No abstract

The synthesis and physical characterization (thermotropic and ferroelectric behavior) of eight ortho-palladated dimers [Pd2(ji-C1)2L*2] is reported. They are derived from chiral imines HL* (HL* = />-R1OC6H,(CH=NQH4-OR* 12-p, with R1, R2, or both equal to (R)or (5)-l-methylheptyl). The chiral imines, which contain one or two stereogenic centers, are not liquid crystals themselves. However, the dimeric complexes, which contain two or four stereogenic centers in their structure, exhibit both SmA and SmC* mesophases and enable the first comparative structure-activity study on metal-containing ferroelectric liquid crystals to be made. The ferroelectric properties obtained are better when there are chiral chains on the ortho-metalated aromatic rings, because the fixed conformation of these rings diminishes the chiral tail freedom, thus allowing a better coupling of molecular dipoles. The complexes with two chiral tails show important Psmax values in the range 44-131 nC*cm-2. The complex with four chiral chains (R1 = R2 = (R)-methylheptyl) is the first such compound ever reported containing four stereogenic centers; furthermore, it shows a remarkably high Psmax value of 206 nC-cnr2, the highest value reported so far for a metal-containing liquid crystal.

Our data suggest that obesity susceptibility or resistance may depend on the genetic make up related to inflammatory features, and support a role for omega-3 fatty acids in the prevention of obesity-associated inflammation in adipose tissue. In addition, our data do not support the hypothesis that serum haptoglobin is an acute phase protein expected to be positively related to increased adiposity in rats, at least in early and medium stages of DIO.

2] Sequence notations principally concern oligodeoxynucleotide derivatives ; the prefix d for deoxy is omitted here. Abbreviations: M e = 5'-0-methyl, M T M = S-0-methylthiomethyl. q 3 = 5'-azido-5'-deoxy. H2N = 5'-amino-5'deoxy. Ho = 5'-hydroxy, p = 3-phosphate. p = 3'-(2-chlorophenyl)phosphate, pPT1: = 3'-(2-phenylthioethyI)phosphate, pn = 3'-5'-phosphoamidate (the sequences, when not otherwise specified, are always in the 5' + 3' direction); HPLC = high-performance liquid chromatography, RPC' = reversed-phase column. (31 G . von Kiedrowski, Angrn.. Chem. 1986, 98, 932-934; Angew. Chem. 1121. Ed. Engl. 1986. 25, 932-935.[4] a ) For the theory of the square root law and parabolic growth see: G. von Kiedrowski. Bioorg. Chern. Front. 1993, 3, 113-146. b) Interestlngly, parabolic growth is also described in connection with the propagation of computer viruses: b)P. A. Angew Chcm I n / . Ed. Engl. 1993. 32, N o . 8 VCH VeriugsgeselBrhufi mhH. 0-69451 Weinheim, 1993 O57O-O833j93jOSO~-l20l 3 IO.OO+ .25:0 [S] The phases observed were characterized with a polarizing microscope; the abbreviation S, that appears later in the text refers to a smectic A phase characterized by an untilted, liquid-crystalline layer structure. 1202 0 VCH Verlagsgesellschafi mhH. 0-69451 Weinhem, 1993 0570

: A series of twelve mononuclear ortho-ualladated comulexes incornorating a Schiff base and a /I-diketone ligand have been synthesised. These compounds have four nonequivalent terminal chain positions and differ in the number and position(s) of chiral chains [(R)-2-methylheptyl] in the structure. A study of the ferroelectnc properties of the compounds has been performed. It is found that the spontaneous polarisation is highly dependent not only on the number of chiral carbons present, but also on the plexesIn recent years interest in metal-containing liquid crystals has been increasing, and several review articles have appeared describing this field."] Investigation into ferroelectricity in metallomesogens (metal-containing liquid crystals) is a relatively recent development, and the first transition-metal compound to exhibit ferroelectric behaviour was reported in 1 989.L21 Since this first example, a number of other compounds have been reported, including paramagnetic ferroelectric copper(n), vanadium(1v) and palladium ~alicylaldiminates,[~~ mononuclear P-diketonate ortho-palladated imine~,'~] and dimeric chloro-bridged ortho-palladated imine complexes containing either two or four chiral chains.*5]The most common problem associated with metal-containing mesogens is the high transition temperatures often encountered. At these elevated temperatures thermal decomposition often occurs, which hinders the study of the physical properties of the mesophases. An approach that has been successfully applied to obtain systems with lower transition temperatures is the synthesis of molecules with less symmetrical shapes.[61 On changing from a dinuclear to a mononuclear complex, reductions of around 100 "C in the clearing points are obtained (Fig. 1).The mononuclear complex shown in Figure 1 is of particular interest because it combines relatively low transition temperatures with the possibility of incorporating chiral carbons in different positions. The aim of the work described here was to synthesise a series of twelve mononuclear mixed-ligand palladium complexes covering all possible permutations for the incor- poration of one, two, three or four chiral chains (see Fig. 2), in order to study the effect of the position and number of chiral carbons on the liquid crystalline and ferroelectric properties of the compounds. This is the first time, in metallomesogens or in purely organic liquid crystalline systems, that the influence of chiral substituents in four nonequivalent positions has been studied systematically. 8CIO