Integrated fractal analysis of silica: Adsorption, electronic energy transfer, and small-angle x-ray scattering.
Explore the source record for details and available documents.
Journal Article↗
Biomedical subjects
D Huppert
Publications and source records attributed to D Huppert.
Direct measurement of proton transfer as a probing reaction for the microenvironment of the apomyoglobin heme-binding site.
Aromatic alcohols fluoresce at different wavelengths in their neutral (phiOH*) and anionic (phiO-*) excited states. Consequently, time-resolved fluorescence measurements, at the respective wavelengths, can be used for measuring the rates of proton dissociation and recombination of the excited molecule. As the lifetime of the excited state is very short (a few nanoseconds), the measured reaction is that which takes place in a volume corresponding to the diffusion distance of the proton during the lifetime of the excited state. 8-Hydroxypyrene 1,3,6-trisulfonate (pK = 7.7, pK* = 0.5) is bound to apomyoglobin with a stoichiometry of 1:1. In the bound state its neutral form fluorescence increase 20-fold. The binding affinity is pH-dependent. Two protonatable groups, with pK = 6.5, participate in the stabilization of the negatively charged ligand in the binding site. The ligand is bound only to the apoprotein and is displaced from its site by hemin. Thus we suggest that the ligand is bound to the heme binding site of apomyoglobin. Time-resolved fluorescence of the bound ligand yields the rate constants of proton dissociation and recombination as taking place within the heme binding cavity of apomyoglobin. The rate of proton dissociation is slowed to 7% of the rate measured for the free ligand. Such a slow dissociation indicates a strong interaction of the water in the cavity with the walls [Gutman, M., Huppert, D., and Nachliel, E. (1982) Eur. J. Biochem. 121, 637-642]. The water activity in the site is equivalent to alpha (H2O) = 0.67.
Apoproteins↗
Kinetic studies of proton transfer in the microenvironment of a binding site.
Excitation of 8-hydroxypyrene 1,3,6-trisulfonate to its first electronic singlet state converts the compound from weak base (pK degrees = 7.7) into a strong acid (pK* = 0.5). The dissociation of the proton in water or dilute salt solution is a very fast reaction, K12 = 1 X 10(10) S-1. In concentrated salt solutions the dissociation is slowed as an exponential function of the chemical activity of the water in the solution. This kinetic parameter has been used to gauge the properties of the microenvironment of the binding sites of bovine serum albumin at which this compound is bound. Time-resolved fluorometry reveals two distinct steps: a rapid dissociation of the proton with tau = 300 +/- 40 ps which lasts approximately 0.5 ns, followed by a slower reaction with tau = 3.3 ns. The first rapid phase represents proton dissociation taking place in the binding site. From the rate constant K = 3.3 X 10(9) s-1 we estimate that the ability of the water molecules in the site to hydrate the ejected proton is equivalent to a salt solution with water activity of 0.85. The slow phase represents the escape of the proton from the binding site. The rate of the escape, 1.4 X 10(8) s-1, is significantly slower than diffusion-controlled dissociation. It is concluded that the shape of the site or its lowered proton conductivity do not allow a rapid escape of the proton to the bulk. Still it should be remembered that the escape of the proton is 10(5)-10(6)-times faster than a typical turnover of an enzyme.U
Arylsulfonates↗
Probing the micelle/water interface by a rapid laser-induced proton pulse.
The laser-induced pH jump (Gutman, M. and Huppert, D.J. (1979) Biochem. Biophys. Methods 1, 9-19) has a time resolution capable of measuring the diffusion-controlled rate constant of proton binding. In the present study we employed this technique for measuring the kinetics of protonation-deprotonation of surface groups of macromolecules. The heterogeneous surface of proteins excludes them from serving as a simple model, therefore we used micelles of a neutral detergent (Brij 58) as a high molecular weight structure. The charge was varied by the addition of a low concentration of sodium dodecyl sulfate and the surface group with which the protons react was an adsorbed pH indicator (bromocresol green or neutral red). The dissociation of a proton from adsorbed bromocresol green is slower than that from free indicator. This effect is attributed to the enhanced stabilization of the acid form of the indicator in the pallisade region of the micelle. The pK shift of bromocresol green adsorbed on neutral micelles is thus quantitatively accounted for by the decreased rate of proton dissociation. Indicators such as neutral red, which are more lipid soluble in their alkaline form, do not exhibit such decelerated proton dissociation in their adsorbed state nor a pK shift on adsorption to neutral micelles. The protonation of an indicator is a diffusion-controlled reaction, whether it is free in solution or adsorbed on micelles. By varying the electric charge of the micelle this rate can be accelerated or decelerated depending on the total charge of the micelle. The micellar charge calculated from this method was corroborated by other measurements which rely only on equilibrium parameters. The high time resolution of the pH jump is exemplified by the ability to estimate the diffusion coefficient of protons through the hydrated shell of the micelle.
Colloids↗
Rapid pH and deltamuH+ jump by short laser pulse.
The excited state (S1) of sulfononaphthols has a pK value well below that of the ground state, consequently intensive illumination of their aqueous solution should lead to acidification. In this study the second harmonies of a ruby laser pulse (10 MW, 30 ns at 347.2 nm) were used for excitation of a sulfononaphthol solution, resulting in a lowering of the pH from 8 to 4. The change in pH was demonstrated by spectral changes of the pH indicators Bromocresol Green, Bromothymol Blue, Bromocresol Purple and Phenol Red. The magnitude of the pH change was calculated from the kinetics of the changes in the indicators' absorbance and from fluorescence intensity of naphtholate. Sulfononaphthols, due to their hydrophylic nature, cannot permeate across phospholipid membranes. Taking advantage of this property, liposomes containing sulfononaphthol were prepared and irradiated by the laser pulse. Evidence is given that under such conditions the change in pH was limited to the space enclosed in the liposomes. The resulting proton-motive force (deltamuH+ = 180 -- 240 mV) is adequate for perturbing the energy-coupled reactions of oxidative phosphorylation. Possible applications of this technique in chemical physics, chemistry, biochemistry and bioenergetics are discussed.
Hydrogen-Ion Concentration↗
Picosecond dynamics of iron proteins.
The excitation of hemoproteins containing either Fe(2+) or Fe(3+) with a picosecond light pulse resulted in the bleaching and recovery of the iron absorbance bands within 6 psec. A new absorbance band also was observed whose formation and decay rate of less than 6 psec suggests that it is probably due to S(1)-->S(n) absorbance. The Soret band relaxation time is deduced to be approximately 0.5 psec whereas the free base hemoprotein does not show any of the above fast-decay characteristics. Therefore, there is a strong influence of the metal on the energy dissipation process.
Journal Article↗
Picosecond and nanosecond isomerization kinetics of protonated 11-cis retinylidene Schiff bases.
Explore the source record for details and available documents.
Kinetics↗
Picosecond kinetics of chlorophyll and chlorophyll/quinone solutions in ethanol.
The mechanism of quenching by quinones of the lowest excited singlet state of chlorophyll has been investigated using picosecond laser spectroscopy. With chlorophyll alone, laser excitation resulted in immediate (less than 10 ps) bleaching of the 665 nm band and production of new absorption bands in the regions 460-550 and 800-830 nm. The lifetimes of these changes were greater than 500 ps. Addition of 2,6-dimethylbenzoquinone caused quenching of these absorbance changes. No indication of chlorophyll cation radical formation was obtained. Thus, the interaction between quinone and the chlorophyll excited singlet state results in energy dissipation without measurable formation of radical species having lifetimes longer than 10 ps. This is in marked contrast to the quenching of the chlorophyll lowest triplet state by quinones, during which easily detectable stable radical formation has been observed.
Chlorophyll↗
Production of patulin by different strains of Penicillium expansum in pear and apple cultivars stored at different temperatures and modified atmospheres.
It was shown that the ability of three different strains of Penicillium expansum (NRRL 2034, NRRL 6069, and CBS 481.84) to grow and to produce patulin in pears (cv. Spadona) and apples (cv. Starking) varied under the different temperatures tested (0, 3, 6, 17 and 25 degrees C). Strain NRRL 2034 did not produce patulin at 0 or 25 degrees C while the two other strains produced the toxin at all temperatures, the maximum production occurring at 25 degrees C (for pears) and 17 degrees C (for apples). No significant differences in pathogenicity, as determined by lesion diameter, was recorded among the strains. Patulin production was totally inhibited when the fungi were grown in apples stored under 3% CO2/2% O2 (25 degrees C). The weight of infected tissue in apples contaminated with any of the strains and stored at that modified atmosphere was 70% that of the control. Under 3% CO2/10% O2 or 3% CO2/20% O2, strain NRRL 2034 did not produce patulin while the two other strains produced the toxin in different amounts.
Carbon Dioxide↗