Ternary complexes of cyclodextrins with alkali earth cations and amino acids in gas phase investigated by mass spectrometry.

Noncovalent ternary complexes between cyclodextrins (CDs), small molecules and alkali earth cations drew growing attention due to their potential application in many chemical and pharmaceutical fields. To date, the main factors affect the formation mechanism of noncovalent ternary complexes in gas phase have not been fully investigated. In this study, ternary complexes of CDs, divalent metal cations and amino acids (AAs) were investigated by electrospray ionization mass spectrometry (ESI-MS), demonstrating the formation of 1:1:1 stoichiometric noncovalent ternary complex of [CD + cation(II)+AA]2+ in gas phase. The results revealed that only +2 valence cations can form stable ternary complexes in ESI-MS. The ratio of peak intensities for [ß-CD + Mg(II)+AA]2+ to those for [ß-CD + Mg(II)]2+ hydrophobicity of AAs was also determined to discuss the effect of hydrophobicity of AAs. Exceptions exist for Pro, Gly, and Val indicated that other factors such as side-chain structure and rigidity of AAs can also influence the binding strength for ternary complexes. Collision induced dissociations (CID) were performed to further confirm the formation of the ß-CD ternary complexes, revealing the binding strength of [CD + Mg(II)+Phe]2+ decreased in the order of γ-CD, ß-CD, and α-CD. Although Leu and Ile are isomers, the ESI-MS demonstrated the peak intensity for ternary complexe of [ß-CD + Mg(II)+Ile]2+ exhibited stronger than that of [ß-CD + Mg(II)+Leu]2+, DFT theoretical calculations were conducted to explain the phenomenon. The calculation indicated when Mg2+ existing, the conformations of the two ternary complexes could be affected due to the electrostatic force. In the complexes, the Leu and Ile turn a way round, inserting to the cavity with their carboxylic acid side into the large rim side of ß-CD and interacting with Mg2+. This work not only clearly explained the factors influencing the formation of [CD + cation(II)+AA]2+ in gas phase, but it also provides an insight in designing ternary complexes for areas such as drug design and chiral discrimination.

Treatment of thrombosis in KD Patients using tissue plasminogen activator: a single center study.

OBJECTIVE: The most severe complication associated with giant coronary aneurysm in children with Kawasaki disease is ischemic cardiomyopathy (ICM) caused by thrombosis. Addition of tissue plasminogen activator, Alteplase, in the treatment regimen can be an efficient thrombolytic therapy, and therefore can have a significantly positive impact on patients' quality of life in long term. METHODS: Total four male KD patients with central thromboses in coronary aneurysm were treated in Pediatric Cardiology Department of Shengjing Hospital, China Medical University, from January 2020 to August 2021. These patients received thrombolytic treatments including Alteplase once + Heparin for 1 week followed by continuous oral Warfarin + Aspirin + Clopidogrel. RESULTS: 4 young male KD patients had coronary aneurysm (CAA) complicated with total 7 occurrences of central thrombosis. These patients were given alteplase and heparin/oral Warfarin + Aspirin + Clopidogrel treatment. 9 days to 2 months later, thromboses were significantly dissolved. The treatment successfully diminished the thrombosis complication. CONCLUSION: 1. Pediatric KD patients complicated with coronary aneurysm thrombosis are prone to recurrence of thrombosis. 2.  In KD patients complicated with coronary aneurysm thrombosis, treatments described in Method can be used for treating either small thromboses formed less than 1 month with strong echo and convex lumen or large thromboses with mixed strong and weak echo. With these treatments, coronary artery blood flow can be improved or completely recovered. 3. Clinical experiences at our center in treating these KD patients suggest that Alteplase can be considered in thrombolytic treatment beyond the limitation of less than 12 h of thrombosis occurrence.

Correlation Analysis of Anti-Cardiolipin Antibody/D Dimer/C-Reactive Protein and Coronary Artery Lesions/Multiple-Organ Damage in Children With Kawasaki Disease.

Aim: Kawasaki disease (KD) is a systemic vasculitis with unknown etiology. In addition to cardiovascular system involvement, it can also have other multiple organs involved. This study is aimed at investigating the correlation between anti-cardiolipin antibody (ACA)/D dimer/C reactive protein (CRP) and coronary artery lesions (CAL)/multiple-organ lesions in children with KD. Methods: Retrospective analysis was performed in 284 KD/IKD patients from May 2015 to April 2016. Among them, 175 were males (61.6%), with average age of 2 years and 5 months old. Patients were divided into ACA+ group and ACA- group, elevated D dimer group (DDE) and normal D dimer group (DDN), and coronary artery injury (CAL) group and non-coronary artery injury (NCAL) group. Results: ACA was most likely tested positive in younger KD children (p < 0.05). ACA+ and hypoproteinemia were correlated with CAL, thrombocytosis, and granulocytopenia (p < 0.05-0.01). Levels of cTnI and CK in the CAL group were significantly higher than those in the NCAL group (p < 0.05). CAL was more frequently detected in younger patients and patients with prolonged fever, later IVIG treatment, and elevated CRP over 100 mg/l, but there was no statistically significant difference (all p > 0.05). In the KD with DDE group, the incidence of granulopenia, thrombocytosis, myocardial damage, cholestasis, hypoproteinemia, and aseptic urethritis was significantly higher than that in the KD with DDN group (p < 0.05-0.01). However, elevated D dimer was not associated with CAL. CRP elevation was highly correlated with D dimer, but not with CAL. Conclusion: Higher incidence of CAL and myocardial damage occurred in KD patients with positive ACA and hypoproteinemia. In the current study, ACA was only tested for positive and negative, which is a limitation to this study. To further elucidate the association, ACA titers would establish its significance in drawing a conclusion for the significance of ACA in CAL and myocardial damages. In addition, higher incidence of CAL occurred in younger patients. The higher D dimer was associated with increased multiple-organ damage (MOD). CRP was closely correlated with D dimer, but not correlated with ACA and CAL.

Distinction of chiral penicillamine using metal-ion coupled cyclodextrin complex as chiral selector by trapped ion mobility-mass spectrometry and a structure investigation of the complexes.

Penicillamine (Pen) is a common chiral drug that is obtained from penicillin. Between the two enantiomers of Pen, only D-Pen can be used to treat cystinuria and rheumatoid arthritis while L-Pen is toxic. Therefore, it requires great efforts for the research of the rigorous analysis and distinction of the two enantiomers. The non-covalent combination of chiral molecules and chiral selectors (CSs) has been proved as a unique strategy for chiral distinction by ion mobility spectrometry in coupling with -mss spectrometry (IM-MS). Here, we developed a simple method to distinguish D, L-Pen by using special CSs for IM-MS separation. The CSs utilized here include cyclodextrins (CD) and linear chain oligosaccharides plus metal ions. We found that non-covalent complexes [Pen+ß-CD + Li]+ could be easily formed by electrospray ionization of the mixture of the solution, and the chirality of Pen could be effectively recognized by measuring their mobilities due to the different collision cross collision sections of [D-Pen+ß-CD + Li]+ and [L-Pen+ß-CD + Li]+. A detailed analysis of [Pen+ß-CD + Li]+ was then conducted by the optical rotation measurements and NMR experiments to reveal their structural differences. Furthermore, DFT calculation showed the differences of molecular conformation between the complexes. The results provide a new powerful method for fast analysis and recognition of chirality of Pen compounds by IM-MS.

The Complementary Relationship Between Echocardiography and Multi-Slice Spiral CT Coronary Angiography in the Diagnosis of Coronary Artery Thrombosis in Children With Kawasaki Disease.

Aim: To compare the diagnostic values by using transthoracic echocardiography (ECHO) and multi-slice spiral CT coronary angiography (CTCA) for identifying coronary artery thrombosis in children with Kawasaki disease (KD). Methods: Total 97 KD children with coronary artery dilation complications in our hospital from June 2012 to December 2020 were included in the study. CTCA and ECHO were performed after over 1 month of illness. Results: Coronary artery thrombosis was found in 14 out of 97 patients. Among them, 10 were identified as positive by CTCA, 9 were identified as positive by ECHO, and 5 were identified as positive by both CTCA and ECHO. Conclusion: Both CTCA and ECHO can be used to diagnose coronary artery thrombosis. ECHO has advantage in identifying low-density thrombus, and CTCA is better for the clot in distal coronary artery. They can complement each other.

Enantio-separation of pregabalin by ternary complexation using trapped ion mobility spectrometry.

Rationale The rapid identification of small-molecule chiral drugs is challenging due to subtle structural differences. Different enantiomers of chiral drugs may produce inverse biological effects through their different pharmacokinetics. Therefore, it is highly desirable to distinguish the chirality of drug molecules. METHODS: The chirality of pregabalin was distinguished by studying the ion mobility spectra of the ternary non-covalent complexes formed with cyclodextrins (CDs), pregabalin, and alkali-earth cations using trapped ion mobility spectrometry (TIMS). The ternary non-covalent complex ions were determined by electrospray ionization of mixed solutions. The analyzed sample was simply mixed, without derivatization or sample pretreatment. The relative contents of pregabalin enantiomers were derived using a calibration curve method. RESULTS: The ion mobility spectra of several ternary non-covalent complexes formed with α-, ß-, and γ-CD, pregabalin, and alkali-earth cations were obtained. We compared their ability to distinguish the chirality of pregabalin. The best peak-to-peak resolution (Rp-p ) was estimated to be 2.20 for [2ß-CD + pregabalin + Sr]2+ , which can be ascribed as baseline separation. The derived relative contents for S-pregabalin were in agreement with the actual contents. CONCLUSIONS: A novel and convenient method for discriminating the chirality of the pregabalin molecule by TIMS was developed and optimized. The chirality of pregabalin was recognized by studying the ion mobility spectra of the ternary non-covalent complexes, such as [2ß-CD + pregabalin + Sr]2+ . This TIMS method could also be used to quantify the relative contents of pregabalin enantiomers.

Propafenone-Induced QRS Widening in a Child With Arrhythmogenic Right Ventricular Cardiomyopathy: A Case Report and Literatures Review.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a rare cardiac disease in children, and can lead to sudden cardiac death (SCD). Propafenone is classIC antiarrhythmic medication, and its side effects include cardiovascular compromise in the form of hypotension, bradycardia, ventricular dysrhythmias, QRS widening, and heart block. Propafenone has been reported causing QRS widening, but rarely in children. In this article, we presented a boy diagnosed with ARVC who meets diagnosis criteria based on typical symptoms, electrocardiograph (ECG), echocardiography (Echo), cardiac magnetic resonance imaging (CMRI), sudden death of first family member, and genetic mutation in desmosomal DSG2 gene. Antiarrhythmic drugs have been used for treating patients with ARVC, by eliminating or decreasing the occurring frequency of arrhythmias. As his ECG showed frequent premature ventricular contractions (PVC), he was prescribed with oral propafenone. One day after the drug treatment, he presented dizziness accompanied with significant QRS widening in ECG. His dizziness was improved when Propafenone dose was reduced, and resolved after sotalol replacement, with ECG recovered to nearly normal state of QRS. Propafenone may lead to QRS widening and increase the risk of ventricular tachycardia, and it may not reduce ARVC associated mortality. This report may serve as a precaution for clinicians when providing cares for ARVC patients.

Correlation Between Arrhythmia and the Prognosis in Children With EFE/LVNC/DCM.

Aim: To explore the correlation between different phenotypes of arrhythmia and the prognosis in children with EFE/LVNC/DCM. Methods: A total of 167 children with cardiomyopathy diagnosed and treated in Shengjing Hospital between January 2010 and May 2019 were evaluated. After patient screening, 31 patients with endomyocardial fibroelastosis (EFE), left ventricular non-compaction, or dilated cardiomyopathy with significant arrhythmias were selected. In addition, 42 children with primary EFE were selected to evaluate the prognosis with or without arrhythmia. Follow-up was undertaken 0, 1, 3, 6, 9, and 12 months after treatment. Results: We revealed the outcomes for five types of cardiomyopathy: EFE patients with Wolff-Parkinson-White syndrome B and supraventricular tachycardia, intraventricular block and complete left bundle branch block recovered slower than EFE patients with atrial flutter and atrial fibrillation, even slower than EFE with ventricular tachycardia. The average recovering time for LVEF and LVED in EFE patients without arrythmia was 10 months after diagnosis, while 76.9% (3/13 cases) of those with significant arrythmia hadn't recovered until 24 months after diagnosis. Three of patients died at 6, 7, and 6 and half years after diagnosis. Conclusion: The long-term prognosis in children with cardiomyopathy is associated with the type of arrhythmia and time of intervention. The prognosis of EFE patients with arrhythmia is worse than EFE patients without arrhythmia. Patients with Wolff-Parkinson-White syndrome B, especially a significantly widen QRS complex, carry a poor prognosis if radiofrequency ablation is not undertaken. CLBBB patients have similar poor prognosis if proper pacemaker is not implanted timely.

The non-covalent complexes of α- or γ-cyclodextrin with divalent metal cations determined by mass spectrometry.

Noncovalent complexes between cyclodextrin (CD) and divalent metal cations drew growing attentions due to their applications in the pharmaceutical industry for molecular recognition. In this study, gas-phase binding of noncovalent complexes between α-, or γ-CD and divalent metal cations was investigated by electrospray ionization mass spectrometry (ESI-MS), demonstrating the formation of 1:1 stoichiometric noncovalent complexes. The binding of the complexes were furtherly confirmed by collision-induced dissociation (CID) with tandem mass spectrometry. The CID revealed the fragmentation pattern were strongly dependent on the electronic configuration of the cations and the charge separation reaction frequently took place in the cyclodextrin-complexes with transition metal cations. For the non-covalent complexes of α-CD with Mg2+, Ca2+, Sr2+ or Ba2+ at a collision energy of 25 eV, the fragments attributed to [α-CD + cation-nGlucose unit]2+ were observed (named series A). However, for the γ-CD complexes with transition metal cations Co2+, Ni2+, Cu2+ or Zn2+, apart from fragments of series A, it were observed fragment ions of [γ-CD + cation-nGlucose unit]+ (named series B), together with the Glucose unit (m/z 163.2) and its products with loss of H2O (m/z 145.2 and 126.8). The CID performed at a collision energy from 10 to 50 eV showed that the binding strength of complexes increase in the order of [α-CD + Mg]2+, [α-CD + Ca]2+, [α-CD + Sr]2+ and [α-CD + Ba]2+. Through mass spectrometric titrations, the values of dissociation constant Kd (in µmol•L-1) for the complexes of α-CD with Ca2+ or Ni2+ were obtained, which were 4.30 and 4.26, respectively.

Investigation of noncovalent interactions between peptides with potential intrinsic sequence patterns by mass spectrometry.

RATIONALE: The conformation of a protein largely depends on the interactions between peptides. Specific and intrinsic sequence peptide patterns, such as DNA double helix backbones, may be present in proteins. A computational statistical deep learning method has supported this assumption, but it has not been experimentally proven. Mass spectrometry, as a fast and accurate experimental method, could be used to evaluate the interaction of biomolecules. The results would be of great value for further study of the mechanism of protein folding. METHODS: Several potential intrinsic peptides were chosen by the deep learning method, including seven groups of pentapeptides and five groups of nonapeptides. The noncovalent interactions between mixed polypeptides were investigated by electrospray ionization mass spectrometry (ESI-MS) in full-scan and collision-induced dissociation (CID) modes. Molecular dynamics and molecular mechanics Poisson-Boltzmann surface area (MD-MM/PBSA) analyses were also performed to support the results. RESULTS: The ESI-MS spectra showed that 11 of the 12 groups of mixed polypeptides formed binary and ternary complexes with relatively high stability. The binding between nonapeptide groups was stronger than that between pentapeptide groups according to the relative intensity. The binding energies calculated by the MM/PBSA binding energy tool also provided strong evidence for the combination of the complexes. Electrostatic interactions, hydrophobic interactions, and van der Waals forces were thought to stabilize the complexes according to the binding models. CONCLUSIONS: The results implied the formation of stable complexes between polypeptides and identified their noncovalent interactions, proving that specific sequences and combinations with relatively strong binding ability exist in potential intrinsic sequences of peptides in protein structures.

Fabrication and Tribological Properties of Copper Matrix Solid Self-Lubricant Composites Reinforced with Ni/NbSe2 Composites.

This paper presents a facile and effective method for preparing Ni/NbSe2 composites in order to improve the wettability of NbSe2 and copper matrix, which is helpful in enhancing the friction-reducing and anti-wear properties of copper-based composites. The powder metallurgy (P/M) technique was used to fabricate copper-based composites with different weight fractions of Ni/NbSe2, and tribological properties of composites were evaluated by using a ball-on-disk friction-and-wear tester. Results indicated that tribological properties of copper-based composites were improved by the addition of Ni/NbSe2. In particular, copper-based composites containing 15 wt.% Ni/NbSe2 showed the lowest friction coefficient (0.16) and wear rate (4.1 × 10-5 mm3·N-1·m-1) among all composites.

Antibiotic analysis using Electro-Filtering Paper Spray Ionization.

In this work, we analyzed the performance of the Electro-Filtering Paper Spray Ionization (EFSI) method for detecting compounds in unprocessed samples. A relatively rigid and electrically conductive copper filter was used as a substrate to insure sufficient and efficient sample-solvent extraction and to increase the conductivity for paper spraying. The method was demonstrated as applicable for indirect high-throughput analysis of large-volume unprocessed samples, which is not possible with conventional nanoESI or direct paper spray methods. The new method can generate different desired ion signals for a wide range of compounds by selecting different extraction solvents. Moreover, key parameters related to extraction efficiency were optimized in detail to obtain the most satisfactory extraction efficiency during antibiotic analysis. Finally, under optimal conditions, the EFSI method was successfully used to detect four antibiotics in animal products of egg, chicken, and chicken liver, exhibiting good reproducibility with calibration curves between 81.6% and 96.3%, and R2 values above 0.99. Recoveries of 75.0%ￚ94.6% were obtained for the four antibiotics. Hence, the proposed EFSI-MS is a successful, economical, rapid, and high-throughput method that is effective for both unknown and targeted extraction of unprocessed samples by mass spectrometric analysis.

Exploring halide anion affinities to native cyclodextrins by mass spectrometry and molecular modelling.

The binding affinities of cyclodextrins complexation with chlorine (Cl-), bromine (Br-) and iodine (I-), were measured by mass spectrometric titrimetry, and the fitting of the binding constants was based on the concentration measurement of the cyclodextrin equilibrium. The binding constants (lg Ka) for α-, ß- or γ-cyclodextrin with Cl- were 3.99, 4.03 and 4.11, respectively. The gas-phase binding affinity of halide anions for native cyclodextrins was probed by collision-induced dissociation. In collision-induced dissociation, the centre-of-mass frame energy results revealed that in the gas phase, for the same type of cyclodextrin, the stability of the complexes decreased in order: Cl > Br > I, and for the same halide anion, the binding stability of the complex with α-, ß- or γ-cyclodextrin decreased in the order: γ-cyclodextrin >ß-cyclodextrin > α-cyclodextrin. The density functional theory calculations showed that halide anion binding on the primary face had a lower energy than the secondary face and hydrogen bonding was the main driving force for complex formation. The higher stability of the γ-cyclodextrin complex with the Cl anion can be attributed to the higher charge density of the Cl anion and better flexibility of γ-cyclodextrin.

Quantifying non-covalent binding affinity using mass spectrometry: a systematic study on complexes of cyclodextrins with alkali metal cations.

RATIONALE: To date, the quantification of binding affinities for non-covalent complexes between cyclodextrin (CD) and alkali cations including Li(+) , Na(+) , K(+) , Rb(+) , and Cs(+) has not been investigated in detail by electrospray ionization mass spectrometry (ESI-MS) due to the unknown ionization efficiencies of the different species. In this study, the binding constants of CD-Cs(+) complexes were determined by an improved mass spectrometric titration methodology, which was based only on the peak intensities of equilibrium CD. Hence, the discrepancy of ionization efficiencies of CD, alkaline cation and their complex would not affect the measurement. Then the obtained lgKa values were provided as references for competitive ESI-MS. The binding constants for complexes of α-, ß- or γ-CD with Li(+) , Na(+) , K(+) and Rb(+) could be derived directly and quickly. METHODS: The lgKa values between α-, ß- or γ-CD and Cs(+) data were processed by curve fitting. These lgKa values were provided as references for competitive ESI-MS. In addition, linear fit equations for complexes of α-, ß- or γ-CD with Cs(+) were derived. Through the linear fit equations of competitive ESI-MS, the binding constants for complexes of Li(+) , Na(+) , K(+) and Rb(+) with α-, ß- or γ-CD were acquired. RESULTS: Results showed that the binding constant (lgKa ) values for the complexes of Cs(+) with α-, ß- and γ-cyclodextrins were 3.94, 3.88 and 3.80, respectively, revealing that the binding strength decreased with the increase in diameter of cyclodextrins. The competitive ESI-MS results showed a clear trend of decreasing affinity for complexes of cyclodextrins in the order of Li(+) , Na(+) , K(+) , Rb(+) . CONCLUSIONS: The binding constants of non-covalent cyclodextrin-alkali cation complexes have been systematically studied by an improved mass spectrometric titration and competitive ESI-MS. Also, the structural features of the complexes were discussed. Our results are valuable for better understanding of mechanisms driving inclusion chemistry under well-defined conditions.

Multiple mass analysis using an ion trap array (ITA) mass analyzer.

A novel ion trap array (ITA) mass analyzer with six ion trapping and analyzing channels was investigated. It is capable of analyzing multiple samples simultaneously. The ITA was built with several planar electrodes made of stainless steel and 12 identical parallel zirconia ceramic substrates plated with conductive metal layers. Each two of the opposing ceramic electrode plates formed a boundary of an ion trap channel and six identical ion trapping and analyzing channels were placed in parallel without physical electrode between any two adjacent channels. The electric field distribution inside each channel was studied with simulation. The new design took the advantage of high precision machining attributable to the rigidity of ceramic, and the convenience of surface patterning technique. The ITA system was tested by using a two-channel electrospray ionization source, a multichannel simultaneous quadruple ion guide, and two detectors. The simultaneous analysis of two different samples with two adjacent ITA channels was achieved and independent mass spectra were obtained. For each channel, the mass resolution was tested. Additional ion trap functions such as mass-selected ion isolation and collision-induced dissociation (CID) were also tested. The results show that one ITA is well suited for multiple simultaneous mass analyses.

Electrospinning preparation, characterization and magnetic properties of cobalt-nickel ferrite (Co(1-x)Ni(x)Fe2)O4) nanofibers.

Uniform Co(1-)(x)Ni(x)Fe(2)O(4) (x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) nanofibers with average diameter of 110 nm and length up to several millimeters were prepared by calcination of electrospun precursor nanofibers containing polymer and inorganic salts. The as-spun and calcined nanofibers were characterized in detail by TG-DTA, XRD, FE-SEM, TEM, SAED and VSM, respectively. The effect of composition of the nanofibers on the structure and magnetic properties were investigated. The nanofibers are formed through assembling magnetic nanoparticles with poly(vinyl pyrrolidone) as the structure-directing template. The structural characteristics and magnetic properties of the resultant nanofibers vary with chemical composition and can be tuned by adjusting the Co/Ni ratio. Both lattice parameter and particle size decrease gradually with increasing nickel concentration. The saturation magnetization and coercivity lie in the range 29.3-56.4 emu/g and 210-1255 Oe, respectively, and both show a monotonously decreasing behavior with the increase in nickel concentration. Such changes in magnetic properties can mainly be attributed to the lower magnetocrystalline anisotropy and the smaller magnetic moment of Ni(2+) ions compared to Co(2+) ions. Furthermore, the coercivity of Co-Ni ferrite nanofibers is found to be superior to that of the corresponding nanoparticle counterparts, presumably due to their large shape anisotropy. These novel one-dimensional Co-Ni ferrite magnetic nanofibers can potentially be used in micro-/nanoelectronic devices, microwave absorbers and sensing devices.

Studies on the non-covalent interactions between cyclodextrins and aryl alkanol piperazine derivatives by mass spectrometry and fluorescence spectroscopy.

The non-covalent complexes of alpha- and beta-cyclodextrins (alpha-, beta-CDs) with two aryl alkanol piperazine derivatives (Pipe I and Pipe II) have been studied by electrospray ionization mass spectrometry (ESI-MS) and fluorescence spectroscopy. The ESI-MS experimental results demonstrated that Pipe I can conjugate to beta-CD and form 1:1 or 1:2 stoichiometric non-covalent complexes, and Pipe II can only form 1:1 complexes with alpha- or beta-CD. Fluorescence spectra indicated that the fluorescence intensities of Pipe I and Pipe II can be enhanced by increasing the content of beta-CD. The mass spectrometric titration experiments showed that the dissociation constants K(d1) were 5.77 and 9.52 x 10(-4) mol L(-1) for the complexes of alpha-CD with Pipe I and Pipe II, respectively, revealing that the binding of alpha-CD-Pipe I was stronger than alpha-CD-Pipe II. The K(d1) and K(d2) values were 9.81 x 10(-4) mol L(-1) and 1.11 x 10(-7) (mol L(-1))(2) for 1:1 and 1:2 complexes of Pipe I with beta-CD, respectively. The K(d) values obtained from fluorescence spectroscopy were in agreement with those from ESI-MS titration.

Investigation of non-covalent complexes of glutathione with common amino acids by electrospray ionization mass spectrometry.

AIM: To study the non-covalent interaction between glutathione and common amino acids. METHODS: A stoichiometry of glutathione and common amino acids were mixed to reach the equilibrium, and then the mixed solution was investigated by electrospray ionization mass spectrometry (ESI-MS). The binding of the complexes was further examined by collision-induced dissociation (CID) in a tandem mass spectrometer as well as UV spectroscopy. To avoid distinct ionization efficiency discrepancy and signal suppression in the ESI-MS measurements, the interaction between glutathione (GSH) and glutamate (Glu) was quantitatively evaluated. The total concentrations and series of m/z of peak intensities for glutathione and amino acids could be achieved, respectively. Due to the existence of some oligomeric species arising from glutathione or amino acids, an improved calculation formula was proposed to calculate the dissociation constants of glutathione binding to amino acids. RESULTS: The ESI mass spectra revealed that glutathione could interact easily with Met, Phe, Tyr, Ser, or Ile to form non-covalent complexes. The binding of the complexes was further confirmed by CID experiments in a tandem mass spectrometer as well as UV spectroscopy. Moreover, an improved calculation formula was successfully applied to determine the dissociation constants of glutathione binding to Glu, His, or Gln. Finally, a possible formation mechanism for the complexes of glutathione with amino acids was proposed. CONCLUSION: The reduced polypeptide gamma-glutathione can interact with each of 8 common amino acids, including Glu, His, and Gln to form non-covalent complexes with different affinity.