Delving into the complex picture of Ti(IV)-citrate speciation in aqueous media: Synthetic, structural, and electrochemical considerations in mononuclear Ti(IV) complexes containing variably deprotonated citrate ligands

The aqueous reaction of TiCl₄ with citric acid at pH ∼ 4 (KOH), led to the surprising isolation of a species assembly K₃[Ti(C₆H₆O₇)₂(C₆H₅O₇)] · K₄[Ti(C₆H₅O₇)₂(C₆H₆O₇)] · 10H₂O (1). The same system at pH ∼ 3 (neocuproine), led to the crystalline material (C₁₄H₁₃N₂)₂[Ti(C₆H₆O₇)₃] · 5H₂O (2), while at pH 5.0 (NaOH), afforded Na₃[Ti(C₆H₆O₇)₂(C₆H₅O₇)] · 9H₂O (3). Analytical, spectroscopic and structural characterization of 1, 2 and 3 revealed their distinct nature exemplified by mononuclear complexes bearing variably deprotonated citrates bound to Ti(IV). Solid-state ¹³C MAS NMR spectroscopy in concert with solution ¹³C and ¹H NMR on 3 provided ample evidence for the existence of bound citrates of distinct coordination mode to the metal ion. Cyclic voltammetry defined the electrochemical signature of complex 2, thereby projecting the physicochemical profile of the species formulated by the aforementioned properties. Comparison of cyclic voltammetric data on available discrete Ti(IV)-citrate species depicts the electrochemical profile and an E_1/2 value trend of the species in that binary system’s aqueous speciation, further substantiating the redox behavior of mononuclear Ti(IV)-citrate species in a pH-sensitive fashion. Collectively, the well-defined discrete species in 1-3 reflect and corroborate a synthetically challenging yet complex pH-specific picture of the aqueous Ti(IV) chemistry with the physiological citric acid, and shed light on the pH-dependent speciation in the binary Ti(IV)-citrate system.     

Racemic crystallography of synthetic protein enantiomers used to determine the X‐ray structure of plectasin by direct methods

We describe the use of racemic crystallography to determine the X‐ray structure of the natural product plectasin, a potent antimicrobial protein recently isolated from fungus. The protein enantiomers L ‐plectasin and D ‐plectasin were prepared by total chemical synthesis; interestingly, L ‐plectasin showed the expected antimicrobial activity, while D ‐plectasin was devoid of such activity. The mirror image proteins were then used for racemic crystallization. Synchrotron X‐ray diffraction data were collected to atomic resolution from a racemic plectasin crystal; the racemate crystallized in the achiral centrosymmetric space group P1 with one L ‐plectasin molecule and one D ‐plectasin molecule forming the unit cell. Dimer‐like intermolecular interactions between the protein enantiomers were observed, which may account for the observed extremely low solvent content (13%–15%) and more highly ordered nature of the racemic crystals. The structure of the plectasin molecule was well defined for all 40 amino acids and was generally similar to the previously determined NMR structure, suggesting minimal impact of the crystal packing on the plectasin conformation.     

Continental‐scale syntheses of Australian pyromes – misclassification of south‐western eucalypt woodlands misinforms management

Global and continental‐scale analysis of ecological phenomena can offer important insights through the identification of patterns and associations not detectable at smaller scales. However, using proxies for ecological phenomena, such as vegetation mapping for spatially projecting fire regime niches and post‐fire plant responses, require critical examination of predictions to determine utility. Using local studies in south‐western Australia, we demonstrate that while this approach has been largely successful in mallee woodland and shrubland, it has failed in eucalypt woodland, with the consequence that values for a range of fire‐related parameters from the continent‐wide approaches, if adopted in informing management, would result in undesirable conservation outcomes for the world's largest extant temperate woodland.     

Synthesis of lucifensin by native chemical ligation and characteristics of its isomer having different disulfide bridge pattern

The antimicrobial 40‐amino‐acid‐peptide lucifensin was synthesized by native chemical ligation (NCL) using N‐acylbenzimidazolinone (Nbz) as a linker group. NCL is a method in which a peptide bond between two discreet peptide chains is created. This method has been applied to the synthesis of long peptides and proteins when solid‐phase synthesis is imcompatible. Two models of ligation were developed: [15 + 25] Ala‐Cys and [19 + 21] His‐Cys. The [19 + 21] His‐Cys method gives lower yield because of the lower stability of 18‐peptide‐His‐Nbz‐CONH₂ peptide, as suggested by density functional theory calculation. Acetamidomethyl‐deprotection and subsequent oxidation of the ligated linear lucifensin gave a mixture of lucifensin isomers, which differed in the location of their disulfide bridges only. The dominant isomer showed unnatural pairing of cysteines [C1?6], [C3?5], and [C2?4], which limits its ability to form α‐helical structure. The activity of isomeric lucifensin toward Bacillus subtilis, Staphylococcus aureus, and Micrococcus luteus was lower than that of the natural lucifensin. The desired product native lucifensin was prepared from this isomer using a one‐pot reduction with dithiotreitol and subsequent air oxidation in slightly alkaline medium. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.     

在高浓度1,4-丁二醇中酶促合成去B链C端六肽胰岛素

用含80％1,4-丁二醇的混合溶剂,以胰蛋白酶酶促,由去八肽胰岛素(DOI)合成了去六肽胰岛素(DHI),总产率为35％。1,4-丁二醇的溶解性能好,在浓度高达80—90％时不明显抑制酶活力,DOI的氨基无需保护,溶液中无高聚物或沉淀形成。     

在条锈菌侵染早期小麦初生叶内多聚核糖体水平与蛋白质合成能力的变化

小麦初生叶接种条锈菌毒性生理小种（ＣＹ２９）及其弱毒突变菌系（ＣＹ２９－ｍｕｔ３）后,呈不亲和反应的寄主叶片可溶性蛋白质合成能力在接种后２４ｈ显著高于未接种对照,但其后逐渐降低,直至接近对照;而呈亲和性反应的寄主叶片可溶性蛋白质合成在侵染早期与对照相近,但与膜结合蛋白质在９６ｈ时大大高于对照。对接种叶中核糖体的密度梯度分析证实：呈不亲和反应寄主叶片游离多聚核糖体及亲和反应的寄主内与膜结合多聚核糖体均有特异性增加。上述结果表明寄主的抗病和感病反应均与蛋白质合成能力的变化有关。     

Global and local mechanisms sustain axonal proteostasis of transmembrane proteins

The control of neuronal protein homeostasis or proteostasis is tightly regulated both spatially and temporally, assuring accurate and integrated responses to external or intrinsic stimuli. Local or autonomous responses in dendritic and axonal compartments are crucial to sustain function during development, physiology and in response to damage or disease. Axons are responsible for generating and propagating electrical impulses in neurons, and the establishment and maintenance of their molecular composition are subject to extreme constraints exerted by length and size. Proteins that require the secretory pathway, such as receptors, transporters, ion channels or cell adhesion molecules, are fundamental for axonal function, but whether axons regulate their abundance autonomously and how they achieve this is not clear. Evidence supports the role of three complementary mechanisms to maintain proteostasis of these axonal proteins, namely vesicular transport, local translation and trafficking and transfer from supporting cells. Here, we review these mechanisms, their molecular machineries and contribution to neuronal function. We also examine the signaling pathways involved in local translation and their role during development and nerve injury. We discuss the relative contributions of a transport‐controlled proteome directed by the soma (global regulation) versus a local‐controlled proteome based on local translation or cell transfer (local regulation).      

Phytoalexins from Thlaspi arvense, a wild crucifer resistant to virulent Leptosphaeria maculans: structures, syntheses and antifungal activity

Phytoalexins are inducible chemical defenses produced by plants in response to diverse forms of stress, including microbial attack. Our search for phytoalexins from cruciferous plants resistant to economically important fungal diseases led us to examine stinkweed or pennycress (Thlaspi arvense), a potential source of disease resistance to blackleg. We have investigated phytoalexin production in leaves of T. arvense under abiotic (copper chloride) and biotic elicitation by Leptosphaeria maculans (Desm.) Ces. et de Not. [asexual stage Phoma lingam (Tode ex Fr.) Desm.], and report here two phytoalexins, wasalexin A and arvelexin (4-methoxyindolyl-3-acetonitrile), their syntheses and antifungal activity against isolates of P. lingam/L. maculans, as well as the isolation of isovitexin, a constitutive glycosyl flavonoid of stinkweed, having antioxidant properties but devoid of antifungal activity.