A simple and robust LC-MS/MS method for quantification of free 3-nitrotyrosine in human plasma from patients receiving on-pump CABG surgery

We have developed a simple, sensitive, and robust liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) method to determine free 3-nitrotyrosine concentrations in human plasma of patients receiving on-pump coronary artery bypass grafting surgery. A one-step solid-phase extraction protocol was optimized to enrich the analyte at low nanomolar concentrations. The processed samples were analyzed by LC-MS/MS with a 2.1 × 100 mm Kinetex PFP column and a triple quadrupole mass spectrometer. The method was validated for 3-nitrotyrosine concentrations close to real patient plasma levels. The relative standard deviations or relative errors of the intraday and interday determinations were all within 10%. Limit of detection and limit of quantitation were determined to be 0.034 nM and 0.112 nM, respectively, while lower limit of quantitation was below 0.625 nM. No deterioration of the column performance was noticed after running a large number of patient samples. The results showed that the 3-nitrotyrosine concentrations in coronary sinus plasma samples were elevated after cardiopulmonary bypass (CPB) procedure. The pre-CPB and post-CPB concentrations of 3-nitrotyrosine in patient plasmas were 1.494 ± 0.107 nM and 2.167 ± 0.177 nM (mean ± SEM), respectively. Application of this method to more patients in clinical studies may help validate 3-nitrotyrosine as a meaningful biomarker for nitrosative stress and link patient characteristics, clinical outcomes, and cardioprotective treatments to endogenous nitrosative stress levels.     

A new derivatization method coupled with LC-MS/MS to enable baseline separation and quantification of dimethylarginines in human plasma from patients to receive on-pump CABG surgery

Asymmetric dimethylarginine (ADMA) is an inhibitor of nitric oxide synthase and a risk factor for cardiovascular events. We have developed a new derivatization method to enable baseline separation of the regio-isomers, ADMA, and symmetric dimethylarginine (SDMA), within 15 min on a C18 reverse phase column. Reacting naphthalene-2,3-dicarboxaldehyde with ADMA and SDMA in the presence of 2-mercaptoethanol produces corresponding 2,3-dihydro-benzo[f]isoindol-1-ones that are more stable than previously reported ortho-phthaldialdehyde and 2-mercaptoethanol derivatives. LC-MS/MS quantitation of these derivatives can be used to determine ADMA and SDMA concentrations in the plasma of patients to receive on-pump coronary artery bypass grafting (CABG) surgery. The LOD, LOQ and lower LOQ (LLOQ) of this method were determined to be 2.6, 8.7, and 25 nM for ADMA, and 2.5, 8.3, and 25 nM for SDMA, respectively, with consumption of only 50 μL of plasma. The relative standard deviations and relative errors of the intraday and interday determinations, as measurements of reproducibility and accuracy, are all within 15%. The ADMA and SDMA concentrations in patient plasma are 298.1 ± 11.2 nM (mean ± S.E.M., n = 123) and 457.7 ± 19.8 nM (mean ± S.E.M., n = 123), respectively. Upon unblinding of our clinical trial, these predetermined values might explain patient clinical outcomes associated with on-pump CABG surgery, as ADMA is known to inhibit nitric oxide production. Furthermore, this derivatization reaction in conjunction with LC-MS/MS analysis may open a venue to explore alternative chemical labeling modes for LC-MS/MS applications, such as analysis of other amino acids, metabolites, and peptides containing primary amine group(s).     

水合烟酸钡的合成、±结构表征和热化学性质

选择烟酸和氢氧化钡作为反应物, 利用室温固相合成方法, 借助于球磨技术, 合成了一种新的化合物——水合烟酸钡. 利用化学分析、元素分析、FTIR和X射线粉末衍射等方法确定了它的组成和结构为Ba(Nic)2·3H2O(s). 利用精密自动绝热热量计直接测定了此化合物在78-400 K温区的摩尔热容. 在热容曲线上出现了一个明显的吸热峰, 通过对热容曲线的解析, 得到了相变过程的峰温、相变焓和相变熵分别为(327.097±1.082) K、(16.793±0.084) kJ·mol-1和(51.340±0.164) J·K-1·mol-1. 将该温区的摩尔热容实验值用最小二乘法拟合得到摩尔热容(Cp,m)对温度(T)的多项式方程, 并且在此基础上计算出了它的舒平热容值和各种热力学函数值. 另外, 依据Hess定律, 通过设计合理的热化学循环, 选择体积为100 mL、浓度为0.5 mol·L-1的盐酸作为量热溶剂, 利用等温环境溶解-反应热量计分别测量固相反应的反应物和产物在所选溶剂中的溶解焓, 利用溶解焓确定固相反应的反应焓为⊿rH0m=-(84.12±0.38) kJ·mol-1. 最后, 利用固相反应的反应焓和其它反应物和产物已知的热力学数据计算出水合烟酸钡的标准摩尔生成焓为⊿fH0m[Ba(Nic)2·3H2O(s)]=-(2115.13±1.90) kJ·mol-1.     

Frontal analysis in microchip CE: a simple and accurate method for determination of protein-DNA dissociation constant

Equilibrium constants, such as the dissociation constant (K(d)), are a key measurement of noncovalent interactions that are of importance for the proper functioning of molecules in living systems. Frontal analysis (FA) is a simple and accurate CE method for the determination of K(d). Microchip CE coupled with LIF detection was used to determine K(d) of protein-DNA interactions using the FA method. A model system of IgE and the IgE-binding aptamer was selected to demonstrate the capability of FA in microchip CE. Because the fluorescence emission was dependent on the dye migration velocity, the velocity of the free aptamer was adjusted to be the same as that of the aptamer-IgE complex by setting up individual separation voltage configurations for the free and bound aptamers. The ratio of the free and bound aptamers in the equilibrium mixture was directly measured from the heights of their plateaus detected at 1.0 cm from the intersection of the microchip, and no internal standard was needed. The K(d) of the IgE-aptamer pair was determined as 6 +/- 2 nM which is consistent with the reported results (8 nM).     

Association between a photo-intermediate of a M-lacking mutant D75N of pharaonis phoborhodopsin and its cognate transducer

Pharaonis phoborhodopsin (ppR or pharaonis sensory rhodopsin II) is a receptor of the negative phototaxis of Natronobacterium pharaonis and forms a complex with its transducer pHtrII in membranes. Flash-photolyis of a D75N mutant did not yield the M-intermediate, but an O-like intermediate is observed in a ms time range. We examined the interaction between the D75N of ppR and t-Htr (truncated pHtrII). These formed a complex in the presence of 0.1% n-dodecyl-beta-maltoside, and the association accelerated the decay of the O of D75N from 15 to 56 s(-1). From the decay time constants under varying ratios of D75N and t-Htr, n, the molar ratio of D75N/t-Htr in the complex, and K(D), the dissociation constant, were estimated. The value of n was unity and K(D) was estimated to 146 nM. This K(D) value can be considered to be the association between the photo-intermediate and t-Htr, which is deduced by the method of estimation. Previously we (Photochem. Photobiol. 74 (2001) 489) reported a K(D) of 15 microM for the interaction between the wild-type and t-Htr by means of the change in M-decay rates. Therefore, this value should be the K(D) value for the interaction between M of the wild-type and t-Htr.     

Extraction of some univalent salts into 1,2-dichloroethane and nitrobenzene: analysis of overall extraction equilibrium based on elucidating ion-pair formation and evaluation of standard potentials for ion transfers at the interfaces between their diluents and water

Sodium permanganate, sodium picrate (NaPic), Bu(4)NPic, Me(4)NPic, and Et(4)NPic were extracted at an ionic strength of 2 × 10(-5) to 0.08 mol dm(-3) and 25°C from water (w)-phases into the organic (o)-ones, 1,2-dichloroethane (DCE) and nitrobenzene (NB). Thereby, apparent distribution constants (K(D,±)) of the anions (A(-)) or the cations (M(+)) and ion-pair formation ones (K(MA)(org)) of the univalent salts (MA) in the o-phases were determined at 25 °C, where K(D,±) = ([A(-)](o)[M(+)](o)/[A(-)][M(+)])(1/2) = (K(D,A)K(D,M))(1/2) and K(MA)(org) = [MA](o)/[M(+)](o)[A(-)](o). Also, the K(ex) and K(D,MA) values with A(-) = Pic(-), MnO(4)(-) were estimated from the relations K(ex) (= [MA](o)/[M(+)][A(-)]) = K(MA)(org)(K(D,±))(2) and = K(MA)K(D,MA), respectively. Standard potentials (Δψ(tr)(0)) for ion transfers at the w/DCE and w/NB interfaces were evaluated from the log K(D,A) or log K(D,M) values by assuming the relations K(D,Pic) = K(D,Et4N) and = K(D,Me4N), respectively. The thus-obtained Δψ(tr)(0) values, especially for the w/DCE system, were in good agreement with the values based on the extra-thermodynamic assumption for Ph(4)As(+) and BPh(4)(-) transfers at the interfaces. In the present extraction systems, the ion-pair formation of MA in the w- and o-phases was less effective in the determination of their distribution constants into the two o-phases.     

Bioactive steroidal glycosides from the marine sponge Erylus lendenfeldi

Bioassay-guided fractionation of the methanol extract of Erylus lendenfeldi using engineered strains of budding yeast (Saccharomyces cerevisiae) has resulted in the isolation of the known compound eryloside A (1) and two new compounds, erylosides K (2) and L (3). The structures were established based mainly on 1D and 2D NMR data. The absolute stereochemistry of eryloside A, which had never been fully characterized, was determined using the modified Mosher's method. The absolute stereochemistry of eryloside K was determined by comparison with tetrahydroeryloside A. Compounds 1-3 exhibited selective cytotoxicity against a yeast strain (Δrad50) deficient in double strand break (DSB) repair.     

Experimental and computational thermochemical study of barbituric acids: structure-energy relationship in 1,3-dimethylbarbituric acid

This paper reports an experimental and computational thermochemical study on 1,3-dimethylbarbituric acid. The value of the standard (p° = 0.1 MPa) molar enthalpy of formation in the gas phase at T = 298.15 K has been determined. The energy of combustion was measured by static bomb combustion calorimetry, and from the result obtained, the standard molar enthalpy of formation in the crystalline state at T = 298.15 K was calculated as -639.6 ± 1.9 kJ·mol(-1). The enthalpy of sublimation was determined using a transference (transpiration) method in a saturated N(2) stream and a value of the enthalpy of sublimation at T = 298.15 K was derived as 92.3 ± 0.6 kJ·mol(-1). From these results a value of -547.3 ± 2.0 kJ·mol(-1) for the gas-phase enthalpy of formation at T = 298.15 K was determined. Theoretical calculations at the G3 and G4 levels were performed, and a study on molecular and electronic structure of the compound has been carried out. Calculated enthalpies of formation are in very good agreement with the experimental value.     

New pyrazolo[3,4-b]pyridones as selective A(1) adenosine receptor antagonists: synthesis, biological evaluation and molecular modelling studies

A series of ethyl 4-amino-1-(2-chloro-2-phenylethyl)-6-oxo-6,7-dihydro-1H-pyrazolo[3,4-b]pyridine-5-carboxylates () has been synthesized as potential A(1) adenosine receptor (A(1) AR) ligands. Binding affinities of the new compounds were determined for adenosine A(1), A(2A) and A(3) receptors. Compounds and showed good affinity (K(i)= 299 nM and 517 nM, respectively) and selectivity towards A(1) AR, whereas showed good affinity for A(2A) AR (K(i)= 290 nM), higher than towards A(1) AR (K(i)= 1000 nM). The only arylamino derivative of the series displayed high affinity (K(i)= 4.6 nM) and selectivity for A(3) AR. Molecular modelling and 3D-QSAR (CoMFA) studies carried out on the most active compounds gave further support to the pharmacological results.     

t-Bu2SiF-derivatized D2-receptor ligands: the first SiFA-containing small molecule radiotracers for target-specific PET-imaging

The synthesis, radiolabeling and in vitro evaluation of new silicon-fluoride acceptor (SiFA) derivatized D(2)-receptor ligands is reported. The SiFA-technology simplifies the introduction of fluorine-18 into target specific biomolecules for Positron-Emission-Tomography (PET). However, one of the remaining challenges, especially for small molecules such as receptor-ligands, is the bulkiness of the SiFA-moiety. We therefore synthesized four Fallypride SiFA-conjugates derivatized either directly at the benzoic acid ring system (SiFA-DMFP, SiFA-FP, SiFA-DDMFP) or at the butyl-side chain (SiFA-M-FP) and tested their receptor affinities. We found D(2)-receptor affinities for all compounds in the nanomolar range (K(i(SiFA-DMFP)) = 13.6 nM, K(i(SiFA-FP)) = 33.0 nM, K(i(SiFA-DDMFP)) = 62.7 nM and K(i(SiFA-M-FP)) = 4.21 nM). The radiofluorination showed highest yields when 10 nmol of the precursors were reacted with [(18)F]fluoride/TBAHCO(3) in acetonitrile. After a reversed phased cartridge purification the desired products could be isolated as an injectable solution after only 10 min synthesis time with radiochemical yields (RCY) of more than 40% in the case of SiFA-DMFP resulting in specific activities >41 GBq/μmol (>1,100 Ci/mmol). Furthermore, the radiolabeled products were shown to be stable in the injectable solutions, as well as in human plasma, for at least 90 min.     

四氯合镉酸正十一烷铵的合成、晶体结构及低温热容

合成了四氯合镉酸正十一烷铵配合物(C₁₁H₂₃NH₃)₂CdCl₄(s)[简写: C₁₁Cd(s)]. 用X 射线单晶衍射技术、化学分析和元素分析确定其晶体结构和化学组成. 利用其晶体学数据计算出晶格能为: U_POT＝908.18 kJ·mol^-1. 利用精密自动绝热热量计测定了它在78～395 K 温区的低温热容, 结果表明, 该配合物在此温区出现两次连续的固-固相转变, 计算出两次相变的峰温、摩尔焓及摩尔熵分别为: T_trs,1＝(321.88±0.07) K, Δ_trsH_m,1＝(37.59±0.17) kJ·mol^-1, Δ_trsS_m,1＝(117.24±0.12) J·K^-1·mol^-1, T_trs,2＝(323.81±0.30) K, Δ_trsH_m,2＝(12.42±0.02) kJ·mol^-1 和Δ_trsS_m,2＝(38.36±0.09) J·K^-1·mol^-1. 用最小二乘法将实验摩尔热容对温度进行拟合, 得到热容随温度变化的多项式方程. 用此方程进行数值积分,得到此温区每隔5 K 的舒平热容值和相对于298.15 K 时的热力学函数值.     

Experimental and computational thermochemical study of 2-thiobarbituric acid: structure-energy relationship

This paper reports an experimental and computational thermochemical study on 2-thiobarbituric acid (2-thioxodihydropyrimidine-4,6(1H,5H)-dione), [CAS 504-17-6]. The value of the standard (p(0) = 0.1 MPa) molar enthalpy of formation in the gas phase at T = 298.15 K has been determined. The energy of combustion was measured by bomb combustion calorimetry, using a rotatory bomb, and from the result obtained, the standard molar enthalpy of formation in the crystalline state at T = 298.15 K was calculated as -(396.8 ± 0.9) kJ·mol(-1). The enthalpy of sublimation was determined using a transference (transpiration) method in a saturated N(2) stream and a value of the enthalpy of sublimation at T = 298.15 K was derived as (118.3 ± 2.2) kJ·mol(-1). From these results a value of -(278.5 ± 2.4) kJ·mol(-1) for the gas-phase enthalpy of formation at T = 298.15 K was determined. Theoretical calculations at the G3 and G4 levels were performed, and a study of the molecular and electronic structure of the compound has been carried out. Calculated enthalpies of formation are in very good agreement with the experimental value.     

Experimental and computational investigation of the group 11-group 2 diatomic molecules: first determination of the AuSr and AuBa bond energies and thermodynamic stability of the copper- and silver-alkaline earth species

The dissociation energies of the intermetallic molecules AuSr and AuBa were for the first time determined by the Knudsen effusion mass spectrometry method. The two species were produced in the vapor phase equilibrated with apt mixtures of the constituent elements, and the dissociation equilibria were monitored mass-spectrometrically in the temperature range 1406-1971 K (AuSr) and 1505-1971 K (AuBa). The third-law analysis of the equilibrium data gives the following dissociation energies (D(0)°, in kJ/mol): 244.4 ± 4.8 (AuSr) and 273.3 ± 6.3 (AuBa), so completing the series of D(0)°s for the AuAE (AE = group 2 element) diatomics. The AuAE species were also studied computationally at the coupled cluster including single, double and perturbative triple excitation [CCSD(T)] level with basis sets of increasing zeta quality, and various complete basis set limit extrapolations were performed to calculate the dissociation energies. Furthermore, the entire series of the heteronuclear diatomic species formed from one group 11 (Cu, Ag) and one group 2 (Be, Mg, Ca, Sr, Ba) metal was studied by DFT with the hybrid meta-GGA TPSSh functional and the def2-QZVPP basis set, selected after screening a number of functional-basis set combinations using the AuAE species as benchmark. Dissociation energies, internuclear distances, vibrational frequencies, and anharmonic constants were determined for the CuAE and AgAE species and their thermal functions evaluated therefrom. On this basis, a thermodynamic evaluation of the formation of these species was carried out under various conditions.     

Voltammetric determination of bisphenol A in food package by a glassy carbon electrode modified with carboxylated multi-walled carbon nanotubes

A highly sensitive and mercury-free method for determination of bisphenol A (BPA) was established using a glassy carbon electrode that was modified with carboxylated multi-walled carbon nanotubes. A sensitive oxidation peak is found at 550?mV in linear sweep voltammograms at pH?7. Based on this finding, trace levels of bisphenol A can be determined over a concentration range that is linear from 10?nM to 10⁴?nM, the correlation coefficient being 0.9983, and the detection limit (S/N?=?3) being 5.0?nM. The method was successfully applied to the determination of BPA in food package.

硝酸锌与四种α-氨基酸配合物的恒容燃烧能测定

Ten solid complexes of zinc nitrate with L-α-leucine(Leu)， L-α-valine(Val)， L-α-tryptophan(Try) and L-α-threonine(Thr) were prepared in water. The compositions of these complexes are determined by chemical analysis and elemental analysis， which are identified as Zn(Leu)(NO₃)₂·2H₂O(A)， Zn(Leu)₂(NO₃)₂·H₂O(B)， Zn(Val)(NO₃)₂·2H₂O(C)， Zn(Val)₂(NO₃)₂·H₂O(D)， Zn(Val)₃(NO₃)₂·H₂O(E)， Zn(Try)(NO₃)₂·2H₂O(F)， Zn(Try)₂(NO₃)₂·H₂O(G)， Zn(Thr)(NO₃)₂·2H₂O(H)， Zn(Thr)₂(NO₃)₂·H₂O(I) and Zn(Thr)₃(NO₃)·H₂O(J). The constant-volume combustion energies of the complexes， Δ_cU(complex)， were determined by a precise rotating bomb calorimeter at 298.15K. Standard enthalpies of combustion，Δ_cH_m^?(complex， s， 298.15K)， and standard enthalpies of formation， Δ_fH_m^?(complex，s，298.15K) for these complexes were calculated as (4523.22±2.08)， (7208.86±4.28)， (3442.21±1.85)， (5971.21±3.32)， (9007.26±4.24)， (5802.35±2.14)， (10891.58±3.01)， (2147.40±1.28)， (4120.83±0.99)， (6444.68±3.85)kJ·mol^-1 and (615.67±2.27)， (1863.16±4.60)， (1017.34±2.00)， (1742.93±3.61)， (2245.70±4.73)， (1161.18±2.61)， (1829.71±4.20)， (1632.82±1.43)， (1885.55±1.50)， (2770.25±4.21)kJ·mol^-1， respectively.     

ClO radical yields in the reaction of O(1D) with Cl2, HCl, chloromethanes, and chlorofluoromethanes

Absolute ClO radical product yields in the gas-phase reactions of O((1)D) with Cl(2), HCl, CCl(4), CHCl(3), CH(2)Cl(2), CH(3)Cl, CFCl(3), CF(2)Cl(2), CF(3)Cl, CHFCl(2), and CHF(2)Cl are reported. Product yields were measured using pulsed-laser photolysis of O(3) to produce O((1)D) in the presence of excess reactant combined with dual wavelength differential cavity ring-down spectroscopic detection of the ClO radical. ClO radical absorption cross sections for the A(2)Π(v = 10) ← X(2)Π(v = 0) transition band head near 280 nm were determined between 200 and 296 K as part of this work. The ClO product yields obtained at room temperature were Cl(2) (0.77 ± 0.10), HCl (0.20 ± 0.04), CCl(4) (0.79 ± 0.04), CHCl(3) (0.77 ± 0.04), CH(2)Cl(2) (0.73 ± 0.04), CH(3)Cl (0.46 ± 0.06), CFCl(3) (0.79 ± 0.04), CF(2)Cl(2) (0.76 ± 0.06), CF(3)Cl (0.82 ± 0.06), CHFCl(2) (0.73 ± 0.05), and CHF(2)Cl (0.56 ± 0.03), where the quoted error limits are 2σ of the measurement precision. ClO product yields in the O((1)D) + Cl(2) and CFCl(3) reactions were found to be independent of temperature between 200 and 296 K, within the precision of the measurements. The absolute ClO yields obtained in this study are compared with previously reported values determined using relative and indirect methods.     

Stereochemistry and mechanism of the Brønsted acid catalyzed intramolecular hydrofunctionalization of an unactivated cyclic alkene

Through employment of deuterium-labeled substrates, the triflic acid catalyzed intramolecular exo addition of the X-H(D) (X=N, O) bond of a sulfonamide, alcohol, or carboxylic acid across the C=C bond of a pendant cyclohexene moiety was found to occur, in each case, with exclusive formation (≥90%) of the anti-addition product without loss or scrambling of deuterium as determined by (1)H and (2)H NMR spectroscopy and mass spectrometry analysis. Kinetic analysis of the triflic-acid-catalyzed intramolecular hydroamination of N-(2-cyclohex-2'-enyl-2,2-diphenylethyl)-p-toluenesulfonamide (1a) established the second-order rate law: rate=k(2)[HOTf][1a] and the activation parameters ΔH(++)=(9.7±0.5) kcal mol(-1) and ΔS(++)=(-35±5) cal K(-1) mol(-1). An inverse α-secondary kinetic isotope effect of k(D)/k(H) =(1.15±0.03) was observed upon deuteration of the C2' position of 1a, consistent with partial C-N bond formation in the highest energy transition state of catalytic hydroamination. The results of these studies were consistent with a mechanism for the intramolecular hydroamination of 1a involving concerted, intermolecular proton transfer from an N-protonated sulfonamide to the alkenyl C3' position of 1a coupled with intramolecular anti addition of the pendant sulfonamide nitrogen atom to the alkenyl C2' position.     

Development of a rapid and sensitive high-performance liquid chromatographic method to determine CYP2D6 phenotype in human liver microsomes

Dextromethorphan is a probe substrate to determine CYP2D6 phenotype. The conversion of dextromethorphan to dextrorphan by CYP2D6 accounts for approximately 60% of total metabolism. Most analytical methods utilize complicated labor- and time-intensive sample processing methods with several liquid-liquid extraction (LLE) steps. Our goal was to develop a non-LLE based rapid and sensitive HPLC method, to measure dextromethorphan metabolism in human liver microsomes. A solid-phase filtration based reverse-phase HPLC method with fluorescence detection was developed and validated. Human liver (n = 6) microsomal incubations were carried out with dextromethorphan, under optimum conditions. The analytes were separated by one-step centrifugal filtration with Nanosep separation units. The filtrate was injected ( 50 microL) into a Waters Alliance 2690 HPLC system. Metabolic incubations were also conducted to determine levels using LLE for comparisons. The Nanosep separation step reduced the extraction time from 3h to 40 min. The limit of quantitation was 23.8 nM (9.7 ng/mL), recovery was approximately 98%, the mean precision values were <10% RSD for the controls (80, 320 and 640 nM) and mean percentage error was <5%. Michaelis-Menten parameters were determined to distinguish CYP2D6 phenotypes. A rapid and sensitive HPLC method is reported, which may be suitable for automation and allows phenotyping of human liver microsomes.     

紫外-可见吸收光谱结合高斯多峰拟合技术测定甲基红酸离解常数

在一定pH值范围内,甲基红(MR)水溶液紫外-可见吸收光谱特征是酸式甲基红(HMR)最大吸收峰((530±15)nm)与碱式甲基红(MR-)最大吸收峰((435±20)nm)叠合在一起.本文用高斯多峰拟合技术实现了HMR和MR-叠合峰的分峰拟合计算.拟合计算输出两个吸收峰的积分面积即峰强度A1和A2,A1和A2之比与MR-和HMR浓度之比.进而计算甲基红水溶液酸离解平衡常数pKa.用本方法测量298.15K时的pKa值为4.76.拟合优度高,拟合度R2、拟合优度χ2分别达到0.998和10-5以下.深入探讨了表面活性剂十二烷基硫酸钠(SDS)、十六烷基三甲基溴化铵(CTAB)聚集行为对甲基红pKa的影响.与传统分光光度测量方法相比,紫外-可见吸收光谱结合高斯多峰拟合技术结果更可靠,测量步骤和数据处理过程更简单,更具有普适性.     

Protocols for amide high-speed analoging. Preparation of novel, small molecule cathepsin D inhibitors

Procedures for solution phase parallel synthesis of new, small molecule cathepsin D inhibitors by the coupling of acyl chlorides, sulfonyl chlorides and carboxylic acids with nitrogen nucleophiles have been established using polymer-bound reagents to facilitate the chemistry and/or to efficiently scavenge the unreacted starting materials and reaction by-products. Silver(I) benzoate was used to facilitate the coupling of acyl chlorides with less reactive anilines. Compound 4 was identified as a sub-micromolar cathepsin D inhibitor (IC₅₀=320 nM).