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81.
82.
Mariana R. Almeida Rafael S. Alves Laura B. L. R. Nascimbem Rodrigo Stephani Ronei J. Poppi Luiz Fernando C. de Oliveira 《Analytical and bioanalytical chemistry》2010,397(7):2693-2701
Fourier transform Raman spectroscopy and chemometric tools have been used for exploratory analysis of pure corn and cassava starch samples and mixtures of both starches, as well as for the quantification of amylose content in corn and cassava starch samples. The exploratory analysis using principal component analysis shows that two natural groups of similar samples can be obtained, according to the amylose content, and consequently the botanical origins. The Raman band at 480 cm?1, assigned to the ring vibration of starches, has the major contribution to the separation of the corn and cassava starch samples. This region was used as a marker to identify the presence of starch in different samples, as well as to characterize amylose and amylopectin. Two calibration models were developed based on partial least squares regression involving pure corn and cassava, and a third model with both starch samples was also built; the results were compared with the results of the standard colorimetric method. The samples were separated into two groups of calibration and validation by employing the Kennard-Stone algorithm and the optimum number of latent variables was chosen by the root mean square error of cross-validation obtained from the calibration set by internal validation (leave one out). The performance of each model was evaluated by the root mean square errors of calibration and prediction, and the results obtained indicate that Fourier transform Raman spectroscopy can be used for rapid determination of apparent amylose in starch samples with prediction errors similar to those of the standard method. Figure
Raman spectroscopy has been successfully applied to the determination of the amylose content in cassava and corn starches by means of multivariate calibration analysis. 相似文献
83.
84.
Haipei Liu Zhaowei Liu Mariana Sá Santos Michael A. Nash 《Angewandte Chemie (International ed. in English)》2023,62(32):e202304136
Single-molecule force spectroscopy (SMFS) is powerful for studying folding states and mechanical properties of proteins, however, it requires protein immobilization onto force-transducing probes such as cantilevers or microbeads. A common immobilization method relies on coupling lysine residues to carboxylated surfaces using 1-ethyl-3-(3-dimethyl-aminopropyl) carbodiimide and N-hydroxysuccinimide (EDC/NHS). Because proteins typically contain many lysine groups, this strategy results in a heterogeneous distribution of tether positions. Genetically encoded peptide tags (e.g., ybbR) provide alternative chemistries for achieving site-specific immobilization, but thus far a direct comparison of site-specific vs. lysine-based immobilization strategies to assess effects on the observed mechanical properties was lacking. Here, we compared lysine- vs. ybbR-based protein immobilization in SMFS assays using several model polyprotein systems. Our results show that lysine-based immobilization results in significant signal deterioration for monomeric streptavidin-biotin interactions, and loss of the ability to correctly classify unfolding pathways in a multipathway Cohesin-Dockerin system. We developed a mixed immobilization approach where a site-specifically tethered ligand was used to probe surface-bound proteins immobilized through lysine groups, and found partial recovery of specific signals. The mixed immobilization approach represents a viable alternative for mechanical assays on in vivo-derived samples or other proteins of interest where genetically encoded tags are not feasible. 相似文献
85.
Peralta Cecilia Mariana Acosta Gimena Henestrosa Cecilia Gil Raúl Andrés Fernández Liliana Patricia 《Journal of Analytical Chemistry》2022,77(3):308-317
Journal of Analytical Chemistry - The present development involved a flow injection strategy using a mini-column of multiwalled carbon nanotubes and fluorescent detection (λex of 283 nm,... 相似文献
86.
Agnid?Banerjee Mariana?Smit Vega GarciaEmail author Andrew?K.?Zeller 《Calculus of Variations and Partial Differential Equations》2017,56(1):7
We show that the quotient of two caloric functions which vanish on a portion of an \(H^{k+ \alpha }\) regular slit is \(H^{k+ \alpha }\) at the slit, for \(k \ge 2\). In the case \(k=1\), we show that the quotient is in \(H^{1+\alpha }\) if the slit is assumed to be space-time \(C^{1, \alpha }\) regular. This can be thought of as a parabolic analogue of a recent important result in De Silva and Savin (Boundary Harnack estimates in slit domains and applications to thin free boundary problems, 2014), whose ideas inspired us. As an application, we show that the free boundary near a regular point of the parabolic thin obstacle problem studied in Danielli et al. (Optimal regularity and the free boundary in the parabolic Signorini problem. Mem. Am. Math. Soc., 2013) with zero obstacle is \(C^{\infty }\) regular in space and time. 相似文献
87.
In the framework of the Multi-Channel Quantum Defect Theory (MQDT), a theoretical study of the dissociative excitation is
presented. Numerical results for the dissociative excitation cross sections of HD
+, D
2+, and DT
+ with electrons of energy between 2 and 12 eV are reported. The contribution of the vibrational continua of the two lowest
electronic states as explicit ionization channels has been considered. Within a quasi-diabatic representation of the molecular electronic states, the Born expansion of second order is done in the K-matrix evaluation. 相似文献
88.
89.
90.
We consider the Euler equations describing nonlinear waves on the free surface of a two-dimensional inviscid, irrotational
fluid layer of finite depth. For large surface tension, Bond number larger than 1/3, and Froude number close to 1, the system
possesses a one-parameter family of small-amplitude, traveling solitary wave solutions. We show that these solitary waves
are spectrally stable with respect to perturbations of finite wave-number. In particular, we exclude possible unstable eigenvalues
of the linearization at the soliton in the long-wavelength regime, corresponding to small frequency, and unstable eigenvalues
with finite but bounded frequency, arising from non-adiabatic interaction of the infinite-wavelength soliton with finite-wavelength
perturbations.
Received: 7 February 2001 / Accepted: 6 October 2001 相似文献