Biomedical subjects
Publications and source records attributed to S Gao.
The crystal structure of the coordination polymer [Mn3(N3)2(nta)4(H2O)2]n (nta = nicotinate) consists of trinuclear subunits bridged by mixed mu-1,1-azide and mu-carboxylate-O,O groups, which are linked by mu 3-nta-N,O,O ligands into a three-dimensional network exhibiting ferrimagnetic-like ordering.
A novel, three-dimensional copper diphosphonate Cu4(CH3C(OH)(PO3)2)2(C4H4N2)(H2O)4 (1) incorporating an organic pyrazine ligand has been hydrothermally synthesized, which exhibits antiferromagnetic ordering below 4.2 K and metamagnetic behavior.
Three cyano-bridged bimetallic assemblies, [NiL(1)](3)[Cr(CN)(6)](2).7H(2)O (1), [NiL(2)](3)[Cr(CN)(6)](2).9H(2)O (2), and [NiL(2)](3)[Cr(CN)(5)(NO)](2).9H(2)O (3) (L(1) = 3,10-dimethyl-1,3,5,8,10,12-hexaazacycloctadecane and L(2) = 3,10-diethyl-1,3,5,8,10,12-hexaazacycloctadecane), have been prepared and characterized structurally and magnetically. Complex 1 crystallizes in the monoclinic space group of C2/c with a = 25.929 A, b = 15.442(3) A, c = 19.553(4) A, beta = 106.21(3) degrees, and Z = 4, while 2 and 3 are in the trigonal space group P3 with a = b = 14.919(2) A, c = 9.5246(19) A, gamma = 120 degrees, and Z = 1 for 2 and a = b = 14.863(2) A, c = 9.3134(19) A, gamma = 120 degrees, and Z = 1 for 3. The structures of 1-3 are similar and consist of cyano-bridged two-dimensional (2D) honeycomb-like neutral Ni(3)Cr(2) layers. In each complex, [Cr(CN)(6)](3-) or [Cr(CN)(5)(NO)](3-) coordinates to three trans-[Ni(macrocycle)](2+) groups using three fac-CN(-) ligands, providing a 2D layered network. The NO group in [Cr(CN)(5)(NO)](3-) remains monodentate. Magnetic studies show the existence of a short-range ferromagnetic interaction in all of the complexes. Complexes 1 and 2 exhibit long-range antiferromagnetic ordering at 13.0 and 11.9 K, respectively, and a metamagnetic transition with critical field of ca. 1.6 kOe for 1 and 1.5 kOe for 2 at 1.8 K. Complex 3 exhibits long-range ferromagnetic ordering below 4.3 K.
The design, synthesis, and structural and magnetic properties of the two new bimetallic complexes [Sm(DMF)(4)(H(2)O)(2)Cr(CN)(6)].H(2)O and [Sm(DMF)(2)(H(2)O)(3)Cr(CN)(6)].H(2)O (DMF = N,N-dimethylformamide) are presented. [Sm(DMF)(4)(H(2)O)(2)Cr(CN)(6)].H(2)O was prepared by the reaction between Sm(3+) and [Cr(CN)(6)](3-) in a methanol-DMF solution, while [Sm(DMF)(2)(H(2)O)(3)Cr(CN)(6)].H(2)O was prepared by the reaction between Sm(3+), DMF, and [Cr(CN)(6)](3-) in the molar ratio of 1:2:1 in H(2)O. [Sm(DMF)(4)(H(2)O)(2)Cr(CN)(6)].H(2)O crystallizes in the monoclinic space group of P2(1)/c with a = 13.161(3) A, b = 12.928(3) A, c = 19.174(4) A, beta = 109.82(3) degrees, and Z = 4, while [Sm(DMF)(2)(H(2)O)(3)Cr(CN)(6)].H(2)O is in the triclinic space group P1 with a = 7.7535(1) A, b = 9.4307(3) A, c = 16.2905(5) A, alpha = 94.1590(14) degrees, beta = 100.0597(18) degrees, gamma = 100.9154(18) degrees, and Z = 2. The structure of [Sm(DMF)(4)(H(2)O)(2)Cr(CN)(6)].H(2)O possesses a cyano-bridged one-dimensional (1D) zigzag chain structure with alternating Sm(DMF)(4)(H(2)O)(2) and Cr(CN)(6) moieties. [Sm(DMF)(2)(H(2)O)(3)Cr(CN)(6)].H(2)O consists of cyano-bridged neutral brick wall-like layers in which each [Cr(CN)(6)](3-) unit uses three cyanide groups in the meridional arrangement to connect with three [Sm(DMF)(2)(H(2)O)(3)](3+) units. Each [Sm(DMF)(2)(H(2)O)(3)](3+) unit, in turn, links three [Cr(CN)(6)](3-), generating a flat brick wall-like structure. Magnetic studies on [Sm(DMF)(2)(H(2)O)(3)Cr(CN)(6)].H(2)O showed a magnetic-phase transition temperature below 4.2 K and a coercive field of 100 Oe at 1.85 K, while no long-range magnetic ordering was observed in the 1D complex [Sm(DMF)(4)(H(2)O)(2)Cr(CN)(6)].H(2)O.
Reaction of 4,4'-dipyridine dioxide (dpdo) and CuCl(2).6H(2)O in aqueous solution gave an adduct [Cu(H(2)O)(6)]Cl(2).2dpdo.2H(2)O 1, which has a hydrogen-bonded three-dimensional network. While substituting CuCl(2).6H(2)O with Cu(ClO(4))(2).6H(2)O, three pseudopolymorphs, namely, [Cu(dpdo)(6)][ClO(4)](2) 2, [Cu(3)(dpdo)(8)(H(2)O)(6)][ClO(4)](6).2dpdo.6H(2)O 3, and [Cu(dpdo)(H(2)O)(4)][ClO(4)](2).2dpdo 4, were isolated. 2 consists of a mononuclear copper coordinated with six terminal dpdo ligands. Adjacent mononuclear units are overlapped through pi-pi stacking of pyridine rings to give a 2D sheet with a triangular channel. 3 forms a trinuclear cluster bridged by two dpdo molecules. The solvate and terminal dpdo molecules are interwoven through hydrogen bonding and pi-pi stacking to lead to a rectangular channel with a dimensionality of 12.98 A x 13.44 A. 4 has a one-dimensional chain structure bridged by dpdo. Two solvate dpdo ligands link these chains through hydrogen bonding to generate two sets of three-dimensional networks which are interwoven through a common conjunctive point [Cu(H(2)O)(4)](2+), yielding a three-dimensional open framework with triangular channels. ClO(4)(-) anions are included within these channels in 2-4 through weak C-H...O hydrogen bonding. The introduction of the second spacer, 4,4'-bipyridine, generated a 2D architecture [Cu(dpdo)(4,4'-bipy)][ClO(4)](2).2H(2)O.dpdo 5, which is constructed by 4,4'-bipy and 4,4'-dpdo simultaneously, exhibiting a large channel with approximate dimensionality 11.1 A x 12.6 A, in which solvate 4,4'-dpdo ligand and perchlorate anions are accommodated.
BACKGROUND: The epidemiology and natural history of cognitive impairment that is not dementia is important to the understanding of normal aging and dementia. OBJECTIVE: To determine the prevalence and outcome of cognitive impairment that is not dementia in an elderly African American population. METHOD: A two-phase, longitudinal study of aging and dementia. A total of 2212 community-dwelling African American residents of Indianapolis, IN, aged 65 and older were screened, and a subset (n = 351) received full clinical assessment and diagnosis. Subsets of the clinically assessed were seen again for clinical assessment and rediagnosis at 18 and 48 months. Weighted logistic regression was used to generate age-specific prevalence estimates. RESULTS: The overall rate of cognitive impairment among community-dwelling elderly was 23.4%. Age-specific rates indicate increasing prevalence with increasing age: 19.2% for ages 65 to 74 years, 27.6% for ages 75 to 84 years, and 38.0% for ages 85+ years. The most frequent cause of cognitive impairment was medically unexplained memory loss with a community prevalence of 12.5%, followed by medical illness-associated cognitive impairment (4.0% prevalence), stroke (3.6% prevalence), and alcohol abuse (1.5% prevalence). At 18-month follow-up, 26% (17/66) of the subjects had become demented. CONCLUSIONS: Cognitive impairment short of dementia affects nearly one in four community-dwelling elders and is a major risk factor for later development of dementia.
Glutathione peroxidase (GPX) has a powerful role in scavenging reactive oxygen species. In previous papers we have developed a new strategy for generating abzymes: the monoclonal antibody with a substrate-binding site is first prepared, then a catalytic group is incorporated into the monoclonal antibody's binding site by using chemical mutation [Luo, Zhu, Ding, Gao, Sun, Liu, Yang and Shen (1994) Biochem. Biophys. Res. Commun. 198, 1240-1247; Ding, Liu, Zhu, Luo, Zhao and Ni (1998) Biochem. J. 332, 251-255]. Since then we have established a series of catalytic antibodies capable of catalysing the decomposition of hydroperoxides by GSH. The monoclonal antibody 2F3 was raised against GSH-S-2,4-dinitrophenyl t-butyl ester and exhibited high catalytic efficiency, exceeding that of rabbit liver GPX, after chemical mutation. To produce pharmaceutical proteins and to study the reason why it exhibits high catalytic efficiency, we sequenced, cloned and expressed the variable regions of 2F3 antibody as a single-chain Fv fragment (2F3-scFv) in different bacterial strains. The amounts of 2F3-scFv proteins expressed from JM109 (DE3), BL21 (DE3), and BL21 (coden plus) were 5-10%, 15-20% and 25-30% of total bacterial proteins respectively. The 2F3-scFv was expressed as inclusion bodies, purified in the presence of 8 M urea by Co(2+)-immobilized metal-affinity chromatography (IMAC) and renatured to the active form in vitro by gel filtration. The binding constants of the active 2F3-scFv for GSH and GSSG were 2.46 x 10(5) M(-1) and 1.03 x 10(5) M(-1) respectively, which were less by one order of magnitude than that of the intact 2F3 antibody. The active 2F3-scFv was converted into selenium-containing 2F3-scFv (Se-2F3-scFv) by chemical modification of the reactive serine; the GPX activity of the Se-2F3-scFv was 3394 units/micromol, which approaches the activity of rabbit liver GPX.
Two bimetallic assemblies, [Ni(tn)(2)](2)[Cr(CN)(5)(NO)]OH.H(2)O (1) and [Ni(tn)(2)](2)[Co(CN)(6)]NO(3).2H(2)O (2) (tn = 1,3-diaminopropane), have been prepared and structurally and magnetically characterized. Crystal data for 1 (2): space group P1 (P1), a = 8.698(3) (8.937(2)) A, b = 10.001(2) (9.863(1)) A, c = 10.158(2) (10.064(1)) A, alpha = 87.40(2) (86.064(10)) degrees, beta = 65.10(2) (65.489(10)) degrees, gamma = 81.63(2) (81.572(12)) degrees and Z = 1 (1). Both structures consist of two-dimensional grid-like polycations containing Ni-N triple bond C-M linkages (M = Cr or Co) and counteranions (OH, NO(3)). Magnetic studies of 1 showed that the complex displays a metamagnetic behavior originating from intralayer ferromagnetic and interlayer antiferromagnetic interactions. Long-range antiferromagnetic ordering was observed at T(N) = 3.3 K. Complex 2 exhibits intramolecular ferromagnetic interactions through the diamagnetic N triple bond C-Co-N triple bond C bridges, owing to superexchange involving the empty d(sigma) orbital of the diamagnetic Co(III) ion.
2,2'-Biphenanthroline (2,2'-biphen) formed from 1,10-phenanthroline when a new two-dimensional layered vanadium oxide metal coordination complex, [(2,2'-biphen)Co]V3O8.5, which contains novel 4,8,10-net sheets, was hydrothermally synthesized.
A bimetallic cluster complex, [(2,2'-Py2NH)2Co]3V8O23 (2,2'-Py2NH = 2,2'-dipyridylamine) 1, has been hydrothermally synthesized; X-ray crystallography reveals that 1 possesses a novel cage topology structure in which the metal cluster core is constructed from six V4Co pentatomic rings.
In this paper we propose five new tests for the equality of paired means of health care costs. The first two tests are the parametric tests, a Z-score test and a likelihood ratio test, both derived under the bivariate normality assumption for the log-transformed costs. The third test (Z-score with jack-knife) is a semi-parametric Z-score method, which only requires marginal log-normal assumptions. The last two tests are the non-parametric bootstrap tests: one is based on a t-test statistic, and the other is based on Johnson's modified t-test statistic. We conduct a simulation study to compare the performance of these tests, along with some commonly used tests when the sample size is small to moderate. The simulation results demonstrate that the commonly used paired t-test on the log-scale and the Wilcoxon signed rank for differences of the two original scales can yield type I error rates larger than the preset nominal levels. The commonly used paired t-test on the original data performs well with slightly skewed data, but can yield inaccurate results when two populations have different skewness. The likelihood ratio test, the parametric and semi-parametric Z-score tests all have very good type I error control with the likelihood ratio test being the best. However, the semi-parametric Z-score test requires less distributional assumptions than the two parametric tests. The percentile-t bootstrap test and bootstrapped Johnson's modified t-test have better type I error control than the paired t-test on the original-scale and Johnson's modified t-test, respectively. Combining with the propensity-score method, we can also apply the proposed methods to test the mean equality of two cost outcomes in the presence of confounders. Our two applications are from health services research. In the first one, we want to know the effect of Medicaid reimbursement policy change on outpatient health care costs. The second one is to evaluate the effect of a hospitalist programme on health care costs in an observational study, and the imbalanced covariates between intervention and control patients are taken into account using a propensity score approach.
Oligomeric nanoparticle networks, generated by the self-assembly of bis-biotinylated double-stranded DNA fragments and streptavidin, have been studied by scanning force microscopy (SFM). SFM imaging revealed the presence within the networks of irregular thick DNA molecules, which were often associated with distinct, Y-shaped structural elements. Closer analysis revealed that the Y structures are formed by condensation (thickening and shortening) of two DNA fragments, most likely through the supercoiling of two DNA molecules bound to adjacent binding sites of the streptavidin particle. The frequency of supercoiling was found to be dependent on the ionic strength applied during the immobilization of the oligomeric networks on mica surfaces. Potential applications of the structural changes as a means for constructing ion-dependent molecular switches in nanomaterials are discussed.
The dissipative quantum dynamics of a model system, O2 at a Pt(111) surface, has been solved in two dimensions using a stochastic wave packet approach and parallel-computing techniques. It is found that, upon excitation, the dissipation anisotropy creates nonequilibrium and anisotropic energy storage between different reaction channels. The latter determines decisively the short-time reaction dynamics and, in particular, the branching ratio between desorption and dissociation, in agreement with recent experimental findings.
Glycoprotein I(b)alpha (GP I(b)alpha), the ligand binding subunit of the platelet glycoprotein Ib-IX-V complex, is sulfated on three tyrosine residues (Tyr-276, Tyr-278, and Tyr-279). This posttranslational modification is known to be critical for von Willebrand factor (vWF) binding; yet it remains unclear whether it provides a specific structure or merely contributes negative charges. To investigate this issue, we constructed cell lines expressing GP I(b)alpha polypeptides with the three tyrosine residues converted to either Glu or Phe and studied the ability of these mutants to bind vWF in the presence of modulators or shear stress. The mutants were expressed normally on the cell surface as GP Ib-IX complexes, with the conformation of the ligand-binding domain preserved, as judged by the binding of conformation-sensitive monoclonal antibodies. In contrast to their normal expression, both mutants were functionally abnormal. Cells expressing the Phe mutant failed to bind vWF in the presence of either ristocetin or botrocetin. These cells adhered to and rolled on immobilized vWF only when their surface receptor density was increased to twice the level that supported adhesion of cells expressing the wild-type receptor and even then only 20% as many rolled and rolled significantly faster than wild-type cells. Cells expressing the Glu mutant, on the other hand, were normal with respect to ristocetin-induced vWF binding and adhesion to immobilized vWF but were markedly defective in botrocetin-induced vWF binding. These results indicate that GP I(b)alpha tyrosine sulfation influences the interaction of this polypeptide with vWF primarily by contributing negative charges under physiological conditions and when the interaction is induced by ristocetin but contributes a specific structure to the botrocetin-induced interaction.
CONTEXT: Alzheimer disease (AD) represents a major and increasing public health problem. If populations were identified with significantly lower or higher incidence rates of AD, the search for risk factors in the genesis of AD could be greatly enhanced. OBJECTIVE: To compare incidence rates of dementia and AD in 2 diverse, elderly community-dwelling populations. DESIGN: The Indianapolis-Ibadan Dementia Project, a longitudinal, prospective population-based study consisting of a baseline survey (1992-1993) and 2 subsequent follow-up waves after 2 years (1994-1995) and 5 years (1997-1998). Each wave followed a 2-stage design, with an in-home screening interview followed by a full diagnostic workup of a subsample of participants based on screening performance. SETTING AND PARTICIPANTS: A total of 2459 community-dwelling Yoruba residents of Ibadan, Nigeria, without dementia, and 2147 community-dwelling African American residents of Indianapolis, Ind, without dementia (all aged 65 years or older). The cohorts were followed up for a mean of 5.1 years and 4.7 years, respectively. MAIN OUTCOME MEASURES: Incident cases of dementia and AD in each of the 2 populations. RESULTS: The age-standardized annual incidence rates were significantly lower among Yoruba than among African Americans for dementia (Yoruba, 1.35% [95% confidence interval [CI], 1.13%-1.56%]; African Americans, 3.24% [95% CI, 2.11%-4.38%]) and for AD (Yoruba, 1.15% [95% CI, 0.96%-1.35%]; African Americans, 2.52% [95% CI, 1.40%-3.64%]). CONCLUSION: This is the first report of incidence rate differences for dementia and AD in studies of 2 populations from nonindustrialized and industrialized countries using identical methods and the same group of investigators in both sites. Further explorations of these population differences may identify potentially modifiable environmental or genetic factors to account for site differences in dementia and AD.
Cyano-mediated interaction of the alternating high-spin Mn(II) centers and low-spin Ru(III) centers in {Mn[Ru(acac)2 (CN)2 ]2 }n (Hacac=acetylacetone) results in long-range ferromagnetic ordering below 3.6 K. This novel Mn(II) Ru(III) coordination polymer, which has a diamond-like structure, was constructed from [Ru(acac)2 (CN)2 ](-) and Mn(2+) ions.
Boronic acids bind certain 1,2- and 1,3-diols with high affinity through reversible formation of boronate esters. They have been utilized as the recognition moiety for artificial receptors, particularly receptors for carbohydrates that have cis-diol moieties. Therefore, sensors for boronic acids could serve as universal reporters for monitoring boronate formation. This paper reports the design and synthesis of a series of photometric chemosensors for phenylboronic acid using diethanolamine as the recognition moiety. Diethanolamine, which binds strongly to boronic acids, has been linked to three different types of optical reporters. A photoinduced electron transfer system based on the anthracene fluorophore has been used to create sensors that show up to a fivefold increase in fluorescent intensity in the presence of millimolar concentrations of phenylboronic acid. Sensor designs based on the restriction of free rotation of extended pi systems and on the perturbed electronic properties of azo dyes are also included. This work demonstrates that sensors based on several different designs can be used for the detection of boronic acids.
The ability to custom-make fluorescent sensors for different analytes could have a tremendous impact in a variety of areas. Template-directed polymerization or molecular imprinting seems to be a promising approach for the preparation of high-affinity and specific binding sites for different template molecules. However, the application of molecular imprinting in the preparation of fluorescent sensors has been hampered by the lack of suitable fluorescent tags, which would respond to the binding event with significant fluorescence intensity changes. We have designed and synthesized a fluorescent monomer (1) that allows for the preparation of fluorescent sensors of cis diols using molecular imprinting methods. This monomer has been used for the preparation of imprinted polymers as sensitive fluorescent sensors for D-fructose. The imprinted polymers prepared showed significant fluorescence intensity enhancement upon binding with the template carbohydrate.