This paper describes new features implemented in the EXPO2014 software and aimed at assisting crystallographers in the use of quantum-chemistry calculations in combination with experimental powder diffraction data. The implemented tools are useful in particular in two important steps of the process of crystal structure determination from powder diffraction data: (1) preparing accurate structural model suitable for crystal structure determination by real-space methods; (2) validating structure determination. The combination of experimental/quantum-chemical methods in EXPO2014 is now managed easily thanks to the following capabilities: (a) converting crystallographic data in input files and reading molecular geometry from output files of a wide variety of computational chemistry packages (GAMESS-US, NWChem, Gaussian, CRYSTAL, ABINIT, QUANTUM ESPRESSO); (b) optimizing the geometry of a molecule using Open Babel's force fields; (c) a graphical interface to run semi-empirical quantum calculation by MOPAC (Molecular Orbital PACkage); (d) producing input file for dispersion-corrected density functional theory.

A polycrystalline material or 'powder' is an ensemble of several randomly oriented crystallites.The size of the elementary crystals is of the order of micrometer. Microcrystalline compounds cannot be singled out to be characterized in the same way as single crystals. Chemical matter, drugs, minerals, heritage manufacts can be available or can be reduced in the form of crystalline powders.....

alpha-Lithiated epoxides, long considered "fleeting" intermediates in the reactions of epoxides with strong bases, have nowadays proven to be key synthons for asymmetric synthesis. In this study, the solution and the solid state structure of an alpha-lithiated aryloxirane, namely a-lithiated ortho-trifluoromethyl styrene oxide (1-Li), were determined. Single crystal X-ray diffraction analysis of 1-Li performed at 100 K applying the X-TEMP-2 device revealed a self-assembled heterochiral dimeric structure with a rare central six-membered (O-Li-C)(2) planar core, which is unprecedented in Li/oxygen carbenoids. Multinuclear magnetic resonance (H-1, C-13, F-19, Li-7) studies suggested that 1-Li exists in THF solution as a mixture of two interconverting diastereomeric dimeric aggregates, each one featuring a single s-contact between lithium and a carbon atom. Line shape analysis provided activation parameters for both the dynamic interconversion of the two dimers and the enantiomerisation of 1-Li, which proved to be mostly entropy controlled. The structural assignment in solution was supported by density functional theory computations through the investigation of conformers of monomeric and dimeric complexes of 1-Li featuring different degrees of specific solvation. A mechanism based on the equilibration of six-membered homo-and heterochiral dimers was proposed to explain the configurational instability exhibited by 1-Li in THF.

Innovative methodologies, introduced in the software EXPO and working both in the reciprocal and in the direct space, can be successfully adopted for solving crystal structure by X-ray powder diffraction data. The principles underlying these methodologies are summarized. Three representative examples of crystal structure solution of the peptides Z-(Aib)(2)-OH, Z-(Aib)(3)-O-t-Bu and Z-(Aib)(4)-OH are discussed in relation to their different degree of structure complexity.

EXPO2013, the heir of EXPO2009, has been enriched by a variety of new algorithms and graphical tools aiming at strengthening the individual steps of the powder structure solution pathway. Particular attention has been addressed to the procedures devoted to improving structural models provided by direct methods in ab initio approaches. In addition, a new procedure has been implemented, working in direct space, which may be chosen by the user as an alternative to the traditional simulated annealing algorithm. © 2013 International Union of Crystallography Printed in Singapore - all rights reserved.

The functionalization of four-membered cyclic sulfoximine, based on a lithiation/electrophile trapping sequence, led to unprecedented C(2)-substituted N-Boc-1-imino-1. 6-thietane 1-oxide in moderate to good yields. Interestingly, the reaction proceeded with high stereocontrol showing a preferential bias for an introduction of the electrophile syn to the oxygen on the sulfur. Starting from thietan-1-one, by a combination of lithiation/electrophile trapping followed by N-transfer, it is possible to obtain the stereoisomer bearing the electrophile syn to the nitrogen on the sulfur. Thus, all stereoisomers can be accessible for medicinal chemistry studies.

Negli ultimi venticinque anni il metodo della diffrazione da polveri è stato applicato con successo crescente per risolvere strutture cristalline (composti organici, inorganici, metallorganici). Nonostante ciò, la soluzione strutturale da polveri è ancora oggi una sfida perché i problemi del metodo, dovuti principalmente all'interpretazione dei dati sperimentali, devono essere ancora risolti.

The phase identification of a polycrystalline mixture by X-ray powder diffraction data is often requested for studying materials interesting to different scientific and technological fields: chemistry, pharmaceutics, mineralogy, archeometry, forensic science, etc. The availability of user friendly computer programs, able to carry out qualitative phase analysis in efficient and possibly automatic way, is extremely useful to the scientific community involved in powder diffraction. QUALX2.0, the evolution of QUALX, is a freely distributed software for qualitative phase analysis. Based on the traditional search-match method, it is able to manage both a commercial database (PDF-2 maintained by ICDD), and a freely available database (POW_COD generated by the structure information contained in the Crystallography Open Database). QUALX2.0 is continuously improved in terms of computing and graphic tools. Correspondingly, the database POW_COD is suitably modified to make efficient the operations of search. The search-match approach can be facilitated by the use of restraints, when available, involving the chemical composition, the kind of compound(s) (e.g., organic, inorganic, etc.), the symmetry (space group, crystal system), the unit-cell parameters and/or volume, the crystal properties (measured and/or calculated crystal density, crystal color). An outline of the main features of QUALX2.0 and an example of application is described.

To obtain novel muscarinic acetylcholine receptor (mAChR) antagonists, the enantiomers of the hybrid compounds 3-5, in which the quinuclidin-3-yloxy fragment of solifenacin and the 6,6-diphenyl-1,4dioxane-2-yl moiety of 2 linked by an ester or ether spacer were embedded in the same chemical entity, were prepared and evaluated for their affinity at the five mAChR subtypes (M-1-M-5). Stereochemistry and the nature of the linker between the quinuclidine moiety and the 1,4-dioxane nucleus play an important role on the affinities of the compounds. The presence of an ether bridge confers higher affinities for all mAChR subtypes to the ligand. Interestingly, the ether enantiomer (R,S)-5 shows the highest affinity at all mAChR subtypes with K-p(i) values similar to that of solifenacin at M-3 and higher at the other subtypes. Unlike solifenacin, it shows a preference for M-1 mAChR subtype with respect to the other subtypes. This compound, lacking a permanent positive charge on the nitrogen atom, can be a useful tool for the pharmacological study of mAChRs in the central nervous system. (C) 2017 Elsevier Masson SAS. All rights reserved.

In the present work the behavior of different substituted iminic bonds toward the oxidative action of 3-chloroperbenzoic acid is reported. The C=N bond was or was not oxidized to oxaziridines, amides, oximes, nitroso-, nitro-, and azodioxy compounds depending on the substituents at the iminic group and on the imine/MCPBA stoichiometric ratio.

Herein we report a new straightforward synthesis of cis and trans 2,5-disubstituted N,N-dialkylpiperazines, even in enantioenriched form, by reacting non-activated N-alkyl arylaziridines in the presence of a catalytic amount of a Lewis acid. A stereochemical and NMR investigation revealed useful mechanistic insights for this process.

The first structure of an aromatic bis(trifluoroborate) dipotassium salt, elucidated by the combination of crystallography, DFT calculations, topological and non-covalent interaction analysis, discloses a 3D network undergoing spontaneous self-assembly thanks to the massive participation of weak intra- and intermolecular interactions for which fluorine atoms proved to play a leading role.

In this work, the self-cleaning and photocatalytic properties of mesoporousTiO2/AuNRs-SiO2 composites (namely UCA-TiO2Au) prepared by a simple and low-costtechnique were investigated toward application in building materials. Mesoporous photocatalyticnanocomposites coating the surface of stone and other building materials are a very promisingapproach to address relevant questions connected with the increasing atmospheric pollution.We tested three types of preformed TiO2/AuNRs nanostructures in order to evaluate the effectof AuNRs on the photocatalytic activity of resulting coatings deposited on the surface of apopular building limestone. The resulting nanocomposites provide crack-free surface coatingson limestone, effective adhesion, improve the stone mechanical properties and impart hydrophobicand self-cleaning properties. Photocatalytic characterization involved the degradation of a targetcompound (Methylene blue; MB) under direct exposure to simulated solar light using TiO2 P25 Evonik(TiO2 P25) as a reference material. Moreover, these coatings upon irradiation by simulated solarlight were successfully employed for the photocatalytic oxidation of carbon soot. The experimentalresults revealed that UCA-TiO2Au samples are the best performing coating in both MB bleachingand soot degradation.

The reaction of ortho-lithiated aryloxiranes with various enaminones straightforwardly affords new functionalized isochromanes as mixtures of two epimeric stereoisomers in reasonable to very good yields (50-90%). The two diastereomers, which show a high structural variability, can be easily separated by column chromatography.

QUALX2.0 is the new version of QUALX, a computer program for qualitative phase analysis by powder diffraction data. The previous version of QUALX was able to carry out phase identification by querying the PDF-2 commercial database. The main novelty of QUALX2.0 is the possibility of querying also a freely available database, POW_COD. POW_COD has been built up by starting from the structure information contained in the Crystallography Open Database (COD). The latter is a growing collection of diffraction data, freely downloadable from the web, corresponding to inorganic, metal-organic, organic and mineral structures. QUALX2.0 retains the main capabilities of the previous version: (a) automatically estimating and subtracting the background; (b) locating the experimental diffraction peaks; (c) searching the database for single-phase pattern(s) best matching to the experimental powder diffraction data; (d) taking into account suitable restraints in the search; (e) performing a semi-quantitative analysis; (f) enabling the change of default choices and strategies via a user-friendly graphic interface. The advances of QUALX2.0 with respect to QUALX include (i) a wider variety of types of importable ASCII file containing the experimental diffraction pattern and (ii) new search-match options. The program, written in Fortran and C++, runs on PCs under the Windows operating system. The POW_COD database is exported in SQLite3 format.

The regioselective lithiation-functionalization of 2-arylazetidines has been explored. The nature of the N-substituent is mainly responsible for a regioselectivity switch. ortho-Lithiation occurred, using hexyllithium as a greener base, in N-alkylazetidines, while alpha-benzylic lithiation has been observed with N-Boc azetidines.

'Gear-like' rotations of simple C C bonds have been observed in some aziridine methanol derivatives. These restricted rotations have been studied by dynamic and multinuclear magnetic resonance experiments, and the barrier for rotations of Csp(3)-Csp(3) and Csp(3)-Csp(2) bonds have been calculated. The role of an intramolecular hydrogen bond on the stereodynamics has also been demonstrated. (C) 2011 Elsevier Ltd. All rights reserved.

The Shift_and_Fix procedure is a new method which has been developed for improving the quality of a structure model obtained by the ab-initio solution process from powder diffraction data. The main features of the new approach, which is fully automatic, are: a) the structure model usually attained at the end of the phasing process by Direct Methods is shifted partly and randomly; b) a combination of Fourier map calculation and least squares cycles has been suitably designed for relocating the shifted atoms onto positions which can finally be moved onto the true ones by the standard model optimization approaches; c) the Fourier map is calculated using coefficients which depend on the chemical content of the compound under study. When the figure of merit for selecting the best set of phases derived by Direct Methods does not work well, the ALLTRIALS strategy can be applied: it aims at investigating, automatically and sequentially, all the stored Direct Methods phasing sets and picking up the correct solution. The Shift_and_Fix method has been applied for improving the structure model calculated by each one of the phasing sets processed by ALLTRIALS. It has been implemented in the computing program EXPO and proved to be effective in providing a better ALLTRIALS outcome and increasing the probability of succeeding in the ab-initio powder solution.

A direct method to obtain -alkylidene -oxo amides by the palladium-catalyzed carbonylation of -chloro ketones in the presence of aromatic imines has been described. The methodology can be applied to a variety of C-aryl imines bearing N-aryl or N-alkyl substituents. The entire process is highly stereoselective and affords the -alkylidene -oxo amides only as (Z) isomers. A mechanistic hypothesis involving an acyl--lactam intermediate has also been proposed.

Aziridines are widely used as versatile building blocks for the synthesis of a variety of biologically and pharmaceutically importantmolecules [1]. Among the available methodologies for the preparation of functionalised aziridines, the lithiation/trapping sequence of simpleparent aziridines is growing in importance [2]. Present work reports the results concerning the structural study of aziridine-2-methanolderivatives by dynamic nuclear magnetic resonance (DMNR) [3] and single crystal X-ray diffraction. A careful examination of the aziridine2 (see figure 1) by NMR data, shows that at room temperature the meta protons and the protons of the two ortho methyl groups of the mesitylring gives featureless lumps, likely as consequence of a restricted rotation around the Csp3 -Csp2 bond between the carbinolic carbon andthe ipso carbon of the mesityl ring. Also in the solid state, an almost identical arrangement of the mesityl ring, with respect to the other twophenyl rings, has been observed. In this case, the aziridine nitrogen substituent was found in a syn relationship with respect to the carbinolicgroup so preventing the possibility of forming a hydrogen bond with the hydroxyl group. This evidence underlines a slow rotation of themesityl group instead of a nitrogen inversion as usually is expected. By X-ray analysis of 3 and diast-3 (figure 1), it is estimated that thenitrogen substituents set on the opposite side with respect the carbinolic carbon. Via study of crystal structures, the presence of hydrogenbonds between the hydroxyl group and the aziridine nitrogen lone pair was ascertained for aziridine 3 but not for diast-3 (figure 1). Such a hydrogen bond, which is persistent also in solution, could prevent the formation of conformational diastereoisomers by rotation around the bond between the carbinolic carbon and the aziridine quaternary carbon. This hypothesis has been demonstrated by NMR experiments. This investigation allowed us to calcolate some Csp2-Csp3 and Csp3-Csp3 rotational barriers and highlight a sort of "geared" rotation between aryl and alkyl substituents; this is possible if the structure is not in a locked conformation by an hydrogen bond as demonstrated by NMR and X-ray diffraction.

Anatase (TiO?) and multiwalled carbon nanotubes bearing polyethylenimine (PEI) anchored on their surface were hybridized in different proportions according to a sol-gel method. The resulting nanocomposites (TiO?@PEI-MWCNTs), characterized by BET, XRD, XPS, SEM, and UV techniques, were found efficient catalysts for CO? photoreduction into formic and acetic acids in water suspension and under visible light irradiation. PEI-grafted nanotubes co-catalysts are believed to act as CO? activators by forming a carbamate intermediate allowing to accomplish the first example in the literature of polyamines/nanotubes/TiO? mediated CO? photoreduction to carboxylic acids