NMR Structural Studies on Alamethicin Dimers

N labeled alamethicin dimer was synthesized. The structure and dynamics of alamethicin dimers were studied with nuclear magnetic resonance (NMR) spectroscopy. The data from 15 N-labeled alamethicin dimer suggest little differences in conformation between the dimer and monomer in the Aib 1 -Pro 14 region. Significant difference in the conformation of the C-terminus are manifest in the NH chemical shifts in the Val 15 -Pho 20 region.

Conformational Analysis of γ-Butyrolactones by Nuclear Magnetic Resonance Spectroscopy

A series of trans-4, 5-disubstituted -γ-butyrolactones are found to assume two different envelope conformations by means of nuclear magnetic resonance spectroscopy.

Urinary nuclear magnetic resonance spectroscopy of a Bangladeshi cohort with hepatitis-B hepatocellular carcinoma: A biomarker corroboration study

AIM: To establish if a distinct urinary metabolic profile could be identified in Bangladeshi hepatitis-B hepatocellular carcinoma (HCC) patients compared to cirrhosis patients and controls.METHODS: Urine samples from 42 Bangladeshi patients with HCC (39 patients with hepatitis-B HCC), 47 with cirrhosis on a background of hepatitis B, 46 with chronic hepatitis B, and seven ethnically-matched healthy controls were analyzed using nuclear magnetic resonance (NMR) spectroscopy. A full dietary and medication history was recorded for each subject. The urinary NMR data were analyzed using principal component analysis (PCA) and orthogonal partial least squared discriminant analysis (OPLS-DA) techniques. Differences in relative signal levels of the most discriminatory metabolites identified by PCA and OPLS-DA were compared between subject groups using an independent samples Kruskal-Wallis one-way analysis of variance (ANOVA) test with all pairwise multiple comparisons. Within the patient subgroups, the Mann-Whitney U test was used to compare metabolite levels depending on hepatitis B e-antigen (HBeAg) status and treatment with anti-viral therapy. A Benjamini-Hochberg adjustment was applied to acquire the level of significance for multiple testing, with a declared level of statistical significance of P < 0.05.RESULTS: There were significant differences in age (P < 0.001), weight (P < 0.001), and body mass index (P < 0.001) across the four clinical subgroups. Serum alanine aminotransferase (ALT) was significantly higher in the HCC group compared to controls (P < 0.001); serum α-fetoprotein was generally markedly elevated in HCC compared to controls; and serum creatinine levels were significantly reduced in the HCC group compared to the cirrhosis group (P = 0.004). A three-factor PCA scores plot showed clustering of the urinary NMR spectra from the four subgroups. Metabolites that contributed to the discrimination between the subgroups included acetate, creatine, creatinine, dimethyamine (DMA), formate, glycine, hippurate, and trimethylamine-N-oxide (TMAO). A comparison of relative metabolite levels confirmed that carnitine was significantly increased in HCC; and creatinine, hippurate, and TMAO were significantly reduced in HCC compared to the other subgroups. HBeAg negative patients showed a significant increase in creatinine (P = 0.001) compared to HBeAg positive patients in the chronic hepatitis B subgroup, whilst HBeAg negative patients showed a significant decrease in DMA (P = 0.004) in the cirrhosis subgroup compared to HBeAg positive patients. There were no differences in metabolite levels in HCC patients who did or did not receive antiviral treatment.CONCLUSION: Urinary NMR changes in Bangladeshi HCC were identified, corroborating previous findings from Egypt and West Africa. These findings could form the basis for the development of a cost-effective HCC dipstick screening test.

Determination of chlorogenic acid in traditional Chinese prescription Shuanghuanglian capsule using quantitative nuclear magnetic resonance spectroscopy in combination with solid phase extraction

The determination method of chlorogenic acid in traditional Chinese prescription Shuanghuanglian capsule was established by using quantitative nuclear magnetic resonance spectroscopy(q NMR) in combination with solid phase extraction(SPE). As the capsule’s main active component, chlorogenic acid comes from the extraction of Chinese herb medicine Flos Lonicerae. The chlorogenic acid in capsule was ultrasonically extracted at room temperature using pure water as solvent. The extracting solution was enriched and cleaned using HC-C18 SPE cartridge. The effect of ultrasonic extraction, sample pretreatment conditions via SPE and q NMR experimental conditions were investigated. The q NMR experiment conditions were selected using deuterated DMSO as solvent, calibrated 1,4-phthalaldehyde as internal standard, and P1(pulse width) = 14.4 μs, d1(pulse delay time) = 1 s, NS(number of scan) = 512. The 1 H NMR peaks of δ 6.138–6.182(H-8’, d, 1 H) of chlorogenic acid was chosen as the quantitative peaks. Method validation was performed, including precision(the intra-day RSD = 1.2% and the inter-day RSD = 1.5%), linearity(correlation coefficient r>0.9999), LOD(0.0017 mg/g) and LOQ(0.079 mg/g). The recovery of the SPE-q NMR was within the range of 100.2%–103.2%. The result showed that the method was stable, accurate and reliabile. Determined by the method, the chlorogenic acid in a real Shuanghuanglian capsule was within the range of 9.68–10.35 mg/g.

Grade classification of neuroepithelial tumors using high-resolution magic-angle spinning proton nuclear magnetic resonance spectroscopy and pattern recognition

Clinical data have shown that survival rates vary considerably among brain tumor patients,according to the type and grade of the tumor.Metabolite profiles of intact tumor tissues measured with high-resolution magic-angle spinning proton nuclear magnetic resonance spectroscopy (HRMAS 1H NMRS) can provide important information on tumor biology and metabolism.These metabolic fingerprints can then be used for tumor classification and grading,with great potential value for tumor diagnosis.We studied the metabolic characteristics of 30 neuroepithelial tumor biopsies,including two astrocytomas (grade I),12 astrocytomas (grade II),eight anaplastic astrocytomas (grade III),three glioblastomas (grade IV) and five medulloblastomas (grade IV) from 30 patients using HRMAS 1H NMRS.The results were correlated with pathological features using multivariate data analysis,including principal component analysis (PCA).There were significant differences in the levels of N-acetyl-aspartate (NAA),creatine,myo-inositol,glycine and lactate between tumors of different grades (P<0.05).There were also significant differences in the ratios of NAA/creatine,lactate/creatine,myo-inositol/creatine,glycine/creatine,scyllo-inositol/creatine and alanine/creatine (P<0.05).A soft independent modeling of class analogy model produced a predictive accuracy of 87% for high-grade (grade III-IV) brain tumors with a sensitivity of 87% and a specificity of 93%.HRMAS 1H NMR spectroscopy in conjunction with pattern recognition thus provides a potentially useful tool for the rapid and accurate classification of human brain tumor grades.

Using Nuclear Magnetic Resonance and MS/MS Spectroscopy for the Identification of Brodimoprim Metabolites in Rat Urine

Eight metabolites of brodimoprim (BDP) in rat urine were detected by NMR and ESIMS/MS. They were demethyl-BDP glucuronide, demethyl-BDP sulfurate, demethyl-BDP glucuronide sulfurate, alpha -hydroxyl-BDP, alpha -hydroxyl-BDP glucuronide, BDP sulfurate, N-oxide-BDP sulfurate, and alpha -hydroxyl-N-oxide-BDP sulfurate. All the sulfurates are reported for the first time.

Nuclear magnetic resonance spectroscopy is highly sensitive for lipid-soluble metabolites

Although the water-soluble metabolite profile of human mesenchymal stem cells is known, the lipid profile still needs further investigation. In this study, methanol-chloroform was used to extract lipid-soluble metabolites and perchloric acid was used to extract water-soluble metabolites. Fur- thermore, a dual phase extraction method using methanol-chloroform and water was used to obtain both water and lipid fractions simultaneously. All metabolite extractions were analyzed on a 9.4T high-resolution nuclear magnetic resonance spectrometer. Metabolite resonance peaks were as- signed in the acquired spectra according to the chemical shift, and the extraction efficiency of dif- ferent methods was compared. Results showed that in the spectra of water-soluble extracts, major metabolites comprised low molecular weight metabolites, including lactate, acetic acid, fatty acids, threonine, glutamic acid, creatine, choline and its derivatives, while in the spectra of lipid-soluble extracts, most metabolites were assigned to fatty acids. Among the different extraction procedures, perchloric acid was more efficient in extracting water-soluble metabolites and methanol-chloroform was efficient in extracting organic components compared with the dual phase extraction method. Nuclear magnetic resonance spectroscopy showed that as low as 0.7 mg organic yield was enough to obtain clear resonance peaks, while about 6.0 mg water-soluble yield was needed to obtain rela- tively favorable spectral lines. These results show that the efficiency of extracting water and lipid fractions is higher using perchloric acid and methanol-chloroform compared with dual phase ex- traction and that nuclear magnetic resonance spectroscopy is highly sensitive for analyzing lipid-soluble extracts.

Crystallochemical Characterizations, Raman Spectroscopy and Studies Nuclear Magnetic Resonance (NMR) of Cu₂Zn(Sn, Si)S₄Compounds for Photovoltaic Applications

In this study, Si-doped Cu2ZnSnS4 compounds (Cu2ZnSn1-xSixS4, 0 ≤ x ≤ 1) were prepared by solid state reaction method for use of materials for photovoltaic cells. The structural and spectroscopic properties of the as-prepared compounds were studied by X-ray diffraction (XRD), 119Sn, 29Si and 65Cu Magic Angle Spinning nuclear magnetic resonance (MAS NMR) and Raman spectroscopy. The Si-substitution in the Sn-site induces three different types of XRD patterns which depend largely on the Si content in the compound. For 0 ≤ x ≤ 0.5, XRD analysis reveals the presence of a pure tetragonal phase of solid solution with I-42m as a space group. Mixed tetragonal and orthorhombic phases were observed for 0.5 < x < 0.8, followed by a pure orthorhombic structure with a space group Pmn21 at high content of Si (x ≥ 0.8). 119Sn MAS NMR spectra show the presence of Sn/Si disorder as a function of the Si content. The 65Cu MAS NMR spectra of the quadratic solid solution confirm the presence of the two copper sites (Cu-2a and Cu-2c) at 780 ppm while in the case of the orthorhombic solid solution samples, a very broad band is observed. The optical properties were investigated of all compounds by UV-Vis diffuse reflectance and the obtained optical band gap values (1.31 to 2.43 eV) confirm a semiconductor character.

Application of Nuclear Magnetic Resonance Spectroscopy in Metabolic Differences and Potential Biomarkers Screening in Rats with Polycystic Ovary Syndrome

Objective:To investigate the application of nuclear magnetic resonance(NMR)spectroscopy in the exploration of metabolic differences and potential biomarkers in rats with polycystic ovary syndrome(PCOS).Methods:PCOS model was established by subcutaneous injection of deoxy-epiandrosterone(DHEA)in 30 rats randomly selected from sixty 23-day-old SPF female SD rats and set as PCOS group,and the other 30 rats were subcutaneously injected with oil and set as oil group,PCOS model was successfully established by 20 days of injection in both groups,and blood samples were taken for biochemical detection and NMR detection analysis.At the same time,the body weight,ovarian weight and HE staining results of rats in both groups were observed.Results:Compared with the oil group,the rats in the PCOS group had higher body weight,ovarian weight and serum LH,FPG,T,E_(2)and HOMA levels,and lower serum FSH and INS levels(P<0.05).In the oil group,a large number of corpus luteum,follicles at different stages of development and multi-layered granulosa cells were observed under microscope after HE staining;In PCOS group,corpus luteum formation was only visible in some ovaries after HE staining,and all of them showed a higher number of cystic dilated follicles,thickened follicular membrane layer and less granulosa cell layer.The PCA score map of serum NMR profiles of the rats in the two groups showed that the samples were separated between the PCOS group and the oil group but the samples were aggregated within the group,and there were differences in blood metabolism between the PCOS model constructed by surface DHEA and the rats in the oil group.A total of 70 metabolites were detected in the serum samples of rats in the two groups by NMR technique,and 31 of them were different between the two groups,which can be classified into glucose,lipid,and and amino acid.There were significant differences in three metabolites,including isoleucine,valine,and creatine(P<0.01).Conclusion:There are differences in carbohydrate,lipid and amino acid metabolism between normal rats and PCOS rats,among which the levels of serum isoleucine,valine and creatine can be used as important biomarkers in the diagnosis of PCOS.

7.0T nuclear magnetic resonance evaluation of the amyloid beta(1–40) animal model of Alzheimer's disease: comparison of cytology verification

3.0T magnetic resonance spectroscopic imaging brain function in Alzheimer＇s disease. However, is a commonly used method in the research ot the role of 7.0T high-field magnetic resonance spectroscopic imaging in brain function of Alzheimer＇s disease remains unclear. In this study, 7.0T magnetic resonance spectroscopy showed that in the hippocampus of Alzheimer＇s disease rats, the N-acetylaspartate wave crest was reduced, and the creatine and choline wave crest was elevated. This finding was further supported by hematoxylin-eosin staining, which showed a loss of hippocampal neurons and more glial cells. Moreover, electron microscopy showed neuronal shrinkage and mitochondrial rupture, and scanning electron microscopy revealed small size hippocampal synaptic vesicles, incomplete synaptic structure, and reduced number. Overall, the results revealed that 7.0T high-field nuclear magnetic resonance spectroscopy detected the lesions and functional changes in hippocampal neurons of Alzheimer＇s disease rats in vivo, allowing the possibility for assessing the success rate and grading of the amyloid beta （1-40） animal model of Alzheimer＇s disease.

Proton nuclear magnetic resonance-based metabonomic models for non-invasive diagnosis of liver fibrosis in chronic hepatitis C:Optimizing the classification of intermediate fibrosis

AIM To develop metabonomic models(MMs), using 1 H nuclear magnetic resonance(NMR) spectra of serum, to predict significant liver fibrosis(SF: Metavir ≥ F2), advanced liver fibrosis(AF: METAVIR ≥ F3) and cirrhosis(C: METAVIR = F4 or clinical cirrhosis) in chronic hepatitis C(CHC) patients. Additionally, to compare the accuracy of the MMs with the aspartate aminotransferase to platelet ratio index(APRI) and fibrosis index based on four factors(FIB-4). METHODS Sixty-nine patients who had undergone biopsy in the previous 12 mo or had clinical cirrhosis were included. The presence of any other liver disease was a criterion for exclusion. The MMs, constructed using partial least squares discriminant analysis and linear discriminant analysis formalisms, were tested by cross-validation, considering SF, AF and C. RESULTS Results showed that forty-two patients(61%) presented SF, 28(40%) AF and 18(26%) C. The MMs showed sensitivity and specificity of 97.6% and 92.6% to predict SF; 96.4% and 95.1% to predict AF; and 100% and 98.0% to predict C. Besides that, the MMs correctly classified all 27(39.7%) and 25(38.8%) patients with intermediate values of APRI and FIB-4, respectively. CONCLUSION The metabonomic strategy performed excellently in predicting significant and advanced liver fibrosis in CHC patients, including those in the gray zone of APRI and FIB-4, which may contribute to reducing the need for these patients to undergo liver biopsy.

Nuclear magnetic resonance based metabolomics and liverdiseases:Recent advances and future clinical applications

Metabolomics is defined as the quantitative measurement of the dynamic multiparametric metabolic response of living systems to pathophysiological stimuli or genetic modification.It is an"omics"technique that is situated downstream of genomics,transcriptomics and proteomics.Metabolomics is recognized as a promising technique in the field of systems biology for the evaluation of global metabolic changes.During the last decade,metabolomics approaches have become widely used in the study of liver diseases for the detection of early biomarkers and altered metabolic pathways.It is a powerful technique to improve our pathophysiological knowledge of various liver diseases.It can be a useful tool to help clinicians in the diagnostic process especially to distinguish malignant and non-malignant liver disease as well as to determine the etiology or severity of the liver disease.It can also assess therapeutic response or predict drug induced liver injury.Nevertheless,the usefulness of metabolomics is often not understood by clinicians,especially the concept of metabolomics profiling or fingerprinting.In the present work,after a concise description of the different techniques and processes used in metabolomics,we will review the main research on this subject by focusing specifically on in vitro proton nuclear magnetic resonance spectroscopy based metabolomics approaches in human studies.We will first consider the clinical point of view enlighten physicians on this new approach and emphasis its future use in clinical"routine".

Molecular structure characterization of middle-high rank coal via^(13)C NMR,XPS,and FTIR spectroscopy

Elemental analysis,nuclear magnetic resonance carbon spectroscopy(^(13)C-NMR),X-ray photoelectron spectroscopy(XPS)and Fourier transform infrared spectroscopy(FTIR)experiments were carried out to determine the existence of aromatic structure,heteroatom structure and fat structure in coal.MS(materials studio)software was used to optimize and construct a 3D molecular structure model of coal.A method for establishing a coal molecular structure model was formed,which was“determination of key structures in coal,construction of planar molecular structure model,and optimization of three-dimensional molecular structure model”.The structural differences were compared and analyzed.The results show that with the increase of coal rank,the dehydrogenation of cycloalkanes in coal is continuously enhanced,and the content of heteroatoms in the aromatic ring decreases.The heteroatoms and branch chains in the coal are reduced,and the structure is more orderly and tight.The stability of the structure is determined by theπ-πinteraction between the aromatic rings in the nonbonding energy EN.Key Stretching Energy The size of EB determines how tight the structure is.The research results provide a method and reference for the study of the molecular structure of medium and high coal ranks.

Substituent, Temperature and Solvent Effects on the Keto-Enol EQUILIBRIUM in <i>&beta;</i>-Ketoamides: A Nuclear Magnetic Resonance Study

Substituent, temperature and solvent effects on tautomeric equilibria in several β-ketoamides have been investigated by means of nuclear magnetic resonance spectroscopy (NMR). Keto-enol equilibrium predominates over the amide-imidol one. The relative stability of the individual tautomers and the corresponding equilibrium shifts are explained considering electronic and steric effects and tautomer stabilization via internal hydrogen bonds. In solution, these compounds exist mainly as ketoamide and Z-enolamide tautomers, both presenting intramolecular hydrogen bonds.

定量核磁共振波谱法快速测定灭火剂材料中全氟辛烷磺酰基化合物

泡沫灭火剂中全氟辛烷磺酰基化合物(PFOS)的使用受到严格管控.针对灭火剂中PFOS快速测定的需求,建立了基于19F的定量核磁共振波谱(qNMR)检测方法.方法以全氟丁基磺酸钾为标准物质,通过计算全氟丁基磺酸钾的-CF3在化学位移δ-78.94处19F特征峰和PFOS的-CF2在化学位移δ-117.12处19F特征峰的积分面积比值,进而实现PFOS定量分析.经测试,全氟丁基磺酸钾百分含量与定量峰面积线性相关系数为0.9955,检出限为0.024%,定量限为0.080%.8种灭火剂产品的定性测定结果与实际标注情况相吻合,其中4种泡沫灭火剂产品中PFOS含量在0.106%~1.339%之间.研究结果表明,方法受基质干扰小、检测速度快、灵敏度高,可为泡沫灭火剂中PFOS的管控提供可靠的检测方法与数据支撑.

不同溶剂预处理煤在ScCO_(2)作用下的谱学差异及其机制

为了探究溶剂预处理后超临界二氧化碳(ScCO_(2))对煤化学结构的影响,以长治霍尔辛赫贫煤为研究对象,分别用四氢呋喃(THF)、盐酸(HCI)和氢氟酸(HF)对煤样进行预处理,采用傅里叶红外光谱(FTIR)、固体核磁共振(^(13)C-NMR)和X射线衍射(XRD)测试,探讨了ScCO_(2)对预处理煤的化学组成和结构的影响机理。研究表明:①FITR分峰拟合谱图实验曲线基本一致,而各官能团吸收峰位置及峰强度仍出现一定的偏差,酸(HCI、HF)预处理后部分波段脂肪族峰位消失。两类酸预处理顺序不同,对煤中含氧官能团、脂肪结构及芳烃结构作用效果也不相同。HF-HCI处理后芳烃C=C结构和含氧官能团峰强度均增强,而HCI-HF处理后芳烃C=C结构强度减弱,含氧官能团结构峰强度变化不明显。THF预处理后煤样芳烃C=C结构峰强度增强,含氧官能团结构峰强度降低。总体芳烃C=C结构峰强度远大于脂肪族结构和含氧官能团结构的峰强度。②^(13)C-NMR谱中主要官能团谱峰的化学位移出现了一定程度的偏移,芳香碳f_(a)^(B)化学位移向增大的方向偏移。大分子结构参数中,芳香碳含量远大于脂肪碳含量,说明煤大分子结构中芳香碳占主要组成部分。③XRD谱中002峰与101峰衍射强度明显增大,芳香微晶层网面间距d_(002)呈现升高趋势,说明THF、酸(HF、HCI)处理和ScCO_(2)对煤大分子结构产生了一定程度的改造作用,使煤的大分子网络结构变得疏松,进而使微晶结构参数d_(002)整体增大。研究认为,溶剂作用后煤的谱学特征变化不仅与溶剂性质有关,还与无机酸处理顺序有关,由此使得官能团组成和大分子结构不同程度改变,进而影响ScCO_(2)对预处理煤的萃取效果。

qNMR法测定片剂苯磺酸氨氯地平的含量

本文利用定量核磁共振波谱法(qNMR)建立了测定片剂苯磺酸氨氯地平含量的分析方法。片剂样品经研磨称量后,加入氘代甲醇为溶剂、1,3,5-三甲氧基苯作为内标物进行混合。混合物经涡旋、超声和离心后取上清液转移入核磁管,对样品采集核磁共振氢谱(1H-NMR)。氢谱中以苯磺酸氨氯地平位于δ5.41的谱峰为检测定量峰,1,3,5-三甲氧基苯位于δ 6.07的谱峰为内标定量峰建立绝对定量方法。1H-NMR实验参数为:90度单脉冲序列,脉冲延迟时间30 s,扫描次数32次,采样温度308 K。实验结果显示苯磺酸氨氯地平与内标物的摩尔比在0.42~8.38的范围内具有良好的线性关系(R2=0.9973),精密度和稳定性试验的相对标准偏差(RSD)分别为0.45%(n=7)和0.44%。对于片剂样品,整个方法(包括目标组份的提取和定量核磁检测)重复性试验RSD为1.69%(n=6);三个不同浓度的加标回收率分别为103.86%、101.20%和99.69%。应用本方法对8个市售品牌的苯磺酸氨氯地平片剂进行了含量测定,结果显示建立的qNMR方法准确度高,重复性好,简便快捷,为片剂药品绝对含量的测定提供了新方法。

常压下酸催化多元醇液化纤维素反应机理的研究

开发农林废弃物高值化利用路径与“深入推进能源绿色低碳转型”国家重大战略需求高度契合。实验探索农业废弃物玉米秸秆中纤维素组分常压酸(H3PO4)催化多元醇[丙二醇(PG)与二甘醇(DEG)混合液]液化反应路径为研究目标,了解酸催化多元醇作用条件下的木质生物质液化反应机理。采用傅里叶红外光谱(FTIR)、凝胶渗透色谱(GPC)、核磁共振波谱(NMR)及热重分析(TGA)对不同反应时间下纤维素液化所得生物油的化学基团、分子量及其分布、分子结构、热解等进行了分析。FTIR检测表明,不同反应时间所得生物油具有相似FTIR特征;液化初期,纤维素降解生成了较多的烃类、醚类和含羰基化合物;液化后期,纤维素中的糖类降解产物、羟基或烯烃与PG/DEG反应生成了难溶于1,4-二氧六环的有机物。GPC分析表明,随着液化的进行,纤维素分子链发生断裂程度加剧,降解生成低分子量(LMW)物质越来越多,降解反应占主导地位;而当反应时间达到某一值时,其降解产物与PG/DEG发生聚合反应产生越来越多的大分子量物质,使生物油的分子量不再降低,即聚合反应占主导地位。^(1)H-和^(13)C-NMR表明,纤维素在液化作用下发生降解使得分子链断裂,仍保留了部分葡萄糖单元结构;随着液化反应的进行,这些结构单元再次发生转化产生LMW化合物;反应继续进行时,这些产物之间或与PG/DEG之间可进行聚合反应,形成结构趋于一致、性质逐渐稳定的新物质。TGA分析结果:生物油中含有70%~85%碳数小于25和5%~10%碳数高于25的化合物,最终残炭率随着反应时间的延长先降低再升高。实验通过研究纤维素在多元醇液化过程中的结构变化,揭示其液化的反应历程,为探索秸秆全组分的液化机理奠定理论基础。

二元/三元渗透溶液渗透脱水处理对黄桃果块特性的影响

以蔗糖、麦芽糖醇及二者复配的三元溶液为渗透溶液,探究渗透脱水处理对黄桃果块质构特性、介电特性、细胞壁多糖含量以及微观结构的变化,并利用核磁共振氢谱(1H nuclear magnetic resonance,1H NMR)技术测定了可溶性糖含量的变化,明确麦芽糖醇和蔗糖的协同作用在渗透脱水过程中对黄桃果块特性的改善作用。结果表明:相较于对照组,SM14(蔗糖、麦芽糖醇质量比1∶4的溶液)显著降低黄桃果块的硬度、咀嚼性和黏附性。渗透脱水处理导致黄桃果块的阻抗和有效电阻显著降低,同时诱导静电容量显著增加,表明渗透脱水可能作用于细胞壁多糖而使果肉细胞特性改变。1H NMR检测结果发现,与蔗糖组相比,三元渗透液处理显著降低了黄桃果块组织中蔗糖的含量,其中SM14处理组蔗糖信号强度仅为19803.9±156.00,麦芽糖醇信号强度为54934.9±1239.11。此外,相比较对照组,SM14组水溶性果胶和鳌合性果胶含量均显著增加,分别为(26.63±1.80)mg/g和(21.59±0.71)mg/g,碱溶性果胶含量显著降低,为(27.24±0.46)mg/g。微观结构观察发现,SM14处理组细胞圆润且完整度较高,塌陷程度低,细胞壁厚度明显增加,这可能是由于蔗糖与麦芽糖醇之间的交互作用有对细胞的协同保护作用。因此,蔗糖与麦芽糖醇复配的三元渗透溶液可以有效地改善二元渗透脱水导致的黄桃果块品质劣变等问题,同时拓宽了糖醇的应用场景。

俾路支褐煤有机结构特征及大分子模型构建

以巴基斯坦俾路支褐煤(BL)为研究对象,由元素分析得出BL化学式为C_(167)H_(130)O_(53)N_(2)S。经X射线光电子能谱(XPS)分析BL有机结构中氧、氮和硫元素存在形式。利用傅里叶变换红外光谱(FT-IR)研究BL有机结构中主要官能团特征,-CH和-CH^(2)为BL脂肪族结构中主要官能团。BL中苯环主要取代形式为三取代和四取代。运用核磁共振光谱(^(13)C-NMR)探究BL有机结构碳骨架结构。BL分子结构中,芳香桥碳与周碳之比X_(BP)为0.21,碳主要由芳香碳和脂肪碳2部分构成,其中脂肪碳质量分数53.23%,芳香碳占比41.93%。芳香结构以苯环和萘环为主,氧主要以羧基、羰基、醚氧和酚羟基形式存在,而氮主要以吡咯氮形式存在,硫主要为噻吩。建立BL二维分子结构模型,通过Materials Studio对其进行加氢饱和,构建BL分子模型三维立体结构,进一步优化所得分子模型,空间效果显著,得到能量最低的BL三维结构模型,发现范德华能是BL分子结构稳定的关键因素。通过计算得到的BL模型结构^(13)C NMR谱图与试验所测谱图基本一致,验证了所构建BL结构模型的合理性。