Fluoride ion complexation by a B(2)/Hg heteronuclear tridentate Lewis acid.

The reaction of [Li(THF)(4)][1,8-mu-(Mes(2)B)C(10)H(6)] with HgCl(2) affords [1,1'-(Hg)-[8-(Mes(2)B)C(10)H(6)](2)] () or [1-(ClHg)-8-(Mes(2)B)C(10)H(6)] (), depending on the stoichiometry of the reagents. These two new compounds have been characterized by (1)H, (13)C, (11)B and (199)Hg NMR, elemental analysis and X-ray crystallography. The cyclic voltammogram of in THF shows two distinct waves observed at E(1/2) -2.31 V and -2.61 V, corresponding to the sequential reductions of the two boron centers. Fluoride titration experiments monitored by electrochemistry suggest that binds tightly to one fluoride anion and more loosely to a second one. Theses conclusions have been confirmed by a UV-vis titration experiment which indicates that the first fluoride binding constant (K(1)) is greater than 10(8) M(-1) while the second (K(2)) equals 5.2 (+/- 0.4) x 10(3) M(-1). The fluoride binding properties of have been compared to those of [1-(Me(2)B)-8-(Mes(2)B)C(10)H(6)] () and [1-((2,6-Me(2)-4-Me(2)NC(6)H(2))Hg)-8-(Mes(2)B)C(10)H(6)] (). Both experimental and computational results indicate that its affinity for fluoride anions is comparable to that of but significantly lower than that of the diborane . In particular, the fluoride binding constants of , and in chloroform are respectively equal to 5.0 (+/- 0.2) x 10(5) M(-1), 1.0 (+/- 0.2) x 10(3) M(-1) and 1.7 (+/- 0.1) x 10(3) M(-1). Determination of the crystal structures of the fluoride adducts [S(NMe(2))(3)][-mu(2)-F] and [S(NMe(2))(3)][-mu(2)-F] along with computational results indicate that the higher fluoride binding constant of arises from a strong chelate effect involving two fluorophilic boron centers.

Pregnancy and social stress in female rats: influences on blood leukocytes and corticosterone concentrations.

The consequences of pregnancy and social stress on blood immune cells and on plasma corticosterone concentrations were assessed in Long Evans rats. Normal pregnancy in control females was characterized by a progressive increase in corticosterone concentration and increasing numbers of granulocytes. In contrast, CD4 T, CD8 T, and B cell numbers as well as the proliferative response of lymphocytes decreased as pregnancy progressed. Stress was induced in pregnant females by social confrontation for 2 h daily with a female resident opponent over a period of 2 months. Corticosterone concentrations were substantially higher in pregnant stressed than in pregnant control rats. Furthermore, the numbers of monocytes, NK and B cells were lower in stressed females, and there was a strong trend towards suppressed lymphocyte proliferation. Interestingly, pregnant females did not show granulocytosis in response to the stressor. In sum, the social stress paradigm in females appears to be a good model for the investigation of the interactions between stress, pregnancy and the immune system. It also provides an excellent platform for studies on prenatal stress under relatively naturalistic conditions.

Synthesis of B/Ga and B/In heteronuclear bidentate Lewis acids: formation of intramolecular pi-arene-gallium(III) and -indium(III) complexes.

Reaction of 1,8-dilithionaphthalene x TMEDA (TMEDA=tetramethylethylenediamine) with dimesitylboron fluoride in diethyl ether followed by treatment with THF affords the Li(THF)(4) salt of dimesityl-1,8-naphthalenediylborate (1). Compound 1-Li(THF)(4) undergoes a ring-opening reaction with trimethyltin chloride to afford high yields of 1-(dimesitylboron)-8-(trimethyltin)naphthalenediyl (2), a compound in which a boryl and a stannyl moiety coexist at the peri positions of a naphthalene core. Compound 2 has been characterized by multinuclear NMR spectroscopy, elemental analysis, and X-ray single-crystal analysis which reveal the existence of a sterically crowded structure. Compound 2 is a useful starting material for the synthesis of other heteronuclear naphthalene derivatives. Thus, the transmetalation reaction of 2 with GaCl(3) or InCl(3) in THF results in high yields of 1-(dichlorogallium)-8-(dimesitylboron)naphthalenediyl (3) and 1-(dichloroindium)-8-(dimesitylboron)naphthalenediyl (4), respectively. These unprecedented boron/gallium and boron/indium heteronuclear bidentate Lewis acids have been characterized by multinuclear NMR spectroscopy, elemental analysis, and X-ray single-crystal analysis. Owing to the presence of a short contact between the ipso-carbon atom of a mesityl group and the heavy Group 13 element (C(ipso)bondGa 2.279(4) A for 3, C(ipso)bondIn 2.442(6) A for 4), compounds 3 and 4 are best described as intramolecular pi-arene complexes and are the first examples of such complexes. As shown by (1)H and (13)C NMR spectroscopy, this pi interaction subsists in solution.