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1.
    
The study of protein–ionic liquid interactions is very important because of the widespread use of ionic liquids as protein stabilizer in the recent years. In this work, the interaction of bovine serum albumin (BSA) with different imidazolium‐based ionic liquids (ILs) such as [1‐ethyl‐3‐methyl‐imidazolium ethyl sulfate (EmimESO4), 1‐ethyl‐3‐methyl‐imidazolium chloride (EmimCl) and 1‐butyl‐3‐methyl‐imidazolium chloride (BmimCl)] has been investigated using different spectroscopic techniques. The intrinsic fluorescence of BSA is quenched by ILs by the dynamic mechanism. The thermodynamic analysis demonstrates that very weak interactions exist between BSA and ILs. 8‐Anilino‐1‐naphthalenesulfonic acid (ANS) fluorescence and lifetime measurements reveal the formation of the compact structure of BSA in IL medium. The conformational changes of BSA were monitored by CD analysis. Temperature‐dependent ultraviolet (UV) measurements were done to study the thermal stability of BSA. The thermal stability of BSA in the presence of ILs follows the trend EmimESO4 > EmimCl > BmimCl and in the presence of more hydrophobic IL, destabilization increases rapidly as a function of concentration.  相似文献   

2.
Nanomaterials in different form have been thoroughly used in the area of pharmaceutics and medicine for drug delivery. The large scale of nanoparticles (NPs) synthesis from plant extract is much safe, cheap and eco-friendly. Here, we demonstrated a new, one-step, ultra-fast biosynthesis of gold nanoparticles (sc-AuNPs, 19.54?nm) by using aqueous Spathodea campanulata leaf extracts as a reducing and capping agent. And also, we presented the synthesis of citrate capped gold nanoparticles (cit-AuNPs) of approximately same size (19.66?nm). These two NPs were characterized by UV-Visible, dynamic light scattering, transmission electron microscope and energy dispersive X-ray spectroscopy. Fourier transform infrared spectroscopy confirmed that the functional groups like OH, NH, OH of COOH and CO were contributed in the sc-AuNPs formation. The negative zeta potential (?20.5, ?22.8?mV) established the stability and dispersion of the sc- and cit-AuNPs. The anti-bacterial activity of the sc- and cit-AuNPs were checked against Escherichia coli (DH5-Alpha). Minimum inhibitory concentration was 2.4 and 3.0?nM, respectively for sc- and cit-AuNPs. The interaction study of the sc-AuNPs/cit-AuNPs-human serum albumin (HSA) system was done by UV-Visible absorbance, fluorescence, circular dichroism, time resolved fluorescence spectroscopy and the measurement of zeta potential. Absorbance, three dimensional fluorescence, synchronous fluorescence and circular dichroism spectroscopy showed a minor conformational change of HSA upon interaction with the sc-AuNPs compared to cit-AuNPs. The present comparative study will advance our knowledge about the binding mode, mechanism and conformational change of the protein upon interaction with green synthesized sc-AuNPs and cit-AuNPs.

Communicated by Ramaswamy H. Sarma  相似文献   


3.
    
The fluorescence, ultraviolet (UV) absorption, time resolved techniques, circular dichroism (CD), and infrared spectral methods were explored as tools to investigate the interaction between histamine H1 drug, epinastine hydrochloride (EPN), and bovine serum albumin (BSA) under simulated physiological conditions. The experimental results showed that the quenching of the BSA by EPN was static quenching mechanism and also confirmed by lifetime measurements. The value of n close to unity indicated that one molecule of EPN was bound to protein molecule. The binding constants (K) at three different temperatures were calculated (7.1 × 104, 5.5 × 104, and 3.9 × 104M−1). Based on the thermodynamic parameters (ΔH0, ΔG0, and ΔS0), the nature of binding forces operating between drug and protein was proposed. The site of binding of EPN in the protein was proposed to be Sudlow's site I based on displacement experiments using site markers viz, warfarin, ibuprofen, and digitoxin. Based on the Förster's theory of non‐radiation energy transfer, the binding average distance, r between the donor (BSA) and acceptor (EPN) was evaluated and found to be 4.48 nm. The UV–visible, synchronous fluorescence, CD, and three‐dimensional fluorescence spectral results revealed the changes in secondary structure of the protein upon its interaction with EPN. © 2015 Wiley Periodicals, Inc. Biopolymers 103: 646–657, 2015.  相似文献   

4.
    
The interactions of poly‐L ‐glutamic acid and a cationic porphyrin derivative in aqueous solutions were studied by the combination of vibrational circular dichroism (VCD) and electronic circular dichroism (ECD) spectroscopies. It was found that non‐covalent interactions between both agents influence the structure of the polymeric matrix and the guest porphyrins and vice versa, but the physico‐chemical properties of the solutions, especially the pH and the relative permittivity of the solvent, play a key role in the structure of the polypeptide part of the formed complexes. It was shown that the interaction with porphyrins prevents the precipitation of poly‐L ‐glutamic acid in aqueous solution at acidic pH. In special conditions, the porphyrins attached to the polypeptide probably possess face‐to‐face interaction as demonstrated by the enhancement of the characteristic ECD signal and the appearance of sidebands on its short and long wavelength sides. Copyright © 2005 European Peptide Society and John Wiley & Sons, Ltd.  相似文献   

5.
    
The salen‐type ligand prepared with (R,R) diphenylethan‐1,2‐diamine and salicylaldehyde provides stable and inert complexes KLnL2 upon simple reaction with lanthanide halides or pseudohalides LnX3 (Ln = Tb3+‐Lu3+; X = Cl? or TfO?) of its potassium salt. All the complexes were completely characterized through nuclear magnetic resonance (NMR), electronic circular dichroism (ECD) in the UV and some (Er3+, Tm3+, Yb3+) also with Near‐IR ECD (NIR‐ECD) and luminescence (Tb3+, Tm3+). Careful analysis of the NMR shifts demonstrated that the complexes are isostructural in solution and afforded an accurate geometry. This was further confirmed by means of Density Functional Theory (DFT) optimization of the Lu3+ complex, and by comparing the ligand‐centered experimental and time‐dependent TD‐DFT computed UV‐ECD spectra. As final validation, we used the NIR‐ECD spectrum of the Yb3+ derivative calculated by means of Richardson's equations. The excellent match between calculated and experimental ECD spectra confirm the quality of the NMR structure.  Chirality 27:857–863, 2015. © 2015 Wiley Periodicals, Inc.  相似文献   

6.
    
Picosecond time‐resolved crystallography was used to follow the dissociation of carbon monoxide from the heme pocket of a mutant sperm whale myoglobin and the resultant conformational changes. Electron‐density maps have previously been created at various time points and used to describe amino‐acid side‐chain and carbon monoxide movements. In this work, difference refinement was employed to generate atomic coordinates at each time point in order to create a more explicit quantitative representation of the photo‐dissociation process. After photolysis the carbon monoxide moves to a docking site, causing rearrangements in the heme‐pocket residues, the coordinate changes of which can be plotted as a function of time. These include rotations of the heme‐pocket phenylalanine concomitant with movement of the distal histidine toward the solvent, potentially allowing carbon monoxide movement in and out of the protein and proximal displacement of the heme iron. The degree of relaxation toward the intermediate and deoxy states was probed by analysis of the coordinate movements in the time‐resolved models, revealing a non‐linear progression toward the unbound state with coordinate movements that begin in the heme‐pocket area and then propagate throughout the rest of the protein.  相似文献   

7.
    
Variations in the structure of d(GGGA)(5) oligonucleotide in the presence of Li(+), Na(+), and K(+) ions and its temperature stability were studied using electronic and vibrational circular dichroism, IR absorption, and ab initio calculations with the Becke 3-Lee-Yang-Parr functional at the 6-31G** level. The samples were characterized by nondenaturing gel electrophoresis. Oligonucleotide d(GGGA)(5) in the presence of Li(+) forms a nonplanar single tetramer, with angles of 102 degrees and 171 degrees between neighboring guanine bases. This tetramer changes its geometry at temperatures >50 degrees C, but does not form a quadruplex structure. In the presence of Na(+), the d(GGGA)(5) structure was optimized to almost planar tetramers with an angle of 177 degrees between neighboring guanines. The spectral results suggest that it stacks into a quadruplex helical structure. This quadruplex structure decayed to a single tetramer at temperatures >60 degrees C. The Hartree-Fock energies imply that d(GGGA)(5) prefers to form complexes with Na(+) rather than Li(+). The d(GGGA)(5) structure in the presence of monovalent ions is stabilized against thermal denaturation in the order Li(+) < Na(+) < K(+).  相似文献   

8.
    
New efficient catalysts based on electrophilic N‐fluoro quaternary ammonium salts are reported for catalytic allylation of (E)‐N,1‐diphenylmethanimine. The chiral version of the catalyst based on cinchonidine (F‐CD‐BF4) shows high catalytic activity with approximately 94% ee and TOF (>800 h?1). The F‐CD‐BF4 is prepared from cinchonidine and Selectfluor by one‐step transfer fluorination.  相似文献   

9.
Fluorescence anisotropy studies of molecularly imprinted polymers.   总被引：1，自引：0，他引：1  
A molecularly imprinted polymer (MIP) is a biomimetic material that can be used as a biochemical sensing element. We studied the steady-state and time-resolved fluorescence and fluorescence anisotropy of anthracene-imprinted polyurethane. We compared MIPs with imprinted analytes present, MIPs with the imprinted analytes extracted, MIPs with rebound analytes, non-imprinted control polymers (non-MIPs) and non-MIPs bound with analytes to understand MIP's binding behaviour. MIPs and non-MIPs had similar steady-state fluorescence anisotropy in the range 0.11-0.24. Anthracene rebound in MIPs and non-MIPs had a fluorescence lifetime of tau = 0.64 ns and a rotational correlation time of phi(F) = 1.2-1.5 ns, both of which were shorter than that of MIPs with imprinted analytes present (tau = 2.03 ns and phi(F) = 2.7 ns). The steady-state anisotropy of polymer solutions increased exponentially with polymerization time and might be used to characterize the polymerization extent in situ.  相似文献   

10.
    
Polyglutamine repeats in proteins are highly correlated with amyloid formation and neurological disease. To better understand the molecular basis of glutamine repeat diseases, structural analysis of polyglutamine peptides as soluble monomers, oligomers, and insoluble amyloid fibrils is necessary. In this study, fluorescence resonance energy transfer (FRET) experiments and molecular dynamics simulations using different theoretical models of polyglutamine were conducted. This study demonstrates that a previously proposed simple C(α)C(β) model of polyglutamine, denoted as FCO, accurately reproduced the present FRET results and the results of previously published FRET, triplet-state quenching, and fluorescence correlation studies. Other simple C(α)C(β) models with random coil and extended β-strand parameters, and all-atom models with parm96 and parm99SB force fields, did not match the FRET result well. The FCO is an intrinsically disordered model with a high-effective persistence length producing extended peptides at short lengths (Q(N) < 10). Because of an increasing number of attractive Q-Q interactions at longer lengths, the FCO model becomes increasingly more compact at lengths between Q(N) ～ 10-16 and is as compact as many folded proteins at Q(N) > 16.  相似文献   

11.
    
Two couples of enantiomeric platinum(II) complexes: Pt(L1a)Cl ( 1a ), Pt(L1b)Cl ( 1b ) and Pt(L1a)(C ≡ C ? Ph) ( 2a ), Pt(L1b)(C ≡ C ? Ph) ( 2b ) (L1a = (+)‐1,3‐di‐(2‐(4,5‐pinene)pyridyl)benzene, L1b = (?)‐1,3‐di‐(2‐(4,5‐pinene)pyridyl)benzene) were synthesized and characterized. Their absolute configurations were determined by single crystal X‐ray diffraction and further verified by circular dichroism (CD) spectra (including electronic circular dichroism [ECD] and vibrational circular dichroism [VCD]). These complexes show interesting mechanoluminescence and/or vapoluminescence due to crystalline‐to‐amorphous transformation. The crystalline solids, grinding‐induced amorphous powders, and vapor‐induced amorphous powders of complexes 2a and 2b were comparatively investigated by solid‐state ECD and VCD spectra. The transformation from crystalline solids to amorphous powders was accompanied by significant variances of the spectral feature in both ECD and VCD spectra. Chirality 25:384–392, 2013. © 2013 Wiley Periodicals, Inc.  相似文献   

12.
    
In order to determine the origin of the bisignate CD spectra of native purple membrane, heterochromophoric analogues containing bacteriorhodopsin regenerated with native all-trans-retinal and retinal analogues were investigated. The data collected for the purple membrane samples containing two different chromophores suggest the additive character of the CD spectra. This conclusion was supported by a series of spectra using 5,6-dihydroretinal and 3-dehydroretinal and by using 33% regenerated PM in buffer and in presence of osmolytes. Our results support the idea of conformational heterogeneity of the chromophores in the bR in the trimer, suggesting that the three bR subunits in the trimer are not conformationally equal, and therefore, the bisignate CD spectrum of bR in the purple membrane occurs rather due to a superposition of the CD spectra from variously distorted bR subunits in the trimer than interchromophoric exciton-coupling interactions.  相似文献   

13.
Vacuum ultraviolet circular dichroism spectra are reported for poly(galacturonic acid) solution and film, sodium polygalacturonate solution and film, and calcium polygalacturonate gel. In addition to the positive c.d. band near 208 nm previously observed, we find a pair of higher energy bands at 170 180 nm (negative) and 145 nm (positive). The low energy band, assigned to an n-π1 carboxyl transition, is blue-shifted upon gelation or film formation.  相似文献   

14.
本文综述了圆二色谱激子手性法进展及其在天然产物绝对构型确定中的应用.  相似文献   

15.
    
The electronic circular dichroism (ECD) spectrum of the recently synthesized [16]helicene and a derivative comprising two triisopropylsilyloxy protection groups was computed by means of the very efficient simplified time‐dependent density functional theory (sTD‐DFT) approach. Different from many previous ECD studies of helicenes, nonequilibrium structure effects were accounted for by computing ECD spectra on \"snapshots\" obtained from a molecular dynamics (MD) simulation including solvent molecules. The trajectories are based on a molecule specific classical potential as obtained from the recently developed quantum chemically derived force field (QMDFF) scheme. The reduced computational cost in the MD simulation due to the use of the QMDFF (compared to ab‐initio MD) as well as the sTD‐DFT approach make realistic spectral simulations feasible for these compounds that comprise more than 100 atoms. While the ECD spectra of [16]helicene and its derivative computed vertically on the respective gas phase, equilibrium geometries show noticeable differences, these are “washed” out when nonequilibrium structures are taken into account. The computed spectra with two recommended density functionals (ωB97X and BHLYP) and extended basis sets compare very well with the experimental one. In addition we provide an estimate for the missing absolute intensities of the latter. The approach presented here could also be used in future studies to capture nonequilibrium effects, but also to systematically average ECD spectra over different conformations in more flexible molecules. Chirality 28:365–369, 2016. © 2016 Wiley Periodicals, Inc.  相似文献   

16.
    
The increasing interest in peptidomimetics of biological relevance prompted us to synthesize a series of cyclic peptides comprising trans‐2‐aminocyclohexane carboxylic acid (Achc) or trans‐2‐aminocyclopentane carboxylic acid (Acpc). NMR experiments in combination with MD calculations were performed to investigate the three‐dimensional structure of the cyclic peptides. These data were compared to the conformational information obtained by electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) spectroscopy. Experimental VCD spectra were compared to theoretical VCD spectra computed quantum chemically at B3LYP/6‐31G(d) density functional theory (DFT) level. The good agreement between the structural features derived from the VCD spectra and the NMR‐based structures underlines the applicability of VCD in studying the conformation of small cyclic peptides. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd.  相似文献   

17.
    
Model peptides based on -(Aib-Ala)(n)-, and (Aib)(n)-Leu-(Aib)(2) sequences, which have varying amounts of 3(10)-helical character, were studied by use of vibrational and electronic circular dichroism (VCD and ECD) and Fourier transform infrared (FTIR) absorption spectroscopies to test the correlation of spectral response and conformation. The data indicate that these peptides, starting from a length of about four to six residues, predominantly adopt a 3(10)-helical conformation at room temperature. The longest model peptides, depending on the series, may evidence some alpha-helical contribution to the spectra, while the shorter ones, with less than six residues, have much less order. The IR absorption spectra (as supported by theory) showed only small frequency changes between 3(10)- and alpha-helices. By contrast, solvent effects are a source of much bigger perturbations. The ECD results show that the intensity ratio for the approximately 222-nm to approximately 208-nm bands, while useful for distinguishing between these two helical types in some sequences, may have a narrower range of application than VCD. However, the VCD data presented here continue to support the proposed discrimination between alpha- and 3(10)-helices based on qualitative amide I and II bandshape differences. The present study shows the intensities of the 3(10)-helical amide I (peak-to-peak) to its amide II VCD to be of the same order and useful for discriminating them from alpha-helices, whose amide I dominates the amide II in intensity. This qualitative result is experimentally independent of the amount of alphaMe-substituted residues in the sequence. These experimental VCD results are consistent in detail with theoretical spectral simulations for Ac-(Ala)(8)-NH(2), Ac-(Aib-Ala)(4)-NH(2), and Ac-(Aib)(8)-NH(2) in 3(10)- and alpha-helical conformations.  相似文献   

18.
Antigen retrieval (AR), in which formalin-fixed paraffin-embedded tissue sections are briefly heated in buffers at high temperature, often greatly improves immunohistochemical staining. An important unresolved question regarding AR is how formalin treatment affects the conformation of protein epitopes and how heating unmasks these epitopes for subsequent antibody binding. The objective of the current study was to use model proteins to determine the effect of formalin treatment on protein conformation and thermal stability in relation to the mechanism of AR. Sodium dodecyl sulfate polyacrylamide gel electrophoresis was used to identify the presence of protein formaldehyde cross-links, and circular dichroism spectropolarimetry was used to determine the effect of formalin treatment and high-temperature incubation on the secondary and tertiary structure of the model proteins. Results revealed that for some proteins, formalin treatment left the native protein conformation unaltered, whereas for others, formalin denatured tertiary structure, yielding a molten globule protein. In either case, heating to temperatures used in AR methods led to irreversible protein unfolding, which supports a linear epitope model of recovered protein immunoreactivity. Consequently, the core mechanism of AR likely centers on the restoration of normal protein chemical composition coupled with improved accessibility to linear epitopes through protein unfolding.  相似文献   

19.
    
Babenko V  Harada T  Yagi H  Goto Y  Kuroda R  Dzwolak W 《Chirality》2011,23(8):638-646
Hydrodynamic forces are capable of inducing structural order in dispersed solid phases, and of causing symmetry-breaking when chiral crystals precipitate from an achiral liquid phase. Until it was observed upon vortex-assisted fibrillation of insulin, such behavior had been thought to be confined to few unbiological systems. In this paper we are discussing chiroptical properties of two chiral variants of insulin amyloid, termed +ICD and -ICD, which form during the process of chiral bifurcation in vortexed solutions of aggregating insulin. As conventional measurements of circular dichroism of solid, anisotropic substances are particularly vulnerable to overlapping influences of linear birefringence and linear dichroism, we have employed complementary tools including dedicated universal chiroptical spectrophotometer to rule out such artifacts. We propose that the strong chiroptical properties of +ICD and -ICD insulin fibrils are an aspect of genuine superstructural chirality of amyloid fibrils and of powerful excitonic couplings taking place within them. A comparison of thioflavin T complexes with fibrils formed by insulin and polyglutamic acid suggests that the extrinsic Cotton effect stemming from the level of single twisted dye molecules is weaker, although diagnostically useful, and cannot account for the overall magnitude of ICD of the dye bound to ±ICD insulin amyloid.  相似文献   

20.
We have devised an artificial sampling approach generating "absorption flattening" (AF) on the UV-Vis spectrum of a solution of a chiral compound: Tris (ethylendiamine)cobalt(III) chloride (Lambda-Co(en)(3)Cl(3)). We have observed a concomitant red shift of the CD maxima. Related CD and absorption spectra have been calculated from spectra recorded on diluted homogeneous solutions, thus monitoring the effect of AF on both types of data. Experimental data are in good agreement with calculated spectra. Simulations with suitable bandshapes show that the red shift of the CD spectrum is due to AF. On the basis of these results, we conclude that AF is an important cause of distortions in CD spectra for inhomogeneous samples. Plans to compensate or at least to take into account this effect are presented.  相似文献   

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