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31.
Two new rhenium(IV) mononuclear compounds of formula NBu4[ReBr4(OCN)(DMF)] (1) and (NBu4)2[ReBr(OCN)2(NCO)3] (2) (NBu4 = tetrabutylammonium cation, OCN = O-bonded cyanate anion, NCO = N-bonded cyanate anion and DMF = N,N-dimethylformamide) have been synthesized and their crystal structures determined by single-crystal X-ray diffraction. 1 crystallizes in the monoclinic system with the space group P21/n, whereas 2 crystallizes in the triclinic one with as space group. In both complexes the rhenium atom is six-coordinated, in 1 by four Br atoms in the equatorial plane, and two trans-oxygen atoms, one of a DMF molecule and another one from a cyanato group, while in 2 by one bromide anion and five cyanate ligands, two of which are O-bonded and three N-bonded, forming a somewhat distorted octahedral surrounding. Magnetic susceptibility measurements on polycrystalline samples of 1 and 2 in the temperature range 1.9-300 K are interpreted in terms of magnetically isolated spin quartets with large values of the zero-field splitting (|2D| is ca. 41.6 and 39.2 cm−1 for 1 and 2, respectively). 相似文献
32.
Aged individuals exhibit an impairment of T helper and/or T suppressor activity on B cell function in an antibody-specific induction system. Further evidence is now provided that soluble suppressive factors acting on monocytes play a key role in such deficits. In fact, overnight preincubation of isolated monocytes and supplementation of autologous lymphocytes reverses the immunoregulatory imbalance. The suppressive factors are also responsible for a decreased interleukin 2 (IL-2) synthesis since a similar pretreatment of cell suspensions or exogenous human IL-1 and/or IL-2 supplementation of aged cell cultures leads to a recovery of T regulatory effects on B cell differentiation. Similar effects are observed in the presence of thymopentin, a well known IL-2 inducer. Interferon alpha and gamma addition to cultures gives rise to a restoration of T immunoregulatory effects. These findings suggest that several mechanisms are involved in the depressed T immunoregulatory activity in the elderly. 相似文献