Crown ether decorated phthalocyanines were designed to form rigidly eclipsed aggregates with metal ions being sandwiched between the molecules. We studied tetra-18crown-6 ether functionalized zinc ...phthalocyanine (ZnPcTetCr) in the presence of excess NaCl by electrospray ionization mass spectrometry. ZnPcTetCr was found to form aggregates in the gas phase to which several neutral NaCl molecules are attached. Collision-induced dissociation experiments revealed that the ions observed in the positive- and negative-ion modes possess remarkably different structures. Their fragmentation behavior indicates that the sodium ions providing the charge of the positively charged aggregates are strongly bound inside the crown ether moieties, while the neutral salt units are less strongly attached. However, in the negatively charged ions, none of the sodium ions is embedded in the crown ether moieties, and the NaCl molecules were found to be attached as one large, weakly bound cluster.
Singly and doubly charged adducts of LiCl with β-cyclodextrin (βCD) of the type (βCD)(LiCl)
n
Li
+
and (βCD)
2
(LiCl)
p
Li
2
2+
were studied using electrospray ionization mass spectrometry (ESI-MS). ...Insight into their structural composition was gained by analysis of their collision-induced dissociation (CID) mass spectra. The conditions the ions experience in the transfer region interfacing the ESI source and the mass analyzer were found to have a marked influence on the nature of the detected ions. In one instrument incorporating a single skimmer, individually attached LiCl ion pairs were observed, whereas the dual funnel ion guides of the second instrument allow the detection of previously unknown labile inclusion complexes of (LiCl)
n
clusters in βCD.
Graphical Abstract
ᅟ
The in situ metalation of monolayers and multilayers of 2H-tetraphenylporphyrin (2HTPP) with Fe atoms on Ag(111) was studied with scanning tunneling microscopy (STM) and X-ray photoelectron ...spectroscopy (XPS). This surface-confined coordination reaction results in the formation of adsorbed iron(II)-tetraphenylporphyrin (FeTPP). It is demonstrated that metalation of 2HTPP is achieved either by depositing iron atoms onto a monolayer of 2HTPP at room temperature or, alternatively, by depositing 2HTPP onto a Ag(111) surface with predeposited iron. The latter route requires elevated temperatures, indicating that this reaction includes at least one step with an activation barrier. In addition, it is demonstrated that vapor deposited Fe atoms also react with multilayers of the porphyrin at room temperature under the formation of FeTPP.
Crown ether fullerenes, C60H(cr – H), form two different dimers in electrospray ionization mass spectrometry, a noncovalently bound, metal-bridged dimer C60H(cr – H)2M+, and a singly bonded ...fullerene dimer of the type (cr – H)–C60–C60–(cr – H)M n n+, with n = 1, 2. In this work, the dependence of both the formation and the dissociation of these dimers on the respective sizes of the crown ether moiety (12cr4, 15cr5, 18cr6) and of the alkali metal ion (M+ = Li+, Na+, K+, Rb+, Cs+) is studied. The size ratio of crown ether cavity to metal cation size has a profound influence on the formation of the noncovalent dimers, C60H(cr – H)2M+. These are only formed if the cation is larger than the crown ether cavity. Also, the doubly charged, covalent dimers C60(cr – H)2M2 2+ show a dependence on the size ratio. The proposed formation mechanism involves the recombination of two C60(cr – H)M•+ radical cations, which can only occur if the repulsion between the two charges is sufficiently reduced by encapsulating the metal cations within the crown ether moiety. Only the formation of the singly charged covalent dimer C60(cr – H)2M+ was found to be independent of the size ratio, in line with a radical-based dimerization mechanism. The fragmentation behavior, however, is strongly dependent on the size ratio, revealing the influence of intramolecular crown–metal–crown complexes.
The K+ adducts of the crown ether–60fullerene conjugate of the form (12cr4 – H)–C60–H are investigated by electrospray mass spectrometry (ESI-MS), focusing on the dimeric species produced from two ...different solvent mixtures. A singly bonded fullerene dimer of the type (12cr4 – H)–C60–C60–(12cr4 – H)K+ is generated in aprotic solvents, while in protic solvents, a metal-bridged, noncovalently bound dimer predominates. The dimerization reaction is proposed to occur during the ESI process via the radical intermediate (12cr4 – H)–C60 •. The fragmentation behavior of the different dimers is studied by collision-induced dissociation (CID), showing characteristic product ions for each species.
The aggregation of phthalocyanines is well-known in solution but has never before been studied in the gas phase. We investigated the tetra-18crown-6 ether functionalized zinc–phthalocyanine ...(ZnPcTetCr, M) with electrospray ionization mass spectrometry (ESI-MS) in the absence of coordinating metal cations. Apart from the molecular ion M +•, singly and multiply charged aggregates M n z(+•) were observed, bound together by electrostatic interactions, without alkali metal cations inside the crown ethers. Collision-induced dissociation (CID) experiments indicate that these clusters consist of stacked neutral M and radical cations M +•. After the oxidation of individual molecules at the electrospray needle, the aggregation occurs during desolvation of the charged droplets created in the source. Complete evaporation of the solvent and detection of the aggregates was found to require an additional acceleration of the droplets in the transfer region of the instrument, the resulting collisions with neutral gas assisting the desolvation process.
Metalfluoride anions are produced from reaction of fluorinated fullerenes with activated metal surfaces.
Display omitted
•Metalfluoride anions are produced from reaction of fluorinated fullerenes ...with activated metal surfaces.•In a plasma ion source, C60Fx react with the Mo and W of the filament and sample holder yielding MoF5/6− and WF5/6−.•In laser desorption/ionisation (LDI) of C60Fx on Al, Cu and Fe foils, the respective metalfluoride anions are generated.•The metalfluoride yields strongly depend on the fluorine content of the fullerene.
A comparative investigation into the chemical reactions of a series of fluorinated fullerenes (C60F18, C60F36 and C60F48) with a variety of activated metal surfaces is reported. New ways of generating intense beams of metal fluoride anions are demonstrated: either in reactions of fluorinated fullerene vapours with hot W and Mo metal surfaces in a plasma ion source or by laser desorption/ionisation (LDI) of solid fluorinated fullerenes from various metal substrates (Al, Fe, Cu, Pt, W). In both cases, the resulting metal fluorides and their anions are formed in the highest oxidation state, yielding molybdenum and tungsten hexafluoride anions (plasma ion source), aluminium and iron tetrafluoride anions, and copper trifluoride anions (LDI). No reactions were observed with Pt and W in LDI. The reactivity of the metals towards fluorination correlates with their positions in the metal activity series. Relative yields of bare metal cations are dictated by their ionisation energy. The yield of metal fluoride anions is strongly dependent on the fluorine content of the fluorofullerenes.
The ion formation of crown ether-60fullerene conjugates of the type (crown - H)-C60-H with crown = 12cr4, 15cr5 and 18cr6 has been studied with matrix-assisted laser desorption/ionisation (MALDI) and ...electrospray ionisation mass spectrometry (ESI MS). In total five different ways of ion formation are presented, including metalation (MALDI, ESI), protonation and oxidation (both in MALDI) in the positive-ion mode and deprotonation (MALDI, ESI) and reduction (MALDI) in the negative-ion mode. In line with thermochemistry, the deprotonation and electron transfer processes involve the C60 moiety as the charge-carrying entity, while protonation and metalation occur at the crown ether. Particular emphasis has been placed on the study of metal cation attachment in MALDI varying the crown ether size in the conjugate and using different alkali metal chlorides in the target preparation. Dissociation reactions of the metalated conjugates are influenced by the interaction strength of the metal cation to the crown ether fullerene conjugate. The data confirm an increase in bond strength with smaller metal cations, supporting the notion of charge density-driven interactions.
Proteolysis during the storage of UHT milk is associated with major technological problems, particularly bitter off-flavors and age gelation limiting the shelf life of milk. In this study, untargeted ...peptide profiling by MALDI-TOF-MS identified peptides that were formed by proteolysis and reflected the storage of UHT milk. Analysis of nine different commercial UHT samples recorded peptide profiles during and at the end of their shelf life. Relative quantification and sequencing of the peptides revealed that the concentrations of 22 peptides increased significantly during the storage of UHT milk due to the activity of endogenous milk proteases and microbial proteases as well as other unidentified proteolytic mechanisms. Based on highly discriminative AUC values from receiver operator characteristic (ROC) curve analysis, we selected ten peptides as marker candidates. Among those, the peptide β-casein192–206 (m/z 1668.9) was the most suitable marker differentiating expired-UHT from regular-UHT samples with 100% accuracy. Additionally, β-casein191–206 (m/z 1782.0) showed 100% specificity and β-casein139–161 (m/z 2696.4) 100% sensitivity. Thus, β-casein192–206, either by itself or in combination with β-casein191–206 and β-casein139–161, presents a reliable marker to monitor the storage of UHT milk based on proteolytic mechanisms.
Enzymatic hydrolysis is the main reason why processed milk spoils during storage. The present study recorded peptide profiles to monitor the release or degradation of peptides in stored UHT milk. Among the detected peptides, statistical analysis revealed that the relative concentration of β-casein192–206 reflected those proteolytic processes most precisely.
Food authorities can now refer to β-casein192–206 as a reliable marker to differentiate between freshly processed milk and products at the end of their shelf life. Furthermore, the food industry can use this marker peptide to improve production processes by monitoring the proteolysis during storage. The recorded peptide profile helps to explain the basic mechanisms leading to storage-induced proteolysis.
Display omitted
•MALDI-TOF-MS analysis monitored proteolysis leading to spoilage of UHT milk.•Peptide profiling revealed 22 peptides released during storage of UHT milk.•β-Casein192–206 differentiated expired from regular samples with 100% accuracy.•β-Casein191–206 and β-casein139–161 reached 100% specificity and 100% sensitivity.•The release of the peptides was mainly related to endogenous proteases.
To elucidate an antitumor drug exhibiting enhanced activity relative to cisplatin, a novel dinuclear gold(III) complex was synthesized, incorporating 1,5-naphthyridine as a bridging ligand. ...Subsequently, the newly synthesized complex underwent comprehensive characterization using various techniques to validate its structural attributes. The stability of the complex in both water and PBS buffer was assessed through UV–Vis spectroscopy. DNA binding studies were conducted employing UV–Vis, fluorescence spectroscopy, and viscosity measurements. Competitive studies with ethidium bromide (EB) or 4′-hydroxyethidium (HOE) were performed utilizing fluorescence spectroscopy. The findings indicated that the dinuclear gold(III) complex interacts with calf thymus DNA (CT-DNA) through a groove binding mode. Moreover, the investigated complex exhibited significant binding constants for its interaction with human serum albumin (HSA) and bovine serum albumin (BSA) and interactions in the presence of site markers (eosin Y or ibuprofen). The dinuclear gold(III) complex demonstrated notable cytotoxicity against HCT116 and MDA-MB-231 cancer cell lines at 24 and 72 h post-treatment. Furthermore, the complex displayed selectivity by inducing significantly lower cytotoxic activity in healthy cells than in cancerous ones. In support of its antitumor activity, the complex exhibited proapoptotic effects, as evidenced by increased caspase 9 activity and low percentages of necrosis. Molecular docking simulations were employed to corroborate all experimentally obtained results.
PDF
