Charge Reversal Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

We report the first charge reversal experiments performed by tandem-in-time rather than tandem-in-space MS/MS. Precursor odd-electron anions from fullerene C₆₀, and even-electron ions from 2,7-di-tert-butylfluorene-9-carboxylic acid and 3,3′-bicarbazole were converted into positive product ions (^–CR⁺) inside the magnet of a Fourier transform ion cyclotron resonance mass spectrometer. Charge reversal was activated by irradiating precursor ions with high energy electrons or UV photons: the first reported use of those activation methods for charge reversal. We suggest that high energy electrons achieve charge reversal in one step as double electron transfer, whereas UV-activated ^–CR⁺ takes place stepwise through two single electron transfers and formally corresponds to a neutralization-reionization (^–NR⁺) experiment.      

Study of Electron Ionization and Fragmentation of Non-hydrated and Hydrated Tetrahydrofuran Clusters

Mass spectroscopic investigations on tetrahydrofuran (THF, C₄H₈O), a common model molecule of the DNA-backbone, have been carried out. We irradiated isolated THF and (hydrated) THF clusters with low energy electrons (electron energy ~70 eV) in order to study electron ionization and ionic fragmentation. For elucidation of fragmentation pathways, deuterated TDF (C₄D₈O) was investigated as well. One major observation is that the cluster environment shows overall a protective behavior on THF. However, also new fragmentation channels open in the cluster. In this context, we were able to solve a discrepancy in the literature about the fragment ion peak at mass 55 u in the electron ionization mass spectrum of THF. We ascribe this ion yield to the fragmentation of ionized THF clusters.

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Sulfur Pentafluoride is a Preferred Reagent Cation for Negative Electron Transfer Dissociation

Negative mode proteome analysis offers access to unique portions of the proteome and several acidic post-translational modifications; however, traditional collision-based fragmentation methods fail to reliably provide sequence information for peptide anions. Negative electron transfer dissociation (NETD), on the other hand, can sequence precursor anions in a high-throughput manner. Similar to other ion–ion methods, NETD is most efficient with peptides of higher charge state because of the increased electrostatic interaction between reacting molecules. Here we demonstrate that NETD performance for lower charge state precursors can be improved by altering the reagent cation. Specifically, the recombination energy of the NETD reaction—largely dictated by the ionization energy (IE) of the reagent cation—can affect the extent of fragmentation. We compare the NETD reagent cations of C₁₆H₁₀ ^●+ (IE?=?7.9 eV) and SF₅ ^●+ (IE?=?9.6 eV) on a set of standard peptides, concluding that SF₅ ^●+ yields greater sequence ion generation. Subsequent proteome-scale nLC-MS/MS experiments comparing C₁₆H₁₀ ^●+ and SF₅ ^●+ further supported this outcome: analyses using SF₅ ^●+ yielded 4637 peptide spectral matches (PSMs) and 2900 unique peptides, whereas C₁₆H₁₀ ^●+ produced 3563 PSMs and 2231 peptides. The substantive gain in identification power with SF₅ ^●+ was largely driven by improved identification of doubly deprotonated precursors, indicating that increased NETD recombination energy can increase product ion yield for low charge density precursors. This work demonstrates that SF₅ ^●+ is a viable, if not favorable, reagent cation for NETD, and provides improved fragmentation over the commonly used fluoranthene reagent.

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Sequence Ion Structures and Dissociation Chemistry of Deprotonated Sucrose Anions

We investigate the tandem mass spectrometry of regiospecifically labeled, deprotonated sucrose analytes. We utilize density functional theory calculations to model the pertinent gas-phase fragmentation chemistry of the prevalent glycosidic bond cleavages (B₁-Y₁ and C₁-Z₁ reactions) and compare these predictions to infrared spectroscopy experiments on the resulting B₁ and C₁ product anions. For the C₁ anions, barriers to interconversion of the pyranose [α-glucose-H]^?, C₁ anions to entropically favorable ring-open aldehyde-terminated forms were modest (41 kJ mol^?1) consistent with the observation of a band assigned to a carbonyl stretch at ~?1680–1720 cm^?1. For the B₁ anions, our transition structure calculations predict the presence of both deprotonated 1,6-anhydroglucose and carbon 2-ketone ((4S,5S,6R)-4,5-dihydroxy-6-(hydroxymethyl)dihydro-2H-pyran-3(4H)-one) anion structures, with the latter predominating. This hypothesis is supported by our spectroscopic data which show diagnostic bands at 1600, 1674, and 1699 cm^?1 (deprotonated carbon 2-ketone structures), and at ~?1541 cm^?1 (both types of structure) and RRKM rate calculations. The deprotonated carbon 2-ketone structures are also the lowest energy product B₁ anions.

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Si<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/Si Interface Profiles Measured to Sub-Nanometer Precision Using uleSIMS Energy Sequencing

The utility of energy sequencing for extracting an accurate matrix level interface profile using ultra-low energy SIMS (uleSIMS) is reported. Normally incident O₂ ⁺ over an energy range of 0.25–2.5 keV were used to probe the interface between Si_0.73Ge_0.27/Si, which was also studied using high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). All the SIMS profiles were linearized by taking the well understood matrix effects on ion yield and erosion rate into account. A method based on simultaneous fitting of the SIMS profiles measured at different energies is presented, which allows the intrinsic sample profile to be determined to sub-nanometer precision. Excellent agreement was found between the directly imaged HAADF-STEM interface and that derived from SIMS.

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Electron attachment to oxygen and oxygen/ozone clusters studied in a high-resolution crossed beams experiment

Highly monochromatized electrons (with 30 meV FWHM) are used in a crossed beams experiment to investigate electron attachment to oxygen clusters (O₂)_n at electron energies from approximately zero eV up to 2 eV. At energies close to zero the attachment cross section for the reaction (O₂)_n +e → O ₂ ^? varies inversely with the electron energy, indicative of s-wave electron capture to (O₂)_n. Peaks in the attachment cross section present at higher energies can be ascribed to vibrational levels of the oxygen anion. The vibrational spacings observed can be quantitatively accounted for. In addition electron attachment to mixed oxygen/ozone clusters has been studied in the energy range up to 4 eV. Despite the initially large excess of oxygen molecules in the neutral clusters the dominant attachment products are undissociated cluster ions (O₃) _m ^? including the O ₃ ^? monomer while oxygen cluster ions (O₂) _n ^? appear with comparatively low intensity.     

Formation and Characterization of Zr<Superscript>4+</Superscript> Stabilized by Neutral Tridentate Ligands in the Gas Phase

Ligated tetrapositive metal ions are rare gas-phase species which tend to form complexes with lower charges due to the high 4th ionization energies of metals. We report the observation of tetrapositive Zr(TMPDA)₃⁴⁺ and Zr(TMOGA)₃⁴⁺ complexes in the gas phase by electrospray ionization of Zr(ClO₄)₄/TMPDA and Zr(ClO₄)₄/TMOGA mixtures. The Zr⁴⁺ center in both complexes is coordinated by nine atoms from three neutral diamide ligands forming nine-coordinate twisted tricapped trigonal prismatic geometry on the basis of DFT calculations. Collision-induced dissociation of both complexes resulted in the loss of protonated ligands to form tripositive Zr(TMPDA)(TMPDA-H)³⁺ and Zr(TMOGA)(TMOGA-H)³⁺ products which retain the IV oxidation state of zirconium at the cost of charge reduction from 4+ to 3+ of the whole complexes. The very high 4th ionization energy of zirconium (34.34 eV) makes tetrapositive zirconium complex the most challenging tetracation to be stabilized against charge reduction in the gas phase to date.

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Combined Infrared Multiphoton Dissociation with Ultraviolet Photodissociation for Ubiquitin Characterization

Herein we report the successful implementation of the consecutive and simultaneous photodissociation with high (213 nm) and low (10.6 μm) energy photons (HiLoPD, high-low photodissociation) on ubiquitin in a quadrupole-Orbitrap mass spectrometer. Absorption of high-energy UV photon is dispersed over the whole protein and stimulates extensive C–C_α backbone fragmentation, whereas low-energy IR photon gradually increases the internal energy and thus preferentially dissociates the most labile amide (C–N) bonds. We noticed that simultaneous irradiation of UV and IR lasers on intact ubiquitin in a single MS/MS experiment provides a rich and well-balanced fragmentation array of a/x, b/y, and z ions. Moreover, secondary fragmentation from a/x and z ions leads to the formation of satellite side-chain ions (d, v, and w) and can help to distinguish isomeric residues in a protein. Implementation of high-low photodissociation in a high-resolution mass spectrometer may offer considerable benefits to promote a comprehensive portrait of protein characterization.

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Characterization of Electron Transfer Dissociation in the Orbitrap Velos HCD Cell

Electron transfer dissociation (ETD) is commonly employed in ion traps utilizing rf fields that facilitate efficient electron transfer reactions. Here, we explore performing ETD in the HCD collision cell on an Orbitrap Velos instrument by applying a static DC gradient axially to the rods. This gradient enables simultaneous three dimensional, charge sign independent, trapping of cations and anions, initiating electron transfer reactions in the center of the HCD cell where oppositely charged ions clouds overlap. Here, we evaluate this mode of operation for a number of tryptic peptide populations and the top-down sequence analysis of ubiquitin. Our preliminary data show that performing ETD in the HCD cell provides similar fragmentation as ion trap-ETD but requires further optimization to match performance of ion trap-ETD.      

Small-Angle Neutron Scattering Study on Aggregation of 1-Alkyl-3-methylimidazolium Based Ionic Liquids in Aqueous Solution

Aggregation structures of 1-alkyl-3-methylimidazolium based ionic liquids (ILs) in aqueous solution were investigated by small-angle neutron scattering (SANS) from the viewpoint of alkyl chain length, n, and anions (Cl^?, Br^? and trifluoromethanesulfonate, $ {\text{CF}}_{3} {\text{SO}}_{3}^{ - } $ ). In [C₄mIm⁺]-based IL systems, no noticeable SANS intensity was observed for all of the systems examined here, although aqueous [C₄mIm⁺][ $ {\text{BF}}_{4}^{ - } $ ] solutions show a significant SANS profile originating from concentration fluctuations in the solution (Almasy et al. J Phys Chem B 112:2382–2387, 2008). This suggests that [C₄mIm⁺][Cl^?], [C₄mIm⁺][Br^?] and [C₄mIm⁺][ $ {\text{CF}}_{3} {\text{SO}}_{3}^{ - } $ ] homogeneously mix with water, unlike the [C₄mIm⁺][ $ {\text{BF}}_{4}^{ - } $ ] system, due to preferential hydration of the ions. In the case of the C _n mIm cations with longer alkyl chain lengths (n = 8 and 12), SANS profiles were clearly observed in the aqueous solutions at IL concentrations of C _IL > 230 and 20.0 mmol·dm^?3, respectively. For aqueous [C₈mIm⁺][Br^?] solutions, the asymptotic behavior of the scattering function varied largely from I(q) ~ q ^?2 to ~q ^?4 with increasing C _IL, indicating that the solution changes from an inhomogeneous mixing state to a nano-scale micelle state. Aqueous [C₁₂mIm⁺][Br^?] solutions show a typical SANS profile for micelle formation in solution. It was found from a model-fitting analysis that the structure of the [C₁₂mIm⁺][Br^?] micelle is ellipsoidal, not spherical, in solutions over the C _IL range examined here.     

Electron inity of 1,3,5,7-cyclooctatetraene determined by the kinetic method

The kinetic method is used to determine the electron inity (EA) of 1,3,5,7-cyclooctatetraene (COT), a compound that undergoes a significant structural change upon electron attachment. Collision-induced dissociation of anionic clusters of COT with a set of reference compounds (Ref), [COT·Ref]^?·, at various collision energies, allowed deconvolution of the relative enthalpies and entropies of the competitive reactions. The adiabatic EA of COT is determined to be 0.58±0.10 eV, in good agreement with the value, 0.58±0.04 eV, of Wentworth and Ristau (J. Phys. Chem. 1969, 73, 2126) determined by thermal electron detachment as well as the more recent value, 0.55±0.02 eV, of Kato et al. (J. Am. Chem. Soc. 1997, 119, 7863) determined by equilibrium electron transfer with molecular oxygen. A large entropy difference, 25.6±10.0 e.u. (J mol^?1 K^?1), is observed between the two dissociation channels. This entropy difference corresponds to a negative 14.7±13.0 e.u. change for the dissociation of the dimer to give COT^?· and the neutral reference compound and a positive 10.9±8.4 e.u. entropy change for the dissociation of the dimer to give Ref^?· and neutral COT.     

An Improved Measurement of Isotopic Ratios by High Resolution Mass Spectrometry

The study of protein kinetics requires an accurate measurement of isotopic ratios of peptides. Although Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometers yield accurate mass measurements of analytes, the isotopologue ratios are consistently lower than predicted. Recently, we demonstrated that the magnitude of the spectral error in the FT-ICR mass spectrometer is proportional to the scan duration of ions. Here, we present a novel isotopic ratio extrapolation (IRE) method for obtaining accurate isotopic ratio measurements. Accuracy is achieved by performing scans with different duration and extrapolation of the data to the initial moment of the ion rotation; IRE minimizes the absolute isotopic ratio error to ≤1 %. We demonstrate the application of IRE in protein turnover studies using ²H₂O-metabolic labeling. Overall, this technique allows accurate measurements of the isotopic ratios of proteolytic peptides, a critical step for enabling routine studies of proteome dynamics.      

Estimation of the critical rate of temperature rise for thermal explosion of nitrocellulose using non-isothermal DSC

The expressions to calculate the critical rate of temperature rise of thermal explosion $ ({\text{d}}T / {\text{d}}t)_{{\text{T}_{\text{b}} }} $ for energetic materials (EMs) were derived from the Semenov’s thermal explosion theory and autocatalytic reaction rate equation of nth order, C_nB, B_na, first-order, apparent empiric-order, simple first-order, A_u, apparent empiric-order of m = 0, n = 0, p = 1 and m = 0, n = 1, p = 1, using reasonable hypotheses. A method to determine the kinetic parameters in the autocatalytic-decomposing reaction rate equations and the $ ({\text{d}}T / {\text{d}}t)_{{\text{T}_{\text{b}} }} $ in EMs when autocatalytic decomposition converts into thermal explosion from data of DSC curves at different heating rate was presented. Results show that (1) under non-isothermal DSC conditions, the autocatalytic-decomposing reaction of NC (12.97 % N) can be described by the first-order autocatalytic reaction rate equation dα/dt = 10^16.00exp(?174520/RT)(1 ? α) + 10^16.00exp(?163510/RT)α(1 ? α); (2) the value of $ ({\text{d}}T / {\text{d}}t)_{{\text{T}_{\text{b}} }} $ for NC (12.97 % N) when autocatalytic decomposition converts into thermal explosion is 0.354 K s^?1.     

Theoretical study of N–H· · ·O hydrogen bonding properties and cooperativity effects in linear acetamide clusters

We investigated geometry, energy, ${\nu_{{\text{N--H}}}}$ harmonic frequencies, ¹⁴N nuclear quadrupole coupling tensors, and ${n_{\rm O}\to \sigma _{{\text{N--H}}}^\ast}$ charge transfer properties of (acetamide) _n clusters, with n = 1 ? 7, by means of second-order Møller-Plesset perturbation theory (MP2) and DFT method. Dependency of dimer stabilization energies and equilibrium geometries on various levels of theory was examined. B3LYP/6-311++G** calculations revealed that for acetamide clusters, the average hydrogen-bonding energy per monomer increases from ?26.85 kJ mol^?1 in dimer to ?35.12 kJ mol^?1 in heptamer; i.e., 31% cooperativity enhancement. The n-dependent trend of ${\nu_{{\text{N--H}}}\,{and}\,^{14}}$ N nuclear quadrupole coupling values were reasonably correlated with cooperative effects in ${r_{{\text{N--H}}}}$ bond distance. It was also found that intermolecular ${n_{\rm O}\to \sigma_{{\text{N--H}}}^\ast}$ charge transfer plays a key role in cooperative changes of geometry, binding energy, ${\nu_{{\text{N--H}}}}$ harmonic frequencies, and ¹⁴N electric field gradient tensors of acetamide clusters. There is a good linear correlation between ¹⁴N quadrupole coupling constants, C _Q (¹⁴N), and the strength of Fock matrix elements (F _ij ). Regarding the ${n_{\rm O}\to \sigma_{{\text{N--H}}}^\ast}$ interaction, the capability of the acetamide clusters for electron localization, at the N–H· · ·O bond critical point, depends on the cluster size and thereby leads to cooperative changes in the N–H· · ·O length and strength, N–H stretching frequencies, and ¹⁴N quadrupole coupling tensors.     

Fragmentation of clusters induced by collision with a solid surface: comparison of antimony and bismuth cluster ions

Mass-selected antimony cluster ions Sb _n ⁺ (n = 3-12) and bismuth cluster ions Bi _{ntn} ⁺ (n = 3-8) are allowed to collide with the surface of highly oriented pyrolytic graphite at energies up to 350 eV. The resulting fragment ions are analysed in a time-of-flight mass spectrometer. Two main fragmentation channels can be identified. At low impact energies both Sb _n ⁺ and Bi _n ⁺ cluster ions lose neutral tetramer and dimer units upon collision. Above about 150 eV impact energy Sb ₃ ⁺ becomes the predominant fragment ion of all investigated antimony clusters. The enhanced stability of these fragment clusters can be explained in the framework of the polyhedral skeletal electron pair theory. In contrast, Bi _n ⁺ cluster scattering leads to the formation of Bi ₃ ⁺ , Bi ₂ ⁺ and Bi+ with nearly equal abundances, if the collision energy exceeds 75 eV. The integral scattering yield is substantially higher in this case as compared to Sb _n ⁺ clusters.     

Thermodynamic characterization of chromium tellurate

The standard Gibbs energy of formation of chromium tellurate, Cr₂TeO₆ was determined from the vapour pressure measurement of TeO₂(g) over the phase mixture Cr₂TeO₆(s) + Cr₂O₃(s) in the temperature range 1,183–1,293 K. A thermogravimetry (TG)-based transpiration technique was used for the vapour pressure measurement. This technique was validated by measuring the vapour pressure of CdCl₂(g) over CdCl₂(s). The temperature dependence of the vapour pressure of CdCl₂(g) could be represented as logp (Pa) (±0.02) = 12.06 ? 8616.3/T (K) (734 ? 823 K). A ‘third-law’ analysis of the vapour pressure data yielded a mean value of 185.1 ± 0.4 kJ mol^?1 for the enthalpy of sublimation of CdCl₂(s). The temperature dependence of vapour pressure of TeO₂(g) generated by the incongruent vapourisation reaction, $ {\text{Cr}}_{ 2} {\text{TeO}}_{ 6} (\rm s) \to {\text{Cr}}_{ 2} {\text{O}}_{ 3} (\rm s) + {\text{TeO}}_{ 2} (\rm g) + 1/2\,{\text{O}}_{ 2} (\rm g) $ could be represented as logp (Pa) (±0.04) = 18.57 – 21,199/T (K) (1,183 – 1,293 K). The temperature dependence of the Gibbs energy of formation of Cr₂TeO₆ could be expressed as $ \{ \Updelta G_{\text{f}}^{ \circ } ({\text{Cr}}_{ 2} {\text{TeO}}_{ 6} ,{\text{ s}}){\text{ (kJ}}\,{\text{mol}}^{ - 1} )\pm 4. 0 {\text{\} = }} - 1 6 2 5. 6 { \,+\, 0} . 5 3 3 6\,T({\text{K}}) \, (1{,}183 - 1{,}293\,{\text{K}}). $ A drop calorimeter was used for measuring the enthalpy increments of Cr₂TeO₆ in the temperature range 373–973 K. Thermodynamic functions viz., heat capacity, entropy and Gibbs energy functions of Cr₂TeO₆ were derived from the experimentally measured enthalpy increment values. $ \Updelta H_{{{\text{f}},298\,{\text{K}}}}^{ \circ } ({\text{Cr}}_{ 2} {\text{TeO}}_{ 6} ) $ was found to be ?1636.9 ± 0.8 kJ mol^?1.     

Kinetics and mechanism of the collision-activated dissociation of the acetone cation

For center-of-mass collision energies E_cm = 1–60 eV, the major fragment ions for the collision-activated dissociation (CAD) of the acetone cation are the acetyl cation (m / z 43; absolute branching ratios of 0.96–0.60) and the methyl cation (m/ z 15; absolute branching ratios of 0.02–0.26); the absolute total cross-sections were 24–35) Ų. The breakdown curves (viz, plots of the absolute branching ratios versus E_cm) show complex, complementary energy dependences for production of MeCO⁺ and Me⁺, indicating apparent closure of the Me⁺ channel for E_cm > 30 eV. Our observations are consistent with a competition between three fast, primary (direct) reactions, each of which opens sequentially at its respective threshold energy (viz, reactions 8, 10, and 8′). 1 $$Me_2 CO^ + \cdot \to MeCO^ + + Me \cdot (X^2 A''_2 ) \Delta H = 0.82 eV$$ 1 $$ \to MeCO^ + + Me \cdot (B, 1^2 A'_1 ) \Delta H = 6.55 eV$$ 1 $$ \to Me^ + + Me \cdot + CO \Delta H = 4.24 eV$$ That is, the breakdown curves for MeCO⁺ and Me⁺ (and other CAD fragments) are consistent with the interpretation by other authors that the collisional activation of the acetone cation involves electronic transitions, so that CAD occurs primarily from isolated electronic states (i.e., non-quasi-equilibrium theory (QET) behavior). For acetone we found a correspondence between the photoelectron-photoion-coincidence and CAD breakdown curves. This may indicate that collisional activation in non-QET systems corresponds to scattering angles that emphasize optically allowed transitions accessed by photoionization.     

Gas-Phase Oxidation of Neutral Basic Residues in Polypeptide Cations by Periodate

The gas-phase oxidation of doubly protonated peptides containing neutral basic residues to various products, including [M + H + O]⁺, [M – H]⁺, and [M – H – NH₃]⁺, is demonstrated here via ion/ion reactions with periodate. It was previously demonstrated that periodate anions are capable of oxidizing disulfide bonds and methionine, tryptophan, and S-alkyl cysteine residues. However, in the absence of these easily oxidized sites, we show here that systems containing neutral basic residues can undergo oxidation. Furthermore, we show that these neutral basic residues primarily undergo different types of oxidation (e.g., hydrogen abstraction) reactions than those observed previously (i.e., oxygen transfer to yield the [M + H + O]⁺ species) upon gas-phase ion/ion reactions with periodate anions. This chemistry is illustrated with a variety of systems, including a series of model peptides, a cell-penetrating peptide containing a large number of unprotonated basic sites, and ubiquitin, a roughly 8.6 kDa protein.

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Microhydration of Deprotonated Nucleobases

Hydration reactions of deprotonated nucleobases (uracil, thymine, 5-fluorouracil,2-thiouracil, cytosine, adenine, and hypoxanthine) produced by electrospray have been experimentally studied in the gas phase at 10 mbar using a pulsed ion-beam high-pressure mass spectrometer. The thermochemical data, ΔH ^o , ΔS ^o , and ΔG ^o , for the monohydrated systems were determined. The hydration enthalpies were found to be similar for all studied systems and varied between 39.4 and 44.8 kJ/mol. A linear correlation was found between water binding energies in the hydrated complexes and the corresponding acidities of the most acidic site of nucleobases. The structural and energetic aspects of the precursors for the hydrated complexes are discussed in conjunction with available literature data.

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Fluidized-bed Fenton-like oxidation of a textile dye using natural magnetite

Degradation of Acid Orange 7 (AO7) as a model azo dye was investigated in a recirculating pilot fluidized-bed reactor by a Fenton-like process using natural magnetite (NM) and potassium persulfate (K₂S₂O₈). Scanning electron microscopy was performed to characterize the magnetite sample. The heterogeneous Fenton-like process (NM/\({\text{S}}_{2} {\text{O}}_{8}^{2 - }\)) is a modified method owing to its enhanced mass transfer. It can be operated reliably and simply by reducing the produced iron oxide sludge in the conventional Fenton process. Degradation efficiency (DE %) of AO7 by NM/ \({\text{S}}_{2} {\text{O}}_{8}^{2 - }\) process was affected by operational parameters. The DE % of 75 % was obtained for the AO7 treatment (15 mg/L) at the desired conditions, such as pH 5, 0.2 mM \({\text{S}}_{2} {\text{O}}_{8}^{2 - }\), and 0.5 g/L NM after 120 min of reaction time. The dye degradation rate in all the experiments followed the pseudo-second-order kinetic with high correlation coefficients (R ² ≥ 0.98). The low released iron concentration, successive reusability at milder pH and the recirculation mode with the proper mixing are the significant advantages of the NM/\({\text{S}}_{2} {\text{O}}_{8}^{2 - }\) process.