Lie detector

Novel, semicrystalline polyamides and copolyamides were synthesized from a new carbohydrate-based diamine, namely isoidide-2,5-dimethyleneamine (IIDMA). In combination with 1,6-hexamethylene diamine (1,6-HDA) as well as the biobased sebacic acid (SA) or brassylic acid (BrA), the desired copolyamides were obtained via melt polymerization of the nylon salts followed by a solid-state polycondensation (SSPC) process. Depending on the chemical compositions, the number average molecular weights (Mn) of the polyamides were in the range of 4000–49000 g/mol. With increasing IIDMA content in the synthesized copolyamides, their corresponding glass transition temperatures (Tg) increased from 50 °C to approximately 60–67 °C while the melting temperatures (Tm) decreased from 220 to 160 °C. The chemical structures of the polyamides were analyzed by NMR and FT-IR spectroscopy. Both differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) analyses revealed the semicrystalline character of these novel copolyamides. Variable-temperature (VT) 13C{1H} cross-polarization/magic-angle spinning (CP/MAS) NMR and FT-IR techniques were employed to study the crystal structures as well as the distribution of IIDMA moieties over the crystalline and amorphous phases of the copolyamides. The performed ab initio calculations reveal that the stability of the IIDMA moieties is due to a pronounced boat conformation of the bicyclic rings. The incorporation of methylene segments in between the isohexide group and the amide groups enables the hydrogen bonds formation and organization of the polymer chain fragments. Given the sufficiently high Tm values (200 °C) of the copolyamides containing less than 50% of IIDMA, these biobased semicrystalline copolyamides can be useful for engineering plastic applications

De Novo

The crystal structure of form 4 of the drug 4-[4-(2-adamantylcarbamoyl)-5-tert-butyl-pyrazol-1-yl]benzoic acid is determined using a protocol for NMR powder crystallography at natural isotopic abundance combining solid-state 1H NMR spectroscopy, crystal structure prediction, and density functional theory chemical shift calculations. This is the first example of NMR crystal structure determination for a molecular compound of previously unknown structure, and at 422 g/mol this is the largest compound to which this method has been applied so far

An NMR crystallography DFT-D approach to analyse the role of intermolecular hydrogen bonding and π–π interactions in driving cocrystallisation of indomethacin and nicotinamide

Density functional theory (DFT) calculations using the Perdew–Burke–Ernzerhof (PBE) exchange-correlation functional are presented for a 1 : 1 cocrystal formed by indomethacin and nicotinamide (IND-NIC) as well as for crystal structures of the individual components. DFT-D approaches which correct the DFT energy for dispersion effects, specifically the Grimme (G06) and Tkatchenko–Scheffler (TS) schemes, are investigated: for geometry optimisation starting with crystal structures determined experimentally by diffraction and allowing the atomic positions and the unit cell to vary, closest agreement with the experimental unit cell parameters is achieved with the PBE-TS approach (calculated volumes are less than 4% smaller than in experiment). Calculations of solid-state NMR chemical shifts using the GIPAW (gauge including projector augmented wave) approach are presented. Closest agreement between NMR chemical shifts calculated with variable and fixed (experimental) unit cell parameters is also observed for the PBE-TS approach: the root mean squared standard deviation difference is 0.15 ppm (1H) and 0.29 ppm (13C) for PBE-TS, as compared to 0.45 ppm (1H) and 0.68 ppm (13C) with standard PBE. Differences in 1H chemical shifts calculated for the full periodic crystal structure and for isolated molecules extracted from the geometry-optimised crystal structure are presented in conjunction with NICS (nucleus independent chemical shift) maps, so as to separately quantify intermolecular hydrogen bonding and π–π interactions. This analysis is complemented by total energy calculations, including also at the B97D/6-311+G* level of theory with basis set superposition error correction, in order to understand the interactions that drive cocrystallisation

The impact of amide connectivity on the assembly and dynamics of benzene-1,3,5-tricarboxamides in the solid state

Solid-state NMR experiments as well as extensive Car–Parrinello Molecular Dynamics simulations are used to study the dependence of supramolecular self-organization of benzene-1,3,5-tricarboxamides (BTA) on the local orientation of the amide functionality. Unlike the known symmetric co-planar helical arrangement of CO-centered BTAs found in supramolecular architectures like supramolecular polymers in gels, N-centered BTAs adopt an asymmetric helical arrangement in the solid-state. The resulting tilt angle between the aromatic cores of neighboring BTA molecules leads to a breaking of the three-fold molecular symmetry and thus causes a splitting of 1H MAS NMR signals. At elevated temperatures, motional averaging of the split 1H MAS NMR signals is observed, which can be attributed to certain dynamics on the ms time scale of individual BTA molecules in the columnar packing arrangement