Search results for "absorption."
showing 10 items of 2682 documents
A study of electron transfer in Ru(dcbpy)2(NCS)2 sensitized nanocrystalline TiO2 and SnO2 films induced by red-wing excitation.
2008
Excited state dynamics and electron transfer from the Ru(dcbpy)2(NCS)2 (RuN3) sensitizer to semiconductor nanoparticles were studied using time-resolved femtosecond absorption spectroscopy. We found that excitation of the red wing of the absorption spectrum of the sensitizer populates the (3)MLCT state directly, both in solution and attached on semiconductor nanoparticle films. Electron injection is slowed down and becomes gradually less efficient as excitation moves towards red from the absorption maximum at 535 nm. At 675 nm the injection is non-exponential and characterized by 5, 30 and 180 ps time constants. The non-exponential electron injection observed is assigned to injection from a…
Pigment organization and energy transfer dynamics in isolated photosystem I (PSI) complexes from Arabidopsis thaliana depleted of the PSI-G, PSI-K, P…
2002
Abstract Green plant photosystem I (PSI) consists of at least 18 different protein subunits. The roles of some of these protein subunits are not well known, in particular those that do not occur in the well characterized PSI complexes from cyanobacteria. We investigated the spectroscopic properties and excited-state dynamics of isolated PSI-200 particles from wild-type and mutant Arabidopsis thaliana plants devoid of the PSI-G, PSI-K, PSI-L, or PSI-N subunit. Pigment analysis and a comparison of the 5K absorption spectra of the various particles suggests that the PSI-L and PSI-H subunits together bind approximately five chlorophyll a molecules with absorption maxima near 688 and 667nm, that…
Ferricytochrome c encapsulated in silica hydrogels: correlation between active site dynamics and solvent structure.
2003
Ferricytochrome c encapsulated in silica hydrogels has been prepared by the sol-gel technique following, with some modifications, the procedure originally developed by Ellerby et al. (Science 255 1113 (1992)). A suitable preparation of hydrogels enables having both 'wet' and 'dry' samples. Wet samples have a high water content: as the temperature is lowered below approximately 260 K, water freezes and the samples crack. On the contrary, dry samples have a low water content (hydration h approximately equal 0.35): in these conditions water does not freeze even at cryogenic temperatures and the samples remain transparent and non-cracking. The dynamics of ferricytochrome c and its dependence on…
Perpetual proliferation of LYT-1 cells requires repetitive signals for IL-2 receptor induction by antigen-presenting cells.
1984
Abstract T cell lines with specificity for bovine insulin and ovalbumin were maintained by serial stimulation with antigen presented on irradiated syngeneic spleen cells, alternating 3 days later with subculture in IL-2 containing medium (CM). When the cultures were repetitively split in CM, with concomitant dilution of antigen-presenting cells, a gradual loss of proliferative capacity of the cells in the presence of CM was observed. Absorption studies revealed a 20-fold reduction of IL-2 receptors on the surface of T blasts assayed 12 days after antigenic stimulation as compared with day 5 blasts. This decrement in the number of IL-2 acceptor sites reflected an actual decrease in cell surf…
Nortriptyline for smoking cessation: Release and human skin diffusion from patches
2009
Abstract The objective of this work was to develop a simple and inexpensive transdermal formulation containing Nortriptyline Hydrochloride (NTH) for smoking cessation support therapy. Hydroxypropyl-methyl-cellulose was chosen as polymer and a mixture of transdermal enhancers (selected from previous research) was incorporated. The formulations were characterised in terms of appearance, thickness, uniformity of NTH content, release and skin permeation. Release studies demonstrated controlled release for four formulations. Diffusion studies were performed through human heat separated epidermis (HHSE) using Franz Diffusion Cells (FDC). Patches provided different fluxes varying from 20.39 ± 7.09…
Quaternary structure dependence of kinetic hole burning and conformational substates interconversion in hemoglobin.
2003
Using a sol-gel encapsulation technique, we have prepared samples of CO saturated human adult hemoglobin locked in the R or T quaternary conformation. We report time-resolved spectra of these samples in the Soret region following flash photolysis, in the time interval ranging from 250 ns to 200 ms and in the temperature interval of 100-170 K. A suitable analysis of the measured difference spectra enables us to obtain the spectral contribution of deoxyHb and HbCO molecules as a function of time and/or of the fraction N(t) of deoxyHb molecules. In our experimental time window geminate CO rebinding to hemoglobin in the T quaternary conformation is about 2 orders of magnitude slower than to hem…
Associations of Maternal Cell-Phone Use During Pregnancy With Pregnancy Duration and Fetal Growth in 4 Birth Cohorts
2019
Results from studies evaluating potential effects of prenatal exposure to radio-frequency electromagnetic fields from cell phones on birth outcomes have been inconsistent. Using data on 55,507 pregnant women and their children from Denmark (1996-2002), the Netherlands (2003-2004), Spain (2003-2008), and South Korea (2006-2011), we explored whether maternal cell-phone use was associated with pregnancy duration and fetal growth. On the basis of self-reported number of cell-phone calls per day, exposure was grouped as none, low (referent), intermediate, or high. We examined pregnancy duration (gestational age at birth, preterm/postterm birth), fetal growth (birth weight ratio, small/large size…
Copper, iron, and zinc contents in human milk during the first three months of lactation: A longitudinal study
2000
The aim of the study has been to analyze the evolution of copper, iron, and zinc contents in human milk, from colostrum to the third postpartum month, following a longitudinal design, under specific conditions of sample collection and to apply an analytical procedure previously optimized to reduce any variation outside physiological lactation. The copper, iron, and zinc concentrations in 144 milk samples from 39 healthy puerpera women, were analyzed in five stages by flame atomic absorption spectrometry, following a standardized protocol. Copper presented a gradual decrease from 0.38 mg/L to 0.19 mg/L by the 90th day; the particular analysis from colostrum to transitional milk manifested th…
In vitro degradation of porous PLLA/pearl powder composite scaffolds
2013
Abstract The in vitro degradation behavior of poly- l -lactide (PLLA), PLLA/aragonite pearl powder and PLLA/vaterite pearl powder scaffolds was investigated. The scaffolds were soaked in phosphate buffer solution (PBS) up to 200 days. Scanning electron microscopy (SEM), gel permeation chromatography (GPC), and differential scanning calorimetry (DSC) were used to observe any degradation of the scaffolds. Degradation behaviors such as changes in pH, porosity, bulk density, water absorption, weight loss and mechanical properties were discussed. The results show that a gradual increase of the pH in composite scaffolds can decrease the rate of hydrolysis of PLLA. PLLA/vaterite and PLLA/aragonite…
Protein dynamics observed by tunable mid-IR quantum cascade lasers across the time range from 10 ns to 1 s
2017
We have developed a spectrometer based on tunable quantum cascade lasers (QCLs) for recording time-resolved absorption spectra of proteins in the mid-infrared range. We illustrate its performance by recording time-resolved difference spectra of bacteriorhodopsin in the carboxylic range (1800–1700 cm− 1) and on the CO rebinding reaction of myoglobin (1960–1840 cm− 1), at a spectral resolution of 1 cm− 1. The spectrometric setup covers the time range from 4 ns to nearly a second with a response time of 10–15 ns. Absorption changes as low as 1 × 10− 4 are detected in single-shot experiments at t > 1 μs, and of 5 × 10− 6 in kinetics obtained after averaging 100 shots. While previous time-res…