Comparison of collision‐ versus electron‐induced dissociation of sodium chloride cluster cations

The collision‐induced dissociation (CID) and electron‐induced dissociation (EID) spectra of the [(NaCl)_m(Na)_n]ⁿ⁺ clusters of sodium chloride have been examined in a hybrid linear ion trap Fourier transform ion cyclotron resonance mass spectrometer. For singly charged cluster ions (n = 1), mass spectra for CID and EID of the precursor exhibit clear differences, which become more pronounced for the larger cluster ions. Whereas CID yields fewer product ions, EID produces all possible [(NaCl)_xNa]⁺ product ions. In the case of doubly charged cluster ions, EID again leads to a larger variety of product ions. In addition, doubly charged product ions have been observed due to loss of neutral NaCl unit(s). For example, EID of [(NaCl)₁₁(Na)₂]²⁺ leads to formation of [(NaCl)₁₀(Na)₂]²⁺, which appears to be the smallest doubly charged cluster of sodium chloride observed experimentally to date. The most abundant product ions in EID spectra are predominantly magic number cluster ions. Finally, [(NaCl)_m(Na)₂]^{+ .} radical cations, formed via capture of low‐energy electrons, fragment via the loss of [(NaCl)_n(Na)] ^. radical neutrals. Copyright © 2008 John Wiley & Sons, Ltd.     

Electron capture dissociation mass spectrometry of metallo-supramolecular complexes

The electron capture dissociation (ECD) of metallo-supramolecular dinuclear triple-stranded helicate Fe₂L₃⁴⁺ ions was determined by Fourier transform ion cyclotron resonance mass spectrometry. Initial electron capture by the di-iron(II) triple helicate ions produces dinuclear double-stranded complexes analogous to those seen in solution with the monocationic metal centers Cu^I or Ag^I. The gas-phase fragmentation behavior [ECD, collision-induced dissociation (CID), and infrared multiphoton dissociation (IRMPD)] of the di-iron double-stranded complexes, (i.e., MS³ of the ECD product) was compared with the ECD, CID, and IRMPD of the Cu^I and Ag^I complexes generated from solution. The results suggest that iron-bound dimers may be of the form Fe₂^IL₂²⁺ and that ECD by metallo-complexes allows access, in the gas phase, to oxidation states and coordination chemistry that cannot be accessed in solution.     

Fragmentation of Singly,Doubly, and Triply Charged Hydrogen Deficient Peptide Radical Cations in Infrared Multiphoton Dissociation and Electron Induced Dissociation

Gas phase fragmentation of hydrogen deficient peptide radical cations continues to be an active area of research. While collision induced dissociation (CID) of singly charged species is widely examined, dissociation channels of singly and multiply charged radical cations in infrared multiphoton dissociation (IRMPD) and electron induced dissociation (EID) have not been, so far, investigated. Here, we report on the gas phase dissociation of singly, doubly and triply charged hydrogen deficient peptide radicals, [M + nH]^(n+1)+· (n = 0, 1, 2), in MS³ IRMPD and EID and compare the observed fragmentation pathways to those obtained in MS³ CID. Backbone fragmentation in MS³ IRMPD and EID was highly dependent on the charge state of the radical precursor ions, whereas amino acid side chain cleavages were largely independent of the charge state selected for fragmentation. Cleavages at aromatic amino acids, either through side chain loss or backbone fragmentation, were significantly enhanced over other dissociation channels. For singly charged species, the MS³ IRMPD and EID spectra were mainly governed by radical-driven dissociation. Fragmentation of doubly and triply charged radical cations proceeded through both radical- and charge-driven processes, resulting in the formation of a wide range of backbone product ions including, a-, b-, c-, y-, x-, and z-type. While similarities existed between MS³ CID, IRMPD, and EID of the same species, several backbone product ions and side chain losses were unique for each activation method. Furthermore, dominant dissociation pathways in each spectrum were dependent on ion activation method, amino acid composition, and charge state selected for fragmentation.     

Fragmentation of the tryptophan cluster [Trp9-2H]2- induced by different activation methods

Electrospray ionization (ESI) of tryptophan gives rise to multiply charged, non‐covalent tryptophan cluster anions, [Trp_n–xH]^x?, in a linear ion trap mass spectrometer, as confirmed by high‐resolution experiments performed on a Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometer. The smallest multiply charged clusters that can be formed in the linear ion trap as a function of charge state are: x = 2, n = 7; x = 3, n = 16; x = 4, n = 31. The fragmentation of the dianionic cluster [Trp₉–2H]^2? was examined via low‐energy collision‐induced dissociation (CID), ultraviolet photodissociation (UVPD) at 266 nm and electron‐induced dissociation (EID) at electron energies ranging from >0 to 30 eV. CID proceeds mostly via charge separation and evaporation of neutral tryptophan. The smallest doubly charged cluster that can be formed via evaporation of neutral tryptophans is [Trp₇–2H]^2?, consistent with the observation of this cluster in the ESI mass spectrum. UVPD gives singly charged tryptophan clusters ranging from n = 2 to n = 9. The latter ion arises from ejection of an electron to give the radical anion cluster, [Trp₉–2H]^?.. The types of gas‐phase EID reactions observed are dependent on the energy of the electrons. Loss of neutral tryptophan is an important channel at lower energies, with the smallest doubly charged ion, [Trp₇–2H]^2?, being observed at 19.8 eV. Coulomb explosion starts to occur at 19.8 eV to form the singly charged cluster ions [Trp_x–H]^? (x = 1–8) via highly asymmetric fission. At 21.8 eV a small amount of [Trp₂–H–NH₃]^? is observed. Thus CID, UVPD and EID are complementary techniques for the study of the fragmentation reactions of cluster ions. Copyright © 2010 John Wiley & Sons, Ltd.     

Electron capture dissociation and collision-induced dissociation of metal ion (Ag+, Cu2+, Zn2+, Fe2+, and Fe3+) complexes of polyamidoamine (PAMAM) dendrimers

The electron capture dissociation (ECD) and collision-induced dissociation (CID) of complexes of polyamidoamine (PAMAM) dendrimers with metal ions Ag⁺, Cu²⁺, Zn²⁺, Fe²⁺, and Fe³⁺ were determined by Fourier transform ion cyclotron resonance mass spectrometry. Complexes were of the form [PD + M + mH]⁵⁺ where PD = generation two PAMAM dendrimer with amidoethanol surface groups, M = metal ion, m = 2−4. Complementary information regarding the site and coordination chemistry of the metal ions can be obtained from the two techniques. The results suggest that complexes of Fe³⁺ and Cu²⁺ are coordinated via both core tertiary amines, whereas coordination of Ag⁺ involves a single core tertiary amine. The Zn²⁺ and Fe²⁺ complexes do not appear to involve coordination by the dendrimer core.     

Intramolecular Gas‐Phase Reactions of Synthetic Nonheme Oxoiron(IV) Ions: Proximity and Spin‐State Reactivity Rules

The intramolecular gas‐phase reactivity of four oxoiron(IV) complexes supported by tetradentate N₄ ligands ( L ) has been studied by means of tandem mass spectrometry measurements in which the gas‐phase ions [Fe^IV(O)( L )(OTf)]⁺ (OTf=trifluoromethanesulfonate) and [Fe^IV(O)( L )]²⁺ were isolated and then allowed to fragment by collision‐induced decay (CID). CID fragmentation of cations derived from oxoiron(IV) complexes of 1,4,8,11‐tetramethyl‐1,4,8,11‐tetraazacyclotetradecane (tmc) and N,N′‐bis(2‐pyridylmethyl)‐1,5‐diazacyclooctane ( L ⁸Py₂) afforded the same predominant products irrespective of whether they were hexacoordinate or pentacoordinate. These products resulted from the loss of water by dehydrogenation of ethylene or propylene linkers on the tetradentate ligand. In contrast, CID fragmentation of ions derived from oxoiron(IV) complexes of linear tetradentate ligands N,N′‐bis(2‐pyridylmethyl)‐1,2‐diaminoethane (bpmen) and N,N′‐bis(2‐pyridylmethyl)‐1,3‐diaminopropane (bpmpn) showed predominant oxidative N‐dealkylation for the hexacoordinate [Fe^IV(O)( L )(OTf)]⁺ cations and predominant dehydrogenation of the diaminoethane/propane backbone for the pentacoordinate [Fe^IV(O)( L )]²⁺ cations. DFT calculations on [Fe^IV(O)(bpmen)] ions showed that the experimentally observed preference for oxidative N‐dealkylation versus dehydrogenation of the diaminoethane linker for the hexa‐ and pentacoordinate ions, respectively, is dictated by the proximity of the target C? H bond to the oxoiron(IV) moiety and the reactive spin state. Therefore, there must be a difference in ligand topology between the two ions. More importantly, despite the constraints on the geometries of the TS that prohibit the usual upright σ trajectory and prevent optimal σ_CH–σ* overlap, all the reactions still proceed preferentially on the quintet (S=2) state surface, which increases the number of exchange interactions in the d block of iron and leads thereby to exchange enhanced reactivity (EER). As such, EER is responsible for the dominance of the S=2 reactions for both hexa‐ and pentacoordinate complexes.     

Gas-phase reactions of doubly charged alkaline earth and transition metal complexes of acetonitrile, pyridine, and methanol generated by electrospray ionization

Formation and low energy collision-induced dissociation (CID) of doubly charged metal(II) complexes ([metal(II)+L _n ]²⁺, metal(II)=Co(II), Mn(II), Ca(II), Sr(II) and L = acetonitrile, pyridine, and methanol) were investigated. Complexes of [metal(II)+L _n ]²⁺ where n≤7 were obtained using electrospray ionization. Experimental parameters controlling the dissociation pathways for [Co(II)+(CH₃CN)₂]²⁺ were studied and a strong dependence of these processes on the collision energy was found. However, the dissociation pathways appear to be independent of the cone potential, indicating low internal energy of the precursor ions. In order to probe how these processes are related to intrinsic parameters of the ligand such as ionization potential and metal ion coordination, low energy CID spectra of [metal(II)+L _n ]²⁺ for ligands such as acetonitrile, pyridine, and methanol were compared. For L = pyridine, all metals including the alkaline earth metals Ca and Sr were reduced to the bare [metal(I)]⁺ species. Hydride transfer was detected upon low energy CID of [metal(II)+L _n ]²⁺ for metal(II)=Co(II) and Mn(II) and L = methanol, and corroborated by signals for [metal(II)+H^?]⁺ and [metal(II)+H^?+CH₃OH]⁺, as well as by the complementary ion [CH₃O]⁺.     

Intermetallic Competition in the Fragmentation of Trimetallic Au–Zn–Alkali Complexes

Cationization is a valuable tool to enable mass spectrometric studies on neutral transition‐metal complexes (e.g., homogenous catalysts). However, knowledge of potential impacts on the molecular structure and catalytic reactivity induced by the cationization is indispensable to extract information about the neutral complex. In this study, we cationize a bimetallic complex [AuZnCl₃] with alkali metal ions (M⁺) and investigate the charged adducts [AuZnCl₃M]⁺ by electrospray ionization mass spectrometry (ESI‐MS). Infrared multiple photon dissociation (IR‐MPD) in combination with density functional theory (DFT) calculations reveal a μ³ binding motif of all alkali ions to the three chlorido ligands. The cationization induces a reorientation of the organic backbone. Collision‐induced dissociation (CID) studies reveal switches of fragmentation channels by the alkali ion and by the CID amplitude. The Li⁺ and Na⁺ adducts prefer the sole loss of ZnCl₂, whereas the K⁺, Rb⁺, and Cs⁺ adducts preferably split off MCl₂ZnCl. Calculated energetics along the fragmentation coordinate profiles allow us to interpret the experimental findings to a level of subtle details. The Zn²⁺ cation wins the competition for the nitrogen coordination sites against K⁺, Rb⁺, and Cs⁺ , but it loses against Li⁺ and Na⁺ in a remarkable deviation from a naive hard and soft acids and bases (HSAB) concept. The computations indicate expulsion of MCl₂ZnCl rather than of MCl and ZnCl₂.     

Mass spectrometry of coordination compounds of transition metals with tetradentate ligands. 11. isomeric quasi-macrocyclic Ni(II) complexes based on S-substituted isothiocarbohydrazides and the structure of “small” ions derived from them

Two series of bonding isomers of Ni(II) coordination compounds with tetradentate quasimacrocyclic ligands based on S-substituted isothiocarbohydrazides were characterized by electron impact (EI) mass spectrometry and by tandem mass spectrometry methods. Conventional EI mass spectra were more isomer specific than metastable ion (MI) and collision induced dissociation (CID) mass spectra of the molecular ions. The MI (and CID) mass spectra of the isomers were very similar. This effect resulted from a facile randomization of Ni–N bonds in the ions possessing low internal energies, prior to their dissociation. The compounds were found to be convenient precursors for coordinatively unsaturated metal-containing ions, [NiL_n]⁺ and [RNiL_n]⁺ (n = 1, 2; L = NCCH₃, NCSCH₃; R = OH, NO). Most of these species had a structure of mono- or disolvated nickel ion. The dissociation of [HONiNCCH₃]⁺ ions was consistent with the formation of two isomers: one corresponding to the [HONi]⁺ ion solvated by acetonitrile and the other is a complex of H₂O with [NiNCCH₂]⁺. A structure of [HO,Ni,(NCCH₃)₂]⁺ ions was best represented by a five-membered cycle formed by two acetonitrile units and the metal atom with the OH group attached to one of the nitrogen atoms.     

Gas-phase coordination complexes of U(VI)O2(2+), Np(VI)O2(2+), and Pu(VI)O2(2+) with dimethylformamide

Electrospray ionization of actinyl perchlorate solutions in H₂O with 5% by volume of dimethylformamide (DMF) produced the isolatable gas-phase complexes, [An^VIO₂(DMF)₃(H₂O)]²⁺ and [An^VIO₂(DMF)₄]²⁺, where An = U, Np, and Pu. Collision-induced dissociation confirmed the composition of the dipositive coordination complexes, and produced doubly- and singly-charged fragment ions. The fragmentation products reveal differences in underlying chemistries of uranyl, neptunyl, and plutonyl, including the lower stability of Np(VI) and Pu(VI) compared with U(VI).     

Chemical design of heterometallic carboxylate structures with Fe3+ and Ag+ ions as a rational synthetic approach

Solid phase thermolysis of pivalate complex [Fe₃O(Piv)₆(HPiv)₃]Piv generates the [Fe₃O(Piv)₆]⁺ complex cation due to a deficiency of ligands in the coordination sphere of the metal ions. Crystallization of [Fe₃O(Piv)₆]⁺ from THF–EtOH leads to the heteroleptic complex [Fe₃O(Piv)₆(THF)(EtOH)(OH)] · 0.5 THF · 0.5 H₂O in 69% yield, while the reaction of [Fe₃O(Piv)₆]⁺ with AgNO₃ in toluene results in the complex [Fe₄Ag₄O₂(Piv)₁₂] · 2 PhMe with a rare combination of Fe^III and Ag^I atoms. Crystal structures of the two new complexes have been established.     

Dissociation of disulfide‐intact somatostatin ions: the roles of ion type and dissociation method

The dissociation chemistry of somatostatin‐14 was examined using various tandem mass spectrometry techniques including low‐energy beam‐type and ion trap collision‐induced dissociation (CID) of protonated and deprotonated forms of the peptide, CID of peptide‐gold complexes, and electron transfer dissociation (ETD) of cations. Most of the sequence of somatostatin‐14 is present within a loop defined by the disulfide linkage between Cys‐3 and Cys‐14. The generation of readily interpretable sequence‐related ions from within the loop requires the cleavage of at least one of the bonds of the disulfide linkage and the cleavage of one polypeptide backbone bond. CID of the protonated forms of somatostatin did not appear to give rise to an appreciable degree of dissociation of the disulfide linkage. Sequential fragmentation via multiple alternative pathways tended to generate very complex spectra. CID of the anions proceeded through CH₂? S cleavages extensively but relatively few structurally diagnostic ions were generated. The incorporation of Au(I) into the molecule via ion/ion reactions followed by CID gave rise to many structurally relevant dissociation products, particularly for the [M+Au+H]²⁺ species. The products were generated by a combination of S? S bond cleavage and amide bond cleavage. ETD of the [M+3H]³⁺ ion generated rich sequence information, as did CID of the electron transfer products that did not fragment directly upon electron transfer. The electron transfer results suggest that both the S? S bond and an N? C_α bond can be cleaved following a single electron transfer reaction. Copyright © 2009 John Wiley & Sons, Ltd.     

Functional group interaction in the fragmentation of protonated 2,7-octanedione

The fragmentation of 2,7-octanedione, induced by chemical ionization with methane as a reagent gas (CI (CH₄)), is shown to be extensively governed by the interaction of the two carbonyl groups. Tandem mass spectrometry reveals that a sequential loss of H₂O and C₂H₄O from the [M + H]⁺ ion competes with sequential loss of H₂O and C₆H₁₀, and that both processes occur via the same [MH - H₂O]⁺ intermediate. This intermediate is likely to be formed via intramolecular gas-phase aldol condensation and subsequent dehydration. The resulting C(1) protonated 1-acetyl-2-methylcyclopentene structure readily accounts for the observed further decomposition to CH₃C?O⁺ and 1-methylcyclopentene (C₆H₁₀) or, alternatively, to [C₆H₉]⁺ (e. g. 1-methylcyclopentenylium) ions and acetaldehyde (C₂H₄O). Support for this mechanistic rationale is derived from deuterium isotope labelling and low-energy collision-induced dissociation (CID) of the [MH - H₂O]⁺ ion. The common intermediate shows a CID behaviour indistinguishable by these techniques from that of reference ions, which are produced by gas-phase protonation of the authentic cyclic aldol or by gas-phase addition of an acetyl cation to 1-methylcyclopentene in a CI (CH₃COOCH₃) experiment.     

Formation and Characterisation of the Silver Hydride Nanocluster Cation [Ag3H2((Ph2P)2CH2)]+ and Its Release of Hydrogen

Multistage mass spectrometry and density functional theory (DFT) were used to characterise the small silver hydride nanocluster, [Ag₃H₂L]⁺ (where L=(Ph₂P)₂CH₂) and its gas‐phase unimolecular chemistry. Collision‐induced dissociation (CID) yields [Ag₂HL]⁺ as the major product while laser‐induced dissociation (LID) proceeds via H₂ formation and subsequent release from [Ag₃H₂L]⁺, giving rise to [Ag₃L]⁺ as the major product. Deuterium labelling studies on [Ag₃D₂L]⁺ prove that the source of H₂ is from the hydrides and not from the ligand. Comparison of TD‐DFT absorption patterns obtained for the optimised structures with action spectroscopy results, allows assignment of the measured features to structures of precursors and products. Molecular dynamics “on the fly” reveal that AgH loss is favoured in the ground state, but H₂ formation and loss is preferred in the first excited state S₁, in agreement with CID and LID experimental findings. This indicates favourable photo‐induced formation of H₂ and subsequent release from [Ag₃H₂L]⁺, an important finding in context of metal hydrides as a hydrogen storage medium, which can subsequently be released by heating or irradiation with light.     

Characterization of five [C4H7O]+ Ion structures. Fragmentation of the 2-pentanone molecular ion

The [C₄H₇0]⁺ ions [CH₂?CH? C(?OH)CH₃]⁺ (1), [CH₃CH?CH? C(?OH)H]⁺ (2), [CH₂?C(CH₃)C(?OH)H]⁺ (3), [Ch₃CH₂CH₂C?O]⁺ (4) and [(CH₃)₂CHC?O]⁺ (5) have been characterized by their collision-induced dissociation (CID) mass spectra and charge stripping mass spectra. The ions 1–3 were prepared by gas phase protonation of the relevant carbonyl compounds while 4 and 5 were prepared by dissociative electron impact ionization of the appropriate carbonyl compounds. Only 2 and 3 give similar spectra and are difficult to distinguish from each other; the remaining ions can be readily characterized by either their CID mass spectra or their charge stripping mass spectra. The 2-pentanone molecular ion fragments by loss of the C(1) methyl and the C(5) methyl in the ratio 60:40 for metastable ions; at higher internal energies loss of the C(1) methyl becomes more favoured. Metastable ion characteristics, CID mass spectra and charge stripping mass spectra all show that loss of the C(1) methyl leads to formation of the acyl ion 4, while loss of the C(5) methyl leads to formation of protonated vinyl methyl ketone (1). These results are in agreement with the previously proposed potential energy diagram for the [C₅H₁₀O]⁺˙ system.     

Mass-analysed ion kinetic energy and collisionally induced dissociation mass spectra of clusters of acetylated xylo-oligosaecharides with protonated ammonia and methylannine

Per-O-acetylated methyl glycosides of D -xylan-type di- and trisaccharides were studied by mass-analysed ion kinetic energy (MIKE) and collisionally induced dissociation (CID) mass Spectrometry using protonated ammonia and methylamine, respectively, as reaction gases in chemical ionization (CI). The oligosaccharides form abundant cluster ions, [M + NH₄]⁺ or [M + CH₃NH₃]⁺, and the main fragmentation of these ions in the MIKE and CID spectra is the cleavage of interglycosidic linkages. Thus, CI (NH₃) or CI (CH₃NH₂) spectra in combination with the MIKE or CID spectra allow the molecular masses, the masses of monosaccharide units and the branching point in oligosaccharides to be established. In the case of disaccharides, it is possible to distinguish the (1 → 2) linkage from the other types of linkages.     

Generation and dissociation of oxygen‐ and chloride‐bridged iron(III) and manganese(III) tetraphenylporphyrin dimer ions in the gas phase

Electrospray ionization mass spectrometry (ESI/MS) has allowed the discovery of novel dimer ions emerging from solutions of metalloporphyrin salts and their investigation by collision‐induced dissociation (CID) with N₂ molecules. ESI mass spectra have been recorded for the formation of the oxygen or chloride‐bridged dimer ions [(FeTPP)₂OH]⁺, [(MnTPP)₂OH]⁺, [(FeTPP)₂Cl]⁺ and [(MnTPP)₂Cl]⁺ derived from various solutions of FeTPPCl and MnTPPCl salts. The CID of [(FeTPP)₂OH]⁺ proceeds mainly by neutral loss of (FeTPP)OH to form [FeTPP]⁺ and, to a minor extent, to form the charge‐reversed products. The CID of [(MnTPP)₂OH]⁺ exhibits exclusively the product ion [MnTPP]⁺ by loss of neutral (MnTPP)OH. [(FeTPP)₂Cl]⁺ and [(MnTPP)₂Cl]⁺ dissociate by loss of (Fe/MnTPP)Cl to give rise to [Fe/MnTPP]⁺. [(FeTPP)₂O]⁺ and [(FeTPP)₂OH]⁺ were generated from a solution of the dimer, (FeTPP)₂O. Dissociation of [(FeTPP)₂O]⁺ yields two product ions, [FeTPP]⁺ and [(FeTPP)O]⁺, with higher onsets compared to the equivalent fragments formed from [(FeTPP)₂OH]⁺. Copyright © 2009 John Wiley & Sons, Ltd.     

Formation and hydrolysis of gas‐phase [UO2(R)]+: R═CH3, CH2CH3, CH═CH2, and C6H5

The goals of the present study were (a) to create positively charged organo‐uranyl complexes with general formula [UO₂(R)]⁺ (eg, R═CH₃ and CH₂CH₃) by decarboxylation of [UO₂(O₂C─R)]⁺ precursors and (b) to identify the pathways by which the complexes, if formed, dissociate by collisional activation or otherwise react when exposed to gas‐phase H₂O. Collision‐induced dissociation (CID) of both [UO₂(O₂C─CH₃)]⁺ and [UO₂(O₂C─CH₂CH₃)]⁺ causes H⁺ transfer and elimination of a ketene to leave [UO₂(OH)]⁺. However, CID of the alkoxides [UO₂(OCH₂CH₃)]⁺ and [UO₂(OCH₂CH₂CH₃)]⁺ produced [UO₂(CH₃)]⁺ and [UO₂(CH₂CH₃)]⁺, respectively. Isolation of [UO₂(CH₃)]⁺ and [UO₂(CH₂CH₃)]⁺ for reaction with H₂O caused formation of [UO₂(H₂O)]⁺ by elimination of ·CH₃ and ·CH₂CH₃: Hydrolysis was not observed. CID of the acrylate and benzoate versions of the complexes, [UO₂(O₂C─CH═CH₂)]⁺ and [UO₂(O₂C─C₆H₅)]⁺, caused decarboxylation to leave [UO₂(CH═CH₂)]⁺ and [UO₂(C₆H₅)]⁺, respectively. These organometallic species do react with H₂O to produce [UO₂(OH)]⁺, and loss of the respective radicals to leave [UO₂(H₂O)]⁺ was not detected. Density functional theory calculations suggest that formation of [UO₂(OH)]⁺, rather than the hydrated U^VO₂⁺, cation is energetically favored regardless of the precursor ion. However, for the [UO₂(CH₃)]⁺ and [UO₂(CH₂CH₃)]⁺ precursors, the transition state energy for proton transfer to generate [UO₂(OH)]⁺ and the associated neutral alkanes is higher than the path involving direct elimination of the organic neutral to form [UO₂(H₂O)]⁺. The situation is reversed for the [UO₂(CH═CH₂)]⁺ and [UO₂(C₆H₅)]⁺ precursors: The transition state for proton transfer is lower than the energy required for creation of [UO₂(H₂O)]⁺ by elimination of CH═CH₂ or C₆H₅ radical.     

Spectroscopic Investigation on Sonocatalytic Damage of BSA Molecules by FeIII Complexes with Binary Organic Acid Ligands Under Ultrasonic Irradiation

The interaction between bovine serum albumin (BSA) and Fe^III complexes with three binary organic acid (biorga) ligands, [Fe^III(oxa)(H₂O)₄]⁺ (oxa = oxalic acid), [Fe^III(pra)(H₂O)₄]⁺ (pra = propanedioic acid) and [Fe^III(sua)(H₂O)₄]⁺ (sua = succinic acid), as well as the sonocatalytic damage of BSA in the presence of these three Fe^III–biorga complexes under ultrasonic irradiation, were studied by UV–vis and fluorescence spectra. The experimental results show that the fluorescence quenching process of BSA caused by three Fe^III–biorga complexes are all static quenching and the corresponding quenching rate constants (K _q), equilibrium constants (K _A) and the binding site numbers (n) were calculated. The results reveal that, under ultrasonic irradiation, the BSA molecules were obviously damaged by these Fe^III–biorga complexes. In addition, the effects of several factors on the damage of BSA molecules were examined. The experimental results demonstrate that the damage degree of BSA increased with an increase of ultrasonic irradiation time, Fe^III–biorga complex concentration, and ionic strength. In comparison, [Fe^III(pra)(H₂O)₄]⁺ exhibited higher sonocatalytic activity than [Fe^III(oxa)(H₂O)₄]⁺ and [Fe^III(sua)(H₂O)₄]⁺. Finally, the extent of generation of $ \cdot {\text{O}}_{2}^{ - } $ · O 2 ? and ·OH during sonocatalytic processes was estimated. Perhaps, the results will be significant for promoting sonodynamic treatment (SDT) of tumors at the molecular level.