Justinas Ceponkus

Far-Infrared Band Strengths in the Water Dimer: Experiments and Calculations

Most fundamentals modes of the water dimer have been experimentally determined, and the frequencies have been measured in either neon or parahydrogen matrices. The band strengths of all intramolecular and most intermolecular fundamentals of the water dimer have been measured. The results are further corroborated by comparison with the corresponding data for the fully deuterated water dimer. DFT calculations of the mode frequencies and band strength are in qualitative agreement with the experimental observations.

Photochemistry of acetylacetone isolated in parahydrogen matrices upon 266 nm irradiation

The photochemistry of the chelated enol form of acetylacetone (AcAc) was investigated by UV excitation of the S(2) state at 266 nm in parahydrogen matrices, complemented by experiments in neon and normal hydrogen matrices. Infrared (IR) spectroscopy, combined with theoretical calculations, was used to identify the photoproducts. Isomerization towards various non-chelated forms (no intramolecular H-bond) of AcAc is the dominant channel whereas fragmentation is very minor. The isomerization kinetics is monitored by IR spectroscopy. Among the seven non-chelated conformers of AcAc, only three are formed in parahydrogen matrices, whereas four are observed in normal hydrogen matrices. This difference suggests that an active tunnelling process between conformers occurs in parahydrogen but is quenched in normal hydrogen where guest-host interactions are stronger. Fragmentation and isomerization of excited AcAc are discussed in the light of these new data. The role of the intermediate triplet state in the S(2)→ S(0) relaxation is confirmed, as the importance of phonons in the condensed phase.

UV-induced growth of cyanopolyyne chains in cryogenic solids

UV laser excitation of cryogenic solids doped with cyanoethyne, HC(3)N, led to an in situ creation of longer carbon-nitrogen chains, namely HC(5)N, C(4)N(2), and C(6)N(2), heralded by their strong visible luminescence. HC(5)N and C(4)N(2) molecules can form, most probably, within HC(3)N aggregates linked by hydrogen bonds, while the reaction occurring between two isolated, photochemically created C(3)N radicals yields C(6)N(2). This latter species, dicyanobutadiyne, is easily detected in Ar, Kr, N(2), as well as in parahydrogen solids. The C(6)N(2) phosphorescence is identified here for the first time. The reported carbon chain coupling reactions in rigid environments are of interest for astrochemistry of interstellar ices.

Nuclear Spin Conversion to Probe the Methyl Rotation Effect on Hydrogen‐Bond and Vibrational Dynamics

A noteworthy example of a molecule with coupled large-amplitude motions is provided by acetylacetone (methyl group torsions and intramolecular hydrogen bonds). The molecule was trapped in solid parahydrogen to investigate the complex proton tunneling processes. Nuclear spin conversion in methyl groups is observed and, combined with IR spectra, documents the coupling between high frequency modes and large amplitude motions.

Infrared spectroscopic imaging of renal tumor tissue.

Fourier transform infrared (FTIR) spectroscopic imaging has been used to probe the biochemical composition of human renal tumor tissue and adjacent normal tissue. Freshly resected renal tumor tissue from surgery was prepared as a thin cryosection and examined by FTIR spectroscopic imaging. Tissue types could be discriminated by utilizing a combination of fuzzy k-means cluster analysis and a supervised classification algorithm based on a linear discriminant analysis. The spectral classification is compared and contrasted with the histological stained image. It is further shown that renal tumor cells have spread in adjacent normal tissue. This study demonstrates that FTIR spectroscopic imaging can potentially serve as a fast and objective approach for discrimination of renal tumor tissue from normal tissue and even in the detection of tumor infiltration in adjacent tissue.

Microspectroscopic infrared specular reflection chemical imaging of multi-component urinary stones: MIR vs. FIR

AbstractSpecular reflection infrared microspectroscopy was used for chemical imaging of cross-sectioned urinary stones to determine their chemical composition and morphology simultaneously. Absorption spectral bands were recovered from reflection spectra by Kramers-Kronig transform. FUse of far-infrared radiation provides high-contrast images and allows more precise constituent distribution determinations than mid-infrared because band asymmetry after the transform caused by diffuse reflection is less in the far-infrared.

Conformational studies of aliphatic secondary ozonides (propene, 1-butene and 1-heptene) by means of FTIR spectroscopy

Ozonization reaction of simple alkenes was studied by means of FT infrared absorption gas spectroscopy. The reaction was performed at 95 K in neat films of the reactants. IR absorption spectra of the gaseous products were recorded. The spectra were analyzed combining experimental results with theoretical calculations performed at B3LYP 6-311++G (3df, 3pd) level. We found that among all theoretically predicted conformers of propene secondary ozonide, only one which has the O-O half-chair configuration for the five membered ring and the radical attached in the equatorial position was present in the sample. Samples of 1-butene and 1-heptene secondary ozonides consist from two conformers of very similar energy (ΔH=0.3 kJ/mol). The most stable conformer for both ozonides is the one with O-O half-chair configuration of the five membered ring and the radical attached in equatorial position and the aliphatic chain in gauche position. The second stable conformer has the aliphatic chain in anti position.

Matrix isolation FTIR spectroscopical study of ethene secondary ozonide

A new method is used for the separation of ethene secondary ozonide (SOZ) from the other products of ethene ozonization reaction. The reaction was performed in the neat films of the reactants at 77 K. Ethene SOZ was separated from other products of the reaction by vacuum distillation at 190–210 K and analyzed by means of the matrix isolation IR absorption spectroscopy. Spectroscopic data from photolysis of the matrix isolated ozonide was used as an argument for assignment of the infrared spectral bands either to ethene SOZ or to other products of the reaction. The spectra of ethene SOZ isolated in the Ar matrix were analyzed by combining experimental results with the theoretical calculations performed at the MP2 6-311+G (3df, 3pd) level.A new assignment of some experimental fundamental bands is proposed taking in to account the Fermi resonance between CH stretch and the five membered ring vibrations. For the first time more than 30 weak infrared absorption bands were observed and assigned to various combination vibrations and overtones. By using new spectral information concerning the overtones and the combination bands it is concluded that the dissociation of unstable ethene SOZ involving breaking of any of the four CO bonds of the five membered ring of ethene SOZ has low probability. Dissociation of the ring starts from breaking of the OO bond.

Infrared spectroscopic imaging of kidney tumor tissue

Infrared spectroscopic imaging of cancerous kidney tissue was performed by means of FTIR microscopy. The spectra of thin tissue cryosections were collected with 64x64 MCT FPA detector and imaging area was increased up to 5.4×5.4 mm by mapping by means of PC controlled x,y stage. Chemical images of the samples were constructed using statistical treatment of the raw spectra. Several unsupervised and supervised statistical methods were used. The imaging results are compared with results of the standard histopathological analysis. It was concluded that application of method of cluster analysis ensures the best contrast of the images. It was found that border between cancerous and normal tissues visible in the infrared spectroscopic image corresponds with the border visible in histopathological image. Closer examination of the infrared spectroscopic image reveals that small domains of cancerous cells are found beyond the border in areas distant from the border up to 3 mm. Such domains are not visible in the histopathological images. The smallest domains found in the infrared images are approx. 60 μm.

Conformational isomerism of 1-butene secondary ozonide as studied by means of matrix isolation infrared absorption spectroscopy

AbstractTheoretical calculations of structures, stability and vibrational spectra of 1-butene secondary ozonide (SOZ) conformers were performed using DFT method B3LYP with a 6-311++G(3df, 3pd) basis set. The calculations predict six staggered structures of 1-butene SOZ. The FTIR spectra of 1-butene SOZ isolated in Ar, N2 and Xe matrices were recorded. It was found that nitrogen is the best suited for the matrix isolation of 1-butene SOZ. The bandwidth of the spectral bands of the ozonide isolated in nitrogen was as narrow as 2 cm−1. For the first time the existence of five conformers of 1-butene SOZ were confirmed experimentally by means of matrix isolation infrared absorption spectroscopy. The equatorial gauche (∠OCCC=−66.1°) conformer was proved theoretically and experimentally to be the most stable. It was found that due to high potential barriers of the conformational transitions annealing of the matrix is useless for the assignment of spectral bands to various conformers of 1-butene SOZ. Using the hot nozzle technique the van’t Hoff experimental plots were made for three additional conformers of 1-butene SOZ and experimental ΔH values for these additional conformers were established. The crystallization problems of 1-butene SOZ are discussed which accounts for the rich conformational diversity of the ozonide as well as high conformational barriers for axial-equatorial transitions.