Self-assembly of amphiphilic liquid crystal polymers obtained from a cyclopropane-1,1-dicarboxylate bearing a cholesteryl mesogen.

We study the self-assembly of a new family of amphiphilic liquid crystal (LC) copolymers synthesized by the anionic ring-opening polymerization of a new cholesterol-based LC monomer, 4-(cholesteryl)butyl ethyl cyclopropane-1,1-dicarboxylate. Using the t-BuP(4) phosphazene base and thiophenol or a poly(ethylene glycol) (PEG) functionalized with thiol group to generate in situ the initiator during the polymerization, LC homopolymer and amphiphilic copolymers with narrow molecular weight distributions were obtained. The self-assemblies of the LC monomer, homopolymer, and block copolymers in bulk and in solution were studied by small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and transmission electron microscopy (TEM). All polymers exhibit in bulk an interdigitated smectic A (SmA(d)) phase with a lamellar period of 4.6 nm. The amphiphilic copolymers self-organize in solution into vesicles with wavy membrane and nanoribbons with twisted and folded structures, depending on concentration and size of LC hydrophobic block. These new morphologies will help the comprehension of the fascinating organization of thermotropic mesophase in lyotropic structures.

Metal-free activation in the anionic ring-opening polymerization of cyclopropane derivatives.

The successful activation observed when using Bu(t) P(4) phosphazene base and thiophenol or bisthiols for the anionic ring opening polymerization (ROP) of di-n-propyl cyclopropane-1,1-dicarboxylate is described. Well-defined monofunctional or difunctional polymers with a very narrow molecular weight distribution were obtained through a living process. Quantitative end-capping of the propagating malonate carbanion was accessible by using either an electrophilic reagent such as allyl bromide or a strong acid such as HCl. Kinetics studies demonstrated a much higher reactivity compared to the conventional route using alkali metal thiophenolates.

The effects of clonidine added to mepivacaine for paronychia surgery under axillary brachial plexus block.

We hypothesized that onset of sensory block is delayed in infected versus healthy tissues within the same nerve distribution after axillary brachial plexus block (ABPB) and that clonidine added to mepivacaine would enhance anesthesia and postoperative analgesia. Forty-one outpatients undergoing thumb/index paronychia surgery under ABPB were randomly assigned to receive in a double-blind fashion 400 mg mepivacaine plus either 100 microg clonidine (clonidine group, n = 21) or 2 mL saline (placebo group, n = 20). Onset of sensory block in the infected area was delayed compared with healthy areas of the same nerve distribution (24.7 +/- 5.5 min versus 21.3 +/- 7.2; P = 0.02 for median and 21.6 +/- 7.8 min; P = 0.04 for radial) within the placebo group. In the clonidine group, when compared to placebo i) onset of sensory block in both the median and radial nerve territories was accelerated (11.1 +/- 5.6 and 10.5 +/- 5.2 versus 21.3 +/- 7.2 and 21.6 +/- 7.8 min, respectively; P < 0.001), ii) onset of sensory block in the region of infection was accelerated (9.1 +/- 1.9 versus 24.7 +/- 5.5 min; P < 0.001), iii) duration of anesthesia (275 +/- 75 versus 163 +/- 57; P = 0.04) and time to first analgesic requirement (279 +/- 87 versus 197 +/- 84 min; P = 0.002) were prolonged with decreased visual analog scale scores at this time (30 +/- 18 versus 70 +/- 24; P < 0.001), and iv) verbal numeric rating scores were decreased at 24 h (1.7 +/- 2.2 versus 4.1 +/- 3.0; P = 0.002) and 48 h (0.1 +/- 0.5 versus 1.5 +/- 2.4; P = 0.01) postoperatively. Our findings suggest that in the setting of distal infected tissue surgery under ABPB infected tissues are resistant to anesthesia compared with healthy areas within the same nerve distribution and clonidine added to mepivacaine enhances both anesthesia and postoperative analgesia.

Tramadol added to 1.5% mepivacaine for axillary brachial plexus block improves postoperative analgesia dose-dependently.

UNLABELLED: Adjuncts to local anesthetics for peripheral plexus blockade may enhance the quality and duration of anesthesia and postoperative analgesia. The analgesic, tramadol, has a unique mechanism of action that suggests efficacy as such an adjunct. It displays a central analgesic and peripheral local anesthetic effect. We designed a prospective, randomized, controlled and double-blind clinical trial to assess the effect of tramadol added to brachial plexus anesthesia. One-hundred patients scheduled for carpal tunnel release surgery under brachial plexus anesthesia were randomized into four groups. All patients received 1.5% mepivacaine 40 mL plus a study solution containing either isotonic sodium chloride (Group P, n = 17), tramadol 40 mg (Group T(40), n = 22), tramadol 100 mg (Group T(100), n = 20) or tramadol 200 mg (Group T(200), n = 20). We evaluated the time of onset of anesthesia, duration of sensory and motor blockade, duration and quality of postoperative analgesia, and occurrence of adverse effects. Onset and duration of sensory and motor blocks were not different among groups. The number of patients requesting analgesia in the postoperative period was significantly less in the 3 tramadol groups compared with the placebo group (P = 0.02); this was also noted with the placebo and T(40) groups compared with the T(200) group. No statistical significance was demonstrated between the placebo and the T(40) group or the T(100) group and the T(200) group. Furthermore, there was a significant trend effect among groups applying the Cochran-Armitage tendency test (P = 0.003), suggesting a dose-dependent decrease for additional postoperative analgesia requirements when tramadol was added. Side effects did not differ among groups, although they were more frequently recorded in the T groups. Our study suggests that tramadol added to 1.5% mepivacaine for brachial plexus block enhances in a dose-dependent manner the duration of analgesia with acceptable side effects. However, the safety of tramadol has to be investigated before allowing its use in clinical practice. IMPLICATIONS: Tramadol's unique mechanism of action suggests efficacy as a local anesthetic adjunct for peripheral plexus blockade. Our study demonstrates that tramadol, added to mepivacaine for brachial plexus anesthesia, extends the duration and improves the quality of postoperative analgesia in a dose dependent fashion with acceptable side effects.

N,N'-disubstituted ureas: influence of substituents on the formation of supramolecular polymers.

Symmetrical N,N'-disubstituted ureas have been synthesized and characterized. Among them, the branched dialkylureas prepared are highly soluble in organic media. Moreover, the solutions obtained are very viscous in heptane, if the branched alkyl groups are not too bulky (i.e. a methyl group on the alpha carbon, or an ethyl group on the beta carbon). Due to the strong, bifurcated hydrogen bonds between the urea moieties, linear supramolecular polymers are formed. The degree of association of these supramolecular polymers has been determined by FTIR spectroscopy.