We report the detection of the oxygen-bearing complex organic molecules propenal (C2H3CHO), vinyl alcohol (C2H3OH), methyl formate (HCOOCH3), and dimethyl ether (CH3OCH3) toward the cyanopolyyne peak ...of the starless core TMC-1. These molecules are detected through several emission lines in a deep Q-band line survey of TMC-1 carried out with the Yebes 40m telescope. These observations reveal that the cyanopolyyne peak of TMC-1, which is the prototype of cold dark cloud rich in carbon chains, contains also O-bearing complex organic molecules like HCOOCH3 and CH3OCH3, which have been previously seen in a handful of cold interstellar clouds. In addition, this is the first secure detection of C2H3OH in space and the first time that C2H3CHO and C2H3OH are detected in a cold environment, adding new pieces in the puzzle of complex organic molecules in cold sources. We derive column densities of (2.2 ± 0.3) × 1011 cm™2, (2.5 ± 0.5) × 1012 cm-2, (1.1 ± 0.2) × 1012 cm-2, and (2.5 ± 0.7) × 1012 cm-2 for C2H3CHO, C2H3OH, HCOOCH3, and CH3OCH3, respectively. Interestingly, C2H3OH has an abundance similar to that of its well known isomer acetaldehyde (CH3CHO), with C2H3OH/CH3CHO ~ 1 at the cyanopolyyne peak. We discuss potential formation routes to these molecules and recognize that further experimental, theoretical, and astronomical studies are needed to elucidate the true mechanism of formation of these O-bearing complex organic molecules in cold interstellar sources.
We report the detection for the first time in space of three new pure hydrocarbon cycles in TMC-1:
c
-C
3
HCCH (ethynyl cyclopropenylidene),
c
-C
5
H
6
(cyclopentadiene), and
c
-C
9
H
8
(indene). We ...derive a column density of 3.1 × 10
11
cm
−2
for the first cycle and similar values, in the range (1−2) × 10
13
cm
−2
, for the second and third. This means that cyclopentadiene and indene, in spite of their large size, are exceptionally abundant, only a factor of five less abundant than the ubiquitous cyclic hydrocarbon
c
-C
3
H
2
. The high abundance found for these two hydrocarbon cycles together with the high abundance previously found for the propargyl radical (CH
2
CCH) and other hydrocarbons, such as vinyl and allenyl acetylene (Agúndez et al. 2021, A&A, 647, L10; Cernicharo et al. 2021a, A&A, 647, L2; Cernicharo et al. 2021b, A&A, 647, L3), start to allow us to quantify the abundant content of hydrocarbon rings in cold dark clouds and to identify the intermediate species that are probably behind the in situ bottom-up synthesis of aromatic cycles in these environments. While
c
-C
3
HCCH is most likely formed through the reaction between the radical CCH and
c
-C
3
H
2
, the high observed abundances of cyclopentadiene and indene are difficult to explain through currently proposed chemical mechanisms. Further studies are needed to identify how five- and six-membered rings are formed under the cold conditions of a cloud such as TMC-1.
Our observations of TMC-1 with the Yebes 40 m radio telescope in the 31.0–50.3 GHz range allowed us to detect a group of unidentified lines, showing a complex line pattern indicative of an open-shell ...species. The observed frequencies of these lines and the similarity of the spectral pattern with that of the 2
0, 2
–1
0, 1
rotational transition of H
2
CCN indicate that the lines arise from the deuterated cyanomethyl radical, HDCCN. Using Fourier transform microwave spectroscopy experiments combined with electric discharges, we succeeded in producing the radical HDCCN in the laboratory and observed its 1
0, 1
–0
0, 0
and 2
0, 2
–1
0, 1
rotational transitions. From our observations and assuming a rotational temperature of 5 K, we derive an abundance ratio H
2
CCN/HDCCN = 20 ± 4. The high abundance of the deuterated form of H
2
CCN is well accounted for by a standard gas-phase model, in which deuteration is driven by deuteron transfer from the H
2
D
+
molecular ion.
We present a study of the isocyano isomers of the cyanopolyynes HC3N, HC5N, and HC7N in TMC-1 and IRC+10216 carried out with the Yebes 40m radio telescope. This study has enabled us to report the ...detection, for the first time in space, of HCCCCNC in TMC-1 and to give upper limits for HC6NC in the same source. In addition, the deuterated isotopologues of HCCNC and HNCCC were detected, along with all 13C substitutions of HCCNC, also for the first time in space. The abundance ratios of HC3N and HC5N, with their isomers, are very different in TMC-1 and IRC+10216, namely, N(HC5N)/N(HC4NC) is ~300 and ≥2100, respectively. We discuss the chemistry of the metastable isomers of cyanopolyynes in terms of the most likely formation pathways and by comparing observational abundance ratios between different sources.
We present the first identification in interstellar space of the propargyl radical (CH
CCH). This species was observed in the cold dark cloud TMC-1 using the Yebes 40m telescope. The six strongest ...hyperfine components of the 2
-1
rotational transition, lying at 37.46 GHz, were detected with signal-to-noise ratios in the range 4.6-12.3 σ. We derive a column density of 8.7 × 10
cm
for CH
CCH, which translates to a fractional abundance relative to H
of 8.7 × 10
. This radical has a similar abundance to methyl acetylene, with an abundance ratio CH
CCH/CH
CCH close to one. The propargyl radical is thus one of the most abundant radicals detected in TMC-1, and it is probably the most abundant organic radical with a certain chemical complexity ever found in a cold dark cloud. We constructed a gas-phase chemical model and find calculated abundances that agree with, or fall two orders of magnitude below, the observed value depending on the poorly constrained low-temperature reactivity of CH
CCH with neutral atoms. According to the chemical model, the propargyl radical is essentially formed by the C + C
H
reaction and by the dissociative recombination of C
H
ions with
= 4-6. The propargyl radical is believed to control the synthesis of the first aromatic ring in combustion processes, and it probably plays a key role in the synthesis of large organic molecules and cyclization processes to benzene in cold dark clouds.
Aims
Saliva has been previously used as an inoculum for in vitro oral biofilm studies. However, the microbial community profile of saliva is markedly different from hard‐ and soft‐tissue‐associated ...oral biofilms. Here, we investigated the changes in the biofilm architecture and microbial diversity of in vitro oral biofilms developed from saliva, tongue or plaque‐derived inocula under different salivary shear forces.
Methods and Results
Four inoculum types (saliva, bacteria harvested from the tongue, toothbrush and curette‐harvested plaque) were collected and pooled. Biofilms (n ≥ 15) were grown for 20 h in cell‐free human saliva flowing at three different shear forces. Stained biofilms were imaged using a confocal laser scanning microscope. Biomass, thickness and roughness were determined by image analysis and bacterial community composition analysed using Ion Torrent. All developed biofilms showed a significant reduction in observed diversity compared with their respective original inoculum. Shear force altered biofilm architecture of saliva and curette‐collected plaque and community composition of saliva, tongue and curette‐harvested plaque.
Conclusions
Different intraoral inocula served as precursors of in vitro oral polymicrobial biofilms which can be influenced by shear.
Significance and Impact of the Study
Inoculum selection and shear force are key factors to consider when developing multispecies biofilms within in vitro models.
Remineralization of caries lesions is naturally achieved by salivary ions, and it can be enhanced by external factors or elements such as fluoride. Numerous studies have demonstrated the ...remineralizing efficacy of fluoride therapies as well as the limitations with some groups of the population. Consequently, developing new remineralization therapies to close this gap in efficacy has been a priority for the last 2 decades. In this review, we summarize and briefly discuss some of the latest advances in remineralization therapies. Most new therapies try to enhance the effect of fluoride by adding other potentially active ingredients to the formulation, such as calcium, phosphate, stannous, xylitol, and arginine. Other remineralization strategies have focused on creating remineralizing scaffolds within the lesions (e.g., self-assembling peptides). While several of the new remineralization strategies have progressed significantly in recent years, for most of them, the evidence is still insufficient to assess their true clinical potential.
Context.
The reaction between carbon atoms and vinyl cyanide, CH
2
CHCN, is a formation route to interstellar 3-cyano propargyl radical, CH
2
C
3
N, a species that has recently been discovered in ...space. The 1-cyano propargyl radical (HC
3
HCN), an isomer of CH
2
C
3
N, is predicted to be produced in the same reaction at least twice more efficiently than CH
2
C
3
N. Hence, HC
3
HCN is a plausible candidate to be observed in space as well.
Aims.
We aim to generate the HC
3
HCN radical in the gas phase in order to investigate its rotational spectrum. The derived spectroscopic parameters for this species will be used to obtain reliable frequency predictions to support its detection in space.
Methods.
The HC
3
HCN radical was produced by an electric discharge, and its rotational spectrum was characterized using a Balle-Flygare narrowband-type Fourier-transform microwave spectrometer operating in the frequency region of 4–40 GHz. The spectral analysis was supported by high-level ab initio calculations.
Results.
A total of 193 hyperfine components that originated from 12 rotational transitions,
a
- and
b
-type, were measured for the HC
3
HCN radical. The analysis allowed us to accurately determine 22 molecular constants, including rotational and centrifugal distortion constants as well as the fine and hyperfine constants. Transition frequency predictions were used to search for the HC
3
HCN radical in TMC-1 using the QUIJOTE survey between 30 and 50 GHz. We do not detect HC
3
HCN in TMC-1 and derive a 3
σ
upper limit to its column density of 6.0 × 10
11
cm
−2
.
PDF
