Nature Of Hydrogen Bonds Research Articles

Dual dynamic crosslinking of rubber for enhanced mechanical properties and reconfigurable shape memory behavior

AbstractConstructing dynamic covalent bonds (DCBs) in rubbers provides a promising avenue to resolve the trade‐offs between chemical crosslinking and recyclability. The reinforcement of dynamic covalent networks by nanofilling is widely adopted, which, however, inevitably hinders the exchange reaction of DCBs and network rearrangement due to the restrictions on chain mobility imposed by fillers. To date, the reinforcement of dynamic covalent networks without affecting the dynamic properties remains challenging. In this work, we report a dual dynamic crosslinking strategy by engineering reversible noncovalent bonds into dynamic covalent rubbers to improve mechanical performance and simultaneously maintain desirable malleability and reprocessability. Specifically, dynamic boronic ester‐crosslinked styrene–butadiene rubber is firstly prepared and then modified through triazolinedione (TAD) click reaction. The grafted urazole groups can form hydrogen bond interactions that further aggregate to form clusters and phase‐separation structure in the networks. Due to the reversible nature of hydrogen bonds, they can act in a sacrificial manner to dissipate mechanical energy, leading to a combination of improved strength, modulus and toughness of the networks. More importantly, the hydrogen‐bonded clusters are dissociated at elevated temperatures, enabling the network dynamic properties to be largely preserved. In addition, the dynamic features of the dual crosslinks (hydrogen bonds and boronic esters) endow the TAD‐modified networks with reconfigurable shape memory effect. © 2023 Society of Industrial Chemistry.

Nature and Strength of Sulfur-Centered Hydrogen Bond in Methanethiol Aqueous Solutions.

Methanethiol (M) and water (W) clusters like dimers (M1W1, M2, and W2), trimers (M1W2, M2W1, M3, and W3), and tetramers (M1W3, M2W2, M3W1, M4, and W4) were studied to assess the strength of sulfur-centered hydrogen bonding using different levels of theories, viz, HF, MP2, MP3, MP4, B3LYP, B3LYP-D3, CCSD, CCSD(T)-F12, and CCSD(T) along with aug-cc-pVNZ (where N = D, T, and Q) basis sets. Interaction energies were found to be in the range of -3.3 to -5.3 kcal/mol for the dimers, -8.0 to -16.7 kcal/mol for the trimers, and -13.5 to -29.5 kcal/mol for the tetramers at the B3LYP-D3/CBS limit level of theory. Normal modes of vibrations computed at the B3LYP/cc-pVDZ level of theory were seen to be in good agreement with the experimental values. Local energy decomposition calculations using the DLPNO-CCSD(T) level of theory indicated the domination of electrostatic interactions' contribution to the interaction energy in all cluster systems. Furthermore, atoms in molecules and natural bond orbital calculations both carried out at the B3LYP-D3/aug-cc-pVQZ level of theory aided in visualizing the hydrogen bonds besides proving a rationale for the strength of the hydrogen bonds and thereby the stability of these cluster systems.

The disposition of bridge hydrogen bond in the homopolar-diborane and its derivatives

Compounds that comprehend less valence electrons are designated as electron deficient and atoms involved in such compounds occasionally form three-center-two-electron (3c-2e-) bonds to engross all of their available valence orbitals in bonding. Hence, in this study, calculations using M06-2X, MP2, and CCSD(T) method with the inclusion of def2-TZVP basis sets are exploited to reconnoiter the authentic bonding portrayal in diborane (DB) and its derivatives. Molecular electrostatic potential (MEP) analysis on the basis of vSmax and vSmin values indicates that there is a charge transfer between a π-hole that encompasses one monomer and the most negative region of another monomer that results in the formation of bridge bonds between two monomers. QTAIM investigation directed towards the charge depletion at bridging fragment in all the complexes and disclosed the polar covalent nature of bridge hydrogen bond. Additionally, ETS-NOCV examination suggests that charge flow from bridge to boron atom of all the complexes. Additionally, the bonding found to be more through orbital interactions compared to electrostatic interactions.

Catalyst-free, highly sensitive and adjustable photo-responsive azobenzene liquid crystal elastomers based on dynamic multiple hydrogen bond

Photo-responsive liquid crystal elastomers (LCEs) containing azobenzene components have received great attention and are in great demand gap for the development of smart materials. Herein, we have prepared a novel azobenzene photo-responsive liquid crystal elastomer (HAzo-LCEs) through simultaneously introducing azobenzene molecules and 2-ureido-4-pyrimidone (UPy) units into main chain of polyurethane molecule. Utilizing polyurethane system into this HAzo-LCEs has a trade-off between the exceptional mechanical performance and quick response. Especially, the transformation of photo-responsive HAzo-LCEs from polydomain to monodomain liquid crystal structures has been achieved under the catalyst-free and low temperature conditions by exploiting the dynamic nature of multiple hydrogen bond between UPy units. This synthetic method breaks the dilemma that the conventional photo-responsive LCEs require the preparation of monodomain liquid crystal structures at high temperatures or with the help of a large number of catalysts. Importantly, the HAzo-LCEs sample can bend rapidly in response to the UV light, and the maximum bending angle of the sample could reach 144°. Intriguingly, the blended HAzo-LCEs sample can rapidly straighten and finally extended under green light, showing the high sensitivity and flexible adjustability. It is valuable to integrating the high sensitivity, flexible adjustability and complete reversibility into one photo-responsive elastomers of this HAzo-LCEs. Furthermore, the multiple hydrogen bonds from UPy units allows the HAzo-LCEs to regulate its dynamics and stability by increasing the number and binding sites through the advantages of adjustable strength, high selectivity and abundant formation modes, providing great design and application scope for photo-responsive liquid crystal elastomers. This design route of non-toxic PU-based HAzo-LCEs provides a novel approach to broaden photo-responsive LCEs application in sensor and actuator.

Physicochemical fundamentals of processing solutions of thermoplastic poly(ether urethane)s to obtain fibrous-porous polymer composite materials

Objectives. To study the structure and properties of solutions of thermoplastic poly(ether urethane)s (PEUs) to inform their potential use in the production of fibrous-porous polymer composite materials with a given structure and set of performance properties depending on the field of practical application.Methods. The composition of PEUs was studied by attenuated total reflection infrared (ATR-IR) spectroscopy using a program for correcting the spectra on an IR Fourier spectrophotometer, as well by differential scanning calorimetry (DSC) using a heat flow calorimeter. The viscosity of PEU solutions was determined on a rotational viscometer.Results. The chemical composition of PEUs and the nature of the formation of hydrogen bonds were studied. An analysis of the spectra demonstrates the almost complete identity of the PEUs synthesized from the same 4,4'-diphenylmethane diisocyanate. In the studied PEUs of the Vitur and Desmopan® brands, as well as Sanpren, pronounced absorption bands characteristic of urethane groups involved in the formation of hydrogen bonds are visible in the region from 1702 to 1730 cm−1. The temperature transitions and thermal stability of the investigated PEUs were determined by DSC. The influence of the ratio of rigid and flexible blocks, as well as the nature of hydrogen bonds on the melting temperatures of polymers, was shown. Analysis of the DSC curves demonstrated all the studied PEUs to have high melting points ranging from 159 to 215°C. From the studied temperature dependences of the structural viscosity of thermoplastic PEUs solutions, all solutions were established to have a minimum viscosity anomaly; the value of the logarithm of viscosity depends on the chemical composition and structure of the initial PEUs. It is shown that the viscosity anomaly of PEU solutions can be reduced with increasing temperature.Conclusions. A comparison of the chemical composition, structure, thermal and rheological characteristics of thermoplastic PEUs with PEU solutions widely used for the production of fibrous-porous materials and coatings of Sanpren LQ-E-6 and Vitur R 0112 grades demonstrates their practicability as production materials and coatings having a predetermined structure and a set of properties depending on the requirements and operating conditions of finished products.

Unraveling the Nature of Hydrogen Bonds of "Proton Sponges" Based on Car-Parrinello and Metadynamics Approaches.

The nature of intra- and intermolecular non-covalent interactions was studied in four naphthalene derivatives commonly referred to as "proton sponges". Special attention was paid to an intramolecular hydrogen bond present in the protonated form of the compounds. The unsubstituted "proton sponge" served as a reference structure to study the substituent influence on the hydrogen bond (HB) properties. We selected three compounds substituted by methoxy, amino, and nitro groups. The presence of the substituents either retained the parent symmetry or rendered the compounds asymmetric. In order to reveal the non-covalent interaction properties, the Hirshfeld surface (HS) was computed for the crystal structures of the studied compounds. Next, quantum-chemical simulations were performed in vacuo and in the crystalline phase. Car-Parrinello molecular dynamics (CPMD), Path Integral Molecular Dynamics (PIMD), and metadynamics were employed to investigate the time-evolution changes of metric parameters and free energy profile in both phases. Additionally, for selected snapshots obtained from the CPMD trajectories, non-covalent interactions and electronic structure were studied. Quantum theory of atoms in molecules (QTAIM) and the Density Overlap Regions Indicator (DORI) were applied for this purpose. It was found based on Hirshfeld surfaces that, besides intramolecular hydrogen bonds, other non-covalent interactions are present and have a strong impact on the crystal structure organization. The CPMD results obtained in both phases showed frequent proton transfer phenomena. The proton was strongly delocalized in the applied time-scale and temperature, especially in the PIMD framework. The use of metadynamics allowed for tracing the free energy profiles and confirming that the hydrogen bonds present in "proton sponges" are Low-Barrier Hydrogen Bonds (LBHBs). The electronic and topological analysis quantitatively described the temperature dependence and time-evolution changes of the electronic structure. The covalency of the hydrogen bonds was estimated based on QTAIM analysis. It was found that strong hydrogen bonds show greater covalency, which is additionally determined by the proton position in the hydrogen bridge.

Change in students’ explanation of the shape of snowflakes after collaborative immersive virtual reality

In recent years, chemistry educators are increasingly adopting immersive virtual reality (IVR) technology to help learners visualise molecular interactions. However, educational studies on IVR mostly investigated its usability and user perceptions leaving out its impact on improving conceptual understanding. If they evaluated students’ knowledge gains, they tended to use information recall tests to assess knowledge gains. Employing interviews and diagram-drawing tasks, this study explored how students’ conceptual understanding of the nature of hydrogen bonds and the shape of snowflakes changed through a collaborative IVR experience on snowflakes. Participants were 68 undergraduate chemistry students. Videos of pre-/post-interviews and student-generated diagrams were analysed. The results indicated a marked improvement in students’ conceptual understanding of the nature of hydrogen bonds among water molecules in snowflakes. After IVR, 57 students provided scientifically acceptable explanations of the nature of hydrogen bonds. Improvements in students’ understanding were related to the intermolecular nature of hydrogen bonds, the role of lone pairs of electrons in forming hydrogen bonds, and molecular interactions in 3D space. This study suggests that collaborative IVR could be a powerful way for students to visualise molecular interactions, examine their alternative conceptions, and build more coherent understanding. Implications for the design and implementation of IVR activities for science learning are discussed.

Analysis of students’ diagrams of water molecules in snowflakes to reveal their conceptual understanding of hydrogen bonds

Recent studies have reported a growing trend of using student-generated diagrams for assessment in science teaching and research. However, many educators tend to use diagrams to explore students’ perceptions of scientists and their work rather than explore conceptual understanding of abstract concepts. In this study, we used diagrams to investigate students’ conceptual understanding of the nature of hydrogen bonds among water molecules in snowflakes. Participants were 70 first- and second-year university students. Following a sequence of interview prompts, the students drew diagrams to illustrate the interactions amongst water molecules in snowflakes. Sixty students’ diagrams were analyzed inductively using a constant comparison method. Most diagrams showed that the students did not have major challenges drawing the water molecule structure, recognizing polarity of a water molecule, or recognizing the intermolecular nature of hydrogen bonds. However, the diagrams revealed varied ways in which students conceptualized the formation of hydrogen bonds. A third of the diagrams revealed students’ alternative conceptions about the role of lone pairs of electrons in the formation of hydrogen bonds. Most diagrams which showed a good understanding of the nature of a hydrogen bond revealed students’ difficulties in recognizing molecular interactions in a 3D space. Our findings suggest that student-generated diagrams can provide a powerful way to understand students’ conceptions of abstract science concepts.

Bulk and transparent supramolecular glass from evaporation-induced noncovalent polymerization of nucleosides.

Understanding the nature of glass is one of the most important challenges in chemistry, physics, and materials science. In this study, transparent bulk supramolecular glasses with excellent optical behaviors and good mechanical properties were fabricated via the non-covalent polymerization of nucleosides. Hydrogen bonding is the main driving force in the formation of bulk supramolecular glasses. The directional and saturated character of hydrogen bonding enables the formation of a short-range ordered structure, while the weak nature and reversibility of hydrogen bonds allow for the asymmetric and random connections of the short-range ordered structure into a long-range disordered network. Various relaxations, including β, γ, and δ relaxations, are observed at temperatures below the glass transition temperature, demonstrating the metastable nature of bulk supramolecular glasses. This investigation offers supramolecular insights into the nature of glass materials.

A Simple Substitution on Thyroid Hormones Remarkably Alters the Regioselectivity of Deiodination by a Deiodinase Mimic.

The regioselective deiodinations of L-thyroxine (T4) play key roles in the thyroid hormone homeostasis. These reactions are catalyzed by three isoforms of the selenoenzymes, iodothyronine deiodinases (Dio1, Dio2 and Dio3), which are highly homologous in nature. Dio1 mediates 5'- or 5-deiodinations of T4 to produce T3 and rT3, respectively. In contrast, Dio2 and Dio3 are selective to 5'- or 5-deiodination to produce T3 and rT3, respectively. Understanding of the regioselectivity of deiodination at the molecular level is important as abnormal levels of thyroid hormone have been implicated in various clinical conditions, such as hypoxia, myocardial infarction, neuronal ischemia and cancer. In this paper, we report that the electronic properties of the iodine atoms in thyroxine (T4) can be modulated through a simple substitution in the 4'-phenolic moiety. This leads to the change in the regioselectivity of deiodination by different small molecule mimics of Dio enzymes. By using this chemical approach, we also show that the substitution of a strong electron withdrawing group facilitates the removal of all four iodine atoms in the T4 derivative. Theoretical investigations on the hydrogen bonded adducts of T4 with imidazole indicate that the charge on the iodine atoms depend on the nature of hydrogen bond between the -OH group of T4 and the imidazole moiety. While the imidazole can act as either hydrogen bond acceptor (HBA) or hydrogen bond donor (HBD), the protonated imidazole acts exclusively as HBD in T4-imidazole complex. These studies support the earlier observations that the histidine residue at the active sites of the deiodinases play an important role not only in the substrate binding, but also in altering the regioselectivity of the deiodination reactions.

Biaxial Hard Compression, Anisotropic Elastic Property, and Pressure-Induced Isosymmetric Phase Transition in Ammonium Bicarbonate

The elastic property, exceptional anisotropic compression, and pressure-induced isosymmetric phase transition in ammonium bicarbonate (AB) are studied by in situ synchrotron X-ray diffraction, Raman spectroscopy, and computational methods. The exceptional anisotropic compression as a result of biaxial hard compression is induced by stiff hydrogen-bonding “double-wine-rack” geometric motifs. The large values of elastic anisotropy such as Young’s moduli, Shear moduli, and Poisson’s ratio verify the anisotropic nature in AB. The biaxial hard compression further induces an isosymmetric phase transition at 2 GPa through the generation of new N–H···O hydrogen bonds. Our work first demonstrates the stiff mechanical study of “double-wine-rack” geometric hydrogen-bonding networks and its influence on the phase transition, which can be used as a model to investigate the robust nature of hydrogen bonds and the structural origin of isosymmetric phase transition. Moreover, the hydrogen-bonding “double-wine-rack” geometric mechanism also provides an inspiration to construct a covalent-bonding “double-wine-rack” geometric model favoring anomalous biaxial mechanical/thermal responses. The determination of the high-pressure phase of AB provides new information to understand the composition of the ternary system H2O–CO2–NH3.

Cellulose nanocrystal nanocomposites capable of low-temperature and fast self-healing performance

The development of low-temperature self-healing polymers is crucial because high-temperature or softening conditions for rapid self-healing inevitably reduce their mechanical strength. Herein, we first report cellulose nanocrystal (CNC)/polymer nanocomposites with a rapid low-temperature self-healing performance. The nanocomposite was prepared by simple blending of grafted CNC and matrix prepolymer made from the monomers having metal-ligand coordination and lower critical solution temperature functionalities along with the presence of hexamethylene diisocyanate and dibutyltin dilaurate. Owing to the dynamic nature of both hydrogen bonds and metal–ligand coordinated covalent bonds, the resultant nanocomposites showed excellent self-healing efficiency (99 %, within 1 h) at a low temperature (5 °C) with robust mechanical properties including a high stretchability (230 %), high toughness (2538 MJ/m3), enhanced tensile strength (25.49 ± 0.02 MPa), and improved thermomechanical properties. Self-healing performance of the coordinated covalent bonds requiring active hydrogen was considerably improved by the introduction of CNCs with abundant hydrogen bonds.

DFT study of stability and electronic properties of cyclic tetramer involving dinucleobase monomers, comprising acetylene central block substituted at both edges with guanine and cytosine nucleobases

The dinucleobase molecule comprising acetylene central block substituted at both edges with guanine and cytosine nucleobases has previously been synthesised. In this manuscript, the stability and electronic properties of cyclic tetramer involving this ethynylene-linked molecule are theoretically investigated at B3LYP/6-311++G(d,p) level. In addition to gas phase, the influence of aprotic solvents on the stability and electronic properties of cyclic tetramer is also investigated with a focus on its dielectric constant. Here, toluene, diethyl ether, tetrahydrofuran, dichloromethane, acetophenone, acetone, benzonitrile, propanonitrile and acetonitrile are chosen as aprotic solvent. It is observed that the stability of cyclic tetramer is diminished by increasing the dielectric constant of solvent. Whereas the cyclic tetramer is stabilised by hydrogen bonds, the strength and nature of hydrogen bonds are examined using AIM analysis. The relationships between dielectric constant of solvent and some electronic properties of cyclic tetramer such as band gap, electron affinity, electrophilicity index, first ionisation energy, electronic chemical potential, chemical softness and hardness are also investigated.

Life at low Reynolds number Re-visited: The efficiency of microbial propulsion

It has for over 40 years been taken as a truth universally acknowledged that microbial swimming efficiency by flagellar propulsion is fixed by fluid mechanical limitations at 1–2%. And that the missing 98% dissipated as heat is inefficient or wasted. Estimates of such low swimming efficiency make no sense. Microbes have had billions of years to evolve highly efficient swimming; images of microbes in motion show movement with alacrity and maximum speeds of up to 10 body lengths per second, equivalent to the running and swimming speeds of far larger animals. This paradox can be resolved by taking into account the hydrogen-bonded nature of water and how efficient viscous flow over the surface of the animal is established. The minimal requirement for viscous flow is that the activation energy barrier be overcome. The activation energy for viscous flow in water and sea water is the amount of energy required to break 2 hydrogen bonds—breaking apart the dominant water pentamer into the single H2O species, thus greatly reducing the size of the molecular hole required for flow. Microbial swimming efficiency is made highly efficient by devoting some 95% of the energy expended (some must be lost to entropy) into the breaking of hydrogen bonds.

PH- and thermo-responsive Pickering emulsion stabilized by silica nanoparticles and conventional nonionic copolymer surfactants

HypothesisPoly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) could be adsorbed on the silica surface via the hydrogen bonding between PEO and silanol (SiOH) groups. This interaction would be inhibited once SiOH is dissociated to SiO- at an increased pH value. Besides, the adsorption should be affected by temperature considering the nature of hydrogen bond. Hence, we speculate that silica nanoparticles modified in situ by adsorbed PEO-PPO-PEO possess a pH- and thermo-sensitive surface activity, making them a stimuli-responsive Pickering emulsifier. ExperimentsParaffin oil-in-water emulsions stabilized by silica nanoparticles and PEO-PPO-PEO were prepared. Stabilities, droplet morphologies and stimuli-responses were systematically studied using bottle test, optical microscopy and cryo-scanning electron microscopy (cryo-SEM). To clarify the emulsification mechanism, interfacial viscoelastic moduli and desorption energies were determined using the data obtained from drop shape analysis. FindingsSilica nanoparticles are hydrophobized and flocculated by adsorbed PEO-PPO-PEO at a relatively low pH and room temperature. Upon the pH or the temperature increased, particles regain their hydrophilicity and dispersity due to the desorption of surfactants. Emulsions stabilized by these surfactant-modified particles are pH- and thermo-responsive and can be repetitively switched between stabilization and destabilization. The switch temperature is controlled by the PEO length. The emulsification mechanism is verified in view of interfacial viscoelasticity and desorption energy. These findings demonstrate a novel and simple strategy of preparing pH- and thermo-responsive Pickering emulsions desirable to many industrial applications.

Hydrogen Bonds with Fluorine in Ligand-Protein Complexes-the PDB Analysis and Energy Calculations.

Fluorine is a common substituent in medicinal chemistry and is found in up to 50% of the most profitable drugs. In this study, a statistical analysis of the nature, geometry, and frequency of hydrogen bonds (HBs) formed between the aromatic and aliphatic C–F groups of small molecules and biological targets found in the Protein Data Bank (PDB) repository was presented. Interaction energies were calculated for those complexes using three different approaches. The obtained results indicated that the interaction energy of F-containing HBs is determined by the donor–acceptor distance and not by the angles. Moreover, no significant relationship between the energies of HBs with fluorine and the donor type was found, implying that fluorine is a weak HB acceptor for all types of HB donors. However, the statistical analysis of the PDB repository revealed that the most populated geometric parameters of HBs did not match the calculated energetic optima. In a nutshell, HBs containing fluorine are forced to form due to the stronger ligand–receptor neighboring interactions, which make fluorine the “donor’s last resort”.

Nature of excited-state dependent hydrogen bonds and their critical role in determining the photophysical properties of aromatic thioketones.

In this work, how the excited-state dependent hydrogen bond (H-bond) interactions control photophysical processes have been uncovered by accurate electronic structure calculations for the five lowest-lying states (S0, S1, S2, T1, and T2) of three aromatic thioketones and their isomers. The difference in the H-bond nature between S2 and S1 gives rise to ultrafast S2 → S1 internal conversion via the two-state conical intersection. Strong S2 fluorescence observed usually in thiocarbonyl compounds is absent in aromatic thioketones with intramolecular H-bonds. Meanwhile, the relatively weak H-bond interactions in S1 and T1 states make the S1, T2, and T1 states degenerate or quasi-degenerate. As a result, the T2 state acts as a relay and enables both forward S1 → T1 and reverse T1 → S1 processes to occur efficiently, which provides new insights into the mechanism of thermally activated delayed fluorescence (TADF), and could be used to improve the design principle of purely organic TADF materials.

Hydrogen bonding in the crystal of 1,1'-((1E,1'E)-(pyridine-3,4-diylbis(azanylylidene))bis(methanylylidene))-bis(naphthalen-2-ol) acetonitrile solvate: combined experimental and theoretical study

The title compound, 1,1'-((1E,1'E)-(pyridine-3,4-diylbis(azanylylidene))bis(methanylylidene))­bis(naphthalen-2-ol) (1), was synthesized and structurally characterized. The compound cocrystallized with one MeCN molecule. Interestingly, one of two salicylaldehyde Schiff base fragments exists in enol form, while the other one — in a ketone form. Moreover, cocrystallized acetonitrile molecule forms hydrogen bonding with three hydrogen atoms of the dye molecule. The nature and energies of intermolecular and intramolecular hydrogen bonds were studied theoretically using DFT calculations and topological analysis of the electron density distribution within the formalism of Bader's theory (QTAIM method).

Searching for correlations between geometric and spectroscopic parameters of intramolecular hydrogen bonds in porphyrin-like macrocycles.

Chemical bond lengths and angles are characteristic structural parameters of a molecule. Similarly, the frequencies of the vibrational modes and the NMR chemical shifts are unique "chemical fingerprints" specific to a compound. These are the basic parameters describing newly obtained compounds and enabling their identification. Intramolecular hydrogen bonding significantly influences the physicochemical properties of macrocyclic compounds with a porphyrin-like structure. This work presents the verification for correlations between geometric and spectroscopic parameters related to hydrogen bonds in this type of macrocyclic compounds. In particular, such relationships were investigated for a large group of porphyrin, porphycene, and dibenzotetraaza[14]annulene derivatives and a group of other macrocycles with similar structure. A very strong linear correlation was found only between the vibrational frequencies of the NH groups involved in a hydrogen bond and the length of this bond, which applied to all macrocyclic compounds of this type. Several other relationships were found between spectroscopic (IR, Raman, NMR) and geometric (X-ray) parameters, highlighting differences and similarities between different families of macrocycles. Apart from providing a better understanding of the nature of hydrogen bonds and their characteristics in porphyrin-like macrocyclic compounds, these relationships will facilitate the identification of new macrocycles and the extrapolation of their spectroscopic properties.

A substrate-independent isocyanate-modified polydimethylsiloxane coating harvesting mechanical durability, self-healing ability and low surface energy with anti-corrosion/biofouling potential

Polydimethylsiloxane (PDMS)-derived materials have been used as functional coatings in a wide range of industrial and engineering applications owing to their appealing physical and chemical properties. However, most of them cannot harvest mechanical durability, self-healing ability and low surface energy due to the conventional chemical crosslinking method. Herein, a polymer coating featuring multifaceted functionalities is developed by facilely brush-coating isocyanate-modified PDMS (I-PDMS) on diverse substrates, in which the adjacent polymer chains are physically crosslinked by the hydrogen bonds between the urea motifs. The prepared coating can withstand 500 cycles of adhesive tape-peeling or 200 cycles of sandpaper abrasion without losing its hydrophobicity. Besides, the dynamic nature of the intermolecular hydrogen bonds leads to appreciable self-healing ability which can essentially extend the coating’s lifespan. Moreover, the I-PDMS coating possesses low surface energy, i.e., ∼ 13.1 mJ/m2 and ∼ 28.8 mJ/m2 when the PDMS Mw is ∼ 30000 and ∼ 3000, respectively. These appealing properties strongly depend on the PDMS Mw which could be attributed to the variation in mobility of the polymer chains and density of the intermolecular hydrogen bonds. Furthermore, it is found that this I-PDMS coating can effectively mitigate corrosion and biofouling on metal substrates, implying its great potential as a protective coating in practical engineering processes. Our work offers a promising approach to prepare multifunctional PDMS-based coatings with considerable application prospect.