The notes were issued to Darwin as part of the £2.5mln financing deal announced at the end of 2016.
Darwin is to convert the remaining ten notes it holds, worth £250,000, into Graphene shares at 3.601908p per share.
To satisfy the conversion, Malaysia-based Graphene will issue 6.94mln shares, which are expected to be admitted to AIM next Friday (20 April).
Under the terms of the financing agreement, Graphene receives 90% of the par value of the notes. In this case, the company will receive £225,000.
Shares in Graphene NanoChem have more than doubled over the past week as Darwin drew nearer to converting its remaining notes and clearing the stock overhang.
Graphene's share price was up another 1% or so on Thursday afternoon to 7.6p.