Potential Theranostic Boron Neutron Capture Therapy Agents as Multimodal Radiopharmaceuticals.

Boron neutron capture therapy (BNCT) has been extant for decades and continues to be practiced in many centers around the globe. Most of the active clinical trials utilize boronophenylalanine as the drug containing boron atoms. The important aspect that has been added to the BNCT practice is the use of an F-18 radiolabeled analog for ascertaining targeting and monitoring follow-up studies. The recent widespread application of therapeutic radiopharmaceuticals, especially peptides (somatostatin analogs), prostate-specific antigen-binding ligands, or immunomolecules, offers the ambit for invention of new tumor-specific BNCT agents, especially for BNCT-susceptible tumors, that is, locoregional cancers such as head and neck cancer. Such BNCT agents, when radiolabeled, can enable simultaneous imaging and/or therapeutic applications (depending on the radionuclide used) through multimodal approaches. Development of boron-rich moieties such as sodium borocaptate and neutral carboranes combined with tumor-targeting moieties can lead to a new horizon in BNCT. The review covers various aspects of drug design, tumor targeting, and possible future radiopharmaceutical development for multimodal theranostic application in humans.

Synthesis, structure, and magnetic properties of novel B-site ordered double perovskites, SrLaMReO6 (M = Mg, Mn, Co and Ni).

Four new double perovskites, SrLaMReO(6) (M = Mg, Mn, Co, Ni) in which Re(5+) (5d(2)) is present, were prepared via conventional solid state reactions and characterized by X-ray and neutron powder diffraction, XANES, SQUID magnetometry, and muon spin relaxation (µSR). Synchrotron X-ray and neutron diffraction experiments confirmed that all compounds crystallize in the monoclinic P2(1)/n structure type, which consists of alternately corner-shared octahedra of MO(6) and ReO(6). Rietveld refinement results indicated anti-site mixing of less than 7% on the M/Re sites. Bond valence sum calculations (BVS) suggest all M and Re ions are 2+ and 5+, respectively, and for the Mn-containing phase this is also supported by XANES measurements. All of the materials are paramagnetic at room-temperature and their Curie-Weiss temperatures are positive (except for Mg) indicating net ferromagnetic interactions. No evidence for long-range magnetic order is evident in the dc magnetic susceptibility and µSR measurements for SrLaMgReO(6) to 2 K. The Mn-phase shows long-range order at T(C) = 190 K and neutron diffraction revealed a ferromagnetic structure with a refined net moment of ∼3.7µ(B). Both Co- and Ni-containing phases exhibit spin glass behavior at T(G) = 23 and 30 K, respectively, which is supported by neutron diffraction and a.c. susceptibility data. The structure and physical properties of these four new rhenium based ordered double perovskites are compared to the closely related "pillared perovskites", La(5)Re(3)MO(16), the isoelectronic Os(6+) (5d(2)) double perovskite Sr(2)CoOsO(6), and the Re(6+) (5d(1)) double perovskites, Sr(2)MReO(6), (M = Mg, Ca, Mn, Co, Ni).

Orientational ordering, tilting and lone-pair activity in the perovskite methylammonium tin bromide, CH3NH3SnBr3.

Synchrotron powder diffraction data from methylammonium tin bromide, CH(3)NH(3)SnBr(3), taken as a function of temperature, reveal the existence of a phase between 230 and 188 K crystallizing in Pmc2(1), a = 5.8941 (2), b = 8.3862 (2), c = 8.2406 (2) A. Strong ferroelectric distortions of the octahedra, associated with stereochemical activity of the Sn 5s(2) lone pair, are evident. A group analysis and decomposition of the distortion modes of the inorganic framework with respect to the cubic parent is given. The primary order parameters driving this upper transition appear to be an in-phase tilt (rotation) of the octahedra coupled to a ferroelectric mode. The precise nature of the lower-temperature phase remains uncertain, although it appears likely to be triclinic. Density-functional theory calculations on such a triclinic cell suggest that directional bonding of the amine group to the halide cage is coupled to the stereochemical activity of the Sn lone pair via the Br atoms, i.e. that the bonding from the organic component may have a strong effect on the inorganic sublattice (principally via switching the direction of the lone pair with little to no energy cost).

Synthesis, structure, and unexpected magnetic properties of La3Re2O10.

The compound La(3)Re(2)O(10) has been synthesized by solid-state reaction and characterized by powder neutron diffraction, SQUID magnetometry, and heat capacity measurements. Its structure consists of isolated [Re(2)O(10)](9-) dimer units of two edge-shared ReO(6) octahedra, separated by La(3+) within the lattice. The Re-Re distance within the dimer units is 2.488 A, which is indicative of metal-metal bonding with a bond order of 1.5. The average oxidation state of the Re atom is +5.5, leaving one unpaired electron per dimer unit (S = 1/2). Although the closest interdimer distance is 5.561 A, the magnetic susceptibility data and heat capacity measurements indicate this compound exhibits both short- and long-range magnetic order at surprisingly high temperatures. The zero field cooled (ZFC) magnetic susceptibility data show two broad features at 55 and 105 K, indicating short-range order, and a sharper cusp at 18 K, which signifies long-range antiferromagnetic order. The heat capacity of La(3)Re(2)O(10) shows a lambda-type anomaly at 18 K, which is characteristic of long-range magnetic order. DFT calculations determined that the unpaired electron resides in a pi-bonding orbital and that the unpaired electron density is widely delocalized over the atoms within the dimer, with high values at the bridging oxygens. Extended Hückel spin dimer calculations suggest possible interaction pathways between these dimer units within the crystal lattice. Results from the calculations and fits to the susceptibility data indicate that the short-range magnetic ordering may consist of 1-D antiferromagnetic linear chains of coupled S = 1/2 dimers. The magnetic structure of the antiferromagnetic ground state could not be determined by unpolarized neutron powder diffraction.

Tilt and acoustic instabilities in ABX4, A2BX4 and ABX3 perovskite structure types: their role in the incommensurate phases of the organic-inorganic perovskites.

An examination of the tilt modes and other low-frequency modes is made for an isolated, untilted perovskite layer, which maps very simply to the ABX4 perovskites. A sheet of pure tilts exists at the Brillouin Zone boundary at {xi, (1/2), zeta}. An instability is also found at all wavevectors which can be described as continuously varying from pure tilts to pure layer displacements as a function of the wavevector. Analysis is extended by considering the stacking of layers in the I-centered A2BX4-layer perovskites. The effect of freezing in the commensurate tilt required to generate the Cmca tilt system, pertinent to the modulated phases of propylammonium salts, is examined. The zero-frequency modes are restricted to two planes in the Brillouin Zone. All of the observed wavevectors associated with modulated phases, and the commensurately tilted propylammonium tetrachlorocadmate, are consistent with this calculation. The effect of full three-dimensional connectivity is briefly reviewed for the true ABX3 perovskites. While pure tilt incommensurates appear to be hypothetically possible, they do not appear to have been observed to date.

Ammonium cyanate shows N-H...N hydrogen bonding, not N-H...O.

The transformation of ammonium cyanate into urea, first studied over 170 years ago by Wöhler and Liebig, has an important place in the history of chemistry. To understand the nature of this solid state reaction, knowledge of the crystal structure of ammonium cyanate is a prerequisite. Employing neutron powder diffraction, we demonstrate conclusively that, in the structure of ammonium cyanate, the NH(4)(+) cation forms N-H...N hydrogen bonds to four cyanate N atoms at alternate corners of a distorted cube, rather than our previously proposed alternative arrangement with N-H...O hydrogen bonds to cyanate O atoms at the other four corners.

Structure and dynamics of ND3BF3 in the solid and gas phases: a combined NMR, neutron diffraction, and Ab initio study.

The decrease in D-->A bond lengths, previously reported for some Lewis acid/base complexes, in going from the gas to the solid phases is investigated by obtaining an accurate crystal structure of solid ND(3)BF(3) by powder neutron diffraction. The B-N internuclear distance is 1.554(3) A, 0.118 A shorter than the most recent gas-phase microwave value and 0.121 A shorter than the single molecule geometry optimized (1.672 A, CISD/6-311++G(d,p)) bond length. The crystal structure also shows N-D.F-B hydrogen bonds. The effects of this change in structure and of intermolecular hydrogen-bonding on nuclear magnetic shielding (i.e., chemical shifts) and the nuclear quadrupolar coupling constants (QCC) are investigated by ab initio molecular orbital and density functional theory calculations. These calculations show that the nitrogen ((15)N and (14)N) and boron ((11)B and (10)B) chemical shifts should be rather insensitive to changes in r(BN) and that the concomitant changes in molecular structure. Calculations on hydrogen-bonded clusters, based on the crystal structure, indicate that H-bonding should also have very little effect on the chemical shifts. On the other hand, the (11)B and (14)N QCCs show large changes because of both effects. An analysis of the (10)B[(19)F] line shape in solid ND(3)(10)BF(3) yields a (11)B QCC of +/-0.130 MHz. This is reasonably close an earlier value of +/-0.080 MHz and the value of +/-0.050 MHz calculated for a [NH(3)BF(3)](4) cluster. The gas-phase value is 1.20 MHz. Temperature-dependent deuterium T(1) measurements yield an activation energy for rotation of the ND(3) group in solid ND(3)BF(3) of 9.5 +/- 0.1 kJ/mol. Simulations of the temperature-dependent T(1) anisotropy gave an E(a) of 9.5 +/- 0.2 kJ/mol and a preexponential factor, A, of 3.0 +/- 0.1 x 10(12) s(-)(1). Our calculated value for a [NH(3)BF(3)](4) cluster is 16.4 kJ/mol. Both are much higher than the previous value of 3.9 kJ/mol, from solid-state proton T(1) measurements.

Neutron powder-profile study of chlorofluoromethane.

The crystal structure of chlorofluoromethane, CH(2)ClF, has been determined at 100 and 30 K using indexing, packing considerations and Rietveld refinement of neutron powder profiles. There is only one phase, in monoclinic space group P2(1) and with two molecules in the unit cell occupying general positions. The structure has close packing in several directions and there are weak hydrogen bonds forming zigzag chains.