No abstract

Baseline drift always blurs or even swamps signals and deteriorates analytical results, particularly in multivariate analysis. It is necessary to correct baseline drift to perform further data analysis. Simple or modified polynomial fitting has been found to be effective to some extent. However, this method requires user intervention and is prone to variability especially in low signal-to-noise ratio environments. A novel algorithm named adaptive iteratively reweighted Penalized Least Squares (airPLS) that does not require any user intervention and prior information, such as peak detection etc., is proposed in this work. The method works by iteratively changing weights of sum squares errors (SSE) between the fitted baseline and original signals, and the weights of the SSE are obtained adaptively using the difference between the previously fitted baseline and the original signals. The baseline estimator is fast and flexible. Theory, implementation, and applications in simulated and real datasets are presented. The algorithm is implemented in R language and MATLAB, which is available as open source software (http://code.google.com/p/airpls).

Different chromatographic and electrophoretic techniques commonly used in the instrumental inspection of herbal medicines (HM) are first comprehensively reviewed. Chemical fingerprints obtained by chromatographic and electrophoretic techniques, especially by hyphenated chromatographies, are strongly recommended for the purpose of quality control of herbal medicines, since they might represent appropriately the "chemical integrities" of the herbal medicines and therefore be used for authentication and identification of the herbal products. Based on the conception of phytoequivalence, the chromatographic fingerprints of herbal medicines could be utilized for addressing the problem of quality control of herbal medicines. Several novel chemometric methods for evaluating the fingerprints of herbal products, such as the method based on information theory, similarity estimation, chemical pattern recognition, spectral correlative chromatogram (SCC), multivariate resolution, etc. are discussed in detail with examples, which showed that the combination of chromatographic fingerprints of herbal medicines and the chemometric evaluation might be a powerful tool for quality control of herbal products.

No abstract

Fluorescent background is a major problem in recoding the Raman spectra of many samples, which swamps or obscures the Raman signals. The background should be suppressed in order to perform further qualitative or quantitative analysis of the spectra. For this purpose, an intelligent background-correction algorithm is developed, which simulates manual background-correction procedure intelligently. It basically consists of three aspects: (1) accurate peak position detection in the Raman spectrum by continuous wavelet transform (CWT) with the Mexican Hat wavelet as the mother wavelet; (2) peak-width estimation by signal-to-noise ratio (SNR) enhancing derivative calculation based on CWT but with the Haar wavelet as the mother wavelet; and (3) background fitting using penalized least squares with binary masks. This algorithm does not require any preprocessing step for transforming the spectrum into the wavelet space and can suppress the fluorescent background of Raman spectra intelligently and validly. The algorithm is implemented in R language and available as open source software (http://code.google.com/p/baselinewavelet).

No abstract

Supplementary data are available at Bioinformatics online.

In this paper we present a new paradigm for designing hydrogelators that exhibit sharp phase transitions in response to a series of disparate stimuli, including oxidation-reduction reactions (redox), guest-host interactions, and pH changes. We have serendipitously discovered that ferrocenoyl phenylalanine (Fc-F) monomers aggregate in water via a rapid self-assembly mechanism to form stable, multistimuli hydrogels. In comparison to other known mono- and multiresponsive gelators, Fc-F is unique because of its small size, economy of gel-forming components, and exceptionally simple molecular structure. Density functional theory (DFT) ab initio calculations suggest gel formation initially involves an antiparallel, noncovalent dimerization step wherein the ferrocenoyl moiety of one axe-like monomer conjoins with the phenyl group of the second monomer via a π-π stacking interaction to form brick-like dimers. This stacking creates a cavity in which the carboxylic acid groups of each monomer mutually interact via hydrogen bond formation, which affords additional stability to the dimer. On the basis of structural analysis via optical and electrical measurements and additional DFT calculations, we propose a possible stepwise hierachical assembly mechanism for fibril formation. Insights into the self-assembly pathway of Fc-F should prove useful for understanding gelation processes of more complex systems. We expect that Fc-F will serve as a helpful archetypical template for others to use when designing new, stimuli specific hydrogelation agents.