葵花籽油贮藏过程理化性质与LF-NMR弛豫特性的相关性

该文主要对葵花籽油分别在25、65℃避光贮藏过程的理化性质及其低场核磁共振(LF-NMR)弛豫特性的变化规律进行了研究,建立并验证了理化指标与LF-NMR检测结果的相关性模型。结果表明:65℃贮藏时,油样的过氧化值(PV)、共轭二烯值(K232)、共轭三烯值(K270)、p-茴香胺值(p-AV)、总极性化合物(TPC)含量及峰面积比例(S21、S22)随时间延长呈指数关系增加(r20.93),而S23峰及单组分弛豫时间(T2W)则随时间延长呈指数减小趋势(r20.98),通过多元回归分析可建立理化指标与弛豫特性间的相关性模型(r20.94)。25℃贮藏过程中理化性质及其LF-NMR弛豫特性的变化程度均相对较小,但PV、K232及TPC含量仍与贮藏时间呈良好的线性增大关系(r20.95),其余理化指标及LF-NMR弛豫特性则无明显的规律性变化,相关性模型亦较差。     

基于低场核磁共振弛豫特性结合多元线性回归同步评价菜籽煎炸油品质

油脂作为煎炸食品的重要配料,其品质对产品质量安全和行业发展具有重要意义。以菜籽油为研究对象,系统分析了菜籽油在煎炸过程中品质指标的变化规律及其对低场核磁共振(Low-field nuclear magnetic resonance,LF-NMR)弛豫信号的影响,研究了菜籽油品质指标与弛豫特性之间的相关性,通过LF-NMR弛豫特性结合多元线性回归建立了菜籽煎炸油品质指标同步检测模型,并探究了自变量数对模型性能的影响。结果表明,菜籽油的酸价、极性组分、茴香胺值、羰基价、黏度和吸光度均随煎炸时间延长而增大,而碘值逐渐减小;煎炸过程中菜籽油回波衰减曲线的衰减速率呈上升趋势;弛豫特性指标(T_2w、T₂₁、T₂₂、S₂₂和S₂₃)与菜籽煎炸油的品质指标(酸价、极性组分、茴香胺值、羰基价、黏度、吸光度和碘值)呈显著相关(p<0.05);同步检测模型的决定系数(R²)大于0.93,相对平均偏差(RAD)小于0.15,与单变量检测模型相比,除茴香胺值外,其它指标的RA...     

LF-NMR和MRI对干制虾仁复水过程水分状态及品质变化的研究

采用低场核磁(LF-NMR)及其成像技术(MRI)研究干制虾仁在25℃复水过程中的水分含量、分布及状态变化,并通过线性回归分析不同复水时间干制虾仁的LF-NMR参数与质构特性及复水率的相关性。实验结果表明,干制虾仁复水过程中存在结合水、不可移动水和自由水3个组分峰,随着复水时间的增加,结合水无明显变化,而自由水、不易流动水含量增加,且自由度增加,流动性增大。LF-NMR参数(T_(22)、T_(23)、A_(22)、A_(23)和A_(Total))和硬度、咀嚼性、弹性、凝聚性以及复水率有极显著的相关性(R~2≥0.613),为干制虾仁复水过程中品质的快速无损预测提供了一种新方法。     

碳链长度及不饱合度对脂肪酸低场核磁弛豫特性的影响

对不同碳链长度及饱和程度的脂肪酸及二、三元混合脂肪酸体系的低场核磁共振弛豫特性进行了研究。结果表明,除乙酸外,随碳链长度增加,横向弛豫时间(T_2)及单组分弛豫时间(T_(2W))均减小;而随不饱和度增加,二者均相对增大。对棕榈酸-油酸、硬脂酸-油酸混合体系而言,随着油酸比例增加,T_2与T_(2W)均增大;油酸比例大于40%后,会对亚油酸-油酸体系的弛豫响应产生较大影响。随着亚油酸比例增加,各亚油酸-油酸-硬脂酸三元混合体系的T2弛豫时间均增大,峰面积比例(S_(21))减小,而峰面积比例(S_(22))增大,油酸比例越高,峰面积比例的变化幅度减小,T_(2W)均增加,且随体系中油酸(OA)比例的增加变化趋缓。     

颗粒污染物对变压器油粘度的影响

运动粘度是表征变压器油流动性能的重要指标,颗粒污染物的存在对油液的粘度性能会产生较大的影响,甚至导致油液的劣化。按照ISO4406标准,采用均匀设计法配制了24组含Cu、Fe、SiO_2的不同粒径、不同污染度的颗粒污染物油样并对其进行了运动粘度测试(40℃),获得了不同含量的颗粒物对油液运动粘度的影响规律;采用支持向量机法建立了油中不同粒径、含量的Cu、Fe、SiO_2混合颗粒物与油样运动粘度之间的数学模型。结果表明建立的不同粒径、含量的Cu、Fe、SiO_2颗粒与油液运动粘度之间的SVM(Support Vector Machine)模型对验证集的决定系数和均方根误差分别是0.9951、0.0628;随着颗粒含量的增加,油液运动粘度值逐渐减小并趋于稳定;油中Cu、Fe、SiO_2混合颗粒物在粒径为15μm、25μm时对变压器油运动粘度的影响较大,变化幅度分别为0.455mm~2/s、0.56mm~2/s。     

活性炭纤维-固相微萃取-气相色谱/飞行时间质谱法鉴别地沟油与植物油

采用活性炭纤维-固相微萃取(ACF-SPME)与气相色谱/飞行时间质谱(GC/TOFMS)联用技术检测地沟油与植物油中挥发性游离脂肪酸的含量,通过色谱峰分析脂肪酸含量的变化,建立了鉴别地沟油的新方法。检测出6种挥发性脂肪酸:戊酸、己酸、辛酸、壬酸、棕榈酸和硬脂酸;地沟油中棕榈酸的含量远高于植物油中的含量,而己酸含量基本不变。据此提出了地沟油检测指标,即A值指标=棕榈酸的峰面积/己酸的峰面积:地沟油的A值大于0.8,而植物油的A值均小于0.8。通过实验证明了不同纤维、不同品牌植物油对A值没有影响,通过模拟加热食用油实验表明了A值指标的可靠性,适用于煎炸老油的鉴定。     

低场核磁共振法测定五种肉类中不同状态水分含量

利用低场核磁共振技术(Low-field Nuclear Magnetic Resonance,LF-NMR)采集牛、猪、羊、鸡和鸭肉五种肉类中水分子的1H信号,通过T-12(弛豫时间倒数)与CuSO4溶液浓度、峰面积与CuSO4溶液质量2条标准曲线,对肉中结合水、不易流动水与自由水的含量进行定量测定,同时与烘箱干燥法测定的体相水(不易流动水和自由水之和)含量进行对比分析。结果显示,LF-NMR法测定的牛肉、猪肉、羊肉、鸡肉和鸭肉中的结合水含量分别为3.49%、3.33%、4.10%、2.17%和3.96%;不易流动水的含量分别为71.0%、72.30%、76.78%、76.61%和77.78%;自由水的含量分别为2.48%、1.90%、2.85%、2.27%和2.14%。烘箱法测定的五种肉类的体相水含量分别为73.04%、73.47%、76.83%、77.11%和77.56%,与LF-NMR法测定的结果差异不显著(p0.05)。LF-NMR可以准确测定上述五种肉类中不同状态水的含量。     

PEI溶液紫外吸收光谱检测油气田硫化氢气体

建立了一种基于聚乙烯亚胺(PEI)溶液的紫外(UV)吸收光谱检测油气田硫化氢(H2S)气体浓度的方法。利用PEI结构中的氨基可与H2S气体反应的特性,测定通入H2S气体前后PEI溶液的UV吸收光谱,并分析了UV光谱吸收峰在230、365 nm附近的吸光度变化与气体浓度的关系。采用标准浓度的H2S气体样品进行浓度标定实验,建立了H2S气体浓度与吸光度之间的关系模型。实验结果表明:通入高纯度H2S气体时,PEI溶液的UV光谱在230 nm和365 nm处均出现较强吸收峰;通入较低浓度H2S气体时,UV光谱只在230 nm处出现吸收峰,该吸收峰附近的吸光度与H2S气体浓度间存在线性关系(相关系数为0.970 6),系统对H2S气体浓度的检出限可达15.39 mg/m3。基于PEI溶液的UV吸收光谱检测法可为油气田H2S气体浓度的快速、准确测定提供参考。     

无机盐对乙醇-水体系LF-NMR弛豫特性的影响及主成分分析

该文研究了不同浓度(0~9%)的Na Cl,Mg SO4或Na OH对乙醇-水体系LF-NMR弛豫特性的影响,并应用主成分分析(PCA)对样品的弛豫特性进行了分析。研究表明:无机盐种类和浓度会对水及乙醇-水体系的LF-NMR弛豫特性产生影响。无机盐-水二元体系仅存在1个弛豫峰,且弛豫时间:Mg SO4Na OHNa Cl。而无机盐-乙醇-水三元体系则存在2个弛豫峰,Na Cl/Na OH-乙醇-水体系的弛豫峰分别位于200~330 ms和1 300~1 600 ms处;而Mg SO4-乙醇-水体系则位于约250~335 ms和1 620~1 707 ms处。不同种类无机盐、水和乙醇-水体系间的LF-NMR弛豫特性差异均可在PCA得分图上有效反映,且随着无机盐浓度的增加,各浓度梯度在主成分得分图中亦呈规律性分布。说明基于样品的LF-NMR弛豫特性,结合主成分分析法可快速分析无机盐对水/乙醇-水的缔合特性。     

食用/工业明胶的凝胶及LF-NMR弛豫特性的比较

该文研究了食品/工业明胶浓度、混合比例及蔗糖或NaCl对体系的黏度、凝冻强度及LF-NMR弛豫特性的影响。结果发现,与食用明胶相比,工业明胶的凝冻强度与黏度较低。随着明胶浓度的增加,体系的黏度、凝胶强度均相对增大;结合水弛豫时间T_(21)、自由水弛豫时间T_(22)及自由水比例S_(22)均减小,而结合水比例S_(21)增大。随着工业明胶含量的增多,混合体系的黏度与凝冻强度均线性降低,T_(21)、T_(22)及S_(21)均线性增大,S_(22)线性减小;相同蔗糖或NaCl浓度下,食用明胶体系的黏度、凝冻强度最大,混合明胶体系次之,而工业明胶体系的最小;随着蔗糖浓度的增加,体系的黏度均增大,食用、混合体系的凝冻强度增大,而工业明胶变化较小;各体系的T_(22)、S_(22)均减小,S_(21)增大,工业明胶的T_(21)增大,而食用明胶、混合明胶体系的T_(21)变化不大。随着NaCl浓度的增加,各体系的凝冻强度均相对降低,而T_(21)、T_(22)、S_(21)均相对增大,S_(22)减小。     

A carbanion induced synthesis of highly congested pyrazole and imidazole containing heterocycles

An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet–Spengler reaction

An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a–g and imidazo[1,5-a]quinoxalines 7a–h by the reaction of 2-imidazolyl anilines 4a–c with aryl aldehydes 5a–k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a–b was found to be instrumental for the success of the reaction.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.     

Synthesis of N-substituted carbazolones from α-iodo enaminones via Pd(0)-catalyzed intramolecular coupling under microwave irradiation

A variety of N-aryl and N-alkyl carbazolones were conveniently achieved in good to high yields via Pd₂(dba)₃-mediated intramolecular coupling of N-substituted α-iodo enaminones under microwave irradiation. The Pd(0)-catalyzed cyclization was found to proceed favorably with the more electron-deficient phenyl ring during the reactions involving unsymmetrical N,N-diaryl α-iodo enaminones. This unique property enables the construction of carbazolone skeleton containing nitro substituted benzenoid ring.     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.     

Synthesis of substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles by intramolecular nitrilimine cycloaddition

Both substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles have been synthesized by the 3+2 intramolecular dipolar cycloaddition of nitrilimines to alkynes. This cyclization has been extended to more versatile 3-bromo derivatives by the use of alkynylbromides as dipolarophiles.