- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Eu3+ as a luminescence probe in DNA studies: Structural and conformational implications
摘要： 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.
关键词： infrared (IR),DNA condensation,lanthanide ions,DNA structure,luminescence probe,vibrational circular dichroism (VCD)
更新于2025-09-19 17:15:36
-
Analysis of Vibrational Circular Dichroism Spectra of Peptides: a Generalised Coupled Oscillator Approach of a Small Peptide Model Using VCDtools
摘要： Vibrational Circular Dichroism (VCD) is one of the major spectroscopic tools to study peptides. Nevertheless, a full understanding of what determines the signs and intensities of VCD bands of these compounds in the amide I and amide II spectral regions is still far from complete. In the present work we study the origin of these VCD signals using the General Coupled Oscillator (GCO) analysis, a novel approach that has recently been developed. We apply this approach to the ForValNHMe model peptide in both α-helix and β-sheet configurations. We show that the intense VCD signals observed in the amide I and amide II spectral regions essentially have the same underlying mechanism, namely, the through-space coupling of electric dipoles. The crucial role played by intra-molecular hydrogen bonds in determining VCD intensities is also illustrated. Moreover, we find that contributions to the rotational strengths considered to be insignificant in standard VCD models may have sizable magnitudes and can thus not always be neglected. In addition, the VCD robustness of amide I and II modes has been investigated by monitoring the variation of the rotational strength and its contributing terms during linear transit scans and by performing calculations with different computational parameters. From these studies -and in particular the decomposition of the rotational strength made possible by the GCO analysis- it becomes clear that one should be cautious when employing measures of robustness as proposed previously.
关键词： amide I,Vibrational Circular Dichroism,amide II,VCD robustness,peptides,General Coupled Oscillator analysis
更新于2025-09-19 17:13:59
-
Chiral Analysis || Vibrational Optical Activity in Chiral Analysis
摘要： Chiral analysis encompasses all analytical techniques focused on quantitative measures of the chiral properties of molecules. The properties unique to chiral molecules are absolute configuration (AC) and enantiomeric excess (ee). As will be discussed below, vibrational optical activity (VOA) can provide information on samples of chiral molecules by direct spectroscopic investigation without modifying the molecules by reacting them, sometimes irreversibly, with other chiral molecules or substrates. From a molecular point of view, VOA chiral analysis may be regarded as noninvasive in that the molecule is not changed or altered from its natural solution or solid-state condition in order to carry out the analysis. An important property of VOA is its sensitivity to the conformational states of chiral molecules, both in solution and in the solid state. Apart from the determination of the absolute chirality of a molecule, VOA can be used to specify these states, in conjunction with quantum mechanical calculations, and determine populations of solution-state conformers that are interconverting faster than the nuclear magnetic resonance (NMR) timescale. VOA can also be used to probe the solid-state conformations of chiral molecules as well as their polymorphic crystal forms. Although this information is not strictly chiral in nature, VOA has extraordinary sensitivity to both the absolute structure and the conformation of chiral molecules and this aspect of chiral analysis by VOA should not be overlooked.
关键词： absolute configuration (AC),Raman optical activity (ROA),enantiomeric excess (ee),Chiral analysis,vibrational optical activity (VOA),vibrational circular dichroism (VCD)
更新于2025-09-09 09:28:46
-
Smithsonian Astrophysical Observatory Ozone Mapping and Profiler Suite (SAO OMPS) formaldehyde retrieval
摘要： This paper presents our new formaldehyde (H2CO) retrievals, obtained from spectra recorded by the nadir instrument of the Ozone Mapping and Profiler Suite (OMPS) flown on board NASA’s Suomi National Polar-orbiting Partnership (SUOMI-NPP) satellite. Our algorithm is similar to the one currently in place for the production of NASA’s Ozone Monitoring Instrument (OMI) operational H2CO product. We are now able to produce a set of long-term data from two different instruments that share a similar concept and a similar retrieval approach. The ongoing overlap period between OMI and OMPS offers a perfect opportunity to study the consistency between both data sets. The different spatial and spectral resolution of the instruments is a source of discrepancy in the retrievals despite the similarity of the physic assumptions of the algorithm. We have concluded that the reduced spectral resolution of OMPS in comparison with OMI is not a significant obstacle in obtaining good-quality retrievals. Indeed, the improved signal-to-noise ratio of OMPS with respect to OMI helps to reduce the noise of the retrievals performed using OMPS spectra. However, the size of OMPS spatial pixels imposes a limitation in the capability to distinguish particular features of H2CO that are discernible with OMI. With root mean square (RMS) residuals ～ 5×10?4 for individual pixels we estimate the detection limit to be about 7.5 × 1015 molecules cm?2. Total vertical column density (VCD) errors for individual pixels range between 40 % for pixels with high concentrations to 100 % or more for pixels with concentrations at or below the detection limit. We compare different OMI products (SAO OMI v3.0.2 and BIRA OMI v14) with our OMPS product using 1 year of data, between September 2012 and September 2013. The seasonality of the retrieved slant columns is captured similarly by all products but there are discrepancies in the values of the VCDs. The mean biases among the two OMI products and our OMPS product are 23 % between OMI SAO and OMPS SAO and 28 % between OMI BIRA and OMPS SAO for eight selected regions.
关键词： formaldehyde,OMPS,H2CO,retrieval,AMFs,vertical column density,air mass factors,spectral fitting,OMI,VCD
更新于2025-09-04 15:30:14
-
Spectroscopic Investigation of the Stimulus of NLO Property on Acetone Thiosemicarbazone Using Computational [HF and DFT] Confinement
摘要： In this attempt of research work, the inducement of NLO property on the compound Acetone thiosemicarbazone has been analyzed using computational calculations. The FT-IR, FT-Raman, FT-NMR and UV-Visible spectra have been recorded in specified region. The optimized inducement of NLO activity by the molecular structural deformation due to the addition of acetone compound has been investigated. The supportive analyses such as Mulliken charge levels, first order and second order polarization, vibrational confirmation, frontier molecular interactions, thermodynamic function (Gibbs energy) and VCD profile for proving NLO mechanism in the compound have been carried out. The chemical environment of the compound was simultaneously monitored by simulating and recording 1H and 13C NMR spectra. The isotropic and anisotropic chemical shift related to carbons and hydrogens after the formation of target compound have been carefully interpreted. The stabilization of orbitals by interchanging of energy between donor and acceptor was observed by NBO perturbation calculations.
关键词： NLO activity,Acetone thiosemicarbazone,Isotropic,NBO perturbation,VCD
更新于2025-09-04 15:30:14