A streamlined metabolic pathway for the biosynthesis of moenomycin A

Moenomycin A (MmA) is a member of the phosphoglycolipid family of antibiotics, which are the only natural products known to directly target the extracellular peptidoglycan glycosyltransferases involved in bacterial cell wall biosynthesis. The structural and biological uniqueness of MmA make it an attractive starting point for the development of new antibacterial drugs. In order both to elucidate the biosynthesis of this unusual compound and to develop tools to manipulate its structure, we have identified the MmA biosynthetic genes in Streptomyces ghanaensis (ATCC14672). We show via heterologous expression of a subset of moe genes that the economy of the MmA pathway is enabled through the use of sugar-nucleotide and isoprenoid building blocks derived from primary metabolism. The work reported lays the foundation for genetic engineering of MmA biosynthesis to produce novel derivatives.     

Synthesis and Fluorescence Quenching Study of the Novel Cationic Probe Derived from Luminarosine

A simple and efficient transformation of the zwitterionic luminarosine into a brightly fluorescent cationic analogue, namely 1‐amino‐9‐methoxy‐2,4,10‐triaza‐4b‐azoniaphenanthrene ( 3 ), is reported. The fluorescence quenching of 3 by common nucleotides, calf‐thymus (CT) DNA, and halide ions was investigated by means of spectrophotometric and spectrofluorometric methods. Intermolecular static and dynamic fluorescence‐quenching constants for quenching of 3 by nucleotides and halide ions were determined in aqueous solution. Evidence for formation of nonfluorescent ground‐state complexes of 3 with nucleotides and CT‐DNA is presented. Scatchard analysis of the CT‐DNA quenching data resulted in a binding constant of 2.8×10⁴ M ⁻¹ and a number of binding sites per base pair of 0.049.     

Fluid penetration effects in porous media contact

The contact boundary conditions at the interface between two fluid-saturated porous bodies are derived. The general derivation is performed within the well-founded framework of the Theory of Porous Media (TPM) based on the constituent balance relations of mass, momentum, and energy accounting for finite discontinuities at the contact surface. Particular attention is drawn to the effects associated with the interstitial fluid flux across the interface. The derived contact conditions include two kinematic continuity conditions for the solid velocity and the fluid seepage velocity as well as two jump conditions for the effective solid stress and the pore-fluid pressure. As an application, the common case of biphasic porous media contact proceeding from materially incompressible constituents and inviscid fluid properties is discussed in detail.      

Dynamic covalent chemistry in live cells for organelle targeting and enhanced photodynamic action

Organelle-specific targeting enables increasing the therapeutic index of drugs and localizing probes for better visualization of cellular processes. Current targeting strategies require conjugation of a molecule of interest with organelle-targeting ligands. Here, we propose a concept of dynamic covalent targeting of organelles where the molecule is conjugated with its ligand directly inside live cells through a dynamic covalent bond. For this purpose, we prepared a series of organelle-targeting ligands with a hydrazide residue for reacting with dyes and drugs bearing a ketone group. We show that dynamic hydrazone bond can be formed between these hydrazide ligands and a ketone-functionalized Nile Red dye (NRK) in situ in model lipid membranes or nanoemulsion droplets. Fluorescence imaging in live cells reveals that the targeting hydrazide ligands can induce preferential localization of NRK dye and an anti-cancer drug doxorubicin in plasma membranes, mitochondria and lipid droplets. Thus, with help of the dynamic covalent targeting, it becomes possible to direct a given bioactive molecule to any desired organelle inside the cell without its initial functionalization by the targeting ligand. Localizing the same NRK dye in different organelles by the hydrazide ligands is found to affect drastically its photodynamic activity, with the most pronounced phototoxic effects in mitochondria and plasma membranes. The capacity of this approach to tune biological activity of molecules can improve efficacy of drugs and help to understand better their intracellular mechanisms.

We introduce a concept of dynamic covalent targeting of organelles, where a dye/drug molecule is conjugated with its targeting ligand inside live cells by a reversible hydrazone bond, revealing organelle-dependent photodynamic action.     

Search strategies for non-standard Higgs bosons at future ee colliders

Already in the simplest two-Higgs-doublet model with CP violation in the Higgs sector, the 3×3 mixing matrix for the neutral Higgs bosons can substantially modify their couplings, thereby endangering the “classical” Higgs search strategies. However, there are sum rules relating Yukawa and Higgs–Z couplings which ensure that the ZZ, and couplings of a given neutral 2HDM Higgs boson cannot all be simultaneously suppressed. This result implies that any single Higgs boson will be detectable at an e⁺e⁻ collider if the Z+Higgs, Higgs and Higgs production channels are all kinematically accessible and if the integrated luminosity is sufficient. We explore, as a function of Higgs mass, the luminosity required to guarantee Higgs boson detection, and find that for moderate tanβ values the needed luminosity is unlikely to be available for all possible mixing scenarios. Implications of the sum rules for Higgs discovery at the Tevatron and LHC are briefly discussed.     

How to Identify Roast Defects in Coffee Beans Based on the Volatile Compound Profile

The aim of this study was to detect and identify the volatile compounds in coffee that was obtained in defect roast processes versus standard roasting and to determine the type and strength of the correlations between the roast defects and the volatile compound profile in roasted coffee beans. In order to achieve this goal, the process of coffee bean roasting was set to produce an underdeveloped coffee defect, an overdeveloped coffee defect, and defectless coffee. The “Typica” variety of Arabica coffee beans was used in this study. The study material originated from a plantation that is located at an altitude of 1400–2000 m a.s.l. in Huehuetenango Department, Guatemala. The analyses were carried out with the use of gas chromatography/mass spectrometry (GC–MS) and an electronic nose. This study revealed a correlation between the identified groups of volatile compounds and the following coffee roasting parameters: the time to the first crack, the drying time, and the mean temperatures of the coffee beans and the heating air. The electronic nose helped to identify the roast defects.     

On the different coordination of Ni, Zn and Cd cations in their model Schiff base complexes - Single crystal X-ray and solid state NMR studies

Three model metal complexes: Ni(NCS)L, Zn₂(NCS)₂L₂ and Cd₂(NCS)₂L₂, consisting of the SCN⁻ anion(s) and L = 2-[(2-dimethylaminoethylimino)-methyl]-phenolate, have been studied by X-ray diffraction and solid state NMR spectroscopy. The metal cations in these complexes have different coordination modes: Ni²⁺ is almost square-planar, the Zn²⁺ cation in Zn₂(NCS)₂L₂ is pentacoordinated, whereas Cd²⁺ is penta- and hexacoordinated in [Cd₂(NCS)₂L₂]. The different coordination of the metal cations influences the chemical shifts of the metal cations and also the nitrogen atoms. These chemical shifts can be correlated with the M-N and M-O bond lengths (M = Ni²⁺, Zn²⁺, Cd²⁺).     

Experimental and quantum-chemical studies of 15N NMR coordination shifts in palladium and platinum chloride complexes with pyridine, 2,2'-bipyridine and 1,10-phenanthroline

A series of Pd and Pt chloride complexes with pyridine (py), 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen), of general formulae trans-/cis-[M(py)2Cl2], [M(py)4]Cl2, trans-/cis-[M(py)2Cl4], [M(bpy)Cl2], [M(bpy)Cl4], [M(phen)Cl2], [M(phen)Cl4], where M = Pd, Pt, was studied by 1H, 195Pt, and 15N NMR. The 90-140 ppm low-frequency 15N coordination shifts are discussed in terms of such structural features of the complexes as the type of platinide metal, oxidation state, coordination sphere geometry and the type of ligand. The results of quantum-chemical NMR calculations were compared with the experimental 15N coordination shifts, well reproducing their magnitude and correlation with the molecular structure.     

Calculation of structural behavior of indirect NMR spin-spin couplings in the backbone of nucleic acids

Calculated indirect NMR spin-spin coupling constants (J-couplings) between (31)P, (13)C, and (1)H nuclei were related to the backbone torsion angles of nucleic acids (NAs), and it was shown that J-couplings can facilitate accurate and reliable structural interpretation of NMR measurements and help to discriminate between their distinct conformational classes. A proposed stepwise procedure suggests assignment of the J-couplings to torsion angles from the sugar part to the phosphodiester link. Some J-couplings show multidimensional dependence on torsion angles, the most prominent of which is the effect of the sugar pucker. J-couplings were calculated in 16 distinct nucleic acid conformations, two principal double-helical DNAs, B- and A-, the main RNA form, A-RNA, as well as in 13 other RNA conformations. High-level quantum mechanics calculations used a baseless dinucleoside phosphate as a molecular model, and the effect of solvent was included. The predicted J-couplings correlate reliably with available experimental data from the literature.