Methyl, hydrochalcogenido, and phenylchalcogenolate complexes of zinc in a sulfur rich coordination environment: syntheses and structural characterization of the tris(2-mercapto-1-tert-butylimidazolyl)hydroboratozinc complexes [TmBut]ZnMe, [TmBut]ZnEH (E = S, Se) and [TmBut]ZnEPh (E = O, S, Se, Te)

A series of hydrochalcogenido and phenylchalcogenolate complexes of zinc supported by tris(2-mercapto-1-tert-butylimidazolyl)hydroborato ligation, [Tm(Bu(t))]ZnEH (E = S, Se) and [Tm(Bu(t))]ZnEPh (E = O, S, Se, Te) have been synthesized from [Tm(Bu(t))]ZnMe; structural characterization by X-ray diffraction indicates that the variation in Zn-E bonding as a function of the chalcogen is significantly different from that in other series of metal-chalcogenolate compounds.     

Pincer-porphyrin hybrids

[reaction: see text] Starting from tetrakis(3,5-bis(bromomethyl)phenyl)porphyrin, pincer-porphyrin hybrid molecules (tetrakis(ECE-pincer)porphyrin; E = N, P, S) based on a tetraphenylporphyrin skeleton have been prepared in high yields. These multi-ligand site compounds could be selectively metalated at their peripheries, which was shown by X-ray crystallography.     

Formation of organolithium hetero-aggregates [Li4Ar2(nBu)2] (Ar=C6H4CH(Me)NMe2-2) during the directed ortho-lithiation of [1-(dimethylamino)ethyl]benzene

(R)-[1-(Dimethylamino)ethyl]benzene reacts with nBuLi in a 1:1 molar ratio in pentane to quantitatively yield a unique hetero-aggregate (2 a) containing the lithiated arene, unreacted nBuLi, and the complexed parent arene in a 1:1:1 ratio. As a model compound, [Li(4)(C(6)H(4)CH(Me)NMe(2)-2)(2)(nBu)(2)] (2 b) was prepared from the quantitative redistribution reaction of the parent lithiated arene Li(C(6)H(4)CH(Me)NMe(2)-2) with nBuLi in a 1:1 molar ratio. The mono-Et(2)O adduct [Li(4)(C(6)H(4)CH(Me)NMe(2)-2)(2)(nBu)(2)(OEt(2))] (2 c) and the bis-Et(2)O adduct [Li(4)(C(6)H(4)CH(Me)NMe(2)-2)(2)(nBu)(2)(OEt(2))(2)] (2 d) were obtained by re-crystallization of 2 b from pentane/Et(2)O and pure Et(2)O, respectively. The single-crystal X-ray structure determinations of 2 b-d show that the overall structural motifs of all three derivatives are closely related. They are all tetranuclear Li aggregates in which the four Li atoms are arranged in an almost regular tetrahedron. These structures can be described as consisting of two linked dimeric units: one Li(2)Ar(2) dimer and a hypothetical Li(2)nBu(2) dimer. The stereochemical aspects of the chiral Li(2)Ar(2) fragment are discussed. The structures as observed in the solid state are apparently retained in solution as revealed by a combination of cryoscopy and (1)H, (13)C, and (6)Li NMR spectroscopy.     

Analysis of the pi-pi stacking interactions between the aminoglycoside antibiotic kinase APH(3')-IIIa and its nucleotide ligands

A key contact in the active site of an aminoglycoside phosphotransferase enzyme (APH(3')-IIIa) is a pi-pi stacking interaction between Tyr42 and the adenine ring of bound nucleotides. We investigated the prevalence of similar Tyr-adenine contacts and found that many different protein systems employ Tyr residues in the recognition of the adenine ring. The geometry of these stacking interactions suggests that electrostatics play a role in the attraction between these aromatic systems. Kinetic and calorimetric experiments on wild-type and mutant forms of APH(3')-IIIa yielded further experimental evidence of the importance of electrostatics in the adenine binding region and suggested that the stacking interaction contributes approximately 2 kcal/mol of binding energy. This type of information concerning the forces that govern nucleotide binding in APH(3')-IIIa will facilitate inhibitor design strategies that target the nucleotide binding site of APH-type enzymes.     

An experimental study of chromatographic dynamics in open and packed non-cylindrical conduits

A systematic investigation of the influence of the perimeter shape of open and particle packed fused silica capillaries on chromatographic properties such as resistance to flow and dispersion of solutes propelled through these channels has been conducted. Verifications of these uncommon experiments with existing theoretical treatments are presented and the insights transferred to a novel polymer chip design with integrated facilities for complex separations. A comparison of the chromatographic performance of a real life proteomics sample on this chip with a capillary column of "similar" dimensions is presented.     

Probing the glycosidic linkage: UV and IR ion-dip spectroscopy of a lactoside

The beta(1-->4) glycosidic linkage found in lactose is a prevalent structural motif in many carbohydrates and glycoconjugates. Using UV and IR ion-dip spectroscopies to probe benzyl lactoside isolated in the gas phase, we find that the disaccharide unit adopts only a single, rigid structure. Its fully resolved infrared ion-dip spectrum is in excellent agreement with that of the global minimum structure computed ab initio. This has glycosidic torsion angles of phi(H) (H1-C1-O-C4') approximately 180 degrees and psi(H) (C1-O-C4'-H4') approximately 0 degrees which correspond to a rotation of approximately 150 degrees about the glycosidic bond compared to the accepted solution-phase conformation. We discuss the biological implications of this discovery and the generality of the strategies employed in making it.     

Morphology and molten-state rheology of polylactide and polyhydroxyalkanoate blends

Polylactide (PLA) and poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) blends were prepared at different compositions by melt mixing. First, the rheological properties of each individual component are briefly presented focusing on the most important aspects to be taken into account during blends preparation and investigation. The kinetics of PHBV viscosity decrease due to strong polymer degradation in the molten state was recorded. This helped making a choice of the blending parameters and of the way of performing the rheological frequency sweeps. DSC showed that components are immiscible in the whole range of compositions studied. Blends morphology was studied using high-resolution scanning electron microscope and optical microscopy in reflection mode. Nodular and co-continuous morphologies were observed depending on the composition, and minor phase size was roughly estimated. The rheology of PLA/PHBV blends was investigated in the dynamic mode and correlated with the morphology observed. The results showed an important role of the interfaces between PLA and PHBV and a peculiar behaviour of the viscosity of some mixtures at low frequencies. At medium and high frequencies mixture dynamic viscosity follows the mixing law.     

(3R,4S)‐3‐Phenyl‐1‐[(R)‐1‐phenyl­ethyl]‐4‐[(R)‐1‐phenylethyliminomethyl]azetidin‐2‐one

The configuration of the chiral ring atoms of the title compound, C₂₆H₂₆N₂O, obtained in an enantioselective synthesis, has been established relative to the known R configuration of the α‐methyl­benzyl moieties. The crystal packing involves a two‐dimensional network of C—H?π interactions between the aromatic rings.     

Nanomolar Inhibitors for Two Distinct Biological Target Families from a Single Synthetic Sequence: A Next Step in Combinatorial Library Design?

One common synthetic route creates small-molecule libraries directed toward two functionally distinct target families. The novel structural template 1 can independently display the necessary pharmacophore patterns for inhibition of members of two different biomolecular target families, the matrix metalloproteinases (MMPs) or the phosphodiesterases (PDEs). The incorporation of multiple target family directed design elements into combinatorial library design could help expedite the pharmaceutical lead discovery process. Z=OR′ (PDE4), H (MMPs).     

catena‐Poly­[[bis­(nitrato)(pyrimidine)­copper(II)]‐μ‐pyrimidine‐N:N′]

The title compound, [Cu(NO₃)₂(C₄H₄N₂)₂]_n, crystallizes as a linear polymeric compound with one pyrimidine ligand bridging between two Cu^II atoms and a second pyrimidine ligand coordinated in a monodentate manner. The distorted octahedral geometry around the Cu^II atom consists of two pyrimidine N atoms at distances of 2.033 (4) and 2.025 (4) Å, and two nitrate O atoms at distances at 1.987 (3) and 1.973 (3) Å. The apical positions are occupied by an N atom of a bridging pyrimidine ligand [2.291 (4) Å] and a nitrate O atom at a long distance of 2.781 (3) Å. The basal plane is almost planar, with trans angles of 176.23 (14) and 165.34 (15)°.