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BY 4.0 license Open Access Published by De Gruyter Open Access December 31, 2019

Photophysical and antibacterial activity of light-activated quaternary eosin Y

  • Desislava Staneva , Stanislava Yordanova EMAIL logo , Evgenia Vasileva-Tonkova , Stanimir Stoyanov and Ivo Grabchev
From the journal Open Chemistry

Abstract

The functional characteristics of a new eosin dye with biocidal quaternary ammonium group (E) were studied in aqueous solution and in organic solvents of different polarity. The spectral properties depend on the nature and polarity of the respective solvents. The antimicrobial activity of compound E has been tested in vitro against Gram-negative bacteria (Escherichia coli, Acinetobacter johnsoni and Pseudomonas aeruginosa), Gram-positive bacteria (Sarcina lutea and Bacillus cereus) and the antifungal activity was tested against the yeasts Candida lipolytica in solution and after treated on cotton fabric. Broth dilution test has been used for quantitative evaluation of the antimicrobial activity of compound E against the model strains. The ability of compound E to inhibit the growth of model Gram-negative P. aeruginosa strain was assessed after 16 h of incubation in presence and absence of light. These experiments were conducted in planktonic format in solution and on cotton fabric. The results suggest that the new compound is effective in treating the relevant pathogens with better results being obtained by irradiation with light. In this case the quaternary ammonium group promotes the binding of eosin Y moiety to the bacterial cell wall thus accelerating bacterial photo inactivation.

1 Introduction

Fluorescent compounds are often used in medicine, pharmacy, biology and environmental protection [1,2]. Among the known fluorophore structures used in these fields, the eosin Y and its derivatives are very important. They belong to the group of xanthene fluorescent dyes with a wide range of photophysical and biological applications, due to their low toxicity in vivo, and high water solubility [3]. The utility of eosin derivatives is associated to their good spectral characteristics and the possibility to interact with different type of biomolecules [4, 5, 6, 7, 8]. Photophysical properties of eosin in solution strongly depend on the solvents polarity and possibility of hydrogen bond formations. Depending on pH eosin Y exhibit tautomeric structures with different proteolytic forms, and its colour depends on the respective forms [9,10]. In recent years, eosin Y was also successfully used as photoredox catalyst in organic synthesis [11,12].

A new scientific area of research is the combination of dyeing process with antibacterial properties in one compound [13]. This can be achieved through the introduction of specific groups into the dye chromophore systems to give antibacterial properties without changing their colour characteristics. In this case quaternary ammonium group can be bonded to the fluorophores by incorporating alkyl chain into the chromophore system through covalent bonds. The cationic dyes thus obtained show good colour characteristics and high antibacterial activity in solutions [14, 15, 16, 17, 18]. In the last years in our laboratory, fluorophores with different chemical structure having ammonium quaternary groups have been synthesized and their antibacterial and antifungal activity were investigated in solution or after their incorporation into polylactide matrix, or on the textile fabrics [19, 20, 21]. The relevance of such studies is due to the fact than in the last years the antimicrobial resistance of different pathogens has become a major problem in medicine and clinical practice. This encouraged many research laboratories to start searching for and investigating novel and more active antibacterial drugs [22, 23, 24].

Scheme 1 Chemical structure of quaternary eosin Y (E).
Scheme 1

Chemical structure of quaternary eosin Y (E).

In the last few years, photodynamic therapy has been used against the resistance of pathogens to the medicines administered in practice. In this case, the microbiological activity of the preparations used is due to the generation of reactive oxygen species upon irradiation with visible light, which kill the bacteria by oxidative burst [25]. It has been reported that eosin Y has some antibacterial photoactivity [26].

In this paper we present the results on photophysical characterization of a new ammonium quaternary eosin Y in organic solvents of different polarity and evaluation of its antimicrobial activity against different pathogens. The effect of visible light on the antimicrobial activity of the new eosin Y derivative has also been tested in solution and after its deposition on cotton fabric.

2 Experimental part

2.1 Materials and methods

The synthesis and application of a quaternary ammonium eosin Y (E) as photoinitiator of polymerization of acrylate monomers has been described recently (Scheme 1) [27]. The light source of lamp used for irradiation was with the parameters: HL 8325, 25 w, 1230 Lumen, 6400 K, Horoz. Absorption spectra were performed using “Thermo Spectronic Unicam UV 500” spectrophotometer. The fluorescence spectra were taken on a “Cary Eclipse” spectrophotometer. All spectra were recorded using 1 cm path length synthetic quartz glass cells. Absorption and fluorescence measurements of the eosin compound E were carried out at 10-6 mol.L-1 concentration. Organic solvents: acetonitrile (MeCN), methanol (MeOH), ethanol (EtOH), dimethylsulfoxide (DMSO), N,N-dimethylformamide (DMF), dichloromethane (CH2Cl2), 1,4-dioxane and ethylacetate (EtOAc) used in this study were of spectroscopic grade. Fluorescence quantum yield was determined on the basis of the absorption and fluorescence spectra, using Rhodamine 6G as reference (Φst = 0.94 in ethanol [28]).

2.2 Preliminary antimicrobial screening

The antibacterial activity of the investigated compound E was determined against Gram-positive bacteria (Sarcina lutea and Bacillus cereus), Gram-negative bacteria (Acinetobacter johnsonii, Escherichia coli and Pseudomonas aeruginosa) and the antifungal activity was tested against the yeasts Candida lipolytica. Microbial cultures were maintained at 4°C on Mueller-Hinton agar (MHA) slants and transferred monthly.

2.3 In vitro antimicrobial assay

Broth dilution test was used for quantitative evaluation of the antimicrobial activity of compound E against the model strains. Тhe concentration of compound E dissolved in water was 5 mg/ml (0.623 μM) and was further diluted in each consecutive test tube in sterile meat-peptone broth (MPB, pH 7.0) to final concentrations of 0.018, 0.038, 0.077, 0.156, 0.249 and 0.312 and 0.623 mM. After inoculation with 2% (v/v) of each standardized cell suspension, the tubes were incubated at appropriate temperature for 24 h under shaking (at 240 rpm). The microbial growth was assessed by measuring the optical density of the medium at 600 nm (OD600). The growth control, sterility control and control of the compound E were used. The % survival of the test cultures was determined on the basis of the positive control which was considered as 100%. The experiments were conducted in triplicate. The light source used for irradiation was with the parameters: HL 8325, 25 w, 1230 Lumen, 6400 K, Horoz [27].

2.4 Antimicrobial activity of cotton fabrics

The antimicrobial effectiveness of cotton fabrics treated with 0.5% solution of the compound E was investigated by the shaking flask method. C. lipolytica, B. cereus and A. johnsonii were used as model strains. Test tubes containing sterile MPB (1.0 ml) and square specimens (10 mm x 10 mm) were inoculated with each overnight grown microbial culture. Tubes with untreated cotton and without specimens were also prepared as controls. After 24 h incubation at appropriate temperature under shaking, microbial growth was determined by measuring OD600. To evaluate the antimicrobial activities of the samples, the reduction in cell density between the untreated and treated samples after incubation was compared. All antimicrobial activity tests were done in triplicate.

2.5 Treatment of cotton fabrics with E

In 5 ml of water the compound E (5 mg) was dissolved and 1g of cotton fabric (weight 140 g/m2) was added in the solution for 30 min at 25°C. Then cotton sample was dried at ambient temperature.

Ethical approval: The conducted research is not related to either human or animal use.

3 Results and Discussion

3.1 Photophysical characteristics of ammonium quaternary eosin Y (E)

Photophysical properties of the eosin Y derivatives as a part of xanthene dyes are characterized by heterocyclic system containing a dibenzo-1,4-pyran ring. Its basic spectral characteristics depend from the solvent polarity and for formation of hydrogen bonds with solvents.

All spectral measurements of the compound E were investigated at a concentration of c = 1 x 10-6 mol.L-1 and in this concentration the solution is highly coloured in red-pink colour. Table 1 presents its spectral characteristics in different organic solvents: the fluorescence (lF) and absorption (lA) maxima, Stokes shift (nA -n F), quantum yield of fluorescence (FF) and the molar absorptivity (e).

Table 1

Photophysical characteristics of compound E in solvents with different polarity.

SolventlA nmlF nmnA - nF cm-1ε l mol-1 cm-1FF
Water5155357261100000.22
MeOH5225406391100000.59
EtOH5295465891200000.54
DMF5385524711100000.36
MeCN538556602980000.71
DMSO545562555951000.68
CH2Cl2543561590951000.22
EtOAc540556533942000.40
Dioxane540555501921000.20

From the data in Table 1 it is seen than the ammonium quaternary eosin E has absorption maxima at 515-540 nm and the respective fluorescence maxima are at 540-562 nm. All absorption spectra exhibit bands with a well pronounced maximum and short-wavelength shoulder as it can be seen from Figure 1 as an example. Also Figure 1 shows that the fluorescence curve is approximately mirror images of the absorption curves which is typical for such structures with allowed transitions and similar geometries in excited and ground state.

Figure 1 Normalized absorption (black) and fluorescence (red) spectra of the compound E in N,N-dimethylformamide solution.
Figure 1

Normalized absorption (black) and fluorescence (red) spectra of the compound E in N,N-dimethylformamide solution.

The position of the absorption and fluorescence maxima depend from the polarity of solvents (Figures 2 and 3). In the case of solvents containing hydroxyl group such as alcohols and water both absorption and emission maxima are hypsochromically shifted compared to the other solvents. The difference is due to the enhancing the dipole moment of the molecule upon excitation due to the electron density distribution and from other hand the possibility for formation of hydrogen bonds.

Figure 2 Absorption (A) and fluorescence (B) spectra of compound E in solvents with different polarity.
Figure 2

Absorption (A) and fluorescence (B) spectra of compound E in solvents with different polarity.

Figure 3 Normalized excitation (black) and fluorescence (red) spectra of compound E loaded on the cotton fabric.
Figure 3

Normalized excitation (black) and fluorescence (red) spectra of compound E loaded on the cotton fabric.

Stokes shift (nA - nF) is important parameters of the fluorescent compounds which indicate the difference in properties and structure between the ground S0 and the first excited state S1 and it has been estimated according to Equation (1):

(1)(vAvF)=(1/λA1/λF)×107

From Table 1 it is seen that the Stokes shift is in a narrow range (between 501 and 726 cm-1) and it depends on the solvents. Larger values were obtained at nonpolar solvents and the results are very typical to this class of compounds [29, 30, 31, 32].

The ability of the photoactive molecules to emit the absorbed light energy is characterized quantitatively by the fluorescence quantum yield FF.. It has been calculated on the basis of the absorption and fluorescence spectra using Rhodamine 6G as a standard according to Equation (2).

(2)ΦF=ΦstSuSstAstAunDu2nDst2

The calculated FF were in the region 0.20-0.68 and its values depend on the polarity and chemical nature of the solvents. In polar solvents the obtained yields are more than three times higher compared to these in non-polar solvents.

3.2 Absorption and fluorescence investigations of coloured cotton fabric

To investigate the antimicrobial activity of compound E, it has been superficially deposited on a cotton fabric, giving it intense red colour and fluorescence. Figure 3 plots the normalized excitation spectrum and fluorescence spectrum having maxima at (l = 526 nm) and (l = 562 nm) respectively. These results show that in solid state compound E has similar absorption wavelength value to these in alcohol solution, probably due to the fact that cotton cellulose molecules are enriched with hydroxyl groups that have a similar behaviour as the alcoholic hydroxyl groups at formation of intermolecular bonds. The fluorescence maximum is bathochromically shifted compared to that in alcohol, which can be explained by the strong fixation of the fluorophore molecule to the textile matrix and hence for the lack of conformational changes in the transition from excited S1 to the ground state S0.

The release of compound E from the surface of cotton fabric has been measured in aqueous solution at pH = 7.2 by absorption and fluorescence spectroscopy in the condition of dropping method for 60 minutes.

Through the contact of coloured cotton fabric with water solvent the hydrophilic dye E is released from the surface cotton matrix to the aqueous solution, which becomes colourful. Figure 4 shows that the absorption and respective fluorescence intensity of compound E increase with time then it reaches a plateau. It is seen that in the beginning the cotton fabric releases a large amounts of E, and accordingly the absorption and fluorescence intensity increase drastically, and with time this effect disappear. This indicates that compound Е leaves the cotton fabric and passes into the aqueous solution. The respective maxima of Е in this solution are lA = 515 nm and lF = 535 nm, matching these in freshly prepared water solution. The observation that there is no change of the absorption and fluorescence maxima positions during the extraction, but only the intensity is increased, give evidence that the dye didn’t undergo any chemical change during the deposition and the release. This is a new important characteristic of coloured cotton fabric, which indicate that E release into the water solution exhibiting a prolonged antimicrobial activity.

Figure 4 Absorption (A) and fluorescence (B) release profile of E from cotton matrix in aqueous solution at pH = 7.2 at 25oC for 60 min.
Figure 4

Absorption (A) and fluorescence (B) release profile of E from cotton matrix in aqueous solution at pH = 7.2 at 25oC for 60 min.

4 Antimicrobial activity

4.1 Growth inhibitory activity in aqueous solution

A quantitative evaluation of the antimicrobial activity of the synthesized compound was carried out by the shaking flask test against two Gram-positive bacteria (B. cereus, S. lutea), three Gram-negative bacteria P. aeruginosa, A. johnsonii, E. coli) and the yeasts C. lipolytica. Figure 5 shows changes in the growth of the strains in presence of different concentrations of E ranging from 0.018 μM to 0.623 μM. As can be seen, the compound E redused the growth of all test cultures with increasingof its concentrations as compared to the negative control.. The relative order of sensitivity to the compound was found to be a function of the strain. The compound exhibited highest antimicrobial efficiency against the test Gram-positive bacterium S. lutea and the yeasts C. lipolytica (MICs at 0.156 μM) followed by Gram-negative bacterium A. johnsonii (MIC at 0.249 μM) and Gram-positive B. cereus (MIC at 0.312 μM). P. aeruginosa and E. coli exhibited highest resistance to the compound E than the other cultures and MICs were not reached up to 0.623 μM.

Figure 5 Growth of the tested model microbial strains in presence of different concentrations of compound E.
Figure 5

Growth of the tested model microbial strains in presence of different concentrations of compound E.

4.2 Antimicrobial activity of modified cotton fabric

The antimicrobial activity of cotton fabric treated with E has been evaluated by the reduction in bacterial growth. Gram-positive B. cereus, Gram-negative A. johnsonii, and the yeasts C. lipolytica were used as model strains. It was found that the treated cotton textile leads to slight reduction of the growth of B. cereus and C. lipolytica by about 14% and 22%, respectively, and no growth reduction of A. johnsonii was observed (Figure 6) In thsi case the slow release of compound E from the cotton matrix into the aqueous medium, and direct contact with matogenic cells contributed to the antimicrobial effect of the modifed cotton fabric.

Figure 6 Effect of cotton fabric treated with compound E on growth development (quantified by OD at 600 nm) of the indicated model microbial strains.
Figure 6

Effect of cotton fabric treated with compound E on growth development (quantified by OD at 600 nm) of the indicated model microbial strains.

5 Effect of light irradiation on bacterial growth

The ability of E to inhibit the growth of model Gram-negative P. aeruginosa strain was assessed after 16 h of incubation in presence and absence of light. The experiments were conducted in planktonic format in solution and applied on cotton fabric. In solution, without illumination, we observed higher density of P. aeruginosa cells compared to the illuminated sample (Figure 7). With light irradiation, the antibacterial effect was significantly higher at concentration of eosin Y 0.25 μM than observed for the 0.125 μM concentration. In the experiments with eosin-treated and non-treated cotton fabrics, about 41% reduction of cell density of P. aeruginosa was established in the absence of illumination, while almost complete growth inhibition was observed in the illuminated sample (Figure 8). Similarly to some findings reported previously [33, 34], it can be assumed that eosin Y produce large amount of singlet oxygen near the outer membrane of bacteria leading to membrane damage. Quaternary ammonium group promotes the binding of eosin Y moiety to the bacterial cell wall thus accelerating bacterial photo-inactivation.

Figure 7 Effect of visible light on planktonic cultures of P. aeruginosa in presence of compound E.
Figure 7

Effect of visible light on planktonic cultures of P. aeruginosa in presence of compound E.

Figure 8 Effect of light irradiation on the antibacterial effect of cotton fabric treated with compound E.
Figure 8

Effect of light irradiation on the antibacterial effect of cotton fabric treated with compound E.

6 Conclusions

The photophysical characteristics of a new eosin Y functionalised with quaternary ammonium biocidal group have been investigated in different media. The results demonstrated than the modified eosin Y exhibits intense fluorescence in solutions which was retained after its deposition on the surface of cotton fabric. The results showed good inhibitory activity of the novel eosin compound E towards the tested microbial cultures. Antimicrobial activity of cotton fabric treated with the new eosin derivative E was investigated against the strains A. johnsonii, B. cereus and C. lipolytica. The results showed that the compound E has released slowly into the aqueous solution and exhibits a prolonged antimicrobial activity. The modified cotton fabric exhibited higher bioactivity against B. cereus and C. lipolytica, suggesting its suitability for application as a new additive in preparation of antibacterial textile fabric. The new compound E can be use for the photodynamic bacterial inactivation.

Acknowledgements

The authors acknowledge Grant № KOST 1/3-2017, Scientific Research Fund, Ministry of Education and Science of Bulgaria

The authors are grateful to Operational programme “Science and Education for Smart Growth”, project BG05M2OP001-2.009-0028.

  1. Conflict of interest: Authors declare no conflict of interest.

References

[1] Zheng Q., Lavis L., Development of photostable fluorophores for molecular imaging, Curr. Opin. Chem. Biol., 2017, 39, 32-38.10.1016/j.cbpa.2017.04.017Search in Google Scholar PubMed

[2] Mizukami S., Targetable fluorescent sensors for advanced cell function analysis, J. Photochem. Photobiol. C: Photochem. Rev., 2017, 30, 24-35.10.1016/j.jphotochemrev.2017.01.003Search in Google Scholar

[3] Derayea S., Nagy D., Application of a xanthene dye, eosin Y, as spectroscopic probe in chemical and pharmaceutical analysis; a review, Rev. Analyt. Chem., 2018, 20170020.10.1515/revac-2017-0020Search in Google Scholar

[4] Seema A., Babulal R., Fluorescence spectrometric study of eosin yellow dye–surfactant interactions, Arab. J. Chem., 2009, 2, 7-12.10.1016/j.arabjc.2009.07.010Search in Google Scholar

[5] Waheed A., Rao K., Gupta P., Mechanism of dye binding in the protein assay using eosin dyes, Anal. Biochem., 2000, 287, 73-79.10.1006/abio.2000.4793Search in Google Scholar PubMed

[6] Waheed A., Gupta P., Estimation of protein using eosin B dye, Anal. Biochem., 1996, 233, 249-252.10.1006/abio.1996.0037Search in Google Scholar PubMed

[7] Kristen M., Michael T., Lanxuan T., Chloe E., Stephan G., Worachart S., Eosin B as a novel antimalarial agent for drug-resistant Plasmodium falciparum Antimicrob. Agents Chemother., 2006, 50, 3132-3141.10.1128/AAC.00621-06Search in Google Scholar PubMed PubMed Central

[8] Rahman H., Utilization of eosin dye as an ion pairing agent for determination of pharmaceuticals: a brief review, Int. J. Pharm. Pharm. Sci., 2017, 9, 1-9.10.22159/ijpps.2017v9i12.21220Search in Google Scholar

[9] Vanzin D., Freitas C., Pellosi D., Batistela A., Machado A., Pontes R., Experimental and computational studies of protolytic and tautomeric equilibria of erythrosin B and eosin Y in water/DMSO, RSC Adv., 2016, 6, 110312-110328.10.1039/C6RA12198ESearch in Google Scholar

[10] Nikitina N., Reshetnyak E., Svetlova N., Petrossyan N., Protolytic properties of dyes embedded in gelatin films, J. Braz. Chem. Soc., 2011, 22, 857-866.10.1590/S0103-50532011000500007Search in Google Scholar

[11] Srivastava V., Singh P., Eosin Y catalyzed photoredox synthesis: a review, RSC Adv., 2017, 7, 31377-31392.10.1039/C7RA05444KSearch in Google Scholar

[12] Hari D., Koning B., Synthetic applications of eosin Y in photoredox catalysis, Chem. Commun., 2014, 50, 6688-6699.10.1039/C4CC00751DSearch in Google Scholar

[13] Gutarowska B., Machnowski W., Kowzowicz Ł., Antimicrobial activity of textiles with selected dyes and finishing agents used in the textile industry, Fibers Polym., 2013, 14, 415-422.10.1007/s12221-013-0415-xSearch in Google Scholar

[14] Simoncic B., Tomsic B., Structure of novel antimicrobial agents for textiles-A review, Text. Res. J., 2010, 80, 1721-1737.10.1177/0040517510363193Search in Google Scholar

[15] Ma M., Sun Y., Sun G., Antimicrobial cationic dyes: part 1: synthesis and characterization, Dyes Pigments, 2003, 58, 27-35.10.1016/S0143-7208(03)00025-1Search in Google Scholar

[16] Liu S., Ma J., Zhao D., Synthesis and characterization of cationic monoazo dyes incorporating quaternary ammonium salts, Dyes Pigments, 2007, 75, 255-262.10.1016/j.dyepig.2006.05.004Search in Google Scholar

[17] Caruso E., Banfi S., Barbieri P., Leva B., Orlandi V., Synthesis and antibacterial activity of novel cationic BODIPY photosensitizers, J. Photochem. Photobiol. B: Biology, 2012, 114, 44-51.10.1016/j.jphotobiol.2012.05.007Search in Google Scholar PubMed

[18] Chan K., Zhang J., Chang C., Mode of action investigation for the antibacterial cationic anthraquinone analogs, Bioorg. Med. Chem. Lett., 2011, 21, 6353-6356.10.1016/j.bmcl.2011.08.107Search in Google Scholar PubMed

[19] Staneva D., Betcheva R., Chovelon J.-M., Fluorescent benzo[de]anthracen-7-one pH-sensor in aqueous solution and immobilized on viscose fabrics, J. Photochem. Photobiol. A, 2006, 183, 159-164.10.1016/j.jphotochem.2006.03.011Search in Google Scholar

[20] Makki T., Staneva D., Vasileva-Tonkova E., Sobahi T., Abdеl-Rahman R., Asiri A.M, Grabchev I., Antimicrobial activity of fluorescent benzanthrone in aqueous solution and in polylactic acid film, Int. J. Pharm., Biol. Chem. Sci., 2014, 3, 66-74.Search in Google Scholar

[21] Staneva D., Vasileva-Tonkova E., Makki M., Sobahi T., Abdulrahman R.M., Asiri A.M., Grabchev I., Synthesis, photophysical and antimicrobial activity of new water soluble ammonium quaternary benzanthrone in solution and in polylactide film, J. Photochem. Photobiol. B, 2015, 143, 44-51.10.1016/j.jphotobiol.2014.12.024Search in Google Scholar PubMed

[22] Silver L.L., Challenges of Antibacterial Discovery, Clinical Microbiology Review, 2011, 71-109.10.1128/CMR.00030-10Search in Google Scholar

[23] Lv J.S., Peng X.-M., Kishore B., Zhou C.-H, 1,2,3-Triazole-derived naphthalimides as a novel type of potential antimicrobial agents: Synthesis, antimicrobial activity, interaction with calf thymus DNA and human serum albumin, Bioorg. Med. Chem. Lett., 2014, 24, 308-313.10.1016/j.bmcl.2013.11.013Search in Google Scholar

[24] Zhang Y.-Y., Zhou C.-H., Synthesis and activities of naphthalimide azoles as a new type of antibacterial and antifungal agents, Bioorg. Med. Chem. Lett., 2011, 21, 4349-4352.10.1016/j.bmcl.2011.05.042Search in Google Scholar

[25] Cieplik F., Deng D., Crielaard W., Buchalla W., Hellwig E, Al-Ahmad A., Maisch T. Antimicrobial photodynamic therapy - what we know and what we don’t. Crit Rev Microbiol., 2018, 44, 571-589.10.1080/1040841X.2018.1467876Search in Google Scholar

[26] Pileggi G., Wataha J.C., Girard M., Grad I., Schrenzel J., Lange N., Bouillaguet S., Blue light-mediated inactivation of Enterococcus faecalis in vitro, Photodiagnosis and Photodynamic Therapy, 2013, 10, 134-140.10.1016/j.pdpdt.2012.11.002Search in Google Scholar

[27] Staneva D., Grabchev I., Bosch P., Fluorescent hydrogel–textile composite material synthesized by photopolymerization, Int. J. Polym. Mater. Biomat., 2015, 64, 838-847.10.1080/00914037.2015.1030654Search in Google Scholar

[28] Fischer M., George J., Fluorescence quantum yield of rhodamine 6G in ethanol as a function of concentration using thermal lens spectroscopy, Chem. Phys. Lett., 1996, 260, 115-118.10.1016/0009-2614(96)00838-XSearch in Google Scholar

[29] Georgiev N., Dimitrova M., Asiri A., Alamry K., Bojinov V., Synthesis, sensor activity and logic behaviour of a novel bichromophoric system based on rhodamine 6G and 1,8-naphthalimide, Dyes Pigments, 2015, 115, 172-180.10.1016/j.dyepig.2015.01.001Search in Google Scholar

[30] Soh J., Swamy K., Kim S., Lee S., Yoon J., Rhodamine urea derivatives as fluorescent chemosensors for Hg2þ, Tetrahedron Lett., 2007, 48, 5966-5969.10.1016/j.tetlet.2007.06.114Search in Google Scholar

[31] Georgiev N., Asiri A., Qusti A., Alamry K., Bojinov V., A pH sensitive and selective ratiometric PAMAM wavelength-shifting bichromophoric system based on PET, FRET and ICT, Dyes Pigments, 2014, 102, 35-45.10.1016/j.dyepig.2013.10.007Search in Google Scholar

[32] Khalid A., Alamry A., Georgiev N., El-Daly S., Taib L., Bojinov V., A ratiometric rhodamine–naphthalimide pH selective probe built on the basis of a PAMAM light-harvesting architecture, J. Lumin., 2015, 158, 50-59.10.1016/j.jlumin.2014.09.014Search in Google Scholar

[33] Marinic K., Daniel Manoil D., Filieri A., John C. Wataha J.C., Schrenzel J., Lange N., Bouillaguet S. Repeated exposures to blue light-activated eosin Y enhance inactivation of E. faecalis biofilms, in vitro Photodiagnosis and Photodynamic Therapy, 2015, 12, 393-400.10.1016/j.pdpdt.2015.06.004Search in Google Scholar PubMed

[34] Johnson G.A., Ellis E.A, Kim H, Muthukrishnan N, Snavely T, Pellois JP. Photoinduced membrane damage of E. coli and S. aureus by the photosensitizer-antimicrobial peptide conjugate eosin-(KLAKLAK)2. PLoS One, 2014, 9, e91220.10.1371/journal.pone.0091220Search in Google Scholar PubMed PubMed Central

Received: 2018-12-03
Accepted: 2019-05-09
Published Online: 2019-12-31

© 2019 Desislava Staneva et al., published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 Public License.

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