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NMR T1 relaxation times have been measured for 13C nuclei in the alkyl chains of symmetric tetra-n-alkylstannanes dissolved in CDCl3. The results are interpreted in terms of conformational transitions occurring in the aliphatic chains superimposed to rotational diffusion of the whole molecule. A comparison with analogous tetra-n-alkylammonium salts is performed. Differences are ascribed to changes in the overall rotational diffusion deriving from effects of charge upon formation of ion-pairs and larger aggregates.

The conformational dynamics of alkyl chains is usually analysed within the framework of the rotational isomeric state (RIS) approximation, where only the conformers corresponding to the configurational potential minima are considered, and torsional fluctuations about the minima are ignored. In order to test the validity of this procedure, 13 C NMR T 1 relaxation times have been measured in the series of symmetric tetra- n -alkylammonium ions (C N H 2 N +1 ) 4 N + , with N = 8, 10, 12, 16 and 18, and compared with theoretical results predicted by the RIS model. Spin relaxation rates of the terminal carbon atoms show a tendency to level off for increasing chain length, in contrast with the monotonic increase predicted by the RIS model. The experimental behaviour reveals that deviations from RIS results appear for chains with more than ten carbon atoms.

Butyrolactone I (BLI) can be used to maintain meiosis blocked during transport of oocytes to the laboratory, aiming to maintain their quality and competence. This work evaluated the effect of BLI during transport of bovine oocytes on the cortical granules (CG) distribution, and fertilization. Meiotic block culture was in basic medium (TCM-199 with 0.2 mM pyruvate, 25 mM sodium bicarbonate, and 75 mg mL-1 gentamicin) with 10 μLM BLI (B10) or 100 (AM BLI + 0.3% BSA (B100). During meiotic block, oocytes were cultured in cryogenic vials (15/vial) containing 60 μLL of medium recovered with mineral oil, packed in a portable incubator (Thawing Unit MT 35/42, Minitub) at 38.5°C during the first 5 h, and then transferred to a incubator at 38.5°C and 5% CO2 in air for the remaining 19 h. Then, they were matured at 38.5°C and 5% CO2 in basic medium supplemented with 0.6% BSA and hormones (maturation medium, MM) for 20 h. As controls, a group of oocytes was matured in MM during 24 h, without prior meiotic block. Control oocytes were cultured at 38.5°C and 5% CO2 (control 1, C1) or in the same portable incubator conditions in which the blocked oocytes were cultured (C2). A group of oocytes was fixed immediately after follicular aspiration (C0). At the end of cultures, a group of oocytes (n = 853) were stained with 1 μg mL-1 Lens culinaris (FITC-LCA) and assessed for the distribution of CG (arrangement in clusters = immature; peripheral = mature). The remaining oocytes (n = 563) were fertilized for 18 h, and zygotes were stained with 10 μg mL-1 Hoechst 33342 and assessed for sperm penetration and pronuclear formation. Oocytes with 2 pronuclei (2PN) were considered to present normal fertilization, and oocytes with >2PN were considered to be polyspermic. The data were analyzed by ANOVA and Tukey’s test, and correlation between CG positioning and pronuclear formation was analyzed with the Pearson correlation test. After meiotic block, the proportion of immature CG were higher (P < 0.05) in B100 (90.7%) and C0 (88.2%) than in B10 (69.0%). After maturation, mature CG rates in C2 (61.7%) were similar to B10 (52.3%) and B100 (72.9%), but only B100 was similar to C1 (83.6%). Irrespective of the presence or absence of BLI, culture of oocytes in the portable incubator adversely affected the normal pronuclear formation rates, which were higher (P < 0.05) in C1 (78.9%) than in C2 (56.8%), B10 (56.0%), and B100 (51.8%). The incidence of >2PN was higher (P < 0.05) in B10 (5.9%) than in C1, C2, and B100 (0.0, 1.4, and 0.0%, respectively). There was a fine correlation between mature CG and normal pronuclear formation (R = 0.5; P < 0.05). We conclude that (1) CG migration is reversibly blocked by BLI at a concentration of 100 μLM during transport; (2) oocyte transport in the portable incubator, but not BLI itself, adversely affects the normal pronuclear formation; and (3) CG maturation is essential for normal pronuclear formation. Financial support: FAPESP.