Theoretical Investigation of Normal to Strong Hydrogen Bonds

Manipulating Hydrogen-Bonding Donor/Acceptor in Ultra-Robust Isoreticular Zr(IV) Metal-Organic Frameworks for Efficient Regulation of Water Sorption Inflection Point and Steepness

The development of porous materials exhibiting steep and stepwise adsorption of water vapor at desired humidity is crucial for implementing diverse applications such as humidity control, heat allocation, and atmospheric water harvesting. The precise molecular-level elucidation of structural characteristics and chemical components that dictate the water sorption behaviors in confined nanospaces, metal-organic frameworks (MOFs) in particular, is fundamentally important, but this has yet to be largely explored. In this work, by leveraging the isoreticular principle, we crafted two pairs of isostructural Zr-MOFs with linker backbones of benzene and pyrazine acting as hydrogen-bonding donor and acceptor, respectively. The outstanding water sorption cyclic durability of the four Zr-MOFs permits persuasive investigation of the correlation of the water sorption inflection point and steepness (the two central figures-of-merit for water sorption) with the linker functionality. The two pyrazine-carrying Zr-MOFs both show steep water uptake at lower relative pressure and slightly decreased steepness, which are quantitatively described by the Dubinin-Astakhov relation. We deciphered the privileged water clusters through single-crystal X-ray diffraction studies in which the pyrazine moiety formed stronger hydrogen-bonding interactions with guest water molecules and favored the formation of water pentamers instead of hexamers that are observed in the benzene analog. The hydrogen-bonding donor/acceptor manipulation approach presented in this work may facilitate future research endeavors focusing on molecular attribute engineering in predeterminedly ultrawater-resistant MOF platforms for efficient regulation of water sorption behaviors toward customized applications.

Stabilization of the Alkylammonium Cations in Halide Perovskite Thin Films by Water-Mediated Proton Transfer

The development of alkylammonium lead trihalide perovskite (ALHP) photovoltaics has grown rapidly over the past decade. However, there are remaining critical challenges, such as proton defects, which can lead to the material instability of ALHPs. Although specific strategies, including the use of halide additives, have significantly reduced the defects, a fundamental understanding of the defect passivation mechanism remains elusive. Herein, an approach and mechanism for minimizing proton defects in ALHP crystals by adding ionized halides to the perovskite precursor solution are reported. This work clarifies that the ionized halides induced proton transfer from H₂ O to the alkylammonium cation in the precursor solution, stabilizing the ALHP crystals. The fundamental characteristics of ALHP and its precursors are examined by X-ray diffraction, transmittance electron microscopy, in situ extended X-ray absorption fine structure, Fourier transform NMR spectroscopy, and Fourier transform infrared spectroscopy. The findings from this work will guide the development of highly stable ALHP crystals, enabling efficient and stable optoelectronic ALHP devices.

Matrix effects on hydrogen bonding and proton transfer in fluoropyridine - HCl complexes

We report an extensive computational and spectroscopic study of several fluoropyridine-HCl complexes, and the parent, pyridine-HCl system. Matrix-IR spectra for pentafluoropyridine-HCl, 2,6-difluororpyridine-HCl, and 3,5-difluororpyridine-HCl in solid neon exhibit shifts for the H-Cl stretching band that parallel the effects of fluorination on hydrogen-bond strength. Analogous spectral shifts observed across various host environments (solid neon, argon, and nitrogen) for pentafluoropyridine-HCl and 2,6-difluororpyridine-HCl convey a systematically varying degree of matrix stabilization on the hydrogen bonds in these complexes. An extended quantum-chemical study of pyridine-HCl and eight fluorinated analogs, including 2-, 3-, and 4-fluoropyridine-HCl, 2,6- and 3,5-difluororpyridine-HCl, 2,4,6- and 3,4,5-trifluropyridine-HCl, as well as pentafluoropyridine-HCl, was also performed. Equilibrium structures and binding energies for the gas-phase complexes illustrate two clear trends in how fluorine substitution affects hydrogen bond strength; increasing fluorination weakens these interactions, yet substitution at the 2- and 6-positions has the most pronounced effect. Bonding analyses for a select subset of these systems reveal shifts in electron density that accompany hydrogen bonding, and most notably, the values of the electron density at the N-H bond critical points among the stronger systems in this subset significantly exceed those typical for moderately strong hydrogen-bonds. We also explored the effects of dielectric media on the structural and bonding properties of these systems. For pyridine-HCl, 3-fluoropyridine-HCl, and 3,5-difluororpyridine-HCl, a transition to proton transfer-type structures is observed at ε-values of 1.2, 1.5, and 2.0, respectively. This is signaled by key structural changes, as well as an increase in the negative charge on the chorine, and dramatic shifts in topological properties of the H-Cl and N-H bonds. In the case of pentafluoropyridine-HCl, and 2,6-difluororpyridine-HCl, we do not predict proton transfer in dielectric media up to ε = 20.0. However, there are clear indications that the media enhance hydrogen-bond strength, and moreover, these observations are completely consistent with the experimental IR spectra.

Assessment of hydrogen bond strengths and cooperativity in self- and cross-associating cyclic (HF)m(H2O)n (m + n = 2 to 8) clusters

In this work, we investigated the strengths of various self- and cross-associating hydrogen bonds (HBs) in mixed hydrogen fluoride–water cyclic (HF)m(H2O)n (m + n = 2 to 8) clusters, employing a molecular tailoring approach (MTA)-based method.

ABEEM/MM OH- Models for OH-(H2O)n Clusters and Aqueous OH-: Structures, Charge Distributions, and Binding Energies

Based on the atom-bond electronegativity equalization method fused into molecular mechanics (ABEEM/MM), two fluctuating charge models of OH^--water system were proposed. The difference between these two models is whether there is charge transfer between OH^- and its first-shell water molecules. The structures, charge distributions, charge transfer, and binding energies of the OH^-(H₂O)_n (n = 1-8, 10, 15, 23) clusters were studied by these two ABEEM/MM models, the OPLS/AA force field, the OPLS-SMOOTH/AA force field, and the QM methods. The results demonstrate that two ABEEM/MM models can search out all stable structures just as the QM methods, and the structures and charge distributions agree well with those from the QM calculations. The structures, the charge transfer, and the strength of hydrogen bonds in the first hydration shell are closely related to the coordination number of OH^-. Molecular dynamics simulations on the aqueous OH^- solution are performed at 298 and 278 K using ABEEM/MM-I model. The MD results show that the populations of three-, four-, and five-coordinated OH^- are 29.6%, 67.1%, and 3.4% at 298 K, respectively, and those of two-, three-, four-, and five-coordinated OH^- are 10.8%, 44.9%, 39.2%, and 4.9% at 278 K, respectively; the average hydrogen bond lengths and the hydrogen bond angle in the first shell increase with the temperature decreasing.

Hydrogen bonding effect between active site and protein environment on catalysis performance in H2-producing [NiFe] hydrogenases

The interaction between the active site and the surrounding protein environment plays a fundamental role in the hydrogen evolution reaction (HER) in [NiFe] hydrogenases. Our density functional theory (DFT) findings demonstrate that the reaction Gibbs free energy required for the rate determining step decreases by 7.1 kcal mol^-1 when the surrounding protein environment is taken into account, which is chiefly due to free energy decreases for the two H⁺/e^- addition steps (the so-called Ni-SIa to I1, and Ni-C to Ni-R), being the largest thermodynamic impediments of the whole reaction. The variety of hydrogen bonds (H-bonds) between the amino acids and the active site is hypothesised to be the main reason for such stability: H-bonds not only work as electrostatic attractive forces that influence the charge redistribution, but more importantly, they act as an electron 'pull' taking electrons from the active site towards the amino acids. Moreover, the electron 'pull' effect through H-bonds via the S^- in cysteine residues shows a larger influence on the energy profile than that via the CN^- ligands on Fe.

Anisotropic and amphoteric characteristics of diverse carbenes

The singlet/triplet stabilities and amphoteric behaviors of diverse carbenes are elucidated with the anisotropic natures of their electron configurations.

Prediction of strong O-H/M hydrogen bonding between water and square-planar Ir and Rh complexes

Intermolecular O-H/M interactions, between a water molecule and square-planar acac complexes ([M(acac)L₂]), with different types of L ligands (en, H₂O, CO, CN^-, and OH^-) and different types of metal atoms (Ir(i), Rh(i), Pt(ii), and Pd(ii)) were studied by high level ab initio calculations. Among the studied neutral complexes, the [Pd(acac)(CN)(CO)] complex forms the weakest interaction, -0.62 kcal mol^-1, while the [Ir(acac)(en)] complex forms the strongest interaction, -9.83 kcal mol^-1, which is remarkably stronger than the conventional hydrogen bond between two water molecules (-4.84 kcal mol^-1).

CRANAD-1 as a cyanide sensor in aqueous media: a theoretical study

The lethal toxicity of cyanide ions to animals and the environment has led to considerable research into the development of methods for rapid and sensitive cyanide detection.

Temperature-responsive properties of poly(4-vinylpyridine) coatings: influence of temperature on the wettability, morphology, and protein adsorption

Poly(4-vinylpyridine)-grafted brushes demonstrate a thermal response of their wettability (stronger than that for spin-coated films), surface morphology, and protein adsorption.

Density functional theory based study of molecular interactions, recognition, engineering, and quantum transport in π molecular systems

CONSPECTUS: In chemical and biological systems, various interactions that govern the chemical and physical properties of molecules, assembling phenomena, and electronic transport properties compete and control the microscopic structure of materials. The well-controlled manipulation of each component can allow researchers to design receptors or sensors, new molecular architectures, structures with novel morphology, and functional molecules or devices. In this Account, we describe the structures and electronic and spintronic properties of π-molecular systems that are important for controlling the architecture of a variety of carbon-based systems. Although DFT is an important tool for describing molecular interactions, the inability of DFT to accurately represent dispersion interactions has made it difficult to properly describe π-interactions. However, the recently developed dispersion corrections for DFT have allowed us to include these dispersion interactions cost-effectively. We have investigated noncovalent interactions of various π-systems including aromatic-π, aliphatic-π, and non-π systems based on dispersion-corrected DFT (DFT-D). In addition, we have addressed the validity of DFT-D compared with the complete basis set (CBS) limit values of coupled cluster theory with single, double, and perturbative triple excitations [CCSD(T)] and Møller-Plesset second order perturbation theory (MP2). The DFT-D methods are still unable to predict the correct ordering in binding energies within the benzene dimer and the cyclohexane dimer. Nevertheless, the overall DFT-D predicted binding energies are in reasonable agreement with the CCSD(T) results. In most cases, results using the B97-D3 method closely reproduce the CCSD(T) results with the optimized energy-fitting parameters. On the other hand, vdW-DF2 and PBE0-TS methods estimate the dispersion energies from the calculated electron density. In these approximations, the interaction energies around the equilibrium point are reasonably close to the CCSD(T) results but sometimes slightly deviate from them because interaction energies were not particularly optimized with parameters. Nevertheless, because the electron cloud deforms when neighboring atoms/ions induce an electric field, both vdW-DF2 and PBE0-TS seem to properly reproduce the resulting change of dispersion interaction. Thus, improvements are needed in both vdW-DF2 and PBE0-TS to better describe the interaction energies, while the B97-D3 method could benefit from the incorporation of polarization-driven energy changes that show highly anisotropic behavior. Although the current DFT-D methods need further improvement, DFT-D is very useful for computer-aided molecular design. We have used these newly developed DFT-D methods to calculate the interactions between graphene and DNA nucleobases. Using DFT-D, we describe the design of molecular receptors of π-systems, graphene based electronic devices, metalloporphyrin half-metal based spintronic devices as graphene nanoribbon (GNR) analogs, and graphene based molecular electronic devices for DNA sequencing. DFT-D has also helped us understand quantum phenomena in materials and devices of π-systems including graphene.

Exceptional superhydrophobicity and low velocity impact icephobicity of acetone-functionalized carbon nanotube films

We present a simple method to produce carbon nanotube-based films with exceptional superhydrophobicity and impact icephobicity by depositing acetone-treated single-walled carbon nanotubes on glass substrates. This method is scalable and can be adopted for any substrate, both flexible and rigid. These films have indicated a high contact angle, in the vicinity of 170°, proved both by static and dynamic analysis processes. The dynamic evaporation studies indicated that a droplet deposited on the treated films evaporated in the constant contact angle mode for more than 80% of the total evaporation time, which is definitely a characteristic of superhydrophobic surfaces. Furthermore, the acetone-functionalized films showed a strong ability to mitigate ice accretion from supercooled water droplets (-8 °C), when the droplets were found to bounce off the films tilted at 30°. The untreated nanotube films did not indicate similar behavior, and the supercooled water droplets remained attached to the films' surfaces. Such studies could be the foundation of highly versatile technologies for both water and ice mitigation.

Supramolecular assembly of Mg(II) complexes directed by associative lone pair-pi/pi-pi/pi-anion-pi/pi-lone pair interactions

Two Mg(II) malonate complexes with protonated 2-aminopyridine and protonated 2-amino-4-picoline as counterions, namely, (C(5)H(7)N(2))(4)[Mg(C(3)H(2)O(4))(2)(H(2)O)(2)](ClO(4))(2) (1) and (C(6)H(8)N(2)H)(2)[Mg(C(3)H(2)O(4))(2)(H(2)O)(2)] x 4 H(2)O (2) [C(5)H(7)N(2) = protonated 2-aminopyridine, C(3)H(4)O(4) = malonic acid, C(6)H(8)N(2)H = protonated 2-amino-4-picoline], have been synthesized from purely aqueous media, and their crystal structures have been determined by single-crystal X-ray diffraction. The role of lone pair...pi interactions in stabilizing the self-assembly process appears to be of great importance in both complexes. Additional weak forces like anion...pi and noncovalent O...O interactions are also found to be operating in 1. A rare combination of lone pair...pi and anion...pi interactions in 1, of the type lone pair...pi/pi...pi/pi...anion...pi/pi...lone pair, is observed, and this unusual supramolecular network is fully described here. An attempt to prepare an analogous complex with 2-amino-4-picoline resulted in 2, which is isomorphous with our recently reported transition-metal complexes of the type (C(6)H(8)N(2)H)(2)[M(C(3)H(2)O(4))(2)(H(2)O)(2)] x 4 H(2)O (M = Ni/Co/Mn). A high-level DFT-D study (RI-B97-D/TZVP) has been used to characterize the different noncovalent interactions present in the solid state. We have also analyzed some crystal fragments to examine energetically some important assemblies that drive the crystal packing. Finally, we have studied the influence of magnesium on some hydrogen-bonding interactions.

Comparison of cationic, anionic and neutral hydrogen bonded dimers

Short Strong Hydrogen Bonds (SSHBs) play an important role in many fields of physics, chemistry and biology. Since it is known that SSHBs exist in many biological systems, the role of hydrogen bonding motifs has been particularly interesting in enzyme catalysis, bio-metabolism, protein folding and proton transport phenomena. To explore the characteristic features of neutral, anionic and cationic hydrogen bonds, we have carried out theoretical studies of diverse homogeneous and heterogeneous hydrogen bonded dimers including water, peroxides, alcohols, ethers, aldehydes, ketones, carboxylic acids, anhydrides, and nitriles. Geometry optimization and harmonic frequency calculations are performed at the levels of Density Functional Theory (DFT) and Møller-Plesset second order perturbation (MP2) theory. First principles Car-Parrinello molecular dynamics (CPMD) simulations are performed to obtain IR spectra derived from velocity- and dipole-autocorrelation functions. We find that the hydrogen bond energy is roughly inversely proportional to the fourth power of the r(O/N-H) distance. Namely, the polarization of the proton accepting O/N atom by the proton-donating H atom reflects most of the binding energy in these diverse cation/anion/neutral hydrogen bonds. The present study gives deeper insight into the nature of hydrogen-bonded dimers including SSHBs.

Binding mechanisms in supramolecular complexes

Supramolecular chemistry has expanded dramatically in recent years both in terms of potential applications and in its relevance to analogous biological systems. The formation and function of supramolecular complexes occur through a multiplicity of often difficult to differentiate noncovalent forces. The aim of this Review is to describe the crucial interaction mechanisms in context, and thus classify the entire subject. In most cases, organic host-guest complexes have been selected as examples, but biologically relevant problems are also considered. An understanding and quantification of intermolecular interactions is of importance both for the rational planning of new supramolecular systems, including intelligent materials, as well as for developing new biologically active agents.