Finding crystal structures from few diffraction data by a combination of a random search with genetic algorithms

A new procedure for performing structural analysis of crystalline materials from diffraction data by random search and genetic algorithms is described

Crystal structure of the stereoregular ethylene-alt-styrene copolymer synthesized with a zirconocene-based catalyst

A stereoregular alternating ethylene-styrene copolymer, also stretchable in fiber form, has been obtained with rac-isopropylidenebis( l-indenyl)zirconium dimethyldiamide activated by the methylalumoxane catalytic system. From X-ray diffraction fiber spectra, an isotactic structure has been assigned to this copolymer as well as the previously described stereoregular ethylene-styrene copolymers. The polymer has zigzag planar chain conformation with phenyl groups oriented perpendicularly to the chain axis. The crystallographic symmetry in B2/m. Lattice constants (monoclinic, unique axis c): a = 10.23, b = 15.53, c = 5.12 Angstrom; gamma = 98.6 degrees. The disagreement index for measured reflections is R-1 = 0.10

Self-Assembly and Gelation Study of Dipeptide Isomers with Norvaline and Phenylalanine

Dipeptides have emerged as attractive building blocks for supramolecular materials thanks to their low-cost, inherent biocompatibility, ease of preparation, and environmental friendliness as they do not persist in the environment. In particular, hydrophobic amino acids are ideal candidates for self-assembly in polar and green solvents, as a certain level of hydrophobicity is required to favor their aggregation and reduce the peptide solubility. In this work, we analyzed the ability to self-assemble and the gel of dipeptides based on the amino acids norvaline (Nva) and phenylalanine (Phe), studying all their combinations and not yielding to enantiomers, which display the same physicochemical properties, and hence the same self-assembly behavior in achiral environments as those studied herein. A single-crystal X-ray diffraction of all the compounds revealed fine details over their molecular packing and non-covalent interactions

Self-Assembly of Homo- and Hetero-Chiral Cyclodipeptides into Supramolecular Polymers towards Antimicrobial Gels

There is an increasing interest towards the development of new antimicrobial coatings, especially in light of the emergence of antimicrobial resistance (AMR) towards common antibiotics. Cyclodipeptides (CDPs) or diketopiperazines (DKPs) are attractive candidates for their ability to self-assemble into supramolecular polymers and yield gel coatings that do not persist in the environment. In this work, we compare the antimicrobial cyclo(Leu-Phe) with its heterochiral analogs cyclo(D-Leu-L-Phe) and cyclo(L-Leu-D-Phe), as well as cyclo(L-Phe-D-Phe), for their ability to gel. The compounds were synthesized, purified by HPLC, and characterized by 1H-NMR, 13C-NMR, and ESI-MS. Single-crystal X-ray diffraction (XRD) revealed details of the intermolecular interactions within the supramolecular polymers. The DKPs were then tested for their cytocompatibility on fibroblast cells and for their antimicrobial activity on S. aureus. Overall, DKPs displayed good cytocompatibility and very mild antimicrobial activity, which requires improvement towards applications

Ring size effect on the solid state assembly of propargyl substituted hexa- and octacyclic peptoids

The investigation of the solid state assembly of propargyl substituted hexa- and octacyclic peptoids highlights the effect of ring size in determining the packing arrangement of the macrocycles. A layered arrangement is obtained in the case of the hexacyclic peptoid 1 and a tubular arrangement in the case of the octacyclic peptoid 2. Guest molecules either intercalate between the layers as in 1 or are located within the peptoid nanotube as in 2

Cyclic Peptoids as Mycotoxin Mimics: An Exploration of Their Structural and Biological Properties

Cyclic peptoids have recently emerged as important examples of peptidomimetics for their interesting complexing properties and innate ability to permeate biological barriers. In the present contribution, experimental and theoretical data evidence the intricate conformational and stereochemical properties of five novel hexameric peptoids decorated with N-isopropyl, N-isobutyl, and N-benzyl substituents. Complexation studies by NMR, in the presence of sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaTFPB), theoretical calculations, and single-crystal X-ray analyses indicate that the conformationally stable host/guest metal adducts display architectural ordering comparable to that of the enniatins and beauvericin mycotoxins. Similarly to the natural depsipeptides, the synthetic oligolactam analogues show a correlation between ion transport abilities in artificial liposomes and cytotoxic activity on human cancer cell lines. The reported results demonstrate that the versatile cyclic peptoid scaffold, for its remarkable conformational and complexing properties, can morphologically mimic related natural products and elicit powerful biological activities

X-ray Powder Diffraction

X-ray powder diffraction (XRPD) as a powerful nondestructive analytical technique finds applications in various field as mineralogy, metallurgy, materials science, forensic science, archeometry, biology, pharmaceutical industry, and, of course, supramolecular chemistry. The most recent applications of XRPD in the field of supramolecular chemistry are reported with the aim to outline the advantages of the technique and its complementarity with other analytical tools, as spectroscopic techniques, and also computational methods. The main aspects of the structure analysis from XRPD data, including pair distribution function analysis, are briefly described. Main applications as qualitative and quantitative phase analysis by means of XRPD are also detailed. Selected examples in the structure determination of metal-organic frameworks, fullerenes, inclusion compounds, but also in the study of phase transitions, adsorption processes, polymorphism, and solvatomorphism are provided. Keywords: Direct space methods; Dual space methods; High-resolution X-ray powder diffraction; In situ X-ray powder diffraction; Metal-organic frameworks; Pair distribution function; Phase identification; Phase transformations; Qualitative phase analysis; Quantitative phase analysis; Reciprocal space methods; Rietveld refinement; Supramolecular zeolite; Synchrotron radiation; X-ray powder diffractio

Analisi diffrattometriche di materiali policristallini

Dottorato di ricerca in chimica. 12. ciclo. A.a. 1998-99. Relatore Attilio Immirzi. Coordinatore Arrigo ScettriConsiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome; Biblioteca Nazionale Centrale - P.za Cavalleggeri, 1, Florence / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

La diffrazione dei cristalli

Numerosi e ottimi testi trattano la diffrazione dei raggi X e il suo uso nelle indagini strutturali, essi però sono per lo più in lingua inglese e poco si prestano come testi didattici. Questo libro si propone di colmare tale lacuna. Di particolare rilievo il capitolo sull’uso delle coordinate interne nella modellazione delle molecole nelle procedure di risoluzione delle strutture per tentativo, un argomento poco trattato da altri testi, anche perché, in anni recenti, ha ricevuto nuovi impulsi proprio grazie agli autori