ESI Mass Spectra Research Articles

A novel chemical probe based on the salamo-Co(II) complex for the highly selective fluorescence detection of tyrosine

A new and rare Salamo-Co(II) complex probe L-Co2+ was designed and synthesised. The structure of the [Co3(L)2(μ-OAc)2(MeOH)2]⋅2H2O complex was obtained by X-ray diffraction experiments. Three Co(II) atoms are in a line in the complex, and all Co(II) atoms form a 6-coordinated octahedral configuration. The probe L-Co2+ selectively recognises tyrosine in DMF/H2O (8:2, v/v). Upon addition of tyrosine, the fluorescence intensity of L-Co2+ was enhanced in a short time. The probe showed high selectivity and sensitivity for tyrosine, detection limit is 4.27 × 10−8 M. The recognition mechanism of probe L-Co2+ for Tyr was inferred by FT-IR spectra, UV spectroscopy, ESI mass spectra and DFT calculations. Finally, due to the simplicity and specificity of the identification process, the probe was also subjected to a test paper experiment and a milk assay.

Transition metal (II) complexes of 2-(2,5-dimethoxy-benzylidene)hydrazine-1-carbothioamide: synthesis, characterization and their biological evaluation

<p>The current study involved synthesizing Schiff base ligand, 2-(2,5-dimethoxybenzylidene)hydrazine-1-carbothioamide (L) by combining thiosemicarbazide (Th) with 2,5-dimethoxybenzaldehyde (2,5-Dmb), and synthesizing its novel complexes of Co(II), Ni(II), and Cu(II) ions. Elemental analysis, conductance measurements, magnetic susceptibility, molecular weight estimations, FT-IR, ESI-Mass, and UV-Vis spectrum analysis have confirmed the ligand and its metal complexes. The experiment data demonstrated that the ligand binds to the metal atom in a bidentate manner through the N and S atoms. The cytotoxic activity of the synthesized complexes was tested against brine shrimp. All the complexes showed cytotoxic activity; among them, ligands showed a better result with LC<sub>50</sub> value of 36.93 µg/mL than complexes. Using disc diffusion, the antibacterial action was tested against two Gram-positive bacteria and two Gram-negative bacteria. [Ni(L)<sub>2</sub>] was more effective against <em>E. coli</em> than the other compounds. The results verified the formation of the novel complexes, and the Ni-complex has the potential to generate novel antibacterial compounds for use in biomedical applications.</p>

Design, Synthesis, Characterization and Biological Evaluation of Novel Depsides as Potential Antibacterials

Sixteen depsides were synthesized to screen for their antibacterial activity. All of them were reported for the first time. Their chemical structures were clearly determined by FTIR, 1H NMR, ESI mass spectra. All the compounds were assayed for antibacterial and antifungal activities against two Gram-positive bacterial strains (Bacillus subtilis ATCC 6633) and (Staphylococcus aureus ATCC 29747)and two gram-negative bacterial strains (Escherichia coli ATCC 8739) and (Pseudomonas aeruginosa ATCC 25619) the MIC and zone of inhibition calculated by cup-plate method and serial dilution method and two fungal strains (Aspergillus niger ATCC 90292) and (Candida albicans ATCC 24433)by the micro-broth dilution method.Compound2-(2- propoxy -2-oxoethylphenyl (4-methoxyphenyl)acetate(P6) and 2-(2- propoxy-2-oxoethylphenyl(4-methylphenyl)acetate(P7) showed powerful antibacterial activities against E. coli with MIC of 2.0 40mg/ml while compound 2-(2- propoxy -2-oxoethylphenyl(4-methylphenyl)acetate (P7) and 2-(2- propoxy -2-oxoethylphenyl and (3-methoxyphenyl)acetate (P8) exhibited significant antibacterial activities against B. subtilis with MIC of 3.12 40mg/ml, which were superior to the positive controls amoxycillin trihydrate and ciprofloxacin HCl, respectively and compound 2-(2- propoxy -2-oxoethyl) phenyl 4-methylbenzoate (P8) was found to have highest antifungal activity against Candida albicans ATCC 24433. On the basis of the biological results, quantitative structure activity relationships were discussed.
 Keywords: Depsides, Antibacterials, Antifungal, Quantitative structure activity relationship.

Imidazole-centred cupric ions sensor: Experimental validation, theoretical understanding, and zebrafish bioimaging

In this study, we have developed an imidazole centered fluorescent probe 3-(2-(2-(5-bromo-2-hydroxyphenyl)-4,5-diphenyl-1H-imidazol-1-yl)thiazol-4-yl)-6-chloro-2H-chromen-2-one (SICT), achieving exceptional selectivity for Cu2+ ion detection. These probes exhibit rapid responsiveness (109 nM detection limit) and strong binding constants (0.214 × 105 M−1). Employing an aqueous ethanol system, we assessed their sensing capabilities through both in vitro and in vivo studies, using zebrafish as our model organism. Notably, the SICT probe displays a high quantum yield of 0.62 and follows a 1:1 binding mechanism with Cu2+ ions, validated by Job's plot and ESI-Mass spectrum analyses. Furthermore, our probe demonstrates minimal cytotoxicity in both in vitro (MDA-MB-231 cells) experiments. These promising results motivate us to apply the SICT probe for intracellular Cu2+ ion tracking in zebrafish embryos, showcasing its potential in diverse fields like biomedicine and environmental monitoring.

Fluorescent imidazole derived sensor for selective in vitro and in vivo Fe2+ detection and bioimaging in zebrafish with DFT studies

Herein, we have developed imidazole derivatized fluorescent probes IM-1 and IM-2 for extremely selective detection of Fe2+ with rapid response (LOD: 3.245 μM for IM-1 and 0.297 μM for IM-2) and excellent binding constants (0.214 × 105 M−1 and 1.004 × 105 M−1). Aqueous ethanol system was employed to assess the sensing potency of the probes both in vitro and in vivo in zebrafish is the main highlight of this work. The synthesized fluorophores possess admirable quantum yields of 0.61 and 0.78. The 1:1 binding mechanism of ligands with Fe2+ ions is supported by Job's plot and ESI-Mass spectrum. The synthesized probes demonstrated limited cytotoxicity both in vitro (MDA-MB-231 cells) and in vivo (zebrafish, Danio Rerio) studies. These results prompted us to employ the probes IM-1 and IM-2 to trace out intra cellular Fe2+ ions in zebrafish embryos.

Solid-liquid-vapour equilibrium conditions of tetra-iso-amyl ammonium bromide (TiAAB) semiclathrates formed from H2

The tetra-iso-amyl ammonium bromide (TiAAB) is synthesized according to Menschutkin's reaction and the fundamental characterization of TiAAB is conducted using ESI mass spectrum and 13C NMR spectra, respectively. Using an isochoric equilibrium cell the H2 semi-clathrates were formed in the presence of three different TiAAB solutions; a 15 wt% solution, a 30 wt% solution, and a 45 wt% solution. Using TiAAB allows for the formation of H2 semi-clathrates at much milder P-T conditions as compared to other quaternary ammonium salts such as TBAB, TBAN, TBPB, and TBAF. The mixed H2/TiAAB semi-clathrates were found to form over a narrow range of temperatures from 303 K to 304 K, and the pressure ranged from atmospheric pressure to above 4 MPa. The experimental results obtained in the current work contribute to developing a method to store hydrogen gas with mixed H2/TiAAB semi-clathrate.

Mutual induced‐fit controlled signal amplification of hydrogen‐bonded capsule formation

AbstractMutual induced‐fit is well known process in biological system and playing crucial role in enzymatic catalysis, peptide‐bond synthesis, protein synthesis, etc…, proceeds by mutual interactions of two or more than two components. However, in an artificial system, to mimic such process is challenging, especially by purely organic components. In this report, we have shown importance of mutual induced‐fit in signal amplification of hydrogen‐bonded capsule formation. Two different types of highly flexible ligands (one N‐bridged and another triazine‐bridged) are used. N‐bridged tripodal ligand acting as clip over the adduct obtained from triazine‐bridged ligand, bringing the resultant adduct in the cone‐shape conformation. The resulting cone‐shape conformation undergo solvent polarity dependent hydrogen‐bonded capsule formation as a sole product. In absence of N‐bridged tripodal ligand, only 50% capsule formation is observed through 1H NMR at 100 mM concentration. However, in the presence of N‐bridged tripodal ligand, organic components undergo mutual interactions to opt the cone‐shape conformation and 100% capsule is formed (independent of concentration). The complete process is characterized by IR‐spectra, 1H and 13C NMR spectra, concentration dependent 1H NMR titration spectra, 1H‐1H COSY, 1H‐1H NOESY, DOSY NMR, high resolution ESI mass spectra, and also by energy‐minimized structure.

Identification of metabolites from complex mixtures by 3D correlation of 1H NMR, MS and LC data using the SCORE-metabolite-ID approach

Not only in metabolomics studies, but also in natural product chemistry, reliable identification of metabolites usually requires laborious steps of isolation and purification and remains a bottleneck in many studies. Direct metabolite identification from a complex mixture without individual isolation is therefore a preferred approach, but due to the large number of metabolites present in natural products, this approach is often hampered by signal overlap in the respective 1H NMR spectra. This paper presents a method for the three-dimensional mathematical correlation of NMR with MS data over the third dimension of the time course of a chromatographic fractionation. The MATLAB application SCORE-metabolite-ID (Semi-automatic COrrelation analysis for REliable metabolite IDentification) provides semi-automatic detection of correlated NMR and MS data, allowing NMR signals to be related to associated mass-to-charge ratios from ESI mass spectra. This approach enables fast and reliable dereplication of known metabolites and facilitates the dynamic analysis for the identification of unknown compounds in any complex mixture. The strategy was validated using an artificial mixture and further tested on a polar extract of a pine nut sample. Straightforward identification of 40 metabolites could be shown, including the identification of β-d-glucopyranosyl-1-N-indole-3-acetyl-N-l-aspartic acid (1) and Nα-(2-hydroxy-2-carboxymethylsuccinyl)-l-arginine (2), the latter being identified in a food sample for the first time.

In vitro and in vivo nanomolar Hg2+ detection in live cells and zebrafish, theoretical studies

A worldwide contaminant that has an impact on both environment and human health is mercury. Neurological disorders are eventually caused by mercury bioaccumulation in the nervous system and ultimately affecting other parts of the body. It has been an indispensable task to sensitively and selectively sense mercury in order to control the damage. In this regard, an effectual chemosensor for the trace detection of Hg2+ ions has been synthesized appertaining to imidazole-coumarin cores with extremely lower cytotoxicity (15±0.15 µM).The sensing efficiency of IMCT was assessed in aqueous acetonitrile medium. The probe IMCT demonstrated its high sensitivity towards Hg2+ ions with a limit of detection (LOD) of 23.64 nM, which is extremely lower than the World Health Organization (WHO) international norms acceptable mercury level in drinking water (6.0 µg/L). ESI-Mass spectrum and Job’s result substantiates the complex formation of IMCT with Hg2+in 1:1 ratio. In vitro and in vivo imaging was carried out in zebrafish and human cancer cells. These results illustrate the effectiveness of IMCT as a fluorescent biomarker for Hg2+ has been effectively demonstrated.

Co(II), Ni(II), Cu(II), and Zn(II) complexes with Benzothiazole Schiff base ligand: Preparation, Spectral Characterization, DNA Binding, and In Vitro Cytotoxic Activities

2-((E)-(6-ethoxybenzo[d]thiazol-2-ylimino)methyl)-4-chlorophenol (2-EBTMCP) of Schiff base (HL) which would be produced from 6-ethoxy-2-amino benzothiazole and 5-Chloro-2-hydroxybenzaldehyde was prepared and characterised using 1H NMR, Infrared, ESI-mass spectra, elemental analysis, SEM, EDX and powder XRD spectroscopic methods. Its complexes with Ni(II), Co(II), Zn(II) and Cu(III) were made, isolated as solid compounds, and identified by various spectroscopic methods. The research of metal complexes here includes the intercalative form of DNA binding studies with CT (Calf thymus) DNA. The UV–Vis electron absorption spectroscopy approach has been used to explore the DNA-binding capabilities of transition metal complexes. Additionally, a MTT assay was performed to investigate their in vitro cytotoxic potential.

A rhodamine based chemodosimeter for the detection of Group 13 metal ions.

A new rhodamine derivative, HL-CIN, derived from a reaction between N-(rhodamine-6G)lactam-ethylenediamine (L1) and trans-cinnamaldehyde, is reported here for the colorimetric and fluorogenic sensing of Group 13 trivalent cations, namely Al3+, Ga3+, In3+ and Tl3+. The absorption intensity of the probe increases significantly at 530 nm whereas the fluorescence intensity enhances massively at 558 nm upon interaction with these metal ions. Other relevant metal ions could not impart any noticeable color change or fluorescence enhancement. The quantum yield or fluorescence life time of HL-CIN increases considerably in the presence of these Group 13 metal ions. Different spectral studies such as ESI-mass, FT-IR, 1H and 13C NMR spectra, establish that HL-CIN undergoes hydrolysis in the presence of the trivalent cations and a rhodamine species in its ring opened form (i.e. N-(2-aminoethyl)-2-((6Z)-3-(ethylamino)-6-(ethylimino)-2,7-dimethyl-6H-xanthen-9-yl)benzamide, (L2)) along with cinnamaldehyde are produced. The rhodamine species in its ring opened form (L2) is responsible for the color change and strong increment in the absorbance and fluorescence of HL-CIN with Group 13 cations. Interaction between L1 and these metal ions could not produce the same outcome. It has been used in test paper strips and to detect these cations in real samples.

Amidoquinoline-based xylofuranose derivative for selective detection of Cu2+ in aqueous medium

The amide derivatives of quinoline 1 and naphthalene 2 were synthesized after incorporating D(+) xylose moiety to recognize cations and anions in the aqueous medium. Amidoquinoline-based xylofuranose derivative 1 showed absorbance and fluorescence responses towards Cu2+ ions over other metal ions and anions in an aqueous medium. Sensor 1 showed a sensitivity limit of 0.87 µM with a 1:1 binding ratio for Cu2+ ions. The binding stoichiometry of the complex was established from Job plot and supported by the ESI-mass spectrum of the complex. Amidonaphthalene-based reference compound 2 was used to establish the binding mechanism between 1 and Cu2+ ion. Finally, FT-IR spectroscopy and DFT calculation executed the binding mode of 1 with Cu2+ in an aqueous medium. The effective fluorescence quenching of 1 with the presence of Cu2+ ions could be restored from Na2EDTA experiment. Sensor 1 showed selective and effective fluorescence quenching responses towards Cu2+ ions in an aqueous solution.

Selective detection of BF3 in living cells and environmental water samples using Schiff-base fluorescent probe

A new pyrazole naphthalene-based Schiff base (3c) as a colorimetric and turn-on fluorescent sensor for rapid detection of BF3 was developed. Ligand 3c showed a significant fast response and superior selectivity for BF3 with significant color change by naked eye over other competitive species. Sensor probe 3c showed low detection limit (LOD) of 2.46 nM, which was far lower than the previous reports. Based on the Job’s plot, the binding association ratio of 3c with BF3 was found to be 1:1. The sensing mechanism of 3c with BF3 based on the intramolecular charge transfer (ICT) was confirmed by FTIR, 1H NMR titration, ESI mass spectra, and DFT calculation. Moreover, the sensing probe 3c was found to be reversible with the addition of triethylamine (NEt3), which revealed that 3c could behave as a good candidate for BF3 and NEt3 controlled “ON-OFF-ON” mode. Most importantly, probe 3c has been successfully applied to quantitatively detect BF3 species in various water samples, and using low-cost test paper strips as well as living cells.

In-Situ Analysis of Anionic Coordination Polymerizations by Electrospray-Ionization Mass Spectrometry.

Anionic coordination polymerizations proceed via highly reactive intermediates, whose in situ analysis has remained difficult. Here, we show that electrospray-ionization mass spectrometry is a promising method to obtain detailed information on the polymerization process. Focusing on polymerization reactions of 1,3-dienes initiated by CoCl2 /RLi (R=Me, nBu, tBu, Ph), we directly observe the growing polymer chains and characterize the active anionic cobalt centers by gas-phase fragmentation experiments. On the basis of these results, we suggest a plausible mechanism for the polymerization reaction. Moreover, the ESI mass spectra permit the determination of molecular weight distributions, which are in good agreement with those derived from NMR-spectroscopic as well as MALDI mass-spectrometric measurements, and afford a wealth of kinetic data.

Derivatization to increase the detectability of small peptides in blood serum in the analysis by ESI and MALDI high resolution mass spectrometric methods

This work highlights the efficient approach to highly sensitive determination of dipeptides that can present in biological liquids at very low and trace quantities. The approach involves preliminary derivatization of peptides with tris(2,4,6-trimethoxyphenyl)-methyl carbenium hexafluoroborate followed by ESI and MALDI high-resolution mass spectrometry. Using model dipeptides with various amino acid compositions and sequences, it was shown that the derivatization reaction proceeded smoothly in mild conditions and gave rise to pink-red colored salt derivatives. Ready cations of interest for the analysis are easily desorbed from the salt-derivatives providing strong signals in ESI and MALDI mass spectra and this ensures high sensitivity of the analysis. Another positive aspect is the removal of the target signal from the region of a matrix noise, since the introduced fragment possesses a large mass increment (359 Da). High resolution mass spectrometry, which provides the determination of accurate weights and elemental compositions of ions, was used to reliably detect model dipeptides added to artificial urine and blood serum. A number of these dipeptides was shown to be present in real blood serum collected from volunteers. Collision induced dissociation of precursor cations composed of derivatizing reagent and dipeptide moieties gives rise to characteristic and simple fragmentation mass spectra. A comparison of limits of detection (LOD) measured for non-modified and derivatized dipeptides showed that the latter derivatives provide the highest sensitivity when LOD is determined by using multiple reaction monitoring (MRM) transitions. The suggested derivatization approach was shown to be useful for unambiguous identification of special dipeptides in artificial media and dietary supplements.

Organo-rhodium and -iridium complexes containing the thiosulfate (S2O32−) ligand

Reaction of the complexes [M2(μ-Cl)2(cod)2] (M = Rh, Ir) with sodium thiosulfate pentahydrate gives the dinuclear thiosulfate complexes [M2(μ-S2O3)2(cod)2]2−, which were isolated as their Ph3PCH2Ph+ salts. An X-ray structure determination on the Rh complex confirms the dimeric nature of the complex, with the two Rh(I) centres bridged by the terminal sulfurs of the thiosulfate ligands. Using ESI mass spectrometry, the dimer [M2(μ-S2O3)2(cod)2]2− and monomer [M(S2O3)(cod)]− are both observed, depending on the metal and capillary exit voltage. Reaction of sodium thiosulfate pentahydrate with the complexes trans-[RhCl(CX)(PPh3)2] (X = O or S) gave the anionic complexes Na[Rh(S2O3)(CX)(PPh3)], which were characterised by 31P{1H} NMR and IR spectroscopies, ESI MS, and in the case of the thiocarbonyl complex, by elemental analysis. Pentamethylcyclopentadienyl (Cp*) rhodium(III) and iridium(III) thiosulfate complexes [(Cp*M)2(μ -S2O3)3]2− were also synthesised by reaction of the chloride-bridged dimers [Cp*MCl2]2 with sodium thiosulfate, and isolated as their Ph3PCH2Ph+ salts. The complexes gave the expected parent dianions in ESI mass spectra, which underwent fragmentation of a thiosulfate ligand at higher capillary exit voltages to give ions [(Cp*M)2(S2O3)2S + H]−.

Solvent directed fluorometric discrimination of Cu2+ and Ni2+ ions by a quinoline-based glucopyranosyl derivative

The reversible fluorescence sensor 1 has been reported for the discrimination of metal ions in aqueous medium after excitation at a higher wavelength. Sensor 1 showed specific sensing properties towards Cu2+ and Ni2+ in aqueous solutions of DMSO and CH3CN. The discrimination of Cu2+ and Ni2+ions was carried out by controlling the testing media. Sensor 1 exhibited high selectivity and excellent sensitivity (LOD: 0.17 µM for Cu2+ and 0.18 µM for Ni2+) towards Cu2+ and Ni2+ in two different analytical techniques (absorbance and fluorescence). The 1:1 complexation for both Cu2+ and Ni2+ was established from Job plots and ESI-mass spectra of the complexes. Model compound 2 and FTIR spectroscopy were used to know the binding mechanism of sensor 1 with Cu2+ and Ni2+ ions. Finally, DFT calculations were performed to establish the binding mode of 1 with Cu2+ and Ni2+.

Metal complexes of thiosemicarbazones derived by 2-quinolones with Cu(I), Cu(II) and Ni(II); Identification by NMR, IR, ESI mass spectra and in silico approach as potential tools against SARS-CoV-2

Substituted thiosemicarbazones derived by 2-quinolone were synthesized to investigate their complexation capability towards Cu(I), Cu(II) and Ni(II) salts. The structure of the complexes was established by ESI, IR and NMR spectra in addition to elemental analyses. Monodetate Cu(I) quinoloyl-substituted ligands were observed, whereas Ni(II) and Cu(II) formed bidentate-thiosemicarbazone derived by 2-quinolones. Subsequently, molecular docking was used to evaluate each analog's binding affinity as well as the inhibition constant (ki) to RdRp complex of SARS-CoV-2. Docking results supported the ability of the tested complexes that potentially inhibit the RdRp of SARSCov-2 show binding energy higher than their corresponding ligands. Additionally, ADMET prediction revealed that some compounds stratify to Lipinski's rule, indicating a good oral absorption, high bioavailability good permeability, and transport via biological membranes. Therefore, these metals-based complexes are suggested to be potentially good candidates as anti-covid agents.

Molecular Rearrangement of Pyrazino[2,3-c]quinolin-5(6H)-ones during Their Reaction with Isocyanic Acid.

New tetrahydropyrazino[2,3-c]quinolin-5(6H)-ones were prepared from 3-chloroquinoline-2,4(1H,3H)-diones and ethylene diamine. In their reaction with HNCO, an unprecedented molecular rearrangement produced new types of hydantoin derivatives. All prepared compounds were characterized on the basis of their 1H, 13C, and 15N NMR and ESI mass spectra and some were authenticated by X-ray analysis of single crystalline material. A proposed mechanism for rearrangement is discussed in this essay. The CDK and ABL inhibition activity as well as in vitro cytotoxicity of the prepared compounds was also tested.

Investigation of new schiff base transition metal (II) complexes theoretical, antidiabetic and molecular docking studies

A new Schiff base ligand, 2-((Z)-(4-((furan-2-ylmethylene)amino)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-ylidene)amino)pyridine-3-ol have been synthesized by the condensation of 4-((furan-2-ylmethylene)amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one with 2-amino-3-hydroxypyridine. Its divalent metal complexes of Cu(II), Ni(II), Co(II) and Zn(II) were also synthesized. The ligand and its metal complexes were characterized by Elemental analysis, UV-Visible, FT-IR, 1H NMR, 13C NMR, EPR, ESI-Mass spectra and thermal analysis (TGA & DTA). The consequences of antidiabetic studies showed that the complexes are potentially more active. The experimental and molecular docking studies revealed that the ligand and all the complexes can interact with a human pancreatic α-amylase (PDB: 1HNY) protein and they showed promising docking score value. The DFT calculations of quantum parameters and geometry optimization of ligand and complexes are done.