RESUMO
Characterization of surface adsorbed species using infrared (IR) spectroscopy provides valuable information concerning interfacial chemical and physical processes. However, in situ infrared studies of surface areas approaching the IR diffraction limit, such as micrometer scale electrodes, require a hitherto unrealized means to obtain high signal-to-noise (S/N) spectra from femtomole quantities of adsorbed molecules. A major methodological breakthrough is described that couples the high brilliance of synchrotron-sourced infrared microscopy with attenuated total reflection surface enhanced infrared spectroscopy (ATR-SEIRAS). The method is shown to allow the spectral measurement of a monolayer of 4-methoxypyridine (MOP) adsorbed on a surface enhancing gold film electrode under fully operational electrochemistry conditions. A factor of 15 noise improvement is achieved with small apertures using synchrotron IR relative to a thermal IR source. The very low noise levels allow the measurement of high quality IR spectra of 2.5 fmol of molecules confined to a 125 µm2 beam spot.
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Solvent properties play a central role in mediating the aggregation and self-assembly of molecular gelators and their growth into fibers. Numerous attempts have been made to correlate the solubility parameters of solvents and gelation abilities of molecular gelators, but a comprehensive comparison of the most important parameters has yet to appear. Here, the degree to which partition coefficients (log P), Henry's law constants (HLC), dipole moments, static relative permittivities (ε(r)), solvatochromic E(T)(30) parameters, Kamlet-Taft parameters (ß, α, and π), Catalan's solvatochromic parameters (SPP, SB, and SA), Hildebrand solubility parameters (δ(i)), and Hansen solubility parameters (δ(p), δ(d), δ(h)) and the associated Hansen distance (R(ij)) of 62 solvents (covering a wide range of properties) can be correlated with the self-assembly and gelation of 1,3:2,4-dibenzylidene sorbitol (DBS) gelation, a classic molecular gelator, is assessed systematically. The approach presented describes the basis for each of the parameters and how it can be applied. As such, it is an instructional blueprint for how to assess the appropriate type of solvent parameter for use with other molecular gelators as well as with molecules forming other types of self-assembled materials. The results also reveal several important insights into the factors favoring the gelation of solvents by DBS. The ability of a solvent to accept or donate a hydrogen bond is much more important than solvent polarity in determining whether mixtures with DBS become solutions, clear gels, or opaque gels. Thermodynamically derived parameters could not be correlated to the physical properties of the molecular gels unless they were dissected into their individual HSPs. The DBS solvent phases tend to cluster in regions of Hansen space and are highly influenced by the hydrogen-bonding HSP, δ(h). It is also found that the fate of this molecular gelator, unlike that of polymers, is influenced not only by the magnitude of the distance between the HSPs for DBS and the HSPs of the solvent, R(ij), but also by the directionality of R(ij): if the solvent has a larger hydrogen-bonding HSP (indicating stronger H-bonding) than that of the DBS, then clear gels are formed; opaque gels form when the solvent has a lower δ(h) than does DBS.
Assuntos
Sorbitol/análogos & derivados , Géis/química , Ligação de Hidrogênio , Solubilidade , Solventes/química , Sorbitol/químicaRESUMO
The result of interfacing step-scan spectroelectrochemistry with an IR microscope and synchrotron infrared (SIR) radiation is provided here. An external reflectance cell containing a 25 µm gold ultramicroelectrode is employed to achieve an electrochemical time constant less than one microsecond. The use of a prototypical electrochemical system, i.e., the mass-transport controlled reduction of ferricyanide, allows for a proof of principle evaluation of the viability of SIR for step-scan spectroelectrochemistry. An analysis of the importance of accounting for synchrotron source variation over the prolonged duration of a step-scan experiment is provided. Modeling of the material flux in the restricted diffusion space afforded by the external reflectance cell allows the quantitative IR results to be compared to theoretical predictions. The results indicate that only at very short times does linear diffusion within the cavity dominate the electrode response and the majority of the transient signal operates under conditions of quasi-hemispherical diffusion. The analytical information provided by the IR signal is found to be considerably less than that derived from the current response due the latter's pronounced edge effects. The results provide a detection limit of 36 fmol for step-scan SIR measurements of ferrocyanide. Implications for future IR spectroelectrochemical studies in the microsecond domain are discussed.
Assuntos
Técnicas Eletroquímicas/métodos , Microquímica/métodos , Microeletrodos , Síncrotrons , Técnicas Eletroquímicas/instrumentação , Espectrofotometria Infravermelho/métodosRESUMO
Synchrotron infrared radiation has been successfully coupled through an infrared (IR) microscope to a thin-cavity external reflectance cell to study the diffusion controlled redox of a ferrocyanide solution. Excellent signal-to-noise ratios were achieved even at aperture settings close to the diffraction limit. Comparisons of noise levels as a function of aperture size demonstrate that this can be attributed to the high brilliance of synchrotron radiation relative to a conventional thermal source. Time resolved spectroscopic studies of diffusion controlled redox behavior have been measured and compared to purely electrochemical responses of the thin-cavity cell. Marked differences between the two measurements have been explained by analyzing diffusion in both the axial (linear) and radial dimensions. Whereas both terms contribute to the measured current and charge, only species that originate in the volume element above the electrode and diffuse in the direction perpendicular to the electrode surface are interrogated by IR radiation. Implications for the use of ultramicroelectrodes and synchrotron IR (SIR) to study electrochemical processes in the submillisecond time domain are discussed.
Assuntos
Ferrocianetos/química , Espectrofotometria Infravermelho/métodos , Difusão , Técnicas Eletroquímicas/métodos , Eletrodos , Oxirredução , Espectrofotometria Infravermelho/instrumentação , SíncrotronsRESUMO
Tragic its consequences, the Covid-19 pandemic has ripped through societies with, at the time of writing, global death rates exceeding two and a half million people. In the process, there has been variability in terms of how effectively governments have dealt with the pandemic. Differences between political responses, forms of governance and the relationships between science and politics are apparent. This article investigates these relations in the United Kingdom with a particular focus upon the interpretations that informed the response of the English Government and their interactions with the scientific community. For this purpose, it provides an exploration of the political and socio-economic conditions prevailing in the United Kingdom prior to the pandemic. It then examines the interactions between science and politics as the pandemic unfolded during 2020. Then, building on these discussions it views the tensions that arose through a clash between two characteristics within democratic societies: the redemptive and pragmatic. What becomes apparent is the tendency for a form of the redemptive to be favoured over the pragmatic which results in an exposure of limits to usual and narrow political ways of governing.
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We produced coherent synchrotron radiation at the Canadian Light Source between about 5 and 30 cm(-1) in bursting and continuous emission modes and used it to acquire photoacoustic spectra of solids. A band was observed in the spectrum of α-lactose monohydrate at 18 cm(-1) and attributed to a rotational mode, in agreement with published data obtained using other numerical and experimental techniques.
Assuntos
Acústica , Lactose/análogos & derivados , Lactose/química , Análise Espectral/instrumentação , Síncrotrons , Luz , Fuligem/químicaRESUMO
The formation kinetics of self-assembling tubules composed of phytosterol:gamma-oryzanol mixtures were investigated at the Canadian Light Source on the mid-IR beamline using synchrotron radiation and Fourier transform infrared spectroscopy (FT-IR). The Avrami model was fitted to the changing hydrogen bonding density occurring at 3450 cm(-1). The nucleation process was found to be highly dependent on the molecular structure of the phytosterol. The nucleation event for cholesterol:gamma-oryzanol was determined to be sporadic whereas 5alpha-cholestan-3beta-ol:gamma-oryzanol and beta-sitosterol:gamma-oryzanol underwent instantaneous nucleation. One-dimensional growth occurred for each phytosterol:gamma-oryzanol mixture and involved the evolution of highly specific intermolecular hydrogen bonds. More detailed studies on the cholesterol:gamma-oryzanol system indicated that the nucleation activation energy, determined from multiple rate constants, obtained using the Avrami model, was at a minimum when the two compounds were at a 1:1 weight ratio. This resulted in drastic differences to the microscopic structures and affected the macroscopic properties such as turbidity. The formation of the phytosterol:gamma-oryzanol complex was due to intermolecular hydrogen bonding, which was in agreement with the infrared spectroscopic evidence.
Assuntos
Fenilpropionatos/química , Fitosteróis/química , Varredura Diferencial de Calorimetria , Ligação de Hidrogênio , Cinética , Microscopia , Espectroscopia de Infravermelho com Transformada de FourierRESUMO
Limitations of conventional light microscopy in pathological diagnosis of brain tumors include subjective bias in interpretation and discordance of nomenclature. A study using mid-infrared (IR) spectromicroscopy was undertaken to determine whether meningiomas, a group of brain tumors prone to recurrence, could be identified by the unique spectral 'fingerprints' of their chemical composition. Paired, thin (5-microm) cryosections of snap-frozen human meningioma tumor samples removed at elective surgery were mounted on glass (hematoxylin and eosin-stained tissue section) and infrared (unstained tissue section) reflectance slides, respectively. Concordance of the tumor-bearing areas identified in the stained section by a pathologist with the unstained IR tissue section was ensured using a novel digital grid and tumor-mapping system developed in our laboratory. Compared with the normal control, tumor samples from four meningioma patients revealed a marked decrease in bands associated with unsaturated fatty acids, particularly in the bands at 3010, 2920, 2850, and 1735 cm(-1). Spectral datasets were subjected to hierarchical cluster analyses (HCA) using Ward's algorithm for comparison and grouping of similar data groups, and were converted into color-coded digital maps for matching spectra with their respective clusters. False color images of 5 and 6 clusters obtained by HCA identified dominant clusters corresponding to tumor tissue. Corroboration of these findings in a larger number of meningiomas may allow for more precise identification of these and other types of brain tumors.
Assuntos
Neoplasias Meníngeas/diagnóstico , Neoplasias Meníngeas/patologia , Meningioma/diagnóstico , Meningioma/patologia , Idoso , Análise por Conglomerados , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Espectroscopia de Infravermelho com Transformada de FourierRESUMO
Arabidopsis thaliana lines expressing only one cruciferin subunit type (double-knockout; CRUAbc, CRUaBc, or CRUabC) or devoid of cruciferin (triple-knockout; CRU-) or napin (napin-RNAi) were generated using combined T-DNA insertions or RNA interference approaches. Seeds of double-knockout lines accumulated homohexameric cruciferin and contained similar protein levels as the wild type (WT). Chemical imaging of WT and double-knockout seeds using synchrotron FT-IR spectromicroscopy (amide I band, 1650 cm(-1), νCâO) showed that proteins were concentrated in the cell center and protein storage vacuoles. Protein secondary structure features of the homohexameric cruciferin lines showed predominant ß-sheet content. The napin-RNAi line had lower α-helix content than the WT. Lines entirely devoid of cruciferin had high α-helix and low ß-sheet levels, indicating that structurally different proteins compensate for the loss of cruciferin. Lines producing homohexameric CRUC showed minimal changes in protein secondary structure after pepsin treatment, indicating low enzyme accessibility. The Synchrotron FT-IR technique provides information on protein secondary structure and changes to the structure within the cell.
Assuntos
Arabidopsis/química , Arabidopsis/genética , Proteínas de Armazenamento de Sementes/análise , Espectroscopia de Infravermelho com Transformada de Fourier/métodos , Proteínas de Arabidopsis/química , Proteínas de Arabidopsis/genética , Técnicas de Inativação de Genes , Globulinas/química , Globulinas/genética , Estrutura Secundária de Proteína , Proteínas de Armazenamento de Sementes/química , Proteínas de Armazenamento de Sementes/genética , Sementes/química , SíncrotronsRESUMO
A description of a coupled electrochemical and spectrometer interface using synchrotron infrared radiation is provided. The interface described allows for the precise and accurate timing needed for time-resolved IR spectroscopic studies of electrochemical systems. The overall interface uses a series of transistor-transistor logic trigger signals generated from the commercial FTIR spectrometer to regulate the recording of control, electrochemical, and IR signals with reproducible and adjustable timing. The instrument has been tested using a thin-layer electrochemical cell with synchrotron light focused through microscope optics. The time-resolved response of the benzoquinone/dihydroxybenzoquinone redox couple is illustrated as an example of the instrument's capability.
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Glioblastoma multiforme (GBM) is one of the most malignant human tumors, with a uniformly poor outcome. One obstacle in curing malignant brain tumors is the limitation of conventional light microscopy in detecting microscopic residual tumor in biopsy samples from the perimeter of the surgically resected tumor. We further refined the identification of GBM tumor tissue at the sub-cellular level, utilising the technique of Synchrotron, sourced mid-infrared (mid-IR) spectromicroscopy. Paired, thin (5 microm) cryosections of snap-frozen human GBM tumor samples removed at elective surgery were mounted on glass slides (hematoxylin and eosin-stained tissue section) and calcium fluoride (CaF2) windows (unstained tissue section for transmission spectromicroscopy), respectively. Concordance of tumor bearing areas identified in the stained section with the unstained IR tissue section was confirmed by the pathologist of the study. Compared with molecular signatures obtained from normal control brain tissue, unique spectroscopic patterns were detected in GBM tumor samples from 6 patients. The identifying features of GBM were: i) high protein-to-lipid ratios (amide I+II/CH2 symmetric stretch; amide I+II/CH2+CH3 symmetric and asymmetric stretch), and ii) considerable enhancement of the intensities of characteristic peaks at 2,957 and 2,871 cm(-1) representing CH3 asymmetric and symmetric stretch, respectively. Spectral data sets were subjected to Ward's algorithm for assignment to similar groups, and then subjected to hierarchical cluster analysis (HCA) by means of false color digital maps. False color images of 5 clusters obtained by HCA identified dominant clusters corresponding to tumor tissue. Corroboration of these findings in a larger number of GBM may allow for more precise identification of these and other types of brain tumors.
Assuntos
Neoplasias Encefálicas/diagnóstico , Glioblastoma/diagnóstico , Espectrofotometria Infravermelho/métodos , Síncrotrons , Adulto , Idoso , Neoplasias Encefálicas/metabolismo , Fluoreto de Cálcio/química , Criança , Análise por Conglomerados , Crioultramicrotomia/métodos , Feminino , Glioblastoma/metabolismo , Histocitoquímica/métodos , Humanos , Lipídeos/análise , Lipídeos/química , Masculino , Pessoa de Meia-Idade , Proteínas/análise , Proteínas/química , Espectrofotometria Infravermelho/instrumentaçãoRESUMO
Partindo de aspectos aparentemente comuns da vida amor, atos de consumo, trabalho, lazer, religião , Bauman e May escreveram esse livro com o objetivo de ajudar as pessoas a entender suas vivências individuais e com os outros. Revelam como a sociologia fornece uma série de observações sobre nossas experiências e mostram as implicações de nossos atos sobre a maneira como conduzimos nossa existência. A edição original, publicada nos Estados Unidos em 1990, foi revista pelos autores e inclui temas atuais como corpo, intimidade, tempo, espaço, desordem, risco, globalização, identidade e novas tecnologias. Cada capítulo aborda problemas que constituem parte de nossa vida cotidiana, dilemas e escolhas com os quais nos deparamos, mas não chegamos a refletir. Os autores ainda sugerem questões que podem servir de orientação para o leitor ou de plano de estudos para professores e alunos. Pensar sociologicamente significa entender aqueles que nos cercam em suas esperanças, desejos, inquietações e preocupações.