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Jide Xu

Publications and source records attributed to Jide Xu.

At least 19 recordsLinked to original sources
PubMed2007

Brilliant Sm, Eu, Tb, and Dy chiral lanthanide complexes with strong circularly polarized luminescence.

The synthesis, characterization, and luminescent behavior of trivalent Sm, Eu, Dy, and Tb complexes of two enantiomeric, octadentate, chiral, 2-hydroxyisophthalamide ligands are reported. These complexes are highly luminescent in solution. Functionalization of the achiral parent ligand with a chiral 1-phenylethylamine substituent on the open face of the complex in close proximity to the metal center yields complexes with strong circularly polarized luminescence (CPL) activity. This appears to be the first example of a system utilizing the same ligand architecture to sensitize four different lanthanide cations and display CPL activity. The luminescence dissymmetry factor, g(lum), recorded for the Eu(III) complex is one of the highest values reported, and this is the first time the CPL effect has been demonstrated for a Sm(III) complex with a chiral ligand. The combination of high luminescence intensity with CPL activity should enable new bioanalytical applications of macromolecules in chiral environments.

Circular Dichroism↗
PubMed2006

"Cymothoe sangaris": an extremely stable and highly luminescent 1,2-hydroxypyridinonate chelate of Eu(III).

The synthesis, structure, and characterization of a new class of luminescent agents based on the 1,2-hydroxypyridinone chelator are reported. The prototype complex, [Eu(5LIO-1,2-HOPO)2]-, demonstrates superb aqueous stability [pEu = 18.64(10)] and is highly emissive [Phit = 0.21(3)], emitting almost pure "red" light (lambdaem = 612 nm). The crystal structure reveals a coordination geometry reminiscent of a "butterfly", hence the soubriquet of "Cymothoe sangaris" to identify with the unique species of red butterfly found only in Central Africa.

Chelating Agents↗
PubMed2006

Tren-based analogues of bacillibactin: structure and stability.

Synthetic analogues were designed to highlight the effect of the glycine moiety of bacillibactin on the overall stability of the ferric complex as compared to synthetic analogues of enterobactin. Insertion of a variety of amino acids to catecholamide analogues based on a Tren (tris(2-aminoethyl)amine) backbone increased the overall acidity of the ligands, causing an enhancement of the stability of the resulting ferric complex as compared to TRENCAM. Solution thermodynamic behavior of these siderophores and their synthetic analogues was investigated through potentiometric and spectrophotometric titrations. X-ray crystallography, circular dichroism, and molecular modeling were used to determine the chirality and geometry of the ferric complexes of bacillibactin and its analogues. In contrast to the Tren scaffold, addition of a glycine to the catechol chelating arms causes an inversion of the trilactone backbone, resulting in opposite chiralities of the two siderophores and a destabilization of the ferric complex of bacillibactin compared to ferric enterobactin.

Circular Dichroism↗
PubMed2006

Bacillibactin-mediated iron transport in Bacillus subtilis.

The hexadentate triscatecholamide bacillibactin delivers iron to Bacillus subtilis and is structurally similar to enterobactin, although in a more oblate conformation. B. subtilis uses two partially overlapping permeases (1 and 2) to acquire iron from its endogenous siderophores (bacillibactin and itoic acid). Enterobactin and bacillibactin have opposite metal chiralities, different affinity for ferric ion, and dissimilar iron transport behaviors. The solution thermodynamic stability of ferric bacillibactin has been investigated through potentiometric and spectrophotometric titrations. The addition of a glycine to the catechol chelating arms causes a destabilization of the ferric complex of bacillibactin compared to ferric enterobactin. B. subtilis appears to express a separate receptor for enterobactin (permease 3), although enterobactin can also be transported through the permease for bacillibactin (permease 2).

Bacillus subtilis↗
PubMed2005

Large M4L4 (M = Al(III), Ga(III), In(III), Ti(IV)) tetrahedral coordination cages: an extension of symmetry-based design.

As an extension to a rational design for the formation of self-assembled coordination cages, the syntheses for very large M4L4 tetrahedra based on a hexadentate 3-fold symmetric ligand (1,3,5-tris(4'-(2' ',3' '-dihydroxybenzamido)phenyl)benzene (H6L2)) are described. Four tetrahedral M4L2(4) assemblies (M = Al(III), Ga(III), In(III), Ti(IV)), with cavity sizes of around 450 A3, have been characterized by elemental analysis, NMR spectroscopy, and high-resolution electrospray mass spectrometry. Differences in chiral resolution and dynamic behavior of host-guest interactions with previously reported tetrahedral M4L(N)6 and M4L1(4) architectures are highlighted for the ligands 1,5-bis(2',3'-dihydroxybenzamido)naphthalene (H4L(N)) and 1,3,5-tris(2',3'-dihydroxybenzamido)benzene (H6L1). An even larger 3-fold symmetric ligand, 1,3,5-tris(4'-(2' '',3' ''-dihydroxybenzamido)-1',1' '-biphenyl)benzene (H6L3) has been prepared but, due to increased flexibility and deviation from the intended 3-fold symmetry, does not undergo self-assembly to form the M4L3(4) structure.

Journal Article↗
PubMed2005

Sequestered plutonium: [Pu(IV){5LIO(Me-3,2-HOPO)}2]--the first structurally characterized plutonium hydroxypyridonate complex.

The first single-crystal X-ray diffraction analysis of a hydroxypyridonate plutonium(IV) complex is presented, that of the tetradentate ligand 5LIO(Me-3,2-HOPO) with Pu(IV). The [Pu(IV){5LIO(Me-3,2-HOPO)}(2)] complex crystallizes in the space group Pna2(1) with the asymmetric unit cell containing two unique eight-coordinate plutonium complexes and one perchlorate anion. According to shape measure analysis, the geometry of both Pu centers is closest to a bicapped trigonal prism (C(2v) symmetry, for Pu 1: S(C(2v))=13.48 degrees , S(D(4d))=15.43 degrees , S(D(4d))=16.10 degrees ). The average bond length for the Pu--O(phenolic) is 2.31(4) A, whereas the Pu--O(amide) distances are slightly longer, averaging 2.40(2) A. The preparative chemistry of this compound and the implications of the structure are discussed.

Journal Article↗
PubMed2005

Incorporation of hydroxypyridinone ligands into self-assembled monolayers on mesoporous supports for selective actinide sequestration.

In this study, three isomers of hydroxypyridinones (1,2-HOPO, 3,2-HOPO, and 3,4-HOPO) were attached to self-assembled monolayers on mesoporous silica (SAMMS). The HOPO-SAMMS materials have superior solid adsorbents properties: they do not suffer from solvent swelling; their rigid, open pore structure allows rapid sorption kinetics; their extremely high surface area enables the installation of high functional density; and being silica-based, they are compatible with vitrification into a final vitreous waste form. Kinetics, equilibrium, and selectivity of the adsorptions of actinide on the HOPO-SAMMS at various pH values and in the presence of other metal cations, anions, and competing ligands are reported. Rapid sequestration of U(VI), Np(V), and Pu(IV) was observed. Very little competition from transition metal cations and common species was observed.

Adsorption↗
PubMed2005

Hydroxypyridinone functionalized self-assembled monolayers on nanoporous silica for sequestering lanthanide cations.

1,2-Hydroxypyridinone (1,2-HOPO) ligands were installed as self-assembled monolayers on nanoporous silica (MCM-41) to create a superior class of sorbent materials for lanthanide cations. Lanthanides were used as a model system for the radioactive, expensive, and highly hazardous actinides in preliminary screening studies. The ligand properties of the 1,2-HOPO ligand field and the extremely large surface area of MCM-41, coupled with the dense monolayer coating, contribute to the extremely high lanthanide binding capacity of the 1,2-HOPO nanoporous sorbent. At pH 4-5.9, the mass-weighted partition coefficients (Kd) for La, Nd, Eu, and Lu were 354,000, 344,000, 210,800, and 419,800, respectively. The rigid, open pore structure of the silica also allows for very rapid sorption. Being silica-based, the sorbent is compatible with vitrification processing into a final glasseous waste form, for subsequent disposition in a deep geological repository.

Cations↗
PubMed2004

Time gating improves sensitivity in energy transfer assays with terbium chelate/dark quencher oligonucleotide probes.

Lanthanides are attractive as biolabels because their long luminescence decay rates allow time-gated detection, which separates background scattering and fluorescence from the lanthanide emission. A stable and highly luminescent terbium complex based on a tetraisophthalamide (TIAM) chelate is paired with a polyaromatic-azo dark quencher (referred to as a Black Hole Quencher or BHQ) to prepare a series of 5'TIAM(Tb)/3'BHQ dual-labeled oligonucleotide probes with no secondary structure. Luminescence quenching efficiency within terbium/BHQ probes is very dependent on the terbium-BHQ distance. In an intact probe, the average terbium-BHQ distance is short, and Tb --> BHQ energy transfer is efficient, decreasing both the terbium emission intensity and lifetime. Upon hybridization or nuclease digestion, which spatially separate the Tb and BHQ moieties, the Tb luminescence intensity and lifetime increase. As a result, time-gated detection increases the emission intensity ratio of the unquenched probe/quenched probe due to the shorter lifetime of the quenched species. A 40-mer probe that has a 3-fold increase in steady-state luminescence upon digestion has a 50-fold increase when gated detection is used. This study demonstrates that time gating with lanthanide/dark quencher probes in energy transfer assays is an effective means of improving sensitivity.

Amides↗
PubMed2004

Gadolinium(III) 1,2-hydroxypyridonate-based complexes: toward MRI contrast agents of high relaxivity.

Prospective gadolinium(III) MRI contrast agent precursors [Gd-TREN-1,2-HOPO] (1) [TREN-1,2-HOPO = tris[(1-hydroxy-2-oxo-1,2-dihydropyridine-6-carboxamido)ethyl]amine] and [Gd-TREN-bis(Me-3,2-HOPO)-1,2-HOPO] (2) have been synthesized and characterized by relaxometric measurements. The water proton relaxivity values of 1 and 2 (20 MHz and 25 degrees C) are 9.5 and 9.3 mM(-)(1)s(-)(1), respectively, suggesting the presence of two coordinated water molecules. The molecular structure of [1.DMF](2) was obtained and reveals a similar eight-coordinate geometry to [Gd-TREN-Me-3,2-HOPO.2H(2)O] ([3.2H(2)O]). A shape analysis of the coordination polyhedron of 1 reveals that this geometry is best described as a bicapped trigonal prism, poised to accommodate an additional donor atom to give a tricapped trigonal prismatic intermediate. This geometry supports the model that formation of a tris-aquo intermediate for 1 enables fast and associative water exchange.

Chelating Agents↗
PubMed2003

Toward optimized high-relaxivity MRI agents: the effect of ligand basicity on the thermodynamic stability of hexadentate hydroxypyridonate/catecholate gadolinium(III) complexes.

The thermodynamic stabilities of the Gd(III) complexes of five hexadentate ligands, which incorporate the 2,3-dihydroxyterephthalamide and 2,3-hydroxypyridonate chelating moieties, have been determined by potentiometric and spectrophotometric titration. The ligands were chosen to span a range of basicities while maintaining a similar tripodal structural motif, facilitating a study of the effect of ligand basicity on the thermodynamic stability of the Gd(III) complexes. The relative stability of the five complexes is found to be highly pH dependent, with the most acidic ligands forming the most stable complexes at low pH and more basic ligands forming more stable complexes at high pH. The most stable Gd(III) complex at a physiological pH of 7.4 is formed with a ligand of intermediate basicity and is of stability comparable to that of Gd(III) complexes that feature eight-coordinate amino-carboxylate ligands and are currently used as magnetic resonance imaging contrast agents in diagnostic medicine. A single-crystal X-ray structure of the intermediate compound 3-hydroxy-6-methyl-2-oxo-1,2-dihydropyridine-4-carboxylic acid ethyl ester is described: This compound crystallizes in the triclinic space group P1 with a = 7.4801(3) A, b = 8.0671(3) A, c = 8.3457(4) A, alpha = 72.242(2) degrees, beta = 80.693(2) degrees, gamma = 69.943(3) degrees, V = 449.60(3) A(3), Z = 2, and R = 0.042.

Catechols↗
PubMed2003

Thorium(IV) complexes of bidentate hydroxypyridinonates.

The coordination chemistry of actinide(IV) ions with hydroxypyridinone ligands has been initially explored by examining the complexation of Th(IV) ion with bidentate PR-1,2-HOPO (HL(1)()), PR-Me-3,2-HOPO (HL(2)()), and PR-3,4-HOPO-N (HL(3)()) ligands. The complexes Th(L(1)())(4), Th(L(2)())(4), and Th(L(3)())(4) were prepared in methanol solution from Th(acac)(4) and the corresponding ligand. Single-crystal X-ray diffraction analyses are reported for the free ligand PR-Me-3,2-HOPO (HL(2)()) [Ponemacr;, Z = 8, a = 8.1492(7) A, b = 11.1260(9) A, c = 23.402(2) A, alpha = 87.569(1) degrees, beta = 86.592(1) degrees, gamma = 87.480(1) degrees ], and the complex Th(L(2)())(4).H(2)O [Pna2(1) (No. 33), Z = 4, a = 17.1250(5) A, b = 12.3036(7) A, c = 23.880 (1) A]. A comparison of the structure of the metal complex Th-PR-Me-3,2-HOPO with that of free ligand PR-Me-3,2-HOPO reveals that the ligand geometry is the same in the free ligand and in the metal complex. Amide hydrogen bonds enhance the rigidity and stability of the complex and demonstrate that the Me-3,2-HOPO ligands are predisposed for metal chelation. Solution thermodynamic studies determined overall formation constants (log beta(140)) for Th(L(1)())(4), Th(L(2)())(4), and Th(L(3)())(4) of 36.0(3), 38.3(3), and 41.8(5), respectively. Species distribution calculations show that the 4:1 metal complex Th(L)(4) is the dominant species in the acidic range (pH < 6) for PR-1,2-HOPO, in weakly acidic to physiological pH range for PR-Me-3,2-HOPO and in the high-pH range (>8) for PR-3,4-HOPO-N. This finding parallels the relative acidity of these structurally related ligands. In the crystal of [Th(L(2)())(4)].H(2)O, the chiral complex forms an unusual linear coordination polymer composed of linked, alternating enantiomers.

Algorithms↗
PubMed2003

The effect of ligand scaffold size on the stability of tripodal hydroxypyridonate gadolinium complexes.

The variation of the size of the capping scaffold which connects the hydroxypyridonate (HOPO) binding units in a series of tripodal chelators for gadolinium (Gd) complexes has been investigated. A new analogue of TREN-1-Me-3,2-HOPO (1) (TREN = tri(ethylamine)amine) was synthesized: TREN-Gly-1-Me-3,2-HOPO (2) features a glycine spacer between the TREN cap and HOPO binding unit. TRPN-1-Me-3,2-HOPO (3) has a propylene-bridged cap, as compared to the ethylene bridges within the TREN cap of the parent complex. Thermodynamic equilibrium constants for the acid-base properties of 2 and the Gd(3+) complexation strength of 2 and 3 were measured and are compared with that of the parent ligand. The most basic ligand is 2 while 3 is the most acidic. Both 2 and 3 form Gd(3+) complexes of similar stability (pGd = 16.7 and 15.6, respectively) and are less stable than the parent complex Gd-1 (pGd = 19.2). Two of the three complexes are more stable than the bis(methylamide)diethylenetriamine pentaacetate complex Gd(DTPA-BMA) (pGd = 15.7) while the other is of comparable stability. Enlargement of the ligand scaffold decreases the stability of the Gd(3+) complexes and indicates that the TREN scaffold is superior to the TRPN and TREN-Gly scaffolds. The proton relaxivity of Gd-2 is 6.6 mM(-)(1) s(-)(1) (20 MHz, 25 degrees C, pH 7.3), somewhat lower than the parent Gd-1 but higher than that of the MRI contrast agents in clinical practice. The pH-independent relaxivity of Gd-2 is uncharacteristic of this family of complexes and is discussed.

Contrast Media↗
PubMed2002

Hexadentate hydroxypyridonate iron chelators based on TREN-Me-3,2-HOPO: variation of cap size.

TREN-Me-3,2-HOPO, TR322-Me-3,2-HOPO, TR332-Me-3,2-HOPO, and TRPN-Me-3,2-HOPO correspond to stepwise replacement of ethylene by propylene bridges. A series of tripodal, hexadentate hydroxypyridinone ligands are reported. These incorporate 1-methyl-3,2-hydroxypyridinone (Me-3,2-HOPO) bidentate chelating units for metal binding. They are varied by systematic enlargement of the capping scaffold which connects the binding units. The series of ligands and their iron complexes are reported. Single crystal X-ray structures are reported for the ferric complexes of all four tripodal ligands: FeTREN-Me-3,2-HOPO.0.375C(4)H(10)O.0.5CH(2)Cl(2) [P2(1)/n (No. 14), Z = 8, a = 20.478(3) A, b = 12.353(2) A, c = 27.360(3) A; beta = 91.60(1) degrees ]; FeTR322-Me-3,2-HOPO.CHCl(3).0.5C(6)H(14).CH(3)OH.0.5H(2)O [P2(1)/n (No. 14), Z = 4, a = 12.520(3) A, b = 22.577(5) A, c = 16.525(3) A; beta = 111.37(3) degrees ]; FeTR332-Me-3,2-HOPO.3.5CH(3)OH [C2/c (No. 15), Z = 8, a = 13.5294(3) A, b = 19.7831(4) A, c = 27.2439(4) A; beta = 101.15(3) degrees ]; FeTRPN-Me-3,2-HOPO.C(3)H(7)NO.2C(4)H(10)O [P1 (No. 2), Z = 2, a = 11.4891(2) A, b = 12.3583(2) A, c = 15.0473(2) A; alpha = 86.857(1) degrees, beta = 88.414(1) degrees, gamma = 70.124(1) degrees ]. The structures show the importance of intermolecular hydrogen bonds and the effect of cap enlargement to the stability and geometry of the metal complexes throughout the series. All protonation and iron complex formation constants have been determined from solution thermodynamic studies. The TREN-capped derivative is the most acidic, with a cumulative protonation constant, log beta(014), of 25.95. Corresponding values of 26.35, 26.93, and 27.53 were obtained for the TR322, TR332, and TRPN derivatives, respectively. The protonation constants and NMR spectroscopic data are interpreted as being due to the influence of specific hydrogen-bond interactions. The incremental enlargement of ligand size results in a decrease in iron-chelate stability, as reflected in the log beta(110) values of 26.8, 26.2, 26.42, and 24.48 for the TREN, TR322, TR332, and TRPN derivatives, respectively. The metal complex formation constants are also affected by the acidity of a proximal (non-metal-binding) amine in the complexes, a trend consistent with the effects of internal hydrogen bonding. The ferric complexes display reversible reduction potentials (measured relative to the normal hydrogen electrode (NHE)) between -0.170 and -0.223 V.

Algorithms↗
PubMed2002

Synthesis and initial evaluation for in vivo chelation of Pu(IV) of a mixed octadentate spermine-based ligand containing 4-carbamoyl-3-hydroxy-1-methyl-2(1H)-pyridinone and 6-carbamoyl-1-hydroxy-2(1H)-pyridinone.

An improved synthesis for a series of 1-hydroxy-2(1H)-pyridinone-based octadentate ligands is reported. The mixed chelate, octadentate ligand, 3,4,3-LI(1,2-Me-3,2-HOPO), was designed, synthesized, and tested for in vivo chelation of Pu in a mouse model. This ligand incorporates both 1,2-HOPO and Me-3,2-HOPO metal chelating units; the latter has higher affinity toward actinide ions than does 1,2-HOPO at physiological pH. Injected or administered orally to fasted or normally fed mice at the standard clinical dose 30 micromol/kg, both 3,4,3-LI(1,2-HOPO) and 3,4,3-LI(1,2-Me-3,2-HOPO) remove significantly more Pu than injected CaNa(3)DTPA. Injected doses of 0.1 micromol/kg of these HOPO ligands are as effective as 30 micromol/kg of injected CaNa(3)DTPA. Ten daily injections of 30 micromol/kg of a HOPO ligand did not induce detectable acute toxicity in mice. The mixed HOPO ligand is somewhat more effective than 3,4,3-LI(1,2-HOPO) when given orally, and the enhanced reduction of liver Pu by the mixed ligand is statistically significant. Thus, both octadentate HOPO ligands meet the criterion of low toxicity at doses that are more effective than the standard dose of CaNa(3)DTPA. Their improved effectiveness at low dose along with great oral activity (despite low gastrointestinal absorption) implies that new treatment regimens can be developed using the HOPO ligands alone or as adjuncts to CaNa(3)DTPA therapy, which will greatly exceed the amount of Pu excretion that is achievable with CaNa(3)DTPA alone.

Administration, Oral↗