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Dimer/tetramer motifs determine amphiphilic hydrazine fibril structures on graphite.

ABSTRACT: Fibril structures are produced at a solvent-graphite interface by self-assembly of custom-designed symmetric and asymmetric amphiphilic benzamide derivatives bearing C(10) aliphatic chains. Scanning tunnelling microscopy (STM) studies reveal geometry-dependent internal structures for the elementary fibrils of the two molecules that are distinctly different from known mesophase bulk structures. The structures are described by building-block models based on hydrogen-bonded dimer and tetramer precursors of hydrazines. The closure and growth in length of building units into fibrils takes place through van der Waals forces acting between the dangling alkyl chains. The nanoscale morphology is a consequence of the basic molecular geometry, where it follows that a closure to form a fibril is not always likely for the doubly substituted hydrazine. Therefore, we also observe crystallite formation.

SUBMITTER: Thomas LK

PROVIDER: S-EPMC3458612 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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Dimer/tetramer motifs determine amphiphilic hydrazine fibril structures on graphite.

Thomas Loji K LK Diek Nadine N Beginn Uwe U Reichling Michael M

Beilstein journal of nanotechnology 20120919

Fibril structures are produced at a solvent-graphite interface by self-assembly of custom-designed symmetric and asymmetric amphiphilic benzamide derivatives bearing C(10) aliphatic chains. Scanning tunnelling microscopy (STM) studies reveal geometry-dependent internal structures for the elementary fibrils of the two molecules that are distinctly different from known mesophase bulk structures. The structures are described by building-block models based on hydrogen-bonded dimer and tetramer precu ...[more]

PMID: 23019562

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Project description:The ground-state properties of (NO)(2) and (NO)(4) have been investigated using multireference second-order perturbation theory (MRMP2) and include a two-tier extrapolation to the complete basis set (CBS) limit. For the NO dimer the MRMP2(18,14)/CBS predicted structure, binding energy (with respect to 2NO; D(e) = 3.46 kcal/mol), and dipole moment (u(e) = 0.169 D) are in excellent agreement with experimental measurements (D(e) = 2.8-3.8 kcal/mol; u(e) = 0.171 D). Additionally, three of four intermolecular anharmonic MRMP2(18,14)/CBS-estimated frequencies (143 cm(-1), 238 cm(-1), 421 cm(-1)) are in excellent agreement with recent gas-phase experimental measurements (135 cm(-1), 239 cm(-1), 429/428 cm(-1)); however, the predicted value of 151 cm(-1) for the out-of-plane torsion (A(2)) is elevated compared to recent experimental estimates of 97-117 cm(-1). Our finding that this infrared-forbidden vibration is also predicted to have an extremely low Raman activity (0.04 Å/amu at the MP2/QZ level of theory) conflicts with Raman measurements of a strong intensity for a low frequency band; however, these studies were performed for low temperature solid and liquid phases. Probing the possibility of the presence of higher order clusters we investigated the stability of (NO)(4) and discovered three isomers, each resembling pairs of dimers, that were stable to dissociation to 2(NO)(2), with the lowest-energy isomer (C(i) structure) having a predicted binding energy almost identical to that of the dimer. Computed vibrational frequencies of the C(i) isomer indicate that the 12 highest-frequency modes resemble barely shifted NO dimer-combined bands while the 13th highest-frequency mode at ~100 cm(-1) is exclusive to (NO)(4). Moreover, this tetramer-unique vibration is infrared inactive but has a very high predicted Raman activity of some 24 Å/amu. Guided by the theoretical results, we reexamined and reassigned experimental Raman and infrared data going back to 1951 and determined that our best predictions of vibrational frequencies of (NO)(2) and (NO)(4) are consistent with experimental observations. We thus postulate the existence and observation of (NO)(4).

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Dimer/tetramer motifs determine amphiphilic hydrazine fibril structures on graphite.

Publications

Dimer/tetramer motifs determine amphiphilic hydrazine fibril structures on graphite.

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