Modulating the Amine-CO Interaction Strength: Toward Efficient Carbon Capture.

This study contributes to a comprehensive understanding of the interactions between CO and amines at the molecular level by exploring the rotational spectra of binary complexes between CO and eight different amines through pulsed-jet Fourier transform microwave spectroscopy and quantum chemical calculations. The findings reveal a consistent pattern in which CO is bonded to the amino group, primarily through a C···N tetrel bond, while being supported by C-H···O/C hydrogen bonds. Notably, the binding energies increase from primary through tertiary amines and with increasing chain length of the alkyl groups.

How Nonpolar CO Aggregates on Cycloalkenes: A Case Study with Cyclopentene-(CO) Clusters.

This study explores the molecular clusters of cyclopentene (CPE) with one to three CO molecules (CPE-(CO)) through their jet-cooled rotational spectra using Fourier transform microwave spectroscopy with supplementary quantum chemical calculations. The assembly of CPE-(CO) clusters is predominantly driven by tetrel bonding networks, notably C···π(C═C) and C···O interactions, with additional stabilization from weak C─H(CH)···C═O hydrogen bonds. Critically, the dispersive forces play a pivotal role in stabilizing CO aggregation on CPE, eclipsing the effects of electrostatic and orbital interactions.

Fluorination effects on non-covalent binding forces: A rotational study on the 2-(trifluoromethyl)acrylic acid-water complex.

This study explores the effects of the -CF group on non-covalent interactions through a comprehensive rotational investigation of the 2-(trifluoromethyl)acrylic acid-water complex. Employing Fourier transform microwave spectroscopy complemented by quantum chemical calculations, two isomers, i.e.

Adaptive Response to Solvation in Flexible Molecules: Oligo Hydrates of 4-Hydroxy-2-butanone.

Structural changes induced by water play a pivotal role in chemistry and biology but remain challenging to predict, measure, and control at molecular level. Here we explore size-governed gas-phase water aggregation in the flexible molecule 4-hydroxy-2-butanone, modeling the conformational adaptability of flexible substrates to host water scaffolds and the preference for sequential droplet growth. The experiment was conducted using broadband rotational spectroscopy, rationalized with quantum chemical calculations.

n → π* Interaction Enabling Transient Inversion of Chirality.

This study reports the observation and characterization of two isomers of the acrolein dimer by using high-resolution rotational spectroscopy in pulsed jets. The first isomer is stabilized by two hydrogen bonds, adopting a planar configuration, and is energetically favored over the second isomer, which exhibits a dominant n → π* interaction in a nearly orthogonal arrangement. Surprisingly, the n → π* interaction was revealed to enable a concerted tunneling motion of two moieties along the carbonyl group.

Probing the n → π* carbonyl-carbonyl interactions in the formaldehyde-trifluoroacetone dimer by rotational spectroscopy.

The non-covalent bonding features of carbonyl-carbonyl interactions have been investigated in the dimer of formaldehyde and trifluoroacetone using high resolution rotational spectroscopy combined with quantum chemical calculations. The observation of all possible isotopic substitutions for the heavy atoms in the complex enabled the determination of the accurate structure, characterized by the antiparallel arrangement of the two C=O bonds. The two moieties are connected through a dominant n → π* interaction enhanced by one weak C-H⋯O hydrogen bond, as revealed by supporting natural bond orbital analysis and symmetry-adapted perturbation theory analysis.

Insights into the Diels-Alder Reaction of Furan with Maleic Anhydride from Its Prereactive Intermediate.

The prereactive intermediate in the furan-maleic anhydride cycloaddition, a classical Diels-Alder reaction, has been captured and characterized in pulsed jets by Fourier transform microwave spectroscopy for the first time. The observed species is stabilized by the π-π* interaction between the two moieties, which connects to the channel of the cycloaddition. The secondary interactions between the C=C and C=O in the observed isomer are accountable for its lower energy with respect to the one with the channel.

Scissor-like Face to Face π-π Stacking: A Surprising Preference Induced by the Isocyano Group in the Self-Assembled Dimer of Phenyl Isocyanide.

Phenyl isocyanide has been chosen as a prototype to probe the π-π interaction modulated by the -NC group, which has a chameleonic nature with two main resonance forms showing a triple bond and being carbenoid. The rotational spectroscopic investigation complemented with theoretical analyses indicates that the phenyl isocyanide dimer has a scissor-like configuration controlled by dispersive forces along with the formation of π-π stacking. This is the first rotational spectroscopic evidence, to the best of our knowledge, that the -substitution by an -NC group on benzene can activate the position in forming noncovalent interactions.

Preparation of SrTiO nanocubes by CO laser vaporization (LAVA) and hydrothermal maturation.

SrTiO is of particular interest for numerous applications such as photocatalytic water splitting, as an electrode material for thermoelectrics or as piezoceramics for sensors. Here we report on an advanced CO laser vaporization (LAVA) method for the production of faceted, single-phase SrTiO nanoparticles with an average particle size of 35 nm. Starting from a coarse SrTiO raw powder, spherical SrTiO nanoparticles were obtained by a laser-induced gas-phase condensation process.

Aqueous microsolvation of 4-hydroxy-2-butanone: competition between intra- and inter-molecular hydrogen bonds.

The rotational spectra of 4-hydroxy-2-butanone and its monohydrate were investigated by Fourier transform microwave spectroscopy complemented by quantum chemical calculations. One conformer of 4-hydroxy-2-butanone, with the intramolecular O-H⋯O hydrogen bond, has been observed in the pulsed jet. Rotational spectra of the six isotopologues (including four C and one O mono-substitution species) in natural abundance were measured and assigned, enabling the accurate structural determination of the molecular skeleton.

The LAM of the Rings: Large Amplitude Motions in Aromatic Molecules Studied by Microwave Spectroscopy.

Large amplitude motions (LAMs) form a fundamental phenomenon that demands the development of specific theoretical and Hamiltonian models. In recent years, along with the strong progress in instrumental techniques on high-resolution microwave spectroscopy and computational capacity in quantum chemistry, studies on LAMs have become very diverse. Larger and more complex molecular systems have been taken under investigation, ranging from series of heteroaromatic molecules from five- and six-membered rings to polycyclic-aromatic-hydrocarbon derivatives.

Spectroscopic Characterization of 3-Aminoisoxazole, a Prebiotic Precursor of Ribonucleotides.

The processes and reactions that led to the formation of the first biomolecules on Earth play a key role in the highly debated theme of the origin of life. Whether the first chemical building blocks were generated on Earth (endogenous synthesis) or brought from space (exogenous delivery) is still unanswered. The detection of complex organic molecules in the interstellar medium provides valuable support to the latter hypothesis.

Methyl Internal Rotation in Fruit Esters: Chain-Length Effect Observed in the Microwave Spectrum of Methyl Hexanoate.

The gas-phase structures of the fruit ester methyl hexanoate, CH-O-(C=O)-CH, have been determined using a combination of molecular jet Fourier-transform microwave spectroscopy and quantum chemistry. The microwave spectrum was measured in the frequency range of 3 to 23 GHz. Two conformers were assigned, one with C symmetry and the other with C symmetry where the γ-carbon atom of the hexyl chain is in a orientation in relation to the carbonyl bond.

Biopolymer-based nanocarriers for sustained release of agrochemicals: A review on materials and social science perspectives for a sustainable future of agri- and horticulture.

Devastating plant diseases and soil depletion rationalize an extensive use of agrochemicals to secure the food production worldwide. The sustained release of fertilizers and pesticides in agriculture is a promising solution to the eco-toxicological impacts and it might reduce the amount and increase the effectiveness of agrochemicals administration in the field. This review article focusses on carriers with diameters below 1 μm, such as capsules, spheres, tubes and micelles that promote the sustained release of actives.

Interaction Types in CH(CH)OH-CO ( = 0-4) Determined by the Length of the Side Alkyl Chain.

CH(CH)OH-CO complexes have been investigated using rotational spectroscopy ( = 0-2) complemented by quantum chemical calculations ( = 0-4), which implies that the side alkyl chain length can determine the types of intermolecular interactions. Unlike the in-plane C···O tetrel bond in phenol-CO, the π*···π interaction has been shown to link CO to phenylmethanol and 2-phenylethanol, which is, to the best of our knowledge, the first time it has been demonstrated by rotational spectroscopy. Further elongations of the side alkyl chain gradually increase the energies of intramolecular hydrogen bonds in 3-phenylpropanol and 4-phenylbutanol so that CO cannot break it.

Stacked but not Stuck: Unveiling the Role of π→π* Interactions with the Help of the Benzofuran-Formaldehyde Complex.

The 1:1 benzofuran-formaldehyde complex has been chosen as model system for analyzing π→π* interactions in supramolecular organizations involving heteroaromatic rings and carbonyl groups. A joint "rotational spectroscopy-quantum chemistry" strategy unveiled the dominant role of π→π* interactions in tuning the intermolecular interactions of such adduct. The exploration of the intermolecular potential energy surface led to the identification of 14 low-energy minima, with 4 stacked isomers being more stable than those linked by hydrogen bond or lone-pair→π interactions.

Determination of the "Privileged Structure" of 8-Hydroxyquinoline.

An accurate semi-experimental equilibrium structure of 8-hydroxyquinoline (8-HQ) has been determined combining experiment and theory. The cm-wave rotational spectrum of 8-HQ was recorded in a pulsed supersonic jet using broadband dual-path reflection and narrowband Fabry-Perot-type resonator Fourier-transform microwave spectrometers. Accurate rotational and quartic centrifugal distortion constants and N quadrupole coupling constants are determined.

Switching Aromatic Character by Complexation: π to π* Change Seen in Molecular Rotation Spectra.

A dominating F···π* interaction is found to govern the benzaldehyde···tetrafluoromethane complex, as revealed by this rotational spectroscopic investigation. Secondary F···π* and C σ*···π interactions also contribute to the stability of the observed isomer. Narrow splittings have been observed in the rotational spectrum originating from a 3-fold internal rotation of CF above the aromatic moiety, and a corresponding barrier was determined to be 1.

Convenient Syntheses of Trivalent Uranium Halide Starting Materials without Uranium Metal.

Low-valent uranium coordination chemistry continues to rely heavily on access to trivalent starting materials, but these reagents are typically prepared from uranium turnings, which are becoming increasingly difficult to acquire. Here we report convenient syntheses of UI(THF) (THF = tetrahydrofuran) and UBr(THF) from UCl, a more accessible uranium starting material that can be prepared from commercially available uranium oxides. UCl(THF) (), UBr(THF) (), and UI(THF) () were prepared by single-pot reductions from UCl using KH and KC and converted to or by halide exchange with the corresponding MeSiX (where X = Br or I).

Chlorine "Equatorial Belt" Activation of CFCl by CO: The C···Cl Tetrel Bond Dominance in CFCl-CO.

Besides its typical halogen donor behavior (exhibiting a Cl σ-hole) in forming Cl···B halogen bonds (B is an electron-rich region), CFCl reveals a new interaction site in its complex with CO when explored by rotational spectroscopy. Experimental evidence and theoretical analyses point out irrefutably that CFCl prefers to link to CO through its Cl "equatorial belt" consisting of the lone pairs of the Cl atom, resulting in a C···Cl tetrel bond. In addition, a secondary plausible C···O tetrel bond and a F···O halogen bond might contribute to the relative orientation of the moieties forming the complex.

Van der Waals interactions of the disulfide bond revealed: A microwave spectroscopic study of the diethyl disulfide-argon complex.

The van der Waals complex formed between diethyl disulfide (DEDS) and an argon atom was investigated by pulsed-jet Fourier transform microwave spectroscopy in conjunction with quantum chemical computations. One set of transition lines belonging to the configuration of the global potential energy minimum was measured and assigned. The rotational constants A, B, and C were accurately determined to be 1262.

The Characteristics of Disulfide-Centered Hydrogen Bonds.

The disulfide-centered hydrogen bonds in the three different model systems of diethyl disulfide⋅⋅⋅H O/H CO/HCONH clusters were characterized by high-resolution Fourier transform microwave spectroscopy and quantum chemical computations. The global minimum energy structures for each cluster are experimentally observed and are characterized by one of the three different S-S⋅⋅⋅H-C/N/O disulfide-centered hydrogen bonds and two O⋅⋅⋅H-C hydrogen bonds. Non-covalent interaction and natural bond orbital analyses further confirm the experimental observations.

Internal rotation and chlorine nuclear quadrupole coupling in 2-chloro-4-fluorotoluene explored by microwave spectroscopy and quantum chemistry.

2-Chloro-4-fluorotoluene was investigated using a combination of molecular jet Fourier transform microwave spectroscopy in the frequency range from 5 to 21 GHz and quantum chemistry. The molecule experiences an internal rotation of the methyl group, which causes fine splittings of all rotational transitions into doublets with separation on the order of a few tens of kHz. In addition, hyperfine effects originating from the chlorine nuclear quadrupole moment coupling its nuclear spin to the end-over-end rotation of the molecule are observed.

The structure and low-barrier methyl torsion of 3-fluorotoluene.

The rotational spectra of 3-fluorotoluene and its seven C isotopic species have been recorded at natural abundance in the frequency range from 4 to 26 GHz using a pulsed molecular jet Fourier transform microwave spectrometer. The molecular structure comprising bond lengths and angles as well as parameters describing the methyl torsion were determined with high accuracy. Due to the very low torsional barrier of 17 cm, the lowest torsional states of the vibrational ground state exhibited large splittings in the spectrum, which were modeled satisfactorily with a modified version of the program XIAM and the program aixPAM, both developed to treat the methyl internal rotation effects.