| 1. |
- Schäffer, Tilman E, et al.
(author)
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Does abalone nacre form by heteroepitaxial nucleation or by growth through mineral bridges?
- 1997
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In: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 9:8, s. 1731-1740
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Journal article (peer-reviewed)abstract
- We present experimental support for a model of abalone nacre growth that is based on mineral bridges between successive aragonite tablets rather than on heteroepitaxial nucleation. Interlamellar sheets of organic polymers delineate the aragonite tablets but allow the tablets to grow mineral bridges through pores in the sheets. Atomic force microscope images of interlamellar organic sheets from flat pearls made by Haliotis rufescens (red abalone; marine gastropod mollusk) reveal a fibrous core and holes of 5-50 nm in diameter. Scanning ion conductance microscopy shows that these holes are actually pores through the interlamellar sheets. With the help of statistical analysis we can associate the pore-to-pore spacings in the interlamellar sheets with the observed offsets of successive nacre tablets. These results, supplemented by AFM, SEM, and TEM images, support and extend the model of biofabrication of gastropod nacre which is based on mineral bridges between the aragonite tablets.
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| 2. |
- Edholm, O., et al.
(author)
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The barrier for heme-protein separation estimated by non-equilibrium molecular dynamics simulations
- 1998
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In: Chemical Physics Letters. - 0009-2614 .- 1873-4448. ; 291:5-6, s. 501-508
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Journal article (peer-reviewed)abstract
- In heme-containing proteins the heme group is usually non-covalently bound in a pocket. Molecular dynamics (MD) simulations have been performed to estimate the barrier height for heme-protein separation. In simulations of myoglobin dissolved in water, a force has been applied to pull the heme out of the binding pocket. With forces above 0.5 nN, the heme group is easily pulled out of the pocket in times of the order of tens of picoseconds. With weaker forces, heme release becomes too slow to be monitored in an MD simulation covering a couple of hundred picoseconds. These results are consistent with a free energy barrier to heme release of about 100 kJ/mol. The results show that the main energetic change that occurs during the release is a conversion of heme/protein Lennard-Jones energy into heme/water Lennard-Jones energy. The release is essentially barrierless in energy indicating that the main part of the barrier is entropic.
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| 3. |
- Lundin, Anders, et al.
(author)
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Compressibility of C61D2 up to 1 GPa in the temperature range 175 - 345 K
- 1996
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In: Carbon. - : Elsevier Science Ltd.. - 0008-6223 .- 1873-3891. ; 34:9, s. 1119-1121
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Journal article (peer-reviewed)abstract
- We have measured the bulk modulus K for C61D2 up to 1 GPa in the temperature range 175–343 K. For face-centered cubic C61D2 above 290 K, we find an anomalously low value for K below about 0.15 GPa, possibly indicating pressure-induced changes in the structure. The (extrapolated) zero-p bulk modulus K(0) decreases with increasing T from 6.7 GPa at 175 K to 5.2 GPa at 343 K. A comparison with hypothetical expanded f.c.c. C60 with the same lattice constant shows that K(0) values are similar, indicating that the main intermolecular interactions are still between molecular bellies, not the sidegroups.
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| 4. |
- Smith, M.L., et al.
(author)
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The spontaneous hemin release from Lumbricus terrestris hemoglobin
- 1997
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In: Comparative Biochemistry and Physiology. P. A, Physiology. - 1096-4940. ; 118:4, s. 1241-1245
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Journal article (peer-reviewed)abstract
- The slow, spontaneous release of hemin from earthworm, Lumbricus terrestris, hemoglobin has been studied under mild conditions in the presence of excess apomyoglobin. This important protein is surprisingly unstable. The reaction is best described as hemin released from the globin into water, followed by quick engulfment by apomyoglobin. The energetics of this reaction are compared with those of other types of hemoglobins. Anomalously low activation energy and enthalpy are counterbalanced by a negative entropy. These values reflect significant low frequency protein motion and dynamics of earthworm hemoglobin and may also indicate an open structure distal to the heme. This is also supported by the infrared spectrum of the carbonyl hemoprotein, which indicates several types of distal interactions with the bound CO. The reported low heme to polypeptide ratio for this protein may be due to facile heme and hemin release by the circulating protein.
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