A stereoselective synthesis of verbalactone—determination of absolute stereochemistry

A total synthesis of verbalactone has been achieved starting from l-malic acid. The two appropriately protected acid and alcohol segments were prepared from l-malic acid and lactonized under Yamaguchi conditions.     

Factors governing fibrillogenesis of polypeptide chains revealed by lattice models

Using lattice models we explore the factors that determine the tendencies of polypeptide chains to aggregate by exhaustively sampling the sequence and conformational space. The morphologies of the fibril-like structures and the time scales (τ(fib)) for their formation depend on a balance between hydrophobic and Coulomb interactions. The extent of population of an ensemble of N* structures, which are fibril-prone structures in the spectrum of conformations of an isolated protein, is the major determinant of τ(fib). This observation is used to determine the aggregating sequences by exhaustively exploring the sequence space, thus providing a basis for genome wide search of fragments that are aggregation prone.     

Integral equation theory for symmetric nonadditive hard sphere mixtures

An integral equation theory is presented for the pair correlation functions and phase behavior of symmetric nonadditive hard sphere mixtures with hard sphere diameters given by sigma(A)(A)() = sigma(BB) = lambdad and sigma(AB) = d. This mixture exhibits a fluid-fluid phase separation into an A-rich phase and a B-rich phase at high densities. The theory incorporates, into the closure approximation, all terms that can be calculated exactly in the density expansion of the direct correlation functions. We find that the closure approximation developed in this work is accurate for the structure and phase behavior over the entire range of lambda, when compared to computer simulations, and is significantly more accurate than the previous theories.     

The behavior of fluids near solutes: a density functional theory and computer simulation study

The density distribution of solvent near a solute particle is studied using density functional theory and Monte Carlo simulation. The fluid atoms interact with each other via a hard sphere plus Yukawa potential, and interact with the solute via a hard sphere potential. For small solute sizes, the solvent displays liquidlike ordering near the particle. When the solute become larger, a drying transition is observed at state points near the coexistence conditions of the solvent. These predictions are similar to those of a recent theory for the hydrophobic effect by Lum, Chandler, and Weeks [J. Phys. Chem. 103, 4570 (1999)], although a comparison with simulations shows that the theory of this work is quantitatively more accurate. The connection between density functional methods and the LCW approach is also established.     

A Fast and Highly Efficient Protocol for Reductive Amination of Aromatic Aldehydes Using NaBH4 and Isoxazole Amines in an Ionic Liquid Medium

Reductive amination of aromatic aldehydes using NaBH₄ and isoxazole amines is carried out in a Brønsted acidic ionic liquid 1‐methylimidazolium tetrafluoroborate [(HMIm)BF₄]. The ionic liquid plays dual roles of solvent as well as catalyst for the efficient transformation of aromatic aldehydes to heterocyclic substituted amines in excellent yields without any undesired side product formation. The newly synthesized compounds ( 3 , 6 and 7 ) were characterized by IR, ¹H NMR and mass spectral techniques.     

Single Crystal‐to‐Single Crystal Site‐Selective Postsynthetic Metal Exchange in a Zn–MOF Based on Semi‐Rigid Tricarboxylic Acid and Access to Bimetallic MOFs

The metal ions in a neutral Zn–MOF constructed from tritopic triacid H₃L with inherent concave features, rigid core, and peripheral flexibility are found to exist in two distinct SBUs, that is, 0D and 1D. This has allowed site‐selective postsynthetic metal exchange (PSME) to be investigated and reactivities of the metal ions in two different environments in coordination polymers to be contrasted for the first time. Site‐selective transmetalation of Zn ions in the discrete environment is shown to occur in a single crystal‐to‐single crystal (SCSC) fashion, with metal ions such as Fe³⁺, Ru³⁺, Cu²⁺, Co²⁺, etc., whereas those that are part of 1D SBU sustain structural integrity, leading to novel bimetallic MOFs, which are inaccessible by conventional approaches. To the best of our knowledge, site‐selective postsynthetic exchange of an intraframework metal ion in a MOF that contains metal ions in discrete as well as polymeric SBUs is heretofore unprecedented.