Physicochemical, in-vitro therapeutic activity and biomolecular interaction studies of Mn(II), Ni(II) and Cu(II) complexes tethered with O2N2 ligand backbone

Two major health crisis of today's world are antimicrobial drug resistance and type II diabetes. To tackle them, there is an immediate requirement for the development of new and safer drugs and the present work is one such quest for novel and efficient drug candidates. We have developed three trace metal coordination compounds tethered with a reduced salen ligand {H₂(hpdbal)₂-an} (L), namely, a manganese-salan complex, [Mn^II(H₂O)₂{(hpdbal)₂-an}] (1), a nickel-salan complex, [Ni^II{(hpdbal)₂-an}] (2) and a copper-salan complex, [Cu^II{(hpdbal)₂-an}] (3). The compounds were characterized by elemental analysis, vibrational spectroscopy, electronic spectroscopy, thermogravimetric analysis, nuclear magnetic resonance and electron-paramagnetic resonance techniques. The compounds were evaluated for antimicrobial activity against seven pathogens (Escherichia coli, Klebsiella pneumonia, Acinetobacter baumannii, Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans and Cryptococcus neoformans) and antidiabetic activity by mimicking diabetic environment on the immortal human liver cancer cells, HepG2. Complexes 1 and 2 were additionally tested for their reactivity and stability in biological media mimic conditions. The nickel(II) salan complex (2) exhibited noteworthy antifungal activity against Candida albicans and the manganese(II) salan complex (1) induced increased glucose uptake by the insulin resistant cells. Both compounds were found to be stable when solution pH conditions were varied from 3 to 9. They exhibited strong affinity of binding towards a carrier protein, bovine serum albumin which was evaluated with the aid of multi-spectroscopic techniques.

Near-infrared spectroscopy as a potential non-invasive tool in the assessment of disease activity in vitiligo patients

Vitiligo is a common chronic depigmenting skin disease. We explored the utility of near-infrared (NIR) spectroscopy in the identification of spectral changes associated with disease activity in vitiligo patients. In vivo spectral measurements were performed directly on the perilesional skin of 70 vitiligo patients. Relative intensities (second derivative) at 1139, 1344, 1646 and 1839 nm appeared to be significantly lower in the perilesional region of patients with active vitiligo compared with stable disease, while the intensity at 1884 nm seemed to be significantly higher. A classification model based on the spectral ranges around those peaks generated a correct prediction in 82.9% of the cases. In conclusion, we can state that NIR spectroscopy could have potential in the assessment of disease activity. However, large-scale prospective studies are necessary to confirm our preliminary results.

Potent drug candidature of an ONS donor tethered copper (II) complex: Anticancer activity, cytotoxicity and spectroscopically approached BSA binding studies

In our continued efforts to develop metal based therapeutic agents, we have synthesized a novel copper(II) complex, [{Cu(hpdbal-sbdt)}₂] (2) tethered with a biocompatible ONS^2- donor backbone [H₂hpdbal-sbdt] (1) [H₂hpdbal-sbdt is a tridentate ligand derived from S-benzyldithiocarbazate (Hsbdt) and 2-hydroxy-5-(phenyldiazenyl)benzaldehyde (Hhpdbal)]. The metal complex (2) was characterized using attenuated total reflection-infrared (ATR-IR) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, thermogravimetry and differential scanning calorimetric (TG-DSC) analysis, field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS) and elemental (CHNS) analysis. The antineoplastic ability of copper complex was evaluated in vitro against human cervical cancer (HeLa) cells. MTT assay results showed that the copper complex exhibited significant growth inhibition of HeLa cells with an IC₅₀ value of 4.46 μM and this value was compared with reported standards. Cytotoxicity of the copper complex towards human embryonic kidney cells (HEK-293) was also evaluated. The potentially active copper complex was studied for its solution state stability at a pH range of 3-9. Following this, the interactive behaviour of the bioactive copper complex with a drug transporter protein (BSA) was deciphered through multi-spectrosopic investigations like steady-state fluorescence, three-dimensional fluorescence, deconvoluted-IR and UV-Visible techniques.

In vitro apoptosis-induction, antiproliferative and BSA binding studies of a oxidovanadium(V) complex

In our ongoing efforts to develop novel trace metal complexes with therapeutically interesting properties, a neutral mono nuclear oxidomethoxidovanadium(V) complex, [V^VO(OCH₃)(hpdbal-sbdt)] (1) and a μ-O bridged dinuclear oxidovanadium(V) complex, [{V^VO(hpdbal-sbdt)}₂μ-O] (2) [H₂hpdbal-sbdt (I) is a tridentate and dibasic ONS^2- donor ligand obtained through the Schiff base reaction of 2-hydroxy-5-(phenyldiazenyl)benzaldehyde (Hhpdbal) and S-benzyldithiocarbazate (Hsbdt)] have been synthesized and characterized by various analytical techniques such as TGA, EDS, ATR-IR, UV-Vis, CV, ¹H NMR, ¹³C NMR and ⁵¹V NMR. Single-crystal X-ray diffraction analysis of 1 confirms the coordination of phenolate oxygen, imine nitrogen and thioenolate sulfur of the ligand to the vanadium center with a distorted tetragonal-pyramidal geometry. The compound 2 triggered apoptotic and reproductive death of the cancer cells in vitro with 76% and 62% growth inhibition of human breast adenocarcinoma (MCF-7) and human lung carcinoma cells (A549) respectively. The compound 2 was found to be sufficiently stable over a wide window of physiological pH. The complex 2 was studied further for its interaction with a drug carrier protein BSA with the aid of spectroscopic techniques viz. fluorescence, temperature controlled UV-vis and deconvoluted IR techniques.

A novel biocompatible NiII tethered moiety as a glucose uptake agent and a hit against methicillin-resistant Staphylococcus aureus

In the efforts to develop a biocompatible transition metal complex as a drug alike for some of the prevailing non-communicable diseases (NCDs) and communicable diseases (CDs), a novel binuclear Ni^II compound [{Ni^II(hpdbal-sbdt)}₂] (2) has been synthesized by the reaction of Ni(OAc)₂.4H₂O and H₂hpdbal-sbdt (1) [1 is a dibasic tridentate ONS^2- donor Schiff base ligand obtained by the condensation of 2-hydroxy-5-(phenyldiazenyl)benzaldehyde (Hhpdbal) and S-benzyldithiocarbazate (Hsbdt)]. Both ligand 1 and compound 2 were structurally characterized in the solid and solution state using various spectroscopic techniques like ATIR, ¹H NMR, ¹³C NMR, TGA, FESEM, EDS and CHNS analysis. The antidiabetic activity of H₂hpdbal-sbdt (1) and [{Ni^II(hpdbal-sbdt)}₂] (2) were assessed using 2-NBDG uptake assay. The assay results showed 85% and 95% of fluorescent glucose uptake by insulin resistant HePG2 cells treated with compounds 1 and 2 respectively. The 2-NBDG uptake by the cells treated with the compound 2 was observed to be comparable to the standard antidiabetic drug metformin. Compounds 1 and 2 were also tested against five bacterial and two fungi strains in order to evaluate pathogen killing activity. Compound 2 showed significant inhibitory action towards the methicillin-resistant Staphylococcus aureus (MRSA) strain with an MIC value of 2 μg/mL whereas the ligand 1 was found to be inactive. Furthermore, the interactive nature of compound 2 with a model serum carrier protein bovine serum albumin (BSA) was studied using a multi-spectroscopic approach which provided an insight into the nature and extent of binding, conformational changes and the quenching of amino acid residues of the protein.

A robust spectroscopic method for the determination of protein conformational composition - Application to the annealing of silk

The physical and mechanical properties of structural proteins such as silk fibroin can be modified by controlled conformational change, which is regularly monitored by Fourier transform infrared spectroscopy by peak fitting of the amide I band envelope. Although many variables affecting peak shape are well established, there is no fixed methodology to compare and follow secondary structural differences without significant operator input especially where low frequency spectral noise is a problem. The aim of this contribution is to establish a method for such analyses to be carried at high levels of autonomy to prevent subjective or erroneous fitting. A range of approaches was trialled with optimal peak parameters selected based on overall goodness of fit and reproducibility of fit of replicate sample spectra. The method was successfully tested against reference proteins having contrasting β content and the rationale for parameter selection is presented. Further, we applied this method to measure the effect of conformational change on the energy of the amide I band of silk fibroin during annealing. Energy changes were ca. 400 kJ mol^-1 of fibroin. To confirm that this energy change was a consequence of increased hydrogen bonding we used a Thioflavin T staining method typically used to identify β aggregate type structures in amyloid plaques. We propose that the approach described herein can aid in the development of silk based materials for biomedical applications where tuning of the physical and mechanical properties of the silk are needed to guarantee optimum activity.

STATEMENT OF SIGNIFICANCE

The physical and mechanical properties of proteins including silk fibroin can be modified by controlled structural change, which is regularly monitored by Fourier transform infrared spectroscopy (FTIR) by peak fitting of the amide I band. Currently there is no fixed methodology to compare and follow secondary structural differences without significant operator input leading to subjectivity and error. This contribution establishes a method for such analyses to be carried at high levels of autonomy applicable to a wide range of proteins and the conformational changes have been quantified as a single energy change output, which clearly shows the progression of the annealing process used. We propose that the approach can help in the development of silk based materials for biomedical applications where tuning of the physical and mechanical properties of the silk are needed to guarantee optimum activity.

Analysis of protein structure changes and quality regulation of surimi during gelation based on infrared spectroscopy and microscopic imaging

A developed Fourier transform infrared spectroscopy (FT-IR) was employed to investigate changes of protein conformation, which played significant roles in maintaining stable protein networks of white croaker surimi gel, exploring the relationship between protein conformation and surimi gel networks. Spectra of surimi and gels with different grades (A, AA, FA and SA) were analyzed by tri-step FT-IR method and peak-fitting of deconvolved and baseline corrected amide I bands (1600~1700 cm⁻¹). The result showed that α-helix was the main conformation of surimi proteins. During surimi gelation, α-helix of myosin partially transformed into β-sheet, β-turn and random coil structures. β-sheet and random coil structures were the main protein conformations maintaining the structure of surimi gel, of which β-sheet made the main contribution to gel strength. Scanning electron microscopy (SEM) result revealed that surimi gels had a fibrous and homogeneous network structure. Moreover, ordered interconnections between three-dimensional proteins networks of gels were inclined to emerge in higher grade surimi, in agreement with the gel strength results. It was demonstrated that the tri-step FT-IR spectroscopy combined with peak-fitting could be applicable for exploration of surimi protein conformation changes during gelation to deepen understanding of its effect on gel quality.

Insights into Biochemical Alteration in Cancer-Associated Fibroblasts by using Novel Correlative Spectroscopy

The microenvironment of a tumor changes chemically and morphologically during cancer progression. Cancer‐stimulated fibroblasts promote tumor growth, however, the mechanism of the transition to a cancer‐stimulated fibroblast remains elusive. Here, the multi‐modal spectroscopic methods Fourier transform infrared imaging (FTIRI), X‐ray absorption spectroscopy (XAS) and X‐ray fluorescence imaging (XFI) are used to characterize molecular and atomic alterations that occur in cancer‐stimulated fibroblasts. In addition to chemical changes in lipids (olefinic and acyl chain) and protein aggregation observed with FTIRI, a new infrared biomarker for oxidative stress in stimulated fibroblasts is reported. Oxidative stress is observed to cause lipid peroxidation, which leads to the appearance of a new band at 1721 cm⁻¹, assigned to 4‐hydroxynonenal. Complementary to FTIRI, XFI is well suited to determining atom concentrations and XAS can reveal the speciation of individual elements. XFI reveals increased concentrations of P, S, K, Ca within stimulated fibroblasts. Furthermore, XAS studies reveal alterations in the speciation of S and Ca in stimulated fibroblasts, which might provide insight into the mechanisms of cancer progression. Using XFI, not only is the concentration change of individual elements observed, but also the subcellular localization. This study demonstrates the wealth of biochemical information provided by a multi‐modal imaging approach and highlights new avenues for future research into the microenvironment of breast tumors.

Mid-infrared spectroscopy for protein analysis: potential and challenges

Mid-infrared (MIR) spectroscopy investigates the interaction of MIR photons with both organic and inorganic molecules via the excitation of vibrational and rotational modes, providing inherent molecular selectivity. In general, infrared (IR) spectroscopy is particularly sensitive to protein structure and structural changes via vibrational resonances originating from the polypeptide backbone or side chains; hence information on the secondary structure of proteins can be obtained in a label-free fashion. In this review, the challenges for IR spectroscopy for protein analysis are discussed as are the potential and limitations of different IR spectroscopic techniques enabling protein analysis. In particular, the amide I spectral range has been widely used to study protein secondary structure, conformational changes, protein aggregation, protein adsorption, and the formation of amyloid fibrils. In addition to representative examples of the potential of IR spectroscopy in various fields related to protein analysis, the potential of protein analysis taking advantage of miniaturized MIR systems, including waveguide-enhanced MIR sensors, is detailed.

Simultaneous Fitting of Absorption Spectra and Their Second Derivatives for an Improved Analysis of Protein Infrared Spectra

Infrared spectroscopy is a powerful tool in protein science due to its sensitivity to changes in secondary structure or conformation. In order to take advantage of the full power of infrared spectroscopy in structural studies of proteins, complex band contours, such as the amide I band, have to be decomposed into their main component bands, a process referred to as curve fitting. In this paper, we report on an improved curve fitting approach in which absorption spectra and second derivative spectra are fitted simultaneously. Our approach, which we name co-fitting, leads to a more reliable modelling of the experimental data because it uses more spectral information than the standard approach of fitting only the absorption spectrum. It also avoids that the fitting routine becomes trapped in local minima. We have tested the proposed approach using infrared absorption spectra of three mixed α/β proteins with different degrees of spectral overlap in the amide I region: ribonuclease A, pyruvate kinase, and aconitase.

The Melibiose Transporter of Escherichia coli: CRITICAL CONTRIBUTION OF LYS-377 TO THE STRUCTURAL ORGANIZATION OF THE INTERACTING SUBSTRATE BINDING SITES

We examine the role of Lys-377, the only charged residue in helix XI, on the functional mechanism of the Na(+)-sugar melibiose symporter from Escherichia coli. Intrinsic fluorescence, FRET, and Fourier transform infrared difference spectroscopy reveal that replacement of Lys-377 with either Cys, Val, Arg, or Asp disables both Na(+) and melibiose binding. On the other hand, molecular dynamics simulations extending up to 200-330 ns reveal that Lys-377 (helix XI) interacts with the anionic side chains of two of the three putative ligands for cation binding (Asp-55 and Asp-59 in helix II). When Asp-59 is protonated during the simulations, Lys-377 preferentially interacts with Asp-55. Interestingly, when a Na(+) ion is positioned in the Asp-55-Asp-59 environment, Asp-124 in helix IV (a residue essential for melibiose binding) reorients and approximates the Asp-55-Asp-59 pair, and all three acidic side chains act as Na(+) ligands. Under these conditions, the side chain of Lys-377 interacts with the carboxylic moiety of these three Asp residues. These data highlight the crucial role of the Lys-377 residue in the spatial organization of the Na(+) binding site. Finally, the analysis of the second-site revertants of K377C reveals that mutation of Ile-22 (in helix I) preserves Na(+) binding, whereas that of melibiose is largely abolished according to spectroscopic measurements. This amino acid is located in the border of the sugar-binding site and might participate in sugar binding through apolar interactions.

Effects of domains modification on the catalytic potential of chitinase from Pseudomonas aeruginosa

Chitinase, an important enzyme in chitin-degrading, have extensive biophysiological functions and immense potential applications. Here, a chitinase gene pachi was cloned from Pseudomonas aeruginosa and overexpressed in E. coli (DE3). The structural analysis showed that chitinase pachi consists of catalytic domain (CHC), chitin binding domain (CBD) and both of these are linked by connective domain (FN3). In this study, Pachi displayed optimal activity at temperature 65 °C and pH 6.5. To understand the structural and functional relationship of chitin-binding domain with catalytic domain, two mutants, CHA (without CBD) and CBD+FN3-pachi with additional CBD have been constructed. Though the results showed that the two mutants have similar characteristics with Pachi, it is interesting to note that the deficiency of CBD caused an increase in expression level as well as solubility of the CHA. Moreover, the catalytic efficiency of CHA was increased 1.26-fold and substrate affinity in the absence of CBD was decreased 1.85-fold. Thus, the improved solubility and activity of CHA by domain deficiency is an interesting pathway to study the relationship of structure and function of chitinase and support its potential use in commercial applications.