Fluorescent mesogenic boron difluoride complexes derived from heterocyclic benzoxazoles.

One new series of boron difluoride complexes 1 derived from heterocyclic benzoxazoles 2 was reported, and their mesomorphic and optical properties were also investigated. One single crystal of the mesogenic BF2 complex 1a (m = 12, n = 8) was obtained, and its single crystal and molecular structure were resolved. The geometry coordination at the central boron atom is tetrahedral. It crystallizes in a triclinic space group P1[combining macron] with Z = 4. The overall molecular shape was described as slightly bent Z-shapes, and the molecular length was ca. 34.06 Å. Weak intramolecular and intermolecular H-bonds observed in the crystal lattice were attributed to the formation of mesophases. The results indicated that benzoxazoles 2a (n = 6, 8, 12) formed monotropic SmA phases, while boron difluoride complexes 1a (n = 6, 8, 12, 16) exhibited monotropic SmC mesophases. In contrast, all compounds of 2b and 1b (m = 1, n = 12 for all) were not mesogenic. Boron complexes 1 emitted a pronounced violet emission at λmax = 399 nm in solution at room temperature.

Cervical spine clearance in obtunded patients after blunt traumatic injury: a systematic review.

BACKGROUND: Cervical spine clearance protocols are controversial for unconscious patients after blunt traumatic injury and negative findings on computed tomography (CT). PURPOSE: To review evidence about the utility of different cervical spine clearance protocols in excluding significant cervical spine injury after negative CT results in obtunded adults with blunt traumatic injury. DATA SOURCES: MEDLINE, EMBASE, CINAHL, Google Scholar, and the Cochrane Library were searched from January 2000 through November 2014. STUDY SELECTION: English-language studies that examined patients with negative CT results having confirmatory routine testing with magnetic resonance imaging (MRI), dynamic radiography, or clinical examination and that reported outcome measures of missed cervical spine injury, need for operative stabilization, or prolonged use of cervical collars. DATA EXTRACTION: Independent reviewers evaluated the quality of studies and abstracted the data according to a predefined protocol. DATA SYNTHESIS: Of 28 observational studies (3627 patients) that met eligibility criteria, 7 were prospective studies (1686 patients) with low risk of bias and well-interpreted, high-quality CT scans. These 7 studies showed that 0% of significant injuries were missed after negative CT results. The overall studies using confirmatory routine testing with MRI showed incidence rates of 0% to 1.5% for cervical spine instability (16 studies; 1799 patients), 0% to 7.3% for need for operative fixation (17 studies; 1555 patients), and 0% to 29.5% for prolonged collar use (16 studies; 1453 patients). LIMITATIONS: Most studies were retrospective. Approaches to management of soft tissue changes with collars varied markedly. CONCLUSION: Cervical spine clearance in obtunded adults after blunt traumatic injury with negative results from a well-interpreted, high-quality CT scan is probably a safe and efficient practice. PRIMARY FUNDING SOURCE: None.

Functionalized dibenzo[g,p]chrysenes: variable photophysical and electronic properties and liquid-crystal chemistry.

The photophysical and electronic properties of dibenzo[ g, p]chrysenes bearing electron-rich and -deficient substituents vary markedly with these substituents. The chemistry of the first liquid-crystalline dibenzo[ g, p]chrysene is also described.

Supramolecular metallomesogens. Self-organization of an H-bonded tetrameric assembly into columnar phase from single component.

The first example of supramolecular metallomesogens derived from palladium complexes exhibiting columnar phase is reported, and the formation of the mesophase is induced by H-bonding in a tetrameric assembly.

Liquid crystals of silver complexes derived from simple 1-alkylimidazoles.

A homologous series of silver complexes of 1-alkylimidazoles (R-im, R = CnH(2n+1), where n= 10, 12, 14, 16 and 18) was synthesized. All the CnH(2n+1)-im ligands are non-mesomorphic. Upon complexation, all the [Ag(CnH(2n+1)-im)2]-[NO3], except for n = 10, exhibit liquid crystalline properties. The crystal structure of [Ag(C12H25-im)2][NO3] shows that the silver center is two-coordinate and adopts a U-shaped conformation with bilayer packing. The non-mesomorphic [Ag(C16H33-bim)2][NO3](bim = benzimidazole) has a three-coordinate silver ion and has a chair conformation with monolayer stacking. Non-mesomorphic [Ag(C16H33-bim)2][BF4] has a linear geometry around the silver ion and also has a chair conformation. The mesophase for the Ag-(CnH(2n+1)-im) complexes has been identified as the smectic A (SmA) phase. [Ag(C16H33-im)2]+ with four different anions, NO3-, BF4-, PF6- and CF3SO3- were compared. Of the four Ag-im complexes, only that with the CF3SO3- anion does not show liquid-crystal behavior.