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PubMed1976

The binding of poly(rA) and poly(rU) to denatured DNA. I. Model studies with homopolymers.

We have compared the properties of the poly(rA).oligo(dT) complex with those of the poly(rU).oligo(dA)n complex. Three main differences were found. First, poly(rA) and oligo(dT)n do not form a complex in concentrations of CsCl exceeding 2 M because the poly(rA) is insoluble in high salt. If the complex is made in low salt, it is destabilized if the CsCl concentration is raised. Complexes between poly(rU) and oligo(dA)n, on the other hand, can be formed in CsCl concentrations up to 6.6 M. Second, complexes between poly(rA) and oligo(dT)n are more rapidly destabilized with decreasing chain length than complexes between poly(rU) and oligo(dA)n. Third, the density of the complex between poly(rA) and poly(dT) in CsCl is slightly lower than that of poly(dT), whereas the density of the complex between poly(rU) and poly(dA) in CsCl is at least 300 g/cm3 higher than that of poly(dA). These results explain why denatured natural DNAs that bind poly(rU) in a CsCl gradient usually do not bind poly(rA).

Binding Sites↗
PubMed1996

Use of a fibrillar polylactic acid homopolymer in sheep cranial defects.

Guided tissue regeneration has been shown to permit osteoconduction in otherwise nonhealing cranial defects. The relative importance of preventing the prolapse of soft tissue versus the infiltration of individual connective tissue cells has not been determined. A fibrillar form of polylactic acid (PLA) was tested in 13-mm-diameter defects in the parietal bones of 12 sheep. The polymer was hypothesized to prevent the prolapse of dura and periosteum but allow entrance of individual cells. Control defects in the same sheep were either filled with autogenous bone shavings or left unfilled. The animals were killed at times ranging from 6 to 25 weeks and the defects examined grossly, radiologically, and histologically. The autogenous bone-filled defects were spanned by trabeculated bone by 6 weeks. The unfilled defects demonstrated prolapse of soft tissues into the defect; however, progressive centripetal bone growth was evident. The fibrillar PLA-filled defects were occupied by a full-thickness mixture of fibrous tissue interspersed with PLA. After 19 weeks, small "fingers" of bone were seen to minimally infiltrate the fibrous tissue. Although separation of the dura and periosteum was maintained by the fibrillar PLA, invasion of fibrous tissue restricted osteoconduction.

Animals↗
PubMed2001

Self-generated disorder and structural glass formation in homopolymer globules.

We have investigated the interrelation between spin glasses and structural glasses. Spin glasses in this case are p-spin interaction spin glasses (at p>2) or Potts glasses that contain quenched disorder, whereas the structural glasses are here exemplified by a homopolymeric globule, which can be viewed as a liquid of connected units on a nanoscale. It is argued that the homopolymeric globule problem can be mapped onto a disorder field theoretical model whose effective Hamiltonian resembles the corresponding one for the spin glass model. In this sense the disorder in the globule is self-generated (in contrast to spin glasses) and can be related to competing interactions (virial coefficients of different signs) and the chain connectivity. The work is aimed at giving a quantitative description of this analogy. We have investigated in the mean-field approximation the phase diagram of the homopolymeric globule where the transition line from the liquid to glassy globule is treated in terms of the replica symmetry breaking paradigm. The configurational entropy temperature dependence is also discussed.

Journal Article↗
PubMed2003

Interacting growth walk: a model for hyperquenched homopolymer glass?

We show that the compact self-avoiding walk configurations, kinetically generated by the recently introduced interacting growth walk (IGW) model, can be considered as members of a canonical ensemble if they are assigned random values of energy. Such a mapping is necessary for studying the thermodynamic behavior of this system. We have presented the specific heat data for the IGW, obtained from extensive simulations on a square lattice; we observe a broad hump in the specific heat above the theta point, contrary to expectation.

Journal Article↗