Browsing by Author "Sosa, Jose M."
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Item A study of the chain transfer reactions of poly(methyl methacrylate) radicals with substituted phenols(1969) Sosa, Jose M.; Seymour, Raymond B.; Wentworth, Wayne E.; Hurley, E. J.; Zlatkis, Albert; McElrath, Eby N.The chain transfer constants (C[lowered s]) of nineteen phenols with poly-(methyl methacrylate) radicals and the extent of retardation (R[lowered e]) of the polymerization reaction by these phenols were determined at 50.0[degrees]C. Attempts were made to correlate both C[lowered s] and R[lowered e] values with previously published antioxidant ratings of the phenols. R[lowered e] values correlated well with antioxidant ratings obtained from the oxidation of petroleum and with the oxidation potentials of the phenols. C[lowered s] values did not correlate well with antioxidant ratings for disubstituted phenols with bulky ortho substituents or with phenols possessing groups with benzylic hydrogens. The poor correlation of Cs values with antioxidant efficiencies appears to be due to the inability of the poly(methyl methacrylate) radicals to abstract phenolic hydrogens from phenols with bulky ortho substituents and to the sluggishness of this radical toward phenolic hydrogen atoms. The latter may result in the abstraction of benzylic and phenolic hydrogen atoms at comparable rates. This premise is supported by a poor correlation of C[lowered s] values with Hammett a substituent values, and by the fact that C[lowered s] values increase as the bond strength of the benzylic hydrogens decrease. Polymerization rates of methyl methacrylate in several phenols and the rates of decomposition of azobisisobutyronitrile in the presence of several phenols were also determined. These investigations showed that phenols affect the rate of decomposition of the initiator, and this may be another factor affecting the correlation of C[lowered s] values with antioxidant ratings and with the Hammett parameter. Inhibition times of the polymerization reaction by phenols in the presence of oxygen correlated well with Hammett a values and indicate that electron donating groups increase the activity of the phenol.Item The relationship between red blood cell deformability metrics and perfusion of an artificial microvascular network(Clinical Hemorheology and Microcirculation, 9/10/2014) Sosa, Jose M.; Nielsen, Nathan D.; Vignes, Seth M.; Chen, Tanya G.; Shevkoplyas, Sergey S.The ability of red blood cells (RBC) to undergo a wide range of deformations while traversing the microvasculature is crucial for adequate perfusion. Interpretation of RBC deformability measurements performed in vitro in the context of microvascular perfusion has been notoriously difficult. This study compares the measurements of RBC deformability performed using micropore filtration and ektacytometry with the RBC ability to perfuse an artificial microvascular network (AMVN). Human RBCs were collected from healthy consenting volunteers, leukoreduced, washed and exposed to graded concentrations (0% – 0.08%) of glutaraldehyde (a non-specific protein cross-linker) and diamide (a spectrin-specific protein cross-linker) to impair the deformability of RBCs. Samples comprising cells with two different levels of deformability were created by adding non-deformable RBCs (hardened by exposure to 0.08% glutaraldehyde) to the sample of normal healthy RBCs. Ektacytometry indicated a nearly linear decline in RBC deformability with increasing glutaraldehyde concentration. Micropore filtration showed a significant reduction only for concentrations of glutaraldehyde higher than 0.04%. Neither micropore filtration nor ektacytometry measurements could accurately predict the AMVN perfusion. Treatment with diamide reduced RBC deformability as indicated by ektacytometry, but had no significant effect on either micropore filtration or the AMVN perfusion. Both micropore filtration and ektacytometry showed a linear decline in effective RBC deformability with increasing fraction of non-deformable RBCs in the sample. The corresponding decline in the AMVN perfusion plateaued above 50%, reflecting the innate ability of blood flow in the microvasculature to bypass occluded capillaries. Our results suggest that in vitro measurements of RBC deformability performed using either micropore filtration or ektacytometry may not represent the ability of same RBCs to perfuse microvascular networks. Further development of biomimetic tools for measuring RBC deformability (e.g. the AMVN) could enable a more functionally relevant testing of RBC mechanical properties.