DETERM INATION OF THE STABILITY CONSTANTS OF COMPLEXES OF HISTIDINE,SOME DIPEPTIDES AND TRIGLYCINE WITH Zn(Ⅱ)AND Cd(Ⅱ)USING SMALL-SCALE PH-METRIC TITRATIONS

A potentiometric study on the complexes of His,Gly-His,ALa-His,Gly-Gly and Gly—Gly—Gly with Zn(Ⅱ)and Cd(Ⅱ)has been reported.Small-scale potentiometric titrations were car- ried out to determine stabil ity constants of complexes at 25℃ with I=0.10 mol dm^(-3)(KNO_3).The com- puter programs SUPERQUAD were applied for data treatment with satisfactory results.

A COMPARISON OF THE DETERMINATION OF STABILITY CONSTANTS OF COMPLEXES OF Cd(Ⅱ)WITH AMINO ACIDS AND SIMPLE PEPTIDES USING MICRO—pH—METRIC TITRATIONS AND CYCLIC VOLTAMMETRY

This paper reports the determination of stability constants for complexes of Cd(Ⅱ)with Gly, Ala,Val,Asp,Gly—Asp,Asp Gly,Gly—Gly and Gly—Gly—Gly using both micro—pH—metric titra- tions and the application of convolution—deconvolution cyclic voltammetry at 25℃ and I=0.10 mol· dm^(-3)(KNO_3).Stability constants were calculated from pH—metric data using the SUPERQUAD com- puter program and cyclic voltammograms were collected,stored and manipulated using the EG and G CONDECON 300 software.A considerably larger ligand:metal ratio(e,g.50:1)was possible using voltammetry.Evaluation of results from the two techniques suggests that stability constants for the species[CdL_2]and[CdL_3]are reliable when calculated fromvoltammetry while those for[CdL]are more reliable when determined by pH-metric titration.

A Multiparameter Colloidal Titrations for the Determination of Cationic Polyelectrolytes

In water treatment processes and conditioning drinking water, PEs are widely used;however, their environmental impact is still doubtful, since residual concentrations increase organic matter content and represents a potential health hazard. This paper demonstrates a multiparametric study of two colloidal titration methods: spectrophotometric and zeta potential end point detection. The first one was optimized to guarantee the accuracy of cationic commercial PE quantification. It includes the indicator dose optimization using analytical criteria for competing equilibria, a calibration curve for two ranges of CPE concentration (1 - 5 ppm and 5 - 100 ppm) and the interference study of flocculant and Sn in the CPE quantification. The second method provides a physicochemical validation of the electric surface phenomena occurring during the colloidal titration and the end point detection. As an additional contribution the zeta potential titration was discussed and proposed as an alternative method for quantifying CPE when the sample is metal free.

Exploring the taste presentation and receptor perception mechanism of salty peptides from Stropharia rugosoannulata based on molecular dynamics and thermodynamics simulation

The taste presentation and receptor perception mechanism of the salty peptide of Stropharia rugosoannulata were predicted and verified using peptide omics and molecular interaction techniques.The combination of aspartic acid(D)and glutamic acid(E),or peptide fragments composed of arginine(R),constitute the characteristic taste structural basis of salty peptides of S.rugosoannulata.The taste intensity of the salty peptide positively correlates with its concentration within a specific concentration range(0.25–1.0 mg/mL).The receptor more easily recognizes the first amino acid residue at the N-terminal of salty peptides and the aspartic acid residue in the peptides.GLU513,ASP707,and VAL508 are the critical amino acid residues for the receptor to recognize salty peptides.TRPV1 is specifically the receptor for recognizing salty peptides.Hydrogen bonds and electrostatic interactions are the main driving forces for the interactions between salty peptides and TRPV1 receptors.KSWDDFFTR has the most potent binding capacity with the receptor and has tremendous potential for application in sodium salt substitution.This study confirmed the taste receptor that specifically recognizes salty peptides,analyzed the receptor-peptide binding interaction,and provided a new idea for understanding the taste receptor perception of salty peptides.

Analysis of the electron transfer pathway in small laccase by EPR and UV-vis spectroscopy coupled with redox titration

Bacterial small laccases(SLAC) are promising industrial biocatalysts due to their ability to oxidize a broad range of substrates with exceptional thermostability and tolerance for alkaline p H. Electron transfer between substrate, copper centers, and O2is one of the key steps in the catalytic turnover of SLAC. However, limited research has been conducted on the electron transfer pathway of SLAC and SLAC-catalyzed reactions, hindering further engineering of SLAC to produce tunable biocatalysts for novel applications. Herein, the combinational use of electron paramagnetic resonance(EPR) and ultraviolet-visible(UV-vis) spectroscopic methods coupled with redox titration were employed to monitor the electron transfer processes and obtain further insights into the electron transfer pathway in SLAC. The reduction potentials for type 1 copper(T1Cu), type 2 copper(T2Cu) and type 3copper(T3Cu) were determined to be 367 ± 2 mV, 378 ± 5 m V and 403 ± 2 mV,respectively. Moreover, the reduction potential of a selected substrate of SLAC, hydroquinone(HQ), was determined to be 288 mV using cyclic voltammetry(CV). In this way, an electron transfer pathway was identified based on the reduction potentials. Specifically,electrons are transferred from HQ to T1Cu, then to T2Cu and T3Cu, and finally to O2.Furthermore, superhyperfine splitting observed via EPR during redox titration indicated a modification in the covalency of T2Cu upon electron uptake, suggesting a conformational alteration in the protein environment surrounding the copper sites, which could potentially influence the reduction potential of the copper sites during catalytic processes. The results presented here not only provide a comprehensive method for analyzing the electron transfer pathway in metalloenzymes through reduction potential measurements, but also offer valuable insights for further engineering and directed evolution studies of SLAC in the aim for biotechnological and industrial applications.

The Sigma-1 Receptor as a Pharmacologic Chaperone: Energetics

Initially thought to be an opioid receptor subtype, Sigma-1 receptors (S1R) are now known to be unique proteins that have chaperone-like properties. As such, they play critical roles in cellular signaling, homeostasis, and cell survival. These roles offer significant insight for understanding homeostasis of normal physiologic processes, and the pathophysiologic consequences of disruption of normal function. Because of the broad nature of chaperone action, S1R agonists and antagonists represent potential drug discovery goals for the pharmacotherapeutic treatment of a variety of disorders that result from dysfunctional proteins. The present study summarizes the S1R as a pharmacologic chaperone crucial for protein folding and cellular homeostasis. Through literature review and thermodynamic analysis, it explores how S1R stabilizes target proteins, influencing neuroprotection and potential drug therapies. The binding of chaperones to target proteins is thermodynamically favorable, offering insights into treating diseases linked to protein misfolding.

Physicochemical Analysis of Locally Made Yoghurt (Kossam) Commercialised in the City of Douala-Cameroon

Yogurt is a traditional dairy product well known in all the regions of the world. In Cameroon, the most popularly known type is “kossam” also called curdled milk. Kossam is a set of milk based beverage from northern Cameroon presenting great symbolic, economic and social values for local population [1]. 150 Kossam samples were collected from neighborhoods of PK8, Bonamoussadi, Nyalla, cite des palmier, Deido and Bedi community and later on reconstituted into 50 different samples of 350 mL, each containing 1/3 of 3 individual samples. They were analyzed for their physiochemical properties such as: PH, titratable acidity, density, brix and dry matter using most at times the standard Association of Official Analytical Chemists (AOAC) methods with slight modifications and results compared to a licensed brand sold in the Cameroonian market. The results of the study showed that, the physico-chemical properties of the locally made yogurts were different within the different samples. Analysis of variance revealed a significant difference in the levels of the parameters analyzed in the different yogurt samples (p −1 Kg/L), Brix (8˚ - 24˚B), Dornic (23˚ - 160˚D). others contents per 100 g fresh matter are as follows: dry matter (average mean of 16.54%). Hence, the significant variations in the physico-chemical properties of kossam are a call for concern since as it impacts on the health of the population consuming this product.

A comparison of the determination of stability constants of complexes of Pb(II) with amino acids using micro-pH-metric titrations and cyclic voltammetry

This paper reports the determination of stability constants for complexes of Pb(Ⅱ) with Gly, Ala, Asp and Gly-Gly using both micro-pH-metric titrations and the application of convolution-de- convolution cyclic voltammetry at 25℃ and I = 0.10 mol.dm^(-3)(KNO_3). Stability constants were calculated from pH-metric data using the SUPERQUAD computer program and cyclic voltammograms were collected, stored and manipulated using the E G and G CONDECON 300 software. A consider- ably larger ligand: metal ratio (e.g. 50:1) was possible using voltammetry. Under these conditions, hydroxy complex formation was minimised and the formation of bis-complexes optimised. Computer based calculations were carried out on PC-compatible microcomputers fitted with mathematics co- processors. Evaluation of results from the two techniques suggests that stability constants for the species [PbL_2] are reliable when calculated from voltammetry while those for [PbL] are mote reliable when determined by pH-metric titration.

Isomerization and bioaccessibility of cypermethrin and fenpropathrin in Pacific oyster during simulated digestion as influenced by domestic cooking methods

Pyrethroids can be ingested by humans through eating contaminated oysters,which is potentially harmful to health.This study aimed to investigate the effects of raw,steaming,and roasting on cypermethrin(CP)and fenpropathrin(FP)in oysters during simulated digestion.Results showed that the amount of released CP and FP was different from raw(CP:0.617μg·g−1,FP:0.266μg·g−1),steaming(CP:0.498μg·g−1,FP:0.660μg·g−1),and roasting(CP:1.186μg·g−1,FP:0.588μg·g−1)at the end of simulated digestion.The share of cis-CP and low-efficiency CP increased significantly(p<0.05),and the share of high-efficiency trans-CP did not maintain a high level for a long time during simulated digestion.The fluorimetric titration and isothermal titration calorimetry confirmed that CP and FP could spontaneously interact with oyster actin,and CP could bind with oyster actin more tightly than FP.This study reveals that cooking methods affect the binding capacity of CP and FP to oyster tissues and influence the changes of CP and FP in oysters during digestion.Furthermore,the current study provides a reference for assessing the potential harm of pyrethroids in oysters to consumers.

A Colorimetric Receptor Based on SchiffoBase Bearing Azo-Phenolic Hydroxy Group

A novel N-（2-hydroxy-5-chlorodibenzophenone）-N＇-[2-hydroxy-5-azophenyl-benzaldehyde]- 1,2-diaminobenzene receptor has been synthesized by simple steps with good yields. The anion recognition properties were studied by ultraviolet-visible spectroscopy. The results showed that the receptor had a higher affinity to F-, AcO-, and H2PO4-, but no evident binding with Cl-, Br-, and l-. Upon addition of the three former anions to the receptors in DMSO, the solution exhibited an obvious color change from colorless to yellow, which could be observed by the naked eye, thus the receptor could act as a fluoride ion sensor even in the presence of other halide ions. The UV-Vis data indicates that a 1：1 stoichiometric complex is formed through hydrogen bonding interactions between receptor and anions.

Surface Acidity of Amorphous Aluminum Hydroxide

The surface acidity of synthetic amorphous AI hydroxide was determined by acid/base titration with several complementary methods including solution analyses of the reacted solutions and XRD characterization of the reacted solids. The synthetic specimen was characterized to be the amorphous material showing four broad peaks in XRD pattern. XRD analyses of reacted solids after the titration experiments showed that amorphous AI hydroxide rapidly transformed to crystalline bayerite at the alkaline condition （pH〉10）. The solution analyses after and during the titration Ksp=^aAl^3＋/aH^＋^3 ,was 10^10.3. The amount of consumption of added acid or base during the titration experiment was attributed to both the protonation/deprotonation of dissolved AI species and surface hydroxyl group. The surface acidity constants, surface hydroxyl density and specific surface area were estimated by FITEQL 4.0.

Determination of aniline in environmental water samples by alternating-current oscillopolarographic titration

A new method for the determination of aniline in environmental water based on oscillopolarographic titration was presented in this paper. Several factors including the kind, concentration, and volume of acid, the dosage of potassium bromide, the temperature and concentration of concomitant substances were investigated in detail. The experimental results indicated that this method was simple, rapid, and sensitive. The linear range was 8.367 × 10(?4) to 2.789 × 10(?2) mol L(?1), the relative standard deviation (R.S.D.) was lower than 0.96%, and the spiked recoveries of aniline in environmental water samples were in the range of 99.4–106.9% under the optimal conditions. The results indicated that the present method could be used as an alternative method for aniline determination in realworld water samples.

Analysis of an improved acquisition method for high-dynamic BOC signal

To reach a compromise between short acquisition time and excellent detection probability for the high-dynamic binary offset carrier (BOC) signal, an overall algorithm based on discrete polynomial-phase transform (DPT) and partial matching filter (PMF)-fast Fourier transform (FFT) algorithm is given. The high order items of received signals are removed by the method of DPT, and the PMF-FFT algorithm is redesigned for the BOC signal. The simulation experiments and theoretical analyses verify that the improved algorithm has attained improvement in acquisition performance. © 2016 Beijing Institute of Aerospace Information.

Measurement and Correlation of Equilibrium Data for Aqueous Two-phase System Ethanol+Water+ K_2HPO_4

The isothermal solubility data of aqueous two-phase system ethanol+water+K 2HPO 4 were determined with the turbidity titration method at 303.2 K. The binodal curves were described by using the Mistry equation very well. An experimental procedure for measuring the liquid-liquid equilibrium data of the aqueous two-phase system was proposed, in which the concentrations of the coexisting phases were determined with the corresponding densities of the solution. The tie lines were satisfactorily described by using the Othmer-Tobias and Bancroft equations.

Mechanical Fault Diagnosis Based on Band-phase-randomized Surrogate Data and Multifractal

The vibration signals of machinery with various faults often show clear nonlinear characteristics.Currently,fractal dimension analysis as the common useful method for nonlinear signal analysis,is a kind of single fractal form,which only reflects the overall irregularity of signals,but cannot describe its local scaling properties.For comprehensive revealing of internal properties,a combinatorial method based on band-phase-randomized（BPR） surrogate data and multifractal is introduced.BPR surrogate data method is effective to eliminate nonlinearity in specified frequency band for a fault signal,which can be utilized to detect nonlinear degree in whole fault signal by nonlinear titration method,and the overall nonlinear distribution of fault signal is displayed in nonlinear characteristic curve that can be used to analyze the fault signal qualitatively.Then multifractal theory as a quantitative analysis method is used to describe geometrical characteristics and local scaling properties,and asymmetry coefficient of multifractal spectrum and multifractal entropy for fault signals are extracted as new criterions to diagnose machinery faults.Several typical faults include rotor misalignment,transversal crack,and static-dynamic rubbing fault are analyzed,and the results indicate that those faults can be distinguished by the proposed method effectively,which provides a qualitative and quantitative analysis way in the field of machinery fault diagnosis.

Structural requirements and interaction mechanisms of ACE inhibitory peptides:molecular simulation and thermodynamics studies on LAPYK and its modifi ed peptides

The understanding of the structural requirements and the intermolecular-interaction mechanism are important for discovering potent angiotensin-converting enzyme(ACE)inhibitory peptides.In this study,we modifi ed an egg-white derived peptide,LAPYK,using the amino acids with different properties to produce the LAPYK-modified peptides.The ACE inhibitory activities of the modified peptides were determined to explore the structural requirements of ACE inhibitory peptides(ACEIPs).Molecular simulation and isothermal titration calorimetry analysis were used to investigate interactions between the peptides and ACE.We found that hydrophobicity and the amino acids with ring structures were benefi cial for the ACE inhibitory activities of the peptides.The results of the molecular mechanics poisson boltzmann surface area(MMPBSA)binding free energy calculations indicated that the polar solvation free energy(ΔG_(polar))of the charged peptides(LAPYK,LAPYE)were unfavorable for binding to ACE.On the other hand,the results of isothermal titration calorimetry analyses suggested that the enthalpy-driven ACE-peptide interactions were more favorable than the entropy-driven ACE-peptide interaction counterparts.

Preparation of CS-CMC Bipolar Membrane and its Application in Electro-generated FeO_4^(2-)

CS-CMC bipolar membrane was prepared and the cross-section photograph of CS-CMC BM was observed by SEM. FT-IR spectrum indicated that CS-CMC BM contained -N=CRH2^＋ and -COO^- functional groups. The charge density of -N--CRH2^＋ in CS membrane was about 14.13 mmol/g and the charge density of -COO in CMC membrane was about 9.01 mmol/g. The electrochemistry properties of CS-CMC BM were also studied. CS-CMC BM not only can effectively stop FeO4^2- from diffusing into the cathode chamber, but also plays an important role in the supply of OH＂ consumed during the electro-generated FeO4^2- process.

Determination of pKa values of alendronate sodium in aqueous solution by piecewise linear regression based on acid-base potentiometric titration

As a mono-sodium salt form of alendronic acid,alendronate sodium presents multi-level ionization for the dissociation of its four hydroxyl groups.The dissociation constants of alendronate sodium were determined in this work by studying the piecewise linear relationship between volume of titrant and p H value based on acidbase potentiometric titration reaction.The distribution curves of alendronate sodium were drawn according to the determined p Ka values.There were 4 dissociation constants(pKa_1=2.43,pKa_2=7.55,pKa_3=10.80,pKa_4=11.99,respectively) of alendronate sodium,and 12 existing forms,of which 4 could be ignored,existing in different p H environments.

Starting glargine in insulin-nave type 2 diabetic patients based on body mass index is safe

AIM:To evaluate the safety of four insulin titration algorithms in a homogeneous population of insulin-na ve type 2 diabetic patients.METHODS:We conducted a 24-wk,open,single-center study with 92 insulin-na ve type 2 diabetes patients who failed treatment with one or two oral drugs.The patients were randomized to one of the four following algorithms:LANMET(n=26)and LANMET PLUS(n=22)algorithms,whose patients received a fixed initial insulin dose of 10 U,and DeGold(n=23)and DeGold PLUS(n=21)algorithms,whose patients’initial insulin dose was based on their body mass index(BMI).In addition,patients in the PLUS groups had their insulin titrated twice a week from 2 to 8 U.In the other two groups,the titration was also performed also twice a week,but in a fixed increments of 2 U.The target fasting glucose levels for both groups was 100 mg/dL.RESULTS:There was no significant difference in efficacy parameters.There was no significant difference when comparing moderate hypoglycemia events in algorithms starting with a 10 U fixed dose and algorithms based on BMI.However,there was a significant increase in moderate hypoglycemia events among the PLUS treated patients when the LANMET and DeGold algorithms were compared with the 2 fast-titration PLUS algorithms.We observed 12 hypoglycemia events in the first group,which corresponded to 0.94 events/patient per year,and we observed 42 events in the second group,which corresponded to 2.81 events/patient per year(P<0.037).No further significant differences were observed when other comparisons between the algorithms were carried out.CONCLUSION:Starting insulin glargine based on BMI is safe,but fast titration algorithms increase the risk of moderate hypoglycemia.