A study of hydrogen bonded vibrational spectra of (R)-(+)-Methylsuccinic acid, as aided by DFT dimer analysis

Evolution of Hydrogen-Bond Interactions within Single Levitated Metastable Aerosols Studied by In Situ Raman Spectroscopy

Atmospheric aerosols can exist as supersaturated (metastable) liquid or glassy states, with physical and chemical properties that are distinct from the solid or liquid phases. These unique properties of aerosols have substantial implications on climate and health effects. Direct investigations on metastable aerosols remain a challenge because any interfacial contact can cause heterogeneous nucleation. In this study, in situ Raman spectroscopic and Mie scattering imaging analysis is applied to metastable aerosols in the absence of physical contact using an environment-controlled electrodynamic balance (EDB). This has allowed a detailed study of the O-H stretching regions of the Raman spectrum, revealing evidence for the rearrangement of hydrogen-bonding structures of levitated aqueous citric acid (CA) and aqueous sucrose droplets at metastable liquid states. We found that carboxyl groups in a CA droplet yield distinctive dynamics of strong and weak hydrogen bonds, whereas hydroxyl groups in a sucrose droplet show correlated strong and weak interactions. Such effects are particularly important in a supersaturated solution. These results indicate that metastable liquid aerosols from different sources may exhibit distinct physical and chemical behavior.

DL-3-Aminoisobutyric acid: vibrational, NBO and AIM analysis of N-H⋯O bonded-zwitterionic dimer model

A zwitterionic dimer model constructed of inter-molecular -N-H⋯O bonding has been proposed for the solid sample of DL-3-Aminoisobutyric acid consistent with IR absorption and Raman spectral features measured in the 3500-400/50 cm^-1. This zwitterionic dimer model in water as solvent has been computed at B3LYP/6-311++G(d,p) and B3LYP-D3/6-311++G(d,p) levels including Grimme's dispersion correction associated with the -N-H⋯O interaction and SCRF-SMD method. Of the several possible monomer and dimer conformational structures, the most stable dimer constructed of two zwitterion monomer units has produced vibrational modes due to the -NH₃ ⁺ cation and -CO₂‾ anion involved in the -N-H⋯O bonding in fair agreement with the observed broad but composite IR modal features near the 3500-2000 cm^-1. Except for the frequency of asymmetric stretching mode of the -NH₃ ⁺ cation, its symmetric and bending modes agree with the observed values. As for the -CO₂‾ anion, the frequencies of all of its modes are in good agreement with the experiment. Natural bond orbital (NBO), molecular electrostatic potential (MEP), atoms-in-molecules (AIM) and non-covalent interaction (NCI) analyses have been used to understand electronic characterization of the -N-H⋯O bonding.

Experimental and theoretical investigation of the complexation of methacrylic acid and diisopropyl urea

The present paper explores the complexation ability of methacrylic acid which is one of the most abundant functional monomer for the preparation of molecularly imprinted polymers. Host-guest interactions and the mechanism of complex formation between methacrylic acid and potentially genotoxic 1,3-diisopropylurea were investigated in the pre-polymerization solution featuring both experimental (NMR, IR) and in silico density functional theory (DFT) tools. The continuous variation method revealed the presence of higher-order complexes and the appearance of self-association which were both taken into account during the determination of the association constants. The quantum chemical calculations - performed at B3LYP 6-311++G(d,p) level with basis set superposition error (BSSE) corrections - are in agreement with the experimental observations, reaffirming the association constants and justifying the validity of computational investigation of such systems. Furthermore, natural bond orbital analysis was carried out to appraise the binding properties of the complexes.