Determination of divalent metal ion-regulated proton concentration and polarity at the interface of anionic phospholipid membranes.

We studied the influence of trace quantities of divalent metal ions (M: Ca, Mg, and Zn) on proton concentration (-log[H], designated as pH') and polarity at the interface of anionic PG-phospholipid membranes comprising saturated and unsaturated acrylic chains. A spiro-rhodamine-6G-gallic acid (RGG) pH-probe was synthesized to monitor the interfacial pH' of large unilamellar vesicles (LUVs) at a physiologically appropriate bulk pH (6.0-7.

Fluorometric trace methanol detection in ethanol and isopropanol in a water medium for application in alcoholic beverages and hand sanitizers.

Detection of methanol (MeOH) in an ethanol (EtOH)/isopropanol ( PrOH) medium containing water is crucial to recognize MeOH poisoning in alcoholic beverages and hand sanitizers. Although chemical sensing methods are very sensitive and easy to perform, the chemical similarities between the alcohols make MeOH detection very challenging particularly in the presence of water. Herein, the fluorometric detection of a trace amount of MeOH in EtOH/ PrOH in the presence of water using alcohol coordinated Al(iii)-complexes of an aldehydic phenol ligand containing a dangling pyrazole unit is described.

Aza-Crown-Based Macrocyclic Probe Design for "PET-off" Multi-Cu Responsive and "CHEF-on" Multi-Zn Sensor: Application in Biological Cell Imaging and Theoretical Studies.

The work represents a rare example of an aza-crown-based macrocyclic chemosensor, H (H = 1,16-dihydroxy-tetraaza-30-crown-8) for the selective detection of both Zn and Cu in HEPES buffer medium (pH 7.4). H exhibits a fluorescence response for both Zn and Cu ions.

An aluminium fluorosensor for the early detection of micro-level alcoholate corrosion.

The detection of the dry alcoholate corrosion of aluminium is vital to design a corrosion resistive aluminium alloy for the storage and transportation of biofuel (methanol or ethanol). By synthesizing an Al fluorescent probe operable in an alcoholic medium, we quantified the alcoholate corrosion in terms of the fluorometrically estimated soluble alkoxide (Al(OR)) generation under nitrogen atmosphere. With time, a linear increase in corrosion with specific aluminium dissolution rate constants ∼2.

Protonation-induced pH increase at the triblock copolymer micelle interface for transient membrane permeability at neutral pH.

Achieving controlled membrane permeability using pH-responsive block copolymers is crucial for selective intercellular uptake. We have shown that the pH at the triblock-copolymer micelle interface as compared to its bulk pH can help regulate membrane permeability. The pH-dependent acid/base equilibriums of two different interface-interacting pH probes were determined in order to measure the interfacial pH for a pH-responsive triblock copolymer (TBP) micelle under a wide range of bulk pH (4.

Determination of proton concentration at cardiolipin-containing membrane interfaces and its relation with the peroxidase activity of cytochrome .

The activities of biomolecules are affected by the proton concentrations at biological membranes. Here, we succeeded in evaluating the interface proton concentration (-log[H] defined as pH') of cardiolipin (CL)-enriched membrane models of the inner mitochondrial membrane (IMM) using a spiro-rhodamine-glucose molecule (RHG). According to fluorescence microscopy and H-NMR studies, RHG interacted with the Stern layer of the membrane.

Porphyrin-Based Probe for Simultaneous Detection of Interface Acidity and Polarity during Lipid-Phase Transition of Vesicles.

Biochemical activities at a membrane interface are affected by local pH/polarity related to membrane lipid properties including lipid dynamics. pH and polarity at the interface are two highly interdependent parameters, depending on various locations from the water-exposed outer surface to the less polar inner surface. The optical response of common pH or polarity probes is affected by both the local pH and polarity; therefore, estimation of these values using two separate probes localized at different interface depths can be erroneous.

Detection of Curvature-Radius-Dependent Interfacial pH/Polarity for Amphiphilic Self-Assemblies: Positive versus Negative Curvature.

It is possible that a defined curvature at the membrane interface controls its pH/polarity to exhibit specific bioactivity. By utilizing an interface-interacting spiro-rhodamine pH probe and the Schiff base polarity probe, we have shown that the pH deviation from the bulk phase to the interface (ΔpH)/interfacial dielectric constant (κ(i)) for amphiphilic self-assemblies can be regulated by the curvature geometry (positive/negative) and its radius. According to H NMR and fluorescence anisotropy investigations, the probes selectively interact with an anionic interfacial Stern layer.

A ratiometric solvent polarity sensing Schiff base molecule for estimating the interfacial polarity of versatile amphiphilic self-assemblies.

A newly synthesised Schiff base molecule (PMP) existing in equilibrium between non-ionic and zwitterionic forms displays solvent polarity induced ratiometric interconversion from one form to another, such novelty being useful to detect the medium polarity. The specific interface localisation of PMP in versatile amphiphilic self-assembled systems has been exploited to monitor their interfacial polarity by evaluating such interconversion equilibrium with simple UV-Vis spectroscopy. In spite of the large differences in pH and/or viscosity between the bulk and interface, the unchanged equilibrium between the two molecular forms on varying the medium pH or viscosity provides a huge advantage for the exclusive detection of interfacial polarity.

A simple interfacial pH detection method for cationic amphiphilic self-assemblies utilizing a Schiff-base molecule.

A simple pH-sensing method for cationic micelle and vesicle interfaces is introduced, utilizing a Schiff-base molecule, 2-((4H-1,2,4-triazol-4-ylimino)methyl)-6-(hydroxymethyl)-4-methylphenol (AH). AH containing a phenolic moiety was obtained by the reaction between 4-amino-4H-1,2,4-triazole containing polar O- and N-centres with opposite polarity to the cationic interface and 2-hydroxy-3-(hydroxymethyl)-5-methylbenzaldehyde. The acid/base equilibrium of AH was investigated at the interfaces of cetrimonium bromide (CTAB) micelles, tri-block-copolymeric micelles (TBPs) and large unilamellar vesicles (LUVs) of different lipid compositions using steady state UV-Vis absorption spectroscopy.

Formation of domain-swapped oligomer of cytochrome C from its molten globule state oligomer.

Many proteins, including cytochrome c (cyt c), have been shown to form domain-swapped oligomers, but the factors governing the oligomerization process remain unrevealed. We obtained oligomers of cyt c by refolding cyt c from its acid molten globule state to neutral pH state under high protein and ion concentrations. The amount of oligomeric cyt c obtained depended on the nature of the anion (chaotropic or kosmotropic) in the solution: ClO4(-) (oligomers, 11% ± 2% (heme unit)), SCN(-) (10% ± 2%), I(-) (6% ± 2%), NO3(-) (3% ± 1%), Br(-) (2% ± 1%), Cl(-) (2% ± 1%), and SO4(2-) (3% ± 1%) for refolding of 2 mM cyt c (anion concentration 125 mM).

Formation of oligomeric cytochrome c during folding by intermolecular hydrophobic interaction between N- and C-terminal α-helices.

We have previously shown that horse cytochrome c (cyt c) forms oligomers by domain swapping its C-terminal α-helix when interacting with ethanol. Although folding of cyt c has been studied extensively, formation of domain-swapped oligomers of cyt c during folding has never been reported. We found that domain-swapped oligomeric cyt c is produced during refolding from its guanidinium ion-induced unfolded state at high protein concentrations and low temperatures.

Fluorescence correlation spectroscopy at single molecule level on the Tat-TAR complex and its inhibitors.

The TAR element of HIV and the viral protein Tat form a molecular switch regulating transcriptional efficiency in HIV. We show that fluorescence correlation spectroscopy at the single molecule level is a powerful method to study the association between a Tat-derived peptide and TAR fragments. We also investigated the inhibition of the peptide-RNA complex by different ligands.