Autocorrelation infrared analysis of mineralogical samples: the influence of user controllable experimental parameters

Autocorrelation infrared (ACIR) analysis is based upon the application of the autocorrelation function corr(alpha,omega') = integral(-infinity)(infinity) alpha(omega + omega') alpha(omega) d omega to standard Fourier transform infrared (FTIR) transmission spectra. We present a rigorous examination of the effect of experimental parameters such as dilution ratio, spectral resolution, grinding time and pressing conditions upon the ACIR analysis of haematite. Results were found to vary by less than 4.5% irrespective of sample preparation, instrumental and data collection parameters. For a series of perovskite samples, the relationship between the measured effective linewidth and material composition appears to be reproducible, even though the absolute magnitudes of delta corr values do not. Our results further indicate that the ACIR technique is indeed valid for comparative analysis of synthetic sample sequences that vary slightly in composition or structural state, provided that primary spectra are all recorded by the same instrument.     

Diastereoselective synthesis of glutamate-appended oxolane rings: synthesis of (s)-(+)-lycoperdic acid

The stereocontrolled synthesis of the glutamate-containing natural product (S)-(+)-lycoperdic acid is described. The key transformation in the synthetic route was an efficient diastereoselective annulation of an oxolane ring onto a pyroglutamate scaffold to construct either a gamma,gamma-disubstituted glutamate-appended tetrahydrofuran or a gamma-lactone. The reaction sequence also featured an improved method for the halogenation of pyroglutamate derivatives in high yield with enhanced stereoselection.     

Curcumin Loaded Dendrimers Specifically Reduce Viability of Glioblastoma Cell Lines

Glioblastoma (GB) is a deadly and aggressive cancer of the CNS. Even with extensive resection and chemoradiotherapy, patient survival is still only 15 months. To maintain growth and proliferation, cancer cells require a high oxidative state. Curcumin, a well-known anti-inflammatory antioxidant, is a potential candidate for treatment of GB. To facilitate efficient delivery of therapeutic doses of curcumin into cells, we encapsulated the drug in surface-modified polyamidoamine (PAMAM) dendrimers. We studied the in vitro effectiveness of a traditional PAMAM dendrimer (100% amine surface, G4 NH₂), surface-modified dendrimer (10% amine and 90% hydroxyl-G4 90/10-Cys), and curcumin (Cur)-encapsulated dendrimer (G4 90/10-Cys-Cur) on three species of glioblastoma cell lines: mouse-GL261, rat-F98, and human-U87. Using an MTT assay for cell viability, we found that G4 90/10-Cys-Cur reduced viability of all three glioblastoma cell lines compared to non-cancerous control cells. Under similar conditions, unencapsulated curcumin was not effective, while the non-modified dendrimer (G4 NH₂) caused significant death of both cancerous and normal cells. By harnessing and optimizing the components of PAMAM dendrimers, we are providing a promising new route for delivering cancer therapeutics. Our results with curcumin suggest that antioxidants are good candidates for treating glioblastoma.     

Coinage metal aluminyl complexes: probing regiochemistry and mechanism in the insertion and reduction of carbon dioxide

The synthesis of coinage metal aluminyl complexes, featuring M–Al covalent bonds, is reported via a salt metathesis approach employing an anionic Al(i) (‘aluminyl’) nucleophile and group 11 electrophiles. This approach allows access to both bimetallic (1 : 1) systems of the type (^tBu₃P)MAl(NON) (M = Cu, Ag, Au; NON = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene) and a 2 : 1 di(aluminyl)cuprate system, K[Cu{Al(NON)}₂]. The bimetallic complexes readily insert heteroallenes (CO₂, carbodiimides) into the unsupported M–Al bonds to give systems containing a M(CE₂)Al bridging unit (E = O, NR), with the μ-κ¹(C):κ²(E,E′) mode of heteroallene binding being demonstrated crystallographically for carbodiimide insertion in the cases of all three metals, Cu, Ag and Au. The regiochemistry of these processes, leading to the formation of M–C bonds, is rationalized computationally, and is consistent with addition of CO₂ across the M–Al covalent bond with the group 11 metal acting as the nucleophilic partner and Al as the electrophile. While the products of carbodiimide insertion are stable to further reaction, their CO₂ analogues have the potential to react further, depending on the identity of the group 11 metal. (^tBu₃P)Au(CO)₂Al(NON) is inert to further reaction, but its silver counterpart reacts slowly with CO₂ to give the corresponding carbonate complex (and CO), and the copper system proceeds rapidly to the carbonate even at low temperatures. Experimental and quantum chemical investigations of the mechanism of the CO₂ to CO/carbonate transformation are consistent with rate-determining extrusion of CO from the initially-formed M(CO)₂Al fragment to give a bimetallic oxide that rapidly assimilates a second molecule of CO₂. The calculated energetic barriers for the most feasible CO extrusion step (ΔG^‡ = 26.6, 33.1, 44.5 kcal mol⁻¹ for M = Cu, Ag and Au, respectively) are consistent not only with the observed experimental labilities of the respective M(CO)₂Al motifs, but also with the opposing trends in M–C (increasing) and M–O bond strengths (decreasing) on transitioning from Cu to Au.

The differential reactivity of copper, silver and gold aluminyl compounds towards CO₂ and other heteroallenes are probed by experimental and quantum chemical methods.     

CO‐irredundant Ramsey numbers for graphs

The study of the CO‐irredundant Ramsey numbers t(n₁, ···, n_k) is initiated. It is shown that several values and bounds for these numbers may be obtained from the well‐studied generalized graph Ramsey numbers and the values of t(4, 5), t(4, 6) and t(3, 3, m) are calculated. © 2000 John Wiley & Sons, Inc. J Graph Theory 34: 258–268, 2000     

Structural Classification and General Principles for the Design of Spherical Molecular Hosts

Cryptands, carcerands, polyoxometalates, and molecular capsules are cagelike hosts that complex guests through encapsulation. Following the discovery of a nanometer scale supramolecular shell-like spheroid, these and other shell-like hosts were structurally classified. Their frameworks may be catalogued according to principles of solid geometry. This has led to the identification of hosts that have not yet been synthesized or discovered (such as the cuboctahedron shown; X=O, S) and should lead to the design of additional container assemblies.     

Electrophysiological Responses of Bactrocera kraussi (Hardy) (Tephritidae) to Rectal Gland Secretions and Headspace Volatiles Emitted by Conspecific Males and Females

Pheromones are biologically important in fruit fly mating systems, and also have potential applications as attractants or mating disrupters for pest management. Bactrocera kraussi (Hardy) (Diptera: Tephritidae) is a polyphagous pest fruit fly for which the chemical profile of rectal glands is available for males but not for females. There have been no studies of the volatile emissions of either sex or of electrophysiological responses to these compounds. The present study (i) establishes the chemical profiles of rectal gland contents and volatiles emitted by both sexes of B. kraussi by gas chromatography–mass spectrometry (GC–MS) and (ii) evaluates the detection of the identified compounds by gas chromatography–electroantennogram detection (GC–EAD) and –electropalpogram detection (GC–EPD). Sixteen compounds are identified in the rectal glands of male B. kraussi and 29 compounds are identified in the rectal glands of females. Of these compounds, 5 were detected in the headspace of males and 13 were detected in the headspace of females. GC–EPD assays recorded strong signals in both sexes against (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane, 2-ethyl-7-mehtyl-1,6-dioxaspiro[4.5]decane isomer 2, (E,Z)/(Z,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane, and (Z,Z)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane. Male antennae responded to (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane, 2-methyl-6-pentyl-3,4-dihydro-2H-pyran, 6-hexyl-2-methyl-3,4-dihydro-2H-pyran, 6-oxononan-1-ol, ethyl dodecanoate, ethyl tetradecanoate and ethyl (Z)-hexadec-9-enoate, whereas female antennae responded to (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane and 2-methyl-6-pentyl-3,4-dihydro-2H-pyran only. These compounds are candidates as pheromones mediating sexual interactions in B. kraussi.     

Particle size distributions of silver nanoparticles at environmentally relevant conditions

Silver nanoparticles (Ag NPs) are becoming increasingly popular as antimicrobial agents in consumer goods with consequent risk to environmental health from discharges. Environmentally relevant fate and transport investigations are limited but essential to gain understanding towards bioavailability and toxicology. In this study, monodisperse 15 nm citrate-stabilised Ag NPs were synthesised, characterised and then fractionated by flow field-flow fractionation (FlFFF) at environmentally relevant conditions (pH 5 or 8, presence of natural organic macromolecules (NOM) and presence of sodium or calcium). At low ionic strength, Ag NPs particle size increased as pH increased from 5 to 8. However, changing the ionic strength from 10⁻³ to 10⁻² M Na increased instability of the Ag NPs, and loss of peak at pH 5 but in the presence of humic substance (HS), a reduction in NP size was seen, most likely due to a reduction in the diffuse layer. The presence of Ca²⁺ ions, at the higher ionic strengths caused complete loss of the solution Ag NPs with or without HS, most likely due to aggregation. At the lower Ca²⁺ ionic strength the Ag NPs were still unstable, but again, in the presence of HS the NPs were largely dispersed. The presence of HS improved stability of Ag NPs under these conditions by forming a surface coating resulting in both steric and charge stabilisation. This work implies that Ag NPs could have long residence times in aquatic systems in the presence of HS potentially resulting in increased bioavailability.