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Xu WL, Zeng P, Wu B, Zheng F, Zhu F, Smith TA, Ghiggino KP, Hao XT. Effects of Processing Solvent on the Photophysics and Nanomorphology of Poly(3-butyl-thiophene) Nanowires:PCBM Blends. J Phys Chem Lett 2016; 7:1872-1879. [PMID: 27140304 DOI: 10.1021/acs.jpclett.6b00808] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We report the effect of the processing solvent on the nanoscale morphology and photophysical dynamics of poly(3-butyl-thiophene) nanowires (P3BT-nw). P3BT-nw assembled in ortho-dichlorobenzene (ODCB) show higher crystallization and a longer conjugation length with increased exciton delocalization compared with those assembled in chlorobenzene (CB). It is proposed that this solvent effect is associated with the higher ordered structures formed from ODCB solution state. Charge-transfer dynamics and phase separation for P3BT-nw:PCBM blends were investigated by ultrafast fluorescence techniques. The more efficient fluorescence quenching observed in P3BT-nw:PCBM blend films processed from ODCB suggests that there is intimate contact between P3BT-nw and PCBM that facilitates charge transfer. The superior performance of organic photovoltaic devices based on P3BT-nw:PCBM bulk heterojunctions processed using ODCB is attributed to the higher crystallization of P3BT-nw, optimized phase separation, and more efficient charge transfer from P3BT-nw to PCBM.
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Zeng P, Cadusch J, Chakraborty D, Smith TA, Roberts A, Sader JE, Davis TJ, Gómez DE. Photoinduced Electron Transfer in the Strong Coupling Regime: Waveguide-Plasmon Polaritons. NANO LETTERS 2016; 16:2651-6. [PMID: 26963038 DOI: 10.1021/acs.nanolett.6b00310] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Reversible exchange of photons between a material and an optical cavity can lead to the formation of hybrid light-matter states where material properties such as the work function [ Hutchison et al. Adv. Mater. 2013 , 25 , 2481 - 2485 ], chemical reactivity [ Hutchison et al. Angew. Chem., Int. Ed. 2012 , 51 , 1592 - 1596 ], ultrafast energy relaxation [ Salomon et al. Angew. Chem., Int. Ed. 2009 , 48 , 8748 - 8751 ; Gomez et al. J. Phys. Chem. B 2013 , 117 , 4340 - 4346 ], and electrical conductivity [ Orgiu et al. Nat. Mater. 2015 , 14 , 1123 - 1129 ] of matter differ significantly to those of the same material in the absence of strong interactions with the electromagnetic fields. Here we show that strong light-matter coupling between confined photons on a semiconductor waveguide and localized plasmon resonances on metal nanowires modifies the efficiency of the photoinduced charge-transfer rate of plasmonic derived (hot) electrons into accepting states in the semiconductor material. Ultrafast spectroscopy measurements reveal a strong correlation between the amplitude of the transient signals, attributed to electrons residing in the semiconductor and the hybridization of waveguide and plasmon excitations.
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Connell TU, White JM, Smith TA, Donnelly PS. Luminescent Iridium(III) Cyclometalated Complexes with 1,2,3-Triazole "Click" Ligands. Inorg Chem 2016; 55:2776-90. [PMID: 26938838 DOI: 10.1021/acs.inorgchem.5b02607] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
A series of cyclometalated iridium(III) complexes with either 4-(2-pyridyl)-1,2,3-triazole or 1-(2-picolyl)-1,2,3-triazole ancillary ligands to give complexes with either 5- or 6-membered chelate rings were synthesized and characterized by a combination of X-ray crystallography, electron spin ionization-high-resolution mass spectroscopy (ESI-HRMS), and nuclear magnetic resonance (NMR) spectroscopy. The electronic properties of the complexes were probed using absorption and emission spectroscopy, as well as cyclic voltammetry. The relative stability of the complexes formed from each ligand class was measured, and their excited-state properties were compared. The emissive properties are, with the exception of complexes that contain a nitroaromatic substituent, insensitive to functionalization of the ancillary pyridyl-1,2,3-triazole ligand but tuning of the emission maxima was possible by modification of the cyclometalating ligands. It is possible to prepare a wide range of optimally substituted pyridyl-1,2,3-triazoles using copper Cu(I)-catalyzed azide alkyne cycloaddition, which is a commonly used "click" reaction, and this family of ligands represent an useful alternative to bipyridine ligands for the preparation of luminescent iridium(III) complexes.
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Burton MG, Whitchurch CB, Turnbull L, Rogers K, Orth R, Brien Simpson NO, Gee M, Clayton AH, Smith TA. Fluorescence Investigations on the Attack of Cell-Wall-Deficient Bacteria by Antimicrobial Peptides. Biophys J 2016. [DOI: 10.1016/j.bpj.2015.11.489] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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55
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Dryza V, Smith TA, Bieske EJ. Blue to near-IR energy transfer cascade within a dye-doped polymer matrix, mediated by a photochromic molecular switch. Phys Chem Chem Phys 2016; 18:5095-8. [PMID: 26816320 DOI: 10.1039/c5cp07400b] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The spectroscopic properties of a poly(methyl methacrylate) matrix doped with a coumarin dye, a cyanine dye, and a photochromic spiropyran dye have been investigated. Before UV irradiation of the matrix, excitation of the coumarin dye results in minimal energy transfer to the cyanine dye. The energy transfer is substantially enhanced following UV irradiation of the matrix, which converts the colourless spiropyran isomer to the coloured merocyanine isomer, which then acts as an intermediate bridge by accepting energy from the coumarin dye and then donating energy to the cyanine dye. This demonstration of a switchable energy transfer cascade should help initiate new research directions in molecular photonics.
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Schwarz KN, Farley SB, Smith TA, Ghiggino KP. Charge generation and morphology in P3HT:PCBM nanoparticles prepared by mini-emulsion and reprecipitation methods. NANOSCALE 2015; 7:19899-19904. [PMID: 26567986 DOI: 10.1039/c5nr06244f] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Organic semiconductor nanoparticles provide a potentially scalable approach for photovoltaics that can be processed from aqueous media. Particles of poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester (PCBM) were prepared using two techniques; those produced by a mini-emulsion method contained greater amounts of crystalline P3HT domains with charge generation resembling phase-separated annealed solvent-cast films.
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Hickey JL, James JL, Henderson CA, Price KA, Mot AI, Buncic G, Crouch PJ, White JM, White AR, Smith TA, Donnelly PS. Intracellular Distribution of Fluorescent Copper and Zinc Bis(thiosemicarbazonato) Complexes Measured with Fluorescence Lifetime Spectroscopy. Inorg Chem 2015; 54:9556-67. [DOI: 10.1021/acs.inorgchem.5b01599] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
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58
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Smith TA, Ghiggino KP. A review of the analysis of complex time-resolved fluorescence anisotropy data. Methods Appl Fluoresc 2015; 3:022001. [DOI: 10.1088/2050-6120/3/2/022001] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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59
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60
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Henderson CA, Nagul EA, Cattrall RW, Kolev SD, Smith TA. Imaging chemical extraction by polymer inclusion membranes using fluorescence microscopy. Methods Appl Fluoresc 2014; 2:024008. [PMID: 29148458 DOI: 10.1088/2050-6120/2/2/024008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Polymer inclusion membranes (PIMs) transport chemicals between bodies of liquid by simultaneously performing chemical extraction and back-extraction. The internal chemical and physical mechanisms by which this transport occurs are, however, poorly understood. Also, some PIMs, which are otherwise optimal for their task, age and lose function after only days, limiting their feasibility for industrial upscaling. Through the application of fluorescence imaging methods we are able for the first time to see where chemical extraction occurs in the membrane. Extraction of fluorescein from solution by PIMs demonstrates inhomogeneities that do not correlate to surface morphology. Fluorescence lifetime imaging demonstrates that regions of increased extraction have distinctly different fluorescence lifetimes to that of the surrounding PIM indicating localized chemical environments, and this is observed to change with membrane age. Fluorescence imaging is shown to allow probing and novel understanding of PIM internal chemical morphology.
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61
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Yang H, Peng S, Hao X, Smith TA, Qiao GG, Zhang X. Surfactant-mediated formation of polymeric microlenses from interfacial microdroplets. SOFT MATTER 2014; 10:957-64. [PMID: 24983104 DOI: 10.1039/c3sm52568f] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Nano- and micro-scale lenses have a range of potential applications, such as in antireflective layers in photovoltaic or light emission devices, and in super resolution imaging in the near field modes. One of the protocols to mass produce polymeric microlenses is through the polymerization of microdroplets of a monomer precursor that are produced at solid–liquid interfaces by a solvent exchange technique. In this work, we have advanced this protocol by using surfactants. A cationic surfactant was added to the liquid phase for the control over the formation and morphology of polymerisable microdroplets and their resultant microlenses (i.e. the polymerized microdroplets). The results demonstrate that the surfactant could enable the production of polymerizable microdroplets on hydrophilic substrates by the solvent exchange technique, and eliminate the restriction by the substrate wettability on the microlens fabrication. Furthermore, the size distribution and aspect ratio of microlenses could be tuned by the surfactant concentration.
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Briët OJT, Smith TA. Response to 'Applying the ICMJE authorship criteria to operational research in low-income countries: the need to engage programme managers and policy makers' by Zachariah et al. (2013) TMIH 18, pp. 1025-1028. Trop Med Int Health 2013; 19:128. [PMID: 24147785 DOI: 10.1111/tmi.12213] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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63
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Hao XT, Hirvonen LM, Smith TA. Nanomorphology of polythiophene–fullerene bulk-heterojunction films investigated by structured illumination optical imaging and time-resolved confocal microscopy. Methods Appl Fluoresc 2013; 1:015004. [DOI: 10.1088/2050-6120/1/1/015004] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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64
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Dias DA, Smith TA, Ghiggino KP, Scollary GR. The role of light, temperature and wine bottle colour on pigment enhancement in white wine. Food Chem 2012; 135:2934-41. [PMID: 22980893 DOI: 10.1016/j.foodchem.2012.07.068] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2012] [Revised: 07/04/2012] [Accepted: 07/10/2012] [Indexed: 11/30/2022]
Abstract
Pigmentation enhancement in a Chardonnay wine with high flavan-3-ol concentration was examined by irradiating the wine under controlled conditions. Heating the wine in darkness required temperatures in excess of 50°C before enhanced pigmentation became apparent. It was found that ultraviolet and, to a lesser extent, low wavelength visible light contributed to pigment production. The development of pigmentation depended on wine bottle glass colour: Flint>Arctic Blue>French Green>Antique Green. This is in agreement with the transmission characteristics of the bottles with even the darkest (Antique Green) allowing the transmission of some ultraviolet light. Riboflavin, when added to the wine, degraded rapidly when exposed to radiation <400 nm. The degradation of riboflavin and the onset of colour development depended on the actual amounts as well as the ratio of riboflavin to flavan-3-ol, suggesting that a complex series of reactions are occurring. A degradation product of riboflavin may be contributing to the increase in absorbance in the visible region observed during light exposure.
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65
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Dao LV, Hall C, Vu HL, Dinh KB, Balaur E, Hannaford P, Smith TA. Phase-matched generation of highly coherent radiation in water window region. APPLIED OPTICS 2012; 51:4240-4245. [PMID: 22722304 DOI: 10.1364/ao.51.004240] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2012] [Accepted: 05/15/2012] [Indexed: 06/01/2023]
Abstract
Highly coherent extreme ultraviolet radiation around the water window region (~4.4 nm) is generated in a semi-infinitive helium gas cell using infrared pulses of wavelength 1300 nm, energy 2.5 mJ, duration 40 fs, and repetition rate 1 kHz. The pressure-squared dependence of the intensity and the almost-perfect Gaussian profile and low divergence of the high harmonic source indicate a phase-matched generation process. The spatial coherence of the source is studied using Young's double-slit measurements.
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66
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Smith TA, Kim M, Piza M, Davidson PM, Jenkins CR, Ingham JM, Clayton JM. Advance care planning by respiratory physicians with patients with COPD. A pilot survey. BMJ Support Palliat Care 2012. [DOI: 10.1136/bmjspcare-2012-000250.78] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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67
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Heskes AM, Lincoln CN, Goodger JQD, Woodrow IE, Smith TA. Multiphoton fluorescence lifetime imaging shows spatial segregation of secondary metabolites in Eucalyptus secretory cavities. J Microsc 2012; 247:33-42. [PMID: 22394321 DOI: 10.1111/j.1365-2818.2011.03593.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Multiphoton fluorescence lifetime imaging provides an excellent tool for imaging deep within plant tissues while providing a means to distinguish between fluorophores with high spatial and temporal resolution. Ideal candidates for the application of multiphoton fluorescence lifetime imaging to plants are the embedded secretory cavities found in numerous species because they house complex mixtures of secondary metabolites within extracellular lumina. Previous investigations of this type of structure have been restricted by the use of sectioned material resulting in the loss of lumen contents and often disorganization of the delicate secretory cells; thus it is not known if there is spatial segregation of secondary metabolites within these structures. In this paper, we apply multiphoton fluorescence lifetime imaging to investigate the spatial arrangement of metabolites within intact secretory cavities isolated from Eucalyptus polybractea R.T. Baker leaves. The secretory cavities of this species are abundant (up to 10 000 per leaf), large (up to 6 nL) and importantly house volatile essential oil rich in the monoterpene 1,8-cineole, together with an immiscible, non-volatile component comprised largely of autofluorescent oleuropeic acid glucose esters. We have been able to optically section into the lumina of secretory cavities to a depth of ∼80 μm, revealing a unique spatial organization of cavity metabolites whereby the non-volatile component forms a layer between the secretory cells lining the lumen and the essential oil. This finding could be indicative of a functional role of the non-volatile component in providing a protective region of low diffusivity between the secretory cells and potentially autotoxic essential oil.
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68
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Chan NY, Hao XT, Smith TA, Dunstan DE. Conformational and photophysical changes in conjugated polymers exposed to Couette shear. J Phys Chem B 2011; 115:6838-42. [PMID: 21553834 DOI: 10.1021/jp111787b] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Conjugated polymers in solution exhibit interesting photophysical behavior, which is dictated by their molecular conformation. The conformations and resulting photophysics can be altered by deformational flows such as simple shear. Solutions of poly[2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) in dimethylformamide (DMF) show large decreases in fluorescence intensity as a function of shear rate, combined with significant spectral shifts upon exposure to shear. The excitation and emission spectra shift toward shorter wavelengths, indicating a change in conformation with shortened conjugated segment lengths attributed to compressive hydrodynamic forces in flow. Addition of poly(methyl methacrylate) to the solutions is shown to alter the fluorescence emission spectral behavior, which we ascribe to energy transfer from the higher energy, short segments to a small population of lower energy conjugated segments. The measured fluorescence changes were not reversible upon cessation of shear, demonstrating that permanent conformational changes are induced by flow.
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69
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Rapson AC, Hossain MA, Wade JD, Nice EC, Smith TA, Clayton AHA, Gee ML. Structural dynamics of a lytic peptide interacting with a supported lipid bilayer. Biophys J 2011; 100:1353-61. [PMID: 21354409 DOI: 10.1016/j.bpj.2011.01.026] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2010] [Accepted: 12/15/2010] [Indexed: 11/26/2022] Open
Abstract
The interaction of a melittin mutant with a 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC)-supported lipid bilayer was studied with the use of time-resolved evanescent wave-induced fluorescence spectroscopy (TREWIFS) and evanescent wave-induced time-resolved fluorescence anisotropy measurements (EW-TRAMs). The mutant peptide was labeled at position K14 with AlexaFluor 430 and retained the lytic activity characteristic of native melittin. The fluorescence decay kinetics of the conjugate was found to be biexponential with a short-lived component, τ(1), due to photoinduced electron transfer between AlexaFluor 430 and proximal side chains within or between the peptides. The longer-lived component, τ(2), was sensitive to the polarity of the microenvironment at or near the K14 position of the peptide. Upon interaction with a DPPC-supported bilayer, the proportional contribution of τ(1) increased, indicating a conformational change of the peptide. The values of τ(1) and τ(2) indicate that the AlexaFluor 430 probe experienced an environment with an equivalent polarity no less than that of methanol. EW-TRAMs data from the melittin mutant revealed hindered rotational motions of the AlexaFluor 430 probe both in the plane and perpendicular to the plane of the supported lipid bilayer. The data indicate a highly ordered and polar environment near the center of the melittin helix consistent with the formation of a toroidal pore.
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Clark AC, Dias DA, Smith TA, Ghiggino KP, Scollary GR. Iron(III) tartrate as a potential precursor of light-induced oxidative degradation of white wine: studies in a model wine system. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2011; 59:3575-3581. [PMID: 21381783 DOI: 10.1021/jf104897z] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The potential for iron(III) tartrate to act as a photoactivator in light-induced oxidative degradation of white wine is described. Using a tartaric-acid-based model wine system containing 5 mg/L iron, exposure to light from a xenon arc lamp led to the oxidative degradation of tartaric acid and the production of glyoxylic acid. The critical wavelength of light for the degradation process was found to be below 520 nm. No glyoxylic acid was formed in the absence of iron and/or light. Flint glass offered little protection from the light-induced photodegradation of tartaric acid. Antique Green glass offered more protection but did not stop the photodegradation process.
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Scholes CA, Millar DP, Gee ML, Smith TA. Resonance energy-transfer studies of the conformational change on the adsorption of oligonucleotides to a silica interface. J Phys Chem B 2011; 115:6329-39. [PMID: 21500794 DOI: 10.1021/jp201332w] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Time-resolved evanescent wave-induced fluorescence studies have been carried out on a series of fluorescently labeled oligonucleotide sequences adsorbed to a silica surface from solution. The fluorescence decay profiles of a fluorescent energy donor group undergoing resonance energy transfer to a nonemissive energy-acceptor molecule have been analyzed in terms of a distribution of donor-acceptor distances to reveal the conformational changes that occur in these oligonucleotides upon adsorption. Evanescent wave-induced time-resolved Förster resonance energy-transfer (EW-TRFRET) measurements indicate that at a high electrolyte concentration, there is localized separation of the oligonucleotide strands, and the helical structure adopts an "unraveled" conformation as a result of adsorption. This is attributed to the flexibility within the oligonucleotide at high electrolyte concentration allowing multiple segments of the oligonucleotide to have direct surface interaction. In contrast, the EW-TRFRET measurements at a lower electrolyte concentration reveal that the oligonucleotide retains its helical conformation in a localized extended state. This behavior implies that the rigidity of the oligonucleotide at this electrolyte concentration restricts direct interaction with the silica to a few segments, which correspondingly introduces kinks in the double helix conformation and results in significant oligonucleotide segmental extension into solution.
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Tilley AJ, Danczak SM, Browne C, Young T, Tan T, Ghiggino KP, Smith TA, White J. Synthesis and Fluorescence Characterization of MEHPPV Oligomers. J Org Chem 2011; 76:3372-80. [DOI: 10.1021/jo200336m] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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73
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Hirvonen LM, Smith TA. Imaging on the Nanoscale: Super-Resolution Fluorescence Microscopy. Aust J Chem 2011. [DOI: 10.1071/ch10333] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Although the resolution of a light microscope is fundamentally limited by diffraction to about half of the wavelength of light, in recent years several techniques have been developed that can overcome this limitation in fluorescence microscopy, allowing imaging with nanometre scale resolution. Many of these techniques are based on photoswitchable molecules that can switch between a bright, fluorescent and a dark, nonfluorescent state. Some of these techniques, as well as their limitations, are discussed.
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McLean SC, Scholes CA, Smith TA, Gee ML. Monitoring Supramolecular Self-Assembly using Time-Resolved Fluorescence Spectroscopy. Aust J Chem 2011. [DOI: 10.1071/ch11066] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Time-resolved fluorescence spectroscopy is used to observe subtleties in supramolecular structure during the self-assembly of polymers in solution. Lifetime distribution analysis of the fluorescence decay kinetics of the solvent-sensitive fluorescent probe 1-anilino-8-naphthalene sulfonic acid associated with the di-block copolymer poly(2-vinylpyridine)41–poly(ethylene oxide)204 (P2VP-PEO) as it self-assembles enabled identification of three microdomains, distinguishable on the basis of micropolarity. These microdomains can be assigned to different supramolecular substructures: the micelle corona (high polarity), the micelle core and the P2VP globule (both low polarity), and the core–corona interface and the globule–PEO junction (both intermediate polarity). Changes in the relative population distributions of these sub-structures as a function of P2VP-PEO pinpoint the onset of micellization corresponding to the critical micelle concentration (CMC) of the copolymer, but indicate significant variation in supramolecular structure, including micelle formation, well below the CMC. This suggests that supramolecular self-assembly in polymeric systems has characteristics of a second order phase transition.
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Teoh CL, Pham CLL, Todorova N, Hung A, Lincoln CN, Lees E, Lam YH, Binger KJ, Thomson NH, Radford SE, Smith TA, Müller SA, Engel A, Griffin MDW, Yarovsky I, Gooley PR, Howlett GJ. A structural model for apolipoprotein C-II amyloid fibrils: experimental characterization and molecular dynamics simulations. J Mol Biol 2010; 405:1246-66. [PMID: 21146539 DOI: 10.1016/j.jmb.2010.12.006] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2010] [Revised: 12/02/2010] [Accepted: 12/03/2010] [Indexed: 10/18/2022]
Abstract
The self-assembly of specific proteins to form insoluble amyloid fibrils is a characteristic feature of a number of age-related and debilitating diseases. Lipid-free human apolipoprotein C-II (apoC-II) forms characteristic amyloid fibrils and is one of several apolipoproteins that accumulate in amyloid deposits located within atherosclerotic plaques. X-ray diffraction analysis of aligned apoC-II fibrils indicated a simple cross-β-structure composed of two parallel β-sheets. Examination of apoC-II fibrils using transmission electron microscopy, scanning transmission electron microscopy, and atomic force microscopy indicated that the fibrils are flat ribbons composed of one apoC-II molecule per 4.7-Å rise of the cross-β-structure. Cross-linking results using single-cysteine substitution mutants are consistent with a parallel in-register structural model for apoC-II fibrils. Fluorescence resonance energy transfer analysis of apoC-II fibrils labeled with specific fluorophores provided distance constraints for selected donor-acceptor pairs located within the fibrils. These findings were used to develop a simple 'letter-G-like' β-strand-loop-β-strand model for apoC-II fibrils. Fully solvated all-atom molecular dynamics (MD) simulations showed that the model contained a stable cross-β-core with a flexible connecting loop devoid of persistent secondary structure. The time course of the MD simulations revealed that charge clusters in the fibril rearrange to minimize the effects of same-charge interactions inherent in parallel in-register models. Our structural model for apoC-II fibrils suggests that apoC-II monomers fold and self-assemble to form a stable cross-β-scaffold containing relatively unstructured connecting loops.
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