Structure And Dynamics Of Methacrylamide

Methacrylamide (CH$_{2}$=C(CH$_{3}$)-CONH$_{2}$) is formed by an allyl non-polar frame and an amide polar frame connected by a rotatable bond. Despite the relatively reduced size of the molecule, the presence of four nearby functional groups causes complex internal dynamics. The underlying conformational space has been explored by quantum mechanical modeling and surveyed with millimeter-wave rotational spectroscopy using a Stark-modulated free-jet absorption spectrometer, in the 59.6-104 GHz frequency range. According to the relative orientation of the two unsaturated bonds (defined by the dihedral angle $\tau$, C=C-C=O), two conformers were observed, namely s-$trans$ and s-$cis$. In the s-$cis$ form, the methylene and carbonyl groups lie on the same side and the overall symmetry is $C_{s}$ ($\tau=0^{\circ}$), whereas s-$trans$-methacrylamide consists of two equivalent non-planar minima ($\tau= \pm 151^{\circ}$), which are enantiomers and are separated by a low energy barrier corresponding to a planar skeletal arrangement ($\tau=180^{\circ}$). From relative intensity measurements, s-$cis$-methacrylamide is estimated to lie 4(2) kJ mol$^{-1}$ above s-$trans$-methacrylamide. The rotational spectra are characterized by a complex hyperfine structure which allowed the determination of the methyl internal rotation barrier and the $^{14}$N nuclear quadrupole coupling constants for both conformers. Moreover, the tunneling spliting related to the double minimum potential of s-$trans$-methacrylamide was determined. A one-dimensional flexible model of the vibro-rotational interaction suggests that the corresponding interconversion barrier is about 2.4 kJ mol$^{-1}$ and the first torsional quantum state lies 55 cm$^{-1}$ above the ground state

Interplay of Rotational and Pseudorotational Motions in Flexible Cyclic Molecules

Solutions to the time-independent nuclear Schrodinger equation associated with the pseudorotational motion of three flexible cyclic molecules are presented and discussed. Structural relaxations related to the pseudorotational motion are described as functions of a pseudorotation angle phi which is formulated according to the definition of ring-puckering coordinates originally proposed by Cremer and Pople ( J. Am. Chem. Soc. 1975, 97 (6), 1354-1358). In order to take into account the interplay between pseudorotational and rotational motions, the rovibrational Hamiltonian matrices are formulated for the rotational quantum numbers J = 0 and J = 1. The rovibrational Hamiltonian matrices are constructed and diagonalized using a Python program developed by the authors. Suitable algorithms for (i) the construction of one-dimensional cuts of potential energy surfaces along the pseudorotation angle phi and (ii) the assignment of the vibrorotational wave functions (which are needed for the automatic calculation of rotational transition energies J = 0 -> J = 1) are described and discussed

The structure of 2,6-di-tert-butylphenol–argon by rotational spectroscopy

Producción CientíficaThe molecular structure of a van der Waals-bonded complex involving 2,6-di-tert-butylphenol and a single argon atom has been determined through rotational spectroscopy. The experimentally derived structural parameters were compared to the outcomes of quantum chemical calculations that can accurately account for dispersive interactions in the cluster. The findings revealed a π-bound configuration for the complex, with the argon atom engaging the aromatic ring. The microwave spectrum reveals both fine and hyperfine tunneling components. The main spectral doubling is evident as two distinct clusters of lines, with an approximate separation of 179 MHz, attributed to the torsional motion associated with the hydroxyl group. Additionally, each component of this doublet further splits into three components, each with separations measuring less than 1 MHz. Investigation into intramolecular dynamics using a one-dimensional flexible model suggests that the main tunneling phenomenon originates from equivalent positions of the hydroxyl group. A double-minimum potential function with a barrier of 1000 (100) cm−1 effectively describes this extensive amplitude motion. However, the three-fold fine structure, potentially linked to internal motions within the tert-butyl group, requires additional scrutiny for a comprehensive understanding.Ministerio de Ciencia e Innovación y Fondo Europeo de Desarrollo Regional (FEDER) - (grant PID2021-125015NBI00)Junta de Castilla y León y Fondo Europeo de Desarrollo Regional (FEDER) - (grants INFRARED IR2020-1-UVa02 and INFRARED IR2021-UVa13

UPS, XPS, NEXAFS and Computational Investigation of Acrylamide Monomer

Acrylamide is a small conjugated organic compound widely used in industrial processes and agriculture, generally in the form of a polymer. It can also be formed from food and tobacco as a result of Maillard reaction from reducing sugars and asparagine during heat treatment. Due to its toxicity and possible carcinogenicity, there is a risk in its release into the environment or human intake. In order to provide molecular and energetic information, we use synchrotron radiation to record the UV and X-ray photoelectron and photoabsorption spectra of acrylamide. The data are rationalized with the support of density functional theory and ab initio calculations, providing precise assignment of the observed features

Structure, Dynamics, and Accurate Laboratory Rotational Frequencies of the Acrylonitrile–Methanol Complex

The hydrogen-bonded complex between acrylonitrile (CH2=CHCN) and methanol has been characterized spectroscopically in the millimeter wave range (59.6-74.4 GHz) using a free jet absorption millimeter wave spectrometer. Precise values of the rotational and centrifugal distortion constants were obtained from the measured frequencies of the complex of acrylonitrile with CH3OH and CD3OD. The analysis of the splittings of the rotational lines due to the hindered internal rotation of the methanol methyl group led to the determination of a V-3 value of 221.9(7) and 218(5) cm(-1) for the complexes of CH3OH and CD3OD, respectively, and these values are about 40% lower than that of free methanol. The structure of the observed conformation is in agreement with the global minimum determined at the MP2/aug-cc-pVTZ level of calculation, and the counterpoise corrected intermolecular binding energy, obtained at the same theoretical level, is D-e = 26.3 kJ mol(-1)We thank the University of Bologna for funding (RFO). C.C. acknowledges the Spanish Government (MINECO, Project Code CTQ2017-89150-R) for a postdoctoral contract. W.D.G. acknowledges support from the Swedish Research Council (Vetenskapsradet), Grant Number 2019-04332. We thank R. A. Boto and J. Contreras-Garcia for the availability of the NCI 2D plot script

Exploring the conformational landscape through rotational spectroscopy and computational modelling: The tunneling dynamics in 2,6-diethylphenol

Phenol and some of its derivatives exhibit interesting tunneling motions consisting of two groups of transitions separated by a few hundred MHz. Recently, one of its derivatives, 2,6-di-tert-butylphenol, has shown additional hyperfine tunneling components, the origin of which remains unclear. In this work, another member of the family, 2,6-diethylphenol, has been investigated through its rotational spectrum. The jet-cooled broadband chirped-pulse Fourier transform microwave spectra in the 2–8 GHz frequency region revealed the presence of two conformers. The comparison with the equilibrium structure obtained by computational calculations at the B3LYP-D3(BJ)/Def2-TZVP level validates the structural determination and the orientation of the lateral ethyl groups. Additional observation of all the singly-substituted 13C isotopologues for the most stable ones allowed the determination of the substitution structure by means of the Kraitchman equations. Both conformers exhibited tunneling that was reproduced using an advanced 1D model, which provides an estimate of the barrier height for both conformersWe acknowledge funding from the Spanish Ministerio de Ciencia e Innovaci\u00F3n and the European Regional Development Fund (MICINN\u2013ERDF, Grant No. PID2021-125015NBI00) and the Junta de Castilla y Le\u00F3n (Grant No. INFRARED IR2021-UVa13). M. J. thanks the University of Valladolid for a \u201CMargarita Salas\u201D postdoc contract. W.L. thanks the China Scholarship Council for a research scholarship. We acknowledge the CINECA award under the ISCRA initiative, for the availability of high-performance computing resources and support. This work was supported by University of Bologna (RFO). L.P. and A.P. acknowledge the Spanish Ministry of Science, Innovation and Universities & the State Research Agency through grants refs. PID2021-126560NB-I00 and CNS2022-135803 (MCIU/AEI/FEDER, UE), and the \u201CMar\u00EDa de Maeztu\u201D Programme for Units of Excellence in R&D (CEX2023-001316-M), and FASLIGHT network (RED2022-134391-T), and computer resources and assistance provided by Centro de Computaci\u00F3n Cient\u00EDfica de la Universidad Aut\u00F3noma de Madrid and Barcelona Supercomputing Center (FI-2023-1-0035 and FI-2023-2-0012)

Can hyperspectral imaging be used to map corrosion products on outdoor bronze sculptures?

The application of hyperspectral imaging in the field of cultural heritage investigation is growing rapidly. In this study, short wavelength infrared hyperspectral imaging (960–2500 nm) has been explored as a potential non-invasive technique for in situ mapping of corrosion products on bronze sculptures. Two corrosion products, brochantite and antlerite, commonly found on the surfaces of outdoor bronze monuments, were considered. Their spatial distribution was investigated on the surface of the bronze sculpture The Man with the Key by Auguste Rodin in Oslo. The results demonstrate that hyperspectral imaging combined with image analysis algorithms can display the distribution of the two corrosion products in different areas (unsheltered and partially sheltered) of the sculpture

A Competition between Relative Stability and Binding Energy in Caffeine Phenyl-Glucose Aggregates: Implications in Biological Mechanisms

Hydrogen bonds and stacking interactions are pivotal in biological mechanisms, although their proper characterisation within a molecular complex remains a difficult task. We used quantum mechanical calculations to characterise the complex between caffeine and phenyl-β-D-glucopyranoside, in which several functional groups of the sugar derivative compete with each other to attract caffeine. Calculations at different levels of theory (M06-2X/6-311++G(d,p) and B3LYP-ED=GD3BJ/def2TZVP) agree to predict several structures similar in stability (relative energy) but with different affinity (binding energy). These computational results were experimentally verified by laser infrared spectroscopy, through which the caffeine·phenyl-β-D-glucopyranoside complex was identified in an isolated environment, produced under supersonic expansion conditions. The experimental observations correlate with the computational results. Caffeine shows intermolecular interaction preferences that combine both hydrogen bonding and stacking interactions. This dual behaviour had already been observed with phenol, and now with phenyl-β-D-glucopyranoside, it is confirmed and maximised. In fact, the size of the complex’s counterparts affects the maximisation of the intermolecular bond strength because of the conformational adaptability given by the stacking interaction. Comparison with the binding of caffeine within the orthosteric site of the A2A adenosine receptor shows that the more strongly bound caffeine·phenyl-β-D-glucopyranoside conformer mimics the interactions occurring within the receptor.Grants PGC2018-098561 and PID2021-127918NB-I00 funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe”. Grant IT1491-22 funded by the Basque Government

High Resolution Millimeter Wave Absorption Spectroscopy of Flexi- ble Complex Organic Molecules: Laboratory Spectrum of 1, 2-butanediol

The enhancing sensibility of radioastronomical observations allows for detec- tion of complex organic molecules (COMs) with increasing size. Observations performed by the Atacama Large Millimeter Array (ALMA) open up new oppor- tunities to reveal the COMs, at the same time, the huge amount of data collected and the extremely rich surveys represent a challenge for the astrochemistry community. Among all the detected molecules, the diols are object of chemical interest, because of their similarity with important biological building block molecules such as sugar alcohols. The simplest of them, ethylene glycol (EG), is one of the largest COMs detected in space thus far. Lines attributable to the most stable conformer of EG were detected in different environments and recently also the higher energy conformer has been observed both towards IRAS 16293-2422 and the Orion KL. Observations of 1, 2- and 1, 3-propanediol toward Sgr B2 (N-LMH) were attempted as part of the GBT Prebiotic Interstellar Molecule Sur- vey Legacy Project, but no transitions were detected. Although up to now, due the fact that the column densities of molecules tend to decrease with increasing molecular weight, no large diols have been observed in interstellar space, owing to the raising sensitivity of the radioastronomy observations, their future detection can not be excluded. In this context we report, for the first time, the laboratory millimeter spectrum of 1, 2-butanediol (BD) recorded in the 59.6-103.6 GHz frequency region (5.03-2.89 mm). BD (the ethylated form of EG) is a flexible molecule characterized by a great conformational complexity, thus at room condi- tions the population is distributed in a large number of species, leading to a very congested spectrum. This problem has been overcome exploiting the rotational and conformational cooling produced by the supersonic expansion technique. Six conformers of BD, including the global minimum, have been assigned yielding the rotational constants and centrifugal distortion constants up to the forth- or sixth-order. The experimental spectroscopic constants and theoretical electric dipole moment components were used to predict the rotational spectrum of each of the observed conformers up to 163 GHz. Making use of the training received by the ALMA Regional Center in Bologna, selected lines of the most stable conformer of BD were searched toward the IRAS 16293-2422 A source exploiting Band 3 observations performed during the ALMA-project 2012.1.00712.S. No match was found, however further observations, aimed specifically to its search, could be more successful. Moreover considering that the maximum spectral signal of heavy molecules is predicted at higher frequencies, additional laboratory measurements at sub-millimeter wavelengths can be performed, starting from the present assignments. The new data could be used to attempt new observations in COMs-reach sources

Reference data for isolated pyrrole

The dataset includes input and output files for the fitting of the rotational and vibrorotational transition lines related to the v=0,1,2 vibrational states of the NH out-of-plane bending motion of pyrrole in the gas phase using the SPFIT program of the CALPGM suite. The following information is provided: (i) fitting files for the normal species including pure rotational line transition of the ground and first excited vibrational state and vibrorotational bands of the fundamental, first overtone, and first hot band using the S-reduction and the Watson's III-l representation. (ii) fitting files for the normal species including pure rotational line transition of the ground and first excited vibrational state and vibrorotational bands of the fundamental, first overtone, and first hot band using the Watson's S-reduction and the I-r representation. (iii) fitting files for the rotational transition lines of the 13C2 isotopologue using the Watson's S-reduction and the III-l representation. (iv) fitting files for the rotational transition lines of the 13C3 isotopologue using the Watson's S-reduction and the III-l representation