Magnetic order in CaMn2Sb2 studied via powder neutron diffraction

This paper reports a neutron powder diffraction study of CaMn₂Sb₂ in the temperature range of 20–300 K. Collinear long-range antiferromagnetic order of manganese ions occurs below 85 K, where a transition is observed in the dc magnetic susceptibility measured with a single crystal. Short-range magnetic order, characterized by a broad diffraction peak corresponding to a d-spacing of approximately 4 Å (2θ≈22°), is also observed above 20 K. The long-range antiferromagnetic order is indexed by the chemical unit cell, indicating a propagation vector k=(0 0 0), with a refined magnetic moment of 3.38 μ_B at 20 K. Two possible magnetic models have been identified, which differ in spin orientation for the two manganese ions with respect to the ab plane. The model with spins oriented at a 25±2° angle relative to the ab plane gives an improved fit compared to the other model in which the spins are constrained to the ab plane. Representational analysis can account for a model involving a c-axis component only by the mixing of two irreducible representations.     

活细胞中的化学物理-光学观测和控制细胞内信号转导

Cells are crowded microenvironments filled with macromolecules undergoing constant physical and chemical interactions. The physicochemical makeup of the cells affects various cellular responses, determines cell-cell interactions and influences cell decisions. Chemical and physical properties differ between cells and within cells. Moreover, these properties are subject to dynamic changes in response to environmental signals, which often demand adjustments in the chemical or physical states of intracellular molecules. Indeed, cellular responses such as gene expression rely on the faithful relay of information from the outside to the inside of the cell, a process termed signal transduction. The signal often traverses a complex path across subcellular spaces with variable physical chemistry, sometimes even influencing it. Understanding the molecular states of such signaling molecules and their intracellular environments is vital to our understanding of the cell. Exploring such intricate spaces is possible today largely because of experimental and theoretical tools. Here, we focus on one tool that is commonly used in chemical physics studies-light. We summarize recent work which uses light to both visualize the cellular environment and also control intracellular processes along the axis of signal transduction. We highlight recent accomplishments in optical microscopy and optogenetics, an emerging experimental strategy which utilizes light to control the molecular processes in live cells. We believe that optogenetics lends unprecedented spatiotemporal precision to the manipulation of physicochemical properties in biological contexts. We hope to use this work to demonstrate new opportunities for chemical physicists who are interested in pursuing biological and biomedical questions.     

Unsymmetrical and symmetrical diphosphazane ligands derived from o-phenylene phosphorochloridite

Two new diphosphazane ligands, PrⁱN(PPh₂)(PO₂C₆H₄) ( 1 ) and PrⁱN{P(O₂C₆H₄)}₂ ( 3 ), have been synthesized and characterized by spectroscopic data. The structure of 1 has been confirmed by single crystal X-ray diffraction. Crystal data: Monoclinic, C2/c, Z = 16, a = 34.149(5) Å, b = 9.717(6) Å, c = 29.439(5) Å, β = 125.11(2)°, V = 7991 ų, R = 0.058, R_w = 0.061. This compound shows two different P–N bond lengths (1.654 (4) and 1.743(4) Å) and a P–N–P angle of 120.7(2)°. Variable temperature ³¹P NMR measurements for 1 and 3 throw light on the nature of the conformers present in solution.     

Analysis of plasma polymerization of allylamine by FTIR

The plasma polymerization of allylamine in an inductively coupled rf plasma reactor is analyzed by Fourier transform infrared spectroscopy. Comparison of the infrared spectra of the as-received monomer and the plasma polymerized film reveals a conversion of the primary amine in the monomer (? CH₂? NH₂) to an imine (? CH?NH) and a nitrile (C?N). Plasma polymerization of ethylenediamine yields the same results, suggesting that this polymerization scheme may be typical of primary amines. Increasing the plasma power seems to increase the proportion of nitrile groups in relation to the imine groups. The infrared spectra of the vapor phase polymerized monomer was similar to that of the substrate-grafted allylamine film implying a similar structure. Aging of this vapor phase polymer at 120°C for 1 h in vacuum and at 295°C for 15 min in an oxygen free environment reveals nitrile group reaction similar to that observed in polyacrylonitrile. Thermogravimetric analyses of the vapor phase polymers in a nitrogen atmosphere at 20°C/min demonstrated the thermal stability, with the polymer produced at a plasma power level of 50 W retaining 20% of its weight at 1000°C. This was better than the stability shown by the polymer produced at 150 W and is attributed to the ease of nitrile group polymerization in the former.     

Titrimetric micro determination of some phenothiazine neuroleptics with potassium hexacyanoferrate(III)

Three simple, rapid and accurate titrimetric procedures using potassium hexacyanoferrate(III) have been developed for the micro determination of five phenothiazine drugs in pure form and in dosage forms. The procedures are based on the oxidation of phenothiazines in an acid medium to colourless sulphoxides via orange or purple coloured products. In the first procedure, phenothiazines are titrated directly in H(2)SO(4)-H(3)PO(4) medium to a colourless end point. In the second method, a known excess of the oxidant is added and after a specified time, the residual oxidant is determined iodometrically. The third method employs electrometric end-point detection. The optimum reactions conditions and other analytical parameters are evaluated. The influence of the substrates commonly employed as excipients with phenothiazine drugs has been studied. Statistical comparison of the results with those of an official method shows excellent agreement and indicates no significant difference in precision.     

N-甲基甲酰胺与醇的氢键相互作用

The hydrogen bonding interactions between N-methylformamide and primary, secondary, and tertiary alcohols have been studied using the FT1R spectroscopic method. The most likely association complex between alcohol and N-methylformamide is the 1:1 stoichiometric complex formed between the hydroxyl group of alcohol and the carbonyl group of N-methylformamide. The formation constant of the 1:1 complexes has been calculated using the Nash method. It appears that the primary alcohols have larger formation constant compared with the secondary and tertiary alcohols. The results showed that the proton-donating ability of the alcohols decreased in the order: primary＞secondary＞tertiary, and that the association constant increased with the increase in carbon chain of the alkyl group of alcohols.     

Strong light fields coax intramolecular reactions on femtosecond time scales

Energetic H(2) (+) ions are formed as a result of intramolecular rearrangement during fragmentation of linear alcohols (methanol, ethanol, propanol, hexanol, and dodecanol) induced by intense, pulsed optical fields. The laser intensity regime that is accessed in these experiments (peak intensity of 8 x 10(15) W cm(-2)) ensures multiple ionization of the irradiated alcohol molecules such that Coulomb explosions would be expected to dominate the overall fragmentation dynamics. Polarization dependent measurements show, counterintuitively, that rearrangement is induced by the strong optical field within a single, 100 fs long laser pulse, and that it occurs before Coulomb explosion of the field-ionized multiply charged alcohols.