Influence Of Halogen Substituents Research Articles

Synthesis of novel benzylamine antimycotics and evaluation of their antimycotic potency.

A series of 23 novel benzylamines was synthesized by reductive amination from halogen-substituted 3- and 4-benzyloxybenzaldehyde derivatives and 6-methylhept-2-yl amine or n-octylamine. The antimycotic activity of the resulting amines was evaluated in a microdilution assay against the apathogenic yeast Yarrowia lipolytica as test microorganism. Promising compounds were also tested against human pathogenic Candida species. The influence of halogen substituents at the benzyl ether side chain was studied in this screening, as well as the influence of the branched side chain of (±)-6-methylhept-2-yl amine in comparison with the n-octyl side chain.

Halogen and structure sensitivity of halobenzene adsorption on copper surfaces.

The adsorption orientation of molecules on surfaces influences their reactivity, but it is still challenging to tailor the interactions that govern their orientation. Here, we investigate how the substituent and the surface structure alter the adsorption orientation of halogenated benzene molecules from parallel to tilted relative to the surface plane. The deviation of the parallel orientation of bromo-, chloro-, and fluorobenzene molecules adsorbed on Cu(111) and Cu(110) surfaces is determined, utilising the surface selection rule in reflection-absorption infrared spectroscopy. On Cu(111), all three halogenated molecules are adsorbed with their molecular plane almost parallel to the surface at low coverages. However, they are tilted at higher coverages; yet, the threshold coverages differ. On Cu(110), merely bromo- and chlorobenzene follow this trend, albeit with a lower threshold for both. In contrast, fluorobenzene molecules are tilted already at low coverages. The substantial influence of the halogen atom and the surface structure on the adsorption orientation, resulting from an interplay of molecule-molecule and molecule-surface interactions, is highly relevant for reactivity confined to two dimensions.

Halogen bond in high-performance liquid chromatography enantioseparations: Description, features and modelling

Halogen bond (XB)-driven enantioseparations involve halogen-centred regions of electronic charge depletion (σ-hole) as electrophilic recognition sites. The knowledge in this field is still in its infancy. Indeed, although the influence of halogens on enantioseparation have been often considered, only recently the function of electrophilic halogens (Cl, Br, I) as enantioseparations ‘drivers’ has been demonstrated by our groups. Further to these studies, in this paper we focus on some unexplored issues. First, as XB-driven chiral recognition mechanisms are at an early stage of comprehension, a theoretical investigation based on a series of 32 molecular dynamic (MD) simulations was performed by using polyhalogenated 4,4′-bipyridines and polysaccharide-based polymers as ligands and receptors, respectively. Enantiomer elution orders (EEOs) were derived from calculations and the theoretical model accounted for some analyte- and chiral stationary phase (CSP)-dependent experimental EEO inversions. Then, the function of halogen-centred σ-holes in competitive systems, presenting also hydrogen bond (HB) centres as recognition sites, was considered. In this regard, Pirkle’s enantioseparations of halogenated compounds performed on Whelk-O1 were theoretically re-examined and electrostatic potentials (EPs) associated with both σ-holes on halogens and HB centres were computed and compared. Then, the enantioseparation of halogenated 2-nitro-1-arylethanols was performed on cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC) and the influence of halogen substituents on the chromatographic results was evaluated by correlating theoretical and experimental data.

The influence of halogen substituents on the biological properties of sulfur-containing flavonoids

A series of halogen-substituted tricyclic flavonoids containing a 1,3-dithiol-2-ylium moiety has been synthesized from the corresponding 3-dithiocarbamic flavanones. The influence of halogen substituents on the antibacterial properties of the tricyclic flavonoids has been investigated against Staphylococcus aureus and Escherichia coli. On going from fluorine to iodine, these compounds exhibit good to excellent inhibitory properties against both Gram-positive and Gram-negative pathogens. These results suggest that size is the main factor for the change in potency rather than polarity/electronics.

Perylene Derivatives As Useful SERRS Reporters, Including Multiplexing Analysis.

Five perylene bisimide (PBI) derivatives were designed and synthesized, on the basis of quantum-chemical calculations. The influence of halogen substituents on the shape and energy of the frontier orbitals and the Raman spectra were calculated, in the prospect use in surface-enhanced resonance Raman scattering (SERRS) studies. The corresponding experiments confirmed a very strong SERRS response in the presence of pristine (i.e., uncoated) gold nanoparticles. These spectra can be used for multiplexing measurements, namely measurements in which, by using a single laser excitation, one can recognize the simultaneous presence of several analytes.

Influence of halogen substituent on the mesomorphic properties of five-ring banana-shaped molecules with azobenzene wings

Three new series of bent-shaped molecules with 4-chlororesorcinol, 4-bromoresorcinol or 4-fluororesorcinol as the central unit, and azobenzene with different alkoxy chain length as side arms were synthesised. The mesophase behaviour was investigated by polarising optical microscopy, and differential scanning calorimetry. A representative example has also been characterised by X-ray diffraction (XRD) studies. It is found that almost all of the materials prepared are monotropic liquid crystalline. Depending on the substituent at the central unit and on the chain length nematic phases, B6 phases, a B4-like dark conglomerate phase and a modulated/undulated anticlinic SmC phase were found. As a unique feature, upon reducing the chain length a transition from nematic to B6-type smectic phases was observed, which is reverse to usually observed phase sequences. The UV–vis absorption spectroscopy was also performed to study the effect of light-induced trans–cis-isomerisation on the prepared compounds.

Influence of halogen substituents on the catalytic oxidation of 2,4,6-halogenated phenols by Fe(III)-tetrakis(p-hydroxyphenyl) porphyrins and potassium monopersulfate.

The influence of halogen substituents on the catalytic oxidation of 2,4,6-trihalogenated phenols (TrXPs) by iron(III)-porphyrin/KHSO5 catalytic systems was investigated. Iron(III)-5,10,15,20-tetrakis(p-hydroxyphenyl)porphyrin (FeTHP) and its supported variants were employed, where the supported catalysts were synthesized by introducing FeTHP into hydroquinone-derived humic acids via formaldehyde poly-condensation. F (TrFP), Cl (TrCP), Br (TrBP) and I (TrIP) were examined as halogen substituents for TrXPs. Although the supported catalysts significantly enhanced the degradation and dehalogenation of TrFP and TrCP, the oxidation of TrBP and TrIP was not enhanced, compared to the FeTHP catalytic system. These results indicate that the degree of oxidation of TrXPs is strongly dependent on the types of halogen substituent. The order of dehalogenation levels for halogen substituents in TrXPs was F > Cl > Br > I, consistent with their order of electronegativity. The electronegativity of a halogen substituent affects the nucleophilicity of the carbon to which it is attached. The levels of oxidation products in the reaction mixtures were analyzed by GC/MS after extraction with n-hexane. The most abundant dimer product from TrFP via 2,6-difluoroquinone is consistent with a scenario where TrXP, with a more electronegative halogen substituent, is readily oxidized, while less electronegative halogen substituents are oxidized less readily by iron(III)-porphyrin/KHSO5 catalytic systems.

The influence of halogen substituents on the course of hydrogallation and hydroalumination reactions

Treatment of trimethylsilylethynylbenzene derivatives with HGaCl(2) afforded products, [C(6)H(6-x){C(H)=C(SiMe(3))GaCl(2)}(x)], in which by a very fast cis/trans-rearrangement the Ga and H atoms occupied opposite sides of the resulting C=C double bonds. The stability of the cis-forms considerably increased upon application of 1,3-dibromo- and pentafluorophenylalkyne derivatives. Two pairs of cis/trans-isomers could be characterized by crystal structure determinations and allow the direct comparison of structural parameters. For the first time an equilibrium was detected between cis- and trans-forms in solution. Treatment of 1,4-di(tert-butylalkynyl)benzene with HAlR(2) (R = CMe(3), CH(2)CMe(3)) afforded cyclophane-type molecules by the release of AlR(3). Only the neopentyl derivative could be isolated and characterized by crystal structure determination. In contrast, the dibromo compound, 1,4-Br(2)-2,5-(Me(3)CC[triple bond]C)(2)C(6)H(2), yielded the simple addition product, C(6)H(2)Br(2){C(AlR(2))=C(H)CMe(3)}(2) (R = CMe(3)). Condensation was hindered in this case by intramolecular Al-Br interactions. Surprisingly, the simple addition product was also isolated from the reaction of 1,4-(Me(3)CC[triple bond]C)(2)C(6)H(4) with the relatively small hydride HAlEt(2). Solid-state NMR spectra of the product revealed strong intermolecular Al-C interactions involving the negatively charged terminal vinylic carbon atoms, to give one-dimensional coordination polymers.

Influence of Halogen Substituents on the Self-Assembly of Oligothiophenes−A Combined STM and Theoretical Approach

Iodinated quaterthiophenes 2-3 have been synthesized and their self-assembling behavior investigated at the liquid-solid interface by means of high-resolution scanning tunneling microscopy in comparison to parent oligothiophene 1. All three compounds spontaneously give well-ordered 2D crystalline monolayers at the graphite surface and order in a lamella-type arrangement of the conjugated backbones concomitant with an interlocking of the alkyl side chains. Symmetrically substituted oligothiophenes 1 and 3 without a relevant dipole moment self-assemble in a similar fashion, exhibiting comparable unit cells, whereas monoiodo derivative 2 arranges as pairs along the lamella axis due to the presence of a permanent dipole moment induced by the polarizable halogen group. Corroborated by quantum chemical calculations, novel head-to-head (iodo-iodo) intermolecular interactions were found to take place for this unsymmetrical derivative. The investigation of mixed solutions clearly reveals that at the solid-liquid interface a homogeneous layer of this compound is formed, which comprises the highest packing density leading to a separation process at the interface.

Synthesis, Characterization, and Magnetism of Binuclear Iron(III) Complexes with Iodanilato as Bridging Ligand

Three new μ‐iodanilato‐bridged binuclear iron(III) complexes were synthesized and characterized, namely [Fe2(IA)(Me2phen)4](ClO4)4 (1), [Fe2(IA)(Ph2phen)4](ClO4)4 (2), and [Fe2(IA)(Phphen)4]‐(ClO4)4 (3), where IA represents the dianion of iodanilic acid; Me2phen, Ph2phen, and Phphen denotes 2,9‐dimethyl‐1,10‐phenanthroline; 4,7‐diphenyl‐1,10‐phenanthroline or 5‐phenyl‐1,10‐phenanthroline, respectively. Based on elemental analyses, molar conductivity and room‐temperature magnetic moment measurements, IR and electronic spectral studies, it is proposed that these complexes have extended IA‐bridged structures consisting of two iron(III) ions, each in a distorted octahedral environment. The complexes (1) and (2) were further characterized by variable‐temperature (4.2–300 K) magnetic susceptibility measurements and the observed data were successfully simulated by the equation based on the spin Hamiltonian operator, Ĥ = −2JŜ 1 Ŝ 2, giving the exchange parameter J = −9.21 cm−1 for (1) and J = −10.85 cm−1 for (2). These results are commensurate with weak antiferromagnetic spin‐exchange interaction between the two iron(III) ions within each molecule. The influence of halogen substituents in the bridging ligand on magnetic interactions between the metal ions of this kind of complexes is preliminarily discussed.

The influence of halogen substituents at the ligand framework of (α-diimine)nickel(II) catalyst precursors on their behavior in ethylene oligomerization and polymerization

Abstract The ligand structure of (α-diimine)nickel(II) catalyst precursors has a significant influence on the behavior of these catalysts in the polymerization of ethylene. After activation with MAO, homogeneous nickel catalysts of this type are suitable to polymerize olefins to low molecular oligomers and/or more or less branched polymers. The variation of the ligand framework of the catalysts with halogen substituents in different positions shows clear dependencies between these substituents and the properties of the polymerization products. Unsaturated oligomers with an even number of carbon atoms (4–50) and all possible isomers as well as polymers up to a molecular weight of 36,000 g/mol can be obtained.

Ab initio studies of the gas-phase thermodynamic properties and bond dissociation energies for haloethanes and halomethyl radicals

Ab initio molecular orbital calculations have been performed on fluorine- and chlorine-substituted ethanes and radicals. The molecular equilibrium characteristics (energies, structural parameters and vibrational frequencies) of all the species were estimated at the MP2/6-311G** level of theory. A rigid harmonic oscillator model was used for the development of a data base for the ideal gas thermodynamic properties: Cp°, S°, − (G° − H0°)/T, ΔfH°, ΔfG° and log Kf, of the haloethanes and halomethyl radicals over a temperature range 0–1500 K. From the estimated enthalpies of formation at 298.15 K and 1 atm, bond dissociation energies for the homolytic cleavage of C–C bonds for the haloethanes were obtained. The results of the MP2/6-311G** calculations of the heats of formation at 298.15 K, ΔfH298.15K°, of the halogenated methyl radicals have been compared with those obtained using the CBS-RAD procedure and a modification of this called CBS-RAD(B3-LYP,B3-LYP). Finally, the influence of halogen substituents on reactivity has been interpreted in terms of polar and hyperconjugation effects.

Long-chain haloalkanes are incorporated into fatty acids by Rhodococcus rhodochrous NCIMB 13064

Summary: The fatty acid composition of the cellular lipids of Rhodococcus rhodochrous NCIMB 13064 grown on various long-chain haloalkanes has been investigated and the influence of halogen substituents, carbon chain length and the position of halogen substitution in the growth substrate explored. Of the total fatty acids present in cells grown on 1-chloro-, 1-bromo- and 1-iodohexadecane, 75, 90 and 81%, respectively, were substituted in the w position by the corresponding halogen but only 1% of the fatty acids present after growth on 1-fluorotetradecane were fluorinated in this position. The extent of the halofatty acid incorporation with different halogen substituents in the growth substrate appears to reflect the degree to which oxygenase attack is restricted to the non-halogenated end of the haloalkane. Studies of the fatty acid composition of cells after growth on a series of 1-chloroalkanes containing an even number of carbon atoms between C10 and C18 indicated chlorofatty acid incorporation from C12 to C18 substrates at levels ranging from 21% with C12 to 75% with C16. The chlorofatty acids formed by initial oxidation of the chloroalkane were chain-lengthened or chain-shortened by from two to eight carbon atoms, with accompanying desaturation in some instances. Substantial quantities of a methyl-branched C19:0 chlorofatty acid were also present with several chloroalkane substrates. When the fatty acid composition of cells after growth on 1-bromoalkanes containing an odd number of carbon atoms between C11 and C17 was examined, the incorporation of bromofatty acids was observed with C13, C15 and C17 substrates; a maximum of 76% was recorded for the C15 bromoalkane. As with even chain-length chloroalkanes, both chain-lengthening and -shortening occurred predominantly via two-carbon units so that most bromoacids present possessed an odd number of carbon atoms. When 1-bromododecane or 2-bromododecane were substrates, overall incorporations of bromofatty acids into the lipid fraction were very similar, demonstrating that the position of halogen substitution in the haloalkane was not critical in determining the extent of incorporation of the haloacids into cellular lipids. The results of the study indicate a mechanism by which degradation products of chlorinated paraffins could enter the biological food chain.

Symmetrically disubstituted poly(bithiophene)s: influence of halogen substituents

Poly(3,3′-dibromo-2,2′-bithiophene)(PBr2BT) and poly(3,3′-dichloro-2,2′-bithiophene)(PCl2BT) can be readily deposited on electrodes via electrochemical polymerization of the respective monomers. Visible cracks observed on the resulting PCl2BT and PBr2BT films were related to the steric influence of the substituents. The redox potentials of polymers were found to decrease in the order PBr2BT PCl2BT > poly(bithiophene)(PBT), suggesting that the steric hindrance and electronegative nature of the halogen groups impart a negative effect on the inculator-to-conductor transition in PBr2BT and PCl2BT. In addition, the less extended π-conjugation, together with the electrochemically unfavourable doped state and discontinuous macroscopic structure, prevent the solid-state PBr2BT and PCl2BT from achieving conductivity comparable to the parent PBT. However, the enhanced solubility with consequent improved processibility, coupled with the presence of reactive pendant halogens would make these systems useful as functional polymers for further modifications in the post-polymerization stage.

Spectrophotometric studies of some charge-transfer complexes of tetracyanoethylene with poly(N-vinyl halogenocarbazoles)

The results and numerical analysis of measurements of absorption spectra of charge-transfer complexes of poly(N-vinyl halogenocarbazoles) with tetracyanoethylene are presented. The absorption bands result from donor–acceptor interaction together with values of equilibrium constants, enthalpy, and oscillators strengths of investigated complexes allowed us to conclude that isomerism of complexing took place. The influence of halogen substituents (mono- and disubstitution) in positions 3 and 6 of the carbazole ring (polymeric donor) on the spectral properties of its complexes was observed.

Chemical structure and biodegradability of halogenated aromatic compounds. Substituent effects on 1,2-dioxygenation of catechol.

1. The influence of halogen substituents on the 1,2-dioxygenation of catechols was investigated. The results obtained with the two isoenzymes pyrocatechase I and pyrocatechase II from the haloarene-utilizing Pseudomonas sp. B 13 and the pyrocatechase from benzoate-induced cells of Alcaligenes eutrophus B.9 were compared. 2. Substituents on catechol were found to interfere with O2 binding by the two isoenzymes from Pseudomonas sp. B 13, whereas the Km value for catechol kept constant at different O2 concentrations. 3. Electron-attracting substituents decreased the Km values for catechols. 4. Results from binding studies with substituted catechols demonstrated narrow stereospecificities of pyrocatechase I from pseudomonas sp. B 13 and the pyrocatechase from alcaligenes eutrophus B.9. In contrast, a low steric hindrance by substituents in the binding of catechols with pyrocatechase II was observed. 5. Low pK'1 values of substituted catechols resulted in low Michaelis constants. 6. Electron-attracting substituents such as halogen decreased the reaction rates of catechol 1,2-dioxygenation. The correlation of the Vmax. values observed with pyrocatechase II from Pseudomonas sp. B 13 with the substituent constant sigma+ (Okamoto--Brown equation) was distinctly greater than with Hammett's sigma values. The corresponding logVmax. against sigma+ correlation for pyrocatechase I was considerably disturbed by steric influences of the substituents.