Tubular Assemblies DOI: 10.1002/ange.201204776 Solution-Phase and Magnetic Approach towards Understanding Iron Gall Ink-like Nanoassemblies** Harshita Kumari, Steven R. Kline,* Cindi L. Dennis,* Andrew V. Mossine, Rick L. Paul, Carol A. Deakyne,* and Jerry L. Atwood* The degradative oxidation of Leonardo da Vinci)s oeuvre, the works of Galileo, and many other imperiled ancient manu- scripts is, ironically, catalyzed by the very ink that was used to write them. [1] Historical artifacts such as these are charac- terized by the extensive use of “iron gall ink”, an ink commonly used prior to the twentieth century. Regardless of the specific composition, iron gall inks are complexes of various polyphenolic gallic acids, a class of tannins, and ferric/ ferrous ions, along with other agents such as gypsum and gum arabic. In the interest of preserving such invaluable works of ancient prose, Fe complexes with polyphenolic compounds, such as gallic acid, catechin, ellagic acid and pyrogallol, have been extensively studied by IR, ESR, NMR, XANES and Mçssbauer spectroscopy. [2] However, structural elucidation of these complexes has proven difficult. Our interest in this field stems from the difficulty in characterizing similar Fe-poly- phenolic complexes, namely the complexes with the bowl- shaped pyrogallol[4]arenes (PgC n , n = alkyl chain length). Compared to other PgC-transition metal capsular entities, which have been thoroughly studied and characterized by XRD, the structure of the PgC n Fe complexes has largely remained a mystery, much like that of the chemically similar gall inks. [3] Herein, we present a new approach towards the characterization of these unique complexes through the combination of solid-state magnetic and in situ neutron scattering methods. In our previous studies, solid-state properties aided our understanding of solution-phase behavior. [4] For example, solid-state PgC n M entities (M = Zn, Cu, Ni, Co) are spherical, and our small-angle neutron scattering (SANS) experiments indicate that they retain that architecture when dissolved in non-polar solvents. [5] In contrast, solid-state PgC 4 Ga and PgC 4 GaZn entities have rugby-ball and spherical shapes, respectively, which convert to toroids of different metric dimensions in solution. [6] Thus, SANS allows differentiation between architectures of similar metric dimensions and between varying metric dimensions of similar architectur- es. [5a, 6] The current study addresses our three-fold interest in investigating solution structures of magnetically interesting self-assembled frameworks, obtaining solid-state insight from solution-phase studies and exploring the parameters that direct self-assembly. Specifically, the stability, elemental ratios and magnetic properties of Fe-containing C-alkylpyro- gallol[4]arene (PgC n Fe) nanoassemblies were examined. PgC 1 Fe or PgC 3 Fe was synthesized by mixing 4 equiv of Fe(NO 3 ) 3 with 1 equiv of PgC n and 14 equiv of C 5 H 5 N (Py) in a variety of solvent systems. The blue-black precipitates obtained could not be crystallized; thus, structural studies were conducted using SANS. The solid-state magnetic behavior of these entities was investigated using a SQUID magnetometer. The composition of these nanoframeworks was measured with prompt gamma activation analysis (PGAA). The PGAA results for solid-state PgC 1 Fe and PgC 3 Fe reveal C :Fe ratios of 27.8 :1 and 28.5 :1 and C :N ratios of 28.1:1 and 29.2 :1, respectively (see Supporting Information). The 1:1 ratio between Fe and C 5 H 5 N-derived nitrogen agrees with the metal:Py ratios typically found in metal-seamed pyrogallol- [4]arene dimeric host capsules. [5b,c] However, in contrast to the typical capsular metal:PgC n ratio of 4:1, the Fe:PgC n ratio was unexpectedly deduced to be 1.3:1. [5a] This ratio also differs from those for the tubular and dimeric PgC 1  ferrocene (PgC 1 Fc) hydrogen-bonded inclusion complexes, for which the Fc:PgC 1 ratios are 1:3 and 1:2, respectively. [4c, 7] In the SANS study, the [D 6 ]DMSO-solubilized PgC 1 Fe (3 % mass fraction) was measured on the NG7 30 m SANS instrument at the NIST Center for Neutron Research (NCNR) in Gaithersburg, MD [8] and analyzed with IGOR Pro. [9] The scattering length density (SLD) of PgC 1 Fe was calculated at the molar ratio of 1:1.3:1.3 (PgC 1 :Fe:Py) obtained from the PGAA results, and the scattering data was fitted to spherical, [10] cylindrical [11] and ellipsoidal models. [12] The data analysis revealed distinct structural differences between previously investigated metal-seamed spherical [4a,c] nanoassemblies and the Fe-containing pyrogal- lol[4]arene nanoassemblies (Figure 1). The scattering for PgC 1 Fe was higher at low scattering angles (q) and fitted [*] Dr. H. Kumari, A. V. Mossine, Prof. C. A. Deakyne, Prof. J. L. Atwood Department of Chemistry, University of Missouri-Columbia 601 S. College Avenue, Columbia, MO 65211 (USA) E-mail: deakynec@missouri.edu atwoodj@missouri.edu Dr. S. R. Kline NIST Center for Neutron Research National Institute of Standards and Technology 100 Bureau Drive, Gaithersburg, MD 20899 (USA) E-mail: steven.kline@nist.gov Dr. C. L. Dennis, Dr. R. L. Paul Material Measurement Laboratory National Institute of Standards and Technology 100 Bureau Drive, Gaithersburg, MD 20899 (USA) E-mail: cindi.dennis@nist.gov [**] We thank NSF for support of this work (J.L.A.) and NIBIB for training grant T21 EB004822 (A.V.M.). This work utilized facilities supported in part by the NSF under Agreement No. DMR-0944772 (S.R.K.). Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/anie.201204776. A ngewandte Chemi e 1 Angew. Chem. 2012, 124,1–5  2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim These are not the final page numbers! Ü Ü