PubMed · 1734513
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G E Lienhard, J W Slot, D E James, M M Mueckler. 1992. How cells absorb glucose.. https://doi.org/10.1038/scientificamerican0192-86
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The electronic absorption spectra, photobleaching property, emission, and triplet excited state characteristics of a pentaazadentate porphyrin-like gadolinium(III) complex have been investigated at acidic and basic conditions. The electronic absorption spectrum of this complex exhibits a Soret band at ca. 449 nm and a Q-like band at ca. 880 nm when the pH value of the solution is lower than 6.6. At basic conditions, the Q-like band blue shifts to ca. 624 nm, while the Soret band only shows an approximate 20 nm hyposochromic shift. The acidic solution is relatively stable upon exposure to ambient light, but the basic solution photobleached to colorless in approximately 3 hours. Irradiation of the Soret band of basic solutions at 420 nm causes faster photobleaching than irradiation of the Q-like band (624 nm). The emission of this complex at pH = 6.5 appears at ca. 915 nm (max.) and 1016 nm, which is a mirror image of the Q-like band, indicating the nature of the emitting state being the lowest singlet excited state. At pH = 9.0, the emission band shifts to ca. 585 nm (max.) and 630 nm (shoulder). The triplet transient difference absorption spectrum of the solution at pH = 6.5 exhibits a bleaching band at ca. 460 nm, a narrow positive band at ca. 450 nm, and a broad, moderately intense absorption band from 480 nm extending to the near-IR region (700 nm). The triplet excited state lifetime deduced from the decay of the transient absorption is approximately 81 ns.
Ribonuclease A (RNase A) is immobilized on silver surfaces in oriented and random form via self-assembled monolayers (SAMs) of alkanethiols. The immobilization process is characterized step-by-step using chemically selective near-edge X-ray absorption fine structure spectroscopy (NEXAFS) at the C, N, and S K-edges. Causes of imperfect immobilization are pinpointed, such as oxidation and partial desorption of the alkanethiol SAMs and incomplete coverage. The orientation of the protein layer manifests itself in an 18% polarization dependence of the NEXAFS signal from the N 1s to pi* transition of the peptide bond, which is not seen for a random orientation. The S 1s to C-S sigma* transition exhibits an even larger polarization dependence of 41%, which is reduced to 5% for a random orientation. A quantitative model is developed that explains the sign and magnitude of the polarization dependence at both edges. The results demonstrate that NEXAFS is able to characterize surface reactions during the immobilization of proteins and to provide insight into their orientations on surfaces.
The sorptions of three basic dyes, Astrazon((R)) Blue FGRL (AB), Astrazon((R)) Red GTLN (AR), and methylene blue (MB) onto green macroalga Caulerpa lentillifera were investigated. The results were compared to the sorption performance of a commercial activated carbon (CARBON). The results revealed that the alga exhibited greater sorption capacities than activated carbon for the three basic dyes investigated in this work. The sorption process for all mixture systems (ALGA/AB, ALGA/AR, ALGA/MB, CARBON/AB, CARBON/AR, and CARBON/MB) obeyed the pseudo-second order kinetic model. C. lentillifera could more rapidly sequester AR when compared with activated carbon, but was more slowly in the sorption of AB. For the sorption of MB, both ALGA and CARBON seemed to have the same sorption rate. The sorption processes were initially controlled by both film and pore-diffusion, and only were limited by pore diffusion in the later stage. The isotherms followed Langmuir model which suggested that the sorption was monolayer coverage.