Induced‐Fit Mechanism in Class I Terpene Cyclases

We present crystallographic and functional data of selina‐4(15),7(11)‐diene synthase (SdS) from Streptomyces pristinaespiralis in its open and closed (ligand‐bound) conformation. We could identify an induced‐fit mechanism by elucidating a rearrangement of the G1/2 helix‐break motif upon substrate binding. This rearrangement highlights a novel effector triad comprising the pyrophosphate sensor Arg178, the linker Asp181, and the effector Gly182‐O. This structural motif is strictly conserved in class I terpene cyclases from bacteria, fungi, and plants, including epi‐isozizaene synthase (3KB9), aristolochene synthase (4KUX), bornyl diphosphate synthase (1N20), limonene synthase (2ONG), 5‐epi‐aristolochene synthase (5EAT), and taxa‐4(5),11(12)‐diene synthase (3P5R). An elaborate structure‐based mutagenesis in combination with analysis of the distinct product spectra confirmed the mechanistic models of carbocation formation and stabilization in SdS.     

Nickel‐Catalyzed Csp2Csp3 Bond Formation by CarbonFluorine Activation

We report herein a general catalytic method for Csp²?Csp³ bond formation through C?F activation. The process uses an inexpensive nickel complex with either diorganozinc or alkylzinc halide reagents, including those with β‐hydrogen atoms. A variety of fluorine substitution patterns and functional groups can be readily incorporated. Sequential reactions involving different precatalysts and coupling partners permit the synthesis of densely functionalized fluorinated building blocks.     

Restriction of Intramolecular Motions: The General Mechanism behind Aggregation‐Induced Emission

Aggregation‐induced emission (AIE) has been harnessed in many systems through the principle of restriction of intramolecular rotations (RIR) based on mechanistic understanding from archetypal AIE molecules such as tetraphenylethene (TPE). However, as the family of AIE‐active molecules grows, the RIR model cannot fully explain some AIE phenomena. Here, we report a broadening of the AIE mechanism through analysis of 10,10′,11,11′‐tetrahydro‐5,5′‐bidibenzo[a,d][7]annulenylidene (THBDBA), and 5,5′‐bidibenzo[a,d][7]annulenylidene (BDBA). Analyses of the computational QM/MM model reveal that the novel mechanism behind the AIE of THBDBA and BDBA is the restriction of intramolecular vibration (RIV). A more generalized mechanistic understanding of AIE results by combining RIR and RIV into the principle of restriction of intramolecular motions (RIM).     

In situ photoreduction of Ag+-ions by TiO2 nanoparticles deposited on cotton and cotton/PET fabrics

The possibility of in situ photoreduction of Ag⁺-ions using TiO₂ nanoparticles deposited on cotton and cotton/PET fabrics in the presence of amino acid alanine and methyl alcohol has been discussed. The possible interaction between TiO₂, alanine and Ag⁺-ions was evaluated by FTIR analysis. The fabrication of TiO₂/Ag nanoparticles on both fabrics was confirmed by SEM, EDX, XRD, XPS and AAS analyses. Cotton and cotton/PET fabrics impregnated with TiO₂/Ag nanoparticles provided maximum reduction of Gram-negative bacteria Escherichia coli and Gram-positive bacteria Staphylococcus aureus. Although excellent antibacterial activity was preserved after ten washing cycles, a significant amount of silver leached out from the fabrics into the washing bath. The perspiration fastness assessment revealed that smaller amounts of silver were also released from the fabrics into artificial sweat at pH 5.50 and 8.00. In addition, deposited TiO₂/Ag nanoparticles imparted maximum UV protection to fabrics.     

A novel reversed-phase HPLC method for the determination of urinary creatinine by pre-column derivatization with ethyl chloroformate: comparative studies with the standard Jaffé and isotope-dilution mass spectrometric assays

Creatinine is an important biomarker for renal function diagnosis and normalizing variations in urinary drug/metabolites concentration. Quantification of creatinine in biological fluids such as urine and plasma is important for clinical diagnosis as well as in biomonitoring programs and urinary metabolomics/metabonomics research. Current methods for creatinine determination either are nonselective or involve the use of expensive mass spectrometers. In this paper, a novel reversed-phase high-performance liquid chromatographic (HPLC) method for the determination of creatinine of high hydrophilicity by pre-column derivatization with ethyl chloroformate is presented. N-Ethyloxycarbonylation of creatinine significantly enhanced the hydrophobicity of creatinine, facilitating its chromatographic retention as well as quantification by HPLC. Factors governing the derivatization reaction were studied and optimized. The developed method was validated and applied for the determination of creatinine in rat urine samples. Comparative studies with isotope-dilution mass spectrometric method revealed that the two methods do not yield systematic differences in creatinine concentrations, indicating the HPLC method is suitable for the determination of creatinine in urine samples.

Structure-Based Evolution of Subtype-Selective Neurotensin Receptor Ligands

Subtype-selective agonists of the neurotensin receptor NTS2 represent a promising option for the treatment of neuropathic pain, as NTS2 is involved in the mediation of μ-opioid-independent anti-nociceptive effects. Based on the crystal structure of the subtype NTS1 and previous structure–activity relationships (SARs) indicating a potential role for the sub-pocket around Tyr11 of NT(8–13) in subtype-specific ligand recognition, we have developed new NTS2-selective ligands. Starting from NT(8–13), we replaced the tyrosine unit by β²-amino acids (type 1), by heterocyclic tyrosine bioisosteres (type 2) and peptoid analogues (type 3). We were able to evolve an asymmetric synthesis of a 5-substituted azaindolylalanine and its application as a bioisostere of tyrosine capable of enhancing NTS2 selectivity. The S-configured test compound 2 a, [(S)-3-(pyrazolo[1,5-a]pyridine-5-yl)-propionyl¹¹]NT(8–13), exhibits substantial NTS2 affinity (4.8 nm) and has a nearly 30-fold NTS2 selectivity over NTS1. The (R)-epimer 2 b showed lower NTS2 affinity but more than 600-fold selectivity over NTS1.     

Embedology

Mathematical formulations of the embedding methods commonly used for the reconstruction of attractors from data series are discussed. Embedding theorems, based on previous work by H. Whitney and F. Takens, are established for compact subsetsA of Euclidean space R^k. Ifn is an integer larger than twice the box-counting dimension ofA, then almost every map fromR ^k toR ⁿ , in the sense of prevalence, is one-to-one onA, and moreover is an embedding on smooth manifolds contained withinA. IfA is a chaotic attractor of a typical dynamical system, then the same is true for almost everydelay-coordinate map fromR ^k toR ⁿ . These results are extended in two other directions. Similar results are proved in the more general case of reconstructions which use moving averages of delay coordinates. Second, information is given on the self-intersection set that exists whenn is less than or equal to twice the box-counting dimension ofA.     

Ovoids with a pencil of translation ovals

We show that if an ovoid of PG(3, q), where q>2 is even, has a pencil of translation ovals and if the carrier of the pencil is not an axis of at least one of the ovals in the pencil, then the ovoid is a Tits ovoid. It follows, as a corollary of this and a result of Penttila and Praeger, that if an ovoid of PG(3, q), where q>2 is even, has a pencil of translation ovals then the ovoid is either an elliptic quadric or a Tits ovoid.     

Hyperdeformation and clustering in the actinide region

The excitation energy spectrum of fission resonances has been measured with high energy resolution using the ²³⁵U(d,pf) reaction in order to study hyperdeformed (HD) rotational bands and HD nuclear shapes. The moments of inertia of the rotational bands and the energy of the ground state in the third minimum were determined. Another signature of these highly deformed states, their enhanced α decay, was also observed. By studying cold or compact fission in the ²³²Th(n,f) reaction around HD resonances, we obtained data for heavy clustering.