Solvent Effect on the Preparation of Ionic Cocrystals of dl -Amino Acids with Lithium Chloride: Conglomerate versus Racemate Formation

The hydrophobic dl-amino acids alanine, valine, leucine, and isoleucine have been cocrystallized with LiCl via solid-state and solution methods, and the effect of preparation conditions and solvent choice on the racemic versus conglomerate formation has been investigated. For the sake of comparison, enantiopure l-amino acids have also been reacted with LiCl in the same experimental conditions. With dl-alanine only, a racemic ionic cocrystal of formula dl-alanine·LiCl·H2O is obtained, irrespective of the preparation conditions, while the amino acids dl-valine and dl-leucine undergo spontaneous chiral resolution when MeOH is used in ball milling conditions, yielding monohydrated conglomerates, which at ambient conditions convert over time into the racemic ionic cocrystals dl-Val·LiCl·H2O and dl-Leu·LiCl·1.5H2O; these racemic ionic cocrystals (ICCs) are otherwise obtained in a single step if water is employed instead of MeOH, both in ball milling and solution conditions. dl-Isoleucine behaves differently, and product characterization is complicated by the presence of dl-alloisoleucine (dl-aIle) in the commercial starting material; solution crystallization in the presence of excess LiCl, however, unexpectedly results in the formation of the alloisoleucine conglomerate d-aIle·LiCl·H2O and l-aIle·LiCl·H2O, together with unreacted dl-isoleucine. Solid-state syntheses of the ionic cocrystals proceed in most cases via formation of intermediate metastable polymorphs; phase identification and structural characterization for all ICCs have been conducted via single crystal and/or powder X-ray diffraction

Assembling photoactive materials from polycyclic aromatic hydrocarbons (PAHs): room temperature phosphorescence and excimer-emission in co-crystals with 1,4-diiodotetrafluorobenzene

Co-crystallization between the polycyclic aromatic hydrocarbons anthracene (A) and 9-methylanthracene (MA) with 1,4-diiodotetrafluorobenzene (I2F4) afforded three novel co-crystals, viz. A·(I2F4)2 and an unexpectedly complex system with two distinct compositions, namely MA·I2F4 and (MA)4·I2F4, which can be mechanochemically interconverted by a change in the stoichiometry of the reactive mixtures. Interestingly, all co-crystals are dual-emissive materials and exhibit different mechanisms of emission. A·(I2F4)2 and MA·I2F4 fluoresce from isolated molecules, whereas the luminescence of (MA)4·I2F4 is dominated by excimer emission. In all cases, phosphorescence at RT (RTP) is observed and interpreted as a direct consequence of the interactions between the iodine atoms of the I2F4 co-former and the π-electron density of the anthracene aromatic rings. Furthermore, [4 + 4] photoactivity within (MA)4·I2F4 was also investigated by means of FTIR/NMR spectroscopy and PXRD. The photophysical and photochemical behaviors of all solids are discussed and rationalized based on their structural features

Environmentally Friendly Sunscreens: Mechanochemical Synthesis and Characterization of β-CD Inclusion Complexes of Avobenzone and Octinoxate with Improved Photostability

We report on the mechanochemical synthesis of inclusion complexes obtained by reacting β-cyclodextrin (β-CD) with two widely used sunscreens, namely, avobenzone (AVO) and octinoxate (OCT). Formation of crystalline inclusion complexes was confirmed via a combination of solid-state techniques, including X-ray diffraction (XRD), Raman, and ATR-FTIR spectroscopies. A new, metastable polymorph of avobenzone was also isolated and characterized. NMR spectroscopy and thermal analyses (TGA and DSC) allowed us to evaluate the host/guest ratio and the water content (ca. 8H2O) in crystalline (β-CD)2·AVO and (β-CD)3·OCT2. Photodegradation of the two sunscreens upon inclusion in the hydrophobic cavity of β-CD was evaluated in solution via mass spectrometry (ESI-MS) and UV-vis spectroscopy and found to be sharply reduced. All findings indicate that the inclusion of AVO and OCT in β-CD might represent a viable route for the preparation of environmentally friendly sunscreens with improved photostability to be used in formulations of sun creams

Unexpected one-pot synthesis of highly conjugated pentacyclic diquinoid compounds

A new class of pentacyclic diquinoid compounds has been synthesized with a facile one-pot reaction of two molecules of 2-hydroxynaphthoquinone and 1-bromoalkanes in the presence of ferrocene. These molecules were isolated as enol tautomers that exhibit intramolecular hydrogen bond and extended electronic conjugation as proved by the intense absorption spectrum with a broad band between 400 and 600 nm. The spectroscopic and electrochemical characterization of this new class of compounds has been performed. One of the synthesized diquinoid derivatives showed a significant cytotoxicity with IC50 values of 25−50 μM against Cisplatin-Resistant SKOV3 and colon carcinoma SW480 cell lines. The results of our study provide a valuable tool to a one-pot synthesis of highly conjugated polyquinones, analogous to important biological systems, with significant antitumoral activity

Thiocarbamoyl Disulfides as Inhibitors of Urease and Ammonia Monooxygenase: Crystal Engineering for Novel Materials

The environmental sustainability of soil nitrogen fertilization is essential for the primary production of food for an expanding human population. In this framework, the control of soil enzymatic activities that impact the release of N-based compounds either in the atmosphere or in the underground waters is critical. The two enzymes that act as key players in the biogeochemical cycle of nitrogen are urease and ammonia monooxygenase (AMO), respectively, nickel- and copper-dependent enzymes. This article reveals the high efficacy of three molecules of the thiurams family, namely, thiram (tetramethylthiuram disulfide, TMTD), disulfiram (tetraethylthiuram disulfide, TETD), and tetraisopropylthiuram disulfide (TIPTD) as inhibitors of both the activities of jack bean (Canavalia ensiformis) urease (JBU) and Nitrosomonas europaea AMO. The water solubility of these compounds was significantly improved by the preparation of three novel inclusion complexes of beta-cydodextrin with TMTD, TETD, and TIPTD by mechanochemical synthesis, using green technology. The resulting beta-CD.thiuram complexes beta-CD.TMTD, (beta-CD)(2)-TETD, and (beta-CD)(2).TIPTD were all characterized by powder X-ray diffraction, thermogravimetric analysis, and solid-state NMR. A conformational polymorph of TIPTD was also detected and isolated via hot stage microscopy, and structurally characterized by single-crystal X-ray diffraction. Biological tests of enzymatic inhibition performed on JBU and AMO with the beta-CD.thiuram complexes showed the same inhibition efficacy as the isolated molecules, suggesting that the active species is, in all cases, the free thiuram, likely in equilibrium with the adduct in solution. These results have a great potential for improving the nitrogen use efficiency of soil fertilizers for a greener environment

Facile And Reversible Co Insertion Into The Ir-ch3 Bond Of [ir4(ch3)(co)8(μ4- η3-ph2pccph)(μ-pph2)]

Reaction of [Ir4H(CO)10 (μ-PPh2)] with BuLi, Ph2PC≡CPh and then Mel gives [Ir4 (CH 3)(CO)8 (μ4-η3-Ph 2PCCPh)(μ-PPh2)], which undergoes a reversible two-step CO insertion under extremely mild conditions to yield Ir4{(CH 3C(O)}(CO)8-(μ4:η3-Ph 2PCCPh)(μ-PPh2)] as the final product; the structures of both species have been established by X-ray diffraction studies.121008101

Synthesis And Structural Characterisation Of [ir4(co)8(ch3)(μ4-η 3-ph2pccph)(μ-pph2)] And Of The Carbonylation Product [ir4(co)8{c(o)ch3}(μ4-η 3-ph2pccph)(μ-pph2)]

Deprotonation of [(μ-H)Ir4(CO)10(μ-PPh2)], 1, gives [Ir4(CO)10(μ-PPh2)]- that reacts with Ph2PCCPh and CH3I to afford [Ir4(CO)8(CH3)(μ4-η 3-Ph2PCCPh)(μ-PPh2)], 2 (34%), besides [Ir4(CO)9(μ3-η3-Ph 2PC(H)CPh)(μ-PPh2)] and [(μ-H)Ir4(CO)9(Ph2PC≡CPh)(μ-PPh2)]. Compound 2 was characterised by a single crystal X-ray diffraction analysis and exhibits a flat butterfly of metal atoms, with the Ph2PCCPh ligand interacting with all four Ir atoms and the methyl group bonded terminally to a wingtip Ir atom. Carbonylation of 2 yields initially (25°C, 20 min) a CO addition product that, according to VT 31P{1H} and 13C{1H} studies, exists in solution in the form of two isomers 4A and 4B (8:1), and then (40°C, 7 h), the CO insertion product [Ir4(CO)8{C(O)CH3}-(μ4-η 3-Ph2PCCPh)(μ-PPh2)], 5. The molecular structure of 5, established by an X-ray analysis, is similar to that of 2, except for the acyl group that remains bound to the same Ir atom. The process is reversible at both stages. Treatment of 2 with PPh3 and P(OMe)3 affords the CO substitution products [Ir4(CO)7L(CH3)(μ4-η 3-Ph2PCCPh)(μ-PPh2)] (L = PPh3, 6 and P(OMe)3, 7), instead of the expected CO inserted products. According to the 1H and 31P{1H} NMR studies, the PPh3 derivative 6 exists in the form of two isomers (1:1) that differ with respect to the position of this ligand.1013545Hoffmann, R., (1982) Angew. Chem. Int. Ed. Engl., 21, p. 711Bau, R., Chiang, M.Y., Wei, C.-Y., Garlaschelli, L., Martinengo, S., Koestzle, T.F., (1984) Inorg. Chem., 23, p. 4758Ragaini, F., Porta, F., Demartin, F., (1991) Organometallics, 10, p. 185Albano, V.G., Canziani, F., Ciani, G., Chini, P., Martinengo, S., Manassero, M., Giordano, G., (1978) J. Organomet. Chem., 150, pp. C17Chinara, T., Aoki, K., Yamazaki, H., (1990) J. Organomet. Chem., 353, p. 367Chinara, T., Aoki, K., Yamazaki, H., (1994) J. Organomet. Chem., 473, p. 273González-Moraga, (1993) Cluster Chemistry, , Chapter 3, Springer-Verlag, BerlinBenvenutti, M.H.A., Vargas, M.D., Braga, D., Grepioni, F., Parisini, E., Mann, B.E., (1993) Organometallics, 12, p. 2955Benvenutti, M.H.A., Vargas, M.D., Braga, D., Grepioni, F., Mann, B.E., Naylor, S., (1993) Organometallics, 12, p. 2947Yamamoto, A., (1986) Organotransition Metal Chemistry, , WileyMorison, E.D., Bassner, L.S.L., Geoffroy, G.L., (1986) Organometallics, 5, p. 408Pereira, R.M.S., Fujiwara, F.Y., Vargas, M.D., Braga, D., Grepioni, F., (1997) Organometallics, 16, p. 4833Delgado, E., Chi, Y., Wang, W., Horgath, G., Low, P.J., Enright, G.D., Peng, S.-M., Carty, A.J., (1998) Organometallics, 17, p. 2936Vargas, M.D., Pereira, R.M.S., Braga, D., Grepioni, F., (1993) J. Chem. Soc. Chem. Commun., p. 1008Hengefelt, A., Nast, R., (1983) Chem. Ber., 116, p. 2025Livotto, F.S., Raithby, P.R., Vargas, M.D., (1993) J. Chem. Soc. Dalton Trans., p. 1797Brauer, G., (1965) Handboock of Preparative Inorganic Chemistry, 1, p. 645Sheldrick, G.M., (1990) Acta Crystallogr., A46, p. 467Sheldrick, G.M., (1976) SHELX76, Program for Crystal Structure Determination, , University of Cambridge, Cambridge, EnglandWalker, N., Stuart, D., (1983) Acta Crystallogr., Sect. B, 39, p. 158Keller, E., (1992) SHAKAL92, Graphical Representation of Molecular Models, , University of Freiburg, FRGKubota, M., McClesky, T.M., Hayashi, R.K., Carl, G., (1987) J. Am. Chem. Soc., 109, p. 7569Wade, K., (1976) Adv. Inorg. Chem. Radiochem., 18, p. 1Benvenutti, M.H.A., Vargas, M.D., Hitchcock, P.B., Nixon, J.F., (1995) J. Chem. Soc. Chem. Commun., p. 866Carty, A.J., Mac Laughlin, S.A., Nucciaroni, D., (1987) Phosphorus 31-NMR Spectroscopy in Steereochemical Analysis of Organic Compounds and Metal Complexes, , Chapter 16Verkade, J. G.Quin, L. D. EdsVCHKeister, J.B., (1980) J. Organomet. Chem., 190, pp. C36Aime, S., Dastrù, W., Gobetto, R., Viale, A., (1998) Organometallics, 17, p. 3182Johnson, B.F.G., Lewis, J., Orpen, A.G., Raithby, P.R., Süss, G., (1979) J. Organomet. Chem., 173, p. 187Araujo, M.H., Vargas, M.D., unpublished resultsMonti, D., Frachey, G., Bassetti, M., Haynes, A., Sunley, G.J., Maitlis, P.M., Cantoni, A., Bocelli, G., (1995) Inorg. Chim. Acta, 240, p. 485Garcia Alonso, J., Llamazares, A., Riera, V., Diaz, M.R., García Grande, S., (1991) J. Chem. Soc. Chem. Commun., p. 1058Cotton, J.D., Crisp, G.T., Daly, V.A., (1981) Inorg. Chim. Acta, 47, p. 165Bondietti, G., Laurenczy, G., Ross, R., Roulet, R., (1994) Helv. Chim. Acta, 77, p. 1869Laurenczy, G., Bondietti, G., Merbach, A.E., Moulet, B., Roulet, R., (1994) Helv. Chim. Acta, 77, p. 547Braga, D., Grepioni, F., Vargas, M.D., Ziglio, C.M., manuscript in preparatio

Making crystals from crystals: a green route to crystal engineering and polymorphism.

Supramol. reactions between cryst. materials as well as reactions between a cryst. material and a vapor can be used to generate new cryst. substances. These solvent-free processes can be exploited to prep. both hydrogen-bonded co-crystals and coordination networks. Solid-vapor reactions do not differ from solid-vapor uptake/release processes, and can also be used to prep. polymorphs and solvates. It is argued that solvent-less reactions involving mol. crystals represent a green route to supramol. solid-state chem. and crystal engineering. [on SciFinder (R)