New insights into the degradation mechanism of ibuprofen in the UV/H2O2 process: role of natural dissolved matter in hydrogen transfer reactions

Ibuprofen (IBU), a widely used antipyretic and analgesic, has been frequently detected in various natural water systems. Advanced oxidation processes (AOPs) are effective ways to remove pollutants from water. The degradation of IBU under UV/H2O2 conditions in the presence of various kinds of natural dissolved matter was investigated using density functional theory (DFT). The eco-toxicological properties were predicted based on a quantitative structure-activity relationship (QSAR) model. The calculated results showed that two H-abstraction reactions occurring at the side chain are predominant pathways in the initial reaction. H2O, NH3, CH3OH, C2H5OH, HCOOH and CH3COOH can catalyze the H transfer in the degradation process through decreasing the energy barriers and the catalysis effects follow the order of NH3 > alcohols > acids > H2O. The catalysis effects differ under acid or alkaline conditions. The overall rate coefficient of the reaction of IBU with ˙OH is calculated to be 5.04 × 109 M-1 s-1 at 298 K. IBU has harmful effects on aquatic organisms and human beings and the degradation process cannot significantly reduce its toxicity. Among all products, 2-(4-formylphenyl)propanoic acid, which is more toxic than IBU, is the most toxic with acute and chronic toxicity, developmental toxicity, mutagenicity, genotoxic carcinogenicity and irritation/corrosivity to skin. The findings in this work provide new insights into the degradation of IBU and can help to assess its environmental risks.

The many forms of alpha-methoxy phenylacetic acid in the gas phase: flexibility, internal dynamics, and their intramolecular interactions

Five conformers of the flexible molecule alpha-methoxy phenylacetic acid were identified using rotational spectroscopy. The conformational landscape, internal dynamics, and intramolecular interactions were investigated.

Using photoelectron elliptical dichroism (PEELD) to determine real-time variation of enantiomeric excess

In this work, the photoionization of chiral molecules by an elliptically polarized, high repetition rate, femtosecond laser is probed. The resulting 3D photoelectron angular distribution shows a strong forward-backward asymmetry, which is highly dependent not only on the molecular structure but also on the ellipticity of the laser pulse. By continuously varying the laser ellipticity, we can observe molecular and enantiomer changes in real time at a previously unseen speed and precision. The technique allows enantiomeric excess of a pure compound to be measured with a 5% precision within 3 s, and a 10-min acquisition yields a precision of 0.4%. The isomers camphor and fenchone can be easily distinguished, unlike with conventional mass spectrometry. Preliminary results for the pharmaceutically interesting ibuprofen are also given, showing the capability of photoionization as a means of distinguishing larger molecular systems.

Conformational impact of aliphatic side chains in local anaesthetics: benzocaine, butamben and isobutamben

We studied the impact of aliphatic side chains on the stability and conformational landscape of the local anaesthetics benzocaine, butamben and isobutamben, combining high-resolution rotational spectroscopy in the microwave and millimetre regions and molecular modelling. The study reveals the connections between alkyl chain flexibility and molecular conformations.

Millimeter-wave emission spectrometer based on direct digital synthesis

We present a millimeter-wave Fourier transform emission spectrometer whose design is based on the application of a direct digital synthesizer (DDS) up-converted into the Ku-band with subsequent frequency multiplication. The spectrometer covers the frequency range from 50 GHz to 110 GHz and from 150 GHz to 330 GHz. Owing to the fast frequency switching ability of the DDS in the spectrometer, the same radiation source is used both as a generator of short polarizing pulses and as a local oscillator for the heterodyne receiving system. Such a design provides intrinsically coherent reception that allows very long-term data averaging in the time domain, which improves considerably the maximum sensitivity of the spectrometer. The performances of the spectrometer including the data acquisition rate, the sensitivity, and the accuracy of line frequency measurements were tested on the rotational spectra of OCS, NH₂CHO, and CH₃CH₂CN. We show that in the frequency range of 150-300 GHz, the maximum sensitivity of the spectrometer for a 10 min integration time is around 10^-9 cm^-1 (the minimal value of the absorption coefficient of detectable rotational transition) in the case of narrowband single frequency pulse excitation, and around 10^-8 cm^-1 in the case of broadband chirped-pulse excitation.

On the applicability of functional-group symmetry-adapted perturbation theory and other partitioning models for chiral recognition - the case of popular drug molecules interacting with chiral phases

The applicability of symmetry-adapted perturbation theory (SAPT) and functional-group SAPT (F-SAPT) to study chiral recognition is investigated on an example of three popular chiral drug molecules: ibuprofen, norepinephrine, and baclofen, interacting with phenethylamine or proline - two molecules that are often used as chiral phases in chromatography. The comparison of the F-SAPT with the interacting quantum atoms (IQA) approach is also provided. Accurate estimation of energetic differences of the non-covalent intermolecular complexes composed of two chiral molecules is a necessary prerequisite for the possibility of a prediction of the chiral recognition. The SAPT method with interacting molecules described on the density functional theory level provides accurate total interaction energies, while the F-SAPT approach is the most useful in determining which functional groups are responsible for strengthening or weakening of the interaction between chiral molecules. The largest difference in the interaction energies has been calculated for the baclofen-phenethylamine and norepinephrine-phenethylamine pairs, while the smallest for the ibuprofen-proline and baclofen-proline ones. In most cases, the intermolecular interaction is found to be composed of a strong directional hydrogen bond, which was stabilized by two or more weaker non-covalent interactions between groups (in accordance with the phenomological three-point rule), but in several cases more subtle factors are responsible for larger stability of one diastereoisomer, like the stabilization of the conformation involving two noninteracting functional groups attached to a chiral atom through intramolecular attraction. Additionally, the simulated IR spectra were analyzed for all pairs of diastereoisomeric complexes and the red- and blue-shifts of characteristic bond vibrations were discussed in the context of inter-group interactions.

Correlation analysis based on the hydropathy properties of non-steroidal anti-inflammatory drugs in solid-phase extraction (SPE) and reversed-phase high performance liquid chromatography (HPLC) with photodiode array detection and their applications to biological samples

In the present work we analyzed the hydrophobicity and hydrophilicity properties of several non-steroidal anti-inflammatory drugs (NSAIDs) by investigating the structural changes of the dynamic hydrogen bond network in order to predict the extraction recovery of NSAIDs from biological fluids set by solid phase extraction (SPE). This work allows investigating the relationship between theoretical descriptors and experimental data using a parameter free method with a strong correlation (Pearson correlation 0.95, p-value 0.0003). The identification and quantification of analytes in human plasma were carried out by high performance liquid chromatography coupled with photodiode array detection (HPLC-PDA) using a Kinetex Evo C₁₈ (150 x 4.6 mm I.D) protected by a guard column and a mixture of acetonitrile and 10 mM phosphate buffer (pH 2.5) (50:50, v/v) as mobile phase at isocratic conditions. Accuracy (BIAS%) ranged within -2.33% and + 8.05% while precision (RSD%) was less than 5.73%.The mean extraction recovery of the carprofen (IS) was 84.1% and the recovery of NSAIDs from human plasma ranged between 81.9% to 86.6%. LODs and LOQs for all the investigated NSAIDs were 0.003 and 0.01 μg/mL, respectively. The method was validated according to the ICH guide line in the range 0.010-20.0 μg/mL.

Flexibility unleashed in acyclic monoterpenes: conformational space of citronellal revealed by broadband rotational spectroscopy

Conformational flexibility is intrinsically related to the functionality of biomolecules. Elucidation of the potential energy surface is thus a necessary step towards understanding the mechanisms for molecular recognition such as docking of small organic molecules to larger macromolecular systems. In this work, we use broadband rotational spectroscopy in a molecular jet experiment to unravel the complex conformational space of citronellal. We observe fifteen conformations in the experimental conditions of the molecular jet, the highest number of conformers reported to date for a chiral molecule of this size using microwave spectroscopy. Studies of relative stability using different carrier gases in the supersonic expansion reveal conformational relaxation pathways that strongly favour ground-state structures with globular conformations. This study provides a blueprint of the complex conformational space of an important biosynthetic precursor and gives insights on the relation between its structure and biological functionality.

Microsolvated complexes of ibuprofen as revealed by high-resolution rotational spectroscopy

Four conformers of microsolvated ibuprofen have been characterized using high-resolution microwave spectroscopy.

Chiral Analysis Using Broadband Rotational Spectroscopy

broadband microwave spectroscopy is a proven tool to precisely determine molecular properties of gas-phase molecules. Recent developments make it applicable to investigate chiral molecules. Enantiomers can be differentiated, and the enantiomeric excess and, indirectly, the absolute configuration can be determined in a molecule-selective manner. The resonant character and high resolution of rotational spectroscopy provide a unique mixture compatibility. Future directions, such as extending the technique to chemical analysis, are discussed.

Phase Dependence of Double-Resonance Experiments in Rotational Spectroscopy

We here report on double-resonance experiments using broadband chirped pulse Fourier transform microwave spectroscopy that can facilitate spectral assignment and yield information about weak transitions with high resolution and sensitivity. Using the diastereomers menthone and isomenthone, we investigate the dependence of pumping a radio frequency transition on both the amplitude and phase of the signal from a microwave transition with which it shares a common rotational level. We observe a strong phase change when scanning the radio frequency through molecular resonance. The direction of the phase change depends on the energy level arrangement, that is, if it is progressive or regressive. The experimental results can be simulated using the three-level optical Bloch equations and described with the AC Stark effect, giving rise to an Autler-Townes splitting.