1,721,084 research outputs found
REDUCTIVE TRANSFORMATIONS OF THE NITRO GROUP: FROM HOMOGENEOUS TO HETEROGENEOUS CATALYSIS
Full text linkThis thesis focuses its attention into two different aspects of catalysis. In the first part, transition-metal complexes were used as homogeneous catalysts for the preparation nitrogen-containing heterocycles (especially indoles) using liquid sources of carbon monoxide. In the second part, in collaboration with Prof. Matthias Beller (Leibniz Institute for Catalysis-LIKAT, Rostock), doped-carbon heterogeneous non-noble metal catalysts were employed as catalytic materials in the hydrogenation of nitroaromatics. In both cases, nitro compounds were used as valuable starting materials corroborating their central role in organic chemistry. Equally, mechanistic aspects (especially kinetics) were taken into account showing how they can play a pivotal role in understanding not only the specific reaction mechanism but also how a catalytic system can be further improved
Pd-Catalyzed Synthesis of Heterocycles from Nitro Compounds using Liquid CO Sources
No full textCatalytic carbonylation processes represent a key synthetic tool for the preparation of bulk and fine chemicals. Furthermore, the CO molecule can be even employed as a stoichiometric reductant towards many functional groups. In particular, the transition-metal catalysed reductive cyclization of substituted aromatic nitro compounds allows for the synthesis of a large variety of N-containing heterocycles. However, from a laboratory-scale point of view, the use of pressurized CO requires the installation of expensive safety measures and high-pressure equipments. A solution to this problem is represented by the use of molecules capable of releasing an equivalent CO in situ. Among the various alternatives, formate esters (both alkyl and aryl) are the most promising one given their relative low cost, availability and functional group tolerance. Herein, we reported the use of formate esters as effective CO surrogates in the Pd-catalyzed reductive cyclization of substituted nitro compounds for the synthesis of heterocycles. Key for the success was the use of phenyl formate that, under optimal conditions, enable the synthesis of substituted indoles with excellent selectivities, while performing the reactions in an economical pressure tube without the need for autoclaves and/or a CO gas line. In addition, mechanistic investigations of the formate activation were performed in order to discriminate between a base-mediated and a metal-catalyzed process
Indole synthesis by reductive cyclization of ortho-nitrostyrenes: formate ester as CO surrogates
No full textThe palladium catalyzed reductive cyclization of substituted ortho-nitrostyrenes is a powerful method for the synthesis of indoles. The reaction proceeds using CO as the reductant [1]. However CO is a highly toxic gas and its use implies the installation of expensive safety measures and high-pressure equipments. Therefore carbonylation reactions using non-gaseous CO precursors are highly desirable [2].
For our purpose we chose formate esters as the CO sources due their commercial availability and low cost. Thus, we developed a one-pot two-catalysts system composed of Ru3(CO)12 and [Pd(Phen)2][BF4]2 for the decarbonylation and the reductive cyclization step respectively. As the result various 2,6-substituted indoles were synthesized in good yields using a cheap and safe CO source [3]
EXERCISE-ASSOCIATED SKIN TEMPERATURE DYNAMICS BY INFRARED THERMOGRAPHY. METHODS AND APPLICATIONS.
No full textHeat dissipation during sport exercise is an important physiological mechanism that may influence athletic performance. Therefore, monitoring skin temperature during exercise provides important physiological information about thermoregulatory processes. Skin temperature measurements through infrared thermography have the advantages to be non-invasive and to record temperature data simultaneously from different points on a wide area of the body.
The aim of the present investigation were: first, to compare three methods of thermal images analysis in skin temperature evaluation, and second to study the skin temperature dynamics during two types of physical exercise. In the present thesis three studies will be presented and discussed.
The analysis of thermographic images, with the goal of obtaining a temperature value representative of a specific area, is usually performed by different methods of averaging temperature values inside a selected Region of Interest (Troi and Tot). A comparison between the methods mainly used in literature in the specific case of a muscular group of calves on a population of 33 healthy subjects is presented. Here, it is presented an alternative method (Tmax) to obtain a temperature value of a specific area based on maximal temperature detection instead of considering the average temperature on the selected area. No meaningful difference in mean temperature between Troi and Ttot was found (p = 0.9), while temperature values calculated using Tmax were higher than the above methods (p < 0.001). The high correlation among the compared methods prove that they can equally represent temperature trends in cutaneous thermographic analyses.
The second and the third study presented here are applicative study investigating the skin temperature response during physical exercise.
The aim of the second study was to test the hypothesis that differences exist in the dynamics of exercise-associated skin temperature changes between trained and untrained subjects. Thermoregulation of a local muscle area (muscle–tendon unit) involved in a localized steady-load exercise (standing heels raise) using infrared thermography was investigated. Seven trained female subjects and seven untrained female controls were studied. Each subject performed standing heels raise exercise for 2 min. Thermal images were recorded prior to exercise (1 min), during exercise (2 min), and after exercise (7 min). The analysis of thermal images provided the skin temperature time course, which was characterized by a set of descriptive parameters. Two-way ANOVA for repeated measures detected a significant interaction (p = 0.03) between group and time, thus indicating that athletic subjects increased their skin temperature differently with respect to untrained subjects. This was confirmed by comparing the parameters describing the speed of rise of skin temperature. It was found that trained subjects responded to exercise more quickly than untrained controls (p<0.05). In conclusion, physical training improves the ability to rapidly elevate skin temperature in response to a localized exercise in female subjects.
The third study presented here is a preliminary report, since the data analysis is still in progress. It aimed to investigate the skin temperature response by using infrared thermography during slow speed low intensity exercise as compared to normal speed low intensity exercise in squat trial. We hypothesized that low intensity resistance exercise with slow movement would result in a skin temperature response slower than the one of the normal speed exercise with the same intensity.
13 active males performed 2 sessions of deep squat exercise until exhaustion, with 50% of 1 RM. The pace of movement was set in 1s eccentric / 1s concentric and 5s eccentric / 5s concentric phase in the 1st and in the 2nd session respectively. Thermal images were recorded every 20s before exercise (2min), during exercise (until exhaustion), and after exercise (10min).
Surprisingly, a different behaviour of skin temperature during and after exercise was observed among subjects: a decrease in skin temperature in 9 subjects (down group) and an increase in the other 4 (up group). Thus, statistics will be performed in each group separately.
It was shown that the response of cutaneous circulation to dynamic exercise is characterized by a initial vasoconstriction to dissipate heat from the core through the skin followed by vasodilation driving the blood flow from inactive tissue (including the skin) to active muscles involved in exercise. We speculate that the unexpected different behaviour of the skin temperature response in the 2 sub-groups was probably due to a time-dependent predominance of vasoconstriction over vasodilation or viceversa
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Fe2O3/NGr@C- and Co–Co3O4/NGr@C-catalysed hydrogenation of nitroarenes under mild conditions
Full text linkAn improved hydrogenation of nitroarenes using nano-structured iron- and cobalt-based catalysts is
presented. Modifications of the heterogeneous catalysts by N-doped graphene-flakes are crucial for the
success of selective reductions. The use of polar solvents and basic additives has a significant positive influence
on the rate of reduction of nitroarenes. This allows performing non-noble metal-catalysed hydrogenations
under very mild reaction conditions (e.g. 70 °C and 20 bar). On the basis of the obtained catalytic
results a heterolytic mechanism for the hydrogenation process is postulated, to
The chronotype can influence the perceived exertion during self-paced exercise performed at different times of day
No full textAim: Individual differences can influence circadian rhythms, resulting in a person’s preference for morning or evening activities. The aim of this study was to analyze the psychophysiological responses during morning (M) (0830 hours) and afternoon (A) (1530 hours) self-paced walking session in different chronotypes.
Method: Forty-six college students (24.81 ± 7.18 years) filled in the Morningness–Eveningness Questionnaire (MEQ) to determine their chronotype. In order to evaluate the psychophysiological responses during the walking sessions (1530 m long, uphill altitude gap 127.5 m and downhill altitude gap 85 m) at different times of day, the heart rate (HR) and the walking times were recorded; moreover, the subjects reported their rate of perceived exertion (RPE) using Borg’s scale at completion of the every walking session.
Results: The results showed that both M-types and E-types tended to walk slower during the M session, while presenting opposite trend in HR and RPE; M-types, as expected, had higher HR and lower RPE, while, E-types had lower HR and higher RPE during the morning session. Based on the multivariate analysis of covariance (MANCOVA) we found an effect for the individual chronotype (as an ordinal covariate) on HR mean, RPE and walking speed parameters (p = .05). A post hoc analysis showed a significant difference (p = .02; Cohen’s d = -1.21) between M-types vs. E-types for RPE in the morning, while no differences were found in the afternoon.
Conclusion: This study draws attention to the possibility that psychophysiological responses to physical activity can be influenced by individual chronotype. The subjects had lower perceived exertion in accordance with their chronotype. Knowledge of chronotypes could be important when prescribing physical exercise with the aim to increase the health and well-being in the population.
References
Adan A (1994) Chronotype and personality factors in the daily consumption of alcohol and psychostimulants. Addiction 89:455–462 Borg GA (1982) Psychophysical bases of perceived exertion. Med Sci Sports Exerc 14:377–38 Horne H, Ostberg O (1976) A self-assessment questionnaire to determine morningness–eveningness in human circadian rhythms. Int J Chronobiol 4:97–11
The slow strip set resistance training
No full textAim: In order to enhance muscular power and strength, the American College of Sports Medicine recommends performing high intensity resistance training (HI-RT) lifting 70% of 1RM. However, the same achievements could be obtained performing low intensity resistance exercise (20% of 1RM) in conjunction with external wrapping devices to restrict the blood flow (BFRRT)1. Similar effects are also produced by relatively low intensity resistance training (50% of 1RM) with slow movement and tonic force generation (LST)2. Alberti et al.3 suggest performing low intensity resistance training with slow movement until exhaustion using two overload strip (from 50% to 30% of 1RM) to obtain the same power and strength gain and to decrease the injury risks. The aim of this study was to investigate the effect of a new resistance training method on power and strength levels.
Methods: 22 amateur male Wing Chun martial artists (31.82 ± 11.17 yrs; 23.64 ± 2.14 kg/m2) were recruited and randomly divided into two groups: experimental group (EG) performed 4 weeks, 3 session per week, of slow strip set (SSS) on bench press in addition to the baseline training while control group (CG) continued their baseline training. Peak power (PP) and 1RM were assessed before and after the training period. Paired t-test and effect size (ES) were used for statistical analysis, with confidence interval set at 95%.
Results: Significant difference was not found between the 2 groups before the training period in PP and 1RM. The EG improved PP (p<0.001; ES=0.63, moderate) and 1RM (p<0.001; ES=0.53, moderate), while the CG did not improve strength and power values from pre to post training period.
Discussion: As expected, after 4 weeks of SSS training, 1RM and PP on bench press were improved. The SSS resistance training permitted to achieve the same power and strength gains of HI-RT, to obtain the same neuromuscular adaptation of BFRRT and to decrease the injury risk like in LST
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