Photophysical properties of Kuratowski-type coordination compounds [M(II)Zn4Cl4(Me2bta)6] (M(II) = Zn or Ru) featuring long-lived excited electronic states

The syntheses of Kuratowski-type pentanuclear clusters featuring {MZn(4)Cl(4)} cores (M(II) = Ru or Zn) that incorporate triazolate ligands are described. The coordination compounds are characterized by single-crystal X-ray diffraction, X-ray powder diffraction (XRD), FTIR- and UV-vis spectroscopy. [Ru(II)Zn(4)Cl(4)(Me(2)bta)(6)]·2DMF (Me(2)bta(-) = 5,6-dimethyl-1,2,3-benzotriazolate) (1) crystallizes in the cubic system, while [Zn(5)Cl(4)(ta)(6)] (ta(-) = 1,2,3-triazolate) (3) crystallizes in the tetragonal system. Both compounds feature structurally similar cluster topologies in which the central octahedrally coordinated metal ion is coordinated to six triazolate ligands. Each triazolate ligand is coordinated with two zinc ions (μ(3)-bridging mode), leading altogether to a pentanuclear cluster of T(d) point group symmetry. Photophysical investigations reveal that compound [Zn(5)Cl(4)(Me(2)bta)(6)]·2DMF (2) shows a short-lived excited electronic state, which can be populated with high quantum yield. The isostructural compound [Ru(II)Zn(4)Cl(4)(Me(2)bta)(6)]·2DMF (1), on the other hand, shows a long-lived photoexcited state, owing to an internal singlet to triplet conversion of the electronic states, as revealed by time-resolved fluorescence spectroscopy. Insights gained from these studies open up novel design strategies towards photocatalytically active metal-organic frameworks incorporating photoactive Kuratowski-type secondary building units such as MFU-4 (Metal-Organic Framework Ulm University-4).     

Conversion of methane into C1 oxygenates by deep-UV photolysis on solid surfaces: influence of the nature of the solid and optimization of photolysis conditions

Deep-UV photolysis (either 165 or 185 nm) of surface hydroxy groups leads to homolytic O-H bond-cleavage with the generation of oxyl radicals that can initiate the room-temperature radical-chain methane activation. Whilst in the absence of oxygen, radical coupling reactions to give low-molecular-weight alkanes are observed in the gas phase, the presence of some oxygen quenches these radicals and increases the selectivity towards C1 oxygenates (methanol, formaldehyde, and formic acid species). The nature of the solid influences the efficiency of the photochemical process and the distribution between products in the gas and solid phases. Using Beta-, delaminated ITQ2 and ITQ6, and medium-pore ZSM5 zeolites, mesoporous MCM41 silicates, and non-porous TiO(2), we observed that confinement and porosity increased the proportion of C1 oxygenates adsorbed onto the solid and reduced the contribution of the gas-phase products. In addition, the presence of aluminum in the zeolite framework, which is responsible for the generation of acid sites, increased overoxidation of methanol and methoxy groups into formaldehyde and formic acids. For a given amount of methane and unchanged photolysis conditions, the conversion increased with the amount of the solid used as photocatalyst. In this way, methane conversions of up to 7% were achieved for the 185 nm photolysis of methane for 1 h with a 76 MJ mol(-1) energy consumption.     

The Hessenberg matrix and the Riemann mapping function

We consider a Jordan arc Γ in the complex plane ${\mathbb C}$ and a regular measure μ whose support is Γ. We denote by D the upper Hessenberg matrix of the multiplication by z operator with respect to the orthonormal polynomial basis associated with μ. We show in this work that, if the Hessenberg matrix D is uniformly asymptotically Toeplitz, then the symbol of the limit operator is the restriction to the unit circle of the Riemann mapping function ?(z) which maps conformally the exterior of the unit disk onto the exterior of the support of the measure μ. We use this result to show how to approximate the Riemann mapping function for the support of μ from the entries of the Hessenberg matrix D.     

Computing matrix functions solving coupled differential models

In this paper a modification of the method proposed in [E. Defez, L. Jódar, Some applications of Hermite matrix polynomials series expansions, Journal of Computational and Applied Mathematics 99 (1998) 105–117] for computing matrix sine and cosine based on Hermite matrix polynomial expansions is presented. An algorithm and illustrative examples demonstrate the performance of the new proposed method.     

Ion‐Mobility Spectrometry Can Assign Exact Fucosyl Positions in Glycans and Prevent Misinterpretation of Mass‐Spectrometry Data After Gas‐Phase Rearrangement

The fucosylation of glycans leads to diverse structures and is associated with many biological and disease processes. The exact determination of fucoside positions by tandem mass spectrometry (MS/MS) is complicated because rearrangements in the gas phase lead to erroneous structural assignments. Here, we demonstrate that the combined use of ion‐mobility MS and well‐defined synthetic glycan standards can prevent misinterpretation of MS/MS spectra and incorrect structural assignments of fucosylated glycans. We show that fucosyl residues do not migrate to hydroxyl groups but to acetamido moieties of N‐acetylneuraminic acid as well as N‐acetylglucosamine residues and nucleophilic sites of an anomeric tag, yielding specific isomeric fragment ions. This mechanistic insight enables the characterization of unique IMS arrival‐time distributions of the isomers which can be used to accurately determine fucosyl positions in glycans.     

Excited‐State Charge Transfer in Covalently Functionalized MoS2 with a Zinc Phthalocyanine Donor–Acceptor Hybrid

The functionalization of MoS₂ is of paramount importance for tailoring its properties towards optoelectronic applications and unlocking its full potential. Zinc phthalocyanine (ZnPc) carrying an 1,2‐dithiolane oxide linker was used to functionalize MoS₂ at defect sites located at the edges. The structure of ZnPc‐MoS₂ was fully assessed by complementary spectroscopic, thermal, and microscopy imaging techniques. An energy‐level diagram visualizing different photochemical events in ZnPc‐MoS₂ was established and revealed a bidirectional electron transfer leading to a charge separated state ZnPc^{. +} ‐MoS₂^.?. Markedly, evidence of the charge transfer in the hybrid material was demonstrated using fluorescence spectroelectrochemistry. Systematic studies performed by femtosecond transient absorption revealed the involvement of excitons generated in MoS₂ in promoting the charge transfer, while the transfer was also possible when ZnPc was excited, signifying their potential in light‐energy‐harvesting devices.     

Photochemical behavior of p-dimethylaminobenzoylated polystyrene as polymerization photoinitiator: Synthesis of graft copolymers

The photochemical behavior of p-dimethylaminobenzoylated polystyrene (PS-MI) in benzene solution has been investigated, both in the presence and absence of methyl methacrylate (MMA). This behavior has been compared with that of the model compound, 4-isopropyl-4′-N,N-dimethylaminobenzophenone (CU-MI). PS-MI photoreduction takes place only through excimer formation due to the high local chromophore concentration, and therefore, PS-MI disappearance quantum yield is close to the previously calculated limiting value (0.02) and independent of chromophore concentration. Several parameters that characterize the polymerization process have been determined; it has been found that the obtained PMMA is photografted onto PS-MI backbone. This is in agreement with the proposed mechanism for radical generation. No homo-PMMA formation has been detected. © 1993 John Wiley & Sons, Inc.     

New photopolymer with trifunctional monomer for holographic applications

New holographic recording materials based on photopolymerizable systems have contributed significantly to the recent growth of holographic applications. Previously, we reported that in photopolymerizable systems with a difunctional monomer, Ethylene Glycol DiMethAcrylate (EGDMA) improves the behaviour of the system and explains the role played by an eosin ester that has an oxo-oxime group in the production of amine initiator radicals. This comparative study was carried out in our laboratory using differential scanning photo-calorimetry and holography. The results of the new photosensitive recording materials for holography indicate that this system can be used for the formulation of very promising photopolymers that have a better performance. The aim of this study was to change the crosslinking monomer in order to increase the energetic sensitivity and discover the rest of the behavior. The new photo-polymerizable mixture contains PentaErythritol TriAcrylate (PETA) in a 1:1 ratio of volume and a 2-Hydroxy-Ethylene MethAcrylate monomer (HEMA). A diffraction efficiency of 80% is achieved with an energetic sensitivity of 3 J/cm² at 514 nm, and the spatial resolution is up to 2000 lines/mm.Part of this paper was presented at the IS&T/SPIE Symposium in Electronic Imaging, Science and Technology (Holographic Materials), February 5–10, San Jose, CA, USA     

4-N,N-Dimethylamino-4'-Isopropylbenzophenone as polymerization photoinitiator. Effect of solvent and photoinitiator concentration on its photoreactivity and on the polymerization process

Several kinetics aspects of the methyl methacrylate (MMA) polymerization using 4-dimethylamino-4'-isopropylbenzophenone (PI) as photoinitiator have been studied. The order of the polymerization reaction with respect to monomer and initiator concentrations have been investigated, as well as the polymerization behavior under well-stirred and unstirred conditions; values of initiation quantum yield (?_i) and k_p/k_t^1/2 have also been determined. It has been found that the nature of the polymerization-initiating radicals depends on the type of solvent and the photoinitiator concentration ([PI]). In cyclohexane solution and at low [PI] (< 5 x 10^-5M), the cyclohexyl radical is practically the only polymerization initiating radical, while at higher [PI] both radicals, cyclohexyl and the aminoalkyl derived from PI, participate in the initiation step, increasing the participation of the later as the [PI] increases. When benzene is used as solvent both phenyl and aminoalkyl radicals participate in the initiation step at any [PI] employed. Efficiencies of the radicals derived from solvent and photoinitiator have been determined.     

High-performance liquid chromatographic method with ultraviolet detection for the determination of dapsone and its hydroxylated metabolite in human plasma

A validated high-performance liquid chromatographic method with ultraviolet detection for the quantitative determination of dapsone (4,4'-diaminodifenyl sulfone, DDS) and a metabolite, hydroxylaminodapsone (4-amino-4-hydroxylaminodiphenyl sulfone, DDS-NOH), in human plasma is described. Human plasma was deproteinized with acetone and the clear supernatant solution after centrifugation was evaporated to dryness under a gentle stream of nitrogen at 70 degrees C. The residue was dissolved in a mixture of HPLC eluent and acetone (18:5 v/v) and an aliquot of this solution (50 microL) was injected onto the HPLC column. Dapsone, hydroxylaminodapsone and diazoxide as internal standard, were separated within 10 min by isocratic elution with water:acetonitrile:glacial acetic acid:triethylamine (80:20:1.0:0.5 by volume) as eluent. Detection was by ultraviolet at the wavelength of 295 nm. The within-day repeatability coefficients of variation were 3-5% for dapsone (0.301-20.0 mg/L, n = 5) and 3-5% for hydroxylaminodapsone (0.0948-6.32 mg/L, n = 5), whereas the between-day repeatability coefficients of variation were 3-8% (0.301-20.0 mg/L, n = 5) for dapsone and 4-10% for hydroxylaminodapsone (0.0948-6.32 mg/L, n = 5). The mean recoveries -were 92-107% (0.301-20.0 mg/L, n = 2), 80-82% (0.0948-6.32 mg/L, n = 2) and 88% (0.0200 mg/mL, n = 5), for dapsone, hydroxylaminodapsone and diazoxide, respectively. The average correlation coefficient of the calibration curve was 0.99988 (n = 5) for dapsone at a concentration range of 0.301-20.0 mg/L, whereas the average correlation coefficient of the hydroxylaminodapsone calibration curve was 0.99981 (n = 5) at a concentration range of 0.0948-6.32 mg/L. The limits of detection were 0.00200 and 0.0470 mg/L for dapsone and hydroxylaminodapsone, respectively. The method is suitable for drug level monitoring and for pharmacokinetic studies.