1,633 research outputs found
Tunnelling dominates the reactions of hydrogen atoms with unsaturated alcohols and aldehydes in the dense medium
Hydrogen addition and abstraction reactions play an important role as surface
reactions in the buildup of complex organic molecules in the dense interstellar
medium. Addition reactions allow unsaturated bonds to be fully hydrogenated,
while abstraction reactions recreate radicals that may undergo radical-radical
recombination reactions. Previous experimental work has indicated that double
and triple C--C bonds are easily hydrogenated, but aldehyde -C=O bonds are not.
Here, we investigate a total of 29 reactions of the hydrogen atom with
propynal, propargyl alcohol, propenal, allyl alcohol, and propanal by means of
quantum chemical methods to quantify the reaction rate constants involved.
First of all, our results are in good agreement with and can explain the
observed experimental findings. The hydrogen addition to the aldehyde group,
either on the C or O side, is indeed slow for all molecules considered.
Abstraction of the H atom of the aldehyde group, on the other hand, is among
the faster reactions. Furthermore, hydrogen addition to C--C double bonds is
generally faster than to triple bonds. In both cases, addition on the terminal
carbon atom that is not connected to other functional groups is easiest.
Finally, we wish to stress that it is not possible to predict rate constants
based solely on the type of reaction: the specific functional groups attached
to a backbone play a crucial role and can lead to a spread of several orders of
magnitude in the rate constant.Comment: Accepted for publication in A&
In active acromegaly, IGF1 bioactivity is related to soluble Klotho levels and quality of life
The value of measuring IGF1 bioactivity in active acromegaly is unknown. Soluble Klotho (S-Klotho) level is elevated in active acromegaly and it has been suggested that S-Klotho can inhibit activation of the IGF1 receptor (IGF1R). A cross-sectional study was carried out in 15 patients with active acromegaly based on clinical presentation, unsuppressed GH during an oral glucose tolerance test, and elevated total IGF1 levels (>+2 s.d.). Total IGF1 was measured by immunoassay, IGF1 bioactivity by the IGF1R kinase receptor activation assay and S-Klotho by an ELISA. Quality of Life (QoL) was assessed by Acromegaly QoL (AcroQoL) Questionnaire and Short-Form-36 Health Survey Questionnaire (SF-36). Out of 15 patients, nine had IGF1 bioactivity values within the reference range. S-Klotho was higher in active acromegaly compared with controls. Age-adjusted S-Klotho was significantly related to IGF1 bioactivity (r=0.75, P=0.002) and to total IGF1 (r=0.62, P=0.02). IGF1 bioactivity and total IGF1 were inversely related to the physical component summary of the SF-36 (r=−0.78, P=0.002 vs r=−0.60, P=0.03). Moreover, IGF1 bioactivity, but not total IGF1, was significantly inversely related to the physical dimension of the AcroQoL Questionnaire (r=−0.60, P=0.02 vs r=−0.37, P=0.19). In contrast to total IGF1, IGF1 bioactivity was within the reference range in a considerable number of subjects with active acromegaly. Elevated S-Klotho levels may have reduced IGF1 bioactivity. Moreover, IGF1 bioactivity was more strongly related to physical measures of QoL than total IGF1, suggesting that IGF1 bioactivity may better reflect physical limitations perceived in active acromegaly
Self-Awareness After Brain Injury:Relation with Emotion Recognition and Effects of Treatment
Item does not contain fulltextSelf-awareness is often impaired after acquired brain injury (ABI) and this hampers rehabilitation, in general: unrealistic reports by patients about their functioning and poor motivation and compliance with treatment. We evaluated a self-awareness treatment that was part of a treatment protocol on executive dysfunction (Spikman, Boelen, Lamberts, Brouwer, & Fasotti, 2010). A total of 63 patients were included, aged 17-70, suffering non-progressive ABI, and minimum time post-onset of 3 months. Self-awareness was measured by comparing the patient's Dysexecutive Questionnaire (Wilson, Alderman, Burgess, Emslie, & Evans, 1996) score with that of an independent other. As emotion recognition is associated with self-awareness and influences the effect of rehabilitation treatment, we assessed this function using the Facial Expressions of Emotion-Stimuli and Tests (Young, Perrett, Calder, Sprengelmeyer, & Ekman, 2002). Results showed that patients in the experimental treatment group (n = 29) had better self-awareness after training than control patients (n = 34). Moreover, our results confirmed that the level of self-awareness before treatment was related to emotion recognition. Hence, self-awareness can improve after neuropsychological treatment fostering self-monitoring. Since neuropsychological treatment involves social learning, impairments in social cognition should be taken into account before starting and during treatment.8 p
Relevance of the H_2 + O reaction pathway for the surface formation of interstellar water. Combined experimental and modeling study
The formation of interstellar water is commonly accepted to occur on the surfaces of icy dust grains in dark molecular clouds at low temperatures (10–20 K), involving hydrogenation reactions of oxygen allotropes. As a result of the large abundances of molecular hydrogen and atomic oxygen in these regions, the reaction H_2 + O has been proposed to contribute significantly to the formation of water as well. However, gas-phase experiments and calculations, as well as solid-phase experimental work contradict this hypothesis. Here, we use precisely executed temperature-programmed desorption (TPD) experiments in an ultra-high vacuum setup combined with kinetic Monte Carlo simulations to establish an upper limit of the water production starting from H_2 and O. These reactants were brought together in a matrix of CO_2 in a series of (control) experiments at different temperatures and with different isotopological compositions. The water detected with the quadrupole mass spectrometer upon TPD was found to originate mainly from contamination in the chamber itself. However, if water is produced in small quantities on the surface through H_2 + O, this can only be explained by a combined classical and tunneled reaction mechanism. An absolutely conservative upper limit for the reaction rate was derived with a microscopic kinetic Monte Carlo model that converts the upper limit into the highest possible reaction rate. Incorporating this rate into simulation runs for astrochemically relevant parameters shows that the upper limit to the contribution of the reaction H_2 + O in OH, and hence water formation, is 11% in dense interstellar clouds. Our combined experimental and theoretical results indicate, however, that this contribution is most likely much lower
Formation of COMs through CO hydrogenation on interstellar grains
Glycoaldehyde, ethylene glycol, and methyl formate are complex organic
molecules that have been observed in dark molecular clouds. Because there is no
efficient gas-phase route to produce these species, it is expected that a
low-temperature surface route existst that does not require energetic
processing. CO hydrogenation experiments at low temperatures showed that this
is indeed the case. Glyoxal can form through recombination of two HCO radicals
and is then further hydrogenated. Here we aim to constrain the methyl formate,
glycolaldehyde, and ethylene glycol formation on the surface of interstellar
dust grains through this cold and dark formation route. We also probe the
dependence of the grain mantle composition on the initial gas-phase composition
and the dust temperature. A full CO hydrogenation reaction network was built
based on quantum chemical calculations for the rate constants and branching
ratios. This network was used in combination with a microscopic kinetic Monte
Carlo simulation to simulate ice chemistry, taking into account all positional
information. After benchmarking the model against CO-hydrogenation experiments,
simulations under molecular cloud conditions were performed. COMs are formed in
all interstellar conditions we studied, even at temperatures as low as 8 K.
This is because the HCO + HCO reaction can occur when HCO radicals are formed
close to each other and do not require to diffuse. Relatively low abundances of
methyl formate are formed. The final COM abundances depend more on the H-to-CO
ratio and less on temperature. Only above 16 K, where CO build-up is less
efficient, does temperature start to play a role. Molecular hydrogen is
predominantly formed through abstraction reactions on the surface. Our
simulations are in agreement with observed COM ratios for mantles that have
been formed at low temperatures
Massive Star Cluster Formation and Destruction in Luminous Infrared Galaxies in GOALS
We present the results of a {\it Hubble Space Telescope} ACS/HRC FUV, ACS/WFC
optical study into the cluster populations of a sample of 22 Luminous Infrared
Galaxies in the Great Observatories All-Sky LIRG Survey. Through integrated
broadband photometry we have derived ages and masses for a total of 484 star
clusters contained within these systems. This allows us to examine the
properties of star clusters found in the extreme environments of LIRGs relative
to lower luminosity star-forming galaxies in the local Universe. We find that
by adopting a Bruzual \& Charlot simple stellar population (SSP) model and
Salpeter initial mass function, the age distribution of clusters declines as
, consistent with the age distribution derived
for the Antennae Galaxies, and interpreted as evidence for rapid cluster
disruption occuring in the strong tidal fields of merging galaxies. The large
number of young clusters identified in the sample also
suggests that LIRGs are capable of producing more high-mass clusters than what
is observed to date in any lower luminosity star-forming galaxy in the local
Universe. The observed cluster mass distribution of is consistent with the canonical -2 power law used to describe the
underlying initial cluster mass function (ICMF) for a wide range of galactic
environments. We interpret this as evidence against mass-dependent cluster
disruption, which would flatten the observed CMF relative to the underlying
ICMF distribution.Comment: 63 pages, 58 Figures, 56 Tables, Accepted for publication in Ap
Episodic abdominal pain characteristics are not associated with clinically relevant improvement of health status after cholecystectomy
BACKGROUND: Cholecystectomy is the therapy of first choice in patients with uncomplicated symptomatic cholecystolithiasis, but it remains unclear which patients truly benefit in terms of health status improvement. Patients generally present with episodic abdominal pain of varying frequency, duration, and intensity. We assessed whether characteristics of abdominal pain episodes are determinants of clinically relevant improvement of health status after cholecystectomy. METHODS: In a post hoc analysis of a prospective multicenter cohort study, patients of ≥18 years of age with uncomplicated symptomatic cholecystolithiasis subjected to cholecystectomy were included. Preoperatively, patients received a structured interview and a questionnaire consisting of the visual analogue scale (VAS; range 0–100) and gastrointestinal quality of life index (GIQLI). At 12 weeks after cholecystectomy, the GIQLI was again administered. Logistic regression analyses were performed to determine significant associations. RESULTS: Questionnaires were sent to 261 and returned by 166 (63.6 %) patients (128 females, mean age at surgery 49.5 ± 13.8). A total of 131 (78.9 %) patients reported a clinically relevant improvement of health status. The median (interquartile range) frequency, duration, and intensity of abdominal pain episodes were 0.38 (0.18–0.75) a week, 4.00 (2.00–8.00) hours, and 92 (77–99), respectively. None of the characteristics was associated with a clinically relevant improvement of health status at 12 weeks after cholecystectomy. CONCLUSIONS: Characteristics of abdominal pain episodes cannot be used to inform patients with symptomatic cholecystolithiasis who are skeptic about the timing of cholecystectomy for optimal benefit. Timing of cholecystectomy should therefore be based on other characteristics and preferences
Internalization of the radioiodinated somatostatin analog [125I-Tyr3]octreotide by mouse and human pituitary tumor cells: increase by unlabeled octreotide
Recently, we developed a technique that allows the in vivo visualization
in man of somatostatin receptor-positive neuroendocrine tumors after i.v.
injection of [125I-Tyr3]octreotide or [111In-DTPA-D-Phe1]octreotide.
Radiotherapy of such tumors using somatostatin analogs coupled to alpha-
or beta-emitting radionuclides has been proposed as an application for
radiolabeled somatostatin analogs. To develop this concept further, it is
of importance to know whether the above-mentioned radiolabeled
somatostatin analogs are internalized by the tumor cells, and whether it
might be possible to manipulate the degree of internalization. In the
present study we investigated the internalization of a stable somatostatin
analog, [125I-Tyr3]octreotide, by mouse AtT20/D16V pituitary tumor cells
and primary cultures of human GH-secreting pituitary tumor cells.
Treatment of the cells with low pH was used to distinguish between
membrane-bound (acid-releasable) and internalize (acid-resistant)
radioligand. [125I-Tyr3]octreotide showed a time-dependent increasing
accumulation in AtT20 cells; after 4 h of incubation, values up to 6-8% of
the dose of radioligand added were obtained. Binding and internalization
of [125I-Tyr3]octreotide were temperature dependent and inhibited by
pertussis toxin. Inhibitors of lysosomal degradation did not increase the
amount of internalized radioligand. After 4 h of incubation, 88% of the
radioactivity present in the cells was still peptide bound, suggesting a
low intracellular breakdown of this radioligand. Six of seven human
GH-secreting adenoma cell cultures also internalized [125I-Tyr3]octreotide
(variation between 0.24-4.98% of the dose radioligand added). Displacement
of binding and internalization of [125I-Tyr3]octreotide by unlabeled
octreotide showed a bell-shaped curve in AtT20 cells. At low
concentrations (0.1 and 1 nM), binding and internalization were increased,
whereas at higher concentrations, saturation occurred. In contrast to
this, binding of [125I-Tyr3]octreotide to a broken cell preparation of
AtT20 cells was displaced in a dose-dependent manner by unlabeled
octreotide, with an IC50 of 0.1 nM. Similar observations were made in the
human GH-secreting adenoma cell cultures. In conclusion, a high amount of
[125I-Tyr3]octreotide is internalized in a specific-, time-, temperature-,
and pertussis toxin-sensitive GTP-binding protein-dependent manner by
mouse AtT20 and human GH-secreting pituitary tumor cells. In the presence
of a low concentration of unlabeled octreotide, a rapid increase in the
amount of [125I-Tyr3]octreotide internalized by AtT20 cells and by the
majority of the human GH-secreting adenoma cell cultures was
found.(ABSTRACT TRUNCATED AT 400 WORDS
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