Activation volume measurement for C[bond]H activation. Evidence for associative benzene substitution at a platinum(II) center

The reaction of the platinum(II) methyl cation [(N-N)Pt(CH(3))(solv)](+) (N-N = ArN[double bond]C(Me)C(Me)[double bond]NAr, Ar = 2,6-(CH(3))(2)C(6)H(3), solv = H(2)O (1a) or TFE = CF(3)CH(2)OH (1b)) with benzene in TFE/H(2)O solutions cleanly affords the platinum(II) phenyl cation [(N-N)Pt(C(6)H(5))(solv)](+) (2). High-pressure kinetic studies were performed to resolve the mechanism for the entrance of benzene into the coordination sphere. The pressure dependence of the overall second-order rate constant for the reaction resulted in Delta V(++) = -(14.3 +/- 0.6) cm(3) mol(-1). Since the overall second order rate constant k = K(eq)k(2), Delta V(++) = Delta V degrees (K(eq)) + Delta V(++)(k(2)). The thermodynamic parameters for the equilibrium constant between 1a and 1b, K(eq) = [1b][H(2)O]/[1a][TFE] = 8.4 x 10(-4) at 25 degrees C, were found to be Delta H degrees = 13.6 +/- 0.5 kJ mol(-1), Delta S degrees = -10.4 +/- 1.4 J K(-1) mol(-1), and Delta V degrees = -4.8 +/- 0.7 cm(3) mol(-1). Thus DeltaV(++)(k(2)) for the activation of benzene by the TFE solvento complex equals -9.5 +/- 1.3 cm(3) mol(-1). This significantly negative activation volume, along with the negative activation entropy for the coordination of benzene, clearly supports the operation of an associative mechanism.     

Local dense structural heterogeneities in liquid water from ambient to 300 MPa pressure: evidence for multiple liquid-liquid transitions.

Difference and double-difference near-infrared DO-D and HO-H stretching overtone (2nuOD and 2nuOH) spectroscopy and a rigorous (physically substantiated) band deconvolution technique were applied to reveal three different kinds of inherent (interstitial) structures of liquid water, which determine its high density (compared to ice lh under ambient conditions), its compressibility (under hydrostatic pressure, up to 300MPa), and its high fragility (manifested under temperature variation). Our data processing allowed the rigorous discrimination of up to six vibrational components. On the basis of an extensive comparative analysis combined with available structural data (X-ray and neutron scattering) and molecular dynamics (MD) simulations for liquid water, as well as with experimental and computed data for small non-tetrahedrally arranged water clusters, the major four components could be ascribed to: i) The basic lh icelike substructure; ii) the temperature-dependent remote interstitial "defects" due to tetrahedral displacements (primarily responsible for transport properties); iii) the interstitial "defects" most probably arranged in quasiplanar noncyclic tetramers (totally absent in the ice structure); and iv) the interstitial "defects" formed with increasing pressure, probably arranged in cubic water octamers and composed of two pairs of noncyclic and cyclic tetramer fragments. The latter structures include, essentially, bent hydrogen bonds stabilized by resonance effects.     

Reductive PET-fragmentation-cyclization processes of bicyclo[n.3.0]alkanones: synthesis of angular quasi-triquinane and propellane systems

Bicyclo[3.3.0]octanone and bicyclo[4.3.0]nonanone derivatives with a cyclopropane unit in the α-position and an unsaturated side chain in the γ-position of the carbonyl group undergo fragmentation-cyclization processes leading to quasi-triquinane systems upon reductive photoinduced electron transfer (PET). For example, the new angular triquinane derivative 6 and the new propellane derivative 12 were synthesized in one step from these starting materials in moderate to good yields.     

Systematic Comparison of Peptidic Proteasome Inhibitors Highlights the α‐Ketoamide Electrophile as an Auspicious Reversible Lead Motif

The ubiquitin–proteasome system (UPS) has been successfully targeted by both academia and the pharmaceutical industry for oncological and immunological applications. Typical proteasome inhibitors are based on a peptidic backbone endowed with an electrophilic C‐terminus by which they react with the active proteolytic sites. Although the peptide moiety has attracted much attention in terms of subunit selectivity, the target specificity and biological stability of the compounds are largely determined by the reactive warheads. In this study, we have carried out a systematic investigation of described electrophiles by a combination of in vitro, in vivo, and structural methods in order to disclose the implications of altered functionality and chemical reactivity. Thereby, we were able to introduce and characterize the class of α‐ketoamides as the most potent reversible inhibitors with possible applications for the therapy of solid tumors as well as autoimmune disorders.     

Regioselective Ring‐Opening Polymerization of a Polyhydroxycarboxylic Acid for the Synthesis of a Nanoscale Carrier Material with pH‐Dependent Stability and Sustained Drug Release

Synthetic polyesters are usually composed of monohydroxycarboxylic acids to avoid the problem of regioselectivity during ring‐opening polymerization. In contrast, the linear polyester BICpoly contains four secondary OH groups and is nevertheless esterified regioselectively at only one of these positions. Neither the synthesis of the tricyclic monomers nor the ring‐opening polymerization requires protecting groups, making BICpoly an attractive novel and biocompatible polymer. BICpoly nanoparticles can be loaded with low‐molecular weight drugs or coated onto surfaces as thin films. The release of loaded compounds makes BICpoly an attractive depot for drug release, as shown herein by loading BICpoly with dyes or the cytostatic drug doxorubicin. BICpoly is distinguishable from other polymers by its characteristic pH‐dependent degradation.     

Cation behavior at an artificial cell interface: binding distinguished by ion hydration energetics and size

The unique molybdenum oxide-based nucleophilic porous capsule/artificial cell [{(MoVI)MoVI5O21(H2O)6}12{MoV2O4(SO4)30}]72-, according to an X-ray crystallographic study, traps [Al(H2O)6]3+ complexes above the pores while interacting with the latter via hydrogen bonds; this is supported by 27Al NMR studies of the interaction of the capsule with hydrated Al3+ cations in aqueous solution.