An overview of analytical methodologies for the determination of antibiotics in environmental waters

The widespread occurrence of antibiotics as contaminants in the aquatic environment has increased attention in the last years. The concern over the release of antibiotics into the environment is related primarily to the potential for the development of antimicrobial resistance among microorganisms. This article presents an overview of analytical methodologies for the determination of quinolone (Qs) and fluoroquinolone (FQs), macrolide (MLs), tetracycline (TCs), sulfonamide (SAs) antibiotics and trimethoprim (TMP) in different environmental waters. The analysis of these antibiotics has usually been carried out by high-performance liquid chromatography (HPLC) coupled to mass spectrometry (MS) or tandem mass spectrometry (MS/MS) and to a lesser extent by ultraviolet (UV) or fluorescence detection (FD). A very important step before LC analysis is sample preparation and extraction leading to elimination of interferences and prevention of matrix effect and preconcentration of target analytes.     

Modeling study of non-line-narrowed hole-burned spectra in weakly coupled dimers and multi-chromophoric molecular assemblies

Several different models have been proposed to explain the origin of the complex anti-hole features observed in hole-burned (HB) spectra of excitonically coupled systems such as photosynthetic complexes. This lack of consensus presents a serious constraint on the interpretation of HB spectra and the underlying electronic structures of these systems. To resolve this problem we present results of modeling studies of non-resonant HB spectra taking uncorrelated excitation energy transfer and excitonic interactions into account. Simplified analytical results are compared with Monte Carlo simulations in which excitonic interactions are explicitly taken into account in order to disentangle a number of distinct effects. It is shown that these effects can accurately account for both hole shapes and the broad anti-hole structure observed in excitonically coupled systems. We argue that these models will provide a necessary framework for probing the electronic structure of these systems via HB spectroscopy.     

利用三能级光谱技术研究^235U的高激发态,超精细结构

本文报道用两台连续激光级联共振的方法,测量了(255)~U的→16900→33625cm~(-1)跃迁的超精细光谱结构,给出了33625cm~(-1)能级的超精细结构常数A、B,从而给出一种测量难熔、有毒金属高激发态能级结构的简单且精确的方法.     

Disrupting the MAD2L2-Rev1 Complex Enhances Cell Death upon DNA Damage

DNA-damaging chemotherapy agents such as cisplatin have been the first line of treatment for cancer for decades. While chemotherapy can be very effective, its long-term success is often reduced by intrinsic and acquired drug resistance, accompanied by chemotherapy-resistant secondary malignancies. Although the mechanisms causing drug resistance are quite distinct, they are directly connected to mutagenic translesion synthesis (TLS). The TLS pathway promotes DNA damage tolerance by supporting both replication opposite to a lesion and inaccurate single-strand gap filling. Interestingly, inhibiting TLS reduces both cisplatin resistance and secondary tumor formation. Therefore, TLS targeting is a promising strategy for improving chemotherapy. MAD2L2 (i.e., Rev7) is a central protein in TLS. It is an essential component of the TLS polymerase zeta (ζ), and it forms a regulatory complex with Rev1 polymerase. Here we present the discovery of two small molecules, c#2 and c#3, that directly bind both in vitro and in vivo to MAD2L2 and influence its activity. Both molecules sensitize lung cancer cell lines to cisplatin, disrupt the formation of the MAD2L2-Rev1 complex and increase DNA damage, hence underlining their potential as lead compounds for developing novel TLS inhibitors for improving chemotherapy treatments.     

Two and multilevel spectral switching of single molecules in polystyrene at room temperature

Various switching processes with jumps between two or more spectral states were observed for single molecules of the fluorescent dyes PI and DAPI in polystyrene at room temperature. Switching processes were found in the temporal trajectories of almost each spectral parameter. Statistical analyses on the distribution of jumpwidths and on correlations between them were performed. By this means a discrimination between extrinsic and intrinsic mechanisms, which trigger the observed switching dynamic, has been possible in some cases even without anticipated assumption on the nature of the mechanism itself. It has been found that PI and DAPI behave considerably different in single molecule spectroscopy, opposed to their almost identical appearance on bulk level.     

On the weighting method for mixed least squares–total least squares problems

It is well known that the standard algorithm for the mixed least squares–total least squares (MTLS) problem uses the QR factorization to reduce the original problem into a standard total least squares problem with smaller size, which can be solved based on the singular value decomposition (SVD). In this paper, the MTLS problem is proven to be closely related to a weighted total least squares problem with its error‐free columns multiplied by a large weighting factor. A criterion for choosing the weighting factor is given; and for the sake of stability in solving the MTLS problem, the Cholesky factorization‐based inverse (Cho‐INV) iteration and Rayleigh quotient iteration are also considered. For large‐scale MTLS problems, numerical tests show that Cho‐INV is superior to the standard QR‐SVD method, especially for the case with big gap between the desired and undesired singular values and the case when the coefficient matrix has much more error‐contaminated columns. Rayleigh quotient iteration behaves more efficient than QR‐SVD for most cases and fails occasionally, and in some cases, it converges much faster than Cho‐INV but still less efficient due to its higher computation cost.     

特征荧光光谱法定量检测水质的研究

讨论了一种可同时检测自然水体中有机物和叶绿素a含量的快速分析方法。以武汉东湖水为样品,采用激光诱导荧光(LIF)的方法测量了水体的总荧光光谱(TLS);并用特征光谱荧光标记(SFS)技术对水体中溶解的有机物(DOM)及叶绿素a (Chl-a)的荧光光谱特征进行了分析和指认。并利用水的拉曼散射信号强度进行归一化的方法,分别得到较低浓度腐殖酸和叶绿素a的特征光谱归一化荧光强度以及它们在水体中浓度的标定曲线和线性关系式。另外, 对于较高浓度的腐殖酸溶液,确定了其特征光谱的荧光强度与浓度之间满足的函数关系。结果表明,在一定的浓度范围内,特征光谱的荧光强度与浓度之间仍然有很好的线性关系。该方法在自然水体质量的检测方面有广泛的应用前景,它能快速识别水体中的污染物,定量测量它们在水体中的含量,实现对自然水体的质量状况进行大范围的实时动态监测。     

Ultrasensitive assays of trans- and cis-β-carotenes in vegetable oils by high-performance liquid chromatography–thermal lens detection

The fact that β-carotene might be the protective factor against various cancers, suggests the need for a rapid reliable assay for this potential marker. We have proposed the method for selective, precise and simple profiling of carotenoids as well as for simultaneous ultrasensitive assaying of trans-β-carotene (TBC) and cis-β-carotene(s) (CBC) in five vegetable oils. The oil samples diluted 20 or 100 times were directly injected and analysed by means of the isocratic non-aqueous reversed-phase high-performance liquid chromatography (HPLC) combined with ultrasensitive thermal lens detection (TLS).

Elution of TBC was followed by CBC; both were identified and determined in olive, safflower, sesame, wheat germ and linseed oil by standard addition method. The presence of lutein/zeaxanthin, some xanthophyll and/or early eluting carotene may be also presumed in the aforementioned oils. The examined oils showed different and characteristic carotenoid/carotene profiles and characteristic TBC-to-CBC ratios. Both analytes were selectively detected in the presence of palmitic, oleic, linoleic, linolenic and stearic acid, β-sitosterol and --tocopherol. This extends applicability of the method to other vegetable oils as well.

Favourable analytical performances (high sensitivity, low limits of detection (LODs) and wide linearity span) enabled the direct analyses of highly diluted oils. This resulted in several major benefits of the proposed method, among which (i) reduced risk of stationary phase deterioration, (ii) avoiding the risk of carotenoids transformations and (iii) substantial labour and time savings. The TBC and CBC in diluted vegetable oils were reliably measured at ultratrace level (1–26 ng ml⁻¹) with the S/N ratio ranging from 4 to 140 and precisely determined (imprecision 0.4–8.3%). The concentrations of TBC+CBC estimated in the original oils were as follows: 90.5+51.2 ng ml⁻¹ in sesame oil, 146.0+164 ng ml⁻¹in safflower oil, 464.6+206.1 ng ml⁻¹in linseed oil, 453.7+143.3 ng ml⁻¹ in olive oil and 2.31+2.63 μg ml⁻¹ in wheat germ oil. The characteristic and variable portion of TBC within total β-carotene may serve as a reliable indicator of both, quality and authenticity of the vegetable oil. The HPLC–TLS assay proposed may therefore be successfully applied in nutritional, agricultural and epidemiological studies.