The j–pH diagram of interfacial reactions involving H+ and OH-

For aqueous interfacial reactions involving H+and OH-, the interfacial pH varies dynamically during the reaction process, which is a key factor determining the reaction performance. Herein, the kinetic relevance between the interfacial pH and reaction rate is deciphered owing to the success in establishing the transport equations of H+/OH- in unbuffered solutions, and is charted as a current(j)–pH diagram in the form of an electrochemical response. The as-described j–pH interplay is experimentally verified by the oxygen reduction and hydrogen evolution reactions. This diagram serves to form a panoramic graphic view of pH function working on the interfacial reactions in conjunction with the Pourbaix’s potential–pH diagram, and particularly enables a kinetic understanding of the transport effect of H+and OH-on the reaction rate and valuable instruction toward associated pH control and buffering manipulation.

Preparation of bromfenac-loaded liposomes modified with chitosan for ophthalmic drug delivery and evaluation of physicochemical properties and drug release profile

The purpose of this study was to design a submicron-sized liposomal non-steroidal antiinflammatory drug(NSAID)preparation that targets the retina via topical instillation of eye drops.Bromfenac(BRF)-loaded liposomes were prepared using the calcium acetate gradient method.Liposome sizes and encapsulation efficiencies were optimized by screening several liposome formulations of lipid,drug concentration,and buffer solution.BRF entrapment efficiency was greater than 90%using this method,and was low using conventional hydration methods.High initial BRF loading using the pH gradient method caused aggregation of liposomes.To circumvent aggregation,the negatively charged lipid dicetylphosphate was incorporated into liposomes,which formed anion layer preventing coalescence.Release of BRF from liposomes was sustained for several hours depending on lipid concentration,inner water phase,initial drug amounts,and surface properties.Surface modification with chitosan(CS),a mucoadhesive cationic polymer,was achieved using electrostatic interactions of negatively charged liposomes.The optimal concentration of CS for evasion of liposome aggregation was 0.15%.

Non-phospholipid liposomes with high sterol content display a very limited permeability

We demonstrate that it is possible to form non-phospholipid fluid bilayers in aqueous milieu with a mixture of palmitic acid (PA),cholesterol (Chol),and cholesterol sulfate (Schol) in a molar proportion of 30/28/42.These self-assemblies are shown to be bilayers in the liquid ordered phase.They are stable between pH 5 and 9.Over this pH range,the protonation/deprotonation of PA carboxylic group is observed but this change does not appear to alter the stability of these bilayers,a behavior contrasting with that observed for binary mixtures of PA/Chol,and PA/Schol.The multilamellar dispersions formed spontaneously from the PA/Chol/Schol mixture could be successfully extruded to form Large Unilamellar Vesicles (LUVs).These LUVs show interesting permeability properties,linked with their high sterol content.These non-phospholipid liposomes can sustain a pH gradient (pH internal 8/pH external 6) 100 times longer than LUVs made of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and cholesterol,with a molar ratio of 60/40.Moreover,the non-phospholipid LUVs are shown to protect ascorbic acid from an oxidizing environment (1 mM iron(III)).Once entrapped in liposomes,ascorbic acid displays a degradation rate similar to that obtained in the absence of iron(III).These results show the possibility to form novel nanocontainers from a mixture of a monoalkylated amphiphile and sterols,with a good pH stability and showing interesting permeability properties.

The complex relationship between multiple drug resistance and the tumor pH gradient:a review

Multiple drug resistance(MDR)is the tumor’s way of escaping the cytotoxic effects of various unrelated chemotherapeutic drugs.It can be either innate or acquired.MDR represents the end of the therapeutic pathway,and it practically leaves no treatment alternatives.Reversing MDR is an unfulfilled goal,despite the important recent advances in cancer research.MDR,the main cause of death in cancer patients,is a multi-factorial development,and most of its known causes have been thoroughly discussed in the literature.However,there is one aspect that has not received adequate consideration-intracellular alkalosis-which is part of wider pH deregulation where the pH gradient is inverted,meaning that extracellular pH is decreased and intracellular pH increased.This situation interacts with MDR and with the proteins involved,such as P-gp,breast cancer resistance protein,and multidrug associated resistance protein 1.However,there are also situations in which these proteins play no role at all,and where pH takes the lead.This is the case in ion trapping.Reversing the pH gradient to normal can be an important contribution to managing MDR.The drugs to manipulate pH exist,and most of them are FDA approved and in clinical use for other purposes.Furthermore,they have low or no toxicity and are inexpensive compared with any chemotherapeutic treatment.Repurposing these drugs and combining them in a reasonable fashion is one of the points proposed in this paper,which discusses the relationship between cancer’s peculiar pH and MDR.

pH Overpotential for Unveiling the pH Gradient Effect of H^(+)/OH^(−)Transport in Electrode Reaction Kinetics

The pH gradient caused by H^(+)/OH^(−)transport on an electrode surface is the key factor determining reaction performance,but its detailed impact on the electrode reaction kinetics has yet to be clarified.Here,the pH gradient effect was determined by developing electrode reaction equations,considering the overpotential assigned to the pH gradient called pH overpotential.The pH gradient effect was revealed to involve two aspects:(1)the Nernst pH overpotential,accounting for the common Nernst relationship with pH,and(2)the pH-dependent function of the electron-transfer coefficient(α_(pH)).Both parts were verified experimentally using oxygen reduction reaction and hydrogen evolution reaction,obviously,with differentα_(pH) functions.Detailedα_(pH) function effect was clarified based on numerical calculations of the electrode reaction equations.We found that the effect could be assessed suitably by an apparent constant(α_(app))and a nonlinear fitting method proposed forα_(app) value estimation.The results of this study provide the kinetic fundamentals of electrode reactions involving H^(+)/OH^(−)and contribute to the understanding and assessment of their performance with the H^(+)/OH^(−)transport effect.

Swimming Behavior Analysis Based on Bacterial Chemotaxis in Solution

Microrobots is playing more and more important roles for medical applications, such as targeting tumoral lesions for therapeutic purposes, Minimally Invasive Surgery （MIS） and highly localized drug delivery. However, energy efficient pro- pulsion system poses significant challenges for the implementation of such mobile robots. Flagellated chemotactic bacteria can be used as an effective integrated propulsion system for microrobots. In this paper, we proposed a new type of propulsion method that is inspired by the motility mechanism of flagellated chemotactic bacteria in different pH gradients. The pH gradient field was established in solution through electrolysis method. The distribution of the pH values in solution was measured with pH indicator and analyzed with image processing technology, and the mechanism by which the pH values changed was also discussed. The swimming speed and direction of the bacteria were studied experimentally. Through analyzing the key pa- rameters, such as stabilization time and electrode voltage, the optimal design of propulsion mechanism based on bacteria motion in the pH gradient field was proven.