Extensive Intermolecular Interactions Research Articles

Exploring a Solvent Dependent Strategy to Control Self-Assembling Behavior and Cellular Interaction in Laminin-Mimetic Short Peptide based Supramolecular Hydrogels.

Self-assembled hydrogels, fabricated through diverse non-covalent interactions, have been extensively studied in regenerative medicines. Inspired from bioactive functional motifs of ECM protein, short peptide sequences have shown remarkable abilities to replicate the intrinsic features of the natural extracellular milieu. In this direction, we have fabricated two short hydrophobic bioactive sequences derived from the laminin protein i. e., IKVAV and YIGSR. Based on the substantial hydrophobicity of these peptides, we selected a co-solvent approach as a suitable gelation technique that included different concentrations of DMSO as an organic phase along with an aqueous solution containing 0.1 % TFA. These hydrophobic laminin-based bioactive peptides with limited solubility in aqueous physiological environment showed significantly enhanced solubility with higher DMSO content in water. The enhanced solubility resulted in extensive intermolecular interactions that led to the formation of hydrogels with a higher-order entangled network along with improved mechanical properties. Interestingly, by simply modulating DMSO content, highly tunable gels were accessed in the same gelator domain that displayed differential physicochemical properties. Further, the cellular studies substantiated the potential of these laminin-derived hydrogels in enhancing cell-matrix interactions, thereby reinforcing their applications in tissue engineering.

In-situ polymerization of PANI on hydrogel electrolyte enabling all-in-one supercapacitors mechanically stable at low temperatures

Flexible supercapacitors are becoming increasingly popular in portable and wearable electronics. However, conventional flexible supercapacitors typically exhibit laminated multilayer configurations, inevitably causing the irreversibly interfacial slippage or even delamination under deformations. In this study, an all-in-one supercapacitor with highly integrated structure is constructed through in-situ polymerization of conducting polyaniline on a hydrogel electrolyte. Because the extensive intermolecular interactions between polymer chains and nanoparticles can dissipate energy, the prepared hydrogel electrolyte shows outstanding mechanical properties. At the same time, the introduction of ethylene glycol endows hydrogel electrolyte with a higher binding energy between ethylene glycol and water molecule to break hydrogen bonds between water molecules, thus enabling the hydrogel electrolyte to be anti-freezing. Benefiting from the novel all-in-one structure, the device maintains 100% and 97.5% of its initial capacitance after 6000 charging/discharging cycles at room temperature and −20 ℃ respectively. Besides, the highly integrated structure endows the device with excellent capacitance retentions of 99.2% and 97.5% after 5000 bending and stretching cycles respectively. More importantly, the device still works well under bending, twisting, and stretching states at −20 ℃. This work provides an inspiring pathway to develop flexible all-in-one supercapacitors and broadens the practical application range of energy storage devices in various fields.

Structural basis for the broad and potent cross-reactivity of an N501Y-centric antibody against sarbecoviruses.

More than 80% of SARS-CoV-2 variants, including Alpha and Omicron, contain an N501Y mutation in the receptor-binding domain (RBD) of the spike protein. The N501Y change is an adaptive mutation enabling tighter interaction with the human ACE2 receptor. We have developed a broadly neutralizing antibody (nAb), D27LEY, whose binding affinity was intentionally optimized for Y501. This N501Y-centric antibody not only interacts with the Y501-containing RBDs of SARS-CoV-2 variants, including Omicron, with pico- or subnanomolar binding affinity, but also binds tightly to the RBDs with a different amino acid at residue 501. The crystal structure of the Fab fragment of D27LEY bound to the RBD of the Alpha variant reveals that the Y501-containing loop adopts a ribbon-like topology and serves as a small but major epitope in which Y501 is a part of extensive intermolecular interactions. A hydrophobic cleft on the most conserved surface of the RBD core serves as another major binding epitope. These data explain the broad and potent cross-reactivity of this N501Y-centric antibody, and suggest that a vaccine antigenic component composed of the RBD core and a part of receptor-binding motif (RBM) containing tyrosine at residue 501 might elicit broad and potent humoral responses across sarbecoviruses.

Supramolecular association of (1,4-phenylenedimethanaminium) bis(perchlorate) monohydrate: A combined experimental and theoretical study

This paper deals with the crystal structure of the new material (1,4-phenylenedimethanaminium) bis(perchlorate) monohydrate, (C8H14N2)(ClO4)2·H2O that was prepared in crystalline form by solvent evaporation method at room temperature. Single crystal X-ray diffraction analysis shows that this compound crystallizes in the monoclinic system, with the space group P21/c. The title structure benefits from extensive intermolecular interactions such as C-H… π interactions and hydrogen bonds which are the major forces to make it more stable in the solid-state.The interactions in the solid-state have been also studied using Hirshfeld surface analyses (dnorm, curvedness, and shape index), as well as its 2D fingerprint plots. To reinforce experimental results, DFT calculations have been performed via the B3LYP/LanL2DZ method. HOMO-LUMO energies and the chemical quantum descriptors were taken into account. AIM and RDG analysis has been explored to reveal the steadiness of the molecule. Molecular electrostatic potential inspection has also been submitted in the study.

Growth, single crystal investigation and physico-chemical properties of thiocyanate coordination compounds based on 1,4-dimethylpiperazine

Four new hybrid organic-inorganic compounds based on 1,4-cimethylpiperazinium, [C6H16N2M(SCN)4]·2H2O (M = Co(1), Ni(2)), [(C6H16N2)Cd(SCN)4] (3), and [C6H16N2(SCN)2] (4), were prepared by the evaporation crystal growth method at room temperature. These complexes were characterized by their X-ray crystal structure; spectroscopic methods such as FTIR analysis supported the presence of surface ligand groups of thiocyanates and identified the vibrational absorption bands. The piperazinium ring adopts a slightly distorted chair conformation which is more stable because it does not have any steric hindrance or steric repulsion between the hydrogen bonds and which favors the entities coordination. Intermolecular interactions were investigated by Hirshfeld surfaces and contact enrichment tools. In the crystals, extensive intermolecular interactions have been used in the self-assembly of motifs, including strong H-bonds. The components are linked mainly by N-H…S, O-H…S, and N-H…N hydrogen-bonding interactions, resulting in a three-dimensional network. The arrangements of the anions and cations in the solids are governed not only by the size and symmetry of the cations, but also by the non-covalent bonds in the crystal structures.

Intra- and Intermolecular Synergistic Engineering of Aggregation-Induced Emission Luminogens to Boost Three-Photon Absorption for Through-Skull Brain Imaging.

Three-photon fluorescence microscopic (3PFM) bioimaging is a promising imaging technique for visualizing the brain in its native environment thanks to its advantages of high spatial resolution and large imaging depth. However, developing fluorophores with strong three-photon absorption (3PA) and bright emission that meets the requirements for efficient three-photon fluorescence microscopic (3PFM) bioimaging is still challenging. Herein, four bright fluorophores with aggregation-induced emission features are facilely synthesized, and their powders exhibit high quantum yields of up to 56.4%. The intramolecular engineering of luminogens endows (E)-2-(benzo[d]thiazol-2-yl)-3-(7-(diphenylamino)-9-ethyl-9H-carbazol-2-yl)acrylonitrile (DCBT) molecules with bright near-infrared emission and large 3PA cross sections of up to 1.57 × 10-78 cm6 s2 photon-2 at 1550 nm, which is boosted by 3.6-fold to 5.61 × 10-78 cm6 s2 photon-2 in DCBT dots benefiting from the extensive intermolecular interactions in molecular stacking. DCBT dots are successfully applied for 3PFM imaging of brain vasculature on mice with a removed or intact skull, providing images with high spatial resolution, and even small capillaries can be recognized below the skull. This study will inspire more insights for developing advanced multiphoton absorbing materials for biomedical applications.

Syntheses and structure characterization of seven inorganic-organic hybrids based on N-Brønsted bases and perhalometallates

Seven organic-inorganic hybrids [(H2L1)3(Bi2Br9)(BiBr6)(H2O)] (1) (L1 = N,N,N′,N′-tetramethylethylenediamine), [(HL2)3(SbCl5)] · Cl (2) (L2 = 4-chlorobenzylamine), [(HL3)3(SbCl4)] · Cl2 (3) (L3 = 2,6-dimethylaniline), [(HL3)2(ZnCl4)] · 2H2O (4), [(HL4)4(Bi2Br10)] (5) (L4 = 2-methylquinoline), [(HL4)2(SbCl5)] (6) and [(H2L5)2(SbCl5)2] · H2O (7) (L5 = bis(N-imidazolyl)methane) were prepared and characterized by IR, XRD, EA and TG analysis. XRD analysis told that all complexes were built from non-covalent bonds between the cations and the perhalometallates anions. The lattice H2O also played crucial role in structure extension in the respective hybrids. Extensive intermolecular interactions have been used in the self-assembly of diverse motifs, ranging from strong X-H···Y (X = O, N; Y = Br, Cl, O) H-bonds to weak CH-M (M = Cl, Br), CH2-M (M = Cl, Br), CH3-M (M = O, Cl, Br), CH3-CH3/CH3-CH/CH2-CH/CH-CH, Cl-Cl, CH3-π and π-π associations. Among them, 3 D architectures are found in 1–2 and 4–7, but only 2 D motif is appeared in 3. The arrangements of the anions and cations in the solid mode are ruled not only by the size and symmetry of the cations, but also by the non-covalent bonds in the crystals.

Syntheses and structural characterization of eight inorganic-organic hybrid solids based on N-Brønsted bases and halometallates of Zn, Cu, Sb and Bi

Eight organic-inorganic hybrid salts [(HL1)(SbCl4)] (1) (L1 = N,N-dimethylbenzylamine), [(HL2)2(ZnCl4)] (2) (L2 = 4-chlorobenzylamine), [(HL2)(L2)(CuCl3)(H2O)2] (3), [(HL3)2(Sb2OCl6)] (4) (L3 = quinoline), [(HL4)4(Bi2Cl10)] (5) (L4 = 2-methylquinoline), [(HL5)(SbCl4)] (6) (L5 = 5,7-dimethyl-1,8-naphthyridine-2-amine), [(H2L6)(SbCl5)] (7) (L6 = 3,6-bis(imidazol-1-yl)pyridazine) and [(H2L7)2(CuBr4)2] · 7H2O (8) (L7 = di(2-benzimidazol-1-ylethyl)ether) were prepared and characterized by IR, XRD, EA and TG analysis. XRD analysis told that all of the complexes were 3 D net built from non-covalent bonds from the cations and the halometallates. The aryl rings of the cations in all of the compounds are essentially planar. The H2O also had crucial role in structure extension in 3 and 8. Extensive intermolecular interactions have been used in the self-assembly of diverse motifs, ranging from strong N-H···X (X = Br, Cl), N-H···O, N-H···N, O-H···O, O-H···Br H-bonds to weak CH2···O, CH3-Cl/CH2-Cl/CH-Cl, Cl-Cl, O-Br, CH3-π, CH2-π, Cl-π and π-π associations. The arrangements of the anions and cations in the solid are ruled not only by the size and symmetry of the cations, but also by the non-covalent bonds in the crystal structures.

Zinc(II) complexes of N(4)-monosubstituted thiosemicarbazones derived from pyridine-2-carbaldehyde: Structural and spectroscopic studies

• Five new Zn(II) complexes of two thiosemicarbazone ligands are reported. • Spectroscopic studies reveal thione and deprotonated thiolate coordination of the ligands. • Crystal structure of a complex shows distorted square pyramidal geometry around Zn(II). • Extensive intermolecular interactions are quantified by Hirshfeld surface analysis. Five zinc(II) complexes of pyridine-2-carbaldehyde-N(4)-p-methoxyphenyl thiosemicarbazone [HL 1 ] and pyridine-2-carbaldehyde-N(4)-2-phenylethyl thiosemicarbazone [HL 2 ] were synthesized and physico-chemically characterized by means of partial elemental analyses, molar conductance measurements, electronic and infrared spectral studies. The complexes were given the formulae as [Zn(HL 1 )Cl 2 ] ( 1 ), [Zn(HL 1 ) 2 ] ⋅ (NO 3 ) 2 ( 2 ), [Zn(L 2 )Br] ⋅ C 2 H 5 OH ( 3 ), [Zn 2 (L 2 ) 2 SO 4 ] ⋅ 2H 2 O ( 4 ) and [Zn(HL 2 )Cl 2 ] ( 5 ). In the complexes 1, 2 and 5 the thiosemicarbazones are coordinated in the thione form, while complexes 3 and 4 were formed through the coordination of the thiolate form of HL 2 . The structure of the complex 1 is solved by single crystal X-ray crystallography and was found to be a distorted square pyramidal geometry around Zn(II). Extensive intermolecular hydrogen bonding interactions found in the packing of the crystal lattice are mutually complemented and reinforced by π … π stacking interactions, which are further confirmed quantitatively by Hirshfeld surface analysis.

In vivo reconstitution finds multivalent RNA-RNA interactions as drivers of mesh-like condensates.

Liquid-like condensates have been thought to be sphere-like. Recently, various condensates with filamentous morphology have been observed in cells. One such condensate is the TIS granule network that shares a large surface area with the rough endoplasmic reticulum and is important for membrane protein trafficking. It has been unclear how condensates with mesh-like shapes but dynamic protein components are formed. In vitro and in vivo reconstitution experiments revealed that the minimal components are a multivalent RNA-binding protein that concentrates RNAs that are able to form extensive intermolecular mRNA-mRNA interactions. mRNAs with large unstructured regions have a high propensity to form a pervasive intermolecular interaction network that acts as condensate skeleton. The underlying RNA matrix prevents full fusion of spherical liquid-like condensates, thus driving the formation of irregularly shaped membraneless organelles. The resulting large surface area may promote interactions at the condensate surface and at the interface with other organelles.

Syntheses and structural characterizations of six ionic inorganic-organic salts from heterocyclic aromatic bases and tetrachlorometallates of Zn, Cu and Cd

Six organic-inorganic hybrid salts, ([(HL1)2(CdCl4)(H2O)] (1) (L1 = 2-(imidazol-1-yl)-1-phenylethanone), [(HL2)2(ZnCl4)(H2O)] (2) (L2 = 6-bromobenzo[d]thiazol-2-amine), [(H2L3)2(CdCl4)2(CH3OH)] (3) (L3 = bis(N-imidazolyl)methane), [(H2L4)(ZnCl4)(H2O)2] (4) (L4 = bis(N-imidazolyl)butane), [(H2L5)2(CuCl4)2]·7H2O (5) (L5 = di(2-benzimidazol-1-ylethyl)ether) and [(H2L6)4(ZnCl4)4]·7H2O (6) (L6 = 1,2-bis(2-benzimidazolyl)-1,2-ethanediol)), were prepared and characterized by IR, XRD, EA and TG analyses. The aryl rings of the cations in all salts are essentially planar. XRD analysis indicated that all of the complexes are built from non-covalent bonds between the cations and the tetrachlorometallate anions. The lattice solvent (H2O/CH3OH) molecules also played crucial roles in structure extension of all salts. Extensive intermolecular interactions have been used in the self-assembly of motifs, ranging from strong X-H···Y (X = O, N; Y = Cl, O) H-bonds to weak CH···A (A = O, Cl, Br), CH2···A (A = O, Cl), O···O, Cl···O, Cl···S, Cl···π, Br···Cl, CH3···π and π···π associations. 3 D architectures are found in 1 and 3-6, but only a 2 D architecture appeared in 2. The arrangements of the anions and cations in the solid are governed not only by the size and symmetry of the cations, but also by the non-covalent bonds in the crystal structures.

Mono- and poly-nuclear copper(II) carboxylates with flourous ligands: Synthesis, structure and improved properties

Polynuclear copper(II) complexes [Cu(para-fluorophenyl acetate)2]n (1) and [Cu(para-nitrophenyl acetate)2]n (2) were converted in-situ to mono-nuclear complexes [Cu(para-fluorophenyl acetate)2(1,10-Phenanthroline)(H2O)] (3) and [Cu(para-nitrophenyl acetate)2(2,2́-Bipyridine)(H2O)].3H2O (4). The complexes were isolated in quantitative yield, purified and characterized using FT-IR, absorption, electrochemical, electron paramagnetic resonance and powder XRD techniques yielding results in accordance with structural data. Structures of 1 and 2 consist of directly interlinked paddlewheel units with square pyramidal geometry while those of 3 and 4 are mononuclear with octahedral and square pyramidal geometry around Cu. Fluorinated complexes 1 and 3 were found to consist of extensive intermolecular interactions while 2 and 4 contained no such interactions. Their optical band gap was around 1.4 eV which indicates semiconducting property of the complexes. Moreover, the flourous complex 3 was found to possess significant activity against Bacillus subtilis and Escherichia coli and good activity against Micrococcus luteus. A similar trend was observed in their DNA-binding potency studied through absorption as well as electrochemical solution studies yielding Kb values 1.494 × 104, 1.342 × 104 and 1.411 × 104 M−1 and 7.547 × 104, 2.457 × 104 and 3.667 × 104 M−1 for 1–3, respectively. The electronic structures of the complexes elucidated using density functional theory ab-initio calculations confirmed the Intermediate states which play important role in the enhancement of the optoelectronic properties. The structure and properties of the flourous complexes were found different than their non-flourous analogues which was attributable to fluorine.

Two fluorophore compounds based on 1, 8-naphthalimide: Synthesis, crystal structure, and optical properties

Two new 1, 8-naphthalimide-based fluorophore compounds, 4-piperazinyl-N-(4-Pyr-idinyl)-1, 8-naphthalimide (RB1) and 4-phenyl-N-(3-hydroxyphenyl)-1, 8-naphth- alimide (RB2) were synthesized via two-steps nucleophilic substitution reactions and Suzuki coupling reaction. The chemical structures of the title compounds were characterized by 1H NMR, 13C NMR, HRMS and FT-IR spectral analysis. Thermogravimetric analysis results show that the degradation temperatures of two compounds were about 300 °C. The single-crystal XRD analysis revealed that both RB1 and RB2 crystallize in the monoclinic P21/c (No. 14) space group, with lattice parameters of RB1a = 15.3016(10), b = 15.4468(9), c = 7.1919(4) Å, β = 95.384(2)°, V = 1692.38(18) Å3, Z = 4 and RB2a = 16.1990(3), b = 15.9460(3), c = 7.5870(15) Å, β = 98.718(5)°, V = 1937.2(7) Å3, Z = 4 respectively. Both crystals of two compounds have parallel offset stacking with extensive intermolecular interactions (hydrogen bond, C–H⋅⋅⋅π interaction), which are correspondence with the molecular packing of J-aggregation. The UV–vis and fluorescence properties of two compounds in different solvents were investigated, indicated that ICT characteristics of RB1 in organic solvents. Moreover, RB1 crystal can excite the strong green fluorescence with good thermal and optical stability qualifying it as a potential application in the fields of crystal luminescent functional materials.

Supramolecular salts of 5,7-dimethyl-1,8-naphthyridine-2-amine and acids through classical H-Bonds and other intermolecular interactions

This article demonstrates 5,7-dimethyl-1,8-naphthyridine-2-amine based organic salts formation of crystalline solids 1–9, in which the acidic units have been integrated via a variety of non-covalent bonds. Addition of equivalents of the acidic units to the solution of 5,7-dimethyl-1,8-naphthyridine-2-amine generates the single protonated species which direct the anions. The nine compounds crystallize as their salts with the acidic H transferred to the aromatic N of the 5,7-dimethyl-1,8-naphthyridine-2-amine. In 2, 3, 4, and 7 the methyl substituted N-rings were protonated, while others were protonated at the NH2 substituted N-ring. All salts have been characterized via IR, mp, EA and XRD technique. The major driving force for the salt formation is attributed to the classical H-bonds from 5,7-dimethyl-1,8-naphthyridine-2-amine and the acids. Other extensive intermolecular interactions also play great functions in space association of the molecular assemblies in the relevant crystals. The common R22(8) graph set has been observed in all salts due to the H-bonds and other intermolecular interactions, except 2, 4, and 6. For the synergistic interactions of the various non-covalent bonds, all salts displayed 3D structures.

Structural characterization of the bent metallocenes, [C5H3(SiMe3)2]2Sm and [C5H3(CMe3)2]2Ln (Ln = Eu, Sm), and the mono(cyclopentadienyl) tetraphenylborate complex, [C5H3(CMe3)2]Eu(μ-η6:η1-Ph)2BPh2

Efforts to generate Ln2+ precursors suitable for reduction to Ln1+ compounds have provided the X-ray crystal structures of Cp″2Sm, 1-Sm, and Cptt2Ln, 2-Ln [Ln = Eu, Sm; Cp″ = C5H3(SiMe3)2; Cptt = C5H3(CMe3)2], allowing direct comparisons of these similar cyclopentadienyl rings in Ln2+ complexes. In the solid state, these complexes exhibit extensive intermolecular interactions. Bridging cyclopentadienyl ligands are found with both types of ligands and the Cp″ ligand engages in silyl-methyl-metal interactions. The compounds display bent metallocene structures with (ring centroid)–Ln–(ring centroid) angles ranging from 110.0° to 147.9°. Complex 2-Eu reacts with [HNEt3][BPh4] to form the mono(cyclopentadienyl) tetraphenylborate complex, (η5-Cptt)Eu(μ-η6:η1-Ph)2BPh2, 3-Eu, in which the Eu2+ ion is coordinated by three carbocyclic ligands in a nearly trigonal planar geometry.

Adsorption, Assembly, and Oligomerization of Aspartic Acid on Pd(111)

The surface chemistry of l-aspartic acid is studied on Pd(111) in ultrahigh vacuum using reflection absorption infrared spectroscopy (RAIRS) and scanning tunneling microscopy (STM) as a function of sample temperature and coverage. Density functional theory (DFT) calculations are carried out to supplement the experimental results. At low temperatures, the dominant surface species was found to be monoaspartate species at all the experimental coverages. The monoaspartate species undergo extensive intermolecular hydrogen-bonding interactions and form extended two-dimensional ordered structures, forming either a honeycomb pattern or linear-row structures. At room temperature, aspartic acid undergoes a self-polymerization reaction to form oligosuccinimide networks, although some individual monoaspartate species are also observed.

Effects of Anionic Geometries on Hydrogen-Bonding Networks of 1-(4-pyridyl) Piperazine

A series of new salts have been obtained by the self-assembly of 1-(4-pyridyl) piperazine and inorganic ions or metal chloride in the hydrochloric acid medium, i.e. (C9H15N3 2+)·(Cl−)2 (1) (C9H15N3 2+)·(NO3 −)2 (2), (C9H15N3 2+)·(CuCl4 2−) (3), (C9H15N3 2+)·(CoCl4 2−) (4), (C9H15N3 2+)·(ZnCl4 2−) (5), {(C9H15N3 2+)·[Mn(H2O)2Cl4 2−]}·H2O (6), (C9H14N3 +)·(Sb2Cl7 −) (7) and (C9H15N3 2+)·(PbCl4 2−) (8). Structural analyses indicate that different anionic structure (e.g. spherical, trigonal planar, tetrahedral, octahedral, polyhedral and chain) can induce the formation of diverse architectures, influencing the crystallization ratio, the protonated number and the final structures. Extensive intermolecular interactions have been utilized for the self-assembly of diverse frameworks, ranging from strong X–H···Y (X=O, N; Y=Cl, O) hydrogen bonds to weak C–H···M (M=O, Cl) interactions. Among them, 3D hydrogen-bonding architectures are observed in 1–7 but only a 2D hydrogen-bonding architecture is observed in 8. Salt 6 crystallizes with water molecules but the others do not. Interestingly, the anions of salts 7 and 8 are dinuclear and 1D complex ions, respectively. A series of supramolecular salts have been obtained by the self-assembly of 1-(4-pyridyl) piperazine and inorganic acids or metal chloride in the hydrochloric acid medium. Structural analyses indicate that different anionic structure (e.g. spherical, trigonal planar, tetrahedral, octahedral, polyhedral and chain) can induce the formation of diverse supramolecular architectures, influencing the crystallization ratio, the protonated number and the final structures.

Mechano‐Responsive, Thermo‐Reversible, Luminescent Organogels Derived from a Long‐Chained, Naturally Occurring Fatty Acid

The gelating ability of an α-diketo derivative of oleic acid, 9,10-dioxooctadecanoic acid (DODA), is investigated. DODA can gelate aromatic liquids and many other organic liquids. By contrast, none of the liquids examined can be gelated by the methyl ester of DODA. DODA is a more efficient gelator than stearic acid and the monoketo derivative due to its more extensive intermolecular dipole-dipole interactions. Formation of organogels of DODA can be induced by both thermal and mechanical stimuli, during which the luminescent and mechanical properties can be modulated significantly. The emission from DODA in 1-octanol exhibits a large, reversible, hypsochromic shift (≈25 nm) between its thermally cycled gel and sol states. The emission changes have been exploited to probe the kinetics of the aggregation and deaggregation processes. DODA is the simplest gelator of which we are aware that exhibits a reversible shift in the emission. Although the self-assembled fibrillar networks of the DODA gels in 1-octanol, benzonitrile, or silicone oil are crystalline, isothermal mechanical cycling between the gel and the sol states is rapid and can be repeated several times (i.e., they are thixotropic). The single-crystal structure of DODA indicates that extended intermolecular dipole-dipole interactions are crucial to the thermal and mechanical formation of DODA gels and the consequential changes in emissive and mechanical properties. From analyses of structural information, gelator packing, and morphology differences, we hypothesize that the mechanical destruction and reformation of the gel networks involves interconversion between the 3D networks and 1D fiber bundles. The thermal processes allow the fibrillar 3D networks and their 0D components (i.e., isolated molecules or small aggregates of DODA) to be interconverted. These results describe a facile approach to the design of mechano-responsive, thermo-reversible gels with control over their emission wavelengths.

Solid state 13C-NMR, infrared, X-ray powder diffraction and differential thermal studies of the homologous series of some mono-valent metal (Li, Na, K, Ag) n-alkanoates: A comparative study

A comparative study of the molecular packing, lattice structures and phase behaviors of the homologous series of some mono-valent metal carboxylates (Li, Na, K and Ag) is carried out via solid state FT-infrared and 13C-NMR spectroscopes, X-rays powder diffraction, density measurements, differential scanning calorimetry, polarizing light microscopy and variable temperature infrared spectroscopy. It is proposed that, for lithium, sodium and potassium carboxylates, metal-carboxyl coordination is via asymmetric chelating bidentate bonding with extensive intermolecular interactions to form tetrahedral metal centers, irrespective of chain length. However, for silver n-alkanoates, carboxyl moieties are bound to silver ions via syn–syn type bridging bidentate coordination to form dimeric units held together by extensive head group inter-molecular interactions. Furthermore, the fully extended hydrocarbon chains which are crystallized in the all-trans conformation are tilted at ca. 30°, 27°, 15° and 31° with respect to a normal to the metal plane, for lithium, sodium, silver and potassium carboxylates, respectively. All compounds are packed as lamellar bilayer structures, however, lithium compounds are crystallized in a triclinic crystal system whilst silver, sodium and potassium n-alkanoates are all monoclinic with possible P1 bravais lattice. Odd–even alternation observed in various physical features is associated with different inter-planar spacing between closely packed layers in the bilayer which are not in the same plane; a phenomenon controlled by lattice packing symmetry requirements.All compounds, except silver carboxylates, show partially reversibly first order pre-melting transitions; the number of which increases with increasing chain length. These transitions are associated, for the most part, with lamellar collapse followed by increased gauche-trans isomerism in the methylene group assembly, irrespective of chain length. It is proposed that the absence of mesomorphic transitions in their phase sequences is due to a lack of sufficient balance between attractive and repulsive electrostatic and van der Waals forces during phase change. The evidence presented in this study shows that phase behaviors of mono-valent metal carboxylates are controlled, mainly, by head group bonding.

Effects of strong hydrogen bonds and weak intermolecular interactions on supramolecular assemblies of 4-fluorobenzylamine

A series of supramolecular salts have been obtained by the self-assembly of 4-fluorobenzylamine and halide ions or metal chloride with 18-crown-6 as the host in the hydrochloric acid medium, i.e. (C7H9FN)+⋅X− (X=Cl−, 1; Br−, 2), [(C7H9FN)2⋅(18-crown-6)2]2+⋅(MCl4)2− (M=Mn, 3; Co, 5; Zn, 7; Cd, 8), [(C7H9FN)⋅(18-crown-6)]+⋅(FeCl4)− (4) and [(C7H9FN)⋅(18-crown-6)]+⋅1/2(CuCl4)2− (6). Structural analyses indicate that 1–2 crystallize in the triclinic space group P−1, 4 in orthorhombic space group Pnma and 3, 5, 6–8 in the monoclinic space group P21/c or C2/c. In these compounds, extensive intermolecular interactions have been utilized for the self-assembly of diverse supramolecular architectures, ranging from strong N–H⋯X (X=O, Cl, Br) hydrogen bonds to weak C–H⋯Y (Y=F, Cl, π) interactions. N–H⋯Cl/Br hydrogen bonds offer the major driving force in the crystal packing of salts 1–2 while N–H⋯O hydrogen bonds are found in salts 3–8.