Gas-phase reactions of aryl radicals with 2-butyne: experimental and theoretical investigation employing the N-methyl-pyridinium-4-yl radical cation

Aromatic radicals form in a variety of reacting gas-phase systems, where their molecular weight growth reactions with unsaturated hydrocarbons are of considerable importance. We have investigated the ion-molecule reaction of the aromatic distonic N-methyl-pyridinium-4-yl (NMP) radical cation with 2-butyne (CH(3)C≡CCH(3)) using ion trap mass spectrometry. Comparison is made to high-level ab initio energy surfaces for the reaction of NMP and for the neutral phenyl radical system. The NMP radical cation reacts rapidly with 2-butyne at ambient temperature, due to the apparent absence of any barrier. The activated vinyl radical adduct predominantly dissociates via loss of a H atom, with lesser amounts of CH(3) loss. High-resolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry allows us to identify small quantities of the collisionally deactivated reaction adduct. Statistical reaction rate theory calculations (master equation/RRKM theory) on the NMP+2-butyne system support our experimental findings, and indicate a mechanism that predominantly involves an allylic resonance-stabilized radical formed via H atom shuttling between the aromatic ring and the C(4) side-chain, followed by cyclization and/or low-energy H atom β-scission reactions. A similar mechanism is demonstrated for the neutral phenyl radical (Ph˙)+2-butyne reaction, forming products that include 3-methylindene. The collisionally deactivated reaction adduct is predicted to be quenched in the form of a resonance-stabilized methylphenylallyl radical. Experiments using a 2,5-dichloro substituted methyl-pyridiniumyl radical cation revealed that in this case CH(3) loss from the 2-butyne adduct is favoured over H atom loss, verifying the key role of ortho H atoms, and the shuttling mechanism, in the reactions of aromatic radicals with alkynes. As well as being useful phenyl radical analogues, pyridiniumyl radical cations may form in the ionosphere of Titan, where they could undergo rapid molecular weight growth reactions to yield polycyclic aromatic nitrogen hydrocarbons (PANHs).     

Investigation of the electrophilic reactivity of the cytotoxic marine alkaloid discorhabdin B

The mechanisms of action of the cytotoxic marine pyrroloiminoquinone alkaloids the discorhabdins are unknown. We have determined that discorhabdin B acts as an electrophile towards biomimetic thiol nucleophiles leading to debrominated adducts. In contrast, less potent cytotoxins discorhabdins D and Q failed to react, supporting an SAR model of cytotoxicity requiring an orchestrated combination of an electrophilic Δ(1) carbon centre and a nucleophilic N-18 amine for potent activity. The stereospecific nature of nucleophile trapping exhibited by both enantiomers of discorhabdin B implies the biogenesis of ovothiol A substituted discorhabdins H, H(2), K and K(2) need not be mediated by enzymatic processes.     

Anion-dependent construction of two hexanuclear 3d-4f complexes with a flexible Schiff base ligand

Two hexanuclear 3d-4f Ni-Eu and Cu-Eu complexes [Eu(4)Ni(2)L(2)(OAc)(12)(EtOH)(2)] (1) and [Eu(4)Cu(2)L(2)(OAc)(12)]·2H(2)O (2) are reported which are formed from the salen type Schiff-base ligand H(2)L (H(2)L = N,N'-bis(3-methoxysalicylidene)butane-1,4-diamine). In both complexes, four Eu(3+) cations are bridged by eight OAc(-) groups and the chain is terminated at each end by two ML (M = Ni and Cu) units. The structures of 1 and 2 were determined by single crystal X-ray crystallographic studies and the luminescence properties of the free ligand and metal complexes in solution were measured.     

Tin(II) amide/alkoxide coordination compounds for production of Sn-based nanowires for lithium ion battery anode materials

A series of tin(II) amide alkoxides ([(OR)Sn(NMe(2))](n)) and tin(II) alkoxides ([Sn(OR)(2)](n)) were investigated as precursors for the production of tin oxide (SnO(x)) nanowires. The precursors were synthesized from the metathesis of tin dimethylamide ([Sn(NMe(2))(2)](2)) and a series of aryl alcohols {H-OAr = H-OC(6)H(4)(R)-2: R = CH(3) (H-oMP), CH(CH(3))(2) (H-oPP), C(CH(3))(3) (H-oBP)] or [H-OC(6)H(3)(R)(2)-2,6: R = CH(3) (H-DMP), CH(CH(3))(2) (H-DIP), C(CH(3))(3) (H-DBP)]}. The 1:1 products were all identified as the dinuclear species [(OAr)Sn(μ-NMe(2))](2) where OAr = oMP (1), oPP (2), oBP (3), DMP (4), DIP (5), DBP (6). The 1:2 products were identified as either a polymer ([Sn(μ-OAr)(2)](∞) (where OAr = oMP (7), oPP (8)), dinuclear [(OAr)Sn(μ-OAr)](2) (where OAr = oBP (9), DMP (10) or DIP/HNMe(2) (11)), or mononuclear [Sn(DBP)(2)] (12) complexes. These novel families of compounds (heteroleptic 1-6, and homoleptic 7-12) were evaluated for the production of SnO(x) nanowires using solution precipitation (SPPT; oleylamine/octadecene solvent system) or electrospinning (ES; THF solvent) processing conditions. The SPPT route that employed the heteroleptic precursors yielded mixed phases of Sn(o):romarchite [1 (100:0); 2 (80:20); 3 (68:32); 4 (86:14); 5 (66:35); 6 (88:12)], with a variety of spherical sized particles [1 (350-900 nm); 2 (150-1200 nm); 3 (250-950 nm); 4 (20-180 nm); 5 (80-400 nm); 6 (40-200 nm)]. For the homoleptic precursors, similar phased [7 (80:20); 8 (23:77); 9 (15:85); 10 (34:66); 11 (77:23); 12 (77:23)] spherical nanodots were isolated [7 (50-300 nm); 8: (irregular); 10 (200-800 nm); 11 (50-150 nm); 12 (50-450 nm)], except for 9 which formed polycrystalline rods [Sn(o):romarchite (15:85)] with aspect ratios >100. From ES routes, the heteroleptic species were found to form 'tadpole-shaped' materials whereas the homoleptic species formed electrosprayed nanodots. The one exception noted was for 7, where, without use of a polymer matrix, nanowires of Sn(o), decorated with micron sized 'balls' were observed. Due to the small amount of material generated, PXRD patterns were inconclusive to the identity of the generated material; however, cyclic voltammetry on select samples was used to tentatively identify the final Sn(o) (from 7) with the other sample identified as SnO(x) (from 1).     

Fully automatable two-dimensional hydrophilic interaction liquid chromatography-reversed phase liquid chromatography with online tandem mass spectrometry for shotgun proteomics

We have developed a fully automatable two-dimensional liquid chromatography platform for shotgun proteomics analyses based on the online coupling of hydrophilic interaction liquid chromatography (HILIC) - using a nonionic type of TSKgel Amide 80 at either pH 6.8 (neutral) or 2.7 (acidic) - with conventional low-pH reversed-phase chromatography. Online coupling of the neutral-pH HILIC and reversed phase chromatography systems outperformed the acidic HILIC-reversed phase chromatography combination, resulting in 18.4% (1914 versus 1617 nonredundant proteins) and 41.6% (12,989 versus 9172 unique peptides) increases in the number of identified peptides and proteins from duplicate analyses of Rat pheochromocytoma lysates. Armed with this optimized HILIC-reversed phase liquid chromatography platform, we identified 2554 nonredundant proteins from duplicate analyses of a Saccharomyces cerevisiae lysate, with the detected protein abundances spanning from approximately 41 to 10(6) copies per cell, which contained up to approximately 2092 different validated protein species with a dynamic range of concentrations of up to approximately 10(4) . This present study establishes a fully automated platform as a promising methodology to enable online coupling of different hydrophilic HILIC and reversed phase chromatography systems, thereby expanding the repertoire of multidimensional liquid chromatography for shotgun proteomics.     

Benzothiazolium-functionalized tetraphenylethene: an AIE luminogen with tunable solid-state emission

Melding a benzothiazolium unit with tetraphenylethene generates a new hemicyanine luminogen with aggregation-induced emission characteristics; the luminogen exhibits crystochromism and its solid-state emission can be repeatedly tuned from yellow or orange to red by grinding-fuming or grinding-heating processes due to the transformation from the crystalline to the amorphous state and vice versa.     

A strong two-photon induced phosphorescent Golgi-specific in vitro marker based on a heteroleptic iridium complex

A new heteroleptic iridium complex demonstrated low cytotoxicity and near-infrared excitation (via two-photon absorption) for target-specific in vitro Golgi imaging in various cell lines (HeLa and A549 cells) with two-photon absorption cross section (~350 GM) in DMSO.     

Road traffic noise exposure in residential complexes built at different times between 1950 and 2000 in Hong Kong

This paper attempts to determine the exposure of the urban population to road traffic noise living in residential complexes built at different times between 1950 and 2000 in Hong Kong. Noise exposure was estimated at the residents’ dwelling, neighborhood and community by noise mapping. The purpose of the study is to find out if the noise exposure levels of these residential complexes have improved as a result of stepped up noise control and reduction efforts. A total of 212 residential complexes built at different times, by the government and private sector in different districts, were selected for noise assessment. The results show that, compared to private housing, public housing estates are generally exposed to less road traffic noise. The study has also found that, over the 50-year period, the dwelling noise exposure levels of the recently built residential complexes are lower than the older ones, showing some improvement over time. This is particularly more noticeable at the high exposure end. There is however only some small differences in noise level between recent and old developments at the community scale both for public and private housing estates.     

Experimental investigation of the sound absorption performance of compartmented Helmholtz resonators

An experiment was derived in the present study to investigate the effects of coupling up two Helmholtz resonators on their overall sound absorption performance. The effect of compartmenting the cavity of a resonator on its sound absorption property was also discussed. Such cavity compartmentation in fact creates a coupled resonator with a front and a rear resonator. The results show that the coupling in many cases can improve the sound absorption capacity and widen the working bandwidth of the resonators provided that the uncoupled resonance frequency of the front resonator is larger than or equal to that of the rear resonator. Results also suggest that the best compartmentation is that with these uncoupled resonance frequencies very close to each other. It is also found that the undamped plane wave approach is sufficient to predict the resonance frequencies of the coupled resonators within engineering tolerance.     

Subfrequency noise signal extraction in fiber-optic strain sensors using postprocessing

Laser frequency fluctuations typically limit the performance of high-resolution interferometric fiber strain sensors. Using time delay interferometry, we demonstrate a frequency noise immune fiber sensing system, where strain signals were extracted well below the noise floor normally imposed by the frequency fluctuations of the laser. Initial measurements show a reduction in the noise floor by a factor of 30, with strain sensitivities of a nanostrain/Hz at 100 mHz and reaching 100 ps/Hz at 1 Hz. Further characterization of the system indicates the potential for at least 4.5 orders of magnitude frequency fluctuation rejection.