scholarly journals Porphyrin-Based Supramolecular Flags in the Thermal Gradients’ Wind: What Breaks the Symmetry, How and Why

Nanomaterials ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 1673
Author(s):  
Angelo Nicosia ◽  
Fabiana Vento ◽  
Giovanni Marletta ◽  
Grazia M. L. Messina ◽  
Cristina Satriano ◽  
...  
Keyword(s):  
Circular Dichroism ◽  
Building Blocks ◽  
Thermal Gradients ◽  
Thermally Induced ◽  
Force Microscopy ◽  
Natural Event ◽  
Transmission Electron ◽  
Harvesting Systems ◽  
Supramolecular Aggregates ◽  
Circular Dichroïsm

The Spontaneous Symmetry Breaking (SSB) phenomenon is a natural event in which a system changes its symmetric state, apparently reasonless, in an asymmetrical one. Nevertheless, this occurrence could be hiding unknown inductive forces. An intriguing investigation pathway uses supramolecular aggregates of suitable achiral porphyrins, useful to mimic the natural light-harvesting systems (as chlorophyll). Using as SSB probe supramolecular aggregates of 5,10,15,20-tetrakis[p(ω-methoxypolyethyleneoxy)phenyl]porphyrin (StarP), a non-ionic achiral PEGylated porphyrin, we explore here its interaction with weak asymmetric thermal gradients fields. The cross-correlation of the experimental data (circular dichroism, confocal microscopy, atomic force microscopy, and cryo-transmission electron microscopy) revealed that the used building blocks aggregate spontaneously, organizing in flag-like structures whose thermally-induced circular dichroism depends on their features. Finally, thermal gradient-induced enantioselectivity of the supramolecular flag-like aggregates has been shown and linked to their size-dependence mesoscopic deformation, which could be visualized as waving flags in the wind.

scholarly journals The effects of Ca2+ and Cd2+ on the secondary and tertiary structure of bovine testis calmodulin. A circular-dichroism study

1986 ◽  
Vol 238 (2) ◽  
pp. 485-490 ◽  
Author(s):  
S R Martin ◽  
P M Bayley
Keyword(s):  
Circular Dichroism ◽  
Conformational Changes ◽  
Metal Ion ◽  
Tertiary Structure ◽  
Thermal Unfolding ◽  
Apparent Effect ◽  
Thermally Induced ◽  
Circular Dichroïsm ◽  
Secondary And Tertiary Structure

Near-u.v. and far-u.v. c.d. spectra of bovine testis calmodulin and its tryptic fragments (TR1C, N-terminal half, residues 1-77, and TR2C, C-terminal half, residues 78-148) were recorded in metal-ion-free buffer and in the presence of saturating concentrations of Ca2+ or Cd2+ under a range of different solvent conditions. The results show the following: if there is any interaction between the N-terminal and C-terminal halves of calmodulin, it has not apparent effect on the secondary or tertiary structure of either half; the conformational changes induced by Ca2+ or Cd2+ are substantially greater in TR2C than they are in TR1C; the presence of Ca2+ or Cd2+ confers considerable stability with respect to urea-induced denaturation, both for the whole molecule and for either of the tryptic fragments; a thermally induced transition occurs in whole calmodulin at temperatures substantially below the temperature of major thermal unfolding, both in the presence and in the absence of added metal ion; the effects of Cd2+ are identical with those of Ca2+ under all conditions studied.

Circular Dichroism of C-Phycoerythrin: A Conformational Analysis

1980 ◽  
Vol 35 (5-6) ◽  
pp. 367-375 ◽  
Author(s):  
Elisabeth Langer ◽  
Harald Lehner ◽  
Wolfhart Rüdiger ◽  
Barbara Zickendraht-Wendelstadt
Keyword(s):  
Circular Dichroism ◽  
Secondary Structure ◽  
Conformational Changes ◽  
Spectral Region ◽  
Protein Unfolding ◽  
Extensive Study ◽  
Random Coil ◽  
Linear Superposition ◽  
Thermally Induced ◽  
Circular Dichroïsm

Abstract An extensive study of the chiroptical properties of C-phycoerythrin and the α-and β-subunits in the spectral region from 700 -200 nm is presented. Based on the VIS-circular dichroism inherently chiral conform ations are proposed for the co­ valently linked chromophores. By means of mean residue ellipticities and the experimental circular dichroism spectra in the region of the n → π* peptide transition the a-helix contents of the apoproteins of the ac-and ß-subunits are estimated to amount to 60% and 40%, respectively. The circular dichroism spectrum of native C-phycoerythrin is congruent with a linear superposition of the α-and β-subspectra, in the whole spectral region studied. Since a-and β-subunits are associated in native C-phycoery-thrin as revealed by sedim entation analysis the interactions between the subunits in the native chromoprotein are not accom panied by substantial conform ational changes. In the temperature range 0°-40°C the thermally induced changes of the chrom ophores in native C-phycoerythrin are not associated with changes of the secondary structure of the apoprotein. Unfolding occurs at 60°-70°C but slowly leads to irreversible denaturation. Protein unfolding starts at 3 M urea. The random coil secondary structure of the apoproteins is reached at 8 M urea. At this concentration the absorbance and the optical activity of the chrom o­ phores are reduced by a factor 3 and 10, respectively. The conformational changes in the peptide with increasing denaturant concentration are not synchronous with those induced in the Chromo­ phore indicating that a m ultistep process is operative during unfolding. The C D results on dena­ turation are supplem ented by absorption and em ission spectroscopy.

Tunable Organogelator from Alkyl-Polypeptide Diblock Prepared by Ring-Opening Polymerization

2014 ◽  
Vol 67 (1) ◽  
pp. 59 ◽  
Author(s):  
Chongyi Chen ◽  
Decheng Wu ◽  
Wenxin Fu ◽  
Zhibo Li
Keyword(s):  
Atomic Force Microscopy ◽  
Organic Solvents ◽  
Ring Opening ◽  
Ring Opening Polymerization ◽  
Low Concentration ◽  
Force Microscopy ◽  
Atomic Force ◽  
Transmission Electron ◽  
Circular Dichroïsm ◽  
Β Sheet

Three alkyl-polypeptide hybrid amphiphiles were synthesized by the ring-opening polymerization (ROP) of γ-(2-methoxyethoxy)esteryl-l-glutamate N-carboxyanhydride (l-EG1Glu NCA) using alkylamine, i.e. C6H13NH2, C14H29NH2, and C16H33NH2, as initiators. As-prepared alkyl-poly-l-EG1Glu hybrids were found to form clear organogels in several organic solvents at low concentration. FTIR and circular dichroism characterizations suggested that poly-l-EG1Glu formed a predominantly β-sheet conformation, which accounted for the gelation. Transmission electron and atomic force microscopy characterizations revealed that these copolymers formed nanoribbon structures in THF.

Optical anisotropy and sign reversal in layer-by-layer assembled films from chiral nanoparticles

2016 ◽  
Vol 191 ◽  
pp. 141-157 ◽  
Author(s):  
Zhumei Liang ◽  
Kalil Bernardino ◽  
Jishu Han ◽  
Yunlong Zhou ◽  
Kai Sun ◽  
...  
Keyword(s):  
Circular Dichroism ◽  
Optical Activity ◽  
Metallic Nanoparticles ◽  
Density Functional ◽  
Structural Changes ◽  
Building Blocks ◽  
Layer By Layer ◽  
Semiconductor Films ◽  
Surface Ligands ◽  
Circular Dichroïsm

Chiral anisotropy and related optical effects at the nanoscale represent some of the most dynamic areas of nanomaterials today. Translation of optical activity of chiral semiconductor and metallic nanoparticles (NPs) into optoelectronic devices requires preparation of thin films from chiral NPs on both flat and curved surfaces. In this paper we demonstrate that chiral NP films can be made via layer-by-layer assembly (LBL) using negatively charged chiral CdS NPs, stabilized by d- and l-cysteine and positively charged polyelectrolytes, as building blocks. LBL coatings from NPs combine simplicity of preparation and strong optical activity. Circular extinction measurements using circular dichroism instruments indicate that the film possess four chiroptical bands at 280, 320, 350, and 390 nm. The latter two bands at 390 and 350 nm are associated with the band gap transitions (chiral excitons), while the former two are attributed to transitions involving surface ligands. When NPs are assembled in LBL films, the rotatory activity and the sign for circular extinction associated with the electronic transition in the inorganic core of the NPs is conserved. However, this is not true for circular extinction bands at short wavelengths: the sign of the rotatory optical activity is reversed. This effect is attributed to the change of the conformation of surface ligands in the polyelectrolyte matrix, which was confirmed both by semi-empirical and density functional (DFT) quantum mechanical calculations. Circular dichroism spectra calculated using a DFT algorithm closely match the experimental spectra of CdS NPs. These findings indicate that the spectroscopic methods sensitive to chirality of the surface ligands can be used to investigate fine structural changes in the surface layer of nanocolloids. Strong rotatory optical activity of nanostructured semiconductor films opens the possibilities for new polarization-based optical devices.

Sign in / Sign up

Export Citation Format

Share Document