Infrared and Raman spectra of phtalic, isophtalic and terephtalic acids

Investigating the stability of aromatic carboxylic acids in hydrated magnesium sulfate under UV irradiation to assist detection of organics on Mars

The Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) instrument onboard the Mars 2020 Perseverance rover detected so far some of the most intense fluorescence signals in association with sulfates analyzing abraded patches of rocks at Jezero crater, Mars. To assess the plausibility of an organic origin of these signals, it is key to understand if organics can survive exposure to ambient Martian UV after exposure by the Perseverance abrasion tool and prior to analysis by SHERLOC. In this work, we investigated the stability of organo-sulfate assemblages under Martian-like UV irradiation and we observed that the spectroscopic features of phthalic and mellitic acid embedded into hydrated magnesium sulfate do not change for UV exposures corresponding to at least 48 Martian sols and, thus, should still be detectable in fluorescence when the SHERLOC analysis takes place, thanks to the photoprotective properties of magnesium sulfate. In addition, different photoproduct bands diagnostic of the parent carboxylic acid molecules could be observed. The photoprotective behavior of hydrated magnesium sulfate corroborates the hypothesis that sulfates might have played a key role in the preservation of organics on Mars, and that the fluorescence signals detected by SHERLOC in association with sulfates could potentially arise from organic compounds.

Dramatic change in the properties of magnetite-modified MOF particles depending on the synthesis approach

Iron-containing metal-organic frameworks are promising Fenton catalysts. However, the absence of additional modifiers has proven difficult due to the low reaction rates and the inability to manipulate the catalysts. We hypothesize that the production of iron oxide NPs in the presence of a metal-organic framework will increase the rate of the Fenton reaction and lead to the production of particles that can be magnetically manipulated without changing the structure of the components. A comprehensive approach lead to a metal organic framework using the example of MIL-88b (Materials of Institute Lavoisier) modified with iron oxides NPs: formulation of iron oxide in the presence of MIL-88b and vice versa. The synthesis of MIL-88b consists of preparing a complexation compound with the respective structure and addition of terephthalic acid. The synthesis of MIL-88b facilitates to control the topology of the resulting material. Both methods for composite formulation lead to the preservation of the structure of iron oxide, however, a more technologically complex approach to obtaining MIL-88b in the presence of Fe3O4 suddenly turned out to be the more efficient for the release of iron ions.

Developing boron carbon nitride/boron carbon nitride-citric acid quantum dot metal-free photocatalyst and evaluating the degradation performance difference of photo-induced species for tetracycline via theoretical and experimental study

For opening a way to synthesize novel metal-free catalysts and clarifying the photodegradation performance difference of photoactive species (such as ·O₂^-, h⁺), a series of metal-free photocatalysts have been synthesized by using different existing forms of the same materials (boron carbon nitride (BCN) and boron carbon nitride-citric acid quantum dot (BCQD)) as precursors via calcinating their mixture at 350 °C. BCQD has good fluorescence and up-conversion fluorescence performance. BCN/BCQD-350 has the highest removal efficiency (90%, including adsorption 60% and photodegradation 30%) for tetracycline (TC) among all samples under visible light irradiation. TC adsorption by BCN/BCQD-350 conforms to pseudo-second-order kinetic and Langmuir isotherm models. TC photodegradation by BCN/BCQD-350 conforms to type II heterojunction mechanism. Photoactive species capture experiments suggest that·O₂^- makes a higher contribution for TC photodegradation, followed by h⁺, ·OH, ¹O₂ and e^-. From LC-MS results, TC photodegradation is initiated by the dehydration step. TC dehydration activated by ·O₂^- has the lowest barrier (43.4 kcal/mol) than that (50.1 kcal/mol) activated by h⁺, that (64.8 kcal/mol) without the activation by photoactive species. TC removal rate of BCN/BCQD-350 (0.01563 min^-1) is higher than that of g-C₃N₄, P25 (TiO₂), BNPA, BCNPA, etc. Furthermore, BCN/BCQD-350 can also photodegrade TC under infrared light irradiation (λ > 800 nm).

Structures, Bonding and Sensor Properties of Some Alkaline o-Phthalatocuprates

Comprehensive study of the structure and bonding of disodium, dipotassium and diammonium di-o-phthalatocuprates(II) dihydrates has been undertaken. The crystal structure of ammonium o-phthalatocuprate has been determined. The identity of structures of phthalatocuprate chains in potassium and ammonium salts has been revealed. Vibrational spectra of all three compounds have been recorded, and the assignment of vibrational bands has been made. Force field calculations have shown a minor effect of outer-sphere cations (Na+, K+, NH4+) on both intraligand (C-O) and metal-ligand bond strengths. Synthesized compounds have been tested as electrochemical sensors on D-glucose, dopamine and paracetamol. Their sensitivity to analytes varied in the order of Na+ > K+ > NH4+. This effect has been explained by the more pronounced steric hindrance of copper ions in potassium and ammonium salts.

Structure-Dependent Anchoring of Organic Molecules to Atomically Defined Oxide Surfaces: Phthalic Acid on Co3O4(111), CoO(100), and CoO(111)

We have performed a model study to explore the influence of surface structure on the anchoring of organic molecules on oxide materials. Specifically, we have investigated the adsorption of phthalic acid (PA) on three different, well-ordered, and atomically defined cobalt oxide surfaces, namely 1) Co3O4(111), 2) CoO(111), and 3) CoO(100) on Ir(100). PA was deposited by physical vapor deposition (PVD). The formation of the PA films and interfacial reactions were monitored in situ during growth by isothermal time-resolved IR reflection absorption spectroscopy (TR-IRAS) under ultrahigh vacuum (UHV) conditions. We observed a pronounced structure dependence on the three surfaces with three distinctively different binding geometries and characteristic differences depending on the temperature and coverage. 1) PA initially binds to Co3O4(111) through the formation of a chelating bis-carboxylate with the molecular plane oriented perpendicularly to the surface. Similar species were observed both at low temperature (130 K) and at room temperature (300 K). With increasing exposure, chelating mono-carboxylates became more abundant and partially replaced the bis-carboxylate. 2) PA binds to CoO(100) in the form of a bridging bis-carboxylate for low coverage. Upon prolonged deposition of PA at low temperature, the bis-carboxylates were converted into mono-carboxylate species. In contrast, the bis-carboxylate layer was very stable at 300 K. 3) For CoO(111) we observed a temperature-dependent change in the adsorption mechanism. Although PA binds as a mono-carboxylate in a bridging bidentate fashion at low temperature (130 K), a strongly distorted bis-carboxylate was formed at 300 K, possibly as a result of temperature-dependent restructuring of the surface. The results show that the adsorption geometry of PA depends on the atomic structure of the oxide surface. The structure dependence can be rationalized by the different arrangements of cobalt ions at the three surfaces.

The surface structure matters: thermal stability of phthalic acid anchored to atomically-defined cobalt oxide films

The atomic structure of cobalt oxide surfaces influence the ordering and thermal stability of anchored phthalic acid.

Molecular structure and vibrational spectra of Bis(melaminium) terephthalate dihydrate: a DFT computational study

The experimental and theoretical vibrational spectra of Bis(melaminium) terephthalate dihydrate were studied. The Fourier transform infrared (FT-IR) spectra of the Bis(melaminium) terephthalate dihydrate and its deuterated analogue were recorded in the solid phase. The molecular geometry and vibrational frequencies of Bis(melaminium) terephthalate dihydrate in the ground state have been calculated by using the density functional method (B3LYP) with 6-31++G(d,p) basis set. The results of the optimized molecular structure are presented and compared with the experimental X-ray diffraction. The molecule contains the weak hydrogen bonds of N-H···O, N-H···N and O-H···O types, and those bonds are calculated with DFT method. In addition, molecular electrostatic potential, frontier molecular orbitals and natural bond orbital analysis of the title compound were investigated by theoretical calculations. The lack of the second harmonic generation (SHG) confirms the presence of macroscopic center of inversion.

Ethylenediammonium dication: H-bonded complexes with terephthalate, chloroacetate, phosphite, selenite and sulfamate anions. Detailed vibrational spectroscopic and theoretical studies of ethylenediammonium terephthalate

Crystalline complexes between ethylenediammonium dication and terephthalate, chloroacetate, phosphite, selenite and sulfamate anions were obtained by slow evaporation from water solution method. Room temperature powder infrared and Raman measurements were carried out. For ethylenediammonium terephthalate theoretical calculations of structure were performed by two ways: ab-initio HF and semiempirical PM3. In this case the PM3 method gave more accurate structure (closer to X-ray results). The additional PM3 calculations of vibrational spectra were performed. On the basis theoretical approach and earlier vibrational studies of similar compounds the vibrational assignments for observed bands have been proposed. All compounds were checked for second harmonic generation (SHG).

Feasibility of Raman microspectroscopic identification of biomarkers through gypsum crystals

The miniaturized Raman spectrometer is considered to be a candidate instrument for the Pasteur payload (the ExoMars mission scheduled for 2018). This mission will, for the first time, combine mobility and access to subsurface locations where organic molecules might be well preserved. Evaporitic crystals are among the potential protected habitats that have been postulated. Various concentrations of biomarkers (beta-carotene, glycine and phthalic acid) dispersed in a gypsum matrix were analyzed through transparent mineral (gypsum) plates of different thicknesses. By doing so, conditions were simulated in which biomarkers were trapped within evaporitic crystals. Using a long-working distance objective, all studied concentrations of biomarkers mixed in gypsum powder were detected. The characteristic Raman bands were easily observable for a 10% mixture of all chosen biomarkers not only through a 3.3 mm plate and but even through a 5.2 mm plate. It was possible to detect key Raman bands of 1% phthalic acid/gypsum mixture and 1% beta-carotene/gypsum mixture even through a 5.2 mm gypsum plate. The 1% beta-carotene/gypsum mixture was still clearly distinguishable through an 8.5mm gypsum crystal due to the known resonance Raman effect of the molecule.

Raman spectroscopic identification of phthalic and mellitic acids in mineral matrices

Raman spectroscopy has many advantages for planetary exploration, and the Raman technique is currently being developed for future space missions. The Raman microspectroscopic study of organic acids (phthalic and mellitic acids) in experimentally prepared mixtures with halite and gypsum was performed using near infrared 785 nm and visible 514 nm excitation wavelengths. Gypsum and halite matrices were chosen as analogues of Martian minerals. Carboxylic acids mixed with mineral powders were also investigated through a UV-transparent crystal of gypsum and halite (approximately 2 mm, resp. 5 mm thick), thereby creating a type of artificial inclusion that could potentially be present in Martian minerals. The detection limit of phthalic acid mixed in mineral matrices and analyzed through crystals was 1 wt% using both excitation wavelengths. A Raman mellitic acid signal was obtained at a concentration as low as 1 wt% in halite matrix, and at a concentration of 5 wt% when analyzed through halite crystal. In the case of mellitic acid mixed with gypsum and for analyses through a gypsum crystal, the detection limit is 5 wt% using both excitation wavelengths.

Using portable Raman spectrometers for the identification of organic compounds at low temperatures and high altitudes: exobiological applications

Organic minerals, organic acids and NH-containing organic molecules represent important target molecules for astrobiology. Here, we present the results of the evaluation of a portable hand-held Raman spectrometer to detect these organic compounds outdoors under field conditions. These measurements were carried out during the February-March 2009 winter period in Austrian Alpine sites at temperatures ranging between -5 and -25 degrees C. The compounds investigated were detected under field conditions and their main Raman spectral features were observed unambiguously at their correct reference wavenumber positions. The results obtained demonstrate that a miniaturized Raman spectrometer equipped with 785 nm excitation could be applied with advantage as a key instrument for investigating the presence of organic minerals, organic acids and nitrogen-containing organic compounds outdoors under terrestrial low-temperature conditions. Within the payload designed by ESA and NASA for several missions focusing on Mars, Titan, Europa and other extraterrestrial bodies, Raman spectroscopy can be proposed as an important non-destructive analytical tool for the in situ identification of organic compounds relevant to life detection on planetary and moon surfaces or near subsurfaces.

Molecular structure and vibrational assignment of melaminium phthalate by density functional theory (DFT) and ab initio Hartree-Fock (HF) calculations

The molecular geometry, the normal mode frequencies and corresponding vibrational assignment of melaminium phthalate (C3H7N6+.C8H5O4(-)) in the ground state were performed by HF and B3LYP levels of theory using the 6-31G(d) basis set. The optimized bond length numbers with bond angles are in good agreement with the X-ray data. The vibrational spectra of melaminium phthalate which is calculated by HF and B3LYP methods, reproduces vibrational wave numbers with an accuracy which allows reliable vibrational assignments. The title compound has been studied in the 4000-100 cm(-1) region where the theoretical evaluation and assignment of all observed bands were made.

IR, Raman and SERS spectra of disodium terephthalate

The IR and Raman spectra of disodium terephthalate were recorded and analysed. Surface enhanced Raman scattering (SERS) spectrum was recorded in silver colloid. The vibrational wavenumber of the compound have been computed using the Hartree-Fock/6-31G* basis and compared with the experimental values. SERS studies suggest a flat orientation of the molecule at the metal surface.

Effect of pH on the Viscosity of Titanium Dioxide Aqueous Dispersions with Carboxylic Acids

Dispersions of titanium dioxide nanoparticles with terephthalic acid, isophthalic acid, salicylic acid, benzoic acid, and pyridine-2,5-dicarboxylic acid were prepared by aqueous grinding. The pH of the dispersions was adjusted by adding either HCl or NaOH, and the viscosity of the dispersions was measured. It was found that the viscosity of the system depends strongly on pH. The qualitative interpretation of the results based on the DLVO theory is presented. The evidence of the effect of bridging interactions on the viscosity of titanium dioxide-dicarboxylic acid dispersions is discussed.

Infrared spectra of phthalic acid, the hydrogen phthalate ion, and the phthalate ion in aqueous solution

The infrared spectra of a series of aqueous solutions containing phthalic acid (1,2-benzenedicarboxylic acid) and varying pH were examined using attenuated total reflection Fourier transform infrared spectroscopy and potentiometry. The basis spectra of phthalic acid, the hydrogen phthalate ion, and the phthalate ion were isolated using a factor analysis in which the absorbance of these species varies with pH and total phthalate concentration according to equilibrium and mass balance relations. Assignments of these basis spectra were made by comparison with spectra calculated ab initio. The conditional formation constants of phthalic acid and the hydrogen phthalate ion were determined at 25.0+/-0.1 degrees C in 0.6 M NaCl ionic media using infrared spectroscopy and in 1.5 M NaCl ionic media using both infrared spectroscopy and potentiometry.