The potentiostatic intermittent titration technique(PITT)is widely used to determine the diffusion coefficient of ions in electrode materials for rechargeable batteries such as lithium-ion or sodium-ion batteries,pred...The potentiostatic intermittent titration technique(PITT)is widely used to determine the diffusion coefficient of ions in electrode materials for rechargeable batteries such as lithium-ion or sodium-ion batteries,predicated on the assumption that the insertion/extraction of ions in the host materials is governed by diffusion.However,in practical scenarios,the electrochemical process might be dominated by interfacial reaction kinetics rather than diffusion.The present work derives analytical equations for electric current by considering the finite interfacial reaction kinetics and small overpotentials during PITT measurements and further studies the chemical stress field induced by the interfacial reaction-controlled ion insertion.The exchange current density(j_(0))can be ascertained using the analytical equation,which dictates the magnitude and decay rate of the electric current during a PITT process.The electric current decays more rapidly,and consequently,the lithium concentration reaches equilibrium faster for larger values of j_(0).The magnitude of the chemical stress is independent of j_(0) but depends on the overpotential.展开更多
BACKGROUND Effective pain management after radical gastrectomy is crucial for patient recovery.With the promotion of enhanced recovery after surgery protocols,postoperative pain management has become a core component ...BACKGROUND Effective pain management after radical gastrectomy is crucial for patient recovery.With the promotion of enhanced recovery after surgery protocols,postoperative pain management has become a core component of perioperative care.However,controversy remains regarding the optimal frequency of analgesic titration for pain control.AIM To compare the efficacy of 12-hour vs 24-hour titration regimens in postoperative pain management following radical gastrectomy for gastric cancer.METHODS This retrospective comparative study analyzed data from 120 patients who underwent radical gastrectomy between January 2021 and December 2022,with 52 patients receiving a 12-hour titration regimen and 68 patients receiving a 24-hour titration regimen.All patients received patient-controlled intravenous analgesia containing sufentanil and tropisetron postoperatively with identical initial settings.RESULTS The 12-hour titration group demonstrated significantly lower pain scores at 12 hours postoperatively compared to the 24-hour group(3.2 vs 4.8,P<0.001);total analgesic consumption(morphine equivalents)was reduced by 28.6%(30 mg vs 42 mg,P<0.001);postoperative nausea and vomiting decreased by 50%(15%vs 30%,P=0.02);respiratory depression was less frequent(2%vs 8%,P=0.04);patient satisfaction was higher(85%vs 65%reporting“very satisfied”or“satisfied”,P<0.001);and hospital stay was shortened by 12.5%(4.2 days vs 4.8 days,P=0.02).Cox regression analysis showed that the 12-hour regimen was associated with a lower risk of prolonged high-intensity pain(hazard ratio=0.65,95%confidence interval:0.45-0.93,P=0.02),and multivariate regression analysis confirmed that the 12-hour regimen was an independent predictor of better overall recovery(β=-0.32,P=0.01).CONCLUSION Compared to the 24-hour titration regimen,the 12-hour titration regimen provided more effective control of early postoperative pain after radical gastrectomy,reduced total analgesic consumption,lowered the incidence of related adverse reactions,improved patient satisfaction,and shortened hospital stays.展开更多
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 betwe...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.展开更多
A new on line titration method and device based on a new technique continuous flow titration is described. By the means of electronically controlled switching of a solenoid valve, the main component of the system, t...A new on line titration method and device based on a new technique continuous flow titration is described. By the means of electronically controlled switching of a solenoid valve, the main component of the system, the equivalent point of the titration is easily determined. Several kinds of mixing tools were examined, whereby a self made mixing chamber with minimum volume gave best results and was therefore used in the device. The error of the titration is within 0.2% and the relative standard deviation (RSD) is below 1.2%. The results show no difference compared with a commercial device, meanwhile the new on line titration system is cheaper and fully automated and thus easy to hand and less solvent consumption.展开更多
Introduction: Only vindication of a nasal continuous positive airway pressure (CPAP) retitration procedure will be an actual change in the optimal CPAP pressure after that test. The purpose of this study was to identi...Introduction: Only vindication of a nasal continuous positive airway pressure (CPAP) retitration procedure will be an actual change in the optimal CPAP pressure after that test. The purpose of this study was to identify any items in patient characteristics, clinical features, baseline PSG and initial CPAP titration as predictors of change in optimal pressure on CPAP retitration. Methods: 46 patients with obstructive sleep apnea (OSA) were divided in two groups: Group I (optimal pressure was changed on CPAP retitration): N = 30, M 22 and F 8, age 31-72, BMI 26-50 Kg/m2, neck size 15 – 20', tonsillectomy in 8, narrow oropharynx in 15, uvuvlopalatopharyngoplasty (UP3) in 2, abnormal chin in 3, deviated nasal septum (DNS) and prior nose surgery in 1 each, initial CPAP pressure 6-19 cm, sleep efficiency 65%-98%, REM latency 0-304 minutes and residual apnea hypopnea index (AHI) 0-23/hour. Group II (optimal pressure unchanged after CPAP retitration): N = 16, M 11 and 5 F, age 32-69, BMI 23-62 Kg/m2, neck size 14.5-20', tonsillectomy in 6, narrow oropharynx in 5, abnormal chin in 4, corrective nasal surgery in 2, DNS in 1, initial CPAP pressure 8-13 cm of H2O, sleep efficiency 69%-95%, REM latency 0-270 minutes and residual AHI 0-19/hour. The statistical analyses were performed using two-tailed Fisher’s t test and unpaired t test. A p value of <0.05 was considered statistically significant. Results: Patient characteristics (age, gender, neck size, and BMI), clinical features (tonsillar status, oropharyngeal narrowing, chin abnormality, DNS/nasal surgery or UP3), baseline PSG or initial CPAP titration (sleep efficiency, REM latency, residual AHI and initial CPAP pressure) did not differ significantly between the 2 groups (p = 0.09-0.99). Conclusion: Patient characteristics, clinical features or variables on baseline PSG and initial CPAP titration do not predict a change in optimal pressure on CPAP retitration. The results suggest that 1) Significant weight change;2) Patient’s subjective feeling of pressure being too high or insufficient;3) Residual or recurrent daytime sleepiness uncorrected by interface readjustments;4)展开更多
Objective: to compare the difference between potentiometric titration and indicator titration in the determination of total organic acids in hawthorn. Methods: potentiometric titration and indicator titration were use...Objective: to compare the difference between potentiometric titration and indicator titration in the determination of total organic acids in hawthorn. Methods: potentiometric titration and indicator titration were used to determine the content of total organic acids in different batches of hawthorn, and the differences in precision, repeatability, stability and recovery between the two methods were compared. Results: the repeatability and stability of potentiometric titration were higher than that of indicator titration. The recovery rate of potentiometric titration was 97.61%, and that of indicator titration was 96.96%. Potentiometric titration is easier to eliminate the interference of Hawthorn water extract color on titration end point. Conclusion: potentiometric titration is better than indicator method in the determination of total organic acids in hawthorn with color interference.展开更多
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 dosa...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.展开更多
Paraquat （PQ）, a nonselective herbicide, is non-fluorescent in aqueous solutions. Thus, its determination through direct fluorescent methods is not feasible. The supramolecular inclusion interaction of PQ with cucur...Paraquat （PQ）, a nonselective herbicide, is non-fluorescent in aqueous solutions. Thus, its determination through direct fluorescent methods is not feasible. The supramolecular inclusion interaction of PQ with cucurbit[7]uril was studied by a fluorescent probe titration method. Significant quenching of the fluorescence intensity of the cucurbit[7]uril-coptisine fluorescent probe was observed with the addition of PQ. A new fluorescent probe titration method with high selectivity and sensitivity at the ng/mL level was developed to determine PQ in aqueous solutions with good precision and accuracy based on the significant quenching of the supramolecular complex fluorescence intensity. The proposed method was successfully used in the determination of PQ in lake water, tap water, well water, and ditch water in an agricultural area, with recoveries of 96.73% to 105.77%. The fluorescence quenching values （AF） showed a good linear relationship with PQ concentrations from 1.0 × 10^-8 to 1.2× 10^-5 mol/L with a detection limit of 3.35 x 10-9 mol/L. In addition, the interaction models of the supramolecular complexes formed between the host and the vip were established using theoretical calculations. The interaction mechanism between the cucurbit[7]uril and PQ was confirmed by 1H NMR spectroscopy.展开更多
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 thi...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.展开更多
Rocky desertification has become a major environmental issue in the karst region of southwestern China.Karst rocky desertification was more severe in regions of limestone soil than in adjacent regions of other soils,d...Rocky desertification has become a major environmental issue in the karst region of southwestern China.Karst rocky desertification was more severe in regions of limestone soil than in adjacent regions of other soils,despite the relatively higher soil organic matter(SOM)content in limestone soil.The underlying mechanism remains ambiguous.We speculated that the geochemical characteristics of limestone soils in the karst region plays an essential role,especially the high calcium content of limestone soil.To test this hypothesis,we collected limestone soil samples from a limestone soil profile in the southwestern China karst region and extracted humic acid(HA)from these limestone soil samples.We investigated the interaction of Ca^(2+)and three HA samples on a joint experimental platform,which consists of an automatic potentiometric titrator,a UV–visible spectrometer,and a Fluorescence spectrometer.HA solutions were titrated by Ca^(2+)and optical spectra of the HA solutions were monitored during the titration experiments.The results indicated that:(1)the interaction of Ca^(2+)and HA is a combined process of adsorption and complexation.Adsorption dominated the overall distribution behavior of Ca^(2+),which could be fit by Langmuir and Freundlich isotherm models.Complexation was distinguished only when the concentration of Ca2+is low;(2)the changes of UV–visible spectroscopy and excitation–emission matrix fluorescencespectroscopy spectra of HA samples when they were binding with Ca^(2+)implied the apparent molecular size and structure of HA became larger and more complex;(3)the combination of Ca^(2+)and HA plays an important role in the SOM preservation of limestone soils but the stability of the Ca–HA association was relatively weak.The present study draws attention to maintaining the relatively higher Ca^(2+)concentration in limestone soils in ecologic restoration attempts in karst regions.展开更多
The stability constants and thermodynamic functions for complexes of lanthanum with eight kind of amino acids according to 1∶1 and 1∶2 in proportion have been determined by titration calorimeter at 298.15 K. The ent...The stability constants and thermodynamic functions for complexes of lanthanum with eight kind of amino acids according to 1∶1 and 1∶2 in proportion have been determined by titration calorimeter at 298.15 K. The enthalpy change makes a predominant contribution to the stability of these complexes. The ring in amino acid associated with lanthanum ion helps to enhance the stability of complexes. Steric effects between rings in complexes leads to that the equilibrium constants of reaction of the complexes (1∶2) is much less than that of the complexes (1∶1).展开更多
By using calcium ion selective elatrode (Ca ISE) as indicating electrode, saturated calomel electrode (SCE) as reference electrode and EGTA as titrant, calcium in seawater was determined by potentiometric titration in...By using calcium ion selective elatrode (Ca ISE) as indicating electrode, saturated calomel electrode (SCE) as reference electrode and EGTA as titrant, calcium in seawater was determined by potentiometric titration in borate buffer solution. This method can reduce observation errors in the determination of the endpoint, and thus provide better analytical precision(<0.08%) than present complexometric titration.展开更多
The compositions of the extracted complexes of La, Gd, Er and Y with sec octyl phenoxy acetic acid in heptane and the related apparent extraction equilibrium constants K M were determined using two phase titration...The compositions of the extracted complexes of La, Gd, Er and Y with sec octyl phenoxy acetic acid in heptane and the related apparent extraction equilibrium constants K M were determined using two phase titration technique. The stoichiometric compounds for La, Gd, Er and Y should be LaA 3·2.5HA, GdA 3·3HA, ErA 3·3.1HA and YA 3·4.3HA respectively. And their p K M are 3.43, 3.46, 3.08 and 2.58 respectively.展开更多
The content of dimethylallylamine was determined using glacial acetic acid as solvent, acetic-formic mixture as an anhydrite, perchloric acid-glacial acetic acid as titrant, and 1% crystal violet in acetic acid as ind...The content of dimethylallylamine was determined using glacial acetic acid as solvent, acetic-formic mixture as an anhydrite, perchloric acid-glacial acetic acid as titrant, and 1% crystal violet in acetic acid as indicator in the presence of methylamine and dimethylamine The influences of inert constituents and water on the titration were investigated, and a complete analytical method was determined. The results showed that the determination error of total amines increased with water increasing, while the effect of water on the determination of dimethylallylamine was little when the amount of water was within 5%, the relative error was generally within 1%, and that the end-point was acutely when about 10% chloroform was added. Compared with gas chromatography, this method is simple, convenient and accurate.展开更多
The formation constants of Co￣(2+), Ni￣(2+), Cu￣(2+) and Zn￣(2+) complexes with humic acid (HA) and fulvicacid (FA) in red soil were determined by the potentiometric titration method. The constants as a functionof...The formation constants of Co￣(2+), Ni￣(2+), Cu￣(2+) and Zn￣(2+) complexes with humic acid (HA) and fulvicacid (FA) in red soil were determined by the potentiometric titration method. The constants as a functionof composition of the complexation solutions were obtained by two graphical approaches respectively Theformation constants decreased with increasing concentration of metal in the solution. The results provideunambiguous evidence for the heterogeneity of the function groups of humic substances. The formationconstants of FA were much smaller than those of HA, and the formation constants of Cu￣(2+) were muchgreater than those of Co￣(2+) , Ni￣(2+) and Zn￣(2+) . The potentiometric titration method for determining formationconstants are also discussed in the article.展开更多
The analytical technique of conductometric titration is used to characterize polymeric materials.This technique allows obtaining the polymer dry weight capacity(DWC)and the extent of reaction and establishing the opti...The analytical technique of conductometric titration is used to characterize polymeric materials.This technique allows obtaining the polymer dry weight capacity(DWC)and the extent of reaction and establishing the optimal number of water molecules per sulfonic groups.In this particular case the polymer material under study was Nafion?117.Two different reactions were made:Neutralization and exchange.Both of them allow obtaining the same result.Conductometric titrations could be considered as a good method to study the neutralization and exchange reactions for polymeric materials used in fuel cells or electrolyzers.The implementation of this analytical technique allows reducing operation time of those types of materials.The waiting time between determinations permits to say that the amount of reactant consumed and products obtained were the same after each addition of titrant.展开更多
The precursors of La0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ(LSCCF, x=0.05, 0.10, 0.15, 0.20) as the cathode materials for intermediate temperature solid oxide fuel cell (ITSOFC) were prepared by reverse titration co-precipitatio...The precursors of La0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ(LSCCF, x=0.05, 0.10, 0.15, 0.20) as the cathode materials for intermediate temperature solid oxide fuel cell (ITSOFC) were prepared by reverse titration co-precipitation method with metal-nitrates as starting materials and mixed alkali (NaOH and Na2CO3) as a precipitating agent. The formation process of LSCCF from the precursors was monitored by TG-DSC, and the crystal structure and particles morphology of the precursors which were calcined at 600, 800, 1000 ℃ for 3 h were characterized using XRD, SEM technologies. Compared with the solid state reaction of constituent oxides, when the pH value of the precipitating solution was in the range of 9.1～9.5, the LSCCF powders from the precursors caclined at 800 ℃ for 3 h had high purity, homogeneous and single perovskite phase. The electrical conductivity of the LSCCF samples sintered at 1200 ℃ for 3 h, which was measured as a function of temperatures from 100 to 800 ℃ by DC four-probe method in air, decreased with x from 0.05 to 0.20. The value of electrical conductivity was almost equal because of Ca2+, Sr2+ co-dopant resulting in the 'mix effect' while x=0.10 or 0.15. The electrical conductivity of all doped samples was higher than 100 S·cm-1 at intermediate temperatures from 500 to 800 ℃, and there was good compatibility between the LSCCF cathode and Ce0.8Sm0.2O2 electrolyte.展开更多
A rapid, simple and sensitive method was demonstrated for the determination of phenolic compounds in water samples by alternating-current oscillopolarographic titration. With the presence of sulfuric acid, phenol coul...A rapid, simple and sensitive method was demonstrated for the determination of phenolic compounds in water samples by alternating-current oscillopolarographic titration. With the presence of sulfuric acid, phenol could be transferred into a nitroso-compound by reacting with NaNO2. The titration end-point was obtained by the formation of a sharp cut in the oscillopolarographic with infinitesimal NaNO2 on double platinum electrodes. The results showed that phenol had an excellent linear relationship over the range of 4.82×10^-6 -9.65×10^-3 mol/L, the RSD of the proposed method was lower than 1.5%, and the spiked recoveries of three real water samples were in the range of 95.6%-106.9%.展开更多
Amount and properties of roots surface charge are important for nutrient uptake and balance in plants. Roots surface charge markedly varies at different rizosphere conditions (particularly pH and ionic strength), whic...Amount and properties of roots surface charge are important for nutrient uptake and balance in plants. Roots surface charge markedly varies at different rizosphere conditions (particularly pH and ionic strength), which can markedly alter during vegetation season. Among recently available measuring methods, surface charge-pH dependence of roots (as well as other biological objects) is most easily evaluated by potentiometric titration. Use of this method is also easy at different ionic strengths. Potentiometric titration also allows for estimation of the distribution of charge generating surface groups. However, many applications of this method seem to be based either on incorrect methodical or theoretical approaches. In this paper we discuss the methodical and theoretical backgrounds of the titration method. Basing on experimental titration curves of roots of barley grown in nutrient solution, we show inconsistency of surface charge results obtained at different measuring conditions. Limitations of theoretical interpretations of the results are outlined also.展开更多
基金supported by the National Natural Science Foundation of China(No.12374003)the Guangdong Basic and Applied Basic Research Foundation(No.2024A1515030256)the Shenzhen Science and Technology Program(Grant Nos.JCYJ20220531095208019 and GXWD20231129103124001).
文摘The potentiostatic intermittent titration technique(PITT)is widely used to determine the diffusion coefficient of ions in electrode materials for rechargeable batteries such as lithium-ion or sodium-ion batteries,predicated on the assumption that the insertion/extraction of ions in the host materials is governed by diffusion.However,in practical scenarios,the electrochemical process might be dominated by interfacial reaction kinetics rather than diffusion.The present work derives analytical equations for electric current by considering the finite interfacial reaction kinetics and small overpotentials during PITT measurements and further studies the chemical stress field induced by the interfacial reaction-controlled ion insertion.The exchange current density(j_(0))can be ascertained using the analytical equation,which dictates the magnitude and decay rate of the electric current during a PITT process.The electric current decays more rapidly,and consequently,the lithium concentration reaches equilibrium faster for larger values of j_(0).The magnitude of the chemical stress is independent of j_(0) but depends on the overpotential.
基金Supported by Wenzhou Science and Technology Bureau,No.Y20220877.
文摘BACKGROUND Effective pain management after radical gastrectomy is crucial for patient recovery.With the promotion of enhanced recovery after surgery protocols,postoperative pain management has become a core component of perioperative care.However,controversy remains regarding the optimal frequency of analgesic titration for pain control.AIM To compare the efficacy of 12-hour vs 24-hour titration regimens in postoperative pain management following radical gastrectomy for gastric cancer.METHODS This retrospective comparative study analyzed data from 120 patients who underwent radical gastrectomy between January 2021 and December 2022,with 52 patients receiving a 12-hour titration regimen and 68 patients receiving a 24-hour titration regimen.All patients received patient-controlled intravenous analgesia containing sufentanil and tropisetron postoperatively with identical initial settings.RESULTS The 12-hour titration group demonstrated significantly lower pain scores at 12 hours postoperatively compared to the 24-hour group(3.2 vs 4.8,P<0.001);total analgesic consumption(morphine equivalents)was reduced by 28.6%(30 mg vs 42 mg,P<0.001);postoperative nausea and vomiting decreased by 50%(15%vs 30%,P=0.02);respiratory depression was less frequent(2%vs 8%,P=0.04);patient satisfaction was higher(85%vs 65%reporting“very satisfied”or“satisfied”,P<0.001);and hospital stay was shortened by 12.5%(4.2 days vs 4.8 days,P=0.02).Cox regression analysis showed that the 12-hour regimen was associated with a lower risk of prolonged high-intensity pain(hazard ratio=0.65,95%confidence interval:0.45-0.93,P=0.02),and multivariate regression analysis confirmed that the 12-hour regimen was an independent predictor of better overall recovery(β=-0.32,P=0.01).CONCLUSION Compared to the 24-hour titration regimen,the 12-hour titration regimen provided more effective control of early postoperative pain after radical gastrectomy,reduced total analgesic consumption,lowered the incidence of related adverse reactions,improved patient satisfaction,and shortened hospital stays.
基金supported by the National Natural Science Foundation of China (21825703, 21927814)the National Key R&D Program of China (2019YFA0405600, 2019YFA0706900, 2021YFA1200104, 2022YFC3400500)+3 种基金the Strategic Priority Research Program of Chinese Academy of Sciences (XDB0540200, XDB37040201)Plans for Major Provincial Science&Technology Projects (202303a07020004)Basic Research Program Based on Major Scientific Infrastructures,CAS (JZHKYPT-2021-05)the Youth Innovation Promotion Association,CAS (2022455)
文摘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.
文摘A new on line titration method and device based on a new technique continuous flow titration is described. By the means of electronically controlled switching of a solenoid valve, the main component of the system, the equivalent point of the titration is easily determined. Several kinds of mixing tools were examined, whereby a self made mixing chamber with minimum volume gave best results and was therefore used in the device. The error of the titration is within 0.2% and the relative standard deviation (RSD) is below 1.2%. The results show no difference compared with a commercial device, meanwhile the new on line titration system is cheaper and fully automated and thus easy to hand and less solvent consumption.
文摘Introduction: Only vindication of a nasal continuous positive airway pressure (CPAP) retitration procedure will be an actual change in the optimal CPAP pressure after that test. The purpose of this study was to identify any items in patient characteristics, clinical features, baseline PSG and initial CPAP titration as predictors of change in optimal pressure on CPAP retitration. Methods: 46 patients with obstructive sleep apnea (OSA) were divided in two groups: Group I (optimal pressure was changed on CPAP retitration): N = 30, M 22 and F 8, age 31-72, BMI 26-50 Kg/m2, neck size 15 – 20', tonsillectomy in 8, narrow oropharynx in 15, uvuvlopalatopharyngoplasty (UP3) in 2, abnormal chin in 3, deviated nasal septum (DNS) and prior nose surgery in 1 each, initial CPAP pressure 6-19 cm, sleep efficiency 65%-98%, REM latency 0-304 minutes and residual apnea hypopnea index (AHI) 0-23/hour. Group II (optimal pressure unchanged after CPAP retitration): N = 16, M 11 and 5 F, age 32-69, BMI 23-62 Kg/m2, neck size 14.5-20', tonsillectomy in 6, narrow oropharynx in 5, abnormal chin in 4, corrective nasal surgery in 2, DNS in 1, initial CPAP pressure 8-13 cm of H2O, sleep efficiency 69%-95%, REM latency 0-270 minutes and residual AHI 0-19/hour. The statistical analyses were performed using two-tailed Fisher’s t test and unpaired t test. A p value of <0.05 was considered statistically significant. Results: Patient characteristics (age, gender, neck size, and BMI), clinical features (tonsillar status, oropharyngeal narrowing, chin abnormality, DNS/nasal surgery or UP3), baseline PSG or initial CPAP titration (sleep efficiency, REM latency, residual AHI and initial CPAP pressure) did not differ significantly between the 2 groups (p = 0.09-0.99). Conclusion: Patient characteristics, clinical features or variables on baseline PSG and initial CPAP titration do not predict a change in optimal pressure on CPAP retitration. The results suggest that 1) Significant weight change;2) Patient’s subjective feeling of pressure being too high or insufficient;3) Residual or recurrent daytime sleepiness uncorrected by interface readjustments;4)
文摘Objective: to compare the difference between potentiometric titration and indicator titration in the determination of total organic acids in hawthorn. Methods: potentiometric titration and indicator titration were used to determine the content of total organic acids in different batches of hawthorn, and the differences in precision, repeatability, stability and recovery between the two methods were compared. Results: the repeatability and stability of potentiometric titration were higher than that of indicator titration. The recovery rate of potentiometric titration was 97.61%, and that of indicator titration was 96.96%. Potentiometric titration is easier to eliminate the interference of Hawthorn water extract color on titration end point. Conclusion: potentiometric titration is better than indicator method in the determination of total organic acids in hawthorn with color interference.
文摘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.
基金supported by the National Natural ScienceFoundation of China (No. 21171110)the Research Fund for the Doctoral Program of Higher Education of China (No. 20091404110001)
文摘Paraquat （PQ）, a nonselective herbicide, is non-fluorescent in aqueous solutions. Thus, its determination through direct fluorescent methods is not feasible. The supramolecular inclusion interaction of PQ with cucurbit[7]uril was studied by a fluorescent probe titration method. Significant quenching of the fluorescence intensity of the cucurbit[7]uril-coptisine fluorescent probe was observed with the addition of PQ. A new fluorescent probe titration method with high selectivity and sensitivity at the ng/mL level was developed to determine PQ in aqueous solutions with good precision and accuracy based on the significant quenching of the supramolecular complex fluorescence intensity. The proposed method was successfully used in the determination of PQ in lake water, tap water, well water, and ditch water in an agricultural area, with recoveries of 96.73% to 105.77%. The fluorescence quenching values （AF） showed a good linear relationship with PQ concentrations from 1.0 × 10^-8 to 1.2× 10^-5 mol/L with a detection limit of 3.35 x 10-9 mol/L. In addition, the interaction models of the supramolecular complexes formed between the host and the vip were established using theoretical calculations. The interaction mechanism between the cucurbit[7]uril and PQ was confirmed by 1H NMR spectroscopy.
基金the support of Key Laboratory of Chinese Medicine Preparation of Solid Dispersion,Gansu Longshenrongfa Pharmaceutical Industry Co.,Ltd.,Gansu Province,China
文摘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.
基金supported by the National Natural Science Foundation of China (U1701241, U1612441,41773147, and 41273149)the Science Foundation of Guizhou(20113109) 。
文摘Rocky desertification has become a major environmental issue in the karst region of southwestern China.Karst rocky desertification was more severe in regions of limestone soil than in adjacent regions of other soils,despite the relatively higher soil organic matter(SOM)content in limestone soil.The underlying mechanism remains ambiguous.We speculated that the geochemical characteristics of limestone soils in the karst region plays an essential role,especially the high calcium content of limestone soil.To test this hypothesis,we collected limestone soil samples from a limestone soil profile in the southwestern China karst region and extracted humic acid(HA)from these limestone soil samples.We investigated the interaction of Ca^(2+)and three HA samples on a joint experimental platform,which consists of an automatic potentiometric titrator,a UV–visible spectrometer,and a Fluorescence spectrometer.HA solutions were titrated by Ca^(2+)and optical spectra of the HA solutions were monitored during the titration experiments.The results indicated that:(1)the interaction of Ca^(2+)and HA is a combined process of adsorption and complexation.Adsorption dominated the overall distribution behavior of Ca^(2+),which could be fit by Langmuir and Freundlich isotherm models.Complexation was distinguished only when the concentration of Ca2+is low;(2)the changes of UV–visible spectroscopy and excitation–emission matrix fluorescencespectroscopy spectra of HA samples when they were binding with Ca^(2+)implied the apparent molecular size and structure of HA became larger and more complex;(3)the combination of Ca^(2+)and HA plays an important role in the SOM preservation of limestone soils but the stability of the Ca–HA association was relatively weak.The present study draws attention to maintaining the relatively higher Ca^(2+)concentration in limestone soils in ecologic restoration attempts in karst regions.
基金Supported by the National Nature Science Foundation of China(29873036)
文摘The stability constants and thermodynamic functions for complexes of lanthanum with eight kind of amino acids according to 1∶1 and 1∶2 in proportion have been determined by titration calorimeter at 298.15 K. The enthalpy change makes a predominant contribution to the stability of these complexes. The ring in amino acid associated with lanthanum ion helps to enhance the stability of complexes. Steric effects between rings in complexes leads to that the equilibrium constants of reaction of the complexes (1∶2) is much less than that of the complexes (1∶1).
文摘By using calcium ion selective elatrode (Ca ISE) as indicating electrode, saturated calomel electrode (SCE) as reference electrode and EGTA as titrant, calcium in seawater was determined by potentiometric titration in borate buffer solution. This method can reduce observation errors in the determination of the endpoint, and thus provide better analytical precision(<0.08%) than present complexometric titration.
文摘The compositions of the extracted complexes of La, Gd, Er and Y with sec octyl phenoxy acetic acid in heptane and the related apparent extraction equilibrium constants K M were determined using two phase titration technique. The stoichiometric compounds for La, Gd, Er and Y should be LaA 3·2.5HA, GdA 3·3HA, ErA 3·3.1HA and YA 3·4.3HA respectively. And their p K M are 3.43, 3.46, 3.08 and 2.58 respectively.
文摘The content of dimethylallylamine was determined using glacial acetic acid as solvent, acetic-formic mixture as an anhydrite, perchloric acid-glacial acetic acid as titrant, and 1% crystal violet in acetic acid as indicator in the presence of methylamine and dimethylamine The influences of inert constituents and water on the titration were investigated, and a complete analytical method was determined. The results showed that the determination error of total amines increased with water increasing, while the effect of water on the determination of dimethylallylamine was little when the amount of water was within 5%, the relative error was generally within 1%, and that the end-point was acutely when about 10% chloroform was added. Compared with gas chromatography, this method is simple, convenient and accurate.
文摘The formation constants of Co￣(2+), Ni￣(2+), Cu￣(2+) and Zn￣(2+) complexes with humic acid (HA) and fulvicacid (FA) in red soil were determined by the potentiometric titration method. The constants as a functionof composition of the complexation solutions were obtained by two graphical approaches respectively Theformation constants decreased with increasing concentration of metal in the solution. The results provideunambiguous evidence for the heterogeneity of the function groups of humic substances. The formationconstants of FA were much smaller than those of HA, and the formation constants of Cu￣(2+) were muchgreater than those of Co￣(2+) , Ni￣(2+) and Zn￣(2+) . The potentiometric titration method for determining formationconstants are also discussed in the article.
基金supported by the Defense Ministry of Argentina under Grant PIDDEF No.22/11
文摘The analytical technique of conductometric titration is used to characterize polymeric materials.This technique allows obtaining the polymer dry weight capacity(DWC)and the extent of reaction and establishing the optimal number of water molecules per sulfonic groups.In this particular case the polymer material under study was Nafion?117.Two different reactions were made:Neutralization and exchange.Both of them allow obtaining the same result.Conductometric titrations could be considered as a good method to study the neutralization and exchange reactions for polymeric materials used in fuel cells or electrolyzers.The implementation of this analytical technique allows reducing operation time of those types of materials.The waiting time between determinations permits to say that the amount of reactant consumed and products obtained were the same after each addition of titrant.
基金the National High-Tech Development Plan (2006AA05Z417)the Natural Science Foundation of Lia-oning Province (20062145)the Education department of Liaoning Province (05L073)
文摘The precursors of La0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ(LSCCF, x=0.05, 0.10, 0.15, 0.20) as the cathode materials for intermediate temperature solid oxide fuel cell (ITSOFC) were prepared by reverse titration co-precipitation method with metal-nitrates as starting materials and mixed alkali (NaOH and Na2CO3) as a precipitating agent. The formation process of LSCCF from the precursors was monitored by TG-DSC, and the crystal structure and particles morphology of the precursors which were calcined at 600, 800, 1000 ℃ for 3 h were characterized using XRD, SEM technologies. Compared with the solid state reaction of constituent oxides, when the pH value of the precipitating solution was in the range of 9.1～9.5, the LSCCF powders from the precursors caclined at 800 ℃ for 3 h had high purity, homogeneous and single perovskite phase. The electrical conductivity of the LSCCF samples sintered at 1200 ℃ for 3 h, which was measured as a function of temperatures from 100 to 800 ℃ by DC four-probe method in air, decreased with x from 0.05 to 0.20. The value of electrical conductivity was almost equal because of Ca2+, Sr2+ co-dopant resulting in the 'mix effect' while x=0.10 or 0.15. The electrical conductivity of all doped samples was higher than 100 S·cm-1 at intermediate temperatures from 500 to 800 ℃, and there was good compatibility between the LSCCF cathode and Ce0.8Sm0.2O2 electrolyte.
基金Project supported by the Creative Talented Person's Fund of Henan Province (High Teaching [2005]-126)the Natural Science Foundation of Henan Province (No. 0511053000)+1 种基金the Youth Science Foundation of Henan Normal University (No. 2004005)the Henan Key Laboratory for Environmental Pollution Control.
文摘A rapid, simple and sensitive method was demonstrated for the determination of phenolic compounds in water samples by alternating-current oscillopolarographic titration. With the presence of sulfuric acid, phenol could be transferred into a nitroso-compound by reacting with NaNO2. The titration end-point was obtained by the formation of a sharp cut in the oscillopolarographic with infinitesimal NaNO2 on double platinum electrodes. The results showed that phenol had an excellent linear relationship over the range of 4.82×10^-6 -9.65×10^-3 mol/L, the RSD of the proposed method was lower than 1.5%, and the spiked recoveries of three real water samples were in the range of 95.6%-106.9%.
文摘Amount and properties of roots surface charge are important for nutrient uptake and balance in plants. Roots surface charge markedly varies at different rizosphere conditions (particularly pH and ionic strength), which can markedly alter during vegetation season. Among recently available measuring methods, surface charge-pH dependence of roots (as well as other biological objects) is most easily evaluated by potentiometric titration. Use of this method is also easy at different ionic strengths. Potentiometric titration also allows for estimation of the distribution of charge generating surface groups. However, many applications of this method seem to be based either on incorrect methodical or theoretical approaches. In this paper we discuss the methodical and theoretical backgrounds of the titration method. Basing on experimental titration curves of roots of barley grown in nutrient solution, we show inconsistency of surface charge results obtained at different measuring conditions. Limitations of theoretical interpretations of the results are outlined also.
