Effects of surface roughness on reflection spectra obtained by terahertz time-domain spectroscopy

We present an analytical model that shows that reflection from a rough surface causes a Gaussian frequency roll-off for the spectral magnitude of a terahertz wave and reduces the signal-to-noise ratio of terahertz time-domain spectroscopy. The parameter that determines the width of the frequency roll-off is the standard deviation of the surface height distribution. Measurements of terahertz waves reflected from copper powder samples provide experimental evidence for this effect.     

Helices versus zigzag chains: one-dimensional coordination polymers of Ag(I) and Bis(4-pyridyl)amine

Five one-dimensional coordination polymers were prepared by the reaction of a bent bridging ligand, bis(4-pyridyl)amine (bpa), with an extensive series of AgX salts (X = CF3SO3, PF6, ClO4, NO3). The 1D polymer networks formed with AgCF3SO3 (1), AgPF6 (2.MeCN), and AgClO4 (3.2MeCN) all incorporated MeCN and were found to adopt a zigzag arrangement. The networks formed with AgClO4 (4) and AgNO3 (5) did not contain any solvent and adopted a single-stranded helical arrangement. Two-dimensional H-bonding networks were formed for 1 and 3.2MeCN, with network topologies 4.8(2) and (4, 4), respectively, whereas three-dimensional H-bonded networks of helices were formed for 4, showing an (8, 3)-a network topology, and 5, showing the topology of the alpha-polonium net. The three-dimensional networks both exhibited 4-fold interpenetration. The NO3- anion in 5 appeared to be acting as a template for the 3D structure.     

Lower main-group element complexes with a soft scorpionate ligand: the structural influence of stereochemically active lone pairs

The syntheses and structures of complexes of the fifth period elements indium and antimony, and the sixth period element bismuth with the soft scorpionate ligand, hydrotris(methimazolyl)borate (Tm(Me)) are reported. A considerable variety of structural motifs were obtained by reaction of the main-group element halide and NaTm(Me). The indium(III) complexes took the form [In(kappa(3)-Tm(Me))(2)](+). This motif could not, however, be isolated for antimony(III), the dominant product being [Sb(kappa(3)-Tm(Me))(kappa(1)-Tm(Me))X] (X = Br, I). An iodo-bridged species [Sb(kappa(3)-Tm(Me))I(mu(2)-I)](2), analogous to a previously reported bismuth complex, was also isolated. Reaction of antimony(III) acetate with NaTm(Me) results in a remarkable species in which three different ligand binding modes are observed. In each antimony complex the influence of the nonbonded electron pair is observed in the structure. Bismuth halides form complexes analogous to those of antimony, with directional lone pairs, but in addition, reaction of Bi(NO(3))(3) with NaTm(Me) results in a complex with a regular S(6) coordination sphere and a nonstereochemically active lone pair. Comparisons are drawn with known Tm(Me) complexes of As, Sn, and Bi in which the stereochemical influence of the lone pairs is negligible and with Tm(Me) complexes of Te and Bi in which the lone pairs are stereochemically active. This study highlights the ability of Tm(Me) to coordinate in a variety of modes as dictated by the metal centre with no adverse effects on the stability of the complexes formed.     

石荠苧不同药用部位总黄酮及微量元素含量的测定

采用分光光度法测定了石荠芋不同药用部位总黄酮的含量,采用电感耦合等离子发射光谱法测定了其中微量元素的含量。结果表明,叶中总黄酮含量最高,根次之,茎最少;根、茎、叶中均含有Cu、Fe、Mn、Zn、Co等多种人体必需的微量元素,其中Fe含量最高,且叶中明显高于根、茎;3个部位均未检出有害重金属As,而Hg、Pb含量均未超标。该结果可为石荠芋不同药用部位的利用和药材的开发提供科学依据。     

Insight into ortho-boronoaldehyde conjugation via a FRET-based reporter assay

Ortho-boronoaldehydes react with amine-based nucleophiles with dramatically increased rates and product stabilities, relative to unfunctionalised benzaldehydes, leading to exciting applications across biological and material chemistry. We have developed a novel Förster resonance energy transfer (FRET)-based assay to provide key new insights into the reactivity of these boronoaldehydes, allowing us to track conjugation with unprecedented sensitivity and accuracy under standardised conditions. Our results highlight the key role played by reaction pH, buffer additives, and boronoaldehyde structure in controlling conjugation speed and stability, providing design criteria for further innovations and applications in the field.

A FRET-based platform has been developed to allow the rapid reactions between ortho-boronoaldehydes and amine-based nucleophiles to be precisely studied.

Reactions between ortho-boronoaldehydes (oBAs) and amine-based nucleophiles have emerged as powerful tools for bioconjugation and materials chemistry over the last decade, due to a combination of rapid reaction rates and tunable product stability. The ortho-boronoimines, and related derivatives (collectively oBIDs), that form have shown high potential in drug delivery,¹in vivo labelling,² and responsive materials.³ To allow further evolution of these technologies and drive innovative new applications, there is a pressing need for increased understanding of the formation of oBIDs and their responsive behaviour. In this work, we deliver a sensitive and versatile platform to realise such understanding, through a Förster resonance energy transfer (FRET) reporter assay of oBID formation. This assay allows us to probe the rapid kinetics of oBID formation in detail, under complex and biomedically relevant conditions.The ortho-boronic acid accelerates the rate of oBID formation (k₁), relative to unfunctionalised benzaldehyde, by both activating the aldehyde to nucleophilic attack and accelerating the rate-determining dehydration step. Though the rate of hydrolysis (k₋₁) is also accelerated, stabilising B–N interactions lead to a significant overall shift in equilibrium towards product formation (decrease in dissociation constant, K_d). For example, while benzaldehyde reacts with alkyl amines with k₁ ∼ 0.1 M⁻¹ s⁻¹ and K_d ∼ 300 M,⁴ the ortho-borono analogue ortho-formylphenylboronic acid (FBPA) forms analogous iminoboronates with a k₁ ∼ 1000 M⁻¹ s⁻¹ and K_d ∼ 10 mM (Fig. 1a).⁵ This 5-order of magnitude increase in reaction rate, and 4-order of magnitude decrease in dissociation constant, typifies the unique reactivity of oBAs.Open in a separate windowFig. 1(a) Comparison of benzaldehyde and ortho-boronoaldehyde reactivity, with the ortho-borono group both accelerating and stabilising imine formation; (b) schematic overview of the FRET platform developed in this work, allowing sensitive monitoring of rapid oBID formation (k₁ > 10⁵ M⁻¹ s⁻¹).Through variation of the oBA and nucleophile coupling partners, K_ds spanning 10⁻²–10⁻⁹ M have been reported.⁶ When coupled with high biocompatibility and potential for stimuli-responsive behaviour, this tunability greatly enhances the potential for biomedical applications of oBIDs. Despite this potential, much of our understanding of oBID chemistry comes from simple, unsubstituted model compounds such as FPBA, which poorly reflect the stereo-electronic characteristics of the functionalised oBAs necessary for translational applications.Moreover, much of this understanding is pieced together from a large number of independent studies, performed and analysed under varying conditions, making comparison challenging. This is particularly important given the highly dynamic nature of oBID linkages, leading to a high sensitivity to environmental conditions and choice of analytical technique. Ultimately, this leads to significant discrepancies in reported rates of formation and stabilities of oBIDs, due to subtle differences in substrate choice, reaction conditions, or analysis method.^7,8To address this, we herein describe a versatile and sensitive FRET-assay for studying oBID formation, stability, and cleavage. This assay is highly tolerant of environmental conditions, allowing us to provide critical new insights into the effects of pH, additives, media, and oBA structure on conjugation. We therefore anticipate that this assay will find future use for the high-throughput screening of novel oBIDs and their stimuli-responsive behaviour.