Variations In Relative Intensities Research Articles

Subsurface Probing in Diffusely Scattering Media Using Spatially Offset Raman Spectroscopy

We describe a simple methodology for the effective retrieval of Raman spectra of subsurface layers in diffusely scattering media. The technique is based on the collection of Raman scattered light from surface regions that are laterally offset away from the excitation laser spot on the sample. The Raman spectra obtained in this way exhibit a variation in relative spectral intensities of the surface and subsurface layers of the sample being investigated. The data set is processed using a multivariate data analysis to yield pure Raman spectra of the individual sample layers, providing a method for the effective elimination of surface Raman scatter. The methodology is applicable to the retrieval of pure Raman spectra from depths well in excess of those accessible with conventional confocal microscopy. In this first feasibility study we have differentiated between surface and subsurface Raman signals within a diffusely scattering sample composed of two layers: trans-stilbene powder beneath a 1 mm thick over-layer of PMMA (poly(methyl methacrylate)) powder. The improvement in contrast of the subsurface trans-stilbene layer without numerical processing was 19 times. The potential applications include biomedical subsurface probing of specific tissues through different overlying tissues such as assessment of bone quality through skin, providing an effective noninvasive means of screening for bone degeneration, other skeletal disease diagnosis, and dermatology studies, as well as materials and catalyst research.

Myosin lever disposition during length oscillations when power stroke tilting is reduced

M3 reflection intensity (I(M3)) from tetanized, intact skeletal muscle fiber bundles was measured during sinusoidal length oscillations at 2.8 kHz, a frequency at which the myosin motor's power stroke is greatly reduced. I(M3) signals were approximately sinusoidal, but showed a "double peak" distortion previously observed only at lower oscillation frequencies. A tilting lever arm model simulated this distortion, where I(M3) was calculated from the molecular structure of myosin subfragment 1 (S1). Simulations showed an isometric lever arm disposition close to normal to the filament axis at isometric tension, similar to that found using lower oscillation frequencies, where the power stroke contributes more toward total S1 movement. Inclusion of a second detached S1 in each actin-bound myosin dimer increased simulated I(M3) signal amplitude and improved agreement with the experimental data. The best agreement was obtained when detached heads have a fixed orientation, insensitive to length changes, and similar to that of attached heads at tetanus plateau. This configuration also accounts for the variations in relative intensity of the two main peaks of the M3 reflection substructure after a length change. This evidence of an I(M3) signal distortion when power stroke tilting is suppressed, provided that a large enough amplitude of length oscillation is used, is consistent with the tilting lever arm model of the power stroke.

Anion and cation-yield spectroscopy of core-excited SF6

We report an extensive study on total and partial-ion-yield spectroscopy around both the S 2p and F 1s thresholds in SF(6). All positive and negative single-ion channels have been measured. Below the F 1s threshold we detect a large variation in relative intensity of the resonant structures according to the specific channel monitored, indicating selective fragmentation. Above threshold, at variance with previous cases described by us, we detect high-intensity structures related to shape resonances not only in the cation channels but also for the anions. We discuss the applicability and limits of a model we have developed for the analysis of shape resonances in anion yields as a function of molecular size.

Mixed-ligand copper(II) complexes of dipicolylamine and 1,10-phenanthrolines: The role of diimines in the interaction of the complexes with DNA

Mixed-ligand copper(II) complexes of the type [Cu(dipica)(diimine)](ClO4)2, where dipica is di(2-picolyl)amine and diimine is 1,10-phenanthroline (phen), 5,6-dimethyl-1,10-phenanthroline (5,6-dmp), 2,9-dimethyl-1,10-phenanthroline (2,9-dmp) or dipyridoquinoxaline (dpq), have been isolated and characterized by analytical and spectral methods. The copper(II) complexes exhibit a broad band in the visible region around 675 nm and axial EPR spectra in acetonitrile glass (77 K) with g∥ and A∥ values of ∼2·22 and 185 × 10−4 cm−1 respectively, suggesting the presence of a square-based coordination geometry for the CuN5 chromophore involving strong axial interaction. The interaction of the complexes with CT DNA has been studied using absorption, emission and circular dichroic spectral methods and viscosity measurements. Absorption spectral titrations reveal that the intrinsic DNA binding affinities are dependent upon the nature of the diimine ligand: dpq > 5,6-dmp > phen > 2,9-dmp. This suggests the involvement of the diimine rather than the dipica ‘face’ of the complexes in DNA binding. An intercalative mode of DNA interaction, which involves the insertion of dpq and to a lesser extent the phen ring of the complexes in between the DNA base pairs, is proposed. However, interestingly, the 5,6-dmp complex is involved in hydrophobic interaction of the 5,6-dmp ring in the grooves of DNA. The large enhancement in the relative viscosity of DNA on binding to the dpq and 5,6-dmp complexes supports the proposed DNA binding modes. Further, remarkably, the 5,6-dmp complex is selective in exhibiting a positive-induced CD band on binding to DNA suggesting the transition of the B form of CT DNA to A-like conformation. The variation in relative emission intensities of DNA-bound ethidium bromide observed upon treatment with the complexes parallels the trend in DNA binding affinities.

On the band-to-continuum intensity ratio in the infrared spectra of interstellar carbonaceous dust

Published interpretations of the relative intensity variations of the Unidentified Infrared Bands (UIBs) and their underlying continuum are discussed. An alternative model is proposed, in which a single carrier for both emits a) mostly a continuum when it is electronically excited by photons (visible or UV), or b) exclusively the UIBs, when only chemical energy is deposited by H capture on its surface, inducing only nuclear vibrations. The bands will dominate in atomic H regions but will be overcome by thermal continuum radiation when the ambient field is strong but lacks dissociating photons (900-1100 Angstroms). The model applies to PDRs as well as to limbs of molecular clouds in the ISM and agrees quantitatively with recent satellite observations. It gives indications on atomic H density and UIB intensity provided the ambient radiation field is known. It invokes no chemical, electronic, structural or size change in order to interpret the observed intensity variations.

Glycoform composition profiling of O-glycopeptides derived from human serum IgA1 by matrix-assisted laser desorption ionization-time of flight-mass spectrometry

Pools of O-glycopeptides prepared from trypsin-digested reduced and alkylated human serum IgA1 have been analyzed using matrix-assisted laser desorption ionization-time of flight-mass spectrometry (MALDI-ToF-MS) in the positive-ion mode, using 2,4,6-trihydroxy acetophenone–ammonium citrate matrix. Dozens of such pools prepared from normal serum IgA1 and from serum of patients with a number of different medical conditions have been routinely analyzed in this manner. The glycopeptides present in these pools possess identical amino acid sequences but are substituted with a variety of neutral and sialylated glycans and the spectra obtained were such that individual compositional glycoforms were baseline resolved. In addition, the spectra were reproducible, exhibiting a relative peak intensity and area variation of around 11–16%, enabling the technique to be used for the relative quantitation of the different compositional glycoforms present. This could be achieved manually or by applying a Java program especially developed for this purpose. The MS analysis described here is a major improvement over present MALDI methods used for profiling the O-glycosylation of IgA1. The MS methodology together with the Java data analysis are expected to be generally applicable for profiling O-linked glycopeptides derived from other glycoproteins and probably for N-linked glycopeptide pools.

Glycoform composition profiling of O-glycopeptides derived from human serum IgA1 by matrix-assisted laser desorption ionization-time of flight-mass spectrometry*1

Pools of O-glycopeptides prepared from trypsin-digested reduced and alkylated human serum IgA1 have been analyzed using matrix-assisted laser desorption ionization-time of flight-mass spectrometry (MALDI-ToF-MS) in the positive-ion mode, using 2,4,6-trihydroxy acetophenone–ammonium citrate matrix. Dozens of such pools prepared from normal serum IgA1 and from serum of patients with a number of different medical conditions have been routinely analyzed in this manner. The glycopeptides present in these pools possess identical amino acid sequences but are substituted with a variety of neutral and sialylated glycans and the spectra obtained were such that individual compositional glycoforms were baseline resolved. In addition, the spectra were reproducible, exhibiting a relative peak intensity and area variation of around 11–16%, enabling the technique to be used for the relative quantitation of the different compositional glycoforms present. This could be achieved manually or by applying a Java program especially developed for this purpose. The MS analysis described here is a major improvement over present MALDI methods used for profiling the O-glycosylation of IgA1. The MS methodology together with the Java data analysis are expected to be generally applicable for profiling O-linked glycopeptides derived from other glycoproteins and probably for N-linked glycopeptide pools.

Studies of oxidized hexagonal SiC surfaces and theSiC/SiO2 interface using photoemission and synchrotron radiation

Results of recent photoemission studies of oxidation of hexagonal SiC surfaces andSiO2/SiC interfaces are reviewed and discussed. These investigations have focused on two mainquestions thought to have a significant effect on MOS device characteristics: the existenceof carbon clusters or carbon-containing by-products and the existence of sub-oxides at theSiO2/SiC interface. The presentation is focused on Si-terminated surfaces of hexagonal n-typeSiC(0001) crystals since they to date have been considered the most promising for deviceapplications. The results reviewed show that no carbon clusters or carbon-containingby-product can be detected at the interface of in situ or ex situ grown samples with anoxide layer thickness larger than about 10 Å. Since the presence of carbon clusters wassuggested in a recent scanning microscopy study it appears that they may exist, possiblydepending on the sample preparation method used, but in such low concentrations thatthey are not detectable using photoemission. The presence of sub-oxides at theSiO2/SiC interface has been revealed in recorded Si 2p core level spectra by several groups. Theresults were not unanimous, however. The number of sub-oxides present andthe shifts reported were different. The results of a recent study including alsothe Si 1s core level and Si KLL Auger transitions are therefore examined. Thesetogether with earlier Si 2p data show the presence of only one sub-oxide, assigned toSi1+ oxidation states, besidesthe fully developed SiO2 (Si4+). Possible reasons for the differences obtained earlier are discussed. That the sub-oxide islocated at the interface is concluded from the relative intensity variations observed for thedifferent components versus electron emission angle. An oxide thickness dependence of theSiO2 chemical shift in the core levels and Auger transitions is shown, similar tobut smaller in magnitude than the thickness dependence revealed earlier forSiO2/Si. On cooled SiC(0001) substrates, adsorption of metastable molecularoxygen is suggested to occur in the initial oxidation stage like on theSi(111)-7 × 7 surface. Oxidation results from the C-terminated surface and some preliminary results for the non-polar and surfaces are included and they show distinct differences both as regards the sub-oxidespresent and the amount of carbon-containing by-products at the interface in the initialoxidation stage compared to the Si-terminated SiC(0001) surface.

Determination of spin distributions in ion-beam magnetic textured iron films by magnetic orientation Mössbauer spectroscopy

A promising approach by which to gain information about the spin distributions in different sample layers using depth-sensitive angle-dependent conversion electron Mössbauer spectroscopy is presented in combination with magneto-optical Kerr effect, Rutherford backscattering spectrometry and x-ray diffraction investigations. Three 77 nm thick Fe films containing a 15 nm Fe57 marker layer at different depths were deposited on Si(100) substrates and irradiated under well defined mechanical stress with 200 keV Xe ions. The distribution of the spins in the sample plane was analyzed by Mössbauer spectroscopy and by tilting the sample toward the incident γ beam and observing the variation in angle-dependent relative intensity of the sextet lines. For the sample with the sensitive marker layer in the middle of the ferromagnetic film, all spins were found to be oriented exactly along the mechanical stress axis. This agrees with the angular properties of the macroscopic hysteresis curves measured by the magneto-optic Kerr effect.

Electrochromic modulation of excited-state intramolecular proton transfer: the new principle in design of fluorescence sensors.

Internal Stark effect (or internal electrochromy) consists of the shift of light absorption and emission bands under the influence of electric field produced by proximal charges. In the studies of 3-hydroxyflavone (3HF) derivatives exhibiting the excited-state intramolecular proton transfer (ESIPT), we describe a new phenomenon - a very strong internal electrochromic modulation of this reaction. Fluorescence spectra of 3HF derivatives with charged groups attached to the chromophore from the opposite sides without pi-electronic conjugation, N-[(4'-diethylamino)-3-hydroxy-6-flavonyl]methyl-N,N-dimethyloctylammonium bromide and 4-[4-[4'-(3-hydroxyflavonyl)]piperazino]-1-(3-sulfopropyl)pyridinium, were compared with those of their neutral analogues in a series of representative solvents. The introduction of the proximal charge results in shifts of absorption spectrum and of both normal (N) and tautomer (T) emission bands, which correspond to initial and phototautomer states of the ESIPT reaction. The observed shifts are in accordance with the Stark effect theory. The direction of the shift depends on the position of the proximal charge with respect to the chromophore. The magnitude of the shift depends strongly on the solvent dielectric constant and on screening or unscreening produced by addition of the hydrophobic salts. In all of these cases, the spectral shifts are accompanied by extremely strong variations of relative intensities of N and T emission bands. This signifies a strong influence of internal electric field on the ESIPT reaction, which produces a dramatic change of emission color. Thus, the coupling of the initial electrochromic sensory signal with the ESIPT reaction allows for the breaking of the limit in magnitude of response inherent to common electrochromic dyes. This suggests a new principle of designing the ultrasensitive electrochromic two-wavelength fluorescence sensors and probes for analytical chemistry, macromolecular science, and cellular biology.

Natural variations and reproducibility of in vivo near‐infrared Fourier transform Raman spectroscopy of normal human skin

AbstractWe examined variations of in vivo near‐infrared Fourier transform Raman spectra on healthy human skin. Diurnal and day‐to‐day variation, variation between persons, variation between different spots in the same body region and variation in spectra obtained on the same spot was studied in 13 volunteers. In 140 volunteers we examined variations in Raman spectra caused by skin pigmentation. In our spectral analysis we concentrated on the wavenumbers and relative intensities of the water band around 3250 cm−1, the amide I and amide III bands in the regions around 1645–1680 and 1230–1300 cm−1, respectively, and on the wavenumbers of the strong bands at 1450 and 2940 cm−1 that were used as reference bands. The results showed a diurnal variation and interpersonal variation in relative water intensity. In relative amide I intensity there was a variation between persons and between repeated measurements on the same spot. Between persons the variation might arise from different hydration of proteins, but it is difficult to explain why this variation is seen when repeated measurements are made on the same spot. Day‐to‐day variations were seen in the relative amide III intensity. Variations in amide III band wavenumbers were seen between persons, probably because of different collagen structure. Pigmentation did not influence wavenumbers or intensities considerably, but a regression analysis showed a correlation between background height and pigmentation. The conclusion of our study is that Raman spectra obtained on healthy human skin are reproducible and show mostly small variations. Copyright © 2002 John Wiley & Sons, Ltd.

Formation of [18]trannulenes derived via Bingel reactions between C60F18O isomers and CHBr(CO2Et)2 and between C60F18 and CHX(CO2R)2 (X = Br, Cl; R = Me, Et)

Through extended SN2′ nucleophilic substitution of three fluorine atoms in two isomers of C60F18O by alkyl halogenomalonate anions −CBr(CO2Et)2, (obtained from diethyl bromomalonate in the presence of DBU) we have prepared and characterised the [18]trannulenes, C60F15O[CBr(CO2Et)2]3. Likewise we have prepared [18]trannulenes by the reactions between C60F18 and either −CBr(CO2Me)2 or −CCl(CO2Et)2 (obtained from the corresponding esters 1, 2 and DBU). The formation of the trannulenes from either 1 or 2 shows that the CBr(CO2Me)2 and CCl(CO2Et)2 substituents, though smaller than CBr(CO2Et)2 are still large enough to bring about the extended SN2′ substitution, rather than direct nucleophilic substitution. The products from the oxides show that oxygen does not inhibit trannulene formation either sterically or electronically. Each derivative has the brilliant emerald-green colour of the corresponding [18]trannulene prepared from C60F18 and diethyl bromomalonate, arising from the presence of bands at ca. 615 and 660 nm; minor variations in wavenumber and relative intensities occur according to the derivative. Under less forcing conditions, mono- and bis-substitution products were obtained from the more available symmetrical oxide and from the reaction of the chloro- and bromo-esters with C60F18.

Crystal defects and optical transitions in high purity, high resistivity CdTe for device applications

The structural and optical properties of high purity undoped semi-insulating (SI) Cadmium Telluride (CdTe) crystals, grown by Physical Vapour Transport (PVT) and by modified Vertical Bridgman (BG) techniques have been studied. The samples were obtained from 7N source elements by direct synthesis followed by heat treatment to adjust the stoichiometry. The experimental measurements have been systematically performed using high resolution X-ray diffraction (HRXRD) and cathodoluminescence (CL) techniques, before and after the thermal annealing procedures. The CL emissions from low and high resistivity samples have been studied in order to correlate the CL bands to the presence and concentration of native defects in the crystals. Two broad luminescence bands have been found in addition to the expected emission related to the excitonic recombination. The nature of the defects involved in the transitions was studied by analysing the position of the energy levels and the relative intensity variation of the CL peaks. The effect of the thermal treatments, performed at different temperatures, on the optical and electrical properties of the specimens was also analysed.

Second-Sphere Contributions to Substrate-Analogue Binding in Iron(III) Superoxide Dismutase

A combination of spectroscopic and computational methods has been employed to explore the nature of the yellow and pink low-temperature azide adducts of iron(III) superoxide dismutase (N(3)-FeSOD), which have been known for more than two decades. Variable-temperature variable-field magnetic circular dichroism (MCD) data suggest that both species possess similar ferric centers with a single azide ligand bound, contradicting previous proposals invoking two azide ligands in the pink form. Complementary data obtained on the azide complex of the Q69E FeSOD mutant reveal that relatively minor perturbations in the metal-center environment are sufficient to produce significant spectral changes; the Q69E N(3)-FeSOD species is red in color at all temperatures. Resonance Raman (RR) spectra of the wild-type and Q69E mutant N(3)-FeSOD complexes are consistent with similar Fe-N(3) units in all three species; however, variations in energies and relative intensities of the RR features associated with this unit reveal subtle differences in (N(3)(-))-Fe(3+) bonding. To understand these differences on a quantitative level, density functional theory and semiempirical INDO/S-CI calculations have been performed on N(3)-FeSOD models. These computations support our model that a single azide ligand is present in all three N(3)-FeSOD adducts and suggest that their different appearances reflect differences in the Fe-N-N bond angle. A 10 degrees increase in the Fe-N-N bond angle is sufficient to account for the spectral differences between the yellow and pink wild-type N(3)-FeSOD species. We show that this bond angle is strongly affected by the second coordination sphere, which therefore might also play an important role in orienting incoming substrate for reaction with the FeSOD active site.

Solid State Inclusion of the Nonionic Surfactant C12E4 in β-Cyclodextrin, at Various Humidities: A Combined Raman and 13C CP MAS NMR Study

The inclusion of the nonionic surfactant α-n-dodecyl-ω-hydroxytetra(oxyethylene), C12E4, in β-cyclodextrin (βCD), has been prepared in the solid state and its structure characterized by powder X-ray diffraction, thermogravimetry, and Raman and 13C CP/MAS NMR spectroscopies. Stepwise dehydration was observed in the thermogram, indicating the presence of energetically distinct water molecules. Comparison of the dispersions of 13C chemical shift values for C1 and C4 atoms of the βCD macrocycle, within a series of inclusion compounds of CnEm homologues, reveals a rather complete symmetrization of the βCD macrocycle, and the dispersions of 13C shifts for C6 atoms point to the particular sensitivity of these atoms to hydrogen-bonding type of interactions. The integrated intensity of the O−H Raman stretching band for the βCD inclusion compound of C12E4 is approximately constant for humidities between 20% and 80%. In passing from 15% to 20% of humidity, one observes abrupt relative intensity variations of some Ra...

XPS characterization of xα-Fe 2O 3–(1− x)ZrO 2 for oxygen gas sensing application

XPS characterization was carried out for the solid-solution xα-Fe 2O 3–(1− x)ZrO 2 which is a potential low temperature oxygen gas sensing material. The significant variation of relative intensity of the two peaks in O 1s spectra provides us a unique way to estimate the oxygen vacancy concentrations of xα-Fe 2O 3–(1− x)ZrO 2 with x ranging from 0 to 0.3. The estimation result from XPS coincides with the calculated values from the substitutional model. The relationship between the sensitivity of the fabricated oxygen gas sensor and the oxygen vacancy concentration in the sensing material was established.

Neutral fluorescence probe with strong ratiometric response to surface charge of phospholipid membranes

We report on dramatic differences in fluorescence spectra of 4′-dimethylamino-3-hydroxyflavone (probe F) studied in phospholipid membranes of different charge (phosphatidyl glycerol, phosphatidylcholine (PC), their mixture and the mixture of PC with a cationic lipid). The effect consists in variations of relative intensities at two well-separated band maxima at 520 and 570 nm belonging to normal (N*) and tautomer (T*) excited states of flavone chromophore. Based on these studies we propose a new approach to measure electrostatic potential at the surface layer of phospholipid membranes, which is based on potential-dependent changes of bilayer hydration and involves very sensitive and convenient ratiometric measurements in fluorescence emission.

Collective excitations in alkali metals on Al(111)

The photon-excited multipole and the bulklike modes have been studied in Na/Al(111) and K/Al(111). These collective modes appear for a coverage of ≥2 monolayers. Both the multipole and the bulklike modes exhibit interesting variations in frequency, line shape, and relative intensity with adlayer coverage. The reasons for such behavior are discussed on the basis of existing theoretical results. The substrate Al multipole is found to be attenuated by smooth adlayer growth. Deposition of K on two monolayer Na/Al(111) results in the growth of K related collective excitation at the expense of the Na modes. For complicated surface structures like Al(111)-(√3×√3)R30°:K or the Al(111)-(2×2):Na surface alloy, electron charge-density profiles at the surface are calculated based on ab initio density-functional theory-local-density approximation method to explain the photoyield data. The importance of the shape of the charge-density profile in determining the collective excitations is demonstrated. For Al(111)-(√3×√3)R30°:K, a strong increase in intensity in the energy region of the K plasmons is observed in the on-top structure which is attributed to a mixed plasmon mode. These results show that while the experimental observations for smooth alkali-metal adlayers are in good agreement with existing theory, more theoretical work, especially for the complicated surface structures, is desirable.

Forward degenerate four-wave-mixing spectra of NO in the strong-field regime including polarization, line coupling, and multipole effects. II. Experiments

The behavior of forward degenerate four-wave-mixing spectra of NO $\~A\ensuremath{-}\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{X}(0,0)$ in the presence of strong optical fields is observed for two crossed-polarization arrangements. The NO features in terms of coupled and isolated lines are interpreted with the complete model described in the preceding paper [V. Kr\"uger et al., paper I, Phys. Rev. 63, 012716 (2001)]. In the intermediate regime of saturation, the variation of relative line intensities with input energy is properly reproduced for NO. Thanks to these fits, we have been able to determine saturation threshold with a good accuracy. Important properties of the different polarization schemes are observed and discussed.

Electric-field-induced charge-density variations in covalently bonded binary compounds

Extended data sets for the relative intensity variation of x-ray Bragg reflections of GaAs and ZnSe caused by an external electric field were collected using a modulation demodulation technique. In particular, the functional dependence of the intensity variation on field strength and wavelength of the synchrotron radiation was determined. The wavelength dependence allows to determine the phases of the difference-structure factors. An interpretation of all data using a semiempirical model leads to the following conclusions: The main contribution to the measured effects comes from a displacement of the anion sublattice relative to the cation sublattice. The response of the electron density to an external electric field is negligibly small according to density functional theory calculations with both, clamped and ``free'' ions. This effect is much smaller than the redistribution of the electron density in the bond region associated with the displacements of the atoms causing a change in overlap. The dependence of the sublattice displacement on the strength of the external electric field $\mathbf{E}\ensuremath{\parallel}[111]$ is estimated to be $1.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}\AA{}/{\mathrm{V}\mathrm{}\mathrm{mm}}^{\mathrm{\ensuremath{-}}1}$ for GaAs and $13.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}\AA{}/{\mathrm{V}\mathrm{}\mathrm{mm}}^{\mathrm{\ensuremath{-}}1}$ for ZnSe. For the mainly covalent GaAs the inverse piezoelectric effect can be explained by this bond-length variation, in contrast to the much more ionic compound ZnSe for which this is not the case.