Liurukara D. Sanjeewa

Multifunctional Yolk-in-Shell Nanoparticles for pH-triggered Drug Release and Imaging

Multifunctional nanoparticles are synthesized for both pH-triggered drug release and imaging with radioluminescence, upconversion luminescent, and magnetic resonance imaging (MRI). The particles have a yolk-in-shell morphology, with a radioluminescent core, an upconverting shell, and a hollow region between the core and shell for loading drugs. They are synthesized by controlled encapsulation of a radioluminescent nanophosphor yolk in a silica shell, partial etching of the yolk in acid, and encapsulation of the silica with an upconverting luminescent shell. Metroxantrone, a chemotherapy drug, was loaded into the hollow space between X-ray phosphor yolk and up-conversion phosphor shell through pores in the shell. To encapsulate the drug and control the release rate, the nanoparticles are coated with pH-responsive biocompatible polyelectrolyte layers of charged hyaluronic acid sodium salt and chitosan. The nanophosphors display bright luminescence under X-ray, blue light (480 nm), and near infrared light (980 nm). They also served as T1 and T2 MRI contrast agents with relaxivities of 3.5 mM(-1) s(-1) (r1 ) and 64 mM(-1) s(-1) (r2 ). These multifunctional nanocapsules have applications in controlled drug delivery and multimodal imaging.

Honeycomb-like S = 5/2 Spin-Lattices in Manganese(II) Vanadates.

New complex manganese vanadate materials were synthesized as high-quality single crystals in multi-millimeter lengths using a high-temperature, high-pressure hydrothermal method. One compound, Mn5(VO4)2(OH)4, was grown from Mn2O3 and V2O5 in 3 M CsOH at 580 °C and 1.5 kbar. Changing the mineralizer to 1 M CsOH/3MCsCl leads to the formation of another product, Mn6O(VO4)2(OH). Both compounds were structurally characterized by single-crystal X-ray diffraction (Mn5(VO4)2(OH)4: C2/m, Z = 2, a = 9.6568(9) Å, b = 9.5627(9) Å, c = 5.4139(6) Å, β = 98.529(8)°; Mn6O(VO4)2(OH): P21/m, Z = 2, a = 8.9363(12) Å, b = 6.4678(8) Å, c = 10.4478(13) Å, β = 99.798(3)°), revealing interesting low-dimensional transition-metal features. Mn5(VO4)2(OH)4 possesses complex honeycomb-type Mn-O layers, built from edge-sharing [MnO6] octahedra in the bc plane, with bridging vanadate groups connecting these layers along the a-axis. Mn6O(VO4)2(OH) presents a more complicated structure with both octahedral [MnO6] and trigonal bipyramidal [MnO5] units. A different pattern of planar honeycomb sheets are formed by edge-shared [MnO6] octahedra, and these sublattices are connected through edge-shared dimers of [MnO5] trigonal bipyramids to form corrugated sheets. Vanadate groups again condense the sheets into a three-dimensional framework. Infrared and Raman spectroscopies indicated the presence of OH groups and displayed characteristic Raman scattering due to vanadate groups. Temperature-dependent magnetic studies indicated Curie-Weiss behavior above 100 K with significant anti-ferromagnetic coupling for both compounds, with further complex magnetic behavior at lower temperatures. The data indicate canted anti-ferromagnetic order below 57 K in Mn5(VO4)2(OH)4 and below 45 K in Mn6O(VO4)2(OH). Members of another class of compounds, K2M3(VO4)2(OH)2 (M = Mn, Co), also containing a honeycomb-type sublattice, were also synthesized to allow a comparison of the structural features across all three structure types and to demonstrate extension to other transition metals.

Hydrothermal Synthesis and Characterization of Novel Brackebuschite-Type Transition Metal Vanadates: Ba2M(VO4)2(OH), M = V3+, Mn3+, and Fe3+, with Interesting Jahn–Teller and Spin-Liquid Behavior

A new series of transition metal vanadates, namely, Ba2M(VO4)2(OH) (M = V(3+), Mn(3+), and Fe(3+)), was synthesized as large single crystals hydrothermally in 5 M NaOH solution at 580 °C and 1 kbar. This new series of compounds is structurally reminiscent of the brackebuschite mineral type. The structure of Ba2V(VO4)2(OH) is monoclinic in space group P21/m, a = 7.8783(2) Å, b = 6.1369(1) Å, c = 9.1836(2) Å, β = 113.07(3)°, V = 408.51(2) Å(3). The other structures are similar and consist of one-dimensional trans edge-shared distorted octahedral chains running along the b-axis. The vanadate groups bridge across edges of their tetrahedra. Structural analysis of the Ba2Mn(VO4)2(OH) analogue yielded a new understanding of the Jahn-Teller effect in this structure type. Raman and infrared spectra were investigated to observe the fundamental vanadate and hydroxide vibrational modes. Single-crystal temperature-dependent magnetic studies on Ba2V(VO4)2(OH) reveal a broad feature over a wide temperature range with maximum at ∼100 K indicating that an energy gap could exist between the antiferromagnetic singlet ground state and excited triplet states, making it potentially of interest for quantum magnetism studies.

Structural and magnetic characterization of the one-dimensional S = 5/2 antiferromagnetic chain system SrMn(VO4)(OH)

The descloizite-type compound, SrMn(VO4)(OH), was synthesized as large single crystals (1-2mm) using a high-temperature high-pressure hydrothermal technique. X-ray single crystal structure analysis reveals that the material crystallizes in the acentric orthorhombic space group of P212121 (no. 19), Z = 4. The structure exhibits a one-dimensional feature, with [MnO4] chains propagating along the a-axis which are interconnected by VO4 tetrahedra. Raman and infrared spectra were obtained to identify the fundamental vanadate and hydroxide vibrational modes. Magnetization data reveal a broad maximum at approximately 80 K, arising from one-dimensional magnetic correlations with intrachain exchange constant of J/kB = 9.97(3) K between nearest Mn neighbors and a canted antiferromagnetic behavior below TN = 30 K. Single crystal neutron diffraction at 4 K yielded a magnetic structure solution in the lower symmetry of the magnetic space group P21 with two unique chains displaying antiferromagnetically ordered Mn moments oriented nearly perpendicular to the chain axis. Lastly, the presence of the Dzyaloshinskii Moriya antisymmetric exchange interaction leads to a slight canting of the spins and gives rise to a weak ferromagnetic component along the chain direction.

One-Pot Hydrothermal Synthesis of TbIII13(GeO4)6O7(OH) and K2TbIVGe2O7: Preparation of a Stable Terbium(4+) Complex

Two terbium germanates have been synthesized via high-temperature and high-pressure hydrothermal synthesis with 20 M KOH as a mineralizer using Tb4O7 as a starting material. Tb13(GeO4)6O7(OH) crystallizes in trigonal space group R3̅, is built up of isolated GeO4 units, and contains a complex arrangement of terbium oxide polyhedra. K2TbGe2O7 is a terbium(4+) pyrogermanate that is isostructural with K2ZrGe2O7 and displays a rare stable Tb4+ oxidation state in the solid state.

Hydrogen-bonding patterns in 5-fluoro-cytosine-melamine co-crystal (4/1).

The asymmetric unit of the title compound comprises two independent 5-fluorocytosine molecules and one half-molecule of melamine. The 5-fluorocytosine molecules are linked through two different homosynthons; one is formed via a pair of N—H⋯O hydrogen bonds and the second via a pair of N—H⋯N hydrogen bonds. The 5-fluorocytosine and melamine molecules interact via N—H⋯O, N—H⋯N and N—H⋯O, N—H⋯N, C—H⋯F hydrogen bonds.

Crystal chemistry of hydrothermally grown ternary alkali rare earth fluorides.

The structural variations of several alkali metal rare earth fluoride single crystals are summarized. Two different stoichiometric formulations are considered, namely those of ARE2F7 and ARE3F10 (A = K, Rb, Cs; RE = Y, La-Lu), over a wide range of ionic radii of both the alkali and rare earth (RE) ions. Previously reported and several new single-crystal structures are considered. The new single crystals are grown using hydrothermal methods and the structures are compared with literature reports of structures grown from both melts and hydrothermal fluids. The data reported here are combined with the literature data to gain a greater understanding of structural subtleties surrounding these systems. The work underscores the importance of the size of the cations to the observed structure type and also introduces synthetic technique as a contributor to the same. New insights based on single-crystal structure analysis in the work introduce a new disordered structure type in the case of ARE2F7, and examine the trends and boundaries of the ARE3F10 stoichiometry. Such fundamental structural information is useful in understanding the potential applications of these compounds as optical materials.

Single Crystals of Cubic Rare-Earth Pyrochlore Germanates: RE2Ge2O7 (RE = Yb and Lu) Grown by a High-Temperature Hydrothermal Technique

Large single crystals of Yb2Ge2O7 in the cubic Fd3̅ m space group, are synthesized and characterized from a high-temperature hydrothermal method (650°C/200 MPa in 1 M KF). The cubic phase displays spin frustration and possibly nonclassical quantum-spin behavior at low temperature. This is the first report of single crystals of this important phase of size and quality suitable for single-crystal neutron diffraction.

The magnetic order of a manganese vanadate system with two-dimensional striped triangular lattice

Results of magnetization and neutron diffraction measurements of the manganese vanadate system Mn5(VO4)2(OH)4 are reported. The crystal structure of this compound contains triangular [Mn3O13] building blocks that produce two-dimensional Mn2+ magnetic networks with striped triangular topologies. The Mn sheets are connected through the nonmagnetic vanadate tetrahedra extending along the a-axis. Magnetization measurements performed on single crystals reveal the onset of a long-range antiferromagnetic order below approximately 45 K. The magnetic structure is Neel-type with nearest-neighbor Mn atoms coupled via three or four antiferromagnetic bonds. The magnetic moments are confined within the layers and are oriented parallel to the b direction. The magnitudes of ordered moments are reduced, presumably by geometrical frustration and the low-dimensionality of the lattice structure.Results of magnetization and neutron diffraction measurements of the manganese vanadate system Mn5(VO4)2(OH)4 are reported. The crystal structure of this compound contains triangular [Mn3O13] building blocks that produce two-dimensional Mn2+ magnetic networks with striped triangular topologies. The Mn sheets are connected through the nonmagnetic vanadate tetrahedra extending along the a-axis. Magnetization measurements performed on single crystals reveal the onset of a long-range antiferromagnetic order below approximately 45 K. The magnetic structure is Neel-type with nearest-neighbor Mn atoms coupled via three or four antiferromagnetic bonds. The magnetic moments are confined within the layers and are oriented parallel to the b direction. The magnitudes of ordered moments are reduced, presumably by geometrical frustration and the low-dimensionality of the lattice structure.

Crystal chemistry and the role of ionic radius in rare earth tetrasilicates: Ba2RE2Si4O12F2 (RE = Er3+–Lu3+) and Ba2RE2Si4O13 (RE = La3+–Ho3+)

Structural variations across a series of barium rare earth (RE) tetrasilicates are studied. Two different formulas are observed, namely those of a new cyclo-silicate fluoride, BaRE2Si4O12F2 (RE = Er3+-Lu3+) and new compounds in the Ba2RE2Si4O13 (RE = La3+-Ho3+) family, covering the whole range of ionic radii for the rare earth ions. The Ba2RE2Si4O13 series is further subdivided into two polymorphs, also showing a dependence on rare earth ionic radius (space group P{\overline 1} for La3+-Nd3+, and space group C2/c for Sm3+-Ho3+). Two of the structure types identified are based on dinuclear rare earth units that differ in their crystal chemistries, particularly with respect to the role of fluorine as a structural director. The broad study of rare earth ions provides greater insight into understanding structural variations within silicate frameworks and the nature of f-block incorporation in oxyanion frameworks. The single crystals are grown from high-temperature (ca 953 K) hydrothermal fluids, demonstrating the versatility of the technique to access new phases containing recalcitrant rare earth oxides, enabling the study of structural trends.