Determining the composition of aqueous microdroplets with broad-band cavity enhanced Raman scattering

We demonstrate that broad-band cavity enhanced Raman scattering (CERS) can be used to determine the composition of binary alcohol-water aerosol droplets over a wide compositional range from 10% v/v to 90% v/v. In contrast to conventional CERS using narrow-band laser excitation, the excitation is provided by a broad-band Nd:YAG pumped dye laser. A change in the spontaneous spectrum resulting from the change of the linewidth of the excitation laser permits tuning of the sensitivity range over which the droplet composition can be determined by CERS. We demonstrate that this change in sensitivity can be estimated using a simulation of the change in the sensitivity to the species in spontaneous bulk phase measurements. We further show that the compositional calibration is independent of droplet radius in the range 33-56 microm. The compositional range over which CERS is sensitive can be controlled and optimised for any particular application by exploiting the dependence of the stimulated Raman scattering on the laser linewidth and wavelength. Thus, quantitative measurements of droplet composition can be made in situ with high accuracy, providing a valuable new tool for analysing aerosol composition.     

Probing spin-orbit mixing and the singlet-triplet gap in dichloromethylene via Ka-sorted emission spectra

The magnitude of the singlet-triplet gap in dichloromethylene (CCl(2)) has been a point of controversy in the recent literature. In this study, we report single vibronic level emission spectra of the A(1)B(1)-->X[combining tilde](1)A(1) system of the carbene C(35)Cl(2), which probes the vibrational structure of the X[combining tilde](1)A(1) state up to approximately 10,000 cm(-1) above the vibrationless level. By the careful selection of bands where complete isotope and K(a)' selectivity in excitation was possible, we measured K(a)'-sorted emission spectra in order to test the previously established hypothesis [M.-L. Liu, C.-L. Lee, A. Bezant, G. Tarczay, R. J. Clark, T. A. Miller and B.-C. Chang, Phys. Chem. Chem. Phys., 2003, 5, 1352] that unassigned lines lying above approximately 5,000 cm(-1) belong to levels of the ?(3)B(1) state. The K(a)'-sorting method discriminates between singlet and triplet levels via the (A'-B[combining macron]') rotational constant, which is significantly larger for pure triplet levels due to the larger equilibrium bond angle. In the region between 3,500 and 9,000 cm(-1) above the vibrationless level of the X[combining tilde](1)A(1) state, we find only a very modest increase in (A'-B[combining macron]'), and approximately 86% of the lines observed between 5,000 and 9,000 cm(-1) can be assigned to X[combining tilde](1)A(1) levels within 3 standard deviations of our Dunham expansion fit, which included more than 140 levels in total. A nearly complete set of Dunham parameters was determined for the C(35)Cl(2) isotopomer, and the X[combining tilde](1)A(1) state term energies up to 4,000 cm(-1) are in excellent agreement with recent variational calculations of Tarczay, et al. [G. Tarczay, T. A. Miller, G, Czakó and A. G. Császár, Phys. Chem. Chem. Phys., 2005, 7, 2881]. Finally, the implication of our results for the singlet-triplet gap in dichloromethylene is discussed.     

Eremostachiin: a new furanolabdane diterpene glycoside from Eremostachys glabra

The reversed-phase preparative HPLC analysis of the methanol extract of the rhizomes of Eremostachys glabra (Lamiaceae) led to the isolation of two furanolabdane diterpene glycosides, phlomisoside II, and beta-D-glucopyranosyl-(1-->2)-beta-D-glucopyranosyl ester of phlomisoic acid (named eremostachiin), the latter being a novel natural product. The structure of the new compound has been elucidated unambiguously by HRMS and a series of 1D- and 2D-NMR spectroscopic techniques. The free radical scavenging activity of these compounds was assessed using the DPPH assay.     

Analysis of the ambruticin and jerangolid gene clusters of Sorangium cellulosum reveals unusual mechanisms of polyketide biosynthesis

Ambruticins and jerangolids are structurally related antifungal polyketides produced by Sorangium cellulosum strains. Comparative analysis of the gene clusters and characterization of compounds produced by gene knockout strains suggested hypothetical schemes for biosynthesis of these compounds. Polyketide synthase (PKS) architecture suggests that the pyran ring structure common to ambruticins and jerangolids forms by an intramolecular reaction on a PKS-bound intermediate. Disrupting ambM, encoding a discrete enzyme homologous to PKS C-methyltransferase domains, gave 15-desmethylambruticins. Thus, AmbM is required for C-methylation, but not pyran ring formation. Several steps in the post-PKS modification of ambruticin involve new enzymology. Remarkably, the methylcyclopropane ring and putative carbon atom excision during ambruticin biosynthesis apparently occur on the PKS assembly line. The mechanism probably involves a Favorskii rearrangement, but further work is required to elucidate these complex events.     

The vibrational spectrum of the stable free radical 1,1,3,3-tetramethylisoindolin-2-yloxyl

Solid and solution IR and Raman spectra of a stable nitroxide radical, 1,1,3,3-tetramethylisoindolin-2-yloxyl (TMIO), are reported and compared to ab initio density functional theory calculations of the vibrational frequencies to obtain unequivocal band assignments, in particular of the NO stretching frequency, nu(NO). The band position was found to be at 1431 cm(-1) for the solid, which is well outside the previously published range of 1310-1380 cm(-1) for nitroxide radicals. This apparently anomalous peak position was confirmed by undertaking isotopic substitution studies through the preparation and recording of vibrational spectra of tetrakis(trideuteriomethyl)isoindolin-2-yloxyl ([2H12]-TMIO) and [2H12,15N]-TMIO analogues. Solution spectra of TMIO in methanol and CCl4 are assessed for possible solvent-dependent spin density distribution effects in the NO bond.     

Electronic spectroscopy of the A1A" <--> X1A' system of CDBr

We report fluorescence excitation and single vibronic level emission spectra of jet-cooled CDBr in the 450-750 nm region. A total of 32 cold bands involving the pure bending levels 2(0)n with n=3-10 and combination bands 2(0)n3(0)1 (n=2-10), 2(0)n3(0)2 (n=2-9), 1(0)(1)2(0)n (n=7-10), and 1(0)(1)2(0)n3(0)(1) (n=6,8-9) in the A1A" <-- X1A' system of this carbene were observed; most of these are reported and/or rotationally analyzed here for the first time. Rotational analysis yielded band origins and effective (B) rotational constants for both bromine isotopomers (CD79Br and CD81Br). The derived A1A" vibrational intervals are combined with results of Yu et al. [J. Chem. Phys. 115, 5433 (2001)] to derive barriers to linearity for the 2n, 2n3(1), and 2n3(2) progressions. The A1A" state C-D stretching frequency (2350 cm(-1)) is determined for the first time, in excellent agreement with theory, as are the 79Br-81Br isotope splittings in the excited state. Our emission spectra probe the vibrational structure of the X1A' and a3A" states up to approximately 9000 cm(-1) above the vibrationless level of the X1A' state; the total number of levels observed is around twice that previously reported. Unlike CHBr, where even the lowest bending levels are perturbed by spin-orbit interaction with the triplet origin, the term energy of every level save one below 3000 cm(-1) in CDBr is reproduced by a Dunham expansion to within a standard deviation of 1 cm(-1), and a spin-orbit coupling matrix element of approximately 330 cm(-1) is derived from a deperturbation analysis of the triplet origin. The multireference configuration interaction (MRCI) calculations of Yu et al. [J. Chem. Phys. 115, 5433 (2001)] well reproduce triplet perturbations in the pure bending manifold, and globally, the vibrational frequencies of X1A', a3A", and A1A" are in excellent agreement with theoretical predictions.     

Characterization of ornithine and glutamine lipids extracted from cell membranes of Rhodobacter sphaeroides

The identification and structural characterization of a series of ornithine lipids extracted from the cell membranes of wild-type Rhodobacter sphaeroides, as well as from a glycerophosphocholine-deficient strain, have been achieved by multistage tandem mass spectrometry of their protonated and deprotonated precursor ions in a linear quadrupole ion trap. Systematic examination of the multistage gas-phase fragmentation reactions of these ions, combined with the use of hydrogen/deuterium exchange, has enabled the pathways responsible for sequential losses of the 3-hydroxy linked fatty acyl chain and the amide linked 3-OH fatty acyl chain from these lipids, as well as for formation of the previously reported ornithine specific positively charged "fingerprint" ion at m/z 115, to be determined. Additionally, the fragmentation pathways responsible for formation of a previously unreported ornithine lipid head group-specific product ion at m/z 131 in negative ion mode have been examined. Based on these results, and by comparison with the fragmentation behavior of model lipoamino acid standard compounds, a series of novel glutamine containing lipids have also been identified, with analogous structures but with masses 14 Da higher than those of several of the ornithine lipids observed in this study. Characteristic "fingerprint" ions indicative of these glutamine lipids were found at m/z 147, 130, and 129 in positive ion mode and at m/z 145 and 127 in negative ion mode. The results from this study establish an experimental basis for future efforts aimed at the sensitive identification, characterization, and quantitative analysis of ornithine and glutamine lipids in complex unfractionated cellular extracts.     

Role of community tolerance level (CTL) in predicting the prevalence of the annoyance of road and rail noise

Fidell et al. [(2011), J. Acoust. Soc. Am. 130(2), 791-806] have shown (1) that the rate of growth of annoyance with noise exposure reported in attitudinal surveys of the annoyance of aircraft noise closely resembles the exponential rate of change of loudness with sound level, and (2) that the proportion of a community highly annoyed and the variability in annoyance prevalence rates in communities are well accounted for by a simple model with a single free parameter: a community tolerance level (abbreviated CTL, and represented symbolically in mathematical expressions as L(ct)), expressed in units of DNL. The current study applies the same modeling approach to predicting the prevalence of annoyance of road traffic and rail noise. The prevalence of noise-induced annoyance of all forms of transportation noise is well accounted for by a simple, loudness-like exponential function with community-specific offsets. The model fits all of the road traffic findings well, but the prevalence of annoyance due to rail noise is more accurately predicted separately for interviewing sites with and without high levels of vibration and/or rattle.     

Phase behaviour of SMA/PMMA blends: the influence of processing at low and high deformation rates

The influence of processing parameters (deformations) on SMA/PMMA blend phase behaviour is studied. It is found that injection moulding does change polymer blend phase behaviour. Phase separation kinetics are important to understand the injection moulding experiments and the kinetics are probably influenced by the deformations caused by the injection moulding proces. Capillary flow causes a complex change of polymer blend phase behaviour showing both deformation induced mixing and redemixing. Short capillaries, causing almost only uniaxial elongation in combination with pressure, cause no change to polymer blend phase behaviour. This is probably due to the short time the deformation is imposed to the material: it is expected that elongation is a main parameter causing changes in polymer blend phase behaviour. Parallel plate rheometer experiments show that applying only shear causes a complex change of phase behaviour showing both shear induced mixing and redemixing.