The electrostatic field created by the inward pointing dipole moments of an oriented membrane leaflet has never been measured directly, but is thought to have an important influence on membrane function. Here we present the first direct measurement of the membrane dipole field in lipid bicelles using vibrational Stark effect spectroscopy which is based on the sensitivity of a nitrile oscillator’s vibrational frequency to its local electrostatic environment. The nitrile probe was introduced as the artificial amino acid p-cyanophenylalanine (CN-Phe) in four different locations of a α-helical peptide composed of alternating alanine and leucine residues. This peptide was intercalated into bicelles composed of mixtures of the long chain lipids 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), or 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), and the short chain lipid 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC) formed in two different sizes, 5 nm and 15 nm in radius. Formation of the bicelle above the phase transition temperature of the lipid mixture was confirmed by ³¹P NMR, and the structure of the [alpha]-helix within the bicelle was confirmed by circular dichroic spectroscopy. The absorption energy of the nitrile probe at 4 positions along the helical axis was measured by Fourier transform infrared spectroscopy, from which we estimate the magnitude of the membrane dipole electrostatic field to be -6 MV/cm. Then we successfully manipulated the dipole field in q = 0.5 DMPC/DHPC bicelles by incorporating the small molecule phloretin into the membrane and measured the corresponding ratiometric fluorescence signal of the co-intercalated voltage gated dye di-8-ANEPPS. We measured 0.7 ± 0.2 cm⁻¹ blue shift in absorption energy of the nitrile probe due to the decrease in dipole field caused by phloretin, corresponding to a dipole field of -4.2 MV/cm. This change was essentially identical to what has been estimated through ratiometric fluorescence methods, indicating that VSE spectroscopy will be useful tool for measurement of the biological effects of electrostatic fields in lipid membranes. / text

In atomic force microscopy (AFM), the measured force between tip and substrate is used to produce images with subatomic resolution. In this thesis, plausible electrostatic interactions between tip-substrate is studied and compared with the experimental results in the report Vibrations of a molecule in an external force field by Okabayashi et al.. A simplified model gives by hand that the interaction between substrate and tip is dominated by a point charge - point charge relation due to the interatomic distances in AFM. We find that the electrostatic interaction can reproduce the experiment down to a limit of z ~ 3 Å. Further, we find that the tip interacts with the sample as a point charge with an induced dipole moment obtained by the electric field of the substrate. By analyzing electrostatic forces and compare them with the results in the Okabayashi et al. report, the AFM images in the report could be reproduced. / <p>Rättande lärare: Cecilia Holmqvist</p>

α-Tocopherol has a well known antioxidant action but is also considered likely to exert significant non-antioxidant effects in cell membranes. Due to its lipophilic nature α-tocopherol inserts into biological membranes where it influences the organisation of the component lipids and may therefore influence biophysical parameters including the membrane dipole potential. The dipole potential has been demonstrated to modulate the function of several membrane associated proteins and perturbation of this physical parameter by α-tocopherol may prove to be a significant non-antioxidant mechanism underlying several of its cellular effects. This study investigates the influence of α-tocopherol, and the non-antioxidant structural analogue α-tocopherol succinate, on the membrane dipole potential employing fluorescence spectroscopy techniques with the dipole potential sensitive probe Di-8-ANEPPS. Similar techniques are utilised with the surface potential sensitive probe FPE to investigate the interaction of the charged α-tocopherol succinate molecule with membranes. α-Tocopherol and α-tocopherol succinate are shown to decrease the dipole potential of egg-phosphatidylcholine vesicles and Jurkat T-lymphocyte cell membranes. This effect is placed in the context of the significant influence of membrane cholesterol oxidation on the dipole potential. 7-ketocholesterol, an oxidised form of cholesterol, significantly influences several cellular processes and is thought to mediate these effects, in part, through its physical effects on the cell membrane. These include altering the composition, and therefore biophysical properties, of rafts; structures which are considered to support the function of a host of membrane proteins. This study attempts to correlate the effect of 7-ketocholesterol on the dipole potential of microdomains with the influence of the oxysterol on the function of two microdomains associated receptors: P-glycoprotein and the insulin receptor, assessed by determining the extent of ligand binding using flow fluorocytometry. α-Tocopherol has been suggested to inhibit the raft-mediated effects of 7-ketocholesterol and the influence of this molecule on the effect of 7-ketocholesterol on the dipole potential are investigated as a potential mechanism for this inhibition. It is hypothesized that α-tocopherols may protect against the deleterious effects of cholesterol oxidation in cell membranes by excluding 7-ketocholesterol from specific microdomains, of which rafts are a subset, acting to preserve their dipole potential and maintain the function of the proteins they support. However, where significant cholesterol oxidation has previously occured the concurrent changes in the microdomain landscape of the membrane is suggested to prevent α-tocopherol succinate from eliciting this protective effect.

Orientadores: Michel Zamboni Rached, Guillermo Gerardo Cabrera Oyarzún / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-09-01T02:33:12Z (GMT). No. of bitstreams: 1 Pachon_EdwinGermanPinilla_D.pdf: 4993091 bytes, checksum: 788c9fb47dfe7b9fea6cc0935ad94d54 (MD5) Previous issue date: 2016 / Resumo: Nesta tese, propõe-se um novo método para realizar guiamento de átomos neutros resfriados. Este método envolve o uso da pressão de radiação por ressonância para efetuar o guiamento dos átomos através de um campo óptico (feixe) oco. Particularmente, usa-se a força de dipolo óptico e um tipo específico de campo óptico não difrativo, chamado de "Frozen Wave" (FW), na versão tradicional e estendida, para estudar o guiamento atômico. Os campos ópticos FW¿s, que são uma solução exata da equação de onda, surgem como uma resposta aos problemas relacionados com a difração e com a impossibilidade de fazer qualquer tipo de modelamento (ou localização) longitudinal e transversal de intensidade, dos campos ópticos tradicionais usados no guiamento de átomos, como por exemplo, nos campos Laguerre-Gauss e Bessel. Assim, planejam-se algumas soluções mediante os métodos tradicional e estendido que permitem criar estruturas de luz (localizadas) resistentes à difração e nas quais o padrão de intensidade longitudinal e transversal (restringido) pode ser modelado a priori. De acordo com isso, o estudo teórico do método tradicional e da generalização das FW¿s foi realizado junto com sua comprovação experimental e foram calculados os respectivos potenciais de dipolo óptico junto com a profundidade de penetração dos átomos na barreira de potencial para cada campo óptico. Nos resultados conseguiu-se modelar algumas estruturas de luz (tanto no método tradicional como no estendido) tais como um cilindro, três cilindros concatenados, um tipo de cilindro com tampa e um funil óptico, entre outras; e mostrou-se as vantagens do uso deste tipo de estruturas de luz quando comparadas com os campos ópticos tradicionais para o guiamento atômico. Finalmente, concluiu-se que usar este tipo de campos não difrativos elimina as restrições dos campos tradicionais e é possível fazer o guiamento de átomos neutros resfriados com estes tipos de estruturas de luz. O método estendido dá uma generalização que permite pensar estes tipos de estruturas de luz para aplicações mais globais nas diferentes áreas da óptica e fotônica / Abstract: This thesis proposes a new method to perform cold neutral atom guiding. This method involves the use of resonance radiation pressure to make the atom guiding along a hollow (beam) optical field. Particularly, it uses the optical dipole force and a specific type of non-diffracting optical field, called "Frozen Wave" (FW), in these traditional and extended versions, to study the atom guiding. The FW¿s optical fields, which are an exact solution of the wave equation, appear as an answer to the problems related to the high diffraction and impossibility of any type of longitudinal and transverse intensity modeling (or location) of traditional optical fields used in atom guiding, for example the Laguerre-Gaussian and Bessel optical fields. Thus, some solutions were planned by the traditional and extended methods, which allow to create localized light structures resistant to diffraction and model a priori longitudinal and transverse (restricted) intensity pattern. Accordingly, the theoretical study of the traditional method and his generalization were carried out with their experimental evidence. Also, his respective optical dipole potential was calculated with the atom penetration depth in the potential barrier for each optical field. In the results was possible to model some light structures (both in the traditional and extended method) such as a cylinder, three concatenated cylinders, one cylinder with a lid and an optical funnel, among others; and it is showed the advantages of using this type of light structures when it is compared with the conventional optical fields for the atom guiding. Finally, it is concluded that use this type of non-diffracting fields eliminates the restrictions of the traditional fields and it is possible the cold neutral atoms guiding with this type of light structures. The FW¿s extended method gives a generalization and it permits to suggest this type of light structures for more complete applications in different areas of optics and photonics / Doutorado / Física / Doutor em Ciências / 141977/2013-2 / CNPQ