Effect of intramolecular charge transfer on fluorescence and singlet oxygen production of phthalocyanine analogues

Intramolecular charge transfer (ICT) was studied on a series of magnesium, metal-free and zinc complexes of unsymmetrical tetrapyrazinoporphyrazines and tribenzopyrazinoporphyrazines bearing two dialkylamino substituents (donors) and six alkylsulfanyl or aryloxy substituents (non-donors). The dialkylamino substituents were responsible for ICT that deactivated excited states and led to considerable decrease of fluorescence and singlet oxygen quantum yields. Photophysical and photochemical properties were compared to corresponding macrocycles that do not bear any donor centers. The data showed high feasibility of ICT in the tetrapyrazinoporphyrazine macrocycle and significantly lower efficiency of this deactivation process in the tribenzopyrazinoporphyrazine type molecules. Considerable effect of non-donor peripheral substituents on ICT was also described. The results imply that tetrapyrazinoporphyrazines may be more suitable for development of new molecules investigated in applications based on ICT.     

ChemInform Abstract: Synthesis and Structural Characterization of ACu9Tt4 (A: Ca,Sr, Ba,Eu; Tt: Si,Ge, Sn) — Tetragonally Distorted Ternary Variants of the Cubic NaZn13 Structure Type. Improved Structure Refinement of SrCu2Ge2.

The title compounds are synthesized from the elements using excess Cu and Si, Ge, or Sn as a flux (alumina crucibles, 1100 °C, 2 h).     

In‐situ enrichment of phosphopeptides on MALDI plates modified by ambient ion landing

We report substantial in‐situ enrichment of phosphopeptides in peptide mixtures using titanium and zirconium dioxide‐coated matrix assisted laser desorption‐ionization (MALDI) plates prepared by recently reported ambient ion landing deposition technique. The technique was able to modify four common materials currently used for MALDI targets (stainless steel, aluminum, indium‐tin oxide glass and polymeric anchor chip). The structure of the deposited dioxide was investigated by electron microscopy, and different surfaces were compared and discussed in this study. Two standard proteins were used to test the enrichment capabilities of modified MALDI plates: casein and in‐vitro phosphorylated trehalase. The enrichment of casein tryptic digest resulted in identification of 20 phosphopeptides (including miscleavages). Trehalase was used as a suitable model of larger protein that provided more complex peptide mixture after the trypsin digestion. All four possible phosphorylation sites in trehalase were identified and up to seven phosphopetides were found (including methionine oxidations and miscleavages). Two different mass spectrometers, MALDI‐Fourier transform ion cyclotron resonance (FTICR) and MALDI‐time of flight, were used to detect the phosphopeptides from modified MALDI plates after the enrichment procedure. It was observed that the desorption‐ionization phenomena on the modified surfaces are not critically influenced by the parameters of the different MALDI ion sources (e.g. different pressure, different extraction voltages), and thus the presence of dioxide layer on the standard MALDI plate does not significantly interfere with the main MALDI processes. The detection of phosphopeptides after the enrichment could be done by both instruments. Desorption electrospray ionization coupled to the FTICR was also tested, but, unlike MALDI, it did not provide satisfactory results. Copyright © 2012 John Wiley & Sons, Ltd.     

Primary investigation of the preparation of nanoparticles by precipitation

The absorption, distribution, biotransformation and excretion of a drug involve its transport across cell membranes. This process is essential and influenced by the characteristics of the drug, especially its molecular size and shape, solubility at the site of its absorption, relative lipid solubility, etc. One of the progressive ways for increasing bioavaibility is a nanoparticle preparation technique. Cholesterol, cholestenolone and pregnenolone acetate as model active pharmaceutical ingredients and some of the commonly used excipients as nanoparticle stabilizers were used in the investigated precipitation method that was modified and simplified and can be used as an effective and an affordable technique for the preparation of nanoparticles. All 120 prepared samples were analyzed by means of dynamic light scattering (Nanophox). The range of the particle size of the determined 100 nanoparticle samples was from 1 nm to 773 nm, whereas 82 samples contained nanoparticles of less than 200 nm. Relationships between solvents and used excipients and their amount are discussed.     

Minimum required signal-to-noise ratio for optimal precision in HPLC and CE

In a survey, results of more than 100 assay determinations of various analytes (active pharmaceutical ingredients, methylparabene, chlorthalidone, and proteins) at different concentration levels were collected with signal-to-noise ratio (S/N) levels between 2 and higher than 10?000. It must be concluded that without having a S/N of at least 50, repeatabilities (combination of injection, separation process, and integration) of 2% cannot be achieved, in contrast to the general assumption that a S/N of 10 is sufficient for analytical HPLC. These data now confirm an earlier assumption with a much broader fundamental of measurements. The empirical functions %RSD = 58/(S/N) + 0.30 (for HPLC data) and %RSD = 73/(S/N) + 1.07 (for CE data) could be derived. It was shown that a S/N of greater than 100 is necessary for optimal precision. Before optimizing HPLC or CE methods, for example, for sample pretreatment, S/N > 100 should be the prerequisite, else optimal precision will not be achieved. Only after the detection-related scatter is sufficiently reduced, other sources of variation can be successfully tackled.     

Synthesis and structure of bis- and tris-ferrocene containing N-methylimide foldamers

The synthesis and conformational analysis of dimer Fc–CO–NMe–CO–Fc (5) and trimer Fc–CO–NMe–CO–Fn–CO–NMe–CO–Fc (6) have been described. It has been shown by means of spectroscopic studies, X-ray crystallography, and molecular modeling, that these molecules are dominated by cis–cis conformation. Furthermore, we recognized for the first time, that such type of organometallics possess elements of chiral helicity. Their crystal lattices are characterized by π–π and CH–π intermolecular interactions (5) and by CH?OC intermolecular hydrogen bonds (6). We believe that foldamers 5/6 are stabilized by the special type of aromatic π–π interactions between the closer cyclopentadienyl rings of the juxtaposed ferrocene units.     

Efficient synthesis of N-alkyl-2,7-dihalocarbazoles by simultaneous carbazole ring closure and N-alkylation

The N-alkyl-2,7-dihalocarbazole as the main product was formed by the reaction of 4,4′-dihalo-2-nitrobiphenyl with aromatic nitro compound and trialkyl phosphite. The presence and crucial role of aromatic nitro compound causes simultaneous carbazole ring closure and N-alkylation unlike the Cadogan ring closure where non-alkylated carbazole is formed as a main product. In addition, the mixture of aromatic nitro compound and trialkyl phosphite was found to be a possible N-alkylating agent for heterocycles, such as carbazole or indole.     

New spin probes starting from 4-amino-2,2,6,6-tetramethylpiperidine-1-yloxyl

This Letter describes four new 4-trimethylammonio-2,2,6,6-tetramethylpiperidine-1-yloxyls bearing camphorsulfonate, triflate, tosylate, or lactate as counter ions. These spin probes were made by anion metathesis of 4-trimethylammonio-2,2,6,6-tetramethylpiperidine-1-yloxyl iodide using the corresponding silver salts. The latter is made by the alkylation of 4-amino-2,2,6,6-tetramethylpiperidine-1-yloxyl. Furthermore, the Letter gives an improved synthetic way to 4-sulfonamido-2,2,6,6-tetramethylpiperidine-1-yloxyl using chlorosulfuric acid trimethylsilylester and 4-amino-2,2,6,6-tetramethylpiperidine-1-yloxyl. All the spin probes are highly interesting for the investigation of ionic liquids.     

Molecular imprinting of natural flavonoid antioxidants: application in solid-phase extraction for the sample pretreatment of natural products prior to HPLC analysis

As shown in the past years, SPE based on molecularly imprinted polymers (MIPs) may provide significant enhancement of selectivity in sample preparation and analyte preconcentration. The objective of this work was the fabrication of MIPs for the specific adsorption of rutin and quercetin. The two flavonoids were used as the template molecules for the preparation of MIP phases in a self-assembly (noncovalent) approach. The produced MIPs were validated with regard to the imprinting efficiency as media for LC and SPE. The retention behavior of several flavonoid compounds was studied using as stationary phases imprinted, control nonimprinted polymers, and commercial silica-based materials. MIPs were applied as materials for the selective SPE and preconcentration of the flavonoids from white and red wine, orange juice, and tea. The collected fractions were analyzed by high-pressure LC. MIP-SPE facilitated specific analyte isolation and effective sample clean-up. The results show that molecularly imprinted SPE can be a useful tool for the simple, selective, and cost-effective pretreatment of samples containing natural antioxidants.     

Pre-treatment of HT-29 cells with 5-LOX inhibitor (MK-886) induces changes in cell cycle and increases apoptosis after photodynamic therapy with hypericin

It may be hypothesized that the lipoxygenase (LOX) metabolic pathway plays an important role in photodynamic therapy (PDT) of malignant tumours, and modification of this pathway may result in administration of lower doses of photodynamic active agents accompanied by reduced side effects. In this study, we examine in more detail the cytokinetic parameters of human colon adenocarcinoma HT-29 cells pre-treated for 48 or 24h with LOX inhibitor MK-886, followed by PDT induced by hypericin. Based on MTT assay the concentrations of both agents (MK-886 and hypericin) with relatively slight (non-significant) cytotoxic effects were selected. These concentrations were used for combined treatment, where MTT response, total cell number, floating cells quantification, viability, cell cycle progression and DNA synthesis were detected. Hoechst/PI staining, PARP fragmentation and mitochondrial membrane potential (MMP) were evaluated to determine the extent of apoptosis. While MK-886 alone caused mainly necrosis, 48h pre-treatment of cells with MK-886 followed by PDT with hypericin clearly shifted the type of cell death to apoptosis. PDT with hypericin alone caused apoptosis in 19% of the cell population. Some combined modalities significantly potentiated the apoptotic effect (31% of apoptotic cells; 2.5microM MK-886/0.1microM hypericin), i.e., by 60% more than after single treatment with hypericin. Increased apoptosis was confirmed by PARP (116kDa) cleavage to characteristic 89kDa fragments and changes in MMP. Increasing concentration of MK-886 was accompanied by massive changes in the cell cycle progression. Combined treatment with lower concentrations of MK-886 and hypericin increased accumulation of cells in the S phase, accompanied by inhibition of DNA synthesis. Increasing concentration of MK-886 in this combination caused the opposite effect, manifesting significant accumulation of cells in the G0/G1 phase. More pronounced effects were observed after the 48h pre-treatment schedule. This anti-proliferative effect was confirmed by BrdU incorporation. These results indicate that combined treatment involving PDT and LOX inhibitor MK-886 may improve the therapeutic effectiveness of PDT.