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101.
Quezada E Delogu G Viña D Santana L Picciau C Podda G Uriarte E 《Magnetic resonance in chemistry : MRC》2008,46(7):701-705
The synthesis of four pyranocoumarins starting from phloroglucinol and the complete (1)H and (13)C NMR assignment of seven pyranocoumarins has been performed using 1D and 2D NMR techniques including COSY, HMQC and HMBC experiments. 相似文献
102.
Tonidandel L Ragazzi E Roghi G Traldi P 《Rapid communications in mass spectrometry : RCM》2008,22(5):630-638
Amber is a fossil resin constituted of organic polymers derived through complex maturation processes of the original plant resin. A classification of eight samples of amber of different geological age (Miocene to Triassic) and geographical origin is here proposed using direct mass spectrometric techniques, i.e. laser desorption ionization (LDI), atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI), in order to obtain a fingerprint related to the amber origin. Differences and similarities were detected among the spectra with the four methods, showing quite complex spectra, full of ionic species in the mass range investigated (up to m/z 2000). The evaluation required statistical analysis involving multivariate techniques. Cluster analysis or principal component analysis (PCA) generally did not show a clear clustering with respect to the age of samples, except for the APPI method, which allowed a satisfying clustering. Using the total ion current (TIC) obtained by the different analytical approaches on equal quantities of the different amber samples and plotted against the age, the only significant correlation appeared to be that involving APPI. To validate the method, four amber samples from Cretaceous of Spain were analyzed. Also in this case a significant correlation with age was found only with APPI data. PCA obtained with TIC values from all the MS methods showed a fair grouping of samples, according to their age. Three main clusters could be detected, belonging to younger, intermediate and older fossil resins, respectively. This MS analysis on crude amber, either solid or extract, followed by appropriate multivariate statistical evaluation, can provide useful information on amber age. The best results are those obtained by APPI, indicating that the quantity of amber soluble components that can be photoionized decreases with increasing age, in agreement with the formation of highly stable, insoluble polymers. 相似文献
103.
Aldamen MA Clemente-Juan JM Coronado E Martí-Gastaldo C Gaita-Ariño A 《Journal of the American Chemical Society》2008,130(28):8874-8875
[ErW10O36]9- is the first polyoxometalate behaving as a single-molecule magnet (SMM). It shows frequency-dependent out-of-phase magnetization and a thermally activated single relaxation process with an effective barrier of 55.8 K. This single lanthanide ion polyoxometalate is the inorganic analogue of the bis(phthalocyaninato)lanthanide SMMs, both exhibiting very similar ligand field symmetries around the lanthanide ion (idealized D4d). It is chemically stable and offers new avenues for organization and processing of single-molecule magnets. Furthermore, it can be made free from nuclear spins and opens the possibility to be used for studies of decoherence on unimolecular qubits. 相似文献
104.
Coronado E Galán-Mascarós JR Martí-Gastaldo C 《Journal of the American Chemical Society》2008,130(45):14987-14989
The anionic oxalate-bridged bimetallic chain [Co(H2O)2Cr(ox)3]- shows slow relaxation of the magnetization, typical of the so-called single-chain magnets, when crystallized in segregated layers in a mixed salt with the supramolecular cations [C12H24O6K]+ and [(C12H24O6)(FC6H4NH3)]+. This is the first time that such phenomenon has been observed in an oxalate-bridge material. In view of the wide synthetic versatility exhibited by the oxalate ligand, it opens the door for the realization of a complete family of SCM materials whose physical properties might be tuned by the suitable replacement of M3+ ions within the chain. The information extracted from the systematic study of these compounds should provide important information concerning the main parameters that affect the slow-relaxation phenomena in this sort of 1D nanomagnets. 相似文献
105.
Thakurta S Chakraborty J Rosair G Tercero J El Fallah MS Garribba E Mitra S 《Inorganic chemistry》2008,47(14):6227-6235
Two new Cu(II) linear trinuclear Schiff base complexes, [Cu3(L)2(CH3COO)2] (1) and [Cu3(L)2(CF3COO)2] (2), have been prepared using a symmetrical Schiff base ligand H2L [where H2L = N,N'-bis(2-hydroxyacetophenone)propylenediimine]. Both of the complexes have been characterized by elemental analyses, Fourier transform IR, UV/vis, and electron paramagnetic resonance spectroscopy. Single-crystal X-ray structures show that the adjacent Cu(II) ions are linked by double phenoxo bridges and a mu(2)-eta(1):eta(1) carboxylato bridge. In each complex, the central copper atom is located in an inversion center with distorted octahedral coordination geometry, while the terminal copper atoms have square-pyramidal geometry. Cryomagnetic susceptibility measurements over a wide range of temperature exhibit a distinct antiferromagnetic interaction of J = -36.5 and -72.3 cm(-1) for 1 and 2, respectively. Density functional theory calculations (B3LYP functional) and continuous-shape measurement (CShM) studies have been performed on the trinuclear unit to provide a qualitative theoretical interpretation of the antiferromagnetic behavior shown by the complexes. 相似文献
106.
Coronado E Galán-Mascarós JR Martí-Gastaldo C Ribera A Palacios E Castro M Burriel R 《Inorganic chemistry》2008,47(19):9103-9110
Layered double hydroxides containing paramagnetic Ni (II) and diamagnetic/paramagnetic Al (III)/Fe (III) ions have been prepared and characterized. Ni 2Al(OH) 6(NO 3). nH 2O ( 1), Ni 2Fe(OH) 6(NO 3). nH 2O ( 2), Ni 2Fe(OH) 6(C 6H 8O 4) 0.5. nH 2O ( 3), and Ni 2Fe(OH) 6(C 10H 16O 4) 0.5. nH 2O ( 4) were prepared by coprecipitation at controlled pH as polycrystalline materials with the typical brucite-like structure, with alternating layers of hydroxide and the corresponding anions, which determine the interlayer separation. Magnetic studies show the appearance of spontaneous magnetization between 2 and 15 K for these compounds. Interestingly, the onset temperature for spontaneous magnetization follows a direct relationship with interlayer separation, since this is the only magnetic difference between compounds 2, 3, and 4. Magnetic and calorimetric data indicate that long-range magnetic ordering is not occurring in any of these materials, but rather a freezing of the magnetic system in 3D due to the magnetic disorder and competing intra- and interlayer interactions. Thus, these hydrotalcite-like magnetic materials can be regarded as spin glasses. 相似文献
107.
Katarzyna Brodowska Anna Sykuła Eugenio Garribba Elżbieta Łodyga-Chruścińska Michał Sójka 《Transition Metal Chemistry》2016,41(2):179-189
A Schiff base derived from naringenin (NTSC) and its complex with Cu(II) ([Cu(H3L)(OAc)]·H2O, Cu(II)–NTSC) have been synthesized and characterized by physicochemical and spectroscopic methods. EPR studies confirmed that nitrogen, oxygen, and sulfur are the donor atoms bound to Cu(II) in the complex. The geometry of the complex has been modelled using DFT methods. Furthermore, naringenin and NTSC were used for the formation of Cu(II) complexes in solution, for comparison of biological activities. Antioxidant studies confirmed better radical scavenging activity of both NTSC and its Cu(II) complex compared to naringenin. The interaction of these compounds with calf thymus DNA was monitored by UV–Vis spectroscopy. 相似文献
108.
Tannya R. Ibarra-Rivera Manuel Alejandro Rentería-Gómez Eduardo Nieto-Sepúlveda Rocío Gámez-Montaño Verónica M. Rivas Galindo Eugenio Hernandez-Fernandez 《合成通讯》2016,46(6):509-515
Novel tetrahydroindeno[1,2-b]pyrrolidines were conveniently prepared in moderate to good yields via a sequential Ugi multicomponent reaction or Staudinger/aza-Wittig/Ugi combination, followed by the palladium-catalyzed aerobic oxidative cyclization of the resulting Ugi adducts. 相似文献
109.
We discussed three dissimilarity measures between dendrograms defined over the same set, they are triples, partition, and cluster indices. All of them decompose the dendrograms into subsets. In the case of triples and partition indices, these subsets correspond to binary partitions containing some clusters, while in the cluster index, a novel dissimilarity method introduced in this paper, the subsets are exclusively clusters. In chemical applications, the dendrograms gather clusters that contain similarity information of the data set under study. Thereby, the cluster index is the most suitable dissimilarity measure between dendrograms resulting from chemical investigation. An application example of the three measures is shown to remark upon the advantages of the cluster index over the other two methods in similarity studies. Finally, the cluster index is used to measure the differences between five dendrograms obtained when applying five common hierarchical clustering algorithms on a database of 1000 molecules. 相似文献