Degradation of Methyl 2-Aminobenzoate (Methyl Anthranilate) by H₂O₂/UV: Effect of Inorganic Anions and Derived Radicals

Synthesis of Ursolic Acid-based Hybrids: In Vitro Antibacterial, Cytotoxicity Studies, In Silico Physicochemical and Pharmacokinetic Properties

BACKGROUND

There is a critical need for the discovery of novel and effective antibacterial or anticancer molecules.

OBJECTIVES

Amine-linked ursolic acid-based hybrid compounds were prepared in good yields in the range of 60-68%.

METHODS

Their molecular structures were successfully confirmed using different spectroscopic methods including 1H/13C NMR, UHPLC-HRMS and FTIR spectroscopy. The in vitro cytotoxicity of some of these hybrid molecules against three human tumour cells, such as MDA-MB23, MCF7, and HeLa was evaluated using the MTT colorimetric method.

RESULT

Their antibacterial efficacy was evaluated against eleven bacterial pathogens using a serial dilution assay. Majority of the bacterial strains were inhibited significantly by compounds 17 and 24, with the lowest MIC values in the range of 15.3-31.25 μg/mL. Compound 16 exhibited higher cytotoxicity against HeLa cells than ursolic acid, with an IC50 value of 43.64 g/mL.

CONCLUSION

The in vitro antibacterial activity and cytotoxicity of these hybrid compounds demonstrated that ursolic acid-based hybrid molecules are promising compounds. Further research into ursolic acid-based hybrid compounds is required.

Implementation of laser flash photolysis for radical-induced reactions and environmental implications

Confronted with the imperative crisis of water quality deterioration, the pursuit of state-of-the-art decontamination technologies for a sustainable future never stops. Fitting into the framework of suitability, advanced oxidation processes have been demonstrated as powerful technologies to produce highly reactive radicals for the degradation of toxic and refractory contaminants. Therefore, investigations on their radical-induced degradation have been the subject of scientistic and engineering interests for decades. To better understand the transient nature of these radical species and rapid degradation processes, laser flash photolysis (LFP) has been considered as a viable and powerful technique due to its high temporal resolution and rapid response. Although a number of studies exploited LFP for one (or one class of) specific reaction(s), reactions of many possible contaminants with radicals are largely unknown. Therefore, there is a pressing need to critically review its implementation for kinetic quantification and mechanism elucidation. Within this context, we introduce the development process and milestones of LFP with emphasis on compositions and operation principles. We then compare the specificity and suitability of different spectral modes for monitoring radicals and their decay kinetics. Radicals with high environmental relevance, namely hydroxyl radical, sulfate radical, and reactive chlorine species, are selected, and we discuss their generation, detection, and implications within the frame of LFP. Finally, we highlight remaining challenges and future perspectives. This review aims to advance our understandings of the implementation of LFP in radical-induced transient processes, and yield new insights for extrapolating this pump-probe technique to make significant strides in environmental implications.

Flavour compounds affect protein structure: The effect of methyl anthranilate on bovine serum albumin conformation

This study aims to understand possible effects of flavour compounds on the structure and conformation of endogenous proteins. Using methyl anthranilate (a grape flavour compound added to drinks, confectionery, and vape-liquids) and bovine serum albumin (BSA, a model serum protein) we designed experimental investigations using analytical ultracentrifugation, size exclusion chromatography small angle X-ray scattering, and fluorescence spectroscopy to reveal that methyl anthranilate spontaneously binds to BSA (ΔG°, ca. -21 KJ mol^-1) which induces a conformational compactness (ca. 10 %) in the monomer structure. Complementary molecular modelling and dynamics simulations suggested the binding occurs at Sudlow II of BSA via establishment of hydrogen bonds with arginine⁴⁰⁹, lysine⁴¹³ and serine⁴⁸⁸ leading to an increased conformational order in domains IA, IIB and IIIB. This work aims to set the foundation for future research on flavour-protein interactions and offer new sets of opportunities for understanding the effects of small compounds on protein structure.

Prediction of Second-Order Rate Constants of Sulfate Radical with Aromatic Contaminants Using Quantitative Structure-Activity Relationship Model

Predicting the second-order rate constants between aromatic contaminants and a sulfate radical (kSO4•−) is vital for the screening of pollutants resistant to sulfate radical-based advanced oxidation processes. In this study, a quantitative structure-activity relationship (QSAR) model was developed to predict the values for aromatic contaminants. The relationship between logkSO4•− and three molecular descriptors (electron density, steric energy, and ratio between oxygen atoms and carbon atoms) was built through multiple linear regression. The goodness-of-fit, robustness, and predictive ability of the model were characterized statistically with indicators showing that the model was reliable and applicable. Electron density was found to be the most influential descriptor that contributed the most to logkSO4•−. All data points fell within the applicability domain, and no outliers existed in the training set. The comparison with other models indicates that the QSAR model performs well in elucidating the mechanism of the reaction between aromatic compounds and sulfate radicals.

Chemical-damage MINE: A database of curated and predicted spontaneous metabolic reactions

Spontaneous reactions between metabolites are often neglected in favor of emphasizing enzyme-catalyzed chemistry because spontaneous reaction rates are assumed to be insignificant under physiological conditions. However, synthetic biology and engineering efforts can raise natural metabolites' levels or introduce unnatural ones, so that previously innocuous or nonexistent spontaneous reactions become an issue. Problems arise when spontaneous reaction rates exceed the capacity of a platform organism to dispose of toxic or chemically active reaction products. While various reliable sources list competing or toxic enzymatic pathways' side-reactions, no corresponding compilation of spontaneous side-reactions exists, nor is it possible to predict their occurrence. We addressed this deficiency by creating the Chemical Damage (CD)-MINE resource. First, we used literature data to construct a comprehensive database of metabolite reactions that occur spontaneously in physiological conditions. We then leveraged this data to construct 148 reaction rules describing the known spontaneous chemistry in a substrate-generic way. We applied these rules to all compounds in the ModelSEED database, predicting 180,891 spontaneous reactions. The resulting (CD)-MINE is available at https://minedatabase.mcs.anl.gov/cdmine/#/home and through developer tools. We also demonstrate how damage-prone intermediates and end products are widely distributed among metabolic pathways, and how predicting spontaneous chemical damage helps rationalize toxicity and carbon loss using examples from published pathways to commercial products. We explain how analyzing damage-prone areas in metabolism helps design effective engineering strategies. Finally, we use the CD-MINE toolset to predict the formation of the novel damage product N-carbamoyl proline, and present mass spectrometric evidence for its presence in Escherichia coli.

Rate constants of dichloride radical anion reactions with molecules of environmental interest in aqueous solution: a review

Natural waters, water droplets in the air at coastal regions and wastewaters usually contain chloride ions (Cl-) in relatively high concentrations in the milimolar range. In the reactions of highly oxidizing radicals (e.g., •OH, •NO3, or SO4•-) in the nature or during wastewater treatment in advanced oxidation processes the chloride ions easily transform to chlorine containing radicals, such as Cl•, Cl2•-, and ClO•. This transformation basically affects the degradation of organic molecules. In this review about 400 rate constants of the dichloride radical anion (Cl2•-) with about 300 organic molecules is discussed together with the reaction mechanisms. The reactions with phenols, anilines, sulfur compounds (with sulfur atom in lower oxidation state), and molecules with conjugated electron systems are suggested to take place with electron transfer mechanism. The rate constant is high (107-109 M-1 s-1) when the reduction potential the one-electron oxidized species/molecule couple is well below that of the Cl2•-/2Cl- couple.

An Electrochemical Route for Special Oxidative Ring-Opening of Indoles

A novel electrochemical protocol for the oxidative cleavage of indoles has been developed, which offers a simple way to access synthetically useful anthranilic acid derivatives. In undivided cells, a wide variety of indoles and alcohol compounds are examined to afford amide ester aromatics without using extra oxidants and stoichiometric metal catalysts, which avoids the formation of undesired by-products and exhibits high atom economy. The products we described in this perspective represent a synthetic intermediate in numerous drug molecules and industrial chemical reagents and remarkably show potential application in the future.

An overview of homogeneous and heterogeneous photocatalysis applications for the removal of pharmaceutical compounds from real or synthetic hospital wastewaters under lab or pilot scale

The last few decades, Pharmaceutical Active Compounds (PhACs) have been considered as emerging contaminants due to their continuous release and persistence to aquatic environment even at low concentrations. A growing number of research articles have shown the occurrence of numerous PhACs in various wastewater treatment plant influents, hospital effluents, and surface waters all over the world. The rising concern regarding PhACs, which present high recalcitrance towards conventional treatment methods, has provoked extensive research in the field of their effective remediation. This review provides a comprehensive assessment of homogeneous and heterogeneous photocatalytic applications for the removal of PhACs, from real or artificial hospital wastewater effluents. These two representative advanced oxidation processes (AOPs) are assessed in terms of their efficiency to remove PhACs, reduce the COD and toxicity as well as increase the biodegradability of the effluent. Simultaneously with their efficiency the operational costs of the processes are considered. Their potential combination with other processes is critically discussed, as this option seems to enhance the treatment efficiency and simultaneously overcome the limitations of each individual process. Moreover, the type of reactors as well as the main parameters that should be considered for the design and the development of photoreactors for wastewater treatment are reviewed. Finally, based on the literature survey, indications for future work are provided.

Ni2 P Nanoalloy as an Air-Stable and Versatile Hydrogenation Catalyst in Water: P-Alloying Strategy for Designing Smart Catalysts

Non-noble metal-based hydrogenation catalysts have limited practical applications because they exhibit low activity, require harsh reaction conditions, and are unstable in air. To overcome these limitations, herein we propose the alloying of non-noble metal nanoparticles with phosphorus as a promising strategy for developing smart catalysts that exhibit both excellent activity and air stability. We synthesized a novel nickel phosphide nanoalloy (nano-Ni₂ P) with coordinatively unsaturated Ni active sites. Unlike conventional air-unstable non-noble metal catalysts, nano-Ni₂ P retained its metallic nature in air, and exhibited a high activity for the hydrogenation of various substrates with polar functional groups, such as aldehydes, ketones, nitriles, and nitroarenes to the desired products in excellent yields in water. Furthermore, the used nano-Ni₂ P catalyst was easy to handle in air and could be reused without pretreatment, providing a simple and clean catalyst system for general hydrogenation reactions.

Natural Macromolecules as Carriers for Essential Oils: From Extraction to Biomedical Application

Essential oils (EOs) and their main constituents, the terpenes, are widely studied, mostly relating to their antioxidant ability and bioactivity, such as antimicrobial, anticancer, anti-inflammatory, and range of other actions in the living systems. However, there is limited information on their bioavailability, especially upon clinical studies. Having in mind both strong biological effects and health benefits of EOs and their specific physicochemical properties (volatility, lipophilic character, low water solubility or insolubility, viscosity, expressed odor, concentration-dependent toxicity, etc.), there is a need for their encapsulation for target delivery. Encapsulation of EOs and their constituents is the prerequisite for enhancing their oxidative stability, thermostability, photostability, shelf life, and biological activity. We considered various carrier types such a (1) monophase and polyphase polysaccharide hydrogel carriers, (2) polysaccharide-protein carriers, and (3) lipid carriers in the context of physicochemical and engineering factors. Physicochemical factors are encapsulation efficiency, chemical stability under gastric conditions, mechanical stability, and thermal stability of carrier matrices. Choice of carrier material also determines the encapsulation technique. Consequently, the engineering factors are related to the advantage and disadvantage of various encapsulation techniques frequently used in the literature. In addition, it was intended to address the interactions between (1) main carrier components, such as polysaccharides, proteins, and lipids themselves (in order to form chemically and mechanically stable structure); (2) main carrier components with pepsin under gastric conditions (in order to form resistant material under gastric conditions); and (3) main carrier components with EOs (in order to enhance encapsulation efficiency), as a necessary precondition for whole process optimization. Finally, different sources for obtaining natural carrier macromolecules are surveyed, especially the agro-waste materials and agricultural and food by-products. This review article highlights the bioavailability aspects of encapsulated EOs and physicochemical and engineering factors concerning natural macromolecule carriers for their target delivery and application.

The Effect of Electrolytes on the Photodegradation Kinetics of Caffeine

Unsuccessfully treated by the existing wastewater-treatment processes, caffeine concentrations in wastewater effluents and natural reservoirs are constantly rising. Photodegradation treatment processes are drawing much attention due to their potential to oxidize and remove such, and similar contaminating compounds from treated waters. In continuation to our previous work on the photodegradation kinetics of caffeine in water by UV/H2O2 and UV/TiO2, this work evaluates the influence of various electrolytes, including NaCl, KCl, MgCl2, NaBr, and KBr, on the kinetics of the UV/H2O2 photodegradation of caffeine, aiming at estimating the efficiency of the method in more complex water systems. Results show that the efficiency of the UV/H2O2 photodegradation reactions is strongly affected by ionic strength and the presence of electrolytes in the solution. While chloride electrolytes were shown to optimize or reduce the process efficiency pending on their concentration. The sole presence of NaBr and KBr shows an immediate reduction in the efficiency of the photodegradation. Empirical apparent-rate-coefficients and curves describing the effect of the different electrolytes on the photodegradation kinetics of caffeine are presented.

Rate constants of carbonate radical anion reactions with molecules of environmental interest in aqueous solution: A review

The rate constants of carbonate radical anion (CO₃^-) reaction with organic molecules, mainly of environmental interest, were collected from the literature and structure effects were discussed together with methods of rate constant determination and reaction mechanisms. These rate constants are essential for modelling chemical processes taking place with participation of reactive radicals in the environment determining the persistence of certain toxic compounds. The rate constants span over a very wide range from 10² to 10⁹ mol^-1 dm³ s^-1, but, even the highest values are smaller by a factor of 2-5 as the diffusion controlled limit. This survey shows that only those molecules have high rate constants in the 10⁷-10⁹ mol^-1 dm³ s^-1 range which have special electron rich part(s). These molecules are removed selectively in CO₃^- reactions. Such electron rich moiety is the NH₂ group attached to an aromatic ring. High vales were measured e.g., for most of anilines or the sulfonamide antibiotics. -CO group attached to the N-atom (in acetanilides and in phenylurea herbicides), or strong electron withdrawing substituents on benzene ring strongly decrease the rate constant. High values were also measured for aromatic molecules with dissociated -OH group (O^-, phenoxides). The thioether group (e.g., in amino acids, or in fenthion or phorate insecticides) also activates the molecules in CO₃^- reactions.

UV-induced transformation of 2,3-dibromo-5,6-dimethyl-1,4-benzoquinone in water and treated wastewater

In this work, we investigate the photolysis behavior of 2,3-dibromo-5,6-dimethyl-1,4-benzoquinone (DDBQ), the only dibrominated benzoquinone detected in treated water so far. DDBQ solutions prepared in ultra-pure water were exposed to UV radiation centered at 254 nm (UV₂₅₄), and the photolysis of the parent compound was monitored together with by-product formation. The DDBQ pseudo-first order photolysis rate constants decreased when increasing the initial DDBQ concentration, and this behavior was caused by saturation of absorption. The photodegradation kinetics was found not to depend on pH and 1-butanol addition, but was affected by humic acids and components that occur in both natural waters and treated wastewater. For the first time with this class of compounds, photolysis studies were also performed using natural and treated wastewater matrices, where photodegradation was always found to proceed significantly slower than in ultra-pure water. The implications for the radiation dose that is required to reach a given treatment target are discussed, and a numerical approach by which to foresee the extent of degradation inhibition is provided that should be taken into account when planning the UV₂₅₄ treatment of DDBQ. The phototransformation of DDBQ yielded hydroxyderivatives, most likely via a debromination-hydroxylation pathway. In-silico toxicity screening suggested that the transformation of DDBQ into the detected hydroxyderivatives would not eliminate toxicity. Although the monohydroxylated derivative underwent relatively fast transformation, the dihydroxylated compound was found to accumulate during irradiation. As a compromise, the irradiation conditions that produce over 90% degradation of DDBQ in the studied samples, and at the same time keep by-product formation low are discussed.

Rate constants of sulfate radical anion reactions with organic molecules: A review

The rate constants of sulfate radical anion reaction (k_SO4-) with about 230 organic molecules of environmental interest are tabulated and discussed, together with both the methods of rate constant determinations and the reaction mechanisms. k_SO4-'s were collected from the original publications. The highest values in the ∼10⁹ M^-1 s^-1 range are published for aromatic molecules. There is a tendency that electron donating substituents increase and electron withdrawing substituents decrease these values. There are just a few compounds with rate constants established using different techniques in different laboratories. k_SO4-'s determined in different laboratories by the direct techniques, pulse radiolysis or laser flash photolysis, in most cases agree reasonably. The values determined by competitive experimental techniques, by complex kinetics calculations, or by modelling show a large scatter. Some of these techniques seem to be questionable for k_SO4- determination. The sulfate radical anion reacts with ketone and amine moieties of molecules by electron transfer. The same mechanism is also suggested for the reaction with aromatic rings. However, in a few cases addition to the double bond and sulfate anion elimination reactions were distinguished. A typical reaction with the aliphatic parts of the molecule is H-abstraction.

Degradation of pharmaceuticals in different water matrices by a solar homo/heterogeneous photo-Fenton process over modified alginate spheres

A solar homo/heterogeneous photo-Fenton process using five materials (Fe(II), Fe(III), mining waste, Fe(II)/mining waste, and Fe(III)/mining waste) supported on sodium alginate was used as a strategy to iron dosage for the degradation of eight pharmaceuticals in three different water matrices (distilled water, simulated wastewater, and hospital wastewater). Experiments were carried out in a photoreactor with a capacity of 1 L, using 3 g of iron-alginate spheres and an initial hydrogen peroxide concentration of 25 mg L^-1, at pH 5.0. All the materials prepared were characterized by different techniques. The Fe(III)-alginate spheres presented the best pharmaceutical degradation after a treatment time of 116 min. Nineteen transformation products generated during the solar photo-Fenton process were identified by liquid chromatography coupled to quadrupole time-of-flight mass spectrometry, using a purpose-built database developed for detecting these transformation products. Finally, the transformation products identified were classified according to their toxicity and predicted biodegradability.

Insight into the Degradation of Two Benzophenone-Type UV Filters by the UV/H2O2 Advanced Oxidation Process

Environmental problems caused by UV filters, a group of emerging contaminants, have attracted much attention. The removal of two typical UV filters benzophenone (BP) and 4,4′-dihydroxy-benzophenone (HBP) in water was investigated by the UV/H2O2 process. The response surface methodology (RSM) and central composite design (CCD) were applied to investigate the effects of the process parameters on the degradation rate constants, including the initial contaminant concentration, H2O2 dose, and UV light intensity. BP is more easily degraded by the UV/H2O2 process. Both processes followed pseudo-first-order kinetics. The results obtained with the built RSM model are in accordance with the experimental results (adjusted coefficients R2(adj)= 0.9835 and 0.9778 for BP and HBP, respectively). For both processes, the initial contaminant concentration (exerting a negative effect) were the most important factors controlling the degradation, followed by H2O2 dose and UV intensity (exerting positive effects). A total of 15 BP degradation products and 13 HBP degradation products during the UV/H2O2 process were identified by LC/MS and GC/MS. A series of OH radical irritated reactions, including hydroxylation, carboxylation, and ring cleavage, led to the final degradation of BP and HBP. Degradation pathways of BP and HBP were also proposed. On the whole, this work is a unique contribution to the systematic elucidation of BP and HBP degradation by the UV/H2O2 process.