The
ground state millimeter/submillimeter rotational spectrum of
pyruvic acid, a potential interstellar precursor to alanine, was collected
and assigned from 90 GHz to 1 THz with extension of the assignments
up to maximum J = 99, K
a
= 49, and K
c
= 99. Previous work on pyruvic acid collected and assigned
its spectrum up to 314 GHz with maximum J = 70, K
a
= 42, and K
c
= 70. Fitting was conducted using the
ERHAM program due to the presence of an internally rotating methyl
group. This fit resulted in the refinement of the rotational constants
making the spectrum of pyruvic acid well-predicted across the entire
spectral range of ground-based far-IR telescopes. A subsequent search
for pyruvic acid in 30 different astronomical sources was conducted
using the results from the experimental spectrum. No definitive detection
of pyruvic acid was identified. The results of the laboratory and
observational work are presented herein and discussed in the context
of prebiotic astrochemistry.
Pyruvic acid (C 3 H 4 O 3 , or HOOCOCCH 3 ) is one of the main reactants in the Krebs Cycle of biological systems where sugar is metabolized and glucose is converted to lactic acid. Its presence in carbonaceous meteorites has already been confirmed, and its abiotic formation in experimental ice analogs implies the potential for exogenous delivery to planets via comets and asteroids. Therefore, it is important to have a complete experimental spectrum within the same wavelengths of astronomical telescopes to facilitate detections of pyruvic acid. Previous work on pyruvic acid reported the spectrum from 160 GHz to 314 GHz. At room temperature, these measurements only cover part of the Boltzmann peak. Additionally, with the spectral coverage now available at telescopes ranging up to and beyond 1 THz, measurements covering a significantly broader region of the molecular spectrum are required. Newly-developed experimental capabilities and sensitivities have since allowed for more sensitive measurement of the rotational transitions in this same wavelength regime and beyond. This work remeasures and extends the spectrum of pyruvic acid from 90 GHz up to 1 THz. Spectral prediction and fitting was conducted using the ERHAM program based on the previous work. Reanalysis using XIAM was then performed due to key advantages and disadvantages in each program. The results of the spectral study and analysis of pyruvic acid from 90 GHz to 1 THz will be presented.
Crystals were obtained from a solution containing 3,4-dichlorophenol and imidazole in 1:1 stoichiometric proportions. These are of a 2:1 co-crystal [P-1, a = 7.6731(7) Å, b = 8.2007(7) Å, c = 14.229(2) Å, α = 80.320(1)°, β = 84.070(1)°, γ = 68.699(1)°] of 3,4-dichlorophenol and imidazole. One of the phenol molecules donates a hydrogen bond to the imidazole molecule and is a hydrogen bond acceptor from the second phenol. A second reaction mixture (in which equal moles of 3,4-dichlorophenol and tetramethylammonium hydroxide were added together) resulted in other crystals. These are of a 2:1 co-crystal [P21/n, a = 10.3392(4) Å, b = 16.6235(5) Å, c = 14.7074(5) Å, β = 91.602(3)°] of 3,4-dichlorophenol and tetramethylammonium 3,4dichlorophenolate. In these crystals, one of the phenols is disordered while the second phenol molecule is not, and the phenolate is accepting hydrogen bonds from two phenol molecules. The structures of the 3,4-dichlorophenol(ate) moieties will be compared to each other and to that of pure 3,4-dichlorophenol.
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