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

Packing Interactions in Hydrated and Anhydrous Forms of the Antibiotic Ciprofloxacin: a Solid-State NMR, X-ray Diffraction, and Computer Simulation Study

We present an experimental NMR, X-ray diffraction (XRD), and computational study of the supramolecular assemblies of two crystalline forms of Ciprofloxacin: one anhydrate and one hydrate forming water wormholes. The resonance assignment of up to 51 and 54 distinct ¹³C and ¹H resonances for the hydrate is reported. The effect of crystal packing, identified by XRD, on the ¹H and ¹³C chemical shifts including weak interionic H-bonds, is quantified; ¹H chemical shift changes up to ∼−3.5 ppm for CH···π contacts and ∼+2 ppm (CH···O⁽⁻⁾); ∼+4.7 ppm (⁽⁺⁾NH···O⁽⁻⁾) for H-bonds. Water intake induces chemical shift changes up to 2 and 5 ppm for ¹H and ¹³C nuclei, respectively. Such chemical shifts are found to be sensitive detectors of hydration/dehydration in highly insoluble hydrates

Packing Interactions in Hydrated and Anhydrous Forms of the Antibiotic Ciprofloxacin: a Solid-State NMR, X-ray Diffraction, and Computer Simulation Study

We present an experimental NMR, X-ray diffraction (XRD), and computational study of the supramolecular assemblies of two crystalline forms of Ciprofloxacin: one anhydrate and one hydrate forming water wormholes. The resonance assignment of up to 51 and 54 distinct ¹³C and ¹H resonances for the hydrate is reported. The effect of crystal packing, identified by XRD, on the ¹H and ¹³C chemical shifts including weak interionic H-bonds, is quantified; ¹H chemical shift changes up to ∼−3.5 ppm for CH···π contacts and ∼+2 ppm (CH···O⁽⁻⁾); ∼+4.7 ppm (⁽⁺⁾NH···O⁽⁻⁾) for H-bonds. Water intake induces chemical shift changes up to 2 and 5 ppm for ¹H and ¹³C nuclei, respectively. Such chemical shifts are found to be sensitive detectors of hydration/dehydration in highly insoluble hydrates

Recent Advances on Mass Spectrometry Analysis of Nitrated Phospholipids

In recent years, there has been an increasing interest in nitro fatty acids (NO₂-FA) as signaling molecules formed under nitroxidative stress. NO₂-FA were detected <i>in vivo</i> in a free form, although it is assumed that they may also be esterified to phospholipids (PL). Nevertheless, insufficient discussion about the nature, origin, or role of nitro phospholipids (NO₂-PL) was reported up to now. The aim of this study was to develop a mass spectrometry (MS) based approach which allows identifying nitroalkenes derivatives of three major PL classes found in living systems: phosphatidylcholines (PCs), phosphatidylethanolamine (PEs), and phosphatidylserines (PSs). NO₂-PLs were generated by NO₂BF₄ in hydrophobic environment, mimicking biological systems. The NO₂-PLs were then detected by electrospray ionization (ESI-MS) and ESI-MS coupled to hydrophilic interaction liquid chromatography (HILIC). Identified NO₂-PLs were further analyzed by tandem MS in positive (as [M + H]⁺ ions for all PL classes) and negative-ion mode (as [M – H]⁻ ions for PEs and PSs and [M + OAc]⁻ ions for PCs). Typical MS/MS fragmentation pattern of all NO₂-PL included a neutral loss of HNO₂, product ions arising from the combined loss of polar headgroup and HNO₂, [NO₂-FA + H]⁺ and [NO₂-FA – H]⁻ product ions, and cleavages on the fatty acid backbone near the nitro group, allowing its localization within the FA akyl chain. Developed MS method was used to identify NO₂-PL in cardiac mitochondria from a well-characterized animal model of type 1 diabetes mellitus. We identified nine NO₂-PCs and one NO₂-PE species. The physiological relevance of these findings is still unknown

Packing Interactions and Physicochemical Properties of Novel Multicomponent Crystal Forms of the Anti-Inflammatory Azelaic Acid Studied by X‑ray and Solid-State NMR

The reactivity of the active pharmaceutical ingredient azelaic acid (AA) with carboxylic acid, alcohol, amine, and amide based co-formers was screened. Five new multicomponent crystal forms of AA were obtained by liquid assisted grinding and conventional solution methods. The obtained forms: (i) a co-crystal with 4,4′-bipyridine (AA:BIP, <b>1</b>), (ii) an anhydrous and an hydrated molecular salt with piperazine (AA:PIP, <b>2</b> and <b>3</b>), and (iii) two anhydrous molecular salts with morpholine (AA:MORPH, <b>4</b>) and 1,4-diazobicyclo­[2.2.2]­octane (AA:DABCO, <b>5</b>), were fully characterized by X-ray diffraction and solid-state (SS) NMR. In all new forms the carboxylic-carboxylic <i>R</i>₂²(8) homosynthon present in AA is broken, and NH₂···O_COOH or ⁺NH₂···O_COO- hydrogen bonds (HBs) become the fundamental pillars in the new supramolecular arrangements. The X-ray structure of <b>4</b> exhibits a static disorder in the hydrogen atoms engaged in an HB between two COOH moieties of AA. Density functional theory geometry optimization of the hydrogen positions followed by GIPAW-DFT calculations of ¹H chemical shifts showed that such disordered atoms refer to O···H···O hydrogens, roughly equidistant from both proton acceptor and donor atoms. ¹H SSNMR detected unusually strong HBs associated with such disordered hydrogens through the presence of ¹H resonances shifted to very high frequencies (up to <i>ca</i>. 20.1 ppm). These results clearly show the advantageous use of both X-ray diffraction and SSNMR techniques for structural elucidation. We concluded that the hydrated piperazine salt <b>3</b> readily converted to <b>2</b> at ambient RH and that their thermal behavior is strongly determined by both the supramolecular arrangement and strength of HB network. Piperazine salt <b>2</b> presents an improved aqueous solubility bestowing a promising opportunity to avoid the use of alcoholic solutions in the final formulations

<i>meso</i>‑Tetraphenylbenzoporphyrin‑2²,2³‑dicarboxylic Anhydride: A Platform to Benzoporphyrin Derivatives

A method to synthesize <i>meso</i>-tetraphenylbenzoporphyrin-2²,2³-dicarboxylic anhydride is reported. This compound reacts with alkylamines and arylamines to afford the corresponding “phthalimides” in moderate to excellent yields. The reaction of the title compound with benzene-1,4-diamine or with benzene-1,3-diamine yields the corresponding <i>N</i>,<i>N</i>′-(phenylene)­bisphthalimides, whereas with benzene-1,2-diamine or naphthalene-1,8-diamine it affords heterocyclic-fused porphyrins. Molecular mechanics simulations elucidates the multiplicity of signals observed in the NMR spectra of the <i>N</i>,<i>N</i>′-(1,4-phenylene)­bisphthalimide <b>11</b>. This molecule exhibits two preferential conformations corresponding to a coplanar and an almost perpendicular arrangement of the benzoporphyrin units relative to the central benzenic ring

Synthesis, Spectroscopy Studies, and Theoretical Calculations of New Fluorescent Probes Based on Pyrazole Containing Porphyrins for Zn(II), Cd(II), and Hg(II) Optical Detection

New pyrazole–porphyrin conjugates were successfully prepared from a reaction of β-porphyrin–chalcone derivatives with phenylhydrazine in acetic acid followed by an oxidative step. This fast and efficient synthetic approach provided the expected compounds in yields up to 82%. The sensing ability of the new porphyrin–pyrazole derivatives to detect the metal ions Ag⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Pb²⁺, and Cr³⁺ was studied by spectrophotometric and spectrofluorimetric titrations. In the presence of Zn²⁺, the conjugates exhibit changes in the emission spectra that are desired for a ratiometric-type fluoroionophoric detection probe. The studies were extended to gas phase, where the pyrazole–porphyrin conjugates show ability to sense metal ions with high selectivity toward Cu²⁺ and Ag⁺, and in poly­(methyl methacrylate) doped films with promising results for Zn²⁺ detection