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1.
Sci Total Environ ; 742: 140597, 2020 Nov 10.
Artigo em Inglês | MEDLINE | ID: mdl-32629271

RESUMO

Polychlorinated biphenyls (PCBs) and halogen flame retardants (HFRs) are major pollutants in e-waste recycling area. High internal exposure levels of PCBs and HFRs are harmful to human thyroid hormone (TH) equilibrium. To examine their disrupting effects on TH, we conducted a study on children (n = 114) of an e-waste recycling and a control area in South China. Concentrations of PCBs, HFRs, and TH levels were determined in serum samples. TH related proteins and their corresponding gene were also monitored as markers of such disruption. Levels of these chemicals in the exposed group were much greater than those in the control group. Results of the linear regression and generalized additive model indicated the presence of close relationships between the internal exposure levels and the responses of TH related proteins, gene expression. More extensive exposure concentrations of these chemicals led to higher expression of iodothyronine deiodinase I and decreased the concentrations of thyroid-stimulating hormone, expression of TH receptor α, indicating the exertion of discrepant and even contrary influences on equilibrium of TH, and a compensation of these mechanisms may kept the homeostasis of TH. These results for children warrant further investigation on the health risks of PCBs and HFRs exposure in e-waste area.


Assuntos
Resíduo Eletrônico/análise , Retardadores de Chama , Bifenilos Policlorados/análise , Criança , China , Halogênios , Humanos , Proteínas , Reciclagem , Hormônios Tireóideos
2.
Chemosphere ; 251: 126452, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32443227

RESUMO

Microplastics (MPs) are prevalent global pollutants that are being detected in aquatic ecosystems and drinking water sources around the world. In addition to plastic polymers, MPs contain various chemical substances (known as "additives") that can leach and risk water quality. In this paper, we investigated for the first time the potential release of disinfection byproducts (DBPs) precursors when MPs are exposed to hydrolysis and/or degradation by simulated sunlight. Seventeen MPs with seven different polymer types were collected either as commercial products (e.g. drinking water bottles, shopping bags, recycled plastics, etc.) or pure/virgin polymers. Results showed high release of dissolved organic carbon (DOC) from five MP samples and a significant increase in bromide concentrations from four MPs. DBPs formation potential (DBPFP) experiments with MPs' leachates showed higher concentrations of chlorinated trihalomethanes (THMs), haloacetonitriles (HANs), and total organic halogens (TOX) in three samples, while a significant shift to brominated DBPs was observed in samples containing bromide. Extending the leaching experiments to four consecutive cycles showed that the leaching of DOC and DBPs' precursor significantly decreased after the second leaching cycle. Further analysis revealed that the reactivity of the leached DOC - indicated by THMFP yields - was comparable to those of several raw waters that supply drinking water treatment plants. The leached THMs and TOX from MPs that were exposed to UVA irradiation were in general higher than MPs that were run under dark conditions.


Assuntos
Monitoramento Ambiental , Microplásticos/análise , Poluentes Químicos da Água/análise , Brometos/análise , Desinfetantes/química , Desinfecção , Água Potável/análise , Ecossistema , Halogenação , Halogênios/análise , Plásticos , Trialometanos/análise , Qualidade da Água
3.
J Chromatogr A ; 1621: 461052, 2020 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-32268956

RESUMO

Ion chromatography-electrospray tandem mass spectrometry (IC-ESI-MS/MS) is used to determine nine haloacetic acids (HAAs), bromate, and dalapon in drinking water samples in U.S. EPA Method 557. In this method, all target analytes are separated and measured with good sensitivity without the need for sample preconcentration or derivatization. However, the separation time is relatively long. In order to reduce the sample analysis time in EPA Method 557, a new anion exchange column has been developed to perform fast separation of the target analytes. Using this new anion exchange column, nine HAAs, bromate, and dalapon can be resolved and separated from interfering matrix ions within 40 minutes, about 33% faster than the analysis time obtained using an earlier anion exchange column reported in EPA Method 557. The new anion exchange column has unique selectivity and high exchange capacity. Method optimization, simplification and improvements in robustness are demonstrated while validating the new column suitability for the determine of HAAs, bromate and dalapon according to EPA Method 557.


Assuntos
Acetatos/análise , Bromatos/análise , Cromatografia por Troca Iônica/métodos , Água Potável/química , Propionatos/análise , Espectrometria de Massas por Ionização por Electrospray/métodos , Espectrometria de Massas em Tandem/métodos , Acetatos/química , Halogênios
4.
Biochemistry (Mosc) ; 85(Suppl 1): S34-S55, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-32087053

RESUMO

This review discusses formation of reactive halogen species (RHS) catalyzed by myeloperoxidase (MPO), an enzyme mostly present in leukocytes. An imbalance between the RHS production and body's ability to remove or neutralize them leads to the development of halogenative stress. RHS reactions with proteins, lipids, carbohydrates, and antioxidants in the content of low-density lipoproteins (LDLs) of the human blood are described. MPO binds site-specifically to the LDL surface and modifies LDL properties and structural organization, which leads to the LDL conversion into proatherogenic forms captured by monocytes/macrophages, which causes accumulation of cholesterol and its esters in these cells and their transformation into foam cells, the basis of atherosclerotic plaques. The review describes the biomarkers of MPO enzymatic activity and halogenative stress, as well as the involvement of the latter in the development of atherosclerosis.


Assuntos
Aterosclerose/metabolismo , Halogenação , Halogênios/metabolismo , Lipoproteínas LDL/metabolismo , Placa Aterosclerótica/metabolismo , Sítios de Ligação , Biomarcadores/metabolismo , Colesterol/metabolismo , Ácidos Graxos Insaturados/metabolismo , Células Espumosas/metabolismo , Radicais Livres/metabolismo , Humanos , Ácido Hipocloroso/metabolismo , Leucócitos/metabolismo , Peroxidase/metabolismo
5.
Biochemistry (Mosc) ; 85(Suppl 1): S56-S78, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-32087054

RESUMO

Oxidative stress resulting from accumulation of reactive oxygen, nitrogen, and halogen species (ROS, RNS, and RHS, respectively) causes the damage of cells and biomolecules. However, over the long evolutionary time, living organisms have developed the mechanisms for adaptation to oxidative stress conditions including the activity of the antioxidant system (AOS), which maintains low intracellular levels of RONS (ROS and RNS) and RHS. Moreover, living organisms have adapted to use low concentrations of these electrophiles for the regulation of cell functions through the reversible post-translational chemical modifications of redox-sensitive amino acid residues in intracellular effectors of signal transduction pathways (protein kinases and protein phosphatases), transcription factors, etc. An important fine-tuning mechanism that ensures involvement of RONS and RHS in the regulation of physiological processes is interconversion between different reactive species. This review focuses on the complex networks of interacting RONS and RHS types and their endogenous sources, such as NOX family of NADPH oxidases, complexes I and III of the mitochondrial electron transport chain, NO synthases, cytochrome P450-containing monooxygenase system, xanthine oxidoreductase, and myeloperoxidases. We highlight that kinetic parameters of reactions involving RONS and RHS determine the effects of these reactive species on cell functions. We also describe the functioning of enzymatic and non-enzymatic AOS components and the mechanisms of RONS and RHS scavenging under physiological conditions. We believe that analysis of interactions between RONS and relationships between different endogenous sources of these compounds will contribute to better understanding of their role in the maintenance of cell redox homeostasis as well as initiation and progression of diseases.


Assuntos
Halogênios/metabolismo , Espécies Reativas de Nitrogênio/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Transdução de Sinais/fisiologia , Antioxidantes/metabolismo , Sistema Enzimático do Citocromo P-450/metabolismo , Complexo de Proteínas da Cadeia de Transporte de Elétrons/metabolismo , Radicais Livres/metabolismo , Halogenação , Humanos , Mitocôndrias/enzimologia , NADPH Oxidases/metabolismo , Óxido Nítrico Sintase/metabolismo , Oxirredução , Estresse Oxidativo , Peroxidase/metabolismo , Xantina Desidrogenase/metabolismo
6.
J Environ Sci (China) ; 89: 90-101, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-31892405

RESUMO

This study investigated the speciation of halogen-specific total organic halogen and disinfection byproducts (DBPs) upon chlorination of natural organic matter (NOM) in the presence of iopamidol and bromide (Br-). Experiments were conducted with low bromide source waters with different NOM characteristics from Northeast Ohio, USA and varied spiked levels of bromide (2-30 µmol/L) and iopamidol (1-5 µmol/L). Iopamidol was found to be a direct precursor to trihalomethane (THM) and haloacetic acid formation, and in the presence of Br- favored brominated analogs. The concentration and speciation of DBPs formed were impacted by iopamidol and bromide concentrations, as well as the presence of NOM. As iopamidol increased the concentration of iodinated DBPs (iodo-DBPs) and THMs increased. However, as Br- concentrations increased, the concentrations of non-brominated iodo- and chloro-DBPs decreased while brominated-DBPs increased. Regardless of the concentration of either iopamidol or bromide, bromochloroiodomethane (CHBrClI) was the most predominant iodo-DBP formed except at the lowest bromide concentration studied. At relevant concentrations of iopamidol (1 µmol/L) and bromide (2 µmol/L), significant quantities of highly toxic iodinated and brominated DBPs were formed. However, the rapid oxidation and incorporation of bromide appear to inhibit iodo-DBP formation under conditions relevant to drinking water treatment.


Assuntos
Brometos/análise , Desinfetantes , Iopamidol/análise , Poluentes Químicos da Água , Purificação da Água , Desinfecção , Halogenação , Halogênios , Trialometanos
7.
J Phys Chem Lett ; 11(3): 877-884, 2020 Feb 06.
Artigo em Inglês | MEDLINE | ID: mdl-31931562

RESUMO

BODIPY chromophores can serve as organic-based triplet photosensitizers for a wide range of applications. To perform this function, the formation of the triplet state is critical, and a better understanding of how to modulate the formation of the triplet state could lead to further advances in BODIPY-based sensitizers for solar energy conversion and photodynamic therapy. In this work we investigate the ability of halogen bonding, a noncovalent solvent interaction, to facilitate intersystem crossing in a diiodo-BODIPY. Ultrafast transient absorption spectroscopy is applied to diiodo-BODIPY in the presence of pyridine-based halogen bonding solvent molecules to determine the rate constants for intersystem crossing. We find that halogen bonding facilitates the formation of the triplet state by increasing the intersystem crossing rate constant of diiodo-BODIPY. The results are interpreted in terms of the Marcus expression for intersystem crossing. Quantum chemical calculations show that halogen bonding acts to alter both the spin-orbit coupling terms and the relative energetics of the singlet and triplet states.


Assuntos
Compostos de Boro/química , Halogênios/química , Cinética , Piridinas/química , Teoria Quântica , Solventes/química
8.
Macromol Rapid Commun ; 41(4): e1900468, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31880037

RESUMO

Catalytic dehydropolymerization of halogen-functionalized phosphine-boranes (4-X-C6 H4 )PH2 ⋅BH3 (1a: X = Br, 1b: X = I) with [CpFe(CO)2 (OTf)] at 100 °C provides convenient access to halogen-functionalized polyphosphinoboranes [(4-X-C6 H4 )PH-BH2 ]n (2a: X = Br, 2b: X = I). These polymers are useful precursors for post-polymerization functionalization, which is demonstrated by Sonogashira coupling under mild conditions to yield the alkynyl-functionalized polyphosphinoborane [(4-PhCC-C6 H4 )PH-BH2 ]n (3).


Assuntos
Boranos/química , Halogênios/química , Fosfinas/química , Polímeros/química , Polímeros/síntese química , Alquinos/química , Catálise , Polimerização
9.
Environ Sci Pollut Res Int ; 27(5): 4917-4926, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31845272

RESUMO

Six elemental chlorine-free bleaching sequences were studied to see their effect on quality of pulp produced and quantity of pollutants generated during bleaching of wheat straw soda pulp. Impact of parameters like adsorbable organic halogens (AOX), chemical oxygen demand (COD), biochemical oxygen demand (BOD) and sodium adsorption ratio, pH and total dissolved solids generated during bleaching on environment as index of global pollution (IGP) was also studied. The purpose of the study was to investigate six elemental chlorine-free bleaching sequences to compare the pulp quality, effluent properties and their impact on environment. An oxygen delignification stage before D0EOPD bleaching sequence reduced the AOX, COD, colour and BOD by 44%, 42%, 36% and 33%, respectively, whereas an ozonation stage before bleaching reduced the same by 70%, 66%, 73% and 60%, respectively, as compared to those of control. The generation of pollutants as AOX, COD, colour and BOD was reduced further by 88%, 80%, 90% and 77%, respectively, with the use of short bleaching sequences (DD, DP and PD) as compared to those of control. The environmental impact as IGP with D0EOPD bleaching sequence was 2.65 which got reduced to 1.44 with bleaching sequence OZPD. Bleaching sequence OZD0EOPD was found the most effective for improving brightness and whiteness of the pulp, whereas short bleaching sequence OZPD found the most effective for reducing generation of pollutants during bleaching among different bleaching sequences studied. Graphical abstract.


Assuntos
Cloro , Resíduos Industriais , Adsorção , Cloro/química , Halogênios/química , Ácido Hipocloroso , Resíduos Industriais/análise , Papel , Eliminação de Resíduos Líquidos
10.
J Oral Biosci ; 62(1): 107-113, 2020 03.
Artigo em Inglês | MEDLINE | ID: mdl-31863827

RESUMO

OBJECTIVES: The degree of monomer conversion is crucial in determining the mechanical and clinical performance of dental resin composites. This study investigated the polymerization adequacy of two bulk-fill resin composites polymerized by Quartz-Tungsten-Halogen (QTH) and Light Emitting Diode (LED) light curing units at different depths. METHODS: Two bulk-fill resin composites (X-tra Fil; Voco and Tetric N-Ceram Bulk-fill; Ivoclar-Vivadent) with diameters of 7 mm and thicknesses of 1-4 mm were prepared and light-cured by LED or QTH. Then, the degree of conversion (DC) and microhardness of the two bulk-fill composites were evaluated. RESULTS: The microhardness of X-tra fill was significantly higher than that of Tetric N-Ceram polymerized by LED or QTH. The microhardness and DC of X-tra fil exhibited no significant difference among the increments regardless of type of light source. The DC, however, significantly decreased in deep increments for Tetric N-Ceram polymerized by QTH. CONCLUSIONS: The polymerization efficacies of the two bulk-fill composites were different in terms of the depth of cure and type of light source. The DC and microhardness of the X-tra fill bulk-fill composite polymerized by either QTH or LED did not decrease up to a thickness of 4 mm. Thus, new generations of LED light sources are better options for polymerizing the bulk-fill resin composites than QTH.


Assuntos
Luzes de Cura Dentária , Quartzo , Resinas Compostas , Halogênios , Dureza , Teste de Materiais , Polimerização , Tungstênio
11.
Chemistry ; 26(23): 5200-5207, 2020 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-31849117

RESUMO

Polychlorinated biphenyl (PCB) flame retardants are persistent pollutants and inhibit neurodevelopment, particularly in the early stages of life. Halogen bonding (XB) to the iodothyronine deiodinases (Dio) that modulate thyroid hormones (THs) is a potential mechanism for endocrine disruption. Cl⋅⋅⋅Se XB interactions of PCBs with SeMe- , a small model of the Dio active site selenocysteine, are compared with previous results on polybrominated diphenylethers (PBDEs) and THs using density functional theory. PCBs generally display weaker XB interactions compared to PBDEs and THs, consistent with the dependence of XB strength on the size of the halogen (I>Br>Cl). PCBs also do not meet a proposed energy threshold for substrates to undergo dehalogenation, suggesting they may behave as competitive inhibitors of Dio in addition to other mechanisms of endocrine disruption. XB interactions in PCBs are position-dependent, with ortho interactions slightly more favorable than meta and para interactions, suggesting that PCBs may have a greater effect on certain classes of Dio. Flexibility of PCBs around the biphenyl C-C bond is limited by ortho substitutions relative to the biphenyl linkage, which may contribute to the ability to inhibit Dio and other TH-related proteins.


Assuntos
Iodeto Peroxidase/metabolismo , Bifenilos Policlorados/química , Glândula Tireoide/química , Hormônios Tireóideos/química , Poluentes Ambientais/análise , Halogênios/química , Humanos , Iodeto Peroxidase/química , Glândula Tireoide/metabolismo , Hormônios Tireóideos/metabolismo
12.
J Chromatogr A ; 1616: 460788, 2020 Apr 12.
Artigo em Inglês | MEDLINE | ID: mdl-31866134

RESUMO

The halogen bond (XB) is a noncovalent interaction involving a halogen acting as electrophile and a Lewis base. In the last decades XB has found practical application in several fields. Nevertheless, despite the pivotal role of noncovalent interactions in separation science, investigations of XB in this field are still in their infancy, and so far a limited number of studies focusing on solid phase extraction, liquid-liquid microextraction, liquid-phase chromatography, and gas chromatography separation have been published. In addition, in the last few years, our groups have been systematically studying the potentiality of XB for HPLC enantioseparations. On this basis, in the present paper up-to-date results emerging from focused experiments and theoretical analyses performed by our laboratories are integrated with a descriptive presentation of XB features and the few studies published until now in separation science. Then, the aim of this article is to provide a comprehensive and critical discussion of the topic, and account for some still open issues in the application of XB to separate chemical mixtures.


Assuntos
Halogênios/química , Modelos Teóricos , Cromatografia Líquida , Microextração em Fase Líquida , Conformação Molecular , Impressão Molecular , Eletricidade Estática , Estereoisomerismo
13.
Molecules ; 24(23)2019 Nov 29.
Artigo em Inglês | MEDLINE | ID: mdl-31795316

RESUMO

The formation of a halogen-bond (XB) complex in the excited state was recently reported with a quadrupolar acceptor-donor-acceptor dye in two iodine-based liquids (J. Phys. Chem. Lett. 2017, 8, 3927-3932). The ultrafast decay of this excited complex to the ground state was ascribed to an electron transfer quenching by the XB donors. We examined the mechanism of this process by investigating the quenching dynamics of the dye in the S1 state using the same two iodo-compounds diluted in inert solvents. The results were compared with those obtained with a non-halogenated electron acceptor, fumaronitrile. Whereas quenching by fumaronitrile was found to be diffusion controlled, that by the two XB compounds is slower, despite a larger driving force for electron transfer. A Smoluchowski-Collins-Kimball analysis of the excited-state population decays reveals that both the intrinsic quenching rate constant and the quenching radius are significantly smaller with the XB compounds. These results point to much stronger orientational constraint for quenching with the XB compounds, indicating that electron transfer occurs upon formation of the halogen bond.


Assuntos
Fumaratos/química , Halogênios/química , Modelos Químicos , Transporte de Elétrons
14.
Molecules ; 24(23)2019 Dec 02.
Artigo em Inglês | MEDLINE | ID: mdl-31810199

RESUMO

Relativistic effects are found to be important for the estimation of NMR parameters in halogen-bonded complexes, mainly when they involve the heavier elements, iodine and astatine. A detailed study of 60 binary complexes formed between dihalogen molecules (XY with X, Y = F, Cl, Br, I and At) and four Lewis bases (NH3, H2O, PH3 and SH2) was carried out at the MP2/aug-cc-pVTZ/aug-cc-pVTZ-PP computational level to show the extent of these effects. The NMR parameters (shielding and nuclear quadrupolar coupling constants) were computed using the relativistic Hamiltonian ZORA and compared to the values obtained with a non-relativistic Hamiltonian. The results show a mixture of the importance of the relativistic corrections as both the size of the halogen atom and the proximity of this atom to the basic site of the Lewis base increase.


Assuntos
Halogênios/química , Espectroscopia de Ressonância Magnética , Algoritmos , Astato/química , Ligação de Hidrogênio , Modelos Moleculares , Solubilidade , Eletricidade Estática
15.
Molecules ; 25(1)2019 Dec 25.
Artigo em Inglês | MEDLINE | ID: mdl-31881785

RESUMO

Recently, a computational approach combining a structure-activity relationship library containing pairs of halogenated ligands and their corresponding unsubstituted ligands (called XSAR) with QM-based molecular docking and binding free energy calculations was developed and used to search for amino acids frequently targeted by halogen bonding, also known as XB hot spots. However, the analysis of ligand-receptor complexes with halogen bonds obtained by molecular docking provides a limited ability to study the role and significance of halogen bonding in biological systems. Thus, a set of molecular dynamics simulations for the dopamine D4 receptor, recently crystallized with the antipsychotic drug nemonapride (5WIU), and the five XSAR sets were performed to verify the identified hot spots for halogen bonding, in other words, primary (V5x40), and secondary (S5x43, S5x461 and H6x55). The simulations confirmed the key role of halogen bonding with V5x40 and H6x55 and supported S5x43 and S5x461. The results showed that steric restrictions and the topology of the molecular core have a crucial impact on the stabilization of the ligand-receptor complex by halogen bonding.


Assuntos
Halogênios/metabolismo , Simulação de Dinâmica Molecular , Receptores de Dopamina D4/metabolismo , Ligantes , Relação Estrutura-Atividade
16.
Molecules ; 24(22)2019 Nov 13.
Artigo em Inglês | MEDLINE | ID: mdl-31766108

RESUMO

Since hyperactivity of the protein kinase DYRK1A is linked to several neurodegenerative disorders, DYRK1A inhibitors have been suggested as potential therapeutics for Down syndrome and Alzheimer's disease. Most published inhibitors to date suffer from low selectivity against related kinases or from unfavorable physicochemical properties. In order to identify DYRK1A inhibitors with improved properties, a series of new chemicals based on [b]-annulated halogenated indoles were designed, synthesized, and evaluated for biological activity. Analysis of crystal structures revealed a typical type-I binding mode of the new inhibitor 4-chlorocyclohepta[b]indol-10(5H)-one in DYRK1A, exploiting mainly shape complementarity for tight binding. Conversion of the DYRK1A inhibitor 8-chloro-1,2,3,9-tetrahydro-4H-carbazol-4-one into a corresponding Mannich base hydrochloride improved the aqueous solubility but abrogated kinase inhibitory activity.


Assuntos
Halogênios/química , Indóis/química , Indóis/farmacologia , Inibidores de Proteínas Quinases/química , Inibidores de Proteínas Quinases/farmacologia , Proteínas Serina-Treonina Quinases/química , Proteínas Tirosina Quinases/química , Desenho de Fármacos , Humanos , Simulação de Acoplamento Molecular , Simulação de Dinâmica Molecular , Estrutura Molecular , Proteínas Serina-Treonina Quinases/antagonistas & inibidores , Proteínas Tirosina Quinases/antagonistas & inibidores , Solubilidade , Análise Espectral , Relação Estrutura-Atividade
17.
Molecules ; 24(23)2019 Nov 22.
Artigo em Inglês | MEDLINE | ID: mdl-31766716

RESUMO

A halogen-bonded complex formed between methane and chlorine monofluoride has been isolated in the gas phase before the reaction between the components and has been characterised through its rotational spectrum, which is of the symmetric-top type but only exhibits K = 0 type transitions at the low effective temperature of the pulsed-jet experiment. Spectroscopic constants for two low-lying states that result from internal rotation of the CH4 subunit were detected for each of the two isotopic varieties H4C···35ClF and H4C···37ClF and were analysed to show that ClF lies on the symmetry axis with Cl located closer than F to the C atom, at the distance r0(C···Cl) ≅ 3.28 Å and with an intermolecular stretching force constant kσ ≅ 4 N m-1. Ab initio calculations at the explicitly correlated level CCSD(T)(F12c)/cc-pVTZ-F12 show that in the equilibrium geometry, the ClF molecule lies along a C3 axis of CH4 and Cl is involved in a halogen bond. The Cl atom points at the nucleophilic region identified on the C3 axis, opposite the unique C-H bond and somewhere near the C atom and the tetrahedron face centre, with re(C···Cl) = 3.191 Å. Atoms-in-molecules (AIM) theory shows a bond critical point between Cl and C, confirming the presence of a halogen bond. The energy that is required to dissociate the complex from the equilibrium conformation into its CH4 and ClF components is only De ≅ 5 kJ mol-1. A likely path for the internal rotation of the CH4 subunit is identified by calculations at the same level of theory, which also provide the variation of the energy of the system as a function of the motion along that path. The barrier to the motion along the path is only ≅ 20 cm-1.


Assuntos
Cloro/química , Fluoretos/química , Metano/química , Halogênios/química , Conformação Molecular , Análise Espectral
18.
Molecules ; 24(22)2019 Nov 18.
Artigo em Inglês | MEDLINE | ID: mdl-31752140

RESUMO

We first reported the new application of a translate metal chelating ligand α-benzoin oxime for improving Cu-catalyzed C-N coupling reactions. The system could catalyse coupling reactions of (hetero)aryl halides with a wide of nucleophiles (e.g., azoles, piperidine, pyrrolidine and amino acids) in moderate to excellent yields. The protocol allows rapid access to the most common scaffolds found in FDA-approved pharmaceuticals.


Assuntos
Benzoína/análogos & derivados , Cobre/química , Halogênios/química , Oximas/química , Azóis/química , Benzoína/química , Carbono/química , Catálise , Nitrogênio/química , Piperidinas/química , Pirrolidinas/química
19.
Molecules ; 24(23)2019 Nov 23.
Artigo em Inglês | MEDLINE | ID: mdl-31771210

RESUMO

In order to clarify the nature of the halogen bond (XB), we considered the prototype noble gas-dihalogen molecule (Ng-X2) systems, focusing on the nature, range, and strength of the interaction. We exploited data gained from molecular beam scattering experiments with the measure of interference effects to obtain a suitable formulation of the interaction potential, with the support of high-level ab initio calculations, and charge displacement analysis. The essential interaction components involved in the Ng-X2 adducts were characterized, pointing at their critical balance in the definition of the XB. Particular emphasis is devoted to the energy stability of the orientational Ng-X2 isomers, the barrier for the X2 hindered rotation, and the influence of the X2 electronic state. The present integrated study returns reliable force fields for molecular dynamic simulations in Ng-X2 complexes that can be extended to systems with increasing complexity and whose properties depend on the selective formation of XB.


Assuntos
Halogênios/química , Gases Nobres/química , Isomerismo , Simulação de Dinâmica Molecular , Teoria Quântica
20.
Molecules ; 24(21)2019 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-31694313

RESUMO

Halogens can be very important for active agents as vital parts of their binding mode, on the one hand, but are on the other hand instrumental in the synthesis of most active agents. However, the primary halogenating compound is molecular chlorine which has two major drawbacks, high energy consumption and hazardous handling. Nature bypassed molecular halogens and evolved at least six halogenating enzymes: Three kind of haloperoxidases, flavin-dependent halogenases as well as α-ketoglutarate and S-adenosylmethionine (SAM)-dependent halogenases. This review shows what is known today on these enzymes in terms of biocatalytic usage. The reader may understand this review as a plea for the usage of halogenating enzymes for fine chemical syntheses, but there are many steps to take until halogenating enzymes are reliable, flexible, and sustainable catalysts for halogenation.


Assuntos
Halogenação/fisiologia , Halogênios/química , Biocatálise , Catálise , Flavina-Adenina Dinucleotídeo/metabolismo , Flavinas/química , Humanos , Ácidos Cetoglutáricos/metabolismo , Peroxidases/metabolismo , S-Adenosilmetionina/metabolismo
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