Quantum cluster equilibrium theory applied to liquid ammonia.

Through this paper, the authors propose using the quantum cluster equilibrium (QCE) theory to reinvestigate ammonia clusters in the liquid phase. The ammonia clusters from size monomer to hexadecamer were considered to simulate the liquid ammonia in this approach. The clusterset used to model the liquid ammonia is an ensemble of different structures of ammonia clusters. After studious research of the representative configurations of ammonia clusters through the cluster research program ABCluster, the configurations have been optimized at the MN15/6-31++G(d,p) level of theory. These optimizations lead to geometries and frequencies as inputs for the Peacemaker code. The QCE study of this molecular system permits us to get the liquid phase populations in a temperature range of 190-260 K, covering the temperatures from the melting point to the boiling point. The results show that the population of liquid ammonia comprises mainly the ammonia hexadecamer followed by pentadecamer, tetradecamer, and tridecamer. We noted that the small-sized ammonia clusters do not contribute to the population of liquid ammonia. In addition, the thermodynamic properties, such as heat of vaporization, heat capacity, entropy, enthalpy, and free energies, obtained by the QCE theory have been compared to the experiment given some relatively good agreements in the gas phase and show considerable discrepancies in liquid phase except the density. Finally, based on the predicted population, we calculated the infrared spectrum of liquid ammonia at 215 K temperature. It comes out that the calculated infrared spectrum qualitatively agrees with the experiment.

Ecotoxicological impact of dinotefuran insecticide and its metabolites on non-targets in agroecosystem: Harnessing nanotechnology- and bio-based management strategies to reduce its impact on non-target ecosystems.

The class of insecticides known as neonicotinoid insecticides has gained extensive application worldwide. Two characteristics of neonicotinoid pesticides are excellent insecticidal activity and a wide insecticidal spectrum for problematic insects. Neonicotinoid pesticides can also successfully manage pest insects that have developed resistance to other insecticide classes. Due to its powerful insecticidal properties and rapid plant absorption and translocation, dinotefuran, the most recent generation of neonicotinoid insecticides, has been widely used against biting and sucking insects. Dinotefuran has a wide range of potential applications and is often used globally. However, there is growing evidence that they negatively impact the biodiversity of organisms in agricultural settings as well as non-target organisms. The objective of this review is to present an updated summary of current understanding regarding the non-target effects of dinotefuran; we also enumerated nano- and bio-based mitigation and management strategies to reduce the impact of dinotefuran on non-target organisms and to pinpoint knowledge gaps. Finally, future study directions are suggested based on the limitations of the existing studies, with the goal of providing a scientific basis for risk assessment and the prudent use of these insecticides.

Solvation of Manganese(III) Ion in Water and in Ammonia.

In this work, we have studied the solvation of manganese(III) ion in water and in ammonia using three levels of theory: MP2, MN15, and ωB97XD associated with the aug-cc-pVDZ basis set. The studied systems are constituted of Mn3+(H2O)6 and Mn3+(NH3)6 in gas and solvent phases as well as Mn3+(H2O)18 and Mn3+(NH3)18 in the gas phase. Four aspects of the solvation of manganese(III) ion have been examined for the aforementioned systems at the three levels of theory. First, we started by locating the Jahn-Teller elongated and compressed configuration in Mn3+(H2O)6 and Mn3+(NH3)6. Second, we calculated the spin state energies and the spin state free energies for temperatures ranging from 50 to 400 K to look at possible spin crossover in the studied systems. Third, we carried out a quantum theory of atoms in molecules (QTAIM) analysis, and we determined the ionic radii of manganese(III) ion in water and in ammonia. Fourth, we calculated the solvation free energies and the solvation enthalpies of manganese(III) ion in water and in ammonia using the cluster continuum solvation model. For these four aspects of the solvation of manganese(III) ion, most of the reported properties are provided in this work for the first time. We particularly found that the calculated solvation enthalpy of the manganese(III) ion in water is in good agreement with an experimental estimate.

Large-Sized Ammonia Clusters and Solvation Energies of the Proton in Ammonia.

The absolute solvation energies (free energies and enthalpies) of the proton in ammonia are used to compute the pKa of species embedded in ammonia. They are also used to compute the solvation energies of other ions in ammonia. Despite their importance, it is not possible to determine experimentally the solvation energies of the proton in a given solvent. We propose in this work a direct approach to compute the solvation energies of the proton in ammonia from large-sized neutral and protonated ammonia clusters. To undertake this investigation, we performed a geometry optimization of neutral and protonated ammonia 30-mer, 40-mer, and 50 mer to locate stable structures. These structures have been fully optimized at both APFD/6-31++g(d,p) and M06-2X/6-31++g(d,p) levels of theory. An infrared spectroscopic study of these structures has been provided to assess the reliability of our investigation. Using these structures, we have computed the absolute solvation free energy and the absolute solvation enthalpy of the proton in ammonia. It comes out that the absolute solvation free energy of the proton in ammonia is calculated to be -1192 kJ mol-1 , whereas the absolute solvation enthalpy is evaluated to be -1214 kJ mol-1 . © 2019 Wiley Periodicals, Inc.

Exploration of the potential energy surfaces of small ethanol clusters.

The potential energy surfaces (PESs) of the ethanol clusters become increasingly complex as the cluster size increases. This is mainly due to the fact that there are up to three stable structures on the PES of the ethanol monomer yielding a huge number of possible structures of the ethanol clusters. In this work, we have thoroughly explored the PESs of neutral ethanol clusters from dimer to pentamer. For each cluster size, we have identified all possible combinations of the three monomers to build a structure of that cluster size. For each combination, we have used ABCluster to generate initial guessed geometries. These geometries have been fully optimized at the MP2/aug-cc-pVDZ level of theory. The results show that the PESs of the neutral ethanol clusters are symmetric due to enantiomerism of the clusters. For each cluster size, several isomers have been located as global minima energy structures. Globally, we have found that cyclic structures are the most stable, followed by branched cyclic and linear structures. The branched linear structures are found to be among the least stable structures on the PESs of the neutral ethanol clusters. The infrared spectra of the most stable structures are calculated and compared to experiment. The calculated infrared spectra are found to be in qualitative agreement with experiment. In addition, we have calculated the binding energies of the investigated ethanol clusters using MP2, some density functional theory (DFT) functionals (MN15, ωB97XD and PW6B95D3) and DLPNO-CCSD(T)/CBS levels of theory. As a result, we have found that the PW6B95D3 functional has the smallest mean absolute deviation (MAD) as compared to ωB97XD and MN15, when benchmarked to the DLPNO-CCSD(T)/CBS. Thus, we recommend the PW6B95D3 functional for affordable, yet accurate, exploration of neutral ethanol clusters.

Structures, binding energies, temperature effects, infrared spectroscopy of [Mg(NH3 )n = 1-10 ]+ clusters from DFT and MP2 investigations.

The possible isomers of [Mg(NH3 )n = 1 - 10 ]+ clusters have been investigated using both M06-2X/6-31++G(d,p) and MP2/6-31++G(d,p) levels of theory. The isomeric distribution for each n size has been studied as a function of temperatures ranging from 25 to 400 K. To the best of our knowledge, for clusters size n > 6, this is the first theoretical study available in the literature. From the calculated values in the considered clusters and using a fitting procedure, we have evaluated the binding energies (-14.0 kcal/mol), clustering energies (-10.1 kcal/mol), clustering free energies (-2.8 kcal/mol), and clustering enthalpies (-10.3 kcal/mol). On the basis of our structural and infrared (IR) spectroscopy outcomes, we find that the first solvation shell can hold up to six ammonia molecules. © 2019 Wiley Periodicals, Inc.

Exploration of the potential energy surface of the ethanol hexamer.

The potential energy surfaces (PESs) of the neutral ethanol clusters is among the complex PESs of the neutral clusters. This is due to the fact that the ethanol monomer has three different isomers. In this work, we propose a systematic procedure to thoroughly explore the PES of the neutral ethanol hexamer that can be extended to other ethanol clusters. Thus, we started with a thorough exploration using the ABCluster code which uses the Lennard-Jones potential model. The resulting structures are further optimized at the APFD/6-31++g(d,p) level of theory {APFD refers to the initials of the first four authors in Austin et al. [J. Chem. Theory Comput. 8, 4989-5007 (2012)]}. Finally, 68 APFD structures have been fully re-optimized using the second order Møller-Plesset perturbation (MP2) method associated to the aug-cc-pVDZ basis set As a result, an isomer constituted of two trans ethanol monomers, two gauche+ ethanol monomers, and two gauche- ethanol monomers, is predicted to be the most stable structure using ABCluster. Full optimizations at the APFD/6-31++g(d,p) and MP2/aug-cc-pVDZ levels of theory confirm that this isomer is among the iso-energetic most stable structures of the ethanol hexamer. We found that most of the iso-energetic most stable structures are constituted of at least two different ethanol monomers. This highlights the importance of taking into account all the possible monomers in the exploration of the neutral ethanol clusters. In addition, we found that all the structures having their relative energies within 1.7 kcal mol-1 are cyclic structures. The results show that the most stable branched cyclic structures lies 1.7 kcal mol-1 above the most stable at the APFD/6-31++g(d,p) level of theory.

Solvation energies of the proton in methanol revisited and temperature effects.

We report in this work the absolute solvation enthalpies and the absolute solvation free energies of the proton in methanol at temperatures ranging from 20 to 340 K and an extrapolation to a desired temperature. To achieve this, we thoroughly investigated the structures of neutral methanol clusters (MeOH)n=2-10 and those of the protonated methanol decamer H+(MeOH)n=10 at the M06-2X/6-31++g(d,p) level of theory. As a result, we noted that up to the octamer, the population of the neutral methanol clusters is constituted by cyclic isomers. For nonamers and decamers, both cyclic and branched cyclic isomers contribute to the population of the clusters. Moreover, folded or distorted cyclic isomers are the most favored at low temperatures, while higher temperatures favored the flat cyclic isomers for n = 7-9. For the methanol decamer, a branched cyclic isomer is found to be the most favored at low temperatures. Elsewhere, the infrared spectra of all the investigated structures are provided and compared against experiment. The binding energy of neutral methanol is calculated at the X/6-31++g(d,p) levels of theory, where X represents the DFT functionals M062X, APFD, MN15, ωB97XD and M08HX. It is observed that these functionals provide results in good agreement with the experimental vaporization enthalpy. However, the APFD functional shows the best performance followed by the other functionals in the order of M062X, MN15 and ωB97XD. Furthermore, the calculated solvation energies of the proton in methanol at these various levels of theory and at MP2/6-31++g(d,p) show that the ωB97XD functional shows the best performance in evaluating the solvation enthalpy and the solvation free energy of the proton in methanol and the calculated values are respectively -1140.5 kJ mol-1 and -1100.7 kJ mol-1 at room temperature. Elsewhere, we noted that the absolute solvation enthalpy of the proton in methanol is less affected by a change in temperature. However, the absolute solvation free energy of the proton in methanol remains constant only at temperatures lower than 180 K. For higher temperatures, the absolute solvation free energy of the proton in methanol increases as a linear function of the temperature and can be approximated by ΔGm(H+,T) = 0.200T - 1161.4.

Structures and infrared spectroscopy of large sized protonated ammonia clusters.

We investigated in this work the structures and relative population of large sized protonated ammonia clusters, H + ( NH 3 ) n , n = 18, 20, 25, 30. To this end, we generated initial geometries using the ABCluster code. The 30 most stable geometries for each of the clusters have been fully optimized at the APFD/6-31++g(d,p) level of theory. The results show that the proton is asymmetrically shared by two ammonia molecules to form the NH 4 + ⋯ NH 3 complex. The NH 4 + ⋯ NH 3 complex occupies the center of the structures, and it is gradually solvated with increasing cluster size. For n = 25 and n = 30, the first solvation shell of NH 4 + ⋯ NH 3 is completely filled with some ammonia molecules present in the second solvation shell. Besides, we have reported the relative population of the investigated clusters at the thermodynamic equilibrium. As a result, the three most stable structures dominate the population of the clusters. For each cluster size, we found that the IR spectra of these three most stable structures are in agreement with experiments. This agreement could be an indication of the reliability of our investigations. Overall, the structures of large sized protonated ammonia clusters are cage-like and exhibit an amorphous behavior.

Structures and spectroscopy of the ammonia eicosamer, (NH3)n=20.

In this work, we reported structures and relative stabilities of the neutral ammonia eicosamer at the APFD/6-31++g(d,p) level of theory. Furthermore, we have examined the temperature dependence isomer distribution and reported the relative population of the ammonia eicosamer for temperatures ranging from 20 to 400 K. Moreover, a theoretical infrared (IR) spectroscopic study is performed to confirm our results. As a result, several stable structures have been identified as isomers of the ammonia eicosamer. The most stable structure is a cage-like isomer with two central solvated ammonia molecules. It is found that cage-like isomers with central solvated ammonia molecules are more stable than other types of structures. Besides, two fused tetrameric cyclic structures belonging to the C2 symmetry point group are also located. Moreover, other reported isomers exhibit an amorphous behavior with no definite symmetry. When considering the temperature dependence isomer distribution, we found that only cage-like isomers contribute to the population of the ammonia eicosamer. The most stable isomer dominates the population of the cluster for all the investigated temperatures. Our analysis shows that only the IR spectra of isomers that contribute to the relative population have their peaks in agreement with the experiment. This agreement could be an indication of the reliability of our proposed structures of the ammonia eicosamer and their relative stability.

Structures and spectroscopy of medium size protonated ammonia clusters at different temperatures, H+(NH3)10-16.

Structures of protonated ammonia clusters (H+(NH3)n) are very important for the determination of pKa's and solvation energies of the proton in ammonia. In this work, their structures were investigated at M06-2X/6-31++g(d,p) level of theory, for n=10-16 and for temperatures ranging from 0 to 400 K. In the cluster community, this is the first theoretical study on the protonated ammonia clusters larger than the nonamer. We noted that the population of the investigated clusters is reproduced by branched cage or cage like structures at low temperatures, while branched linear and branched cyclic or branched double cyclic isomers are the only isomers responsible for the population at higher temperatures. In these isomers, the proton is highly and entirely solvated at the center of the cluster. In addition, protonated ammonia clusters are all Eigen structures and the first solvation shell of the related ammonium ion core is saturated by four ammonia molecules. Moreover, infrared (IR) spectra of all isomers have been investigated and these spectra show good agreement with the experiment. This allowed us to assign experimental peaks and to provide the constitution of the populations of the various clusters.

Solvation energies of the proton in ammonia explicitly versus temperature.

We provide in this work, the absolute solvation enthalpies and the absolute solvation free energies of the proton in ammonia explicitly versus temperature. As a result, the absolute solvation free energy of the proton remains quite constant for temperatures below 200 K. Above this temperature, it increases as a linear function of the temperature: ΔGam(H+,T)=-1265.832+0.210 T. This indicates that a temperature change of 100 K would induce a solvation free energy change of 21 kJ mol-1. Thus, ignoring this free energy change would lead to a bad description of hydrogen bonds and an unacceptable error higher than 3.7 pKa units. However, the absolute solvation enthalpy of the proton in ammonia is not significantly affected by a temperature change and, the room temperature value is -1217 kJ mol-1. The change of the solvation enthalpy is only within 3 kJ mol-1 for a temperature change up to 200 K.

Structures and spectroscopy of protonated ammonia clusters at different temperatures.

The accurate determination of the solvation energies of a proton in ammonia is based on the precise knowledge of the structures of neutral and protonated ammonia clusters. In this work, we have investigated all the possible and stable structures of protonated ammonia clusters H+(NH3)n=2-9, along with their isomeric distribution at a specific temperature. New significant isomers are reported here for the first time and show that the structures of protonated ammonia clusters are not only branched linear as assumed by all previous authors. Branched linear structures are the only ones responsible for the population of protonated ammonia clusters for n = 4-6 at any temperature. However, for larger cluster sizes, these types of structures compete with branched cyclic, double cyclic, branched double cyclic and triple cyclic structures depending on the temperature. In addition, we have shown that protonated ammonia clusters are all Eigen structures and the first solvation shell of the related ammonium ion core is saturated by four ammonia molecules. We have also carried out a study of the hydrogen bond network of protonated ammonia clusters establishing the stability rule governing the various isomers of each cluster from estimated energies of the hydrogen bond types in H+(NH3)n=2-9. With all these results, a route for the accurate determination of the solvation energies of a proton in ammonia at a given temperature could be conceivable.

Structures and relative stabilities of ammonia clusters at different temperatures: DFT vs. ab initio.

A hydrogen bond network in ammonia clusters plays a key role in understanding the properties of species embedded in ammonia. This network is dictated by the structures of neutral ammonia clusters. In this work, structures of neutral ammonia clusters (NH3)n(=2-10) have been studied at M06-2X/6-31++G(d,p) and MP2/6-31++g(d,p) levels of theory. The analysis of the relative stabilities of various hydrogen bond types has also been studied and vibrational spectroscopy of the ammonia pentamer and decamer is investigated. We noted that M06-2X provides lower electronic energies, greater binding energies and higher structural resolution than MP2. We also noted that at the M06-2X level of theory, the binding energy converges to the experimental vaporization enthalpy faster than that at the MP2 level of theory. As a result, it is found that the M06-2X functional could be more suitable than the MP2 ab initio method in the description of structures and energies of ammonia clusters. However, we found that the electronic energy differences obtained at both levels of computation follow a linear relation with n (number of ammonia molecules in a cluster). As far as the structures of ammonia clusters are concerned, we proposed new "significant" isomers that have not been reported previously. The most remarkable is the global minimum electronic energy structure of the ammonia hexamer, which has an inversion centre and confirms experimental observation. Moreover, we reported the relative stabilities of neutral ammonia clusters for temperatures ranging from 25 to 400 K. The stability of isomers changes with the increase of the temperature. As a result, the branched and less bonded isomers are the most favored at high temperatures and disfavored at low temperatures, while compact and symmetric isomers dominate the population of clusters at low temperatures. In fine, from this work, the global minimum energy structures of ammonia clusters are known for the first time at a given temperature (T ∼ 0-400 K) and at a reliable computational level of theory.

Structures of DMSO clusters and quantum cluster equilibrium (QCE).

Dimethylsulfoxide (DMSO) clusters are crucial for understanding processes in liquid DMSO. Despite its importance, DMSO clusters have received negligible attention due to the complexity of their potential energy surfaces (PESs). In this work, we explored the PESs of the DMSO clusters from dimer to decamer, starting with classical molecular dynamics, followed by full optimizations at the PW6B95-D3/def2-TZVP level of theory. In addition, the binding energies, the binding enthalpy per DMSO, and the quantum theory of atoms in molecules (QTAIM) analysis of the most stable isomers are reported. Temperature effects on the stability of the isomers have also been assessed. After thoroughly exploring the PESs of the DMSO clusters, 159 configurations have been used to apply the quantum cluster equilibrium (QCE) theory to liquid DMSO. The quantum cluster equilibrium theory has been applied to determine the liquid properties of DMSO from DMSO clusters. Thus, using the QCE, the population of the liquid DMSO, its infrared spectrum, and some thermodynamic properties of the liquid DMSO are predicted. The QCE results show that the population of the liquid DMSO is mainly dominated by the DMSO dimer and decamer, with the contribution in trace of the DMSO monomer, trimer, tetramer, pentamer, and octamer. More interestingly, the predicted infrared spectrum of liquid DMSO is in qualitative agreement with the experiment.

Clusters of solvated ferrous ion in water-ammonia mixture: Structures and noncovalent interactions.

The behavior of metal ions is commonly studied in pure solvent although, in our daily life, these metals are involved in mixtures of solvents. In the present study, we investigated structures, relative stabilities and temperature dependance of solvated ferrous ion in water-ammonia mixture solvent at 0K and at various temperatures ranging from 25K to 400K. All the calculations are performed at the MN15 level of theory associated with the aug-cc-pVDZ basis set. For deep understanding of binding patterns in solvated ferrous ion in water-ammonia mixture solvent, noncovalent interactions are presented based on the QTAIM analysis using AIMAll. Our results prove that the ferrous ion is more stable when it is solvated by ammonia instead of water. In addition, hydrogen bonds are weakened by the presence of ammonia molecules. The temperature dependence of the different obtained geometries indicates that from s=6 (s is the sum of water and ammonia molecules around the ferrous ion), when the number of water molecules is almost equal to that of ammonia, the structures with coordination number 5 are dominant. However, the coordination number is six when there are a maximum water molecules (rich water solution) or maximum ammonia molecules (rich ammonia solution) around the ferrous ion (for s≥6). The QTAIM analysis shows that there are two coordination bondings and four hydrogen bondings. Furthermore, it is found that the Fe2+⋯N coordination bondings are stronger than the Fe2+⋯O confirming that the ferrous ion prefers to be solvated by ammonia instead of water.

Hydration of [Formula: see text]aminobenzoic acid: structures and non-covalent bondings of aminobenzoic acid-water clusters.

CONTEXT: Micro-hydration of the aminobenzoic acid is essential to understand its interaction with surrounding water molecules. Understanding the micro-hydration of the aminobenzoic acid is also essential to study its remediation from wastewater. Therefore, we explored the potential energy surfaces (PESs) of the para-aminobenzoic acid-water clusters, ABW[Formula: see text], [Formula: see text], to study the microsolvation of the aminobenzoic acid in water. In addition, we performed a quantum theory of atoms in molecules (QTAIM) analysis to identify the nature of non-covalent bondings in the aminobenzoic acid-water clusters. Furthermore, temperature effects on the stability of the located isomers have been examined. The located structures have been used to calculate the hydration free energy and the hydration enthalpy of the aminobenzoic acid using the cluster continuum solvation model. The hydration free energy and the hydration enthalpy of the aminobenzoic acid at room temperature are evaluated to be -7.0 kcal/mol and -18.1 kcal/mol, respectively. The hydration enthalpy is in perfect agreement with a previous experimental estimate. Besides, temperature effects on the calculated hydration enthalpy and free energy are reported. Finally, we calculated the gas phase binding energies of the most stable structures of the ABW[Formula: see text] clusters using twelve functionals of density functional theory (DFT), including empirical dispersion. The DFT functionals are benchmarked against the DLPNO-CCSD(T)/CBS. We have found that the three most suitable DFT functionals are classified in the following order: PW6B95D3 > MN15 > [Formula: see text]B97XD. Therefore, the PW6B95D3 functional is recommended for further study of the aminobenzoic acid-water clusters and similar systems. METHODS: The exploration started with classical molecular dynamics simulations followed by complete optimization at the PW6B95D3/def2-TZVP level of theory. Optimizations are performed using Gaussian 16 suite of codes. QTAIM analysis is performed using the AIMAll program.

Corrigendum to Spectroscopic properties (FT-IR, NMR and UV) and DFT studies of amodiaquine [Heliyon Volume 9, Issue 12, December 2023, e22187].

[This corrects the article DOI: 10.1016/j.heliyon.2023.e22187.].

Effect of physicochemical parameters on the occurrence of per- and polyfluoroalkyl substances (PFAS) in aquatic environment.

Perfluoroalkyl substances (PFAS) and their distribution in aquatic environments have been studied extensively, but more information is needed to link these occurrences to their physicochemical characteristics. Understanding how these parameters influence PFAS can help predict their fate, mobility, and occurrences in water. This study reviewed the influence of physicochemical parameters on the occurrences of PFAS in aquatic environment using the relevant keywords to retrieve articles from databases spanning mostly between 2017 and 2024. The result suggests that high pH, turbidity, and dissolved oxygen, give high concentration of PFAS, while high electrical conductivity, temperature and salinity give low PFAS concentration in the water. Therefore, monitoring and safeguarding the aquatic bodies for human and environmental safety is imperative. Future studies should include the effects of the physicochemical properties on PFAS occurrences in the natural environment and focus on an organism's distinctive characteristics to comprehend the bioaccumulation and biomagnification of PFAS in them and environmental matrices.

Scientometric trends and knowledge maps of global polychlorinated naphthalenes research over the past four decades.

Polychlorinated naphthalenes (PCNs) were included in the banned list of the Stockholm Convention due to their potential to provoke a wide range of adverse effects on living organisms and the environment. Many reviews have been written to clarify the state of knowledge and identify the research needs of this pollutant class. However, studies have yet to analyse the scientometric complexities of PCN literature. In this study, we used bibliometric R and vosviewer programs as a scientometric tool to fill this gap by focusing on articles indexed on Web of Science and Scopus databases and those published between 1973 and 2022. A total of 707 articles were published within this period with a publication/author, author/publication, and co-authors/publication ratios of 0.45, 2.19, and 4.86, respectively. Developed countries dominated most scientometric indices (number of publications, citations, and collaboration networks) in the survey period. Lotka's inverse square rule of author productivity showed that Lotka's laws do not fit PCN literature. An annual percentage growth rate of 7.46% and a Kolmogorov-Smirnoff goodness-of-fit of 0.88 suggests that more output on PCNs is likely in years to come. More research is needed from scholars from developing countries to measure the supremacy of the developed nations and to effectively comply with the Stockholm Convention agreement.