Synthesis, crystal structure determination, spectroscopic and electrochemical studies of trans-[Ru(PPh3)2(bbpH2)Cl]Cl·CHCl3·H20 (bbpH2=2,6-bis(benzimidazolyl) pyridine) – an infinite double columnar supramolecule in the solid state

The synthesis, crystal structure, redox and spectroscopic properties of trans-[Ru(bbpH₂)(PPh₃)₂Cl]Cl are reported. In the crystalline solvate trans-[Ru(bbpH₂)(PPh₃)₂cCl]Cl CHCl₃ H₂O, the molecular components are connected by strong intermolecular hydrogen bonding to form an infinite double column.     

Solution study of a structurally characterized monoalkoxo-bound monooxo-vanadium(V) complex: spontaneous generation of the corresponding oxobridged divanadium(V,V) complex and its electroreduction to a mixed-valence species in solution

An interesting transformation of a structurally characterized monooxoalkoxovanadium(V) complex [VO(OEt)L] (LH 2 = a dibasic tridentate ONO donor ligand) in solution leading to the formation of the corresponding monooxobridged divanadium(V,V) complex (VOL) 2O is reported. This binuclear species in solution is adequately characterized by elemental analysis, measurement of conductance (in solution), various spectroscopic (UV-vis, IR, NMR, and mass spectrometry) techiniques and by cyclic voltammetry. The corresponding mixed-valence vanadium(IV,V) species has been generated in CH 3CN solution by controlled potential electrolysis of (VOL) 2O. This mixed-valence species is identified and studied by EPR technique (at room temperature and at liquid nitrogen temperature) and also by UV-vis spectroscopy. This study may be regarded as a general method of obtaining monooxo-bridged binuclear vanadium(V,V) species from the corresponding mononuclear monooxoalkoxovanadium(V) complexes of some selected dibasic tridentate ONO chelating ligands, which can be utilized as the precursor of monooxobridged divanadium(IV,V) mixed-valence species in solution obtainable by controlled potential electrolysis.     

theK L-K S mass difference in left-right symmetric models and the right-handed Kobayashi-Maskawa matrix

Zeitschrift für Physik C Particles and Fields - K L-K S mass difference is computed in a left-right symmetric model with three generations of quarks. Under the assumption of...     

Organosilicon backbone containing pyridyl/quinolyl ligands: Synthesis, complexation reactions and single crystal structures of metallamacrocyclic Pd(II) and Cu(II) complexes

Organosilicon backbone containing ligands 1,2-bis(dimethyl(2-pyridyl)silyl)ethane (L¹) and 1,2-bis(dimethyl(3-quinolyl)silyl) ethane (L²) have been synthesized by treating 2-bromopyridine and 3-bromoquinoline with n-butyllithium and reacting the resulting lithiated products with 1,2-bis(chlorodimethylsilyl)ethane. The ligation of L¹ and L² with Pd(II), Ag(I) and Cu(II) has been investigated. The single crystal structures of L², [Pd(L¹)Cl₂] (1), [Cu(L¹)Br₂] (3) and [PdCl₂(L²)]₂ (4) have been solved. All the three complexes are metallamacrocyclic in nature. The last one is 22-membered and the first example which has ligands containing organosilicon backbone. The geometry of Pd as well as Cu is very close to square planar. The Pd–N, Pd–Cl, Cu–N and Cu–Br bond distances (2.010(1)–2.027(3), 2.3063(10)–2.3114(4), 2.004(4)–2.018(5) and 2.4137(10)–2.4172(10) Å) are very close to sum of covalent radii, indicating strong ligation of L¹ and L² with the metal ions.     

Spacer flexibility in bis(pyridyl) ligands: chelating organosilicon pyridylethynyl ligands

Two new bis(pyridylethynyl) ligands with organosilicon spacers have been synthesized. The ligands react readily with silver(I) to form crystalline complexes, both of which are revealed to be triflate-bridged dimers by X-ray crystallographic analysis. The complex with the flexible siloxane-based ligand possesses considerably less bond angle distortion.     

Periodic cosmic evolution in f(Q) gravity formalism

We study the periodic cosmic transit behavior of the accelerated universe in the framework of symmetric teleparallelism. The exact solution of field equations is obtained by employing a well-known deceleration parameter (DP) called periodic varying DP, $q=m\cos {kt}-1$. The viability and physical reliability of the DP are studied by using observational constraints. The dynamics of periodicity and singularity are addressed in detail with respect to time and redshift parameter. Several energy conditions are discussed in this setting.     

Role of foldability and stability in designing real protein sequences

This work explores the effects of two different fitness criteria, the free energy of folding (ΔG(folding)) and foldability (Φ) of mutated sequences, by measuring the designed protein's robustness via cumulative random point mutations. The results of a self-consistent mean-field based theory are used to design 'wild type' protein sequences corresponding to a specified target structure for a given foldability criteria Φ. The theory is applied on three 36-mer real protein conformations and the 'wild type' sequences are identified in terms of site specific monomer probabilities corresponding to a given foldability. Unlike the stability criteria, ΔG(folding) < 0, the foldability criteria Φ(mutated) < -1 effectively identifies sequences of different site-specific monomer identities by specifying the mean and variance of the energy of the unfolded state ensemble. The results depict a distinct difference in the pattern of mutational robustness of the neutral sequence space, Φ(mutated) < -1 scans more number of neutral sequences compared to ΔG(folding) < 0 to find the evolutionary fit sequences. Φ(mutated) < -1 also accounts for marginally stable sequences which are not effectively scanned by ΔG(folding) < 0 to determine evolutionary fitness. The results clearly point out that viable mutated sequences that are foldable, may not always conform to ΔG(fold) < 0, hence assessing the role of foldability in addition to stability for determining protein's robustness towards cumulative random point mutations. These observations may be used in engineering and designing de novo protein sequences which are more robust towards random point mutations.     

Shape, flexibility and packing of proteins and nucleic acids in complexes

Determining the change in topological properties like shape, flexibility and packing of proteins and nucleic acids on complexation is important in characterizing the role of induced structural changes and various interactions which control the functional specificity of proteins and nucleic acids. To this end, we have analyzed and compared the three dimensional structures of several protein-protein, protein-DNA and protein-RNA complexes available in the Protein Data Bank (PDB) and the Nucleic Acid Data Bank (NDB). The size of complexed proteins and nucleic acids, as measured by the radius of gyration, follows Flory's scaling law. The change in the scaling exponents for proteins, RNA and DNA reflects the changes in their respective sizes due to complexation. The anisotropy in the shape of proteins, DNA and RNA in complexes is measured by considering the asphericity and shape parameter, which are calculated from the eigenvalues of the moment of inertia tensor. The distribution of asphericity and shape shows that complexed proteins are mostly spherically symmetrical, while DNA and RNA in complexed states are largely prolate and considerably more aspherical compared to the proteins. Persistence length characterizes the intrinsic flexibility/rigidity of proteins and nucleic acids. The flexibility of all biomolecules decreases with the chain length. For small DNA molecules (6-147 base pairs), persistence length is larger compared to RNA and proteins in protein-protein and protein-RNA complexes. The flexibility of DNA increases, while RNA decreases, in their respective complexed states as compared to that of proteins which remain almost unchanged. The two body contact analysis confirms that the side-chain-backbone contacts are predominant compared to sidechain-sidechain and backbone-backbone contacts in the complexed proteins. The average packing density of proteins decreases in their complexed states, which is measured by the mean value of the contact density of their alpha carbon atoms. The average number of hydrogen bonds are found to be less in the interface region of protein-protein complexes compared to that in protein-DNA and protein-RNA complexes.     

The reactivity of a ruthenium(III) ammine complex, [Ru(NH3)5Cl]Cl2, towards α-N-heterocyclic mono- and di-carboxylic acids. The synthesis and characterisation of biologically active mixed ligand ruthenium(III) complexes

Ruthenium(III) complexes containing one, two or three -N-heterocyclic mono- and di-carboxylic acid groups were prepared from the ammine complex, [Ru(NH₃)₅Cl]Cl₂ by judicious interplay of controlling factors such as the metal:ligand ratio, reflux time etc. All the complexes were characterised by elemental analyses, spectroscopic (u.v.-vis., i.r., e.p.r.) techniques, magnetic measurements (at room temperature) and conductance measurements in solution. The electrochemical behaviour of the soluble complexes was studied by cyclic voltammetry. Their biological activity, in terms of the growth inhibition of Escherichia coli 10536, has been examined.