Investigation of Mixed Chiral Selectors of Different Metal Ion-L-Alanine Complex and β-Cyclodextrin on the Chiral Separation of Dansyl Amino Acids with Capillary Electrophoresis

Chiral separation of dausyl amino acids by capillary electrophoresis using mixed selectors of Mn(ll)-L-alanine complex and β-cyclodextrin (β-CD) was studied. Resolution was considerably superior to that obtained by using either Mn (Ⅱ)-L-alanine complex or β-CD alone. The effects of separation parameters, such as pH value of buffer solution, capillary temperature, the concentration of Mn (Ⅱ)-L-alanine complex, the types of CD and ligand on the migration times and resolutions were investigated. Six different transition metal complexes,Cu(Ⅱ), Zn(Ⅱ), Co(Ⅱ), Ni(Ⅱ), Hg(Ⅱ) and Cd(Ⅱ)-L-alanine complexes have been employed and compared with Mn(Ⅱ)complex. Differences in retention and selectivity were found.The substitution of Cu(Ⅱ), Zn(Ⅱ), Co(Ⅱ) and Ni(Ⅱ) for Mn(Ⅱ) resulted in a better chiral resolution while Hg(Ⅱ) and Cd(Ⅱ) showed poorer resolution abilities. The chiral separation mechanism was also discussed briefly.     

A Study on the Interaction of the DAS-K with Bovine Serum Albumin by On-line Ultrafiltration and Chemiluminescence

Potassium dehydroandrographolide succinate （DAS-K） has antibacterial and antiviral effects. It has been used widely for the treatment of virus pneumonia, malaria and respiratory infections. In this work, a novel flow-injection chemiluminescence （CL） method for the determination of DAS-K was proposed. The method is based on the reaction between DAS-K and hexacyanoferrate（III） in alkaline solution to give weak CL signal, which is enhanced by rhodamine B. The experimental conditions for the CL reaction were optimized and the possible reaction mechanism was discussed. Under the optimum conditions, the concentration of DAS-K is proportional to the CL intensity in the range of 0.1-80 μmol·L^-1 with a detection limit of 0.05 μmol·L^-1. The interaction of the DAS-K with bovine serum albumin by on-line ultrafiltration and flow-injection chemiluminescence was studied. The concentrations of unbound DAS-K from ultra filter tube were determined by the flow-injection CL method. The binding parameters were estimated by the Scatchard plot and Klotz plot. The proposed system proved that FIA-CL coupled with on-line ultrafiltration sampling was a fast and simple technique for the study of drug-protein interaction.     

Experimental and Theoretical Study of the Stability of the Complex Fisetin–Cu(II) and A Comparative Study of Free Ligand and Complex Interaction with Molecular Singlet Oxygen

In this work, the flavonol fisetin was selected in order to study its reactivity against Cu(II), a metal ion of interest in biological media and industry. The stoichiometry and apparent formation constant of the complex in ethanolic medium at 25°C were evaluated using spectrophotometric techniques. The resulting stoichiometry was a 1:1 ligand:metal complex, and a log K = 5.17 ± 0.12 was determined. Since two possible chelation sites can be proposed for the complex formation, quantum chemistry calculations were performed on these structures. Calculations suggest that the hydroxyl-keto site is more stable for the complex formation than the catechol site. Flavonoids could exert protection against oxidative damage caused by reactive oxygen species, and this biological activity could be affected by chelation with metal ions. This led us to perform a study on the interaction of both, free flavonoid and complex, with reactive oxygen species. Our results showed both compounds quench molecular singlet oxygen photogenerated with visible light, mainly in a physical fashion. In order to analyze a possible protective effect of flavonoid and its complex against oxidative damage in biological environments, the amino acid tryptophan was selected as a model oxidation system. Free flavonoid does not have a marked protective effect, whereas its complex showed a relevant protective effect.     

Interplay between Molecular Recognition and Redox Properties: A Theoretical Study of the Inclusion Complexation of β-Cyclodextrin with Phenothiazine and its Radical Cation

The PM3 molecular orbital method was employed in the conformational analysis of the inclusion complexation of -cyclodextrin with phenothiazine and its radical cation from a complete and unrestricted geometry optimization. Ab initio calculations at the level of HF/3-21G(d) and B3LYP/3-21G(d) were utilized to determine the electronic structures of the host, guest and their complexes. The results indicated that the complexation of -cyclodextrin with the phenothiazineradical cation was significantly more favorable than that with the neutral one, in good agreement with the experimental observation. The charge-transfer interaction was proposed as a physical reason for such behavior. It is suggested that caution should be given when extrapolating one oxidation state behavior to the supramolecular systems in their other oxidation states.     

Study on the complexation of isoquercitrin with β-cyclodextrin and its derivatives by spectroscopy

The inclusion complexes of isoquercitrin (IQ) with cyclodextrins (CDs) including β-cyclodextrin (β-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD) and dimethyl-β-cyclodextrin (DM-β-CD) have been investigated using the methods of steady-state fluorescence, UV-vis absorption and induced circular dichroism. The stoichiometric ratio of the three complexes was found to be 1:1 and the stability constants (K) were estimated from spectrofluorometric titrations, as well as the thermodynamic parameters. Maximum inclusion ability was measured in the case of DM-β-CD due to the increased hydrophobicity of the host cavity, followed by HP-β-CD and β-CD. The effect of pH on the complexation process was also quantitatively assessed. IQ exists in different molecular forms depending on pH and β-CDs were most suitable for inclusion of the neutral form of IQ. The phase-solubility diagrams obtained with β-CD, HP-β-CD and DM-β-CD were all classical A_L type. And DM-β-CD provided the best solubility enhancement, 12.3-fold increase compared to 2.8- and 7.5-fold increase for β-CD and HP-β-CD. The apparent stability constants obtained from the solubility data at 25 °C were comparable with those obtained from the fluorescence assays. Moreover, ¹H NMR was carried out, which revealed that the IQ favorably inserted into the inner cavity from the chromone part instead of the phenyl part, which was in agreement with molecular modeling studies.     

Molecular Mechanics Study of the Complexes of β-Cyclodextrin with 4-(dimethylamino)benzonitrile and Benzonitrile

Molecular Mechanics calculations with the Tripos Force Field were employed to study the complexation of 4-(dimethylamino)benzonitrile (DMABN) and/or benzonitrile (BN) with -cyclodextrin (CD). The systems studied have 1 : 1 (DMABN : CD and BN : CD), 2 : 2 (DMABN : CD) and 1 : 1 : 2 (DMABN : BN : CD) stoichiometries. Evidence for the formation of such complexes, binding constants and other thermodynamic parameters were extracted from the analysis of the steady state fluorescence measurements performed in a previous work. The Molecular Mechanics study, based on the energy changes upon guest-host approaching, was performed in vacuo and in the presence of water as a solvent. Results show that the driving forces for 1 : 1 complexation are mainly dominated by non-bonded van der Waals host : guest interactions. However, the driving forces for association between 1 : 1 complexes to give 2 : 2 homo- or 1 : 1 : 2 heterodimers are dominated by non-bonded electrostatic interactions. Head-to-head electrostatic interactions between CDs, which are presumably due to the hydrogen bonding formation between secondary hydroxyl groups of CDs, are responsible for most of the stability of the dimers.     

Structural Features of the β-CD Complexes with Naringin and its Dihydrochalcone and Aglycon Derivatives by 1H NMR

The -CD inclusion complexes of naringin 1, naringin dihydrochalcone 2 and the aglycon of naringin dihydrochalcone 3 have been investigated by ¹H NMR spectroscopy. Continuous variation plots show the stoichiometry of all complexes to be 1 : 1. Thestructure of complexes was determined from 2D ROESY and 1D ROE experiments. For 1 and 2 the inclusion involves the aromatic rings leaving the disaccharide unit -L-Rha-(1-2)--D-Glc outside the -CD cavity. For naringin 1 the inclusion occurs preferentially from the wider rim of the -CD truncated cone with the terminal phenolic ring deeply inserted into the -CD cavity while for naringin dihydrochalcon 2 it occurs from the side of the -CD narrower rim. The -CD/aglycon 3 complex exists as an equilibrium of the two inclusion modes.     

Uncovering the Shuttle Effect in Organic Batteries and Counter-Strategies Thereof: A Case Study of the N,N′-Dimethylphenazine Cathode

The main drawback of organic electrode materials is their solubility in the electrolyte, leading to the shuttle effect. Using N,N′-dimethylphenazine (DMPZ) as a highly soluble cathode material, and its PF₆⁻ and triflimide salts as models for its first oxidation state, a poor correlation was found between solubility and battery operability. Extensive electrochemical experiments suggest that the shuttle effect is unlikely to be mediated by molecular diffusion as commonly understood, but rather by electron-hopping via the electron self-exchange reaction based on spectroscopic results. These findings led to two counter-strategies to prevent the hopping process: the pre-treatment of the anode to form a solid–electrolyte interface and using DMPZ salt rather than neutral DMPZ as the active material. These strategies improved coulombic efficiency and capacity retention, demonstrating that solubility of organic materials does not necessarily exclude their applications in batteries.     

Structural Characterization of Missense Mutations Using High Resolution Mass Spectrometry: A Case Study of the Parkinson’s-Related Protein,DJ-1

Missense mutations that lead to the expression of mutant proteins carrying single amino acid substitutions are the cause of numerous diseases. Unlike gene lesions, insertions, deletions, nonsense mutations, or modified RNA splicing, which affect the length of a polypeptide, or determine whether a polypeptide is translated at all, missense mutations exert more subtle effects on protein structure, which are often difficult to evaluate. Here, we took advantage of the spectral resolution afforded by the EMR Orbitrap platform, to generate a mass spectrometry-based approach relying on simultaneous measurements of the wild-type protein and the missense variants. This approach not only considerably shortens the analysis time due to the concurrent acquisition but, more importantly, enables direct comparisons between the wild-type protein and the variants, allowing identification of even subtle structural changes. We demonstrate our approach using the Parkinson’s-associated protein, DJ-1. Together with the wild-type protein, we examined two missense mutants, DJ-1_A104T and DJ-1_D149A, which lead to early-onset familial Parkinson’s disease. Gas-phase, thermal, and chemical stability assays indicate clear alterations in the conformational stability of the two mutants: the structural stability of DJ-1_D149A is reduced, whereas that of DJ-1_A104T is enhanced. Overall, we anticipate that the methodology presented here will be applicable to numerous other missense mutants, promoting the structural investigations of multiple variants of the same protein.

Open image in new window

Graphical Abstract ?

     

Identification of Indigo Dyes in Painting Layers by Pyrolysis Methylation and Silylation. A Case Study: “The Dinner of Emmaus” by G. Preti

Reactive pyrolysis, under methylating or silylating conditions, in combination with gas chromatography-mass spectrometry (GC-MS) was evaluated as an analytical method for the detection of indigo dyes in painting layers. Samples with the addition of tetramethylammonium hydroxide (TMAH) or hexamethyldisilazane (HMDS), for pyrolysis/methylation and pyrolysis/silylation experiments, respectively, were pyrolysed at 600 °C by means of a heated filament pyrolyser and the evolved products were analysed on-line by GC-MS. Methyl and silylated pyrolytic markers, related to 2-aminobenzoic acid and the indoxyl moiety, were established from the analysis of synthetic indigo, neat or as a pigment of artificial painting layers containing a siccative oil. The occurrence of these markers was investigated in a real sample, taken from the painting The dinner of Emmaus by G.Preti (XVII century), in order to identify the blu pigment. Positive identification of indigo was achieved by pyrolysis/silylation and confirmed by RAMAN spectroscopy.     

A Molecular Modeling for the Complexation of Cyclobis(paraquat-p-phenylene) with Substituted Benzenes and Biphenyls

The molecular recognition of cyclobis(paraquat-p-phenylene), 14+, has drawn great attention recently, due to its important applications in the design and synthesis of electrochemically and chemically switchable rotaxanes, photoactive rotaxanes, and other molecular devices1. Usually, this type of molecular recognition was investigated with the methods including X-ray, NMR, UV, and IR. However, since these methods usually have difficulties in providing a detailed understanding of the energeti…     

Study on the inclusion interaction of methylated-β-cyclodextrins with albendazole by spectrofluorimetry and its application

The inclusion interaction between three types of methylated-β-cyclodextrins （Me-β-CDs） and albendazole （ABZ） was studied by spectrofluorimetry. The result showed that Me-β-CDs reacted with ABZ to form an inclusion complex, 1： 1 stoichiometry for Me- β-CDs-ABZ complex was established and its association constant have been determined from fluorescence data by Benesi- Hildebrand＇s method （double reciprocal plots）. It was noted that 2,6-DM-β-CD exhibited stronger binding ability than other Me-β- CDs. Based on the significant enhancement of fluorescence intensity of inclusion complex, a simple and highly sensitive fluorimetric method is proposed for the determination of ABZ in the presence of 2,6-DM-β-CD. The proposed method was successfully applied to the determination of ABZ in tablets and human urine.     

Relative Stabilities and Molecular Structures of the Geometrical Isomers of α,α′-Dioxasubstituted Cycloalkylidenecycloalkanes. A DFT Study

The relative stabilities and molecular structures of the geometrical isomers of seven ,-dioxa derivatives of cycloalkylidenecycloalkanes with 3to 6-membered rings have been studied by DFT calculations at the B3LYP/6-31G* level of theory. In each case, the E form was calculated to have the lower total energy. The relative energy of the Z isomer proved to increase regularly with increasing sizes of the two heterocyclic rings, ranging from 1.1 to 13.8 kJ mol^–1 on going from the 3,3to the 6,6-membered rings. Intermediate values of the relative energy were calculated for the Z forms of compounds containing two dissimilar rings. The relative energy of the Z isomer was found to be proportional to d ^–9.3, where d = the distance separating the two O atoms of the Z compound. The molecular structures, electric dipole moments, and atomic charges on the O atoms are also discussed.     

Separation and Concentration of Rare Earths by Recycling Liquid–Liquid Chromatography with Multiple Sample Injection: A Computational Study

Our computational studies into the separation of two- and three-component mixtures of rareearth salts by recycling liquid–liquid chromatography (RLC) with multiple sample injection show that this method considerably enhances metal separation efficiency and makes it possible to concentrate one of the components of mixture.     

A novel reversed-phase HPLC method for the determination of urinary creatinine by pre-column derivatization with ethyl chloroformate: comparative studies with the standard Jaffé and isotope-dilution mass spectrometric assays

Creatinine is an important biomarker for renal function diagnosis and normalizing variations in urinary drug/metabolites concentration. Quantification of creatinine in biological fluids such as urine and plasma is important for clinical diagnosis as well as in biomonitoring programs and urinary metabolomics/metabonomics research. Current methods for creatinine determination either are nonselective or involve the use of expensive mass spectrometers. In this paper, a novel reversed-phase high-performance liquid chromatographic (HPLC) method for the determination of creatinine of high hydrophilicity by pre-column derivatization with ethyl chloroformate is presented. N-Ethyloxycarbonylation of creatinine significantly enhanced the hydrophobicity of creatinine, facilitating its chromatographic retention as well as quantification by HPLC. Factors governing the derivatization reaction were studied and optimized. The developed method was validated and applied for the determination of creatinine in rat urine samples. Comparative studies with isotope-dilution mass spectrometric method revealed that the two methods do not yield systematic differences in creatinine concentrations, indicating the HPLC method is suitable for the determination of creatinine in urine samples.

Study on the Inclusion Interactions of β‐Cyclodextrin and Its Derivative with Clomipramine by Spectroscopy and Its Analytic Application

Abstract

The inclusion interactions of β‐cyclodextrin (β‐CD) and its derivative, namely hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD) with clomipramine (CLOM) have been investigated. The guest molecule was clomipramine and inclusion complexes were characterized by UV, ¹H NMR, ¹³C NMR, and 2D NMR spectroscopy. The main factors affecting the inclusion interaction were discussed in detail. The inclusion complexation behaviour of cyclodextrins with clomipramine was studied in an aqueous buffer solution of pH 4 and pH 5 at room temperature. According to the continuous variation method (Job's plot) applied to spectroscopy measurements a 1∶1 stoichiometry has been proposed for the complexes. Based on the significant enhancement of absorption intensity of clomipramine, a sensitive UV spectrophotometric methods with high sensitivity and selectivity were developed for determination of substance in bulk aqueous solution in the presence of β‐CD and HP‐β‐CD. The apparent association constant of the complex was 9.42 · 10³ mol^?1 L and 9.58 · 10³ mol^?1 L and the linear range was 17.6–70 µg mL^?1 with a correlation coefficient of 0.9997 and a relative standard deviation (R.S.D.) of 0.97% and 1.02% using β‐CD and HP‐β‐CD, respectively. There was no interference from the excipients normally used in tablets and capsules. The proposed methods were successfully applied to the analysis of clomipramine in pharmaceuticals with satisfactory results.     

A Computational Study of Asymmetric Hydrogenation of 2-Phenyl Acrylic Acids Catalyzed by a Rh(Ⅰ)Catalyst with Ferrocenyl Chiral Bisphosphorus Ligand:The Role of Ion-Pair Interaction

Main observation and conclusion Asymmetric hydrogenation reaction is one of the most efficient synthetic methods to form useful chiral compounds for synthetic c...     

A Comparison Study on the Interaction of Sunset Yellow and β-Carotene with Bovine Serum Albumin

在模拟生理pH条件（pH=7．4）下,采用多种光谱法研究日落黄和β-胡萝卜素与BSA的相互作用,并比较两者与BSA相互作用过程的差异性．通过荧光光谱法和紫外吸收光谱法确定了日落黄和β-胡萝卜素对牛血清白蛋白的荧光猝灭机制,采用Stern—Volmer、双对数方程和热力学公式求出相互作用的猝灭常数、结合常数配、结合位点数月和作用力类型．结果表明：日落黄和β-胡萝卜素对BSA的猝灭属于静态猝灭,两者与BSA的民都达到10^5L／mol,结合位点数均为1,日落黄与BSA的作用力以静电引力为主,而β-胡萝卜素则是通过氢键和范德华力与BSA作用．通过红外光谱法和圆二色谱法研究了二者对BSA构象的影响,结果表明,日落黄与BSA作用的过程中,会引起BSA二级结构的改变,而β-胡萝卜素则对BSA的构象基本不产生影响．