The collagen type I segment long spacing (SLS) and fibrillar forms: Formation by ATP and sulphonated diazo dyes

The collagen type I segment long spacing (SLS) crystallite is a well-ordered rod-like molecular aggregate, ∼300 nm in length, which is produced in vitro under mildly acidic conditions (pH 2.5–3.5) in the presence of 1 mM ATP. The formation of the SLS crystallite amplifies the inherent linear structural features of individual collagen heterotrimers, due to the punctate linear distribution and summation of the bulkier amino acid side chains along the length of individual collagen heterotrimers. This can be correlated structurally with the 67 nm D-banded collagen fibril that is found in vivo, and formed in vitro. Although first described many years ago, the range of conditions required for ATP-induced SLS crystallite formation from acid-soluble collagen have not been explored extensively. Consequently, we have addressed biochemical parameters such as the ATP concentration, pH, speed of formation and stability so as to provide a more complete structural understanding of the SLS crystallite. Treatment of collagen type I with 1 mM ATP at neutral and higher pH (6.0–9.0) also induced the formation of D-banded fibrils. Contrary to previous studies, we have shown that the polysulphonated diazo dyes Direct red (Sirius red) and Evans blue, but not Congo red and Methyl blue, can also induce the formation of SLS-like aggregates of collagen, but under markedly different ionic conditions to those employed in the presence of ATP. Specifically, pre-formed D-banded collagen fibrils, prepared in a higher than the usual physiological NaCl concentration (e.g. 500 mM NaCl, 20 mM Tris-HCl pH7.4 or x3 PBS), readily form SLS aggregates when treated with 0.1 mM Direct red and Evans blue, but this did not occur at lower NaCl concentrations. These new data are discussed in relation to the anion (Cl⁻) and polyanion (phosphate and sulphonate) binding by the collagen heterotrimer and their likely role in collagen fibrillogenesis and SLS formation.     

Utility of 2-Diphenylphosphoryloxy-1,3-Dienes in Multicomponent Hetero-Diels–Alder Reactions to Construct Functionalized Six-Membered Nitrogen Heterocycles

The utility of 2-diphenylphosphoryloxy-1,3-dienes for the construction of substituted six-membered nitrogen heterocycles is presented. These dienes undergo boron trifluoride-promoted aza-Diels–Alder reactions when reacted with imines or related species formed in situ using aldehydes and amine derivatives. The stability of the dienes allows this three-component reaction to be carried out with no special precautions to eliminate water or air. Thirty-one examples of this process are presented. The usefulness of the enol phosphate functional group is highlighted in further reactions after the cycloaddition step to generate functionalized piperidenes or pyridines.     

Fluorotrimethyl[(Z)-pentafluoropropen-1-yl]phosphorane: Structure,Bonding, and Reactivity

In this contribution we report on fluorotrimethyl[(Z)-pentafluoropropen-1-yl]phosphorane as a phosphorus based fluorinating reagent. Its solid state structure can be described as a trigonal bipyramid featuring elongated axial bonds due to the formation of a 3-center 4-electron bond. Abstraction of the fluoride ion leads to a shortening of the axial P–C bond. Thus the title compound can be utilized for substitution of bromine with fluorine and for the transfer of fluoride ions onto electrophilic compounds. Reaction with Sn(C₂F₅)₂Br₂ afforded salt [P(CH₃)₃(C₃F₅)]₂[Sn(C₂F₅)₂F₄]. When fluorotrimethyl[(Z)-pentafluoropropen-1-yl]phosphorane was treated with P(C₂F₅)₂F the primarily produced anion is sufficiently nucleophilic to attack the propenyl group of the cation in β-position to the phosphorus atom to yield zwitterionic [Me₃PCF=C(CF₃)–PF₃(C₂F₅)₂].     

Biological applications of amide and amino acid containing synthetic macrocycles

ABSTRACT

Amino acid derived macrocycles with elaborate well-defined stereochemistry are a unique class of compounds that have been isolated from natural sources. Macrocycles like cyclosporine, octreotide, and valinomycin have been used in multiple applications, like drugs or ion sensors. Chemists have long been fascinated by the unique molecular recognition capabilities of these macrocycles and tried to design synthetic analogs with similar functions. This article is focused on reviewing current research on amide and amino acid containing macrocycles that have been developed in research laboratories for biological recognition, specifically for anion sensing, ion transport, carbohydrate sensing, and peptide sensing.     

Co3+-Rich Na1.95CoP2O7 Phosphates as Efficient Bifunctional Catalysts for Oxygen Evolution and Reduction Reactions in Alkaline Solution

Implementing sustainable energy conversion and storage technologies is highly reliant on crucial oxygen electrocatalysis, such as the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). However, the pursuit of low cost, energetic efficient and robust bifunctional catalysts for OER and ORR remains a great challenge. Herein, the novel Na-ion-deficient Na_2−xCoP₂O₇ catalysts are proposed to efficiently electrocatalyze OER and ORR in alkaline solution. The engineering of Na-ion deficiency can tune the electronic structure of Co, and thus tailor the intrinsically electrocatalytic performance. Among the sodium cobalt phosphate catalysts, the Na_1.95CoP₂O₇ (NCPO5) catalyst exhibits the lowest ΔE (E_J10,OER−E_J−1,ORR) of only 0.86 V, which favorably outperforms most of the reported non-noble metal catalysts. Moreover, the Na-ion deficiency can stabilize the phase structure and morphology of NCPO5 during the OER and ORR processes. This study highlights the Na-ion deficient Na_2−xCoP₂O₇ as a promising class of low-cost, highly active and robust bifunctional catalysts for OER and ORR.     

Novel tantalum phosphate Na13Sr2Ta2(PO4)9: synthesis,crystal structure,DFT calculations and Dy3+‐activated fluorescence performance

A new tantalum phosphate, tridecasodium distrontium ditantalum nonaphosphate, Na₁₃Sr₂Ta₂(PO₄)₉, was prepared using the high‐temperature flux method. The structure can be described as a three‐dimensional open framework containing isolated [Ta^V₂(PO₄)₉]¹⁷⁻ units that are interlocked by Na and Sr ions. Band structure studies by the first‐principles method revealed that Na₁₃Sr₂Ta₂(PO₄)₉ is an insulator with an indirect band gap of 4.78 eV, which makes it suitable as a luminescent host matrix. A series of solid solutions, i.e. Na₁₃Sr_2–xTa₂(PO₄)₉:xDy³⁺ (x = 0.01, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12 and 0.14), were prepared and their photoluminescence properties studied. Under 350 nm light excitation, these emit two typical emissions of the Dy³⁺ ion, i.e. the ⁴F_9/2→⁶H_15/2 transition centred at 476 nm and the ⁴F_9/2→⁶H_13/2 transition centred at 570 nm.     

gem-Heteroatom-Substituted Fluoroalkenes as Mimics of Amide Derivatives or Phosphates: A Comprehensive Review

gem-Heteroatom-substituted fluoroalkenes have received little attention despite their great potential in medicinal chemistry or in fine chemistry. Indeed, due to the electronic and steric similarity between the fluoroalkene moiety and the amide bond as well as the high strength of the carbon-fluorine bond, these gem-heteroatom-substituted fluoroalkenes could be envisioned as stable mimics of various important organic functions, such as phosphates, carbamates, S-thiocarbamates and ureas. We present herein an overview describing the syntheses over the last decade of heteroatom-substituted fluoroalkenes in geminal position. This review will be divided into several sections covering each the common following heteroatom: oxygen-, nitrogen-, sulfur-, phosphorus-, boron- and silicon-substituted fluoroalkenes.     

MASS SPECTROMETRIC FRAGMENTATION OF UNSYMMETRICALLY SUBSTITUTED METHYLPHOSPHONATE DIESTERS

Abstract

A series of structurally related unsymmetrically substituted methylphosphonate diesters have been synthesised and subjected to electron impact (El) mass spectral studies. These studies though aimed at total identification of the compounds, resulted in certain interesting observations and hence are being reported. In order to confirm the observations under electron impact and to support the mechanism of fragmentation we have also performed MSNS experiments in both daughter ion and parent ion modes.     

PHOSPHORORGANISCHE VERBINDUNGEN 921

Abstract

Optisch aktive Phosphinigsäureamide R¹R²PNR₂ 4 (R¹ [dbnd] Ph, R² [dbnd] Me bzw. Et, R [dbnd] Et) sind durch kathodische Spaltung bzw.Cyanolyse optisch aktiver Amidophosphoniumsalze [R¹R²R³PNR₂]X (R¹ [dbnd] Ph. R² [dbnd] Me bzw. Et. R³ [dbnd] Bz bzw. All, R [dbnd] Et) unter Erhaltung der Konfiguration in hohen Ausbeuten zugänglich.

Optisch aktive Amidophosphoniumverbindungen, z.B. Ethyl-methyl-phenyl-diethylamido-phosphoniumiodid 10 oder Benzyl-ethyl-phenyl-diethylamido-phosphoniumbromid 12 werden erhalten:

a) aus den optisch aktiven tertiären Phosphinen, z.B. R-(+)Benzyl-methyl-phenyl-phosphin 6 bzw. S-(-)Ethyl-methyl-phenyl-phosphin 13 durch Umsetzung mit Alkyl- oder Arylaziden über die Phosphinimine 7 mit anschließender Alkylierung.

b) durch Alkylierung der optisch aktiven Phosphinigsäureamide 4. Die unter a) und b) genannten Umsetzungen verlaufen unter Erhaltung der Konfiguration.

c) Bei der Umsetzung optisch aktiver tertiärer Phosphine mit N-Halogenaminen entstehen nur racemische Amidophosphoniumsalze.

Optisch aktive Amidophosphoniumsalze, z.B. S(+)-Benzyl-methyl-phenyl-diethylamido-phosphoniumbromid 8 oder R-(-)-Ethyl-methyl-phenyl-diethylamido-phosphoniumiodid 10 werden bei der Einwirkung wäßriger Alkalien unter Inversion zu den entsprechenden Phosphinoxiden 9 bzw. 11 abgebaut. Optisch aktive Amidophosphoniumsalze, z.B. S(+)-Benzyl-ethyl-phenyl-diethylamido-phosphoniumbromid 12, werden mit LiAlH₄ retentiv unter Abspaltung des Aminliganden in die zugrundeliegenden optisch aktiven tertiären Phosphine übergeführt. Die Olefinierung von Benzaldehyd mit S(+)-Benzyl-ethyl-phenyl-diethylamido-phosphoniumbromid 5 ergibt unter Retention Stilben und optisch aktives Ethyl-phenyl-phosphinsäure-diethylamid 17, das auch durch Oxidation von R(-)-4 mit H₂O₂ erhalten wird. Schwefelung von R(-)-4 liefert das optisch aktive Ethyl-phenyl-thiophosphinsäure-diethylamid 18.

Das optisch aktive Phosphinigsäure-diethylamid 4 racemisiert allein und in Kohlenwasserstoffen gelöst bei 130°C nach einer Reaktion nullter Ordnung. Die Racemisierung wird durch Austausch der sekundären Aminogruppe über cyclische Assoziate verursacht. Beweis: Verbindungen mit unterschiedlichen. Substituenten am Phosphor- und Stickstoff tauschen beim dreistündigen Erhitzen auf 200°C die sekundären Aminogruppen aus. Es entstehen neue Phosphinigsäureamide in annähernd äquivalenten Mengen.

In Nitrobenzol bildet sich mit Phosphinigsäureamiden ein Charge-Transfer-Komplex, der im Falle des optisch aktiven Ethyl-phenyl-phosphinigsäure-diethylamids 4 bereits bei Zimmertemperatur eine schnelle Racemisierung bewirkt.

Optisch aktives Ethyl-phenyl-phosphinigsäure-diethylamid 4 liefert als Co-Katalysator bei der Homogenhydrierung von α-Ethylstyrol mit (RhCl-Hexadien-1,5)₂ 2-Phenylbutan mit einer optischen Ausbeute von 34%.