ESI-MS Data Research Articles

Isolation and identification of three new isomer impurities in milbemycin oxime drug substance.

In an effort to identification of the unknown impurities in milbemycin oxime (MO) bulk drug, three impurities 1, 2 and 3 were isolated by two-dimensional (2 D) preparation method (Agilent Zorbax-C3 preparative column and Sepax Amethyst C18-H preparative column). Based on the extensive NMR analysis and ESIMS data, the structures of the three impurities were established as 14-desmethyl-14-ethyl-MO A4 (1), 24-desmethyl-24-ethyl-MO A4 (2) and 12-desmethyl-12-ethyl-MO A4 (3), respectively. They are the new isomer impurities of MO D and most likely originate from the oxidation and oximation of natural milbemycin homologs present in the original fermentation broth.

Spectroscopic Properties and Reactivity of a MnIII-Hydroperoxo Complex that is Stable at Room Temperature.

Manganese catalysts that activate hydrogen peroxide have seen increased use in organic transformations, such as olefin epoxidation and alkane C-H bond oxidation. Proposed mechanisms for these catalysts involve the formation and activation of MnIII-hydroperoxo intermediates. Examples of well-defined MnIII-hydroperoxo complexes are rare, and the properties of these species are often inferred from MnIII-alkylperoxo analogues. In this study, we show that the reaction of the MnIII-hydroxo complex [MnIII(OH)(6Medpaq)]+ (1) with hydrogen peroxide and acid results in the formation of a dark-green MnIII-hydroperoxo species [MnIII(OOH)(6Medpaq)]+ (2). The formulation of 2 is based on electronic absorption, 1H NMR, IR, and ESI-MS data. The thermal decay of 2 follows a first order process, and variable-temperature kinetic studies of the decay of 2 yielded activation parameters that could be compared with those of a MnIII-alkylperoxo analogue. Complex 2 reacts with the hydrogen-atom donor TEMPOH two-fold faster than the MnIII-hydroxo complex 1. Complex 2 also oxidizes PPh3, and this MnIII-hydroperoxo species is 600-fold more reactive with this substrate than its MnIII-alkylperoxo analogue [MnIII(OOtBu)(6Medpaq)]+. DFT and time-dependent (TD) DFT computations are used to compare the electronic structure of 2 with similar MnIII-hydroperoxo and MnIII-alkylperoxo complexes.

Synthesis, Spectroscopic Characterization, DFT, Molecular Docking, Catechol Oxidase Activity, and Anti-SARS-CoV-2 of Acylhydrazone Derivatives

In the present work, five pyrazole-hydrazone biomolecule ligands (L1–L5) were synthesized by condensation between 1H-pyrazole-3-carbohydrazide (2) and aromatic benzaldehydes. Their corresponding structures were elucidated employing NMR and FT-IR spectra and ESI-MS data. Li-Cu(II) complexes (i = 1–5) were evaluated for catecholase activity in situ at standard conditions. The findings disclose that the catecholase oxidation rate varies with the substituted functional groups in ligand and the anion type in the copper (II) salt. Catecholase activity results showed that the L(i = 1–5) -Cu(II)SO4 complexes exhibited efficient catalytic activity, and a maximum activity of 105 ± 42 µM.min−1 is obtained with L5-Cu(II)SO4. DFT and NBO calculations have been carried out to identify the global reactivity and the strength of interaction bonds between the donors and acceptors in L1–L5. The optimized structure of L1–L3 and L5 were found planar, while that of L4 is out of the molecular plan and forms a torsion angle of 18 degrees due to the presence of methoxy and hydroxyl group at meta and para. In L4, the 5-methyl-1H-pyrazole moiety. NBO findings show that the strongest interactions in L1–L5 are those involved in the electronic transition from π-bonding → π*-antibonding and LP → π*- antibonding molecular orbitals. Further, the anti-SARS-CoV-2 of L1–L5 are investigated by estimating their binding affinities into its binding. The docking results reveal that L1–L5 may act as SARS-CoV-2 main protease inhibitors with estimated binding energies in the −6.00 to −8.0 kcal.mol−1 range.

2-hydroxy-1- Naphthaldehyde Based Colorimetric Probe for the Simultaneous Detection of Bivalent Copper and Nickel with High Sensitivity and Selectivity.

A neoteric colorimetric probe based on 2-hydroxy-1-naphthaldehyde (PMB3) was designed and synthesized for the real-time as well as on-site naked-eye detection of Cu2+/Ni2+ ions. Various physicochemical methods were employed to characterize the probe, and its colorimetric response to different metal ions was meticulously investigated. The probe, PMB3, exhibited a sensitive colorimetric response to Cu2+/Ni2+ ions among other competing metal ions, culminating in a prominent colour change from colourless to yellow. The stoichiometry of the ligand metal complexes was ascertained to be in a 1:1 ratio using Job's plot analysis, which was further corroborated by ESI-MS data. With detection limits of 4.56µM for Cu2+ and 2.68µM for Ni2+, the method was effectively extended to real sample analysis, ensuring propitious results that closely aligned with the actual values.

Cu(I) binds to Zn7-MT2 via two parallel pathways.

Metallothionein proteins are essential for Cu(I) and Zn(II) homeostasis as well as heavy metal detoxification. The metallation properties of MT2 are of great interest due to their wide patterns of expression and correlation with multiple diseases including cancers, neurological disorders, and respiratory diseases. Use of isotopically pure 63Cu(I) and 68Zn(II) eliminates the complexity of the Cu, Zn-MT2 mass spectral peaks due to significant overlap of naturally abundant isotopes. This allows for the resolution of the precise Cu(I) and Zn(II) stoichiometries when both Cu(I) and Zn(II) are bound to MT2 at physiological pH as expected in vivo. Exact Cu: Zn ratios were determined from mass spectral simulations carried out for every point in the titration. We report that Cu(I) metallation of Zn7-MT2 can only be understood in terms of two pathways occurring in parallel with pathway ① resulting in Cu5Zn5-MT2 and Cu9Zn3-MT2. Pathway ② results in Cu6Zn4-MT2 and Cu10Zn2-MT2, which are the major products of the reaction. From the electrospray ionization (ESI)-mass spectral data we report a series of formation constants (KF) for species starting from Zn7-MT2 up to Cu11Zn2-MT2. Room temperature phosphorescence and circular dichroism (CD) spectra were measured in parallel with the ESI-mass spectrometry data allowing for the assignment of specific species to specific spectral bands. Through analysis of the CD spectral bands, we propose that Cu(I) binds to the β domain first to form a Cu5Zn1 cluster or Cu6 cluster with emission at 670 and 750nm, respectively, leaving the Zn4 cluster in the α domain.

Synthesis, X-ray crystallography, antimicrobial, molecular docking, and DFT study of bis-triazoles linked ampyrone

A new class of bis-triazoles linked with ampyrone molecules was synthesized from ampyrone-linked bis-alkyne with different benzyl azides under Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. All compounds were characterized by FTIR, 1H NMR, 13C NMR, and ESI-MS data. However, the structures of solid crystalline compounds 4a and 4h were finally supported by X-ray crystallographic data. In vitro, antimicrobial activity results of synthesized alkyne 2 and bis-1,2,3-triazoles 4a-4k showed that the incorporation of triazole units has augmented the antimicrobial activity of all compounds, except 4a for E. coli. Also, compound 4f was found potent against all bacterial strains (E. coli, S. aureus, and P. aeruginosa, each with MIC: 0.0178 µmol/mL) with superior efficacy to B. subtilis (MIC: 0.0089 µmol/mL) compared to standard antibacterial drug ciprofloxacin (MIC: 0.0094 µmol/m). Almost all synthesized triazoles showed superior potency to both fungal strains except 4a, 4g, and 4k against R. oryaze, C. albicans, and R. oryaze, respectively. Computational molecular docking and DFT results supported experimental antimicrobial results for improvement in the activity of all triazoles except 4a.

Protein Metalation by Medicinal Gold Compounds: Identification of the Main Features of the Metalation Process through ESI MS Experiments.

Gold compounds form a new class of promising anticancer agents with innovative modes of action. It is generally believed that anticancer gold compounds, at variance with clinically established platinum drugs, preferentially target proteins rather than nucleic acids. The reactions of several gold compounds with a few model proteins have been systematically explored in recent years through ESI MS measurements to reveal adduct formation and identify the main features of those reactions. Here, we focus our attention on a group of five gold compounds of remarkable medicinal interest, i.e., Auranofin, Au(NHC)Cl, [Au(NHC)2]PF6, Aubipyc, and Auoxo6, and on their reactions with four different biomolecular targets, i.e., the proteins HEWL, hCA I, HSA and the C-terminal dodecapeptide of the enzyme thioredoxin reductase. Complete ESI MS data are available for those reactions due to previous experimental work conducted in our laboratory. From the comparative analysis of the ESI MS reaction profiles, some characteristic trends in the metallodrug-protein reactivity may be identified as detailed below. The main features are described and analyzed in this review. Overall, all these observations are broadly consistent with the concept that cytotoxic gold drugs preferentially target cancer cell proteins, with a remarkable selectivity for the cysteine and selenocysteine proteome. These interactions typically result in severe damage to cancer cell metabolism and profound alterations in the redox state, leading to eventual cancer cell death.

Synthesis of the chelated axially chiral 1,2,3-Triazol-5-ylidene-Pd(II), Ni(II) and Ru(II) complexes and exploration of Bis-MIC-Pd(II) catalyst's application in coupling reaction

A series of chelated (R)-binaphthyl-2,2-diamine (BINAM) based chiral mesoionic Pd(II), Ni(II) and Ru(II) complexes, including three chelated bis-1,2,3-triazol-5-ylidene Pd(II) complexes, one chelated bis-1,2,3-triazol-5-ylidene Ni(II) complex and one chelated mono-1,2,3-triazol-5-ylidene Ru(II) complex, have been developed through either direct metalation (Ni(II) complex) or silver(I) transmetallation (Pd(II) and Ru(II) complexes) methods. These MIC-Pd(II), Ni(II) and Ru(II) complexes have been fully characterized by NMR, ESI-MS data, in which, the structures of (R)-5a, (R)-7, and (R)-9 have been further determined by X-ray diffraction studies of their single crystals. The catalytic activities of the chiral bis-MIC-Pd(II) complexes were explored in Pd(II)-catalyzed Suzuki–Miyaura coupling reaction, in which, bisaryl coupling products could be synthesized in good to excellent yields from the reactions of various aryl boronic acids with aryl iodides. Asymmetric coupling reaction was also tested, but no enantioselectivity was obtained. Scale–up reaction and mercury poisoning experiment were then performed. The catalytic activity of (R)-5a was partly inhibited by a large excess of elemental mercury, indicating the presence of heterogeneous Pd nanoparticles in the reaction mixture.

Two Benzocoumarin-based hydrazine chemodosimeters and their application in monitoring trace levels of hydrazine in soil, water, and urine samples

Hydrazine is used widely in various sectors. This intensified environmental degradation during storage, transit, and sewage disposal. Hydrazine, a category 2B toxin, can go into the body via the skin and nasal passages. It could permanently harm the body. Developing selective recognition mechanisms is critical. In this study, two reaction-based sensors, Coumarin- benzobromobutanoate (CnBr) and Coumarin-Chalcone (CnBC) were developed for the selective detection of N2H4. When exposed to N2H4, CnBr and CnBC in H2O/DMSO (1:1) both produced green fluorescence with highest emission at 528 nm and 532 nm, respectively. The absence of a buffer would greatly simplify and facilitate real-time sample sensing. The addition-cyclisation-elimination cascade reaction supports the sensing mechanism for both CnBr and CnBC, as confirmed by 1H NMR and ESI-MS data. Other ions, amines, and amino acids didn't affect the probes’ hydrazine detection. CnBr and CnBC detects N2H4 at 1.05 µM and 1.01 µM respectively. The probe's practical application was demonstrated by its capacity to sense hydrazine in different soil samples, real water, and urine samples.

Isomerization-induced fluorescence enhancement of two new viologen derivatives: mechanism insight and DFT calculations.

The dark-colored viologen radical cations are unstable in air and easily fade, thus greatly limiting their applications. If a suitable substituent is introduced into the structure, it will have the dual function of chromism and luminescence, which will broaden its application field. Here, Vio1·2Cl and Vio2·2Br were synthesized by introducing aromatic acetophenone and naphthophenone substituents into the viologen structure. The keto group (-CH2CO-) on the substituents is prone to isomerize into the enol structure (-CH[double bond, length as m-dash]COH-) in organic solvents, especially in DMSO, resulting in a larger conjugated system to stabilize the molecular structure and enhance fluorescence. The time-dependent fluorescence spectrum shows obvious keto-to-enol isomerization-induced fluorescence enhancement. The quantum yield also increased significantly (T = 1 day, ΦVio1 = 25.81%, ΦVio2 = 41.44%; T = 7 days, ΦVio1 = 31.48%, and ΦVio2 = 54.40%) in DMSO. The NMR and ESI-MS data at different times further confirmed that the fluorescence enhancement was caused by isomerization, and no other fluorescent impurities were produced in solution. DFT calculations show that the enol form is almost coplanar throughout the molecular structure, which is conducive to stabilizing the structure and enhancing fluorescence. The fluorescence emission peaks of the keto and enol structures of Vio12+ and Vio22+ were at 416-417 nm and 563-582 nm, respectively. The fluorescence relative oscillator strength of Vio12+ and Vio22+ enol structures is significantly higher than that of keto structures (f value changes from 1.53 to 2.63 for Vio12+ and from 1.62 to 2.81 for Vio22+), indicating stronger fluorescence emission of the enol structure. The calculated results are in good agreement with the experimental results. Vio1·2Cl and Vio2·2Br are the first examples of isomerization-induced fluorescence enhancement of viologen derivatives, which shows strong solvatofluorochromism under UV light, making up for the disadvantage that it is easy for a viologen radical to fade in air, and providing a new strategy for designing and synthesizing viologen materials with strong fluorescence.

Синтез производных N-(5-(метилсульфанил)- 4H-1,2,4-триазол-3-ил)пиридин-2-амина и их 1,2,4-триазиновых предшественников

A solvent-free interaction between 5-cyano-1.2.4-triazines and 5-methylsulfanyl-4H-1,2,4-triazol-3-amines has been studied. The structure of the product of ipso-substitution of cyano-group with the corresponding heterocyclic amine residue has been proven by 1Н NMR and ESI-MS data. Thus, in the 1Н NMR spectra a three-proton singlet at 2.61 ppm is present, which can be interpreted as the signal of the methylsulfanyl group protons. Subsequent transformation of 1,2,4-triazine scaffold of the resulting product into a pyridine one has been successfully per-formed under autoclave conditions. It has been found that methylsulfanyl group undergoes no transformations in both stages of synthesis. This fact is also proven by X-Ray crystallography data of the obtained functionalised bypyridines. According to the X-Ray crystallography data, compound 4 crystallizes as two crystallographically independent molecules in non-centrosymmetric space group P-1 with triclinic system. The crystal structure is formed by numerous intermolecular N∙∙∙H contacts between two crystallographically independent molecules of triazolylpyridine-2-amine. The 1Н NMR spectra of compound 4 contain two doublets of the new pyridine cycle at 7.37 and 7.61 ppm. Thus, properties of 5-methysulfanyl-4H-1,2,4-triazol-3-amine are different from these of its analogue with mercaptogroup at C5 position. Namely, in accordance to our previous results ipso-substitution of C5-cyanogroup of 1,2,4-triazine with moiety of the latter amine is accompanied by desulfurization reaction.

CHEMICAL CONSTITUENTS OF DICHLOROMETHANE EXTRACT FROM THE STEM BARK OF GARCINIA FAGRAEOIDES

The Garcinia genus belonging to the Clusiaceae family (Guttiferae) has been reported to be a rich source of polyisoprenylated benzophenones, xanthones and biflavonoids with various biological activities. Garcinia fagraeoides A.Chev is an evergreen hardwood tree found only in the north provinces of Viet Nam and Guangxi province of China. Its stem bark and leaves have been used in Vietnamese traditional medicine for treatment of malaria and dermatitis diseases. In our continuing studies on chemical constituents and biological activities from the genus Garcinia, the phytochemical of Garcinia fagraeoides’s stem bark collected from Thua Thien Hue province was investigated. Repeated chromatography steps over silica gel and Sephadex LH-20 of the dichloromethane partition from the methanol extract of Garcinia fagraeoides’s stem bark led to the isolation of five compounds including one polyisoprenylated benzophenone (isogarcinol (1)), two tetraoxygenated xanthones (rubraxanthone (2), a-mangostin (3)), ferulic acid (4), and pyromeconic acid (5). Their structures were elucidated mainly by analysis of their 1D, 2D NMR spectroscopy and ESI-MS data, and by comparison with reported data. The absolute configuration of isogarcinol (1) was determined by comparison of its experimental optical rotation and NMR data with the values of its stereoisomer. This is the first reported isolation of compounds 1-5 from the stem bark of Garcinia fagraeoides.

Manipulation of the cyanido-bridged Fe2W2 rhombus in the crystalline state: Co-crystallization, desolvation and thermal treatment

We present the new cyanido-bridged rhombus {[FeII(TPMA)]2[WV(CN)8]2}2– (Fe2W2) (TPMA = tris(2-pyridylmethyl)amine) cluster as a potential Secondary Building Block (SBB) for construction of polynuclear molecular materials. Fe2W2 is formed easily in self-assembly process between [FeII(TPMA)]Cl2 and TBA3[W(CN)8] in H2O/MeOH media, and was co-crystallized in (TBA)2{Fe2W2}⋅2H2O (1), and (TBA)2{Fe2W2}⋅mMeOH⋅nH2O (2) solvated salts, and in (TBA)2{Fe2W2}⋅H3PG⋅mMeOH⋅nH2O (3) (H3PG = phloroglucinol, 1,3,5-trihydroxybenzene; co-former) solvated co-crystal salt. Crystals of 1 undergo reversible SCSC transformation 1 ⇄ 1deh upon controlled dehydration and rehydration processes, whereas crystals of 2 reveal anisotropic thermal expansion during heating from 100 K to room temperature. Both processes involve changes of the selected intermolecular distances or local molecular reorientation involving intermolecular cation–anion and anion-anion contacts. [FeII(TPMA)(µ-NC)2] moieties reveal low-spin (LS) state in each case, however, conformation of the Fe2W2 rings varies from the “staggered” in 1, nearly “eclipsed” in 2 to fully “eclipsed” in 3, which is attributed to various hydrogen bond CNN⋅⋅⋅HO schemes involving the terminal cyanido ligands in [W(CN)8]3– and co-crystallizing molecules. In particular, the conformation of Fe2W2 in 3 is fully controlled by an unprecedented cyclic double hydrogen bond {Fe2W2}⋅⋅⋅H3PG synthon, H3PG forming a bridge over the Fe2W2 rhombus plane through binding the opposite [W(CN)8] corners. This arrangement is co-stabilized by close-to-parallel contacts of H3PG with TPMA walls protruding out of the rhombus plane. The Fe2W2 rhombus is stable in MeOH solution and shows notable affinity to H3PG in the gas phase, which was confirmed by ESI-MS data. UV–Vis-NIR spectroscopy discloses an optical FeII → WV MMCT transition and mixed-valence FeII//III-WV/IV electronic ground state.

Tying Up a Loose End: On the Role of the C-Terminal CCHHRAG Fragment of the Metalloregulator CueR.

The transcriptional regulator CueR is activated by the binding of CuI, AgI, or AuI to two cysteinates in a near‐linear fashion. The C‐terminal CCHHRAG sequence in Escherichia coli CueR present potential additional metal binding ligands and here we explore the effect of deleting this fragment on the binding of AgI to CueR. CD spectroscopic and ESI‐MS data indicate that the high AgI‐binding affinity of WT‐CueR is significantly reduced in Δ7C‐CueR.[111 Ag PAC spectroscopy demonstrates that the WT‐CueR metal site structure (AgS2) is conserved, but less populated in the truncated variant. Thus, the function of the C‐terminal fragment may be to stabilize the two‐coordinate metal site for cognate monovalent metal ions. In a broader perspective this is an example of residues beyond the second coordination sphere affecting metal site physicochemical properties while leaving the structure unperturbed.

The Use of Liquid Chromatography and Mass Spectrometry to Identify and Quantify Chemical Components in Tea Extracts

A fast, straightforward, efficient, and high throughput reverse-phase high-performance liquid chromatography and electrospray ionization mass spectrometry method has been developed to analyze tea extracts containing polyphenols. The polyphenols detected in green tea (GT), black tea (BT), and paradise tropical tea (PTT) were separated in 18 min at wavelengths 254 nm, 260 nm, and 280 nm with a gradient elution on the RP-HPLC system. Our approach detected, identified, and quantified three catechins in the tea extracts analyzed, and the response at 280 nm wavelength was the best. The ESI-MS data confirmed the fragmentation patterns of the catechins detected in the tea extract. The validation data showed that the limit of detection (LOD) and limit of quantitation (LOQ) of catechins ranged from 5.26 ± 0.02 to 36.44 ± 0.02 ppb, and 17.52 ± 0.03 to 121.45 ± 0.16 ppb, respectively, for six catechins studied. The standard addition calibration approach used to quantify the catechin content in the tea extract simultaneously showed that PTT has a higher catechin content than GT and BT. The content of polyphenols in GT, BT, and PTT are summarized. This approach holds great promise for quality control studies to quantify polyphenols in nutritional products.

Complex Mixture of Arvensic Acids Isolated from Convolvulus arvensis Roots Identified as Inhibitors of Radicle Growth of Broomrape Weeds

Broomrape weeds (Orobanche and Phelipanche spp.) are noxious parasites that infect crops using haustoria formed at the tip of their radicles. Dichloromethane extract obtained from the roots of Convolvulus arvensis strongly inhibits the radicle growth of broomrape weeds. A complex mixture of arvensic acids was isolated as the metabolites responsible of the inhibitory activity of C. arvensis extract against broomrape radicle growth via activity-guided fractionation and 1H NMR and ESI MS data. We showed that the exposure of broomrape seedlings to this arvensic acids mixture results in a strong phytotoxic effect on their radicles in four broomrape species infecting a wide range of crops worldwide. This discovery paves the way for the synthesis of new bioherbicides and could contribute to the development of efficient and sustainable management strategies for broomrape weeds, for which control in many crops is limited or non-existing.

Vanadium(IV) coordination complexes with excellent biological activities: a synthetic, characterization, and density functional theory approach

A set of new oxidovanadium(IV) complexes, [VO(4-NO2C6H4CH = CHCONHO)2] (1), [VO(4-NO2C6H4CH = CHCONHO)2(2–CNC5H4N)] (2) and [VO(4-NO2C6H4CH = CHCONHO)2(4-CNC6H4NH2)] (3), have been synthesized and characterized by different analytical techniques (magnetic susceptibility, molar conductivity, elemental analysis) and spectroscopic techniques, viz. FTIR, UV–vis, EPR, and mass spectrometry. The magnetic susceptibility, EPR, and ESI-MS data indicate that 1 exists as monomer and a distorted square pyramidal geometry around vanadium is ascertained. The electrochemical study of 1 has shown that it is electrochemically active exhibiting VOV/VOIV quasi-reversible redox couple. The biological activity of 1–3 has been studied against various pathogenic bacteria Staphylococcus epidermidis, Klebsiella pneumoniae, Staphylococcus aureus, Escherichia coli, Salmonella paratyphi, and Salmonella typhi, and fungi Brachypsectra fulva, Candida albicans, and Fusarium oxysporum by minimum inhibitory concentration (MIC) method. In some cases, the synthesized complexes showed superior antibacterial and antifungal activity than the well-known standard drugs tetracycline hydrochloride and fluconazole. The cytotoxicity of 1–3 has been studied on a human cervix carcinoma HeLa cell derivative (mammalian transformed cell line Hep2c) by MTT assay. Density functional theory (DFT) studies have been carried out to determine their relative free energy of formation and optimized molecular structures of 1–3. Time-dependent density functional theory (TD-DFT) based calculations have been performed to find out the frontier molecular orbitals and corroborate with the experimentally observed electronic transitions of 1. Other parameters like HOMO, LUMO energies, and global reactivity descriptors clearly support higher biological activity of 2 and 3 than 1.

Highly selective and sensitive fluorometric probe for Cd2+ ions based on 4-(quinolin-2-ylmethylene)aminoanisole Schiff base

Herein, we report a reversible and easy assembled fluorometric probe (4-(quinolin-2-ylmethylene)aminoanisole, QMAA) for the highly selective and sensitive detection of cadmium ion (Cd2+) in DMF solution with PBS buffer (0.01 M, pH = 7.30). The strong fluorescence response of QMAA to Cd2+ along with a bright blue fluorescence was mainly ascribed to the formation of the complex QMAA–CdCl2. The results show that the complexation can inhibit the CN isomerisation and photo–induced electron transfer (PET), and further lead to the occurrence of chelation fluorescence enhancement. The 1:1 stoichiometry of the complex between QMAA and cadmium ion was studied by fluorescence titration, Job’s plot analysis, 1H NMR, FT–IR, and ESI–MS data, and was further confirmed by the single crystal structure of the complex QMAA–CdCl2. Density functional theory (DFT) calculations have verified the mechanism of fluorescence enhancement. In addition, the limit of detection of QMAA for Cd2+ was as low as 0.1547 µM (at 10–7 M level), which was lower than the acceptable limit of Cd2+ level in drinking water defined by World Health Organization. The analog experiments about nature contamination of Cd2+ in real samples were finished.

New merosesquiterpenes from the Vietnamese sponge Hippospongia fistulosa and their cytotoxic activity

• Hippomeroterpenes A–B, two new merosesquiterpenes isolated from the sponge Hippospongia fistulosa . • Chemical structures were successfully determined by HR-ESI-MS and NMR spectroscopic methods. • Isolated compounds (100 μM) exhibited cytotoxic effects (8.3–36.3 %) on Hep-G2, MCF-7, SK-LU-1, and SK-Mel-2 cells. Two new merosesquiterpenes, hippomeroterpenes A and B ( 1 and 2 ), and four known compounds langconol B ( 3 ), 20-demethoxy-20-methylaminodactyloquinone D ( 4 ), smenospongidine ( 5 ), and smenospongic acid ( 6 ) were isolated from the sponge Hippospongia fistulosa . Their structures were determined by extensive analyses of HR ESI MS and NMR spectral data. At concentration of 100 μM, compounds 1 - 6 exhibited weak cytotoxic effects on Hep-G2, MCF-7, SK-LU-1, and SK-Mel-2 human cancer cells with percentages of dead cells ranging from 8.3 ± 0.3%–36.3 ± 1.5 %.

Spectroscopic and Theoretical Studies of Hg(II) Complexation with Some Dicysteinyl Tetrapeptides.

Tetrapeptides containing a Cys-Gly-Cys motif and a propensity to adopt a reverse-turn structure were synthesized to evaluate how O-, N-, H-, and aromatic π donor groups might contribute to mercury(II) complex formation. Tetrapeptides Xaa-Cys-Gly-Cys, where Xaa is glycine, glutamate, histidine, or tryptophan, were prepared and reacted with mercury(II) chloride. Their complexation with mercury(II) was studied by spectroscopic methods and computational modeling. UV-vis studies confirmed that mercury(II) binds to the cysteinyl thiolates as indicated by characteristic ligand-to-metal-charge-transfer transitions for bisthiolated S-Hg-S complexes, which correspond to 1 : 1 mercury-peptide complex formation. ESI-MS data also showed dominant 1 : 1 mercury-peptide adducts that are consistent with double deprotonations from the cysteinyl thiols to form thiolates. These complexes exhibited a strong positive circular dichroism band at 210 nm and a negative band at 193 nm, indicating that these peptides adopted a β-turn structure after binding mercury(II). Theoretical studies confirmed that optimized 1 : 1 mercury-peptide complexes adopt β-turns stabilized by intramolecular hydrogen bonds. These optimized structures also illustrate how specific N-terminal side-chain donor groups can assume intramolecular interactions and contribute to complex stability. Fluorescence quenching results provided supporting data that the indole donor group could interact with the coordinated mercury. The results from this study indicate that N-terminal side-chain residues containing carboxylate, imidazole, or indole groups can participate in stabilizing dithiolated mercury(II) complexes. These structural insights on peripheral mercury-peptide interactions provide additional understanding of the chemistry of mercury(II) with side-chain donor groups in peptides.