dyes for cancer cell photoacoustic imaging

Novel pH-responsive Cy7.5 dyes bearing various amino groups were developed for cancer cell photoacoustic (PA) imaging. Among structurally diverse dyes, pH-dependent absorption spectral changes were observed for those carrying a diazaalkyl group. DFT calculations and absorbance measurements of the dyes revealed that these spectral changes depended on the electron density of the pH-sensing moiety. The PA spectra of the dyes also changed pH-dependent fashion and were largely consistent with the absorption spectra. In PA imaging experiments with cultured cancer cells, the pH-responsive dyes conjugated with a cancer specific antibody accumulated in cancer cells and changed their PA signals depending on the acidic lysosome pH. Overall, these results demonstrated that pH-responsive Cy7.5 dyes can be useful for detecting cancer, and the elucidated mechanism of the absorption spectral changes could contribute to designing new PA imaging agents.

Coconut husk-lignin derived carbon dots incorporated carrageenan based functional film for intelligent food packaging

Carbon dots (CDs) derived from sustainable natural feed-stocks like lignin have gained wide acceptance by virtue of their renewability and promising potential in intelligent sensing applications. The precursor lignin is isolated from agro-biomass waste, coconut husk through sodium hydroxide based extraction process. CDs are synthesised from amine functionalized lignin through solvothermal process and integrated into carrageenan biopolymer matrix (1, 2 and 3 wt%). The composite film with 2 wt% CDs (CARR2CD) showed optimum fluorescent emission intensity, excellent pH dependent fluorescent color change in the food pH range, reasonable tensile strength (46.50 ± 1.32 MPa) and 27 % increase in elongation at break. CDs imparted UV-light blocking properties (70 % UV-light) and enhanced hydrophobicity of the carrageenan matrix. CARR2CD film showed 84 % visible light transparency, 79 % reduction in oxygen transmittance rate (OTR), 81 % reduction in CO2 gas permeability and excellent antioxidant and antibacterial properties (against E. coli and S. aureus). As a practical application, the developed responsive packaging material is used to track pH change associated with milk spoilage via noticeable color change in fluorescent emission of the composite film. Thus, the developed responsive composite film paves a way for use as green and sustainable transparent intelligent food packaging material.

Unraveling pH-Dependent Changes in Adsorption Structure of Uranyl on Alumina (012).

Mitigating uranium transport in groundwater is imperative for ensuring access to clean water across the globe. Here, in situ resonant anomalous X-ray reflectivity is used to investigate the adsorption of uranyl on alumina (012) in acidic aqueous solutions, representing typical UVI concentrations of contaminated water near mining sites. The analyses reveal that UVI adsorbs at two distinct heights of 2.4-3.2 and 5-5.3 Å from the surface terminal oxygens. The former is interpreted as the mixture of inner-sphere and outer-sphere complexes that adsorb closest to the surface. The latter is interpreted as an outer-sphere complex that shares one equatorial H2O with the terminal surface oxygen. With increasing pH, we observe an increasing prevalence of these outer-sphere complexes, indicating the enhanced role of the hydrogen bond that stabilizes adsorbed uranyl species. The presented work provides a molecular-scale understanding of sorption of uranyl on Al-based-oxide surfaces that has implications for environmental chemistry and materials science.