Dedicated to Professor K. Barry Sharpless
Nanochemistry is the synthesis and study of well-defined structures with dimensions of 1 ยฑ 100 nanometers (nm), and thus spans the size range between molecules and materials. [1] While supramolecular chemistry (making small molecules bigger) and microfabrication techniques (making big structures smaller) attack from the flanks, biology employs many constructs of this size. Examples include the photosynthetic reaction center, the ribosome, and membrane-bound receptor-signaling complexes, all notable because of their sophisticated yet modular function. The burgeoning field of nanotechnology [2] seeks to mimic the information-handling, materials-building, and responsive sensing capabilities of biological systems at the nanometer scale. The special requirements of this enterprise would be well served by building blocks of the proper size with predictable and programmable chemistry.
Cowpea mosaic virus (CPMV) particles are 30 nm-diameter icosahedra, formed by 60 copies of two different types of protein subunits (Figure 1 a). [3] The physical, biological, and genetic properties of CPMV have been well characterized. [4] Approximately one gram of virus is easily and routinely obtained from a kilogram of infected leaves of the black-eye pea plant. The structure of CPMV has been characterized at 2.8 รค resolution by X-ray crystallography and an atomic model of the particle has been constructed. [5] The virion displays icosahedral symmetry to the resolution of the crystal structure and an infectious clone of the virus allows sitedirected and insertional mutagenesis to be performed in a straightforward and rapid manner. [6] The particles are remarkably stable; they maintain their integrity at 60 8C (pH 7) for at least one hour and at pH values from 3.5 to 9 indefinitely at room temperature. Different crystal forms of the virus can be readily produced under well-defined conditions (Figure 1 d). [7, 8] Here we report on the selective
Experimental Section
Single crystals: Succinic acid (0.20 g; Aldrich) was dissolved in cyclohexanol (4.0 g; Acros) and carefully layered above water (5.0 g) containing Ni(acetate) 2 ยฅ 6 H 2 O (0.20 g; Alfa Aesar) inside a Teflon autoclave liner (23 mL). The autoclave was heated under autogenous pressure to 150 8C for 3 days and the product, pale blue-green hexagonal platelets, was separated by filtration. Powder samples for physical characterization were prepared in a similar manner by combining Ni(acetate) 2 ยฅ 6 H 2 O (Alfa Aesar), succinic acid (Aldrich), and water in a 1:2:50 molar ratio. In situ X-ray powder diffraction data were collected every 25 8C on a Phillips X-Pert powder diffractometer using Cu Ka radiation. Elemental analysis (%) calcd: C 24.5, H 2.6; found: C 23.7, H 2.4; the calculation assumes 0.6 surface water molecules per formula unit, as measured by TGA. 040(1),c 45.860(4) รค,V 17 581(2) รค 3 ,Z 18,1 1.995 Mg m ร3 , R 1 0.0444 for 3290 reflections, I > 4sI for 267 least-squares parameters. Single-crystal diffraction data were collected to 0.75 รค on a clear, hexagonal crystal (0.12 ร 0.12 ร 0.08 mm) using a Bruker SMART CCD system with Mo Ka radiation (0.71073 รค). An absorption correction was made using SADABS. [20] Lorentz and polarization corrections were made, the structure was solved using direct methods, and the data were refined against j F 2 j using the SHELXTL suite. [21] All non-hydrogen atoms were refined anisotropically, and hydrogen atoms were placed in calculated positions with isotropic U values 20 % higher than the atom to which they were bound. Crystallographic data (excluding structure factors) for the structure reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-169140. Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK