Sungmin Kang

Synthesis of diphenyl-diacetylene-based nematic liquid crystals and their high birefringence properties

We synthesized two series of diphenyl-diacetylene (DPDA)-based materials with alkoxy and alkyl tails of length m (DPDA–OCm and DPDA–Cm, respectively), and measured their nematic-phase birefringence (Δn) as a function of wavelength and temperature. We found that Δn decreases with an increase in m, possibly by a dilution effect of the low-Δn alkyl tail. Further, of the two series, Δn was found to be relatively higher in the DPDA–OCm materials, with the highest value of 0.4 obtained for DPDA–OC1 at 550 nm at 10 °C below the isotropic-to-nematic transition temperature. Further, we observed the temperature dependence for Δn, which is proportional to the order parameter (s). From extrapolation to s = 1 (the perfect orientation state), it is speculated that the DPDA–O moiety has the potential to afford a very large Δn of 0.9.

Incidental pituitary uptake on whole-body 18F-FDG PET/CT: a multicentre study

PurposeThe purpose of this study was to determine the incidence of incidental pituitary uptake on whole-body 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) and to investigate its clinical significance.MethodsThe files of 40,967 patients who underwent whole-body FDG PET/CT were retrospectively reviewed. Quantification of pituitary metabolic activity was obtained by using the maximum standardized uptake value (SUVmax). Hormone assays and pituitary MRIs were performed to assess pituitary lesions.ResultsFocally increased pituitary FDG uptake on PET/CT was found in 30 of 40,967 patients, accounting for an incidence of 0.073%. The mean SUVmax of 30 patients was 8.9 ± 6.6 (range: 3.2–32.6). Histological diagnosis was obtained in three patients and included two growth hormone-secreting adenomas and one non-functioning adenoma. Hormone assays were performed on serum samples from 11 patients, 2 of whom were shown to have hypersecretion of pituitary hormone. MRI was performed on 19 patients. Abnormal MRI findings suggesting a pituitary mass were found in 18 of 19 cases (94.7%). The mean SUVmax calculated without correction for partial volume effect for macroadenomas was significantly higher than the SUVmax for microadenomas (11.5 ± 8.4 vs 4.8 ± 1.3; p < 0.05). There were no cases diagnosed with metastasis to the pituitary gland during clinical follow-up.ConclusionIncidental pituitary FDG uptake was a very rare finding. Cases with incidental pituitary FDG uptake were diagnosed primarily with clinically non-functioning adenomas, and there were also a few functioning adenomas. Further evaluations, including hormone assays and pituitary MRI, are warranted when pituitary uptake is found on FDG PET/CT.

Formation of banana phases in bent-shaped molecules with unusual bent angles as low as 60°

We prepared a homologous series of bent-shaped molecules with a low bent angle of about 60° using a 1,7-naphthalene central core, a long side wing in which one phenyl ring is attached to the classical wing via an ester linkage and alkoxy tail groups with numbers of carbons of 4 to 14. All the compounds form well-defined mesophases. Two calamitic nematic (N) and SmA phases, and two banana SmAPA and B4 phases were identified with a sequence of N–SmA–SmAPA–B4 upon decreasing temperature. In all these phases, molecules behave as bent molecules irrespective of the low bent angle of approximately 60°, and are packed with the bent direction perpendicular to the n-director. SmAPA is different from SmA only by having biaxiality, and exhibits antiferroelectric switching characteristic of banana smectic phases.

Notable formation of a cubic phase from small bent-angle molecules based on the 1,7-naphthalene central core and alkylthio tails

The mesomorphic properties of small angle, bent-shaped molecules [N(1,7)-S-n] consisting of a 1,7-naphthalene central core, typical Schiff-base side wings, and alkylthio tails with the carbon number n have been investigated, and a notable formation of a cubic (Cub) phase in addition to a distinct hexagonal columnar (Colh) phase was observed. The Cub phase can form when the terminal chain length is longer than 22 and is stable over a wider temperature range (25 °C) as the length increases up to 30. The space symmetry of the Cub phase was determined as Pmn with a lattice size of 160–170 A regardless of the terminal chain length. Assuming that the cubic unit cell is composed of a spherical assembly with a spatial electron density distribution, it can be described as containing eight spheres, each having a radius of 53 A and comprising 300 molecules. This formation of a novel Cub phase, like the micellar assembly phases, was understood as an enclosed layer formation caused by layer deformation with significant curvature resulting from the asymmetric packing of bent molecules in combination with the longer alkylthio tail groups of N(1,7)-S-n. It is noteworthy that the present observation of a Cub phase with unequivocal experimental evidence establishing both its lattice structure and size is the first example of a novel self-assembly mode in a bent-core liquid crystal (LC) molecular system.

Prognostic Value of Primary Tumor Uptake on F-18 FDG PET/CT in Patients with Invasive Ductal Breast Cancer

PurposeTo determine the prognostic implications of pretreatment F-18 FDG PET/CT in patients with invasive ductal breast cancer (IDC), we evaluated the relationship between FDG uptake of the primary tumor and known prognostic parameters of breast cancer. Prognostic significance of tumoral FDG uptake for the prediction of progression-free survival (PFS) was also assessed.Materials and MethodsFifty-five female patients with IDC who underwent pretreatment F-18 FDG PET/CT were enrolled. The maximum standardized uptake value of the primary tumor (pSUVmax) was compared with clinicopathological parameters including tumor size, grade, estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor2 (HER2), axillary lymph node (LN) metastasis, and stage. The prognostic value of pSUVmax for PFS was assessed using the Kaplan-Meier method.ResultsA high pSUVmax was significantly related to a higher stage of tumor size (P < 0.05), grade (P < 0.001), and stage (P < 0.001). pSUVmax was significantly higher in ER-negative tumors (P < 0.001), PR-negative tumors (P < 0.001), and positive LN metastasis (P < 0.01), but not different according to HER2 status. pSUVmax was significantly higher in patients with progression compared to patients who were disease-free (10.6 ± 5.1 vs. 4.7 ± 3.5, P < 0.001). A receiver-operating characteristic curve demonstrated a pSUVmax of 6.6 to be the optimal cutoff for predicting PFS (sensitivity; 86.7%, specificity; 82.5%). The patients with a high pSUVmax (more than 6.6) had significantly shorter PFS compared to patients with a low pSUVmax (P < 0.0001).ConclusionspSUVmax on pretreatment F-18 FDG PET/CT could be used as a good surrogate marker for the prediction of progression in patients with IDC.

Synthesis and evaluation of dinaphthylacetylene nematic liquid crystals for high-birefringence materials

We synthesised 1,2-bis(6-alkoxy-2-naphthyl)acetylene as a new dinaphthylacetylene liquid crystal (LC) compound with alkoxy tails of length m (DNA–OCm) and characterised their phase behaviour by polarising optical microscopy and differential scanning calorimetry, where all compounds exhibited a nematic phase. Also, we measured the actual, and not extrapolated, Δn values of this target compound, and our results show the birefringence potential of the pure LC compound. They have high birefringence values, with the highest value of approximately 0.5 obtained for DNA–OC2 at 550 nm at 10°C above the nematic−crystal transition temperature.

High speed parallel synthesis of banana-shaped molecules and phase transition behaviour of 4-bromo-substituted derivatives

Novel derivative series of the well known bent-shaped P-n-O-PIMB liquid crystal mesogens, referred to as ‘4Br-P-n-O-PIMB’, ‘4Cl-P-n-O-PIMB’ and ‘5Cl-P-n-O-PIMB’, having halogen atoms substituted on the phenyl ring in the central core, were synthesized by solution phase parallel synthesis based on a combinatorial approach. The mesomorphic behaviour and physical properties of all the new compounds were studied by means of optical microscopy, differential scanning calorimetry, X-ray and circular dichroism spectroscopy. We found interesting transitional behaviour for the 4Br-P-n-O-PIMB homologous series. The homologues with alkyl tails having carbon numbers of n=3–10, 12, 14 exhibit rather complicated mesomorphic behaviour, which is strongly sensitive to n. The chiral fluid smectic B2 phase with SmCAPA structure and unidentified smectic Bx phase were observed in the homologues with n=9, 10, 12, 14 and n=3–5, respectively. Interestingly, every member exhibits frustrated and/or helical ordered phases at low temperatures, designated as X1, X2, and X3 phases, which result from a spontaneous escape from a macroscopic polarization. The mesomorphic behaviour and mesophase structures differ remarkably from those of the parent P-n-O-PIMB homologues, suggesting that substitution of the halogen atoms at the central core essentially creates a particular interaction between molecules.

Unusual Formation of Switchable Hexagonal Columnar Phase by Bent-Shaped Molecules with Low Bent-Angle Naphthalene Central Core and Alkylthio Tail

The low-angle bent-shaped molecules with 1,7-naphthalene central core and alkylthio tails can form a novel hexagonal columnar phase and a dark B4 phase. The columnar phase has a large two-dimensional hexagonal lattice with edges of 65–75 A and exhibits polar switching with spontaneous polarization along the column axis. Calculated from the density (∼1 g·cm-3) and unit volume, the number of molecules that are necessary to fill a 4.6-A stratum of each column were found to be ∼11. Such a large number of molecules can be accommodated only in the tube-like assembly, which may be the first example as formed by the usual bent-shaped molecule with a single alkylthio tail.

Assembly of thioether-containing rod-like liquid crystalline materials assisted by hydrogen-bonding terminal carboxyl groups

We designed a hydrogen-bonding tolane-based molecule with terminal carboxyl and alkylsulfanyl groups in an effort to realize thioether-containing rod-like liquid crystalline materials. The molecule successfully exhibits a stable enantiotropic mesophase, in contrast to non-hydrogen bonding derivatives, including tolane and diphenyldiacetylene. In addition, it shows two remarkable characteristics compared to analogues with alkyl or alkoxy groups. First, the mesophase of the alkylsulfanyl derivative shows strong long-range correlation. Second, the birefringence of the alkylsulfanyl derivative is highly temperature-dependent, achieving a maximum value of 0.36. These remarkable characteristics are believed to be due to the high polarisability of sulfur atoms and S–S contacts. These findings will be helpful for the design of novel sulfur-containing rod-like liquid crystalline materials.

Smectic mesophase behavior of dimeric compounds showing antiferroelectricity, frustration and chirality

We have prepared a series of dimeric compounds, mOAM5AMOm, which comprise two Schiffs base mesogens. These compounds formed three types of fluid smectic liquid crystals. When the alkoxy tail length is short (m=4 and 6), the alkoxy tail groups mix randomly with the alkyl spacer groups, resulting in the SmCAs phase. The compounds with m longer than 14 form the SmCAb phase with a bilayer character, in which the spacer and tail groups segregate from each other and consequently two mesogenic layers (so-called bilayer) are included within a repeat unit. In such a bilayer association of twin dimers, spontaneous polarization appears in each bilayer. In this SmCAb phase, furthermore, the molecules are tilted to the layer so that chirality is spontaneously formed in addition to ferroelectricity. The structure was identified as SmCAPA type. The compounds with intermediate m of 8–12 formed the frustrated SmCAf phase with a density modulation (frustration) along the layer. On cooling from the smectic phases, crystallization takes place for mOAM5AMOm with m=4–8, while the chiral Crblue phase with the TGB-like helical structure was clearly identified with m=14–18. The structure and properties of these exotic phases in twin dimers are described in detail.