How Accurate Are Circular Dichroism Based Secondary Structure Estimates?

Circular dichroism (CD) spectroscopy is highly sensitive to the secondary structure (SS) composition of proteins. Several methods exist to either estimate the SS composition of a protein or to validate existing structural models using its CD spectrum. The accuracy and precision of these methods depend on the quality of both the measured CD spectrum and the used reference structure. Using a large reference protein set with high quality CD spectra and synthetic data derived from this set, we quantified deviations from both ideal spectra and reference structures due to experimental limitations. We also determined the impact of these deviations on SS estimation, CD prediction, and SS validation methods of the SESCA analysis package. With regard to the CD spectra, our results suggest intensity scaling errors and non-SS contributions as the main causes of inaccuracies. These factors also can lead to overestimated model errors during validation. The errors of the used reference structures combine non-additively with errors caused by the CD spectrum, which increases the uncertainty of model validation. We have further shown that the effects of scaling errors in the CD spectrum can be nearly eliminated by appropriate re-scaling, and that the accuracy of model validation methods can be improved by accounting for typical non-SS contributions. These improvements have now been implemented within the SESCA package.

In-vitro Release Evaluation of Growth Hormone from an Injectable In-Situ Forming Gel Using PCL-PEG-PCL Thermosensitive Triblock

Objective: An injectable long acting In-Situ Forming Gel (ISFG) of human Growth Hormone (hGH) was prepared by using triblock PCL-­‐PEG-­‐PCL (Mw 1500-1500-1500). Ring-Opening Polymerization (ROP) of triblock using microwave was applied. Methods: The BCA protein assay Kit was used to determine the concentration of hGH in the in-vitro release medium. Finally, Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis (SDS-PAGE) tests and Circular Dichroism (CD) spectrum were done to approve the stability of released hGH. The result of ROP demonstrated that the proportion of PCL to PEG accorded with the initial molar ratio of the monomers. The cross-section of the Surface Electron Microscopy (SEM) indicated the porous framework of the hydrogel could load the drug into its tridimensional matrixes structure. There is the low initial burst release of hGH from the supramolecular hydrogel. Results: The maximum in-vitro release of hGH was 71.2 % ± 1.5 that were due to hGH degrading after this time (21 days). The CD spectrum and SDS-PAGE results confirmed the stability of hGH during invitro release evaluation. Conclusion: The results suggest that the sustained-release formulation using PCL-PEG-PCL can be applied to control the release of hGH.

Giant Tunable Circular Dichroism of Large-Area Extrinsic Chiral Metal Nanocrescent Arrays

Circular dichroism (CD) is an interesting phenomenon originating from the interaction of light with chiral molecules or other nanostructures lacking mirror symmetries in three-dimensional (3D) or two-dimensional (2D) space. While the observable effects of optical chirality are very weak in most of the natural materials, they can be designed and significantly enhanced in synthetic chiral structures, where the spatial symmetry of their component are broken on a nanoscale. Therefore, fabrication of composites capable of cheap, time-saving, and giant CD is desirable for the advanced optical technologies. Here, the giant CD of large-area metal nanocrescent array structures was investigated theoretically and experimentally. The largest value of the CD spectrum measured was larger than 0.5, and the CD spectrum was tuned effectively and extensively while maintaining a large peak intensity, which can be attributed to the selective excitation of the lattice surface modes (LSMs) by circularly polarized light. The analysis of the extrinsic chiral structure shows potential applications in chiral molecule sensing and polarizing imaging.

Galewone, an Anti-Fibrotic Polyketide from Daldinia eschscholzii with an Undescribed Carbon Skeleton

A novel polyphenolic natural product, galewone, with undescribed carbon skeleton, was isolated as a racemate from the culture of Daldinia eschscholzii IFB-TL01, a fungus obtained from the mantis (Tenodera aridifolia) gut. The galewone structure was elucidated by a combination of MS and NMR spectra, and substantiated by X-ray crystallographic diffraction. The absolute stereochemistry of each galewone enantiomers was determined by the CD spectrum. In compliance of the structural similarities, galewone might be the shunt products of the dalesconol biosynthetic pathway. Both (−)- and ( + )-galewones were evaluated to be anti-fibrotic against activated hepatic stellate cell line, CFSC-8B, with the IC50 values being 3.73 ± 0.21 and 10.10 ± 0.41 μM, respectively. Thus, galewone may serve as a starting molecule for the discovery of new anti-fibrotic drug.

Pseudo-enantiomeric chiral components and formation of the helical micro- and nanostructures in charge-transfer complexes

Helical organic micro- and nanostructures are formed by a charge-transfer complex, cinchonidine-TCNQ. These unusual forms result from the chirality, the steric structure and specific interactions of cinchonidine molecules. These materials are semiconductors (10 −4 S cm −1 ), with the typical absorption spectra in IR and UV-vis, but also have a characteristic of CD spectrum. Surprisingly, conductive micro and nano helices are not formed in pseudo-enantiomeric cinchonine, i.e. the complex of cinchonine and TCNQ.

DNA-BASED HYBRID LIQUID CRYSTALLINE NANO ORGANOMETALLIC COMPOSITES FOR TARGETED DRUG DELIVERY IN NEUTRON CAPTURE THERAPY

Objective: The aim of this work was focused on the obtaining a DNA-based hybrid nano liquid crystalline organometallic composites for targeted drug delivery in neutron capture therapy.Methods: The formation of a cholesteric liquid crystalline DNA (CLCD-DNA) dispersion has performed using ultrasonic depolymerized calf thymus DNA(MW-0.6-0.8×106Da)2×10-7M, mixing with polyethylene glycol8.5×10-5M, dissolved in the 0.3 M NaCl solution and incubated over 1,0 h at 20 °C. CLCD-DNA formation process was determined and controlled by measuring absorption value of circular dichroism (CD) spectrum in the range of 350-600 nm. The organometallic DNA-Gd compound was formed by processing the obtained CLCD-DNA with 2.49 × 10-4M, 4.97 × 10-4M, 9.8 × 10-4 M, 1.48× 10-3M, 2.92 × 10-3M GdCl3 aqueous solutions. CLCD-DNA-gadolinium complex formation process was registered over the appearance of 2nd amplitude in the CD spectrum. DNA-Gd complex dispersion toxicity was evaluated over 40 min, 24h and 72h incubation with 1×106cells in the RPMI-40 medium supplemented with 3×10-4 M Gd3+.Results: The obtained CLCD-DNA-Gd (d~500 nm) particles was shown less toxicity and higher viability percentage of macrophages after 40 min incubation with CLCD-DNA-Gd contains Gd3+ions concentration 3×10-4 M showed 100% viability and after 72 h ours approximately 89%. The cells immobilized with CLCD-DNA-Gd particles contains 3×10-4M Gd3+, neutron irritation was caused a 100% cell deaths.Conclusion: Obtained relatively stable, non-cytotoxic drug forms with a maximum local concentration of gadolinium (400 µg/ml). The effectiveness of these nanosystems for targeted drug delivery has markedly superior efficacy than 10B and other products were based on gadolinium.

Alkaloids from the Tuber of Stephania cf. rotunda

Chemical investigation of the tuber of Stephania cf. rotunda collected in Vietnam led to the isolation of a new stephaoxocane-type alkaloid, stepharotudine (1), twenty-eight known alkaloids, and two known amides. The chemical structures of the isolated compounds were determined by spectroscopic and chemical methods. The absolute configuration of the new compound was determined from its CD spectrum and by 1H NMR analyses of its MPA esters. For the known alkaloids (-)-crebanine-β- N-oxide (2), uthongine (3), and palmatrubine (4), fully assigned NMR data are also reported for the first time.