NMR Crystallography: Toward Chemical Shift-Driven Crystal Structure Determination of the β‑Lactam Antibiotic Amoxicillin Trihydrate

We report a new strategy for NMR crystallography of multiple-component molecular crystals in which ¹H NMR chemical shifts enter directly in the structure generation step, governed by a genetic algorithm. Chemical shifts are also used in the structure-refinement step as pseudoforces acting on the models, leading to the lowest-energy structure. This methodology, which avoids the use of time-consuming <i>ab initio</i> chemical shift calculations, is successfully applied to powdered amoxicillin trihydrate, a widely used β-lactamic antibiotic

Formation of Photoluminescent Lead Bromide Nanoparticles on Aluminoborosilicate Glass

A multicomponent aluminoborosilicate photoluminescent glass was synthesized by introducing Pb­(II) and NaBr in its composition. The room-temperature photoluminescence is due to the existence of 4 nm nanocrystals, shown using TEM imaging and XRD analysis, which are assigned to PbBr₂ nanocrystals. The glasses display a broad emission band with a peak at 2.85 eV by exciting at 3.35 eV, with an anisotropy equal to 0.19 at room temperature. At 77 K, the emission intensity increases 1 order of magnitude and a vibronic structure appears, indicating an electron–phonon coupling with the glass matrix. Time-resolved luminescence measurements of these nanocrystals reveal mixed-order kinetics, with second-order recombination of self-trapped electron centers and a first-order temperature-dependent nonradiative rate constant connected with pathways due to confinement of self-trapped centers

Photoluminescent Thermometer Based on a Phase-Transition Lanthanide Silicate with Unusual Structural Disorder

The hydrothermal synthesis of the novel Na­[LnSiO₄] (Ln = Gd, Eu, Tb) disordered orthorhombic system is reported. At 100 K, and above, these materials are best described in the centrosymmetric orthorhombic <i>Pnma</i> space group. At lower temperatures (structure solved at 30 K) the unit cell changes to body-centered with <i>Imma</i> symmetry. The materials exhibit unique photophysical properties, arising from both, this phase transformation, and the disorder of the Ln³⁺ ions, located at a site with <i>D</i>_<i>2d</i> point symmetry. Na­[(Gd_0.8Eu_0.1Tb_0.1)­SiO₄] is an unprecedented case of a luminescent ratiometric thermometer based on a very stable silicate matrix. Moreover, it is the first example of an optical thermometer whose performance (viz., excellent sensitivity at cryogenic temperatures <100 K) is determined mainly by a structural transition, opening up new opportunities for designing such devices

Metal–Organic Frameworks Assembled From Erbium Tetramers and 2,5-Pyridinedicarboxylic Acid

Two novel three-dimensional lanthanide-organic frameworks, [Er₆(OH)₈(pydc)₅(H₂O)₃]­·2.5H₂O (<b>1</b>) and [Er₃(OH)₆(pydc)­Cl] (<b>2</b>) (pydc^2– is the deprotonated residue of 2,5-pyridinedicarboxylic acid - 2,5-H₂pydc), were prepared by hydrothermal synthesis. Compound <b>1</b> consists of an unique one-dimensional (1D) cationic [Er₆(OH)₈(H₂O)₃]_<i>n</i>^10<i>n</i>+ inorganic chain embedded into an organic matrix formed by the linker. Individual chains are disposed in the <i>ab</i> plane of the unit cell in a brick-wall fashion and result from the coalescence of cubane-type clusters of Er³⁺. Compound <b>2</b> comprises densely packed cationic [Er₃(OH)₆Cl]_<i>n</i>^2<i>n</i>+ inorganic layers, constructed by the lateral coalescence of 1D chains identical to those found in <b>1</b>. These layers are pillared by the organic linkers along the [001] direction of the unit cell yielding the crystal structure of <b>2</b>. Considering the metallic tetramers and the ligands as framework nodes, compounds <b>1</b> and <b>2</b> are 7- and 2-nodal networks, respectively. While the former is unprecedented among metal–organic framework (MOF) structures, the latter is reminiscent of the known <b>tcj/hc</b> topological type. The crystal structures and properties of the two compounds have been investigated by (single-crystal and powder) X-ray diffraction, electron microscopy (SEM and EDX), vibrational spectroscopy, CHN elemental analyses, and thermogravimetry. The magnetic properties of <b>1</b> also have been investigated

Antimosquito Activity of a Titanium–Organic Framework Supported on Fabrics

Waste swamps, stagnant water, and poor hygiene practices result in the proliferation of mosquitoes that may cause transmissible and infectious diseases such as malaria, typhoid, cholera, and Zika virus sickness. It has been shown that composites of the traditional natural fibers cotton, viscose, and linen and a Ti-bearing metal–organic framework, NH₂-MIL-125, are very effective against mosquitoes in the absence of any conventional insecticides. In our study, prior to coating with NH₂-MIL-125 crystals, the fabrics were modified with 3-glycidyloxypropyltrimethoxysilane. The composite materials were characterized by powder X-ray diffraction, UV–vis spectroscopy, Fourier transform infrared spectroscopy, and scanning electron microscopy with energy-dispersive X-ray spectroscopy analysis. The latter, in particular, has shown the uniform coating of the fabrics with NH₂-MIL-125 crystals. The modified fabrics have excellent antimosquito properties, attracting and killing them

Photoluminescent Lanthanide-Organic Framework Based on a Tetraphosphonic Acid Linker

A new metal–organic framework based on the highly flexible tetraphosphonic acid linker hexamethylenediamine-<i>N,N,N</i>′<i>,N</i>′-tetrakis­(methylphosphonic acid) (H₈htp) is reported. [Ln₂(SO₄)₂(H₆htp)­(H₂O)₄]·10H₂O [Ln³⁺= Eu³⁺ (<b>1</b>), Sm³⁺ (<b>2</b>), and Gd³⁺ (<b>3</b>)] was readily obtained by microwave heating at moderate temperatures (80 °C) and low reaction time (15 min). The reaction was carried out in aqueous medium and, because of the high flexibility of the organic linker, sulfuric acid was added in small quantities. This acid delays the coordination process and blocks access of the phosphonic acid groups by coordinating the sulfate anion to the metal center, leading to the formation of a compact 3D network. Sulfuric acid further proved to be crucial for the formation of the materials because the use of different acids led to either no precipitation or amorphous compounds. When compared to the only known and reported material based on the same building blocks, this approach allowed us to significantly reduce the reaction time to just 15 min with an immediate crystal formation (compared to the 2 months reported). Crystals were obtained with sizes suitable for single-crystal X-ray diffraction analysis for <b>1</b>. Materials consist of a 3D network with the metal centers forming a close packed layer, being interconnected by the organic linker, forming cavities which are filled with solvent water molecules. Topologically, <b>1</b>–<b>3</b> are binodal networks with a 4,8-connectivity and a Schäfli point symbol of {4¹²·6¹²·8⁴}­{4⁶}₂. This topology is unusual for MOFs, especially for phosphonic acid based linkers, resembling the known mineral fluorite. The photoluminescence properties of <b>1</b> were studied showing an emission lifetime of 0.43 ± 0.01 ms and 0.57 ± 0.01 at 297 and 13 K, respectively

Metal–Organic Frameworks Assembled From Erbium Tetramers and 2,5-Pyridinedicarboxylic Acid

Two novel three-dimensional lanthanide-organic frameworks, [Er₆(OH)₈(pydc)₅(H₂O)₃]­·2.5H₂O (<b>1</b>) and [Er₃(OH)₆(pydc)­Cl] (<b>2</b>) (pydc^2– is the deprotonated residue of 2,5-pyridinedicarboxylic acid - 2,5-H₂pydc), were prepared by hydrothermal synthesis. Compound <b>1</b> consists of an unique one-dimensional (1D) cationic [Er₆(OH)₈(H₂O)₃]_<i>n</i>^10<i>n</i>+ inorganic chain embedded into an organic matrix formed by the linker. Individual chains are disposed in the <i>ab</i> plane of the unit cell in a brick-wall fashion and result from the coalescence of cubane-type clusters of Er³⁺. Compound <b>2</b> comprises densely packed cationic [Er₃(OH)₆Cl]_<i>n</i>^2<i>n</i>+ inorganic layers, constructed by the lateral coalescence of 1D chains identical to those found in <b>1</b>. These layers are pillared by the organic linkers along the [001] direction of the unit cell yielding the crystal structure of <b>2</b>. Considering the metallic tetramers and the ligands as framework nodes, compounds <b>1</b> and <b>2</b> are 7- and 2-nodal networks, respectively. While the former is unprecedented among metal–organic framework (MOF) structures, the latter is reminiscent of the known <b>tcj/hc</b> topological type. The crystal structures and properties of the two compounds have been investigated by (single-crystal and powder) X-ray diffraction, electron microscopy (SEM and EDX), vibrational spectroscopy, CHN elemental analyses, and thermogravimetry. The magnetic properties of <b>1</b> also have been investigated

Photoluminescent Nanocrystals in a Multicomponent Aluminoborosilicate Glass

In this study, stable and nonexpensive aluminoborosilicate glasses with different photoluminescence colors were synthesized by doping with Pb­(II), Ba­(II) and sodium halides. While glasses with NaF and NaCl exhibit no (or very low) luminescence, glasses doped with NaBr and NaI display room-temperature photoluminescence at 435 and 530 nm, respectively. The observed room-temperature photoluminescence is attributed to nanocrystals whose presence is revealed by transmission electron microscopy. The crystalline nature of the particles, which are pointed out as barium-lead halides, is also revealed by anisotropy measurements for Br and I doped samples. Time-resolved luminescence measurements show a second-order kinetics component combined with a first-order nonradiative rate constant. The photoluminescence properties here described are important for the future design of new optical materials or devices based on lead halide nanocrystals

Combining Multinuclear High-Resolution Solid-State MAS NMR and Computational Methods for Resonance Assignment of Glutathione Tripeptide

We present a complete set of experimental approaches for the NMR assignment of powdered tripeptide glutathione at natural isotopic abundance, based on <i>J</i>-coupling and dipolar NMR techniques combined with ¹H CRAMPS decoupling. To fully assign the spectra, two-dimensional (2D) high-resolution methods, such as ¹H–¹³C INEPT-HSQC/PRESTO heteronuclear correlations (HETCOR), ¹H–¹H double-quantum (DQ), and ¹H–¹⁴N <i>D</i>-HMQC correlation experiments, have been used. To support the interpretation of the experimental data, periodic density functional theory calculations together with the GIPAW approach have been used to calculate the ¹H and ¹³C chemical shifts. It is found that the shifts calculated with two popular plane wave codes (CASTEP and Quantum ESPRESSO) are in excellent agreement with the experimental results

Calcium Phosphonate Frameworks for Treating Bone Tissue Disorders

Two new examples of uncommon three-dimensional Ca-bearing metal organic frameworks, [Ca­(H₂O)₃(HPXBP)] (<b>CaP1</b>) and [Ca₂(H₂O)₂(HPXBP)_1.5] (<b>CaP2</b>) (PXBP: <i>p</i>-xylylenebisphosphonate), were prepared and their structures characterized by single crystal X-ray diffraction. <b>CaP1</b> crystallizes in the monoclinic <i>C</i>2/<i>c</i> space group, with three water molecules occupying a half coordination sphere on one side of the Ca atom, while <b>CaP2</b> crystallizes in the triclinic <i>P</i>1̅ space group, with two crystallographic unique Ca atoms, each coordinated by a single water molecule. In contrast with <b>CaP2</b>, which exhibits very low bioactivity, <b>CaP1</b> readily precipitates bone-precursor phases (octacalcium phosphate, OCP, and hydroxyapatite) in SBF solutions. Moreover, studies with MG63 osteoblast-like cells indicate that <b>CaP1</b> is not toxic and stimulates bone mineralization and, thus, holds considerable potential for treating bone diseases, such as osteoporosis