Cold-spray Ionization Mass Spectrometry Research Articles

Intramolecular C-H Oxidation in Iron(V)-oxo-carboxylato Species Relevant in the γ-Lactonization of Alkyl Carboxylic Acids.

High-valent oxoiron species have been invoked as oxidizing agents in a variety of iron-dependent oxygenases. Taking inspiration from nature, selected nonheme iron complexes have been developed as catalysts to elicit C-H oxidation through the mediation of putative oxoiron(V) species, akin to those proposed for Rieske oxygenases. The addition of carboxylic acids in these iron-catalyzed C-H oxidations has proved highly beneficial in terms of product yields and selectivities, suggesting the direct involvement of iron(V)-oxo-carboxylato species. When the carboxylic acid functionality is present in the alkane substrate, it acts as a directing group, enabling the selective intramolecular γ-C-H hydroxylation that eventually affords γ-lactones. While this mechanistic frame is solidly supported by previous mechanistic studies, direct spectroscopic detection of the key iron(V)-oxo-carboxylato intermediate and its competence for engaging in the selective γ-C-H oxidation leading to lactonization have not been accomplished. In this work, we generate a series of well-defined iron(V)-oxo-carboxylato species (2c-2f) differing in the nature of the bound carboxylate ligand. Species 2c-2f are characterized by a set of spectroscopic techniques, including UV-vis spectroscopy, cold-spray ionization mass spectrometry (CSI-MS), and, in selected cases, EPR and Mössbauer spectroscopies. We demonstrate that 2c-2f undergo site-selective γ-lactonization of the carboxylate ligand in a stereoretentive manner, thus unequivocally identifying metal-oxo-carboxylato species as the powerful yet selective C-H cleaving species in catalytic γ-lactonization reactions of carboxylic acids. Reactivity experiments confirm that the intramolecular formation of γ-lactones is in competition with the intermolecular oxidation of external alkanes and olefins. Finally, mechanistic studies, together with DFT calculations, support a mechanism involving a site-selective C-H cleavage in the γ-position of the carboxylate ligand by the oxo moiety, followed by a fast carboxylate rebound, eventually leading to the selective formation of γ-lactones.

Coordination Variations within Binuclear Copper Dioxygen-Derived (Hydro)Peroxo and Superoxo Species; Influences upon Thermodynamic and Electronic Properties.

Copper ion is a versatile and ubiquitous facilitator of redox chemical and biochemical processes. These include the binding of molecular oxygen to copper(I) complexes where it undergoes stepwise reduction-protonation. A detailed understanding of thermodynamic relationships between such reduced/protonated states is key to elucidate the fundamentals of the chemical/biochemical processes involved. The dicopper(I) complex [CuI2(BPMPO-)]1+ {BPMPOH = 2,6-bis{[(bis(2-pyridylmethyl)amino]methyl}-4-methylphenol)} undergoes cryogenic dioxygen addition; further manipulations in 2-methyltetrahydrofuran generate dicopper(II) peroxo [CuII2(BPMPO-)(O22-)]1+, hydroperoxo [CuII2(BPMPO-)(-OOH)]2+, and superoxo [CuII2(BPMPO-)(O2•-)]2+ species, characterized by UV-vis, resonance Raman and electron paramagnetic resonance (EPR) spectroscopies, and cold spray ionization mass spectrometry. An unexpected EPR spectrum for [CuII2(BPMPO-)(O2•-)]2+ is explained by the analysis of its exchange-coupled three-spin frustrated system and DFT calculations. A redox equilibrium, [CuII2(BPMPO-)(O22-)]1+ ⇄ [CuII2(BPMPO-)(O2•-)]2+, is established utilizing Me8Fc+/Cr(η6-C6H6)2, allowing for [CuII2(BPMPO-)(O2•-)]2+/[CuII2(BPMPO-)(O22-)]1+ reduction potential calculation, E°' = -0.44 ± 0.01 V vs Fc+/0, also confirmed by cryoelectrochemical measurements (E°' = -0.40 ± 0.01 V). 2,6-Lutidinium triflate addition to [CuII2(BPMPO-)(O22-)]1+ produces [CuII2(BPMPO-)(-OOH)]2+; using a phosphazene base, an acid-base equilibrium was achieved, pKa = 22.3 ± 0.7 for [CuII2(BPMPO-)(-OOH)]2+. The BDFEOO-H = 80.3 ± 1.2 kcal/mol, as calculated for [CuII2(BPMPO-)(-OOH)]2+; this is further substantiated by H atom abstraction from O-H substrates by [CuII2(BPMPO-)(O2•-)]2+ forming [CuII2(BPMPO-)(-OOH)]2+. In comparison to known analogues, the thermodynamic and spectroscopic properties of [CuII2(BPMPO-)] O2-derived adducts can be accounted for based on chelate ring size variations built into the BPMPO- framework and the resulting enhanced CuII-ion Lewis acidity.

General Synthesis of meso-1,4-Dialdehydes and Their Application in Ir-Catalyzed Asymmetric Tishchenko Reactions.

A practical synthesis of meso-1,4-dialdehydes based on the oxidative cleavage of cyclobutanediol derivatives using polymer-supported periodate was developed. The meso-1,4-dialdehydes were obtained in up to >99% yield and subsequently employed in Ir-catalyzed asymmetric Tishchenko reactions to give the corresponding chiral lactones, which are versatile synthetic intermediates, in good yield with moderate enantiomeric excess. The catalytically active species was identified by means of cold-spray ionization mass spectrometry and 1H NMR spectroscopy.

Comprehensive analysis of Sini decoction and investigation of acid-base self-assembled complexes using cold spray ionization mass spectrometry

Decoctions are a staple of traditional Chinese medicine. This study reports on a comprehensive analysis of the chemical compositions of both the supernatant and naturally-occurring precipitate of Sini decoction using ultra-high-performance liquid chromatography (UHPLC) hyphenated with quadrupole-Orbitrap high-resolution mass spectrometry (Q-Orbitrap HRMS). A total of 99 compounds (40 flavonoids, 34 alkaloids, 7 terpenoids, 3 phenolic acids and 15 other compounds) were tentatively identified in the full-scan MS/data-dependent MS/MS (full-scan MS1/dd-MS2) acquisition mode. Moreover, cold spray ionization-mass spectrometry (CSI-MS) was used to explore the presence of self-assembled complexes between phytochemical ingredients. As a proof-of-concept demonstration, the complexation between one acidic compound (glycyrrhizic acid) and three basic compounds (aconitine, hypaconitine, and mesaconitine) was characterized. This study may present inspiring scientific evidence for the formation of naturally-occurring precipitate, enabling a better understanding of Sini decoction and its therapeutic relevance.

Cold‐spray ionization mass spectrometry of the choline chloride‐urea deep eutectic solvent (reline)

Cold-Spray Ionization mass spectrometry (CSI-MS) that can be compared to an electrospray ionization (ESI) source acting with a nebulizing gas cooled by liquid nitrogen is used for analyzing reline as Deep Eutectic Solvent (DES). The association of cholinium chloride salts with urea molecules is evidenced in negative CSI-MS through the chloride adduct formation. The structure of the supramolecular assemblies forming the reline ions that are observed on CSI mass spectra is rationalized by chemical quantum calculations. The theoretical studies indicate that the ionic network organization is only supported by a maximization of hydrogen bonds of the chlorides with the hydroxyl and methyl moieties of the cholinium cations and the amino groups of urea. The studies of gas-phase fragmentation of the supra-molecular ionic assemblies detected in CSI-MS are performed using the in-source collision-induced dissociation experiments. The experimental measurements in CSI-MS, interpreted at the light of the molecular modelization results, suggest that the insertion of urea in adducts of chlorides with cholinium cations does not lead to the most stable ions.

An Octanuclear Cobalt Cluster Protected by Macrocyclic Ligand: In Situ Ligand-Transformation-Assisted Assembly and Single-Molecule Magnet Behavior.

Macrocyclic molecules with multiple coordination sites have been widely used as promising ligands to build polynuclear metal clusters; however, cyclic silsesquioxane-based metal clusters are still rare. Herein, we report a new octanuclear Co-silsesquioxane cluster [Co8(OH)2{(MeSiO2)6}2(bpy)2(Obpy)2] (SD/Co8c; SD = SunDi), wherein the Co8 disc-like core is sandwiched by two hexamethylcyclohexasiloxanolate ligands (MeSiO2)6 at two poles and finally encircled by two bpy (bpy = 2,2'-bipyridine) and two Obpy (HObpy = 6-hydroxy-2,2'-bipyridine) ligands at the equatorial region. Interestingly, both MeSi(OMe)3 and bpy undergo in situ transformations to generate hexameric cyclic (MeSiO2)6 and Obpy, respectively. The unusual hydroxylation of bpy and the OH- anion in the center of Co8 core provide additional binding sites to induce the formation of the larger cluster instead of the traditional hexanuclear cluster. The solution stability and fragmentation route in the gas phase were studied by cold-spray ionization and collision-induced dissociation mass spectrometry, respectively. Both results reveal that the Co8 core is quite stable in solution as well as in the gas phase, even with increased collision voltage. Magnetic susceptibility studies of SD/Co8c show the slow magnetization relaxation indicative of single-molecule magnet (SMM) behavior. This work not only presents the multiple in situ ligand-transformation-assisted assembly of polynuclear cobalt cluster but also provides some new insights into the magnetism-structure relationship for SMMs.

Study of the noncovalent interactions between phenolic acid and lysozyme by cold spray ionization mass spectrometry (CSI-MS), multi-spectroscopic and molecular docking approaches

Elucidating the recognition mechanisms of the noncovalent interactions between pharmaceutical molecules and proteins is important for understanding drug delivery in vivo, and for the further rapid screening of clinical drug candidates and biomarkers. In this work, a strategy based on cold spray ionization mass spectrometry (CSI-MS), combined with fluorescence, circular dichroism (CD), Fourier transform infrared spectroscopy (FTIR), and molecular docking methods, was developed and applied to the study of the noncovalent interactions between phenolic acid and lysozyme (Lys). Based on the real characterization of noncovalent complex, the detailed binding parameters, as well as the protein conformational changes and specific binding sites could be obtained. CSI-MS and tandem mass spectrometry (MS/MS) technique were used to investigate the phenolic acid-Lys complexes and the structure-affinity relationship, and to assess their structural composition and gas phase stability. The binding affinity was obtained by direct and indirect MS methods. The fluorescence spectra showed that the intrinsic fluorescence quenching of Lys in solution was a static quenching mechanism caused by complex formation, which supported the MS results. The CD and FTIR spectra revealed that phenolic acid changed the secondary structure of Lys and increased the α-helix content, indicating an increase in the tryptophan (W) hydrophobicity near the protein binding site resulting in a conformational alteration of the protein. In addition, molecular docking studies were performed to investigate the binding sites and binding modes of phenolic acid on Lys. This strategy can more comprehensively and truly characterize the noncovalent interactions and can guide further research on the interactions of phenolic acid with other proteins.

Mechanism study on the abnormal accumulation and deposition of islet amyloid polypeptide by cold-spray ionization mass spectrometry.

The abnormal accumulation and deposition of islet amyloid polypeptide (IAPP) are important causes of type-2 diabetes mellitus (T2DM). The common anti-amyloid strategy employs inhibitors to prevent the formation of oligomers and the cytotoxicity caused by them, thus reducing the production of amyloid fibres. Therefore, the real characterization of the oligomers formed at the early stage of aggregation is crucial to understanding the structure of IAPP and the drug development of T2DM. For the first time, in this study, native cold-spray ionization mass spectrometry (CSI-MS) technology was employed to characterize the oligomers. It was found that CSI was more suitable for the determination of these unstable species compared to traditional ESI-MS. The ionic strengths, organic solvent and pH all had effects on the characterization of oligomers and the stability of protein conformation. The MS/MS experiments showed that odd-charge dimer ions were mainly composed of two monomer products. Moreover, a CSI-MS method for the rapid screening of IAPP-inhibitors was established and two of the most potential inhibitors (rutin and quercitrin) were screened from a series of flavonoids. Then, the structure-activity relationship and the mechanism between flavonoids and IAPP were studied. The results showed that 3-OH and sugar chains play a vital role and hydrogen bonds are the main binding force. We further confirmed that rutin and quercitrin could effectively inhibit the fibre formation of IAPP by fluorescence and TEM experiments. This study provides a new insight for analyzing the structure of IAPP and screening potential drugs for T2DM.

Study of the noncovalent interactions of ginsenosides and amyloid-β-peptide by CSI-MS and molecular docking.

Noncovalent interactions between drugs and proteins play significant roles for drug metabolisms and drug discoveries. Mass spectrometry has been a commonly used method for studying noncovalent interactions. However, the harsh ionization process in electrospray ionization mass spectrometry (ESI-MS) is not conducive to the preservation of noncovalent and unstable biomolecular complexes compared with the cold spray ionization mass spectrometry (CSI-MS). A cold spray ionization providing a stable solvation-ionization at low temperature is milder than ESI, which was more suitable for studying noncovalent drug-protein complexes with exact stoichiometries. In this paper, we apply CSI-MS to explore the interactions of ginsenosides toward amyloid-β-peptide (Aβ) and clarify the therapeutic effect of ginsenosides on Alzheimer's disease (AD) at the molecular level for the first time. The interactions of ginsenosides with Aβ were performed by CSI-MS and ESI-MS, respectively. The ginsenosides Rg1 bounded to Aβ at the stoichiometries of 1:1 to 5:1 could be characterized by CSI-MS, while dehydration products are more readily available by ESI-MS. The binding force depends on the number of glycosyls and the type of ginsenosides. The relative binding affinities were sorted in order as follows: Rg1 ≈ Re > Rd ≈ Rg2 > Rh2, protopanaxatriol by competition experiments, which were supported by molecular docking experiment. CSI-MS is expected to be a more appropriate approach to determine the weak but specific interactions of proteins with other natural products especially polyhydroxy compounds.

A triangular palladium(II) supramolecular coordination complex based on 1,4-bis(1H-imidazol-1-yl)benzene and (2,2'-bipyridyl)palladium(II) nitrate: synthesis and crystal structure.

The self-assembly of ditopic bis(1H-imidazol-1-yl)benzene ligands (LH) and the complex (2,2'-bipyridyl-κ2N,N')bis(nitrato-κO)palladium(II) affords the supramolecular coordination complex tris[μ-bis(1H-imidazol-1-yl)benzene-κ2N3:N3']-triangulo-tris[(2,2'-bipyridyl-κ2N,N')palladium(II)] hexakis(hexafluoridophosphate) acetonitrile heptasolvate, [Pd3(C10H8N2)3(C12H10N4)3](PF6)6·7CH3CN, 2. The structure of 2 was characterized in acetonitrile-d3 by 1H/13C NMR spectroscopy and a DOSY experiment. The trimeric nature of supramolecular coordination complex 2 in solution was ascertained by cold spray ionization mass spectrometry (CSI-MS) and confirmed in the solid state by X-ray structure analysis. The asymmetric unit of 2 comprises the trimetallic Pd complex, six PF6- counter-ions and seven acetonitrile solvent molecules. Moreover, there is one cavity within the unit cell which could contain diethyl ether solvent molecules, as suggested by the crystallization process. The packing is stabilized by weak inter- and intramolecular C-H...N and C-H...F interactions. Interestingly, the crystal structure displays two distinct conformations for the LH ligand (i.e. syn and anti), with an all-syn-[Pd] coordination mode. This result is in contrast to the solution behaviour, where multiple structures with syn/anti-LH and syn/anti-[Pd] are a priori possible and expected to be in rapid equilibrium.

Characterization of structural requirement for binding of gigantol and aldose reductase.

We previously reported that gigantol extracted from Caulis Dendrobii has significant therapeutic benefits for the treatment of galactosemic cataracts through its ability to inhibit aldose reductase (AR) activity. In this study, we identified the binding sites and structurally characterized the interaction between gigantol and AR, to understand the mechanism (s) of the effects of gigantol on cataracts. Gigantol was found to be protective against diabetic cataracts (DC) in rats induced by streptozotocin. Molecular docking predicted the binding sites between AR and gigantol to be residues Trp111, His110, Tyr48 and Trp20. Mutation of each of these residues led to a significant reduction in AR activity. Cold-spray ionization mass spectrometry measurements showed that the binding of gigantol to AR is oncentration-dependent and that the maximum stoichiometric ratio of non-covalent bonding is 1:24.4. pH and temperature did not influence the interaction. Taken together, we provide further mechanistic evidence of the beneficial effects of gigantol on DC.

(Guanidine)copper Complex-Catalyzed Enantioselective Dynamic Kinetic Allylic Alkynylation under Biphasic Condition.

Highly enantioselective allylic alkynylation of racemic bromides under biphasic condition is furnished in this report. This approach employs functionalized terminal alkynes as pro-nucleophiles and provides 6- and 7-membered cyclic 1,4-enynes with high yields and excellent enantioselectivities (up to 96% ee) under mild conditions. Enantioretentive derivatizations highlight the synthetic utility of this transformation. Cold-spray ionization mass spectrometry (CSI-MS) and X-ray crystallography were used to identify some catalytic intermediates, which include guanidinium cuprate ion pairs and a copper-alkynide complex. A linear correlation between the enantiopurity of the catalyst and reaction product indicates the presence of a copper complex bearing a single guanidine ligand at the enantio-determining step. Further experimental and computational studies supported that the alkynylation of allylic bromide underwent an anti-SN2' pathway catalyzed by nucleophilic cuprate species. Moreover, metal-assisted racemization of allylic bromide allowed the reaction to proceed in a dynamic kinetic fashion to afford the major enantiomer in high yield.

One Electron-Initiated Two-Electron Oxidation of Water by Aluminum Porphyrins with Earth's Most Abundant Metal.

We report herein a new molecular catalyst for efficient water splitting, aluminum porphyrins (tetra-methylpyridiniumylporphyrinatealuminum: AlTMPyP), containing earth's most abundant metal as the central ion. One-electron oxidation of the aluminum porphyrin initiates the two-electron oxidation of water to form hydrogen peroxide as the primary reaction product with the lowest known overpotential (97 mV). The aluminum-peroxo complex was detected by a cold-spray ionization mass-spectrometry in high-resolution MS (HRMS) mode and the structure of the intermediate species was further confirmed using laser Raman spectroscopy, indicating the hydroperoxy complex of AlTMPyP to be the key intermediate in the reaction. The two-electron oxidation of water to form hydrogen peroxide was essentially quantitative, with a Faradaic efficiency of 99 %. The catalytic reaction was found to be highly efficient, with a turnover frequency up to ∼2×104 s-1 . A reaction mechanism is proposed involving oxygen-oxygen bond formation by the attack of a hydroxide ion on the oxyl-radical-like axial ligand oxygen atom in the one-electron-oxidized form of AlTMPyP(O- )2 , followed by a second electron transfer to the electrode.

Adamantane-based Bidendate Metal Complexes in Crystalline and Solution State.

Bidentate organic molecules with imidazole or benzimidazole moieties connected to a rigid 1,3-diphenyladamantane spacer are simple and unique building blocks that facilitate the assembly of supramolecular architectures in the solid state via metal-coordination. Single-crystal X-ray analysis revealed that the complexation of bidentate ligand-bearing imidazole moieties with cobalt(II) or cadmium(II) ions in methanol/chloroform produced complexes that showed doubly-interpenetrated two-dimensional (2D) sheets through the formation of coordination bonds between the cobalt or cadmium metal centers and the nitrogen atoms of the imidazole groups. In the complexation of another ligand bearing a bulky benzimidazole group with cobalt(II) ion generated in methanol/chloroform, extended zigzag one-dimensional (1D) chains were formed, indicating that the molecular shape and bulkiness of the ligand design are crucial in the control of coordination polymers. The crystallization solutions were subjected to cold-spray ionization mass spectrometry (CSI-MS), and ion peaks derived from complexes with metal-ligand 1:2 and 1:1 were observed in complexation with ligands bearing the imidazole and benzimidazole moieties, respectively. The metal-ligand ratio in the CSI-MS analysis was identical to that found in the single-crystal X-ray analysis of an independent molecule. In addition, coordination oligomers with large molecular weight were detected as part of the obtained coordination polymers observed by CSI-MS/MS.

Cation-Selective and Anion-Controlled Fluorogenic Behaviors of a Benzothiazole-Attached Macrocycle That Correlate with Structural Coordination Modes.

We report how the metal cation and its counteranions cooperate in the complexation-based macrocyclic chemosensor to monitor the target metal ion via the specific coordination modes. The benzothiazolyl group bearing NO2S2-macrocycle L was synthesized, and its mercury(II) selectivity (for perchlorate salt) as a dual-probe channel (UV-vis and fluorescence) chemosensor exhibiting the largest blue shift and the fluorescence turn-off was observed. In the mercury(II) sensing with different anions, except ClO4(-) and NO3(-), no responses for mercury(II) were observed with other anions such as Cl(-), Br(-), I(-), SCN(-), OAc(-), and SO4(2-). A crystallographic approach for the mononuclear mercury(II) perchlorate complex [Hg(L)(ClO4)2]·0.67CH2Cl2 (1) and polymeric mercury(II) iodide complex [Hg(L)I2]n (2) revealed that the observed anion-controlled mercury(II) sensing in the fluorescence mainly stems from the endo- and exocoordination modes, depending on the anion coordinating ability, which induces either the Hg-Ntert bond formation or not. The detailed complexation process with mercury(II) perchlorate associated with the cation sensing was also monitored with the titration methods by UV-vis, fluorescence spectroscopy, and cold-spray ionization mass spectrometry.

Self-assembly of an organo-palladium molecular basket that encapsulates cobalticarborane anion in water

Two [M3L3]6+-type organo-palladium(II) macrocyclic host molecules, {[(phen)Pd]3(4,7-phen)3}(NO3)6, 1·6NO3−; {[(dtod-phen)Pd]3(4,7-phen)3}(NO3)6, 2·6NO3−, (where M=(4,7-phen)Pd, (dtod-phen)Pd; 4,7-phen=4,7-phenanthroline (L), phen=1,10-phenanthroline, dtod-phen=5,6-di(1′,4′,7′,10′-tetraoxododecanoxy)-1,10-phenanthroline), have been synthesized by metal-directed self-assembly in aqueous solution. These basket-shaped hosts bearing syn, syn, syn orientations and their anion complexes, have been fully characterized by 1H NMR, cold-spray ionization mass spectrometry (CSI-MS) and in the case of basket-shaped host 1*PF6− by X-ray single-crystal diffraction analysis. On the basis of anion binding structure within the cavity of 1, the molecule basket 2 possessing a hydrophobic inner cavity expanded with hydrophilic polyethyleneglycol chains was successfully designed for encapsulating one giant anion [(C2B9H11)2Co]− in water and the host–guest interaction was studied by 1H NMR titration and CSI-MS.

Self-assembly of tri-pyrazolate linked cages with di-palladium coordination motifs.

By employing di-palladium complexes [(N^N)2Pd2(NO3(-))2](NO3(-))2 (where N^N = 2,2'-bipyridine, bpy; 4,4'-dimethylbipyridine, dmbpy; 1,10-phenanthroline, phen) as corners and tripyrazole functional ligands () as linkers, a series of highly-positively-charged tripyrazolate-bridged metallo-cages with different conformations and cavities such as [Pd6L2](6+) ( or , where L = L(1) or L(5)), [Pd10L(2)4](10+) (, and , where L = L(2) or L(4)) and [Pd12L4](12+) ( or , where L = L(3) or L4) have been synthesized through a di-metal coordination directed self-assembly with spontaneous deprotonation of the tripyrazole ligands in aqueous solution. These complexes have been fully characterized by (1)H and (13)C NMR, cold-spray ionization or electron spray ionization mass spectrometry (CSI-MS, ESI-MS) and elemental analysis. Complexes , , , and have also been determined by single-crystal X-ray diffraction structural analysis. In the case of complex , six PF6(-) anions were encapsulated within the cavity composed of adjacent di-Pd corners.

Construction of an M3L2A6 Cage with Small Windows from a Flexible Tripodal Ligand and Cu(hfac)3

An M3L2A6 cage has been prepared with small windows from a tripodal ligand, L, and Cu(hfac)2. Cold spray ionization mass spectrometry of a mixture of L and Cu(hfac)2 revealed the formation of a Cu3L2hfac6 cage in solution. X-ray crystallography showed that the Cu3L2hfac6 cage included neutral molecules such as THF and CHCl3. Furthermore, the six hfac anions have been shown to play an important role in holding neutral guest molecules securely in place.

Solvent-dependent Assembly of Discrete and Continuous CoCl2 Adamantane-based Ligand Complexes: Observations by CSI–Mass Spectrometry and X-ray Crystallography

Discrete and continuous coordination structures were obtained in single crystals of CoCl₂ and an adamantane-based bidentate ligand bearing imidazolyl groups, depending on the methanol concentration in a methanol-chloroform mixture. Single-crystal X-ray structure analysis revealed that the metal centers exhibited a tetrahedral geometry in the discrete complex and an octahedral geometry in the continuous metal complex. Conventional analytical methods, including UV-vis and NMR spectroscopy, could not identify those two complexes in solution. In contrast, cold-spray ionization mass spectrometry could detect differences between the discrete complex and the continuous metal complex, and ion peaks due to continuous ligand adducts were found only in the spectrum of the continuous metal complex.

Double Helices of a Pyridine-Appended Zinc Chlorophyll Derivative

Self-assembled structures formed from a pyridine-appended zinc chlorophyll derivative are reported. While the zinc complex forms cyclic oligomers in chloroform solution, as indicated by (1)H NMR studies (including diffusion-ordered spectroscopy), vapor pressure osmometry, and cold-spray ionization mass spectrometry, it forms double-stranded helical coordination polymers in the solid state, as revealed by single-crystal X-ray analysis.