Spectroscopic studies on the interaction between human hemoglobin and CdS quantum dots.
The interaction between human adult hemoglobin (Hb) and bare CdS quantum dots (QDs) was investigated by fluorescence, synchronous fluorescence, circular dichroism (CD), and Raman spectroscopic techniques under physiological pH 7.43. The intrinsic fluorescence of Hb is statically quenched by CdS QDs. The quenching obeys the Stern-Volmer equation, with an order of magnitude of binding constant (K) of 10(7). The electrostatic adsorption of Hb on the cationic CdS QDs surface is energetically favorable (DeltaS(0)=70.22 Jmol(-1)K(-1), DeltaH(0)=-23.11 kJmol(-1)). The red shift of synchronous fluorescence spectra revealed that the microenvironments of tryptophan and tyrosine residues at the alpha(1)beta(2) interface of Hb are disturbed by CdS QDs, which are induced from hydrophobic cavities to a more exposed or hydrophilic surrounding. The secondary structure of the adsorbed Hb has a loose or extended conformation for which the content of alpha-helix has decreased from 72.5 to 60.8%. Moreover, Raman spectra results indicated that the sulfur atoms of the cysteine residues form direct chemical bonds on the surface of the CdS QDs. The binding does not significantly affect the spin state of the heme iron, and deoxidation is not expected to take place on the coated oxyhemoglobin. The change of orientation of heme vinyl groups was also detected.
Shen
Xing-Can
XC
College of Chemistry and Chemical Engineering, Key Laboratory of Medicinal Chemical Resources and Molecular Engineering, Guangxi Normal University, 15 YuCai Road, Guilin 541004, People's Republic of China. xcshen@mailbox.gxnu.edu.cn
Liou
Xin-Yan
XY
Ye
Li-Ping
LP
Liang
Hong
H
Wang
Zuo-Yuan
ZY
D000327:Adsorption; D000328:Adult; D024322:Amino Acids, Aromatic; D019187:Cadmium Compounds / Q000737:chemistry*; D003545:Cysteine; D005453:Fluorescence; D006454:Hemoglobins / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D011485:Protein Binding; D017433:Protein Structure, Secondary; D045663:Quantum Dots; D013057:Spectrum Analysis; D055672:Static Electricity; D013440:Sulfides / Q000737:chemistry*; D013816:Thermodynamics
D024322:Amino Acids, Aromatic; D019187:Cadmium Compounds; D006454:Hemoglobins; D013440:Sulfides; C034939:cadmium sulfide; D003545:Cysteine