Interaction of the ginsenosides with κ-casein and their effects on amyloid fibril formation by the protein: Multi-spectroscopic approaches.

The interaction of the ginsenosides (GS) including ginsenoside Rg1, Rb1 and Re with κ-casein and the effects of GS inhibiting amyloid fibril formation by κ-casein have been investigated in vitro by fluorescence and ultraviolet spectra. Results showed that Rg1 and Rb1 had dose-dependent inhibitory effects on reduced and carboxymethylated κ-casein (RCMκ-CN) fibril formation, while Re resulted in an increase in the rate of fibril formation. The enhancement in RLS intensity was attributed to the formation of new complex between GS and RCMκ-CN, and the corresponding thermodynamic parameters (ΔH, ΔS and ΔG) were assayed. The steady-state ultraviolet-visible absorption spectra had also been tested to observe if the ground-state complex formed, and it showed the same result as RLS spectra. The binding constants and the number of binding sites between GS and RCMκ-CN at different temperatures had been evaluated from relevant fluorescence data. According to the Förster non-radiation energy transfer theory, the binding distance between RCMκ-CN and GS was calculated. The fluorescence lifetime of RCMκ-CN was longer in the presence of GS than in absence of GS, which was evident that the hydrophobic interaction plays a major role in the binding of GS to RCMκ-CN. From the results of synchronous fluorescence, it could be deduced that the polarity around RCMκ-CN Trp97 residue decreased and the hydrophobicity increased after addition of Rg1 or Rb1. Based on all the above results, it is explained that Rg1 and Rb1 inhibited amyloid fibril formation by κ-casein because the molecular spatial conformation and physical property of κ-casein changed causing by the complex formation between GS and κ-casein.

The effects of ginsenosides to amyloid fibril formation by RCMκ-casein.

When not incorporated into the casein micelle, isolated κ-casein spontaneously forms amyloid fibrils under physiological conditions, and is a convenient model for researching generic aspects of fibril formation. Ginsenosides have recently attracted much research interest because of the effects on aging diseases, which are always associated with amyloid fibril formation, for example, Alzheimer's, Parkinson's, and Huntington's diseases. In addition, the mechanism remains unclear that ginsenosides exert the effects against aging diseases. To address these aspects, we have investigated the ability of ginsenoside Rb1, Rc, Rg1, and Re influencing fibril formation by RCMκ-casein (reduced and carboxymethylated κ-casein), with the methods of Thioflavin T fluorescence assay, transmission electron microscopy (TEM), and intrinsic fluorescence spectroscopy. The results showed that ginsenoside Rb1 and Rg1 inhibited obviously RCMκ-CN fibrillation in both the initial rate and final level of ThT fluorescence. On the contrary, ginsenoside Re had a few effect on promoting RCMκ-CN fibril formation, proved by thick and larger fibrils observed frequently in TEM. While Rc did not influence RCMκ-CN fibrillation. It is demonstrated that Rg1 prevent RCMκ-CN fibril formation by stabilising RCMκ-CN in its native like state. Additional chemical structure difference of ginsenosides and the effects on fibril formation are also implicated.

4,4'-Bipyridine-2,2'-(1,2-phenylene-dioxy)diacetic acid-water (1/1/1).

In the title 1:1:1 adduct, C(10)H(8)N(2)·C(10)H(10)O(6)·H(2)O, the dihedral angle between the rings of the 4,4-bipyridine molecule is 10.981 (8)°. In the crystal, O-H⋯O and O-H⋯N hydrogen bonds link the mol-ecules into a zigzag chain structure.

[The influence of pyridyl-carboxylic acid intermolecular H-bond on photoisomerization and photochemical stabilities].

A new type of liquid crystalline was formed through self-assembly via intermolecular hydrogen bonding between the carboxylic acid and the pyridyl group of the stilbazoles. Cholesteryl butane diacid single ester (CSA) was synthesized for use as H-bond donor and the stilbazole derivatives (NCn) were prepared as H-bond acceptors. The spectroscopic behavior and the photochemical stabilities of these two compounds, NCn and its intermolecular H-bonding complex CSA . NCn were investigated by UV-Vis spectroscopy. The results show that these two compounds easily undergo photoisomerization from trans to cis isomers in alcohol. In chloroform solution, the CSA . NCn only undergoes trans-cis photoisomerization, while NCn exhibits not only trans-cis isomerization but also a special photoreaction. The reason is that in CSA . NCn compounds, the pyridyl N-end group is forms intermolecular H-bonding with CSA, and can't catch the H+ and the radical. It is proved that this intermolecular H-bond was very stable when being exposed to UV light.

[Study on the interaction of PTB and serum albumin by fluorescence method].

A molecular spectroscopic investigation of the interaction of phenacyl thiazolium bromide (PTB) and bovine serum albumin (BSA) or human serum albumin (HSA) is reported employing fluorescence quenching techniques. It is determined that the maximal excitation wavelength is 280 nm for BSA solution, and 290 nm for HAS solution. When PTB was added into these solutions gradually, the emission peaks were decreased obviously, which are typical quenching phenomena. The results obtained reveal that there is a medium-intensity binding affinity for PTB with HSA and BSA. At 15 degrees C, the binding constants of PTB and BSA (HSA) are 3.66 x 10(3) and 3.83 x 10(3), and the numbers of binding sites are 1.02 and 1.06 respectively. At 37 degrees C, the binding constants of PTB and BSA (HSA) are 3.58 x 10(3) and 3.35 x 10(3), and the numbers of binding sites are 0.95 and 0.87 respectively. According to the thermodynamic parameters, the main sort of the binding force between the drug and BSA or HSA was electrostatic force. Based on the Föster non-radiation energy transfer theory, it could be acquired that the distance between BSA or HSA and PTB is 7.5 or 7.9 nm. According to the crystal structure of serum albumin, it can be speculated that subdomain II A was the binding sites for the interaction of PTB and serum albumin, which is the region near Try214.