George R. Dubay

Nanoparticle MALDI-TOF Mass Spectrometry without Fragmentation: Au25(SCH2CH2Ph)18 and Mixed Monolayer Au25(SCH2CH2Ph)18−x(L)x

Intact molecular ions of the organothiolate-protected nanoparticle Au25(SCH2CH2Ph)18, including their isotopic resolution, can be observed at 7391 Da as 1- and 1+ ions in negative and positive mode, respectively, by MALDI-TOF mass spectrometry when using a tactic of threshold laser pulse intensities and trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile (DCTB) as matrix. Previous MALDI-TOF studies of Au nanoparticles using other matrices have encountered extensive fragmentation of nanoparticle as well as thiolate ligands. Absence of fragmentation enables precise determination of the distribution of mixed monolayer compositions on nanoparticles prepared by ligand exchange reactions and by synthesis using thiol mixtures. Reaction conditions producing mixed monolayers containing only one or a small number of usefully functional ligands can be readily identified. At increased laser pulse intensity, the first fragmentation step(s) for the Au25(SCH 2CH2Ph)18 nanoparticle results in losses of AuL units and, in particular, loss of Au4(SCH2CH2Ph)4.

Burkholdines 1097 and 1229, potent antifungal peptides from Burkholderia ambifaria 2.2N

Potent antifungal cyclic lipopeptides, burkholdines (Bk), were isolated from a culture of Burkholderia ambifaria 2.2N. Bk-1229 (1) and Bk-1097 (2) are octapeptides comprised of nonproteinogenic amino acids, including beta-hydroxytyrosine, beta-hydroxyasparagine, and a new fatty acyl amino acid. 1 and 2 are fungicidal against a panel of fungi with potencies 2-60-fold better than amphotericin B control.

The "secret" in secretions: methodological considerations in deciphering primate olfactory communication.

Olfactory communication in primates is gaining recognition; however, studies on the production and perception of primate scent signals are still scant. In general, there are five tasks to be accomplished when deciphering the chemical signals contained in excretions and secretions: (1) obtaining the appropriate samples; (2) extracting the target organic compounds from the biological matrix; (3) separating the extracted compounds from one another (by gas chromatography, GC or liquid chromatography, LC); (4) identifying the compounds (by mass spectrometry, MS and associated procedures); and (5) revealing biologically meaningful patterns in the data. Ultimately, because some of the compounds identified in odorants may not be relevant, associated steps in understanding signal function involve verifying the perception or biological activity of putative semiochemicals via (6) behavioral bioassays or (7) receptor response studies. This review will focus on the chemical analyses and behavioral bioassays of volatile, primate scent signals. Throughout, we highlight the potential pitfalls of working with highly complex, chemical matrices and suggest ways for minimizing problems. A recurring theme in this review is that multiple approaches and instrumentation are required to characterize the full range of information contained in the complex mixtures that typify primate or, indeed, many vertebrate olfactory cues. Only by integrating studies of signal production with those verifying signal perception will we better understand the function of olfactory communication. Am. J. Primatol. 75:621–642, 2013.

FAB mass spectrometry of Au25(SR)18 nanoparticles.

The molecular ion of the nanoparticle Au 25(SCH 2CH 2Ph) 18 (A 25(SR) 18) is observed at 7394 Da in fast atom bombardment (FAB, Xe atoms) ionization mass spectrometry using a 3-nitrobenzyl alcohol matrix. A distinctive pattern of positive fragment ions is evident in the mass interval 5225-7394 Da, where peaks are seen for successive mass losses equivalent to R 2S entities. Because the Au 25(SCH 2CH 2Ph) 18 nanoparticle structure is crystallographically known to consist of a centered Au 13 icosahedral core surrounded by six Au 2(SR) 3 semirings, the R 2S loses are proposed to represent serial rearrangements and decompositions of the semiring structures. Mass losses equivalent to R 2S 2 and R 2 entities also appear at the lower end of this mass interval. The most intense spectral peak, at m/ z = 5246 Da, is assigned to the fragment Au 25S 10, from which all of the CH 2CH 2Ph organic units have been cleaved but from which no gold atoms have been lost. A different pattern of fragmentation is observed at lower masses, producing ions corresponding to serial losses of one gold atom and varied numbers of sulfur atoms, which continues down to a Au 9S 2 fragment. FAB mass spectra of the Au nanoparticle are much easier to interpret than laser desorption/ionization spectra, but they show more extensive fragmentation than do electrospray and low laser pulse intensity MALDI spectra. The loss of R 2S fragmentation in FAB is distinctive and unlike that seen in the other ionization modes. The FAB spectrum for the nanoparticle Au 25(S(CH 2) 9CH 3) 18 is also reported; its fragmentation parallels that for Au 25(SCH 2CH 2Ph) 18, implying that this nanoparticle has the same surprising stellated (staples) structure.

SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS. XVIII. INDOMETHACIN

Abstract— The photochemistry, photophysics, and photosensitization (Type I and II) of indomethacin (IN) (N‐[p‐chlorobenzoyl]‐5‐methoxy‐2‐methylindole‐3‐acetic acid) has been studied in a variety of solvents using NMR, high performance liquid chromatography‐mass spectroscopy, transient spectroscopy, electron paramagnetic resonance in conjunction with the spin trapping technique, and the direct detection of singlet molecular oxygen (l O2) luminescence. Photodecomposition of IN (λex > 330 nm) in degassed or air‐saturated benzene proceeds rapidly to yield a major (2; N‐[p‐chlorobenzoyl]‐5‐methoxy‐2‐methyl‐3‐methylene‐indoline) and a minor (3; N‐[p‐chlorobenzoyl]‐5‐methoxy‐2, 3‐dimethyl‐indole) decarboxylated product and a minor indoline (5; 1‐en‐5‐methoxy‐2‐methyl‐3‐methylene‐in‐doline), which is formed by loss of the p‐chlorobenzoyl moiety. In air‐saturated solvents two minor oxidized products 4 (N‐[p‐chlorobenzoyl]‐5‐methoxy‐2‐methylindol‐3‐aldehyde) and 6 (5‐methoxy‐2‐methyl‐indole‐3‐aldehyde) are also formed. When photolysis was carried out in 18O2‐saturated benzene, the oxidized products 4 and 6 contained 18O, indicating that oxidation was mediated by dissolved oxygen in the solvent. In more polar solvents such as acetonitrile or ethanol, photodecomposition is extremely slow and inefficient. Phosphorescence of IN at 77 K shows strong solvent dependence and its emission is greatly reduced as polarity of solvent is increased. Flash excitation of IN in degassed ethanol or acetonitrile produces no transients. A weak transient is observed at 375 nm in degassed benzene, which is not quenched by oxygen. Irradiation of IN (λex > 325 nm) in N2‐gassed C6H6 in the presence of 5, 5‐dimethyl‐1‐pyrroline‐N‐oxide (DMPO) results in the trapping of two carbon‐centered radicals by DMPO. One adduct was identified as DMPO/.COC6H4‐p‐CI, while the other was probably derived from a radical formed during IN decarboxylation. In air‐saturated benzene, (hydro) peroxyl and alkoxyl radical adducts of DMPO are observed. A very weak luminescence signal from 1O2 at 1268 nm is observed initially upon irradiation (λex= 325 nm) of IN in air‐saturated benzene or chloroform. The intensity of this 1O2 signal increases as irradiation is continued suggesting that the enhancement in 1O2 yield is due to photoproduct(s). Accordingly, when 2 and 3 were tested directly, 2 was found to be a much better sensitizer of 1O2 than IN. In air‐saturated ethanol or acetonitrile no IN 1O2 luminescence is detected even on continuous irradiation. The inability of IN to cause phototoxicity may be related to its photo stability in polar solvents, coupled with the low yield of active oxygen species (1O2, O2−‐) upon UV irradiation.

Social odours covary with bacterial community in the anal secretions of wild meerkats

The fermentation hypothesis for animal signalling posits that bacteria dwelling in an animal’s scent glands metabolize the glands’ primary products into odorous compounds used by the host to communicate with conspecifics. There is, however, little evidence of the predicted covariation between an animal’s olfactory cues and its glandular bacterial communities. Using gas chromatography-mass spectrometry, we first identified the volatile compounds present in ‘pure’ versus ‘mixed’ anal-gland secretions (‘paste’) of adult meerkats (Suricata suricatta) living in the wild. Low-molecular-weight chemicals that likely derive from bacterial metabolism were more prominent in mixed than pure secretions. Focusing thereafter on mixed secretions, we showed that chemical composition varied by sex and was more similar between members of the same group than between members of different groups. Subsequently, using next-generation sequencing, we identified the bacterial assemblages present in meerkat paste and documented relationships between these assemblages and the host’s sex, social status and group membership. Lastly, we found significant covariation between the volatile compounds and bacterial assemblages in meerkat paste, particularly in males. Together, these results are consistent with a role for bacteria in the production of sex- and group-specific scents, and with the evolution of mutualism between meerkats and their glandular microbiota.