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1. Thermodynamics and Spectroscopy of Halogen- and Hydrogen-Bonded Complexes of Haloforms with Aromatic and Aliphatic Amines

   https://doi.org/10.3390/molecules27186124  

   Adeniyi, Emmanuel; Grounds, Olivia; Stephens, Zachary; Zeller, Matthias; Rosokha, Sergiy V. (September 2022, Molecules)

   Similarities and differences of halogen and hydrogen bonding were explored via UV–Vis and 1H NMR measurements, X-ray crystallography and computational analysis of the associations of CHX3 (X=I, Br, Cl) with aromatic (tetramethyl-p-phenylenediamine) and aliphatic (4-diazabicyclo[2,2,2]octane) amines. When the polarization of haloforms was taken into account, the strengths of these complexes followed the same correlation with the electrostatic potentials on the surfaces of the interacting atoms. However, their spectral properties were quite distinct. While the halogen-bonded complexes showed new intense absorption bands in the UV–Vis spectra, the absorptions of their hydrogen-bonded analogues were close to the superposition of the absorption of reactants. Additionally, halogen bonding led to a shift in the NMR signal of haloform protons to lower ppm values compared with the individual haloforms, whereas hydrogen bonding of CHX3 with aliphatic amines resulted in a shift in the opposite direction. The effects of hydrogen bonding with aromatic amines on the NMR spectra of haloforms were ambivalent. Titration of all CHX3 with these nucleophiles produced consistent shifts in their protons’ signals to lower ppm values, whereas calculations of these pairs produced multiple hydrogen-bonded minima with similar structures and energies, but opposite directions of the NMR signals’ shifts. Experimental and computational data were used for the evaluation of formation constants of some halogen- and hydrogen-bonded complexes between haloforms and amines co-existing in solutions. 

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2. Exact Interpolation, Spurious Poles, and Uniform Convergence of Multipoint Pade Approximants

   Lubinsky, Doron (July 2018, Sbornik : Mathematics)

   We prove that for most entire functions f in the sense of category, a strong form of the Baker-Gammel-Wills Conjecture holds. More precisely, there is an infinite sequence S of positive integers n, such that given any r>0, and multipoint Padé approximants R_{n} to f with interpolation points in {z:|z|≤r}, {R_{n}}_{n∈S} converges locally uniformly to f in the plane. The sequence S does not depend on r, nor on the interpolation points. For entire functions with smooth rapidly decreasing coefficients, full diagonal sequences of multipoint Padé approximants converge. 

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3. On Uniform Convergence of Diagonal Multipoint Pad� Approximants For Entire Functions

   Lubinsky, Doron S (January 2019, Constructive approximation)

   We prove that for most entire functions f in the sense of category, a strong form of the Baker-Gammel-Wills Conjecture holds. More precisely, there is an inÖnite sequence S of positive integers n, such that given any r > 0, and multipoint PadÈ approximants Rn to f with interpolation points in fz : jzj  rg, fRngn2S converges locally uniformly to f in the plane. The sequence S does not depend on r, nor on the interpolation points. For entire functions with smooth rapidly decreasing coe¢ cients, full diagonal sequences of multipoint PadÈ approximants converge. 

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4. Structural insights into supramolecular interactions in isostructural salts of 2,4,6-triaminopyrimidinium with various heterocyclic carboxylates

   https://doi.org/10.1107/S2053229624008787  

   Mohana, Marimuthu; Gomathi, Sundaramoorthy; Thomas_Muthiah, Packianathan; Butcher, Ray J (November 2024, Acta Crystallographica Section C Structural Chemistry)

   2,4,6-Triaminopyrimidine is an interesting and challenging molecule due to the presence of multiple hydrogen-bond donors and acceptors. Its noncovalent interactions with a variety of carboxylic acids provide several supramolecular aggregates with frequently occurring molecular synthons. The present work focuses on the supramolecular interactions of 2,4,6-triaminopyrimidinium 3-(indol-3-yl)propionate–3-(indol-3-yl)propionic acid (1/1), C₄H₈N₅⁺·C₁₁H₁₀NO₂⁻·C₁₁H₁₁NO₂, (I), 2,4,6-triaminopyrimidinium 2-(indol-3-yl)acetate, C₄H₈N₅⁺·C₁₀H₈NO₂⁻, (II), 2,4,6-triaminopyrimidinium 5-bromothiophene-2-carboxylate, C₄H₈N₅⁺·C₅H₂BrO₂S⁻, (III), and 2,4,6-triaminopyrimidinium 5-chlorothiophene-2-carboxylate, C₄H₈N₅⁺·C₅H₂ClO₂S⁻, (IV). All four salts exhibit robust homomeric and heteromericR₂²(8) ring motifs. Salts (I) and (II) develop sextuple [in (I)] and quadruple [in (I) and (II)] hydrogen-bonded arrays through fused-ring motifs. Salt (II) exhibits a rosette-like architecture. Salt (IV) is isostructural and isomorphous with salt (III), exhibiting an identical crystal structure with a different composition and an identical supramolecular architecture. In salts (III) and (IV), a linear hetero-tetrameric motif is formed and, in addition, both salts exhibit halogen–π interactions which enhance the crystal stability. All four salts develop a supramolecular hydrogen-bonded pattern facilitated by several N—H...O and N—H...N hydrogen bonds with multiple furcated donors and acceptors. 

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5. The Structure of Liquid and Glassy Carbamazepine

   https://doi.org/10.3390/qubs6040031  

   Benmore, Chris J.; Edwards, Angela; Alderman, Oliver L.; Cherry, Brian R.; Smith, Pamela; Smith, Daniel; Byrn, Stephen; Weber, Richard; Yarger, Jeffery L. (December 2022, Quantum Beam Science)

   Punzo, Francesco (Ed.)

   To enhance the solubility of orally administered pharmaceuticals, liquid capsules or amorphous tablets are often preferred over crystalline drug products. However, little is known regarding the variation in bonding mechanisms between pharmaceutical molecules in their different disordered forms. In this study, liquid and melt-quenched glassy carbamazepine have been studied using high energy X-ray diffraction and modeled using Empirical Potential Structure Refinement. The results show significant structural differences between the liquid and glassy states. The liquid shows a wide range of structures; from isolated molecules, to aromatic ring correlations and NH-O hydrogen bonding. Upon quenching from the liquid to the glass the number of hydrogen bonds per molecule increases by ~50% at the expense of a ~30% decrease in the close contact (non-bonded) carbon-carbon interactions between aromatic rings. During the cooling process, there is an increase in both singly and doubly hydrogen-bonded adjacent molecules. Although hydrogen-bonded dimers found in the crystalline states persist in the glassy state, the absence of a crystalline lattice also allows small, hydrogen-bonded NH-O trimers and tetramers to form. This proposed model for the structure of glassy carbamazepine is consistent with the results from vibrational spectroscopy and nuclear magnetic resonance. 

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