Biomedical subjects

A Xia

Publications and source records attributed to A Xia.

6 recordsLinked to original sources

PubMed2001

Platinum(II) hydrazido complexes.

Reaction of 1,2-dimethylhydrazine with the platinum hydroxo complex [(dppp)Pt(mu-OH)](2)(BF(4))(2) gives the bridging 1,2-dimethylhydrazido(-2) product [(dppp)(2)Pt(2)(mu-eta(2):eta(2)-MeNNMe)](BF(4))(2) 1. Crystals of 1.CH(2)Cl(2) from CH(2)Cl(2)/Et(2)O are monoclinic (C/2) with a = 19.690(1), b = 18.886(1), c = 17.170 (1) A, and beta = 92.111(1) degrees. Treatment of [(dppp)Pt(mu-OH)](2)(OTf)(2) with 1,1-dimethylhydrazine gives [(dppp)(2)Pt(2)(mu-OH)(mu-NHNMe(2))](OTf)(2) 2. Crystals of 2.CH(2)Cl(2) from CH(2)Cl(2)/Et(2)O are triclinic (P-1) with a = 12.910 (3), b = 13.927(3), c = 17.5872 (3) A, alpha = 87.121(3), beta = 89.997(4), and gamma = 84.728(3) degrees. Reaction of [(dppp)Pt(mu-OH)](2)(OTf)(2) with 1 equiv of phenylhydrazine in CH(2)Cl(2) gives [(dppp)(2)Pt(2)(mu-OH)(mu-NHNHPh)](OTf)(2) 3. Two equivalents of phenylhydrazine with [(dppp)Pt(mu-OH)](2)(X)(2) gives [(dppp)Pt(mu-NHNHPh)](2)(X)(2) 4 (X = BF(4), OTf). Crystals of 3.ClCH(2)CH(2)Cl from ClCH(2)CH(2)Cl/(i)()Pr(2)O are monoclinic (P2(1)/n) with a = 20.990(2), b = 13.098(1), c = 25.773 (2) A, and beta = 112.944(2) degrees. Crystals of 4(X = BF(4)).ClCH(2)CH(2)Cl(.)()2((t)()BuOMe) from ClCH(2)CH(2)Cl/(t)()BuOMe are monoclinic (C2/m) with a = 30.508(1), b = 15.203(1), c = 19.049 (1) A, and beta = 118.505(2) degrees.

Journal Article↗

PubMed2001

Two fluoradene derivatives: pseudosymmetry, eccentric ellipsoids and a phase transition.

Structures of two derivatives of the curved fluoradene ring system (C(19)H(12)) have been determined. Both have phases that are highly pseudosymmetric. At room temperature crystals of 7b-triisopropylsilylfluoradene (C(28)H(32)Si) have a P1 cell that contains two independent molecules (Z' = 2) and that is almost centered. Crystals of 7b-(2,4-dinitrophenyl)fluoradene (C(25)H(14)N(2)O(4)) have both a P2(1)/c cell with Z' = 1 and a P2(1)/c cell with Z' = 2. The molecular volumes in these two P2(1)/c structures differ by 0.7%, but the structures are otherwise virtually the same; the two independent molecules in the larger cell are related by a pseudotranslation. Some of the atomic ellipsoids in the P2(1)/c, Z' = 1 structure are very large and eccentric, and there are some hints in the diffraction pattern of an incipient phase transition, but the Z' = 1 and Z' = 2 phases are clearly different. The P2(1)/c, Z' = 2 crystal at 295 K probably contains some volume fraction of the Z' = 1 phase; when the temperature is lowered to 273 K this fraction is decreased markedly. The pronounced pseudosymmetry in the P1 and P2(1)/c structures that have Z' = 2 has been investigated by analysing the atomic coordinates, by performing refinements in the smaller pseudocells and by making separate Wilson plots for the classes of reflections which are systematically strong and systematically weak. All three approaches are informative, but they reveal different information. Least-squares fits of coordinates of corresponding atoms measure the similarity of the molecular conformations. The Wilson plots allow a quantitative comparison of the intensities of the strong and weak reflections and thus an assessment of the deviations of the true structure from the smaller pseudocell structure. Comparison of the atomic displacements obtained in the full and pseudocell refinements shows where the structural distortions are largest and provides an indication of their directions.

Journal Article↗

PubMed2001

Expression of connexin 30 in the developing mouse cochlea.

Mutations in the GJB6 gene encoding connexin 30 (Cx30) can cause dominant forms of nonsyndromic deafness. By studying immunohistochemical localization of Cx30 in the mouse cochlea at different ages from 0 to 30 days after birth, we found that the expression of Cx30 is nearly the same as that of Cx26. These findings suggest that as well as Cx26, Cx30 may also contribute to the generation and maturation of endocochlear potential.

Age Factors↗

PubMed2001

[Two-photon fluorescence from recombinant green fluorescent protein].

The photoconversion process of recombinant green fluorescent protein (rGFP) was investigated by two-photon excitation. The results indicated that the rGFP had very strong two-photon excitation fluorescence. The changes of two-photon-induced fluorescence polarization suggest that there is a proton transfer process between two different proton states of rGFP chromophores. The conformation of rGFP chromophores could be changed upon illumination, which partly block the energy transfer processes from amino acid residues to chromophores in rGFP, and result in the decrease of two-photon-induced fluorescence intensity. The fluorescence from amino acid residues in rGFP was also observed by three-photon excitation, which resulted from the blocked amino acid residues in rGFP. These results suggested that it is necessary to optimize rGFP excitation and detection for quantitative fluorescence microscopy.

Energy Transfer↗

PubMed1999

Expression of connexin 26 and Na,K-ATPase in the developing mouse cochlear lateral wall: functional implications.

The immunohistochemical localization of connexin 26 (a gap junction protein) and Na,K-ATPase in the mouse cochlear lateral wall was studied at different ages between 0 and 30 days after birth (DAB). Connexin 26-like immunoreactivity was sparsely distributed among the connective tissue cells just lateral to the future marginal cells of the stria vascularis on 0 DAB. In the mice of 3-6 DAB, connexin 26 was observed in the strial basal cell area, and was increased in its distribution density on 10 DAB. Connexin 26 was sparsely distributed among the fibrocytes in the spiral ligament and the suprastrial zone on 10 DAB, and its distribution density increased rapidly in the mouse on 12 DAB. The immunohistochemical distribution reached the adult pattern in the cochlear lateral wall on 15 DAB. Weak Na, K-ATPase-like immunoreactivity was observed in the epithelial cells, corresponding to the future strial marginal cells, on 0 DAB. Its staining intensity was enhanced with the increase of age, and reached the adult pattern on 10 DAB. In contrast, Na,K-ATPase-like immunoreactivity in the type II fibrocytes and suprastrial fibrocytes was first detected on 12 DAB, and reached the mature level on 15 DAB. It is well known that the endolymphatic potential (EP) reaches the adult level 2 weeks after birth. The expression patterns of connexin 26 and Na,K-ATPase in the fibrocytes of the spiral ligament and the suprastrial zone coincided with the rapid growth and maturation of EP. These findings may suggest a role for the gap junctional communications and Na,K-ATPase activity of the fibrocytes within the cochlear lateral wall in the generation and maturation of EP.

Age Factors↗

PubMed1998

Trends in anemia treatment with erythropoietin usage and patient outcomes.

Recombinant erythropoietin, first approved for Medicare reimbursement in June 1989, was prescribed at initial doses for dialysis patients of 2,500 to 2,700 U per administration independent of hematocrit level. By 1997, however, patients with hematocrits less than 30% were administered 6,000 U/dose, compared with 4,500 U administered to patients with hematocrits of 33% to 36%. Since 1990, the percentage of patients with hematocrits less than 30% decreased from 60% to 22% in 1997, whereas the percentage of patients with hematocrits of 33% to 36% increased from 10% to 30%. In 1997, Medicare initiated the Hematocrit Measurement Audit (HMA) policy, which was directed at reducing the percentage of claims for hematocrits greater than 36% and increasing the stability of the hematocrit levels. The policy change achieved the initial effect but resulted in a reduction of the mean hematocrit as well. The policy was changed in 1998 in response to patient and provider concerns. Mortality studies show that hematocrits less than 30% (or hemoglobin levels < 110 g/L) are associated with an 18% to 40% increased associated risk for death. Higher hematocrits of 33% to 36% appear to be associated with a 7% reduced risk for death. The risk for hospitalization parallels that of mortality. Patients with sustained hematocrits of 33% to 36% over 1 year appear to have the best outcome compared with patients with hematocrits that decrease. The latter are at greater risk than those patients in whom the hematocrits increase. In conclusion, dramatic improvements in hemodialysis patient hematocrits have occurred since 1989. Mortality and hospitalization studies support the National Kidney Foundation Dialysis Outcomes Quality Initiative (NKF DOQI) target hematocrit range of 33% to 36% as providing the best associated outcomes.

Anemia↗