HPLC determination of acidic d‐amino acids and their N‐methyl derivatives in biological tissues

d ‐Aspartate (d ‐Asp) and N‐methyl‐d ‐aspartate (NMDA) occur in the neuroendocrine systems of vertebrates and invertebrates, where they play a role in hormone release and synthesis, neurotransmission, and memory and learning. N‐methyl‐d ‐glutamate (NMDG) has also been detected in marine bivalves. Several methods have been used to detect these amino acids, but they require pretreatment of tissue samples with o‐phthaldialdehyde (OPA) to remove primary amino acids that interfere with the detection of NMDA and NMDG. We report here a one‐step derivatization procedure with the chiral reagent N‐α‐(5‐fluoro‐2,4‐dinitrophenyl)‐(d or l )‐valine amide, FDNP‐Val‐NH₂, a close analog of Marfey's reagent but with better resolution and higher molar absorptivity. The diastereomers formed were separated by HPLC on an ODS‐Hypersil column eluted with TFA/water–TFA/MeCN. UV absorption at 340 nm permitted detection levels as low as 5–10 pmol. d ‐Asp, NMDA and NMDG peaks were not obscured by other primary or secondary amino acids; hence pretreatment of tissues with OPA was not required. This method is highly reliable and fast (less than 40 min HPLC run). Using this method, we detected d ‐Asp, NMDA and NMDG in several biological tissues (octopus brain, optical lobe and bucchal mass; foot and mantle of the mollusk Scapharca broughtonii), confirming the results of other researchers. Copyright © 2009 John Wiley & Sons, Ltd.     

Recombination of Coordination Bonds of a Mononuclear Precursor into a 3D d‐d′ Heterometallic Coordination Polymer with Double Helices

Abstract. Based on a mononuclear precursor [Mn(Hstp)₂(4,4′‐Hbpy)₂] ( 1 ), a hetero‐metallic complex, [Mn₂Ni(stp)₂(4,4′‐bpy)(H₂O)₄] ( 2 ) [stp = 2‐sulfoterephthalate, 4,4′‐bpy = 4,4′‐bpyridine] was synthesized by solvothermal reaction. Single‐crystal X‐ray diffraction analysis reveals that the Mn^II ion of the precursor 1 is hexacoordinate by four oxygen atoms from two Hstp^2– anions and two nitrogen atoms from two protonated 4, 4′‐Hbpy, and hydrogen bonding plays a significant role in constructing 3D supramolecular structure. While complex 2 features a self‐weaving framework from 1D straight chains and 2D wavy networks with double helical chains. Magnetic behavior of complex 2 was analyzed in connection with its crystal structure, which exhibits the weak antiferromagnetic interactions between the Mn^II and Ni^II ions.     

A feasible strategy to constructing hybrid conductive networks in PLA‐based composites modified by CNT‐d‐RGO particles and PEG for mechanical and electrical properties

Carbon nanotubes (CNTs) and reduced graphene oxide (RGO) were successfully assembled by chemical reaction to obtain CNT‐d‐RGO particles. Then, a home‐made dynamic impregnating device was used to prepare hybrid CNT‐d‐RGO/polyethylene glycol (PEG). Next, the different modifiers, including CNTs, GO, CNT‐d‐RGO, PEG, and CNT‐d‐RGO/PEG, were, respectively, added into poly‐(lactic acid) (PLA) matrix via melt‐compounding. The dispersed morphology for these different modifiers within the PLA matrix was confirmed by SEM and TEM observations. Especially, compared with the identical weight ratio of CNT‐d‐RGO, the hybrid CNT‐d‐RGO/PEG within the PLA matrix exhibited an excellent exfoliated and interconnected networks morphology. Moreover, compared with pure PLA, not only the crystallinity of all PLA‐based composites notably improved, but half‐crystallization time was also shortened. Furthermore, despite the addition of different modifiers, the crystal form of PLA‐based composites remained unchanged. Noticeably, compared with those of pure PLA, the tensile stress, strain, and modulus of PLA composite added with CNT‐d‐RGO/PEG increased by 29.4%, 4.1%, and 56.1%, respectively, and the V‐notch impact strength slightly improved. In addition, compared with pure PLA, volume resistivity of the PLA composite added with 1 wt% CNT‐d‐RGO/PEG decreased by 93.1%, and its volume conductivity increased by five orders of magnitude.     

Single‐Molecule Determination of the Isomers of d‐Glucose and d‐Fructose that Bind to Boronic Acids

Monosaccharides, such as d ‐glucose and d ‐fructose, exist in aqueous solution as an equilibrium mixture of cyclic isomers and can be detected with boronic acids by the reversible formation of boronate esters. The engineering of accurate, discriminating and continuous monitoring devices relies on knowledge of which cyclic isomer of a sugar binds to a boronic acid receptor. Herein, by monitoring fluctuations in ionic current, we show that an engineered α‐hemolysin (αHL) nanopore modified with a boronic acid reacts reversibly with d ‐glucose as the pyranose isomer (α‐d ‐glucopyranose) and d ‐fructose as either the furanose (β‐d ‐fructofuranose) or the pyranose (β‐d ‐fructopyranose). Both of these binding modes contradict current binding models. With this knowledge, we distinguished the individual sugars in a mixture of d ‐maltose, d ‐glucose, and d ‐fructose.     

α‐d‐Glucofuranose and α‐d‐allofuranose diacetonides and silyl ether of α‐d‐glucofuranose diacetonide in dithiophosphorylation reactions

α‐d ‐Glucofuranose and α‐d ‐allofuranose diacetonides react with 2,4‐diorganyl 1,3,2,4‐dithiadiphosphetane‐2,4‐disulfides to form optically active dithiophosphonates in 78–81% yields, which are transformed into the corresponding ammonium salts in 90–97% yields by the treatment of n‐hexadecylamine. The S‐silyldithiophosphonate was prepared in 93% yield by the reaction of 2,4‐bis(butoxyphenyl) 1,3,2,4‐dithiadiphosphetane‐2,4‐disulfide with silyl ether of α‐d ‐glucofuranose diacetonide. One of the salts obtained possesses antibacterial activity against Staphylococcus aureus ATCC 6538‐P.     

d‐Secoestrone derivatives. V

The two title 16,17‐secoestrone derivatives, 3‐methoxy‐17‐oxo‐17‐phenyl‐16,17‐secoestra‐1,3,5(10)‐triene‐16‐nitrile, C₂₅H₂₇NO₂, (I) (17‐oxo substituent), and 17‐hydroxy‐3‐methoxy‐17‐phenyl‐16,17‐secoestra‐1,3,5(10)‐triene‐16‐nitrile, C₂₅H₂₉NO₂, (II) (17‐hydroxy substituent), have quite different conformations in the solid state. These conformational differences can be minimized by molecular mechanics calculations. Thus, the remarkable difference in the biological activity of the two compounds, e.g. the strong oestrogenic characteristics of (I) and the moderate antioestrogenic action of (II), must be caused by the difference in substitution at C17. In (II), the mol­ecules are linked by O—H?N hydrogen bonds, forming spirals along the b direction.     

Partially renewable copolyesters prepared from acetalized d‐glucitol by solid‐state modification of poly(butylene terephthalate)

The backbone of poly(butylene terephthalate) (PBT) was modified with 2,4:3,5‐di‐O‐methylene‐D ‐glucitol (Glux) using solid‐state modification (SSM). The obtained copolyesters proved to have a non‐random overall chemical microstructure. The thermal properties of these semicrystalline, block‐like, Glux‐based materials were extraordinary, showing higher melting points, and glass transition temperatures compared with other sugar‐based copolyesters prepared by SSM. These remarkable thermal properties were a direct result of the inherently rigid structure of Glux and the relatively slow randomization of the block‐like chemical microstructure of the Glux‐based copolyesters in the melt. SSM proved to be a versatile tool for preparing partially biobased copolyesters with superior thermal properties. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 164–177     

The low‐temperature study of d‐ and dl‐camphoric anhydride

The low‐temperature crystal stuctures of d ‐ and dl ‐camphoric anhydride, C₁₀H₁₄O₃, have been determined by X‐ray diffraction methods. Although the two enantiomers crystallize in different space groups, the cell volumes and densities are essentially the same. The six‐membered rings deviate significantly from planarity, both exhibiting half‐boat conformations. The dihedral angle between the six‐ and five‐membered rings is 80.3 (1)° in both cases. The main difference in the molecular stuctures can be described by two torsion angles associated with the H atoms of the methyl substituents. The packing of the racemic and chiral structures are essentially the same.     

Butelase‐Mediated Macrocyclization of d‐Amino‐Acid‐Containing Peptides

Macrocyclic compounds have received increasing attention in recent years. With their large surface area, they hold promise for inhibiting protein–protein interactions, a chemical space that was thought to be undruggable. Although many chemical methods have been developed for peptide macrocyclization, enzymatic methods have emerged as a promising new economical approach. Thus far, most enzymes have been shown to act on l ‐peptides; their ability to cyclize d ‐amino‐acid‐containing peptides has rarely been documented. Herein we show that macrocycles consisting of d ‐amino acids, except for the Asn residue at the ligating site, were efficiently synthesized by butelase 1, an Asn/Asp‐specific ligase. Furthermore, by using a peptide‐library approach, we show that butelase 1 tolerates most of the d ‐amino acid residues at the P1′′ and P2′′ positions.