pH-Dependence of Manganese (II) Oxidation Reaction by Novel Wild-Type and Mutants Recombinant Phlebia radiata Manganese Peroxidase 3 (rPr-MnP3) Enzymes

The goal of this study was to determine whether mutation of the Mn-binding site of wild-type recombinant Phlebia radiata manganese peroxidase 3 affected the pH-dependence kinetic parameters. pH range investigated was 2.5 – 12.0. The catalytic efficiency of the mutant enzymes at high and low pH in comparison to the wild-type was investigated using standard rPr-MnP3 protocol. Wild-type recombinant Phlebia radiata MnP3 enzyme showed optimal activity with Mn (II) as substrate at pH 5.0 and remained moderately active (approximately 40%) in the pH range of 6.0 - 9.0. The rPr-MnP3 mutants’ maximum activity ranged between 5.5 and 8.0. Wild-type and mutants rPr-MnP3 enzymes exhibited a similar pH profile with optimum pH of 3.0 for ABTS oxidation. Mutation has severely decreased the catalytic efficiency for Mn (II) oxidation at pH 5.0. The rPr-MnP3 enzymes showed enhanced affinity for Mn (II) at alkaline pH and a more alkaline range for catalysis than ever reported for any Manganese Peroxidase. This study reveals that at higher pH, rPr-MnP3 can function with alternative ligands in the Mn (II) site and does not have an absolutely obligate requirement for an all carboxylate ligand set. These results further strongly confirm that Mn2+ binding site is the only productive catalytic site for Mn (II) oxidation.

Modeling solubility of oxaprozin and irbesartan in biorelevant complex solutions based on a combination of pH-dependent and micellar solubilization models

Biological solubility is one of the important basic parameters in the development process of poorly soluble drugs,but the current measurement methods are mainly based on a large number of experiments,which are time-consuming and cost-intensive.There is still a lack of effective theoretical models to accurately describe and predict the biological solubility of drugs to reduce costs.Therefore,in this study,osaprazole and irbesartan were selected as model drugs,and their solubility in solutions containing surfactants and biorelevant media was measured experimentally.By calculating the parameters of each component using the perturbed-chain statistical associating fluid theory(PC-SAFT)model,combined with pH-dependent and micellar solubilization models,the thermodynamic phase behavior of the two drugs was successfully modeled,and the predicted results were in good agreement with the experimental values.These results demonstrate that the model combination used provides important basic parameters and theoretical guidance for the development and screening of poorly soluble drugs and related formulations.

In Silico Investigation of pH-Dependence of Prolactin and Human Growth Hormone Binding to Human Prolactin Receptor

Experimental data shows that the binding of human prolactin(hPRL)to human prolactin receptor(hPRLr-ECD)is strongly pH-dependent,while the binding of the same receptor to human growth hormone(hGH)is pH-independent.Here we carry in silico analysis of the molecular effects causing such a difference and reveal the role of individual amino acids.It is shown that the computational modeling correctly predicts experimentally determined pKa’s of histidine residues in an unbound state in the majority of the cases and the pH-dependence of the binding free energy.Structural analysis carried in conjunction with calculated pH-dependence of the binding revealed that the main reason for pH-dependence of the binding of hPRL-hPRLr-ECD is a number of salt-bridges across the interface of the complex,while no salt-bridges are formed in the hGH-hPRlr-ECD.Specifically,most of the salt-bridges involve histidine residues and this is the reason for the pH-dependence across a physiological range of pH.The analysis not only revealed the molecular mechanism of the pH-dependence of the hPRL-hPRLr-ECD,but also provided critical insight into the underlying physicchemical mechanism.

水泥固化铅污染粘土的pH-Dependent试验研究

通过pH-dependent试验,研究水泥固化铅污染土的溶出特性.对滤出液pH的研究结果表明,滤出液pH随加酸量增加而下降,且试样C12Pb2较C12Pb0、试样C18Pb2较C18Pb0的碱性/酸缓冲能力弱.对滤出液中铅浓度([Pb])随滤出液pH、水泥掺量的变化特征进行分析,结果表明,[Pb]随滤出液pH增大而先减小后增加;且试样C18Pb2较C12Pb2,其溶出的[Pb]显著减小,铅最大溶出率小5个百分点,表明水泥掺量的增大使得水泥对铅的固定效果更好,使固化土中可溶出的铅减少.

pH-Dependent Assembly of Hybrid Materials Based on Molybdates and Copper/imidazole Complexes

Three novel inorganic-organic hybrid materials, [Cu（imi）2（H2O）（MoO4）]n 1, [Cuz（imi）3（MoO4）E]n.nH2O 2 and [Cu3（imi）2（OH）2（MoO4）2]n 3 （imi = imidazole）, were synthesized and characterized by X-ray single-crystal structure determination. 1 crystallizes in orthorhombic, space group Pca21 with a = 13.382（4）, b = 8.527（2）, c = 9.622（3）A, V = 1098.0（5） A^3 Z = 4, C6H10CuMoN4O5, Mr = 377.66, Dc = 2.285 g/cm^3, F（000） = 740,μ（MoKa） = 3.095 mm^-1, the final R = 0.0256 and wR = 0.0722 for 1896 observed reflections with I 〉 2σ（I）. 2 crystallizes in monoclinic, space group P2t/c with a= 11.170（2）, b = 7.8244（15）, c = 22.631（4）A, β = 115.790（7）°, V = 1780.9（6）A^3 Z = 4, C9H14Cu2Mo2N6O9, Mr = 669.24, Dc= 2.496 g/cm^3, F（000）=1295,μ（MoKa） = 3.792 mm^-1, the final R = 0.0225 and wR = 0.0615 for 3838 observed reflections with I 〉 2σ（I）. 3 crystallizes in monoclinic, space group P21/c with a = 5.5599（19）, b = 23.771（8）, c = 7.3044（18）A , β = 129.356（16）°, V = 746.5（4）A^3, Z = 2, C6H10Cu3Mo2N4O10, Mr = 680.71, Dc = 3.029 g/cm^3, F（000） = 650,μ（MoKa） = 5.900 mm^-1, the final R = 0.0215 and wR = 0.0524 for 1620 observed reflections with I 〉 2σ（I）.

pH-Dependent Assembly of Molecular Capsule,2D and 3D Coordination Polymers

Three lanthanum/4-sulfocalix[4]arene complexes,namely,H2[（H4CAS）La（H2O）7]2· H2[（H4CAS）La（H2O）7]2·2C2H5OH·12H2O（1）,[H（H4CAS）La（H2O）5]·5H2O（2）and [（H4CAS）La-（H2O）4（NO3）La（H2O）5]·7H2O（3）,have been synthesized at different pH conditions.Complex 1,which exhibits the structure of ＂molecular capsule＂ containing the guest of C2H5OH molecule,is formed at pH = 1.At pH = 2～3,a two-dimensional（2D）coordination polymer of 2 is formed.Further increase of the pH value to 5 leads to the three-dimensional（3D）coordination polymer of 3.Crystal data for 1：monoclinic,space group P21/n,a = 10.8743（16）,b = 25.957（4）,c = 15.863（2）,β = 94.763（2）°,V = 4462.1（11）3,Mr = 1160.87,Z = 4,F（000）= 2376,R = 0.0370 and wR = 0.0936;Crystal data for 2：tetragonal,space group P4/n,a = 11.6593（16）,c = 14.069（4）,V = 1912.5（6）3,Mr = 1114.81,Z = 2,F（000）= 1136,R = 0.0849 and wR = 0.1906;and those for 3：triclinic,space group P1,a = 10.4588（16）,b = 14.995（2）,c = 16.699（3）,α = 65.446（3）,β = 83.487（3）,γ = 73.305（3）°,V = 2281.6（6）3,Mr = 1367.76,Z = 2,F（000）= 1368,R = 0.0423 and wR = 0.1183.

The Roles of pH in the Modification of Wild-Type Recombinant Phlebia radiata Manganese Peroxidase 3 Activities and Stability of Secondary Structures

This investigation is aimed at understanding the specific role of pH and calcium ions on the activity and stability of wild-type recombinant Phlebia radiata manganese peroxidase 3 (rPr-MnP3). The pH-dependent cycle of reactions for rPr-MnP3 was evaluated by investigating time-dependent changes in the activity and electronic absorption spectrum of rPr-MnP3.The rPr-MnP3 had maximum efficacy (kcat/Km) for Mn (II) oxidation at pH 5.0 and 3.0 for oxidation of ABTS. Raising the pH of a solution of resting rPr-MnP3 from pH 6.7 (form XH) to pH 8.6 (form X−), a rapid alkaline transition occurs. Leaving the X− form of the enzyme at pH 8.6, it slowly becomes converted to a third form of the enzyme Y−, which returned to the original XH form of the enzyme at pH 6.7. Recovery of form XH from form Y− occurred through an intermediate Z form. The pH inactivation of rPr-MnP3 followed first-order kinetics. The rate of formation of XH from Z is pH-dependent and biphasic in nature, with measured rate constants (k) = 0.25 min−1, and half-life (T1/2) = 2.8 min. The pH-dependent properties observed may be indicative of a greater degree of conformational flexibility at rPr-MnP3 active site due to disruption of the haem-linked hydrogen-bonding network in the distal haem pocket. Calcium ions were observed to significantly stabilised the enzyme’s spectral features and reduce the loss of activity during the alkaline pH transition. Calcium ions enhance the recovery of the initial activity but cannot prevent the final time-dependent irreversible denaturation and aggregation.

Characteristics of Some Heavy Metals in Acid Sulfate Topsoils, Eastern Australia

Forty-five acid sulfate topsoil samples (depth < 0.5 m) from 15 soil cores at 11 locations along the New South Wales coast, Australia, were selected to investigate the chemical behavior of Zn, Mn, Cr, Co and Pb in these soils. The amount of HCI-extractable Mn was much smaller than the mean value of the total Mn documented for other soils. This may be attributed to enhanced mobilization of Mn from the soils under the extremely acidic and seasonally flooded conditions encountered in the investigated soils. The pH-dependency of soluble Zn and Mn was strongly affected by the availability of acid reactive Zn and Mn compounds. There were fairly good relationships between soluble Zn and acid reactive Zn compounds, and between soluble Mn and acid reactive Mn compounds. Soluble Zn and soluble Mn concentrations were important controls on exchangeable Zn and Mn concentrations, respectively. In contrast to the suggestion by other authors that adsorption of Co was closely associated with Mn oxides present in soils, the exchangeable Co in the investigated acid sulfate soils was not clearly related to the abundance of Mn minerals. In addition to the fact that there are few Mn minerals present in the soils, this might also be because the availability of canon exchange sites on the crystal surfaces of Mn oxides was reduced under extremely acidic conditions.

Development of phosphonate-terminated magnetic mesoporous silica nanoparticles for pH-controlled release of doxorubicin and improved tumor accumulation

In this study,phosphonate-terminated magnetic mesoporous nanoparticles(pMMSNs)was designed by incorporation of MNPs in the center of mesoporous silica nanoparticles(MSNs)and followed by grafting phosphonate group on to the surface of MMSNs.The carrier exhibited a typical superparamagnetic feature and the saturation magnetization was 4.89 emu/g measured by vibrating sample magnetometer(VSM).pMMSNs had a spherical morphology and a pore size of 2.2 nm.FromN2 adsorption-desorption analysis,pMMSNs had a surface area of 613.4 m^(2)/g and a pore volume of 0.78 cm^(3)/g.Phosphonate modification improved the colloidal stability of MMSNs,and the hydrodynamic diameter of pMMSNs was around 175 nm.The hydrophilic phosphonate group significantly enhanced the negative surface charge of MMSNs from -19.3 mV to -28.8 mV pMMSNs with more negative surface charge had a 2.3-fold higher drug loading capacity than that of MMSNs.In addition,the rate and amount of release of doxorubicin(DOX)from DOX/pMMSNs was pH-dependent and increased with the decrease of pH.At pH 7.4,the release amount was quite low and only approximately 17wt%ofDOXwasreleasedin48h.AtpH5.0and3.0,the release rate increased significantly and the release amount achieved 31 wt%and 60 wt%in 48 h,respectively.To evaluate the magnetic targeting performance ofpMMSNs,FITC labeledpMMSNswas injected into mice bearing S180 solid tumor.FITC labeledpMMSNscontrolled by an external magnetic field showed higher tumor accumulation and lower normal tissue distribution.

Swelling and Drug Release Characteristics of Poly （methacrylic acid-co-poloxamer） hydrogels

Poly (methacrylic acid-co-poloxamer) hydrogel networks were synthesized byfree-radical solution polymerization, and the dynamic swelling and in vitro release properties ofmodel drugs, dextromethorphan hydrobromide (DMP) and vitamin B_(12) (VB_(12)) were studied. Thesegels exhibited pH-dependant swelling and sustained drug release properties, and the water uptakerate and drug release rate in neutral or basic media were higher than that in acidic media. Theresults showed that the water uptake followed non-Fickian or zero order process in neutral or basicmedia, and the release of model drugs from hydrogels of appropriate composition was of zero orderkinetics over a period of several hours.

Multi-organelle-targeting pH-dependent NIR fluorescent probe for lysosomal viscosity

The normal operation of lysosome, mitochondria, Golgi apparatus and endoplasmic reticulum plays a significant role in maintaining cell homeostasis. Reflecting the state and function of lysosomes, viscosity is a pivotal parameter to assess the stability of microenvironment. Herein, based on TICT mechanism,a new NIR pH-dependent fluorescent probe DCIC with push-pull electronic moiety was synthesized to identify the lysosomes viscosity. In viscous media, DCIC was highly sensitive to viscosity, fluorescence intensity increased by 180 times as viscosity increased from 1.0 cp to 438.4 cp. In addition, DCIC have high localization ability for lysosome, mitochondria, Golgi apparatus, and endoplasmic reticulum and can monitor lysosomal viscosity fluctuations with laser confocal microscopy.

pH-Dependent binding energy-induced inflection-point behaviors for pH-universal hydrogen oxidation reaction

The kinetics of hydrogen oxidation reaction(HOR)declines with orders of magnitude when the electrolyte varies from acid to base.Therefore,unveiling the mechanism of pH-dependent HOR and narrowing the acid-base kinetic gap are indispensable and challenging.Here,the HOR behaviors of palladium phosphides and their counterpart(PdP_2/C,Pd_5P_2/C,Pd_3P/C,and Pd/C)in the whole pH region(from pH 1 to 13)are explored.Unexpectedly,there are non-monotonous relationships between their HOR kinetics and varied pHs,showing distinct inflection-point behaviors(inflection points and acid-base kinetic gaps).We find the inflection-point behaviors can be explained by the discrepant role of pH-dependent hydroxyl binding energy(OHBE)and hydrogen binding energy(HBE)induced HOR kinetics under the entire pH range.We further reveal that the strengthened OHBE is responsible for the earlier appearance of the inflection point and much narrower acid-base kinetic gap.These findings are conducive to understanding the mechanism of the pH-targeted HOR process,and provide a new strategy for rational designing advanced HOR electrocatalysts under alkaline electrolyte.

Insight into the development of electrolytes for aqueous zinc metal batteries from alkaline to neutral

Aqueous zinc metal batteries are considered as promising candidates for next-generation electrochemical energy storage devices,especially for large-scale energy storage,due to the advantages of high-safety,high energy density and low cost.As the bridge connecting cathode and anode,electrolyte provides a realistic operating environment.In alkaline and neutral aqueous zinc metal batteries,issues associated with electrolyte and anode are still intractable.In this review,we reveal the development and evolution of electrolytes for aqueous zinc metal batteries from alkaline to neutral via the description of fundamentals and challenges in terms of comparison and connection.We also elaborate the strategies in electrolytes regulation and highlight the basic roles and progresses in additives engineering.

Calculating pH-dependent free energy of proteins by using Monte Carlo protonation probabilities of ionizable residues

Protein folding,stability,and function are usually in-fluenced by pH.And free energy plays a fundamental role in analysis of such pH-dependent properties.Elec-trostatics-based theoretical framework using dielectric solvent continuum model and solving Poisson-Boltzm-ann equation numerically has been shown to be very successful in understanding the pH-dependent proper-ties.However,in this approach the exact computation of pH-dependent free energy becomes impractical for proteins possessing more than several tens of ioni-zable sites(e.g.>30),because exact evaluation of the partition function requires a summation over a vast number of possible protonation microstates.Here we present a method which computes the free energy us-ing the average energy and the protonation probabili-ties of ionizable sites obtained by the well-established Monte Carlo sampling procedure.The key feature is to calculate the entropy by using the protonation prob-abilities.We used this method to examine a well-studied protein(lysozyme)and produced results which agree very well with the exact calculations.Applications to the optimum pH of maximal stability of proteins and pro-tein-DNA interactions have also resulted in good agreement with experimental data.These examples recommend our method for application to the elucidation of the pH-dependent properties of proteins.

Drug release behavior of chitosan/gelatin network polymer microsphere

Recently, more attention has been attracted by intelligent drug delivery systems (DDS), because the release of drug can be controlled via the system feedback responding to pathologic environment signals. Using natural polymers such as chitosan to compose this kind of pulsed DDS will be of benefit, because chitosan [.α(1→4)2-amino-2-deoxy-β-Dglucan] is one of the abundantly available polysaccharides in nature. As we know, chitosan is usually obtained by alkaline deacetylation of chitin, the principal component of shells