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1. Experimental and theoretical investigations of infrared multiple photon dissociation spectra of arginine complexes with Zn 2+ and Cd 2+

   https://doi.org/10.1039/c8cp03484b  

   Chalifoux, Aaron M. ; Boles, Georgia C. ; Berden, Giel ; Oomens, Jos ; Armentrout, P. B. ( January 2018 , Physical Chemistry Chemical Physics)

   Arginine (Arg) complexes with Zn 2+ and Cd 2+ were examined by infrared multiple photon dissociation (IRMPD) action spectroscopy using light from a free electron laser. Electrospray ionization generated complexes of deprotonated Arg with Zn 2+ , [Zn(Arg–H)] + , and Arg with CdCl + , CdCl + (Arg). Possible low-energy conformers of these species were found using quantum chemical calculations, and their calculated IR spectra were compared to experimentally measured IRMPD spectra. Calculations were performed at the B3LYP/6-311+G(d,p) level for Zn 2+ complexes and B3LYP/def2-TZVP with an SDD effective core potential on cadmium for CdCl + complexes. [Zn(Arg–H)] + was found to adopt a charge-solvated, tridentate [N,CO − ,N ω ′] structure where Zn 2+ binds to the backbone amine, carbonyl oxygen, and side-chain terminal guanidine nitrogen (N ω ′). The CdCl + (Arg) species was suggested to be a mixture of a dominant (∼85%) charge-solvated, tridentate [N,CO,N ω ′] structure where the CdCl + binds to the backbone amine, carbonyl, and side-chain imine (N ω ′) and a minor (∼15%) bidentate [N,CO − ](N ω ′H 2 + ) zwitterionic structure where the metal center binds to the backbone amine and carbonyl oxygen with intramolecular proton migration from the hydroxyl to the N ω ′ guanidine nitrogen (as designated in parenthesis). 

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2. Structural determination of arginine-linked cisplatin complexes via IRMPD action spectroscopy: arginine binds to platinum via NO − binding mode

   https://doi.org/10.1039/d1cp03407c  

   He, C. C. ; Hamlow, L. A. ; Kimutai, B. ; Roy, H. A. ; Devereaux, Zachary J. ; Cunningham, N. A. ; Martens, J. ; Berden, G. ; Oomens, J. ; Chow, C. S. ; et al ( October 2021 , Physical Chemistry Chemical Physics)

   Cisplatin, (NH 3 ) 2 PtCl 2 , has been known as a successful metal-based anticancer drug for more than half a century. Its analogue, Argplatin, arginine-linked cisplatin, (Arg)PtCl 2 , is being investigated because it exhibits reactivity towards DNA and RNA that differs from that of cisplatin. In order to understand the basis for its altered reactivity, the deprotonated and sodium cationized forms of Argplatin, [(Arg-H)PtCl 2 ] − and [(Arg)PtCl 2 + Na] + , are examined by infrared multiple photon dissociation (IRMPD) action spectroscopy in the IR fingerprint and hydrogen-stretching regions. Complementary electronic structure calculations are performed using density functional theory approaches to characterize the stable structures of these complexes and to predict their infrared spectra. Comparison of the theoretical IR spectra predicted for various stable conformations of these Argplatin complexes to their measured IRMPD spectra enables determination of the binding mode(s) of Arg to the Pt metal center to be identified. Arginine is found to bind to Pt in a bidentate fashion to the backbone amino nitrogen and carboxylate oxygen atoms in both the [(Arg-H)PtCl 2 ] − and [(Arg)PtCl 2 + Na] + complexes, the NO − binding mode. The neutral side chain of Arg also interacts with the Pt center to achieve additional stabilization in the [(Arg-H)PtCl 2 ] − complex. In contrast, Na + binds to both chlorido ligands in the [(Arg)PtCl 2 + Na] + complex and the protonated side chain of Arg is stabilized via hydrogen-bonding interactions with the carboxylate moiety. These findings are consistent with condensed-phase results, indicating that the NO − binding mode of arginine to Pt is preserved in the electrospray ionization process even under variable pH and ionic strength. 

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3. Collision cross‐section analysis of self‐assembled metallomacrocycle isomers and isobars via ion mobility mass spectrometry

   https://doi.org/10.1002/rcm.8717  

   Endres, Kevin J. ; Barthelmes, Kevin ; Winter, Andreas ; Antolovich, Robert ; Schubert, Ulrich S. ; Wesdemiotis, Chrys ( February 2020 , Rapid Communications in Mass Spectrometry)

   Coordinatively driven self‐assembly of transition metal ions and bidentate ligands gives rise to organometallic complexes that usually contain superimposed isobars, isomers, and conformers. In this study, the double dispersion ability of ion mobility mass spectrometry (IM‐MS) was used to provide a comprehensive structural characterization of the self‐assembled supramolecular complexes by their mass and charge, revealed by the MS event, and their shape and collision cross‐section (Ω), revealed by the IM event.

   Self‐assembled complexes were synthesized by reacting a bis(terpyridine) ligand exhibiting a 60^odihedral angle between the two ligating terpyridine sites (T) with divalent Zn, Ni, Cd, or Fe. The products were isolated as (Metal²⁺[T])_n(PF₆)_2nsalts and analyzed using IM‐MS after electrospray ionization (ESI) which produced several charge states from eachn‐mer, depending on the number of PF₆ˉ anions lost upon ESI. Experimental Ω data, derived using IM‐MS, and computational Ω predictions were used to elucidate the size and architecture of the complexes.

   Only macrocyclic dimers, trimers, and tetramers were observed with Cd²⁺, whereas Zn²⁺formed the same plus hexameric complexes. These two metals led to the simplest product distributions and no linear isomers. In sharp contrast, Ni²⁺and Fe²⁺formed all possible ring sizes from dimer to hexamer as well as various linear isomers. The experimental and theoretical Ω data indicated rather planar macrocyclic geometries for the dimers and trimers, twisted 3D architectures for the larger rings, and substantially larger sizes with spiral conformation for the linear congeners. Adding PF₆ˉ to the same complex was found to mainly cause size contraction due to new stabilizing anion–cation interactions.

   Complete structural identification could be accomplished using ESI‐IM‐MS. Our results affirm that self‐assembly with Cd²⁺and Zn²⁺proceeds through reversible equilibria that generate the thermodynamically most stable structures, encompassing exclusively macrocyclic architectures that readily accommodate the 60^oligand used. In contrast, complexation with Ni²⁺and Fe²⁺, which form stronger coordinative bonds, proceeds through kinetic control, leading to more complex mixtures and kinetically trapped less stable architectures, such as macrocyclic pentamers and linear isomers.

    

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4. Multipurpose made colorimetric materials for amines, pH change and metal ion detection

   https://doi.org/10.1039/d1ra07811a  

   Bao, Lihong ; Jones, Leighton O. ; Garrote Cañas, Ana M. ; Yan, Yunhan ; Pask, Christopher M. ; Hardie, Michaele J. ; Mosquera, Martin A. ; Schatz, George C. ; Sergeeva, Natalia N. ( January 2022 , RSC Advances)

   Sensors are routinely developed for specific applications, but multipurpose sensors are challenging, due to stability and poor functional design. We report organic materials that operate in solution and gas phase. They show a strong response behaviour to at least three types of environmental changes: pH, amine and metal ion binding/detection. We have confirmed and validated our findings using various analytical and computational methods. We found that the changes in polarity of the solvent and pH not only red shift the tail of the absorption spectra, but also extend the peak optical absorption of these structures by up to 100 nm, with consequential effects on the optical gap and colour changes of the materials. Acid–base response has been studied by spectrophotometric titrations with trifluoroacetic acid (TFA) and triethyl amine (TEA). The experiments show excellent reversibility with greater sensitivity to base than acid for all compounds. Analysis into metal sensing using Zn( ii ) and Cu( ii ) ions as analytes show that the materials can successfully bind the cations forming stable complexes. Moreover, a strong suppression of signal with copper gives an operative modality to detect the copper ion as low as 2.5 × 10 −6 M. The formation of the metal complexes was also confirmed by growing crystals using a slow diffusion method; subsequent single crystal X-ray analysis reveals the ratio of ligand to metal to be 2 to 1. To test sensitivity towards various amine vapours, paper-based sensors have been fabricated. The sensors show a detection capability at 1 ppm of amine concentration. We have employed CIE L * a * b * colour space as the evaluation method, this provides numeric comparison of the samples from different series and allows comparison of small colour differences, which are generally undetectable by the human-eye. It shows that the CIE L * a * b * method can assess both sensitivity to a particular class of analytes and a specificity response to individual amines in this subclass offering an inexpensive and versatile methodology. 

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5. Isothermal Titration Calorimetry for Characterizing the Zinc(II)‐Binding Properties of Photocaged Complexes with Micromolar Affinity

   https://doi.org/10.1002/anse.202200043  

   Hickey, Erin E. ; Shigemoto, Austin ; Gericke, Arne ; Burdette, Shawn C. ( September 2022 , Analysis & Sensing)

   MorphDeCage (2‐(4‐methoxy‐3‐nitrophenyl)‐2‐morpholinoacetic acid) and PyrDeCage (2‐(4‐methoxy‐3‐nitrophenyl)‐2‐(methyl(pyridin‐2‐ylmethyl)amino)acetic) are Zn²⁺photocages that utilize photodecarboxylation of the methoxy derivative ofmeta‐nitrophenylacetic acid as the release mechanism. Isothermal titration calorimetry (ITC) was used an alternative to usual approaches to measure the Zn²⁺binding affinities of these new compounds owing to unsuccessful measurement by competitive titration with 4‐(2‐pyridylazo)resorcinol (PAR). MorphDeCage forms a 1 : 1 ligand‐metal complex with a 106 μM K_dvalue. PyrDeCage forms both a 1 : 1 and 1 : 2 metal: ligand complexes with 3.2 and 21.7 μM K_dvalues respectively. To further demonstrate the efficacy of the ITC methodology and provide a comparison to direct UV‐vis titrations data, two photocages based on Sanger's reagent (SRPs) were prepared. The K_dvalues of the SRPs measured by UV‐vis titration and ITC were internally consistent and support the retraction of the original report (J. Am. Chem. Soc.2020,142, 3806–3813), which was withdrawn due to errors in binding affinity measurements.

    

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