Refractive index-assisted UV/Vis spectrophotometry to overcome spectral interference by impurities

Development of a potential primary method for protein quantification via electrospray differential mobility analysis

Accurate protein quantification is the basis for establishing the metrological traceability of in vitro diagnostics or drug products. In this study, we established and validated a potential primary method for protein quantification based on electrospray-differential mobility analysis coupled with a condensation particle counter (ES-DMA-CPC). The analytical performance of this method was assessed using the certified reference material NIMCmAb, and the uncertainty of measurement was evaluated. The method was applied to the quantification of three other protein reference materials and one highly purified protein, including myoglobin, bovine serum albumin, IgG monoclonal antibody, and one highly purified fibrinogen, with a molecular weight range between 17 kDa and 340 kDa. In addition, when compared with isotope dilution mass spectrometry (IDMS) and UV‒VIS spectrophotometry approaches, the ES-DMA-CPC method showed good agreement with IDMS method for the quantification of these protein reference materials. Our proposed method provided an accurate quantification of proteins, especially those with large molecular weights. Moreover, our method could be a potential primary method for protein quantification and serve as a complement to IDMS method.

Comparative Investigation of the Spectroscopic Behavior Based on High-Concentrated Solution in Nitrogen and Air Atmospheres

In order to accurately obtain photometric information of high concentration SO42- and other substances in the process industry, the spectroscopy behavior of SO42-, S2-, Ni2+ and Cu2+ in air and nitrogen atmosphere was compared based on the UV-visible spectrophotometer with a nitrogen replacing the oxygen. Different from Ni2+ and Cu2+, the accuracy of SO42- and S2- in the ultraviolet region was effectively improved by using a nitrogen atmosphere (P detection results were regressed within the limited standard range, RE < 5%). The nitrogen atmosphere suppressed the additional light attenuation caused by its absorption of ultraviolet rays by isolating oxygen and was also reflected in the decrease in the degree of red shift of the characteristic wavelength for SO42- with increasing concentration. Therefore, the detection results of SO42- showed an effective improvement in sensitivity. Nevertheless, according to the complementary experimental results and theoretical calculations, in addition to oxygen absorption, the low detection accuracy of SO42- high concentration is also attributed to the reduction of the energy required for electronic excitation per unit group caused by the interaction between SO42- groups, resulting in a deviation of the C-A curve from linearity at high concentrations. The influence of this intermolecular force on the detection results is far more important than oxygen absorption. The research can provide reliable theoretical guidance and technical support for the pollution-free direct measurement of high-concentration solutions in the process industry and promote the sustainable development of the process industry.

The characteristics of ultraviolet absorption and electronic excitation of sulfate at high concentrations

The variation of spectra and the characteristics of electronic excitation are critical for establishing a model for quantifying sulfate at high concentrations. The absorption characteristics of sulfate are affected by the optical pathlength and sulfate concentration. The absorption coefficient declines by approximately 86.09-96.20% with an increasing concentration (0-130 g/L) at different optical pathlengths (1-100 mm). Moreover, a high sensitivity and accuracy can be achieved at weak absorption wavelengths or at lower optical pathlengths when high concentrations of sulfate are detected. In addition, the maximum absorption wavelength of sulfate redshifts by approximately 0-10 nm with an increasing concentration and optical pathlength, which is significantly affected by the optical pathlength. The (H₂SO₄)_n‧(H₂O)_4-n models were established at the PBEPBE/6-311++G(d, p) level of theory. There absorption spectra were calculated by the time-dependent density functional theory (TD-DFT) method. As a result, the maximum absorption wavelength redshifted from 180.16 nm to 192.71 nm with an increasing sulfate concentration, and the corresponding absorption coefficient demonstrated a declining trend. Furthermore, the electron-hole and natural bond orbital (NBO) analysis indicate that the type of electronic excitation changes from a n(O) → σ*(S-O) localized excitation to n → σ* charge-transfer excitation as the sulfate concentration increases. This study provides a theoretical foundation for understanding the spectral behavior of sulfates and constructing the quantification models or methods that can also be applied to analyze the spectroscopy of other chemicals.

4mCBERT: A computing tool for the identification of DNA N4-methylcytosine sites by sequence- and chemical-derived information based on ensemble learning strategies

N4-methylcytosine (4mC) is an important DNA chemical modification pattern which is a new methylation modification discovered in recent years and plays critical roles in gene expression regulation, defense against invading genetic elements, genomic imprinting, and so on. Identifying 4mC site from DNA sequence segment contributes to discovering more novel modification patterns. In this paper, we present a model called 4mCBERT that encodes DNA sequence segments by sequence characteristics including one-hot, electron-ion interaction pseudopotential, nucleotide chemical property, word2vec and chemical information containing physicochemical properties (PCP), chemical bidirectional encoder representations from transformers (chemical BERT) and employs ensemble learning framework to develop a prediction model. PCP and chemical BERT features are firstly constructed and applied to predict 4mC sites and show positive contributions to identifying 4mC. For the Matthew's Correlation Coefficient, 4mCBERT significantly outperformed other state-of-the-art models on six independent benchmark datasets including A. thaliana, C. elegans, D. melanogaster, E. coli, G. Pickering, and G. subterraneous by 4.32 % to 24.39 %, 2.52 % to 31.65 %, 2 % to 16.49 %, 6.63 % to 35.15, 8.59 % to 61.85 %, and 8.45 % to 34.45 %. Moreover, 4mCBERT is designed to allow users to predict 4mC sites and retrain 4mC prediction models. In brief, 4mCBERT shows higher performance on six benchmark datasets by incorporating sequence- and chemical-driven information and is available at http://cczubio.top/4mCBERT and https://github.com/abcair/4mCBERT.

Direct-determination of high-concentration sulfate by serial differential spectrophotometry with multiple optical pathlengths

Direct-determination is a fast and free of contamination method for analysis of substances in water samples. However, direct-determination of SO₄^2- with high concentration in environmental systems is still challenging due to deviation from Beer-Lambert law is generally observed when a substance with high concentration is directly determined, resulting in poor accuracy, sensitivity, and narrow linear range. In this study, a simple and rapid method for the direct-determination of SO₄^2- with high concentration was proposed. Serial high-absorbance differential spectrophotometry was applied to incrementally widen the determination range under different optical pathlengths. In this process, the effects of optical pathlength and reference concentration on sensitivity were further investigated. The results showed that SO₄^2- could be accurately quantified within a concentration range of 0-4.10 g/L, and the determination range by this method was 10-fold and 19.5-fold wider than those by conventional differential spectrophotometry and conventional spectrophotometry, respectively. And the applicable ranges of sensitivity were obtained at various optical pathlengths by adjusting the reference solution concentration. This approach exhibited several advantages over conventional methods, including high accuracy, excellent precision, low cost, less time consumption, and easy operation. This method is promising and can provide accurate and reliable data support for environmental monitoring and pollution control.