Mn12_{12}-Acetate Complexes Studied as Single Molecules

The phenomenon of single molecule magnet (SMM) behavior of mixed valent Mn12 coordination clusters of general formula [Mn$^{III}$$_{8}$Mn$^{IV}$$_{4}$O$_{12}$(RCOO)$_{16}$(H$_{2}$O)$_{4}$] had been exemplified by bulk samples of the archetypal [Mn$^{III}$$_{8}$Mn$^{IV}$$_{4}$O$_{12}$(CH$_{3}$COO)$_{16}$(H$_{2}$O)$_{4}$] (4) molecule, and the molecular origin of the observed magnetic behavior has found support from extensive studies on the Mn12 system within crystalline material or on molecules attached to a variety of surfaces. Here we report the magnetic signature of the isolated cationic species [Mn$_{12}$O$_{12}$(CH$_{3}$COO)$_{15}$(CH$_{3}$CN)]$^{+}$ (1) by gas phase X-ray Magnetic Circular Dichroism (XMCD) spectroscopy, and we find it closely resembling that of the corresponding bulk samples. Furthermore, we report broken symmetry DFT calculations of spin densities and single ion tensors of the isolated, optimized complexes [Mn$_{12}$O$_{12}$(CH$_{3}$COO)$_{15}$(CH$_{3}$CN)]$^{+}$ (1), [[Mn$_{12}$O$_{12}$(CH$_{3}$COO)$_{16}$] (2), [Mn$_{12}$O$_{12}$(CH$_{3}$COO)$_{16}$(H$_{2}$O)$_{4}$] (3), and the complex in bulk geometry [Mn$^{III}$$_{8}$Mn$^{IV}$$_{4}$O$_{12}$(CH$_{3}$COO)$_{16}$(H$_{2}$O)$_{4}$] (5). The found magnetic fingerprints – experiment and theory alike – are of a remarkable robustness: The Mn$^{IV}$$_{4}$ core bears almost no magnetic anisotropy while the surrounding MnIII8 ring is highly anisotropic. These signatures are truly intrinsic properties of the Mn$_{12}$ core scaffold within all of these complexes and largely void of the environment. This likely holds irrespective of bulk packing effects

On the contentious sequence and glycosylation motif of the ribosome inactivating plant protein gelonin

International audienceThe amino acid sequence and the glycosylation motif of the ribosome inactivating protein (RIP) gelonin are identified by Fourier transform ion cyclotron resonance mass spectrometry. Intact gelonin as isolated from the seeds of Gelonium multiflorum consists of at least three different post-translational modified forms: analysis of gelonin peptides as obtained by proteolytic digestion is consistent with the amino acid sequence published by Nolan et al. High resolution mass determination established a glycosylation pattern of GlcNAc2Man3-5Xyl. N189 was identified as glycosylation site. The proposed glycan structure is consistent with a standard plant N-glycosylation pattern as found in other RIP. Based on these results we suggest that gelonin is located in the vacuole of Gelonium multiflorum seeds. © 2005 Elsevier Inc. All rights reserved

Diffusion of hydrogen in rare gas solids: neutral H atoms and H⁺ protons

In this letter we review and compare the available information about the stability and spectroscopy of the hydrogen atoms and protons in rare-gas solids. Mechanism of the H⁺ duffusion involving protonated rare-gas dimer Rg₂H⁺ formation in the lattice is discussed. We suggest that the puzzling differences in their behavior and the stability are due to the fact that diffusion of hydrogen atoms is thermally activated, while that of the protons is activated by vibrational excitation of the Rg₂H⁺ under ambient temperature black body radiation

Cryo kinetics of N-2 adsorption onto bimetallic rhodium-iron clusters in isolation

We report the N2 cryo adsorption kinetics of selected gas phase mixed rhodium–iron clusters [RhiFej]+ in the range of i = 3–8 and j = 3–8 in 26 K He buffer gas by the use of a cryo tandem RF-hexapole trap–Fourier transform ion cyclotron resonance mass spectrometer. From kinetic data and fits, we extract relative rate constants for each N2 adsorption step and possible desorption steps. We find significant trends in adsorption behavior, which reveal adsorption limits, intermittent adsorption limits, and equilibrium reactions. For those steps, which are in equilibrium, we determine the Gibbs free energies. We conclude on likely ligand shell reorganization and some weakly bound N2 ligands for clusters where multiple N2 adsorbates are in equilibrium. The relative rate constants are transferred to absolute rate constants, which are slightly smaller than the collision rate constants calculated by the average dipole orientation (Langevin) theory. The calculated sticking probabilities increase, in general, with the size of the clusters and decrease with the level of N2 adsorption, in particular, when reaching an adsorption/desorption equilibrium. We receive further evidence on cluster size dependent properties, such as cluster geometries and metal atom distributions within the clusters through the accompanying spectroscopic and computational study on the equiatomic i = j clusters [Klein et al., J. Chem. Phys. 156, 014302 (2022)]

Energy transfer and photoactivity of photozymes included in polyacrylate hydrogels

Two photozymes poly(vinylnaphthalene/sodium styrenesulfonate) (PZ1) and poly(vinylnaphthalene/sodium styrenesulfonate/N,N'-dimethyl methacryloyloxyethyl propanesulfonate) (PZ2) were synthesized and used for the modification of hydrogels. The hydrogels were composed of acrylamide and 2-acrylamido-2- methylpropanesulfonic acid monomers, and modified with sodium bentonite (NB). The fluorescence properties and photoactivity of the photozymes were examined. Both photozymes demonstrated high self-assembly in both aqueous solutions and hydrogel matrices, which is of great importance for the antenna effect. For the NB-reinforced hydrogel, strong energy transfer from the excited chromophores to the NB was observed and assigned to the high surface conductivity of clay. PZ2 exhibited higher photocatalytic activity for the methylene blue (MB) photodegradation than PZ1. This is most likely due to the better self-assembly and thus enhanced antenna effect of the zwitterionic PZ2. MB a bsorbed by the hydrogel from aqueous solution was efficiently decomposed in a photozyme-catalyzed photochemical process