Antibacterial Photodynamic Therapy of the Metallosurfactant-Fluorescein Conjugate under Visible Light Illumination

Antibacterial photodynamic therapy (APDT) has received increased attention as a treatment for multidrug-resistant bacterial infections caused by antibiotic abuse. However, photosensitizers used in APDT have disadvantages such as water insolubility, self-aggregation, and photobleaching. To address these limitations, metal complexes have been explored. However, the use of such complexes tends to confine their antibacterial effectiveness specific bacterial strains. In this study, we report iron (Fe)- and copper (Cu)-based metallosurfactants as unique moieties for antibacterial photodynamic therapy (PDT) under the illumination of visible light. Briefly, our formulated Fe and Cu metallosurfactants, when combined with a fluorescein photosensitizer, exhibit nearly 100% antibacterial efficacy. This high efficiency is primarily attributed to the enhanced generation of singlet oxygen using FL in the presence of metallosurfactants when targeting bacteria such as Escherichia coli and Staphylococcus aureus under laser light. In vitro experiments further confirmed the superior antimicrobial activity of these metallosurfactants against a diverse range of microbial cultures, encompassing Gram-negative and Gram-positive bacteria as well as fungi. This performance outpaces conventional surfactants like cetyltrimethylammonium chloride and cetylpyridinium chloride. The compelling results from MTT assays and flow cytometry endorsed the substantial enhancement in antimicrobial properties achieved through Fe and Cu doping, all without the need for additional secondary agents. Notably, this synergistic antibacterial approach using metallosurfactants in PDT holds significant promise for the elimination of various bacteria in vivo, with the added advantage of mitigating the emergence of multidrug resistance.

Transition Metal-Based Dimeric Metallosurfactants: From Organic-Inorganic Hybrid Structures and Low-Dimensional Magnets to Metallomicelles

The dimeric (gemini) as well as metallosurfactants exhibit enhanced physicochemical properties compared with conventional surfactants. By uniting the benefits of both, a series of novel dimeric metallosurfactants of the type (12-2-12)[MBr4] (M = Co, Ni, Cu and Zn) was successfully prepared by the reaction of the dimeric surfactant bis(N,N-dimethyl-N-dodecyl)ethylene-1,2-diammonium dibromide, 12-2-12, and the MBr2 salt. Structures and magnetic properties of the materials were studied comprehensively in the solid state, while their micellization was explored in solution. The obtained results unveil that the incorporation and the choice of transition metal more significantly influence surfactants' structures ((12-2-12)2+ cations adopt V-, U-, or trans-conformations) and the magnetic features (metal ions form 1D or 2D magnetic lattice) than their solution properties. However, all synthesized metallosurfactants display improved self-assembly properties compared with the metal-free precursor. The investigated systems represent a fruitful platform for the development of multifunctional materials as they are simple to produce, can be obtained in high yields, and show advanced properties both in solution and in the solid state. Notably, this work unveils a simple approach to the design and synthesis of novel low-dimensional magnetic systems of great potential for future spintronic and optoelectronic devices.

Biocompatible metallosurfactant-based nanocolloid-loaded Rose Bengal with excellent singlet oxygen-induced phototoxicity efficiency against cancer cells

Photodynamic therapy (PDT) is facing challenges such as poor solubility, precise delivery, self-aggregation, and photobleaching of photosensitizers with cancer cells due to their less tendency to accumulate in tumor tissues. To address these challenges, we have explored a Rose Bengal (RB)-loaded metallocatanionic vesicles (MCVs) nanosystem for the phototoxicity of cancer cells. Different sets of MCVs were prepared by two different cationic single-chain metallosurfactants, i.e., hexadecylpyridinium trichlorocuprate (CuCPC I) and hexadecylpyridinium trichloroferrate (FeCPC I) in combination with anionic double-chain sodium bis(2-ethylhexyl)sulfosuccinate (AOT) surfactant in phosphate buffer saline of pH 7.4. The RB-loaded CuCPC I:AOT and FeCPC I:AOT vesicles enhanced the maximum singlet oxygen (¹O₂) generation by 1-fold and 3-fold, respectively, compared to pure RB. Upon irradiation with a 532 nm laser for 10 min, these RB-loaded CuCPC I:AOT and FeCPC I:AOT MCVs significantly decreased the metabolic activity of U-251 cells by 70% and 85% at MCVs concentration of 0.75 μM, respectively. Furthermore, RB-loaded MCVs showed the highest intracellular ¹O₂-mediated membrane damage and cell-killing effect as confirmed by singlet oxygen sensor green and differential nuclear staining assay, which is attributed to the cellular uptake profile of different RB-loaded MCVs fractions. Caspase 3/7 assay confirmed the apoptotic pathway of cell death by activating caspase. Therefore, the photoactivation of RB-loaded MCVs led to a significant reduction in the viability of U-251 cells (maximum 85%), which resulted in cell death. Our study demonstrated the advantage of using these dual-charge and biocompatible metallocatanionic vesicles as a promising delivery system of photodynamic therapy that can enhance ¹O₂ generation from PS and can be further utilized in photomedicine.

Self-Assembling Metallocomplexes of the Amphiphilic 1,4-Diazabicyclo[2.2.2]octane Derivative as a Platform for the Development of Nonplatinum Anticancer Drugs

New 1-cetyl-4-aza-1-azoniabicyclo[2.2.2]octane bromide complexes with copper(II) bromide and lanthanum(III) nitrate were characterized using dynamic light scattering and transmission electron microscopy, with self-assembly and the morphological behavior elucidated. For the lanthanum(III) nitrate complex, the 3D crystal structure was characterized using X-ray diffractometry. These metallosurfactants were tested as antitumor agents, and a high cytotoxic effect comparable with doxorubicin was revealed against the M-HeLa and A-549 cell lines. Both complexes were 2 times more active toward the MCF-7 cell line than the breast cancer drug tamoxifen. The cytotoxic mechanism of complexes is assumed to be related to the induction of apoptosis through the mitochondrial pathway.

Cetylpyridinium Trichlorostannate: Synthesis, Antimicrobial Properties, and Controlled-Release Properties via Electrical Resistance Tomography

Cetylpyridinium trichlorostannate (CPC-Sn), comprising cetylpyridinium chloride (CPC) and stannous chloride, was synthesized and characterized via single-crystal X-ray diffraction measurements indicating stoichiometry of C₂₁H₃₈NSnCl₃ where the molecules are arranged in a 1:1 ratio with a cetylpyridinium cation and a [SnCl₃]^- anion. CPC-Sn has shown potential for application as a broad-spectrum antimicrobial agent, to reduce bacteria-generated volatile sulfur compounds and to produce advanced functional materials. In order to investigate its controlled-release properties, electrical resistance tomography was implemented. The results demonstrate that CPC-Sn exhibits extended-release properties in an aqueous environment as opposed to the CPC counterpart.

Tuning the surface using palladium based metallosurfactant for hydrogen evolution reaction

Synthesis of a novel electrocatalyst for hydrogen evolution reaction (HER) is highly demanding for renewable energy production. This research reports the design and development of novel palladium based metallosurfactant (PdCPC(I)) that belongs to the unique class of inorganic-organic hybrid with striking structural features that are explored for the first time in the HER. The formation of the micelle, molecular orientation and surface characteristics of the metallosurfactant are calculated by conductivity and contact angle measurements. The reduction of palladium in metallomicelles during electrolysis accelerates the HER. Metallosurfactant makes the substrate hydrophilic, which in turn enhances the activity of the modified substrate. The 269 mV and 400 mV (vs RHE) overpotential is required to achieve the 10 mA cm^-2 of current density for PdCPC(I) and CPC, respectively. Tafel slope of PdCPC(I) is 57 mV dec^-1, which signifies that the reaction follows the Volmer- Heyrovsky mechanism in the presence of catalyst. The presence of the palladium in the core of the micelle is certified by ICPMS study. The present electrocatalyst also demonstrates 40 h of electrochemical durability. This work opens the doors toward the enhancement of HER, which fulfills the dreams for future energy resources.

Optimization and utilization of single chain metallocatanionic vesicles for antibacterial photodynamic therapy (aPDT) against E. coli

Currently, bacterial infection due to multi-drug-resistant bacteria is one of the foremost problems in public health. Photodynamic therapy plays a significant role against bacterial infection, without causing any side effects. But the photosensitizers are associated with many drawbacks, which lessen their photodynamic efficiency. In this context, the current study describes the synthesis of new metallocatanionic vesicles and employs them in photodynamic therapy. These vesicles were synthesized by using a single-chain cationic metallosurfactant (CuCPC I) and sodium oleate (NaOl) as an anionic component. These vesicles were characterized from conductivity, dynamic light scattering, zeta potential, field emission scanning electron microscopy, and confocal microscopy measurements. Methylene blue (MB) was used as a photosensitizer and its singlet oxygen quantum yield in the presence of these vesicles was determined by irradiating with 650 nm wavelength laser light. These vesicles play a dual-functional role, one helping in delivering the photosensitizer and the second doubling their singlet oxygen production capability due to the presence of metal ions. Antibacterial photodynamic therapy (aPDT) was studied against E. coli bacteria (Gram-negative bacteria). These vesicles also inherit their antibacterial activity and MB-encapsulated metallocatanionic vesicles on irradiation have shown 100% killing efficiency. In summary, we offer metallocatanionic vesicles prepared via a facile approach, which encapsulate a photosensitizer and can be used to combat E. coli infection through photodynamic therapy. We envisage that these synthesized metallocatanionic vesicles will provide a new modification to the catanionic mixture family and could be used for various applications in the future.

Fluorescein-Metal Hybrid Surfactant Conjugates as a Smart Material for Antimicrobial Photodynamic Therapy against Staphylococcus aureus

Photodynamic therapy (PDT) has been extensively used as an effective alternative for the treatment of bacterial infection using photosensitizers (PSs) in the presence of appropriate light. However, the limitation in the effectiveness of PDT is because of the low yield of singlet oxygen from existing PSs because of their low solubility. Thus, we have developed a platform to enhance the solubility and the photodynamic activity of PSs against bacterial cells using metallosurfactants. Herein, we have used manganese metal-containing single- (MnC I) and double-chain metallosurfactants (MnC II) which show an interplay of electrostatic/hydrophobic interactions with fluorescein (FL) dye (as a PS) and when used in the presence of light enhances the PDT. These interactions play a significant role in enhancing the singlet oxygen generation efficiency of FL. MnC I and MnC II have shown good antimicrobial activity against Gram-positive Staphylococcus aureus (S. aureus) bacteria. More interestingly, these metallosurfactants when combined with FL significantly enhanced the affectivity against S. aureus, wherein 100% killing was achieved. As compared to experiments performed in the dark, the metallosurfactant, by enhancing the solubility of FL, increases the formation of singlet oxygen upon light irradiation and thus increases cell death. Therefore, the synergistic effect of FL (light toxicity) and metallosurfactants (dark toxicity) defined excellent reduction in the colony formation of bacteria. These results were corroborated through field-emission scanning electron microscopy and optical microscopy, where the rupturing of the cell wall of bacterial cells was observed during this therapy. Moreover, the binding of metallosurfactants to the genomic DNA of S. aureus was also evaluated by gel retardation analysis and UV-visible spectroscopy. The outcomes from this study will deliver formulations for PDT which can be used in clinical medical applications and cancer therapy in the future.

Synthesis, Characterization, and Investigation of the Antimicrobial Activity of Cetylpyridinium Tetrachlorozincate

Cetylpyridinium tetrachlorozincate (referred to herein as (CP)₂ZnCl₄) was synthesized and its solid-state structure was elucidated via single-crystal X-ray diffraction (SC-XRD), revealing a stoichiometry of C₄₂H₇₆Cl₄N₂Zn with two cetylpyridinium (CP) cations per [ZnCl₄]^2- tetrahedra. Crystal structures at 100 and 298 K exhibited a zig-zag pattern with alternating alkyl chains and zinc units. The material showed potential for application as a broad-spectrum antimicrobial agent, to reduce volatile sulfur compounds (VSCs) generated by bacteria, and in the fabrication of advanced functional materials. Minimum inhibitory concentration (MIC) of (CP)₂ZnCl₄ was 60, 6, and 6 μg mL^-1 for Salmonella enterica, Staphylococcus aureus, and Streptococcus mutans, respectively. The MIC values of (CP)₂ZnCl₄ were comparable to that of pure cetylpyridinium chloride (CPC), despite the fact that approximately 16% of the bactericidal CPC is replaced with bacteriostatic ZnCl₂ in the structure. A modified layer-by-layer deposition technique was implemented to synthesize mesoporous silica (i.e., SBA-15) loaded with approximately 9.0 wt % CPC and 8.9 wt % Zn.

High antimicrobial photodynamic activity of photosensitizer encapsulated dual-functional metallocatanionic vesicles against drug-resistant bacteria S. aureus

Developments in the field of photodynamic therapy (PDT) are being made by investigating appropriate photosensitizers (PSs) and enhancing the penetration effect of light by developing new nano-carriers. So, to boost the PDT effect, in the present work, new metallocatanionic vesicles were fabricated by a convenient, efficient, green and inexpensive method to encapsulate PSs and evaluate their antimicrobial PDT against the drug-resistant bacterium Staphylococcus aureus. They were prepared from a combination of a double-chained copper-based cationic metallosurfactant (CuCPCII) and an anionic surfactant sodium bis(2-ethylhexyl)sulfosuccinate (Aerosol OT or AOT). The surface charge, structure and ability to encapsulate oppositely charged photosensitizers are some crucial factors that need to be controlled for their effective utilization in PDT. In this approach, two of the fractions, one each from a cationic rich and anionic rich side, were selected to encapsulate cationic (methylene blue; MB) and anionic (rose bengal (RB)) PSs after characterization by SAXS, AFM, FESEM, DLS, and zeta-potential, and conductivity measurements. Afterwards, PDT was performed on S. aureus (a multidrug-resistant bacterium) by the colony forming unit (CFU) method using PS encapsulated metallocatanionic vesicles that demonstrated high bactericidal activity by using visible light (532 nm) and facilitated the generation of singlet oxygen. The singlet oxygen generation capability of both the PSs was enhanced under irradiation when encapsulated in metallocatanionic vesicles because the presence of metal accelerated the intersystem crossing of triplet oxygen to singlet oxygen. Furthermore, these studies reveal that the metallocatanionic vesicles have dual functionality i.e. encapsulate PSs and even show dark toxicity against S. aureus. To study the killing of S. aureus, bacterial DNA was extracted and its interactions and conformational changes in the presence of metallocatanionic vesicles were analyzed via., UV-Visible, and circular dichroism (CD) spectroscopy. Comet assay (single-cell gel-electrophoresis) demonstrated the DNA damage after PDT treatment in an individual cell. The bacterial DNA damage was more with the metallosurfactant rich 70 : 30 fraction than with the 30 : 70 fraction, in combination with RB under irradiation. This work provides a new metal hybrid smart material that possesses dual functionality and is prepared by an easy, economical and feasible procedure which resulted in enhanced PDT against a drug-resistant bacterium, thus, providing an alternative for antibacterial therapy.

Investigating affordable cobalt based metallosurfactant as an efficient electrocatalyst for hydrogen evolution reaction

The implementation of hydrogen evolution reaction (HER) is an essential requirement of a stable electrocatalyst that competes for the performance of noble metals (Pt, Pd), especially in acidic conditions. This research reports the design and development of affordable cobalt (Co) based metallosurfactant (CoCPC(I)) which performs under acidic medium (0.5 N H₂SO₄) for HER. Such a fabricated catalyst is able to lower the cathodic potentials efficiently and exhibits 130 mV onset potential and Tafel slope of 104 mVdec^-1 that depicts the presence of Volmer-Heyrovsky mechanism. The results of the studies confirm that our synthesized metallosurfactant forms metallomicelles on the surface of electrode and surface remains stable even after the electrochemical cycle. Further, the surfactant protects the metal centre as an active site for a longer time via forming metallo-micelles which helps to sustain activity. These outcomes reveal the efficient mass and charge transfer capability of CoCPC(I) which results in faster charge transfer kinetics. Therefore, the utilization of Co based metallosurfactant can split water easily, cost-effectively, and without using hazardous chemicals. Our demonstrated technology seems suitable for industrial applications due to features of large-scale production possibilities.

Synthesis, thermal and surface activity of cationic single chain metal hybrid surfactants and their interaction with microbes and proteins

A series of water-soluble metal functionalized surfactants have been prepared using commercially available surfactant cetyl pyridinium chloride and transition metal salts. These complexes were characterized in the solid state by elemental analysis, FTIR, 1H NMR and thermogravimetric analysis. The interfacial surface activity and aggregation behaviour of the metallosurfactants were analysed through conductivity, surface tension and small angle neutron scattering measurements. Our results show that the presence of metal ions as co-ions along with counter ions favours micellization at a low critical micellization concentration (CMC). Small angle neutron scattering revealed that the metallomicelles are of a prolate ellipsoidal shape and exhibit strong counterion binding. This article further describes the interaction of the metallosurfactants with transport protein Bovine Serum Albumin (BSA) using different spectroscopic techniques. A spectroscopic study was used to study the binding, interaction and quenching mechanism of BSA with the metallosurfactants. Gel electrophoresis (SDS-PAGE) and circular dichroism (CD) investigated the structural and conformational changes produced in BSA due to the metallosurfactants. The results indicate that there is an alteration in the secondary structure of BSA due to the electrostatic interaction between positive head groups and metal co-ions of the metallosurfactants and negatively charged amino acids of BSA. As the concentration increases, the α-helicity of BSA decreases and all the three studied metallosurfactants gave comparable results. Finally, the in vitro cytotoxicity and antimicrobial activity of the metallosurfactants were evaluated against erythrocytes and microorganisms, which showed prominent effects related to the presence of a metal ion in metallomicelles of the hybrid surfactants.

Cationic double chained metallosurfactants: synthesis, aggregation, cytotoxicity, antimicrobial activity and their impact on the structure of bovine serum albumin

Bovine serum albumin (BSA) is one of the most copious and significant blood proteins with dynamic structure. The understanding of the structural functionality of BSA and its interaction with metal ions is desired for various biological functions. Herein, three different metallosurfactants containing different transition metals and the same hydrophobic tail were engaged to investigate the structural transition of BSA. The metallosurfactants have been prepared by a combination of metal ions (M = Fe, Co and Ni) with cetylpyridinium chloride surfactant via the ligand insertion method and were characterized by elemental, FTIR, 1H-NMR, and thermogravimetric analysis (TGA). The obtained results reveal that insertion of a metal ion perturbs the aggregation behavior of the surfactant. Incorporation of a metal-ion has been found to decrease the CMC value of the surfactant, which has been supported by conductivity, surface tension and small angle X-ray scattering (SAXS). These metallosurfactants were employed to study the interaction and binding mechanism of BSA under physiological conditions. SDS-PAGE analysis points out a weak effect of metallosurfactants on the primary structure of BSA, whereas CD spectra implied a significant change in secondary structure with the decreased α-helical content of BSA. Fluorescence spectroscopy indicates the effect of metallosurfactants on the tertiary structure of BSA, whereas absorption spectra demonstrated static quenching with a blue shift in the presence of metallosurfactants. Moreover, unfolding of BSA in the presence of metallosurfactants has also been confirmed by SAXS studies. The overall results indicate that insertion of the metal ion into the framework of the surfactant structure enhances its protein binding/folding/unfolding abilities, which would be helpful in clinical as well as in life sciences.

In vitro assessment of antimicrobial and genotoxic effect of metallosurfactant based nickel hydroxide nanoparticles against Escherichia coli and its genomic DNA

In the present study, we have synthesized nickel hydroxide nanosuspensions (Ns) using microemulsion technique. This approach is eco-friendly and makes use of Tween 80 (a non-ionic biocompatible surfactant) and newly synthesized metallosurfactants for the formation of uniform nanoparticles in the form of nanosuspensions (Ns). The nickel hydroxide Ns's were derived from three different metallosurfactants i.e. NiCTAC (Bishexadecyltrimethylammonium nickel tetrachloride), NiDDA (Bisdodecylamine nickel dichloride) and NiHEXA (bishexadecylamine nickel dichloride). Three different nickel-based metallosurfactants were synthesized and characterized using various methods such as CHN, ¹HNMR, and FTIR. Fabrication of nanosuspension was confirmed using different characterization methods such as Transmission electron microscopy (TEM), Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-ray Spectroscopy (EDX), X-ray Diffraction (XRD), pH and Zeta potential. These particles were further investigated for their genotoxic and cytotoxic effects on gram-negative bacteria, Escherichia coli (E. coli). Effect of nanosuspensions on E. coli was confirmed using colony forming unit count, agar well diffusion, and gram staining method. Through colony forming unit count method, nanosuspensions influence on the colony-forming capacity of E. coli cells was confirmed. Agar well diffusion method provides the estimation of antimicrobial activity, and the largest inhibition zone was observed for NiCTAC Ns and smallest for NiHEXA Ns which is related to maximum and minimum bactericidal properties of Ns, respectively. The interaction behavior of bacterial DNA with Ni nanosuspension was analyzed using agarose gel electrophoresis and circular dichroism. Along with, the role of different chemical scavengers was also evaluated in DNA damage using gel electrophoresis. Furthermore, the antioxidant activity of Ni nanosuspension was also confirmed using DPPH assay.

Chromium-based metallosurfactants: synthesis, physicochemical characterization and probing of their interactions with xanthene dyes

The solubilization of xanthene dyes of variable solubility has been estimated in chromium based metallosurfactants.

Copper as an alternative antimicrobial coating for implants - An in vitro study

AIM

To investigate osteoconductive and antimicrobial properties of a titanium-copper-nitride (TiCuN) film and an additional BONIT^® coating on titanium substrates.

METHODS

For micro-structuring, the surface of titanium test samples was modified by titanium plasma spray (TPS). On the TPS-coated samples, the TiCuN layer was deposited by physical vapor deposition. The BONIT^® layer was coated electrochemically. The concentration of copper ions released from TiCuN films was measured by atomic absorption spectrometry. MG-63 osteoblasts on TiCuN and BONIT^® were analyzed for cell adhesion, viability and spreading. In parallel, Staphylococcus epidermidis (S. epidermidis) were cultivated on the samples and planktonic and biofilm-bound bacteria were quantified by counting of the colony-forming units.

RESULTS

Field emission scanning electron microscopy (FESEM) revealed rough surfaces for TPS and TiCuN and a special crystalline surface structure on TiCuN + BONIT^®. TiCuN released high amounts of copper quickly within 24 h. These release dynamics were accompanied by complete growth inhibition of bacteria and after 2 d, no planktonic or adherent S. epidermidis were found on these samples. On the other hand viability of MG-63 cells was impaired during direct cultivation on the samples within 24 h. However, high cell colonization could be found after a 24 h pre-incubation step in cell culture medium simulating the in vivo dynamics closer. On pre-incubated TiCuN, the osteoblasts span the ridges and demonstrate a flattened, well-spread phenotype. The additional BONIT^®coating reduced the copper release of the TiCuN layer significantly and showed a positive effect on the initial cell adhesion.

CONCLUSION

The TiCuNcoating inhibits the formation of bacterial biofilms on orthopedic implants by influencing the “race for the surface” to the advantage of osteoblasts.

Fabrication of metalosomes (metal containing cationic liposomes) using single chain surfactants as a precursor via formation of inorganic organic hybrids

This work reveals a methodology to modify a single chain surfactant to fabricate a liposome-like assembly by controlling the stoichiometry by virtue of a metallic counter ion. It is a noteworthy advancement in the area of self-assembled molecular structures.

Transition metal based single chained surfactants: synthesis, aggregation behavior and enhanced photoluminescence properties of fluorescein

Four different transition metal based surfactants were synthesized. The effect of presence of metal as a part of counter ion on the aggregation behaviour of metallosurfactants and on the photophysical properties of fluorescein was explored.