Monoarsine-protected icosahedral cluster [Au13(AsPh3)8Cl4]+: comparative studies on ligand effect and surface reactivity with its stibine analogue.

Ligand shells of gold nanoclusters play important roles in regulating their molecular and electronic structures. However, the similar but distinct impacts of the homologous analogues of the protecting ligands remain elusive. The C2v symmetric monoarsine-protected cluster [Au13(AsPh3)8Cl4]+ (Au13As8) was facilely prepared by direct reduction of (Ph3As)AuCl with NaBH4. This cluster is isostructural with its previously reported stibine analogue [Au13(SbPh3)8Cl4]+ (Au13Sb8), enabling a comparative study between them. Au13As8 exhibits a blue-shifted electronic absorption band, and this is probably related to the stronger π-back donation interactions between the Au13 core and AsPh3 ligands, which destabilize its superatomic 1P and 1D orbitals. In comparison to the thermodynamically less stable Au13Sb8, Au13As8 achieves a better trade-off between catalytic stability and activity, as demonstrated by its excellent catalytic performance towards the aldehyde-alkyne-amine (A3) coupling reaction. Moreover, the ligand exchange reactions between Au13As8 with phosphines, as exemplified by PPh3 and Ph2P(CH2)2PPh2, suggest that Au13As8 may be a good precursor cluster for further cluster preparation through the "cluster-to-cluster" route.

Ag22 Nanoclusters with Thermally Activated Delayed Fluorescence Protected by Ag/Cyanurate/Phosphine Metallamacrocyclic Monolayers through In-Situ Ligand Transesterification.

The composition of protection monolayer exerts great influence on the molecular and electronic structures of atomically precise monolayer protected metal nanoclusters. Four isostructural Ag/cyanurate/phosphine metallamacrocyclic monolayer protected Ag22 nanoclusters are synthesized by kinetically controlled in-situ ligand formation-driven strategy. These eight-electron superatomic silver nanoclusters feature an unprecedented interfacial bonding structure with diverse E-Ag (E=O/N/P/Ag) interactions between the Ag13 core and metallamacrocyclic monolayer, and displays thermally activated delayed fluorescence (TADF), benefiting from their distinct donor-acceptor type electronic structures. This work not only unmasks a new core-shell interface involving cyanurate ligand but also underlines the significance of high-electron-affinity N-heterocyclic ligand in synthesizing TADF metal nanoclusters. This is the first mixed valence Ag0/I nanocluster with TADF characteristic.

Detection of nitroaromatics based on aggregation induced emission of barbituric acid derivatives.

Barbituric acid derivatives with typical aggregation induced emission (AIE) are reported. Their emission wavelengths varied with water fraction of their solution. UV-visible absorption spectroscopy and theoretical calculations revealed the intramolecular charge transfer (ICT) possibility from donor to acceptor and the mechanism was confirmed as a restriction of intramolecular motion (RIM). The AIE properties were affected by the different substituents on barbituric acid. When the molecular volume increased, the AIE effect decreased. Fluorescent quenching mechanism was applied to detect nitroaromatic explosives. For 2,4,6-trinitrophenol (PA), one of the derivatives 5-(4-diphenylamino styrene)-1,3-diphenyl-barbituric acid in THF/H2O mixture (1:9, v/v), showed amplified fluorescence quenching with a maximum Stern-Volmer quenching constant of 4.1 × 104 M-1. The solid phase paper test based on 5-(4-diphenylamino styrene)-1,3-diphenyl-barbituric acid also showed a superior sensitivity toward PA both in vapor and solution.

New views on the reaction of primary amine and aldehyde from DFT study.

A general theoretical investigation on the reaction of primary amine with aldehyde was carried out by density functional theory. The calculation systems involve three kinds of primary amines (methylamine, vinylamine, and phenylamine) and three kinds of aldehydes (formaldehyde, acetaldehyde, and acrylaldehyde). The steric and electronic inductive effects on the reaction mechanism were studied. Results reveal that the nucleophilic attack of primary amine on aldehyde under neutral conditions leads to carbinolamines, rather than Schiff bases. The nucleophilic attack on the protonated aldehyde produces the protonated Schiff base. The steric hindrance of the aldehyde slows down the nucleophilic attack but allows enough time to abstract a H; consequently, the formation of the protonated Schiff base is preferred. During the carbinolamine protonation, the H(+) preferably locates on the amine nitrogen and then is abstracted by the hydroxyl oxygen over an energy barrier, leaving protonated Schiff base after timely water liberation. The formation of a prereaction potential energy well obviously softens the steric and electronic inductive effects on the active barrier for different reactants.

Solid-state structure of gelatin-mono epoxy terminated polydimethylsiloxane polymer: effect of electrostatic and hydrophobic interactions.

In this study, a hybrid synthetic gelatin-mono epoxy terminated polydimethylsiloxane polymer (PDMS-E grafted gelatin (PGG)) was successfully synthesized on a large scale. Supramolecular structure of gelatin, which was decided by the sophisticated inter- and intra-molecular interactions, significantly affected the self-assembly and phase behavior of PGG. Interestingly, the supramolecular organization of PGG could be tuned finely by negatively charged surfactants, such as sodium dodecyl sulfate (SDS) and sodium tetradecyl sulfonate (STSo), as revealed by high-resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM), light microscopy (LM), and atomic force microscopy (AFM). SEM images exhibited the presence of spherical aggregates in PGG/SDS films while hexagonal array was observed in PGG/STSo films. The results of LM revealed that when PGG/STSo solution was dried, a successive structural transformation from spheres to hexagons, via sticks and butterfly-shaped aggregates as intermediates, was observed. However, the morphologies of the aggregates formed in PGG/SDS system did not exhibit any obvious change upon drying. Attenuated total reflection-Fourier transform infrared spectra combined with AFM observations indicated that the secondary structure and aggregation behavior of gelatin was modified with the change in the electrostatic and hydrophobic interactions, leading to the formation of diversified solid-state structures of PGG.

Effect of anionic surfactants on grafting density of gelatin modified with PDMS-E.

The effect of anionic surfactants on the interfacial compatibility in mono epoxy terminated polydimethylsiloxane (PDMS-E) macromonomer and gelatin mixed system was studied by Gibbs free energy (ΔGM), which played a crucial role in deciding the grafting density of immiscible polymer in heterogeneous system. Aggregation behavior of gelatin chains at boundary between gelatin phase and solvent phase was investigated using viscosity, surface tension and conductivity measurements. Viscosity analysis showed a regular increase in viscosity with the increasing alkyl chain length from C7 to C16 of the homologous alkyl sulfate surfactants. Changes of surface tension exhibited the regular curves of polyelectrolyte-anionic surfactant for alkyl sulfate surfactant systems. The results demonstrated that aggregate structure of gelatin-sulfate surfactants was dominated by electrostatic and hydrophobic interactions, which resulted in a self-assembly process of the hydrophobic segments and hydrophilic segments among gelatin chains and surfactant molecules. However, the interactions between gelatin and alkyl sulfonate surfactants were mainly governed by hydrophobic interactions, which induced conformation change of gelatin molecules. Well-ordered arrangement of gelatin chains at a fluid interface has observed by high-resolution transmission electron microscopy (HR-TEM). It is a key factor to contribute to the reduction of interfacial free energy, which mainly depends on the hydrophobic interaction between gelatin and alkyl sulfate/sulfonate surfactants. MD simulations conclusions are great agreement with our experimental results.

Microstructure transformation of PDMS-E grafted gelatin polymers induced by SDS and SDBS.

Inorganic-organic hybrid materials with tunable chemical and physical properties were prepared from mono epoxy terminated polydimethylsiloxane (PDMS) macromonomer and gelatin for improving their flexibility and hydrophobicity. Sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS) were used to enhance the compatibility of two polymers phases. Measurement of grafting density indicated that anionic surfactants played a crucial role in deciding the detailed microstructure of PDMS-E grafted gelatin (PGG) polymers in alkaline solution. The interaction between gelatin and SDS/SDBS was investigated by viscosity and SEM. Viscosity analysis showed a regular increase in SDS system and a steeper change in the case of SDBS. SEM micrographs displayed a series of structural transitions (spherical, spindle, irregular granular and spherical aggregates) with the increase of SDS concentration, but spindle and granular aggregates appeared alternately as varying SDBS concentrations. The results demonstrated that both the electrostatic and hydrophobic interactions between anionic surfactant and gelatin controlled the aggregate structure of gelatin-SDS/SDBS, which affected the compatibility between gelatin and PDMS. Thermal properties of PGG polymers had changed with the modification of polymer microstructure. The results above revealed that microstructure transformation of PGG polymers was determined by the compatibility of two polymers in anionic surfactant aqueous solution and the chemical nature of their monomers.

Effect of aggregation behavior of gelatin in aqueous solution on the grafting density of gelatin modified with glycidol.

The effect of aggregation behavior of gelatin in aqueous solution on the grafting density of glycidol grafted gelatin polymers (GGG polymers) was investigated. The grafting density was measured using the Van Slyke method by calculating the conversion rate of free - NH(2) groups of gelatin. The conversion rate reached peak values at 6% and 14% of the gelatin aqueous solution. SEM micrographs displayed a series of structural transitions (i.e., spherical, spindle, butterfly, irregular and dendritic aggregates) at varying concentrations from 2% to 16% (w/w) at an interval of 2% (w/w). The spindle aggregates reappeared at the concentrations of 6% and 14%. Viscosity measurements indicated that the physicochemical properties of the gelatin solution had changed with increasing concentration. UV and CD analysis indicated that hydrophobic interactions competed with hydrogen bonding, and the random coils partly transformed to ß-sheet structure by changing the concentration. Zeta potential and pH data confirmed the increasing electrostatic repulsion associated with increasing the hydrophobic region. XPS analysis revealed that the elemental composition of the gelatin particle surface changed with variation in the aggregate structure, determining the monotonic variation of the grafting density with increasing concentration. Results demonstrate that aggregation behavior of gelatin in aqueous solution plays a crucial role in deciding the grafting density of gelatin modified products.

N,N,N',N'-Tetra-kis(2-hy-droxy-5-methyl-benz-yl)ethane-1,2-diamine dimethyl-formamide disolvate.

The title compound, C(34)H(40)N(2)O(4)·2C(3)H(7)NO, was synthesized by the Mannich condensation of ethane-diamine, formaldehyde and p-cresol. In the crystal, the tetra-phenol mol-ecule is arranged around an inversion center. The mol-ecule and the dimethyl-formamide solvate are linked through an O-H⋯O hydrogen bond. An intra-molecular O-H⋯N hydrogen bond occurs in the tetra-phenol mol-ecule, which may influence the mol-ecular confomation. Futhermore, C-H⋯O and π-π stacking inter-actions [centroid-centroid distance = 3.7081 (14) Å] stabilize the crystal packing, building a three-dimensional network.

9-{4-[(E)-2-(4,6-Dimethyl-1,3,5-triazin-2-yl)ethen-yl]phen-yl}-9H-carbazole.

In the crystal structure of the title compound, C(25)H(20)N(4), the triazinyl ring is nearly coplanar with the planar (r.m.s. deviation = 0.028 Å) phenyl-ethenyl unit, the twist being only 5.8 (2)°; however, the planar carbazolyl unit (r.m.s. deviation = 0.008 Å) is twisted by 47.8 (1)° with respect to the phenyl-ethenyl unit. The nonplanar nature of the mol-ecule explains the phenomenon of light emission at short wavelengths in the solid state but at long wavelengths in solution.