Gotowa bibliografia na temat „Spectroscopie-γ prompte”

In this work, polyvinylidene fluoride (PVDF) aerogels with a tailorable phase composition were prepared by following the crystallization-induced gelation principle. A series of PVDF wet gels (5 to 12 wt.%) were prepared from either PVDF–DMF solutions or a mixture of DMF and ethanol as non-solvent. The effects of the non-solvent concentration on the crystalline composition of the PVDF aerogels were thoroughly investigated. It was found that the nucleating role of ethanol can be adjusted to produce low-density PVDF aerogels, whereas the changes in composition by the addition of small amounts of water to the solution promote the stabilization of the valuable β and γ phases. These phases of the aerogels were monitored by FTIR and Raman spectroscopies. Furthermore, the crystallization process was followed by in-time and in situ ATR–FTIR spectroscopy. The obtained aerogels displayed specific surface areas > 150 m2 g−1, with variable particle morphologies that are dependent on the non-solvent composition, as observed by using SEM and Synchrotron Radiation Computed micro-Tomography (SR-μCT).

Recent studies have shown that the catalytic performance (activity and/or selectivity) of Pt-group metal (PGM) catalysts for the CO and hydrocarbons oxidation as well as for the (CO, HCs or H2)-SCR of NOx or N2O can be remarkably affected through surface-induced promotion by successful application of electropositive promoters, such as alkalis or alkaline earths. Two promotion methodologies were implemented for these studies: the Electrochemical Promotion of Catalysis (EPOC) and the Conventional Catalysts Promotion (CCP). Both methodologies were in general found to achieve similar results. Turnover rate enhancements by up to two orders of magnitude were typically achievable for the reduction of NOx by hydrocarbons or CO, in the presence or absence of oxygen. Subsequent improvements (ca. 30–60 additional percentage units) in selectivity towards N2 were also observed. Electropositively promoted PGMs were also found to be significantly more active for CO and hydrocarbons oxidations, either when these reactions occur simultaneously with deNOx reactions or not. The aforementioned direct (via surface) promotion was also found to act synergistically with support-mediated promotion (structural promotion); the latter is typically implemented in TWCs through the complex (Ce–La–Zr)-modified γ-Al2O3 washcoats used. These attractive findings prompt to the development of novel catalyst formulations for a more efficient and cost-effective control of the emissions of automotives and stationary combustion processes. In this report the literature findings in the relevant area are summarized, classified and discussed. The mechanism and the mode of action of the electropositive promoters are consistently interpreted with all the observed promoting phenomena, by means of indirect (kinetics) and direct (spectroscopic) evidences.

The aim of this study was to discover bioactive constituents of Angelica reflexa that improve glucose-stimulated insulin secretion (GSIS) in pancreatic β-cells. Herein, three new compounds, namely, koseonolin A (1), koseonolin B (2), and isohydroxylomatin (3), along with 28 compounds (4–31) were isolated from the roots of A. reflexa by chromatographic methods. The chemical structures of new compounds (1–3) were elucidated through spectroscopic/spectrometric methods such as NMR and HRESIMS. In particular, the absolute configuration of the new compounds (1 and 3) was performed by electronic circular dichroism (ECD) studies. The effects of the root extract of A. reflexa (KH2E) and isolated compounds (1–31) on GSIS were detected by GSIS assay, ADP/ATP ratio assay, and Western blot assay. We observed that KH2E enhanced GSIS. Among the compounds 1–31, isohydroxylomatin (3), (−)-marmesin (17), and marmesinin (19) increased GSIS. In particular, marmesinin (19) was the most effective; this effect was superior to treatment with gliclazide. GSI values were: 13.21 ± 0.12 and 7.02 ± 0.32 for marmesinin (19) and gliclazide at a same concentration of 10 μM, respectively. Gliclazide is often performed in patients with type 2 diabetes (T2D). KH2E and marmesinin (19) enhanced the protein expressions associated with pancreatic β-cell metabolism such as peroxisome proliferator-activated receptor γ, pancreatic and duodenal homeobox 1, and insulin receptor substrate-2. The effect of marmesinin (19) on GSIS was improved by an L-type Ca2+ channel agonist and K+ channel blocker and was inhibited by an L-type Ca2+ channel blocker and K+ channel activator. Marmesinin (19) may improve hyperglycemia by enhancing GSIS in pancreatic β-cells. Thus, marmesinin (19) may have potential use in developing novel anti-T2D therapy. These findings promote the potential application of marmesinin (19) toward the management of hyperglycemia in T2D.

Isolation, characterization of natural products dimeric amide alkaloids from roots of the Piper chaba Hunter. The synthesis of these products using intermolecular [4+2] cycloaddition reaction has been described. Obtained products were characterized using IR, 1HNMR, 13CNMR and Mass Spectroscopy. Introduction The awesome structural diversity and complexity of natural products inspire many chemists to consider how nature creates these molecules. Nature’s biosynthetic enzymes offer a powerful and practical route to many organic compounds, and synthetic chemists sometimes seek to imitate the efficiency and elegance of the biosynthetic machinery by designing biomimetic reactions that approximate natural reaction pathways. Probably the most astonishing biomimetic reactions1 are tandem processes that combine several transformations in sequence and produce complicated structures from comparably simple starting materials in a single laboratory operation. Biosynthesis is described as “the reaction or reaction sequence occurred in organism or its immediate environment will be viewed as biosynthesis” where as biomimetic synthesis describes as “A specific reaction or a sequence of reactions that mimic a proposed biological pathway is defined as bimimetic synthesis. An early example is Sir Robert Robinson’s landmark synthesis of tropinone in 1917.2 Forty-two years later, Gilbert Stork and Albert Eschenmoser independently proposed that the steroid ring system could be formed by tandem cation-π cyclizations of a polyene in an ordered transition state.3 A non-enzymatic version of this reaction type was demonstrated in W. S. Johnson’s classic synthesis of progesterone in 1971.4 Chapman’s synthesis of carpanone is a striking example of the power of biomimetic strategies.5 In 1980, Black proposed that the endiandric acids could arise biosynthetically from linear polyenes.6 In 1982, K. C. Nicolaou gave chemical support to Black’s hypothesis by chemically synthesizing endiandric acids A-G.7 Biomimetic Synthesis of Natural Products which involves, The biomimetic polyene carbocyclizations reaction, The biomimetic cycloaddition reaction, The biomimetic electrocyclization reaction, The polyether biomimetic synthesis, The biomimetic oxidative coupling of phenol, Some other interesting biomimetic synthesis, The present biomimetic synthesis of chabamides or dimeric amide alkaloids involves cycloaddition reactions. The Diels Alder reaction In the Diels-Alder reaction a six membered ring is formed through fusion of a 4 π component, usually a diene and a 2 π component which is commonly referred to as the Figure 1. dienophile. The Diels Alder reaction has proven to be great synthetic value, forming a key-step in the construction of compounds containing six-membered rings. Cyclohexene ring generated all the way through the formation of two new σ-bonds and one π bond with four adjacent stereocenters. The reaction is named after Otto Diels and Kurt Alder, two German chemists who studied the synthetic and theoretical aspects of this reaction in great detail.8 Their efforts have been rewarded with the 1950 Noble prize. Figure 2 Schematic representation of the Diels-Alder reaction. Cis principle In Diels-Alder reactions, the stereoselectivity is generally high due to the “cis principle”, which states that Diels-Alder reactions require a cisoid conformation for the diene and suprafacial-suprafacial mode of reaction, meaning that both ends of the diene attack from the same face of the dienophile in a syn fashion. Frontier Molecular Orbital (FMO) Approach Diels-Alder rections can be devided into, normal electron demand and inverse electron demand additions. This difference is based on the way the rate of the reaction responds to the introduction of electron withdrawing and electron donating substituents. Normal electron demand Diels-Alder reactions are promoted by electron donating substituents on the diene and electron withdrawing substituents on the dienophile. In contrast, inverse electron demand reactions are accelerated by electron withdrawing substituents on the diene and electron donating ones on the dienophile. There also exists an intermediate class, the neutral Diels-alder reaction, which is accelerated by both electron withdrawing and donating substitutents. The way the substituents affect the rate of the reaction can be rationalized with aid of Frontier Molecular Orbital (FMO) theory. This theory was developed during a study of the role of orbital asymmetry in pericyclic reactions by Woodward and Hoffmann9 and, independently, by fukui10 Later, Houk contributed significantly to the understanding of the reactivity and selectivity of these processes.11 The FMO theory states that a reaction between two compounds is controlled by the efficiency with which the molecular orbitals of the individual reaction partners interact. The interaction is most efficient for the reactivity is completely determined by interactions of the electrons that are highest in energy of the of the reaction partners (those in the Highest Occupied Molecular Orbital, the HOMO) with the Lowest Unoccupied Molecular Orbital (LUMO) of the other partner, applied to the Diels-alder reactions, two modes of interaction are possible. The reaction can be controlled by the interaction of the HOMO of the diene and the LUMO of the Dienophile (normal electron demand), or by the interaction between the LUMO of the diene and the HOMO of the dienophile (inverse electron demand), as illustrated in Fig-B. In the former case, a reduction of the diene-HOMO and dienophile-LUMO energy gap can be realized by either raising the energy of the HOMO of the diene by introducing electron donating substituents or lowering the energy of the dienophile LUMO by the introduction of electron donating substituents or lowering the energy of the dienophile LUMO by the introduction of electron withdrawing substituents. A glance at Fig-A confirms that in the formation of two new bonds, orbital symmetry is conserved so that, according to Woodward and Hoffmann, the reaction is concerted. In other words, no intermediate is involved in the pericyclic process such as the Diels-Alder reaction.12 This conclusion is consistent with a number of experimental observations. The cis or trans conformation of the dienophile is fully conserved in the configuration of the cycloadduct, which proves that there is no intermediate involved with a lifetime long enough to allow rotation around C-C bond. Selectivity can arise when substituted dienes and dienophiles are employed in the Diels-Alder reaction. Two different cycloadducts denoted as endo and exo are possible. Under the usual conditions their ratio is kinetically controlled. Alder and Stein already discerned that there usually exists a preference for formation of the endo isomer i.e formulated as tendency of maximum accumulation of unsaturation, (the Alder-Stein rule)13 Indeed, there are only very few examples of Diels-Alder reactions where the exo isomer is major product.14 The interactions underlying this behavior have been subject of intensive research. Since the reactions leading to endo and exo product share the same initial state, the difference between the respective transition-state energies fully account for the observed selectivity. These differences are typically in the range of 10-15 kJ per mole.15 Woodward and Katz16 suggested that secondary orbital interactions are of primary importance. These interactions are illustrated in fig-B for the normal electron demand (HOMO-diene, LUMO-dienophile controlled). The symmetry allowed overlap between π-orbital of the carbonyl group of the dienophile and the diene-HOMO is only possible in the endo activiated complex. Hence, only the endo transition state is stabilized so that the reaction forming the endo adduct is faster than that yielding exo product. This interpretation has been criticized by Mellor, who attributed the endo selectivity to steric interactions. Steric effects are frequently suggested as important in determining the selectivity of Diels-Alder reactions, particularly of α-subsituted dienophiles, and may ultimately lead to exo-selectivity. 17 For other systems, steric effects in the exo activated complex can enhance endo selectivity. 18 In summary, it seems for most Diels-Alder reactions secondary orbital interactions afford a satisfactory rationalization of the endo-exo selectivity. However, since the endo-exo ratio is determined by small differences in transition state energies, the influence of other interactions, most often steric in origin and different for each particular reaction is likely to be felt. The compact character of the Diels-Alder activated complex (the activation volume of the retro Diels-Alder reaction is negative) will attenuate these effects.19 Results and Discussions Chabamides F & G as dimeric amide alkaloids were isolated from this plant Piper chaba Hunter. These two dimers were formed by Diels-Alder reaction employing monomer trichostachine. This hypothesis was further confirmed by the mass spectrum, which showed a significant peak at m/z 294.113 [M++Na], assigned to the trichostachine ion arising by the Retro-Diels–Alder cleavage of molecular ion into two halves. Finally, to confirm the existence of the compounds F and G, we extracted the roots of P.chaba with MeOH at room temperature followed HPLC/electron spray ionization (ESI) MS experiments. In HPLC/ESIMS of the MeOH extract showed the presence of peaks at m/z 563 [M++Na] and 543 [M++1] at about 8.8 min and 10.6 min of LC retention time, respectively. To prove this biosynthetic hypothesis we have carried out the intermolecular [4+2] cycloaddition reaction with the trichostachine under solvent free conditions (Scheme 1). Reaction mixture was analysed by the LC-MS, which clearly indicted the presence of the compounds 1 and 2 (retention time and mass). In HPLC analysis, retention times of the synthetic 1 and 2 were identical to those of chabamide F and G, confirming the structure and stereochemistry are same as that of isolated alkaloids. Based on above result during Diels-Alder reaction of trichostachine, we developed two kinds of methodologies for this biomimetic synthesis of dimeric amide alkaloids based on catalytic. On the basis of a biosynthetic hypothesis (described in Chapter I) by the intermolecular Diels-Alder reaction, we chosen piperine (1a), pellitorine (1c) and trans-fagaramide (1c) as substrates to perform the biomimetic synthesis of the dimeric chabamides (Compound H-K) and this study also identified plausible products between piperine (1a) and pellitorine (1c). This study not only explains formation of cyclo adducts but also explains the different mechanistic aspects in Diels-Alder reaction (endo and exo products) of copper salts in aqueous medium. Under normal conditions only combinations of dienes and dienophiles that have FMO’s of similar energy can be transformed into a Diels-Alder adduct. When the gap between the FMO’s large, forcing conditions are required, and undesired side reactions and retro Diels-Alder reactions can easily take over. These cases challenge the creativity of the organic chemist and have led to the invention of a number of methods for promoting reluctant Diels-Alder reactions under mild conditions.20 Plausible mechanism for Diels-Alder reaction: Sijbren Otto. et. al studied extensively on copper (II) catalyzed Diels-Alder reactions on various moieties. 25, 26 Based on these reports we proposed plausible mechanism for this copper catalyzed Diels-Alder reaction. The first step in the cycle comprises rapid coordination of the lewis acid to the dienophile leading to a complex in which the dienophile is activated for reaction with the diene. The cycloadduct has dissociated from the lewis acid in order to make the catalyst available for another cycle. However we didn’t carry any kinetic studies to prove this mechanism. Plausible mechanism of Diels-Alder reaction catalyzed by copper (II) salts Use of lewis acids in Diels-Alder reaction is to lower LUMO dienophile energy to result in the decrease of the LUMO dienophile-HOMO diene gap (normal electron demand) or reduce LUMO diene energy to result in the decrease of the LUMO diene-HOMO dienophile gap (inverse electron demand). The presence of Lewis acids, the Diels-Alder dimerization of piperine, pellitorine, piperine with fagaramide, peperine with pellitorine, gave much lower combined yields in neat conditions. Wie et al. previously reported 21, 22 Diels-Alder reaction of piperine and in both thermal and by lewis acid of Co(II) Cl2.6H2O/P(Ph)3/Zn (1:10:10 mol %) in 3-octanol at 170oC with isomerised product (24 %) and 77 % over all yield. To find the optimum conditions towards the catalyst, piperine (1a) was taken to perform the Diels-Alder reaction in presence of variety of lewis acids and metal salts (Table 1). The highest catalytic activity was attained for the reaction using 10 mol % of Cu (II) salts. The role of copper salts in this reaction can be attributed to its Lewis acid ability, which enhances both the electron donating capacity of diene and electron withdrawing capacity of the dienophile (required for normal electron demand for Diels-Alder reaction). The The catalytic activitiy of Lewis acids like Cu+2 mainly relies on their coordinating character to assemble both dienophile and diene to such a way that promote the reaction to wards the reaction barrier. To find the optimum conditions towards the solvent several reactions were carried out under the solvents like benzene, toluene, xylene, water and results were tabulated (Table 2). Among organic solvents xylene is better to get considerable yield with copper salts. Later water was found to be the best for both yield and selectivity of this cycloaddition. Cycloaddition reactions of piperine (1a): Lewis acids catalyzed cycloaddition reactions (Scheme 2) of piperine (1a) under organic and aqueous solvent conditions to give resultant cycloadducts 2a, 3a, 4a, 5a and 6a, among them 2a is major ortho-exo cyclohexene type dimeric amide alkaloid and also known as chabamide, which is previously isolated23 from this plant, isomer 3a is previously isolated from Piper nigrum21 Remaining isomers (4a-6a) were synthesized from piperine by Diels-Alder reaction by Kun Wei. et al. its physical and spectroscopic data were identical with reported data22 (1H-NMR, 13C-NMR & Mass spectra). In the cycloaddition of piperine (1a), solvents toluene, xylene and water were used in presence of cuper (II) salts. Reaction showed good overall yield and more exo selectivity in organic solvent like xylene. Water catalyzed reactions were ended with good overall yield and minute decrease in exo selectivity, infinitesimal increase in endo selectivity (Table 2). This reaction showed completely regioselectivity (yield of 2a+3a>4a+5a+6a) due to maximum involvement of α-double bond rather than γ-double bond of 1a during Diels-Alder reaction. Cycloaddition reactions of pellitorine (1b): Same catalytic and solvent conditions were employed for pellitorine (1b) as used in piperine (1a) for the biomimetic synthesis (Scheme 3) of chabamide J & K (Chapter-II). These dimers were plausibly generated by monomer pellitorine by cycloaddtion reactions in biosynthesis. During cycloaddition of pellitorine (1b), solvents like toluene xylene and water were used in presence of cupper (II) salts. In former catalyzed reaction showed good overall yield and more endo selectivity in both organic (xylene) and water. Increase in endo selectivity is more in aqueous medium rather than organic solvent like xylene (Table 2). Cycloaddition of pellitorine under above said catalytic conditions gave corresponding cycloadducts 2b, 3b, 4b and 5b. Physical and spectral data of adducts 2b & 3b are identical with compound J & K (chabamide J & K mentioned in Chapter-II) and all physical and spectral data of adduct 4b is identical with nigramide O which is isolated previously from piper nigrum.21 The structure of 5b a new cycloadduct formed during this biomoimetic synthesis employ pellitorine as monomer, its structure was elucidated by 1D and 2D spectral data. This reaction showed completely regioselectivity (yield of 2b+5b≈3b+4b) due to maximum involvement of α-double bond rather than γ-double bond of 1b during Diels-Alder reaction. Structure elucidation of compound 5b: Compound 5b was obtained as a pale yellow oil, had the molecular formula of C28H50N2O2, as deduced from the HRESIMS (Fig-9) m/z, 447.3958 [M++H]. IR spectrum (Fig-1) implied the presence of carbonyl (1648 cm-1) and NH (3304 cm-1). The 1H NMR spectrum of 5b revealed the presence of a trans double bond at δ 5.28 (dd, J = 15.0, 10.0 Hz, H-4"), 5.63 (m, H-5"), two isobutylamide groups at δ 3.15 (m), 3.17 (m), 3.17 (m, H2-1'), 1.74 (m, H-2'), 0.91 (d, J = 6.7 Hz, H-3'), 0.90 (d, J = 6.7, H- 3'), 5.53 (br t, J = 5.7 Hz, NH) and δ 2.96 (m, H1-1'''), 2.97 (m, H2-1'''), 1.73 (m, H-2'''), 0.87 (d, J = 6.7 Hz, H-3'''), 0.86 (d, J = 6.7 Hz, H-3'''), 3.15 (br t, J = 6.0 Hz, NH), n-amyl group and 1-heptene unit at δ 1.96 (m, H-6), 1.40 (m, H-7), 1.20 (m, H-8), 1.27 (m, H-9), 0.86 ( t, J = 6.5 Hz, H-10) and δ 5.28 (dd, J = 15.0, 10.0 Hz, H-4"), 5.63 (m, H-5"), 1.89 (m, H-6"), 1.30 (m, H-7"), 1.28 (m, H-8"), 1.27 (m, H-9"), 0.88 (t, J = 6.5 Hz, H-10"), respectively (Table 3). The 13C NMR spectrum (Fig-3) displayed the presence of 28 carbon atoms and were further classified by DEPT experiments (Fig-4) into categories of 6 methyls, 10 methylenes, 10 methines and 2 quaternary carbons including two carbonyls (δ 173.80 and 173.04). ' The analyses of the 1H and 13C NMR spectral data of 5b showed a high degree of similarity to dimeric alkaloid, compound J naturally isolated from this plant (Chapter-II) compound is meta-endo while 5b is meta-exo product. Furthermore, the detailed elucidation of the 2D NMR data (COSY, HSQC and HMBC) had determined the planar structure of 5b. The 1H homodecoupling NMR (Fig-7) experiments of 5b revealed the connectivities H-2 (δ 2.45, m) to H-3 (δ 5.56, ddd, J = 10.0, 4.3, 2.6 Hz) to H-4 (δ 5.98, dt, J = 10.0, 1.8 Hz) to H-5 (δ 2.41, m) to H-2"( δ 2.68, dd, J = 11.3, 10.0 Hz) to H-3" (δ 2.82, ddd, J = 10.1, 10.0, 5.0 Hz ) via cyclohexene ring protons. The meta-orientation of the carbonyl and isobutylamide groups were established by HMBC (Fig-6) correlations for δ 2.45 (m, H-2), 5.56 (ddd, J = 10.0, 4.3, 2.6 Hz, H-3), 2.82 (ddd, J = 10.3, 10.0, 5.0 Hz, H-3")/δ 173.80 (C-1) and δ 2.68 (dd, J = 10.3, 10.0 Hz, H-2"), 2.41 (m, H-5), 2.82 (ddd, J = 10.3, 10.0, 5.0 Hz, H-3")/δ 173.04 (C-1"). Furthermore, the 1H-1H COSY (Fig-7) cross-peaks between δ 2.82 (ddd, J = 10.3, 10.0, 5.0 Hz, H-3") and δ 5.28 (dd, J = 15.0, 10.0 Hz, H-4"), and δ 5.63 (m, H-5") and δ 2.41 (m, H-5), 1.96 (m, H-6), 1.40 (m, H-7), coupled with the HMBC correlation for δ 5.63 (m, H-5'') to δ 28.35 (C-7"), δ 1.40 (m, H-7) to δ 37.04 (C-5) established the attachment of the 1-heptene and n-amyl groups at C-3" and C-5, respectively. The analysis of the 1H-1H coupling constants and NOESY (Fig- 8) data allowed us to determine the relative stereochemistry of compound 5b. The coupling constants of H-2"/H-5 and H-2"/H-3" (10.3 Hz) indicated anti relations of H-2"/H-5 and H-2"/H-3". In the NOESY spectrum correlations were observed at δ 2.45 (H-2) δ 2.82 (H-3") and δ 2.41 (H-5) and correlations were not observed at δ 2.68 (H-2") with δ 2.82 (H-3") and δ 2.68 (H-2") with δ 2.41 (H-5). These data were in agreement with the β-orientation for H-2" and α-orientation for H-3" and H-5. Thus, based on these spectral data the stereostructure of 5b was confirmed and trivially named as chabamide L. Cycloaddition reaction between piperine (1a) and pellitorine (1b): Our aim of this cycloaddition reaction is to explain to study different cycloadducts and selectivity of diene among piperine and pellitorine (Scheme 4). This biomimetic synthesis will explain the probability of diene, which participated in Diels-Alder reaction between piperine (1a) and pellitorine (1b) both were isolated from same plant (P. chaba). Nigramide N, which is formed biosynthetically via cycloaddition reaction between piperine and pellitorine, this adduct previously isolated from roots of P. nigrum 21 by Wei. et. al. Lewis acid catalyzed cycloaddition reactions of piperine (1a) and pellitorine (1b) under organic and aqueous solvent conditions to give resultant cycloadducts 2c, 3c, 4c, 2a and 3b. Cycloadduct 2c and 3c is new cycloadducts and their structures were illustrated by 1D and 2D spectral data. Structure elucidation of compound 2c: Compound 2c was obtained as pale yellow liquid. The molecular formula of 2c was established as C31H44N2O4 by HRESIMS (Fig-18), which provided a molecular ion peak at m/z 509.3381 [M++H], in conjunction with its 13C NMR spectrum (Fig-12). The IR spectrum displayed absorption bands diagnostic of carbonyl (1640 cm-1) (Fig-10). The 300 MHz 1H NMR spectrum (in CDCl3) indicated the presence of two signals at δ 5.86 (dd, J = 15.6, 10.1 Hz) and 6.27 (d, J = 15.6 Hz), which were assigned to trans-olefinic protons by the coupling constant of 15.6 Hz. It also displayed aromatic protons due to two 1, 3, 4-trisubstituted aromatic rings at δ 6.82 (1H, br s), 6.76 (1H, dd, J = 7.8, 1.4 Hz), 6.75 (1H, d, J = 7.8 Hz) (Fig-11), (Table 4). In addition to the above-mentioned moieties, combined inspection of 1H NMR and 1H–1H COSY revealed the presence of cyclohexene ring, one isobutylamide and one pyrrolidine ring. The 13C NMR spectrum displayed the presence of 31 carbon atoms and were further confirmed by DEPT experiments into categories of 11 methylenes, 12 methines and 5 quaternary carbons including two carbonyls (δ 173.01 and 172.50). On the basis of these characteristic features, database and literature search led the skeleton of compound 2c as a dimeric alkaloidal framework. A comprehensive analysis of the 2D NMR data of compound 2c facilitated the proton and carbon assignments. 1H–1H COSY spectrum suggested the sequential correlations of δ 3.51 (dq, J = 5.0, 2.6 Hz)/5.62 (dt, J = 9.8, 2.6 Hz)/6.10 (ddd, J = 9.8, 1.5 Hz)/2.20 (m)/2.72 (ddd, J = 11.1, 10.1, 5.2 Hz)/3.35 (dd, J = 11.1, 9.8 Hz) assignable to H-2-H-3-H-4-H-5-H-3"-H-2" of the cyclohexene ring. Concerning the connections of the n-amyl and 3, 4-methylenedioxy styryl groups, HMBC spectrum (Fig-15) showed correlations of H-4, H-6, H-7/C-5; H-5", H-4"/C-3", which implies that these units were bonded to the cyclohexene ring at C-5 and C-3". Further, HMBC correlations of two methylene protons at δ 5.95 with 147.91 (C-8"), 146.87 (C-9"), confirmed the location of methylenedioxy group at C-8", and C-9". Remaining units, isobutylamine and pyrrolidine (rings) were connected through carbonyl groups at C-2 and C-2", which was confirmed by HMBC correlations of H-2 and H-1' to C-1 (δ 173.01) and H-2" and H-1''' to C-1" (δ 172.50). The assignment of the relative configuration of compound 2c, and confirmation of overall structure were achieved by the interpretation of the NOESY spectral data and by analysis of 1H NMR coupling constants. The large vicinal coupling constants of H-2"/H-2 (11.1 Hz) and H-2"/H-3" (11.1 Hz) indicated anti-relations of H-2"/H-2 and H-2"/H-3" and the axial orientations for these protons. In the NOESY spectrum (Fig-17), the occurrence of the correlations between H-2/H-3" and the absence of NOE effects between H-2/H-2" and H-2"/H-3" supported the above result. This data indicated β-orientation for H-2" and α-orientation for H-2 and H-3". The α-orientation of H-5 was suggested by the coupling constant of H-5/H-3" (5.2 Hz) and the absence of the NOESY correlations between H-3" and H-2". On the basis of these spectral data, the structure of compound 2c was unambiguously established and trivially named as chabamide M. Structure elucidation of compound 3c: Compound 3c was obtained as pale yellow liquid. The molecular formula of 3c was established as C31H44N2O4 by HRESIMS (Fig-27), which provided a molecular ion peak at m/z 509.3391 [M++H], in conjunction with its 13C NMR spectrum (Fig-21). The IR spectrum displayed absorption bands diagnostic of carbonyl (1624 cm-1) moiety (Fig-19). The 300 MHz 1H NMR spectrum (in CDCl3) indicated the presence of two signals at δ 4.63 (dd, J = 15.6, 10.0 Hz) and 5.46 (dt, J = 15.6, 6.8 Hz), which were assigned to trans-olefinic protons by the coupling constant of 15.6 Hz. It also displayed aromatic protons due to two 1, 3, 4-trisubstituted aromatic ring at δ 6.75 (1H, br s), 6.73 (1H, d, J = 7.8, 1.4 Hz), 6.71 (1H, d, J = 7.8 Hz) (Fig-20). In addition to the above-mentioned moieties, combined inspection of 1H NMR and 1H–1H COSY revealed the presence of cyclohexene ring, one isobutylamide and one pyrrolidine ring. The 13C NMR spectrum displayed the presence of 31 carbon atoms (Table 5), and were further classified by DEPT experiments (Fig-22) into categories of 11 methylenes, 12 methines and 5 quaternary carbons including two carbonyls (δ 173.34 and 173.88). On the basis of these characteristic features, database and literature searches led the skeleton of compound 3c as a dimeric alkaloidal framework. A comprehensive analysis of the 2D NMR data of compound 3c facilitated the proton and carbon assignments. 1H–1H COSY spectrum (Fig-25) suggested the sequential correlations of δ 2.82 (m)/5.63 (dt, J = 9.7, 1.9 Hz)/5.82 (ddd, J = 9.7, 4.8, 1.9 Hz)/3.94 (dq, J =.10.0, 1.9 Hz)/2.76 (ddd, J = 11.7, 10.0 Hz)/3.36 (dt, J = 11.7, 4.8 Hz) assignable to H-2-H-3-H-4-H-5-H-3"-H-2" of the cyclohexene ring. Concerning the connections of the 3, 4-methylenedioxyphenyl and 1-heptene groups, HMBC spectrum (Fig-24) showed correlations of H-7, H-11, H-3"/C-5; H-5", H-4", H-5/C-3", which implies that these units were bonded to the cyclohexene ring at C-5 and C-3". Further, HMBC correlations of two methylene protons at δ 5.92 with 147.42 (C-8"), 146.49 (C-9"), confirmed the location of methylenedioxy group at C-8", and C-9". Remaining units, pyrrolidine and isobutylamine were connected through carbonyl groups at C-2 and C-2", which was confirmed by HMBC correlations of H-2 and H-1' to C-1 (δ 171.34) and H-2" and H-1''' to C-1" (δ 173.88). The assignment of the relative configuration of compound 3c, and confirmation of overall structure were achieved by the interpretation of the NOESY spectral data and by analysis of 1H NMR coupling constants. The large vicinal coupling constants of H-3"/H-2" (11.7 Hz) and H-5/H-3" (10.0 Hz), indicated anti-relations of H-3"/H-5 and H-3"/H-2" and the axial orientations for these protons. In the NOESY spectrum (Fig-26), the occurrence of the correlations between H-2"/H-5 and the absence of NOE effects between H-3"/H-2" and H-3"/H-5 supported the above result. These data indicated β-orientation for H-2" and α-orientation for H-2 and H-3". The α-orientation of H-2 was suggested by the coupling constant of H-2/H-2" (4.8 Hz) and the occurrence of the NOESY correlations between H-2" and H-2. On the basis of this spectral data, the structure of compound 3c was unambiguously established and trivially named as Chabamide N. Cycloaddition reaction between piperine (1a) and E-fagaramide (1c) Lewis acid catalyzed cycloaddition reactions (Scheme 5) of piperine (1a) and trans-fagaramide (1c) under aqueous solvent conditions to give resultant cycloadducts 2d, 3d and 2a. To carry this biomimetic synthesis to explain compound H and I (mentioned in chapter-II), we taken piperine (1a) which is isolated from same plant and trans fagaramide was synthesized by reported method.24 Cycloaddition reaction between 1a and 1c end up with overall yield 70% in xylene and 75% in water. In both solvents ortho products were formed dominantly compared with meta products. Spectral data 1D and 2D of cycloadducts 2d & 3d were identical with compound H & I (see chapter I, compound H & K). Cycloadduct 2a is identical with chabamide. This cycloaddition reaction practically proved as biomimetic synthesis for compound H and I. Acknowledgements: The authors are thankful to Director IICT for his constant encouragement and CSIR New Delhi for providing the fellowship References and Notes Braun, M. Synth. Highlights 1991, 232 Robinson, R. Chem. Soc. 1917, 762. Stork, G.; Burgstahler, A. W. Am. Chem. Soc. 1955, 38, 1890. Johnson, W. S.; Gravestock, M. B.; McCarry, B. E. Am. Chem. Soc. 1971, 93, 4332. Chapman, O. L.; Engel, M. R.; Springer, J. P.; Clardy, J. C. Am. Chem. Soc. 1971, 93, 6696. Bandaranayake, W. M.; Banfield, J. E.; Black, D. St. C. Chem. Soc., Chem Commun. 1980, 902. Nicolaou, K. C.; Zipkin, R. E.; Petasis, N. A. Am. Chem. Soc. 1982, 104, 5558. O.; Alder, K. Ann. 1928, 460, 98. Woodward, R. B.; Hoffmann, R. Chem. 1969, 81, 797. Fakui, K. Chem. Res. 1971, 4, 57. Houk, K. N. Chem.. Res. 1975, 8, 361. Houk, K. N.; Li, Y.; Evanseck, D. Angew Chem., Ed. Engl. 1992, 31, 682. Alder, K.; Stein, G. Chem. 1937, 50, 510. Fotiadu, F.; Michel, F.; Buono, G. Tetraheron Lett. 1990, 34, 4863. Gleiter, R.; Bohm, M. C. Pure Appl. Chem. 1983, 55, 237. Woodward, R. B.; Katz, T. J. Terahedron 1958, 5, 70. Kakushima, M. J. Chem. 1979, 57, 2564. Houk, K. N. Tetrahedron Lett. 1970, 30, 2621. Houk, K. N.; Luskus, L. J. Am. Chem. Soc. 1971, 93, 4606. Otto, S.; Bertoncin, F.; Engberts, J. F. N. Am. Chem. Soc., 1996, 118, 7702–7707. Wei, K.; Li, W.; Koike, K.; Chen, Y-J.; Nikaido, T. Org. Chem. 2005, 70, 1164. Wei, K.; Li, W.; Koike, K.; Chen, Y-J.; Nikaido, T. Lett. 2005, 7, 2833–2835. Rukachaisirikul, T.; Prabpai, S.; Champung, P.; Suksamrarn, A. Planta Med. 2002, 68, 850-853. Nagao, Y.; Seno, K.; Kawabata, K.; Miyasaka, T.; Takao, S.; Fujita, Tetrahedron Lett. 1980, 21, 841. Otto, S.; Boccaletti, G.; Engberts, J. B. F. N. Am. Chem. Soc. 1998, 120, 4238–4239. Otto, S.; Bertoncin, F.; Engberts, J. B. F. N. Am. Chem. Soc. 1996, 118, 7702–7707. O.; Alder, K. Ann. 1931, 490, 243. Woodward, R. B.; Baer, H. Am. Chem. Soc. 1948, 70, 1161. Breslow, R.; Rideout, D. C. Am. Chem. Soc. 1980, 102, 7816. Breslow, R.; Guo, T. Am. Chem. Soc. 1988, 110, 5613. Grieco, P.A.; Nunes, J. J.; Gaul, M. D. Am. Chem. Soc. 1990, 112, 4595.

Developing novel synthesis technologies is crucial to expanding bifunctional electrocatalysts for energy‐saving hydrogen production. Herein, we report an ambient and controllable γ‐ray radiation reduction to synthesize a series of noble metal nanoparticles anchored on defect‐rich manganese oxides (M@MnO2‐x, M = Ru, Pt, Pd, Ir) for glycerol‐assisted H2 evolution. Benefiting from the strong penetrability of γ‐rays, nanoparticles and defect supports are formed simultaneously and bridged by metal‐oxygen bonds, guaranteeing structural stability and active site exposure. The special Ru‐O‐Mn bonds activate the Ru and Mn sites in Ru@MnO2‐x through strong interfacial coordination, driving glycerol electrolysis at low overpotential. Furthermore, only a low cell voltage of 1.68 V is required to achieve 0.5 A cm‐2 in a continuous‐flow electrolyzer system along with excellent stability. In situ spectroscopic analysis reveals that the strong interfacial coordination in Ru@MnO2‐x balances the competitive adsorption of glycerol and OH* on the catalyst surface. Theoretical calculations further demonstrate that the defect‐rich MnO2 support promotes the dissociation of H2O, while the defect‐regulated Ru sites promote deprotonation and hydrogen desorption, synergistically enhancing glycerol‐assisted hydrogen production.

Developing novel synthesis technologies is crucial to expanding bifunctional electrocatalysts for energy‐saving hydrogen production. Herein, we report an ambient and controllable γ‐ray radiation reduction to synthesize a series of noble metal nanoparticles anchored on defect‐rich manganese oxides (M@MnO2‐x, M = Ru, Pt, Pd, Ir) for glycerol‐assisted H2 evolution. Benefiting from the strong penetrability of γ‐rays, nanoparticles and defect supports are formed simultaneously and bridged by metal‐oxygen bonds, guaranteeing structural stability and active site exposure. The special Ru‐O‐Mn bonds activate the Ru and Mn sites in Ru@MnO2‐x through strong interfacial coordination, driving glycerol electrolysis at low overpotential. Furthermore, only a low cell voltage of 1.68 V is required to achieve 0.5 A cm‐2 in a continuous‐flow electrolyzer system along with excellent stability. In situ spectroscopic analysis reveals that the strong interfacial coordination in Ru@MnO2‐x balances the competitive adsorption of glycerol and OH* on the catalyst surface. Theoretical calculations further demonstrate that the defect‐rich MnO2 support promotes the dissociation of H2O, while the defect‐regulated Ru sites promote deprotonation and hydrogen desorption, synergistically enhancing glycerol‐assisted hydrogen production.

La loi « Bataille » fait obligation au CNRS de développer des recherches sur le retraitement des déchets nucléaires. C’est dans ce cadre que notre équipe GRACE (Groupe de Recherche sur l’Aval du Cycle Electronucléaire) de l’IPHC a entrepris des mesures nécessaires à la mise au point des réacteurs hybrides. Le champ de recherche s’est élargi puisqu’il inclut maintenant des études visant à développer le cycle de Thorium. GRACE s’est plus précisément attaché à mesurer des sections efficaces de réactions (n,xng) mal connues jusqu’à présent ou pour lesquelles aucune mesure n’existe. Les mesures ont été effectuées auprès du faisceau « blanc » de Gelina (IRMM Geel, Euratom). La technique de temps de vol a été appliquée. La spectroscopie g en ligne, utilisée pour étudier les réactions (n,xng), requiert avant tout de mesurer l’énergie des rayons g avec une bonne résolution. A cause de l’existence d’un flash g créé en même temps que le faisceau, il faut aussi un temps mort très faible, de façon à pouvoir détecter les neutrons de haute énergie. GRACE a réussi à concilier ces deux impératifs en mettant au point une nouvelle méthode basée sur la digitalisation et le traitement numérique du signal. Des mesures de section efficaces (n,xng) sur le 206,207,208Pb ont été réalisées ainsi avec succès à Geel, à l’aide des détecteurs coaxiaux de gros volume et à une distance de vol de 200 m. Le travail présenté dans ce mémoire a consisté à adapter la méthode pour rendre possible la spectroscopie g en ligne sur des cibles radioactives. Pour cela, la nouvelle mesure s’est déroulée sur une piste de vol de 30 m, et des détecteurs germanium planaires ont été utilisés. Dans un premier temps, et afin de s’assurer du bon fonctionnement du nouveau dispositif expérimental, des mesures de sections efficaces (n,n’g) sur une cible de plomb naturel ont été effectuées et les résultats sont comparés à ceux de la mesure à 200 m et aux calculs du code TALYS. Ensuite, les sections efficaces inélastiques partielles sur le 182,186W ont été mesurées entre le seuil de la réaction et 8 MeV. Enfin, une cible de 235U enrichie à 93 ,2 % a été bombardée et trois transitions dues à la réaction 235U(n,2ng)234U ont été analysées avec succès dont celle de l’état 8+ vers l’état 6+ jamais mesurée avant. Ce travail est une étape essentielle pour utiliser cette nouvelle méthode afin de mesurer des réactions (n,2ng) sur l’233U
The “Bataille” law obliged the CNRS to develop researches on the reprocessing of the nuclear waste. It is in this frame that our group GRACE (Groupe de Recherche sur l’Aval du Cycle Electronucléaire) of the IPHC began researches that contribute to the development of the hybrid reactors. However, the field of research widened because it now includes studies to develop the Thorium cycle. GRACE has undertaken measurements of (n,xng) reactions cross sections badly known or for which no measurement exists yet. The experiments were performed at the “white” neutron beam generated by GELINA facility in Geel, Belgium. The time of flight technique was applied. The g spectroscopy used for these measurements requires the detection of g rays with a good energy resolution. Because of the existence of a g flash created at the same time as the neutron beam, a short dead time is also required, to be able to detect the high energy neutrons. GRACE managed to conciliate these two imperatives by finalizing a new method based on the digital treatment of the signal. Using large HPGe coaxial detectors, (n,xng) cross sections measurements on the 206,207,208Pb nuclei were successfully realized at a 200 m flight path. The work presented in this thesis consists in adapting the method to highly radioactive targets. For that reason, the new measurement took place on a 30 m flight path and planar germanium detectors were used. In order to check the correct functioning of the new experimental method, (n,n’g) cross section measurements on a natural lead target were done and the results found were compared with the experiments at 200 m and with the theoretical calculations of the TALYS code. After that, the partial inelastic scattering cross sections on the 182,186W were performed from the threshold up to 8 Mev. Finally, a 93,2% enriched 235U target was bombarded and three transitions due to the 235U(n,2ng)234U reaction were successfully analysed including the one from the 8+ to the 6+ state, never measured before. This work is an essential step for using this new method in order to measure the (n,2ng) reaction cross sections on the highly radioactive 233U isotope

Dans le contexte du développement des réacteurs de génération IV, des données nucléaires précises sont requises. Dans ce travail de thèse, on s’intéresse en particulier à la section efficace de diffusion inélastique (n, n’) pour les noyaux d’233U et d’238U. L'analyse des données de GRAPhEME, dispositif combinant les méthodes de la spectroscopie-γ prompte et du temps de vol, ont permis d’obtenir, pour la première fois, 12 sections efficaces 233U(n, n’γ). Une modélisation des sections efficaces de ces deux isotopes (233U et 238U) a été réalisée avec le code de réaction nucléaire TALYS. Dans le cas de l’238U, l’implémentation de nouveaux modèles permet un meilleur accord calcul/mesure pour les sections efficaces (n, n’γ). Il a été montré cependant que cela n’influe pas sur la section efficace (n, n’). Enfin, une évaluation des incertitudes des sections efficaces de réaction pour l’238U menée avec CONRAD compare différentes méthodes afin de propager les incertitudes expérimentales aux paramètres des modèles via l’inférence Bayésienne
In the context of the development of generation IV nuclear reactors, precise nuclear data are needed. In this work, we study in particular inelastic scattering cross section for 233U and 238U nuclei. From the analysis of data from GRAPhEME, an experimental device combining prompt γ- spectroscopy and time of flight, we obtained for the first time 12 233U(n, n’γ) reaction cross sections. Cross sections modelling has been performed for both isotopes (233U et 238U) with the nuclear reaction code TALYS. In the 238U case, the implementation of new model in the code highlighted better agreement calculation/experiment for (n, n’γ) reaction cross sections. Despite this result, no change in the total inelastic scattering cross section has been seen. Finally, a cross sections uncertainties evaluation has been done with CONRAD, comparing different methods of propagating experimental uncertainties to model parameters via the Bayesian inference

Le travail présenté dans ce mémoire se situe dans le contexte du programme de nouvelles mesures de sections efficaces de réactions induites par neutron. Ce programme est motivé par les perspectives offertes depuis peu de temps par les projets innovants de traitement des déchets nucléaires et de production d’énergie. Cette motivation est présentée dans l’introduction. Il existe des bases de données diverses pour les sections efficaces de toutes les réactions sur tous les matériaux présents dans les réacteurs actuels. Pour ces réactions, ces bases reposent sur des données expérimentales évaluées et diffèrent donc peu entre elles. Par contre, il y a un manque évident de données dans trois cas :pour les isotopes très radioactifs qui constituent les déchets des réacteurs en fonctionnement:pour des réactions qui n’interviennent qu’à des énergies de plusieurs MeV, et ont donc peu d’importance pour les réacteurs à spectre thermique:pour des réactions (n,xn) parce qu’il n’existe aucune méthode applicable à tous les isotopesDans certains cas, il n’existe pas de données du tout : c’est le cas par exemple pour la réaction 233U(n,2n). Cette réaction est pourtant très importante dans le cycle du Thorium, puisque 233U est l’élément fissile. Elle détermine en grande partie la radiotoxicité de ce cycle. Lorsqu’il n’existe aucune donnée mesurée, les bases de données font appel à des modèles, et diffèrent alors fortement entre elles. Pour effectuer des mesures de section efficace lorsque la cible est très active, il est indispensable d’avoir un faisceau à très haut flux instantané mais pulsé à basse fréquence. C’est dans ce but que le CERN a développé le faisceau de neutrons baptisé n_TOF. Lorsque le faisceau n’est pas monoénergétique mais « blanc » comme celui de n_TOF, les méthodes utilisées jusqu’ici pour mesurer les sections efficaces (n,xn) sont inapplicables. La seule méthode possible est la spectroscopie γ prompte. Cependant, cette méthode est très difficile à adapter à une intensité instantanée très élevée, du moins avec la technique utilisée jusqu’ici. Outre la pixellisation, la solution réside dans une diminution du temps mort entre deux détections de rayon γ. Ce mémoire présente la solution qui a été mise au point à l’IReS et utilisée pour la mesure des sections efficaces de la diffusion inélastique et des réactions (n,2n) dans le plomb naturel auprès de l’accélérateur GELINA (IRMM, Geel). [. . . ]
The work of this thesis is situated in the context of GEDEON program of new neutron-induced reactions cross-section measurements. This program is motivated by the perspectives recently opened by innovating projects of nuclear waste treatment and energy production. This motivation is presented in the introduction. Different databases exist for all reactions on all the materials present in currently operating reactors. For those reactions, the databases rely on experimental data and, consequently, the differences among them are small. On the other hand, there is a shortage of experimental data in the following three cases:For very active isotopes that constitute the waste of currently operating reactors:For reactions that occur only above several MeV of neutron energy and, therefore, have little importance for thermal spectrum reactors:For (n,xn) reactions because there is no universal method applicable to all isotopes. In some cases, there are no data at all. For example, this is the case of 233U(n,2n) reaction. This reaction is, however, very important for the Thorium cycle because 233U is the fissile isotope. This reaction determines the radiotoxicity of the cycle. Where there are no experimental data, the databases rely on theoretical models and differ significantly among themselves. In order to perform cross-section measurements with very active samples, it is indispensable to dispose of a neutron beam facility with very high instantaneous flux, but pulsed at a low frequency. It is for this purpose that n_TOF neutron beam was developed at CERN. When the beam is not monoenergetic but “white” as the one of n_TOF, the only applicable method is prompt γ-spectroscopy. However, this method is a very difficult one to adapt to a high instantaneous beam flux, at least with conventional techniques. Besides detector segmentation, a good solution also requires a reduction of the dead-time per pulse. This thesis presents a technique that was developed in IReS and used to measure inelastic and (n,2n) reaction cross-sections on natural lead at GELINA facility in IRMM Geel, Belgium (a EURATOM research center in Geel, Belgium). [. . . ]