Аннотация:Non-covalent modification of carbon based nanomaterials with biopolymers is of
fundamental importance to improve the profile of its technological and environmental
application. Modern developments of chemistry of nanomaterials pointed us at the study of
sorption ability of carbon-based nanomaterials to globular proteins and humic substances and
to determine properties of formed complexes.
Three types of carbon-based nanomaterials with different hydrophobic properties were
under the test. They are graphene, single-walled carbon nanotubes and detonated
nanodiamonds. The adsorption capacity carbon-based nanomaterials was studied in relation to
brown coal humic acids (commercially available preparation Powhumus (Humintech, Germany))
and fulvic acids separated from Suwannee River (recommended as a standard by IHSS) and
two globular proteins lysozyme from chicken egg white and human serum albumin (MP
Biomedicals). Tritium label was used to determine or “trace” the amount of biopolymers
adsorbed on solids. For this purpose tritium labeled humic substances and globular proteins
were obtained by means of tritium thermal activation method [1, 2].
5-12 mg sample of nanomaterial powder was placed in the Eppendorf tube followed by the
addition of 0.8 ml of 3H-compound solution in phosphate buffer. The bulk radioactivity of
compounds solutions was ca 55 MBq L-1. Ultrasonication of the dispersion was carried out for
2 hours using a bath sonicator (GRAD, Model 28-35, Russia) with rated power of 110 W
followed by incubation at room temperature for 24 hours. The solutions thus obtained were
subjected to centrifugation at 2400g (Vortex) for 60 min. The upper 75 % of the supernatant
after ultracentrifugation was filtered through 13 mm syringe filter with 0.2 μm PVDF membrane
(Acrodisc LC, Life Sciences). A sample of filtered solution was stirred in 7 ml of scintillation
cocktail OptiPhase HiSafe 3 (PerkinElmer). Counting rate was measured by liquid scintillation
spectrometer RackBeta 1215 (Finland). Adsorption Γ was calculated according to following
equation
Here I is counting rate, ε is registration efficiency of tritium β-radiation (from 40 to 50%), Va is
volume of an aliquot, V = 0.8 ml, asp is specific radioactivity of the compound, c0 is initial
concentration of the compound solution, m is mass of solids.
Since radiotracer method was used adsorption isotherms were obtained in wide
concentration range from 10 to 3000 mg L-1 for proteins and from 0.02 to 200 mg L-1 for humic
substances. The values of the adsorption in plateau regions (in the cases of the Langmuir type
adsorption isotherms) were about 0.5-1 g g-1 for proteins and reaches 40 g g-1 in the cases of
humic substances. Besides determination of nanomaterial-conjugate composition, each
nanomaterial-conjugate sample was subjected to dynamic light scattering analysis that allowed
us to reveal the aggregation stability suspensions on nanomaterial-conjugate composition.