In this article we describe the synthesis and dynamic behavior of two new molecular rotors with 1,4-diethynylphenylene rotators axially linked to two conformationally rigid steroidal norethisterone acetate or ethisterone frames. The resulting 1,4-bis(19-nor-17alpha-ethynyltestosterone-17beta-acetate)benzene (1) and 1,4-bis(17alpha-ethynyltestosterone)benzene (2) were fully characterized in solution and in the solid state, and the rotational dynamics of the central phenylene were explored with the help of (13)C NMR with cross polarization and magic angle spinning (CPMAS), and with quadrupolar echo variable temperature (VT) (2)H NMR in the case of 1. Splitting of signals from the aromatic ring on the (13)C CPMAS NMR and a broad quadrupolar spin echo (2)H spectrum of polycrystalline samples indicated that the rotation of the central aromatic ring in these compounds was limited at ambient temperature in the solid state. Variable temperature (2)H NMR experiments at 350 K in the case of 1-d(4) suggested a 2-fold rotational exchange with upper frequency limit of ca. 10 kHz. Single crystal X-ray analysis of this compound revealed that a crowded environment around the prospective phenylene rotator is responsible of the restricted rotation in the solid state.

In this study, we present apatite fission-track results obtained for ten rock samples collected from three different areas across the Sierra Madre del Sur, southern Mexico. The central objective of our study is the timing of the exhumation event that took place in southern Mexico during Late Cretaceous–Palaeogene time. The thermochronometric data obtained during this work indicate that a Late Cretaceous–Eocene cooling is recorded within the Sierra Madre del Sur, and this is interpreted as resulting from exhumation, an orogenic event that is contemporaneous with the Laramide sensu lato (or the Mexican Orogeny). The fission-track ages become younger from west to east across the Sierra Madre del Sur, whereas the cooling rates also increased in the same direction approximately during Campanian–middle Eocene time. Here, we suggest that the activity of the major fault systems of southern Mexico, such as the Caltepec and the Oaxaca faults, played a primary role in the development of geological structures and the exhumation of the Sierra Madre del Sur. Active magmatism during the evolution of the Mexican Orogen implicates the subducted Farallon slab as the main driver of crustal thickening. Moreover, the possible influence of the eastward movement of the Chortis Block on the deformation of the Sierra Madre del Sur cannot be ruled out.

Road from Azumbilla to Coxcatlán, Puebla (18°35'06''N; 97°14'44''W)Chivillas Formation is characterized by a finning and thinning-upward succession of 1.0-1.5meter-thick quartz-pebble conglomerate with black shale intraclasts and normal gradding. It's followed by a medium to coarse-grained sandstone with planar lamination and laminated black calcareous shale. The succession is cyclic and represents Tad and Tabd Bouma Sequence. Samples RN-3 and RN-4 were collected in this succession, separated by ~2.5 km from each other over the road.

La Unión pluton (LUP) belongs to the metamorphic and igneous Sula Terrane (ST) of Central Guatemala, limited to the north by the Motagua fault (MF) and to the south by the Jocotán-Chamelecón fault system (J-CH-FS). The basement of the ST is characterized by the high-grade metamorphic rocks belonging to the Las Ovejas Complex and the extensive low-grade San Diego phyllite, the latter in tectonic contact with LUP. A combination of field data, petrographic and geochemical analyses as well as geochronologic dating by U-Pb method, allow to classify LUP as a monzogranite with an age of 170 Ma (average of two dated samples), characterized by high-K calcalkaline and peraluminous affinity and with a REE pattern typical of a continental magmatic arc. Some trace-elements behavior and a comparison of similar-age units found elsewhere in eastern, central and southern Mexico, allow to associate its formation to the lithospheric thinning and extension that occurred during the breakup of Pangea and the opening of the Gulf of Mexico.