Terminal Bromine Atom Research Articles

Adaptive Planar Chirality of Pillar[5]arenes Invertible by n-Alkane Lengths

Chirality of host molecules can be induced and/or inverted by the guest molecules. However, the adapting chirality of hosts to the length of n-alkanes remains a great challenge because n-alkanes are neutral, achiral, and linear molecules, resulting in a weak interaction with most compounds. Herein, we report a system with chirality adapted to n-alkane lengths, using a pillar[5]arene-based macrocyclic host, S-Br, which contains five stereogenic carbons and five terminal bromine atoms on each rim. The electron-rich cavity of S-Br could include n-alkanes and the planar-chiral isomers sensitively inverted in response to the lengths of the complexed n-alkanes. The inclusion of a short n-alkane such as n-pentane made S-Br more inclined to be in the pS-form, whereas the inclusion of long n-alkanes such as n-heptane made the pR-form more favorable. The difference in the stability of the isomers was supported by the crystal structures and the theoretical calculations. Furthermore, temperature drives the adaptive chirality of S-Br with n-alkanes. An n-alkane with middle length, n-hexane, showed the dominance of the pR-form of S-Br at a higher temperature, whereas the pS-form was shown at a lower temperature.

Synthesis of quaternary ammonium salts based on quinuclidin-3-ol and pyridine-4-aldoxime with alkyl chains

Aim: In search of a new class of potential antimicrobial agents, novel ammonium salts based on quinuclidine-3-ol and pyridine-4-aldoxime with different lengths of alkyl chains were synthesized and analyzed. In addition to their potential biological application, newly synthesized salts containing terminal bromine could possibly be used for the synthesis of more potent bisquaternary salts. Methods: The commercially available quinuclidine-3-ol and pyridine-4-aldoxime were used for the synthesis of new derivatives with the appropriate alkyl chains. The purity of the synthesized salts was tested by thin-layer chromatography on an aluminum plate where aluminum oxide was used as a stationary phase. Melting points were determined in open capillaries using an instrument for melting point determination and the obtained values were left uncorrected. The FTIR spectra were recorded with a spectrometer and the data were analyzed in cm-1. Results: All the synthesized compounds, which contained heterocyclic moiety and alkyl chains (with or without a terminal bromine atom), were obtained in very good yields under the simple quaternization conditions. The better product yields were observed in reactions with quinuclidine3-ol (46-95%) compared to those with pyridine-4-aldoxime (49-59%). The obtained products were analyzed and confirmed by the thin-layer chromatography, the melting point measurement and the FTIR spectra. Conclusion: The observed difference in product yields could be explained by the different basicity of the nitrogen atom of quinuclidin-3-ol than that of pyridine-4-aldoxime. All prepared salts have a positively charged nitrogen atom as a part of their polar “head” and a long hydrocarbon chain as the non-polar “tail”. Such a structure allows electrostatic interaction with the negatively charged bacterial membrane and causes it to be disrupted. The structure of the prepared salts containing long alkyl chains could be crucial for their antimicrobial activity.

From the Unimolecuclar Template of Water-Soluble Multiarm Star Brush Copolymers to One-Dimensional Colloidal Nanocrystal Clusters: Facile Synthesis via a Combination of Magnetic Assembly with Photoinduced Cross-Linking

An effective process for the fabrication of one-dimensional (1D) colloidal superparamagnetic magnetite (Fe3O4) nanocrystal clusters was developed by combining magnetic assembly and photoinduced cross-linking under an external magnetic field. First, a series of water-soluble multiarm star brush copolymers with different molecular weights using α-cyclodextrin as a multifunctional initiator, star brush copolymer PEO-g-PAA, which consisted of poly(ethylene oxide) (PEO) as the main chain and poly(acrylic acid) (PAA) as functional side chains, were prepared by combining anionic ring-opening copolymerization with atom transfer radical polymerization (ATRP). Sequentially, star brush copolymer PEO-g-PAA as a spherical unimolecuclar template was utilized to structure-direct the in situ formation of spherical superparamagnetic Fe3O4 colloidal nanocrystal clusters by loading precursors of Fe3O4 (FeCl3 and FeCl2) into the PAA compartment. Surface-tethered PAA grafting chains of spherical Fe3O4 colloidal nanocrystal clusters, produced by ATRP, retain terminal bromine atoms that were subsequently converted into photo-cross-linkable azide groups (-N3) through nucleophilic substitution. The spherical Fe3O4 colloidal nanocrystal clusters coated with photo-cross-linkable azide groups were assembled into temporary 1D secondary nanostructures by being exposed to external magnetic fields. The resulting temporary 1D nanoclusters were efficiently cross-linked by exposure to UV light to stabilize the 1D secondary nanostructures of Fe3O4 nanocrystals. The dimension of the resulting stable and cross-linked 1D clusters can be tuned by adjusting the strength of the external magnetic field.

Intramolecular and intermolecular bromine⋯polyfluoroarene interactions: The crystal structure of bis{κC-1-(2,3,5,6-tetrafluoropyridyl)-3-benzylimidazolin-2-ylidene}tetrabromodimercury

Abstract In the crystal structure of bis{κC-1-(2,3,5,6-tetrafluoro-pyridyl)-3-benzylimidazolin-2-ylidene}tetrabromodimercury each terminal bromine atom is involved in two lone pair–π interactions with tetrafluoropyridyl rings: one intramolecular, the other intermolecular. NCI index theory calculations confirm the attractive nature of these. The interactions give rise to a zigzagged chain of alternating bromine atoms and tetrafluoropyridyl rings.

Fabrication of Two-Component, Brush-on-Brush Topographical Microstructures by Combination of Atom-Transfer Radical Polymerization with Polymer End-Functionalization and Photopatterning.

Poly(oligoethylene glycol methyl ether methacrylate) (POEGMEMA) brushes, grown from silicon oxide surfaces by surface-initiated atom transfer radical polymerization (SI-ATRP), were end-capped by reaction with sodium azide leading to effective termination of polymerization. Reduction of the terminal azide to an amine, followed by derivatization with the reagent of choice, enabled end-functionalization of the polymers. Reaction with bromoisobutryl bromide yielded a terminal bromine atom that could be used as an initiator for ATRP with a second, contrasting monomer (methacrylic acid). Attachment of a nitrophenyl protecting group to the amine facilitated photopatterning: when the sample was exposed to UV light through a mask, the amine was deprotected in exposed regions, enabling selective bromination and the growth of a patterned brush by ATRP. Using this approach, micropatterned pH-responsive poly(methacrylic acid) (PMAA) brushes were grown on a protein resistant planar poly(oligoethylene glycol methyl ether methacrylate) (POEGMEMA) brush. Atomic force microscopy analysis by tapping mode and PeakForce quantitative nanomechanical mapping (QNM) mode allowed topographical verification of the spatially specific secondary brush growth and its stimulus responsiveness. Chemical confirmation of selective polymer growth was achieved by secondary ion mass spectrometry (SIMS).

Hydrothermal Synthesis of Two Zinc Coordination Polymers with 1‐(1H‐Tetrazol‐5‐ylmethyl)‐1H‐benzotriazole Ligands

AbstractThe direct reaction of ZnBr2 with H‐1‐mbtz [1‐mbtz = 1‐(1H‐tetrazol‐5‐ylmethyl)‐1H‐benzotriazole] gives the two‐dimensional complex [Zn(Br)(1‐mbtz)] (1), whereas the reaction of benzotriazol‐1‐yl‐acetonitrile with NaN3 in the presence of water and a Lewis acid (ZnBr2) affords the 2D coordination polymer [Zn2(OH)(1‐mbtz)3H2O] (2). The central zinc atom in 1 is bonded to one terminal bromine atom and three different nitrogen atoms from two tetrazole ligands and one BTA group (BTA = benzotriazole), and each 1‐mbtz ligand is coordinated to three zinc atoms forming a 2D framework. The coordination polyhedron around the metal atom in 2 is a slightly distorted trigonal bipyramid made up by one zinc atom, four nitrogen atoms as well as one oxygen atom, two of the 1‐mbtz ligands coordinated to three zinc atoms and the third 1‐mbtz ligand acts in a bidentate fashion, which leads to the formation of a complicated 2D network. The syntheses and solid‐state structures of the two coordination polymers are reported.

Nucleophile-Dependent Regioselective Reaction of (S)-4-Benzyl-2-Fluoroalkyl-1,3-Oxazolines

Nucleophile-dependent regioselectivities in the nucleophilic reaction of (S)-4-benzyl-2-fluoroalkyl-1,3-oxazoline to different types of fluorinated compounds were investigated experimentally and theoretically. The ring opening of (S)-4-benzyl-2-bromodifluoromethyl-1,3-oxazoline by arenethiolates exclusively occurred at the C5 position of the 1,3-oxazoline ring, whereas completely different regioselectivity was observed for a unimolecular radical nucleophilic substitution (S(RN)1) at the terminal bromine atom of the CF2Br group when arenolates were employed as the nucleophiles. The reaction of (S)-4-benzyl-2-trifluoromethyl-1,3-oxazoline with nucleophiles such as arenethiols, arenols, and TMSCl underwent nucleophilic ring opening in a regiospecific way, while the use of TMSCF3 was determined to proceed through nucleophilic addition to the C═N bond.

Thermal 8π electrocyclic reaction of heteroarene tetramers: new efficient access to π-extended cyclooctatetraenes

Bromo-substituted acyclic thiazole tetramers selectively underwent an 8π thermal electrocyclic reaction at high temperatures of 280–300 °C without solvent, producing π-extended thiazole-fused cyclooctatetraenes (COTs) in high yields. A quantum chemical study provided a rationale for the lower activation barrier and high selectivity of the 8π electrocyclic reaction mode over a competitive 6π electrocyclic reaction. The terminal bromine atom acts as a leaving group to trigger the rearomatization of the electrocyclized intermediate, which leads to the formation of the energetically stable COT products. This synthetic protocol enables us to synthesize a series of thiazole-fused COTs, including a derivative that can form loosely stacked columnar arrays in the crystalline state and shows fluorescence in the solid state.

Synthesis and antibacterial evaluation of a new series of N-Alkyl-2-alkynyl/(E)-alkenyl-4-(1H)-quinolones.

To gain further insight into the structural requirements of the aliphatic group at position 2 for their antimycobacterial activity, some N-alkyl-4-(1H)-quinolones bearing position 2 alkynyls with various chain length and triple bond positions were prepared and tested for in vitro antibacterial activity against rapidly-growing strains of mycobacteria, the vaccine strain Mycobacterium bovis BCG, and methicillin-resistant Staphylococcus aureus strains, EMRSA-15 and -16. The compounds were also evaluated for inhibition of ATP-dependent MurE ligase of Mycobacterium tuberculosis. The lowest MIC value of 0.5 mg/L (1.2–1.5 µM) was found against M. fortuitum and M. smegmatis. These compounds displayed no or only weak toxicity to the human lung fibroblast cell line MRC-5 at 100 µM concentration. The quinolone derivatives exhibited pronounced activity against the epidemic MRSA strains (EMRSA-15 and -16) with MIC values of 2–128 mg/L (5.3–364.7 µM), and M. bovis BCG with an MIC value of 25 mg/L (66.0–77.4 µM). In addition, the compounds inhibited the MurE ligase of M. tuberculosis with moderate to weak activity showing IC50 values of 200–774 µM. The increased selectivity towards mycobacterial bacilli with reference to MRC-5 cells observed for 2-alkynyl quinolones compared to their corresponding 2-alkenyl analogues serves to highlight the mycobacterial specific effect of the triple bond. Exploration of a terminal bromine atom at the side chain of N-alkyl-2-(E)-alkenyl-4-(1H)-quinolones showed improved antimycobacterial activity whereas a cyclopropyl residue at N-1 was suggested to be detrimental to antibacterial activity.

Multibrominated Hyperbranched Polymers: Synthesis and Further Functionalizations by ARGET ATRP or Click Chemistry

Hyperbranched polymers with multiple alkyl bromide peripheral groups were synthesized by the copolymerization of styrene with ethylene glycol dimethacrylate (2.5, 5.0, 7.5, or 10.0 mol% relative to styrene) in the presence of CBr(4) (10-20-fold excess vs. the radical initiator). The latter compound markedly delayed the gelation and served as the source of terminal bromine atoms via transfer to the propagating radicals. The degree of branching increased with the amount of crosslinker. The alkyl bromide groups were used in further chemical modifications (ATRP at low catalyst concentration or azidation with NaN(3) followed by CuBr-catalyzed click coupling of an alkyne-terminated polymer) that yielded star copolymers with hyperbranched cores.

Vibrational investigations of new functionalized fullerenes

The vibrational properties of two fullerene derivatives: C60-fused N-methylpyrrolidine-5-(12-bromododecyl)thiophenyl (C60TH-DcB) and its modification (C60TH-Dc) has been studied. The vibrational properties were determined using the Raman scattering and infrared absorption spectroscopies supported by the quantum chemical calculations. The difference between two investigated molecules is very subtle. In the C60TH-DcB there is a terminal bromine atom attached to the end of the alkyl chain, while in C60TH-Dc this one atom is absent. The differences in the experimental spectra of both molecules are rather small but clear and they correspond quite well with the calculation results. The quantum chemical calculations of the normal modes of vibration let us describe these fingerprints and assign them to the specific vibrations of various functional groups of the molecule.

Surface active benzodiazepine-bromo-alkyl conjugate for potential GABAA-receptor purification

A conjugable analogue of the benzodiazepine 5-(2-hydroxyphenyl)-7-nitro-benzo[e][1,4]diazepin-2(3H)-one containing a bromide C(12)-aliphatic chain (BDC) at nitrogen N1 was synthesized. One-pot preparation of this benzodiazepine derivative was achieved using microwave irradiation giving 49% yield of the desired product. BDC inhibited FNZ binding to GABA(A)-R with an inhibition binding constant K(i) = 0.89 μM and expanded a model membrane packed up to 35 mN m(-1) when penetrating in it from the aqueous phase. BDC exhibited surface activity, with a collapse pressure π = 9.8 mN m(-1) and minimal molecular area A(min) = 52 Å(2)/molecule at the closest molecular packing, resulted fully and non-ideally mixed with a phospholipid in a monolayer up to a molar fraction x≅ 0.1. A geometrical-thermodynamic analysis along the π-A phase diagram predicted that at low x(BDC) (<0.1) and at all π, including the equilibrium surface pressures of bilayers, dpPC-BDC mixtures dispersed in water were compatible with the formation of planar-like structures. These findings suggest that, in a potential surface grafted BDC, this compound could be stabilize though London-type interactions within a phospholipidic coating layer and/or through halogen bonding with an electron-donor surface via its terminal bromine atom while GABA(A)-R might be recognized through the CNZ moiety.

Ring contraction of 1,3-bis(5-bromopentyl)alloxazine

The reaction of 1,3-bis(5-bromopentyl)alloxazine with ethylamine in propan-2-ol resulted in replacement of the terminal bromine atoms by ethylamino groups and was accompanied by contraction of the pyrimidine ring so that the products were 1,3-bis[5-(ethylamino)pentyl]alloxazine and 1,3-bis[5-(ethylamino)-pentyl]imidazo[4,5-b]quinoxalin-2-one.

Sodium dithionite initiated fluoroalkylation of trimethoxybenzenes, mesitylene and pyrroles with BrCF 2CF 2Br

Sodium dithionite initiated reaction of 1,2-dibromotetrafluoroethane with 1,3,5-trimethoxybenzene ( 1a) in an acetonitrile–water mixture proceeded efficiently at ambient temperature to give 1-(2-bromotetrafluoroethyl)-2,4,6-trimethoxybenzene ( 2) almost quantitatively. Similar reaction with 1,2,3-trimethoxybenzene ( 1b) gave only reasonable yield of regioisomers of (2-bromotetrafluoroethyl)-trimethoxybenzenes 3 and 4 and small amount of a substitution product of the central trimethoxy group, 1-(2-bromotetrafluoroethyl)-2,6-dimethoxybenzene ( 5). The reaction with mesitylene ( 6) gave complex mixtures from which, depending on the temperature and a mesitylene/BrCF 2CF 2Br ratio, the expected (2-bromotetrafluoroethyl)mesitylene ( 8) or a dimeric product, 4,4′-bis(2-bromo-1,1,2,2-tetrafluoroethyl)-1,3,5,1′,3′,5′-hexamethylbicyclohexyl-2,5,2′,5′-tetraene ( 7), were isolated in a yield of 18 and 13%, respectively. The reactions of BrCF 2CF 2Br with pyrrole ( 9) and 1-methylpyrrole ( 11) gave the respective alkylated compounds, 2-(2-bromotetrafluoroethyl)pyrrole ( 10) and 2-(2-bromotetrafluoroethyl)-1-methylpyrrole ( 12) in over 70% yields; the former was found to be fairly unstable. The reactivity of the terminal bromine atom in 1-(2-bromotetrafluoroethyl)-2,4,6-trimethoxybenzene ( 2) was also investigated.

A Facile Strategy for Preparation of α‐Heterobifunctional Polystyrenes with Well‐Defined Molecular Weight

A facile strategy for synthesis of α-heterobifunctional polystyrenes is reported. The novel functional polystyrenes have been successfully synthesized via a combination of atom transfer radical polymerization (ATRP) and chemical modification of end-functional groups. First, ε-caprolactone end-capped polystyrenes with controlled molecular weight and low polydispersity were prepared by ATRP of styrene using α-bromo-ε-caprolactone (αBrCL) as an initiator. Then, removal of the terminal bromine atom was performed with iso-propylbenzene in the presence of CuBr/PMDETA. Finally, ring-opening modifications of the caprolactone group were carried out with amines, n-butanol and H(2) O to produce novel polystyrenes containing two different functional groups at one end.

Intrinsic Gas-Phase Reactivity toward Methanol of Trinuclear Tungsten W3S4 Complexes Bearing W−X (X = Br, OH) Groups

Electrospray ionization (ESI) tandem mass spectrometry is used to investigate the gas-phase dissociation of trinuclear sulfide W(3)S(4) complexes containing three diphosphane ligands and three terminal bromine atoms, namely, [W(3)S(4)(dmpe)(3)(Br)(3)](+) (1(+)) or hydroxo groups, [W(3)S(4)(dmpe)(3)(OH)(3)](+) (2(+)) (dmpe = 1,2-bis(dimethylphosphanyl)ethane). Sequential evaporation of two diphosphane ligands is the sole fragmentation channel for the 1(+) cation that yields product ions with one or two unsaturated W-Br functional groups, respectively. Conversely, evaporation of one diphosphane ligand followed by two water molecules is observed for cation 2(+). Complementary deuterium-labeling experiments in conjunction with computational studies provide deep insight into the thermodynamically favored product ion structures found along the fragmentation pathways. From these results, the formation of a series of cluster cations with WBr, WOH, and WO functional groups either on saturated or unsaturated metal sites is proposed. The effect of the properties of these cluster cations, among them chemical composition and coordinative saturation, on their reactivity toward methanol is discussed.

Acceptability of blood and blood substitutes

Alternatives to donor blood have been developed in part to meet increasing demand. However, new biotechnologies are often associated with increased perceptions of risk and low acceptance. This paper reviews developments of alternatives and presents data, from a field-based experiment in the UK and Holland, on the risks and acceptance of donor blood and alternatives (chemical, genetically modified and bovine). UK groups perceived all substitutes as riskier than the Dutch. There is a negative association between perceived risk and acceptability. Solutions to increasing acceptance are discussed in terms of implicit attitudes, product naming and emotional responses.

Synthesis and Structure of Ta4S9Br8. An Emergent Family of Early Transition Metal Chalcogenide Clusters.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis and Structure of Ta4S9Br8. An Emergent Family of Early Transition Metal Chalcogenide Clusters

Single crystals of Ta4S9Br8 are obtained by heating Ta, S, and Br2 at 400 degrees C in a 4.0:9.0:4.0 molar ratio in a 44% yield. The structure was determined by X-ray analysis and consists of molecular clusters [Ta4(mu4-S)(mu-S2)4Br8]. The tantalum atoms form a square with long Ta...Ta distances (3.30 angstroms), with four S2 ligands bridging the Ta-Ta edges and one capping the square. Each Ta atom has two terminal bromine atoms. The compound is diamagnetic and has only two electrons for metal-metal bonding. IR and Raman spectral studies with the use of 34S allow to identify characteristic vibrations S-S (537 cm(-1)) and Ta4-mu4-S (407 cm(-1)). The compound is soluble in CH3CN, giving a dark-red solution with a characteristic electronic spectrum, which was assigned on the base of DFT calculations. ESI-MS spectra of the solutions show formation of [[Ta4S9Br8]Br]- associates.

Synthesis of Amphiphilic Graft Copolymers of n-Butyl Acrylate and Acrylic Acid by Atom Transfer Radical Copolymerization of Macromonomers

ω-Methacryloyl-functionalized poly(tert-butyl acrylate) (PtBA) and poly(n-butyl acrylate) (PnBA) macromonomers with different chain lengths were synthesized by atom transfer radical polymerization (ATRP). The terminal bromine atoms were removed by a chain transfer reaction and esterification. PnBA-g-PtBA graft copolymers and their “inverse” PtBA-g-PnBA counterparts with different chemical compositions were achieved by the “grafting through” approach via ATRP. The reactivity ratios of macromonomer and comonomer are close to unity, enabling the synthesis of graft copolymers with a statistical distribution of side chains. Amphiphilic PnBA-g-PAA graft copolymers and their “inverse” PAA-g-PnBA counterparts were achieved by quantitative hydrolysis of the poly(tert-butyl acrylate) segments to poly(acrylic acid) (PAA).