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At least 235 records · Page 13Linked to original sources
PubMed2005

Ubiquitous strategy for probing ATR surface-enhanced infrared absorption at platinum group metal-electrolyte interfaces.

A versatile two-step wet process to fabricate Pt, Pd, Rh, and Ru nanoparticle films (simplified as nanofilms hereafter) for in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) study of electrochemical interfaces is presented, which incorporates an initial chemical deposition of a gold nanofilm on the basal plane of a silicon prism with the subsequent electrodepostion of desired platinum group metal overlayers. Galvanostatic electrodeposition of Pt, Rh, and Pd from phosphate or perchloric acid electrolytes, or potentiostatic electrodeposition of Ru from a sulfuric acid electrolyte, yields sufficiently "pinhole-free" overlayers as evidenced by electrochemical and spectroscopic characterizations. The Pt group metal nanofilms thus obtained exhibit strongly enhanced IR absorption. In contrast to the corresponding metal films electrochemically deposited directly on glassy carbon and bulk metal electrodes, the observed enhanced absorption for the probe molecule CO exhibits normal unipolar band shapes. Scanning tunneling microscopic (STM) images reveal that fine nanoparticles of Pt group metals are deposited around wavy and stepped bunches of Au nanoparticles of relatively large sizes. This ubiquitous strategy is expected to open a wide avenue for extending ATR surface-enhanced IR absorption spectroscopy to explore molecular adsorption and reactions on technologically important transition metals, as exemplified by successful real-time spectroscopic and electrochemical monitoring of the oxidation of CO at Pd and that of methanol at Pt nanofilm electrodes. The spectral features of free water molecules coadsorbed with CO on Pt, Pd, Rh, and Ru are also discussed.

Journal Article↗
PubMed2005

Determination of anisotropic optical constants and surface coverage of molecular films using polarized visible ATR spectroscopy. Application to adsorbed cytochrome c films.

This article describes a method to determine the anisotropic optical constants and surface coverage of molecular films using polarized attenuated total reflectance (ATR) absorbance measurements. We have extended the transfer-matrix formalism to describe birefringent and dichroic films in ATR geometries and have combined it with an iterative numerical procedure to determine the anisotropic values of both the real (n) and imaginary (k) parts of the complex refractive index of the film under investigation. Anisotropic values of the imaginary part of the refractive index (k) allow for the determination of the surface coverage and one order parameter of the film. To illustrate this approach, we have used cytochrome c (cyt c) protein films adsorbed to glass and indium tin oxide (ITO) surfaces. Experimental results show that cyt c films on these surfaces, which were formed under identical conditions, have significant differences in their surface coverages (11.2 +/- 0.4 pmol/cm(2) on glass and 21.7 +/- 0.9 pmol/cm(2) on ITO); however, their order parameters are similar (0.30 +/- 0.02 on glass and 0.36 +/- 0.04 on ITO).

Adsorption↗
PubMed2006

Raman and in situ FTIR-ATR characterization of polyazulene films and its derivate.

Polymers from azulene (A) and 2-[(E)-2-azulen-1-ylvinyl]thiophene (B) electrochemically synthesized are materials with a broad absorbance in the UV-vis spectral region. An experimental approach to correlate the Raman and in situ FTIR spectra from azulene based polymers according to the effective conjugation coordinate theory (ECC) is presented. Film characterization was made by Raman and Fourier transform infrared attenuated total reflectance, FTIR-ATR spectroscopy. Throughout the whole work A was used as a model compound. The polymers were synthesized at different polymerization potentials in order to create different structures. Polyazulene showed a divergent Raman response upon change in excitation wavelength, lambda(exc)= 514 nm and lambda(exc)= 780 nm, in comparison to common conducting polymers. The FTIR-ATR measurements were made during charging-discharging of the polymers. The IR spectra of the conducting state show new doping induced infrared active vibrations (IRAV) in the region between 1600 and 700 cm(-1) and a broad electronic absorption in the high energy range (4000-8000 cm(-1)). Two different structures of the polymer from B are formed, and both follow the trends for conducting polymers upon charging.

Journal Article↗
PubMed2005

Evidence for the mechanism of photocatalytic degradation of the bacterial wall membrane at the TiO2 interface by ATR-FTIR and laser kinetic spectroscopy.

The photocatalytic peroxidation of E. coli cell, lipo-polysaccharide (LPS), phosphatidyl-ethanolcholine (PE), and peptidoglycan (PGN) of the E. coli membrane wall has been investigated on TiO2 porous films by ATR-FTIR spectroscopy. The fast reactions of the photogenerated charge carriers in TiO2 with E. coli, LPS, and PE were monitored by laser kinetic spectroscopy. ATR-FTIR spectroscopy allowed the identification of E. coli, LPS, PE, and PGN as photocatalytic peroxidation products. The PGN was observed to be the most resistant membrane wall component. Shorter peroxidation times were observed for LPS and PE. Laser photolysis shows that E. coli, LPS, and PE compete in the scavenging of a surface trapped holes (h+) with the recombination reaction of h+ with the generated electrons (e-) within times > 50 ns. This scavenging leads to the formation of organic radicals initiating the radical chain peroxidation of E. coli, LPS, PE, and PE.

Cell Wall↗
PubMed2004

Adsorption of Suwannee River fulvic acid on aluminum oxyhydroxide surfaces: an in situ ATR-FTIR study.

The adsorption of Suwannee River fulvic acid (SRFA) on boehmite, gamma-AlO(OH), has been examined by both macroscopic adsorption and in situ ATR-FTIR spectroscopic techniques. At a SRFA concentration approaching surface saturation (F = 5.3 micromol m(-2)), adsorption is at a maximum at low pH and decreases as pH is increased. The ATR-FTIR spectral features of adsorbed SRFA are very similar to those measured approximately 1-2 pH units higher in solution, indicating that (i) the SRFA appears to be predominantly adsorbed at the boehmite/water interface in an outer-sphere complexation mode and (ii) the positively charged boehmite/water interface stabilizes SRFA molecules against protonation at low pH.

Adsorption↗
PubMed2006

Multivariate analysis of ATR-IR spectroscopic data: applications to the solid-liquid catalytic interface.

It is demonstrated that attenuated total reflection infrared (ATR-IR) spectroscopy coupled with multivariate data analysis can be effectively used for in situ investigation of supported catalyst-liquid interfaces. Both formaldehyde adsorption/dissociation in water and acetonitrile adsorption in hexane on thin (ca 10 mum) films of 5 wt % Pt/gamma-Al(2)O(3) deposited on a germanium waveguide have been investigated. The multivariate analysis applies classical least squares (CLS) and partial least squares (PLS) methods to the ATR-IR data in order to correlate spectral changes with known sources of experimental variation (i.e., time, concentration of solution species, etc.). The formaldehyde adsorption experiments revealed no spectroscopic evidence for adsorbed molecular formaldehyde under the conditions examined. However, the dissociation product carbon monoxide was observed to form in atop configuration on Pt, likely on edges and terrace sites. Isotope labeling experiments suggest that a pair of peaks observed at 1990 and 2060 cm(-)(1) during treatments of Pt in H(2)-saturated water arise at least in part from nu(Pt)(-)(H) stretching of adsorbed atomic hydrogen. Acetonitrile was found to adsorb on the Pt catalyst by sigma-bonding of the CN group with the platinum, yielding apparent surface peaks that are almost identical to that observed in the liquid phase. A peak at 1641 cm(-)(1) was observed which was assigned to the adsorption of the CN group in a tilted configuration involving a combination of end-on and pi interaction with the surface. This species was found to be reactive toward hydrogen, suggesting that it might play a role in nitrile hydrogenation. The prospects of using this approach to examine solid-catalyzed liquid-phase reactions are discussed in light of these findings.

Journal Article↗
PubMed2007

Biochemical interaction analysis on ATR devices: a wet chemistry approach for surface functionalization.

A new generic device suitable for the investigation of ligand-receptor interactions is presented. In particular, the research focused on optical waveguides constituted by an attenuated total internal reflection (ATR) element, transparent in the infrared and whose surfaces were activated in view of covalently binding a receptor. Silicon and germanium ATR elements were considered. The original method is based on the grafting of bifunctional spacer molecules directly at the surface of the germanium crystal, avoiding the deposition of an intermediate metal layer. The grafting of these binding molecules (under their N-hydroxysuccinimidyl ester forms) was performed either by wet chemistry or by photochemistry. The functionalized surfaces, which allow the binding of molecules bearing peripherical NH2 groups, were successfully used, e.g., for the detection of proteins (streptavidin) or of small molecules (biotin). In the latter case, the biotin was readily detected for concentrations as low as 10(-12) M.

Adsorption↗
PubMed1995

Use of ATR-FTIR spectroscopy to study the diffusion of ethanol through glycerogelatin films.

The use of ATR-FTIR spectroscopy to study the permeability of a glycerogelatin film is described. Measurement of the diffusion coefficient of ethyl alcohol-d in the film showed excellent reproducibility. Comparison of results from this technique with those previously obtained using an air-flow receptor phase diffusion cell show good agreement in terms of lag time assessed diffusion coefficients. ATR-FTIR spectroscopy revealed time-dependent changes in the composition of the glycerogelatin film during the diffusional process. It was also demonstrated that the concurrent assessment of both diffusant penetration and film composition is feasible.

Diffusion↗
PubMed1998

Duplication of ATR inhibits MyoD, induces aneuploidy and eliminates radiation-induced G1 arrest.

Chromosome 3q alterations occur frequently in many types of tumours. In a genetic screen for loci present in rhabdomyosarcomas, we identified an isochromosome 3q [i(3q)], which inhibits muscle differentiation when transferred into myoblasts. The i(3q) inhibits MyoD function, resulting in a non-differentiating phenotype. Furthermore, the i(3q) induces a 'cut' phenotype, abnormal centrosome amplification, aneuploidy and loss of G1 arrest following gamma-irradiation. Testing candidate genes within this region reveals that forced expression of ataxia-telangiectasia and rad3-related (ATR) results in a phenocopy of the i(3q). Thus, genetic alteration of ATR leads to loss of differentiation as well as cell-cycle abnormalities.

Aneuploidy↗
PubMed2006

ATR-dependent radiation-induced gamma H2AX foci in bystander primary human astrocytes and glioma cells.

Radiotherapy is an important treatment for patients suffering from high-grade malignant gliomas. Non-targeted (bystander) effects may influence these cells' response to radiation and the investigation of these effects may therefore provide new insights into mechanisms of radiosensitivity and responses to radiotherapy as well as define new targets for therapeutic approaches. Normal primary human astrocytes (NHA) and T98G glioma cells were irradiated with helium ions using the Gray Cancer Institute microbeam facility targeting individual cells. Irradiated NHA and T98G glioma cells generated signals that induced gammaH2AX foci in neighbouring non-targeted bystander cells up to 48 h after irradiation. gammaH2AX bystander foci were also observed in co-cultures targeting either NHA or T98G cells and in medium transfer experiments. Dimethyl sulphoxide, Filipin and anti-transforming growth factor (TGF)-beta 1 could suppress gammaH2AX foci in bystander cells, confirming that reactive oxygen species (ROS) and membrane-mediated signals are involved in the bystander signalling pathways. Also, TGF-beta 1 induced gammaH2AX in an ROS-dependent manner similar to bystander foci. ROS and membrane signalling-dependent differences in bystander foci induction between T98G glioma cells and normal human astrocytes have been observed. Inhibition of ataxia telangiectasia mutated (ATM) protein and DNA-PK could not suppress the induction of bystander gammaH2AX foci whereas the mutation of ATM- and rad3-related (ATR) abrogated bystander foci induction. Furthermore, ATR-dependent bystander foci induction was restricted to S-phase cells. These observations may provide additional therapeutic targets for the exploitation of the bystander effect.

Astrocytes↗
PubMed2001

Determination of carbonate in marine solid samples by FTIR-ATR spectroscopy.

A method for detecting carbonate in marine solid samples (sediments, corals) by Fourier transform infrared spectroscopy (FTIR) coupled to the total attenuated reflectance (ATR) technique is described. Compared to other techniques, the proposed method is not based on the measurement of CO2 evolved by combustion or acidification of the sample, but on the direct measurement of carbonate present in the sample. For this reason, the method by FTIR-ATR spectroscopy does not require any chemical pre-treatment. The proposed method allows determination of carbonate in the range 6-100% (w/w) as Na2CO3 and gives comparable results with the determination of inorganic carbon by elemental analysis.

Animals↗
PubMed2004

A new FTIR-ATR cell for drug diffusion studies.

The drug diffusion of most compounds, particularly hydrophilic molecules through the skin is limited by the permeation of the outermost cell layers of the epidermis, the stratum corneum(SC). For this reason it is of interest to characterize drug diffusion processes through this skin layer. A new FTIR-ATR cell was developed for non-invasive real time measurements of drug diffusion. The diffusion of water through an artificial polyethyleneglycol-polydimethylsiloxane membrane was studied. Additionally the diffusion of urea in human SC was analyzed. Based on a mathematical model the diffusion coefficients were derived. We could reveal that this cell associates the advantages of the Franz diffusion cell and the FTIR-ATR spectroscopy as a new powerful method for determining drug diffusion through biological membranes.

Diffusion↗
PubMed2005

Adsorption kinetics of L-glutathione on gold and structural changes during self-assembly: an in situ ATR-IR and QCM study.

The adsorption of L-glutathione (gamma-Glu-Cys-Gly) from ethanol on gold surfaces was studied in situ by both attenuated total reflection infrared (ATR-IR) spectroscopy and using a quartz crystal microbalance (QCM). The molecule is firmly anchored to the gold surface through the thiol group. Different IR signals of adsorbed L-glutathione, notably the amide I and nu(-COOH), show significantly different behavior with time, which reveals that their increase is not related to adsorption (mass uptake) alone. This indicates that structural transformations take place during the formation of the self-assembled monolayer (SAM). In particular, the intensity of the acid signal increases quickly only within the first couple of minutes. The complexity of the self-assembling process is confirmed by QCM measurements, which show fast mass uptake within about 100 s followed by a considerably slower regime. The structural change superimposed on the mass uptake is, based on the in situ time-resolved ATR-IR measurements, assigned to the interaction of the acid group of the Gly moiety with the surface. The latter group is protonated in ethanol but deprotonates upon interaction with the gold surface. The protonation-deprotonation equilibrium is sensitive to external stimuli, such as the presence of dissolved L-glutathione molecules. The interaction of the acid group with the surface and concomitant deprotonation proceeds via two distinguishable steps, the first being a reorientation of the molecule, followed by the deprotonation.

Adsorption↗
PubMed2002

Cellular responses to the DNA strand-scission enediyne C-1027 can be independent of ATM, ATR, and DNA-PK kinases.

The current paradigm based upon ionizing radiation (IR) studies states that cells deficient in either ataxia-telangiectasia-mutated kinase (ATM) or related phosphatidylinositol 3 (PI 3) -kinases (ATR and DNA-PK) are hypersensitive to DNA strand breaks because they are unable to rapidly activate downstream effectors such as p53. Here we have contrasted cell responses to IR and C-1027, a radiomimetic antibiotic that induces DNA strand breaks. At equal levels of DNA double strand breaks, cell lines with inactive ATM or other phosphatidylinositol 3-kinases displayed classical hypersensitivity to IR but not to C-1027. Moreover, phosphorylation of p53 Ser-15 induced by C-1027 was independent of ATM, ATR, or DNA-PK function. We have concluded that the model based on IR studies cannot always be directly applied to DNA damage induced by other strand-scission agents.

Aminoglycosides↗
PubMed2003

Phosphorylated claspin interacts with a phosphate-binding site in the kinase domain of Chk1 during ATR-mediated activation.

Claspin is essential for the ATR-dependent activation of Chk1 in Xenopus egg extracts containing incompletely replicated or UV-damaged DNA. The activated form of Claspin contains two repeated phosphopeptide motifs that mediate its binding to Chk1. We show that these phosphopeptide motifs bind to Chk1 by means of its N-terminal kinase domain. The binding site on Chk1 involves a positively charged cluster of amino acids that contains lysine 54, arginine 129, threonine 153, and arginine 162. Mutagenesis of these residues strongly compromises the ability of Chk1 to interact with Claspin. These amino acids lie within regions of Chk1 that are involved in various aspects of its catalytic function. The predicted position on Chk1 of the phosphate group from Claspin corresponds to the location of activation-loop phosphorylation in various kinases. In addition, we have obtained evidence that the C-terminal regulatory domain of Chk1, which does not form a stable complex with Claspin under our assay conditions, nonetheless has some role in Claspin-dependent activation. Overall, these results indicate that Claspin docks with a phosphate-binding site in the catalytic domain of Chk1 during activation by ATR. Phosphorylated Claspin may mimic an activating phosphorylation of Chk1 during this process.

Adaptor Proteins, Signal Transducing↗
PubMed2004

Control of replication origin density and firing time in Xenopus egg extracts: role of a caffeine-sensitive, ATR-dependent checkpoint.

A strict control of replication origin density and firing time is essential to chromosomal stability. Replication origins in early frog embryos are located at apparently random sequences, are spaced at close ( approximately 10-kb) intervals, and are activated in clusters that fire at different times throughout a very brief S phase. Using molecular combing of DNA from sperm nuclei replicating in Xenopus egg extracts, we show that the temporal order of origin firing can be modulated by the nucleocytoplasmic ratio and the checkpoint-abrogating agent caffeine in the absence of external challenge. Increasing the concentration of nuclei in the extract increases S phase length. Contrary to a previous interpretation, this does not result from a change in local origin spacing but from a spreading of the time over which distinct origin clusters fire and from a decrease in replication fork velocity. Caffeine addition or ATR inhibition with a specific neutralizing antibody increases origin firing early in S phase, suggesting that a checkpoint controls the time of origin firing during unperturbed S phase. Furthermore, fork progression is impaired when excess forks are assembled after caffeine treatment. We also show that caffeine allows more early origin firing with low levels of aphidicolin treatment but not higher levels. We propose that a caffeine-sensitive, ATR-dependent checkpoint adjusts the frequency of initiation to the supply of replication factors and optimizes fork density for safe and efficient chromosomal replication during normal S phase.

Animals↗
PubMed2006

ATR, PML, and CHK2 play a role in arsenic trioxide-induced apoptosis.

Arsenic trioxide (ATO) is a potent anti-leukemic chemotherapeutic agent for acute promyelocytic leukemia (APL) that results from a t (15, 17) chromosomal translocation that produces PML-RARalpha, a fusion protein between a tumor suppressor PML and the retinoic acid receptor RARalpha. APL patients are initially treated with retinoic acid, but most develop resistance and relapse. In contrast, ATO induces prolonged remissions even in the relapsed cases. However, the molecular mechanisms by which ATO kills the leukemic cells are not fully understood. We find that ATO induces apoptosis, at least in part, by activating proapoptotic kinase Chk2. ATO does this by stimulating ATR (ataxia telangiectasia mutated and Rad3-related) kinase, a Chk2-activating kinase. In conjunction, ATO degrades PML-RARalpha, resulting in the restoration of PML, which is required for autophosphorylation and full activation of Chk2. As a result, the p53-dependent apoptosis pathway is activated. Based on this, we propose that a pathway composed of ATR, PML, Chk2, and p53 plays a role in ATO-mediated apoptosis, a notion that is consistent with the observation that Chk2 is genetically intact and mutations in the p53 gene are extremely rare in APL.

Animals↗
PubMedDate not supplied

Translocation of amino acyl residues from the membrane interface to the hydrophobic core: thermodynamic model and experimental analysis using ATR-FTIR spectroscopy.

The interactions of a series of histidine-containing peptides with biological model membranes have been investigated by attenuated total reflection Fourier transform infra red (ATR-FTIR) spectroscopy. Related peptides have previously been shown to exhibit antibiotic and DNA transfection activities. The 26-residue LAH4X4 peptides were designed in such a manner to form amphipathic helical structures in membrane environments. Four histidines and four variable amino acids X constitute one face of the helix whereas leucines and alanines characterize the opposite hydrophobic surface. The dichroic ratio of ATR-FTIR spectra has been used to follow the pH-dependent transition from in-plane to transmembrane alignments upon increase in pH. A theoretical model of the topological modulations is presented and the experimental transition curves analysed in order to reveal the Gibbs free energy of transition. The novel concept provides access to the free energy changes associated with the amino acids X incorporated into an extended alpha-helix and in the context of phospholipid bilayers. For the peptides of the series the Gibbs free energies associated with the transition from the membrane interface to the bilayer interior follow the sequence of amino acids: L<A approximately I<S approximately F<T approximately G<V approximately W<<Y.

Amino Acids↗