Exploring atmospheric nucleation processes: Hydration and fluoroalcoholic complexation of pyruvic acid.

This study examines the intermolecular interactions between small molecules and solvents, with a particular focus on pyruvic acid (PA). PA plays a significant role in biochemistry, astrochemistry, and atmospheric chemistry, particularly in aerosol particle formation. Previous studies on PA have been expanded upon by exploring its hydration and complexation with 2,2,2-trifluoroethanol (TFE).

Shape and interactions of the synthetic repellent DEET.

,-Diethyl-3-methylbenzamide (DEET) is the most widely used insect repellent, exhibiting high efficiency against a wide variety of species. In this work, a comprehensive isolated-molecule investigation of DEET was conducted using chirp-excitation Fourier transform microwave (CP-FTMW) spectroscopy within the frequency range of 7-14 GHz. Four out of the eight theoretically predicted conformers were detected and grouped in pairs based on their rotational constants and planar moments of inertia.

Structural effects of oxidation on sugars: glucose as a precursor of gluconolactone and glucuronolactone.

Although structural information on sugars is wide, experimental studies on the oxidation products of sugars in the gas phase, free from solvent interactions, have been rarely reported. We present an experimental work on the changes in the structure and interactions of two products of glucose oxidation (D-glucono-1,5-lactone (GlcL) and D-glucurono-6,3-lactone (GlcurL)) with respect to their precursor. Features such as intramolecular interactions, ring puckering and tautomerism were observed.

Conformationally Restricted β-Sheet Breaker Peptides Incorporating Cyclic α-Methylisoserine Sulfamidates.

Peptides containing variations of the β-amyloid hydrophobic core and five-membered sulfamidates derived from β-amino acid α-methylisoserine have been synthesized and fully characterized in the gas phase, solid state and in aqueous solution by a combination of experimental and computational techniques. The cyclic sulfamidate group effectively locks the secondary structure at the N-terminus of such hybrid peptides imposing a conformational restriction and stabilizing non-extended structures. This conformational bias, which is maintained in the gas phase, solid state and aqueous solution, is shown to be resistant to structure templating through assays of in vitro β-amyloid aggregation, acting as β-sheet breaker peptides with moderate activity.

Bond Length Alternation and Internal Dynamics in Model Aromatic Substituents of Lignin.

Broadband microwave spectra were recorded over the 2-18 GHz frequency range for a series of four model aromatic components of lignin; namely, guaiacol (ortho-methoxy phenol, G), syringol (2,6-dimethoxy phenol, S), 4-methyl guaiacol (MG), and 4-vinyl guaiacol (VG), under jet-cooled conditions in the gas phase. Using a combination of C isotopic data and electronic structure calculations, distortions of the phenyl ring by the substituents on the ring are identified. In all four molecules, the r bond between the two substituted C-atoms lengthens, leading to clear bond alternation that reflects an increase in the phenyl ring resonance structure with double bonds at r , r and r .

The Role of Non-Covalent Interactions on Cluster Formation: Pentamer, Hexamers and Heptamer of Difluoromethane.

The role of non-covalent interactions (NCIs) has broadened with the inclusion of new types of interactions and a plethora of weak donor/acceptor partners. This work illustrates the potential of chirped-pulse Fourier transform microwave technique, which has revolutionized the field of rotational spectroscopy. In particular, it has been exploited to reveal the role of NCIs' in the molecular self-aggregation of difluoromethane where a pentamer, two hexamers and a heptamer were detected.

Laboratory Observation of, Astrochemical Search for, and Structure of Elusive Erythrulose in the Interstellar Medium.

Rotational spectroscopy provides the most powerful means of identifying molecules of biological interest in the interstellar medium (ISM), but despite their importance, the detection of carbohydrates has remained rather elusive. Here, we present a comprehensive Fourier transform rotational spectroscopic study of elusive erythrulose, a sugar building block likely to be present in the ISM, employing a novel method of transferring the hygroscopic oily carbohydrate into the gas phase. The high sensitivity of the experiment allowed the rotational spectra of all monosubstituted isotopologue species of C-CHO to be recorded, which, together with quantum chemical calculations, enabled us to determine their equilibrium geometries () with great precision.

Toward the RNA-World in the Interstellar Medium-Detection of Urea and Search of 2-Amino-oxazole and Simple Sugars.

In the past decade, astrochemistry has witnessed an impressive increase in the number of detections of complex organic molecules. Some of these species are of prebiotic interest such as glycolaldehyde, the simplest sugar, or aminoacetonitrile, a possible precursor of glycine. Recently, we have reported the detection of two new nitrogen-bearing complex organics, glycolonitrile and Z-cyanomethanimine, known to be intermediate species in the formation process of ribonucleotides within theories of a primordial RNA-world for the origin of life.

Observation of the Unbiased Conformers of Putative DNA-Scaffold Ribosugars.

The constitution, configuration, and flexibility of the core sugars of DNA molecules alter their function in diverse roles. Conformational itineraries of the ribofuranosides (s) have long been known to finely determine rates of processing, yet we also know that, strikingly, semifunctional DNAs containing pyranosides (s) or other configurations can be created, suggesting sufficient but incompletely understood plasticity. The multiple conformers involved in such processes are necessarily influenced by context and environment: solvent, hosts, ligands.

Bond Length Alternation Observed Experimentally: The Case of 1H-Indazole.

Bond length alternation is a chemical phenomenon in benzene rings fused to other rings, which has been mainly predicted theoretically. Its physical origin is still not clear and has generated discussion. Here, by using a strategy that combines microwave spectroscopy, custom-made synthesis and high-level ab initio calculations, we demonstrate that this phenomenon is clearly observed in the prototype indazole molecule isolated in the gas phase.

Conformational Behavior of d-Lyxose in Gas and Solution Phases by Rotational and NMR Spectroscopies.

Understanding the conformational preferences of carbohydrates is crucial to explain the interactions with their biological targets and to improve their use as therapeutic agents. We present experimental data resolving the conformational landscape of the monosaccharide d-lyxose, for which quantum mechanical (QM) calculations offer model-dependent results. This study compares the structural preferences in the gas phase, determined by rotational spectroscopy, with those in solution, resolved by nuclear magnetic resonance (NMR) and molecular dynamics (MD) simulations.

A General Treatment to Study Molecular Complexes Stabilized by Hydrogen-, Halogen-, and Carbon-Bond Networks: Experiment and Theory of (CH F ) ⋅⋅⋅(H O).

Rotational spectra of several difluoromethane-water adducts have been observed using two broadband chirped-pulse Fourier-transform microwave (CP-FTMW) spectrometers. The experimental structures of (CH F )⋅⋅⋅(H O) , (CH F ) ⋅⋅⋅(H O), (CH F )⋅⋅⋅(H O) , and (CH F ) ⋅⋅⋅(H O) were unambiguously identified with the aid of 18 isotopic substituted species. A subtle competition between hydrogen, halogen, and carbon bonds is observed and a detailed analysis was performed on the complex network of non-covalent interactions which stabilize each cluster.

Degradation Mechanism and Relative Stability of Methylammonium Halide Based Perovskites Analyzed on the Basis of Acid-Base Theory.

The correct identification of all gases released during hybrid perovskite degradation is of great significance to develop strategies to extend the lifespan of any device based on this semiconductor. CHX (X = Br/I) is a released degradation gas/low boiling point liquid arising from methylammonium (MA) based perovskites, which has been largely overlooked in the literature focusing on stability of perovskite solar cells. Herein, we present an unambiguous identification of CHI release using microwave (rotational) spectroscopy.

Competing Dispersive Interactions: From Small Energy Differences to Large Structural Effects in Methyl Jasmonate and Zingerone.

Modern structural studies of biologically relevant molecules require an exhaustive interplay between experiment and theory. In this work, we present two examples where a poor choice of the theoretical method led to a misinterpretation of experimental results. We do that by performing a rotational spectroscopy study on two large and flexible biomolecules: methyl jasmonate and zingerone.

Interactions between azines and alcohols: a rotational study of pyridine-tert-butyl alcohol.

We assigned the rotational spectra of the parent and the OD isotopologues of the intermolecular complex pyridine-tert-butyl alcohol. The rotational and 14N quadrupole coupling constants are in agreement with a σ-type shape and a Cs symmetry of the complex. The two subunits are held together by a "classical" O-HN intermolecular hydrogen bond.

Water Sculpts the Distinctive Shapes and Dynamics of the Tumor-Associated Carbohydrate Tn Antigens: Implications for Their Molecular Recognition.

The tumor-associated carbohydrate Tn antigens include two variants, αGalNAc- O-Thr and αGalNAc- O-Ser. In solution, they exhibit dissimilar shapes and dynamics and bind differently to the same protein receptor. Here, we demonstrate experimentally and theoretically that their conformational preferences in the gas phase are highly similar, revealing the essential role of water.

Shapes, Dynamics, and Stability of β-Ionone and Its Two Mutants Evidenced by High-Resolution Spectroscopy in the Gas Phase.

The conformational landscapes of β-ionone and two mutants (α-ionone and β-damascone) have been analyzed by means of state-of-the-art rotational spectroscopy and quantum-chemical calculations. The experiments performed at high resolution and sensitivity have provided a deep insight into their conformational spaces, assigning more than 8000 transitions corresponding to the rotational structures of 54 different species (3 isomers, 14 conformers, and 40 isotopologues). Methyl internal rotation dynamics were also observed and analyzed.

Investigating the Conformation of the Bridged Monosaccharide Levoglucosan.

Levoglucosan is one of the main products of the thermal degradation of glucose and cellulose and is commonly used as a tracer for biomass burning. Herein we report a conformational analysis of levoglucosan under isolation conditions, by means of microwave spectroscopy coupled with ultrafast laser vaporization in supersonic expansions. We observed three different conformations of levoglucosan in the gas phase.

N-Methyl Inversion and Accurate Equilibrium Structures in Alkaloids: Pseudopelletierine.

A rotational spectroscopy investigation has resolved the conformational equilibrium and structural properties of the alkaloid pseudopelletierine. Two different conformers, which originate from inversion of the N-methyl group from an axial to an equatorial position, have been unambiguously identified in the gas phase, and nine independent isotopologues have been recorded by Fourier-transform microwave spectroscopy in a jet expansion. Both conformers share a chair-chair configuration of the two bridged six-membered rings.

Understanding the role of tyrosine in glycogenin.

We explored the molecular basis of tyrosine as the docking amino acid for the first glucose molecule during the synthesis of glycogen. The IR spectra show that the aromatic ring acts as bait to keep the position where the next glucose unit has to bind clear, by luring non-desirable molecules towards the aromatic ring. Only, α-/β-glucose shows particular affinity for the O3H and O4H moieties.

High conductance values in π-folded molecular junctions.

Folding processes play a crucial role in the development of function in biomacromolecules. Recreating this feature on synthetic systems would not only allow understanding and reproducing biological functions but also developing new functions. This has inspired the development of conformationally ordered synthetic oligomers known as foldamers.

Influence of the Anomeric Conformation in the Intermolecular Interactions of Glucose.

Carbohydrates are, together with amino acids, DNA bases, and lipids, the building blocks of living beings. They play a central role in basic functions such as immunity and signaling, which are governed by noncovalent interactions between sugar units and other biomolecules. To get insights into such interactions between monosaccharide units, we used a combination of mass-resolved laser spectroscopy in supersonic expansions and molecular structure calculations.

Structural Studies of Nicotinoids: Cotinine versus Nicotine.

Nicotinoids are agonists of the acetylcholine receptor (nAChR) and play important biochemical and pharmacological roles. Herein, we report on the structure and conformation of cotinine, and compare its molecular properties with the nicotine prototype, from which it only differs in the addition of a carbonyl group. This investigation included a theoretical survey of the effects of rotamerization of the pyridine moiety, the puckering of the pyrrolidinone ring and the internal rotation of the methyl group.

Effects of Chlorination on the Tautomeric Equilibrium of 2-Hydroxypyridine: Experiment and Theory.

The effects of halogenation on the tautomeric and conformational equilibria of the model system 2-hydroxypyridine/2-pyridone have been investigated through chlorine substitution at positions 3, 4, 5, and 6. In the gas phase, the lactim syn-periplanar tautomer (OH ) was the predominant species for all compounds over the lactam form (C=O) and the less abundant anti-periplanar lactim (OH ). However, the population of the three species was shown to be dependent on the position of the chlorine substitution.

Scopine Isolated in the Gas Phase.

The rotational spectrum of the tropane alkaloid scopine is detected by Fourier transform microwave spectroscopy in a pulsed supersonic jet. A nonconventional method for bringing the molecules intact into the gas phase is used in which scopine syrup is mixed with glycine powder and the solid mixture is vaporized with an ultrafast UV laser beam. Laser vaporization prevents the easy isomerization to scopoline previously observed with conventional heating methods.