Kai-Chung Lau

A bioaccumulative cyclometalated platinum(II) complex with two-photon-induced emission for live cell imaging

The cyclometalated platinum(II) complex [Pt(L)Cl], where HL is a new cyclometalating ligand 2-phenyl-6-(1H-pyrazol-3-yl)pyridine containing C(phenyl), N(pyridyl), and N(pyrazolyl) donor moieties, was found to possess two-photon-induced luminescent properties. The two-photon-absorption cross section of the complex in N,N-dimethylformamide at room temperature was measured to be 20.8 GM. Upon two-photon excitation at 730 nm from a Ti:sapphire laser, bright-green emission was observed. Besides its two-photon-induced luminescent properties, [Pt(L)Cl] was able to be rapidly accumulated in live HeLa and NIH3T3 cells. The two-photon-induced luminescence of the complex was retained after live cell internalization and can be observed by two-photon confocal microscopy. Its bioaccumulation properties enabled time-lapse imaging of the internalization process of the dye into living cells. Cytotoxicity of [Pt(L)Cl] to both tested cell lines was low, according to MTT assays, even at loadings as high as 20 times the dose concentration for imaging for 6 h.

Lewis acid-activated oxidation of alcohols by permanganate

The oxidation of alcohols by KMnO(4) is greatly accelerated by various Lewis acids. Notably the rate is increased by 4 orders of magnitude in the presence of Ca(2+). The mechanisms of the oxidation of CH(3)OH and PhCH(OH)CH(3) by MnO(4)(-) and BF(3)·MnO(4)(-) have also been studied computationally by the DFT method.

Reactivity of a Disilylene [{PhC(NBut)2}Si]2 toward Bromine: Synthesis and Characterization of a Stable Monomeric Bromosilylene

The reaction of the disilylene [{PhC(NBu(t))(2)}Si](2) (1) with 1 equiv of bromine in toluene afforded novel monomeric bromosilylene [{PhC(NBu(t))(2)}SiBr] (2). The result shows that the Si(I)-Si(I) bond in 1 was cleaved by bromine. An X-ray structure of compound 2 has been determined.

High-Level ab Initio Predictions for the Ionization Energy, Bond Dissociation Energies, and Heats of Formations of Iron Carbide (FeC) and Its Cation (FeC+)

The ionization energy (IE) of FeC and the 0 K bond dissociation energies (D(0)) and the heats of formation at 0 K (DeltaH(o)(f0)) and 298 K (DeltaH(o)(f298)) for FeC and FeC(+) are predicted by the single-reference wave function based CCSDTQ(Full)/CBS approach, which involves the approximation to the complete basis set (CBS) limit at the coupled cluster level up to full quadruple excitations. The zero-point vibrational energy (ZPVE) correction, the core-valence electronic corrections (up to CCSDT level), spin-orbit couplings, and relativistic effects (up to CCSDTQ level) are included in the calculations. The present calculations provide the correct symmetry predictions for the ground states of FeC and FeC(+) to be (3)Delta and (2)Delta, respectively. We have also examined the theoretical harmonic vibrational frequencies of FeC/FeC(+) at the ROHF-UCCSD(T) and UHF-UCCSD(T) levels. While the UHF-UCCSD(T) harmonic frequencies are in good agreement with the experimental measurements, the ROHF-UCCSD(T) yields significantly higher harmonic frequency predictions for FeC/FeC(+). The CCSDTQ(Full)/CBS IE(FeC) = 7.565 eV is found to compare favorably with the experimental IE value of 7.59318 +/- 0.00006 eV, suggesting that the single-reference-based coupled cluster theory is capable of providing reliable IE prediction for FeC, despite its multireference character. The CCSDTQ(Full)/CBS D(0)(Fe(+)-C) and D(0)(Fe-C) give the prediction of D(0)(Fe(+)-C) - D(0)(Fe-C) = 0.334 eV, which is consistent with the experimental determination of 0.3094 +/- 0.0001 eV. The D(0) calculations also support the experimental D(0)(Fe(+)-C) = 4.1 +/- 0.3 eV and D(0)(Fe-C) = 3.8 +/- 0.3 eV determined by the previous ion photodissociation study. The present calculations also provide the DeltaH(o)(f0)(DeltaH(o)(f298)) predictions for FeC/FeC(+). The analysis of the correction terms in these calculations shows that the core-valence and valence-valence electronic correlations beyond CCSD(T) wave function and the relativistic effects make significant contributions to the calculated thermochemical properties of FeC/FeC(+). For the experimental D(0) and DeltaH(o)(f0) values of FeC/FeC(+), which are not known to high precision, we recommend the CCSDTQ(Full)/CBS predictions [D(0)(Fe-C) = 3.778 eV, D(0)(Fe(+)-C) = 4.112 eV, DeltaH(o)(f0)(FeC) = 760.8 kJ/mol and DeltaH(o)(f0)(FeC(+)) = 1490.6 kJ/mol] based on the ZPVE corrections using the experimental vibrational frequencies of FeC and FeC(+).

C-N bond cleavage of anilines by a (salen)ruthenium(VI) nitrido complex.

We report experimental and computational studies of the facile oxidative C-N bond cleavage of anilines by a (salen)ruthenium(VI) nitrido complex. We provide evidence that the initial step involves nucleophilic attack of aniline at the nitrido ligand of the ruthenium complex, which is followed by proton and electron transfer to afford a (salen)ruthenium(II) diazonium intermediate. This intermediate then undergoes unimolecular decomposition to generate benzene and N2.

Novel high proton conductive material from liquid crystalline 4-(octadecyloxy)phenylsulfonic acid

Liquid crystal based sulfonic acid, 4-(octadecyloxy)phenylsulfonic acid, 1, effectively transports protons at 80 °C under non-humidified conditions. At its smectic A liquid crystal state, the proton conductivity of 1 was measured to be 1.1 × 10−2 S cm−1. The proton conductivities of 1 at its molten and solid powder states were found to be 1.2 × 10−4 and 1.5 × 10−7 S cm−1, respectively. A lamellar structure of bilayer stacks of 1 with the sulfonic acid groups in a head-to-head configuration was found within the monodomain of SmA phase of 1 from in situ XRD and DFT calculation. We proposed that the efficient proton transporting property of 1 is highly correlated to the formation of supramolecular pathways between the molecules at its liquid crystal phase.

Conformation-Specific Pathways of β-Alanine: A Vacuum Ultraviolet Photoionization and Theoretical Study

We report a photoionization and dissociative photoionization study of beta-alanine using IR laser desorption combined with synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry. Fragments at m/z = 45, 44, 43, and 30 yielded from photoionization are assigned to NH(3)CH(2)CH(2)(+), NH(2)CHCH(3)(+), NH(2)CHCH(2)(+), and NH(2)CH(2)(+), respectively. Some new conformation-specific dissociation channels and corresponding dissociation energies for the observed fragments are established and determined with the help of ab initio G3B3 calculations and measurements of photoionization efficiency (PIE) spectra. The theoretical values are in fair agreement with the experimental results. Three low-lying conformers of the beta-alanine cation, including two gauche conformers G1+, G2+ and one anti conformer A+ are investigated by G3B3 calculations. The conformer G1+ (intramolecular hydrogen bonding N-H...OC) is found to be another precursor in forming the NH(3)CH(2)CH(2)(+) ion, which is complementary to the previously reported formation pathway that only occurs with the conformer G2+ (intramolecular hydrogen bonding O-H...N). Species NH(2)CHCH(2)(+) may come from the contributions of G1+, G2+, and A+ via different dissociation pathways. The most abundant fragment ion, NH(2)CH(2)(+), is formed from a direct C-C bond cleavage. Intramolecular hydrogen transfer processes dominate most of the fragmentation pathways of the beta-alanine cation.

State‐to‐state Photoionization Dynamics of Vanadium Nitride by Two‐color Laser Photoionization and Photoelectron Methods

We have conducted a two‐color visible‐ultraviolet (VIS‐UV) resonance‐enhanced laser photoionization and pulsed field ionization‐photoelectron (PFI‐PE) study of gaseous vanadium mononitride (VN) in the total energy range of 56900–59020 cm−1. The VN molecules were selectively excited to single rotational levels of the intermediate VN(D3Π0, v′=0) state by using a VIS dye laser prior to photoionization by employing a UV laser. This two‐color scheme allows the measurements of rovibronically selected and resolved PFI‐PE spectra for the VN+(X2Δ; v+=0, 1, and 2) ion vibrational bands. By simulating the rotationally resolved PFI‐PE spectra, J+=3/2 is determined to be the lowest rotational level of the ground electronic state, indicating that the symmetry of the ground VN+ electronic state is 2Δ3/2. The analysis of the PFI‐PE spectra for VN+ also yields accurate values for the adiabatic ionization energy for the formation of VN+(X2Δ3/2), IE(VN)=56909.5±0.8 cm−1 (7.05588±0.00010 eV), the vibrational frequency ωe+=10...

Functionalization of Alkynes by a (Salen)ruthenium(VI) Nitrido Complex

Exploring new reactivity of metal nitrides is of great interest because it can give insights to N2 fixation chemistry and provide new methods for nitrogenation of organic substrates. In this work, reaction of a (salen)ruthenium(VI) nitrido complex with various alkynes results in the formation of novel (salen)ruthenium(III) imine complexes. Kinetic and computational studies suggest that the reactions go through an initial ruthenium(IV) aziro intermediate, followed by addition of nucleophiles to give the (salen)ruthenium(III) imine complexes. These unprecedented reactions provide a new pathway for nitrogenation of alkynes based on a metal nitride.

Rotationally Resolved State-to-State Photoelectron Study of Molybdenum Monoxide Cation (MoO+)

By employing the two-color visible–ultraviolet (vis–UV) laser pulsed field ionization–photoelectron (PFI–PE) measurement, we have obtained rotationally selected and resolved photoelectron spectra for the MoO+(X4Σ–; v+ = 0, 1, and 2) and MoO+(a2Δ3/2,5/2; v+ = 0 and 1) cationic states. The unambiguous rotational assignments have made possible the determination of highly precise values for the band origin v00+ = 60 147.9 ± 0.8 cm–1, rotation constant B0+ = 0.4546 ± 0.0006 cm–1, spin–spin coupling constant λ = 26.454 ± 0.017 cm–1, and bond length re+ = 1.642 ± 0.001 A for the MoO+(X4Σ–) ground state; v00+ = 60 556.4 ± 0.8 cm–1, B0+ = 0.4711 ± 0.0005 cm–1, and r0+ = 1.613 ± 0.001 A for the MoO+ (a2Δ3/2) excited state; and v00+ = 61 718.2 ± 0.8 cm–1, B0+ = 0.4695 ± 0.0006 cm–1, and r0+ = 1.616 ± 0.001 A for the MoO+ (a2Δ5/2) excited state. The ionization energy (IE) for MoO is determined to be IE(MoO) = 60 095.1 ± 0.8 cm–1 [7.4508 ± 0.0001 eV]. Furthermore, the vibrational constants are determined as ωe+ = 1000...