Elucidation of the O(1D) + HF → F + OH mechanism by means of quasiclassical trajectories.

The dynamics and mechanism of the O((1)D) + HF → F + OH reaction have been studied through quasi-classical trajectory calculations carried out on the 1(1)A' Potential Energy Surface (PES) fitted by Gómez-Carrasco et al. [Chem. Phys. Lett., 2007, 435, 188]. The influence of the collision energy and the initial rovibrational state on the reaction has been considered. As a result of this study, we conclude that for v = 0 the reactive collisions take place exclusively through an indirect mechanism that involves a long-lived complex. Interestingly and somewhat unexpectedly for a barrierless reaction, vibrational excitation causes a large enhancement of the reactivity due to the concurrence of a direct abstraction mechanism. Unlike other reactions also taking place on a barrierless PES featuring deep wells, no insertion mechanism is observed in O((1)D) + HF reactive collisions.

Dynamics of the D+ + H2 and H+ + D2 reactions: a detailed comparison between theory and experiment.

An extensive set of experimental measurements on the dynamics of the H(+) + D(2) and D(+) + H(2) ion-molecule reactions is compared with the results of quantum mechanical (QM), quasiclassical trajectory (QCT), and statistical quasiclassical trajectory (SQCT) calculations. The dynamical observables considered include specific rate coefficients as a function of the translational energy, E(T), thermal rate coefficients in the 100-500 K temperature range. In addition, kinetic energy spectra (KES) of the D(+) ions reactively scattered in H(+) + D(2) collisions are also presented for translational energies between 0.4 eV and 2.0 eV. For the two reactions, the best global agreement between experiment and theory over the whole energy range corresponds to the QCT calculations using a gaussian binning (GB) procedure, which gives more weight to trajectories whose product vibrational action is closer to the actual integer QM values. The QM calculations also perform well, although somewhat worse over the more limited range of translational energies where they are available (E(T) < 0.6 eV and E(T) < 0.2 eV for the H(+) + D(2) and D(+) + H(2) reactions, respectively). The worst agreement is obtained with the SQCT method, which is only adequate for low translational energies. The comparison between theory and experiment also suggests that the most reliable rate coefficient measurements are those obtained with the merged beams technique. It is worth noting that none of the theoretical approaches can account satisfactorily for the experimental specific rate coefficients of H(+) + D(2) for E(T)≤ 0.2 eV although there is a considerable scatter in the existing measurements. On the whole, the best agreement with the experimental laboratory KES is obtained with the simulations carried out using the state resolved differential cross sections (DCSs) calculated with the QCT-GB method, which seems to account for most of the observed features. In contrast, the simulations with the SQCT data predict kinetic energy spectra (KES) considerably cooler than those experimentally determined.

Energy dependent dynamics of the O(1D) + HCl reaction: a quantum, quasiclassical and statistical study.

The dynamics of the reaction O((1)D) + HCl → ClO + H, OH + Cl has been investigated in detail by means of a time-dependent wave packet (TDWP) method in comparison with quasiclassical trajectory (QCT) and statistical approaches on the ground potential energy surface by Martínez et al. [Phys. Chem. Chem. Phys., 2000, 2, 589]. Fully coupled quantum mechanical (QM) reaction probabilities for high values of the total angular momentum (J≤ 50) are reported for the first time. At the low collision energy regime (E(c)≤ 0.4 eV) the TDWP probabilities are well reproduced by the QCT and statistical results for the ClO forming product channel, but for the OH + Cl arrangement, only QCT probabilities are found to agree with the QM values. The good accordance found between the rigorous statistical models and the dynamical QM and QCT calculations for the O + HCl → ClO + H process underpins the assumption that the reaction pathway leading to ClO is predominantly governed by a complex-forming mechanism. In addition, to further test the statistical character of this reaction channel, the laboratory angular distribution and time-of-flight spectra obtained in a crossed molecular beam study by Balucani et al. [Chem. Phys. Lett. 1991, 180, 34] at a collision energy as high as 0.53 eV have been simulated using the state resolved differential cross section obtained with the statistical approaches yielding a satisfactory agreement with the experimental results. For the other channel, O + HCl → OH + Cl, noticeable differences between the statistical results and those found with the QCT calculation suggest that the dynamics of the reaction are controlled by a direct mechanism. The comparison between the QCT and QM-TDWP results in the whole range of collision energies lends credence to the QCT description of the dynamics of this reaction.

Reaction dynamics of the D+ + H2 system. A comparison of theoretical approaches.

The dynamics of the deuteron-proton exchange D(+) + H(2) → HD + H(+) reaction on its ground 1(1)A' potential energy surface has been the subject of a theoretical study for collision energies below 1.5 eV. The results obtained with three theoretical approaches: quasi-classical trajectory (QCT), statistical quasi-classical trajectory (SQCT), and accurate time-independent quantum mechanical (QM) calculations are compared in the range of collision energies from 5 meV to 0.2 eV. The QM calculations included all total angular momentum quantum numbers, J, up to J(max) ≈ 40 and all the Coriolis couplings. For higher collision energies, the comparison was restricted to the QCT and SQCT results given the enormous computational cost implied in the QM calculations. Reaction cross sections as a function of collision energy (excitation functions) for various initial rovibrational states have been determined and compared with the corresponding results for the endothermic H(+) + D(2) → HD + D(+) isotopic variant. The excitation function for the title reaction decays monotonically with collision energy as expected for an exothermic reaction without a barrier, in contrast to the behaviour observed in the mentioned H(+) + D(2) (v = 0, j ≤ 3). Reaction probabilities as a function of J (opacity functions) at several collision energies calculated with the different approaches were also examined and important differences between them were found. The effect of using the gaussian binning procedure that preserves, to a large extent, the zero point energy, as compared to the standard histogram binning in the QCT calculations, is also examined. At low collision energy, the best agreement with the accurate QM results is given by the SQCT data, although they tend to overestimate the reactivity. The deviations from the statistical behaviour of the QCT data at higher energies are remarkable. Nevertheless, on the whole, the title reaction can be deemed more statistical than the H(+) + D(2) reaction.

The dynamics of the O(1D) + HCl --> OH + Cl reaction at a 0.26 eV collision energy: a comparison between theory and experiment.

The dynamics of the O((1)D) + HCl(v = 0, j = 0) --> Cl + OH reaction at a 0.26 eV collision energy has been investigated by means of a quasiclassical trajectory (QCT) and statistical quantum and quasiclassical methods. State-resolved cross sections and Cl atom velocity distributions have been calculated on two different potential energy surfaces (PESs): the H2 surface (Martinez et al. Phys. Chem. Chem. Phys. 2000, 2, 589) and the latest surface by Peterson, Bowman, and co-workers (PSB2) (J. Chem. Phys. 2000, 113, 6186). The comparison with recent experimental results reveals that the PSB2 PES manages to describe correctly differential cross sections and the velocity distributions of the departing Cl atom. The calculations on the H2 PES seem to overestimate the OH scattering in the forward direction and the fraction of Cl at high recoil velocities. Although the comparison of the corresponding angular distributions is not bad, significant deviations with a statistical description are found, thus ruling out a complex-forming mechanism as the dominant reaction pathway. However, for the ClO + H product channel, the QCT and statistical predictions are found to be in good agreement.

Analysis of the H + D2 reaction mechanism through consideration of the intrinsic reactant polarisation.

The effect of reactant polarisation on the dynamics of the title reaction at collision energies up to 1.6 eV is analysed in depth. The analysis takes advantage of two novel theoretical concepts: intrinsic reaction properties and stereodynamical portraits. Exact quantum methods are used to determine the polarisation moments that quantify the intrinsic reactant polarisation at various levels of detail, including or not product state and/or scattering angle resolution. The data is then examined with the aid of stereodynamical portraits, which facilitate the rationalisation of the stereochemical effects that are relevant for the reaction dynamics. This allows for detailed characterisations of the so-called direct and delayed reaction mechanisms.

Mechanism and control of the F+H2 reaction at low and ultralow collision energies.

This article uses theoretical methods to study the dependence on stereodynamical factors of the mechanism and reactivity of the F+H2 reaction at low and ultralow collision energies. The impact of polarization of the H2 reactant on total and state-to-state integral and differential cross sections is analyzed. This leads to detailed pictures of the reaction mechanism in the cold and ultracold regimes, accounting, in particular, for distinctions associated with the various product states and scattering angles. The extent to which selection of reactant polarization allows for external control of the reactivity and reaction mechanism is assessed. This reveals that even the simplest of reactant polarization schemes allows for fine, product state-selective control of differential and (for reactions involving more than a single, zero orbital angular momentum partial wave) integral cross sections.

Assessment of suitable porcine semen for freezing, according to the ejaculate characteristics in the Iberico x Landrace breed.

A total of 35 ejaculates were studied in order to assess the suitability of porcine semen for freezing according to the ejaculate characteristics. The effects of the freezing procedure were identified; a decrease in motility and acrosome quality was found after thawing. The best results on motility were linked to the ejaculates with a volume of less than 100 ml of the sperm-rich fraction, a concentration lower than 450 x 10(6) spermatozoa/ml and an agglutination score below 2. However, the best normal apical ridge (NAR) was found when the volume of the sperm-rich fraction was greater than 150 ml. For this reason, an intermediate volume of the sperm-rich fraction of the ejaculate for the best motility and the best NAR, a concentration lower than 450 x 106 spermatozoa/ml and a rate of agglutination below 2 should provide the best quality after freezing. This study also attempted to determine whether a positive effect of ejaculate selection on the overall freezing performance might be expected.

Endocrine profiles during doe-litter separation and the subsequent pregnancy in rabbits.

This study was carried out to determine the effects of a transient doe-litter separation on plasma prolactin, LH, FSH, estradiol-17beta and progesterone concentrations before artificial insemination and during the subsequent pregnancy. Control does (n=12) had free access to nursing, whereas separated does (n=12) were kept away from their litters for 48 hours before artificial insemination. Both groups were inseminated on day 11 after parturition. Teat stimulation by suckling caused a high increase in prolactin concentrations in separated does (p < 0.0001). Basal prolactin concentrations were observed in both groups on days 8 and 18 of pregnancy. No effect of the treatment was detected on LH and FSH concentrations during the sampling period. A rise of estradiol-17beta concentrations was observed 48 hours after doe-litter separation, compared to control does and to previous values (p < 0.003). Both groups showed low progesterone concentrations before artificial insemination. Pregnant rabbits in both groups showed increased progesterone concentrations on days 8 and 18 of pregnancy. Lower estradiol-17beta concentrations were observed in control does on day 18 of pregnancy compared with separated rabbits (p < 0.003). The results suggest that a transient separation of nursing does from their litters before artificial insemination may promote high follicular steroidogenesis activity leading to increased estradiol-17beta concentrations. This hormonal change could be a result of several stimulatory actions probably triggered by the absence of suckling episodes and may affect the luteotrophic function during the subsequent pregnancy.

Endocrine profiles during doe-litter separation and the subsequent pregnancy in rabbits.

This study was carried out to determine the effects of a transient doe-litter separation on plasma prolactin, LH, FSH, estradiol-17beta and progesterone concentrations before artificial insemination and during the subsequent pregnancy. Control does (n=12) had free access to nursing, whereas separated does (n=12) were kept away from their litters for 48 hours before artificial insemination. Both groups were inseminated on day 11 after parturition. Teat stimulation by suckling caused a high increase in prolactin concentrations in separated does (p < 0.0001). Basal prolactin concentrations were observed in both groups on days 8 and 18 of pregnancy. No effect of the treatment was detected on LH and FSH concentrations during the sampling period. A rise of estradiol-17beta concentrations was observed 48 hours after doe-litter separation, compared to control does and to previous values (p < 0.003). Both groups showed low progesterone concentrations before artificial insemination. Pregnant rabbits in both groups showed increased progesterone concentrations on days 8 and 18 of pregnancy. Lower estradiol-17beta concentrations were observed in control does on day 18 of pregnancy compared with separated rabbits (p < 0.003). The results suggest that a transient separation of nursing does from their litters before artificial insemination may promote high follicular steroidogenesis activity leading to increased estradiol-17beta concentrations. This hormonal change could be a result of several stimulatory actions probably triggered by the absence of suckling episodes and may affect the luteotrophic function during the subsequent pregnancy.

Pituitary and ovarian response to transient doe-litter separation in nursing rabbits.

The effects of a transient doe-litter separation on plasma prolactin, FSH and oestradiol concentrations, as well as the effect on LH response to exogenous GnRH administered at the time of artificial insemination, were determined in nursing rabbits. The effects on fertility, and litter size after parturition, as well as litter survival after doe-litter separation, were also studied. Control does (n = 12) had free access to nursing, whereas biostimulated does (n = 12) were separated from their litters for 48 h before artificial insemination. Plasma prolactin concentrations were decreased 24 h after the doe-litter separation (P < 0.05). The response of prolactin to suckling reached 10 times the basal values measured on day 10 after parturition (P < 0.0001). Increased oestradiol concentrations were found during the 48 h after the doe-litter separation: at 0 h, before artificial insemination (P< 0. 0001), 1.0-2.0 h after artificial insemination (P < 0.001), at 2.5 h (P < 0.05), 3.0 h (P < 0.01), and at 3.5 h (P < 0.05) after artificial insemination. Exogenous GnRH administered at the time of artificial insemination caused a greater LH response in does previously separated from their litters during 48 h (P < 0.01). The transient doe-litter separation did not affect plasma FSH concentrations, fertility, litter size or litter survival. These results suggest that a transient separation of nursing does from their litters before artificial insemination results in a decrease in plasma prolactin concentrations that could promote growth of follicular waves, and high steroidogenesis activity, leading to increased oestradiol concentrations and inducing higher sensitivity of the pituitary gland to exogenous GnRH. These findings associated to the absence of suckling episodes would lead to higher LH response and, therefore, exert a major effect on fertility.

Effects of added caffeine on results following artificial insemination with fresh and refrigerated rabbit semen.

Lactating rabbits (n=1335) were artificially inseminated to study the effect of the addition of caffeine on rabbit semen stored for up to 96 h. Concentration of 0-5 mM/l were tested. Whereas a concentration of 0.2 mM/l increased spermatozoa motility, higher concentration values adversely affected reproductive parameters. Spermatozoa stored at 18 degrees C for 72-96 h did not have the capacity to react with caffeine when it was added before insemination. Caffeine did not enhance fertility or prolificacy, regardless of its ability to increase sperm motility.

Plasma estradiol-17beta levels and gonadosomatic index in tench (Tinca tinca L.) reared in natural and controlled conditions.

The plasma estradiol-17beta levels (E2-17beta) and gonadosomatic index (GSI) of female tench (Tinca tinca L.) reared outdoors and indoors were studied from December 1996 to April 1997. Water temperature and daylight were gradually increased (from 10 to 25 degrees C and from 9 to 16 hours per day, respectively) in the indoor group. Animals reared in natural conditions had similar plasma levels throughout the experiment but animals under controlled conditions experienced an increase in these levels in March in relation to previous months (4.81+/-0.73 ng/ml in March vs. 0.29+/-0.03 ng/ml and 0.99+/-0.31 ng/ml in January and February, respectively; P < 0.05) and in relation to animals reared outdoors (4.81+/-0.73 ng/ml vs. 0.47+/-0.19 ng/ml, respectively; P < 0.05). In April, a sharp decrease in estradiol-17beta in these animals was observed, probably associated with the end of vitellogenesis. GSI increased in both groups through the experiment and indoor animals showed greater values in March vs outdoor fishes (7.57+/-2.18 vs. 4.05+/-0.63; P < 0.05). No significant correlation was found between E2-17beta and GSI, (r = 0.35). It is concluded that manipulation of the photoperiod and temperature can modify gonadal development in tench, and this is similar to the situation in other Teleostei species. This research is the first step towards achieving, out of season, spawning in tench.

Determination of plasma melatonin levels by enzyme-linked immunosorbent assay (EIA) in turbot (Scophtalmus maximus L.) and tench (Tinca tinca L.).

An enzymoimmunoassay (EIA) kit for plasma melatonin (MLT) measurements was employed in tench (Tinca tinca) and in turbot (Scophtalmus maximus). Tench and turbot plasma samples were purified with a C18 reversed phase extraction columns because this kit is designed for human serum measurements. The lowest detection limit of the technique was 11.48 pg/well with a sensitivity at 50% binding of 100 pg/well. Intra-assay and inter-assay CV (%) were always less than 5% (n=8), and 9% (n=6) in tench plasma samples, and less than 5% (n=8) and 13% (n=5) in turbot plasma samples, respectively. Correlation coefficients between EIA and RIA measurements in tench and turbot plasma samples were 0.93 and 0.89 (p<0.001) respectively. Diurnal and nocturnal plasma melatonin mean levels were 14.7+/-2.1 pg/ml and 87.4+/-11 pg/ml in tench (n=15), and 3.5+/-0.4 pg/ml and 28.1+/-2.1 pg/ml in turbot (n=15). These species showed a melatonin circadian rhythm as in other animals studied. The results suggest that the commercial kit used in this experiment could be a suitable and alternative method to RIA for plasma MLT determinations in tench and turbot although it is necessary to increase volumes (1ml) and concentrate daytime samples.

Effects of HCG or gonadoreline on seminal parameters and plasma testosterone levels in young male rabbits.

The effect of successive HCG or Gonadoreline injections on some reproductive parameters in 21 young male rabbits, aged from 4 to 4.5 months, has been studied. Animals were randomly allocated in three groups of seven to receive weekly (on each Monday) i.m. injections of 20 mg Gonadoreline, 50 IU HCG, or 0.5 ml Saline solution, respectively. The ejaculate from each male was collected and analysed twice a week (Tuesday and Friday). Higher sperm volumes were observed on the first week after Gonadoreline administration compared to the other groups (p < 0.05), and lower values during the second week in the Control group vs. Gonadoreline group (p < 0.05). Sperm volume increases after the 3rd week in Control animals (p < 0.05). When considering the global period studied, mean sperm volumes achieved after Gonadoreline treatment were higher than in HCG or Control group. Despite the random distribution of the animals to each treatment, and although throughout the experiment more ejaculates were discarded in the Gonadoreline group, the final number of doses obtained per ejaculate was higher in this group followed by HCG treated animals. Globally, the mean sperm concentration of the Control group during the entire studied period was significatively lower compared to the other groups (p < 0.001). No sperm motility differences were detected among the groups (p < 0.1174). HCG injections caused a significative increase in plasma testosterone concentration during the first and second week (p < 0.001) and similar plasma levels were observed in all groups afterwards. No direct plasma testosterone increasing levels owed to Gonadoreline injections were detected, probably due to the frequency of blood sampling (once a week).

Effect of gonadoreline and naloxone on induction of ovulation and plasma LH in rabbit.

To study the effect of an opiate antagonist receptor (naloxone) on LH secretion, two groups of seven does were randomly allocated to GnRH (gonadoreline, 20 microgram/animal), and GnRH + naloxone (1.8 mg/kg b.w.) treatment, respectively and another group of eight animals was treated with naloxone alone. Blood samples were obtained immediately before treatment (0 minutes) and at 60, 120 and 180 minutes after injection. Plasma levels of LH were determined by a direct, simple and precise sandwich enzyme immunoassay (EIA), adapted for measuring plasma LH in rabbit. Luteinizing hormone reached maximum values 60 minutes after administration of GnRH or GnRH + naloxone (p < 0.05) and all the females of these groups ovulated. Only 25% of naloxone treated rabbit does ovulated and these animals presented a high LH plasma level at 60 minutes post-treatment (p < 0.05). In non ovulated animals no variations in plasma LH concentrations were observed at 60 minutes, in relation to blood samples obtained at 0, 120 and 180 minutes. Results show a limited effect of this naloxone dose on the anterior pituitary of non lactating adult rabbi does in relation to induced ovulation. No synergic effect was detected when naloxone was administered in addition to gonadoreline.

A sensitive EIA for 17 beta-estradiol and progesterone in culture medium for oocyte in vitro maturation procedures.

A sensitive heterologous enzyme immunoassay (EIA) was validated to determine 17 beta-estradiol (E2) and progesterone levels, without previous extraction, in culture medium from rabbit oocytes matured in vitro with and without the addition of IGF-I. Polyclonal E2 (C902), and progesterone (C914) antibodies were raised in rabbits using 6-keto-17 beta-estradiol 6-carboxymethyloxime:BSA, and 11 alpha-hydroxyprogesterone 11 alpha-hemisuccinate:BSA. Horseradish peroxidase was used as label, conjugated to 17 beta-estradiol 3-hemisuccinate, and to progesterone 3-carboxymethyloxime. Standard dose response curves covered a range between 0 and 1 ng/well (100 microliters). The low detection limits of the technique were 1.99 pg/well for E2, and 13.21 pg/well for progesterone. Intra- and interassay coefficient of variation percentage (% CV) were < 6.3 and < 7.8 for E2 and progesterone, respectively (n = 10). The recovery rate of known E2 or progesterone concentrations added to a pool of culture maturation medium averaged 96.39%, and 98.65%, respectively. Compared with RIA, EIA values were in close agreement for E2 (n = 15, R = 0.96, P < 0.001), and progesterone (n = 15, R = 0.99, P < 0.001). Medium samples were obtained after oocyte maturation in vitro for 16 h. Use of IGF-I significantly elevated steroids production in the oocyte surrounded cumulus cells. The EIA described here is highly sensitive and specific assay, and provides a rapid, simple, inexpensive, and non-radiometric alternative to RIA for determining E2 and progesterone levels in oocyte culture medium.

Stimulatory effect of insulin-like growth factor I and epidermal growth factor on the maturation of rabbit oocytes in vitro.

The effects of different combinations of epidermal growth factor (EGF) and insulin-like growth factor I (IGF-I) on cumulus expansion and meiotic maturation were examined in rabbit oocytes. Selected rabbit follicular oocytes were matured in vitro and were classified as cumulus-oocyte complexes or denuded oocytes. They were cultured in TCM 199, and were treated with growth factors at different concentrations: EGF at 0, 1, 10, 50 and 100 ng ml-1, IGF-I at 0, 50, 100 and 200 ng ml-1 and EGF plus IGF-I at 10 + 50; 10 + 100; 50 + 50 and 50 + 100 ng ml-1, respectively. After 6 h of culture, the oocytes were assessed for nuclear maturation and after 16 h of culture, for cumulus expansion and maturation stage. After culture for 6 h, the incidence of germinal vesicle breakdown was higher (P < 0.05) in all of the growth factor treatments tested compared with controls. After culture for 16 h, EGF enhanced the incidence of cumulus expansion at all of the concentrations tested. Cumulus expansion was greatest with 50 mg EGF ml-1 plus 100 ng IGF-I ml-1 (72.0% versus 2.4% in controls). Treatment with IGF-I significantly increased (P < 0.05) the incidence of metaphase II stage, and maximum stimulation occurred at 100 ng IGF-I ml-1 (84.5% versus 31.1% in controls). However, IGF-I did not affect cumulus expansion. When denuded oocytes were used, no positive effects on nuclear maturation rates were observed for any treatment. These results suggest that: (1) EGF, either alone or with IGF-I, stimulates cumulus expansion; (2) the addition of IGF-I or EGF plus IGF-I significantly enhances nuclear maturation in immature rabbit oocytes; and (3) this effect is mediated by the presence of cumulus cells.

[Effect of the level of sexual receptivity on plasma estradiol and the ovulatory response during the postpartum period in the rabbit]. / Influencia del nivel de receptividad sexual sobre el estradiol plasmático y la respuesta ovulatoria durante el postparto en la coneja.

The relation between plasma estradiol 17-beta mean levels (E2), sexual receptivity and ovulation response, as well as the evolution of E2 from day 29 of pregnancy until day 11 of postpartum in rabbits, was studied. The results suggest a direct relation between plasma E2 mean levels and high or low sexual receptivity. With a determined plasma E2 concentration was not able to predict sexual receptivity. The best ovulation response was obtained in rabbits of high or medium receptivity treated with 20 micrograms or 40 micrograms of GnRH. High plasma E2 mean concentrations were detected on day 1 and 9 postpartum. The evolution of E2 levels from day 29 of pregnancy until day 11 postpartum suggests that day 9 is the most favorable breeding day, when rabbits are to be submitted to a semi-intensive reproduction management.