Molecular Halogens Research Articles

Endocrine-Disrupting Compounds in Urban Soils of Malaysia: Occurrence, Contamination, and Impacts on Health and the Environment

Endocrine-disrupting compounds (EDCs) have garnered increasing concern in recent years due to their association with severe health issues and significant environmental impacts. EDCs, which can interfere with endogenous hormone systems, are diverse in structure and are often characterized by low molecular mass and halogen substitutions. Their presence in the environment, originating from both natural and synthetic sources, has been well-documented in water bodies, but studies on their occurrence in soils remain limited. This review provides a comprehensive overview of the occurrence, contamination, and impacts of EDCs in the urban soils of Malaysia. The paper discusses the primary sources of EDCs, including pharmaceuticals, pesticides, industrial chemicals, and combustion byproducts, and examines the pathways through which these compounds enter the soil. Health risks associated with exposure to EDCs, as well as their ecological consequences, are also explored. The review highlights the current status of EDCs contamination in Malaysian soils, identifies gaps in research, and outlines the challenges in monitoring and mitigating these contaminants. Understanding the dynamics of EDCs in soil is crucial for developing effective strategies to protect human health and the environment in urban settings.

Development of Molecular Transformation Reactions Using Visible Light and Main Group Elements

Owing to their ability to induce excitation of specific molecular orbitals or initiate chemical reactions, photochemical reactions have the potential to be more effective at selectively activating target molecules than thermal reactions. The thermal reactions transfer thermal energy to activate molecules, which often leads to the activation of multiple molecular species, including undesired ones, resulting in non-selectivity. This nonselectivity may result in undesirable side reactions or decrease reaction efficiency. Additionally, photochemical reactions can induce selective activation by absorbing specific wavelengths of light. However, visible light-driven photocatalytic reactions typically require expensive transition metal catalysts or organic dyes, leaving plenty of room for improvement. To address the aforementioned issues, the photochemical properties of the main group elements, such as halogens, were optimized and methodologies for visible light-induced reactions were developed. Activation of molecular halogen, halogen-carbon bonds, and halogen bonding interactions were independently investigated and various methodologies were reported. These developed reactions are excellent methodologies that use inexpensive raw materials and are thus predicted to contribute significantly toward sustainability.

Gauging the Strength of the Molecular Halogen Bond via Experimental Electron Density and Spectroscopy.

Strong and weak halogen bonds (XBs) in discrete aggregates involving the same acceptor are addressed by experiments in solution and in the solid state. Unsubstituted and perfluorinated iodobenzenes act as halogen donors of tunable strength; in all cases, quinuclidine represents the acceptor. NMR titrations reliably identify the strong intermolecular interactions in solution, with experimental binding energies of approx. 7 kJ/mol. Interaction of the σ hole at the halogen donor iodine leads to a redshift in the symmetric C-I stretching vibration; this shift reflects the interaction energy in the halogen-bonded adducts and may be assessed by Raman spectroscopy in condensed phase even for weak XBs. An experimental picture of the electronic density for the XBs is achieved by high-resolution X-ray diffraction on suitable crystals. Quantum theory of atoms in molecules (QTAIM) analysis affords the electron densities and energy densities in the bond critical points of the halogen bonds and confirms stronger interaction for the shorter contacts. For the first time, the experimental electron density shows a significant effect on the atomic volumes and Bader charges of the quinuclidine N atoms, the halogen-bond acceptor: strong and weak XBs are reflected in the nature of their acceptor atom. Our experimental findings at the acceptor atom match the discussed effects of halogen bonding and thus the proposed concepts in XB activated organocatalysis.

Halide Chemistry in Tin Perovskite Optoelectronics: Bottlenecks and Opportunities.

Tin halide perovskites (Sn HaPs) are the top lead-free choice for perovskite optoelectronics, but the oxidation of perovskite Sn2+ to Sn4+ remains a key challenge. However, the role of inconspicuous chemical processes remains underexplored. Specifically, the halide component in Sn HaPs (typically iodide) has been shown to play a key role in dictating device performance and stability due to its high reactivity. Here we describe the impact of native halide chemistry on Sn HaPs. Specifically, molecular halogen formation in Sn HaPs and its influence on degradation is reviewed, emphasising the benefits of iodide substitution for improving stability. Next, the ecological impact of halide products of Sn HaP degradation and its mitigation are considered. The development of visible Sn HaP emitters via halide tuning is also summarised. Lastly, halide defect management and interfacial engineering for Sn HaP devices are discussed. These insights will inspire efficient and robust Sn HaP optoelectronics.

Halide Chemistry in Tin Perovskite Optoelectronics: Bottlenecks and Opportunities

AbstractTin halide perovskites (Sn HaPs) are the top lead‐free choice for perovskite optoelectronics, but the oxidation of perovskite Sn2+ to Sn4+ remains a key challenge. However, the role of inconspicuous chemical processes remains underexplored. Specifically, the halide component in Sn HaPs (typically iodide) has been shown to play a key role in dictating device performance and stability due to its high reactivity. Here we describe the impact of native halide chemistry on Sn HaPs. Specifically, molecular halogen formation in Sn HaPs and its influence on degradation is reviewed, emphasising the benefits of iodide substitution for improving stability. Next, the ecological impact of halide products of Sn HaP degradation and its mitigation are considered. The development of visible Sn HaP emitters via halide tuning is also summarised. Lastly, halide defect management and interfacial engineering for Sn HaP devices are discussed. These insights will inspire efficient and robust Sn HaP optoelectronics.

Quantitative Assessment of Structure Reactivity Correlation on Rapid Kinetics of Halogenated Aromatic Compounds: A Hydrodynamic Voltammetry Study

Halogenations are mostly rapid and cannot be studied by the conventional method, hence, hydrodynamic voltammetry which is based on voltammetric principles can be adopted to study these fast reactions, provided either a reactant or a product in the reaction is electro reducible. These reactions are mostly electrophillic substitution reactions and second order when molecular halogens are used as a reagent. Rapid kinetic studies on some important halogenated aromatic compounds at rotating platinum electrode (RPE) using hydrodynamic voltammetry are summarized and reviewed for a period of the last few years. The advancement made to the technique as well as its application for mechanistic purposes, electrode kinetic measurements, pharmaceutical, and analytical applications have been addressed. As an investigative tool, kinetics has been used to obtain thermodynamic data that allows a quantitative comparison of the reactivity of the two substrates such as activation energy, velocity constants, frequency factors, and entropy change. This aids in configuring the mechanistic route, from among those theoretically possible by checking the compatibility with experimentally observed facts.

Selectfluor and TBAX (Cl, Br) Mediated Oxidative Chlorination and Bromination of Olefins.

Herein, we report the first metal-free and molecular halogen reagent-free dihomohalogenation methodology by using Selectfluor as an oxidant and tetrabutylammonium bromide/chloride salts as a halogen source. This effective strategy provides various fluorine-free halogenated products easily in quantitative yields from alkenes, alkynes, and natural products.

Chlorine Substitution in Spirocyclic Derivatives Triggers SHG Response in Noncentrosymmetric Crystal.

Organic-inorganic hybrid phase transition materials with switchable properties have important potential applications in smart devices such as dielectric switches and storage. Nevertheless, it remains challenging to modify molecular structures efficiently to obtain materials simultaneously possessing multiple responsive properties. Herein, different from ordinary halogen substitutions in Metal Halide, we report a halogen regulation design of organic molecular strategy: (ASD)2 MnBr4 (ASD=5-azonia-spiro [4.5] decane) to (CASD)2 MnBr4 (CASD=8-chloro-5-azonia-spiro [4.5] decane). After organic molecular halogen regulation, the SHG response was excited and the dielectric phase transition temperature (Tc ) has also been greatly improved. Furthermore, under the irradiation of UV lamp, both showed green light with quantum yields above 50%. This work is of great significance for further exploration of multifunctional molecular switch materials through halogen modification strategies.

Effects of operating conditions on disinfection by-product formation, calculated toxicity, and changes in organic matter structures during seawater chlorination

This study systematically quantified the impacts of different operation conditions, e.g., pH, chlorine dosages, contact times, and temperatures towards the disinfection by-product (DBP) formation, integrated toxicity, and structural changes in seawater natural organic matter during seawater chlorination. Higher concentrations of total DBPs were found under longer contact times, higher chlorine dosages, higher temperatures, and lower pH. The concentration of tribromomethane, the most abundant DBP, was found lowest at pH 10. Monobromoacetic acid, dibromoacetonitrile, and dibromoacetaldehyde were the three main contributors to integrated cyto- and geno-toxicity, stressing the need to monitor DBPs based on their contributions to integrated toxicity, regardless they are regulated or nonregulated. The concentrations of total organic chlorine remained stable under different conditions, while those of total organic bromine increased with increasing contact times, chlorine dosages, and temperatures, but with decreasing pH, indicating the changes of toxicity in chlorinated seawater compared to drinking water or groundwater. Changes of ultraviolet absorbance at 254 nm and fluorescence excitation emission matrix values are useful indicators for monitoring the concentrations of high molecular weight adsorbable organic bromine and total organic halogen under all operating conditions.

A-X⋯σ Interactions-Halogen Bonds with σ-Electrons as the Lewis Base Centre.

CCSD(T)/aug-cc-pVTZ//ωB97XD/aug-cc-pVTZ calculations were performed for halogen-bonded complexes. Here, the molecular hydrogen, cyclopropane, cyclobutane and cyclopentane act as Lewis base units that interact through the electrons of the H–H or C–C σ-bond. The FCCH, ClCCH, BrCCH and ICCH species, as well as the F2, Cl2, Br2 and I2 molecular halogens, act as Lewis acid units in these complexes, interacting through the σ-hole localised at the halogen centre. The Quantum Theory of Atoms in Molecules (QTAIM), the Natural Bond Orbital (NBO) and the Energy Decomposition Analysis (EDA) approaches were applied to analyse these aforementioned complexes. These complexes may be classified as linked by A–X···σ halogen bonds, where A = C, X (halogen). However, distinct properties of these halogen bonds are observed that depend partly on the kind of electron donor: dihydrogen, cyclopropane, or another cycloalkane. Examples of similar interactions that occur in crystals are presented; Cambridge Structural Database (CSD) searches were carried out to find species linked by the A–X···σ halogen bonds.

Bridging the Void: Halogen Bonding and Aromatic Interactions to Program Luminescence and Electronic Properties of π-Conjugated Materials in the Solid State

π-Conjugated materials are promising candidates for emerging organic optoelectronic devices empowered by molecular design. The unsolved challenges of predicting and controlling their packing as solids, central to their properties and performance, currently limits their practical application. As noncovalent interactions drive packing, control over such interactions are critical to bridging from chemical structure to functional properties. In molecular crystals, halogen bonding and interactions of aromatic rings have emerged as versatile tools for noncovalent control with tailored luminescence and electronic properties. Here, we describe how the interplay of these directional and tunable interactions can engineer properties, including stimuli-responsive behavior. Halogen bonding can provide robust designs for directing 2D molecular assembly, whereas the intentional interactions of aromatic rings can yield metastable, switchable packing modes, as well as programmed stacking between layers of chromophores. Examples, herein, demonstrate clear relationships between assembly by design and resulting solid-state properties, and strategies presented offer guidance for future designs of π-conjugated molecular materials using specific aromatic interactions and halogen bonding.

Tuning optical and electronic properties of graphene oxide by surface adsorption of molecular halogens (X2 = I2, Br2, Cl2, and F2) for light harvesting

Surface adsorption of small molecules modulates both optical and electronic structure, which is beneficial for different applications. The molecular adsorption of halogens X2 (X2 = I2, Br2, Cl2, and F2) was investigated using density functional theory and the dispersion (Wb97xd) module. The electronic structure and optical properties of the pristine graphene oxide (GO) and its molecular complexes with halogens (GOI2, GOBr2, GOCl2, and GOF2) are explored. The adsorption of X2 (X2 = I2, Br2, and Cl2) molecules were stabilized by non-covalent lone pair-π bonding, (O)lp… π, interactions and π-π interactions. The F2 molecule were stabilized by lone pair-π bonding, (O)lp… π, as well as halogen bonding (XB). The GOX2 complexes were energetically stable and optically red shifted in polar solvents. The simulated optical absorption spectra at TD-DFT calculations of GOX2 complexes and TDOS uncover the presence of intermediate sates in the energy gap region, which is beneficial for harvest of visible light and photocatalysis.

Lone pair Halogen (X2)…π Interactions Stabilizes Molecular Halogens (X2=I2, Br2, Cl2, and F2) on Reduced Graphene Oxide surface: Structural, Solvent Effect and optical properties

In this work, we investigate the lone pair (lp)…π interaction for the halogens (X2=I2, Br2, Cl2, and F2) binding to the rGO surface. Electronic and optical properties of rGO significantly tuned upon adsorption of halogen molecules, although the weak nature of (lp)…π forces. The structure and optical properties of rGO, rGOI2, rGOBr2, rGOCl2 and rGOF2 adducts were investigated by density functional theory (DFT) and time-dependent DFT (TD-DFT) method. Halogen molecules (X2) stable structures were planer on rGO surface and stabilized by the lone pair X2(lp)…π(C) interactions. The surface oxygen atoms contributed to the stability by the O(lp)… π(X2) charge transfer process. Bader analysis reveals significant charge transfer and bond length elongation for X2 on rGO monolayer sheet in the order I2 > Br2 > Cl2 > F2. Surface adsorption of X2 molecules on rGO surface tunes both band gap energy and optical properties. The TDOS and PDOS reveal that X2 adsorption on rGO surface forms an intermediate states in band gap region, which decrease the energy values. These results are beneficial for photocatalysis and light harvesting applications.

Weak yet Decisive: Molecular Halogen Bond and Competing Weak Interactions of Iodobenzene and Quinuclidine.

The halogen bonded adduct between the commonly used constituents quinuclidine and iodobenzene is based on a single weak nitrogen-iodine contact, and the isolation of this adduct was initially unexpected. Iodobenzene does not contain any electron-withdrawing group and therefore represents an unconventional halogen bond donor. Based on excellent diffraction data of high resolution, an electron density study was successfully accomplished and confirmed one of the longest N···I molecular halogen bonds with a distance of 2.9301(4) Å. The topological analysis identified the XB as a directional but weak σ hole interaction and revealed secondary contacts between peripheral regions of opposite charge. These additional contacts and their competition with a nitrogen-based interaction were confirmed by NOESY experiments in solution. Integration enabled us to determine the relative NOE ratios and provided insight regarding the existing interactions.

Halogenation Regulates Supramolecular Chirality at Hierarchical Levels of Self-Assembled N-Terminal Aromatic Amino Acids.

Halogenation brings about dramatic variations to the performance of self-assembled organic species, such as luminescence and crystallinity, but it has seldom been utilized for chirality control. Here we show the halogenation effect of self-assembling organic building units on supramolecular chirality and chiroptical responses. N-terminal aromatic amino acids with different substituted halogen atoms at p-phenylalanine residues self-assembled into one-dimensional fibrous structures. Halogenation induced the emergence of macroscopic chirality regardless of halogen properties like electronegativity, generating exclusive homochiral helical structures. Solid-state X-ray structures and time-dependent density functional theory were utilized for calculated electronic circular dichroism spectra, which evidenced the diverse driving forces to enable chiral molecular arrangements, including H-bonds and halogen bonds. Red-shifted luminescence was observed in brominated building units, giving rise to active circularly polarized luminescence. This work elucidates the multiple roles of halogen in chiral self-assembly systems, which provides insight into the rational control over supramolecular chirality and their chiroptical applications.

Probing BrCl from photodissociation of CH2BrCl and CHBr2Cl at 248 nm using cavity ring-down spectroscopy.

Photodissociation of di- and tri-halogenated methanes including CH2BrCl and CHBr2Cl at 248 nm was investigated using cavity ringdown absorption spectroscopy (CRDS). The spectra of the BrCl(v'' = 2, 3) and Br2(v'' = 1, 2) fragments were probed over the wavelength range of 594.5-596 nm in the B3Π+0u ← X1Σ+g and B3Π (0+) ← X1Σ+ transitions, respectively. Their corresponding spectra were simulated for assignment of rotational lines at a given vibrational level. The quantum yields for Br2 eliminated from CHBr2Cl and BrCl from CH2BrCl were determined to be 0.048 ± 0.018 and 0.037 ± 0.014, respectively. The photodissociation of CHBr2Cl yielded only the Br2 fragment, but not the BrCl fragment in the experiments. An ab initio theoretical method based on the CCSD(T)//B3LYP/6-311g(d,p) level was employed to evaluate the potential energy surface for the dissociation pathways to produce Br2 and BrCl from CHBr2Cl, which encountered a transition state barrier of 445 and 484 kJ mol-1, respectively. The corresponding RRKM rate constants were calculated to show that the branching ratio of (Br2/BrCl) is ∼20. The BrCl spectrum is expected to be obscured by the much larger Br2 spectrum, explaining why BrCl fragments cannot be detected in the photolysis of CHBr2Cl.

Orthogonal hydrogen and halogen bonding facilitate intermolecular charge transfer between barbaturic acid and molecular halogens over g-C3N4 nanosheet: A comparative experimental and DFT calculations

Durable photogenerated Charge separation in nanomaterials is an essential parameter in semiconductors application. Here, we immobilized the orthogonal hydrogen bonding (HB) and halogen bonding (XB) stabilized complexes of barbaturic acid with molecular halogens (X2=I2, Br2, Cl2, and F2) on g-C3N4 surface for the decreasing the photogenerated electron/hole recombination process. The BUX2/g-C3N4 composite reveal lower band gap (2.65 eV) than the pristine g-C3N4. Spectroscopic techniques such as UV–Vis, photoluminescence, scanning electron microscopy (SEM), thermal gravimetric analysis (TGA) and energy dispersive X-ray fluorescence (EDXRF) were used to investigate the molecular complexes and BUX2/g-C3N4 composites. Density Functional Theory calculations (rwb97xd/lanl2dz) were used to investigate the molecular interactions and explore the binding noncovalent forces. The cooperative orthogonal HB and XB stabilized the BUX2 complexes in polar solvents. Noncovalent forces (vdW) were the dominant factors for the binding of BUX2 on g-C3N4 nanosheets. The quantative charge transfer from g-C3N4 to BUX2 increases in the order of I2 > Br2 > Cl2 > F2, which in accordance with the complexes stability.

VsFilt: A Tool to Improve Virtual Screening by Structural Filtration of Docking Poses.

The ability of ligands to form crucial interactions with a protein target, characteristic for the substrate and/or inhibitors, could be considered a structural criterion for identifying potent binders among docked compounds. Structural filtration of predicted poses improves the performance of virtual screening and helps in recovering specifically bound ligands. Here, we present vsFilt-a highly automated and easy-to-use Web server for postdocking structural filtration. The new tool can detect various types of interactions that are known to be involved in the molecular recognition, including hydrogen and halogen bonds, ionic interactions, hydrophobic contacts, π-stacking, and cation-π interactions. A case study for poly(ADP-ribose) polymerase 1 ligands illustrates the utility of the software. The Web server is freely available at https://biokinet.belozersky.msu.ru/vsfilt.

Surface Propensity of Aqueous Atmospheric Bromine at the Liquid-Gas Interface.

Multiphase reactions of halide ions in aqueous solutions exposed to the atmosphere initiate the formation of molecular halogen compounds in the gas phase. Their photolysis leads to halogen atoms, which are catalytic sinks for ozone, making these processes relevant for the regional and global tropospheric ozone budget. The affinity of halide ions in aqueous solution for the liquid-gas interface, which may influence their reactivity with gaseous species, has been debated. Our study focuses on the surface properties of the bromide ion and its oxidation products. In situ X-ray photoelectron spectroscopy carried out on a liquid jet combined with classical and first-principles molecular dynamics calculations was used to investigate the interfacial depth profile of bromide, hypobromite, hypobromous acid, and bromate. The simulated core electron binding energies support the experimentally observed values, which follow a correlation with bromine oxidation state for the anion series. Bromide ions are homogeneously distributed in the solution. Hypobromous acid, a key species in the multiphase cycling of bromine, is the only species showing surface propensity, which suggests a more important role of the interface in multiphase bromine chemistry than thought so far.

Synthesis of 3-halochromones with simple KX halogen sources enabled by in situ halide oxidation

An in situ oxidation strategy for generating molecular halogen has been developed for the synthesis of 3-halochromones by employing simple potassium halides as halogen sources.