Vibrational spectroscopy of lapachol, α- and β-lapachone: Theoretical and experimental elucidation of the Raman and infrared spectra

Raman and infrared spectroscopy were applied for the vibrational characterization of lapachol and its pyran derivatives, α-lapachone and β-lapachone. Experimental spectra of solid state samples were acquired between 4000 and 100 cm⁻¹ in Raman experiments, and between 4000 and 600 cm⁻¹ (mid-infrared) and 600–100 cm⁻¹ (far-infrared) with FTIR spectroscopy, respectively. Full structure optimization and theoretical vibrational wavenumbers were calculated at the B3LYP/6-31 + + G(d,p) level. Detailed assignments of vibrational modes in an experimental and theoretical spectra were based on potential energy distribution analyses, using Veda 4.1 software. Clear differentiation between the three compounds was verified in the region between 1725 and 1525 cm⁻¹, in which the ν(CO) and ν(CC) modes of the quinone moiety were assigned.     

Hydrogen-bond transition from the vibration mode of ordinary water to the (H,Na)I hydration states: Molecular interactions and solution viscosity

With the aid of differential phonon spectrometrics (DPS) and surface stress detection, we show that HI and NaI solvation transforms different fractions of the HO stretching phonons from the mode of ordinary water centred at ∼3200 to the mode of hydration shell at ∼3500 cm⁻¹. Observations suggest that an addition of the H ↔ H anti-hydrogen-bond to the Zundel notion, [H(H₂O)₂]⁺, would be necessary as the HO bond due H₃O⁺ has a 4.0 eV energy, and the H ↔ H fragilization disrupts the solution network and the surface stress. The I⁻ and Na⁺ ions form each a charge centre that aligns, stretches, and polarize the O:HO bond, resulting in shortening the HO bond and its phonon blue shift in the hydration shell or at the solute-solvent interface. The solute capabilities of bond-number-fraction transition follow: f_H = 0, f_Na ∝ C, and f_I ∝ 1 − exp(−C/C₀) toward saturation, with C being the solute molar concentration and C₀ the decay constant. The f_H = 0 evidences the non-polarizability of the H⁺ because of the H ↔ H formation. The linear f_Na(C) suggests the invariance of the Na⁺ hydration shell size because of the fully-screened cationic potential by the H₂O dipoles in the hydration shell but the nonlinear f_I(C) fingerprints the I⁻ ↔ I⁻ interactions at higher concentrations. Concentration trend consistency between Jones–Dole’s viscosity and the f_NaI(C) coefficient may evidence the same polarization origin of the solution viscosity and surface stress.     

Structure of the complex of dimethylphenyl betaine with dichloroacetic acid studied by X-ray diffraction,DFT calculations,infrared and Raman spectra

The structure of the complex of dimethylphenyl betaine (DMPB) with dichloroacetic acid (DCA) (1) has been investigated by X-ray diffraction, FTIR and Raman spectroscopy, and B3LYP/6-311 + + G(d,p) calculations. The crystal is monoclinic, space group P2₁. The acid is connected with betaine through the OH⋯O hydrogen bond of 2.480(2) Å. In the optimized structure the short, asymmetric O⋯O distance is 2.491 Å. FTIR spectrum shows a broad absorption in the 1500–400 cm⁻¹ region characteristic of very short OH⋯O hydrogen bond caused by Fermi resonance between νOH and overtones of δOH and γOH. In the Raman spectrum this broad absorption is not observed. The potential energy distributions (PED) were used for the assignments of IR and Raman frequencies in the experimental and calculated spectra. The FTIR and Raman spectra of the crystal complex are consistent with the X-ray results.     

Near-infrared spectroscopy as an effective tool for monitoring the conformation of alkylammonium surfactants in montmorillonite interlayers

Application of near-infrared (NIR) spectroscopy to probing the arrangement of trimethylalkylammonium cations in montmorillonite interlayers has been demonstrated. Detailed analysis of the mid-IR (MIR) and NIR spectra of montmorillonite from Jelšový Potok (JP, Slovakia) saturated with surfactants with varying alkyl chain length (even numbers of carbon atoms from C6 to C18) was performed to show the advantages of the NIR region in characterizing surfactant conformations. The position of the ν_as(CH₂), (∼2930–2920 cm⁻¹), ν_s(CH₂) (∼2860–2850 cm⁻¹), 2ν_as(CH₂) (∼5810–5785 cm⁻¹), (ν + δ)_as(CH₂) (∼4340–4330 cm⁻¹) and (ν + δ)_s(CH₂) (∼4270–4250 cm⁻¹) signals was used as an indicator of the gauche/trans conformer ratio. For all bands, a shift toward lower wavenumber on increasing the alkyl chain length from 6 to 18 carbons suggests a transition from disordered liquid-like to more ordered solid-like structures of the surfactants. The magnitude of the shift was significantly higher for 2ν_as(CH₂) (28 cm⁻¹) than for ν_as(CH₂) (8 cm⁻¹) or ν_s(CH₂) (10 cm⁻¹), showing the NIR region to be a useful tool for examining this issue. Comparison of the IR spectra of crystalline alkylammonium salts and the corresponding organo-montmorillonites demonstrated a confining effect of montmorillonite layers on surfactant ordering. For each alkyl chain length the CH₂ bands of the organo-montmorillonites appeared at higher wavenumbers than for the unconfined surfactant, thus indicating a higher disorder of the alkyl chains. The wavenumber difference between corresponding samples was always higher in the NIR than in the MIR region. All these findings show NIR spectroscopy to be useful for conformational studies.     

Behaviour of Li+ and Cu2+ in heated montmorillonite: Evidence from far-, mid-, and near-IR regions

Infrared spectroscopy in the far (FIR), mid (MIR), and near (NIR) regions was used to study the structural changes of a thermally treated clay mineral montmorillonite saturated with Li⁺ or Cu²⁺ cations (Li-JP and Cu-JP samples). Cation exchange capacity (CEC) values decreased by 89 and 64% in Li- and Cu-samples, respectively, heated at 300 °C. The IR spectra confirm that the charge of exchangeable cations significantly affect their final position after fixation upon heating. No absorption bands related to the vibrations of interlayer cations were observed in the FIR spectra of unheated or heated samples; however, different modification of the complex vibrational mode involving motion of octahedral aluminium relative to the tetrahedral sheet was observed near 197 cm⁻¹. The vibrations of OH groups in both MIR (ν_OH, 3630–3670 cm⁻¹) and NIR (2ν_OH, 7070–7170 cm⁻¹) regions proved that the Li⁺ migrated into the octahedral vacancies, thus creating local trioctahedral domains, such as AlMgLiOH. Though Cu²⁺ has similar ionic radius as Li⁺, no spectral features indicating its presence in the octahedral positions have been found even in the sample heated at 300 °C. Fixed Cu(II) is supposed to be located deep in the ditrigonal cavities of the tetrahedral sheets of Cu-JP. The NIR spectra of heated Cu-JP samples show new components near 7045 and 5170 cm⁻¹. These modes are believed to correspond to overtone bands associated with hydrated Cu²⁺ ions tightly bound in close proximity to the ditrigonal cavities of the basal surface (O_basalCu²⁺H₂O). The NIR spectra confirm that in Cu-JP heated at 200 °C, then saturated with Li⁺ and Cu²⁺ and heated again at 300 °C small Li⁺ ions migrate into the vacant octahedral sites even though Cu(II) have been trapped in the hexagonal cavities of the tetrahedral sheets in the course of previous heat treatment.     

Electronic and vibrational spectra of tourmaline – The impact of electron beam irradiation and heat treatment

Irradiation and heat treatment were performed on tourmalines of various colors from Antandrokomby, Madagascar. The samples were irradiated with 10 MeV electrons to fluencies of 2 ×10¹⁷ cm⁻² for 1 h and were heated at 550 °C for 3 h in air. Their electronic and vibrational spectra were investigated by UV–vis, mid-infrared, and WD-XRF spectroscopy for comparison to pristine samples. Changes in the Mn³⁺ ions after irradiation resulted in darker pink tourmalines, which had absorption peaks at 390 and 520 nm. These samples became colorless after subsequent heat treatment. After irradiation, colorless, light blue and yellow tourmalines displayed a new absorption band at 365 nm. Alteration of the stretching absorption bands and wavenumber after irradiation could be explained by the following reactions:OH⁻ + e⁻ beam irradiation → O⁻ + H°,Mn²⁺ + e⁻ beam irradiation → Mn³⁺ + e⁻ andFe²⁺ + e⁻ beam irradiation → Fe³⁺ + e⁻.Stretching vibration of the BO₃ structure occurred at 1330 cm⁻¹, while the SiO vibration absorption bands were assigned to around 1100 cm⁻¹. Colorless, green, and yellow tourmalines showed high-intensity peaks around 3608 and 3505 cm⁻¹ after irradiation. Pink and dark green tourmalines showed low-intensity peaks at 3605 and 3585 cm⁻¹, respectively. The combination modes of stretching and bending in the range of 4600–4300 cm⁻¹ were split after irradiation and heat treatment, and different color changes occurred after irradiation.     

Effect of inorganic anions on the titanium dioxide-based photocatalytic oxidation of aqueous ammonia and nitrite

In this study, we investigated the effects of four inorganic anions (Cl⁻, SO₄²⁻, H₂PO₄⁻/HPO₄²⁻, and HCO₃⁻/CO₃²⁻) on titanium dioxide (TiO₂)-based photocatalytic oxidation of aqueous ammonia (NH₄⁺/NH₃) at pH ∼ 9 and ∼10 and nitrite (NO₂⁻) over the pH range of 4–11. The initial rates of NH₄⁺/NH₃ and NO₂⁻ photocatalytic oxidation are dependent on both the pH and the anion species. Our results indicate that, except for CO₃²⁻, which decreased the homogeneous oxidation rate of NH₄⁺/NH₃ by UV-illuminated hydrogen peroxide, OH scavenging by anions and/or direct oxidation of NH₄⁺/NH₃ and NO₂⁻ by anion radicals did not affect rates of TiO₂ photocatalytic oxidation. While HPO₄²⁻ enhanced NH₄⁺/NH₃ photocatalytic oxidation at pH ∼ 9 and ∼10, H₂PO₄⁻/HPO₄²⁻ inhibited NO₂⁻ oxidation at low to neutral pH values. The presence of Cl⁻, SO₄²⁻, and HCO₃⁻ had no effect on NH₄⁺/NH₃ and NO₂⁻ photocatalytic oxidation at pH ∼ 9 and ∼10, whereas CO₃²⁻ slowed NH₄⁺/NH₃ but not NO₂⁻ photocatalytic oxidation at pH ∼ 11. Photocatalytic oxidation of NH₄⁺/NH₃ to NO₂⁻ is the rate-limiting step in the complete oxidation of NH₄⁺/NH₃ to NO₃⁻ in the presence of common wastewater anions. Therefore, in photocatalytic oxidation treatment, we should choose conditions such as alkaline pH that will maximize the NH₄⁺/NH₃ oxidation rate.     

Electronic structure and Raman spectroscopy study of dibarium magnesium orthoborate,Ba2Mg(BO3)2

The samples of dibarium magnesium orthoborate Ba₂Mg(BO₃)₂ were synthesized by solid-state reaction. The X-ray diffraction (XRD) patterns and Raman spectra of the samples were collected. Electronic structure and vibrational spectroscopy of Ba₂Mg(BO₃)₂ were systematically investigated by first principle calculation. A direct band gap of 4.4 eV was obtained from the calculated electronic structure results. The top valence band is constructed from O 2p states and the low conduction band mainly consists of Ba 5d states. Raman spectra for Ba₂Mg(BO₃)₂ polycrystalline were obtained at ambient temperature. The factor group analysis results show the total lattice modes are 5E_u + 4A_2u + 5E_g + 4A_1g + 1A_2g + 1A_1u, of which 5E_g + 4A_1g are Raman-active. Furthermore, we obtained the Raman active vibrational modes as well as their eigenfrequencies using first-principle calculation. With the assistance of the first-principle calculation and factor group analysis results, Raman bands of Ba₂Mg(BO₃)₂ were assigned as E_g (42 cm⁻¹), A_1g (85 cm⁻¹), E_g (156 cm⁻¹), E_g (237 cm⁻¹), A_1g (286 cm⁻¹), E_g (564 cm⁻¹), A_1g (761 cm⁻¹), A_1g (909 cm⁻¹), E_g (1165 cm⁻¹). The strongest band at 928 cm⁻¹ in the experimental spectrum is assigned to totally symmetric stretching mode of the BO₃ units.     

Excess molar volumes of binary mixtures of 2,2,2-trifluoroethanol with water,or acetone,or 1,4-difluorobenzene,or 4-fluorotoluene,or α,α,α, trifluorotoluene or 1-alcohols at a temperature of 298.15 K and pressure of 101 kPa

Excess molar volumes V_m^E of binary mixtures of 2,2,2-trifluoroethanol with water, or acetone, or methanol, or ethanol, or 1-alcholos, or 1,4-difluorobenzene, or 4-fluorotoluene or α,α,α-trifluorotoluene were measured in a vibrating tube densimeter at temperature 298.15 K and pressure of 101 kPa. The V_m^E extrema are: 1.540 cm³ · mol⁻¹ for (2,2,2-trifluoroethanol + 1-heptanol); 1.452 cm³ · mol⁻¹ for (2,2,2-trifluoroethanol + 1-hexanol); 1.238 cm³ · mol⁻¹ for (2,2,2-trifluoroethanol + 1-butanol); 0.821 cm³ · mol⁻¹ for (2,2,2-trifluoroethanol + 4-fluorotoluene); 0.817 cm³ · mol⁻¹ for (2,2,2-trifluoroethanol + ethanol); 0.647 cm³ · mol⁻¹ for (2,2,2-trifluoroethanol + methanol); 0.618 cm³ · mol⁻¹ for (2,2,2-trifluoroethanol + acetone); 0.605 cm³ · mol⁻¹ for (2,2,2-trifluoroethanol + α,α,α-trifluorotoluene); 0.485 cm³ · mol⁻¹ for (2,2,2-trifluoroethanol + 1,4-difluorobenzene); and −0.656 cm³ · mol⁻¹ for (2,2,2-trifluoroethanol + water). The limiting excess partial molar volumes are estimated.     

Electronic and vibrational circular dichroism spectroscopic study of non-covalent interactions of meso-5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin with (dG-dC)10 and (dA-dT)10

The non-covalent interactions of (dG-dC)₁₀ and (dA-dT)₁₀ with 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin (TMPyP) were studied using the combination of electronic circular dichroism (ECD), vibrational circular dichroism (VCD) spectroscopy, and UV–vis and IR absorption spectroscopy at different ratios of both components r = [oligonucleotide]/[TMPyP] = 2/1–10/1 where [oligonucleotide] and [TMPyP] are the amount concentrations of oligonucleotide per base-pair and TMPyP, respectively. It was shown that TMPyP with (dG-dC)₁₀ provided hemiintercalative binding mode for r = 4/1 that is manifested in vibrational spectra: The absorption band assigned to the C6O6 stretching vibration of guanine is shifted from 1683 to 1672 cm⁻¹, the corresponding VCD couplet from 1694(−)/1674(+) to 1684(−)/1663(+) cm⁻¹ and its intensity decreases. The absorption band assigned to the C2O2 stretching vibration of cytosine is shifted from 1652 to 1644 cm⁻¹ and its intensity increases. TMPyP with (dA-dT)₁₀ provided three binding modes: (i) external binding to the phosphate backbone, (ii) external minor groove binding for the ratios >6/1 and (iii) external major groove binging associated with the partial B- to Z-transition for the ratios <4/1. The major groove binding is manifested in VCD spectra by the intensity decrease of the bands 1655 and 1638 cm⁻¹ assigned to the thymine vibrations while the bands assigned to the adenine vibrations are unchanged. In the (dA-dT)₁₀–TMPyP complexes, the external binding to the phosphate backbone accompanied by self-stacking of porphyrins along the phosphate backbone chain is preferred at temperatures higher than 40 °C.     

Infrared and Raman spectroscopic characterization of the hydrogen-bonding network in l-serine crystal

The IR spectra (4000–400 cm⁻¹) of neat and isotopically substituted (ND/OD ≤ 10% D and ≅30% D) polycrystalline l-serine (α-amino-β-hydroxypropionic acid; HO–CH₂–CH(NH₃)⁺–COO⁻) were recorded in the temperature range 300–10 K and assigned. The isotopic-doping/low-temperature methodology, which allows for decoupling of individual proton vibrational modes from the crystal bulk vibrations, was used for estimating the lengths and energies of the different H-bonds present in l-serine crystal. To this end, the frequency shifts observed in both the NH/OH stretching and out-of-plane bending spectral regions (relatively to reference values for these vibrations in non-hydrogen-bonded l-serine molecules) were used, together with previously developed empirical correlations between these spectral parameters and the H-bond properties. In addition, the room-temperature Raman spectrum (4000–150 cm⁻¹) of a single crystal of neat l-serine was also recorded and interpreted. A systematic comparison was made between the spectroscopic data obtained currently for l-serine and previously for dl-serine, revealing that the vibrational spectra of the two crystals reflect well the different characteristics of their hydrogen-bond networks, and also correlate accurately with the different susceptibility of the two crystals to pressure-induced strain.     

Phase transition and dynamics of NH3 ligands in [Zn(NH3)4](ReO4)2

One phase transition in [Zn(NH₃)₄](ReO₄)₂ at T_c = 393.5 K (on heating) and 392.0 K (on cooling) was found. Thermal stability of this compound was investigated by thermal analysis methods. It decomposes in three main stages. The first two are connected with deamination process, whereas Re₂O₇ evaporates in the last step. The activation energy for NH₃ loss processes was determined from thermogravimetric (TG) measurements. The vibrational and reorientational dynamics of NH₃ ligands in the low-temperature phase was probed by various complementary techniques. It was found that at temperatures close to 150 K, NH⋯O hydrogen bond is formed. Temperature-dependent band shape analysis of properly chosen infrared (IR) band was performed, whose results showed that activation energy for NH₃ reorientational motion (<300 K) is rather small and is approximately equal to 2 kJ mol⁻¹. Neutron and X-ray powder diffraction patterns did not reveal any drastic change in the crystal structure in a wide temperature range.     

Spectroscopic studies of the 1:1 complex of piperidine-4-carboxylic acid (isonipecotic acid) with 2,6-dichloro-4-nitrophenol

The 1:1 complex of piperidine-4-carboxylic acid (isonipecotic acid, P4C) with 2,6-dichloro-4-nitrophenol (DCNP), has been investigated by single-crystal X-ray analysis, Raman and FTIR spectroscopy and theoretical calculations. The hydrogen-bonded-ion-pair complex is observed in the crystalline state with the O⋯H⋯OOC hydrogen bond of 2.453(16) Å. FTIR spectrum shows a broad absorption in the 1600–400 cm⁻¹ region characteristic of very short OHO hydrogen bond, broken by the Evans holes. The complexes are joined through NH⋯O into a H-bonding network. The NH⋯O mode appears as a broad band in the range of 3100–2000 cm⁻¹. In the structure optimized at the B3LYP/6–311 + +G(d,p) level of theory the proton is transferred from DCNP to P4C, and molecules are joined through the O⋯HOOC hydrogen bond of 2.640 Å. The experimental and theoretical infrared spectra are discussed. Detail interpretation of the vibrational spectra has been carried out with the use of computed Potential Energy Distribution (PED).     

Proton (3 MeV) and copper (120 MeV) ion irradiation effects in low-density polyethylene (LDPE)

Low-density polyethylene (LDPE) was irradiated with proton (3 MeV) and copper (120 MeV) ions to analyze the induced modifications with respect to optical and structural properties. In the present investigation, the fluence for proton irradiation was varied up to 2×10¹⁵ protons cm⁻², while that for copper beam was kept in the range of 1×10¹ to 1×10¹³ ions cm⁻² to study the swift heavy ion-induced modifications in LDPE. Ultraviolet–visible (UV–vis), FTIR and X-ray diffraction (XRD) techniques were utilized to study the induced changes. The analysis of UV–vis absorption studies reveals that there is decrease of optical energy gap up to 43% on proton irradiation (at 2×10¹⁵ ions cm⁻²), whereas the copper beam (at 1×10¹³ ions cm⁻²) leads to a decrease of 51%. FTIR analysis indicated the presence of unsaturations due to vinyl end groups in the irradiated sample. The formation of OH and CO groups has also been observed. XRD analysis revealed that the semi-crystalline LDPE losses its crystallinity on swift ion irradiation. It was found that the proton beam (2×10¹⁵ ions cm⁻²) decreased the crystallite size by 23% whereas this decrease is of 31% in case of the copper ion-irradiated LDPE at 1×10¹³ ions cm⁻².     

Vibrational spectroscopic characterization of the phosphate mineral series eosphorite–childrenite–(Mn,Fe)Al(PO4)(OH)2·(H2O)

The phosphate mineral series eosphorite–childrenite–(Mn,Fe)Al(PO₄)(OH)₂·(H₂O) has been studied using a combination of electron probe analysis and vibrational spectroscopy. Eosphorite is the manganese rich mineral with lower iron content in comparison with the childrenite which has higher iron and lower manganese content. The determined formulae of the two studied minerals are: (Mn_0.72,Fe_0.13,Ca_0.01)(Al)_1.04(PO₄, OHPO₃)_1.07(OH_1.89,F_0.02)·0.94(H₂O) for SAA-090 and (Fe_0.49,Mn_0.35,Mg_0.06,Ca_0.04)(Al)_1.03(PO₄, OHPO₃)_1.05(OH)_1.90·0.95(H₂O) for SAA-072. Raman spectroscopy enabled the observation of bands at 970 cm⁻¹ and 1011 cm⁻¹ assigned to monohydrogen phosphate, phosphate and dihydrogen phosphate units. Differences are observed in the area of the peaks between the two eosphorite minerals. Raman bands at 562 cm⁻¹, 595 cm⁻¹, and 608 cm⁻¹ are assigned to the ν₄ bending modes of the PO₄, HPO₄ and H₂PO₄ units; Raman bands at 405 cm⁻¹, 427 cm⁻¹ and 466 cm⁻¹ are attributed to the ν₂ modes of these units. Raman bands of the hydroxyl and water stretching modes are observed. Vibrational spectroscopy enabled details of the molecular structure of the eosphorite mineral series to be determined.     

Complex formation of HCONH2 in CH3OH environment and investigation of linewidth changes of ν(CO) stretching and NH2 bending modes

The isotropic part of the Raman bands corresponding to NH₂ bending and ν(CO) stretching modes of formamide (HCONH₂) at ∼1593 and 1668 cm⁻¹, respectively, in neat HCONH₂ as well as in binary mixtures with methanol (CH₃OH) were reinvestigated. Variations of their linewidths exclusively with mole fractions of HCONH₂, in the range C = 0.1–0.9 were studied. The linewidth variation of the NH₂ bending mode shows a departure from the trend expected on the basis of concentration fluctuation model and this has been explained using a recently suggested empirical model by invoking the concept of microviscosities of the solute, HCONH₂ and the solvent, CH₃OH. The other peak at ∼1668 cm⁻¹ shows a peculiar variation of the linewidth with concentration having two minima at C = 0.8 and 0.4, which have been explained in terms of formation of hydrogen bonded complexes, NH₂HCO⋯HOCH₃, and NH₂HCO⋯(HOCH₃)₂ and the two phenomena, namely motional narrowing and diffusion dynamics being simultaneously operative. The equilibrium constants have been evaluated from the spectral data and their variation with total molar concentration has been presented.     

Characterization,stability, and origin of natural radiation-induced defects in the biogenic calcite of Belemnitella americana from the Upper Cretaceous: An electron paramagnetic resonance study

The rostrum of Belemnitella americana (Morton) from the Marshalltown formation (Kmt, Upper Cretaceous) of the Chesapeake and Delaware Canal was investigated by electron paramagnetic resonance (EPR) spectroscopy. The rostrum composed of biogenic calcite possessed inorganic radical centers CO₂⁻, SO₂⁻, and SO₃⁻ with isotropic resonances with g values of 2.0007, 2.0057, and 2.0031, respectively. SO₃⁻ was found to also display an axially symmetric resonance typical of that seen in calcite of geologic origin with g_⊥=2.0036 and g_∥=2.0021. Mn²⁺ signals of orthorhombic symmetry and very narrow line width (∼0.1 mT) were also noted (|D|=9.3 mT (∼0.009 cm⁻¹), |E|=3.1 mT (∼0.003 cm⁻¹)). Isochronal annealing studies reveal that these inorganic radical species reside in energy traps that are significantly deeper than previously determined as revealed by their annealing temperatures: SO₂⁻ (isotropic), T^*∼340 °C; SO₃⁻ (isotropic), T^*∼230 °C; SO₃⁻ (axial), T^*∼190 °C. These data suggest that these spin centers may be used to extend the upper limit for dating purposes to times on the order of 1 Ma for SO₃⁻ (axial) and 200–300 Ma for SO₃⁻ (isotropic). Spin–spin and spin–lattice relaxation studies employing progressive microwave saturation were determined for all sulfur-based radical species and found to be consistent with the supposition of the isotropic signals existing in environments that are conducive to dynamic averaging of the g-anisotropy.     

Partial least squares modeling of combined infrared, 1H NMR and 13C NMR spectra to predict long residue properties of crude oils

Research has been carried out to determine the potential of partial least squares (PLS) modeling of mid-infrared (IR) spectra of crude oils combined with the corresponding ¹H and ¹³C nuclear magnetic resonance (NMR) data, to predict the long residue (LR) properties of these substances. The study elaborates further on a recently developed and patented method to predict this type of information from only IR spectra. In the present study, PLS modeling was carried out for 7 different LR properties, i.e., yield long-on-crude (YLC), density (D_LR), viscosity (V_LR), sulfur content (S), pour point (PP), asphaltenes (Asph) and carbon residue (CR). Research was based on the spectra of 48 crude oil samples of which 28 were used to build the PLS models and the remaining 20 for validation. For each property, PLS modeling was carried out on single type IR, ¹³C NMR and ¹H NMR spectra and on 3 sets of merged spectra, i.e., IR + ¹H NMR, IR + ¹³C NMR and IR + ¹H NMR + ¹³C NMR. The merged spectra were created by considering the NMR data as a scaled extension of the IR spectral region. In addition, PLS modeling of coupled spectra was performed after a Principal Component Analysis (PCA) of the IR, ¹³C NMR and ¹H NMR calibration sets. For these models, the 10 most relevant PCA scores of each set were concatenated and scaled prior to PLS modeling. The validation results of the individual IR models, expressed as root-mean-square-error-of-prediction (RMSEP) values, turned out to be slightly better than those obtained for the models using single input ¹³C NMR or ¹H NMR data. For the models based on IR spectra combined with NMR data, a significant improvement of the RMSEP values was not observed neither for the models based on merged spectra nor for those based on the PCA scores. It implies, that the commonly accepted complementary character of NMR and IR is, at least for the crude oil and bitumen samples under study, not reflected in the results of PLS modeling. Regarding these results, the absence of sample preparation and the straightforward way of data acquisition, IR spectroscopy is preferred over NMR for the prediction of LR properties of crude oils at site.     

Optimization of the chemoenzymatic mono-epoxidation of linoleic acid using D-optimal design

Mono-epoxied linoleic acid 9(12)-10(13)-monoepoxy 12(9)-octadecanoic acid (MEOA) was synthesized and optimized by immobilized Candida antarctica lipase (Novozym 435®) using D-optimal design. For optimizing the reaction, response surface methodology (RSM) was employed with four reaction variables such as the effect of amount of hydrogen peroxide (μL), amount of enzyme (w) and reaction time (h). At optimum conditions the experiment to obtain a higher yield% with a medium OOC% of MEOA was predicted at an amount of H₂O₂ μL of 15, Novozym 435® of 0.12 g and 7 h of reaction time. At this condition, the yield of MEOA was 82.14%, 4.91% of OOC and 66.65 mg/g of iodine value (IV). The observed value was reasonably close to the predicted value. Hydrogen peroxide was found to have the most significant effect on the degree of epoxidation OOC% and yield%. The epoxy ring opening (–C–O–C–) has been observed by Fourier Transform Infrared Spectroscopy (FTIR) at 820 cm⁻¹ and the double band (–CC–) at 3009 cm⁻¹. ¹H NMR analyses confirmed that the oxirane ring (–CH–O–CH–) of MEOA at 2.92–3.12 ppm and four signals of methane (–CHCH–) was at 5.38–5.49 ppm while the ¹³C NMR showed the oxirane ring (–C–O–C–) at 54.59–57.29 ppm and the olefinic carbons at 124.02–132.89 ppm.