UV-visible Absorption Spectrophotometry Research Articles

Biosynthesis and characterizations of silver nanoparticles by using green banana peel extract: Evaluation of their antibacterial and electrical performances

Biosynthesized silver nanoparticles (Ag NPs) hold tremendous promise in nano-bioscience, with applications spanning engineering, science, and industry. This study delves into their fabrication process, crystallographic characteristics, and nanostructures. Employing green banana peel extract (GBPE), Ag NPs were synthesized. Various analytical techniques, such as UV–Vis absorption spectrophotometry (UV), X-ray diffraction (XRD), Gas chromatography-mass spectrometry (GC-MS), Field emission scanning electron microscopy (FESEM), Fourier-transform infrared spectroscopy (FTIR), and Transmission electron microscopy (TEM) elucidate their attributes. UV–visible analysis reveals a 413 nm absorption band due to surface plasmon resonance. The Ag NPs exhibit a face-centered cubic structure with an average crystallite size of 45.87 nm. Lattice parameters and dislocation density are also determined. When tested against harmful bacteria, such as E. coli and S. epidermidis, advanced microscopy reveals a median size of particles of 55.12 nm and demonstrates their antibacterial characteristics. These environmentally benign Ag NPs also improve the efficiency of bio-electrochemical cells (BECs), opening the door to large-scale manufacturing at a reasonable cost and broadening the range of possible uses.

Change in Osmotic Pressure Influences the Absorption Spectrum of Hemoglobin inside Red Blood Cells.

Absorption spectra of red blood cell (RBC) suspensions are investigated in an osmolarity range in the medium from 200 mOsm to 900 mOsm. Three spectral parameters are used to characterize the process of swelling or shrinkage of RBC-the absorbance at 700 nm, the Soret peak height relative to the spectrum background, and the Soret peak wavelength. We show that with an increase in the osmolarity, the absorbance at 700 nm increases and the Soret peak relative height decreases. These changes are related to the changes in the RBC volume and the resulting increase in the hemoglobin intracellular concentration and index of refraction. Confocal microscopy and flow cytometry measurements supported these conclusions. The maximum wavelength of the Soret peak increases with increasing osmolarity due to changes in the oxygenation state of hemoglobin. Using these spectrum parameters, the process of osmosis in RBCs can be followed in real time, but it can also be applied to various processes, leading to changes in the volume and shape of RBCs. Therefore, we conclude that UV-Vis absorption spectrophotometry offers a convenient, easily accessible, and cost-effective method to monitor changes in RBC, which can find applications in the field of drug discovery and diagnostics of RBC and hemoglobin disorders.

Comparative analysis of polyol-synthesized ZnO nanoparticles through first−principles calculations and experimental characterization

An extensive investigation was undertaken to examine the crucial properties of zinc oxide (ZnO) in its hexagonal wurtzite crystal structure, with a focus on its structural, electronic, and optical features. The aim of this study is to examine the correlation between the theoretical and experimental properties of ZnO nanoparticles (NPs). The experimental part involved the fabrication of ZnO NPs through the polyol method, followed by their characterization using X-ray crystallography and UV-Vis absorption spectrophotometry. Computational calculations were conducted using density functional theory (DFT), incorporating the local density approximation (LDA) and the Hubbard-U exchange-correlation (XC) function to enhance the structure of ZnO. The DFT calculations thoroughly matched the experimental observations, including lattice constants and Zn−O bond length. Electronic properties, particularly the band structure, and DOS calculations, further confirmed the experimental findings, especially regarding the band gap energy. Partial density of states (PDOS) analysis provided insights into the role of each atom in the chemical bonding of ZnO, while total density of states (TDOS) analysis evaluated the overall contribution of all atoms. This comprehensive study of the polyol synthesis method for ZnO NPs and the properties derived from the first principles of DFT calculations offers valuable insights for researchers and highlights the potential applications of ZnO in future studies, mainly for optoelectronic applications.

Experimental and Theoretical Screening of Core Gold Nanoparticles and Their Binding Mechanism to an Anticancer Drug, 2-Thiouracil.

This study demonstrated the capability of two readily available optical spectroscopy tools, namely UV-Vis absorption spectrophotometry and Raman/surface-enhanced Raman spectroscopy, to select in a rapid and noninvasive manner the most homogenous gold nanoparticle (AuNP) models and to identify their chemical binding mechanism to 2-thiouracil (2-TU). 2-TU is an anticancer drug of great promise in the antiproliferative and photothermal therapies of cancer. The citrate-capped AuNPs emerged as the most stable as well as time- and cost-effective AuNP model out of the three widely used colloidal nanocores (citrate-, borohydride-citrate-, and sodium dodecyl sulfate (SDS)-capped AuNPs) that were examined. 2-TU chemically attached to the relatively monodispersed AuNPs via a chemisorption mechanism. The 2-TU-AuNPs complex formed through the covalent bonding of the S atom of 2-TU to the nanosurface in a vertical orientation. The spectroscopic results were then confirmed with the help of density functional theory (DFT) calculations and other physicochemical characterization tools for nanomaterials such as transmission electron microscopy (TEM), dynamic light scattering (DLS), and zeta potential. Overall, the purified 2-TU-AuNPs were found to be spherical, had an average diameter of 25 ± 2 nm, a narrow size distribution (1-30 nm), a sharp localized surface plasmon resonance (LSPR) peak at 525 nm, and a negative surface charge (-14 mV).

Method for quantifying catechin in a strawberry extract by measuring optical absorbance, at high sensitivity, under the effect of wavelength and concentration

Catechin is considered a powerful antioxidant, and its rapid quantification could help urgently prevent inflammatory and coronary heart diseases. Consequently, the UV–Vis absorption spectrophotometry assay technique could serve this need for rapid detection.For this reason, we have carefully studied the possibility of dosing this antioxidant found in strawberry extract with precision, despite its chemical complexity.In the dosage technique used; sometimes the dilution of the solutions could be the way to resolve a specific quantification problem such as catechin in strawberry extract. This is quite particular, when the optical extinction coefficient of the target substance is very low compared to the extinction coefficients of the other chemical compounds in the complex mixture, because at a certain dilution the absorption spectrum of the molecule could appear, specifically, with its total spectral form or at least at one of these wavelengths.In this article, we will study the possibility of rapidly measuring catechin from strawberry extract by spectrophotometry in UV–VIS, while reformulating the Beer-Lambert law in a new form where the extinction coefficient did not depend not only of the chemical nature of the solute and the solvent but also of the excitation wavelength (ε(λ), Eq. (9)).A catechin-methanol solution is taken as a reference to study the spectral variation due to the various dilutions of the solution and the determination of a limiting concentration where the excitation wavelength becomes constant (203 nm), thus the extinction coefficient of the catechin, denoted ε0, but the measurement sensitivity is suddenly reduced.A semi-empirical relationship is determined by linearization of the absorbance function which depended on the concentration (C) and the excitation wavelength (ε(λ)).A separation process will be exposed to recover the strawberry extract, as well as its spectral analysis. Finally, a procedure for analyzing any strawberry extract will be presented at the end of this scientific article.

Impact of Two Lavender Extracts on Silver Nanoparticle Synthesis, and the Study of Nanoparticles’ Antibiofilm Properties and Their Ability to Transfer them into a Nontoxic Polymer

In this work, we aimed to analyze the impact of extracts prepared from dried Lavandula angustifolia (lavender) flowers and leaves on the synthesis of silver nanoparticles (AgNPs) (wherein the shape and size of AgNPs and the efficiency of the process were analyzed) and to prove the possibility of transferring the AgNPs’ properties into a polymer matrix. An ex situ method was used to incorporate AgNPs and prepare polymer matrix composite (PVP-AgNPs) films (via casting) and fibers (via electrospinning). We used UV-vis absorption spectrophotometry, Fourier Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscopy (TEM), and Scanning Electron Microscopy (SEM) to analyze and characterize the AgNPs and prepared composites. The results of FTIR analysis confirmed the presence of phytochemicals that can reduce silver ions from Ag+ to Ag0 in both extracts. The presence of spherical nanoparticles was confirmed via TEM regardless of the type of extract used. However, leaf extract caused the formation of AgNPs with a narrower size interval (an average size of 20 nm), and with higher efficiency, compared to the nanoparticles prepared using the flower extract. The nanoparticles prepared using the leaf extract were then incorporated into the polymer matrix, and thin polymer composite films and fibers were successfully prepared. The anti-biofilm activity of AgNPs colloids and prepared polymer nanocomposites against green algae Chlorella kessleri was studied. The anti-biofilm properties of the AgNPs were proved, along with the efficient transfer of their toxic properties into nontoxic polymer.

Green Synthesis, Characterization, and Assessment of Iron Oxide Nanoparticles' Antibacterial Activity Using Blumea lacera Root Extract

Iron and copper nanoparticles produced through green methods underwent analysis using UV-visible absorption spectrophotometry, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and EDS. Findings indicated that iron oxide nanoparticles displayed an irregular spherical shape, with sizes ranging from 15.73 nm to 32.37 nm. The antimicrobial efficacy of iron and copper oxide nanoparticles synthesized through green techniques was evaluated against four bacterial strains causing human diseases. Results showed that these nanoparticles exhibited the highest antibacterial activity at a concentration of 20 mm/disc, while their effectiveness was lowest at 13 mm/disc concentrations. This study underscores the potential of iron and copper oxide nanoparticles produced via environmentally friendly methods to serve as antibacterial agents.

Ultra small carbon dots from Crocus cancellatus as a highly fluorescence probe for synthetic Ponceau 4R dye sensing in food samples

In this work, for the first time, natural Crocus cancellatus was adopted for the green, low-cost, and simple synthesis of highly fluorescent ultra-small carbon dots (CDs) with well-distributed size using a one-pot hydrothermal treatment. As-synthesized CDs are used as fluorescence sensing probe for quantitative analysis of Ponceau 4R (E124) synthetic food dye, which is widely used. However, excessive consumption of Ponceau 4R poses potential health risks. To obtain better-quality performance of as-synthesized CDs, the time and temperature of the hydrothermal carbonization reaction of crocus were optimized simply. The as-prepared carbon dots exhibit exceptional advantages including excellent fluorescence, satisfactory chemical stability, low toxicity, and excellent biocompatibility. It produced a strong blue fluorescence when irradiated with UV light at 365 nm, which was subsequently effectively employed for Ponceau 4R sensing based on the quenching of fluorescence. The as-prepared CDs was characterized by EDX, XRD, FTIR, SEM, HRTEM, UV–Visible absorption spectrophotometry, and fluorescence. The effects of carbon dots fluorescence emission wavelength, CDs quantity, pH value, and reaction time were investigated to detect Ponceau 4R under optimum conditions. The synthesized carbon dot's fluorescence intensity allowed quantitative determination of Ponceau 4R in the linear range of 60–6000 nM with a detection limit of 40 nM that is lower than all previously published methods. Several soft drink samples were used to validate the potential use of this new fluorescent probe for P4R detection in actual samples with good precision and accuracy.

UV-Vis absorption spectrophotometry and LC-DAD-MS-ESI(+)-ESI(−) coupled to chemometrics analysis of the monitoring of sulfamethoxazole degradation by chlorination, photodegradation, and chlorination/photodegradation

Sulfamethoxazole (SMX) is one of the most widely used antibiotics worldwide and has been detected at high concentrations in wastewater treatment plant effluents and river waters. In this study, the SMX degradation process combining the simultaneous chlorine oxidation and UV photodegradation is assessed and compared with both photodegradation and chlorine oxidation processes individually. Photodegradation and Chlorine/UV tests were performed using Suntest CPS equipment. Different experimental techniques, including UV–Visible spectrophotometry and liquid chromatography coupled to a diode array detector and positive and negative ionization mass spectrometry (LC-DAD-MS-ESI(+)-ESI(−)), were used to evaluate the degradation reaction of SMX.All the analytical data generated have been processed with the Multivariate Curve Resolution–Alternating Least Squares (MCR-ALS) method to monitor, resolve, and identify the several transformation products generated during the studied degradation processes. A new data fusion analysis strategy is proposed to examine the three processes simultaneously (with only photodegradation, only chlorination, and simultaneous chlorination+photodegradation). Combined with the analysis of different analytical techniques individually (spectrophotometry, LC-DAD, and LC-MS), the fusion of all generated data improved the description of the degradation processes.Detection using DAD allowed a better correspondence among the species monitored spectrophotometrically (UV–Vis) with those analyzed chromatographically. On the other side, detection using MS in both positive and negative acquisition modes allowed resolving a larger number of chemical compounds (specially SMX degradation subproducts) that could not be detected by UV–Vis spectrometry. The results obtained permitted the comparison of the effects produced by the three different degradation processes.

Gold Nanoparticles Functionalized with 2-Thiouracil for Antiproliferative and Photothermal Therapies in Breast Cancer Cells.

Nanoparticles have been used to transport drugs to various body parts to treat cancer. Our interest is in gold nanoparticles (AuNPs) since they have the capacity to absorb light and convert it to heat, inducing cellular damage. This property is known as photothermal therapy (PTT) and has been studied in cancer treatment. In the present study, biocompatible citrate-reduced AuNPs were functionalized with a biologically active compound, 2-thiouracil (2-TU), of potential anticancer activity. Both the unfunctionalized (AuNPs) and functionalized (2-TU-AuNPs) were purified and characterized by UV-Vis absorption spectrophotometry, Zeta potential, and Transmission Electron Microscopy. Results showed monodispersed, spherical AuNPs with a mean core diameter of 20 ± 2 nm, a surface charge of -38 ± 5 mV, and a localized surface plasmon resonance peak at 520 nm. As a result of functionalization, the mean core diameter of 2-TU-AuNPs increased to 24 ± 4 nm, and the surface charge increased to -14 ± 1 mV. The functionalization of AuNPs and the load efficiency were further established through Raman spectroscopy and UV-Vis absorption spectrophotometry. The antiproliferative activities of AuNPs, 2-TU and 2-TU-AuNPs were examined by a 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) assay in the MDA-MB-231 breast cancer cell line. It was established that AuNPs significantly enhanced the antiproliferative activity of 2-TU. Furthermore, the irradiation of the samples with visible light at 520 nm decreased the half-maximal inhibitory concentration by a factor of 2. Thus, the 2-TU drug concentration and its side effect during treatments could be significantly reduced by synergistically exploiting the antiproliferative activity of 2-TU loaded onto AuNPs and the PTT effect of AuNPs.

Violuric acid carbon dots as a highly fluorescence probe for ultrasensitive determination of Zn (II) in tomato paste

Zinc is an essential metal since it plays an important role in biological systems, therefore, determination of zinc in food samples is important. Violuric acid was used to prepare highly fluorescent carbon dots (CDs), when it irradiated with ultraviolet radiation at 365 nm, a strong violet fluorescence was observed which caused by the increased amount of nitrogen in the CD structure, which were then successfully used for sensing zinc ion based on quenching of fluorescence. Violuric acid's hydrothermal carbonization reaction's temperature and time were simply optimized for better-quality performance of the CDs as-synthesized. The probe was characterized by HRTEM, SEM, XRD, EDX, fluorescence, UV–Visible absorption spectrophotometry, and FTIR. With a lower LOD 0.32 nM, the developed approach demonstrates an exceptional sensitivity and good selective response to the Zn2+ at 25℃. Compared to the results from ICP, the sensor was successfully used for determination of Zn2+ ions in tomato paste samples.

Metallo-β-lactamases immobilized by magnetic zeolitic imidazolate frameworks-8 for degradation of β-lactam antibiotics in an aqueous environment.

Residual antibiotics in nature are an important cause of antimicrobial drug resistance, and how to deal with residual β-lactam antibiotics in aqueous environments has become an urgent issue. In this work, magnetic zeolitic imidazolate frameworks-8 (ZIF-8) for immobilizing metallo-β-lactamases (MBLs), or Fe3O4@ZIF-8@MBLs, were successfully synthesized using the one-pot method in aqueous solution. The morphology and chemical structure of Fe3O4@ZIF-8@MBLs were characterized by scanning electron microscopy, energy dispersive spectra, X-ray diffraction, infrared spectra, physical adsorption, and zeta potential. Further, the degradation performance of Fe3O4@ZIF-8@MBLs for β-lactam antibiotics (penicillin G, cefoperazone, meropenem) in an aqueous environment was investigated by UV-visible absorption spectrophotometry. The results indicated that Fe3O4@ZIF-8@MBLs, compared to control ZIF-8, exhibited superior degradation ability, excellent reusability, and better stability under several harsh conditions. The strategy of combining ZIF-8 and MBLs to form magnetic porous polymers may be suitable for removing β-lactam antibiotics from an aqueous environment. This work provided an original insight into future studies on the degradation of β-lactam antibiotics employing MBLs immobilized by magnetic metal-organic frameworks.

Synthesis and Characterization of MWCNT-COOH/Fe3O4 and CNT-COOH/Fe3O4/NiO Nanocomposites: Assessment of Adsorption and Photocatalytic Performance.

In this study the adsorption and photodegradation capabilities of modified multi-walled carbon nanotubes (MWCNTs), using tartrazine as a model pollutant, is demonstrated. MWCNT-COOH/Fe3O4 and MWCNT-COOH/Fe3O4/NiO nanocomposites were prepared by precipitation of metal oxides in the presence of MWCNTs. Their properties were examined by X-ray diffraction in powder (XRD), Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectroscopy, synchrotron-based Scanning PhotoElectron Microscopy (SPEM), and Brunauer-Emmett-Teller (BET) analysis. It was found that the optimal adsorption conditions were pH 4 for MWCNT-COOH/Fe3O4 and pH 3 for MWCNT-COOH/Fe3O4/NiO, temperature 25 °C, adsorbent dose 1 g L−1, initial concentration of tartrazine 5 mg L−1 for MWCNT-COOH/Fe3O4 and 10 mg L−1 for MWCNT-COOH/Fe3O4/NiO and contact time 5 min for MWCNT-COOH/Fe3O4/NiO and 15 min for MWCNT-COOH/Fe3O4. Moreover, the predominant degradation process was elucidated simultaneously, with and without simulated sunlight irradiation, using thermal lens spectrometry (TLS) and UV–Vis absorption spectrophotometry. The results indicated the prevalence of the photodegradation mechanism over adsorption from the beginning of the degradation process.

Biosynthesis of Gold Nanoisotrops Using Carallia brachiata Leaf Extract and Their Catalytic Application in the Reduction of 4-Nitrophenol.

The past decade has observed a significant surge in efforts to discover biological systems for the fabrication of metal nanoparticles. Among these methods, plant-mediated synthesis has garnered sizeable attention due to its rapid, cost-effective, environmentally benign single-step procedure. This study explores a step-wise, room-temperature protocol for the synthesis of gold nanoparticles (AuNPs) using Carallia brachiata, a mangrove species from the west coast of Peninsular Malaysia. The effects of various reaction parameters, such as incubation time, metal ion concentration, amount of extract and pH, on the formation of stable colloids were monitored using UV-visible (UV-Vis) absorption spectrophotometry. Our findings revealed that the physicochemical properties of the AuNPs were significantly dependent on the pH. Changing the pH of the plant extract from acidic to basic appears to have resulted in a blue-shift in the main characteristic feature of the surface plasmon resonance (SPR) band, from 535 to 511 nm. The high-resolution-transmission electron microscopy (HR-TEM) and field emission scanning electron microscopy (FESEM) images revealed the morphologies of the AuNPs synthesized at the inherent pH, varying from isodiametric spheres to exotic polygons and prisms, with sizes ranging from 10 to 120 nm. Contrarily, an optimum pH of 10 generated primarily spherical-shaped AuNPs with narrower size distribution (8–13 nm). The X-ray diffraction (XRD) analysis verified the formation of AuNPs as the diffraction patterns matched well with the standard value of a face-centered cubic (FCC) Au lattice structure. The Fourier-transform infrared (FTIR) spectra suggested that different functional groups are involved in the biosynthetic process, while the phytochemical test revealed a clear role of the phenolic compounds. The reduction of 4-nitrophenol (4-NP) was selected as the model reaction for evaluating the catalytic performance of the green-synthesized AuNPs. The catalytic activity of the small, isotropic AuNPs prepared using basic aqueous extract was more effective than the nanoanisotrops, with more than 90% of 4-NP conversion achieved in under an hour with just 3 mg of the nanocatalyst.

Black phosphorus quantum dots as photocatalyst for dye degradation with a high efficiency and rate constant

A metal-free nanocatalyst was proposed to be applied in the photocatalysis of dye degradation based on black phosphorus quantum dots (BPQDs). BPQDs were prepared by a liquid exfoliation combined with solvothermal method. BPQDs show excellent catalytic performance with higher photocatalytic efficiency and shorter degradation time than those for most of previous works. The morphological, structural, and optical properties and functional groups for BPQDs were characterized by numerous techniques. They are transmission electron microscope (TEM), X-ray diffraction (XRD), Raman, fluorescence and UV–vis absorption spectrophotometry, respectively. To investigate the photocatalytic activity of BPQDs, indigo carmine (IC) was employed as a model dye. The decolorization efficiency of IC can get to 98.22% in the sun. Furthermore, the degradation time is 23 min in the sun, which is shorter than other reports. The degradation rate constant is 0.214 min−1 which is about 10 times higher than most of previous works. More importantly, the species after degradation were confirmed by mass spectrum, which own much lower carbon content than IC. The present BPQDs as nanocatalysts may be explored to degrade more organic molecules in environmental wastewater.

Analysis of Agmatine by UV-Visible Absorption Spectrophotometry and Detailed Interference Study on Biogenic Amines and Salts: Grape Application

The aim of this work is to develop a new method for the analysis of agmatine from UV-Visible absorption spectra. The optimization of the analytical parameters shows that the stoichiometry of the orthophthalaldehyde-agmatine complex is 1:1, the optimal pH is equal to 11 and the stability time is about 10 minutes. The analytical performances obtained are satisfactory with very low limit of detection (LOD) and limit of quantification (LOQ) respectively equal to 0.121 µg/mL and 0.405 µg/mL. The relative standard deviation (RSD) obtained of 2.1% shows the good reproducibility of the measurements. Interference effects show that the aromatic biogenic amines interfere less than linear ones, excepted serotonine. Similarly, a more marked interference is found for chloride salts. Finally, a recovery rate of between 99.4% and 111.7% was found in the grape extract studied, showing the effectiveness of the method.

A Highly Selective Economical Sensor for 4-Nitrophenol

Herein, an inexpensive commercially available sensor is presented for the detection of 4-nitrophenol (4NP) pollutant. Sodium fluorescein (NaFl) is used as a sensor to detect trace amounts of 4NP in acetonitrile (MeCN). The photophysical properties of NaFl were studied in two different solvents, MeCN (aprotic) and water (protic), with varying concentrations of different nitroaromatics using UV-visible absorption and fluorescence spectrophotometry. In an aqueous medium, photophysical properties of NaFl did not change in the presence of nitroaromatics. However, examination of the photodynamics in MeCN demonstrated that NaFl is extremely sensitive to 4NP (limit of detection: 0.29 µg/mL). This extreme specificity of NaFl towards 4NP when dissolved in MeCN, as compared to other nitroaromatics, is attributed to hydrogen bonding of 4NP with NaFl in the absence of water, resulting in both static and dynamic quenching processes. Thus, NaFl is demonstrated as a simple, inexpensive, sensitive, and robust optical turn off sensor for 4NP.

Boron- and nitrogen-doped graphene quantum dots with enhanced supercapacitance

Graphene quantum dots (GQDs) with their very large specific surface area and numerous edges can offer promising novel features as metal-free and inexpensive electrodes of supercapacitors. Here, we investigated the effect of boron and nitrogen doping in GQDs on their electrochemical energy storage properties. The GQDs as well as B-GQDs and N-GQDs were synthesized by a facile hydrothermal method and characterized by X-ray diffractometry, UV-Vis absorption spectrophotometry, transmission electron microscopy, and energy-dispersive X-ray mapping techniques. Electrochemical properties of the nanoparticles were investigated in a three-electrode setup using cyclic voltammetry and galvanostatic charge/discharge techniques in KOH electrolyte. The N-GQDs electrode showed the highest specific capacitance of 283 F/g at 1 A/g as compared to the GQDs and B-GQDs electrodes. The N-GQDs electrode exhibited the specific energy and specific power of 6.2 Wh/Kg and 108 W/Kg, respectively. The N-GQDs electrode showed also better cycling stability (80% capacity retention) than the GQDs and B-GQDs electrodes.

Comparative binding studies on the interaction of the indoloquinoline alkaloid cryptolepine with the B and the non-canonical protonated form of DNA: A spectroscopic insight

BackgroundLow pH induced nucleic acid polymorphism and the interaction of naturally occurring small molecules with different polymorphic forms of DNA have been the focus in developing new drugs. Recent studies have revealed that low pH plays an active role in growth and development of cancer cells. Our target is to find whether and how the indoloquinoline alkaloid cryptolepine (CRP) interact with different polymorphic forms of natural DNA, in hope to explore this group of alkaloids as new therapeutics. MethodsMultiple spectroscopic techniques that include UV–visible absorption spectrophotometry, fluorimetry, CD spectroscopy along with thermal melting studies were employed to characterize the interaction between the alkaloid cryptolepine with the B and protonated forms of DNA. Results & conclusionsCryptolepine has been found to interact with either forms of DNA. The nature of binding is non-cooperative in both cases. Data show that the affinity of CRP to B form of DNA is relatively higher than that for the protonated form of DNA. Circular dichroic studies reveal that the alkaloid converts the left handed protonated DNA into bound right handed form. Fluorescence quenching experiments reveal that cryptolepine intercalates within the DNA base pairs. Thermal melting studies show that the alkaloid stabilises the DNA structures. General significanceSuch non-B DNA structures are often present at the ‘mutation hotspots’ that are associated with genetic instability related diseases such as cancer. The ability of cryptolepine to interact to such non-B DNA structures makes it a useful substrate in the designing of potential chemotherapeutic agents.

Coordination Chemistry of a Bis(Tetrazine) Tweezer: A Case of Host-Guest Behavior with Silver Salts.

The carbon-carbon cross-coupling of phenyl s-tetrazine (Tz) units at their ortho-phenyl positions allows the formation of constrained bis(tetrazines) with original tweezer structures. In these compounds, the face-to-face positioning of the central tetrazine cores is reinforced by π-stacking of the electron-poor nitrogen-containing heteroaromatic moieties. The resulting tetra-aromatic structure can be used as a weak coordinating ligand with cationic silver. This coordination generates a set of bis(tetrazine)-silver(I) coordination complexes tolerating a large variety of counter anions of various geometries, namely, PF6−, BF4−, SbF6−, ClO4−, NTf2−, and OTf−. These compounds were characterized in the solid state by single-crystal X-ray diffraction (XRD) and diffuse reflectance spectroscopy, and in solution by 1H-NMR, mass spectrometry, electroanalysis, and UV-visible absorption spectrophotometry. The X-ray crystal structure of complexes {[Ag(3)][PF6]}∞ (4) and {[Ag(3)][SbF6]}∞ (6), where 3 is 3,3′-[(1,1′-biphenyl)-2,2′-diyl]-6,6′-bis(phenyl)-1,2,4,5-tetrazine, revealed the formation of 1D polymeric chains, characterized by an evolution to a large opening of the original tweezer and a coordination of silver(I) via two chelating nitrogen atom and some C=C π-interactions. Electrochemical and UV spectroscopic properties of the original tweezer and of the corresponding silver complexes are reported and compared. 1H-NMR titrations with AgNTf2 allowed the determination of the stoichiometry and apparent stability of two solution species, namely [Ag(3)]+ and [Ag(3)2]2+, that formed in CDCl3/CD3OD 2:1 v/v mixtures.