Circular Dichroism Spectroscopic Methods Research Articles

A New Concept of Enhancing the Anticancer Activity of Manganese Terpyridine Complex by Oxygen-Containing Substituent Modification.

Eleven manganese 4'-substituted-2,2':6',2″-terpyridine complexes (1a-1c and 2a-2h) with three non-oxygen-containing substituents (L1a-L1c: phenyl, naphthalen-2-yl and naphthalen-1-yl, L1a-L1c) and eight oxygen-containing substituents (L2a-L2h: 4-hydroxyl-phenyl, 3-hydroxyl-phenyl, 2-hydroxyl-phenyl, 4-methoxyl-phenyl, 4-carboxyl-phenyl, 4-(methylsulfonyl)phenyl, 4-nitrophenyl and furan-2-yl) were prepared and characterized by IR, elemental analysis or single crystal X-ray diffraction. In vitro data demonstrate that all of these show higher antiproliferative activities than cisplatin against five human carcinoma cell lines: A549, Bel-7402, Eca-109, HeLa and MCF-7. Compound 2d presents the strongest antiproliferative effect against A549 and HeLa cells, with IC50 values being 0.281 μM and 0.356 μM, respectively. The lowest IC50 values against Bel-7402 (0.523 μM) Eca-109 (0.514 μM) and MCF-7 (0.356 μM) were obtained for compounds 2h, 2g and 2c, respectively. Compound 2g with a nitro group showed the best results on the whole, with relevantly low IC50 values against all the tested tumor cells. The DNA interactions with these compounds were studied by circular dichroism spectroscopic and molecular modeling methods. Spectrophotometric results revealed that the compounds have strong affinities in binding with DNA as intercalators, and the binding induces DNA conformational transition. Molecular docking studies indicate that the binding is contributed by the π-π stacking and hydrogen bonds. The anticancer activities of the compounds are correlated with their DNA binding ability, and the modification of oxygen-containing substituents significantly enhanced the anticancer activity, which could provide a new rationale for the future design of terpyridine-based metal complexes with antitumor potential.

A Novel Azaphilone Muyophilone A From the Endophytic Fungus Muyocopron laterale 0307-2.

Two known azaphilone derivatives, 4,6-dimethylcurvulinic acid (1) and austdiol (2), and their novel heterotrimer, muyophilone A (3), were isolated and identified from an endophytic fungus, Muyocopron laterale 0307-2. Their structures and stereochemistry were established by extensive spectroscopic analyses including HRMS, NMR spectroscopy, electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) spectroscopic methods, as well as single crystal X-ray diffraction. In the structure of 3, two compound 2-derived azaphilone units were connected through an unprecedented five-membered carbon bridge which was proposed to be originated from compound 1. Compound 3 represents the first example of azaphilone heterotrimers.

Circular dichroism spectroscopy and chiral sensing in optical fibers.

Chirality is a property of broken mirror symmetry and detecting the handedness of chiral material in small quantities is an important problem in biology and biochemistry. Here, we present a waveguide-based method to measure chirality and distinguish the enantiomers of molecules. A bi-isotropic core in an optical waveguide lifts the degeneracy of modes in a cylindrically symmetric structure. This modal degeneracy lifting is exploited to measure the chirality of the core. The proposed sensor can determine the value of the chirality parameter of the material under test and it can be utilized for various materials with nonzero chirality parameter in different frequency bands. This approach improves the circular dichroism (CD) response and outperforms conventional CD spectroscopy methods by increasing their differential output signal. To compare the results with conventional CD spectroscopy, the CD parameter is adapted to optical waveguides.

Characterization of the binding between anti-tumor drug 5-fluorouracil and human alpha-2-macroglobulin: spectroscopic and molecular docking analyses

5-Fluorouracil (5-FU) is a well-recognized anticancer drug used in the treatment of tumors of head, neck and breast. Drug pharmacokinetics is affected upon binding with protein, thus, making drug–protein interactions imperative to study. Present work investigates the interaction between 5-FU and human major antiproteinase-alpha-2-macroglobulin (α2M) by multi-spectroscopic, calorimetric and molecular docking techniques. UV/Visible absorption, intrinsic fluorescence and circular dichroism (CD) spectroscopic methods have been employed to unveil the mode and mechanism of 5-FU-α2M interaction. Synchronous fluorescence showed alteration in the microenvironment of tryptophan and tyrosine residues of protein. Far UV-CD spectra suggest slight alterations in the secondary structure of α2M by 5-FU. Thermodynamic parameters determined by fluorescence quenching experiments and isothermal titration calorimetry (ITC) suggested the involvement of hydrogen bonds and hydrophobic interactions. Moreover, ITC corroborate the spontaneous and exothermic nature of the interaction process. Molecular docking illustrates that 5-FU binds with moderate affinity and Asp953, Tyr1264, Lys1236, Thr1232, Tyr1323 and Leu951 were the main residues involved. Molecular dynamics simulation studies suggested that 5-FU was stabilizing the α2M structure and forming a stable complex. It was concluded that 5-FU lower the antiproteolytic activity of α2M significantly and causes disruption in the native structure and conformation of α2M. Communicated by Ramaswamy H. Sarma

An electronic circular dichroism spectroscopy method for the quantification of L- and D-amino acids in enantiomeric mixtures.

Rapid quantitative analysis of single chiral amino acid (aa) was achieved using circular dichroism (CD) with data analysis by standard calibration curve. The absolute concentrations of D- and L-aas in enantiomeric mixtures were determined by CD and achiral liquid chromatography (LC) method. It is worth noting that CD and LC were used independently, not online LC/CD in this study. The errors of the experimental results were less than 10%. The method is also applicable to the quantification of non-aa chiral molecules, such as chiral nucleoside and chiral quinine. With this study, we provide a new method for the chiral quantitative analysis of enantiomeric aas mixtures.

An investigation of the effect of PVP-coated silver nanoparticles on the interaction between clonazepam and bovine serum albumin based on molecular dynamics simulations and molecular docking

Owing to the extensive application of silver nanoparticles (AgNPs) in medicine, the influence of AgNPs on the binding of clonazepam to bovine serum albumin (BSA) has been studied using ultraviolet-visible (UV–Vis), fluorescence, and circular dichroism (CD) spectroscopic methods. Detailed insights into the binding sites of clonazepam on the PVP-AgNP surface in the absence and presence of BSA have been obtained by carrying out molecular dynamics (MD) simulations and molecular docking analysis. UV–Vis results show that the interaction between BSA and AgNPs causes formation of BSA-AgNP complexes. CD studies imply that the formation of BSA-AgNP complexes is accompanied by conformational changes in the secondary structural level of the protein. The intrinsic fluorescence of BSA solution in the simultaneous presence of AgNPs and clonazepam shows that clonazepam interacts considerably more with BSA-AgNP complexes than with BSA. MD simulations results show that clonazepam molecules bind more to the PVP polymer film than to the bare Ag (0) atoms on the PVP-AgNP surface. Molecular docking analysis shows a binding affinity of −19.77 kJ/mol for BSA-AgNP complexes. Also, the results show that, although the IIA and IIIA domains in BSA play an important role in the docking of clonazepam with BSA, in BSA-AgNP complexes, clonazepam molecules bind to the bare Ag(0) atoms, and there is also the possibility of interaction between PVP and BSA via clonazepam.

Comprehensive insight into the molecular interaction of an anticancer drug-ifosfamide with human alpha-2-macroglobulin: biophysical and in silico studies

Ifosfamide is an active alkylating chemotherapeutic drug chemically related to nitrogen mustard. The pharmacokinetics of drugs is affected upon binding with protein, making the studies on drug-protein interaction promising. The present study investigates the interaction between ifosfamide and human antiproteinase-alpha-2-macroglobulin (α2M) by using multi-spectroscopic and in silico techniques. The UV-visible absorption, intrinsic fluorescence and circular dichroism (CD) spectroscopic methods were employed to unveil the mode and mechanism of ifosfamide–α2M interaction. Fluorescence quenching studies performed at three different temperatures indicated that ifosfamide–α2M complex formation involves static quenching. Far UV-CD spectra revealed a minor alteration in the secondary structure of α2M instigated by ifosfamide. The thermodynamic parameters determined by fluorescence quenching experiment and isothermal titration calorimetry (ITC) suggested that the complex between ifosfamide and α2M involves hydrogen bonding and hydrophobic interactions. Molecular docking illustrates that ifosfamide binds with moderate affinity to Lys1240, Asn173, Ser957, Leu955, Asp953, Lys1216 and Thr1236 residues during the interaction. Molecular dynamic (MD) simulation suggested that the ifosfamide forms a stable complex with α2M. Communicated by Ramaswamy H. Sarma

Positional Isomers of Isocyanoazulenes as Axial Ligands Coordinated to Ruthenium(II) Tetraphenylporphyrin: Fine-Tuning Redox and Optical Profiles.

Two isomeric ruthenium(II)/5,10,15,20-tetraphenylporphyrin complexes featuring axially coordinated redox-active, low-optical gap 2- or 6-isocyanoazulene ligands have been isolated and characterized by NMR, UV-vis, and magnetic circular dichroism (MCD) spectroscopic methods, high-resolution mass spectrometry, and single-crystal X-ray crystallography. The UV-vis and MCD spectra support the presence of the low-energy, azulene-centered transitions in the Q band region of the porphyrin chromophore. The first coordination sphere in new L2RuTPP complexes reflects compressed tetragonal geometry. The redox properties of the new compounds were assessed by electrochemical and spectroelectrochemical means and correlated with the electronic structures predicted by density functional theory and CASSCF calculations. Both experimental and theoretical data are consistent with the first two reduction processes involving the axial azulenic ligands, whereas the oxidation profile (in the direction of increasing potential) is exerted by the ruthenium ion, the porphyrin core, and the axial azulenic moieties.

Identification of Two New Phenanthrenes from Dendrobii Herba and Their Cytotoxicity towards Human Hypopharynx Squamous Carcinoma Cell (FaDu).

Two new phenanthrenes, (1R,2R)-1,7-hydroxy-2,8-methoxy-2,3-dihydrophenanthrene-4(1H)-one (1) and 2,7-dihydroxy-phenanthrene-1,4-dione (2), were isolated from the ethyl acetate-soluble fraction of Dendrobii Herba, together with seven known phenanthrenes (3–9), two bibenzyls (10–12), and a lignan (13). Structures of 1 and 2 were elucidated by analyzing one-dimensional (1D) and two-dimensional (2D)-NMR and High-resolution electrospray ionization mass spectra (HR-ESI-MS) data. The absolute configuration of compound 1 was confirmed by the circular dichroism (CD) spectroscopic method. In cytotoxicity assay using FaDu human hypopharynx squamous carcinoma cell line, compounds 3–6, 8, 10, and 12 showed activities, with IC50 values that ranged from 2.55 to 17.70 μM.

Circular Dichroism Spectroscopy: A Facile Approach for Quantitative Analysis of Captopril and Study of Its Degradation.

Simple and selective zero- and second-order derivative circular dichroism (CD) spectroscopic methods have been designed for the assay of captopril in commercially available dosage forms. A normal CD spectroscopic scan (zero order) exhibits a negative band at 208 nm (method A) in distilled water. The calibration curve shows a linear response over the concentration range of 10–80 μg mL–1. The second-order derivative (D2) CD spectrum shows one positive band at 208 nm (method B) and one negative band at 225 nm (method C). Linear calibration curves were obtained in the concentration range of 10–70 μg mL–1 for both the methods (B and C). The detection limits were found to be 1.26, 1.48, and 2.38 μg mL–1 for methods A, B, and C, respectively. The study under stressed acidic, basic, and oxidative conditions showed the degradation of captopril. The proposed methods were validated as per ICH guidelines. All the proposed methods were compared with the reference method to demonstrate its suitability for quality control of captopril in its dosage forms.

Eu3+ as a luminescence probe in DNA studies: Structural and conformational implications.

Lanthanide ions are widely used as luminescent probes for structural studies of various biomolecules, including DNA. Latest developments of circularly polarized luminescence (CPL) methodology further boosted interest to luminescence techniques. However, an effect of the lanthanide probes themselves on the DNA structure and conformation was investigated only partially and not for all lanthanides. In the present work, we performed a detailed spectroscopic study of Eu3+ complexes with native double-stranded DNA and compared them to the relevant complexes with single-stranded DNA. We employed infrared (IR), vibrational circular dichroism (VCD) and electronic circular dichroism (ECD) spectroscopic methods to investigate Eu3+ effect on DNA structure and conformational transitions. It was shown that Eu3+ ions can induce significant alteration of the native DNA structure at the concentrations often used in luminescence studies. While no DNA denaturation was observed at these metal ion concentrations, significant unstacking of the base pairs and disordering of the sugar-phosphate backbone, partial appearance of the A-form backbone geometry, and DNA transition into condensed ψ-type form took place. Eu3+ binding to single-stranded DNA was more pronounced than the binding to double-stranded DNA. We detected the main Eu3+ binding sites and determined the metal ion concentration range in which DNA geometry remains largely unaltered. The results obtained in the current study could be used for tuning the luminescence and CPL structural studies of DNA utilizing Eu3+ ions as probes.

Folding Dynamics of Parallel and Antiparallel G-Triplexes under the Influence of Proximal DNA.

The G-triplex is a kind of DNA structure formed by G-rich sequences. Previous studies have shown that it is an intermediate for the folding of G-quadruplex and has an antiparallel structure. The folding dynamics of this G-triplex structure, however, have not been well studied until now. In addition, whether a parallel G-triplex structure exists, remains unknown. In this study, by using single-molecule fluorescence resonance energy transfer and circular dichroism spectroscopy methods, we have studied the folding dynamics of the G-triplex and revealed at the single-molecule level, for the first time, that G-triplexes have both parallel and antiparallel structures. Moreover, we have investigated the effects of proximal DNA on G-triplex folding. We have found that both single-stranded TTA and double-stranded DNA at either end of a G-triplex sequence can reduce its folding speed. More interestingly, when located at the 5' end of a G-triplex sequence, the proximal DNA will favor the folding of parallel over antiparallel G-triplex structures. As G-triplex is an intermediate for G-quadruplex folding, the present results may also shed new light on the folding properties of G-quadruplex structures, in terms of dynamics, stability, and the effects of proximal DNA.

Probing the stereoselective interaction of ofloxacin enantiomers with corresponding monoclonal antibodies by multiple spectrometry

Although stereoselective antibody has immense potential in chiral compounds detection and separation, the interaction traits between stereoselective antibody and the corresponding antigenic enantiomers are not yet fully exploited. In this study, the stereospecific interactions between ofloxacin isomers and corresponding monoclonal antibodies (McAb-WR1 and McAb-MS1) were investigated using time-resolved fluorescence, steady-state fluorescence, and circular dichroism (CD) spectroscopic methods. The chiral recognition discrepancies of antibodies with ofloxacin isomers were reflected through binding constant, number of binding sites, driving forces and conformational changes. The major interacting forces of McAb-WR1 and McAb-MS1 chiral interaction systems were hydrophobic force and van der Waals forces joined up with hydrogen bonds, respectively. Synchronous fluorescence spectra and CD spectra results showed that the disturbing of tyrosine and tryptophan micro-environments were so slightly that no obvious secondary structure changes were found during the chiral hapten binding. Clarification of stereospecific interaction of antibody will facilitate the application of immunoassay to analyze chiral contaminants in food and other areas.

Discrete SeNPs-Macromolecule Binding Manipulated by Hydrophilic Interaction

Nanoparticle-protein conjugates are promising probes for biological diagnostics and versatile building blocks for nanotechnology. Here we demonstrate the interaction of SeNPs with BSA macromolecule simply by physical adsorption method. The interaction between SeNPs and BSA has been investigated by UV−Vis, fluorescence, circular dichroism (CD) spectroscopic and thermal methods. The esterase-like activity of BSA towards PNPA was investigated in the presence of SeNPs. The effects of SeNPs on the stability and conformational changes of BSA were studied, which indicated that the binding of SeNPs with BSA induced relative changes in secondary structure of protein. SeNPs acted as a structure stabilizer for BSA which was further confirmed by thermal denaturation study. The hydrophilic bonding forces played important roles in the BSA-SeNPs complex formation. The putative binding site of SeNPs on BSA was near to Sudlow’s site II. The hydrophilic interaction of SeNPs on the stability and structure of BSA would find promising application in drug delivery system.

Hitoyol A and B, Two Norsesquiterpenoids from the Basidiomycete Coprinopsis cinerea.

Hitoyol A (1), an unprecedented norsesquiterpenoid with an exo-tricyclo[5.2.1.02,6]decane skeleton, was isolated from the culture broth of Basidiomycete Coprinopsis cinerea along with a novel skeletal hitoyol B (2) containing 4-cyclopentene-1,3-dione. Their structures and absolute configurations were analyzed by single-crystal X-ray diffraction and electronic circular dichroism spectroscopic methods. Compound 1 is possibly biosynthesized through decarboxylation-induced cyclization of lagopodin B, a known cuparene-type sesquiterpenoid. Compound 2 showed weak antimalarial activity with an IC50 of 59 μM.

Experimental and theoretical studies of interaction of aliphatic chain α-aminobisphosphonates with DNA

Abstract The interaction of DNA with four aliphatic chain α-aminobisphosphonate were investigated in a tris–hydrogen chloride buffer (pH 7.4) in the presence and absence of spectroscopic probes (Neutral Red dye (NR) and Hoechest (Ho)) by fluorescence, UV–Vis absorption and circular dichroism (CD) spectroscopic methods, electrochemical techniques and viscometry. The spectroscopic and voltammetric studies showed that the groove binding mode of interaction is predominant in the solution containing DNA and α-aminobisphosphonates. Furthermore, the results indicated that the binding strength of the DNA–α-aminobisphosphonate complexes are dependent on alkyl moiety presented in the structure of α-aminoalkylphosphonic acids A1–A4. The principal component analysis (PCA) and theoretical quantum mechanical and molecular mechanics (QM-DFT/B3LYP/6-31+G* and MM-SYBYL) methods were also applied to determine the number of chemical components presented in complexation equilibrium and identify the structure complexes of DNA with α-aminobisphosphonates, respectively.

Glutathione binding to dirhodium tetraacetate: a spectroscopic, mass spectral and computational study of an anti-tumour compound.

Glutathione (γ-l-glutamyl-l-cysteinyl-glycine) is a ubiquitous tripeptide found in all plants and animals. Glutathione has key roles as a metallochaperone and as a cellular thiol involved in metabolism. Little is known about how glutathione interacts with organometallic compounds in vivo. Here, we report the reactions of glutathione in vitro with dirhodium(ii) tetraacetate (tetrakis(μ-acetato)dirhodium(ii), Rh2(OAc)4), a compound with anti-tumour properties. Electrospray ionization mass spectrometry, UV-Visible absorption and circular dichroism spectroscopic methods were used to determine the stoichiometries and optical properties of the final conjugate. Computational analyses were used to predict the binding modes of glutathione to the Rh2(OAc)4, and report on the orbital assignments for the resulting products. We explored the competition by GSH for methionine-bound axial sites on Rh2(OAc)4 to investigate the use of weak thioether to protect its cellular-based anti-cancer activity. Our study highlights the important role that axial ligation would play in deactivating or significantly decreasing the efficacy of this bimetallic anti-tumor drug. The computational data explain the stability of the mono-adduct and the appearance of new absorption bands in the UV region including retention of the Rh-Rh single bond. Additionally, these data show that glutathione can effectively disable the potency of these metallo-drugs through orbital overlap of the entire Rh-Rh core as a result of the strong binding. Electronic absorption spectroscopy, mass spectrometry and computational analysis are a powerful combination in understanding possible chemical reactions in vivo and this information can be used to synthetically tune dirhodium complexes for use in the fight against cancer.

Cytotoxic Homoisoflavonoids from Ophiopogon japonicus Tubers.

A phytochemical fractionation of a methanol extract of Ophiopogon japonicus tubers led to the isolation of a new homoisoflavanone, homoisopogon A (1), and three new homoisoflavanes, homoisopogon B-D (2-4). Their chemical structures were elucidated by mass, NMR, and circular dichroism (CD) spectroscopic methods. Homoisopogon A (1) exhibited potent cytotoxicity against human lung adenocarcinoma LU-1, human epidermoid carcinoma KB, and human melanoma SK-Mel-2 cancer cells with IC50 values ranging from 0.51 to 0.66 µM.

Green synthesis of silver nanoparticles using Pongamia pinnata seed: Characterization, antibacterial property, and spectroscopic investigation of interaction with human serum albumin

In recent years, green synthesized nanoparticles from plant extract have drawn a great interest due to their prospective nanomedicinal application. This study investigates a proficient, safer, and sustainable way for the preparation of AgNPs using medicinal plant Pongamia pinnata (family: Leguminoseae, species: Pinnata) seeds extract without using any external reducing and stabilizing agent. Both ultraviolet-visible spectrum at λmax =439nm and energy dispersive X-ray spectra proof the formation of AgNPs. An average diameter of the AgNPs was 16.4nm as revealed from transmission electron microscope. Hydrodynamic size (d=~19.6nm) was determined by dynamic light scattering (DLS). Zeta potential of AgNPs was found to be -23.7mV, which supports its dispersion and stability. Fourier transform infrared study revealed that the O─H, C═O, and C-O-C groups were responsible for the formation of AgNPs. The antibacterial activity of the synthesized AgNPs was checked against Escherichia coli ATCC 25922. AgNPs at its LD50 dose exhibited synergistic effect with ampicillin. Because protein-AgNPs association greatly affects its adsorption, distribution, and functionality and can also influence the functions of biomolecules. So in order to understand the adsorption and bioavailability, we investigated by fluorescence, ultraviolet-visible, and circular dichroism spectroscopic methods the interaction of synthesized AgNPs toward human serum albumin. The binding affinity and binding sites of human serum albumin toward AgNPs were measured by using the fluorescence quenching data. The circular dichroism spectroscopic results revealed that there was a negligible change of α-helical content in their native structure. Overall, these AgNPs show versatile biological activities and may be applied in the field of nanomedicine.

Interaction of polyethyleneimine-anchored copper(II) complexes with tRNA studied by spectroscopy methods and biological activities.

Ultraviolet-visible, emission and circular dichroism spectroscopic methods were used in transfer RNA (tRNA) interaction studies performed for polyethyleneimine-copper(II) complexes [Cu(phen)(l-Tyr)BPEI]ClO4 (where phen =1,10-phenanthroline, l-Tyr=l-tyrosine and BPEI = branched polyethyleneimine) with various degrees of coordination (x=0.059, 0.149, 0.182) in the polymer chain. The results indicated that polyethyleneimine-copper(II) complexes bind with tRNA mostly through surface binding, although other binding modes, such as hydrogen bonding and van der Waals interactions, might also be present. Dye-exclusion, sulforhodamine B and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays of a polyethyleneimine-copper(II) complex with a higher degree of coordination against different cancer cell lines proved that the complex exhibited cytotoxic specificity and a significant cancer cell inhibition rate. Antimicrobial screening showed activity against some human pathogens.