CH2 Br Research Articles

Encapsulation Characteristics of Cavitand Type Tetrabromo-Functionalized Resorcin[4]arenes in the Crystal Structure

Single crystal X-ray diffraction analysis of upper rim functionalized tetrabromo-resorcin[4]arenes are presented and their guest encapsulation abilities are discussed. The Br-atoms either attached directly to resorcinarene rim or extended by methylene group (CH2–Br). The substituents on the upper-rim plays an important role in the guest encapsulation characteristic of the resorcinarene cavity. In the crystal structure the host–guest supramolecular systems were stabilized by C–H⋯O, C–H⋯π and C⋯H···Br nonbonding interactions. The Hirshfeld surfaces analysis and the related 2D fingerprint plots provided qualitative and quantitative account of the various supramolecular non-bonding interactions present within the crystal. Guest encapsulation characteristic of tetrabromo-functionalized resorcin[4]arenes.

Substituent Effects on Photoinitiation Ability of Monoaminoanthraquinone-Based Photoinitiating Systems for Free Radical Photopolymerization under LEDs.

Three monoamino-substituted anthraquinone derivatives (AAQs), that is, 1-aminoanthraquinone (AAQ), 1-(methylamino)anthraquinone (MAAQ), and 1-(benzamido)anthraquinone (BAAQ), incorporated with various additives [e.g., triethanolamine (TEAOH) and phenacyl bromide (PhC(═O)CH2 Br)] are investigated for their roles as photoinitiating systems of free radical photopolymerization of (meth)acrylate monomers upon the exposure to UV to green LEDs. The AAQs-based photoinitiating systems, AAQ/TEAOH/PhC(═O)CH2 Br and BAAQ/TEAOH/PhC(═O)CH2 Br photoinitiators exhibit the highest efficiency for the free radical photopolymerization of DPGDA under the irradiation of blue LED and UV LED, respectively, which is consistent with the extent of overlap between their absorption spectra and the emission spectra of the LEDs. AAQ/TEAOH/PhC(═O)CH2 Br photoinitiator can also initiate the free radical photopolymerization of different (meth)acrylate monomers, with an efficiency dependent on the chemical structures of these monomers.

Pseudo-Gated Adsorption with Negligible Volume Change Evoked by Halogen-Bond Interaction in the Nanospace of MOFs.

The enhancement of gas adsorption utilizing weak interactions in porous compounds is highly demanding for the design of energy-efficient storage materials. Here, we present a rational design for such an adsorption process by using synergistic functions between dynamic motion in a local module and weak but specific host-guest interactions, that is, halogen-bond (XB) interactions in metal-organic frameworks (MOFs). We designed a new porous coordination polymer (PCP), that is, Br-PCP, the pore surfaces of which are decorated with -CH2 Br groups and could be useful for interaction with CO2 molecules. In accordance with our anticipation, in-situ studies suggest that the adsorption step at approximately 54 kPa during CO2 adsorption is indeed facilitated by XB interactions with little change in the structural volume. This approach of integrating flexible XB modules in rigid PCPs is applicable for designing advanced gas storage systems.

Functional Hyper-Crosslinked Polypyrene for Reductive Decolorization of Industrial Dyes and Effective Mercury Removal from Aqueous Media.

A rigid and valuable hyper-crosslinked polymer (HCP) has been synthesized from the polycyclic aromatic hydrocarbon pyrene: hyper-crosslinked polypyrene (HCPPy). HCPPy was prepared through a simple one-step Friedel-Crafts alkylation reaction that involves ZnBr2 -catalyzed crosslinking in the presence of an external crosslinker, bromomethyl methyl ether (BME). Interestingly, the unreacted bromomethyl groups (-CH2 Br) on the surface of HCPPy could be quantified, which later aided in modification as per our requirement. We aimed at modifying with disulfide-containing cystamine dihydrochloride (Cys-HCPPy). Cys-HCPPy exhibited an extended π-conjugated system with uniform (∼1 μm diameter) morphology and high porosity (specific surface area: 445 m2 g-1 ). As a fundamental application, the Cys-HCPPy composite was used as a sorbent to remove Hg2+ ions from aqueous media. Thus, at pH 6, the adsorption capacity for mercury ions reached 1124.82 mg g-1 after 24 h. Furthermore, the immobilization of Ag nanoparticles on the surface of Cys-HCPPy (Ag@Cys-HCPPy) enhanced the catalytic properties, which allowed for the reductive decolorization of industrial dyes such as methylene blue, methyl orange, and Congo Red in the presence of NaBH4 as a reducing agent.

Control of Interfacial Cl2 and N2O5 Reactivity by a Zwitterionic Phospholipid in Comparison with Ionic and Uncharged Surfactants.

Gas-liquid scattering experiments reveal that charge-separated but neutral (zwitterionic) surfactants catalyze the oxidation of dissolved Br- to Br2 by gaseous Cl2 at the surface of a 0.3 M NaBr/glycerol solution. Solutions of NaBr dissolved in glycerol with no surfactant were compared with solutions coated with zwitterionic, cationic, and anionic surfactants at dilute surface concentrations of 1.1 to 1.5 × 1014 cm-2 (less than 65% of maximum chain packing). The zwitterionic phospholipid enhances Cl2 conversion of Br- to Br2 by a factor of 1.61 ± 0.15, in comparison with a 14-fold enhancement by a cationic surfactant (tetrahexylammonium) and a five-fold suppression by an anionic surfactant (dodecyl sulfate). Further studies indicate that even an uncharged surfactant, monododecanoylglycerol, enhances Cl2 → Br2 production. Similar behavior is observed for the oxidation of Br- to Br2 by N2O5; it is just slightly suppressed by the phospholipid and strongly enhanced by the cationic surfactant. Collectively, these results suggest that attractions and repulsions between the negative Br- ions and the positive and negative charges of the surfactant headgroups draw Br- ions to the surface or repel them away. At low coverages, ion-induced dipole and dispersion interactions between the CH2 groups and Br- or Cl2 may also enhance reactivity. These results demonstrate that the hydrocarbon chains of loosely packed surfactants do not necessarily block gas-liquid reactions but that positively charged, and even uncharged, groups can instead facilitate reactions by bringing gas-phase and solution-phase reagents together in the interfacial region.

ChemInform Abstract: Functionalized Corannulene Carbocations: A Structural Overview

AbstractReview: [46 refs.

Functionalized corannulene carbocations: a structural overview.

A detailed structural overview of a family of bowl-shaped polycyclic aromatic carbocations of the type [C20 H10 R](+) with different R functionalities tethered to the interior surface of corannulene (C20 H10 ) is provided. Changing the identity of the surface-bound groups through alkyl chains spanning from one to four carbon atoms and incorporating a different degree of halogenation has led to the fine tuning of the bowl structures and properties. The deformation of the corannulene core upon functionalization has been revealed based on X-ray crystallographic analysis and compared for the series of cations with R=CH3 , CH2 Cl, CHCl2 , CCl3 , CH2 CH3 , CH2 CH2 Cl, and CH2 CH2 Br. The resulting carbocations have been isolated with several metal-based counterions, varying in size and coordinating abilities ([AlCl4 ](-) , [AlBr4 ](-) , [(SnCl)(GaCl4 )2 ](-) , and [Al(OC(CF3 )3 )4 ](-) ). A variety of aggregation patterns in the solid state has been revealed based on different intermolecular interactions ranging from cation-anion to π-π stacking and to halogen⋅⋅⋅π interactions. For the [C20 H10 CH2 Cl](+) ion crystallized with several different counterions, the conformation of the R group attached to the central five-membered ring of corannulene moiety was found to depend on the solid-state environment defined by the identity of anions. Solution NMR and UV/Vis investigations have been used to complement the X-ray diffraction studies for this series of corannulene-based cations and to demonstrate their different association patterns with the solvent molecules.

Reconstructing the discontinuous and conformational β1/β3-loop binding site on hFSH/hCG by using highly constrained multicyclic peptides.

Making peptide-based molecules that mimic functional interaction sites on proteins remains a challenge in biomedical sciences. Here, we present a robust technology for the covalent assembly of highly constrained and discontinuous binding site mimics, the potential of which is exemplified for structurally complex binding sites on the "Cys-knot" proteins hFSH and hCG. Peptidic structures were assembled by Ar(CH2 Br)2-promoted peptide cyclizations, combined with oxime ligation and disulfide formation. The technology allows unprotected side chain groups and is applicable to peptides of different lengths and nature. A tetracyclic FSH mimic was constructed, showing >600-fold improved binding compared to linear or monocyclic controls. Binding of a tricyclic hCG mimic to anti-hCG mAb 8G5 was identical to hCG itself (IC50 =260 vs. 470 pM), whereas this mimic displayed an IC50 value of 149 nM for mAb 3468, an hCG-neutralizing antibody with undetectable binding to either linear or monocyclic controls.

Gold and gold–graphene used as cathodic interfaces for scission of carbon–halogen bonds. Application to the building of anthraquinone-Au electrodes

Gold (smooth or covered with a thin layer of graphene) is an efficient free-radical scavenger when used as cathode material. This first work points out the immobilization of anthraquinone (AQ) in organic polar solvents containing tetraalkylammonium salts. It appears that Au and graphene, when negatively polarized (E>−1.0V vs. Ag/AgCl), may react towards 2-bromomethylantraquinone (AQ–CH2–Br) in different ways: with Au, a fast adsorption followed by one-electron transfer leads to a robust radical modification of the interface, whereas the presence of graphene permits the formation of a benzyl-type radical readily trapped by the graphene layer. Two different redox stable electrodes are thus produced. Additionally, stability of gold–graphene–AQ electrodes could be successfully tested in aqueous buffered solutions.

Ultrafast acquirement of combined time and frequency spectroscopic data

The incorporation of spectral resolution in time resolved Four Wave Mixing spectroscopy provides important information for the interpretation of the observed spectra. We demonstrate experimentally a new method whereby the combined time and frequency resolved information may be obtained within a single laser pulse. The method is based on Phase Matching Spectral Filtering for the tuning of the generated nonlinear signal, which in turn utilizes the constraints imposed by strict phase matching of parallel input beams in our geometrical arrangement. The measurements were performed on a simple molecule (CH 2Br 2), and are used for identification of molecular degrees of freedom not otherwise possible in pure time resolved methods.

The relationship between volatile halocarbons and phytoplankton pigments during a Trichodesmium bloom in the coastal eastern Arabian Sea

Eukaryotic phytoplankton such as diatoms and prymnesiophytes produce biogenic halocarbons in the ocean that serve as important sources of chlorine and bromine to the atmosphere, but the role of cyanobacteria in halocarbon production is not well established. We studied distributions of chloroform (CHCl 3), carbon tetrachloride (CCl 4), methylene bromide (CH 2Br 2) and bromoform (CHBr 3) in relation to phytoplankton composition, determined from pigment analysis complemented by microscopic examination, for one month in coastal waters of the eastern Arabian that experienced a Trichodesmium bloom that typically occurs during the Spring Intermonsoon season. High concentrations of zeaxanthin (23 μg l −1), alpha beta betacarotene (6 μg l −1) and chlorophyll a (67 μg l −1) were found within the bloom whereas the marker pigment concentrations were low outside the bloom. CHCl 3 and CCl 4 occurred in relatively high concentrations in surface waters whereas CH 2Br 2 and CHBr 3 were restricted to the subsurface layer. Chlorinated halocarbons were positively inter-correlated and with CHBr 3. The observed spatial and temporal trends in brominated compounds appear to be related to the abundance of Trichodesmium although correlations between concentrations of brominated compounds with various marker pigments were poor and statistically non-significant. The results support the existence of multiple sources and sinks of halogenated compounds, which might obscure the relationship between halocarbons and phytoplankton composition.

Femtosecond photolysis of CH 2Br 2 in acetonitrile: Capturing the bromomethyl radical and bromine-atom charge transfer complex through deep-to-near UV probing

Dibromomethane (CH 2Br 2) in acetonitrile is a suitable precursor to characterize the absorption signatures of the CH 2Br radical and solvent Br charge-transfer complexes. Following irradiation of CH 2Br 2 at 255 nm, the iso-H 2C Br Br isomer product rapidly converts back to the parent species, and transient absorption spectra reveal the bands of solvent-separated radical species, the CH 2Br radical peaking at 235 nm, as well as the CH 3CN·Br complex at 272 nm. The absorption of CH 2Br exhibits minor solvatochromic shifts upon going from acetonitrile to cyclohexane, and the molecular decadic extinction coefficient of CH 3CN·Br is estimated to be 1470 M −1 cm −1.

Mixed-metal single-molecule magnets: Syntheses, structure, and magnetic properties of [Mn 8Fe 4O 12(O 2CR) 16(H 2O) 4] (R = CH 2Cl, CH 2Br, CHCl 2)

Three mixed-metal single-molecule magnets containing [Mn 8Fe 4O 12] 16+ cores are synthesized and characterized. The reaction of FeCl 2·4H 2O with KMnO 4 and RCOOH (R = CH 2Cl, CH 2Br) in H 2O gives [Mn 8Fe 4O 12(O 2CR) 16(H 2O) 4] (R = CH 2Cl ( 1), CH 2Br ( 2)) in yields of 43% and 40%, respectively. Treatment of complex 1 with an excess of CHCl 2COOH in CH 2Cl 2 gives [Mn 8Fe 4O 12(O 2CCHCl 2) 16(H 2O) 4]·CH 2Cl 2·10H 2O ( 3·CH 2Cl 2·10H 2O) in a yield of 83%. The X-ray structure analysis reveals that all three complexes consist of a trapped-valence dodecanuclear core comprising 4Mn III, 4Fe III, and 4Mn IV ions. DC magnetic susceptibility and magnetization measurements indicate that all three complexes exhibit intramolecular antiferromagnetic interaction, resulting in an S = 4 ground state. In addition, frequency-dependent out-of-phase AC magnetic susceptibility signals at low temperature for complexes 1, 2, and 3 are indicative of their single-molecule magnetism behavior.

Studies on oxy-bromination of methane and coke deposition over FePO 4/SiO 2 catalysts

Different FePO 4/SiO 2 catalysts have been synthesized and employed for the oxy-bromination of methane reaction. The long-term stability experiments and the influences of FePO 4 loading and reaction temperature have been investigated. It was demonstrated that the FePO 4/SiO 2 catalysts were very stable during 200 h time-on-stream. High total selectivity for CH 3Br plus CO with equimolar ratio could be achieved by manipulating the reaction variables. However, coke deposition was found on the used catalysts after a long running period. Characterization techniques such as N 2-adsorption, Fourier-transform infrared spectroscopy and temperature-programmed oxidation were employed to investigate the fresh and used samples. The characterization results implied that the accumulation of CH 2Br 2 during the reaction could be the direct cause of coke deposition.

Photoionization of two substituted methyl radicals: Cyanomethyl and bromomethyl

The photoionization of two substituted methyl radicals is presented. Cyanomethyl (CH 2CN) and bromomethyl (CH 2Br) were generated by flash pyrolysis from chloroacetonitrile and bromonitromethane. Mass-selective threshold photoelectron spectra of both radicals were recorded. The adiabatic ionization energies of CH 2CN and CH 2Br have been determined to be 10.28 eV ± 20 meV and 8.62 eV ± 10 meV. CH 2Br shows a vibrational progression upon ionization that is assigned to the C–Br stretch mode. The photoionization of the precursors as well as the dissociative photoionization of CH 2Br were examined. A 0 K heat of formation of 174.5 kJ mol −1 is derived for CH 2Br and a C–Br bond dissociation energy of 334.1 kJ mol −1.

Theoretical study on the hydrogen bond interaction of 1:1 supermolecular complexes of protonated adrenaline with formate anion and its derivatives

The hydrogen bond (H-bond) interaction of 1:1 supermolecular complexes of protonated adrenaline (PAd +) with formate anion and its derivatives (denoted as RCOO −, R H, CH 3, CH 2F, CH 2Cl, and CH 2Br) has been investigated by performing density functional theory calculations at the B3LYP/6-31G+(d) level. We obtained the most stable three conformations for each complex, which are denoted as PAd +–RCOO −(I), PAd +–RCOO −(II), PAd +–RCOO −(III), respectively, and calculated the interaction energy between PAd + and RCOO −. In all PAd +–RCOO − complexes, PAd +–CH 3COO − is found to be the most favorable energetically. There exists low-barrier hydrogen bond (LBHB) in PAd +–HCOO −(III), PAd +–CH 2FCOO −(III), PAd +–CH 2ClCOO −(III), and PAd +–CH 2Br −(III) complexes. The solvent effects on the geometry and energy of the complexes are also considered by using the polarizable continuum model (PCM) model in aqueous solvent. It is found that PAd +–R − complexes in solution are significantly less stable than those in the gas-phase. The theoretical results for the present model systems will be useful for experimental researchers working in this field.

The enthalpies of formation of brominated benzenes and phenols: A theoretical prediction

The enthalpies of formation of brominated benzenes and phenols were predicted using Gaussian-4 (G4), G3X, and G3XMP2 model chemistries and a few popular density functional methods, coupled with homodesmic reactions (HR1) and (HR2) in which C 6H 6, C 6H 5Br, and C 6H 5OH are used as reference compounds. The results from G4, G3X, and G3XMP2 agree closely within 2 kJ/mol for all brominated benzenes and phenols; while the results from density functional methods are systematically higher than the G4 ones. The predicted enthalpies of formation for 2- and 4-bromophenols are in close agreement with the recent experimental measurements. Three reactions (R1)–(R3) were also used to derive Δ f H 298 K ° (g, C 6H 5Br) = 98.7 ± 1.0 kJ/mol by using CH 4, CH 3Br, CH 2Br 2, CH 2CHBr, and C 6H 6 as reference compounds at G4 and G3X levels. The value is significantly lower than the only experimental value of 105.4 kJ/mol given by Cox and Pilcher in 1970, and a re-determination is called.

The formation and back isomerization of iso-H 2C–Br–Br on a 100-ps time scale following 255-nm excitation of CH 2Br 2 in acetonitrile

Following 255-nm excitation of CH 2Br 2 in acetonitrile, the formation and decay of the iso-H 2C–Br–Br species is monitored through its visible transient absorption in the 338–612 nm range. The sub-100 ps decay time constant contrasts the previously reported stability of this isomer on a nanosecond timescale in cyclohexane. Different possible decays channels of iso-H 2C–Br–Br are simulated using CCSD and CCSD(T) calculations and we found that the isomerization back to the CH 2Br 2 structure is the lowest energy decay pathway in acetonitrile. The energy barrier for the reverse isomerization process decreases from 10.6 to 3.7 kcal mol −1, in cyclohexane and acetonitrile, respectively.

Short-term variability in halocarbons in relation to phytoplankton pigments in coastal waters of the central eastern Arabian Sea

Halocarbons released from oceans are known to be important in the atmospheric processes. Their abundance in seawater is influenced by water column conditions and phytoplankton community. In the present study halocarbon abundances together with pigment composition were monitored in the coastal waters of the central eastern Arabian Sea. Short-term variability for the period December 2005–March 2007 was studied for chlorinated hydrocarbons (CHCl 3, CCl 4) and bromocarbons (CH 2Br 2 and CHBr 3) for the first time in the Arabian Sea. Variability in pigments was used to understand the influence of phytoplankton community composition on halocarbon concentrations in this region. Halocarbons and phytoplankton pigments showed strong short-term variability, with maximal values generally associated with southwest (summer) monsoon high productivity. Decreased chlorocarbon abundances in sub-surface layers indicate their possible consumption under oxygen deficient conditions, particularly during the summer monsoon and Fall-Intermonsoon periods. Halocarbon abundances were in the order: CHCl 3, CH 2Br 2, CHBr 3 and CCl 4. The CHCl 3 showed significant positive relationship with fucoxanthin ( r = 0.93, p = 0.001, n = 155) suggesting the importance of diatoms and prymnesiophytes in the Arabian Sea. Among the phytoplankton pigments chlorophyll- a showed a positive relationship with marker pigment fucoxanthin. Of the four phytoplankton groups studied, the percent dominance was in the order: diatoms > nanoflagellates > cyanobacteria > dinoflagellates. Our study shows that the utilization of halocarbons during microbial oxidation of organic matter could be a significant sink of these compounds although they might be produced in significant quantities by biochemical processes during high productivity periods, as can be seen from our observations in summer monsoon in the Arabian Sea.

Vibrational spectra, normal modes, ab initio and DFT calculations for 6-Chloro- and 7-Chloro-4-bromomethylcoumarins

Vibration spectral measurements – Infrared (4000–400 cm −1) and Raman (3500–50 cm −1) spectra – have been made for the solid samples of 6-Chloro- and 7-Chloro-4-bromomethylcoumarins. Ground electronic state energies, equilibrium geometries, harmonic vibrational spectra and normal modes have been computed using ab initio – RHF/6-31G* – and DFT – B3LYP/6-31G* levels of theory. The optimization yielded three structures for each molecule, with one being a transition state structure. Of the remaining two conformers, one belongs to C s symmetry and the other belongs to C 1, the latter being the most stable one. The optimized dihedral angle for –CH 2Br group is 111° in agreement with X-ray diffraction results reported for the similar molecular systems. Assignment of all the observed spectral bands has been proposed. The absorptions show band pattern revealing isomer characteristics and vibrational coupling in varying degrees; the Raman spectra show structural changes associated with the rings as well as lattice modes.