Enhanced photocatalytic and photodynamic activity of chitosan and garlic loaded CdO-TiO2 hybrid bionanomaterials

Herein, the work addresses the synthesis of biomaterials (chitosan and garlic) loaded CdO-TiO₂ hybrid nanocomposites for photocatalytic water treatment and photodynamic cancer therapeutic applications that were reported the first time. CdO-TiO₂ (CT) nanocomposites were synthesized and loaded with the biomaterials such as chitosan and garlic by simple sol-gel method. The nanomaterials were characterized and the photodegradation of three model pollutants, Methylene blue (MB), Methyl orange (MO) and Rhodamine B (Rh-B) was opted to investigate the efficiency of the synthesized photocatalyst under the solar light. From the results, the garlic-loaded CdO-TiO₂ (AS-CT) hybrid nanocomposites exhibit a superior photocatalytic activity than the chitosan-loaded CdO-TiO₂ (CS-CT) and CdO-TiO₂ (CT) nanocomposites under the irradiation of solar light. Additionally, the cell viability of the synthesized nanocomposites was carried out in HeLa cell lines under different concentrations, light doses and incubation periods using an LED light source. Compared to the CS-CT and CT nanocomposites, an efficient photodynamic activity was achieved in the case of AS-CT hybrid nanocomposites. Actually, the end-use properties required for both processes in AS-CT nanocomposites appear similar due to the presence of organo sulphurus compounds.

Mn3O4 nanoparticles bearing 5-amino-2-mercapto benzimidazole moiety as antibacterial and antifungal agents

The antibacterial and antifungal effects of non-functionalized and surface-functionalized Mn₃O₄ nanoparticles were comparatively analyzed to reason out the potential changes in antimicrobial activities due to functionalization with 5-amino-2-mercapto benzimidazole (AMB) molecule. The surface functionalization of Mn₃O₄ nanoparticles with AMB molecule was confirmed by the XRD result, which shows the shift in 2θ values with noticeable peaks. The surface morphology and functionalization of Mn₃O₄ nanoparticles were additionally confirmed by HR-SEM and EDAX studies. Antimicrobial activities were investigated by an agar-well-diffusion method using the bacteria Staphylococcus aureus and Pseudomonas aeruginosa and fungi Aspergillus niger. The functionalized Mn₃O₄ nanoparticles possess remarkable antibacterial and antifungal effect than the non-functionalized Mn₃O₄ nanoparticles and AMB molecule. The coating of low energy surface layer over metal oxide nanoparticles such as Mn₃O₄ offers an active surface toward both transfer of electron and the adsorption or desorption of water, inorganic ions, and other molecules, which leads to the increased antimicrobial activity of f-Mn₃O₄ nanoparticles.Communicated by Ramaswamy H. Sarma.

Photodynamic cancer therapy: role of Ag- and Au-based hybrid nano-photosensitizers

The utilization of photodynamic therapy (PDT) has been rapidly increasing due to its advantage as an effective treatment modality for cancer. The organic photosensitizers employed for PDT have some disadvantages, including high toxicity, non-selectivity toward tumors and poor absorption of light. The low light penetration into the tumor sites resulting from low wavelength of absorption and long-term skin photosensitivity. Hence, the attention toward non-toxic inorganic photosensitizers like noble metal nanoparticles (NPs) has been increasing nowadays. In bioscience, NPs are replacing organic dyes since they have photostability and non-toxicity. Generally, nanomaterials can easily form compounds with other substances as well as organic materials and the modified NPs surface enhances the chemical activity. Among the metal NPs, noble metals, especially gold and silver are attractive because of their size and shape-dependent unique optoelectronic properties. The coating of inorganic/organic materials on top of the noble metal makes the NPs bio-compatible and less toxic. Furthermore, Ag- and Au-based inorganic/organic complex NPs could offer a new possibility because of their unique structures. Meanwhile, the coating of inorganic/organic complex NPs protects the noble metals and stabilizes them against chemical corrosion and enhances the production of reactive oxygen species. Thus, in this review, we have highlighted the role of Ag- and Au-based inorganic/organic hybrid nano-photosensitizers in photodynamic therapy.Communicated by Ramaswamy H. Sarma.

Preparation and characterization of core-shell type Ag@SiO2 nanoparticles for photodynamic cancer therapy

With recent scientific developments, Photodynamic therapy (PDT) offers the promisie to become incorporated into the mainstream of cancer therapy. Noble metal based nano-PDT is increasing due to its advantages in the field of biomedicine. In this study, noble metal based Ag@SiO₂ core-shell nanoparticles were synthesized and to confirm the core-shell structure they were characterized by UV-vis, XRD, FTIR, TEM, and EDX. Our data confirm that core-shell type Ag@SiO₂ nanoparticles maintain its ability to kill cancer cells upon light irradiation. This shows that SiO₂ shell may not only prevent aggregation but it also may enhance the photodynamic activity of Ag nanoparticles.

Photodynamic activity and DNA binding studies of Pd@SiO2 core-shell nanoparticles in vitro

Metal-semiconductor core-shell type Pd@SiO₂ nanoparticles (NPs) were successfully synthesized by Stober's method and the product was characterized by UV-vis, XRD, FT-IR, SEM, HR-TEM and EDX techniques. In vitro Photodynamic activity and DNA binding studies of Pd@SiO₂ core shell nanoparticles were studied. Cell viability of the core-shell nanoparticles against HeLa cell line was screened by MTT assay after exposing at different light doses. The outcome of the present study indicates that the core-shell Pd@SiO₂ NPs are highly stable and exhibited strong photodynamic efficiency under LED light illumination in HeLa cells. The results indicated that SiO₂ supported on the surface of Pd NPs not only prevented the aggregation in addition exhibited remarkable photodynamic activity.

Study of photodynamic activity of Au@SiO2 core-shell nanoparticles in vitro

Metal-semiconductor core-shell type Au@SiO2 nanoparticles were prepared by Stober's method. They were characterized by absorption, XRD, HR-TEM and EDAX techniques. The resulting modified core-shell nanoparticles shows that the formation of singlet oxygen, which was confirmed by ESR technique. The photohemolysis studies were carried out under two different experimental conditions. It is observed that the photohemolysis increases with concentration as well as light dose. Cell viability of the core-shell nanoparticles against HeLa cell lines were studied by MTT assay method. The outcomes of the present study indicate that, the Au@SiO2 core-shell nanoparticles are extremely stable with a very high photodynamic efficiency under visible light illumination.

Enhancing photoluminescent behavior of 2-(naphthalen-1-yl)-1,4,5-triphenyl-1H-imidazole by ZnO and Bi2O3

A fluorophore 2-(naphthalen-1-yl)-1,4,5-triphenyl-1H-imidazole [NTI] has been designed, synthesized and characterized by (1)H NMR, (13)C NMR, mass and single crystal XRD. Absorption, emission, lifetime and cyclic voltammetry have been made to deduce the interaction between NTI and ZnO and Bi2O3 nanocrystals. NTI act as a new host for ZnO and Bi2O3 nanocrystals that enhance its luminescence. The apparent binding constant has been obtained. Adsorption of the NTI on ZnO and Bi2O3 nanocrystals lowers the HOMO energy level of the NTI. The strong adsorption of the NTI on the surface of ZnO and Bi2O3 nanocrystals is likely due to the chemical affinity of the nitrogen atom of the NTI to the zinc ion on the surface of nanocrystals. SEM and EDS spectra confirmed the adsorption of NTI on the surface of nanocrystals.

Dynamics of Solvent Controlled ESIPT of π-Expanded Imidazole Derivatives - pH Effect

A set of π-expanded imidazole derivatives employing excited state intramolecular proton transfer (ESIPT) was designed and synthesized. The relationship between the structure and photophysical properties were thoroughly elucidated by comparing with the analogue blocked with ESIPT functionality. The compound possessing an acidic NH function as part of an intramolecular hydrogen bond system has much higher fluorescence quantum yield and Stokes shift and the π-expansion strongly influences the optical properties. The occurrence of ESIPT for imidazole tosylamide derivatives were less affected by the hydrogen-bonding ability of the solvents compared to the unprotected amine. The low pKa values for the monocation ⇌ neutral equilibrium indicate the presence of intramolecular hydrogen bonding between the amino proton and tertiary nitrogen atom.

Optical properties of 1,2-diaryl benzimidazole derivatives - a combined experimental and theoretical studies

Some novel 1,2-diaryl benzimidazole derivatives have been designed, synthesized and characterized by mass, (1)H, (13)C-NMR spectral studies and single crystal XRD. The charge distribution has been calculated from the atomic charges by non-linear optical (NLO) and natural bond orbital (NBO) analyses have been calculated by abinitio method. Synthesized 1,2-diaryl benzimidazole derivatives have the largest μgβ0 value and can be used as potential NLO materials. Analysis of the molecular electrostatic potential (MEP) energy surface exploited the region for non-covalent interactions in the molecule. Calculated bond lengths, bond angles and dihedral angles are found to be slightly higher than that of X-ray diffraction values of its experimental datas.

Contrasting emission behaviour of phenanthroimidazole with ZnO nanoparticles

A new fluorophore 2-(4-fluorophenyl)-1-phenyl-1H-phenanthro [9,10-d]imidazole has been synthesized and characterized by spectroscopic techniques. Nanoparticulate ZnO enhances the fluorescence of the synthesised fluorophore. The absorption, fluorescence, lifetime, cyclic voltammetry and infrared studies reveal that fluorophore is attached to the surface of ZnO semiconductor. Photo-induced electron transfer (PET) explains the enhancement of fluorescence by nanoparticulate ZnO and the apparent binding constant has been obtained. Adsorption of the fluorophore on ZnO nanoparticle lowers the HOMO and LUMO energy levels of the fluorophore. The strong adsorption of the phenanthrimidazole derivative on the surface of ZnO nanocrystals is likely due to the chemical affinity of the nitrogen atom of the organic molecule to the zinc ion on the surface of nanocrystal.

Optical properties of 1-(4,5-diphenyl-1-p-tolyl-1H-imidazol-2-yl)naphthalen-2-ol--ESIPT process

This article presents optical, electrochemical, and thermal properties of novel class of green fluorescent 1-(4,5-diphenyl-1-p-tolyl-1H-imidazol-2-yl)naphthalen-2-ol. Detailed photo physical and quantum chemical studies have been performed to elucidate the excited state intramolecular proton transfer (ESIPT) reaction leading a large stokes shifted fluorescence emission from the phototautomer. The results of quantum chemical investigations confirmed the intramolecular charge transfer characteristics of the ESIPT tautomers. The high photoluminescence quantum yield is ascribed to twisted chromophores due to phenyl substituents at 1,2-position of the imidazole ring which restricted intramolecular motion, leading to an optically allowed lowest optical transition without self quenching.

Characterization and electronic spectral studies of 2-(naphthalen-1-yl)-4,5-diphenyl-1H-imidazole bound Fe2O3 nanoparticles

Multicomponent, one-pot, highly efficient, indium trifluoride (InF3) catalytic synthesis of 2-(naphthalen-1-yl)-4,5-diphenyl-1H-imidazole under solvent-free condition is reported. Characterization of imidazole has been carried out by spectral techniques. The synthesized phosphated imidazole (PI) and phosphated imidazole bound magnetic nanoparticles (PIBMN) were characterized using Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and powder X-ray diffraction (XRD). The photophysical characteristics of the synthesized phosphated imidazole and phosphated imidazole bound magnetic nanoparticles were investigated by steady-state absorption and emission spectroscopy as well as time resolved fluorometry. From these experiments, the position of the spectral maxima (λabs, λexc and λemi), and lifetime (τ) of the synthesized phosphated imidazole and phosphated imidazole bound magnetic nanoparticle have been determined.

Benzimidazole derivative vs. different phases of TiO2-physico-chemical approach

1-Benzyl-2-phenyl-1H-benzo[d]imidazole (BPBI) has been synthesized by simple steps and characterized by spectral studies. Absorption and fluorescence spectral studies have been employed to investigate the interaction of BPBI with the anatase, hombikat, P25 and rutile phases of TiO2. The emission of the BPBI is efficiently quenched by anatase, hombikat and P25 TiO2 nanoparticles owing to charge injection from the excited singlet state of BPBI to the conduction band of the TiO2 nanoparticles. Surprisingly, rutile phase enhances the fluorescence which is likely due to lowering of LUMO and HOMO levels of the ligand on ducking of the benzimidazole moiety of the BPBI molecule into the void space of rutile TiO2. Electron injection from photoexcited BPBI to the TiO2 conduction band (S*→S(+)+e(-)(CB)) is likely to enhance the fluorescence.

Fluorescence quenching of organic molecule by insulator

A new kind of fluorophore 2-(4-fluorophenyl)-1-phenyl-1H-benzo[d]imidazole (FPPBI) has been synthesized and characterized by (1)H NMR, (13)C NMR, mass spectral studies and single crystal XRD. The energy transfer from FPPBI to Al2O3 nanocrystals has been studied by absorption, fluorescence and lifetime spectroscopic methods. The association between nanoparticles and FPPBI is explained from both absorption and fluorescence quenching data. The distance between FPPBI and Al2O3 as well as the critical energy transfer distance has been deduced.

Fluorescence quenching of bovine serum albumin by NNMB

A new type of fluorophore 2-(naphthalen-1-yl)-1-((naphthalen-1-yl)methyl)-1H-benzimidazole (NNMB) has been prepared and characterized by (1)H NMR, (13)C NMR, mass and IR spectral analysis. Absorption, fluorescence and synchronous fluorescence spectral studies have been made for the mutual interaction of NNMB with bovine serum albumin (BSA). Absorption spectroscopy proved the formation of a ground state BSA…NNMB complex. Fluorescence spectrum of BSA in the presence of NNMB clearly shows that NNMB acts as a quencher. Based on the theory of Forester's non-radiation energy transfer (FRET) binding distance has been deduced. The Stern-Volmer quenching constant (KSV), binding site number (n), apparent binding constant (KA) and corresponding thermodynamic parameters (ΔG, ΔH and ΔS) were determined.

Synthesis, spectral studies and solvatochromism of some novel benzimidazole derivatives--ESIPT process

Some novel benzimidazole derivatives were synthesized and characterized by (1)H, (13)C NMR mass and elemental analysis. XRD analysis was carried out for 1-(4-methylbenzyl)-2-p-tolyl-1H-benzo[d]imidazole. The solvent effect on the absorption and fluorescence bands has been analyzed. The energetic analysis of the potential energy surface (PES), HOMO and LUMO levels [DFT/B3LYP/6-31G(d,p)] evidenced the existence of excited state intramolecular proton transfer (ESIPT) in hydroxy benzimidazole derivative.

1-Phenyl-2-p-tolyl-1H-benzimidazole

In the title compound, C20H16N2, the benzimidazole ring system forms dihedral angles of 28.50 (7) and 72.44 (7)° with the tolyl and phenyl rings, respectively. In the crystal, mol-ecules are linked into chains along the a-axis direction by weak C-H⋯N inter-actions. The crystal structure also features C-H⋯π inter-actions.

1-Phenyl-2-[4-(trifluoro-meth-yl)phen-yl]-1H-benzimidazole

In the title mol­ecule, C₂₀H₁₃F₃N₂, the benzimidazole unit is close to being planar [maximum deviation = 0.012 (1) Å] and forms dihedral angles of 31.43 (7) and 61.45 (9)° with the 4-(trifluoromethyl)phenyl and 1-phenyl rings, respectively; the dihedral angle between these rings is 60.94 (10)°. In the crystal, C—H⋯F hydrogen bonds link the mol­ecules into chains along the c-axis direction. The CF₃ group is rotationally disordered with an occupancy ratio of 0.557 (8):0.443 (8) for the F atoms.

2-(4-Meth-oxy-phen-yl)-1-phenyl-1H-benzimidazole

In the title compound, C₂₀H₁₆N₂O, the 1H-benzimidazole ring forms dihedral angles of 48.00 (6) and 64.48 (6)°, respectively with the benzene and phenyl rings, which are inclined to one another by 58.51 (7)°. In the crystal, weak C—H⋯π inter­actions are the only inter­molecular inter­actions present.

Lifetime time measurements, Kamlet-Taft and Catalan solvatochromism of some 2-aryl benzimidazole derivatives

Some 2-aryl benzimidazole derivatives (1-6) have been prepared and characterized by different spectral techniques. Fluorescence lifetime of synthesized 2-aryl benzimidazole derivatives was calculated. Kamlet-Taft and Catalan solvatochromism of synthesized 2-aryl benzimidazole derivatives have been discussed. Crystal structure of 1-(4-methylbenzyl)-2-p-tolyl-1H-benzo[d]imidazole has been studied.

2-(1-Phenyl-1H-benzimidazol-2-yl)phenol

In the title mol­ecule, C₁₉H₁₄N₂O, the benzimidazole unit is close to being planar [maximum deviation = 0.0253 (11) Å] and forms dihedral angles of 68.98 (6) and 20.38 (7)° with the adjacent phenyl and benzene rings; the dihedral angle between the latter two planes is 64.30 (7)°. An intra­molecular O—H⋯N hydrogen bond generates an S(6) ring motif. In the crystal, mol­ecules are linked by C—H⋯N and C—H⋯O hydrogen bonds, and consolidated into a three-dimensional architecture by π–π stacking inter­actions, with a centroid–centroid distance of 3.8428 (12) Å.

1,2-Diphenyl-1H-benzimidazole

In the title mol­ecule, C₁₉H₁₄N₂, the benzimidazole unit is close to being planar [maximum deviation = 0.0102 (6) Å] and forms dihedral angles of 55.80 (2) and 40.67 (3)° with the adjacent phenyl rings; the dihedral angle between the phenyl rings is 62.37 (3)°. In the crystal, one C—H⋯N hydrogen bond and three weak C—H⋯π inter­actions involving the fused benzene ring and the imidazole ring are observed, leading to a three-dimensional architecture.

Selective quenching of benzimidazole derivatives by Cu²+ metal ion

It is a very big challenge to develop a Cu(2+) selective fluorescent sensor with the ability to exclude the interference of some metal ions such as Fe(3+), Mg(2+), Ag(+), K(+) and Na(+). Herein, we report a fluorescence quenching of some benzimidazole derivatives (1-6) with Cu(2+) metal ion. These benzimidazole derivatives have been shown to bind copper ions resulting in quenching of its fluorescence. The response to Cu(2+) is rapid, selective and reversible upon addition of a copper chelator. These benzimidazole derivatives were characterized by (1)H, (13)C NMR mass and elemental analysis. XRD analysis was carried out for 1-(4-methylbenzyl)-2-p-tolyl-1H-benzo[d]imidazole.

Computational studies of 1,2-disubstituted benzimidazole derivatives

Some 1,2-disubstituted benzimidazole derivatives (1-6) have been synthesized and characterized by mass, (1)H, (13)C NMR and elemental analysis. XRD analysis was carried out for 1-(4-methylbenzyl)-2-p-tolyl-1H-benzo[d]imidazole. Calculated bond lengths, bond angles and thus dihedral angles are found to be slightly higher than that of X-ray diffraction values of its experimental data. The charge distribution has been calculated from the atomic charges by non-linear optical (NLO) and natural bond orbital (NBO) analyses have been calculated by ab initio method. Since the synthesized 1,2-disubstituted benzimidazole derivatives have the largest μ(g)β(0) value and can be used as potential NLO materials. Analysis of the molecular electrostatic potential (MEP) energy surface exploited the region for non-covalent interactions in the molecule. Atom in molecule analysis (AIM) was carried out to show the presence of bond critical points (BCPs).

Electronic spectral studies of some fluorescent probes: a comparison of two approaches

Schiff base derivatives were synthesized and characterized by NMR spectra, mass and CHN analysis. The fluorescence properties of these dyes are strongly solvent dependent and the wavelength of maximum fluorescence emission shifts to red. The Kamlet-Taft and Catalan's solvent scales were found to be the most suitable for describing the solvatochromic shifts of the absorption and fluorescence emission. From the NMR chemical shifts and DFT studies, it was found that the azomethine hydrogen is anti to the amine aryl ring i.e., these dyes exist in anti conformation. DFT calculation was also carried out to determine the orientation of hydroxyl group in more stabilized minimum energy conformation.

Effective fluorescent chemosensors for the detection of Zn²+ metal ion

Benzimidazole derivatives synthesized from three components assembling condensation reaction behaves as a selective fluorescent sensor for Zn(2+) metal ion. These benzimidazole derivatives were characterized by (1)H, (13)C NMR, mass and elemental analysis. XRD analysis was carried out for 1-(4-methylbenzyl)-2-p-tolyl-1H-benzo[d]imidazole. The increase in the fluorescence enhancement can be explained on the basis of photo induced electron transfer (PET) mechanism. The blockage of the photoinduced electron transfer process from benzimidazole ring to aryl fluorophore induced by Zn(2+) co-ordination induced emission enhancement.

2-(4-Fluoro-phen-yl)-1-phenyl-1H-benzimidazole

In the title mol-ecule, C(19)H(13)FN(2), the benzimidazole unit is close to planar [maximum deviation = 0.0342 (9) Å] and forms dihedral angles of 58.94 (3) and 51.43 (3)° with the phenyl and fluoro-benzene rings, respectively; the dihedral angle between the phenyl and fluoro-benzene rings is 60.17 (6)°. In the crystal, three C-H⋯F hydrogen bonds and two weak C-H⋯π inter-actions involving the fused benzene ring lead to a three-dimensional architecture.

Binding interaction of 1-(4-methybenzyl)-2-p-tolyl-1H-benzo[d]imidazole with bovine serum albumin

A promising benzimidazole derivative 1-(4-methybenzyl)-2-p-tolyl-1H-benzo[d]imidazole (MBTBI) has been synthesized and characterized by single crystal XRD, NMR, mass and IR spectral techniques. The mutual interaction of this benzimidazole derivative (MBTBI) with bovine serum albumin (BSA) was investigated using solution spectral studies. The fluorescence quenching mechanism of BSA by MBTBI was analyzed and the binding constant has been calculated. The binding distance between these two was obtained based on the theory of Forester's non-radiation energy transfer (FRET). The effect of some common ions on the binding constant was also examined.