HIGHLIGHTS
Organic chemistry
G. RICHARD STEPHENSON University of East Anglia, UK
Lining up silver ions
The capabilities of DNA make it one of the most important organic molecules in biology, and the patterns of base-pairing across the centre of the famous double helix are well-known. Their role in nature is to carry the genetic code. A remarkable example of putting these DNA bases to an alternative, unnatural, use, has appeared in Nature Chemistry (J. Kondo, Y. Tada, T. Dairaku, Y. Hattori, H. Saneyoshi, A. Ono, Y. Tanaka, Nature Chem., 2017, 9, 956). The results extend earlier studies
of C-Ag-C silver insertion motifs, to include G and T bases as well, in both symmetrical and unsymmetrical combinations. This allows silver ion nanowires to be constructed by using a synthetic DNA dodecamer. A crystallographically (Figure 1)
characterised GGCTCGTCC repeat pattern shows that these 12-base sections of single-stranded DNA line up in an offset pattern with C available at one end of the silver- linked double strand, and G available at the other.
O O O A consequence of this is that the
formation of a G-Ag-C silver-mediated linkage joins the paired dodecamers together to form an extended with lengths with just a single strand of silver ions running through its centre. The silver ions at the centre associate in an argentophilic fashion, helping to hold the wire together and perhaps assisting its formation. The separation between individual silver ions is about 3.2-3.4Å, which is less than the sum of their van der Waals radii.
Polymeric porphyrins form a metal- containing lustrous foil Porphyrins are a classic example of a natural metal-binding class of organic molecules, and, like DNA, are popular in unnatural materials – science applications. Consequently, polymers that
contain in-chain porphyrin rings have become a major field of study, and designs of the repeat motif are becoming ever more sophisticated. The example shown in Figure 2 is remarkable because it allows a self-supporting porphyrin-based foil to form (M. Morisue, Y. Hoshino, M. Shimizu, S. Tomita, S. Sasaki, S.
G
A
G G C T
A
G G C T
G G
N N G N NH2 O Guanine H2N N N N Ag N N Guanine Guanine A
Figure 1 When the 12 base GGCTCGTCC se- quence (left structure) with adenine (A) bases folded out, pairs with the same sequence in the reverse order, the G-Ag-C motif has a free guanine (G) base attached to it as a ‘sticky end’. On the right is an enlargement of the way G-Ag-G can link adjacent GGCTCGTCC se- quences together to form extended wires with an aspect ratio of 0.1mm to 2nm (50,000)
N O O
GG Ag
Ag Ag Ag Ag Ag Ag Ag Ag Ag
C C T
C G A
C T
G A
G C
O H2N N Ag N
N C Cytosine N N G A NH2 A A
G G A C
Ag Ag Ag Ag Ag
G C
A G A A
G C T
G G C T
G G
G C T
G G C T
G G
G C T
G G C T
G G
A
G C T
A
G G C T
G G
N N
Zn
N N
A
G C T
O O O
Figure 2 The porphyrin-alkyne- anthracene repeat pattern occurs in a polymer with Mn = 54000 and Mw/ Mn = 4.2. It forms a porphyrin foil with a green metallic luster.
A
G G C T
G G
GG
Ag Ag Ag Ag Ag Ag Ag Ag Ag Ag
GG
Ag Ag Ag Ag Ag Ag Ag Ag Ag Ag
GG
Ag Ag Ag Ag Ag Ag Ag Ag Ag Ag
GG
Ag Ag Ag Ag Ag Ag Ag Ag Ag Ag
Ag Ag Ag Ag Ag Ag Ag Ag Ag
C C T
C G A
C T
C G A
09 | 2017 43
C C T
C G A
C T
C G A
C C T
C G A
C T
C G A
C C T
C G A
C T
C G A
C C T
C G A
C T
C G A
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52
