Exchange Interactions and Intermolecular Hybridization in a Spin-1/2 Nanographene Dimer.

Phenalenyl is a radical nanographene with a triangular shape hosting an unpaired electron with spin S = 1/2. The open-shell nature of the phenalenyl is expected to be retained in covalently bonded networks. As a first step, we report synthesis of the phenalenyl dimer by combining in-solution synthesis and on-surface activation and its characterization on Au(111) and on a NaCl decoupling layer by means of inelastic electron tunneling spectroscopy (IETS). IETS shows inelastic steps that are identified as singlet-triplet excitation arising from interphenalenyl exchange. Spin excitation energies with and without the NaCl decoupling layer are 48 and 41 meV, respectively, indicating significant renormalization due to exchange with Au(111) electrons. Furthermore, third-neighbor hopping-induced interphenalenyl hybridization is fundamental to explaining the position-dependent bias asymmetry of the inelastic steps and activation of kinetic interphenalenyl exchange. Our results pave the way for bottom-up synthesis of S = 1/2 spin-lattices with large exchange interactions.

[25-hydroxy vitamin D deficiency with reduction of intestinal calcium absorption and bone density in chronic alcoholism]. / Carence en 25-hydroxyvitamine D avec diminution de l'absorption intestinale de calcium et de la densité osseuse dans l'alcoolisme chronique.

Plasma levels of 25-hydroxycalciferol (25-OH-D), 47-calcium intestinal absorption, bone mineral content and the biologic parameters of phospho-calcium metabolism were studied in 30 chronic alcoholics, 15 with Laennec's cirrhosis (group A) and 15 without (group B). These patients were compared with 27 normal subjects. In group A, the mean 25-OH-D plasma level was 23.7 +/- SD 18.5 microgram/l and in group B 35.2 +/- SD 21.8 microgram/l. These mean levels were lower than those of the control group, which were 57.2 +/- SD 22.5 microgram/l (p less than 0.001). The mean value of the 47Ca intestinal absorption, measured as the percentage of the ingested dose per litre of plasma and multiplied by the body weight, was also significantly lower in group A, which was 140 +/- SD 47 (p less than 0.01), and in group B, which was 145 +/- SD 69 (p less than 0.05), compared with the normal subjects whose average was 182 +/- SD 45.6. Similarly, the total plasma calcium was low: 1.99 +/- SD 0.24 mmol/l in all the alcoholics, while that of the control group was 2.22 +/- SD 0.18 mmol/l (p less than 0.001). For the 30 chronic alcoholics there was a positive correlation between 25-OH-D and 47Ca intestinal absorption, (r = 0.484; p less than 0.004). This suggests that in chronic alcoholism the deficiency of 25-OH-D induces a diminution of the intestinal absorption of calcium which, in the long term, can result in bone demineralization evidenced in the patients studied by a bone mineral content lower than normal (p less than 0.001).

[Decrease of intestinal absorption of 47-calcium in chronic alcoholism]. / Diminution de l'absorption intestinale de 47-calcium dans l'alcoolisme chronique.

Intestinal 47-calcium absorption has been studied in 34 chronic alcoholics, 17 of whom were cirrhotics (group A) and 17 non-cirrhotics (group B). These patients were compared with 44 normal subjects (group C). In group C, the 47Ca 2 h plasma % of the dose showed a significant negative correlation to the total body weight (p less than 0.001) and a positive correlation with the serum albumin (p less than 0.05). The mean intestinal absorption of 47Ca expressed as 2 h plasma % of the dose multiplied by total body weight was 131 +/- SD 52 in group A and 136 +/- SD 71 in group B. These two means are significantly low (p less than 0.001 and p less than 0.002 respectively) in relation to that found in group C (168 +/- SD 32). These results suggest that intestinal calcium absorption is diminished in chronic alcoholism even in the absence of hepatic cirrhosis.