Stephen Sin-Yin Chui

Supramolecular Polymers and Chromonic Mesophases Self‐Organized from Phosphorescent Cationic Organoplatinum(II) Complexes in Water

Soft matter with a hard core: Through PtII⋅⋅⋅PtII and hydrophobic interactions, planar organoplatinum(II) cations with chloride or sulfate as counterions self‐organize themselves in water into red‐emissive, chromonic, and viscoelastic mesophases from which aligned films and discrete uniaxial microfibers with cofacial molecular orientations can be readily prepared.

Photoresponsive Supramolecular Organometallic Nanosheets Induced by PtII⋅⋅⋅PtII and CH⋅⋅⋅π Interactions

While graphene, a carbon-based two-dimensional nanomaterials, has received an upsurge of interest, self-assembly of small organic and organometallic molecules into 2D nanostructures could also be harnessed to develop new classes of functional supramolecular nanomaterials. In principle, quasi-2D lamellae or nanosheets are planar structures having a thickness less than 100 nm and lateral dimensions a few orders of magnitude greater than their thickness. Control over the bilateral intermolecular noncovalent interactions is anticipated to organize small molecules into regular 2D nanostructures, which has been a formidable challenge yet to be achieved. Recently, Shelnutt and co-workers obtained discrete porphyrin nanosheets reprecipitated from their solutions; Sathish and co-workers constructed hexagonal C60 nanosheets using a liquid–liquid interfacial precipitation method; the groups of Yao and Hu prepared singlecrystalline nanosheets of polycyclic aromatics using a surfactant-assisted reprecipitation and a physical vapor transporting method, respectively; and Zhang and co-workers suggested that molecules with intramolecular charge-transfer dipole moments could be grown into quasi-2D nanostructures. Moreover, some amphiphiles and organogelators were found to self-organize into sheet-like nanostructures in contact with solvents. Despite these advances, templateand surfactant-free synthesis of free-standing, crystalline, and optoelectronically active nanosheets from small molecules remains elusive. Square-planar platinum(II) complexes containing p-conjugated ligands are particularly attractive building blocks for self-assembly reactions, because cofacial molecular aggregation can maximize the orbital interactions between two p systems, thus leading to rich photophysical and photochemical properties that can be harnessed for optoelectronic applications and light-energy conversion reactions. Intermolecular Pt···Pt interactions play a key role in the close packing of molecules. To date, quasi-one-dimensional nanowires have been obtained by self-organization of organoplatinum(II) complexes, presumably owing to the fact that molecular propagation is faster along the Pt···Pt chain axis than in the lateral directions. We and others have taken advantage of this anisotropic growth mechanism to assemble cationic organoplatinum(II) salts into nanostructures with luminescent, semiconducting, liquid crystalline, and gelating properties. Herein we report free-standing and crystalline nanosheets self-assembled from neutral pincer-type cyclometalated platinum(II) aryl acetylides. Indeed, intermolecular Pt···Pt and C H···p(C C) interactions in an orthogonal configuration account for the quasi-2D molecular organization herein. Notably, these organometallic nanosheets luminesce in the red to near infrared (NIR) region, and their electronic conductivity can be modulated by visible-light irradiation. The charge-neutral organoplatinum(II) complexes herein, namely [4-R-(N^C^N)PtC CC6H4-4’-R] (1–8, N^CH^N = 1,5-bis(2’-pyridyl)benzene), were prepared in quantitative yields by stirring the corresponding precursor, [4-R(N^C^N)PtCl] (R = CF3, [10g] H, or CH3 ), and an excess of aryl acetylene in methanol in the presence of NaOH for one day at room temperature. It is notable that when R is CF3, the solids of complexes 1–6 display various colors, depending on the substituent R on the aryl acetylide ligand (Scheme 1). When R is an electron-withdrawing group (CF3 for 5 and NO2 for 6), an electron-donating group (OCH3 for 3 and N(CH3)2 for 4), or a relatively neutral group (H for 1 and F for 2), the solid is bright yellow, deep red, or dark green in color, respectively. When R is H or CH3, no such color contrast was observed upon varying R from electron-withdrawing to -donating groups; the solids are yellow in color, as depicted for complexes 7 and 8 in Scheme 1.

Semiconducting and electroluminescent nanowires self-assembled from organoplatinum(II) complexes

Organometallic nanowires with luminescent and current‐modulating properties were self‐assembled from cyclometalated/terpyridyl platinum(II) complexes with auxiliary arylisocyanide/arylacetylide ligands and incorporated into a compact organic light‐emitting field‐effect transistor (see picture) by solution‐processable protocols. The nanowires exhibit both electron and hole mobilities of 0.1 cm2 V−1 s−1.

Luminescent cyclometalated platinum(II) complexes containing N-heterocyclic carbene ligands with potent in vitro and in vivo anti-cancer properties accumulate in cytoplasmic structures of cancer cells

Contrary to most platinum-based anti-cancer agents which target DNA, coordination of N-heterocyclic carbene (NHC) ligands to cyclometalated platinum(II) complexes confers these luminescent complexes to other cellular target(s). The strong Pt–Ccarbene bond(s) renders the platinum(II) complexes to display unique photophysical properties and enhanced stability against biological reduction and ligand exchange reactions. The platinum complexes described in this work are highly cytotoxic and display high specificity to cancerous cells. Among them, [(C^N^N)PtII(N,N′-nBu2NHC)]PF6 (1a, where HC^N^N = 6-phenyl-2,2′-bipyridine) with a lipophilic carbon chain on the carbene ligand induces apoptosis in cancer cells, demonstrates an enhancing synergistic effect with cisplatin in vitro, and displays potent in vivo activities using nude mice models. As this complex is strongly emissive, its cellular localization can be traced using emission microscopy. In contrast to common platinum-based anti-cancer agents, 1a does not accumulate in the vicinity of DNA but preferentially accumulates in cytoplasmic structures including sites where active survivin, an inhibitor of apoptosis (IAP), is located. In vitro, 1a significantly inhibits the expression of survivin, activates poly(ADP-ribose) polymerase (PARP) and induces apoptosis in cancer cells. Given the ease of structural modification of NHC ligand to alter the overall biological activities, these [(C^N^N)PtII(NHC)]+ complexes having unique photophysical properties provide an entry to a new class of potential anti-cancer drug leads.

Cooperative magnetic behavior in the coordination polymers [Cu3(TMA)2L3] (L=H2O, pyridine)

The temperature and magnetic field dependent magnetization of the polymeric solids [Cu3(TMA)2L3], where TMA=benzene-1,3-5-tricarboxylate and L=H2O or pyridine have been measured up to 5 T. These polymers contain dimeric [Cu2(O2CR)4] units. Discrete dimers in molecules such as cupric acetate have strong antiferromagnetic coupling between their two Cu d9 centers and at low T their susceptibility diminishes to nearly zero. While at higher T (300–100 K) the magnetism of the [Cu3(TMA)2L3] polymers resembles that of individual the [Cu2] dimer molecules, at low T a new cooperative behavior is found, with a sharp increase in χ seen at temperature below 75 K. In the case of L=pyridine a plot of 1/χ vs T shows linearity from 65 to 20 K and fits the Curie–Weiss law χ=C/(T− Θ ). Θ is found to be +4.7 K, indicative of a weak ferromagnetic coupling between dimers. This interaction may be facilitated by the planar aromatic bridges between the [Cu2] units.

A high-performance organic field-effect transistor based on platinum(II) porphyrin: peripheral substituents on porphyrin ligand significantly affect film structure and charge mobility.

Organic field-effect transistors incorporating planar pi-conjugated metal-free macrocycles and their metal derivatives are fabricated by vacuum deposition. The crystal structures of [H2(OX)] (H(2)OX=etioporphyrin-I), [Cu(OX)], [Pt(OX)], and [Pt(TBP)] (H2TBP=tetra-(n-butyl)porphyrin) as determined by single crystal X-ray diffraction (XRD), reveal the absence of occluded solvent molecules. The field-effect transistors (FETs) made from thin films of all these metal-free macrocycles and their metal derivatives show a p-type semiconductor behavior with a charge mobility (mu) ranging from 10(-6) to 10(-1) cm(2) V(-1) s(-1). Annealing the as-deposited Pt(OX) film leads to the formation of a polycrystalline film that exhibits excellent overall charge transport properties with a charge mobility of up to 3.2 x 10(-1) cm(2) V(-1) s(-1), which is the best value reported for a metalloporphyrin. Compared with their metal derivatives, the field-effect transistors made from thin films of metal-free macrocycles (except tetra-(n-propyl)porphycene) have significantly lower mu values (3.0 x 10(-6)-3.7 x 10(-5) cm(2) V(-1) s(-1)).

Analysis of melamine cyanurate in urine using matrix-assisted laser desorption/ionization mass spectrometry.

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) was applied to the direct analysis of melamine cyanurate (MC). The three commonly used MALDI matrixes, namely, alpha-cyano-4-hydroxycinnamic acid (CHCA), sinapinic acid (SA), and 2,5-dihydroxybenzoic acid (DHB), were able to desorb/ionize melamine from MC upon N(2) laser irradiation, with CHCA showing the highest detection sensitivity in the positive mode. Only DHB and SA were able to desorb/ionize cyanuric acid from MC in the negative mode but with remarkably lower sensitivity. The method is able to detect melamine unambiguously from a small amount of MC (down to 12.5 microg) spiked into urine and was successfully applied for the rapid and sensitive detection of melamine in urine stones/residues of the samples collected from patients clinically confirmed of having kidney stones associated with the consumption of melamine-tainted food products. The urine matrix resulted in interfering ion peaks and suppressed the ion intensity of melamine, while a cleanup process consisting of simply washing with water eliminated such interference and enhanced the ion intensity. The merit of the method is simplicity in sample preparation. The analytical time of the method for high-throughput analysis from the time of sample treatment to analysis is less than 7 minutes per sample, with sensitive detection of the presence of melamine in the urine stones/residues of the patient samples.

Hydrothermal synthesis of three new 3-D framework rare-earth mellitates

Abstract Hydrothermal reaction of rare-earth ions and mellitic acid [MEL-H 6 =C 6 (COOH) 6 ] has been carried out to determine the effects of metal size and ancillary aquation on polymer architecture. Three new 3-D framework rare-earth mellitate polymer types are formed with reduced aquation levels compared to ambient phases. Larger ions Ln=La to Er form 9-coordinate [Ln 2 (MEL)(H 2 O) 6 ] 1 (orthorhombic, Pnnm, for La a =13.642(2), b =6.769(1), c =10.321(2) A, V=953.1 A 3 ) and smaller ions Ln=Tm to Lu form the 7-coordinate [Ln 2 (MEL)(H 2 O) 4 ]H 2 O 2 (tetragonal, P4/ncc, for Tm a =18.443(3), c =10.374(2) A, V=3529 A 3 ). In the case of Ln=Er, Tm a third type with μ-aqua groups is found [Ln 2 (MEL)(μ-H 2 O) 2 (H 2 O) 2 ] 3 (monoclinic P2 1 /c, for Tm a =5.781(1), b =14.840(1), c =8.920(1) A, β =93.46(1)°, V=763.8 A 3 ). This 8-coordinate phase is favored over 1 at higher temperature (200°C) for Er and favored over 2 at lower temperatures (160°C) for Tm.

Copper Stabilization via Spinel Formation during the Sintering of Simulated Copper-Laden Sludge with Aluminum-Rich Ceramic Precursors

The feasibility of incorporating copper-laden sludge into low-cost ceramic products, such as construction ceramics, was investigated by sintering simulated copper-laden sludge with four aluminum-rich ceramic precursors. The results indicated that all of these precursors (γ-Al(2)O(3), corundum, kaolinite, mullite) could crystallochemically stabilize the hazardous copper in the more durable copper aluminate spinel (CuAl(2)O(4)) structure. To simulate the process of copper transformation into a spinel structure, CuO was mixed with the four aluminum-rich precursors, and fired at 650-1150 °C for 3 h. The products were examined using powder X-ray diffraction (XRD) and scanning electron microscopic techniques. The efficiency of copper transformation among crystalline phases was quantitatively determined through Rietveld refinement analysis of the XRD data. The sintering experiment revealed that the optimal sintering temperature for CuAl(2)O(4) formation was around 1000 °C and that the efficiency of copper incorporation into the crystalline CuAl(2)O(4) structure after 3 h of sintering ranged from 40 to 95%, depending on the type of aluminum precursor used. Prolonged leaching tests were carried out by using acetic acid with an initial pH value of 2.9 to leach CuO and CuAl(2)O(4) samples for 22 d. The sample leachability analysis revealed that the CuAl(2)O(4) spinel structure was more superior to stabilize copper, and suggested a promising and reliable technique for incorporating copper-laden sludge or its incineration ash into usable ceramic products. Such results also demonstrated the potential of a waste-to-resource strategy by using waste materials as part of the raw materials with the attainable temperature range used in the production of ceramics.

Synthesis and liquid crystal properties of a new class of calamitic mesogens based on substituted 2,5‐diaryl‐1,3,4‐thiadiazole derivatives with wide mesomorphic temperature ranges

Liquid crystals based on substituted 2,5‐diaryl‐1,3,4‐thiadiazole derivatives (1a–1f, 3a and 3b) and 1,3,4‐oxadiazole analogues (2a–2f, 4a and 4b) were synthesised and characterised by 1H, 13C nuclear magnetic resonance, Fourier transform infrared, mass spectrometry, high‐resolution mass spectrometry techniques and elemental analyses. The X‐ray crystal structure of 1e revealed that it contains tilted lamellar arrangement of molecules in the crystalline solid. The liquid crystal properties have been investigated by polarised‐light optical microscopy, differential scanning calorimetry and in‐situ variable‐temperature X‐ray diffraction. All compounds (except 2e and 2f) exhibited thermotropic liquid crystal behaviours with various mesophases (smectic A and C, nematic N or soft crystal E phases). Notably, the 1,3,4‐thiadiazole derivatives consistently have wider mesomorphic temperature ranges than those of the respective 1,3,4‐oxadiazole analogues. The solutions of all compounds in CH2Cl2 individually displayed one or two absorption bands with λ max values at 297–355 nm and emitted with λ max values at 363–545 nm and quantum yields of 0.12–0.73. Structure–property relationships of these compounds are discussed in the contexts of their molecular structures and weak intermolecular interactions.