Multi-criteria ranking and source apportionment of airborne particulate matter

Particulate matter research is essential because of the well known significant adverse effects of aerosol particles on human health and the environment. In particular, identification of the origin or sources of particulate matter emissions is of paramount importance in assisting efforts to control and reduce air pollution in the atmosphere. This thesis aims to: identify the sources of particulate matter; compare pollution conditions at urban, rural and roadside receptor sites; combine information about the sources with meteorological conditions at the sites to locate the emission sources; compare sources based on particle size or mass; and ultimately, provide the basis for control and reduction in particulate matter concentrations in the atmosphere. To achieve these objectives, data was obtained from assorted local and international receptor sites over long sampling periods. The samples were analysed using Ion Beam Analysis and Scanning Mobility Particle Sizer methods to measure the particle mass with chemical composition and the particle size distribution, respectively. Advanced data analysis techniques were employed to derive information from large, complex data sets. Multi-Criteria Decision Making (MCDM), a ranking method, drew on data variability to examine the overall trends, and provided the rank ordering of the sites and years that sampling was conducted. Coupled with the receptor model Positive Matrix Factorisation (PMF), the pollution emission sources were identified and meaningful information pertinent to the prioritisation of control and reduction strategies was obtained. This thesis is presented in the thesis by publication format. It includes four refereed papers which together demonstrate a novel combination of data analysis techniques that enabled particulate matter sources to be identified and sampling site/year ranked. The strength of this source identification process was corroborated when the analysis procedure was expanded to encompass multiple receptor sites. Initially applied to identify the contributing sources at roadside and suburban sites in Brisbane, the technique was subsequently applied to three receptor sites (roadside, urban and rural) located in Hong Kong. The comparable results from these international and national sites over several sampling periods indicated similarities in source contributions between receptor site-types, irrespective of global location and suggested the need to apply these methods to air pollution investigations worldwide. Furthermore, an investigation into particle size distribution data was conducted to deduce the sources of aerosol emissions based on particle size and elemental composition. Considering the adverse effects on human health caused by small-sized particles, knowledge of particle size distribution and their elemental composition provides a different perspective on the pollution problem. This thesis clearly illustrates that the application of an innovative combination of advanced data interpretation methods to identify particulate matter sources and rank sampling sites/years provides the basis for the prioritisation of future air pollution control measures. Moreover, this study contributes significantly to knowledge based on chemical composition of airborne particulate matter in Brisbane, Australia and on the identity and plausible locations of the contributing sources. Such novel source apportionment and ranking procedures are ultimately applicable to environmental investigations worldwide.

Mechanical bending properties of sodium titanate (Na2Ti3O7) nanowires

We report on the mechanical properties of sodium titanate nanowires (Na2Ti3O7 NW) through a combination of bending experiments and theoretical analysis. Na2Ti3O7 NWs with lateral dimensions ranging from 20–700 nm were synthesized by a hydrothermal approach. A focused ion beam (FIB) was used to manipulate the selected Na2Ti3O7 NW over a hole drilled in an indium tin oxide substrate. After welding the nanowire, a series of bending tests was performed. It was observed that the Na2Ti3O7 NW exhibits a brittle behavior, and a nonlinear elastic deformation was observed before failure. By using the modified Euler–Bernoulli beam theory, such nonlinear elastic deformation is found to originate from a combination of surface effects and axial elongation (arising from the bending deformation). The effective Young's modulus of the Na2Ti3O7 NW was found to be independent of the wire length, and ranges from 21.4 GPa to 45.5 GPa, with an average value of 33 ± 7 GPa. The yield strength of the Na2Ti3O7 NW is measured at 2.7 ± 0.7 GPa.

Hybrid chalcogenide nanoparticles : 2D-WS2 nanocrystals inside nested WS2 fullerenes

The MOCVD assisted formation of nested WS2 inorganic fullerenes (IF-WS2) was performed by enhancing surface diffusion with iodine, and fullerene growth was monitored by taking TEM snapshots of intermediate products. The internal structure of the core-shell nanoparticles was studied using scanning electron microscopy (SEM) after cross-cutting with a focused ion beam (FIB). Lamellar reaction intermediates were found occluded in the fullerene particles. In contrast to carbon fullerenes, layered metal chalcogenides prefer the formation of planar, plate-like structures where the dangling bonds at the edges are stabilized by excess S atoms. The effects of the reaction and annealing temperatures on the composition and morphology of the final product were investigated, and the strength of the WS2 shell was measured by intermittent contact-mode AFM. The encapsulated lamellar structures inside the hollow spheres may lead to enhanced tribological activities.

Wear particle analysis and the evolution of the plastically deformed layer on Australian rail steel

Particle analysis methodology is presented, together with the morphology of the wear debris formed during rolling contact fatigue. Wear particles are characterised by their surface topography and in terms of wear mechanism. Rail-wheel materials are subjected to severe plastic deformation as the contact loading progresses, which contributes to a mechanism of major damage in head-hardened rail steel. Most of the current methodologies involve sectioning of the rail-wheel discs to trace material damage phenomena such as crack propagation and plastic strain accumulation. This paper proposes methodology to analyse the development of the plastically deformed layer by sectioning wear particles using the focussed ion beam (FIB) milling method. Moreover, it highlights the processes of oxidation and rail surface delamination during unlubricated rolling contact fatigue.

Structure of 2',3'-O-Isopropylidene-5'-O-tosyluridine, C19H22N 2Oas

M r = 438.45, trigonal, P32, a = b = 13.385 (4), c = 9.900 (5) A,, V = 1536.0 A 3, Z = 3, D x = 1.42, D m = 1.42 Mg m -3, 2(Cu Ka) = 1.5418 A,,g(CuKa) = .800mm -], T=290K, F(000)=690, R=6.0% for 1222 unique reflections with F o>_2o(Fo). This is the first 2',3'-O-isopropylidene pyrimidine nucleoside with the base in a syn orientation with respect to the ribose [Xcy= 116.0(7)°]. The ribose has a C(3')-endo conformation with the phase angle of pseudorotation P = 16.36 (2) °. The dioxolane ring assumes an envelope conformation with 0(2') displaced from the best four-atom plane by 0.50 (1) k. The crystal structure is possibly stabilized by a bifurcated hydrogen bond between N(3) and the 0(2) and 0(4) atoms of screw-related molecules.

Structure of Disodium Deoxyeytidine 5'-Phosphate Heptahydrate, C9H 12N30TP2-.2N a +. 7H 20

M,=477.3, orthorhombic, P2~2~2~, a= 6.719.(4), b=29.614(15), c= 9.559 (3) ~, Z=4, U-- 1902.0 A 3, D x = 1.67 Mg m -3, 2(Cu Ka) = 1.5418A, /~=l.90mm -1, T=290K. Final R for 1809 observed reflections is 0.045. The structure shows an unusual gauche-trans conformation about the C(4')-C(5') bond, while the sugar pucker [C(3')-exo] and glycosidic torsion angle [)CCN = 70.2 (5) °, anti] are normal. The two Na + ions do not interact with the molecule directly, being completely surrounded by water molecules. The cytosine bases are stacked, with a separation distance of 3.36 (5) A.

2-(p-Chlorophenyl)-3-nitro-2H-chromene

C15H10C1NO3, Mr=287.70, triclinic, PI, Z= 2, F(000)= 296, a = 5.422 (1), b = 9.624 (1), c= 12.636 (2) A, ~= 76.66 (2), fl= 78.67 (2), ~= 87.97 (2) ° , V=629.03 A 3, Din= 1.507 (3), Ox= 1.519Mgm -3, 2(CuKa)=l.5418A, p=26.25mm -~, T= 413 K, final R = 0.0577 for 1859 observed reflections [I>2.5e(/)]. Bond lengths [1.512(5)A] and angles [109.2 (3) °] at the phenyl substitution site are comparable with those in other molecules. The bond angle at the nitro substitution site C(7)-C(8)-C(9) is 122.9 (3) ° owing to the electron-withdrawing character of the nitro group. The pyran ring adapts a half-chair conformation.

Reinvestigation of the structure of Feist's acid 3-methylene-trans-1,2-cyclopropanedicarboxylic acid

C6H604, Mr = 142, triclinic, P[, a = 4.842(1), b = 7.607(1), c = 9.168 (3) A, ~ = 98.41(2), fl = 99.89(2), y = 77.74(1) ° , V = 320.9/k 3, Z = 2, Dm= 1.45 (flotation), D x = 1.470 g cm -3, p(Mo Ktt, 2 = 0.7107 A) = 0.63 cm -~, F(000) = 148. The structure was solved by direct methods and refined to an R value of 0.038 for 723 intensity measurements. The geometrical changes in the cyclopropane ring are discussed in the light of substituent effects. In the crystal structure the carboxylic groups are disordered.

Structural Studies of Analgesics and Their Interactions. VIII.* Rotational Isomerism and Disorder in the Crystal Structure of Meelofenamie Acid

Meclofenamic acid, C I4HIICI2NO2, probably the most potent among analgesic fenamates, crystallizes in the triclinic space group P1, with a = 8.569 (5), b = 8.954(8), c -- 9.371 (4) A, ct = 103.0 (2), fl -- 103.5 (2), y = 92.4 (2) ° , Z = 2, D m = 1.43 (4), D c = 1.41 Mg m -3. The structure was solved by direct methods and refined to R = 0.135 for 1062 observed reflections. The anthranilic acid moiety in the molecule is nearly planar and is nearly perpendicular to the 2,6-dichloro-3-methylphenyl group. The molecules, which exist as hydrogen-bonded dimers, have an internal hydrogen bond involving the imino and the carboxyl groups. The methyl group is disordered and occupies two positions with unequal occupancies. The disorder can be satisfactorily explained in terms of the rotational isomerism of the 2,6-dichloro-3-methylphenyl group about the bond which connects it to the anthranilic acid moiety and the observed occupancies on the basis of packing considerations.

L-Tyrosyl-L-glutarnie Acid Monohydrate, C14H18N206.H20

Mr=328.32, triclinic, P1, a=5.801 (1), b=7.977(1), c=9.110(2)A, ~t=102.33 (1), fl= 97.92 (1), y= 109.82 (1) °, v= 377.2 (1) A 3 at 293 K, Z=I, D x=1.45, D m=1.45 g cm -3, 2(MoKs)= 0.7107 A, ~ = 0.74 cm -1, F(000) = 174.0. R = 0.046 for 990 unique observed [F o > 4O(Fo)] reflections. The crystal structure is stabilized by extensive hydrogen bonding involving all N and O atoms.

Conformational Choices for the Stereochemically Constrained gamma-Amino Acid Residue Gabapentin: Theoretical Studies and Correlation With Experimental Results

Gabapentin (1-aminomethylcyclohexaneacetic acid, Gpn) is an achiral, conformationally constrained gamma amino acid residue. A survey of available crystal structures of Gpn peptides reveals that the torsion angles about the C-gamma-C-beta (theta(1)) and C-beta-C-alpha(theta(2)) bonds are overwhelmingly limited to gauche, gauche (g(+)g(+)/g(-)g(-)) conformations. The Gpn residue forms C-7 and C-9 hydrogen bonds in which the donor and acceptor atoms come from the flanking peptide units. In combination with alpha amino acid residues alpha gamma and gamma alpha segments can adopt C-12 hydrogen bonded structures. The conformational choices available to the Gpn residue have been probed using energy calculations, adopting a grid search strategy. Ramachandran phi-psi maps have been constructed for fixed values of theta(1) and theta(2), corresponding to the gauche and trans conformations. The sterically allowed and energetically favorable regions of conformational space have been defined and experimental observations compared. C-7 and C-9 hydrogen bonded conformational families have been identified using a grid search approach in which theta(1) and theta(2) values are varied over a range of +/- 10 degrees about ideal values at 1 degrees intervals. The theoretical analysis together with experimental observations for 59 Gpn residues from 35 crystal structures permits definition of the limited range of conformational possibilities at this gamma amino acid residue. .

Gabapentin: A Stereochemically Constrained gamma Amino Acid Residue in Hybrid Peptide Design

Nature has used the all-alpha-polypeptide backbone of proteins to create a remarkable diversity of folded structures. Sequential patterns of 20 distinct amino adds, which differ only in their side chains, determine the shape and form of proteins. Our understanding of these specific secondary structures is over half a century old and is based primarily on the fundamental elements: the Pauling alpha-helix and beta-sheet. Researchers can also generate structural diversity through the synthesis of polypeptide chains containing homologated (omega) amino acid residues, which contain a variable number of backbone atoms. However, incorporating amino adds with more atoms within the backbone introduces additional torsional freedom into the structure, which can complicate the structural analysis. Fortunately, gabapentin (Gpn), a readily available bulk drug, is an achiral beta,beta-disubstituted gamma amino add residue that contains a cyclohexyl ring at the C-beta carbon atom, which dramatically limits the range of torsion angles that can be obtained about the flanking C-C bonds. Limiting conformational flexibility also has the desirable effect of increasing peptide crystallinity, which permits unambiguous structural characterization by X-ray diffraction methods. This Account describes studies carried out in our laboratory that establish Gpn as a valuable residue in the design of specifically folded hybrid peptide structures. The insertion of additional atoms into polypeptide backbones facilitates the formation of intramolecular hydrogen bonds whose directionality is opposite to that observed in canonical alpha-peptide helices. If hybrid structures mimic proteins and biologically active peptides, the proteolytic stability conferred by unusual backbones can be a major advantage in the area of medicinal chemistry. We have demonstrated a variety of internally hydrogen-bonded structures in the solid state for Gpn-containing peptides, including the characterization of the C-7 and C-9 hydrogen bonds, which can lead to ribbons in homo-oligomeric sequences. In hybrid alpha gamma sequences, district C-12 hydrogen-bonded turn structures support formation of peptide helices and hairpins in longer sequences. Some peptides that include the Gpn residue have hydrogen-bond directionality that matches alpha-peptide helices, while others have the opposite directionality. We expect that expansion of the polypeptide backbone will lead to new classes of foldamer structures, which are thus far unknown to the world of alpha-polypeptides. The diversity of internally hydrogen-bonded structures observed in hybrid sequences containing Gpn shows promise for the rational design of novel peptide structures incorporating hybrid backbones.

Asymmetric total synthesis of erythromycin. 3. Total synthesis of erythromycin

In the preceding paper' we described the preparation of the key lactone intermediate la in optically active form. In this paper we report the synthesis of erythromycin (2) from la. In essence,this transformation involves the glycosidation of a suitable derivative of la with L-cladinose and D-desosamine and the generation of the C-9 ketone functionality.

Hybrid peptide design. Hydrogen bonded conformations in peptides containing the stereochemically constrained gamma-amino acid residue, gabapentin

he crystal structure of 12 peptides containing the conformationally constrained 1-(aminomethyl)cyclohexaneacetic acid, gabapentin (Gpn), are reported. In all the 39 Gpn residues conformationally characterized so far, the torsion angles about the C-alpha-C-beta and C-beta-C-gamma bonds are restricted to the gauche conformation (+/- 60 degrees). The Gpn residue is constrained to adopt folded conformations resulting in the formation of intramolecularly hydrogen-bonded structures even in short peptides. The peptides Boc-Ac(6)c-Gpn-OMe 1 and Boc-Gpn-Aib-Gpn-Aib-OMe 2 provide examples of C-7 conformation; peptides Boc-Gpn-Aib-OH 3, Boc-Ac(6)c-Gpn-OH 4, Boc-Val-Pro-Gpn-OH 5, Piv-Pro-Gpn-Val-OMe 6, and Boc-Gpn-Gpn-Leu-OMe 7 provide examples of C-9 conformation; peptide Boc-Ala-Aib-Gpn-Aib-Ala-OMe 8 provides an example of C-12 conformation and peptides Boc-beta Leu-Gpn-Val-OMe 9 and Boc-beta Phe-Gpn-Phe-OMe 10 provide examples of C-13 conformation. Gpn peptides provide examples of backbone expanded mimetics for canonical alpha-peptide turns like the gamma (C-7) and the beta (C-10) turns. The hybrid beta gamma sequences provide an example of a mimetic of the C-13 alpha-turn formed by three contiguous alpha-amino acid residues. Two examples of folded tripeptide structures, Boc-Gpn-beta Phe-Leu-OMe 11 and Boc-Aib-Gpn-beta Phg-NHMe 12, lacking internal hydrogen bonds are also presented. An analysis of available Gpn residue conformations provides the basis for future design of folded hybrid peptides.

Molecular dynamics studies of nanoparticle impacts

This thesis concerns the dynamics of nanoparticle impacts on solid surfaces. These impacts occur, for instance, in space, where micro- and nanometeoroids hit surfaces of planets, moons, and spacecraft. On Earth, materials are bombarded with nanoparticles in cluster ion beam devices, in order to clean or smooth their surfaces, or to analyse their elemental composition. In both cases, the result depends on the combined effects of countless single impacts. However, the dynamics of single impacts must be understood before the overall effects of nanoparticle radiation can be modelled. In addition to applications, nanoparticle impacts are also important to basic research in the nanoscience field, because the impacts provide an excellent case to test the applicability of atomic-level interaction models to very dynamic conditions. In this thesis, the stopping of nanoparticles in matter is explored using classical molecular dynamics computer simulations. The materials investigated are gold, silicon, and silica. Impacts on silicon through a native oxide layer and formation of complex craters are also simulated. Nanoparticles up to a diameter of 20 nm (315000 atoms) were used as projectiles. The molecular dynamics method and interatomic potentials for silicon and gold are examined in this thesis. It is shown that the displacement cascade expansionmechanism and crater crown formation are very sensitive to the choice of atomic interaction model. However, the best of the current interatomic models can be utilized in nanoparticle impact simulation, if caution is exercised. The stopping of monatomic ions in matter is understood very well nowadays. However, interactions become very complex when several atoms impact on a surface simultaneously and within a short distance, as happens in a nanoparticle impact. A high energy density is deposited in a relatively small volume, which induces ejection of material and formation of a crater. Very high yields of excavated material are observed experimentally. In addition, the yields scale nonlinearly with the cluster size and impact energy at small cluster sizes, whereas in macroscopic hypervelocity impacts, the scaling 2 is linear. The aim of this thesis is to explore the atomistic mechanisms behind the nonlinear scaling at small cluster sizes. It is shown here that the nonlinear scaling of ejected material yield disappears at large impactor sizes because the stopping mechanism of nanoparticles gradually changes to the same mechanism as in macroscopic hypervelocity impacts. The high yields at small impactor size are due to the early escape of energetic atoms from the hot region. In addition, the sputtering yield is shown to depend very much on the spatial initial energy and momentum distributions that the nanoparticle induces in the material in the first phase of the impact. At the later phases, the ejection of material occurs by several mechanisms. The most important mechanism at high energies or at large cluster sizes is atomic cluster ejection from the transient liquid crown that surrounds the crater. The cluster impact dynamics detected in the simulations are in agreement with several recent experimental results. In addition, it is shown that relatively weak impacts can induce modifications on the surface of an amorphous target over a larger area than was previously expected. This is a probable explanation for the formation of the complex crater shapes observed on these surfaces with atomic force microscopy. Clusters that consist of hundreds of thousands of atoms induce long-range modifications in crystalline gold.