Search

Herein, two atomically precise silver nanoclusters, Ag54 and Ag33, directed by inner anion templates (CrO42− and/or Cl−), are initially isolated as a mixed phase from identical reactants across a wide temperature range (20–80 °C). Interestingly, fine‐tuning the reaction temperature can realize pure phase synthesis of the two nanoclusters; that is, a metastable Ag54 is kinetically formed at a low temperature (20 °C), whereas such a system is steered towards a thermodynamically stable Ag33 at a relatively high temperature (80 °C). Electrospray ionization mass spectrometry illustrates that the stability of Ag33 is superior to that of Ag54, which is further supported by density functional theory calculations. Importantly, the difference in structural stability can influence the pathway of 1,4‐bis(pyrid‐4‐yl)benzene induced transformation reaction starting from Ag54 and Ag33. The former undergoes a dramatic breakage‐reorganization process to form an Ag31 dimer (Ag31), while the same product can be also achieved from the latter following a noninvasive ligand exchange process. Both the Ag54 and Ag33 have the potential for further remote laser ignition applications. This work not only demonstrates how temperature controls the isolation of a specific phase, but also sheds light on the structural transformation pathway of nanoclusters with different stability. [ABSTRACT FROM AUTHOR]

Domino reaction of benzo[d]thiazole‐2‐methylamine (S1) has been developed in the presence of MnCl2 ⋅ 4H2O, leading to tetrasubstituted pyrrole coordinated dinuclear Mn(II) complex 1 ([MnClP]2, P−=2,3,4,5‐tetrakis(benzo[d]thiazol‐2‐yl)pyrrol‐1‐ide). The reaction process has been studied by assigning a series of intermediates based on time‐dependent mass spectrometry, control experiments, crystallography, and density functional theory (DFT) theoretical calculation. A plausible mechanism involving an unprecedented divergent‐convergent domino sequence has been proposed. Compound S1 could be activated by MnCl2 ⋅ 4H2O via coordination, which divergently produces two intermediates imine II (1‐(benzo[d]thiazol‐2‐yl)‐N‐(benzo[d]thiazol‐2‐ylmethyl)methanimine) and alkene C (1,2‐bis(benzo[d]thiazol‐2‐yl)ethene) through oxidative self‐condensation and free radical coupling followed by elimination, respectively. They could then react with each other convergently via formal [3+2] cycloaddition to give deprotonated tetrasubstituted pyrrole coordinated intermediate [MnClP] after aromatization. Dimerization of [MnClP] produces the final product 1. Three C−C bonds and one C−N bond are formed through this six‐step domino sequence. The corresponding organic skeleton (HP: 2,2′,2′′,2′′′‐(1H‐pyrrole‐2,3,4,5‐tetrayl)tetrakis(benzo[d]thiazole)) has been obtained from 1 and shows a higher fluorescent quantum yield (52 %) than the reported 3,4‐diphenyl substituted analogue 2,2′‐(3,4‐diphenyl‐1H‐pyrrole‐2,5‐diyl)bis(benzo[d]thiazole) (DPB) (42 %). [ABSTRACT FROM AUTHOR]

Polyoxometalates (POMs) represent crucial intermediates in the formation of insoluble metal oxides from soluble metal ions, however, the rapid hydrolysis‐condensation kinetics of MoVI or WVI makes the direct characterization of coexisted molecular species in a given medium extremely difficult. Silver nanoclusters have shown versatile capacity to encapsulate diverse POMs, which provides an alternative scene to appreciate landscape of POMs in atomic precision. Here, we report a thiacalix[4]arene protected silver nanocluster (Ag72b) that simultaneously encapsulates three kinds of molybdates (MoO42−, Mo6O228− and Mo7O258−) in situ transformed from classic Lindqvist Mo6O192−, providing more deep understanding on the structural diversity and condensation growth route of POMs in solution. Ag72b is the first silver nanocluster trapping so many kinds of molybdates, which in turn exert collective template effect to aggregate silver atoms into a nanocluster. The post‐reaction of Ag72b with AgOAc or PhCOOAg produces a discrete Ag24 nanocluster (Ag24a) or an Ag28 nanocluster based 1D chain structure (Ag28a), respectively. Moreover, the post‐synthesized Ag28a can be utilized as potential ignition material for further application. This work not only provides an important model for unlocking dynamic features of POMs at atom‐precise level but also pioneers a promising approach to synthesize silver nanoclusters from known to unknown. [ABSTRACT FROM AUTHOR]

Modern medical research develops interest in sophisticated artificial nano‐ and microdevices for future treatment of human diseases related to biological dysfunctions. This covers the design of protocells capable of mimicking the structure and functionality of eukaryotic cells. The authors use artificial organelles based on trypsin‐loaded pH‐sensitive polymeric vesicles to provide macrophage‐like digestive functions under physiological conditions. Herein, an artificial cell is established where digestive artificial organelles (nanosize) are integrated into a protocell (microsize). With this method, mimicking crossing of different biological barriers, capture of model protein pathogens, and compartmentalized digestive function are possible. This allows the integration of different components (e.g., dextran as stabilizing block) and the diffusion of pathogens in simulated cytosolic environment under physiological conditions. An integrated characterization approach is carried out, with identifying electrospray ionization mass spectrometry as an excellent detection method for the degradation of a small peptide such as β‐amyloid. The degradation of model enzymes is measured by enzyme activity assays. This work is an important contribution to effective biomimicry with the design of cell‐like functions having potential for therapeutic action. [ABSTRACT FROM AUTHOR]

Electrospray Ionization Mass Spectrometry (ESI‐MS) technique and density functional theory (DFT) calculations were combined to study the formation of the complexes of lanthanides (Ln = La, Ce, Nd, Sm, Eu, Yb) and actinides (UO22+, Th4+) with CyMe4‐BTBP (6,6′‐bis(5,5,8,8‐tetramethyl‐5,6,7,8‐tetrahydro‐benzo‐[1,2,4‐]triazin‐3‐yl)‐[2,2′]bipyridine) to understand the mechanisms during the extraction process. Mass spectrometry titrations showed the formation of the complexation in acetonitrile. For lanthanides, only 1:2 complexes ([Ln(L)2]3+, [Ln(L)2(CH3CN)]3+), [Ln(L)2(NO3)]2+) were found at low [Ln]/[L] concentration ratios, whereas the 1:1 complexes ([Ln(L)(NO3)2]+) were observed when the [Ln]/[L] concentration ratio reached 1.0. For uranyl complexes, 1:1 complex ([UO2L(NO3)]+) was the only species within the measuring range. Th4+ complexes had two compositions: 1:1 and 1:2, in which 1:2 species was the dominant complex. Collision‐induced dissociation (CID) was employed to characterize the fragmentation process. The fragmentation process was unfolded sequentially on both sides of CyMe4‐BTBP ligand with the loss of alkyl groups and cleavage of triazinyl rings. The CID results of CyMe4‐BTBP complexes revealed a slight difference depending on the metal center. The DFT calculations showed that the stable complexes formed in acetonitrile solution were consistent with the ESI‐MS results. [ABSTRACT FROM AUTHOR]

Human metallothioneins (MTs) are involved in binding the essential elements, Cu(I) and Zn(II), and the toxic element, Cd(II), in metal‐thiolate clusters using 20 reduced cysteines. The brain‐specific MT3 binds a mixture of Cu(I) and Zn(II) in vivo. Its metallation properties are critically important because of potential connections between Cu, Zn and neurodegenerative diseases. We report that the use of isotopically pure 63Cu(I) and 68Zn(II) greatly enhances the element resolution in the ESI‐mass spectral data revealing species with differing Cu:Zn ratios but the same total number of metals. Room temperature phosphorescence and circular dichroism spectral data measured in parallel with ESI‐mass spectral data identified the presence of specific Cu(I)‐thiolate clusters in the presence of Zn(II). A series of Cu(I)‐thiolate clusters form following Cu(I) addition to apo MT3: the two main clusters that form are a Cu6 cluster in the β domain followed by a Cu4 cluster in the α domain. 63Cu(I) addition to 68Zn7‐MT3 results in multiple species, including clustered Cu5Zn5‐MT3 and Cu9Zn3‐MT3. We assign the domain location of the metals for Cu5Zn5‐MT3 as a Cu5Zn1‐β cluster and a Zn4‐α cluster and for Cu9Zn3‐MT3 as a Cu6‐β cluster and a Cu3Zn3‐α cluster. While many reports of the average MT3 metal content exist, determining the exact Cu,Zn stoichiometry has proven very difficult even with native ESI‐MS. The work in this paper solves the ambiguity introduced by the overlap of the naturally abundant Cu(I) and Zn(II) isotopes. Contrary to other reports, there is no indication of a major fraction of Cu4‐β‐Znn‐α‐MT3 forming. [ABSTRACT FROM AUTHOR]

Different oxidative pathways of sulfur dioxide promoted by ZnO(NO3)2−, Zn(NO3)2− and Zn(NO2)(NO3)− are revealed by a joint investigation by mass spectrometry and theoretical calculations. The reactions are triggered by [Zn2+‐O−⋅]+ or by the low‐valence Zn+ through oxygen ion transfer or electron transfer to SO2, respectively. The NOx− ligands intervene in the oxidation only when sulfur dioxide is converted to SO3− or SO2−, leading to the formation of zinc sulfate and zinc sulfite coordinated to nitrate or nitrite anions. Kinetic analyses show that the reactions are fast and efficient, and theory discloses the elementary steps, namely oxygen ion transfer, oxygen atom transfer and electron transfer, occurring through similar energy landscapes for the three reactive anions. [ABSTRACT FROM AUTHOR]

Reactive oxygen species (ROS) are critical for many cellular functions, and dysregulation of ROS involves the development of multiple types of tumors, including pancreatic cancer. However, ROS have been grouped into a single biochemical entity for a long time, and the specific roles of certain types of ROS in tumor cells (e.g. pancreatic ductal adenocarcinoma (PDAC)) have not been systematically investigated. In this work, a highly sensitive and accurate mass spectrometry‐based method was applied to study PDAC cells of humans and of genetically modified animals. The results show that the oncogenic KRAS mutation promotes the accumulation of hydrogen peroxide (H2O2) rather than superoxide or hydroxyl radicals in pancreatic cancer cells. We further identified that the enriched H2O2 modifies cellular metabolites and promotes the survival of pancreatic cancer cells. These findings highlight the specific roles of H2O2 in pancreatic cancer development, which may provide new directions for pancreatic cancer therapy. [ABSTRACT FROM AUTHOR]

The molecular composition of lubricating oils has a strong impact on how automotive engines function, but the techniques used to monitor the quality parameters of these oils only inspect their gross physical–chemical properties such as viscosity, color, and bulk spectroscopy profiles; hence, bad‐quality, adulterated, or counterfeit oils are hard to detect. Herein, we investigated the ability of direct infusion electrospray ionization mass spectrometry (ESI‐MS) to provide simple, rapid but characteristic fingerprint profiles for such oils of the mineral and synthetic types. After a simple aqueous extraction, ESI‐MS analyses, particularly in the positive ion mode, did indeed show characteristic molecular markers with unique profiles, which were confirmed and more clearly visualized by partial least squares‐discriminant analysis (PLS‐DA). Nuclear magnetic resonance and Fourier transform infrared‐attenuated total reflection spectroscopy were also tested for the bulk samples but showed nearly identical spectra, thus failing to reveal their distinct molecular composition and to differentiate the oil samples. To simulate adulteration, mixtures of mineral and synthetic oils were also analyzed by ESI(+)‐MS, and additions as low as 1% of mineral oil to synthetic oil could be detected. The technique therefore offers a simple and fast but powerful tool to monitor the molecular composition of lubricant oils, particularly vias their more polar constituents. [ABSTRACT FROM AUTHOR]

A short 10‐min ultra high performance liquid chromatography (UHPLC) method was used for separation and lipidomic analysis of triacylglycerols (TAGs) in 10 pulses: baby lima beans, black beans, black‐eyed peas, butter beans, cranberry beans, garbanzo beans, green split peas, lentils, navy beans, and pinto beans. The lipids extracted using chloroform/methanol averaged 1.9–2.7% across all pulses except garbanzo beans, which gave 6.2% lipids. TAGs were analyzed using dual parallel mass spectrometry (LC1MS2), areas were integrated using LipidSearch 4.2 software, and percent relative TAG compositions were calculated. Fatty acid response factors were calculated by comparison to calibrated GC‐FID, which were used to calculate response‐factor adjusted TAG compositions. Principal component analysis revealed that the pulses separated into three clusters, which were further highlighted using hierarchical cluster analysis. A subset of TAGs was quantified using calibration curves made from alternating sets of regioisomers in the non‐linear high concentration range (~2.5 nMol/ml to ~300 nMol/ml). A linear calibration curve for the sum of tocopherols detected by fluorescence was constructed with a coefficient of determination, r2, >0.99 for low concentrations (0.50–50 μg/ml), but tocopherols in pulses appeared to be inefficiently extracted. TAG regioisomers were quantified based on a Critical Ratio (CR), [AA]+/[AB]+, interpolated between the CRs of two pure regioisomer standards taken from alternating calibration standards. TAG mole percent relative compositions are reported for the first time for most pulses and the compositions are given with more detail and specificity than previously reported. [ABSTRACT FROM AUTHOR]

Electrospray ionization mass spectrometry was used to investigate the cation‐π interaction of Ag+ cation with [2.2]paracyclophane. It was found that cationic Ag.([2.2]paracyclophane)+ and Ag.([2.2]paracyclophane)2+ complex species are formed in the gas phase. Further, applying quantum mechanical calculations in the frame of the density functional theory, using B3LYP functional with Def2TZVP basis set, the most probable structures of the proved Ag+ ‐ [2.2]paracyclophane complexes were derived. In the Ag.([2.2]paracyclophane)+ complex, the cation Ag+ is bounded to three carbon atoms of one benzene ring of [2.2]paracyclophane ligand via cation‐π interaction. Quite analogously is bonded also second [2.2]paracyclophane molecule in Ag.([2.2]paracyclophane)2+ complex. The interaction energy, E(int), of Ag.([2.2]paracyclophane)+ complex was calculated to be −220.79 kJ/mol, E(int) of Ag.([2.2]paracyclophane)2+ complex is −362.67 kJ/mol. It is consistent with the formation of the considered Ag+ ‐ [2.2]paracyclophane complex species. [ABSTRACT FROM AUTHOR]

Metal ions can be analyzed by ESI‐MS with chelating agents. However, matrix effect and the marginal difference in atomic weight of the isotopes of some metal ions make the analysis of a metal ion mixture not feasible. In this paper, we present the use of IP‐HPLC in conjunction with a metal ion chelating agent to analyze the metal ion mixtures. Hydrophobic (±)‐trans‐1,2‐cyclohexylenedinitrilotetraacetic acid (CDTA) was used to chelate 16 metal ions. The chelates were then separated by IP‐HPLC followed by ESI‐MS analysis. For IP‐HPLC, different combinations of primary amines and their salts were employed as the ion‐pairing reagent in eluent on a high‐pH resistant C‐18 column under basic conditions. For ESI‐MS, Q‐Exactive Focus system was used. Among the metal ions, the results indicated that Al3+ showed the lowest LOD (3.88 × 10−3 μM) while Zn2+ showed the highest (0.227 μM). The sensitivity was close to that of ICP‐AES. The coefficients of determination (R2) were greater than 0.995 except for Sr2+ (R2 = 0.9899), indicating the high accuracy of the method. Finally, this method was used to analyze the black soybean samples from two different sources. Eight metal ions were successfully identified with simultaneous detection of sugars, organic acids, and nucleotides. [ABSTRACT FROM AUTHOR]

An on‐line sample preconcentration technique based on transient trapping (tr‐trapping) in micellar electrokinetic chromatography (MEKC) was applied for steroid detection with UV (tr‐trapping‐UV) and electrospray ionization mass spectrometry detection (tr‐trapping‐ESI‐MS). ESI‐MS was used to improve the sensitivity in MEKC. The MEKC separation was carried out using volatile ammonium formate as a background solution to facilitate the coupling with ESI‐MS. The partial introduction of a sodium dodecyl sulfate (SDS) micellar solution before the introduction of a sample solution to the capillary provided the effective preconcentration of analytes. At the same time, the SDS micelle would not enter the ESI‐MS system, so its interference in ESI‐MS detection was suppressed under the optimal condition, then five steroids can be separated by the developed method. In tr‐trapping‐ESI‐MS, an acidic condition of pH 3.5 was employed to suppress the electroosmotic flow, which can avoid micellar solution migrating to the MS instrument. The developed method showed that the micellar solution requires a twofold slower time than the sample to migrate along the column, which can prohibit the cause of the problem with the MS instrument and interference signal of SDS in the steroid's detection. The tr‐trapping‐ESI‐MS protocol showed up to 540‐fold enhancements of the peak intensity and 50‐fold improvement of the limit of detection compared with capillary zone electrophoresis using androsterone as a model sample. [ABSTRACT FROM AUTHOR]

Thiacalix[4]arenes have emerged as a family of macrocyclic ligands to protect metal nanoparticles, but it remains a great challenge to solve the mystery of their structures at the atomic level, especially for those larger than 2 nm. Here, we report the largest known mixed‐valence silver nanocluster [Ag155(CyS)40(TC4A)5Cl2] (Ag155) protected by deprotonated cyclohexanethiol (CySH) and macrocyclic ligand p‐tert‐butylthiacalix[4]arene (H4TC4A). Its single‐crystal structure consists of a metallic core of four concentric shells, Ag13@Ag42@Ag30@Ag70, lined with a organic skin of 40CyS− and 5TC4A4− and 2Cl−. Ag155 manifests an unusual pseudo‐5‐fold symmetry dictated by the intrinsic metal atom packing and the regioselective distribution of mixed protective ligands. This work not only reveals a macrocyclic ligand effect on the formation of a large silver nanocluster, but also provides a new structural archetype for comprehensively perceiving their interface and metal kernel structures. [ABSTRACT FROM AUTHOR]

Stepwise assembly starting from a preassembled metalloligand is a promising approach to obtain otherwise unattainable silver nanoclusters, but hard to be intrinsically identified due to the lack of convincing evidence to justify such a process. Herein, hexagonal and rectangular Ag18 nanoclusters are constructed from the [Mo2O5(PTC4A)2]6− (H4PTC4A=p‐phenyl‐thiacalix[4]arene) metalloligand through stepwise assembly. The formation of the metalloligand is confirmed by electrospray ionization mass spectrometry, then assembled with silver ions to form two geometrically different Ag18 nanoclusters in different solvents. The cyclization from the metalloligand to [(Mo2O5PTC4A)6]12− can be realized without alcohols and otherwise blocked by them. The installation of this metalloligand not only provides comprehensive understanding of how the solvents regulate the silver nanocluster structures, but also brings new insights for the controllable ligand metallization and subsequent condensation. [ABSTRACT FROM AUTHOR]

Activation of the metallocene complexes (n‐C4H9‐(η5‐C5H4))2ZrCl2 (BuCp2ZrCl2) and rac‐1,2‐ethylenebis(1‐η5‐C9H6)ZrCl2 (EBIZrCl2) using methylaluminoxane (MAO) was investigated by electrospray ionization mass spectrometry (ESI‐MS). Formation of dinuclear complexes at low Al : Zr ratios, which is accompanied by catalyst deactivation, occurs in the former case. In contrast, this behavior was not observed at similar Al : Zr ratios in the case of the EBIZrCl2 complex. Both active [BuCp2ZrMe2AlMe2][MAO(Me)] 3 and deactivated [(BuCp2Zr)2(μ‐CH2)μ‐Cl][MAO(Me)] 9 complexes were detected in leaching experiments using a SiO2‐MAO‐supported BuCp2ZrCl2 catalyst and excess MAO. DFT studies of the structure and UV‐Vis spectra calculated for the dinuclear cations 9 detected by ESI‐MS suggest that these species may account for long‐wavelength absorption seen in experimental spectra of complexes like BuCp2ZrCl2 upon activation with MAO. [ABSTRACT FROM AUTHOR]

Methylaluminoxane (MAO) activators have sheet structures which form ion‐pairs on reaction of neutral donors such as octamethyltrisiloxane (OMTS). The ion‐pairs can be detected by electrospray ionization mass spectrometry (ESI‐MS) in polar media. The growth of these reactive precursors during hydrolysis of Me3Al can be monitored using ESI‐MS. Density functional theory, combined with numerical simulation of growth, indicates that this process involves rapid formation of low MW oligomers, followed by assembly of these species into low MW sheets. These can grow through further addition of low MW oligomers or by fusion into larger sheets. The mechanism of these growth processes leads to the prediction that even‐numbered sheets should be favored, and this surprising result is confirmed by ESI‐MS monitoring experiments of both activator growth and MAO aging. [ABSTRACT FROM AUTHOR]

Hydrolysis of trimethylaluminum (Me3Al) in polar solvents can be monitored by electrospray ionization mass spectrometry (ESI‐MS) using the donor additive octamethyltrisiloxane [(Me3SiO)2SiMe2, OMTS]. Using hydrated salts, hydrolytic methylaluminoxane (h‐MAO) features different anion distributions, depending on the conditions of synthesis, and different activator contents as measured by NMR spectroscopy. Non‐hydrolytic MAO was prepared using trimethylboroxine. The properties of this material, which contains incorporated boron, differ significantly from h‐MAO. In the case of MAO prepared by direct hydrolysis, oligomeric anions are observed to rapidly form, and then more slowly evolve into a mixture dominated by an anion with m/z 1375 with formula [(MeAlO)16(Me3Al)6Me]−. Theoretical calculations predict that sheet structures with composition (MeAlO)n(Me3Al)m are favoured over other motifs for MAO in the size range suggested by the ESI‐MS experiments. A possible precursor to the m/z 1375 anion is a local minimum based on the free energy released upon hydrolysis of Me3Al. [ABSTRACT FROM AUTHOR]

The methyl‐modified nucleosides (methyladenosine, methylguanosine, methylcytidine, and methyluridine) occur widely in nucleic acids and serve as biomarkers for a variety of types of diseases. Their isomers have the same parent ions in MS spectra and need further discrimination. Here, electrospray ionization mass spectrometry (ESI‐MS) coupled with collision induced dissociation (CID) was used to distinguish the common isomerides of methyl‐nucleosides. The various fragmentation patterns had been discussed in comparison of the different methyl modified nucleosides and were studied as a function of normalized collision energy. Then, structurally relevant fragments were obtained to efficiently identify characterization of methyl‐nucleoside isomerides by collision induced dissociation. Therefore, this study provides a promising method using CID‐MS for the discrimination of the isomeric methyl nucleosides, which could be useful to quantitative study of methyl nucleosides and detect of unknown methyl nucleosides. [ABSTRACT FROM AUTHOR]

Herein, the reaction of (1‐methyl‐1 H‐benzo[d]imidazol‐2‐yl)methanamine (L1) with Co(H2O)6Cl2, in CH3CN at 120 °C, leading to the 2,3,5,6‐tetrakis(1‐methyl‐1 H‐benzo[d]imidazol‐2‐yl)pyrazine (3), isolated as a dimeric cluster {[CoII2(3)Cl4]⋅2 CH3CN} (2), is reported. When O2 and H2O are present, (1‐methyl‐1 H‐benzo[d]imidazole‐2‐carbonyl)amide (HL1′) is first formed and crystallized as [CoIII(L1)2(L1′)]Cl2⋅2 H2O (4) before fusion of HL1′ with L1, giving 1‐methyl‐N‐(1‐methyl‐1 H‐benzo[d]imidazol‐2‐carbonyl)‐1 H‐benzo[d]imidazol‐2‐carboxamide (HL2′′) forming a one‐dimensional (1D) chain of [CoII3(L2′′)2Cl4]n (5). The combination of crystallography and mass spectrometry (ESI‐MS) of isolated crystals and the solutions taken from the reaction as a function time reveal seven intermediate steps leading to 2, but six steps for 5, for which a different sequence takes place. Control and isotope labeling experiments confirm the two carbonyl oxygen atoms in 5 originate from both air and water. The dependence on the metals, compared with FeCl3⋅6 H2O leading to a stable triheteroarylmethyl radical, is quite astounding, which could be attributed to the different oxidation states of the metals and coordination modes confirmed by DFT calculations. This metal and valence dependent process is a very useful way for selectively obtaining these large molecules, which are unachievable by common organic synthesis. [ABSTRACT FROM AUTHOR]

The product of a revealed transformation—NHC‐ethynyl coupling—was observed as a catalyst transformation pathway in the Sonogashira cross‐coupling, catalyzed by Pd/NHC complexes. The 2‐ethynylated azolium salt was isolated in individual form and fully characterized, including X‐ray analysis. A number of possible intermediates of this transformation with common formulae (NHC)nPd(C2Ph) (n=1,2) were observed and subjected to collision‐induced dissociation (CID) and infrared multiphoton dissociation (IRMPD) experiments to elucidate their structure. Measured bond dissociation energies (BDEs) and IRMPD spectra were in an excellent agreement with quantum calculations for coupling product π‐complexes with Pd0. Molecular dynamics simulations confirmed the observed multiple CID fragmentation pathways. An unconventional methodology to study catalyst evolution suggests the reported transformation to be considered in the development of new catalytic systems for alkyne functionalization reactions. [ABSTRACT FROM AUTHOR]

A one‐pot synthesis of 2‐amino‐1,3,4‐oxadiazoles has been achieved from the corresponding isothiocyanates and hydrazides in the presence of tert‐butyl hydroperoxide (TBHP) and water under microwave irradiation. The thiosemicarbazides intermediate could be derived in situ which underwent an intramolecular cyclodesulfurization under microwave irradiation. Apart from being simpler and green, this method offers significant advantages, such as short reaction times, economy and no requirement for a catalyst, with easy workup procedures to afford a variety of 2‐amino‐1,3,4‐oxadiazoles in significantly high yields (85–98 %). Spectroscopic techniques were employed to elucidate the chemical structures of the final compounds and ESI‐MS technique was employed to establish the formation of thiosemicarbazide intermediate and requirement of oxygen source for the completion of reaction and the most plausible reaction mechanism. [ABSTRACT FROM AUTHOR]

Phospholipids are one of the most important lipid categories with multiple functions in biological systems. Their analysis can contribute to a better understanding of metabolomic and kinetic processes in living cells. Comprehensive methods based on liquid chromatography coupled to mass spectrometry are available for phospholipid identification and quantification. However, quantification of phospholipids using electrospray ionization‐mass spectrometry with internal standards is still challenging due to several reasons. In particular, the detector response of phospholipid species differs with variation of the head group as well as the fatty acid chain length and double bond number. Inductively coupled plasma‐tandem mass spectrometry (ICP‐MS/MS) provides an alternative approach for their absolute quantification with universal detector response for phosphorus independent of its chemical form and proportional to its quantity. Therefore, a quantification method based on compound‐independent calibration using hydrophilic interaction liquid chromatography (HILIC) coupled to ICP‐MS/MS was developed. An inverse gradient system was implemented for constant mobile phase composition after HILIC separation, which provides steady plasma ionization conditions. Isobaric phosphorus interferences were decreased by using the oxygen reaction mode of the triple quadrupole based ICP‐MS/MS instrument. Complementary molecular information was obtained by ESI‐high‐resolution MS and MS/MS. The applicability of this approach was demonstrated in a proof of concept by complementary analysis of a total lipid extract of baker's yeast. [ABSTRACT FROM AUTHOR]

Tailor‐made photoinitiators play an important role for efficient radical polymerisations in aqueous media, especially in hydrogel manufacturing. Bis(acyl)phosphane oxides (BAPOs) are among the most active initiators. Herein, we show that they display a remarkable photochemistry in aqueous and alcoholic media: Photolysis of BAPOs in the presence of water or alcohols provides a new delocalized π‐radical, which does not participate in the polymerization. It either converts into a monoacylphosphane oxide acting as a secondary photoactive species or it works as a one‐electron reducing agent. Upon the electron‐transfer process, it again produces a dormant photoinitiator. We have established the structure and the chemistry of this π radical using steady‐state and time‐resolved (CIDEP) EPR together with ESI‐MS, NMR spectroscopy, and DFT calculations. Our results show that bis(acyl)phosphane oxides act as bifunctional reagents when applied in aqueous and alcoholic media. [ABSTRACT FROM AUTHOR]

Hepatocellular carcinoma (HCC) is the third most‐common cause of cancer‐related death worldwide. Most cases of HCC develop in patients that already have liver cirrhosis and have been recommended for surveillance for an early onset of HCC. Cirrhosis is the final common pathway for several etiologies of liver disease, including hepatitis B and C, alcohol, and increasingly non‐alcoholic fatty liver disease. Only 20–30% of patients with HCC are eligible for curative therapy due primarily to inadequate early‐detection strategies. Reliable, accurate biomarkers for HCC early detection provide the highest likelihood of curative therapy and survival; however, current early‐detection methods that use abdominal ultrasound and serum alpha fetoprotein are inadequate due to poor adherence and limited sensitivity and specificity. There is an urgent need for convenient and highly accurate validated biomarkers for HCC early detection. The theme of this review is the development of new methods to discover glycoprotein‐based markers for detection of HCC with mass spectrometry approaches. We outline the non‐mass spectrometry based methods that have been used to discover HCC markers including immunoassays, capillary electrophoresis, 2‐D gel electrophoresis, and lectin‐FLISA assays. We describe the development and results of mass spectrometry‐based assays for glycan screening based on either MALDI‐MS or ESI analysis. These analyses might be based on the glycan content of serum or on glycan screening for target molecules from serum. We describe some of the specific markers that have been developed as a result, including for proteins such as Haptoglobin, Hemopexin, Kininogen, and others. We discuss the potential role for other technologies, including PGC chromatography and ion mobility, to separate isoforms of glycan markers. Analyses of glycopeptides based on new technologies and innovative softwares are described and also their potential role in discovery of markers of HCC. These technologies include new fragmentation methods such as EThcD and stepped HCD, which can identify large numbers of glycopeptide structures from serum. The key role of lectin extraction in various assays for intact glycopeptides or their truncated versions is also described, where various core‐fucosylated and hyperfucosylated glycopeptides have been identified as potential markers of HCC. Finally, we describe the role of LC‐MRMs or lectin‐FLISA MRMs as a means to validate these glycoprotein markers from patient samples. These technological advancements in mass spectrometry have the potential to lead to novel biomarkers to improve the early detection of HCC. [ABSTRACT FROM AUTHOR]

Two new YIII containing sandwich‐type heterometallic tungstophosphates: [Y{PM2W10O38(H2O)2}2]11– (M = CoII (1) and ZnII (2)) have been synthesized under mild reaction conditions. Both the molecular complexes 1 a and 2 a were synthesized by reacting Y(NO3)3⋅6H2O, M(NO3)2⋅6H2O (M = CoII and ZnII) with Wells‐Dawson type divacant K14[P2W19O69(H2O)]⋅24H2O precursor. The potassium salts of single crystalline material were collected and further used for characterization with different analytical techniques including single crystal X‐ray diffraction (SC‐XRD), Fourier transform infrared (FT‐IR) spectroscopy, inductively coupled plasma atomic emission spectroscopy (ICP‐AES), 31P, 183W and 89Y nuclear magnetic resonance (NMR) spectroscopy, high‐resolution electro‐spray ionization mass spectrometry (HR‐ESI‐MS) as well as thermogravimetric analysis. Single crystal X‐ray diffraction analysis shows that both polyanions crystallize in the orthorhombic crystal system with space group Iba2. Each polyanion consists of (1,5) isomer of di‐metal substituted α‐Keggin type tungstophosphates, which sandwiched a YIII ion. We have reported two new purely inorganic YIII containing di‐metal substituted sandwich‐type tungstophosphate nanoclusters [Y{PM2W10O38(H2O)2}2]11– (M=CoII (1) and ZnII (2)) followed by one pot reaction procedure under mild reaction conditions. Both compounds were well characterized with different analytical techniques. The polyanion 1 and 2 consist of two units of (1,5) isomers of di‐metal substituted hetero Keggin [PM2W10O38(H2O)2]7– anion, sandwiched by yttrium ion. [ABSTRACT FROM AUTHOR]

Two new YIII containing sandwich‐type heterometallic tungstophosphates: [Y{PM2W10O38(H2O)2}2]11– (M = CoII (1) and ZnII (2)) have been synthesized under mild reaction conditions. Both the molecular complexes 1 a and 2 a were synthesized by reacting Y(NO3)3⋅6H2O, M(NO3)2⋅6H2O (M = CoII and ZnII) with Wells‐Dawson type divacant K14[P2W19O69(H2O)]⋅24H2O precursor. The potassium salts of single crystalline material were collected and further used for characterization with different analytical techniques including single crystal X‐ray diffraction (SC‐XRD), Fourier transform infrared (FT‐IR) spectroscopy, inductively coupled plasma atomic emission spectroscopy (ICP‐AES), 31P, 183W and 89Y nuclear magnetic resonance (NMR) spectroscopy, high‐resolution electro‐spray ionization mass spectrometry (HR‐ESI‐MS) as well as thermogravimetric analysis. Single crystal X‐ray diffraction analysis shows that both polyanions crystallize in the orthorhombic crystal system with space group Iba2. Each polyanion consists of (1,5) isomer of di‐metal substituted α‐Keggin type tungstophosphates, which sandwiched a YIII ion. We have reported two new purely inorganic YIII containing di‐metal substituted sandwich‐type tungstophosphate nanoclusters [Y{PM2W10O38(H2O)2}2]11– (M=CoII (1) and ZnII (2)) followed by one pot reaction procedure under mild reaction conditions. Both compounds were well characterized with different analytical techniques. The polyanion 1 and 2 consist of two units of (1,5) isomers of di‐metal substituted hetero Keggin [PM2W10O38(H2O)2]7– anion, sandwiched by yttrium ion. [ABSTRACT FROM AUTHOR]

Polyoxometalates (POMs) are an intriguing class of compounds due to their tremendous structural variety and the wide spectrum of resulting properties, which make them interesting for applications in fields such as catalysis, material science or nanotechnology. Their ability to form large supramolecular architectures by self‐assembly offers an entry to complex, functional systems. After an introduction into the structure and synthesis of POMs of the early transition metals, recently discovered water‐soluble antimonato polyoxovanadates (Sb‐POVs) and the investigation of their chemical reactivity are discussed. Electrospray ionization mass spectrometry (ESI‐MS) is presented as an analytical technique suitable to investigate the structure of complex POM assemblies in solution and to probe the underlying reactivity and formation mechanisms. This Minireview highlights the first studies on the soluble Sb‐POVs and how the knowledge of their reactivity obtained by ESI‐MS has fostered the syntheses of numerous novel Sb‐POV compounds. First soluble hetero‐polyoxovanadates were discovered and led to the generation of more complex polyoxometalate structures by post‐functionalization reactions. Electrospray ionization mass spectrometry greatly contributed to the understanding of the solution chemistry of this intriguing compound class and is highlighted here as a means to analyze structure and reactivity of polyoxometalates. [ABSTRACT FROM AUTHOR]

Recrystallization of the bismuth oxido cluster [Bi38O45(OMc)24(dmso)9]·2dmso·7H2O (A) (OMc = O2C4H5) from alcohols such as EtOH and iPrOH gave single crystals of the bismuth oxido clusters [Bi38O45(OMc)24(ROH)x(H2O)y] [R = Et, x = 13, y = 0 (1); R = iPr, x = 10, y = 2 (2)]. Both compounds crystallize in the triclinic space group P1 and exhibit minor deviations in their cell parameters [1: a = 17.0156(5) Å, b = 19.0048(5) Å, c = 20.2100(5) Å, α = 111.182(2) °, β = 111.475(2) °, γ = 100.716(2) °, V = 5275.7(3) Å3; 2: a = 17.2512(7) Å, b = 19.3712(7) Å, c = 19.6248(8) Å, α = 112.803(3) °, β = 105.969(3) °, γ = 100.183(3) °, V = 5507.08(40) Å3]. ESI‐MS studies show that the bismuth oxido clusters 1 and 2 are more easily desolvated as reported for the dmso adduct A. Collision‐induced dissociation (CID) experiments on the solvent free cluster ions reveal a new fragmentation path for the methacrylate ligands. They split into C3H4 fragments as the leaving group and a formate remains bound at the cluster core. Bismuth particles are formed after annealing of 1 at 300 °C, whereas a composite consisting of Bi/β‐Bi2O3/C was formed in the temperature range of 400 °C to 600 °C. Calcination of 1 at 300 °C and 400 °C provided the formation of an amorphous material containing bismuth and a composite composed of β‐Bi2O3/Bi2O2CO3/Bi/C, respectively. At higher calcination temperatures, α‐Bi2O3 was obtained. The decomposition products do not show any sulfate incorporation as observed for A. [ABSTRACT FROM AUTHOR]

This paper describes a new method for detecting phenols, by reaction with Gibbs reagent to form indophenols, followed by mass spectrometric detection. Unlike the standard Gibbs reaction, which uses a colorometric approach, the use of mass spectrometry allows for simultaneous detection of differently substituted phenols. The procedure is demonstrated to work for a large variety of phenols without para‐substitution. With para‐substituted phenols, Gibbs products are still often observed, but the specific product depends on the substituent. For para groups with high electronegativity, such as methoxy or halogens, the reaction proceeds by displacement of the substituent. For groups with lower electronegativity, such as amino or alkyl groups, Gibbs products are observed that retain the substituent, indicating that the reaction occurs at the ortho or meta position. In mixtures of phenols, the relative intensities of the Gibbs products are proportional to the relative concentrations, and concentrations as low as 1 μmol/L can be detected. The method is applied to the qualitative analysis of commercial liquid smoke, and it is found that hickory and mesquite flavors have significantly different phenolic composition. [ABSTRACT FROM AUTHOR]

The novel N-1-sulfonylcytosine-cyclam conjugates 1 and 2 conjugates are ionized by electrospray ionization mass spectrometry (ESI MS) in positive and negative modes (ES+ and ES-) as singly protonated/deprotonated species or as singly or doubly charged metal complexes. Their structure and fragmentation behavior is examined by collision induced experiments. It was observed that the structure of the conjugate dictated the mode of the ionization: 1 was analyzed in ES- mode while 2 in positive mode. Complexation with metal ions did not have the influence on the ionization mode. Zn2+ and Cu2+ complexes with ligand 1 followed the similar fragmentation pattern in negative ionization mode. The transformation from 2°-amine in 1 to 3°-amine of cyclam ring in 2 leads to the different fragmentation patterns due to the modification of the protonation priority which changed the fragmentation channels within the conjugate itself. Cu2+ ions formed complexes practically immediately, and the priority had the cyclam portion of the ligand 2. The structure of the formed Zn2+ complexes with ligand 2 depended on the number of 3° amines within the cyclam portion of the conjugate and the ratio of the metal:ligand used. The cleavage of the cyclam ring of metal complexes is driven by the formation of the fragment that suited the coordinating demand of the metal ions and the collision energy applied. Finally, it was shown that the structure of the cyclam conjugate dictates the fragmentation reactions and not the metal ions. [ABSTRACT FROM AUTHOR]

Abstract: Intramolecular, homolytic substitution reactions between iron(II) species and various trialkylsulfonium groups were directly observed in the gas phase upon collision‐induced dissociation. In spite of the notoriously low reduction potential of trialkylsulfonium species and the mismatched oxidation potential of iron(II), the reactions proceed at moderate collision energies, forming an alkyl radical as well as a thioether coordinated to the iron. In contrast to classical homolytic substitutions, the attacking radical is a “metalloradical”, namely iron(II) that is oxidized to iron(III) during the reaction. With this process we demonstrate that the conceptually analogous, putative radical generation step in radical S‐adenosyl methionine (SAM) enzymes is possible and plausible. Further, we show that this kind of reaction only occurs in constrained systems with a defined geometry. Combining experimental measurements with DFT studies and NBO analyses allowed us to gain insights into the reactivity and transition states of these systems. Based on our findings, we challenge the notion of a collinear transition state in the radical generation step of radical SAM enzymes and propose it to be bent instead. [ABSTRACT FROM AUTHOR]

CIGB-300 is a first-in-class synthetic peptide-based drug of 25 amino acids currently undergoing clinical trials in cancer patients. It contains an amidated disulfide cyclic undecapeptide fused to the TAT cell-penetrating peptide through a beta-alanine spacer. CIGB-300 inhibits the CK2-mediated phosphorylation leading to apoptosis of tumor cells in vitro, and in vivo in cancer patients. Despite the clinical development of CIGB-300, the characterization of peptide-related impurities present in the active pharmaceutical ingredient has not been reported earlier. In the decision tree of ICHQ3A(R2) guidelines, the daily doses intake, the abundance, and the identity of the peptide-related species are pivotal nodes that define actions to be taken (reporting, identification, and qualification). For this, purity was first assessed by reverse-phase chromatography (>97%) and low-abundance impurities (=0.27%) were collected and identified by mass spectrometry. Most of the impurities were generated during peptide synthesis, the spontaneous air oxidation of the reduced peptide, and the lyophilization step. The most abundant impurity, with no biological activity, was the full-length peptide containing Met17 transformed into a sulfoxide residue. Interestingly, parallel and antiparallel dimers of CIGB-300 linked by 2 intermolecular disulfide bonds exhibited a higher antiproliferative activity than the CIGB-300 monomer. Likewise, very low abundance trimers and tetramers of CIGB-300 linked by disulfide bonds (=0.01%) were also detected. Here we describe for the first time the presence of active dimeric species whose feasibility as novel CIGB-300 derived entities merits further investigation. [ABSTRACT FROM AUTHOR]

Zinc finger (ZF) protein motifs, stabilized by binding of Zn(II), typically function as interaction modules that bind nucleic acids, proteins and other molecules. The elucidation of the redox states of ZF proteins in cellular conditions, which depend on their midpoint redox potentials, is important for understanding of ZF functioning. In the present study we determined the midpoint redox potentials for representatives of Cys2His2 and Cys4 types of ZF proteins in apo and Zn(II)‐bound forms using electrospray ionization mass spectrometry. The midpoint redox potentials of the apo forms of Cys2His2 and Cys4 ZF proteins were −326 and −365 mV (pH 7.5), respectively. These values are close to the cytosolic redox potential of approx. −350 mV (pH 7.5) and thus we can conclude that the apo form of Cys2His2‐type ZF proteins is predominantly reduced but apo forms of Cys4‐type ZF proteins should be substantially oxidized in the cytoplasm. As expected, Zn(II) binding stabilized the reduced forms of both ZF proteins: the corresponding redox potential values were −284 and −301 mV, respectively. Consequently, binding of Zn(II) ions to ZF motifs can act as a sensitive switch that activates the functioning of the ZF motifs within the cell, and also protects them from oxidation and can function as part of a redox‐sensitive regulation mechanism of cellular functions. [ABSTRACT FROM AUTHOR]

Abstract: A new antimonato polyoxovanadate {Zn(en)3}3[V15Sb6O42(H2O)]⋅3 en⋅10 H2O (en=ethylenediamine) synthesized under hydrothermal conditions exhibits remarkable solubility in water. Electrospray ionization mass spectrometry (ESI‐MS) investigations on an aqueous solution demonstrate that the cluster core remains fully intact for 72 h. At longer times, slow transformation into a {V14Sb8O42} cluster is observed. The conversion reaches 50 % after 14 days and is complete after approximately 20 days. The rate of this {V15Sb6}→{V14Sb8} cluster transformation is significantly increased in the presence of ammonium acetate. Applying the new compound as a synthon in the presence of 1,10‐phenanthroline (phen) led to crystallization of {Zn(phen)3}2[Zn(en)2V15Sb6O42(H2O)]⋅23 H2O after a short reaction time, whereas addition of Sb2O3 led to fast crystallization of {(Zn(en)2(H2O)2)(Zn(en)2)}[Zn(en)2V15Sb6O42(H2O)] ⋅8.5 H2O. In the crystal structure of {Zn(en)3}3 [V15Sb6O42(H2O)]⋅3 en⋅10 H2O, the en molecules are seen to be attached to the cluster anion through Sb−N bonds. In the structures of the two new compounds obtained, the [V15Sb6O42(H2O)]6− anions are expanded by Zn2+‐centered complexes through Zn−O−V bond formation. [ABSTRACT FROM AUTHOR]

Abstract: Ein wasserlöslicher Abkömmling des Polyoxovanadat‐Archetyps {V15E6O42} (E=Halbmetall) ermöglicht die Untersuchung supramolekular induzierter Clusterschalen‐Umwandlungen. Eine für E=Sb spezifische Reaktion, die durch einen Ligandenaustausch in [Ni(ethylendiamin)3]2+‐Gegenionen eingeleitet wird, resultiert in der Bildung des metastabilen α1*‐Konfigurationsisomers des {V14Sb8O42}‐Clustertyps. Im Unterschied zu allen bisher bekannten Polyoxovanadat‐Schalenarchitekturen weist dieses Isomer eine nach innen ausgerichtete Vanadylgruppe auf und ist ca. 50 bzw. 12 kJ mol−1 energiereicher als die zuvor isolierten α‐ und β‐Isomere. Diese unerwartete Reaktion wird im Hinblick auf supramolekulare Sb‐O⋅⋅⋅V‐ und Sb‐O⋅⋅⋅Sb‐Bindungen diskutiert, die sich in {V14Sb8O42}2‐Dimeren im Festkörper manifestieren. ESI‐MS‐Experimente untermauern die Stabilität dieser Dimere auch in Lösung und in der Gasphase. DFT‐Rechnungen zufolge sollten so auch weitere, bislang noch nicht gefundene {V14Sb8}‐Isomere zugänglich sein. [ABSTRACT FROM AUTHOR]

Noncovalent, weak interactions in the second coordination sphere of the copper active site of Pseudoazurin (PAz) from Achromobacter cycloclastes were examined using a series of Met16X variants. In this study, the differences in protein stability due to the changes in the nature of the 16th amino acid (Met, Phe, Val, Ile) were investigated by electrospray ionization mass spectrometry (ESI-MS) and far-UV circular dichroism (CD) as a result of acid denaturation. The percentage of native states (folded holo forms) of Met16Phe variants was estimated to be 75% at pH 2.9 although the wild-type (WT), Met16Val and Met16Ile PAz, became completely unfolded. The high stability under acidic conditions is correlated with the result of the active site being stabilized by the aromatic substitution of the Met16 residue. The π-π interaction in the second coordination sphere makes a significant contribution to the stability of active site and the protein matrix. [ABSTRACT FROM AUTHOR]

Non-enzyme-dependent hydrolysis of the drug cisplatin is important for its mode of action and toxicity. However, up until today, the hydrolysis process of cisplatin is still not completely understood. In the present study, the hydrolysis of cisplatin in an aqueous solutionwas systematically investigated by using electrospray ionization mass spectrometry coupled to liquid chromatography. A variety of previously unreported hydrolysis complexes corresponding to monomeric, dimeric and trimeric species were detected and identified. The characteristics of the Pt-containing complexes were investigated by using collision-induced dissociation (CID). The hydrolysis complexes demonstrate distinctive and correlative CID characteristics, which provides tools for an informative identification. The most frequently observed dissociation mechanismwas sequential loss of NH3, H2O and HCl. Loss of the Pt atom was observed as the final step during the CID process. The formation mechanisms of the observed complexes were explored and experimentally examined. The strongly bound dimeric species, which existed in solution, are assumed to be formed from the clustering of the parent compound and its monohydrated or dihydrated complexes. The role of the electrospray process in the formation of some of the observed ions was also evaluated, and the electrospray ionization-related cold clusters were identified. The previously reported hydrolysis equilibria were tested and subsequently refined via a hydrolysis study resulting in a renewed mechanistic equilibrium system of cisplatin as proposed from our results. [ABSTRACT FROM AUTHOR]

Human metallothionein 1a, a protein with two cysteine-rich metal-binding domains (α with 11 Cys and β with 9), was analyzed in its metal-free form by selective, covalent Cys modification coupled with ESI-MS. The modification profiles of the isolated β- and α-fragments reacted with p-benzoquinone (Bq), N-ethylmalemide (NEM) and iodoacetamide (IAM) were compared with the full length protein using ESI-mass spectral data to follow the reaction pathway. Under denaturing conditions at low pH, the reaction profile with each modifier followed pathways that resulted in stochastic, Normal distributions of species whose maxima was equal to the mol. eq. of modifier added. Our interpretation of modification at this pH is that reaction with the cysteines is unimpeded when the full protein or those of its isolated domains are denatured. At neutral pH, where the protein is expected to be folded in a more compact structure, there is a difference in the larger Bq and NEM modification, whose reaction profiles indicate a cooperative pattern. The reaction profile with IAM under native conditions follows a similar stochastic distribution as at low pH, suggesting that this modifier is small enough to access the cysteines unimpeded by the compact structure. The data emphasize the utility of residue modification coupled with electrospray ionization mass spectrometry for the study of protein structure. [ABSTRACT FROM AUTHOR]

Concentration of the surface active agents in industrial products is a common source of error. In order to compare the efficiency of a number of polyisobutylene succinic anhydride (PIBSA) based surfactants, their concentration needs to be determined with a fair degree of accuracy. Industrial samples of the monoethanolamine adduct of PIBSA (PIBSA-MEA) concentrate were used for chromatographic separation of the functionalized surfactant from the sample matrix. Complete spectroscopic assignments were based on detailed analysis of all the precursors and of the purified mixture of structural isomers. The structures of the double bond isomers were consistent with the expected addition products of the classic Alder-ene reaction-derived PIBSA. The carbon-carbon connectivity of the succinamide head group to the bulky polymer tail of PIBSA-MEA was more complicated than previously thought, pointing towards regioselectivity in the nucleophilic substitution of PIBSA. By analogy, further structural assignments of two other surfactants, branded as PIBSA-IMIDE and PIBSA-UREA were made from the spectroscopic data recorded on crude industrial samples. Detailed nuclear magnetic resonance (NMR) assignments for all three surfactants reported here were utilized to develop a semi-quantitative C-NMR based method for the estimation of the amount of the functionalized surfactant relative to the total PIB content in the industrial concentrates. The results highlight common sources of structure- and concentration-dependent errors in high internal phase emulsion formulations. [ABSTRACT FROM AUTHOR]

The aim of this report is to present the electrospray ionization mass spectrometry results of the non-covalent interaction of two biologically active ligands, N-1-(p-toluenesulfonyl)cytosine, 1-TsC, 1 and N-1-methanesulfonylcytosine, 1-MsC, 2 and their Cu(II) complexes Cu(1-TsC-N3)2Cl2, 3 and Cu(1-MsC-N3)2Cl2 and 4 with biologically important cations: Na+, K+, Ca2+, Mg2+ and Zn2+. The formation of various complex metal ions was observed. The alkali metals Na+ and K+ formed clusters because of electrostatic interactions. Ca2+ and Mg2+ salts produced the tris ligand and mixed ligand complexes. The interaction of Zn2+ with 1–4 produced monometal and dimetal Zn2+ complexes as a result of the affinity of Zn2+ ions toward both O and N atoms. [ABSTRACT FROM AUTHOR]

Short guanine(G)-repeat and cytosine(C)-repeat DNA strands can self-assemble to form four-stranded G-quadruplexes and i-motifs, respectively. Herein, G-rich and C-rich strands with non-G or non-C terminal bases and different lengths of G- or C-repeats are mixed selectively in pH4.5 and 6.7 ammoniumacetate buffer solutions and studied by electrospray ionizationmass spectrometry (ESI-MS). Various strand associations corresponding to bi-, tri- and tetramolecular ions are observed in mass spectra, indicating that the formation of quadruplex structures is a random strand by strand association process. However, with increasing incubation time for the mixtures, initially associated hybrid tetramers will transform into self-assembled conformations, which is mainly driven by the structural stability. The melting temperature values of self-assembled quadruplexes suggest that the length of G-repeats or C-repeats shows more significant effect on the stability of quadruplex structures than that of terminal residues. Accordingly, we can obtain the self-associated tetrameric species generated from the mixtures of various homologous G- or C-strands efficiently by altering the length of G- or C-repeats. Our studies demonstrate that ESI-MS is a very direct, fast and sensitive tool to provide significant information on DNA strand associations and stoichiometric transitions, particularly for complex mixtures. [ABSTRACT FROM AUTHOR]

Five niobium cluster compounds of the AI2[Nb6Cl18] type ( AI = organic cation: [ nPr4N]+, [ nBu4N]+, [BMIm]+, [Ph4P]+, and [PPN]+) are obtained through treatment of [Nb6Cl14(H2O)4] ·4H2O with excess of thionyl chloride in the presence of an organic chloride, AICl. Single-crystal structure studies show that the compounds consist of discrete cations and cluster [Nb6Cl18]2- anions. The cluster unit of the hydrated cluster starting material is oxidized by two electrons. Powder diffraction studies and NMR spectroscopic measurements show all compounds to crystallize without co-crystallized solvent molecules. They are air and water stable. The solubility in organic solvents changes to a great extent on changing the type of cation. The ESI-MS spectra of [ nPr4N]2[Nb6Cl18] and [Ph4P]2[Nb6Cl18] show the pseudomolecular peak of the anionic cluster as well as additional signals, which involve simultaneously chloride mass loss and reduction processes. [ABSTRACT FROM AUTHOR]

The Updated Bottom Up Solution (UBUS) was recently applied to atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) of triacylglycerols (TAG). This report demonstrates that the UBUS applies equally well to atmospheric pressure photoionization (APPI) MS and to electrospray ionization (ESI) MS. Critical Ratio 1 (CR1), the [MH]/Σ[DAG] or [MNH]/Σ[DAG] ratio, does not exhibit the same strongly sigmoidal shape as it does by APCI-MS. CR1 varies more widely for APPI-MS than by APCI-MS, having a maximum value of 11.8, indicating a much greater effect of unsaturation on ion ratios in APPI-MS than APCI-MS. Critical Ratio 2, the [AA]/[AB] ratio for Type II TAG or [AC]/([AB]+[BC]) ratio for Type III TAG, allows quantification of regioisomers of TAG, and shows good agreement for APPI-MS to regioisomer quantification determined by APCI-MS. Critical Ratio 3, the [BC]/[AB] ratio for Type III TAG, reveals new trends relating the degree of unsaturation by APPI-MS, and shows that structural assignments made by ESI-MS are in good agreement to APCI-MS data. In addition to providing valuable structural information, the Critical Ratios also constitute a reduced data set that allows APPI-MS or ESI-MS mass spectra to be reconstructed when processed through the UBUS. Quantification by APPI-MS of vitamin D in the gelcaps gave values of 42.90 ± 0.83 μg, or 1716 ± 33 international units, in good agreement with APCI-MS. [ABSTRACT FROM AUTHOR]

N-substituted glycines constitute mimics of natural amino acids that are of great interest in the peptide-based drug development. Peptoids-oligo( N-substituted glycines) have been recently demonstrated to be highly active peptidomimetics in biological systems, resistant to proteolytic degradation. We developed a method of the deuterium labeling of peptidomimetics containing N-substituted glycine residues via H/D exchange of their α-carbon hydrogen atoms. The labeling was shown to be easy, inexpensive, and without the use of derivatization reagents or the need for a further purification. The deuterons introduced at the α-carbon atoms do not undergo a back exchange under acidic conditions during liquid chromatography mass spectrometry (LC-MS) analysis. The LC-MS analysis of a mixture of isotopologues revealed a co-elution of deuterated and nondeuterated forms of the peptidomimetics, which may be useful in the quantitative isotope dilution analysis of peptoids and other derivatives of N-substituted glycines. Copyright © 2015 European Peptide Society and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A luminescence-sensing process based on coordination compound [H2N(CH3)2]3[Tb(dipic)3] was developed. It shows fast response (within 1 min), high selectivity, and is ultrasensitive to detect Fe3+ or Cr3+ in aqueous solution and living cells ( KSV values are calculated to be 3.6×104 L mol−1 for Fe3+ and 1.9×104 L mol−1 for Cr3+). The whole recognition process has been witnessed through electrospray ionization mass spectrometry (ESI-MS) analysis, and the ligand-transfer-induced luminescence-quenching mechanism is interpreted. This work contributes to extend the potential applications of lanthanide coordination compounds (LnCCs) in the fields of biological and environmental technologies. [ABSTRACT FROM AUTHOR]

The probe electrospray ionization (PESI) is an ESI-based ionization technique that generates electrospray from the tip of a solid metal needle. In the present work, we describe the PESI mass spectra obtained by in situ measurement of soybeans and several nuts (peanuts, walnuts, cashew nuts, macadamia nuts and almonds) using different solid needles as sampling probes. It was found that PESI-MS is a valuable approach for in situ lipid analysis of these seeds. The phospholipid and triacylglycerol PESI spectra of different nuts and soybean were compared by principal component analysis (PCA). PCA shows significant differences among the data of each family of seeds. Methanolic extracts of nuts and soybean were exposed to air and sunlight for several days. PESI mass spectra were recorded before and after the treatment. Along the aging of the oil (rancidification), the formation of oxidated species with variable number of hydroperoxide groups could be observed in the PESI spectra. The relative intensity of oxidated triacylglycerols signals increased with days of exposition. Monitoring sensitivity of PESI-MS was high. This method provides a fast, simple and sensitive technique for the analysis (detection and characterization) of lipids in seed tissue and degree of oxidation of the oil samples. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Polar lipids of bacteria from the class Thermomicrobia are known to contain long-chain 1,2-diols instead of glycerol, although the nature of polar head groups has not been investigated. We have studied phospholipid classes of two species from the class Thermomicrobia- Sphaerobacter thermophilus and Thermomicrobia sp. WKT50.2. TLC and P-NMR analysis of polar lipids revealed that both S. thermophilus and Thermomicrobia sp. WKT50.2 contain the same set of four major phospholipid classes. Structures of the novel phospholipids in S. thermophilus were established as 2-acylalkyldiol-1- O-phosphoinositol, 2-acylalkyldiol-1- O-phosphoinositol mannoside, 2-acylalkyldiol-1- O-phospho-acylmannoside, and 2-acylalkyldiol-1- O-phosphoinositol acylmannoside. To our knowledge, this is the first report of a phospholipid with a mannose directly bound to the phosphate. We also analyzed fatty acids and long-chain 1,2-diols of S. thermophilus and Thermomicrobia sp. WKT50.2 and compared our data with available information for T. roseum. All species share a similar set of fatty acids, with 12-Me 18:0 being the major fatty acid. The major diol in S. thermophilus was identified as 13-Me 19:0 (66.2 %). The 21:0 diol was the major component both in Thermomicrobia sp. WKT50.2 (50.6 %) and in T. roseum (56.6 %). [ABSTRACT FROM AUTHOR]

It has been recognized that human hair lipids play crucial roles in the integrity of cells and matrices, while the details of distribution and structure of the minor lipids are hardly known. Here we investigated the lipids at the hair surface, at the interface between cuticle and cortex and in the interior of hair (cortex, medulla and melanin granules). Hair lipids and fatty acids and their metabolites were detected and characterized by using infrared spectroscopy and several mass spectrometry techniques (FTIR, ToF-SIMS, GCMS, and ESI-MS). As a result, it was found that unsaturated fatty acids were present more in the cortex of hair than at the hair surface. At the interface between cuticle and cortex, it is suggested that steryl glycoside-like lipids containing N-acetylglucosamine were present, and contributing to the adhesion between the cuticle and cortex of hair. Oxidative metabolites derived from integral fatty acids such as linoleic and alpha-linolenic acids were found in the hair bulb and melanin granules. Especially the oxidative metabolites of alpha-linolenic acid were integrated into the lipids non-covalently and tightly bound to melanin granules (namely, melanin lipids) and suggested as being involved in the biosynthetic processes of melanosome. [ABSTRACT FROM AUTHOR]

In order to establish a versatile and convenient method for the analysis of lipids, electrospray ionization tandem mass spectrometry (ESI-MS/MS) was applied to a HPLC separation on a cyanopropyl-bonded stationary phase. A binary gradient mobile phase system consisting of hexane, toluene, methanol and a stable electrospray yielding sodium adduct ions could be used to generate specific product ions in MS/MS mode. By applying the LC/ESI-MS/MS method on an egg yolk sample, 29 different molecular species of phosphatidylethanolamines, phosphatidylcholines, and lysophosphatidylcholines could be detected within 25 min. [ABSTRACT FROM AUTHOR]