Biomedical subjects

James D Martin

Publications and source records attributed to James D Martin.

6 recordsLinked to original sources

PubMed2004

Synthesis of [NH(4)]MnCl(2)(OAc) and [NH(4)](2)MnCl(4)(H(2)O)(2) by solvothermal dehydration and structure/property correlations in a one-dimensional antiferromagnet.

The utility of the solvothermal dehydration strategy whereby superheated acetonitrile reacts with water of hydration to form ammonium acetate is demonstrated in the synthesis of [NH(4)]MnCl(2)(OAc), I, and [NH(4)](2)MnCl(4)(H(2)O)(2), II, from MnCl(2).4H(2)O. The structure of I is shown to crystallize in the monoclinic space group C2/c (No. 15) with a = 15.191(6) A, b = 7.044(2) A, c = 13.603(6) A, beta = 107.31 degrees, V = 1389.7(9) cm(-)(1), and Z = 8. The structure of II crystallizes in the space group I4/mmm (No. 139) with a = 7.5250(5) A, b = 8.276(2) A, V = 468.6(1) cm(-)(1), and Z = 2. Both structures exhibit extensive hydrogen bonding that controls both local Mn-Cl bonding and the interchain organization. I is shown to be a one-dimensional Heisenberg antiferromagnet with an intrachain exchange constant J/k = -2.39 K. This structure exhibits exchange coupling intermediate between the well-studied triply and doubly chloride-bridged one-dimensional manganese Heisenberg antiferromagnets. The structure/property correlation demonstrates a linear dependence of the exchange constant on the Mn-Cl-Mn bond angle, alpha, for alpha < 94 degrees.

Journal Article↗

PubMed2003

Sorptive reconstruction of the CuAlCl(4) framework upon reversible ethylene binding.

Three ethylene adducts to CuAlCl(4) have been characterized by single crystal and/or powder X-ray diffraction, (13)C, (27)Al and (63)Cu MAS NMR and diffuse reflectance UV-vis spectroscopy. (C(2)H(4))(2)CuAlCl(4), a = 7.1274(5) b = 12.509(1) c = 11.997(3) beta = 91.19 degrees, Pc, Z = 4; alpha-(C(2)H(4))CuAlCl(4), a =7.041(3) b = 10.754(8) c =11.742(9) beta = 102.48(6), P2(1), Z = 4 and beta-(C(2)H(4))CuAlCl(4), a = 7.306(2), b = 16.133(3), c = 7.094(1), Pna2(1), Z = 4. Up to 2 equiv of ethylene ( approximately 200 cm(3)/g relative to stp) are sorbed at room temperatures and pressures as low as 300 Torr. The ethylene ligands are bound to copper (I) primarily through a sigma-interaction, because the AlCl(4)(-) groups also bound to copper prevent any significant pi-back-bonding. The olefin binding is reversible and has been characterized by gravimetric and volumetric adsorption analysis and by time and pressure resolved synchrotron powder X-ray diffraction. Comparison of the parent crystal structure to those of the adduct phases provide an atomistic picture of the sorptive reconstruction reactions. These are proposed to proceed by a classic substitution mechanism that is directed by the van der Waals channels of the parent crystalline lattice.

Journal Article↗

PubMed2003

Diabetes, hypertension and birth injuries: a complex interrelationship.

Seemingly coincidental occurrence of various pathological conditions may derive from common etiologic denominators. While reviewing 240 malpractice claims involving shoulder dystocia related fetal injuries, we found two antenatal complications in the background conspicuously often. Chronic or pregnancy induced hypertension was identifiable in 80 instances (33%). Pregnancy induced or preexisting diabetes was diagnosed 48 times (20%). Many of these patients were poorly controlled. The blood pressure was usually checked during the antenatal visits. However, about one-half of all patients received no diabetic screening. Therefore, this study may underestimate the actual incidence of diabetes. It has been calculated that the frequency of diabetes in pregnancy and that of hypertension, is about 5% in the United States. Thus, the rates of these complications in this selected group of gravidas was severalfold higher than in the general population. Since hypertension causes retarded fetal growth, it cannot be a direct cause of arrest of the shoulders at delivery. The likely common denominator is maternal diabetes a known predisposing factor both for preeclampsia and shoulder dystocia at birth. In the course of litigations for fetal injuries, demonstration of the predisposing role of seemingly unrelated shortcomings of the medical management may profoundly influence the outcome. This principle is demonstrated by the presentation of an actual malpractice action which resulted in a substantial settlement.

Adult↗

PubMed2002

Designing intermediate-range order in amorphous materials.

Amorphous materials are commonly understood to consist of random organizations of molecular-type structural units. However, it has long been known that structural organizations intermediate between discrete chemical bonds and periodic crystalline lattices are present even in liquids. Numerous models--including random networks and crystalline-type structures with networks composed of clusters and voids--have been proposed to account for this intermediate-range order. Nevertheless, understanding and controlling structural features that determine intermediate-range order in amorphous materials remain fundamental, yet presently unresolved, issues. The most characteristic signature of such order is the first peak in the total structure factor, referred to as the first sharp diffraction peak or 'low Q' structure. These features correspond to large real-space distances in the materials, and understanding their origin is key to unravelling details of intermediate-range order. Here we employ principles of crystal engineering to design specific patterns of intermediate-range order within amorphous zinc-chloride networks. Using crystalline models, we demonstrate the impact of various structural features on diffraction at low values of Q. Such amorphous network engineering is anticipated to provide the structure/property relationships necessary to tailor specific optical, electronic and mechanical properties.

Journal Article↗

PubMed2002

Electronic structure, electrical and magnetic properties of RMo(8)O(14) compounds (R = La, Ce, Pr, Nd, Sm) containing bicapped Mo(8) clusters.

Magnetic and electrical resistivity properties of RMo(8)O(14) (R = La, Ce, Pr, Nd, Sm) compounds containing different bicapped-octahedral Mo(8) clusters are discussed. Extended Hückel (EH) molecular calculations were carried out in order to study the influence of the position of metal capping atoms on the electronic structure of different Mo(8) isomers. Different optimal metal electron counts are possible for these clusters. Periodic density functional calculations confirm the molecular character of these compounds and allow the understanding of their semiconducting and magnetic properties.

Journal Article↗

PubMed2002

Vascular leukocyte sequestration in decompression sickness and prophylactic hyperbaric oxygen therapy in rats.

BACKGROUND: Evidence for a causal relationship between decompression sickness (DCS) and leukocyte sequestration was assessed in a rat model based on the effects of interventions which impede cell-to-cell adherence, including hyperbaric oxygen therapy (HBO2). HYPOTHESIS: We hypothesized that leukocyte adhesion to vessels may play a role in DCS. METHODS: Rats were subjected to decompression stress and their ability to ambulate on a rotating drum was assessed to quantify functional neurological deficits. Leukocyte adherence in the brain was measured by a myeloperoxidase (MPO) radioimmunoassay. Interventions included infusion of antibodies to render rats neutropenic or to inhibit leukocyte beta2 integrin adhesion molecules. Tissue gas bubbles were imaged and quantified using a transmission ultrasound camera. RESULTS: Decompressed rats manifested a deficit in their ability to ambulate and a five-fold elevation in concentration of MPO in brain. Neutropenic rats, and those infused with antibody fragments to inhibit leukocyte beta2 integrins, did not exhibit brain MPO elevations, nor a deficit in ambulatory function. HBO2 was used in a prophylactic manner to address its ability to inhibit leukocyte beta2 integrin-mediated adherence without reducing the presence of decompression-induced bubbles. Prophylactic HBO2 prevented cerebral leukocyte sequestration and the performance deficit. CONCLUSIONS: The results implicate beta2 integrin-mediated leukocyte adhesion in neurological deterioration after decompression stress, and offer new insight into the therapeutic action of HBO2. Immunomodulatory approaches, including prophylactic HBO2, may improve the safety of decompression procedures in undersea and space exploration.

Animals↗