Oxygen-transport

FIGURE 13.4 (a) The structure of sperm whale myoglobin (from Voet Voet, 2004) and (b) the oxygen binding curves of myoglobin and 

FIGURE 13.5 The haem group and its environment in the deoxy form of the human haemoglobin ct-chain. Only selected side chains are shown and the haem 4 propionate is omitted for clarity. (From Gelin Karplus, 1977.) 

FIGURE 13.7 The ai—p2 interface in (a) human deoxy haemoglobin and (b) oxy-haemoglobin. (Adapted from Voet Voet, 2004.) 

If each subunit is labeled, the dissociation in dilute solution becomes clearer  

The primary function of hemoglobin is to transport oxygen from the lungs to the tissues. Hemoglobin forms a 

Secondary structure of the a chain of human hemoglobin. The helical regions (labeled A-H, after Kendrew), N and C termini, and the histidines located near the heme group are indicated. The axes of the B and C helices are indicated by dashed lines. Note that the a chain lacks helix D present in the /S chain. The amino acid residues are numbered by two different methods from the N terminus of the polypeptide chain and from the N-terminal amino acid residue of each helix. Nonhelical regions are designated by the letters of helices at each end of a region. 

Secondary structure of the p chain of human hemoglobin. The helical regions (labeled A-H, after Kendrew), N and C termini, and the histidines located near the heme group are indicated. The axes of the B, C, and D helices are indicated by dashed lines. 

In the hemoglobin curves, the change from A to B to C is termed a rightward shift. The farther to the right a curve is shifted, the larger is the P50 value and the lower is the oxygen affinity. In this example, the shift is due to an increase in Pco2 since pH, temperature, and 2,3-DPG concentration were held constant. However, the shift could also have been caused by an increase in temperature (as in strenuous exercise or fever), a decrease in pH (as in acidosis or exercise), an increase in 2,3-DPG concentration (see below), or a combination of these variables. For 

In human beings and most animals, hemoglobin is found in the blood and gives blood its characteristic color. (In those species without hemoglobin, the blood is either a different color or colorless.) A vastly oversimplified representation of respiration is given in Equation (6.19)  

Whitten, R. E. Davis, L. Peck, and G.G. Stanley, p. 909. Copyright 2010 Brooks/Cole, a part of Cengage Learning, Inc. Reproduced by permission. www.cengage.com/permi ion ) 

When hemoglobin is exposed to both oxygen and carbon monoxide gas, the carbonyl complex, called carboxyhemoglobin, is formed preferentially. The resulting reaction is represented in Equation (6.20)  

The equilibrium constant for the formation of carboxyhemoglobin is about 250 times larger than that for oxyhemoglobin. The result is that breathing carbon monoxide deprives the cells of oxygen, and the victim is ultimately asphyxiated. A few hemoglobin 

Although simulation has the capability to deconvolute particular microstructural features, which a capability experiment endeavours to achieve, the results can be naively incorrect when compared with experiments because the desirable (in this case oxidative) process will likely be influenced strongly by other factors. This may include, for example, complex microstructures, which are not included in the atomistic model of the pristine material. Accordingly, simulation data needs to be considered carefully in context with experimental findings. 

For oxidative catalysis using ceria, oxygen is necessarily extracted from the surface of the material. Similar to constructing models for the bulk material, symmetry operators can be used to construct atomistic models of surfaces. Generally one needs simply to specify the Miller index of the particular surface in the code, which then constructs an atomistic model an unrelaxed GeO2(310) surfeice is shown in Fig. 5.2. 

Two strategies for simulating surfaces at the atomistic level have been considered. The simplest approach uses 3D periodic boundary conditions and includes a large void to represent the free surface. Alternatively, the surface can be considered explicitly using 2D periodic boundary conditions and requires special consideration of the electrostatics.  

The atomistic structure of a surface is not generally a simple termination of the bulk material the surface atoms undergo relaxation and rumpling. This is hardly surprising as the environment, such as the coordination number, of a surface atom is profoundly different from that of an equivalent atom in the bulk. The surface relaxation can be captured using energy minimisation or molecular dynamics, which direct the (surface) atoms into low-energy 

Calculations performed on ceria have revealed that the (111) surface is energetically the most stable surface followed by (110) and (310). The (100) surface, which is dipolar and therefore inherently unstable, has also been simulated and, via a structural rearrangement of the surface atoms, it was possible to quench the surface dipole.The calculations also predicted the (100) surface to be relatively stable and likely therefore to be present in a real material. Indeed, catalytically reactive cuboidal ceria nanoparticles have recently been synthesised with 100 at each of the six surfaces. It is worth noting that the predictive capability of simulation has proven to be even more relevant now than when these calculations were performed over 15 years ago.  

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Oxygen solubility Oxygen tents Oxygen transfer Oxygen transfer rate Oxygen transport Oxyhalide Oxyhemoglobin... 

Whole blood is seldom used ia modem blood transfusion. Blood is separated into its components. Transfusion therapy optimizes the use of the blood components, using each for a specific need. Red cell concentrates are used for patients needing oxygen transport, platelets are used for hemostasis, and plasma is used as a volume expander or a source of proteins needed for clotting of the blood. 

Oxygen Transport. The most widely used methods for measuring oxygen transport are based upon the Ox-Tran instmment (Modem Controls, Inc.). Several models exist, but they all work on the same principle. The most common apphcation is to measure the permeabihty of a film sample. Typically, oxygen is introduced on one side of the film, and nitrogen gas sweeps the other side of the film to a coulometric detector. The detector measures the rate that oxygen comes through the film. The detector response at steady state can easily be converted to At (eq. 1). Simple... 

Slime is a network of secreted strands (extracellular polymers) intermixed with bacteria, water, gases, and extraneous matter. Slime layers occlude surfaces—the biological mat tends to form on and stick to surfaces. Surface shielding is further accelerated by the gathering of dirt, silt, sand, and other materials into the layer. Slime layers produce a stagnant zone next to surfaces that retards convective oxygen transport and increases diffusion distances. These properties naturally promote oxygen concentration cell formation. 

Flow rate not only raises the rate of oxygen transport by lowering the value in... 

Levels below 19.5% oxygen ean have detrimental effeets if the body is already under stress, e.g. at high altitudes. Exposures below 18% should not be permitted under any eireumstanee. Other ehemieals, e.g. earbon monoxide, result in toxie anoxia due to damage of the body s oxygen transport or utilization meehanism. 

One of the most important reactions of dioxygen is that with the protein haemoglobin which forms the basis of oxygen transport in blood (p. 1099). Other coordination... 

The poisoning effect of molecules such as CO and PF3 (p. 495) arises simply from their ability to bond reversibly to haem in the same manner as O2, but much more strongly, so that oxygen transport is prevented. The cyanide ion CN can also displace O2 from oxyhaemoglobin but its very much greater toxicity at small concentrations stems not from this but from its interference with the action of cytochrome a. 

The second type of behaviour (Fig. 1.89) is much closer to that which one might predict from the regular cracking of successive oxide layers, i.e. the rate decreases to a constant value. Often the oxide-metal volume ratio (Table 1.27) is much greater than unity, and oxidation occurs by oxygen transport in the continuous oxide in some examples the data can be fitted by the paralinear rate law, which is considered later. Destructive oxidation of this type is shown by many metals such as molybdenum, tungsten and tantalum which would otherwise have excellent properties for use at high temperatures. 

Table 12. Parameters of reversible oxygen transport for haemoglobin and a microdisperse form of immobilized haemoglobin (pH 7.4, 37 °C, pC02 = 40 Torr, p02 = 0-150 Torr)...

The influence of pH on the affinity of Hb for oxygen known as the Bohr-effect indicates that protons retain the allosteric regulation of oxygen transport. It is also an indirect confirmation of the ability of Hb and Im Hb for transporting carbon dioxide. The values of the Bohr-effect d log P50/d pH for Hb and Im Hb are close to each other in the pH range 7.1-7.4. It is possible that the effect of the micro-environment of carboxylic CP on immobilized Hb and its polyfunctional interaction represents the interaction between Hb and the structural elements inside the red cell [99]. 

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