Efficient High-Refractive-Index Azobenzene Dendrimers Based on a Hierarchical Supramolecular Approach

Real-time manipulation of light in a diffractive optical element made with an azomaterial, through the light-induced reconfiguration of its surface based on mass transport, is an ambitious goal that may enable new applications and technologies. The speed and the control over photopatterning/reconfiguration of such devices are critically dependent on the photoresponsiveness of the material to the structuring light pattern and on the required extent of mass transport. In this regard, the higher the refractive index (RI) of the optical medium, the lower the total thickness and inscription time can be. In this work, we explore a flexible design of photopatternable azomaterials based on hierarchically ordered supramolecular interactions, used to construct dendrimer-like structures by mixing specially designed sulfur-rich, high-refractive-index photoactive and photopassive components in solution. We demonstrate that thioglycolic-type carboxylic acid groups can be selectively used as part of a supramolecular synthon based on hydrogen bonding or readily converted to carboxylate and participate in a Zn(II)-carboxylate interaction to modify the structure of the material and fine-tune the quality and efficiency of photoinduced mass transport. Compared with a conventional azopolymer, we demonstrate that it is possible to fabricate high-quality, thinner flat diffractive optical elements to reach the desired diffraction efficiency by increasing the RI of the material, achieved by maximizing the content of high molar refraction groups in the chemical structure of the monomers.

New Hg(II) coordination polymers based on a thioimidazole ligand with good performance to detoxify Hg(II) and reversibly capture iodine

In the current paper, we have successfully synthesized three new mercury coordination polymers with fascinating structures and properties via a flexible sulfur donor ligand, namely, {[Hg(μ₂-Cl)(μ₂-Ls)]}_n[BF₄]_n(1), {[Hg(μ₂-Cl)(μ₂-Ls)]}_n[ClO₄]_n(2), and [Hg(SCN)₂(μ₂-Ls)]_n(3) [Ls = 1,1-bis(3-methyl-4-imidazoline-2-thione)methane]. These complexes have been characterized by means of different techniques such as single crystal X-ray crystallography, FT-IR, elemental analysis (CHNS), UV-Vis, PXRD, BET, and TGA. Suitable single crystals of all complexes were obtained using the branch tube method with a very high yield and good stability due to the high affinity of mercury to bind to the thione groups. The cationic moieties of polymers 1 and 2 were isostructural, with a HgCl₂S₂ coordination core structure. The voids of the quasi-hexagonal packing of the columnar chains were occupied by unbonded tetrahedral BF₄^- ions in 1 and perchlorate anions in polymer 2. Polymer 3 has a less distorted tetrahedral geometry than 1 and 2, with a HgS₄ core structure. By considering the thiophilicity of mercury, a thioamide-based Ls ligand was used to detoxify Hg(II) into insoluble polymers 1-3. The results of an MTT assay for (HepG2) liver cells confirmed the excellent cytoprotective effect of this ligand against mercury. Based on IC₅₀ calculations, their toxicity was in order of polymer 1 > polymer 2 > polymer 3. These polymers were also considered as adsorbents for the reversible removal of iodine from solution and the kinetics of the process has been studied in detail. Interestingly, all of them showed an excellent stability and high capacity, in order of 763.53 mg g^-1, 877.10 mg g^-1, and 905.31 mg g^-1 for polymers 1-3, respectively.

Journeys in crystal energy landscapes: actual and virtual structures in polymorphic 5-nitrobenzo[c][1,2,5]thiadiazole

A new polymorph of 5-nitrobenzo[c][1,2,5]thiadiazole, polymorph II, has been discovered. This polymorph is obtained by crystallization from solutions containing Cu(II) ions, that inhibit the formation of the already known polymorph...

Crystal and mesophase structure of a bicyclohexyl cyano mesogen

The phase behaviour of 4-[trans-4-(trans-4-propylcyclohexyl)cyclohexyl]benzonitrile, C22H31N, 1, has been examined. This compound has two different solid phases, denoted I and II, and exhibits thermotropic liquid-crystalline behaviour, with a remarkable interval of stability of the mesophase between the lower melting solid phase (75 °C) and the isotropization temperature (247 °C). The crystal and molecular structures of solid phase I have been determined at 173 K. The cyclohexyl rings both adopt the chair conformation and are equatorially substituted. The packing of 1 in the crystalline state is driven by the antiparallel arrangement of cyano dipoles with the formation of close contacts involving the strong cyano acceptor and weak aromatic C—H or aliphatic C—H donors. The crystal packing is discussed and compared with X-ray diffraction data in the liquid-crystalline state. The combination of thermal analysis, optical polarizing microscopy and X-ray diffraction analysis suggests that the mesophase is a partially ordered smectic phase. The lamellar structure of the mesophase is retained in crystalline solid phase II obtained by cooling the liquid-crystalline phase.

Novel Thienyl DPP derivatives Functionalized with Terminal Electron-Acceptor Groups: Synthesis, Optical Properties and OFET Performance

Three novel diketopyrrolopyrrole (DPP) based small molecules have been synthesized and characterized in terms of their chemical-physical, electrochemical and electrical properties. All the molecules consist of a central DPP electron acceptor core symmetrically functionalized with donor bi-thienyl moieties and flanked in the terminal positions by three different auxiliary electron-acceptor groups. This kind of molecular structure, characterized by an alternation of electron acceptor and donor groups, was purposely designed to provide a significant absorption at the longer wavelengths of the visible spectrum: when analysed as thin films, in fact, the dyes absorb well over 800 nm and exhibit a narrow optical bandgap down to 1.28 eV. A detailed DFT analysis provides useful information on the electronic structure of the dyes and on the features of the main optical transitions. Organic field-effect transistors (OFETs) have been fabricated by depositing the DPP dyes as active layers from solution: the different end-functionalization of the dyes had an effect on the charge-transport properties with two of the dyes acting as n-type semiconductors (electron mobility up to 4.4 ⋅ 10^-2  cm² /V ⋅ s) and the third one as a p-type semiconductor (hole mobility up to 2.3 ⋅ 10^-3  cm² /V ⋅ s). Interestingly, well-balanced ambipolar transistors were achieved by blending the most performant n-type and p-type dyes with hole and electron mobility in the order of 10^-3  cm² /V ⋅ s.

Effect of chalcogen bond on the packing and coordination geometry in hybrid organic-inorganic Cu(II) networks

The effect of chalcogen bond interaction led to interesting crystal packing and coordination geometry of Copper (II) in novel organic-inorganic hybrids. The reactions of organic bridging ligands, 1,2,5-benzothiadiazole (btd) and...

High-Energy-Density Materials: An Amphoteric N-Rich Bis(triazole) and Salts of Its Cationic and Anionic Species

The synthesis and characterization of the N-rich bis(triazole) compound 1H,4′H-[3,3′-bis(1,2,4-triazole)]-4′,5,5′-triamine (C₄H₇N₉) with a N content of 69.6% by weight is reported. The compound exhibits a rich acid–base behavior because it can accept up to two protons, forming a monocation and a dication, and can lose one proton, forming an anion. Measurement of the acid constants has shown that there exist well-defined pH intervals in which each of the four species is predominant in solution, opening the way to their isolation and characterization by single-crystal X-ray analysis as salts with different counterions. Some energetic salts of the monocation or dication containing oxidizing inorganic counterions (dinitramide, perchlorate, and nitrate) were also prepared and characterized in the solid state for their sensitivity. In particular, the neutral compound shows a very remarkable thermal stability in air, with T_d = 347 °C, and is insensitive to impact and friction. Salts of the dication with energetic counterions, in particular perchlorate and nitrate, show increased sensitivities and reduced thermal stability. The salt of the monocation with dinitramide as the counterion outperforms other dinitramide salts reported in the literature because of its higher thermal stability (T_d = 230 °C in air) and friction insensitiveness.

An energetic, N-rich compound that, depending on the pH, can exist as neutral, singly protonated, doubly protonated, and deprotonated species is shown.

Enhanced photoinduced mass migration in supramolecular azopolymers by H-bond driven positional constraint

Here we investigated the role of hydrogen bonding in the design of supramolecular azopolymers with a highly directional and constrained azobenzene-chain interaction involving the aromatic ring of the photoactive molecule, by exploiting the 2-aminopyrimidine/carboxylic acid supramolecular synthon as the tool for molecular recognition. We have shown that this approach is advantageous for producing affordable and versatile photopatternable azomaterials by complexation with polyacrylic acid (PAA). Molecular model complexes were successfully prepared and characterized by X-ray diffraction analysis and FTIR spectroscopy to reveal the multiple, non-ionic interaction occurring between the azobenzene units and the polymer chains. Surface photopatterning of thin films, driven by the typical mass migration phenomenon occurring in azopolymers, resulted strongly enhanced with increasing azobenzene content until equimolar composition. Results show that polymers with synthon-based azobenzenes markedly outperform single H-bonded systems bearing azomolecules with similar structure and electronic properties. We finally demonstrated that the azobenzene units can be easily extracted from a photopatterned film by a simple solvent rinse and without any chemical pre-treatment, leaving the periodicity of the inscribed surface relief gratings unaltered. This result was enabled by the orthogonal solubility of the components in the supramolecular system.

Phase behaviour and crystal structures of 2',3'-difluorinated p-terphenyl derivatives

The crystal structures of difluorine derivatives of p-terphenyls (nTm) have been determined by single-crystal X-ray diffraction. For the unsymmetrical substituted compounds 2',3'-difluoro-4-methyl-p-terphenyl (1T0, C₁₉H₁₄F₂) and 4-ethyl-2',3'-difluoro-4''-methyl-p-terphenyl (1T2, C₂₁H₁₈F₂), the crystal structure is disordered, with molecules statistically entering the crystal in up and down orientations, with full superposition of all the atoms, except for those of the terminal groups (H/methyl for 1T0 and methyl/ethyl for 1T2). For triclinic 2',3'-difluoro-4,4''-dimethyl-p-terphenyl (1T1, C₂₀H₁₆F₂), with the space group P-1, the two crystallographically independent molecules have the same conformation, which is different from monoclinic 1T0 (space group C2) and 1T2 (space group C2/c). A common feature of the conformation of the three compounds is the noncoplanar twisted arrangement of the three rings of the p-terphenyl moiety. Two-dimensional (2D) Hirshfeld fingerprint plots are consistent with H...H and C...H contacts in the crystal packing. For the three compounds, the phase behaviour has been investigated by POM (Petra/Osiris/Molinspiration) and differential scanning calorimetry (DSC) analysis. 1T2 is mesogenic, with enantiotropic nematic behaviour.

Stabilization of an elusive tautomer by metal coordination

The solid-state isolation of the different tautomers of a chemical compound can be a challenging problem. In many cases, tautomers with an energy very close to the most stable one cannot be isolated (elusive tautomers). In this article, with reference to the 4-methyl-7-(pyrazin-2-yl)-2H-[1,2,4]triazolo[3,2-c][1,2,4]triazole ligand, for which the elusive 3H-tautomer has an energy only 1.4 kcal mol^-1 greater than the most stable 2H form, we show that metal complexation is a successful and reliable way for stabilizing the elusive tautomer. We have prepared two complexes of the neutral ligand with CuBr₂ and ZnBr₂, namely, aquabromidobis[4-methyl-7-(pyrazin-2-yl)-3H-[1,2,4]triazolo[3,2-c][1,2,4]triazole]copper(II) bromide trihydrate, [CuBr(C₈H₇N₇)₂(H₂O)]Br·3H₂O, and dibromido[4-methyl-7-(pyrazin-2-yl)-2H-[1,2,4]triazolo[3,2-c][1,2,4]triazole][4-methyl-7-(pyrazin-2-yl)-3H-[1,2,4]triazolo[3,2-c][1,2,4]triazole]zinc(II) monohydrate, [ZnBr₂(C₈H₇N₇)₂]·H₂O. The X-ray analysis shows that, in both cases, the elusive 3H-tautomer is present. The results of the crystallographic analysis of the two complexes reflect the different coordination preferences of Cu^II and Zn^II. The copper(II) complex is homotautomeric as it only contains the elusive 3H-tautomer of the ligand. The complex can be described as octahedral with tetragonal distortion. Two 3H-triazolotriazole ligands are bis-chelated in the equatorial plane, while a water molecule and a bromide ion in elongated axial positions complete the coordination environment. The zinc(II) complex, on the other hand, is heterotautomeric and contains two bromide ions and two monodentate ligand molecules, one in the 2H-tautomeric form and the other in the 3H-tautomeric form, both coordinated to the metal in tetrahedral geometry. The observation of mixed-tautomer complexes is unprecedented for neutral ligands. The analysis of the X-ray molecular structures of the two complexes allows the deduction of possible rules for a rational design of mixed-tautomer complexes.

Tautomeric and conformational switching in a new versatile N-rich heterocyclic ligand

A new N-rich triazolo-triazole derivative, 4-methyl-7-(pyrazin-2-yl)-2H-[1,2,4]triazolo[3,2-c][1,2,4]triazole (C8H7N7), bearing a pyrazine residue at 7-position of the triazolo-triazole bicycle, was synthesized, and its acid-base and metal coordination properties were evaluated in solution. The results showed amphoteric behavior and the formation of stable complexes with Cu(ii) and Zn(ii) in pH intervals in which the ligand is neutral or deprotonated. Computational studies were performed in order to evaluate the stability of the different tautomers/conformers of the ligand, and the proton position in the neutral and acidic forms. Single crystal X-ray analysis of the free neutral ligand (2H/s-trans tautomer/conformer), and of its singly protonated (2H-3H/s-trans), doubly protonated (2H-3H-7H/s-trans) and deprotonated forms showed that the influence of the pyrazine ring on the triazolo-triazole system is mainly as electron withdrawing and chelating group, and proton acceptor. Different coordination modes have been evidenced for the neutral and deprotonated ligand. Upon metal coordination, the neutral ligand switches from 2H/s-trans to 3H/s-cis tautomer/conformer forming five-membered chelate rings, while the anionic deprotonated ligand forms six-membered chelate rings in the s-trans conformation. Altogether, five different tautomers/conformers of the ligand were isolated and characterized. In vitro tests confirmed the general antiproliferative activity of triazolo-triazole compounds and the importance of substitution in position 7 for their selectivity.

Crystal structure and mesogenic behaviour of a new fluorene derivative: 9,9-dimethyl-2,7-bis(4-pentylphenyl)-9H-fluorene

The title compound, C₃₇H₄₂, is a new mesogenic compound containing the fluorene moiety. It exhibits enantiotropic nematic liquid crystalline behaviour with melting at 125 °C and isotropization at 175 °C. The crystallographically independent unit contains two molecules oriented face-to-edge with respect to each other. The two molecules have nearly the same conformation of the bis-phenyl fluorene moiety. The molecular packing in the crystal phase is nematic-like.

A new biologically active molecular scaffold: crystal structure of 7-(3-hydroxyphenyl)-4-methyl-2H-[1,2,4]triazolo[3,2-c][1,2,4]triazole and selective antiproliferative activity of three isomeric triazolo–triazoles

A study of three isomeric compounds containing a phenolic moiety attached to the nitrogen-rich triazolo–triazole bicycle is presented. In the three isomers, the phenolic OH group is in the ortho, meta and para positions. The crystal structure analysis of the meta isomer (C10H9N5O) shows that the 2H-tautomer is present in the crystal and that the molecule adopts a substantially planar geometry. However, the conformation found in the crystal is different compared to the monoprotonated cation of the same compound previously investigated in several salts. The packing of the meta isomer is driven by the formation of strong hydrogen bonds and shows the formation of infinite planar ribbons, parallel to a, formed around 21 crystallographic axes. The three isomers were tested against some cancer cell lines and also against normal cell lines. The ortho isomer shows a weak antiproliferative activity, the meta isomer shows significant antiproliferative activity against some cancer lines and no activity against healthy cell lines, and the para isomer is active against all the tested cell lines.

Research Progress on Photosensitizers for DSSC

Dye sensitized solar cells (DSSC) are considered one of the most promising photovoltaic technologies as an alternative to traditional silicon-based solar cells, for their compatibility with low-cost production methods, their peculiar optical and mechanical properties and the high indoor efficiency. Photosensitizers represent one of the most important components of a DSSC device and probably the most thoroughly investigated in the last twenty years, with thousands of dyes that have been proposed and tested for this kind of application. In this review we aimed to provide an overview of the three main classes of DSSC photosensitizers, namely ruthenium(II) polypyridyl complexes, Zn-porphyrin derivatives and metal-free organic dyes. After a brief introduction about the architecture and operational principles of a DSSC and the state of the art of the other main components of this type of device, we focused our discussion on photosensitizers. We have defined the numerous requirements DSSC photosensitizers should satisfy and have provided an overview of their historical development over the years; by examining specific dyes reported in the literature, we attempted to highlight the molecular design strategies that have been established for the optimization of their performance in real devices both in terms of efficiency (which recently reaches an outstanding 14.3%) and operational stability. Finally, we discussed, in the last section, the possible future developments of this intriguing technology.

Crystal structure of N,N'-bis-(2,4-di-fluoro-benzo-yloxy)benzene-1,2:4,5-tetra-carboximide

Mol-ecules of the title compound, C24H8F4N2O8, have Ci point-group symmetry in the crystal, as they lie on crystallographic inversion centres (Z' = 1/2). The di-fluoro-phenyl ring is disordered over two orientations; the final refined occupancy factors of the two components of disorder are 0.947 (4) and 0.053 (4). In the crystal, some Car-H⋯F inter-actions are present, which involve the most acidic H atom of the mol-ecule.

Crystal structure of an epoxysterol: 9α,11α-epoxy-5α-cholest-7-ene-3β,5,6α-triol 3,6-diacetate

The title compound is a polyoxygenated ep­oxy steroid that crystallizes in the P2₁2₁2₁ space group.

The title compound, C₃₁H₄₈O₆, is a polyoxygenated ep­oxy steroid obtained by a multi-step synthesis involving oxidation of 7-de­hydro­cholesterol. It crystallizes in the P2₁2₁2₁ space group; however, the absolute structure of the molecule in the crystal could not be determined by resonant scattering. The configuration at the C5 and C6 positions is in both cases of the α-type, as is that of the C atoms of the ep­oxy ring. Mol­ecules in the crystal form chains parallel to the b axis by hydrogen bonding between O—H donors and carbonyl O-atom acceptors. Some atoms of the alkyl chain are disordered over two orientations, with a refined occupancy ratio of 0.511 (10):0.489 (10).

Pseudosymmetry and high Z' structures: the case of rac-(2R,2'R,5'S)-2-methyl-5'-[(1R,2R,5S,5'S)-1,4,4,5'-tetra-methyl-dihydro-3'H-3,8-dioxa-spiro-[bi-cyclo-[3.2.1]octane-2,2'-furan]-5'-yl]-3,4,1',2',3',4'-hexa-hydro-[2,2'-bi-furan]-5(2H)-one

The title compound, C22H34O6, is one of the products obtained by oxidation of squalene with the catalytic system RuO4(cat.)/NaIO4. It crystallizes in the P-1 space group, with four crystallographically independent mol-ecules related by a pseudo-C2 symmetry axis. The structural analysis also shows that the title compound is isomeric with two products previously reported in the literature and that are obtained by the same reaction procedure. In particular, out of the seven chiral C atoms present in the mol-ecule, the title compound shows the opposite configuration at, respectively, four and two chiral centres with respect to the isomeric compounds.

Solid State Separation and Isolation of Tautomers of Fused-Ring Triazolotriazoles

Fine control of the tautomeric forms of [1,2,4]triazolo[3,2-c][1,2,4]triazole derivatives in acidic conditions has been achieved by acting on the electronic character of the substituent at position 7 of the heterobicycle and on the counterion. Strong electron releasing or electron withdrawing substituents lead almost exclusively to a single tautomeric form, the 1H-3H or the 2H-3H, respectively. In the case of the phenol substituent, both tautomeric forms are present in comparable amount in solution; the two tautomers can also be selectively precipitated in different crystalline salts using suitable counterions.

Crystal structure of a new spiro-polytetra-hydro-furan compound with translational pseudosymmetry: rac-(2S,2'S,5'R)-2-methyl-5'-[(1R,2R,5S,5'R)-1,4,4,5'-tetra-methyl-dihydro-3'H-3,8-dioxa-spiro[bi-cyclo-[3.2.1]octane-2,2'-furan]-5'-yl]hexa-hydro[2,2'-bi-furan]-5(2H)-one

The title compound crystallizes in the P space group, with two crystallographically independent mol­ecules approximately related by the non-crystallographic translation vector c/2.

The title compound, C₂₂H₃₄O₆, is a product of oxidation of squalene with the catalytic system RuO₄(cat.)/NaIO₄. The asymmetric unit contains two crystallographically independent mol­ecules of very similar geometry approximately related by the non-crystallographic translation vector c/2. As a consequence, the average diffracted intensity in the hkl layers with odd l is systematically lower than in the layers with even l. In one mol­ecule, the lactone ring and part of the adjacent tetra­hydro­furan ring are disordered over two orientations with refined occupancy ratio of 0.831 (10):0.169 (10). The crystal structure is mainly governed by van der Waals forces.

Survey of temperature, reaction time and ultrasound irradiation power on sonochemical synthesis of two new nanostructured lead(II) coordination supramolecule compounds

Nanoparticles of two new 0D, lead(II) coordination supramolecular compounds, [Pb(L)₂(I)₂] (1) and [Pb(L)(L^/)(H₂O)]·3H₂O (2), (L=1,10-phenanthroline monohydrate, L^/=2,6-pyridinedicarboxlic acid), have been synthesized by a sonochemical process and characterized by scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM), X-ray powder diffraction (XRPD), FT-IR spectroscopy and elemental analyses. The single crystal X-ray data of compounds show that the Pb ion is six coordinated in both 1 and 2. The thermal stability of compound 1 and 2 has been studied by thermal gravimetric (TG) and differential thermal analyses (DTA). The role of temperature, reaction time and ultrasound irradiation power on the size and morphology of the nano-structured compound obtained from 1 and 2, have been investigated. Results indicate that an increase of temperature and sonication power and a decrease in time reaction led to a decrease of particle size. Topological analysis shows that the compound 1 and 2 are new topology for net: 1,4M5-1 and nch, respectively.

5-Amino-1-(2',3'-O-iso-propyl-idene-d-ribit-yl)-1H-imidazole-4-carboxamide: a crystal structure with Z' = 4

The title compound, C12H20N4O5, crystallizes in the monoclinic space group P21, with four crystallographically independent mol-ecules in the asymmetric unit. The four mol-ecules have a very similar conformation that is basically determined by the formation of two intra-molecular hydrogen bonds between the amino NH2 donors and the carbonyl and ring O-atom acceptors, forming, respectively, R(6) and R(7) ring motifs.. In the crystal, inter-molecular hydrogen bonding leads to the formation of R22(10) ring patterns, involving one amide CONH2 donor and an imidazole N-atom acceptor. The cluster of the four independent mol-ecules has approximate non-crystallographic C2 point symmetry. The structural analysis also shows that during the synthesis of the title compound, the reductive cleavage of the d-ribose ring of the inosine precursor proceeds stereoselectively, with retention of configuration.

A topotactic transition in a liquid crystal compound

The title compound has two crystal phases related by an enantiotropic single-crystal-to-single-crystal transition and a nematic liquid crystalline phase before transition to the isotropic liquid phase.

The anti-proliferative effect of L-carnosine correlates with a decreased expression of hypoxia inducible factor 1 alpha in human colon cancer cells

In recent years considerable attention has been given to the use of natural substances as anticancer drugs. The natural antioxidant dipeptide L-carnosine belongs to this class of molecules because it has been proved to have a significant anticancer activity both in vitro and in vivo. Previous studies have shown that L-carnosine inhibits the proliferation of human colorectal carcinoma cells by affecting the ATP and Reactive Oxygen Species (ROS) production. In the present study we identified the Hypoxia-Inducible Factor 1α (HIF-1α) as a possible target of L-carnosine in HCT-116 cell line. HIF-1α protein is over-expressed in multiple types of human cancer and is the major cause of resistance to drugs and radiation in solid tumours. Of particular interest are experimental data supporting the concept that generation of ROS provides a redox signal for HIF-1α induction, and it is known that some antioxidants are able to suppress tumorigenesis by inhibiting HIF-1α. In the current study we found that L-carnosine reduces the HIF-1α protein level affecting its stability and decreases the HIF-1 transcriptional activity. In addition, we demonstrated that L-carnosine is involved in ubiquitin-proteasome system promoting HIF-1α degradation. Finally, we compared the antioxidant activity of L-carnosine with that of two synthetic anti-oxidant bis-diaminotriazoles (namely 1 and 2, respectively). Despite these three compounds have the same ability in reducing intracellular ROS, 1 and 2 are more potent scavengers and have no effect on HIF-1α expression and cancer cell proliferation. These findings suggest that an analysis of L-carnosine antioxidant pathway will clarify the mechanism underlying the anti-proliferative effects of this dipeptide on colon cancer cells. However, although the molecular mechanism by which L-carnosine down regulates or inhibits the HIF-1α activity has not been yet elucidated, this ability may be promising in treating hypoxia-related diseases.

(3R,3aR,6R,6aR)-Hexa-hydro-furo[3,2-b]furan-3,6-diyl dibenzoate

The title compound, C₂₀H₁₈O₆, prepared from d-mannitol by a two-step procedure, is a functionalized fused bis-tetra­hydro­furan. In the central fragment, consisting of two fused tetra­hydro­furan rings, one O atom and its two adjacent C atoms, a methyl­ene and a bridgehead C atom, are disordered over two sets of sites with an occupancy ratio of 0.735 (9):0.265 (9). In the major component, the ring containing the disordered O atom is a half-chair conformation with twisted methylene and benzoate-substituted C atoms, whereas the other ring has a half-chair or T-form conformation. In the minor component, the ring with the disordered O atom has an envelope conformation, with the O atom as the flap, and the other ring has a half-chair conformation, with the O atom and the other bridgehead CH atom being twisted. The two aromatic rings are inclined to one another by 20.00 (12)°. In the crystal, adjacent molecules are linked via C—H⋯π interactions, forming chains propagating along [010].

(3S,3aS,6R,6aR)-2-Oxohexa-hydro-furo[3,2-b]furan-3,6-diyl dibenzoate

The title compound, C₂₀H₁₆O₇, contains a cis-fused γ-lactone tetra­hydro­furan ring system functionalized with two benzo­yloxy groups. Both rings adopt an envelope conformation. The mol­ecule assumes an elongated shape and exibits non-crystallographic C₂ symmetry. The benzo­yloxy groups are almost planar [maximum deviations of 0.0491 (15) and 0.0336 (17) Å for the O atoms] and their mean planes are inclined to one another by 16.51 (4)°. The crystal packing features weak C—H⋯O inter­actions. The aryl groups of adjacent mol­ecules are parallel shifted with face-to-face contacts and a shortest inter­molecular C⋯C distance of 3.482 (4) Å.

{4-Bromo-2-[(2-{(ethyl-sulfan-yl)[(2-oxido-benzyl-idene-κO)amino-κN]methyl-idene}hydrazinyl-idene-κN (1))meth-yl]phenolato-κO}(ethanol-κO)dioxido-uranium(VI)

In the title complex, [U(C₁₇H₁₄BrN₃O₂S)O₂(C₂H₅OH)], the U^VI cation has a distorted penta­gonal–bipyramidal environment with the penta­gonal plane defined by two N and two O atoms of the tetra­dentate Schiff base ligand and the O atom of the ethanol mol­ecule. Two oxide O atoms occupy the axial positions. The azomethine C=N group and the Br atom are disordered over two positions in a 0.8356 (18):0.1644 (18) ratio. The ethyl­thiolyl group is disordered over three conformations in a 0.8356 (18):0.085 (6):0.079 (6) ratio, and the ethanol ligand is also disordered over three orientations in a 0.470 (16):0.277 (19):0.253 (18) ratio. In the crystal, mol­ecules form centrosymmetric dimers through hydrogen bonding between ethanol O—H donors and phenolate O-atom acceptors. Weak C—H⋯O inter­actions consolidate the crystal packing.

3β,6α-Diacet-oxy-5,9α-dihy-droxy-5α-cholest-7-en-11-one

The title compound, C₃₁H₄₈O₇, a polyoxygenated steroid, was obtained by chemical oxidation of 7-de­hydro­cholesteryl acetate. The mol­ecular geometry features trans A/B and C/D junctions at the steroid core with the acetyl groups in the equatorial position and a fully extended conformation for the alkyl side chain. A chair conformation is observed for rings A and C while ring B adopts a half-chair conformation. The five-membered ring D has an envelope conformation, with the C atom bearing the methyl group at the flap. The terminal isopropyl group and one acetyl group are disordered over two sets of sites with 0.774 (8):0.226 (8) and 0.843 (7):0.157 (7) ratios, respectively. An intra­molecular S(6) O—H⋯O hydrogen-bonding motif involving a hy­droxy donor and acceptor is observed. In the crystal, chains of mol­ecules running along the b axis are formed via O—H⋯O hydrogen bonds between hy­droxy donors and carbonyl acceptors of the ordered acetyl group, giving rise to a C(14) motif. The chains are wrapped around the 2₁ screw axes.

Structural, electronic and vibrational properties of N,N'-1H,1H-perfluorobutyl dicyanoperylenecarboxydiimide (PDI-FCN2) crystal

We present a theoretical and experimental investigation of the crystalline structure of N,N'-1H,1H-perfluorobutyl dicyanoperylenecarboxydiimide (PDI-FCN2) that has been deduced combining experimental XRD data, obtained from powders, with global-optimization algorithms which allow to identify Bravais lattice, primitive cell parameters, and space group of the crystal. The XRD spectrum calculated for the proposed crystalline structure very well reproduces the measured XRD data. Our results suggest the triclinic lattice structure of spatial groups P1 and P1, respectively, for the crystalline PDI-FCN2-1,7 and PDI-FCN2-1,6 isomers. In both cases, the primitive cell contains a single molecule. On the proposed crystalline structures, KS-DFT cell energy calculations, including van der Waals interactions, have been performed to assign the minimum energy geometrical structure and orientation of the molecule inside the corresponding primitive cell. These calculations evidence the molecular packing that characterizes the strong anisotropy of the PDI-FCN2 crystal. Electronic band-structures calculated for both isomers within the Kohn-Sham density-functional theory indicate that the crystalline P1 structure is an indirect gap semiconductor, while the P1 structure is a direct gap semiconductor. The electronic band structure calculations on the optimized crystal geometries highlight strong anisotropy in the dispersion curves E(k), which roots at the molecular packing in the crystal. Finally, the vibrational spectrum of both crystalline isomers has been calculated in the harmonic approximation and the dominant vibrational frequencies have been associated to collective motions of selected atoms in the molecules.

N,N′-Dihydroxybenzene-1,2:4,5-tetracarboximide dihydrate

In the title compound, C₁₀H₄N₂O₆·2H₂O, the organic mol­ecule has crystallographically imposed inversion symmetry. The atoms of the three fused rings of the mol­ecule are coplanar within 0.0246 (8) Å, while the two hy­droxy O atoms are displaced from the mean plane of the mol­ecule by 0.127 (1) Å. In the crystal, infinite near-planar layers of close-packed mol­ecules are formed by hydrogen bonding between water O—H donor groups and carbonyl O-atom acceptors, and by weak inter­actions between C—H donor groups and water O-atom acceptors. The layers are parallel to the {102} family of planes. The stacked planes are held together by hydrogen bonding between N—OH donor groups and water O-atom acceptors.

4,5-Diamino-3-[(E,E)-4-(4,5-diamino-4H-1,2,4-triazol-3-yl)buta-1,3-dienyl]-4H-1,2,4-triazol-1-ium chloride

The title compound, C₈H₁₃N₁₀⁺·Cl⁻, is the monochlorhydrate salt of an aromatic bis­(di­amino­triazole). The cation is centrosymmetric, lying about an inversion centre (C_i symmetry) because the acidic H atom is disordered over two centrosymmetrically related ring N atoms, with equal multiplicity. It is noteworthy that protonation occurs at an N atom of the ring, instead of at the C—NH₂ or N—NH₂ amino groups. The chloride anions are also in special positions, as they lie on binary axes, and so the crystallographically independent unit contains half of a formula unit. The N atom of the C—NH₂ group is sp²-hybridized and the amino group is coplanar with the triazole ring [dihedral angle = 5 (3)°], while the N atom of the N—NH₂ amino group is pyramidal. The C=C bonds are in E conformations and the cation is flat because the conformation of the carbon chain is fully extended. The chloride anions are hexa­coordinated, in a distorted trigonal–prismatic geometry, and they are involved, as acceptors, in six hydrogen bonds. Chains of hydrogen-bonded cations, running along c and a + c, are generated by c-glide and C₂ rotation, respectively. This combination of N—H⋯Cl and N—H⋯N hydrogen bonds leads to the formation of a three-dimensional network.

3β,6β-Diacet-oxy-5,9α-dihy-droxy-5α-cholest-7-en-11-one acetic acid 0.04-solvate

The title compound, C31H48O7·0.04CH3COOH, is a polyoxy-genated steroid obtained by selective chemical oxidation of 7-de-hydro-cholesteryl acetate. The asymmetric unit comprises three mol-ecules of the steroid (Z' = 3) and a mol-ecule of acetic acid which has occupancy factor 0.131 (5). The geometric parameters of the independent mol-ecules do not reveal significant differences. In one mol-ecule, the terminal isopropyl group is disordered over two sets of sites with occupancy ratio 0.869 (5):0.131 (5). The three mol-ecules reveal different hydrogen-bonding patterns. Each of them is involved in an intra-molecular S(6) hydrogen-bonding motif, involving hy-droxy groups as donor and acceptor. In the crystal, two independent mol-ecules form dimers through hydrogen bonding between an OH donor and an acetate carbonyl acceptor, giving rise to R 2 (2)(16) ring patterns. A single hydrogen bond between the OH group and a ketone carbonyl group is observed between two symmetry-independent mol-ecules.

2-(4-Methyl-phen-yl)-6-nitro-1,3-benzoxazole

The title compound, C14H10N2O3, is a π-conjugated mol-ecule containing a benzoxazole aromatic fused heterobicycle. The benzoxazole ring system is planar within 0.01 Å. The mol-ecule assumes an approximately flat conformation, the benzoxazole ring system forming dihedral angles of 6.52 (12) and 7.4 (3)° with the benzene ring and the nitro group, respectively. In the crystal, mol-ecules are connected by very weak C-H⋯O hydrogen inter-actions, forming chains running parallel to the a or c axes. The methyl H atoms are disordered over two sets of sites of equal occupancy rotated by 60°.