Synthesis and optical characterization of new ketocyanine dyes with extended polymethine chaines

New symmetrical and unsymmetrical near-infrared absorbing ketocyanine-type dyes are synthesized and their optical characterization is done. The relationships between their structure and optical properties are discussed. The synthesized ketocyanine dyes show a positive solvatochromism and are poorly fluorescent. A new procedure for the preparation of N,N,N′,N′-tetramethylvinamidinium perchlorate, which was a very useful reagent for the synthesis of various heterocyclic compounds as well as for the preparation of cyanine dyes is developed.     

Synthesis of the 8,19-Epoxysteroid Eurysterol A

We report the first chemical synthesis of eurysterol A, a cytotoxic and antifungal marine steroidal sulfate with a unique C8−C19 oxy-bridged cholestane skeleton. After C19 hydroxylation of cholesteryl acetate, used as an inexpensive commercial starting material, the challenging oxidative functionalization of ring B was achieved by two different routes to set up a 5α-hydroxy-7-en-6-one moiety. As a key step, an intramolecular oxa-Michael addition was exploited to close the oxy-bridge (8β,19-epoxy unit). DFT calculations show this reversible transformation being exergonic by about −30 kJ mol⁻¹. Along the optimized (scalable) synthetic sequence, the target natural product was obtained in only 11 steps in 5 % overall yield. In addition, an access to (isomeric) 7β,19-epoxy steroids with a previously unknown pentacyclic ring system was discovered.     

Evaluation of Pd→B Interactions in Diphosphinoborane Complexes and Impact on Inner-Sphere Reductive Elimination

The dative Pd→B interaction in a series of ^RDPB^R’ Pd⁰ and Pd^II complexes (^RDPB^R’=(o-PR₂C₆H₄)₂BR’, diphosphinoborane) was analyzed using XRD, ¹¹B NMR spectroscopy and NBO/NLMO calculations. The borane acceptor discriminates between the oxidation state Pd^II and Pd⁰, stabilizing the latter. Reaction of lithium amides with [(^RDPB^R’)Pd^II(4-NO₂C₆H₄)I] chemoselectively yields the C−N coupling product. DFT modelling indicates no significant impact of Pd^II→B coordination on the inner-sphere reductive elimination rate.     

A Fluorescence-Based Assay System for the Determination of Haloperoxidase-Activity Using a Two-Dimensional Calibration Ap-proach

Screening for an interesting biocatalyst and its subsequent kinetic characterization depends on a reliable activity assay. In this work, a fluorometric assay based on the halogenation of 4-methyl-7-diethylamino-coumarin was established to monitor haloperoxidase-activity. Since haloperoxidases utilize hydrogen peroxide and halide ions to halogenate a broad range of substrates by releasing hypohalous acids, a direct quantification of haloperoxidase-activity remains difficult. With the system presented here, 3-bromo-4-methyl-7-diethylaminocoumarin is preferentially formed and monitored by fluorescence measurements. As starting material and product share similar spectroscopical properties, a two-dimensional calibration ap-proach was utilized to allow for quantification of each compound within a single measurement. To validate the system, the two-dimensional Michaelis-Menten kinetics of a vanadium-dependent chloroperoxidase from Curvularia inaequalis were recorded, yielding the first overall kinetic parameters for this enzyme. With limits of detection and quantification in the low μm range, this assay may provide a reliable alternative system for the quantification of haloperoxidase-activity.     

On‐Surface Assembly of Hydrogen‐ and Halogen‐Bonded Supramolecular Graphyne‐Like Networks

Demonstrated here is a supramolecular approach to fabricate highly ordered monolayered hydrogen‐ and halogen‐bonded graphyne‐like two‐dimensional (2D) materials from triethynyltriazine derivatives on Au(111) and Ag(111). The 2D networks are stabilized by N???H?C(sp) bonds and N???Br?C(sp) bonds to the triazine core. The structural properties and the binding energies of the supramolecular graphynes have been investigated by scanning tunneling microscopy in combination with density‐functional theory calculations. It is revealed that the N???Br?C(sp) bonds lead to significantly stronger bonded networks compared to the hydrogen‐bonded networks. A systematic analysis of the binding energies of triethynyltriazine and triethynylbenzene derivatives further demonstrates that the X₃‐synthon, which is commonly observed for bromobenzene derivatives, is weaker than the X₆‐synthon for our bromotriethynyl derivatives.     

Identification of Semiconductive Patches in Thermally Processed Monolayer Oxo‐Functionalized Graphene

The thermal decomposition of graphene oxide (GO) is a complex process at the atomic level and not fully understood. Here, a subclass of GO, oxo‐functionalized graphene (oxo‐G), was used to study its thermal disproportionation. We present the impact of annealing on the electronic properties of a monolayer oxo‐G flake and correlated the chemical composition and topography corrugation by two‐probe transport measurements, XPS, TEM, FTIR and STM. Surprisingly, we found that oxo‐G, processed at 300 °C, displays C?C sp³‐patches and possibly C?O?C bonds, next to graphene domains and holes. It is striking that those C?O?C/C?C sp³‐separated sp²‐patches a few nanometers in diameter possess semiconducting properties with a band gap of about 0.4 eV. We propose that sp³‐patches confine conjugated sp²‐C atoms, which leads to the local semiconductor properties. Accordingly, graphene with sp³‐C in double layer areas is a potential class of semiconductors and a potential target for future chemical modifications.     

The response of a spherical droplet on a wall executing small sinusoidal vibrations

Meccanica - This study concerns the response of a spherical drop, attached to a sinusoidally vibrating wall. Given that the drop is spherical, the model is more realistic than that of a 2D drop...     

Brownian dynamics of polymeric chain in strong external field

The cooperativity of conformational transitions in strained linear polymer chain was investigated by the method of Brownian dynamics. Deformation of a chain consisting of N=32 and 64 bonds was created by strong external field of dipole type. Correlations are discussed in terms of hazard-plot analysis.     

Photoprotection of Mammalian Acid-Soluble Collagen by Cuttlefish Sepia Melanin In Vitro

Several important clinical conditions can result in close association between the pigment melanin and dermal collagen. Because melanin and its precursors can be chemically reactive in ground and excited states, it is important to know whether the resulting melanin-collagen interaction results in photoprotection or photoaggression. Acidic and neutral air-saturated collagen suspensions (0.033%) were irradiated with0–2.6 times 104 J/m2 UVC or with0–83 times 104 J/m2 solar-simulating UV radiation (SSR). Photochemical destruction of a photolabile collagen fluorophore (δ_em 360 nm) and collagen chain degradation were monitored as functions of irradiation time in the presence and absence of added (0–100μg) sepia eumelanin. Melanin retarded collagen photodamage but did not qualitatively alter the fluorescence fading kinetics. Both H202 and 02 can be produced by UV irradiation of eumelanin. Added H202 and K02 destroyed collagen fluorescence and caused 50% chain degradation at ca10–20-fold molar excess. Previous studies have demonstrated that eumelanins efficiently scavenge 02 . We demonstrated that eumelanin also efficiently scavenges H202 as evidenced by its ability to (a) compete with scopoletin for peroxide uptake and (b) directly take up H202 through a dialysis bag. The latter observation suggests that peroxide scavenging could occur in vivo by melanin sequestered in melanophages. Thus, neither UV-generated 02 nor H202 are likely to be present in concentrations high enough to cause measurable collagen damage. Absorption and/or scattering of excitation radiation away from the target chromophore appears to be the primary photoprotection mechanism, although scavenging of active 02 intermediates may play an important, if subtle role.     

核磁共振代谢组学数据的尺度归一化新方法

在核磁共振代谢组学数据预处理中,尺度归一化主要目的是提高特征代谢物信息的权重,减小噪声及无关代谢物信息的影响,从而降低后续模式识别分析的难度. 本文提出一种新的尺度归一化方法,该方法不强调各变量在尺度上的归一,而是在原始数据的基础上,通过提高那些稳定性高、且在不同类别样本中具有显著差异性的变量的权重,以增强与特征代谢物相关的信息. 文中分别采用模拟数据和真实代谢组学数据对新归一化方法的性能进行评估,并与单位方差法(Unit Variance)、变量稳定性(Variable Stability)和尺度缩放法(Level Scaling)等常用的尺度归一化方法做比较. 研究结果表明：新归一化方法能够提高多变量统计模型的预测能力,较好地保留核磁共振谱的分子信息,有助于特征代谢物的识别,并使后续的数据分析结果具有更好的可解释性.