Biomedical subjects
Publications and source records attributed to J D Corbett.
Application of growing degree day-water budget analysis concepts to snail-borne diseases are reviewed to demonstrate use of the unique thermal-hydrological preferences and limits of tolerance of individual parasite-vector systems to define the environmental niche of disease agents in the landscape by modern geospatial analysis tools.
A series of compounds that contain square pyramidal Tt(5) polyanions of tin and lead has been obtained in alkaline-earth or rare-earth metal-tetrel systems by direct fusion of the elements at 570 degrees C (Sr(3)Sn(5)), 1000 degrees C (Ba(3)Pb(5)), or 1300 degrees C (La(3)Sn(5)) followed by slow cooling or annealing. The crystal structures for all three have been refined in the Pu(3)Pd(5) structure type (orthorhombic, Cmcm, Z = 4) with cell dimensions of a = 10.644(2), 11.154(7), and 10.352(5) A, b = 8.588(1), 9.049(7), and 8.290(6) A, and c = 10.895(2), 11.370(5), and 10.652(5) A for Sr(3)Sn(5), Ba(3)Pb(5), and La(3)Sn(5), respectively. Square pyramidal clusters of the tetrel elements are weakly interlinked into chains via two types of longer intercluster interactions that are mediated by bridging cations and substantially influenced by cation size and the free electron count. The new compounds are all metallic (rho(295) approximately 10 (Sr(3)Sn(5)) to approximately 25 (La(3)Sn(5)) muOmega.cm), in agreement with simple valence considerations that predict two and five extra electrons per formula unit, respectively, beyond that necessary for closed-shell nido-Tt(5)(4)(-) anions. Extended Hückel tight-binding calculations on the new compounds as well as on La(3)In(5) reveal that bonding in the regions below and around the Fermi energies are dominated by general cation-anion interactions, that is, lattice covalency. Closed-shell bonding features for the classical Sn(5)(4)(-), In(5)(9)(-), etc. ions are also obvious but subsidiary to the heteroatomic interactions with the cations. The intercluster contacts are relatively unimportant in bonding.
A new phase in the K-Sr-In system was discovered following direct fusion of the neat elements in a niobium tube at 900 degrees C and equilibration at 700 degrees C for 5 days. Single-crystal X-ray diffraction analysis reveals that K(2)SrIn(7) crystallizes in an orthorhombic system, space group Cmcm, Z = 4, a = 5.0455(5) A, b = 11.960(2) A, c = 19.762(4) A. The structure contains a three-dimensional In network built of sheets of condensed pentagonal prismatic columns interbonded along. Two rather different types of channels are separately occupied by K and Sr atoms, the latter centered in 15-atom indium polyhedra. Band structure calculations and resistivity and susceptibility measurements indicate that the compound is metallic and diamagnetic. The one-electron deficiency in the valence band per formula unit brought on by the limited cation count is analyzed in terms of the character of the bonding, some of that from multicenter In bonding falling above E(F).
The title compound with heteratomic anionic chains [Tl(4)Sb(6)(12)(-)] has been discovered in the K-Tl-Sb system. The phase is obtained from a range of compositions near K(3)TlSb(1.5) following reaction first at 750-850 degrees C and then at 550 degrees C for one week or more. It crystallizes in the monoclinic system in space group C2/c, Z = 8, a = 9.951(1) A, b = 17.137(3) A, c = 19.640(6) A, and beta = 104.26(3) degrees. Swing-like (Tl(4)Sb(6))(12)(-) units consisting of alternating Sb and Tl atoms in four- and eight-membered rings are linked through Tl-Tl bonds to form infinite one-dimensional chains along a. EHTB calculations and resistivity measurements show that the compound is a semiconductor.
The new title compound has been synthesized and characterized by physical property measurements and electronic structure calculations. The results ratify the highly uncommon deficiency of one electron that has been long speculated for its Ca3Ga5-type structure on the basis of the simple Zintl electron counting formalism. In the Sr3In5 structure (Cmcm), 4- and 2-bonded indium atoms in a 4:1 ratio form a three-dimensional classical network that encapsulates strontium atoms in its narrow channels. The electrical conductivity of the compound shows typical metallic behavior. The detailed electronic structure analysis suggests that the electron hole is mainly localized on a nonbonding p-orbital on the 2-bonded indium atoms, and that these orbitals, stacked in a sigma-type way along avector (4.97 A), interact only weakly with each other to form highly one-dimensional bands.
Two new tellurides have been synthesized in Ta with particular attention to the use of finely divided Dy (Gd) and a sequence of reactive sintering reactions of pressed pellets up to approximately 1060 degrees C. Both phases disproportionate to Ln and LnTe at only slightly higher temperatures so that arc-melting procedures are relatively unproductive. The two compounds crystallize with a Sc(2)Te-type structure. Single-crystal X-ray diffraction results for Dy(2)Te were detailed in the orthorhombic space group Pnma (No. 62), Z =12, a = 21.922(4) A, b = 4.0650(6) A, and c = 11.428(2) A (Guinier data). There is good evidence for the existence of additional metal-rich binary chalcogenides of the heavy lanthanides. Extended Hückel calculations were performed within the tight binding approximation to aid the understanding of the metal-metal bonding in this system. In terms of metal-metal overlap populations, the isotypic Sc(2)Te is more 1D in aggregation, while the larger atoms and orbitals and stronger bonding in Dy(2)Te make it somewhat more 3D. Electrical resistivity and magnetic susceptibility measurements on polycrystalline Dy(2)Te indicate it is metallic and ferromagnetic (T(c)= 161.3 K) with an effective moment at higher temperatures close to that of ground-state Dy(3+). The connections between heavy lanthanide-rich chalcogenide chemistry and that of the early transition metals seem significant.
The binary systems Ca-Sn, Ba-Sn, Eu-Sn, Yb-Sn, Sr-Pb, Ba-Pb, and Eu-Pb do not contain Cr(5)B(3)-like A(5)Tt(3) phases when care is taken to exclude hydrogen from the reactions (Tt = tetrel, Si-Pb). All form ternary A(5)Tt(3)H(x)() phases (x < or = 1) with "stuffed" Cr(5)B(3)-like structures instead, and all of those tested, Ca-Sn, Ba-Sn, Sr-Pb, and Ba-Pb, also yield the isostructural A(5)Tt(3)F. The structures and compositions of Ca(5)Sn(3)H(x), Ca(5)Sn(3)F(0.89), Eu(5)Sn(3)H(x), and Sr(5)Pb(3)F have been refined from single-crystal X-ray diffraction data and of Ca(5)Sn(3)D from powder neutron data. The interstitial H, F atoms are bound in a tetrahedral (A(2+))(4) cavity in a Cr(5)B(3)-type metal atom structure. Nine previous reports of binary "Ba(5)Sn(3)", "Yb(5)Sn(3)", "Sr(5)Pb(3)", and "Ba(5)Pb(3)" compounds were wrong and presumably concerned the hydrides. The new ternary phases are generally Pauli-paramagnetic, evidently with pi electrons from the characteristic tetrelide dimers in this structure type at least partially delocalized into the conduction band. The Sn-Sn bonds appear correspondingly shortened on oxidation. Other new phases reported are CaSn (CrB type), Yb(5)Sn(4)H(x) (Sm(5)Ge(4)), YbSn ( approximately TlTe), Ba(5)Pb(3) ( approximately W(5)Si(3)), and Yb(31)Pb(20) (Ca(31)Sn(20)).
The R(5)Ga(3) (R = Sc, Y, Ho, Er, Tm, Lu) phases were prepared by high-temperature solid-state techniques. The structure of monoclinic Sc(5)Ga(3) was determined by single-crystal X-ray diffraction means (C2/m, No. 12, Z = 4, a = 8.0793(5) A, b = 14.003(1) A, c = 5.9297(3) A, beta = 90.994(5) degrees ), and those of the isotypic R(5)Ga(3), R = Y, Ho, Er, Tm, Lu, were determined by Guinier powder diffraction. The new Sc(5)Ga(3) structure is a deformation of the hexagonal Mn(5)Si(3) type (P6(3)/mcm) and contains two types of gallium dimers with d(Ga-Ga) = 2.91 and 3.14 A. The closely spaced Sc1 chains in the parent Mn(5)Si(3) type transform to zigzag chains in concert with displacements of the uniformly spaced gallium atoms to form dimers within distorted confacial square antiprisms of Sc. Matrix effects appear important in the different Ga(2) bond lengths. Electronic calculations reveal that the transformation from the hypothetical Mn(5)Si(3) to the Sc(5)Ga(3) type is aided by antibonding Ga-Ga interactions between the dimers that are pushed above E(F) and Ga-Ga and Ga-Sc bonding states just below E(F) that are stabilized. Sc(5)Ga(3) is appropriately metallic. Except for R = Sc, Lu, the arc-melted R(5)Ga(3) compounds above slowly transform on annealing at 1150 degrees C and below into tetragonal Ba(5)Si(3)-type structures.
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This article gives an overview of recent developments in three areas of solid state chemistry: (1) The discovery that centered and originally-adventitious interstitial elements Z are essential for the stability of M6X12-type cluster halides of group 3 and 4 metals has led to a large amount of new chemistry through tuning structures and compositions of AnM6(Z)X12Xn phases with the variables Z, x, and n. The corresponding metal-rich group 3 tellurides exhibit novel and more extensive metal aggregation, reflecting a decreased number of anions and valence electrons. (2) Many intrinsically metallic T5M3 phases with a Mn5Si3-type structure are formed by early transition metals T with main-group elements M. Each characteristically reacts with diverse elements (up to 15-20 each) to form stuffed interstitial versions T5M3Z of the same structure. The ranges of Z and some properties are described. Related reactions of hydrogen (often as an impurity) in Mn5Si3-, beta-Yb5Sb3-, and Cr5B3-type systems are extensive. Substantially all previous reports of beta-Yb5Sb3- and Cr5B3-type phases for divalent metals with pnictogen (As-Bi) and tetrel (Si-Pb) elements, respectively, have been for the hydrides, and about two-thirds do not exist without that hydrogen (or fluorine). (3) The developing chemistry of anionic polymetal cluster compounds of the main-group elements with alkali-metal cations is outlined, particularly for the triel elements In and Tl. These clusters lie to the left of what has been called the Zintl boundary, many are new hypoelectronic polyhedra, some may be centered by the same or another neighboring element, and so far all have been isolated only as neat solid state compounds in which specificity of cation-anion interactions seems important. Extended networks are also encountered.
The compounds Sc6MTe2 (M = Mn, Fe, Co, Ni) have been prepared by high-temperature solid-state techniques and their structures determined to be hexagonal P62m (No. 189), Z = 1, a = 7.662(1) A, 7.6795(2) A, 7.6977(4) A, 7.7235(4) A and c = 3.9041(9) A, 3.8368(2) A, 3.7855(3) A, 3.7656(3) A for M = Mn, Fe, Co, and Ni, respectively. Crystal structures were refined for M = Fe and Ni, while M = Mn and Co were assigned as isostructural on the basis of powder diffraction data. The Sc6MTe2 compounds belong to a large family with the Zr6CoAl2-type structure, an ordered variant of the Fe2P structure. The structure contains confacial tricapped trigonal prisms of scandium centered alternately by the late transition metal or tellurium atoms. The Sc6MTe2 compounds are the electron-poorest examples of this structure type. Extended Hückel band calculations for M = Fe and Ni show that both compounds exhibit largely 1D metal-metal bonding and are predicted to be metallic.
A new anionic thallium cluster chain 1 infinity[Cd2Tl11(5-)] has been discovered in the A-Cd-Tl systems for A = Cs, Rb. The compounds are synthesized by direct fusion of the elements at 700 degrees C and equilibration of the quenched product at 200 degrees C for 1 month. The thallides crystallize in the orthorhombic space group Amm2, Z = 2, a = 56107(7) and 55999(6) A, b = 18090(3) and 17603(3) A, c = 13203(3) and 12896(2) A for A = Cs and Rb, respectively, and contain chains of face-sharing pentagonal Tl10 antiprisms embedded in a matrix of alkali metal cations. Cadmium atoms occupy the center of the antiprisms and donate electrons to the anionic chain. Additional four-bonded Tl atoms on one side of the chain make the structure acentric. The compounds are diamagnetic (chi 296 = -08, -40 (x 10(-4) emu/mol, respectively) and metallic (10-20 mu omega cm at 275 K), and the indirect band gap energy of both compounds is close to zero according to extended Hückel calculations on the isolated chain.
The title compound is synthesized by direct fusion of the elements at 400 degrees C followed by annealing at 330 degrees C, quenching to room temperature, and subsequent annealing at 120 and 100 degrees C for days to weeks. The compound crystallizes in the monoclinic space group P21/c (No. 14), with Z = 4, a = 10.132(1) A, b = 22.323(2) A, c = 13.376(1) A, and beta = 93.14(1)degrees, and consists of Tl7(7-) clusters embedded in a matrix of potassium ions. The cluster is an axially compressed pentagonal bipyramid close to D5h symmetry. The apex-apex bond distance (3.462(1) A) is little longer than the bonds in the pentagonal waist (3.183(1)-3.247(1) A). Structurally the compound is not electron-precise: K10Tl7 has three extra electrons per Tl7 cluster and is Pauli paramagnetic (chi300 = 2.25 x 10(-4) emu/mol).
Exploration of reactions in the La-Br-Z system for Z = Fe, Ru, and Os in welded Nb containers at 900-950 degrees C resulted in only the title phase. The La48Br81Os8 stoichiometry is very close to that of known triclinic Pr6Br10Os but with an approximately 32-times larger cell, 138 independent atoms, and completely different intercluster connectivities in a complex monoclinic superstructure (a = 33.076(5) A, b = 23.466(3) A, c = 23.537(2) A, beta = 110.701(4) degrees, P2(1)/c (No. 14), Z = 4, 23 degrees C). Tetragonally compressed, approximately 16 e- lanthanum octahedra centered by Os are heavily interbridged by Br, including Br(f-a) (f = face) and Br(i-a-a) functions, to increase coordination numbers about some Br (to 4) and La (to 6) and to give an average of 19.63 bonded Br/La6Os vs the usual 18. These result in a cell volume 10% less than for an equivalent (hypothetical) La6Br10Os and Br-Br contacts as short as 3.30 A. Increased polar La-Br interactions presumably drive these changes. Optimal atom sizes for this structure have been found so far only in this novel compound.
Band 4.2 is a human erythrocyte membrane protein of incompletely characterized structure and function. Erythrocytes deficient in band 4.2 protein were used to examine the functional role of band 4.2 in intact erythrocyte membranes. Both the lateral and the rotational mobilities of band 3 were increased in band 4.2-deficient erythrocytes compared to control cells. In contrast, the lateral mobility of neither glycophorins nor a fluorescent phospholipid analog was altered in band 4.2-deficient cells. Compared to controls, band 4.2-deficient erythrocytes manifested a decreased ratio of band 3 to spectrin, and band 4.2-deficient membrane skeletons had decreased extractability of band 3 under low-salt conditions. Normal band 4.2 was found to bind to spectrin in solution and to promote the binding of spectrin to ankyrin-stripped inside-out vesicles. We conclude that band 4.2 provides low-affinity binding sites for both band 3 oligomers and spectrin dimers on the human erythrocyte membrane. Band 4.2 may serve as an accessory linking protein between the membrane skeleton and the overlying lipid bilayer.
Southeast Asian ovalocytosis (SAO) is an asymptomatic trait characterized by rigid, poorly deformable red cells that resist invasion by several strains of malaria parasites. The underlying molecular genetic defect involves simple heterozygous state for a mutant band 3 protein, which contains a deletion of amino acids 400 through 408, linked with a Lys 56-to-Glu substitution (band 3-Memphis polymorphism). To elucidate the contribution of the mutant SAO band 3 protein to increased SAO red blood cell (RBC) rigidity, we examined the participation of the mutant SAO band 3 protein in increased band 3 attachment to the skeleton and band 3 oligomerization. We found first that SAO RBC skeletons retained more band 3 than normal cells and that this increased retention preferentially involved the mutant SAO band 3 protein. Second, SAO RBCs contained a higher percentage of band 3 oligomer-ankyrin complexes than normal cells, and these oligomers were preferentially enriched by the mutant SAO protein. At the ultrastructural level, the increased oligomer formation of SAO RBCs was reflected by stacking of band 3-containing intramembrane particles (IMP) into longitudinal strands. The IMP stacking was not reversed by treating SAO RBCs in alkaline pH (pH 11), which is known to weaken ankyrin-band 3 interactions, or by removing the cytoplasmic domain of band 3 from SAO membranes with trypsin. Finally, we found that band 3 protein in intact SAO RBCs exhibited a markedly decreased rotational mobility, presumably reflecting the increased oligomerization and the membrane skeletal association of the SAO band 3 protein. We propose that the mutant SAO band 3 has an increased propensity to form oligomers, which appear as longitudinal strands of IMP and exhibit increased association with membrane skeleton. This band 3 oligomerization underlies the increase in membrane rigidity by precluding membrane skeletal extension, which is necessary for membrane deformation.
We have used differential polarization imaging microscopy to measure the amount and orientation of aligned sickle hemoglobin polymer in quickly deoxygenated sickle red blood cells. Images of the angular orientation of the aligned polymer at each point in the cell allowed for determination of the inclination of individual domains, providing detailed information regarding the polymerization and elongation of sickle hemoglobin polymers ex vivo. We found that the number of aligned polymer domains increased with increasing mean cell hemoglobin concentration. Sickle and holly leaf-shaped cells contained single or few domains of aligned polymer, while more compact cells such as irreversibly sickled cells contained many domains. A new class of cells was discovered by examination of images of the angular orientation of aligned polymer, which contained a single central nucleation site, with growth of polymer occurring outward in all directions in a spherulite-like domain.
Electroporation involves the application of an electric field pulse that creates transient aqueous pathways in lipid bilayer membranes. Transport through these pathways can occur by different mechanisms during and after a pulse. To determine the time scale of transport and the mechanism(s) by which it occurs, efflux of a fluorescent molecule, calcein, across erythrocyte ghost membranes was measured with a fluorescence microscope photometer with millisecond time resolution during and after electroporation pulses several milliseconds in duration. One of four outcomes was typically observed. Ghosts were: (1) partially emptied of calcein, involving efflux primarily after the pulse; (2) completely emptied of calcein, involving efflux primarily after the pulse; (3) completely emptied of calcein, involving efflux both during and after the pulse; or (4) completely emptied of calcein, involving efflux primarily during the pulse. Partial emptying, involving significant efflux during the pulse, was generally not observed. We conclude that under some conditions transport caused by electroporation occurs predominantly by electrophoresis and/or electroosmosis during a pulse, although under other conditions transport occurs in part or almost completely by diffusion within milliseconds to seconds after a pulse.