P.A. Jacobs

A comparative study of the photosensitizing characteristics of some cyanine dyes

The present work has been carried out to explore the potential application of cyanines in photodynamic therapy. After photosensitization, the in vitro cytotoxic and antiproliferative activity on HeLa cells of a total of 35 cyanines belonging to several chemical subgroups is explored. Most of these cyanines have never been used before in similar experimental work. From a first set of experiments, it is found that none of the krypto-, oxa- and imidacyanines is photobiologically active on HeLa cells. Conversely, five thiacyanines (Thiacl-5), one rhodacyanine (Rhodac) and four indocyanines (Indoc2, Indoc4, Indoc5, Indoc7) show photodependent cytotoxicity or antiproliferative effects. A more detailed study shows that out of the ten selected compounds, eight cyanines feature significant photodependent cytotoxic and antiproliferative effects. All possess maximum absorption ranges between 545 and 824 nm. In particular, Rhodac, a tetramethinemeromonomethine rhodacyanine dye with an absorption maximum of 655 nm (ethanol) and a molar absorption coefficient epsilon = 108000 shows very promising photo-dependent biological activity. In general, the measured singlet oxygen quantum yield of the selected cyanines is low (< 0.08) and does not correlate with the degree of photosensitization. Furthermore, the present study shows that cyanines with a partition coefficient close to 1.5 accumulate to the highest extent in HeLa cells, while the more hydrophobic compounds (e.g., indocyanines) concentrate less intracellularly.

Physicochemical and catalytic properties of titanium silicalites

Abstract Titanium silicalites with different titanium contents were synthesized according to two hydrothermal procedures. The materials were subjected to physicochemical characterization and tested as catalysts for partial oxygenations by aqueous hydrogen peroxide. The role of isolated titanium, finely divided titanium dioxide and residual acidity in the catalytic behavior of titanium silicalites is discussed and a mechanistic model for the oxidation reactions is proposed.

Hydroxylation of phenol with hydrogen peroxide on EUROTS-1 catalyst

Abstract The catalytic performance of a standard titanium molecular sieve catalyst, EUROTS-1, has been evaluated at four European universities. The hydroxylation of phenol into catechol and hydroquinone with aqueous H 2 O 2 solution was selected as catalytic test reaction. The use of standard EUROTS-1 catalyst permitted to establish a reproducible standard reaction procedure. The calcination conditions of the catalyst, the use of internal standards, and the nature and the amount of the solvent added to the reaction mixture were found to be major factors determining phenol conversion, product selectivity and hydrogen peroxide product yield.

Membrane occluded catalysts: a higher order mimic with improved performance

Abstract A general method to immobilise homogeneous catalysts and to improve the performance of heterogeneous catalysts is discussed. The method consists in embedding the catalysts in hydrophobic PDMS (polydimethylsiloxane)-membranes. Inspired on a complete structural mimic of cytochrome P-450 up to the level of the membrane, this technique gives superior properties to the membrane resident catalyst. The scope and limitations of this method are discussed by two examples of heterogeneous catalysts, i.e., FePc-Y (iron phthalocyanine zeolite Y) and [Mn(bpy) 2 ] 2+ -Y (manganese bis(bipyridyl) zeolite Y), and three examples of homogeneous complexes, i.e., FePc, Ru-binap ([2,2′-bis(diphenylphosphino-1,1′-binaphtyl]chloro( p -cymene)-ruthenium chloride) and the Jacobsen catalyst ( N,N′ -bis(3,5-di- tert -butylsalicylidene)-1,2-cyclohexane-diamine manganese chloride). Due to changed sorption in the zeolites, catalyst activity is enhanced and deactivation is suppressed. Furthermore, the membrane incorporation makes the use of a solvent redundant. For homogenous complexes, this procedure represents a general method for heterogenisation. Moreover, the technique opens new ways in the field of oxidation chemistry, where solvents are necessary to homogenise reagents which usually differ in polarity.

Isomerization and disproportionation of m-xylene over zeolite β

Abstract The isomerization and disproportionation of m-xylene has been performed over zeolite β samples with Si/Al ratios in the range from 11 to 42. The selectivity for isomerization versus disproportionation and the selectivities among the isomerization and disproportionation products are contrasted with the micropore structures proposed for zeolite β. The isomerization and disproportionation activity of zeolite β depend strongly on the aluminium content, decreasing with increasing framework aluminium content. Maximum activity is found for Si/Al ratios between 14 and 15, while the p/o selectivity remains constant.

Chapter 14 Introduction to acid catalysis with zeolites in hydrocarbon reactions

Publisher Summary Catalytic conversion of hydrocarbons over crystalline microporous acidic aluminosilicate catalysts is applied in large petroleum refining processes including catalytic cracking, hydro cracking, isomerization, alkylation, and oligomerization. This chapter provides with a conceptual basis for rationalizing this acid zeolite based catalytic hydrocarbon conversion processes. It is recognized that the zeolite acid strength is more in line with conventional strong acids rather than with superacid. In order to explain the reactivity and the selectivity of the zeolite catalyst, it is insufficient to represent the zeolite catalyst by a proton, by analogy to homogeneous strong BrOnsted acids, without considering the chemical and physical interactions of the hydrocarbon molecules with the zeolite framework. The kinetics of the catalytic conversions are dominated by the strong physical adsorption of the molecules on the catalyst being unique to zeolites.

Novel catalytic membranes for selective reactions

A survey is given of the potentials of a new kind of catalytic membranes consisting of a catalyst that is immobilised in a dense polymer matrix. When homogeneous, catalytically active complexes are occluded, these membranes constitute a new way of heterogenation. In the case of solid state catalysts, these composite membranes can improve the activity of the catalyst by changing sorption or by allowing experimental set-ups in which solvents become redundant.

Singlet oxygen generation using PDMS occluded dyes

Abstract Several dyes that generate singlet molecular oxygen ( 1 O 2 ) were occluded in polydimethylsiloxane (PDMS). For the homogeneous dyes, this occlusion forms an easy way of heterogenization, whereas it improves the performance of dyes that are heterogenized already in molecular sieves. These systems were investigated for the singlet oxygenation of test substrates, such as 2,3-dimethyl-2-butene and 1-methyl-1-cyclohexene. The PDMS elastomer was selected for its transparent, hydrophobic and permeability characteristics. The elastomer is ‘wrapped’ around the sensitizing system and hence shields the dyes from polar components, such as water, and balances the sorption of solvents and reagents. This results in an enhanced oxygenate yield for water sensitive dyes. Finally, a new porphyrin, 5,15-(2,6-dichlorophenyl)-10,20-(4-allyloxyphenyl)porphyrin, was synthesized and chemically anchored to PDMS, resulting in a highly active heterogeneous singlet oxygen generating system.

Factors Affecting the Formation of Extra-Framework Species and Mesopores During Dealumination of Zeolite Y

Summary The dealumination of HY, LiY and NaY zeolites with SiCl 4 is interpreted as a two-step process. The first step is the formation of chloride salt of the charge compensating cations and of SiCl 3 species probably bound to the framework. This reaction takes place at reaction temperatures as low as 423 K. The second step is the Al, Si exchange. Changes in the degree of dealumination between HY, LiY and NaY are tentatively explained on the basis of cation distributions. Cloro-aluminium complexes formed from AlCl 3 and the chloride salt during the second step give rise to 27 Al MASNMR resonances at ca. 100 ppm. The micropore system can be preserved if the alkali-chloro-aluminium complexes are not decomposed before washing. No additional dealumination was observed during washing. The extracted aluminium can only be removed partially from the samples.

Alkane Oxygenations By H2O2 On Titanium Silicalite

Abstract The Titanium-Silicalite-1 (TS-1) catalyzed oxidation of n-hexane by aqueous H 2 O 2 with formation of 2- and 3-hexanols and the corresponding hexanones is carried out in presence or absence of solvents, and in stirred and non stirred reaction systems. The observed conversions and ketone/alcohol ratios are explained by the relative rates of the different reaction steps: liquid to liquid diffusion, liquid to solid diffusion, intraporous diffusion and catalytic oxidation.