Terminal Acetyl Group Research Articles

Size-Controlled Synthesis of Modifiable Glycine-Terminated Au Nanoclusters as a Platform for Further Functionalization.

An improved and simple synthetic method for producing stable narrow-sized glycine-cystamine (Gly-CSA)-functionalized Au nanoclusters (NCs) from protected Fmoc-glycine-cystamine (Fmoc-Gly-CSA)-functionalized Au NCs is demonstrated in this study. The NC size and size distribution can be controlled directly as a function of reducing agent concentration with the formation of smaller NC core diameters at higher concentrations of NaBH4. Furthermore, when using 0.30 M NaBH4, three UV-vis absorption peaks at 690, 440, and 390 nm were seen, which are consistent with the formation of Fmoc-Gly-CSA-functionalized Au25L18 NCs. After deprotection of the Gly-CSA-functionalized Au NCs, the reactivity of the primary amine groups was investigated. Methyl acrylate-glycine-cystamine (MA-Gly-CSA)-functionalized Au NCs with terminal acetyl groups were formed via the Michael addition reaction of terminal amine groups with methyl acrylate. This reaction resulted in the formation of ester-terminated Au NCs including atom-precise MA-Gly-CSA Au25(SR)18 NCs. The functionalization of the ligand was confirmed by 1H NMR and UV-vis spectra, and TEM images of MA-Gly-CSA- and Gly-CSA-functionalized Au NCs showed that the size of the NCs remained unchanged after the reaction. With controllable NC size and facile functionalization of the Gly-CSA-functionalized Au NCs, these clusters have promising potential as scaffolds for biomedical applications.

Pyrazine-based hollow spherical self-assemblies: A portable tool for detection of volatile organic amines

Development of easy and efficient sensing tool for instant detection of various organic amines in aqueous media has prime significance. In this context, hollow spherical H-aggregates of pyrazine derivative bearing terminal acetyl groups were demonstrated as a reaction-based vapor phase sensing tool for organic amines. The aggregates displayed ratiometric fluorescence behavior toward aliphatic amines with a detection limit at nanomolar concentrations with concomitant self-assembly modulation from spherical H-aggregates to rod-shaped J-aggregates. Surprisingly, in the presence of p-nitroaniline remarkable quenching response was observed among various aromatic amines, which is attributed to the inner filter effect and energy transfer. Furthermore, a portable efficient tool for sensing various organic amines was constructed using the aggregates, demonstrating the practical applicability of this approach. This work will provide straightforward way for designing multifunctional self-assemblies for efficient selective behavior toward various organic amines in the ground water bodies.

Tunable synthesis and acetylation of dendrimer-entrapped or dendrimer-stabilized gold–silver alloy nanoparticles

In this study, amine-terminated generation 5 poly(amidoamine) dendrimers were used as templates or stabilizers to synthesize dendrimer-entrapped or dendrimer-stabilized Au–Ag alloy nanoparticles (NPs) with different gold atom/silver atom/dendrimer molar ratios with the assistance of sodium borohydride reduction chemistry. Following a one-step acetylation reaction to transform the dendrimer terminal amines to acetyl groups, a series of dendrimer-entrapped or dendrimer-stabilized Au–Ag alloy NPs with terminal acetyl groups were formed. The formed Au–Ag alloy NPs before and after acetylation reaction were characterized using different techniques. We showed that the optical property and the size of the bimetallic NPs were greatly affected by the metal composition. At the constant total metal atom/dendrimer molar ratio, the size of the alloy NPs decreased with the gold content. The formed Au–Ag alloy NPs were stable at different pH (pH 5–8) and temperature (4–50°C) conditions. X-ray absorption coefficient measurements showed that the attenuation of the binary NPs was dependent on both the gold content and the surface modification. With the increase of gold content in the binary NPs, their X-ray attenuation intensity was significantly enhanced. At a given metal composition, the X-ray attenuation intensity of the binary NPs was enhanced after acetylation. Cytotoxicity assays showed that after acetylation, the cytocompatibility of Au–Ag alloy NPs was significantly improved. With the controllable particle size and optical property, metal composition-dependent X-ray attenuation characteristics, and improved cytocompatibility after acetylation, these dendrimer-entrapped or dendrimer-stabilized Au–Ag alloy NPs should have a promising potential for CT imaging and other biomedical applications.

The use of dispersion-corrected DFT calculations to prevent an incorrect structure determination from powder data: the case of acetolone, C11H11N3O3

AbstractThe crystal structure of acetolone (5-(acetoacetylamino)benzimidazolone, C11H11N3O3), was determined from X-ray powder data. Despite strong preferred orientation effects, the structure could be solved with real-space methods and refined by the Rietveld method using restraints. The resulting structure gave a good Rietveld fit with reasonable confidence values; the structure looked chemically sensible and passed all tests including a CSD check and thecheckCIFprocedure. But dispersion-corrected density functional theory (DFT) calculations revealed that this structure was actually wrong, and further work showed that the terminal acetyl group had to be rotated by 180°. The correct crystal structure led to a better Rietveld refinement with improvedR-values. This structure was confirmed by dispersion-corrected DFT calculations. The compound crystallises inP-1 with two molecules per unit cell. The molecules are connected by a 2-dimensional hydrogen bond network.

4-{[(4Z)-5-Oxo-2-phenyl-4,5-dihydro-1,3-oxazol-4-yl-idene]meth-yl}phenyl acetate.

The title mol­ecule, C18H13NO4, shows a dihedral angle between the terminal acetyl group (r.m.s. deviation = 0.0081 Å) and remaining non-H atoms (r.m.s. = 0.0734 Å) of 53.45 (7)°. The configuration about the central olefinic bond is Z and overall the mol­ecule has a U-shaped conformation. Supra­molecular chains along the b-axis direction are found in the crystal structure. These are stabilized by (C=O)⋯π(ring centroid of the 1,3-oxazole ring) inter­actions [3.370 (2) Å].

Molecular orientation of thiol-derivatized tetraphenylporphyrin on gold studied by XPS and NEXAFS

Tetraphenylporphyrins bearing four linkers consisting of thioacetyl-functionalized carbon chains were immobilized on a gold surface via thiolate–gold bonds using two different preparation routes. The structure of these molecular layers was characterized in detail with synchrotron radiation based core-level spectroscopy, X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The results show that the geometry of the molecular layers and the number of linkers that bind to the gold surface depends on the preparation schemes. The deprotection of the linkers through removal of the terminal acetyl group before the molecular adsorption (deprotected systems) resulted in porphyrins bound to the gold surface with on the average three linkers, their normal axis being tilted ∼38° with respect to the surface normal. On the other hand, porphyrin layers prepared directly with the acetyl group still in place on the linkers (protected systems) are made of molecules bound to the gold surface via two linkers on the average. The resulting orientation is more upright, with the normal axis of the porphyrin plane tilted ∼50° with respect to the surface normal. Moreover, NEXAFS measurements revealed that the acetyl deprotected porphyrin layers have a higher degree of ordering than the protected systems.

Synthesis and Characterization of Biodegradable Hyperbranched Poly(ester-amide)s Based on Natural Material

A series of novel AB3-type monomers were prepared from nontoxic natural gallic acid and amino acids. These monomers were then melt-polycondensed in the presence of MgO as a catalyst via a transesterification process at 170-190 degrees C to yield the hyperbranched poly(ester-amide)s bearing terminal acetyl groups. FTIR and NMR spectra confirmed the structures of all the monomers and polymers. The degrees of branching, estimated from 1H NMR and quantitative 13C NMR spectra, were 0.50-0.68. These hyperbranched polymers displayed moderately high molecular weights. Hydrolytic and enzymatic degradation studies were carried out in vitro at 37.5 degrees C in NaOH hydrotropic solution and in Tris-HCl buffer (pH = 8.6) containing proteinase K, respectively. The results indicate that the hyperbranched poly(ester-amide)s are degradable hydrolytically as well as enzymatically, and the rate of hydrolytic degradation increases with the pH value of the solution.

Synthesis and characterization of hyperbranched aromatic poly(ester–imide)s

The synthesis and characterization of hyperbranched aromatic poly(ester–imide)s are described. A variety of AB 2 monomers, N-[3- or 4-bis(4-acetoxyphenyl)toluoyl]-4-carboxyl-phthalimide and N-{3- or 4-[1,1-bis(4-acetooxyphenyl)]ethylphenyl}-4-carboxy phthalimides were prepared starting from condensation of nitrobenzaldehydes or nitroacetophenones with phenol and used for synthesis of hyperbranched poly(ester–imide)s containing terminal acetyl groups by transesterification reaction. These hyperbranched poly(ester–imide)s were produced with weight-average molecular weight of up to 6.87 g/mol. Analysis of 1H NMR and 13C NMR spectroscopy revealed the structure of the four hyperbranched poly(ester–imide)s. These hyperbranched poly(ester–imide)s exhibited excellent solubility in a variety of solvents such as N, N-dimethylacetamide, dimethyl sulfoxide, and tetrahydrofuran and showed glass-transition temperatures between 217 and 255 °C. The thermogravimetric analytic measurement revealed the decomposition temperature at 10% weight-loss temperature ( T d 10) ranging from 365 to 416 °C in nitrogen.

Polymer electrolytes based on hyperbranched polymers

A hyperbranched poly[bis(hexaethylene glycol)benzoate] with terminal acetyl groups was prepared, and ionic conductivity, thermal property, and electrochemical stability of the polymer electrolyte with LiN(CF 3SO 2) 2 were investigated. Ionic conductivity of the polymer electrolyte exhibited a maximum value of 9×10 −5 S/cm at a [LiN(CF 3SO 2) 2]/[repeat unit] ratio of 0.6 (corresponding to a Li/O ratio of 0.04) and 80°C. The effect of a hyperbranched polymer, a poly[bis(triethylene glycol)benzoate] with terminal acetyl groups (poly-Ac1b), as an additive on ionic conductivity of a linear poly(ethylene oxide) (PEO)/LiN(CF 3SO 2) 2 electrolyte was also investigated. Addition of 10 wt.% poly-Ac1b improved ionic conductivity and also ion transference number in the polymer electrolyte.

Blend-based polymer electrolytes of poly(ethylene oxide) and hyperbranched poly[bis(triethylene glycol)benzoate] with terminal acetyl groups

Blend-based polymer electrolytes, with favorable mechanical strength, consisting of a linear poly(ethylene oxide) (PEO), a hyperbranched polymer (poly[bis(triethylene glycol)benzoate] with terminal acetyl groups), and LiN(CF 3SO 2) 2 salt, were prepared by the solvent casting technique. Thermal properties, ionic conductivity, electrochemical stability window, lithium ion transference number, and cyclic voltammetric behavior of the blend-based polymer electrolytes were all evaluated and discussed. In comparison with polymer electrolytes based on PEO, the blend-based polymer electrolytes exhibited improved lithium ionic conductivity and lithium/electrolyte interfacial performance. Blend-based polymer electrolyte with a hyperbranched polymer/PEO ratio of 20/80 in wt% and [LiN(CF 3SO 2) 2] 0.125 exhibited ionic conductivities as high as 8.1×10 −4 S cm −1 at 80°C and 3.8×10 −5 S cm −1 at room temperature. The electrochemical stability window was about 4.9 V. It was also demonstrated that crystallinity of the blend-based polymer electrolytes depends significantly on the hyperbranched polymer/PEO weight ratio as well as the lithium salt content.

Characterization of composite electrolytes based on a hyperbranched polymer

Composite polymer electrolytes composed of a hyperbranched poly[bis(triethylene glycol)benzoate] with terminal acetyl groups, LiN(CF 3SO 2) 2 as a lithium salt, and an inert ceramic filler such as α-LiAlO 2 or γ-LiAlO 2 were prepared by solvent casting method. Addition of an appropriate amount of the fillers to fully amorphous pristine polymer electrolytes led to an increase in ionic conductivities and lithium ion transference numbers. All composite polymer electrolytes exhibited good compatibility with a lithium metal electrode, and also, addition of fillers improved their mechanical performance. The α-LiAlO 2 filler was effective for improving the electrochemical compatibility with a lithium metal electrode, and the γ-LiAlO 2 filler was effective for enhancing the mechanical properties of the pristine polymer electrolytes.

Study of a diastereoisomeric dihydrothiophene derivative at 150K

The crystal and molecular structure of (4R, 5R)-4-(1', 2', 3', 4', 5'-penta-O-acetyl-D-manno-pentitol-1-yl)-5-[N-(4-methoxyphenyl)carbamoyl]-2-(N-methyl-benzylamino)-3-nitro-5-phenyl-4,5-dihydrothiophene {IUPAC name: 1-(2R,3R)-5-(N-benzyl-N-methylamino)-2-[N-(4-methoxyphenyl)carbamoyl]-4-nitro-2-phenyl-2,3-dihydro-3-thienyl]-1,2,3,4,5-penta-O-acetyl-D-manno-pentitol}, C 41 H 45 N 3 O 14 S, has been investigated at 150K. The analysis of the crystal structure allows the definition of the absolute configuration of the products of the cycloaddition reaction between 3,5-diphenyl-2-(N-methylbenzylamine)-1,3-thiazolium-7-olate and (E)-3,4,5,6,7-penta-O-acetyl-1,2-dideoxy-1-C-nitro-D-manno-hept-1-enitol, where only one of the two diastereoisomeric dihydrothiophenes could be isolated. The configurations at the new C4 and C5 stereocentres, with respect to that known at C6, are R,R. Except for a slight overall contraction and a slightly altered geometry of the terminal acetyl group, the structure is virtually the same as at room temperature.

Structure-dependent phytotoxicity of fumonisins and related compounds in a duckweed bioassay

Fumonisins A 1, A 2, B 2, B 2, and B 3 are a series of secondary metabolite analogues produced by Fusarium moniliforme. The A series fumonisins differ from B series by possession of a N terminal acetyl group. Hydrolytic removal of the propanetricarboxylic acid moieties from fumonisins B 1, and B 2 yields the aminoalcohols HB 1, and HB 2, respectively. AAL-toxin is a chemically related phytotoxin (only one propanetricarboxylic acid) produced by Alternaria alternata. In a duckweed (Lemna pausicostata) bioassay, AAL-toxin and the B series fumonisins at 1,μM caused pronounced cellular leakage of electrolytes and photodegradation of chlorophylls. These four compounds also caused the most marked reductions in duckweed growth. HB 1, at 1 μM was a moderate growth inhibitor and caused a low level of cellular leakage. The other compounds were inactive at this concentration. Significant effects on cellular leakage were measured at 0.04 μM for both AAL-toxin and fumonisin B 1, the two most active analogues. The propanetricarboxylic acid groups of fumonisins and AAL-toxin are necessary for significant herbicidal activity of this series of compounds, whereas acetylation of the terminal amine group greatly reduces their activity. The structurally related sphingolipids, phytosphingosine and sphingosine, were about two orders of magnitude less phytotoxic than fumonisin B 1; however, the phytotoxicity symptoms were similar.

Acetylation of histones by a kinase from rat liver nuclei

A variety of proteins have been reported to contain N-acetyl groups ( Harris, 1959, Harris and Hindley, 1961, Margoliash et al. , 1961 , Marshall and Neuberger, 1961, Narita, 1958, Phillips, 1963, Satake et al. , 1963 , Schroeder et al. , 1962 , Titani et al. , 1962) . The reactions which form terminal acetyl groups in proteins and their biological significance are not understood. The detction of acetyl groups in calf thymus histones ( Phillips, 1963) and the finding that chemically acetylated histones are less effective inhibitors of the DNA-dependent RNA polymerase in vitro led to the hypothesis that acetylation of histones could be important in the regulation of RNA synthesis ( Allfrey et al. , 1964 , Pogo et al. , 1966 ). Isolated calf thymus ( Allfrey et al. , 1964 ) and rat liver nuclei (Gallwitz and Sekeris, in prep.) acetylate histones in vitro and enzymes which incorporate C 14-acetate into histones have been demonstrated in pigeon liver ( Nohara et al. , 1966 ). This paper reports the transfer of acetate from coenzyme A to rat liver histones by an acetokinase from pure rat liver nuclei.

Linear oligoethylene urethanes oligourethanes II

AbstractLinear oligoethylene urethanes, A[O(CH2)2NHCO]nOCH3 (n = 2–7, A = Ac; n = 1–6, A = H), were synthesized and their physical properties were studied. The synthesis of acetoxy terminated oligomers was carried out by stepwise addition of 2‐acetoxyethyl isocyanate with a hydroxy terminated oligomer. The terminal acetyl group was eliminated by ester exchange in methanol to give the corresponding hydroxy terminated oligomers.