Daughter Molecule Research Articles

Evidence of Surface Catalytic Effect on Cosmic Dust Grain Analogs: The Ammonia and Carbon Dioxide Surface Reaction

Abstract Surface chemistry on cosmic dust grains plays an important role in the formation of molecules at low temperatures in the interstellar and circumstellar environments. For the first time, we experimentally put in evidence the catalytic role of dust surfaces using the thermal reaction CO2 + 2NH3 → NH2COO−, which is also a proxy of radical–radical reactions. Nanometer-sized amorphous silicate and carbon grains produced in our laboratory were used as grain analogs. Surface catalysis on grains accelerates the kinetics of the reaction studied at a temperature of 80 K by a factor of up to 3 compared to the reaction occurring in the molecular solid. The evidence of the catalytic effect of grain surfaces opens a door for experiments and calculations on the formation of interstellar and circumstellar molecules on dust. Ammonium carbamate on the surface of grains or released intact into protostellar or protoplanetary disk phases can give start to a network of prebiotic reactions. Therefore, there should be a great interest to search for ammonium carbamate and its daughter molecule, carbamic acid, in interstellar clouds, protostellar envelopes, and protoplanetary disks.

Depletion of 15N in the center of L1544: Early transition from atomic to molecular nitrogen?

We performed sensitive observations of the N15ND+(1–0) and 15NND+(1–0) lines toward the prestellar core L1544 using the IRAM 30 m telescope. The lines are not detected down to 3σ levels in 0.2 km s−1 channels of ~6 mK. The non-detection provides the lower limit of the 14N/15N ratio for N2D+ of ~700–800, which is much higher than the elemental abundance ratio in the local interstellar medium of ~200–300. The result indicates that N2 is depleted in 15N in the central part of L1544, because N2D+ preferentially traces the cold dense gas, and because it is a daughter molecule of N2. In situ chemistry is probably not responsible for the 15N depletion in N2; neither low-temperature gas phase chemistry nor isotope selective photodissociation of N2 explains the 15N depletion; the former prefers transferring 15N to N2, while the latter requires the penetration of interstellar far-ultraviolet (FUV) photons into the core center. The most likely explanation is that 15N is preferentially partitioned into ices compared to 14N via the combination of isotope selective photodissociation of N2 and grain surface chemistry in the parent cloud of L1544 or in the outer regions of L1544, which are not fully shielded from the interstellar FUV radiation. The mechanism is most efficient at the chemical transition from atomic to molecular nitrogen. In other words, our result suggests that the gas in the central part of L1544 has previously gone trough the transition from atomic to molecular nitrogen in the earlier evolutionary stage, and that N2 is currently the primary form of gas-phase nitrogen.

Detecting and Analyzing Genetic Recombination Using RDP4.

Recombination between nucleotide sequences is a major process influencing the evolution of most species on Earth. The evolutionary value of recombination has been widely debated and so too has its influence on evolutionary analysis methods that assume nucleotide sequences replicate without recombining. When nucleic acids recombine, the evolution of the daughter or recombinant molecule cannot be accurately described by a single phylogeny. This simple fact can seriously undermine the accuracy of any phylogenetics-based analytical approach which assumes that the evolutionary history of a set of recombining sequences can be adequately described by a single phylogenetic tree. There are presently a large number of available methods and associated computer programs for analyzing and characterizing recombination in various classes of nucleotide sequence datasets. Here we examine the use of some of these methods to derive and test recombination hypotheses using multiple sequence alignments.

First experimental photo-detachment spectrum of H2−

This letter reports the first photo-detachment spectrum of the hydrogen anion, H2−. The spectrum was recorded over the range of excitation energies Ehν=17600–17750cm−1, at known laser fluence and under non-saturation conditions. This permitted us to extract absolute values for the photo-depletion cross-section which varies in the range 1–6×10−18cm2 and exhibits oscillatory behaviour. This interesting behaviour was attributed to an electro-dynamical interaction between of the highly-rotating hydrogen daughter molecule and the detached electron. The presence of such oscillations may open new ways to investigate exotic anions relevant to molecular astrophysics and plasma physics.

A method to measure CO and N2depletion profiles inside prestellar cores

Context. In the dense and cold prestellar cores, many species freeze out onto grains to form ices. The most conspicuous case is that of CO itself. Only upper limits of this depletion amplitude can be estimated because the CO emission from the external undepleted layers mask the emission of CO left inside the depleted region. The finite signal-to-noise ratio of the observations is another limitation. However, depletion and even more desorption mechanisms are not well-known and need observational constraints, i.e., depletion profiles.Aims. We describe a method for retrieving the CO and N2 abundance profiles inside prestellar cores, which is mostly free of initial conditions.Methods. DCO+ is a daughter molecule of CO, which appears inside depleted prestellar cores. The main deuteration partners are the H3 + isotopologues. By determining the abundance of these isotopologues via N2 D+ , N2 H+ , and ortho-H2 D+ observations and a chemical model, we can uniquely constrain the CO abundance, the only free parameter left, to fit the observed DCO+ abundance. The N2 abundance is also determined in the same manner once CO is known. DCO+ –H2 collisional rates including the hyperfine structure were computed in order to determine the DCO+ abundance.Results. To illustrate the method, we apply it to the main L183 prestellar core and find that the CO abundance profile varies from ≥ 2.4 × 10-5 at the core edge to ≤ 6.6 × 10-8 at the center. This represents a relative decrease in abundance by ≥ 360, and by ≥ 2000 compared to the standard undepleted CO abundance (1–2 × 10-4 ). Comparatively, N2 abundance decreases much less, from ≤ 3.7 × 10-7 down to ~2.9 × 10-8 , in contrast to the similar binding properties of the two species. Because the N2 abundance is lower than its steady state value at the edge, while CO is close to its own, a possible explanation is that N2 is still in its production phase in competition with depletion. Conclusions. The method allows the CO and N2 abundance profiles to be retrieved in the depleted zone both without needing extremely high signal-to-noise observations and free of masking effects by extended emission from the cloud envelope. The main uncertainties are linked to the N2 H+ collisional rates and somewhat to the H3 + isotopologue rates, both collisional and chemical, but hardly to the initial conditions of the model. This method opens up possibilities of testing depletion and desorption mechanisms in prestellar cores and time evolution models, and of addressing the debated CO/N2 depletion controversy.

Lenalidomide down regulates the production of interferon-γ and the expression of inhibitory cytotoxic receptors of human Natural Killer cells

Lenalidomide, a daughter molecule of Thalidomide, and IMIDs® are immunomodulatory drugs that have been described as having immunomodulatory properties and anti-tumor activity. The effect of Lenalidomide towards Peripheral Blood Mononuclear Cells (PBMC) has been studied and direct effects towards T cells have been described, such as an increase of interferon-γ (IFN-γ) and interleukin (IL)-2 production. As a consequence, it has been also described that IL-2 subsequently activates Natural Killer (NK) cells. Nevertheless, direct effects of Lenalidomide on NK cells from healthy volunteers have never been described, if searched. Here we show that Lenalidomide can inhibit the production of IFN-γ by NK cells from healthy donors. It also modifies the phenotype of NK cells through a decrease of the expression of Killer cell Immunoglobulin-like Receptors (KIRs) and NKp46. However, we did not detect consequence of these phenotype modifications on the cytotoxic potential of NK cells.

A “Stopper” mutant of Neurospora crassa containing two populations of aberrant mitochondrial DNA

[E35], an extranuclear mutant of Neurospora crassa has all the phenotypic characteristics of the "stopper" mutants (De Vries et al. 1980). In the present work, the mitochondrial DNA as well as the mitochondrial translation products are characterized further. The primary mutational event appears to have been the deletion of about 4 kbp from the wild-type genome. Moreover, after prolonged vegetative growth the mutant accumulates an 8-μm circular mtDNA, which was demonstrated both by electronmicroscopy and by restriction enzyme analysis. Hence, the mutant contains two populations of aberrant mitochondrial DNA, the smaller of which is an amplification of the rRNA-tRNA part of the larger. We propose that the primary deletion has generated a signal in the larger DNA which can cause premature termination of replication at the deletion site, and subsequent circularization of the unfinished daughter molecule. Finally, the deleted part may contain a determinant for synthesis of a protein of 11 kDal. The function of this protein, which is not a subunit of the F0 ATPase, is not yet known.

Isophotometry of Comet Tago-Sato-Kosaka

AbstractNarrow-band filler photographs of comet TSK were taken in the light of C2, CN and C3 by Rahe McCracken and Donn, have been analysed in terms of Haser's model of the coma. The isophotes obtained from these photographs were corrected for sky background. The isophotes were circularly symmetric. Radial intensity profiles were obtained along the sunward, antisun and the two perpendicular directions. In each case, these profiles were the same within the experimental errors in intensity (±5%).Theoretical curves based on Haser's model were computed for different combinations of the parameters β0 and β1 where l/β0 is the scale length for the decay of the unobserved parent molecule and 1/β1 the corresponding quantity for the observed daughter molecule. A comparison of the theoretical and observed intensity profiles, yielded our best estimates for β0 and β1 for the different molecules. These are listed in Table 1. In some cases, we were able to obtain lower limits only to the ratio β0/β1 because the isophotes do not go out far enough, a limitation caused by the sky background. It is to be noted that the same values of the parameters were obtained from observations on different dates indicating no unusual activity in the comet in the intervening period. We believe ours is the first result ever obtained for C3.In Table 2, we summarize all the results for C2 and CN in different comets. It appears that the scale lengths differ between comets, a result which cannot be attributed to different helio-centric distances alone.

Dipole-quadrupole polarization correlation in photo-selection

The intensity and polarization correlation formulas for an electric dipole-electric quadrupole tandem two-photon process are explicitly developed using a general spherical-tensor formulation for multipole-radiation of any order. This is applicable to relative polarization studies in photoselection or photoluminescence studies. The molecules are oriented randomly with respect to the laboratory coordinates defined by the radiation field, and the intensity is written in terms of transition matrix elements taken over coordinates of the parent molecule (assumed to interact with one of the photons through the quadrupole mode) and the daughter molecule (assumed to interact with the other photon through the dipole mode). Some bipolar harmonics through the third order needed in the correlation are computed. As an alternative to the above spherical tensor formulation, we expressed the individual one-photon intensities for electric dipole and electric quadrupole transitions in terms of direction cosines between laboratory and molecular coordinates. Then, the two-photon intensities in terms of sixth power products of direction cosines are averaged over all molecular orientations in space. The two formulations yield identical results in terms of matrix elements over cartesian coordinates. This dipole-quadrupole correlation is evaluated for molecules of a few common point group symmetries.

Theory of Angular and Polarization Correlation in Tandem Two-Photon Processes: Application to Photoselection

To facilitate the interpretation of photoselection and photochemical experiments that depend on light intensity, generalized intensity distribution and polarization correlation formulas are derived. These are expressed in terms of Euler angles and multipole transition moments taking into account (1) molecular multipole radiation up to any order, inclusive of their coherent interference, (2) angular distribution of radiation for a given polarization, (3) application to molecules of arbitrary point-group symmetry, (4) arbitrary orientation of the second photon (pertaining to the daughter molecule) with respect to the first photon (pertaining to the parent molecule). For application to oriented molecular systems, examples of the angular characteristics of multipole moments responsible for a fixed polarization, are given up to quadrupole, inclusive of interference effects. It is emphasized that, in contrast to electric dipole radiation where the polarization is unique, for multipole radiation, both polarization and propagation directions must be specified, and that the commonly known dipole or quadrupole intensity which come from space average must be used with caution. For random molecular systems, the space average of the product of intensities for the two tandem and physically distinct one-photon processes are shown to contain “cross” terms, which otherwise vanish, if the space average of intensity were taken independently for the first (parent) and the second photon (daughter molecule). The cross terms are shown to be the consequence of the definition of light intensity for an arbitrary choice of the molecular coordinate system (vs the choice of the principal coordinate system) and of using the same coordinate system for the parent and the daughter molecule. In the space average over the product of four rotation matrices (vs four direction cosines for dipole radiation), use was made of the Clebsch–Gordan series for the coupling among these rotational transformation matrices. The intensity (or probability) products of the two tandem and distinct one-photon processes were then obtained as functions of bipolar harmonics of the transition moments. The coupling of these bipolar harmonics, in turn, gives rise to the polarization correlation between the parent and the daughter molecule. Specific examples, up to electric and magnetic quadrupole, are given for viewing the daughter molecule in directions parallel as well as perpendicular to the incident (first) photon. Also given are the cases of the two photons being in different radiation modes and of different wavelengths.

A new model of DNA replication

The “speedometer cable” model of DNA replication is a widely used hypothesis. However, it has never been proven. On the contrary, experimental facts have been accumulating which make this model less and less likely. Particularly, the postulated rotation of the entire replicating molecule is highly improbable when the bacterial chromosome is considered. We have suggested another hypothesis which does not involve the rotation of the molecule and seems to be consistent with known experimental observations. It consists of enzymatic disassembling of one strand which is then transferred piece by piece and rebuilt in its original shape as a part of a daughter molecule. The other strand remains available for RNA replication.

Proof that the Replication of DNA involves Separation of the Strands

IN their description of the specific pairing of the nucleotides of deoxyribonucleic acid (DNA), Watson and Crick1 proposed that this pairing was the basis for a mechanism of duplication: if unwinding occurred at the time of replication, each strand of the double helix could act as a template for the creation of a new molecule so that each daughter molecule would be a ‘hybrid’ of a parental strand and a new strand. Since then there have been several demonstrations that DNA replication does indeed result in an equal division of the parent molecule between the two daughters2,3. This, however, has not put the hypothesis beyond the realm of cavil. The DNA which divides between the two daughters might, the argument goes4,5, consist of a pair of double helices : if so, no unwinding of the strands would be necessary to produce the observed result, and the mechanism of replication could be radically different from that proposed by Watson and Crick.

The replication of DNA.

According to the proposal of Watson and Crick (1953a), a DNA molecule consists of two polynucleotide chains wound helically about a common axis. The nitrogen base (adenine, guanine, thymine, or cytosine) at each level on one chain is hydrogen-bonded to the base at the same level on the other chain. Structural requirements allow the occurrence of only the hydrogen-bonded base pairs adenine-thymine and guanine-cytosine, resulting in a detailed complementariness between the two chains. The self-complementariness of this structure suggested to its inventors (Watson and Crick, 1953b) a definite and structurally plausible hypothesis for the replication of the DNA molecule. According to this idea, the elementary replicative act is a molecular duplication. The two chains separate, exposing the hydrogen-bonding sites of the bases. Then, in accord with the base-pairing restrictions, each chain serves as a template for the synthesis of its complement. Accordingly, each daughter molecule contains one...

Molecular Excitation in Beta Decay

The theory of molecular excitation in beta decay is developed for the general case of a polyatomic molecule. Calculations of the daughter molecule vibrational excitation are carried through for diatomic molecules, and the results are presented graphically. Finally, the formation of the ${({\mathrm{He}}^{3}{\mathrm{H}}^{3})}^{+}$ molecule ion in the decay of one nucleus of a tritium molecule is studied in detail. It is concluded that the ${({\mathrm{He}}^{3}{\mathrm{H}}^{3})}^{+}$ ground electronic state vibrational spectrum should be observable in the light spontaneously emitted by tritium. For example, neglecting nonradiative transitions, one expects approximately ${10}^{14}$ photons per second to be radiated at wave number \ensuremath{\cong}2.35\ifmmode\times\else\texttimes\fi{}${10}^{3}$ ${\mathrm{cm}}^{\ensuremath{-}1}$ by every gram of tritium in the 1\ensuremath{\rightarrow}0 vibrational transition.

Excitation and Dissociation of Molecules Due to β Decay of a Constituent Atom

The theory of electronic, vibrational, and rotational excitation of a molecule, specifically a diatomic molecule, due to β decay of a substituent atom is presented. The nature of the vibrational and rotational excitation for certain specific cases is mathematically investigated. The problem of dissociation arising from the excitation of rotations is discussed. It is shown that it is very difficult to obtain exact figures on the probability of dissociation due to the excitation of vibrations and rotations. Molecular orbital wave functions are employed to gain some insight into the electronic excitation of the daughter molecule. A very rough calculation is made of the probability of nondissociation in the decay of C14 labeled ethane.

Immunologically Symmetrical Proteolysis

If 0.1 cc. horse serum is added to 1.9 cc. canine leucocytic extract and the mixture is incubated over night, titration of the resulting lytic products by means of ice-chest ripened rabbit precipitin gives precipitin graphs1 suggesting a 400% to 800% test-tube multiplication of horse proteins, without appreciable horse protein denaturization.The simplest explanation of this apparent increase is to assume that under the influence of leucocytic proteolysin each horse protein molecule is hydrolysed into from 4 to 8 daughter protein molecules, each daughter molecule being of approximate horse protein specificity.