Lanthanides (Lns) have recently been recognized as essential cofactors for certain bacterial enzymes, such as methanol dehydrogenase (MDH), yet their poor bioavailability under physiological conditions has long suggested the existence of Ln-binding metallophores termed lanthanophores. In this context methylolanthanin (MLL), a chelator which is potentially involved in Ln-uptake of methylotrophic bacteria, was recently isolated and characterized. Herein we synthesized two novel MLL derivatives, ortho- and meta-MLL, for comparative studies in order to gain a deeper insight into the unusual 4-hydroxy benzoate moiety of native para-MLL. For this we implemented UV-vis titrations, time-resolved laser-induced fluorescence spectroscopy (TRLFS) and ion mobility spectrometry-mass spectrometry (IMS-MS) complemented by density functional theory (DFT) calculations to investigate metal-binding behavior in both solution and gas phases to trivalent Lns. As our binding studies revealed that both artificial chelators tend to precipitate Lns similar to the native para-MLL under biologically relevant conditions (pH: 6.0), rather than solubilizing them, the solubility products of their Eu3+ complexes were determined. Due to the structural resemblance of the MLL derivatives to the siderophore rhodopetrobactin B (RPB B), we also investigated iron binding. In this regard ortho-MLL stood out in our analysis and showed a distinctly different binding behavior from the other two derivatives.

Over the recent years, lanthanide (Ln)-binding proteins such as lanmodulin, a naturally Ln-binding EF-hand protein from Methylorubrum extorquens AM1, as well as protein-inspired short Ln-binding peptides, have become of increasing interest for the development of separation and recycling methods for rare earth elements. Here, we comprehensively examined a set of head-to-tail cyclized lanmodulin-EF-hand sequence-inspired peptides and their complexation behavior toward Lns using time-resolved laser-induced fluorescence spectroscopy (TRLFS), isothermal titration calorimetry (ITC), nuclear magnetic resonance (NMR), and circular dichroism (CD) spectroscopies, complemented by molecular dynamic (MD) simulations and advanced mass spectrometry methods. Results obtained from this multi-method approach evidence that the head-to-tail cyclization can indeed increase the Ln affinity in some cases and positively impact the pre-organization of the metal-free peptide while predominantly forming 1:1 complexes in comparison to linear analogues, which can form both 1:1 and 1:2 species. Furthermore, the impact of a sequence alteration by inserting glycine at the head-to-tail junction is shown to be useful in NMR experiments for probing alterations in the local environment of neighboring amino acids (AA) potentially involved in coordination. Lastly, KD values for the peptides with the whole Ln series (except Pm) and the actinide curium are presented.

Over the recent years lanthanide-binding proteins such as lanmodulin, a naturally lanthanide-binding EF-hand protein from Methylorubrum extorquens AM1, as well as protein-inspired lanthanide-binding peptides have become of increasing interest for the development of separation and recycling methods for rare earth elements. For the first time, a set of head-to-tail cyclised lanmodulin-inspired peptides and their complexation behaviour towards lanthanides was comprehensively examined in aqueous media using time-resolved laser induced fluorescence spectroscopy (TRLFS), isothermal titration calorimetry (ITC), nuclear magnetic resonance (NMR) and circular dichroism (CD) spectroscopies, complemented by molecular dynamic (MD) simulations and advanced mass spectrometry methods. Results obtained from this multi-method approach evidence that the head-to-tail cyclisation can indeed increase the lanthanide-affinity in natural sequences and positively impact the pre-organisation of the metal-free peptide while limiting the amount of formed complex species in comparison to linear analogues. Furthermore, the impact of minimal sequence alterations by inserting glycine is shown to be useful in NMR experiments for probing alterations in the local environment of neighbouring amino acids potentially involved in coordination. Lastly, KD values for the peptides with the whole Ln series (except Pm) and the actinide curium are presented.

Methylobacterium species are prominent members of the plant phyllosphere, where they are exposed to fluctuating environmental conditions, including intense ultraviolet (UV) radiation. To mitigate such stressors, these bacteria commonly synthesise carotenoids as an oxidative protection. In this study, we investigated the carotenoid production of two closely related methylotrophic strains, Methylobacterium extorquens PA1 and AM1 (short PA1 & AM1), with a particular focus on the influence of iron availability. We identified and comprehensively structurally characterised the main carotenoid produced by both strains by using ultraviolet-visible (UV-Vis) spectroscopy, high-performance liquid chromatography (HPLC), high-resolution mass spectrometry (HRMS) with collision-induced dissociation (CID), ion mobility-mass spectrometry (IM-MS), nuclear magnetic resonance (NMR) spectroscopy, and ultrafast transient absorption (TA) spectroscopy. We show that both strains produce, unaffected by the iron availability, the same carotenoid, identified as 4-[2-O-11Zoctadecenoyl-β-D-glucopyranosyl]-4,4′-diapo-Ψ,Ψ-carotene-4,4′-dioate. However, the iron availability strongly influenced the carotenoid production making it an potentially interesting factor for boosting bacterial carotenogenis in biotechnological settings.

Copper(I) complexes exhibit efficient luminescent properties, such as thermally activated delayed fluorescence (TADF), making them attractive for applications in organic light-emitting diodes or sensors. While copper(I) complexes with 2-pyridyl phosphine ligands have been well studied, this work explores the effect of positional isomerism by using 3-pyridyl phosphine instead of 2-pyridyl phosphine, leading to a previously unreported double-bridged distorted tetrahedral structure with an unusually long average of the Cu···Cu distance of 6.238 Å. This new structural motif, enabled by the unique coordination behavior of the 3-pyridyl ligand, leads to excitation-dependent emission behavior with typical TADF behavior and photoluminescence quantum yields ranging from 0.11 to 0.83. Quantum mechanical calculations indicate that the excited-state transitions exhibit primarily metal-to-ligand and halide-to-ligand charge transfer character or a combination of both, which enhances the TADF response. This study highlights how small changes in the ligand topology can lead to fundamentally different coordination modes and photophysical response. The results offer structure-property relationships for copper(I)-based emitters and the development of future ligand derivatives for tunable optical properties.

Abstract Rare-earth metal triflates can modulate the structure, redox properties, and reactivity of transition-metal complexes when confined in supramolecular hosts. In this paper, we have investigated the inclusion of rare-earth metal triflates (Ln(OTf)3, Ln = Dy, Yb, La, Lu) into a cobalt(II) hemicryptophane tren cage (CoCageHCPT) using high-resolution electrospray ionization mass spectrometry (ESI-MS), cyclic traveling wave ion mobility mass spectrometry (cIM-TWIMS), host–guest exchange experiments, and examined the electrochemical properties using cyclic voltammetry. ESI-MS reveals the formation of dicationic inclusion complexes [CoII(CageHCPT)(Ln(OTf)3)]2+ with additional solvated adducts. Ion mobility measurements revealed the conformational flexibility of the empty cage complex, showing a broad distribution of isomers. In contrast, guest encapsulation yields defined geometries with only two dominant isomers, each with similar abundance and a close collisional cross-section in the range of 371–374 Å2. The DFT calculations revealed that the cap of the cage creates an attractive pocket for the lanthanum ion, while the side openings of the cage accommodate the coordinated triflate ions. In addition, one triflate anion is bridging, anchoring La(OTf)3 to the cobalt center. This rigid structure leads to the formation of two diastereoisomers of the inclusion complex, corresponding to the experimentally detected isomers. Equilibration experiments demonstrated fast host–guest exchange kinetics (kMS ≥ 0.5 s–1), indicating dynamic binding of Ln(OTf)3 within the cage cavity. Furthermore, cyclic voltammetry studies showed anodic shifts of the CoII/I (0.6 V) and CoI/0 (0.5 V) reduction waves upon Dy(OTf)3 inclusion, indicating strong Lewis-acid effects on the cobalt center. Overall, the combined results reveal that lanthanoid triflates form dynamic yet structurally defined inclusion complexes that substantially tune the redox properties of the cobalt cage system.

Isomer interconversion rate probed by ion mobility spectrometry.

Since its discovery, pyrroloquinoline quinone (PQQ) has been under constant investigation regarding its efficiency in biomimetic complexes for alcohol dehydrogenation. The discovery of lanthanide (Ln) dependent methanol dehydrogenases has led to the use of lanthanide complexes bearing PQQ derivatives to oxidize alcohols. However, the mechanism of these oxidations is still a subject of debate. Herein, La3+ and Lu3+ complexes of PQQ dimethyl ester (PQQDME), that are able to stoichiometrically oxidize an alcohol substrate, are reported. In the presence of air, some catalytic turnover is observed, but less than with other, more heavily modified PQQ biomimetics known in the literature. To investigate the reason for this low turnover, the reduced counterpart, PQQDMEH2, is synthesized. It is shown that in the presence of atmospheric oxygen, the complexes of the reduced form undergo oxidation and can then also convert alcohol to aldehyde. Additionally, the involvement of radicals in the alcohol oxidation reaction and the origin and nature of these radicals is investigated.

Ion mobility spectrometry (IMS) (also including IMS-IMS measurements) as well as DFT calculations have been used to study isomer distributions and isomer interconversion in a range of electrospray-generated lanthanide chloride cluster anions, LnxCl3x+1- (where x = 1-6, and Ln corresponds to the 15 lanthanide elements (except for radioactive Pm)). Where measurement and structural rearrangement timescales allow, we obtain almost quantitative agreement between experiment and theory thus confirming isomer predictions and reproducing isomer intensity ratios. LnxCl3x+1- structures reflect strong ionic bonding with limited directionality. Ring and chain motifs dominate for smaller clusters while for larger clusters more compact three-dimensional structures become favourable. At cluster sizes with two or more closely lying isomers, the lanthanide contraction can lead to systematic variations in structure types across the series.

Non-covalent interactions between polyoxometalates (POMs) and cyclodextrins (CDs) are often utilized to build novel supramolecular architectures for diverse applications. However, structure prediction becomes challenging with the increase in size and complexity of the assemblies. Herein, we investigate the conformer space of isolated non-covalent complexes of a Wells-Dawson type POM [P2W18O62]6- with cyclodextrins (γ-CD) using trapped ion mobility spectrometry (TIMS). We found that the 1 : 1 (POM : CD) complex exhibits one conformer whereas the 1 : 2 and 1 : 3 (POM : CD) complexes exhibit multiple conformers in the gas-phase, despite showing one stable form in their crystalline phase. The observation of distinct conformers in precise supramolecular aggregates of their complexes reflects the possible isomeric pathways in the growth of the assemblies. The structures of the conformers were resolved through a combination of TIMS and theoretical studies (DFT and GFN1-xTB). Moreover, we performed anion photoelectron spectroscopy (PES) studies, which revealed significant electronic stabilization of the POM anions upon complexation in the γ-CD cavity. This was evident from the increase in adiabatic detachment energy (ADE) of the [KPOM(γ-CD)1]5- complex compared to the [KPOM]5- anion by ∼2.4 eV. We also estimated gas-phase binding energies between the POM and γ-CD from the PES studies. Our work provides significant insights into the geometrical and electronic gas-phase structures of POM-CD non-covalent complexes. In the future, this would allow us to precisely design their solid-state assemblies from preformed gas-phase units by mass and isomer-selected ion deposition techniques.

A synergistic RECl3/[Cu(CH3CN)4]PF6 catalyst system enables the controlled, ring-opening polymerisation of THF at room temperature without the need for any additional initiators. High-molecular-weight PTHF (Mn = 209 kDa, & Dstrok; = 1.6) is obtained at low catalyst loadings, with tunable chain lengths via a targeted ligand addition.

A new, linear octadentate chelator, "en-pypa," based on 2,2'-bipyridine-6-carboxylic acid, has been developed. This ligand can bind trivalent lanthanoids (e.g., Sm, Eu, Tb, Dy, Tm, Yb, and Lu) very rapidly and yields well-defined complexes that exhibit relatively strong luminescence in aqueous solution. This study reports the synthesis, as well as the structural and photophysical characterization. In addition, nonradiative deactivation of near-infrared luminescence by the ligand N-H oscillators is addressed by comparison of the luminescence from the Yb complexes of en-pypa and its methylated analogue.

The question of lanthanide (Ln)-uptake in Ln-using bacteria has gained a lot of attention in recent years and the existence of specific Ln-binding metallophores, so-called lanthanophores, has been postulated. Here we investigate the recently isolated metallophore methylolanthanin (MLL), which was shown to be involved in Ln-metabolism of Methylobacterium extorquens AM1 along the structurally related siderophore rhodopetrobactin B (RPB B). We report the total synthesis of both chelators as well as Ln-binding investigations employing a multitude of spectroscopic methods. Compared to MLL, RPB B has a higher binding affinity for Fe3+. Unexpectedly, both metallophores seem to precipitate Lns under biologically relevant conditions (pH and concentration range). We used a combination of single-cell (sc)ICP MS and LC MS analysis of bacterial supernatant to investigate the Nd accumulation as well as MLL secretion under Fe limitation in M. extorquens AM1. Finally, we use ion mobility spectrometry-mass spectrometry (IMS-MS) and quantum chemical calculations to investigate the RPB B and MLL complexation in the gas phase with Fe3+ and all rare earth elements (except Pm). Our results challenge the classical siderophore-like Ln-uptake (via simple solubilisation) through MLL and underline again a potential complex interplay between Fe3+ and Ln3+ in microbial Ln-uptake.

Ion mobility spectrometry (IMS) is a powerful technique to determine structures and isomers of gas phase clusters and complex molecules. It is also a valuable tool to investigate ligand-protected atom-precise nanoclusters that cannot be readily crystallized and examined by X-ray diffraction. Here we use IMS to study a diphosphine-protected gold hydride nanocluster, [Au22H3(dppee)7]3+ (dppee = bis(2-diphenylphosphino)ethyl ether), which was synthesized previously and hypothesized to contain two Au11 units with different bridging ligands. Surprisingly, our IMS data revealed the coexistence of two structural isomers in the as-synthesized product with a population of ∼85% for the main isomer and ∼15% for the minor isomer. The two isomers are found to be interconvertible at high activation voltages. Comparison between the IMS data and theoretical calculations confirm that the main and minor isomers consist of one and three bridging ligands, respectively. The isomers and isomerization process uncovered in this work provide opportunities to study the structure-property relationship of atomically precise metal nanoclusters.

Selective peptide ligands for lanthanides (Ln) have multiple applications in, for example, Ln-separation and recycling or as lanthanide-binding tags. Optimizing peptides for Ln-binding can be cumbersome and many techniques need high sample volumes. Here short 12-aminoacid peptides are investigated based on the metal-binding loops of the natural Ln-binding protein lanmodulin with advanced gas-phase techniques such as ion mobility spectrometry, collision-induced dissociation, and electrospray ionization to gain insight into binding residues and possible differences between sequences. Both the natural sequences as well as peptides that are synthesized in "reverse" order are investigated and it is found that the trends observed in solution measurements are well reproduced by gas-phase measurements.

A series of seven-coordinated monoporphyrinate rare-earth(III) complexes featuring a novel tripodal tin-chelated trisphosphineoxide scorpionate ligand with the general formula [(TPP)Ln(PPh2O)3Sn] (Ln = Y, La, Dy, Er, Ho, Yb; TPP = 5,10,15,20-tetraphenylporphyrinate) were synthesized by reactions of the potassium tripodal scorpionate ligand [Sn(PPh2O)3K] with porphyrinate rare-earth metal chlorides [(TPP)LnCl(dme)] (Ln = Y, Dy, Er, Ho, Yb) or porphyrinate lanthanum borohydride [(TPP)LaBH4(thf)2]. The complexes were characterized by single-crystal X-ray diffraction, NMR spectroscopy, and ion mobility mass spectrometry. All complexes emit weak red TPP-based fluorescence, accompanied by near-infrared emission of Er, Ho (rather weak), and Yb (relatively intense with a quantum yield of 1% in dichloromethane solution) of the corresponding complexes. Despite the low intensity, the red fluorescence is characteristic (as referred to the parent free-base TPP) and can be used together with optical absorption for analytical evaluation. Similar photophysical properties can be expected for monoporphyrinate rare-earth metal complexes of other tripodal ligands with a similar binding to the (TPP)Ln moiety.

Collision-induced dissociation and high-resolution cyclic ion mobility mass spectrometry, along with quantum chemical calculations and trajectory simulations, were used to compare the structures of isolated [MAu24(C = CR)(18)](2-), M = Ni, Pd, or Pt, and their associated fragment ions. The three different alkynyl ligand-stabilized (C= CR, R = 3,5-(CF3)2C(6)H(3)), transition metal-doped, gold cluster dianions showed mutually resolvable collision cross sections (CCS), which were ordered consistently with their molecular structures from X-ray crystallography. All three [MAu24(C= CR)(18)](2-) species fragment by sequential diyne loss to form [MAu24(C= CR)(18)-n](2-), with n up to 12. The resultant fragment isomer distributions are significantly n- and M-dependent, and hint at a process involving concerted elimination of adjacent ligands. In particular [NiAu24(C= CR)(18)](2-) also fragments to generate alkyne-oligomers, an inference supported by the parallel observation of precursor dianion isomerization as collision energy is increased.

Some of the authors of the present research group have previously reported mass spectrometric detection of [PdAu9(PPh3)(8)(CN)](2+) (PdAu9CN) by atmospheric pressure plasma (APP) irradiation of [MAu8(PPh3)(8)](2+) (PdAu8) in methanol and proposed based on density functional theory (DFT) calculations that PdAu9CN is constructed by inserting a CNAu or NCAu unit into the Au-PPh3 bond of PdAu8 [Emori et al., J. Chem. Phys. 155, 124312 (2021)]. In this follow-up study, we revisited the structure of PdAu9CN by high-resolution ion mobility spectrometry on an isolated sample of PdAu9CN with the help of dispersion-corrected DFT calculation. In contradiction to the previous proposal, we conclude that isomers in which an AuCN unit is directly bonded to the central Pd atom of PdAu8 are better candidates. This assignment was supported by Fourier transform infrared and ultraviolet-visible spectroscopies of isolated PdAu9CN. The simultaneous formation of [Au(PPh3)(2)](+) and PdAu9CN suggests that the AuCN species are formed by APP irradiation at the expense of a portion of PdAu8. These results indicate that APP may offer a unique method for transforming metal clusters into novel ones by generating in situ active species that were not originally added to the solution.

Vacancy defects are known to have significant effects on the physical and chemical properties of nanomaterials. However, the formation and structural dynamics of vacancy defects in atomically precise coinage metal clusters have hardly been explored due to the challenges associated with isolation of such defected clusters. Herein, we isolate [Ag28(BDT)12]2- (BDT is 1,3-benzenedithiol), a cluster with a "missing atom" site compared to [Ag29(BDT)12]3-, whose precise structure is known from X-ray diffraction. [Ag28(BDT)12]2- was formed in the gas-phase by collisional heating of [Ag28Hg(BDT)12]2-, a Hg-doped analogue of the parent cluster. The structural changes resulting from the loss of the Hg heteroatom were investigated by trapped ion mobility mass spectrometry. Density functional theory calculations were performed to provide further insights into the defect structures, and molecular dynamics simulations revealed defect site-dependent structural relaxation processes.

Fragmentation dynamics of ligated coinage metal clusters reflects their structural and bonding properties. So far methodological challenges limited probing structures of the fragments. Herein, we resolve the geometric structures of the primary fragments of [Ag29L12](3-), i.e. [Ag24L9](2-), [Ag19L6](-) and [Ag5L3](-) (L is 1,3-benzene dithiolate). For this, we used trapped ion mobility mass spectrometry to determine collision cross sections of the fragments and compared them to structures calculated by density functional theory. We also report that following two sequential [Ag5L3](-) elimination steps, further dissociation of [Ag19L6](-) also involves a new channel of Ag-2 loss and Ag-S and C-S bond cleavages. This reflects a competition between retaining the electronic stability of 8 e(-) superatom cluster cores and increasing steric strain of ligands and staples. These results are also of potential interest for future soft-landing deposition studies aimed at probing catalytic behavior of Ag clusters on supports.