Complete assignment of 1H and 13C NMR data for nine protopanaxatriol glycosides

Nine protopanaxatriol glycosides isolated from mild acid hydrolysis products of crude root saponins of Panax notoginseng were identified as 20(R)‐ginsenoside‐Rh1, 20(S)‐ginsenoside‐Rh1, ginsenoside‐Rg1, ‐Re and ‐Rg2, notoginsenoside‐R2 and ‐R1, a mixture of 25‐hydroxy‐20(S)‐ginsenoside‐Rh1 and its C‐20 (R) epimer, ginsenoside‐Rh4. The complete assignments of the ¹H and ¹³C NMR chemical shifts for these glycosides were obtained by means of 2D NMR techniques, including ¹H–¹H COSY, ROESY, HMQC, HMBC and HMQC‐TOCSY spectra. The glycosylation shift effect of protopanaxatriol and the differences in chemical shifts between 20(R)‐ and 20(S)‐protopanaxatriol isomers are also discussed. Except for ginsenoside‐Re and ‐Rg2, complete NMR assignments of the other seven glycosides are reported for the first time. Copyright © 2002 John Wiley & Sons, Ltd.     

Complete assignments of 1H and 13C NMR data for ten phenylpiperazine derivatives

Ten phenylpiperazine derivatives were designed and synthesized. The first complete assignments of (1)H and (13)C NMR chemical shifts for these phenylpiperazine derivatives were achieved by means of 1D and 2D NMR techniques, including (1)H-(1)H COSY, HSQC and HMBC spectra.     

3，5-二甲基金刚胺盐酸盐的NMR研究

NMR核磁共振谱显示3，5-二甲基金刚胺盐酸盐是一个刚性结构，但其分子结构包含2个非对映体的立体构型形式. 我们通过利用DEPT，¹H-¹H COSY，HSQC和HMBC等技术所测得的二维谱图数据对NMR数据进行了完整的归属分析，其中¹³C NMR谱图显示在δ=29~54 ppm之间的十组峰表示所有碳的共振，而且由于不同的分子构象导致在¹³C NMR谱中有3个不同的季碳峰和¹H NMR中的2个不同的甲基峰. 由于H-5的叔碳H原子与邻近CH₂ 的平面二面夹角均约为600，致使耦合常数极其小，波谱仪难以分辨它们从而使¹H NMR峰为单重峰.     

Tunable te-CO2 laser-pumped formaldehyde far-infrared lasers: Offsets, assignment, and superfluorescence

Sixty and three absorption transitions in D₂CO and H₂CO, respectively, have produced a number of far infrared laser lines when they are pumped by an etalon-tuned TE-CO₂ laser. Almost all the absorption transitions pumped previously by a free runing TE-CO₂ laser have been efficiently pumped by the etalon tuned CO₂ laser and found to have offset within ±500 MHz from the line-center of the relevant CO₂ pump lines. 22 (1) absorption and 63 (4) emission lines of D₂CO (H₂CO) are assigned. Some of these lines have generated superfluorescence. In paticular, the D₂CO 319-m line pumped by CO₂-9P(32) delivered an output energy of approximately one half that of the well-known D₂O 66-m. It is shown that a large electric dipole moment and an appreciable amount of fractional population in the lower level of the pump transition of this line are responsible to the superfluorescence.     

Spectral assignments of new diterpenes from Hyptis martiusii Benth

The structural characterization of two new abietanes and a new spiro-fused tricyclic diterpene isolated from the roots of Hyptis martiusii is described. The first member of a new class of rearranged abietane diterpenoids designated martiusane was characterized by the use of 1D NMR and several 2D shift correlated NMR pulse sequences (1H,1H-COSY, HMQC, HMBC and NOESY). Unambiguous 1H and 13C chemical shift assignments for all compounds are reported.     

乙酰苯胺分子的拉曼、红外光谱和简正振动分析

分别在3 500～50和3 500～600 cm-1范围内实验测量了乙酰苯胺(ACN)分子的拉曼和红外光谱。运用密度泛函理论(DFT)采用B3LYP 混合泛函和6-311G(d, p)基函数组,计算了该分子的平衡构型和振动频率。结果表明：理论计算的分子最优化构型参数与以往文献报道的实验数据吻合,优于以往由6-31G(d)基函数组计算得到的参数;理论计算的振动频率值和本实验的观测值吻合得较好。运用简正振动分析方法得到了ACN 分子各振动频率的势能分布(PED),对ACN 分子的振动频率归属做出了全面、准确指认。     

三种缩水蔗糖衍生物的NMR研究及结构确证

采用¹H NMR、¹³C NMR、DEPT及二维谱¹H-¹H COSY、HSQC、HMBC和HRMS对1′, 4′∶3′, 6′-二缩水-4-氯-4-脱氧半乳蔗糖、3, 6∶1′, 4′3′, 6′-三缩水-4-氯-4-脱氧半乳蔗糖和3, 6-缩水-4, 1′, 6′-三氯-4, 1′, 6′-三脱氧半乳蔗糖的结构进行了研究和确证,并对它们的¹H、¹³C NMR全谱给予了准确归属.     

Surface‐enhanced Raman scattering from polystyrene on gold clusters

Surface‐enhanced Raman scattering (SERS) constitutes a spectroscopic method of rapidly growing importance, and polystyrene is a widely used compound of great industrial importance. In this work, SERS data were obtained from polystyrene samples prepared by vapor deposition of gold and plasma‐induced polymerization of styrene gas. A thorough examination of this data is presented. The relationships between sample preparation parameters, gold‐cluster morphology, and SERS intensity were elucidated. Using Wilson's notation, vibrations were assigned to all bands between 250 and 1750 cm⁻¹ in the ordinary Raman and SERS spectra of polystyrene. The correct assignment of these bands would be a significant achievement because they have been controversial in the literature for ∼30 years. Our assignments were made by reviewing the literature and comparing the assignments found there to spectral data acquired during this study; they were confirmed using density functional theory (DFT) calculations performed on the styrene monomer. The orientation of polystyrene's phenyl ring, relative to the gold surface, was determined. It has been suggested that reactions involving silver catalyze polystyrene degradation during SERS, but we found that silver is not necessary for the degradation to occur. Copyright © 2009 John Wiley & Sons, Ltd.     

High sensitivity CW-CRDS of O enriched water near 1.6 μm

The absorption spectrum of ¹⁸O enriched water has been recorded by continuous wave cavity ring down spectroscopy between 5905.7 and 6725.7 cm⁻¹ using a series of fibred DFB lasers. The investigated spectral region corresponds to the important 1.55 μm transparency window of the atmosphere where water absorption is very weak. The typical CRDS sensitivity (noise equivalent absorption of 5×10⁻¹⁰ cm⁻¹) allowed for the detection of lines with intensity as low as 10⁻²⁸ cm/molecule while the minimum intensity value provided by HITRAN in the considered spectral region is 1.7×10⁻²⁴ cm/molecule. The line parameters were retrieved with the help of an interactive least squares multi-lines fitting program assuming a Voigt function as line profile. Overall, 4510 absorption lines belonging to the H₂¹⁸O, H₂¹⁶O, HD¹⁸O, HD¹⁶O and H₂¹⁷O water isotopologues were measured. Their intensities range between 3×10⁻²⁹ and 5×10⁻²³ cm/molecule at 296 K and the typical accuracy on the line positions is 1×10⁻³ cm⁻¹. 2074 of the observed lines attributed to H₂¹⁸O, HD¹⁸O and H₂¹⁷O are reported for the first time. The transitions were assigned on the basis of variational calculations resulting in 288, 135 and 38 newly determined rovibrational energy levels for the H₂¹⁸O, HD¹⁸O and H₂¹⁷O isotopologues, respectively. The new data set includes the band origin of the 4ν₂ bending overtone of H₂¹⁸O at 6110.4239 cm⁻¹ and rovibrational levels corresponding to J and K_a values up to 18 and 12, respectively, for the strongest bands of H₂¹⁸O: 4ν₂, ν₁+2ν₂, 2ν₂+ν₃, 2ν₁, ν₁+ν₃, and ν₂+ν₃. The obtained experimental results have been compared to the spectroscopic parameters provided by the HITRAN database and to the recent IUPAC critical review of the rovibrational spectrum of H₂¹⁸O and H₂¹⁷O as well as to variational calculations. Large discrepancies between the 4ν₂ variationally predicted and experimental intensities have been evidenced for the H₂¹⁸O and H₂¹⁶O molecules.     

Application of Fourier Transform Infrared (FTIR) Spectroscopy in the Characterization of Tannins

Abstract

A review of vibrational frequencies reported for tannin molecules is provided to create a database with typical fingerprints for different types of tannins. This will provide researchers working on vibrational spectroscopy applications and technicians a fast, easy, and reliable method to assess the quality and authenticity of these compounds, both extracted in laboratories and provided from commercial sources. The widespread use of these compounds has highlighted the need for a systematic characterization of the vibrational frequencies and molecular fingerprints for their identification and discrimination. According to our knowledge, this is the first systematic collection of typical peak frequencies for tannins, which can be applied in several research fields and technological applications.