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We report halogen‐bonded complexes between 1‐polyfluoroalkyl‐3‐alkylimidazolium iodides and mono‐iodoperfluoroalkanes of different chain lengths or di‐iodoperfluorooctane. 19F NMR analyses revealed that the preferred stoichiometry between the donors and acceptors is 1 : 1 in the cases of the mono‐iodoperfluoroalkanes, and 2 : 1 with di‐iodoperfluorooctane, as a result of the monodentate behavior of the iodide anion (halogen bond acceptor). Single crystal X‐ray diffraction analyses showed the presence of a perfluorinated superanion, which interdigitates with the cation fluorinated chains, favoring the formation of lamellar structures. All of the obtained supramolecular complexes exhibit enantiotropic liquid crystalline phases over a broad range of temperatures. Most of the obtained complexes show melting points lower than 100 °C, two of them being liquid at room temperature, thus representing a new family of fluorinated ionic liquid crystals. [ABSTRACT FROM AUTHOR]

Novel 1,1′-bis(4-alkylphenyl)-[4,4′-bipyridine]-1,1′-diium salts, with alkyl chains of different lengths (8, 10 and 14 carbon atoms) and with different counteranions (Cl−, NTf2−, OTf−, OTs−, PF6−, BPh4−), have been prepared and fully characterized for their thermotropic behavior by polarized optical microscopy (POM), and calorimetric measurements. Almost all the synthesized compounds showed a high thermal stability, a wide temperature range of liquid-crystalline mesophase and, for some of them, the LC transition temperatures were relatively low. These compounds also exhibited electrochromic properties, which have been studied both in solution and in the LC phase, making the new materials very interesting for different opto-electronic applications. [ABSTRACT FROM AUTHOR]

Abstract: Halogen bonding is an increasingly important tool in crystal engineering, and measuring its influence on the local chemical and electronic environment is necessary to fully understand this interaction. Here, we present a systematic crystallographic and solid‐state NMR study of self‐complementary halogen‐bonded frameworks built from the halide salts (HCl, HBr, HI, HI3) of 2‐iodoethynylpyridine and 3‐iodoethynylpyridine. A series of single crystal X‐ray structures reveals the formation of discrete charged dimers in the solid state, directed by simultaneous X−⋅⋅⋅H−N+ hydrogen bonds and C−I⋅⋅⋅X− halogen bonds (X=Cl, Br, I). Each compound was studied using multinuclear solid‐state magnetic resonance spectroscopy, observing 1H to investigate the hydrogen bonds and 13C, 35Cl, and 79/81Br to investigate the halogen bonds. A natural localized molecular orbital analysis was employed to help interpret the experimental results. 1H SSNMR spectroscopy reveals a decrease in the chemical shift of the proton participating in the hydrogen bond as the halogen increases in size, whereas the 13C SSNMR reveals an increased 13C chemical shift of the C−I carbon for C−I⋅⋅⋅X− relative to C−I⋅⋅⋅N halogen bonds. Additionally, 35Cl and 79/81Br SSNMR, along with computational results, have allowed us to compare the C−I⋅⋅⋅X− halogen bond involving each halide in terms of NMR observables. Due to the isostructural nature of these compounds, they are ideal cases for experimentally assessing the impact of different halogen bond acceptors on the solid‐state NMR response. [ABSTRACT FROM AUTHOR]

Unconventional ionic liquid crystals in which the liquid crystallinity is enabled by halogen-bonded supramolecular anions [C nF2 n+1-I⋅⋅⋅I⋅⋅⋅I-C nF2 n+1]− are reported. The material system is unique in many ways, demonstrating for the first time 1) ionic, halogen-bonded liquid crystals, and 2) imidazolium-based ionic liquid crystals in which the occurrence of liquid crystallinity is not driven by the alkyl chains of the cation. [ABSTRACT FROM AUTHOR]

Unconventional ionic liquid crystals in which the liquid crystallinity is enabled by halogen-bonded supramolecular anions [C nF2 n+1-I⋅⋅⋅I⋅⋅⋅I-C nF2 n+1]− are reported. The material system is unique in many ways, demonstrating for the first time 1) ionic, halogen-bonded liquid crystals, and 2) imidazolium-based ionic liquid crystals in which the occurrence of liquid crystallinity is not driven by the alkyl chains of the cation. [ABSTRACT FROM AUTHOR]

It is proposed that noncovalent interactions,wherein it is possibleto identify an element or moiety working as the electrophile, arenamed by referring to the Group of the Periodic Table the electrophilicatom belongs to. The resulting terminology generalizes a criterionwhich was used in the recent IUPAC definition of halogen bond andinspired the definition of hydrogen bond. A systematic, unambiguous,and periodic naming is obtained and applies to the majority of theattractive interactions formed by the elements of Groups 1, 2, 13–17and, possibly, to some interactions formed by the elements of otherGroups. [ABSTRACT FROM AUTHOR]

Halogen bonding is an emerging noncovalent interaction for constructing supramolecular assemblies. Though similar to the more familiar hydrogen bonding, four primary differences between these two interactions make halogen bonding a unique tool for molecular recognition and the design of functional materials. First, halogen bonds tend to be much more directional than (single) hydrogen bonds. Second, the interaction strength scales with the polarizability of the bond-donor atom, a feature that researchers can tune through single-atom mutation. In addition, halogen bonds are hydrophobic whereas hydrogen bonds are hydrophilic. Lastly, the size of the bond-donor atom (halogen) is significantly larger than hydrogen. As a result, halogen bonding provides supramolecular chemists with design tools that cannot be easily met with other types of noncovalent interactions and opens up unprecedented possibilities in the design of smart functional materials. [ABSTRACT FROM AUTHOR]

Thein situcryocrystallisation technique has been used to obtain four adducts between hexamethylphosphortriamide and 1,2-dihalotetrafluoroethanes having iodine, bromine and chlorine as halogen-bonding donor atoms. These systems allowed for a precise comparison of different C–X…O synthons. The effectiveness and reliability of the pharmacologically important C–Cl…O synthons are proven. [ABSTRACT FROM AUTHOR]

Although the understanding of intermolecular interactions, such as hydrogen bonding, is relatively well-developed, many additional weak interactions work both in tandem and competitively to stabilize a given crystal structure. Due to a wide array of potential applications, a substantial effort has been invested in understanding the halogen bond. Here, we explore the utility of multinuclear (13C, 14/15N, 19F, and 127I) solid-state magnetic resonance experiments in characterizing the electronic and structural changes which take place upon the formation of five halogen-bonded co-crystalline product materials. Single-crystal X-ray diffraction (XRD) structures of three novel co-crystals which exhibit a 1:1 stoichiometry between decamethonium diiodide (i.e., [(CH3)3N+(CH2)10N+(CH3)3][2 I−]) and different para-dihalogen-substituted benzene moieties (i.e., p-C6X2Y4, X=Br, I; Y=H, F) are presented. 13C and 15N NMR experiments carried out on these and related systems validate sample purity, but also serve as indirect probes of the formation of a halogen bond in the co-crystal complexes in the solid state. Long-range changes in the electronic environment, which manifest through changes in the electric field gradient (EFG) tensor, are quantitatively measured using 14N NMR spectroscopy, with a systematic decrease in the 14N quadrupolar coupling constant ( CQ) observed upon halogen bond formation. Attempts at 127I solid-state NMR spectroscopy experiments are presented and variable-temperature 19F NMR experiments are used to distinguish between dynamic and static disorder in selected product materials, which could not be conclusively established using solely XRD. Quantum chemical calculations using the gauge-including projector augmented-wave (GIPAW) or relativistic zeroth-order regular approximation (ZORA) density functional theory (DFT) approaches complement the experimental NMR measurements and provide theoretical corroboration for the changes in NMR parameters observed upon the formation of a halogen bond. [ABSTRACT FROM AUTHOR]

Abstract: Crystalline methylene-1,2-cyclopentane (E-1,2CP) random copolymers, containing up to 15% of cyclic units, are obtained in high yields by copolymerization of ethylene and 1,3-butadiene in the presence of rac-[CH2(3-methyl-1-indenyl)2]ZrCl2/MAO catalyst. The highly selective formation of trans methylene-1,2-cyclopentane units occurs by an intramolecular insertion of the double bond pendant from polymeril chain after an unusual primary vinyl insertion of 1,3-butadiene. Thermal properties and structure of E-1,2CP copolymers, as function of 1,2-cyclopentane molar content, are analyzed and compared with those of other ethylene copolymers. The variation in melting temperature and crystallinity observed in E-1,2CP copolymers is consistent with that observed for ethylene copolymers with comonomers bulkier than propylene. Moreover, the 1,2-cyclopentane units, as well as comonomers bulkier than propylene, cause only slight deformations of polyethylene orthorhombic unit cell parameters. These data are rationalized by assuming that 1,2-cyclopentane units, are confined in amorphous phase, while the polyethylene crystalline phase remains pure. [Copyright &y& Elsevier]

The syntheses and the crystal structures of new multitopicanion-bindingorganic ligands based on a benzenoid scaffold and bearing two or three2-iodo-imidazolium arms are reported. The quite short C–I···Br¯contacts observed in the solid state (0.77 times the normalized contacts)demonstrate the excellent halogen bonding donor ability of iodineatoms in 2-iodoimidazolium cations. The geometric features of obtainedbromide anion adducts afford valuable structural insights for thedesign of effective and selective multitopic anion receptors basedon halogen bonding. [ABSTRACT FROM AUTHOR]

Abstract: The single crystal structures of five co-crystals formed by the reaction of different iodide and bromide salts with di- and triiodoperfluorobenzenes (I-ArF) are reported. All of these perfluorocarbon-hydrocarbon systems are heteromeric three-component systems, wherein the weakly coordinating cations favour the formation of naked halides, which function as electron-donors towards the I-ArF modules. The analysis of the crystal structures shows that I−⋯I–ArF, and Br−⋯I–ArF halogen bonds (XBs) control the self-assembly of the obtained supramolecular architectures. 2D and 3D supramolecular networks have been obtained, wherein naked iodide and bromide anions act as tri-, tetra-, or pentadentate nodes. The selected examples demonstrate that I-ArF modules can be particularly robust and reliable tectons for XB-based coordination of halide ions and afford supramolecular architectures in a rational and predictable way. [ABSTRACT FROM AUTHOR]

This critical reviewdescribes how halocarbons can function as effective binding sites of anions viahalogen bonding, the noncovalent interaction whereby halogen atoms accept electron density. The focus is on the binding and coordination of oxyanions, by far the most numerous class of anions in organic chemistry. It is shown how a large variety of inorganic and organic oxyanions can form discrete adducts and 1D, 2D, or 3D supramolecular networks with chloro-, bromo-, and iodocarbons. Specific examples are discussed in order to identify new supramolecular synthons based on halogen bonding and to outline some general principles for the design of effective and selective receptors based on this interaction. The interaction allows for several other anions to self-assemble with halocarbons and mention is also given to the halogen bonding-based coordination of halides, polycyano- and polyoxometallates (72 references). [ABSTRACT FROM AUTHOR]

This special issue of Supramolecular Chemistry is dedicated to the B 14th International Symposium of Macrocyclic and Supramolecular Chemistry (ISMSC2019) b , which was successfully held in Lecce, Italy, from 2 to 6 June 2019. This symposium clearly showed how supramolecular chemistry is flourishing crossing traditional borders and moving towards new interdisciplinary areas of research at the interface between chemistry, medicine, biology, and materials science. As far as outreach is concerned, during ISMSC2019, a public lecture was delivered by Sir James Fraser Stoddart to present the world of supramolecular chemistry and the long scientific journey that has brought him to receive the Nobel Prize in Chemistry 2016. [Extracted from the article]

Abstract: A comparison between 13C NMR spectra of polymer solutions and Fourier transform infrared spectra of polymer films for several ethene–butadiene copolymers, including most butadiene as 1,2-cyclopropane and 1,2-cyclopentane units, is presented. This spectral comparison, also with the help of a low-molecular-mass model compound specifically synthesized for this purpose, has allowed to locate infrared absorbances associated with the cyclic comonomer units. In particular, a satisfactory calibration curve for evaluation of the amount of the reactive cyclopropane units, from the absorbance of the 1020cm−1 band, has been achieved. An analysis of 1,2-cyclopropane unit reactivity in annealed films, has also pointed out that the presence of remnants of the polymerization catalyst can produce large increase in cyclopropane reactivity. [Copyright &y& Elsevier]

Abstract: The possibility to obtain crosslinked polyethene (XLPE) from new ethene copolymers containing cyclopropane rings (C3), synthesized by ethene/1,3-butadiene copolymerizations with a hindered metallocene catalyst, has been explored. In particular, the thermal crosslinking of these copolymers, for C3 molar content in the range 0.3–2.7%, has been studied for annealing temperatures up to 200°C and compared with the thermal behavior of other ethene–butadiene copolymers. Only for the ethene–C3 copolymers, the annealing procedures in the temperature range 160–200°C lead to high gel fractions. These crosslinking processes occur in reasonable times and leave nearly unaltered the polymer crystallinity. Moreover, annealing procedures up to 140°C do not produce appreciable crosslinking. All these features suggest that these new copolymers could be suitable for possible industrial fabrication processes of XLPE. [Copyright &y& Elsevier]

• An impurities and stability testing study on three different commercial formulations, two formulations each, of sevoflurane was performed. • The analyzed samples show differences in quality and quantity of impurities. • In analyzed batches, the content in sevoflurane, the active principle, is >99.995%, >99.99%, and > 99.9995%, respectively. • Sevoflurane methyl ether and two monochlorinated polyfluoro-2-(fluoromethoxy)propanes were identified as impurities. We report an impurities and stability testing study on two different batches of three different commercial formulations of sevoflurane, the widely used fluorinated inhalation anesthetic agent. Our analyses focused on identifying the starting presence of volatile impurities as well as the formation of degradants after storage also under accelerated ageing conditions. We found that the analyzed samples show differences in quality and quantity of impurities as a likely consequence of the different manufacturing processes. Impurities may vary from one batch to the other of a given formulation, but in all case they are well below limits specified by regulatory agencies for clinical use, the content in sevoflurane being always > 99.99%. Fluoride anion concentrations were below 0.1 mg/L in all analyzed samples, consistent with no degradation occurring in the examined timeframe. [ABSTRACT FROM AUTHOR]

Review: 76 refs. [ABSTRACT FROM AUTHOR]

We describe the synthesis and characterization of new trimeric complexes obtained upon halogen-bond driven self-assembly of 1,4-diiodotetrafluorobenzene or α,ω– diiodoperfluoroalkanes, acting as XB-donors, with an alkoxystilbazole derivative functionalized with a methacrylate terminal group, acting as XB-acceptor. Despite the fact that the starting materials are not mesomorphic in nature, the obtained halogen-bonded complexes exhibit monotropic LC behaviour with smectic A phases possibly resulting from segregation between fluorocarbon and hydrocarbon chains. The obtained supramolecular mesogens possess reactive groups suitable for incorporation into liquid crystalline elastomeric actuators. [ABSTRACT FROM AUTHOR]

After the discovery of a few cases of lower enantioselectivity in the oxidation of aryl benzyl sulfides with hydroperoxides in the presence of a complex between titanium isopropoxide and ( S , S )-hydrobenzoin, a screening of the oxidation of new substrates that are related to the structures that gave low ee values, was performed. From this screening, we confirmed that only a few sulfides remain as exceptions within a framework of exceptionally high stereoselectivity of the oxidation reaction. Moreover, the exceptions are clearly identified and are connected to particular coordinating moieties present on the aryl groups. [ABSTRACT FROM AUTHOR]

Haloprogin is a topical antifungal agent. Its structure does not contain any of the functional groups typically exploited in hydrogen bond based co-crystal design. On the other hand, its 1-iodoalkyne moiety is nicely tailored to a crystal engineering strategy based on halogen bonding. Here we describe the formation of three polymorphs of haloprogin and of three co-crystals that this active pharmaceutical ingredient forms with both neutral and ionic co-crystal formers. The halogen bond plays a major role in all of the six structures and the interaction is thus confirmed to be a valuable tool which may complement the hydrogen bond when polymorphs and co-crystals of active pharmaceutical ingredients are pursued. [ABSTRACT FROM AUTHOR]

Hybrid organic–inorganic halide perovskites (HOIHPs) have recently emerged as a flourishing area of research. Their easy and low‐cost production and their unique optoelectronic properties make them promising materials for many applications. In particular, HOIHPs hold great potential for next‐generation solar cells. However, their practical implementation is still hindered by their poor stability in air and moisture, which is responsible for their short lifetime. Optimizing the chemical composition of materials and exploiting non‐covalent interactions for interfacial and defects engineering, as well as defect passivation, are efficient routes towards enhancing the overall efficiency and stability of perovskite solar cells (PSCs). Due to the rich halogen chemistry of HOIHPs, exploiting halogen bonding, in particular, may pave the way towards the development of highly stable PSCs. Improved crystallization and stability, reduction of the surface trap states, and the possibility of forming ordered structures have already been preliminarily demonstrated. [ABSTRACT FROM AUTHOR]

Hybrid organic–inorganic halide perovskites (HOIHPs) have recently emerged as a flourishing area of research. Their easy and low‐cost production and their unique optoelectronic properties make them promising materials for many applications. In particular, HOIHPs hold great potential for next‐generation solar cells. However, their practical implementation is still hindered by their poor stability in air and moisture, which is responsible for their short lifetime. Optimizing the chemical composition of materials and exploiting non‐covalent interactions for interfacial and defects engineering, as well as defect passivation, are efficient routes towards enhancing the overall efficiency and stability of perovskite solar cells (PSCs). Due to the rich halogen chemistry of HOIHPs, exploiting halogen bonding, in particular, may pave the way towards the development of highly stable PSCs. Improved crystallization and stability, reduction of the surface trap states, and the possibility of forming ordered structures have already been preliminarily demonstrated. [ABSTRACT FROM AUTHOR]

We carried out a systematic evaluation of the packing forces in co-crystals featuring monoiodo- and diiodo-perfluoroalkanes and 1,2,4-oxadiazoles through single crystal X-ray diffraction and theoretical analysis. The molecules assemble via a combination of halogen bonding and specific dispersive interactions involving the perfluorinated units. We quantitatively elucidated the nature and strength of such interactions through solid-state calculations and Hirshfeld surface analysis. One of the co-crystals, formed by two monoiodoperfluorodecane molecules, the longest perfluorinated chain ever solved at the atomic level, allowed us to fully highlight the role of fluorous interactions. [ABSTRACT FROM AUTHOR]

Abstract: The supramolecular organization in six solid assemblies involving iodo- and bromoperfluoroarene derivatives is described. Single crystal X-ray analyses show that the formation of the supramolecular architectures is controlled by I−⋯Br–ArF, I−⋯I–ArF, Br−⋯I–ArF, and Cl−⋯I–ArF halogen bondings thus proving the X−⋯X′–ArF supramolecular synthon, where X can be the same as or different from X′, is particularly robust. In five of the described architectures halide anions form two halogen bondings and form infinite chains wherein dihaloperfluoroarenes, which function as bidentate electron acceptors, and halide anions, which function as bidentate electron donors, alternate. This behaviour shows halide anions have a fair tendency to work as bidentate halogen bonding acceptors. [Copyright &y& Elsevier]

2-Iodoethynylpyridine and 2-iodoethynyl-1-methyl-imidazole self-assemble under halogen-bonding control into discrete macrocycles, viz. supramolecular triangles. [ABSTRACT FROM AUTHOR]

Although intensively studied, the high-resolution crystal structure of the peptide DFNKF, the core-segment of human calcitonin, has never been described. Here we report how the use of iodination as a strategy to promote crystallisation and facilitate phase determination, allowed us to solve, for the first time, the single-crystal X-ray structure of a DFNKF derivative. Computational studies suggest that both the iodinated and the wild-type peptides populate very similar conformations. Furthermore, the conformer found in the solid-state structure is one of the most populated in solution, making the crystal structure a reliable model for the peptide in solution. The crystal structure of DFNKF(I) confirms the overall features of the amyloid cross-β spine and highlights how aromatic-aromatic interactions are important structural factors in the self-assembly of this peptide. A detailed analysis of such interactions is reported. [ABSTRACT FROM AUTHOR]

The title reaction generally proceeds with high yields and provides the products with high stereoselectivity. [ABSTRACT FROM AUTHOR]

Hydrophobins are natural surfactant proteins endowed with exceptional surface activity and film-forming capabilities and their use as effective “fluorine-free fluorosurfactants” has been recently reported. In order to increase their fluorophilicity further, here we report the preparation of a unique fluorous-modified hydrophobin, named F-HFBI. F-HFBI was found to be more effective than its wild-type parent protein HFBI at reducing interface tension of water at both air/water and oil/water interfaces, being particularly effective at the fluorous/water interface. F-HFBI was also found to largely retain the exceptionally good capability of forming strong and elastic films, typical of the hydrophobin family. Further studies by interface shear rheology and isothermal compression, alongside Quartz Crystal Microbalance and Atomic Force Microscopy, demonstrated the tendency of F-HFBI to form thicker films compared to the wild-type protein. These results suggest that F-HFBI may function as an effective compatibilizer for biphasic systems comprising a fluorous phase. [ABSTRACT FROM AUTHOR]

The article presents a study related to fluorine (19F) Magnetic Resonance Imaging (MRI). Topics discussed include fluorinated tracers for 19F MRI such as molecular and polymeric tracers, fluorinated metallic nanoparticles, multimodal imaging agents, applications of 19F MRI such as targeted imaging of physiological factors, targeted drug delivery and cell trafficking,.

The peptide bond model N-methylacetamide self-assembles with a range of dihalotetrafluorobenzenes forming co-crystals that all show the occurrence of orthogonal hydrogen and halogen bonds. [ABSTRACT FROM AUTHOR]

19F-MRI offers unique opportunities to image diseases and track cells and therapeutic agents in vivo. Herein we report a superfluorinated molecular probe, herein called PERFECTA, possessing excellent cellular compatibility, and whose spectral properties, relaxation times, and sensitivity are promising for in vivo 19F-MRI applications. The molecule, which bears 36 equivalent 19F atoms and shows a single intense resonance peak, is easily synthesized via a simple one-step reaction and is formulated in water with high stability using trivial reagents and methods. [ABSTRACT FROM AUTHOR]

Abstract: Herein we present a methodology for improving the power conversion efficiency of organic solar cells made by photoactive layers of poly(3-hexylthiophene) (P3HT) and phenyl-C61 butyric acid methyl ester (PCBM) of non-optimized microstructure. In our study we achieve a 47% improvement in the power conversion efficiency (PCE) of the device by utilizing a thiophene-based quinoid (QBT) moiety as the third component in the P3HT:PCBM:QBT photoactive layers. Based on a set of independent characterization experiments we address the QBT composition dependent photophysical, electrical, thermal, structural and morphology-related properties of the ternary photovoltaic P3HT:PCBM:QBT system for elucidating the origin of the PCE improvement. In small amounts (0.3–0.6wt%), QBT serves as a nucleation agent, it enlarges the size of the P3HT crystallites by 15% and it increases the fraction of well-ordered P3HT chains in the P3HT:PCBM:QBT layer. The improved microstructure of the photoactive layer in combination with the QBT-assisted photo-induced hole transfer step from PCBM to P3HT, lead to an increase of the charge photogeneration yield in the P3HT:PCBM:QBT triple bulk heterojunction. The relatively small optical gap of QBT facilitates a resonant energy transfer step from the photoexcited PCBM to the QBT followed by a charge transfer process between QBT and the P3HT matrix. Based on these findings we propose general guidelines for the design of next generation functional additives to be used in organic photovoltaics. [Copyright &y& Elsevier]

[Display omitted] • A multi-branched fluorinated carboxylic acid (BRFA) was esterified with cellulose. • Hydrophobic and ductile materials were obtained due to BRFA esters. • All cellulose-BRFA esters showed a single glass transition at −11 °C. • Water uptake and breathability were similar to materials used for textile. Cellulose ester films were prepared by esterification of cellulose with a multibranched fluorinated carboxylic acid, "BRFA" (BRanched Fluorinated Acid), at different anhydroglucose unit:BRFA molar ratios (i.e. , 1:0, 10:1, 5:1, and 1:1). Morphological and optical analyses showed that cellulose-BRFA materials at molar ratios 10:1 and 5:1 formed flat and transparent films, while the one at 1:1 M ratio formed rough and translucent films. Degrees of substitution (DS) of 0.06, 0.09, and 0.23 were calculated by NMR for the samples at molar ratios 10:1, 5:1, and 1:1, respectively. ATR-FTIR spectroscopy confirmed the esterification. DSC thermograms showed a single glass transition, typical of amorphous polymers, at −11 °C. The presence of BRFA groups shifted the mechanical behavior from rigid to ductile and soft with increasing DS. Wettability was similar to standard fluoropolymers such as PTFE and PVDF. Finally, breathability and water uptake were characterized and found comparable to materials typically used in textiles. [ABSTRACT FROM AUTHOR]

The X-ray diffraction analysis on single crystals obtained from the self-assembly of 1,8-diiodoperfluorooctane 1 with the tetraazahelicene derivative 2 revealed a site-selective pattern of halogen bonds (XBs) in the solid state. Indeed, two non-equivalent XBs drive the formation of an indefinitely repeating pentameric (1)3·(2)2 unit. Interestingly, the N...I-C bonding formation occurred selectively on the pyridazinic/cinnolinic nitrogen atoms of the tetraazahelicene unit, which were preferred over the pyridinic/quinolinic ones. On the basis of molecular electrostatic potential and molecular orbital analyses, DFT calculations predicted and explained well this site-selective XB formation, thus demonstrating to be efficient tools for the prediction of the XB site selectivity in similar polynitrogen systems. [ABSTRACT FROM AUTHOR]

Invited for the cover of this issue is the group of Pierangelo Metrangolo at the Politecnico di Milano. The image depicts the steric zipper formed by the amyloidogenic peptide, DFNKF. Read the full text of the article at . [ABSTRACT FROM AUTHOR]

The amyloidogenic peptide, DFNKF, forms a steric zipper. Iodination of this widely studied sequence facilitated crystallization and allowed its high‐resolution single crystal structure determination for the first time. The structure unveils the importance of aromatic–aromatic interactions in stabilizing the amyloid self‐assembly. The amino acid side‐chains of facing β‐strands (shown in red and green, respectively) interdigitate like the teeth of a zipper, similar to that of blue jeans. More information can be found in the Full Paper by P. Metrangolo et al. on page 2051 ff. [ABSTRACT FROM AUTHOR]