A methodology for choosing parameters for ESR readout of alanine dosimeters for radiotherapy

Spectrometer settings for ESR readout of alanine dosimeters for radiotherapy have been investigated. Several ESR parameters were studied and determined. The main reason for this work is to choose the suitable parameters to increase signal-to-noise ratio and to reduce the uncertainty on ESR readout, which is one of the main components of uncertainty of alanine/ESR dosimetry system for radiotherapy. The new spectrometer settings have been applied for ESR readout of alanine dosimeters irradiated from 1 to 10 Gy. A higher signal-to-noise ratio has been achieved compared to our old spectrometer settings. The extended uncertainty (k=2) has been evaluated in the dose range 2–10 Gy (maximum uncertainty of 4.9% for 2 Gy, while minimum uncertainty of 1.4% for 10 Gy), which implies that the alanine/ESR dosimetry system can be applied to radiotherapy dose level that needs a global accuracy of 5%.     

Bump-hunting for the proficiency tester--searching for multimodality

Kernel density estimation is a method for producing a smooth density approximation to a dataset and avoiding some of the problems associated with histograms. If it is used with a degree of smoothing determined by a fitness for purpose criterion, it can be applied to proficiency test data in order to test for multimodality in the z-scores. The bootstrap is an essential additional technique to determine how rugged the initially estimated kernel density is: the random resampling of the data in the bootstrap simulates a complete blind repeat of the proficiency test. In addition, useful estimates of the standard error of a mode can be thus obtained. It is suggested that a mode and its standard error can be used as an assigned value and its standard uncertainty.     

Novel nanomaterials used for sample preparation for protein analysis

Sample preparation is of vital importance for proteomic analysis because of the high complexity of biological samples. The rapid development of novel nanomaterials with various compositions, morphologies, and proper surface modifications provides a category of powerful tools for the sample preparation for protein analysis. In this paper, we have summarized recent progresses for the applications of novel nanomaterials in sample preparation for the analysis of proteomes, especially for phosphoproteomes, glycoproteomes, and peptidoms. Several kinds of novel nanomaterials were also discussed for their use in other kinds of proteomics analysis.

Call for nominations for the Heinrich-Emanuel-Merck Award

News and Announcements

Call for nominations for the Heinrich-Emanuel-Merck Award     

Perspectives for microelectrode arrays for biosensing and membrane electroporation

Electrochemical microelectrode devices are among the great challenges for bioelectrochemistry, cell biology and recently also for biomedical research and new clinical electrotherapies. Two representative cases in cell biology and medical research for new trends in the technical devices are selected, heading at new diagnostic and therapeutic clinical applications. One example is from the field of biosensing cholinergic neurotransmitter substances by the nicotinic acetylcholine receptor (AcChoR) in solid-supported lipid bilayer membrane and the other one refers to new developments of electrode systems for the electrochemical delivery of drugs and genes to biological cell aggregates and tissue by the powerful method of membrane electroporation. In both cases addressed to, the new developments include the use of electrical feedback control of electrode arrays for biosensing processes as well as for the extent and duration of tissue electroporation. In line with the impressive advances in medical microsurgery, where increasingly smaller organ targets become accessible, microelectrode systems have become a continuous technical challenge for bioanalytical purposes and, as discussed here in some detail, for the new field of the electroporative delivery of effector substances like drugs and genes, using miniaturized electrochemical electrode arrays.     

Materials for bipolar plates for proton-conducting membrane fuel cells

The review is devoted to the present state of research and development in the field of construction materials for bipolar plates for hydrogen-air fuel cells with polymeric proton-conducting membranes. Principal requirements for such materials are considered and criteria for their selection are formulated.     

Epidemiological Support for an Hypothesis for Melanoma Induction Indicating a Role for UVA Radiation

An hypothesis for melanoma induction is presented: UV radiation absorbed by melanin in melanocytes generates products that may activate the carcinogenic process. Products formed by UV absorption in the upper layers of the epidermis cannot diffuse down as far as to the melanocytes. Thus, melanin in the upper layer of the skin may be protective, while that in melanocytes may be photocarcinogenic. Observations that support this hypothesis include: (1) Africans with dark skin have a reduced risk of getting all types of skin cancer as compared with Caucasians, but the ratio of their incidence rates of cutaneous malignant melanoma to that of squamous cell carcinoma is larger than the corresponding ratio for Caucasians. (2) Albino Africans, as compared with normally pigmented Africans, seem to have a relatively small risk of getting cutaneous malignant melanomas compared to nonmelanomas. This is probably also true for albino and normally pigmented Caucasians. (3) Among sun-sensitive, poorly tanning persons, frequent UV exposures are associated with increased risk of melanoma, whereas among sun-resistant, well-tanning persons, increased frequency of exposure is associated with decreased melanoma risk. (4) It is likely that UVA, being absorbed by melanin, might have a melanoma-inducing effect. This is in agreement with some epidemiological investigations which indicate that sun-screen lotions may not protect sufficiently against melanoma induction. The relative latitude gradient for UVA is much smaller than that for UVB. The same is true for the relative latitude gradient of cutaneous malignant melanoma as compared with squamous cell carcinoma and basal cell carcinoma. Under the assumption that the average slopes of the curves relating incidence rates with fluences of carcinogenic UV radiation are similar for melanomas and nonmelanomas, these facts are in agreement with the assumption that UVA plays a significant role in the induction of melanomas in humans. This is in agreement with the experimental results with Xiphophorus.     

Detectors for Liquid Chromatographic Analysis for Polynuclear Aromatic Hydrocarbons

Abstract

A number of liquid chromatographic detectors of various types have been evaluated for both selectivity and sensitivity for the detection of polynuclear aromatic hydrocarbons (PAH). Detection limits for fixed and variable wavelength UV photometers, filter fluorimeters, and spectrofluorimeters have been determined. The utility of each of these types of detectors for use in the reversed-phase HPLC analysis of environmental extracts containing trace levels of PAH's is discussed.     

Solid-phase sample preparation method for prostaglandins: integration of procedures for isolation and derivatization for gas chromatographic determination

A procedure using a solid-phase support has been developed for the isolation and derivatization of prostaglandins from biological matrices. The styrene-divinylbenzene cross-linked copolymeric macroreticular resin, XAD-2, was used as an adsorbent for prostaglandin E2 from biological samples, as a support for the oximation of the carbonyl group and as a catalyst for pentafluorobenzylation. The reactor bed was then linked to a Florisil column for a final chromatographic clean-up. Matrix effects were found to affect the yield, but recovery of the desired electrophoric products was comparable with methods reported in the literature. The ease of sample preparation suggests that this technique may be a viable approach to automating the processes for preparing prostaglandins from biological matrices for gas chromatographic analysis.     

溶剂化的热力学集团展开理论

把二元溶液的过剩内能（excess energy）分成溶剂-溶剂、溶剂-溶质及溶质-溶质相互作用部分。利用集团展开方法给出了二元溶液在正则系综的配分函数的表达式,利用该表达式得到了溶质的偏摩尔内能(partial molar energy)和偏摩尔熵(partial molar entropy)的表达式。在无限稀溶液情形,过剩偏摩尔内能的溶剂-溶剂部分又称重组织内能（reorganization energy）,它反映了溶质存在时对其周围溶剂分子之间的相互作用能的影响。研究表明,在溶质的粒子数密度相对较大时,溶质分子之间的相互作用将影响过剩偏摩尔内能的溶剂-溶剂部分,对于稀溶液,过剩偏摩尔内能的溶剂-溶剂部分与溶质的摩尔分数成线性关系。对低密度二元溶液,溶质的过剩偏摩尔内能和过剩偏摩尔熵也与溶质的摩尔分数成线性关系。     

Advances for proficiency testing for genetic laboratory science

Nucleic acid based clinical genetic testing has undergone explosive growth in recent years due in large part to the human genome project. Characterization of the human genome has led to a molecular understanding of the pathogenesis of many human diseases, and ultimately to clinical molecular tests becoming routinely used to diagnose a wide diversity of diseases. This rapid growth in clinical molecular genetic testing coupled with the complexity of the analytical procedures underscores the necessity for proficiency testing (i.e. external quality assessment) to allow laboratories offering such services the ability to evaluate their analytical procedures via inter-laboratory comparisons. The American College of Medical Genetics (ACMG) in partnership with the College of American Pathologists (CAP) have been offering proficiency testing for clinical molecular genetics laboratories since 1995, and presently have more than 230 laboratories from 11 countries enrolled in this program. This paper describes the evolution of this program and several challenges encountered in the delivery of a proficiency testing program for laboratories offering clinical molecular genetic services. Received: 13 April 2002 Accepted: 18 July 2002     

Prototype for integrated two-dimensional gel electrophoresis for protein separation

Two-dimensional gel electrophoresis practitioners have long waited for a fully automated system. This article presents an integrated platform that is capable of complete automation from sample introduction to spots detection. The strip gel for the first dimensional separation is fixed on the edge of a discrete planar stage before separation. A pair of platinum pin electrodes for isoelectric focusing (IEF) makes contact from underneath the stage. IEF is performed directly after rehydration and protein loading. After the first dimensional separation, sodium dodecyl sulfate (SDS) equilibration is done on the same stage without moving the gel. The IEF stage is then moved horizontally to couple with a precast second dimensional gel. The <0.5 mm gap between the two gels is filled with poly (ethylene oxide) solution. After SDS-polyacrylamide gel electrohporesis separation, a charge-coupled device camera is used to detect spots via protein native fluorescence excited by a Hg (Xe) lamp with the gel inside the running cell. Potential for full automation is demonstrated with 0.5 microg of Escherichia coli proteins on this miniaturized platform. More than 240 spots are detected in a total experiment time of <2.5 h.     

A single-laboratory validated method for the generation of DNA barcodes for the identification of fish for regulatory compliance

The U.S. Food and Drug Administration is responsible for ensuring that the nation's food supply is safe and accurately labeled. This task is particularly challenging in the case of seafood where a large variety of species are marketed, most of this commodity is imported, and processed product is difficult to identify using traditional morphological methods. Reliable species identification is critical for both foodborne illness investigations and for prevention of deceptive practices, such as those where species are intentionally mislabeled to circumvent import restrictions or for resale as species of higher value. New methods that allow accurate and rapid species identifications are needed, but any new methods to be used for regulatory compliance must be both standardized and adequately validated. "DNA barcoding" is a process by which species discriminations are achieved through the use of short, standardized gene fragments. For animals, a fragment (655 base pairs starting near the 5' end) of the cytochrome c oxidase subunit 1 mitochondrial gene has been shown to provide reliable species level discrimination in most cases. We provide here a protocol with single-laboratory validation for the generation of DNA barcodes suitable for the identification of seafood products, specifically fish, in a manner that is suitable for FDA regulatory use.     

有机化合物脂水分配系数logP 的计算

logP作为有机化合物流水性的量反，在定量的效关系研究中扮演了重要的角色，广泛应用于生物化学、药学以及环境科学等各领域．运用计算的方法获得10gP值由于能够弥补实验方法的不足，在药物分子设计等应用中具有重要意义．随着计算机辅助药物分子设计的发展，高精度、简便易行的IOgPi十算方法日益受到重视．logP的计算方法见诸报导的已有多种［‘－7］．这些方法各具特色，但也都分别存在一些明显的缺点．目前流行的片段加合法［‘一句的出发点是将分手划分为基本片段，每个基本片段对10gP具有特定的贡献，但实际上相同片段对10gP的影响…     

Finite-size scaling for critical conditions for stable quadrupole-bound anions

We present finite-size scaling calculations of the critical parameters for binding an electron to a finite linear quadrupole field. This approach gives very accurate results for the critical parameters by using a systematic expansion in a finite basis set. The model Hamiltonian consists of a charge Q located at the origin of the coordinates and k charges -Q/k located at distances R(i), i=1, em leader,k. After proper scaling of distances and energies, the rescaled Hamiltonian depends only on one free parameter q=QR. Two different linear charge configurations with q>0 and q<0 are studied using basis sets in both spherical and prolate spheroidal coordinates. For the case with q>0, the finite size scaling calculations give an extrapolated critical value of q(c)=1.469 70+/-0.000 05 a.u. by using a basis set with prolate spheroidal coordinates. For the quadrupole case with q<0, we obtained an extrapolated critical value of mid R:q(c)mid R:=3.982 51+/-0.000 01 a.u. for stable quadrupole bound anions. The corresponding critical exponent for the ground state energy alpha=1.9964+/-0.0005, with E approximately (q-q(c))(alpha).     

A strategy for ready preparation of glycolipids for multivalent presentation

The olefinic residue of n-pentenyl glycosides serves as the trigger for regioselective construction of higher saccharides and then for elaboration in multivalent glycolipids. [reaction: see text]     

Piperazine-based buffers for liposome coating of capillaries for electrophoresis

Anionic liposomes can be coated on fused-silica capillaries for electrophoresis in the presence of N-(hydroxyethyl)piperazine-N'-(2-ethanesulfonic acid) (HEPES) as background electrolyte (BGE) solution. In this work, the interaction of various compounds with zwitterionic and anionic phospholipid coatings was studied with HEPES at pH 7.4 as BGE solution. The chromatographic and electrophoretic behavior of three test sample solutions (anionic, cationic, and neutral) was investigated for evaluation of the phospholipid coatings. Our results show that hydrophobic interactions between analytes and the phospholipid coating are important for the migration of charged analytes. In addition, the performances of other piperazine-based buffers, i.e., N-(2-hydroxyethyl)piperazine-N'-(2-hydroxypropanesulfonic acid), piperazine-N,N'-bis(2-ethanesulfonic acid), and piperazine-N,N'-bis(hydroxypropane sulfonic acid), at pH 7.4, as liposome solvent and BGE solution were evaluated and compared with the performance of HEPES at pH 7.4. The anionic liposome solution comprised 80/20 mol% phosphatidylcholine/phosphatidylserine. A simple test solution was selected and the chromatographic and electrophoretic migration behavior of the analytes was evaluated. The results show that, in addition to HEPES, other piperazine-based buffers at pH 7.4 are suitable for coating of fused-silica capillaries with anionic liposomes.     

Gum phases for glass capillary columns; a recommendation for users,a challenge for polymer scientists

Conclusion Based on the above-mentioned fundamental advantages, gums should be considered the ideal phases for capillary GLC. Therefore, we strongly recommend users to select a gum whenever it is not precluded because of critical polarity/selectivity requirements.On the other hand we emphasize the great need for a much wider choice of gum phases. We are convinced that developing new and especially, more polar, gum phases is one of the best services that can be rendered to our analytical field. It is our hope that this may be a challange for some polymer scientists.     

Design criteria for dense permeation-selective membranes for enantiomer separations

Dense enantioselective membranes can distinguish between two enantiomers by different mechanisms. At this moment, it is not clear which mechanism provides the best membranes for large-scale enantiomer separations. Therefore, we studied the design criteria for permeation-selective membranes combining literature data, experiments and model calculations. Literature data on dense permeation-selective membranes for enantiomer separation show that these membranes could be divided into two different classes: diffusion selective and sorption selective. Reviewing the literature on diffusion-selective membranes shows that these membranes have one main disadvantage: the inverse proportionality relation between the permeability and selectivity. This disadvantage is absent for sorption-selective membranes. As a model system, the diffusion of phenylalanine through a packed bed of polypropylene beads coated with N-dodecyl-l-hydroxyproline:Cu(II) was studied. The experiments showed that the material could selectively adsorb phenylalanine (Phe) with a selectivity (d/l) of 1.25. However, no permeation selectivity could be detected. With a dual sorption model these results could be interpreted. These model calculations showed that the permeation selectivity only approaches the intrinsic selectivity of the selector if the selectively adsorbed population is mobile and the non-selective permeation is minimized. Therefore, to our opinion more emphasis should be put on the development of sorption selective membranes.