Academic literature on the topic '1440-1449'

Regesten Kaiser Friedrichs III. (1440-1493). Nach Archiven geordnet, hrsg. v. H. Koller, P.-J. Heinig und A. Niederstätter, Heft 14: Die Urkunden und Briefe aus Archiven und Bibliotheken der Stadt Nürnberg, Teil 1: 1440-1449, bearb. v. D. Rübsamen, Wien/Weimar/Köln (Böhlau) 2000. 371 S.

Abstract Bertoldo di Giovanni (ca. 1440–1491) was the primary sculptor and medal worker for Lorenzo the Magnificent (1449–1492). Despite being one of the most prominent Italian Renaissance artists working in Florence, little is known about his workshop and practice. The Frick Collection, New York, owns a Shield Bearer, one of a small number of bronze statuettes attributed to Bertoldo predominantly based on stylistic grounds. This article presents the results obtained from the scientific analysis of The Frick statuette, including a detailed technical characterization of the casting alloy, gilding, solder, organic coatings, and other later alterations. An array of analytical techniques was employed, including X-radiography, micro- and portable X-ray fluorescence (μXRF and pXRF) spectroscopies, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS), Raman and Fourier-transform infrared (FTIR) spectroscopies, and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). This work supported a larger technical study of Bertoldo’s statuettes and reliefs related to an exhibition organized by The Frick, which brought together a select group of medals, as well as eleven bronzes ascribed to the artist, including the museum’s statuette. Close collaboration between conservators, curators, and scientists was critical throughout the study of the Shield Bearer, which also included extensive visual examination of the object in order to understand details of manufacture, identify sampling sites, and interpret the collected data. This study confirmed that The Frick figure was cast from the same brass alloy as a second very similar Shield Bearer in the Liechtenstein Collection, Vienna, suggesting that the two are a pendant pair that was likely cast simultaneously. In addition, analysis supported the assertion that the copper base on The Frick sculpture is original and assisted in identifying later alterations in both works. This focused research has expanded the current knowledge of the sculptor’s materials and methods, enabling scholars to better contextualize his artistic production within the framework of Italian Renaissance sculpture.

A theoretical study on stereo and electronic properties of a series of six 1,2,4-triazole-derived carbenes bearing different N4-substituents, namely isopropyl (1), benzyl (2), phenyl (3), mesityl (4), 2,6-diisopropylphenyl (5) and 1-naphthyl (6), has been carried out. Structures of the six carbenes were first optimized using Gaussian® 16 at B3LYP level. Their molecular geometries and electronic structures of the frontier orbitals were examined. The results suggest the similarity in nature of their HOMOs, which all posses s symmetry with respect to the heterocycle and essentially be the lone electron pair on the Ccarbene. Steric properties of the NHCs was also quantified using percent volume burried (%Vbur) approach. The NHC 1 with isopropyl N4-substituent was the least bulky one with %Vbur of 27.7 and the most sterically demanding carbene is 6, which has large 2,6-diisopropylphenyl substituent (%Vbur = 38.4). Interestingly, the NHCs with phenyl and 1-naphthyl N4-substituents display flexible steric hindrance due to possible rotation of the phenyl or 1-naphthyl around the N-C single bond. Beside stereoelectronic properties of the NHC, topographic steric map of their complexes with metal were also investigated. Keywords: N-heterocyclic carbene, triazolin-5-ylidene, stereoelectronic properties, percent volume burried. References [1] D. Bourissou, O. Guerret, F.P. Gabbaï, G. Bertrand, Stable Carbene, Chem. Rev. 100 (2000) 39−92. https://doi.org/10.1021/cr940472u.[2] N. Marion, S.P. Nolan, Well-Defined N-Heterocyclic Carbenes-Palladium(II) Precatalysts for Cross-Coupling Reactions, Acc. Chem. Res. 41 (2008) 1440−1449. https://doi.org/10.1021/ar800020y. [3] F.E. Hahn, M.C. Jahnke, Heterocyclic carbenes: synthesis and coordination chemistry, Angew. Chem., Int. Ed. 47 (2008) 3122−3172. http://doi. org/10.1002/anie.200703883. [4] M.N. Hopkinson, C. Richter, M. Schedler, F. 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Gornitzka, V. Romanenko, G. Bertrand, Synthesis and structure of 1,2,4-triazol-2-ium-5-ylidene complexes of Hg(II), Pd(II), Ni(II), Ni(0), Rh(I) and Ir(I), J. Organomet. Chem. 664 (2002) 70-76. https: //doi.org/10.1016/S0022-328X(02)01924-1.[10] S. Guo, H.V. Huynh, Dinuclear Triazole-Derived Janus-Type N-Heterocyclic Carbene Complexes of Palladium: Syntheses, Isomerizations, and Catalytic Studies toward Direct C5-Arylation of Imidazoles, Organometallics, 33 (2014) 2004−2011. https:// doi.org/10.1021/om500139b.[11] A. Zanardi, J.A. Mata, E. Peris, Palladium Complexes with Triazolyldiylidene. Structural Features and Catalytic Applications, Organometallics 28 (2009) 4335−4339. https://doi.org/10.1021/om8010504. [12] C. Dash, M.M. Shaikh, R.J. Butcher, P. Ghosh, A comparison between nickel and palladium precatalysts of 1,2,4-triazole based N-heterocyclic carbenes in hydroamination of activated olefins, Dalton Trans. 39 (2010) 2515-2524. http://doi.org/10.1039/B917892A. [13] H. Clavier, A. 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