A reinvestigation of the boron cluster B: a benchmark of density functionals and consideration of aromaticity models.

This study presents a thorough reinvestigation of the B isomers, first employing coupled-cluster theory CCSD(T) calculations to validate the performance of different DFT functionals. The B cation has two planar lowest-lying isomers, while the first 3D isomer is less stable than the global minimum by ∼10 kcal mol. The PBE functional, within this benchmark survey, has proved to be reliable in predicting relative energies for boron isomers.

Design of Liquid Crystal Materials Based on Palmitate, Oleate, and Linoleate Derivatives for Optoelectronic Applications.

Herein, liquid crystalline derivatives based on palmitate, oleate, and linoleate moieties with azomethine cores were synthesized, and their physical, chemical, optical, and photophysical properties were investigated in detail. The mesomorphic activity of these materials was examined through polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The observed results revealed that the stability of the thermal mesophase depends on the terminal polar as well as on the fatty long-chain substituents.

Autocatalysis in Formose Reaction and Formation of RNA Nucleosides.

Understanding of the abiotic formation of nucleosides under geochemical conditions is currently a major scientific challenge. In this study, free radical pathways for formation of RNA nucleosides with canonical nucleobases are proposed for the first time. The pathways proceed with relatively low energy barriers for the formation of ribose as well as all RNA nucleosides.

Reaction Routes for Experimentally Observed Intermediates in the Prebiotic Formation of Nucleobases under High-Temperature Conditions.

The prebiotic synthesis of nucleobases is of particular interest, given the experimental evidence that indicated formation of the nucleobases under abiotic conditions on the Early Earth under high-temperature conditions. Biomolecules have been formed under meteoritic impact scenarios that lead to high temperature and the generation of high energy. Free radical pathways for the formation of biomolecules are appropriate under these conditions.

Unified reaction pathways for the prebiotic formation of RNA and DNA nucleobases.

The reaction pathways for the prebiotic formation of nucleobases are complex and lead to the formation of a mixture of products. In the past 50 years, there has been a concerted effort for identifying a unified mechanism for the abiotic origin of the biomolecules but with little success. In the present theoretical study, we identified two prominent precursors for the building up of RNA and DNA nucleobases under prebiotic conditions: (a) 1,2-diaminomaleonitrile (DAMN), which is a tetramer of hydrogen cyanide (HCN), and (b) formamide, a hydrolysis product of HCN; it is important to emphasize that HCN is the source of both precursors.

Tandem mass spectrometry and density functional theory of RDX fragmentation pathways: Role of ion-molecule complexes in loss of NO3 and lack of molecular ion peak.

Rationale: Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is an explosive compound that finds a wide range of military and civilian applications. RDX has been a target in environmental matrices by gas chromatography/tandem mass spectrometry (GC/MS/MS). MS/MS in negative chemical ionization (NCI) mode of RDX provides important fragmentation patterns that are useful for structural elucidation.

Acetylene as an essential building block for prebiotic formation of pyrimidine bases on Titan.

Prebiotic building blocks for the formation of biomolecules are important in understanding the abiotic origin of biomolecules. However, there is a limited choice of the building blocks as precursors for the biomolecules. Acetylene (HCCH) is found in Titan's atmosphere and is an abiotic-precursor of pyrimidine bases.

Radical Pathways for the Prebiotic Formation of Pyrimidine Bases from Formamide.

The prebiotic formation of nucleobases, the building blocks of RNA/DNA, is of current interest. Highly reactive radical species present in the atmosphere under irradiation have been suggested to be involved in the prebiotic synthesis of nucleobases from formamide (FM). We studied several free radical reaction pathways for the synthesis of pyrimidine bases (cytosine, uracil, and thymine) from FM under cold conditions.

Collision induced dissociations of non-derivatized and trimethylsilyl-derivatized estradiols: similarities in fragmentation patterns.

Fragmentation mechanisms of estradiol and trimethylsilyl (TMS)-derivatized estradiol were studied by triple quadrupole tandem mass spectrometry (MSMS) and density functional theory (DFT) at B3LYP/6-311G(d,p) level. Collision induced dissociations (CID) of estradiol give product ions that are associated with the cleavage of B, C and D rings. Characteristic fragments from the cleavage of the aromatic ring A were not identified, and this was confirmed with both labeled estradiol and trimethylsilyl (TMS)-derivatized estradiol.

Free radical routes for prebiotic formation of DNA nucleobases from formamide.

Modeling the complicated chemical reactions in the interstellar medium and surface materials of Titan is nontrivial. Since both the atmosphere and the surface are rich in organic molecules, the chemistry may have important implications for the origin of biomolecules. Prebiotic synthesis of DNA nucleobases from simple molecules such as formamide has been known for more than half a century.

Density functional theory and mass spectrometry of phthalate fragmentations mechanisms: modeling hyperconjugated carbocation and radical cation complexes with neutral molecules.

This is the first ab initio study of the energetics of the fragmentation mechanisms of phthalate, by mass spectrometry, leading to protonated phthalic anhydride (m/z 149). Phthalates fragment by two major pathways; namely, the McLafferty + 1 rearrangement and the loss of alkoxy. Both pathways involve a carbonyl oxygen attack to the ortho-carbonyl carbon leading to structures with tetrahedral carbon intermediates that eventually give m/z 149.

Hydrogen rearrangement and ring cleavage reactions study of progesterone by triple quadrupole mass spectrometry and density functional theory.

The fragmentation mechanisms of progesterone have been studied by triple quadrupole tandem mass spectrometry (MSMS) and density functional theory (DFT). Mechanisms leading to major product ions are proposed. The data suggest that progesterone fragments preferentially via hydrogen and other rearrangements lead to neutral losses.

Positive chemical ionization triple-quadrupole mass spectrometry and ab initio computational studies of the multi-pathway fragmentation of phthalates.

We report the first positive chemical ionization (PCI) fragmentation mechanisms of phthalates using triple-quadrupole mass spectrometry and ab initio computational studies using density functional theories (DFT). Methane PCI spectra showed abundant [M + H](+), together with [M + C(2)H(5)](+) and [M + C(3)H(5)](+). Fragmentation of [M + H](+), [M + C(2)H(5)](+) and [M + C(3)H(5)](+) involved characteristic ions at m/z 149, 177 and 189, assigned as protonated phthalic anhydride and an adduct of phthalic anhydride with C(2)H(5)(+) and C(3)H(5)(+), respectively.