Anisotropic Ferromagnetic Organic Nanoflowers

We report a weak anisotropic ferromagnetic behavior in a purely organic molecule at room temperature, a property rarely reported in organic nanomaterials. The reported 1,2-bis(tritylthio)ethane, forming plate- and organic-flower-like morphologies at the nanolevel, is the first organic crystal with an inherent magnetic property at 300 and 2 K. However, at low temperatures, the magnetization value [Mmax(T) ∼116 emu/mol at 2 K] increases drastically at 3 orders higher compared to 300 K. Interestingly, the system exhibits strong anisotropy with an anisotropic constant, K1 ∼3.25 7 103 erg/cc, and anisotropy field, HK ∼3.25 kOe. Below 10 K, this system displays unusual temperature dependence of the coercive field [HC(T)] and remanence magnetization [MR(T)] with a hysteresis-peak anomaly (T∗ ∼10-15 K) due to the enhanced spin-orbit coupling. The maximum HC and MR at T∗ were HC = 220 Oe and MR ∼12 emu/mol, respectively. Beyond T*, HC(T) and MR(T) drop continuously and become negligible as the measurement temperature approaches 300 K. Our results demonstrate that the triphenyl molecules can be further exploited for the design and synthesis of organic magnets for possible applications in spintronics and memory storage devices

Formation of extended sheeted structures and their breaking.

<p>S-3 to S basin shifts indicates formation of sheet as a result of right handed movement of the χ₁ rotor and complimenting counter rotation of ϕ; ψ rotor moves in the counter-direction of the ϕ rotor throughout formation and breaking of sheet. See also Figures A1-A4 in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0163993#pone.0163993.s001" target="_blank">S1 File</a>.</p

Mapping the Geometric Evolution of Protein Folding Motor

<div><p>Polypeptide chain has an invariant main-chain and a variant side-chain sequence. How the side-chain sequence determines fold in terms of its chemical constitution has been scrutinized extensively and verified periodically. However, a focussed investigation on the directive effect of side-chain geometry may provide important insights supplementing existing algorithms in mapping the geometrical evolution of protein chains and its structural preferences. Geometrically, folding of protein structure may be envisaged as the evolution of its geometric variables: ϕ, and ψ dihedral angles of polypeptide main-chain directed by χ₁, and χ₂ of side chain. In this work, protein molecule is metaphorically modelled as a machine with 4 rotors ϕ, ψ, χ₁ and χ₂, with its evolution to the functional fold is directed by combinations of its rotor directions. We observe that differential rotor motions lead to different secondary structure formations and the combinatorial pattern is unique and consistent for particular secondary structure type. Further, we found that combination of rotor geometries of each amino acid is unique which partly explains how different amino acid sequence combinations have unique structural evolution and functional adaptation. Quantification of these amino acid rotor preferences, resulted in the generation of 3 substitution matrices, which later on plugged in the BLAST tool, for evaluating their efficiency in aligning sequences. We have employed BLOSUM62 and PAM30 as standard for primary evaluation. Generation of substitution matrices is a logical extension of the conceptual framework we attempted to build during the development of this work. Optimization of matrices following the conventional routines and possible application with biologically relevant data sets are beyond the scope of this manuscript, though it is a part of the larger project design.</p></div

MIDMAT 2 substitution matrix.

<p>MIDMAT 2 substitution matrix constructed using a different approach than MIDMAT1 as discussed in results section, from the same set of 22,997 non-redundant structures from PISCES server. The amino acids are represented as single letter codes.</p

MIDMAT 1 substitution matrix.

<p>MIDMAT 1 substitution matrix values are calculated based on basin statistics derived from the rotor combinations of amino acids in the structural dataset of 22,997 non-redundant structures from PISCES server. The amino acids are represented as their single letter codes.</p

MIDMAT 3 substitution matrix.

<p>MIDMAT3 substitution matrix constructed by following the third strategy (results section) for calculation of B_i, from the identical data set of 22,997 non-redundant structures from PISCES server.</p

Differential distribution of side-chain and main-chain rotors among representative amino acid sets.

<p>Dissimilar ϕ vs χ₁ basins in protein structures for various amino acid types. Differential basin preferences for different amino-acids are calculated from the entire database of 22,977 non-redundant structures. Localization for the χ₁ and ϕ dihedral rotors in protein structures are evident.</p

Helical structure formation and its breaking.

<p>H-3 to H basin shifts indicate formation of helix as a result of left handed rotation of the χ₁ rotor and right handed rotation of ϕ by 80° while helix breaking the rotors assume reverse orientations. The ψ rotor maintains its right handed rotation throughout helix formation and breaking. See also Figures A1-A4 in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0163993#pone.0163993.s001" target="_blank">S1 File</a>.</p