羧甲基纤维素钠水凝胶的制备及其生物降解性研究

用羧甲基纤维素钠(CMC—Na)制得了含水量高达98％的水凝胶，考察了防腐剂、交联剂、无机态氮素、有机态氮素、碳水化合物的加入量以及环境中pH值等因素对生物降解性的影响。结果表明：制备条件不同，水凝胶的生物降解性不同；环境中一定量铵根离子的存在有利于水凝胶的生物降解；在pH=5．2的环境中纤维素酶活性最高，降解程度最大。     

Diffusion-weighted imaging of bacteria colonies in the STRAFI plane

Imaging colonies of bacteria in water suspension using NMR requires that the water inside the bacteria can be differentiated from the surrounding water. This is commonly carried out by using diffusion-weighted pulsed field gradient techniques. However, it is also possible to use the diffusion sensitivity inherent in stray field imaging (STRAFI). In STRAFI, the subject to be imaged is normally moved along the axis of a superconducting magnet so that it passes through the sensitive slice. However, by moving the sample in the transverse direction and by using a long copper strip in place of a surface induction coil, a diffusion-weighted one-dimensional projection profile can be obtained across the sensitive slice. Profiles from a water phantom and from a bacteria suspension show convincing discrimination between intracellular and extracellular water.     

The Anti-Inflammatory Effect of a γ-Lactone Isolated from Ostrich Oil of Struthio camelus (Ratite) and Its Formulated Nano-Emulsion in Formalin-Induced Paw Edema

The ostrich oil of Struthio camelus (Ratite) found uses in folk medicine as an anti-inflammatory in eczema and contact dermatitis. The anti-inflammatory effect of a γ-lactone (5-hexyl-3H-furan-2-one) isolated from ostrich oil and its formulated nano-emulsion in formalin-induced paw edema was investigated in this study. Ostrich oil was saponified using a standard procedure; the aqueous residue was fractionated, purified, and characterized as γ-lactone (5-hexyl-3H-furan-2-one) through the interpretation of IR, NMR, and MS analyses. The γ-lactone was formulated as nano-emulsion using methylcellulose (MC) for oral solubilized form. The γ-lactone methylcellulose nanoparticles (γ-lactone-MC-NPs) were characterized for their size, shape, and encapsulation efficiency with a uniform size of 300 nm and 59.9% drug content. The γ-lactone was applied topically, while the formulated nanoparticles (NPs) were administered orally to rats. A non-steroidal anti-inflammatory drug (diclofenac gel) was used as a reference drug for topical use and ibuprofen suspension for oral administration. Edema was measured using the plethysmograph method. Both γ-lactone and γ-lactone-MC-NPs showed reduction of formalin-induced paw edema in rats and proved to be better than the reference drugs; diclofenac gel and ibuprofen emulsion. Histological examination of the skin tissue revealed increased skin thickness with subepidermal edema and mixed inflammatory cellular infiltration, which were significantly reduced by the γ-lactone compared to the positive control (p-value = 0.00013). Diuretic and toxicity studies of oral γ-lactone-MC-NPs were performed. No diuretic activity was observed. However, lethargy, drowsiness, and refusal to feeding observed may limit its oral administration.     

A first-principles description of proton-driven spin diffusion

Herein we design a reduced Liouville space for the simulation of proton-driven spin diffusion. Using this approach, the experimentally observed carbon-13 polarisation transfer in a powder sample undergoing magic-angle spinning is quantitatively described, directly from crystal geometry and without any adjustable parameters.     

A practical and flexible implementation of 3D MRI in the Earth's magnetic field

The Earth's magnetic field, though weak, is appealing for NMR applications because it is highly homogeneous, globally available and free. However, the practicality of Earth's field NMR (EFNMR) has long been limited by the need to perform experiments in outdoor locations where the local field homogeneity is not disrupted by ferrous or magnetic objects and where ultra-low frequency (ULF) noise sources are at a minimum. Herein we present a flexible and practical implementation of MRI in the Earth's magnetic field that demonstrates that EFNMR is not as difficult as it was previously thought to be. In this implementation, pre-polarization and ULF noise shielding, achieved using a crude electromagnet, are used to significantly improve signal-to-noise ratio (SNR) even in relatively noisy environments. A three axis gradient coil set, in addition to providing imaging gradients, is used to provide first-order shims such that sub-hertz linewidths can routinely be achieved, even in locations of significant local field inhomogeneity such as indoor scientific laboratories. Temporal fluctuations in the magnitude of the Earth's magnetic field are measured and a regime found within which these variations in Larmor frequency produce no observable artefacts in reconstructed images.     

Quantitative analysis of Earth’s field NMR spectra of strongly-coupled heteronuclear systems

In the Earth’s magnetic field, it is possible to observe spin systems consisting of unlike spins that exhibit strongly coupled second-order NMR spectra. Such spectra result when the J-coupling between two unlike spins is of the same order of magnitude as the difference in their Larmor precession frequencies. Although the analysis of second-order spectra involving only spin-½ nuclei has been discussed since the early days of NMR spectroscopy, NMR spectra involving spin-½ nuclei and quadrupolar (I > ½) nuclei have rarely been treated. Two examples are presented here, the tetrahydroborate anion, , and the ammonium cation, . For the tetrahydroborate anion, ¹J(¹¹B,¹H) = 80.9 Hz, and in an Earth’s field of 53.3 μT, ν(¹H) = 2269 Hz and ν(¹¹B) = 728 Hz. The ¹H NMR spectra exhibit features that both first- and second-order perturbation theory are unable to reproduce. On the other hand, second-order perturbation theory adequately describes ¹H NMR spectra of the ammonium anion, , where ¹J(¹⁴N,¹H) = 52.75 Hz when ν(¹H) = 2269 Hz and ν(¹⁴N) = 164 Hz. Contrary to an early report, we find that the ¹H NMR spectra are independent of the sign of ¹J(¹⁴N,¹H). Exact analysis of two-spin systems consisting of quadrupolar nuclei and spin-½ nuclei are also discussed.     

A study of some parameters relevant to the response of harwell PMMA dosimeters to gamma and electron irradiation

The effects on the radiation response of Harwell polymethylmethacrylate (PMMA) dosimeters of dose-rate, radiation type, temperature during irradiation and post-irradiation storage, and post-irradiation stability, are of importance to the operators of commercial irradiation facilities.

This paper describes recent studies of the effects of some of these parameters on the radiation response of Harwell Red 4034, Amber 3042, and Gammachrome YR Perspex dosimeters, and provides data on batch to batch variation and shelf-life.     

Ti掺杂对α″-Fe16N2相稳定性的影响

研究了掺杂Ti对α″-Fe₁₆N₂相稳定性的影响，发现适量Ti掺杂有利于α″-Fe₁₆N₂相的形成．理论分析表明，掺杂适量Ti元素后含Ti的α″-(Fe,Ti)₁₆N₂相的生成焓降低，使α″相的稳定性提高，也使α″相更易制备．Ti浓度为3—15at％的(FeTi)-N薄膜具有高饱和磁化强度，μ₀M_s=2.3—2.5T． 关键词：