Quorum sensing (QS) is a process that allows bacteria to sense the population density of cells around them by communicating with each other via autoinducer molecules. This cross-communication is crucial in the regulation of bacterial processes such as bioluminescence, virulence, and biofilm formation. Previous research by Milburn and Makemson on Vibrio harveyi suggested that in addition of the known biosynthesis of three well-characterized autoinducers, dozens of unknown molecules are also produced and released to the environment by V. harveyi. This study was performed using electrospray tandem mass spectrometry with the purpose of detection and characterization of the extracellular molecules produced by V. harveyi, and assessment of their relationship to QS. A total of 11 molecules were characterized, from which three could be related to QS. These findings provide a glimpse of the nature of novel secondary metabolites produced by V. harveyi and provide the groundwork for further research.

No description available.

<p> Over recent years, Ion Mobility&ndash;Mass Spectrometry (IMS&ndash;MS) measurements have become a widely used tool in a number of disciplines of scientific relevance, including, in particular, the structural characterization of mass-selected biomolecules such as proteins, peptides, or lipids, brought into the gas-phase using a variety of ionization methods. In these structural studies, the measured electrical mobilities are customarily interpreted in terms of a collision cross-section, based on the classic kinetic theory of ion mobility. For ideal ions interacting as smooth, rigid-elastic hard-spheres with also-spherical gas molecules, this <i>collision cross-section</i> (CCS) is identical to the <i>true</i>, geometric cross section. On the other hand, for real ions with non-perfectly spherical geometries and atomically-rough surfaces, subject to long-range interactions with the gas molecules, the expression for the CCS can become fairly intricate.</p><p> This complexity has frequently led to the use of helium as the drift gas of choice for structural studies, given its small size and mass, its low polarizability (minimizing long-range interactions), and its sphericity and lack of internal degrees of freedom, all of which contribute to reduce departures between measured and true cross-sections. Recently, however, a growing interest has arisen for using moderately-polarizable gases such as air, nitrogen, or carbon dioxide (among others) in these structural studies, due to a number of advantages they present over helium, including their higher breakdown voltages (allowing for higher instrument resolutions) and better pumping characteristics. This shift has, nevertheless, remained objectionable in the eye of those seeking to infer accurate structural information from ion mobility measurements and, accordingly, there is a critical need to study whether or not measurements carried out in such gases may be corrected for the finite size of the gas molecules and their long-range interactions with the ions, in order to provide cross-sections truly representative of ion geometry. A first step to address this matter is undertaken here for the special case of nearly-spherical, nanometer-sized ions.</p><p> In order to attain this goal, we have performed careful and accurate IMS&ndash;MS measurements of hundreds of electrospray-generated nanodrops of the ionic liquid (IL) 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF₄), in a variety of drift gases (air, CO₂, and argon), covering a wide range of temperatures (20-100 &deg;C, for both air and CO₂), and considering nanodrops of both positive and negative polarity (the latter in room-temperature air only). Thanks to the combined measurement of the mass and mobility of these nanodrops, we are able to simultaneously determine a mobility-based collision cross-section and a mass-based diameter (taking into account the finite compressibility of the IL matter) for each of them, which then allows us to establish a comparison between the two.</p><p> Over the entire range of experimental conditions investigated, our measurements show that the electrical mobilities of these nearly-spherical, multiply-charged IL nanodrops are accurately described by an adapted version of the well-known Stokes&mdash;Millikan (SM) law for the mobility of spherical ions, with the nanodrop diameter augmented by an effective gas-molecule collision diameter, and including a correction factor to account for the effect of ion&mdash;induced dipole (polarization) interactions, which result in the mobility decreasing linearly with the ratio between the polarization and thermal energies of the ion&ndash;neutral system at contact. The availability of this empirically-validated relation enables us, in turn, to determine true, geometric cross-sections for globular ions from IMS&mdash;MS measurements performed in gases other than helium, including molecular or atomic gases with moderate polarizabilities. In addition, the observed dependence of the experimentally-determined values for the effective gas-molecule collision diameter and the parameters involved in the polarization correction on drift-gas nature, temperature, and nanodrop polarity, is further evaluated in the light of the results of numerical calculations of the electrical mobilities, in the free-molecule regime, of spherical ions subject to different types of scattering with the gas molecules and interacting with the latter under an ion&ndash;induced dipole potential. Among the number of findings derived from this analysis, a particularly notable one is that nanodrop&ndash;neutral scattering seems to be of a <i>diffuse</i> (cf. elastic and specular) character in all the scenarios investigated, including the case of the monatomic argon, which therefore suggests that the atomic-level surface roughness of our nanodrops and/or the proximity between their internal degrees of freedom, rather than the sphericity (or lack of it) and the absence (or presence) of internal degrees of freedom in the gas molecules, are what chiefly determine the nature of the scattering process.</p>

<p> Energy generation via organic photovoltaic (OPV) cells provide many advantages over alternative processes including flexibility and price. However, more efficient OPVs are required in order to be competitive for applications. One way to enhance efficiency is through manipulation of exciton mechanisms within the OPV, for example by inserting a thin film of bathocuproine (BCP) and gold nanoparticles between the C₆₀/Al and ZnPc/ITO interfaces, respectively. We find that BCP increases efficiencies by 330% due to gains of open circuit voltage (<i>V_oc</i>) by 160% and short circuit current (<i>J_sc</i>) by 130%. However, these gains are complicated by the anomalous photovoltaic effect and an internal chemical potential. Exploration in the tuning of metallic nanoparticle deposition on ITO was done through four techniques. Drop casting Ag nanoparticle solution showed arduous control on deposited morphology. Spin-coating deposited very low densities of nanoparticles. Drop casting and spin-coating methods showed arduous control on Ag nanoparticle morphology due to clustering and low deposition density, respectively. Sputtered gold on glass was initially created to aid the adherence of Ag nanoparticles but instead showed a quick way to deposit aggregated gold nanoparticles. Electrodeposition of gold nanoparticles (AuNP) proved a quick method to tune nanoparticle morphology on ITO substrates. Control of deposition parameters affected AuNP size and distribution. AFM images of electrodeposited AuNPs showed sizes ranging from 39 to 58 nm. UV-Vis spectroscopy showed the presence of localized plasmon resonance through absorption peaks ranging from 503 to 614 nm. A linear correlation between electrodeposited AuNP size and peak absorbance was seen with a slope of 3.26 wavelength(nm)/diameter(nm).</p>

No description available.

This work contains two main areas of research within the field of bonding and spectroscopy. The first is the interactions of metals and metal ions with rare gas atoms; the second concerns vibrational dynamics in para-fluorotoluene(pFT). The research has been carried out as part of a collaboration between the SOCAR and Reid groups at the University of Nottingham and also involved external research teams. The work combines the results from experiments employing several different spectroscopic techniques with theoretical calculations, which support the experimental data, assist in their interpretation and provide new information. Resonance enhanced multiphoton ionisation spectroscopy is employed to investigate the Au–Xe and Au–Ne neutral complexes in the region of the 62PJ ← 62S1/2 Au atomic transition. High-level ab initio calculations provide further insight, which is necessary to explain the unusual spectra obtained. A theoretical study of complexes containing Group 2 metal cations and rare gases also reveals some unexpected trends that are related to some of the effects seen in the Au–RG series. A combination of nanosecond zero electron kinetic energy spectroscopy and time-resolved picosecond photoelectron spectroscopy is employed to investigate the vibrational dynamics of pFT. Excitation via several different vibrational states allows the study of a Fermi resonance, statistical intramolecular vibrational energy redistribution and an intermediate case that shows evidence of so-called “doorway states”.

The work in this thesis looks at the spectroscopy and interactions of metals and metal cation complexes. There are two aspects of this vast subject that are considered: the electronic spectroscopy of Au-RG complexes and the ion-molecule chemistry of metals important in the mesosphere-lower thermosphere (MLT) region of the atmosphere. The spectroscopy of the molecular states in the vicinity of the strong Au 2P3/2, 1/2 ← 2S1/2 atomic transition, have been studied for the Au-RG (RG = Ne, Ar, Kr, Xe) series using resonance enhanced multiphoton ionization (REMPI). The spectroscopy of these systems was more involved than expected and high level ab initio calculations were required to complement and aid interpretation of the REMPI spectra obtained. Two main effects were seen to influence the spectroscopy in this energetic region — the mixing between D2Π1/2 and E2Σ1/2+ states through spin-orbit interactions and the interaction of lower lying states arising from the Au(2D) + RG (1S0) asymptote, resulting in predissociation being observed. The MLT is the only region of the Earth’s atmosphere in which metals exist in a free atomic state. It is known that their presence in this region occurs via the ablation of meteors entering the upper atmosphere, but certain aspects of their chemistry are still unclear. Using high level ab initio theory, spectroscopic constants were determined for metal cation complexes that can be formed in this region. These values are used by collaborators in conjunction with laboratory measurement to establish accurate rate coefficients that will allow the ion-molecule chemistry of calcium and magnesium in the MLT region to be modelled.

New solid-state NMR experiments for measuring internuclear distances are designed using symmetry principles. The “recoupling” sequences described here are intended to reintroduce the MAS-averaged heteronuclear dipole-dipole coupling between a spin-1/2 nucleus (e.g. 1H) and a half-integer quadrupolar nucleus (e.g. 17O, I = 5/2). The magnitude of the dipolar interaction depends on the separation between the coupled nuclei, so the evolution of the spin system under the recoupled Hamiltonian can be used to measure the internuclear distance. Simulations of the spin dynamics are used initially to select candidate sequences and these are subsequently employed to measure both long-range and direct O–H distances in powdered L-Tyrosine.HCl (isotopically enriched with 17O at 20%to 30% at the O$^\eta$ site). Improvements to existing methods for the data analysis for this type of NMR experiment are also discussed, including the restriction and/or removal of certain fit parameters and the explicit inclusion of inhomogeneous radio-frequency fields as part of the fitting procedure. The effects of processing on the uncertainty of experimentally determined distances are considered, and a new analysis method which circumvents several of these effects is presented. Similar recoupling sequences can be used to measure the anisotropy of proton chemical shifts, and some preliminary results are also presented for this application. A systematic method for the assignment of congested spin-1/2 spectra resulting from molecules with large numbers of chemically similar sites is also described. This makes use of a comparison between the chemical shift tensor measured as usual by the 2D-PASS experiment and its principal components calculated from first principles using the density functional theory package CASTEP. The initial peak assignment is generated randomly and then varied using a steepest-ascent hill climbing algorithm with the square sum of the difference between the experimental and calculated principal values of the chemical shift tensor as the target function. The new method is tested on the 13C spectrum of the anti-inflammatory drug flufenamic acid and found to be superior to simple assignments using only the isotropic chemical shift.

Orientador: José Anchieta Gomes Neto / Banca: Pedro Vitoriano Oliveira / Banca: Marcia Andreia Mesquita Silva da Veiga / Resumo: Foi desenvolvido um método para a determinação espectrométrica de fósforo em insumos agroindustriais. O método está baseado na determinação por Espectrometria de Absorção atômica com Fonte Contínua de Alta Resolução (HR-CS AAS) utilizando a linha atômica 213,618 nm e bandas de 246,400 nm e 324,616 nm. Foram estudadas as melhores condições para a análise via absorção pelas bandas de PO e da linha de P atômica. Para a primeira, a melhor forma de análise foi utilizar a chama oxidante ar / acetileno, já para a última situação a atomização foi pela utilização de uma chama oxidante de acetileno / óxido nitroso. As melhores condições de funcionamento, tais como altura do queimador, fluxo de gases e taxa de aspiração da amostra foram definidas, sendo seus valores ideais para cada comprimento de onda respectivamente: 246,400 nm (9 mm - 0,186 - 5 mL min-1), para 324,616 nm (8 mm - 0,170 - 5 mL min-1) e de 213,618 nm (4 mm - 0,450 - 5 mL min-1). Boa linearidade foinobtida para o intervalo de concentração 250 - 4000 mg L-1 P usando o modo de integração do sinal de absorbância CP ± 2 (5 pixels), utilizando-se os sais Na2HPO3.5H2O, NaH2PO4, NH4H2PO4 e H3PO4. Os resultados mostraram que era irrelevante a natureza dos compostos para obter um padrão de P. Quatro diferentes modos de integração de absorbância foram avaliados: CP ± 1 (3 pixels), CP ± 2 (5 pixels), CP ± 3 (7 pixels) e CP ± 4 (9 pixels). Foi observado que a sensibilidade (inclinação da curva e massa característica) melhoraram com o aumento do número de pixels. O método de determinação de P pelo HR-CS FAAS em insumos agroindustriais foi comparada com a titulação. A exatidão e precisão foram de acordo com 95% de confiança, o desvio padrão relativo (RSD) obtido foi de 2,0%. Boas recuperações, cerca de 98%, foi obtida a partir de testes de adição e recuperação. / Abstract: It was developed a method for spectrometry determination of phosphorus in agroindustrial products. The method is based on the determination by high-resolution continuum source flame atomic absorption spectrometry technique (HR-CS FAAS) using the atomic line 213,618 nm and bands of 246,400 nm and 324,616 nm. It was studied the best conditions for the analysis, for the absorption by bands of PO and the line of P atomic. To the first the best form of analysis would be using an oxidizing air/acetylene flame for analyte atomization and the last an oxidizing acetylene/nitrous oxide flame. The best operating conditions was defined as the burner high, the gas flow rate and aspiration rate of the sample. The values for these operations conditions are respectively: to 246,400 nm ( 9 mm - 0,186 - 5 mL min-1), to 324,616 nm ( 8 mm - 0,170 - 5 mL min-1) and to 213,618 nm ( 4 mm - 0,450 - 5 mL min-1). Good linearity was obtained for the concentration range 250 - 4000 mg L-1 P using the wavelength integrate absorbance in CP ± 2 (5 pixels), using the salts Na2HPO3.5H2O, NaH2PO4, NH4H2PO4 e H3PO4. The results showed that the was irrelevant to the nature of the compound to obtain a standard of P. Four different wavelength integrated absorbance were evaluated: CP ± 1 (3 pixels), CP ± 2 (5 pixels), CP ± 3 (7 pixels) and CP ± 4 (9 pixels). It was observed that the sensitivity (slope and characteristic mass) improved with increased number of pixels. The method of analysis of P by HR-CS FAAS in agroindustrial products was compared with the titration. The accuracy and precision was agreement at 95% confidence level, the relative standard deviation (RSD) obtaneid was 2,0%. Good recoveries, about 98%, was obtained using test of addition and recovery. / Mestre

<p> Nanomaterials are the focus of intense research efforts in a variety of fields because of dramatic differences in properties when compared to the corresponding bulk materials. Catalysis is one material property that can become more pronounced at the nanoscale. By lowering energy requirements for chemical reactions, catalysts reduce production costs in diverse sectors of the economy, including medicine, transportation, environmental protection, oil and gas, food, and synthetic materials. Transition metals are an important class of catalysts capable of facilitating reduction and oxidation of molecular species. Since the discovery of transition metal catalysts nearly 200 years ago, certain metals were considered more active as catalysts (i.e., Pt, Pd, and Ru), while others (Au) appeared to have negligible catalytic activity as bulk materials. In recent years, gold nanoparticles (AuNPs) have become a fast-growing field of research owing to their unexpected catalytic properties not present in the bulk material. However, unsupported AuNPs are highly prone to flocculation and subsequent reduced catalytic activity. The choice of an appropriate aggregation-resistant stabilizing ligand for these nanoparticles is an important part of maintaining nanoscale catalytic properties. Additional stability is provided by anchoring AuNPs to support materials, allowing for dramatic improvements in catalyst lifetimes. This work discusses the development of novel diamond support materials for improving the stability of catalytically active AuNPs. Synthetic nanodiamond is a widely available, inexpensive, and robust material that has found applications in a wide range of commercial abrasives, lubricants, and composite materials. By exploiting the rich surface chemistry of nanodiamond, we have developed versatile catalyst support materials that offer unrivaled chemical and mechanical stability. Various nanodiamond surface modifications are readily prepared using a combination of chemical vapor deposition, photo-active polymer chemistry, and synthetic organic chemistry techniques. Control over the surface chemistry and properties of the resulting nanodiamond allow for increased stability of AuNPs via surface anchored thiol and amine moieties. The use of diamond as a support material should allow a wide variety of noble and nonprecious metal composite materials to be used as catalysts in harsh chemical environments not suitable for existing support materials.</p><p>