Fluorescence Spectral Measurements Research Articles

Multidimensional Fluorescence Spectroscopy of Wine Using Synchronous Excitation/Emission Matrices and Time-Resolved Fluorescence Interferometric Detection.

Wines are complex mixtures of chemical compounds with broad and overlapping absorption and emission spectral features in the UV and visible spectral regions, making them challenging to study with conventional optical spectroscopic techniques. Multidimensional fluorescence spectroscopies correlate fluorescence spectra with other degrees of freedom, and have proven useful for studying complex molecular systems, offering a pathway for the analysis of wines utilising their inherent fluorescence. Here we employ steady-state excitation emission matrix (EEM) and time- resolved fluorescence spectral measurements to investigate representative commercial white and red wine samples and a fluorescent "model" wine base. Combining these multidimensional measurement methods provides information on the emission characteristics of the components that wines contain. This investigation illustrates the potential for multidimensional fluorescence techniques as diagnostic tools for the wine industry.

Design and Synthesis of Xanthone Analogues Conjugated with Aza-aromatic Substituents as Promising G-Quadruplex Stabilizing Ligands and their Selective Cancer Cell Cytotoxic Action.

We have examined the stabilization of higher-order noncanonical G-quadruplex (G4) DNA structures formed by the G-rich sequences in the promoter region of oncogenes such as c-MYC, c-KIT, VEGF and BCl2 by newly synthesized, novel nitrogen-containing aromatics conjugated to xanthone moiety. Compounds with N-heterocyclic substituents such as pyridine (XNiso), benzimidazole (XBIm), quinoxaline (XQX) and fluorophore dansyl (XDan) showed greater effectiveness in stabilizing the G4 DNA as well as selective cytotoxicity for cancer cells (mainly A549) over normal cells both in terms of UV-Vis spectral titrations and cytotoxicity assay. Both fluorescence spectral titrimetric measurements and circular dichroism (CD) melting experiments further substantiated the G4 stabilization phenomenon by these small-molecular ligands. In addition, these compounds could induce the formation of parallel G4 structures in the absence of any added salt condition in Tris⋅HCl buffer at 25 °C. In a polymerase stop assay, the formation of stable G4 structures in the promoter of oncogenes and halting of DNA synthesis in the presence of the above-mentioned compounds was demonstrated by using oncogene promoter as the DNA synthesis template. Apoptosis-mediated cell death of the cancer cells was proved by Annexin V-PI dual staining assay and cell-cycle arrest occurred in the S phase of the cell cycles. The plausible mode of binding involves the stacking of the xanthone core on the G4 DNA plane with the possibility of interaction with the 5'-overhang as indicated by molecular dynamics simulation studies.

Spectrofluorometric and computational approaches for the interaction studies of aclonifen and bifenox with human serum albumin

Interaction of two broadly used herbicides, aclonifen (ACF) and bifenox (BIF) with the major transporter in human circulation, human serum albumin (HSA) were examined using fluorescence and absorption spectral measurements combined with in silico analyses. Assessment of the fluorescence and absorption spectral results affirmed the complexation between ACF/BIF and HSA. Increase in the KSV value with temperature characterized the ACF/BIF-induced quenching of the protein fluorescence as dynamic quenching. The moderate binding affinities (Kf = 1.74×104 – 1.95×106 M−1 for ACF–HSA complex; Kf = 2.00×103 – 1.02×106 M−1 for BIF–HSA complex) were pointed out between ACF/BIF and HSA, showing a relatively higher binding constant values with increasing temperatures. Quantitative evaluation of thermodynamic data (ΔS = +0.86 kJ mol−1 K−1 and ΔH = +225.43 kJ mol−1 for ACF–HSA complex; ΔS = +1.11 kJ mol−1 K−1 and ΔH = +304.63 kJ mol−1 for BIF–HSA complex) predicted the contribution of hydrophobic interactions in the ACF–HSA and BIF–HSA association processes, which were well supported by our molecular docking results. In silico analyses were made to acquire insight details into the ACF and BIF binding to HSA at the binding sites and suggested the locations of ACF and BIF binding sites as both subdomain IIA (site I) and subdomain IIIA (site II) of HSA, showing more preference toward site I.

Express method for chlorophyll concentration assessment

We propose this fluorescent express method for the assessment of the chlorophyll a concentration in seawater. The method is based on spectral fluorescence measurements obtained with excitation at different wavelengths. A relatively simple two-channel laser spectrometer is used for measurements. In this case, preliminary preparation of samples is not required. We estimated the errors of the method by comparison with the results of direct measurements of the chlorophyll a concentration. A large array of measurement data obtained in the seas of the North Atlantic and the Arctic was used for the analysis. The possibility of reducing errors in the transition from one-dimensional regression to multidimensional is shown. It has also been shown that the accuracy of the assessment is comparable to the fluorescent extraction methods for determining the chlorophyll a concentration: errors of 40–50% when using the general formula and 20–35% after post-cruise calibration.

A novel hydrazone-based fluorescent “off-on-off” probe for relay sensing of Ga3+ and PPi ions

A novel hydrazone-based fluorescent probe (E)-3-((2-(benzo[d]thiazol-2-yl)hydrazono)methyl)-4H-chromen-4-one (BTC) has been rationally designed and synthesized. BTC can subsequently detect Ga3+ and PPi ions through the absorption and emission off–on-off response with high specificity. Importantly, fluorescent probe BTC can well discriminate Ga3+ from Al3+ and In3+. The association constant (K) was calculated as 2.06 × 104M−1, and the limit of detection (LOD) was calculated as 4.88 × 10-2μM. Competitive binding studies also illustrated good results of the probe BTC towards Ga3+. Job's plot and HRMS results substantiated the 1:1 stoichiometry between BTC and Ga3+ ion. The interaction binding mode of BTC with Ga3+ was proposed by HRMS, 1H NMR spectral titration, UV–vis absorption and fluorescence spectral measurements. The combination of the restraint of the photo-induced electron transfer (PET) process and the chelation enhanced fluorescence (CHEF) process is responsible for the fluorescence enhancement of this probe. The in situ chelated BTC-Ga3+ could further monitor pyrophosphate ion (PPi) by demetallization process with quenching fluorescence emission. Additionally, the BTC and BTC-Ga3+ showed good cell permeability and could detect Ga3+ and PPi ions in onioninner epidermal cells, respectively.

Anthracene based selective Co (II) colorimetric and fluorescent sensor for cytotoxicity studies and real sample analysis

A novel and highly selective fluorescent optical sensor developed from 9-anthracene carboxaldehyde and 2-amino 5-nitro benzophenone (BPAI) was designed and synthesized by ultrasonication for rapid Co2+ detection in ethanol medium by charge transfer and CHEF (Chelation Enhanced Fluorescence) mechanism. The stoichiometry of the complexation was calculated as 1:1 via Job's plot and confirmed by mass spectrum. The structure of both the ligand and the metal complex was confirmed by UV, FT-IR, NMR and mass spectral studies. The mechanism of sensing was observed through experimental calculations. Upon treatment of various metal cations such as Cu2+, Ni2+, Zn2+, Cr3+, Mg2+, Hg2+, Fe2+, Fe3+, Cd2+, Pb2+,Al3+, Pd2+, K+, Na+,As3+ no noticeable changes were observed in both absorbance and fluorescence spectral measurements except that of Co2+. The absorbance of BPAI + Co2+ exhibited two new peaks at 616 nm and 679 nm. The fluorescence response of BPAI at 580 nm was abruptly increased, accompanied by the colour change of the BPAI with Co2+ compared to BPAI. The color change from pale brown to yellow occurred due to the binding of Co2+ with that of BPAI thereby yielding a fluorescence-enhanced product. BPAI exhibited significant selectivity within short response time and strong charge transfer mechanism due to the chelation process. The detection limit was found to be 0.00091 μM which is much lower than the permissible limit recommended by WHO. Real sample analysis was performed for the practical applicability of BPAI in the environment. Furthermore, BPAI can be used as a colorimetric and fluorescent sensor to detect Co2+ in biological environments, demonstrating its low cytotoxicity using MTT assay by MG63 cells and L929 cells.

Electrochemical Properties and Excited-State Dynamics of Azaperylene Derivatives.

A series of azaperylene derivatives such as monoazaperylene (MAPery), 1,6-diazaperylene (1,6-DiAPery), 1,7-diazaperylene (1,7-DiAPery), 1,12-diazaperylene (1,12-DiAPery), triazaperylene (TriAPery), and tetraazaperylene (TetAPery) was synthesized by changing the position and number of nitrogen atoms at the bay region of a perylene skeleton in 1, 6, 7, and 12 positions. The density functional theory (DFT) calculations and electrochemical measurements suggested that the energies of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) states significantly become stabilized with increasing the number of nitrogen atoms, whereas the estimated HOMO-LUMO gaps approximately remain constant. This result is in good agreement with the absorption and fluorescence spectral measurements. Additionally, these steady-state spectroscopic measurements demonstrate the broadened spectra as compared to pristine perylene (Pery). In photophysical measurements, the fluorescence quantum yields (ΦFL) significantly decreased as the number of nitrogen atoms increased, whereas much enhanced quantum yields and rate constants of internal conversion (ΦIC and kIC) were observed. Especially, the increased kIC values of TriAPery (kIC: ∼108 s-1) and TetAPery (kIC: ∼109 s-1) are much larger than those of diazaperylene and monoazaperylene derivatives (kIC: ∼107 s-1). These photophysical trends were successfully explained by time-dependent DFT (TD-DFT) calculations. Finally, the characteristic protonated and deprotonated processes of nitrogen atoms in azaperylenes under acidic conditions were monitored utilizing absorption and fluorescence measurements. The binding constants demonstrate that the nitrogen atoms at 1 and 12 positions of a perylene skeleton are essential for the increased values.

Protective actions of bioactive flavonoids chrysin and luteolin on the glyoxal induced formation of advanced glycation end products and aggregation of human serum albumin: In vitro and molecular docking analysis

The post-translational modification of proteins by nonenzymatic glycation (NEG) and the accumulation of AGEs are the two underlying factors associated with the long-term pathogenesis in diabetes. Glyoxal (GO) is a reactive intermediate which has the ability to modify proteins and generate AGEs at a faster rate. Human serum albumin (HSA) being the most abundant serum protein has a higher chance to be modified by NEG. The key objective of the present study is to investigate the potency of chrysin and luteolin as antiglycating and antifibrillating agents in the GO-mediated glycation and fibril formation of HSA. AGEs formation were confirmed from the absorption and fluorescence spectral measurements. Both the flavonoids were able to quench the AGEs fluorescence intensity in vitro indicating the antiglycating nature of the molecules. The formation of fibrils in the GO-modified HSA was confirmed by the Thioflavin T (ThT) fluorescence assay and the flavonoids were found to exihibit the antifibrillation properties in vitro. Docking results suggested that both the flavonoids interact with various amino acid residues of subdomain IIA including glycation prone lysines and arginines via non-covalent forces and further stabilized the structure of HSA, which further explains their mechanisms of action as antiglycating and antifibrillating agents.

Brush Printing Creates Polarized Green Fluorescence: 3D Orientation Mapping and Stochastic Analysis of Conductive Polymer Films.

Brush printing is a unique method used to obtain uniaxially oriented films, whereby a polymer solution is brushed onto a substrate. However, there have been only a few reports on the brush-printing method. Here, we report the preparation of a uniaxially oriented film of a green light-emitting conductive polymer, poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT). The fluorescence polarization ratio of the oriented F8BT films was as high as 11.3, and the average orientation factor reached 0.74 ± 0.06. The orientation factor and the torsion angle of F8BT were visualized by two mappings of fluorescence and Raman spectral measurements by confocal spectromicroscopy, respectively. These two x-y mapping data with many pixels (∼750 pixels) were evaluated by x-y-z mapping of the film thickness at a single position and were used to reveal the three-dimensional (3D) orientation mechanism from a stochastic approach. Polarized green fluorescence originates from polymer chains uniaxially oriented along the brush direction. The high orientation for a film thickness < 100 nm is established by shear stress, faster capillary flow, and flow-induced chain extension for a thin solution film on a substrate. The high orientation factor was also demonstrated by a high brushing speed, whereas an optimized brushing speed existed. We found that this optimization is attributed to the property of a non-Newtonian fluid. By applying this brush-printing method to the fabrication of an optoelectrical device, polarized green electroluminescence was preliminarily demonstrated by the OLED assembled from an oriented F8BT film.

Facile Synthesis of Aryl-Substituted Cycloarenes via Bismuth(III) Triflate-Catalyzed Cyclization of Vinyl Ethers

Cycloarenes are an essential class of polycyclic aromatic hydrocarbons with unique electronic structure, but their synthesis is very challenging. Herein, we report a facile synthetic strategy prima...

Click‐Derived Uracil‐Appended Organosilatranyl Scaffolds: Synthesis, Antibacterial Characteristics, Pb2+ Binding and Fabrication of Hybrid Silica Nanoparticles

AbstractUsing a simple biocompatible click route Uracil Allied Organosilatranyl frameworks (4 a–4 e) have been obtained. These uracil tethered silatranes have shown judicious fluorescence as compared to the parent nitrogen heterocycle uracil. Through absorption and fluorescence spectral measurements, it was established that the designed analogues were selective towards Pb2+ recognition. Furthermore, for the first time hybrid silica nanoparticles (U‐SiNPs) containing a uracil bis‐triazole linkage in the silica framework is reported. The fabricated organosilatrane (4 d) was subjected to sol‐gel condensation with silica nanospheres for covalent grafting of the organic functionality on to silica. It was of interest that the uracil immobilized nanoparticles presented a high sensing efficacy towards Pb2+ as compared to the bulk material. Also, to investigate their biological potential, organosilatranes were evaluated against different bacterial strains.

Guanine damage by singlet oxygen from SYBR Green I in liquid crystalline DNA.

It is known that double-stranded DNA (dsDNA) turns into a liquid crystalline phase by the addition of a high concentration of polymer with salt. SYBR Green I (SG) is a well-known sensitive fluorescent stain for dsDNA, and is intercalated in liquid crystalline DNA. Formation of the liquid crystalline dsDNA-SG complex has been confirmed by CD spectral measurements, fluorescence spectral measurements and confocal fluorescence microscopy. SG in dsDNA was also used as a singlet oxygen generator. We conducted photoirradiation experiments using three kinds of 42-mer oligonucleotides with SG. The amount of guanine decomposition by selective irradiation of SG was analyzed using HPLC after digestion of dsDNA in each sample solution. We found that singlet oxygen produced in liquid crystalline DNA promoted guanine damage much more efficiently than in homogeneous solution.

Genotype Specific Photosynthesis x Environment Interactions Captured by Automated Fluorescence Canopy Scans Over Two Fluctuating Growing Seasons.

Photosynthesis reacts dynamic and in different time scales to changing conditions. Light and temperature acclimation balance photosynthetic processes in a complex interplay with the fluctuating environment. However, due to limitations in the measurements techniques, these acclimations are often described under steady-state conditions leading to inaccurate photosynthesis estimates in the field. Here we analyze the photosynthetic interaction with the fluctuating environment and canopy architecture over two seasons using a fully automated phenotyping system. We acquired over 700,000 chlorophyll fluorescence transients and spectral measurements under semi-field conditions in four crop species including 28 genotypes. As expected, the quantum efficiency of the photosystem II (Fv/Fm in the dark and Fq'/Fm' in the light) was determined by light intensity. It was further significantly affected by spectral indices representing canopy structure effects. In contrast, a newly established parameter, monitoring the efficiency of electron transport (Fr2/Fv in the dark respective Fr2'/Fq' in the light), was highly responsive to temperature (R2 up to 0.75). This parameter decreased with temperature and enabled the detection of cold tolerant species and genotypes. We demonstrated the ability to capture and model the dynamic photosynthesis response to the environment over entire growth seasons. The improved linkage of photosynthetic performance to canopy structure, temperature and cold tolerance offers great potential for plant breeding and crop growth modeling.

Leaf-Level Spectral Fluorescence Measurements: Comparing Methodologies for Broadleaves and Needles

Successful measurements of chlorophyll fluorescence (ChlF) spectral properties (typically in the wavelength range of 650–850 nm) across plant species, environmental conditions, and stress levels are a first step towards establishing a quantitative link between solar-induced chlorophyll fluorescence (SIF), which can only be measured at discrete ChlF spectral bands, and photosynthetic functionality. Despite its importance and significance, the various methodologies for the estimation of leaf-level ChlF spectral properties have not yet been compared, especially when applied to leaves with complex morphology, such as needles. Here we present, to the best of our knowledge, a first comparison of protocols for measuring leaf-level ChlF spectra: a custom-made system designed to measure ChlF spectra at ambient and 77 K temperatures (optical chamber, OC), the widely used FluoWat leaf clip (FW), and an integrating sphere setup (IS). We test the three methods under low-light conditions, across two broadleaf species and one needle-like species. For the conifer, we characterize the effect of needle arrangements: one needle, three needles, and needle mats with as little gap fraction as technically possible. We also introduce a simple baseline correction method to account for non-fluorescence-related contributions to spectral measurements. Baseline correction was found especially useful in recovering the spectra nearby the filter cut-off. Results show that the shape of the leaf-level ChlF spectra remained largely unaffected by the measurement methodology and geometry in OC and FW methods. Substantially smaller red/far-red ratios were observed in the IS method. The comparison of needle arrangements indicated that needle mats could be a practical solution to investigate temporal changes in ChlF spectra of needle-like leaves as they produced more reproducible results and higher signals.

Comparison of fluorometric and microscopical quantification of phytoplankton in a drinking water reservoir by a one-season monitoring program

Phytoplankton are key components in aquatic ecosystems and therefore an important target of monitoring analyses. Microscopical counting, although providing most detailed results, is time and labor intensive and requires highly skilled analysts. In situ spectral fluorescence measurements provide a much faster analysis with a higher spatiotemporal resolution. A one-season survey of phytoplankton assemblages was performed in order to compare the results of the spectrofluorometric measurements to classical microscopical determination in different sections of a drinking water reservoir. The investigations were performed with the spectrofluorometer FluoroProbe (FP) by bbe Moldaenke GmbH (Kiel, Germany), which is designed to discriminate among diatoms, green algae, Cryptophyta and cyanobacteria. The results of phytoplankton quantification as revealed by total chlorophyll a (Chla) measurements with the FP and total biovolumes determined by microscopy showed a good correlation.The accordance between the two approaches was best for diatoms and much lower for the other spectral groups. The proportion of green algae was generally overestimated by FP measurements in comparison to biovolumes. Contrary, the percentage of cyanobacteria was often underestimated by FP compared to microscopical analyses. A clear underestimation of cyanobacteria by FP measurements even at high abundances of Microcystis sp. was observed in two samples. No influence of species composition on the congruence between microscopical analyses and FP measurements was detected.

Molecular interactions of AL3818 (anlotinib) to human serum albumin as revealed by spectroscopic and molecular docking studies

Anlotinib (ANB) is a novel member of the tyrosine kinase inhibitors approved for different types of cancer, its binding to human serum albumin (HSA) is of significant pharmacological importance. Hence, this study was devoted to understand the nature of the binding between ANB and HSA via the use of a set of conventional spectroscopic tools supplemented by molecular docking analysis. Fluorescence spectral measurements revealed a clear quenching effect of ANB on the HSA intrinsic fluorescence, which was shown to follow the static quenching type via the formation of a non-fluorescent complex. Analyses of this fluorescence data using the Stern–Volmer, Lineweaver-Burk and double-log relations showed that ANB-HSA binding constants ranged from 0.96 to 1.15 × 105 M−1 as resulted from the different relations in three different experimental temperatures. Further interpretation of the data using thermodynamic equations reveled spontaneous reaction between ANB and HSA with negative enthalpy and positive entropy values that propose the contribution of electrostatic forces possibly accompanied by hydrogen bonding. Docking studies confirmed the ANB-HSA complex formation with the ANB bound to Site I on the HSA structure mainly with the amino acid residues LYS 199, ARG 222, LEU 238 and ALA 291.

DNA/BSA binding interactions and VHPO mimicking potential of vanadium(IV) complexes: Synthesis, structural characterization and DFT studies

Vanadium(IV) Schiff base complexes (VOL1‐VOL3) were synthesized and characterized by elemental analysis, various spectral methods and single crystal XRD studies. Structural analysis of VOL2 reveals that the central vanadium ion in the complex is six coordinate with distorted octahedral geometry. Density functional theory (DFT) and time dependent (TD‐DFT) studies were used to understand the electronic transitions observed in the complexes in UV–Vis spectra. The electrochemical behavior of the complexes was investigated in acetonitrile medium exhibit quasi‐reversible one electron transfer. The DNA and BSA protein binding interaction of vanadium complexes has been explored by UV–Vis and fluorescence spectral methods and viscosity measurements reveal that the complexes interact with CT‐DNA through intercalation mode and follows the order VOL1 &lt; VOL3 &lt; VOL2. The complexes exhibit binding interactions with BSA protein. The complexes act as chemical nuclease and cleave DNA in the presence of H2O2. The 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) assay was used to evaluate the radical scavenging activity demonstrate the antioxidant property of the complexes. The antimicrobial activity was screened for several microorganisms, Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli. The mimicking of vanadium haloperoxidase was investigated by the bromination of the organic substrate phenol red by vanadium complexes in the presence of bromide and H2O2.

Synthesis and Biophysical Insights into the Binding of a Potent Anti-Proliferative Non-symmetric Bis-isatin Derivative with Bovine Serum Albumin: Spectroscopic and Molecular Docking Approaches

As part of the research endeavors to combat cancer, a non-symmetric bis-isatin derivative (compound 3) was synthesized and showed a significant anti-proliferative potency. The current study provides a comprehensive characterization of the interaction of compound 3 with the drug-transporting protein bovine serum albumin (BSA) via the use of spectroscopic tools along with molecular docking studies. Fluorescence spectral measurements showed that the BSA intrinsic fluorescence can be significantly quenched by the addition of compound 3 and the formation of a non-fluorescent complex. Further measurements revealed a static type of quenching with Stern–Volmer and Linweaver–Burk constants of 105. The thermodynamic parameters of the binding were calculated to be ΔS° 105.09 ± 5.32 with ΔH° of −0.72 ± 0.71 and negative ΔG° values. In addition, synchronous fluorescence and 3D fluorescence spectroscopy suggested that compound 3 did not induce conformational changes in BSA. Site competition experiments revealed that compound 3 competes with warfarin within the BSA binding domain (Sudlow site I). This was further confirmed by the molecular docking results showing a binding energy of −25.93 kJ/mol for compound 3-BSA. Hence, the observed results in the present study assumed that the compound 3-BSA binding is spontaneous, involving electrostatic forces and hydrogen bonding.

Solid bitumen, bituminite and thermal maturity of the Upper Jurassic-Lower Cretaceous Chia Gara Formation, Kirkuk Oil Field, Zagros Fold Belt, Kurdistan, Iraq

The Upper Jurassic-Lower Cretaceous Chia Gara Formation, a proven marine source rock characterised by predominance of amorphous organic matter (AOM) is known from few outcrops in NE Iraq and a number of exploration wells in the Zagros Fold Belt. This study presents comprehensive organic petrographic and mineralogical investigations of the dispersed organic matter and rock-forming minerals of the Tithonian-Berriasian Chia Gara Formation intersected by the Kirkuk well K-109 drilled in the giant Kirkuk oil field, NE Iraq. The organic petrographic analyses, including incident light microscopy and confocal laser-scanning microscopy (CLSM) were applied to carbonate source rocks with low to moderate organic carbon contents. Our data demonstrate the predominance of bituminite and solid bitumen among the examined dispersed organic matter followed by oil exudates and oil globule inclusions as well as the presence of minor contributions of alginite (i.e., Tasmanites and Leiospheridia), liptodetrinite and vitrinite. Based on optical characteristics and CLSM spectral fluorescence measurements, examinations of bituminite point towards the presence of bituminite type III. The bituminite type III encloses dark orange fluorescent amorphous components suggesting a genetic relationship either with liptodetrinite and/or with solid bitumen. The qualitative assessment of solid bitumen reveals several dissimilar forms identified in the analysed samples. The photometric and spectral fluorescence measurements point to distinct reflectance values ranging between 0.19% and 0.43% SBRr and lambda max values extending from 515nm to 590nm, respectively. The corresponding results of the solid bitumen exhibit (1) a lack of a relationship with depth and, (2) suggest its poor property as a reliable maturity indicator for the examined samples. The presence of oil exudates, oil globule inclusions and their association with solid bitumen suggests a genetic relation with the examined residues of liquid hydrocarbon phase. The performed thermal maturities assessments of dispersed organic matter point towards early-mature to peak-mature oil window with vitrinite reflectance values ranging between 0.52% VRr at 2801m to 0.83% VRr at 3089m depth. Mineralogical analyses revealed the predominance of calcite over dolomite in the examined limestone to marl lithofacies (e.g., clear rimmed dolomite) with localised intensive dolomitisation. In the phyllosilicate-rich matrix, predominance of calcite and siderite is observed, followed by zinc blende and pyrite. The composition of organic matter in the examined Chia Gara Formation with predominance of bituminite and solid bitumen makes the major marine source rock of Iraq's Cretaceous petroleum systems distinctive in terms of hydrocarbon generation and migration at an oil window stage as it provides suitable explanations for its generally low hydrogen index (HI) with only minor terrestrial input. In addition, the results presented herein can be helpful for future evaluation of thermal maturities and characterisation of optical appearances of dispersed organic matter in carbonates by incident light microscopy and especially by CLSM during hydrocarbon prospecting.

Structural and molecular docking studies of biologically active mercaptopyrimidine Schiff bases

Novel Schiff bases derived from the treatment of mercapto-diamino pyrimidine with two different aldehydes are characterized using elemental analysis, single crystal X-ray diffraction and 1H NMR spectroscopy. The pharmacological action of the synthesized compounds viz., antimicrobial, anticancer and antitubercular activities is studied. The Schiff bases show a very good activity against various test pathogens. DNA and β-CD binding interactions of the compounds are studied using UV–Visible absorption and fluorescence spectral measurements. The binding constants of the compounds towards β-CD are in the order of 103 to 104. Molecular docking is done using MOE program on the 3D structure of the enzymes, viz., human thymidylate synthase complexed with dump and raltitrex, candida albicans N-myristoyltransferasepeptidic inhibitor, catalytic domain of protein kinase pKnb from mycobacterium tuberculosis in complex with mitoxantrone, pare, topoisomerase atpase inhibitor, E. coli and lactobacillus casdihydrofolatereductase. The MIC/IC50 values of the Schiff bases are compared with the glide scores from the molecular docking studies. The number of hydrogen bonding interactions between the Schiff bases and amino acid residues are also reported.