Food additives characterization by infrared,Raman, and surface‐enhanced Raman spectroscopies

Fourier‐transform infrared (FT‐IR), Raman (RS), and surface‐enhanced Raman scattering (SERS) spectra of β‐hydroxy‐β‐methylobutanoic acid (HMB), L ‐carnitine, and N‐methylglycocyamine (creatine) have been measured. The SERS spectra have been taken from species adsorbed on a colloidal silver surface. The respective FT‐IR and RS band assignments (solid‐state samples) based on the literature data have been proposed. The strongest absorptions in the FT‐IR spectrum of creatine are observed at 1398, 1615, and 1699 cm⁻¹, which are due to ν_s(COOH) + ν(CN) + δ(CN), ρ_s(NH₂), and ν(C O) modes, respectively, whereas those of L ‐carnitine (at 1396/1586 cm⁻¹ and 1480 cm⁻¹) and HMB (at 1405/1555/1585 cm⁻¹ and 1437–1473 cm⁻¹) are associated with carboxyl and methyl/methylene group vibrations, respectively. On the other hand, the strongest bands in the RS spectrum of HMB observed at 748/1442/1462 cm⁻¹ and 1408 cm⁻¹ are due to methyl/methylene deformations and carboxyl group vibrations, respectively. The strongest Raman band of creatine at 831 cm⁻¹ (ρ_w(R NH₂)) is accompanied by two weaker bands at 1054 and 1397 cm⁻¹ due to ν(CN) + ν(R NH₂) and ν_s(COOH) + ν(CN) + δ(CN) modes, respectively. In the case of L ‐carnitine, its RS spectrum is dominated by bands at 772 and 1461 cm⁻¹ assigned to ρ_r(CH₂) and δ(CH₃), respectively. The analysis of the SERS spectra shows that HMB interacts with the silver surface mainly through the  COO⁻, hydroxyl, and  CH₂ groups, whereas L ‐carnitine binds to the surface via  COO⁻ and  N⁺(CH₃)₃ which is rarely enhanced at pH = 8.3. On the other hand, it seems that creatine binds weakly to the silver surface mainly by  NH₂, and C O from the  COO⁻ group. Copyright © 2006 John Wiley & Sons, Ltd.     

Influence of aliphatic spacer group on adsorption mechanisms of phosphonate derivatives of l-phenylalanine: Surface-enhanced Raman, Raman, and infrared studies

The nature of phosphonopeptides containing N-terminal l-phenylalanine (l-Phe), namely l-Phe-dl-NH-CH(CH(CH₃)₂)-PO₃H₂ (A), l-Phe-l-NH-CH(CH₃)-PO₃H₂ (B), and l-Phe-dl-NH-CH(CH₂CH₂COOH)-PO₃H₂ (C) (Fig. 1 presents molecular structure of these molecules), adsorbed on electrochemically roughened and colloidal silver surfaces has been explored by surface-enhanced Raman spectroscopy (SERS). To reveal adsorption mechanism of these species on the basis of their SERS spectra at first Fourier-transform Raman (FT-RS) and absorption infrared (FT-IR) spectra of non-adsorbed molecules were measured. Examination of enhancement, frequency shifts, and changes in relative intensities of SERS bands due to adsorption and surface roughens variation reveals that the tilted compounds adsorb on the electrochemically roughened silver substrate in similar way, while they behave differently on the colloidal silver surface. A stronger enhancement of in-plane ring vibrations of the l-Phe ring, i.e., ν₃ and ν_18b (B₂), over these of the A₂ symmetry in all SERS spectra on the electrochemically roughened silver substrate suggests that the ring interacts with this surface adopting slightly deflect orientation from the perpendicular one. Also, enhancement of PO and -CH₂-/-CH₃ fragments vibrations points out that they are involved in adsorption process on this substrate. This conclusion was drawn on the basis of the enhancement of 1274-1279 and 1138-1152 (ν(PO)), 1393-1400 (δ(CH) + ρ_b(CNH₂) + ν(C-C_O) + δ(CH₃)), ∼1455 (δ(CCH₃/CCH₂) + ρ_b(CH₃/CH₂), and 1505-1512 cm⁻¹ (δ(CH₂) + Phe(ν_19a)) bands. Although a relative intensity ratio of these bands in the presented SERS spectra is different. On the other hand, on the colloidal silver nanoparticles, the aromatic ring of all molecules is lying flat or takes almost parallel orientation to this surface. Besides, A interacts also via P-terminal group (568, 765, 827, 1040, and 1150 cm⁻¹), whereas B mainly through NH₂-C-(CO)-CNH-(712 and 1255 cm⁻¹). In the case of C, it adsorbs on the silver colloidal surface mainly through the aromatic ring of l-Phe, while other fragments of the molecule are in close proximity to this surface as comes off the weak enhancement of bands due to the aliphatic vibrations.     

Super-hydrophobic surface on pure magnesium substrate by wet chemical method

A layer of flower-like super-hydrophobic film was fabricated on pure Mg surface by chemical etching in H₂SO₄, H₂O₂ and subsequent immersion in stearic acid (CH₃(CH₂)₁₆COOH) ethanol solution. The super-hydrophobic surface showed a static water contact angle of 154° with the sliding angle of about 3°. With scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and Fourier-transform infrared (FT-IR) spectrometer, the microstructure and composition of the sample were analyzed. Results showed that the flower-like structure and the bonding of the CH₃(CH₂)₁₆COO⁻ on Mg surface can be responsible for the superior water-repellent property. Electrochemical impedance spectroscopy revealed that the transfer resistance of super-hydrophobic surface was increased about four times than bare Mg after one-hour immersion in 0.1 mol/L NaCl solution.     

Positioning of cationic silver nanoparticle by using AFM lithography and electrostatic interaction

One-dimensional metal lines of silver nanoparticles with a nano-sized width were generated onto silicon surface by using a nano-level lithography technique, field induced oxidation (FIO) by AFM, on self-assembled monolayer-modified Si wafers. This FIO technique provided SiO₂ lines a width of less than 100 nm. Short-time immersion of partially anodized silicon surface which is covered by a cationic silanol surfactant ((CH₃O)₃SiCH₂CH₂CH₂N(CH₃)₃⁺Cl⁻)-monolayer into quaternary ammonium (HSCH₂CH₂N(CH₃)₃⁺Br⁻)-covered silver nanoparticles readily and reproducibly gave nano-metal lines of silver onto silicon wafers. Hydrophilicity of the whole wafer surface was indispensable for homogeneously wetting the anodized SiO₂ area with a nanodimensional width.     

Radiation damage produced in powder of α-(methylamino)isobutyric acid, α -aminoisobutyric acid methyl ester hydrochloride and diethylmalonic acid

The electron paramagnetic resonance spectra of γ-irradiated powders of α-(methylamino)isobutyric acid – CH₃NHC(CH₃)₂COOH, α -aminoisobutyric acid methyl ester hydrochloride – NH₂(CH₃)₂CCOOCH₃ HCl, and diethylmalonic acid – (CH₃CH₂)₂C(COOH)₂ have been investigated at room temperature. It has been found that γ -irradiation produces the (CH₃)₂C˙COOH radical in the first, the (CH₃)₂C˙COOCH₃ radical in the second and the (CH₃CH₂)₂C˙COOH radical in the third compound. The spectra were computer-simulated. The g values and the hyperfine coupling constants of the unpaired electron with the environmental methyl, methylene protons and OH proton were determined. The results were found to be in good agreement with the existing literature data and theoretical predictions.     

Vibrational characterization of L‐valine phosphonate dipeptides: FT‐IR,FT‐RS,and SERS spectroscopy studies and DFT calculations

Four L ‐valine (L ‐Val) phosphonate dipeptides that are potent inhibitors of zinc metalloproteases, namely, L ‐Val‐C(Me)₂‐PO₃H₂ (V1), L ‐Val‐CH(iP)‐PO₃H₂ (V2), L ‐Val‐CH(iB)‐PO₃H₂ (V3), and L ‐Val‐C(Me)(iP)‐PO₃H₂ (V4), are studied by Fourier‐transform infrared (FT‐IR) spectroscopy, Fourier‐transform Raman spectroscopy (FT‐RS), and surface‐enhanced Raman scattering (SERS). The band assignment (wavenumbers and intensities) is made based on (B3LYP/6‐311 + + G**) calculations. Comparison of theoretical FT‐IR and FT‐RS spectra with those of SERS allows to obtain information on the orientation of these dipeptides as well as specific‐competitive interactions of their functionalities with the silver substrate. More specifically, V1 and V4 appear to interact with the silver substrate mainly via a  C_sgCH₃ moiety localized at the  N_amideC_sg(CH₃)P molecular fragment. In addition, the  POH and isopropyl units of V4 assist in the adsorption process of this molecule. In contrast, the  C_αNH₂ and  PO₃H⁻ groups of V2 and V3 interact with the silver nanoparticles, whereas their isopropyl and isobutyl fragments seem to be repelled by the silver substrate (except for the  CH₂  of V3), similar to the  C_β(CH₃)₂ fragment of L ‐Val for all L ‐Val phosphonate dipeptides investigated in this work. The adsorption mechanism of these molecules onto the colloidal silver surface is also affected by amide bond behavior. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of an aliphatic spacer group on the adsorption mechanism on the colloidal silver surface of L‐proline phosphonodipeptides

A comparative study of molecular structures of five L ‐proline (L ‐Pro) phosphonodipeptides: L ‐Pro‐NH‐C(Me,Me)‐PO₃H₂ (P1), L ‐Pro‐NH‐C(Me,iPr)‐PO₃H₂ (P2), L ‐Pro‐L ‐NH‐CH(iBu)‐PO₃H₂ (P3), L ‐Pro‐L ‐NH‐CH(PA)‐PO₃H₂ (P4) and L ‐Pro‐L ‐NH‐CH(BA)‐PO₃H₂ (P5) has been carried out using Raman and absorption infrared techniques of molecular spectroscopy. The interpretation of the obtained spectra has been supported by density functional theory calculations (DFT) at the B3LYP; 6–31 + + G** level using Gaussian 2003 software. The surface‐enhanced Raman scattering (SERS) on Ag‐sol in aqueous solutions of these phosphonopeptides has also been investigated. The surface geometry of these molecules on a silver colloidal surface has been determined by observing the position and relative intensity changes of the Pro ring, amide, phosphonate and so‐called spacer (−R) groups vibrations of the enhanced bands in their SERS spectra. Results show that P4 and P5 adsorb onto the silver as anionic molecules mainly via the amide bond (∼1630, ∼1533, ∼1248, ∼800 and ∼565 cm⁻¹), Pro ring (∼956, ∼907 and ∼876 cm⁻¹) and carboxylate group (∼1395 and ∼909 cm⁻¹). Coadsorption of the imine nitrogen atom and PO group with the silver surface, possibly by formation of a weaker interaction with the metal, is also suggested by the enhancement of the bands at 1158 and 1248 cm⁻¹. P1, P2 and P3 show two orientations of their main chain on the silver surface resulting from different interactions of the  C CH₃,  NH and  CONH fragments with this surface. Bonding to the Ag surface occurs mainly through the imino atom (1166 cm⁻¹) for P2, while for P1 and P3 it occurs via the methyl group(s) (1194–1208 cm⁻¹). The amide group functionality (CONH) is practically not involved in the adsorption process for P1 and P2, whereas the C_s P bonds do assist in the adsorption. Copyright © 2008 John Wiley & Sons, Ltd.     

The catalytic effects of H2CO3, CH3COOH,HCOOH and H2O on the addition reaction of CH2OO + H2O → CH2(OH)OOH

The addition reaction of CH₂OO + H₂O → CH₂(OH)OOH without and with X (X = H₂CO₃, CH₃COOH and HCOOH) and H₂O was studied at CCSD(T)/6-311+ G(3df,2dp)//B3LYP/6-311+G(2d,2p) level of theory. Our results show that X can catalyse CH₂OO + H₂O → CH₂(OH)OOH reaction both by increasing the number of rings, and by adding the size of the ring in which ring enlargement by COOH moiety of X inserting into CH₂OO···H₂O is favourable one. Water-assisted CH₂OO + H₂O → CH₂(OH)OOH can occur by H₂O moiety of (H₂O)₂ or the whole (H₂O)₂ forming cyclic structure with CH₂OO, where the latter form is more favourable. Because the concentration of H₂CO₃ is unknown, the influence of CH₃COOH, HCOOH and H₂O were calculated within 0–30 km altitude of the Earth's atmosphere. The results calculated within 0–5 km altitude show that H₂O and HCOOH have obvious effect on enhancing the rate with the enhancement factors are, respectively, 62.47%–77.26% and 0.04%–1.76%. Within 5–30 km altitude, HCOOH has obvious effect on enhancing the title rate with the enhancement factor of 2.69%–98.28%. However, compared with the reaction of CH₂OO + HCOOH, the rate of CH₂OO···H₂O + HCOOH is much slower.     

Infrared and Raman Spectra of Sulfur-Nitride Complexes of Nickel(II) and Palladium(II)

Abstract

The infrared and Raman spectra of trans-Ni(S₂N₂CH₃)₂ and Pd(S₃N)₂ were measured from 4000-200 cm^?1. The absorption bands were assigned by comparison to the sulfur nitride complexes of nickel(II), palladium(II) and platinum(II). Normal coordinate analyses on these complexes were carried on these data using molecular parameters taken from X-ray data. To aid in band assignments, isotope shift data on trans-⁶²Ni(S₂N₂CH₃)₂ have also been carried out.     

The Raman and Infrared Spectra and the Structures of Dimethyl,Methyl Germyl and Digermyl Sulfide

Abstract

The Raman and infrared spectra of dimethyl sulfide (CH₃?S-CH₃) have been assigned in terms of a D_3d model¹. The structurally related compounds, digermyl sulfide (GeH₃?S-GeH₃) and methyl germyl sulfide(CH₃?S-GeH₃) are prepared according to the literature^2–4, and their vibrational spectra are measured. The analysis of these spectra comparing with those of CH₃?S-CH₃ allows us to determine the molecular structures to be D_3d for GeH₃?S-GeH₃ and a C_3v for CH₃?S-GeH₃ with a linear—S—.     

Tunable linear nanopatterns of disubstituted alkane derivatives containing bi-components via selective hydrogen bonding

Supramolecular self-assembly on surfaces offers attractive features, which are usually tuned through the choice of the chain-length-varying molecular building blocks and stabilized by hydrogen bonding. Here the linear nanopatterns of bi-component building blocks between 1,18-octadecanedionic acid (HOOC(CH₂)₁₈COOH) and 4,4′-bipyridine (BPy), 1-hydroxyhexadecanoic acid (HO(CH₂)₁₅COOH) and BPy on highly ordered pyrolytic graphite are presented. By merely changing terminal groups, we reveal by using scanning tunneling microscopy (STM) that it is rational to steer the periodicity of the linearly patterned nanostructures with nanometer precision over an extended length scale. Different surface nanopatterns on graphite surface are created by tuning different disubstituted terminal groups and the ratio of them to their complementary recognizing molecules. The STM observations are supported by the reference nanostructure of bi-component 1,16-hexadecandiol (HO(CH₂)₁₆OH) and BPy.     

Habit of long-chain molecular crystals

The quantitative analysis of the temperature dependence of the heat capacity of molecular crystals with chains of different lengths was performed using the theory of diffuse first-order phase transitions. The same chemical structure of the “core” of molecular crystals of {CH₃(CH₂)_nCH₃} normal paraffins, {COH(CH₂)_nCOH} diols, {CH₃(CH₂)_nCOH} normal alcohols, and {CH₃(CH₂)_nCOOH} saturated carboxylic and {COOH(CH₂)_nCOOH} dicarboxylic acids enabled the comparative analysis of phase transition parameters.     

Structures and Vibrational Spectra of the Hydrogen-Bonded Complexes Between Nitrous Acid and Acetone: Ab Initio and DFT Studies

ABSTRACT

The structures, stability, and vibrational spectra of the binary complexes formed between acetone and nitrous (trans and cis) acid have been investigated using ab initio calculations at the SCF and MP2 levels and B3LYP calculations with 6-311++G(d,p) basis set. Full geometry optimization was made for the complexes studied. It was established that the complex (CH₃)₂CO···HONO-trans is more stable than the complex (CH₃)₂CO···HONO-cis by 0.5–0.8 kcal·mol^?1. The accuracy of the calculations has been estimated by comparison between the predicted values of the vibrational characteristics (vibrational frequencies and infrared intensities) and the available experimental data. It was established, that the methods, used in this study are well adapted to the problem under examination. The predicted values with the B3LYP/6-311++G(d,p) calculations are very near to the results, obtained with MP2/6-311++G(d,p). The calculated frequency shift Δν(O[sbnd]H) for the complex (CH₃)₂CO···HONO-trans (1A) is larger than for the complex (CH₃)₂CO···HONO-cis (1B). In the same time the intensity of this vibration increases dramatically upon hydrogen bonding. The calculated increase for the complex 1A is up to 15 times and for the complex 1B is up to 30 times. The changes in the vibrational characteristics (vibrational frequencies and infrared intensities) of (CH₃)₂CO upon the complexation are more insignificant than the changes in the vibrational characteristics of HONO-trans and HONO-cis.     

One-step electrodeposition process to fabricate cathodic superhydrophobic surface

In this work, a rapid one-step process is developed to fabricate superhydrophobic cathodic surface by electrodepositing copper plate in an electrolyte solution containing manganese chloride (MnCl₂·4H₂O), myristic acid (CH₃(CH₂)₁₂COOH) and ethanol. The superhydrophobic surfaces were characterized by means of scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The shortest electrolysis time for fabricating a superhydrophobic surface is about 1 min, the measured maximum contact angle is 163° and rolling angle is less than 3°. Furthermore, this method can be easily extended to other conductive materials. The approach is time-saving and cheap, and it is supposed to have a promising future in industrial fields.     

The oxidation of methanol on a silver (110) catalyst

The oxidation of methanol was studied on a Ag(110) single-crystal by temperature programmed reaction spectroscopy. The Ag(110) surface was preoxidized with oxygen-18, and deuterated methanol, CH₃OD, was used to distinguish the hydroxyl hydrogen from the methyl hydrogens. Very little methanol chemisorbed on the oxygen-free Ag(110) surface, and the ability of the silver surface to dissociatively chemisorb methanol was greatly enhanced by surface oxygen. CH₃OD was selectively oxidized upon adsorption at 180 K to adsorbed CH₃O and D₂¹⁸O, and at high coverages the D₂¹⁸O was displaced from the Ag(110) surface. The methoxide species was the most abundant surface intermediate and decomposed via reaction channels at 250, 300 and 340 K to H₂CO and hydrogen. Adsorbed H₂CO also reacted with adsorbed CH₃O to form H₂COOCH₃which subsequently yielded HCOOCH₃ and hydrogen. The first-order rate constant for the dehydrogenation of D₂COOCH₃ to DCOOCH₃ and deuterium was found to be (2.4 ± 2.0) × 10¹¹ exp(?14.0 ± 0.5 $\text{kcal}\text{mole}$ · RT)sec^?1. This reaction is analogous to alkoxide transfer from metal alkoxides to aldehydes in the liquid phase. Excess surface oxygen atoms on the silver substrate resulted in the further oxidation of adsorbed H₂CO to carbon dioxide and water. The oxidation of methanol on Ag(110) is compared to the previous study on Cu(110).     

81Br NQR Study of [NH3(CH2) n NH3]CdBr4 (n = 4 and 5) and [NH3(CH2) n NH3]ZnBr4 (n = 5 and 6)

⁸¹Br NQR frequencies and differential scanning calorimetry (DSC) were measured as a function of temperature. [NH₃(CH₂)₄ NH₃]CdBr₄ (1) and [NH₃(CH₂)₅NH₃]CdBr₄ (2) showed a doublet and quartet ⁸¹Br NQR spectrum, respectively. [NH₃(CH₂)₅NH₃]ZnBr₄ (3) and [NH₃(CH₂)₆NH₃]ZnBr₄ (4) exhibited a four-line ⁸¹Br NQR spectrum. From the NQR results, it is inferred that (1) and (2) consist of infinite two-dimensional sheets of corner-sharing CdBr₆ octahedra, whereas (3) and (4) have isolated [ZnBr₄]²⁻ tetrahedra. All of the crystals except (1) showed at least one structural phase transition above 380 K.     

The electronic delocalization in para‐substituted β‐nitrostyrenes probed by resonance Raman spectroscopy and quantum‐chemical calculations

The electronic (UV‐vis) and resonance Raman (RR) spectra of a series of para‐substituted trans‐β‐nitrostyrenes were investigated to determine the influence of the electron donating properties of the substituent (X = H, NO₂, COOH, Cl, OCH₃, OH, N(CH₃)₂, and O⁻) on the extent of the charge transfer to the electron‐withdrawing NO₂ group directly linked to the ethylenic (C = C) unit. The Raman spectra and quantum chemical calculations show clearly the correlation of the electron donating power of the X group with the wavenumbers of the ν_s(NO₂) and ν (C = C)_sty normal modes. In conditions of resonance with the lowest excited electronic state, one observes for X = OH and N(CH₃)₂ that the symmetric stretching of the NO₂, ν_s(NO₂), is the most substantially enhanced mode, whereas for X = O⁻, the chromophore is extended over the whole molecule, with substantial enhancement of several carbon backbone modes. Copyright © 2008 John Wiley & Sons, Ltd.     

Fabrication of surface‐enhanced Raman scattering‐active ZnO/Ag composite microspheres

We show in this paper how zinc oxide (ZnO)/silver (Ag) composite microspheres can be prepared by the reduction of Ag(NH₃)₂⁺ with the reducing agent formaldehyde in aqueous solution on the surface of ZnO microspheres. During the preparation, Sn²⁺ was absorbed on the surface of ZnO microspheres for sensitization and activation, and then Ag(NH₃)₂⁺ was reduced to Ag nanoparticles by the reducing agent to obtain ZnO/Ag composite microspheres. SEM and TEM images revealed silver nanoparticles with a diameter ranging from tens to 100 nm. X‐Ray photoelectron spectra (XPS), X‐ray diffraction (XRD) patterns and UV‐vis spectra were used to characterize the structure of the ZnO/Ag composite microspheres. The origin of the surface‐enhanced Raman scattering properties was traced to the surface of the ZnO/Ag composite microspheres. The enhancement factor was estimated in detail, and the enhancement mechanism for the SERS effect was also investigated. Copyright © 2007 John Wiley & Sons, Ltd.     

Raman,Infrared and 1H-NMR Spectra of Hexamethyldisilylchalcogenides

The Raman, infrared and ¹H-NMR spectra of (CH₃)₃ -X-Si (CH₃)₃ (X=O,S,Se,Te) were measured, and the assignment was carried out by comparison with those of the structurally related compounds, (CH₃)₃ SiCl and (CH₃)₃ Si-Si (CH₃)₃. The vibrational spectra of (CH₃)₃ Si-X-Si (CH₃)₃ can be interpreted in terms of a non-rigid D_3d symmetry with internal rotations, because those of skeletones of the molecules indicate the lack of coincidence between Raman and infrared frequencies. The ¹H-NMR spectra also support a non-rigid D_3d model, because only one band for CH₃ group appears.     

Catalytic effect of water,water dimer,water trimer,HCOOH, H2SO4, CH3CH2COOH and HN(NO2)2 on the isomerisation of HN(NO2)2 to O2NNN(O)OH: a mechanism study

In this article, the isomerisation mechanisms of HN(NO₂)₂ to O₂NNN(O)OH without and with catalyst X (X = H₂O, (H₂O)₂, (H₂O)₃, HCOOH, H₂SO₄, CH₃CH₂COOH and HN(NO₂)₂) have been investigated theoretically at the CBS-QB3 level of theory. Our results show that the catalyst X (X = H₂O, (H₂O)₂, (H₂O)₃, HCOOH, H₂SO₄ and CH₃CH₂COOH) shows different positive catalytic effects on reducing the apparent activation energy of the isomerisation reaction processes. Such different catalytic effects are mainly related to the number of hydrogen bonds and the size of the ring structure in X (X = H₂O, (H₂O)₂ and (H₂O)₃)-assisted transition states, as well as different values of pK_a for H₂SO₄, HCOOH and CH₃CH₂COOH. Very interesting is also the fact that H₂SO₄-assisted reaction is the most favourable for the hydrogen transfer from HN(NO₂)₂ to O₂NNN(O)OH, due to the smallest pK_a (?3.0) value of H₂SO₄ than H₂O, HCOOH, H₂SO₄ and CH₃CH₂COOH, and also because of the largest ∠X???H???Y (the angle between the hydrogen bond donor and acceptor) involved in H₂SO₄-assisted transition state. Compared to the self-catalysis of the isomerisation mechanisms of HN(NO₂)₂ to O₂NNN(O)OH, the apparent activation energy of H₂SO₄-assisted channel also reduces by 9.6 kcal?mol^?1, indicating that H₂SO₄ can affect the isomerisation of HN(NO₂)₂ to O₂NNN(O)OH, most obvious among all the catalysts H₂O, (H₂O)₂, (H₂O)₃, HCOOH, H₂SO₄, CH₃CH₂COOH and HN(NO₂)₂.