Katarzyna Kostrzewska

New Fluorescence Probes for Biomolecules

Steady state fluorescence measurements have been used for the investigation of interaction between the bovine serum albumin (BSA) and fluorescence probes: 3-hydroxy-2,4-bis[(3-methyl-1,3-benzoxazol-2(3H)-ylidene)methyl]cyclobut-2-en-1-one (SQ6), 3-hydroxy-2,4-bis[(3-methyl-1,3-benzothiazol-2(3H)-ylidene)methyl]cyclobut-2-en-1-one (SQ7) and 3-hydroxy-2,4-bis[(1,3,3-trimethyl-1,3-dihydro-2H-indol-2-ylidene)methyl]cyclobut-2-en-1-one (SQ8). The binding constant between bovine serum albumin and squarine dyes has been determined by using both the Benesi-Hildebrand and Stern-Volmer equations. The negative value of free energy change indicates the existence of a spontaneous complexation process of BSA with squarine dyes.

Hemicyanine dyes derived from 2,3,3-trimethyl-3H-indolium as candidates for non-covalent protein probes.

Non-covalent interaction of hemicyanine dyes, derivatives of 2,3,3-trimethyl-3H-indolium with bovine serum albumin has been studied by spectral method. For this purpose, three hemicyanine dyes containing N-(2-carboxyethyl)-2,3,3-trimethyl-3H-indolium moiety were synthesized and their UV/Vis and fluorescence spectra, aggregation, photostability and association with bovine serum albumin were studied. The hemicyanine dyes with 2-ethylcarboxylic group was found to interact with bovine serum albumin, which is probably due to negative charge on the dye molecule at the expense of the carboxylic group and the ability to form hydrogen bonds with albumin.

Squaric acid derivative effects on the kinetics of photopolymerization of different monomers

Systems composed of 1,3-bis(phenylamino)squaraine (photosensitizer) and conventional free radical sources, such as tetramethylammonium n-butyltriphenylborate, diphenyliodonium chloride and diphenyliodonium hexafluorophosphate were used for initiation of photopolymerization occurring via a radical or cationic mechanism. The photopolymerization of 1,6-hexanediol diacrylate (HDDA), pentaerythritol triacrylate (PETA), 2-ethyl-2-(hydroxymethyl)-1,3-propanediol triacrylate (TMPTA), cyclohexene oxide (CHO) and 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate (EPOX) were carried out at 300 nm < λ < 500 nm irradiation. The polymerization kinetics was measured using a differential scanning calorimeter equipped with a high-pressure mercury lamp. The effect of co-initiator structure and type of monomer on the kinetics of the photopolymerization process is also presented here. It was found that the photoredox pairs, consisting of 1,3-bis(phenylamino)squaraine and tetramethylammonium n-butyltriphenylborate or diphenyliodonium salts, initiate radical and cationic polymerization in the UV-Vis light region. The photoinitiating ability of these new photoinitiating systems acting in the UV-Vis light region for initiation of polymerization of acrylates and epoxides was compared with a few commercially used photoinitiating systems.

New kinetic and mechanistic aspects of photosensitization of iodonium salts in photopolymerization of acrylates

1,3-Bis(p-bromophenylamino)squaraine which functions as an electron-transfer photosensitizer for a wide range of diphenyliodonium salts radical photoinitiators of triacrylate polymerization under UV-blue light irradiation is presented. The functionality of the photosensitizer is determined by the presence of a suitable co-initiator. For this purpose, several different diphenyliodonium salts were used as a source of active species for radical polymerization. The reactivity of the new iodonium salts was studied with ultraviolet-blue light initiated radical polymerization by photo-DSC using squaraine dye as a sensitizer. The iodonium salts functionated as radical initiators bearing different substitution patterns. Electron transfer from the excited state of the sensitizer to the iodonium salt results in initiating radicals. The ability to initiate free radical polymerization of TMPTA by iodonium salts studied is similar. Most of the iodonium salts exhibit no large differences regarding the reactivity in initiation of TMPTA polymerization. However, an introduction of a nitro group in the para position of the phenyl ring of the co-initiator results in a significant increase in the rate of polymerization and degree of monomer conversion. The dye-sensitized photoreaction mechanism of the SQ/I system was also confirmed.

Visible light photoinitiating systems based on squaraine dye: kinetic, mechanistic and laser flash photolysis studies

New two-component photoinitiator systems for radical polymerization of acrylates are presented. The systems discussed comprise a synthetic dye 1,3-bis(p-bromophenylamino)squaraine and borate and onium salts as coinitiator. The effect of the composition of the system on the photopolymerization kinetics was analyzed. To this end, the photophysics and photochemistry of the dye under polymerization conditions were explored by means of stationary and time-resolved spectroscopic methods. The action mechanism of the different photoinitiators systems is discussed.

Squarylium dye and onium salts as highly sensitive photoradical generators for blue light

2-Ethyl-2-(hydroxymethyl)-1,3-propanediol triacrylate was polymerized in the presence of squarylium dye and various onium salts. The onium salts under study are commercially available or may be easily synthesized and are characterized by light absorption properties below 300 nm and generate phenyl radicals upon blue light exposure. Due to these interesting properties the triacrylate polymerization can be efficiently carried out with or without the presence of any additional photoinitiator. The chemical mechanisms are investigated by steady state photolysis and nanosecond laser flash photolysis experiments. The new photoinitiators yielded a higher visible light photoinitiating polymerization effect than the commercial photoinitiator: camphorquinone/ethyl p-(dimethylamino)benzoate and camphorquinone/N-methyldiethanolamine under experimental conditions.