Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 24.979
Filtrar
1.
Acta Crystallogr D Struct Biol ; 76(Pt 4): 326-331, 2020 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-32254056

RESUMO

The study of ion channels dates back to the 1950s and the groundbreaking electrophysiology work of Hodgin and Huxley, who used giant squid axons to probe how action potentials in neurons were initiated and propagated. More recently, several experiments using different structural biology techniques and approaches have been conducted to try to understand how potassium ions permeate through the selectivity filter of potassium ion channels. Two mechanisms of permeation have been proposed, and each of the two mechanisms is supported by different experiments. The key structural biology experiments conducted so far to try to understand how ion permeation takes place in potassium ion channels are reviewed and discussed. Protein crystallography has made, and continues to make, key contributions in this field, often through the use of anomalous scattering. Other structural biology techniques used to study the contents of the selectivity filter include solid-state nuclear magnetic resonance and two-dimensional infrared spectroscopy, both of which make clever use of isotopic labeling techniques, while molecular-dynamics simulations of ion flow through the selectivity filter have been enabled by the growing number of potassium ion channel structures deposited in the Protein Data Bank.


Assuntos
Simulação de Dinâmica Molecular , Canais de Potássio/química , Potássio/química , Cristalografia por Raios X , Marcação por Isótopo , Modelos Moleculares , Ressonância Magnética Nuclear Biomolecular , Estrutura Terciária de Proteína , Espalhamento de Radiação , Espectrofotometria Infravermelho
2.
Chemosphere ; 252: 126413, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32197171

RESUMO

O3 and alkenes are important reactants in the formation of SOA in the atmosphere. The intermediates and reaction mechanism of ozonation of alkene is an important topic in atmospheric chemistry. In this study, the low-temperature matrix isolation was used to capture the intermediates such as Primary ozonides (POZs), Criegee Intermediates (CIs), and Secondary ozonides (SOZs) generated from ozonation of 2-methyl-1-butene (2M1B) and 2-methyl-2-butene (2M2B). The results have been identified by the vacuum infrared spectroscopy and theoretical calculation. Our results show that during the ozonation of asymmetric alkenes, two kinds of CIs and more than two kinds of SOZs were generated due to the different decomposition modes of POZs. The infrared absorption peaks of (CH3)2COO and CH3CH2C(CH3)OO for O-O telescopic vibration was determined to be 889 cm-1 and 913 cm-1, respectively. Using the merged jet method, it was found that a large amount of HCHO was produced during the ozonation of 2M1B, and glyoxal and methylglyoxal were produced in the ozonation of 2M2B. Our findings highlight the importance of asymmetric alkene ozonolysis reactions in producing CIs, further improving the understanding of the generation of CIs from ozonation of alkenes.


Assuntos
Alcenos/química , Modelos Químicos , Ozônio/química , Atmosfera , Compostos Heterocíclicos , Espectrofotometria Infravermelho , Espectroscopia de Infravermelho com Transformada de Fourier
3.
Phys Chem Chem Phys ; 22(10): 5463-5475, 2020 Mar 11.
Artigo em Inglês | MEDLINE | ID: mdl-32096510

RESUMO

The calcium sensor protein calmodulin is ubiquitous among eukaryotes. It translates intracellular Ca2+ influx (by a decrease of conformational flexibility) into increased target recognition affinity. Here we demonstrate that by using the IR reporter -SCN in combination with 2D-IR spectroscopy, global structure changes and local dynamics, degree of solvent exposure and protein-ligand interaction can be characterised in great detail. The long vibrational lifetime of the -SCN label allows for centerline slope analysis of the 2D-IR line shape up to 120 ps to deduce the frequency-frequency correlation function (FFCF) of the -SCN label in various states and label positions in the protein. Based on that we show clear differences between a solvent exposed site, the environment close to the Ca2+ binding motif and three highly conserved positions for ligand binding. Furthermore, we demonstrate how these dynamics are affected by conformational change induced by the addition of Ca2+ ions and by interaction with a short helical peptide mimicking protein binding. We show that the binding mode is strongly heterogeneous among the probed key binding methionine residues. SCN's vibrational relaxation is dominated by intermolecular contributions. Changes in the vibrational lifetime upon changing between H2O and D2O buffer therefore provide a robust measure for water accessibility of the label. Characterising -SCN's extinction coefficient, vibrational lifetime in light and heavy water and its FFCF we demonstrate the vast potential it has as a label especially for nonlinear spectroscopies, such as 2D-IR spectroscopy.


Assuntos
Calmodulina/química , Espectrofotometria Infravermelho , Calmodulina/metabolismo , Óxido de Deutério/química , Ligação Proteica , Conformação Proteica , Domínios e Motivos de Interação entre Proteínas , Solventes/química , Vibração , Água/química
4.
Chemosphere ; 250: 126272, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32109703

RESUMO

Reduction of harmful nitrogen oxides (NOx) from diesel engine exhausts is one of the key challenges in environmental protection, and can be achieved by NH3-assisted selective catalytic reduction (NH3-SCR) using copper-exchanged chabazite zeolites (i.e. Cu-CHA, including Cu-SSZ-13 and Cu-SAPO-34) as catalysts. Understanding the redox chemistry of Cu-CHA in NH3-SCR catalysis is crucial for further improving the NOx reduction efficiency. Here, a series of Cu-SSZ-13 catalysts with different Cu ion exchange levels were prepared, thoroughly characterized by different techniques such as X-ray diffraction, diffuse reflectance ultraviolet-visible spectroscopy and temperature-programmed desorption using NH3 as a probe molecule, etc., and tested in NH3-SCR reactions under steady-state conditions. In situ studies by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), supplemented with density-functional theory calculations, provided solid evidence for the formation of ammonium ion (NH4+) intermediates resulting from the reduction of Cu2+ to Cu+ by co-adsorbed NH3 and NO molecules on Cu-SSZ-13. Catalytic relevance of the NH4+ intermediates, as demonstrated by an increase of NO conversion over Cu-SSZ-13 pre-treated in NH3/NO atmosphere, can be attributed to the formation of closely coupled Cu+/NH4+ pairs promoting the Cu+ re-oxidation and, consequently, the overall NH3-SCR process. This study thus paves a new route for improving the NH3-SCR efficiency over Cu-CHA zeolite catalyst.


Assuntos
Amônia/química , Cobre/química , Óxidos de Nitrogênio/química , Zeolitas/química , Catálise , Teoria da Densidade Funcional , Poluição Ambiental/prevenção & controle , Oxirredução , Espectrofotometria Infravermelho , Emissões de Veículos/toxicidade
5.
Bioelectrochemistry ; 132: 107416, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-31981968

RESUMO

A hybrid bilayer lipid membrane (hBLM), constructed with a 1-hexadecanethiol self-assembled interior leaflet and a 1,2-dipalmitoyl-sn-glycero-3-cytidine nucleolipid exterior leaflet, was deposited at the surface of a gold (111) electrode. This system was used to investigate the molecular recognition reaction between the cytosine moieties of the lipid head group with guanine molecules in the bulk electrolyte solution. Electrochemical measurements and photon polarization modulation infrared reflection absorption spectroscopy (PMIRRAS) were employed to characterize the system and determine the extent of the molecular recognition reaction. The capacitance of the hBLM-covered gold electrode was very low (~1 µF cm-2), therefore the charge density at the gold surface was small. Changing the electrode potential had a minimal effect on the complexation between the cytosine moieties and guanine molecules due to small changes in the static electric field across the membrane. This behavior favored the formation of the guanine-cytosine complex.


Assuntos
Citosina/química , Eletrodos , Ouro/química , Guanina/química , Bicamadas Lipídicas/química , Espectrofotometria Infravermelho
6.
Bioelectrochemistry ; 132: 107412, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-31889632

RESUMO

The synthesis of a series of methyl 2-alkyl-5-aryl-4-ferrocenoylpyrrolidine-2-carboxylates has been achieved by [3 + 2] dipolar cycloaddition of azomethine ylides to acryloylferrocene. The electrochemical properties of novel products were examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). These techniques revealed the quasi-reversible one-electron oxidation process. The DNA-binding capacity of all the products was also studied using CV and DPV, and significant interactions between synthesized compounds and nucleic acid, mostly of the electrostatic type, were disclosed. DFT calculations and molecular docking tests were carried out to gain a more exhaustive insight into the interactions of the obtained products with nucleic acid. A detailed characterization of the new compounds was performed by IR, NMR and elemental analyses, followed by single-crystal X-ray diffraction experiments for two representatives.


Assuntos
DNA/metabolismo , Técnicas Eletroquímicas/métodos , Compostos Ferrosos/metabolismo , Metalocenos/metabolismo , Cristalografia por Raios X , Teoria da Densidade Funcional , Compostos Ferrosos/química , Espectroscopia de Ressonância Magnética , Metalocenos/química , Estrutura Molecular , Oxirredução , Espectrofotometria Infravermelho
7.
Phytochem Anal ; 31(3): 366-374, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-31943426

RESUMO

In this study, the potentiality of applying attenuated total reflectance near-infrared (ATR-NIR) and attenuated total reflectance mid-infrared (ATR-MIR) techniques combined with a partial least squares (PLS) regression technology to quantify the total polyphenols (TPs) in Dendrobium huoshanense (DHS) was investigated and compared. The real TP contents in the DHS samples were analysed using methods of reference. The capability of the two IR spectroscopic techniques to quantify the TPs in DHS was assessed by the root-mean-square error of calibration (RMSEC) and determination coefficients (R2 ). The results showed that both NIR and MIR might be used as a fast and simple tool to replace traditional chemical assays for the determination of the TP contents in DHS, and the best NIR model showed slightly better prediction performance [root-mean-square error of prediction (RMSEP): 0.307, R2 : 0.9122, ratio performance deviation (RPD): 4.43] than the best MIR model (RMSEP: 0.440, R2 : 0.9069, RPD: 3.09). Results from this study indicated that both the NIR and MIR models could be used to quantify the TP in DHS, and ATR-NIR appeared to be the more predominant and more robust technique for the quantification of the TP in DHS.


Assuntos
Dendrobium , Polifenóis , Calibragem , Análise dos Mínimos Quadrados , Espectrofotometria Infravermelho
8.
Phys Chem Chem Phys ; 22(9): 4896-4904, 2020 Mar 04.
Artigo em Inglês | MEDLINE | ID: mdl-31930249

RESUMO

Ibuprofen is a well-established non-steroidal anti-inflammatory drug, inhibiting the prostaglandin-endoperoxide synthase. One of the key features defining the ibuprofen structure is the doubly intermolecular O-HO[double bond, length as m-dash]C hydrogen bond in cyclic dimers as know from carboxylic acids and confirmed by X-ray analysis. Until now, there was neither information about the vaporization enthalpy of ibuprofen nor about how this thermal property is determined by the subtle balance between different types of intermolecular interaction. In this study we derive the vaporization enthalpy of ibuprofen from thermochemical experiments to be . We dissected the hydrogen bond energy, EHB = 45.0 kJ mol-1, exclusively from measured vaporization enthalpies of related aliphatic carboxylic acids, their homomorph methyl esters and alkyl acetates, respectively. This contribution from hydrogen bonding could be confirmed almost quantitatively from quantum chemical calculations of ibuprofen clusters, which also suggest dispersion interaction of similar order (Edisp = 47 kJ mol-1). Following the full analysis of the gas-vapor transition enthalpy, we studied the changing structural components from the solid to the liquid phase of ibuprofen by means of Attenuated Total Reflection Infrared (ATR-IR) spectroscopy. The cyclic dimers as observed in the X-ray patterns are essentially preserved in the liquid state just above the melting point. However, with increasing temperature the doubly hydrogen-bonded cyclic dimers are replaced by singly hydrogen-bonded linear dimers in the liquid ibuprofen. The transfer enthalpy from the temperature-dependent equilibria of both dimers as obtained from the IR intensity ratios of the vibrational bands quantifies for the first time the energy of the released, single hydrogen bond to be EHB = 21.0 kJ mol-1. Overall, we show that a combination of thermodynamics, infrared spectroscopy and quantum chemistry provides quantification and detailed understanding of structure and molecular interaction in ibuprofen and related compounds.


Assuntos
Gases/química , Ibuprofeno/química , Teoria da Densidade Funcional , Dimerização , Ligação de Hidrogênio , Espectrofotometria Infravermelho , Termodinâmica
9.
Phys Chem Chem Phys ; 22(5): 2999-3007, 2020 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-31957771

RESUMO

Infrared multiple photon dissociation (IRMPD) spectroscopy has been used to probe the structures of the three protonated base-pair mismatches containing 9-ethylguanine (9eG) in the gas phase. Computational chemistry has been used to determine the relative energies and compute the infrared spectra of these complexes. By comparing the IRMPD spectra with the computed spectra, in all cases, it was possible to deduce that what was observed experimentally were the lowest energy computed structures. The protonated complex between 9eG and 1-methylthymine (1mT) is protonated at N7 of 9eG-the most basic site of all three bases in this study-and bound in a Hoogsteen type structure with two hydrogen bonds. The experimental IRMPD spectrum for the protonated complex between 9eG and 9-methyladenine (9mA) is described as arising from a combination of the two lowest energy structures, both which are protonated at N1 of adenine and each containing two hydrogen bonds with 9eG being the acceptor of both. The protonated dimer of 9eG is protonated at N7 with an N7-H+-N7 ionic hydrogen bond. It also contains an interaction between a C-H of protonated guanine and the O6 carbonyl of neutral guanine which is manifested in a slight red shift of that carbonyl stretch. The protonated 9eG/9mA structures have been previously identified by X-ray crystallography in RNA and are contained within the protein database.


Assuntos
Gases/química , Guanina/análogos & derivados , Espectrofotometria Infravermelho , Adenina/análogos & derivados , Adenina/química , Adenina/metabolismo , Pareamento Incorreto de Bases , Cristalografia por Raios X , Guanina/química , Guanina/metabolismo , Ligação de Hidrogênio , Modelos Moleculares , Fótons , Timina/análogos & derivados , Timina/química , Timina/metabolismo
10.
Phys Chem Chem Phys ; 22(5): 3008-3016, 2020 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-31957772

RESUMO

Infrared (IR) spectroscopy is commonly utilized for the investigation of protein structures and protein-mediated processes. While the amide I band provides information on protein secondary structures, amino acid side chains are used as IR probes for the investigation of protein reactions, such as proton pumping in rhodopsins. In this work, we calculate the IR spectra of the solvated aspartic acid, with both zwitterionic and protonated backbones, and of a capped form, i.e. mimicking the aspartic acid residue in proteins, by means of molecular dynamics (MD) simulations and the perturbed matrix method (PMM). This methodology has already proved its good modeling capabilities for the amide I mode and is here extended to the treatment of protein side chains. The computed side chain vibrational signal is in very good agreement with the experimental one, well reproducing both the peak frequency position and the bandwidth. In addition, the MD-PMM approach proposed here is able to reproduce the small frequency shift (5-10 cm-1) experimentally observed between the protonated and zwitterionic forms, showing that such a shift depends on the excitonic coupling between the modes localized on the side chain and on the backbone in the protonated form. The spectrum of the capped form, in which the amide I band is also calculated, agrees well with the corresponding experimental spectrum. The reliable calculation of the vibrational bands of carboxyl-containing side chains provides a useful tool for the interpretation of experimental spectra.


Assuntos
Aminoácidos/química , Simulação de Dinâmica Molecular , Proteínas/química , Espectrofotometria Infravermelho , Ácido Aspártico/química , Ácido Glutâmico/química , Teoria Quântica
11.
Phys Chem Chem Phys ; 22(4): 2307-2318, 2020 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-31930268

RESUMO

We report a study of the primary photo-dissociation dynamics of aqueous alanine, isoleucine and proline by 200 nm UV pump-IR probe transient absorption spectroscopy. Photo-dissociation of the three amino acids predominantly results in decarboxylation, and 38 ± 7% of the excited alanine, 35 ± 10% of the excited isoleucine and 47 ± 10% of the excited proline zwitterions remain dissociated 100 picoseconds after the excitation. The decarboxylation occurs from a transient intermediate with a lifetime of ∼20 picoseconds to which we assign the excited state of the amino acids based on comparison of the measured and calculated IR spectra, and calculated excited state energy surfaces.


Assuntos
Aminoácidos/química , Aminoácidos/efeitos da radiação , Descarboxilação/efeitos da radiação , Espectrofotometria Infravermelho , Raios Ultravioleta
12.
Nature ; 577(7788): 34-35, 2020 01.
Artigo em Inglês | MEDLINE | ID: mdl-31894155
13.
Nature ; 577(7788): 52-59, 2020 01.
Artigo em Inglês | MEDLINE | ID: mdl-31894146

RESUMO

The proper functioning of living systems and physiological phenotypes depends on molecular composition. Yet simultaneous quantitative detection of a wide variety of molecules remains a challenge1-8. Here we show how broadband optical coherence opens up opportunities for fingerprinting complex molecular ensembles in their natural environment. Vibrationally excited molecules emit a coherent electric field following few-cycle infrared laser excitation9-12, and this field is specific to the sample's molecular composition. Employing electro-optic sampling10,12-15, we directly measure this global molecular fingerprint down to field strengths 107 times weaker than that of the excitation. This enables transillumination of intact living systems with thicknesses of the order of 0.1 millimetres, permitting broadband infrared spectroscopic probing of human cells and plant leaves. In a proof-of-concept analysis of human blood serum, temporal isolation of the infrared electric-field fingerprint from its excitation along with its sampling with attosecond timing precision results in detection sensitivity of submicrograms per millilitre of blood serum and a detectable dynamic range of molecular concentration exceeding 105. This technique promises improved molecular sensitivity and molecular coverage for probing complex, real-world biological and medical settings.


Assuntos
Biomarcadores/sangue , Análise Química do Sangue/métodos , Soro/química , Espectrofotometria Infravermelho , Biomarcadores/química , Análise Química do Sangue/instrumentação , Humanos , Sensibilidade e Especificidade , Água/química
14.
J Phys Chem Lett ; 11(4): 1282-1290, 2020 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-31977221

RESUMO

Recent chiral sum-frequency generation vibrational spectroscopy (SFG-VS) measurements revealed that two N-H stretching modes in the 3100-3500 cm-1 range in folded peptide LK7ß exhibit chiral characteristics. Here, we report the first phase-resolved subwavenumber high-resolution broadband SFG-VS (HR-BB-SFG-VS) measurement of the folded peptide LK7ß. The results show that this chiral N-H band consists of four, instead of two, distinctive peaks, and they are with two groups of opposite spectral phases. Moreover, the phases of these N-H peaks completely flip from the l-LK7ß to the d-LK7ß peptide, suggesting that the chirality of the N-H in the folded peptide LK7ß is completely governed by the chirality of the Cα-H of the amino acids. This discovery provides a clue on why proteins in nature are composed of the α-amino acids rather than ß- or γ-amino acids and may help us understand how life works.


Assuntos
Hidrogênio/química , Nitrogênio/química , Peptídeos/química , Sequência de Aminoácidos , Carbono/química , Dobramento de Proteína , Espectrofotometria Infravermelho , Estereoisomerismo
15.
J Chromatogr A ; 1617: 460807, 2020 Apr 26.
Artigo em Inglês | MEDLINE | ID: mdl-31889519

RESUMO

Click chemistry has attracted increasing attention for the synthesis of novel stationary phases. Considering the advantage of click chemistry, a strategy based on thiol-Michael addition was developed for the preparation of a new stationary phase herein, and a phenyl vinyl sulfone stationary phase (M-PVS) was prepared. The resulting M-PVS bonded silica was characterized by elemental analysis, solid-state 13C cross-polarization/magic-angle spinning NMR and infrared spectroscopy, confirming the successful immobilization of phenyl vinyl sulfone on the silica support. The retention properties of M-PVS were investigated and exhibited unambiguous reversed phase retention characteristics. Moreover, shape selectivity and silanol activity were studied to reveal the diverse interactions of M-PVS, including hydrophobic, π-π, hydrogen bonding, and ion-exchange interactions. In addition, de-wetting tolerance and hydrophilic properties were evaluated and a pronounced "U" retention curves were obtained, indicating enhanced retention for polar analytes and transitions of different interaction modes. Selectivity differences between M-PVS column, phenyl column and conventional C18 column were examined using series natural standards. The diverse interactions of M-PVS demonstrated its improved selectivity for the compounds with similar hydrophobic skeleton but different polar substituents.


Assuntos
Cromatografia Líquida , Química Click , Interações Hidrofóbicas e Hidrofílicas , Espectroscopia de Ressonância Magnética , Silanos/química , Dióxido de Silício/química , Espectrofotometria Infravermelho , Compostos de Sulfidrila/química , Sulfonas/química
16.
J Agric Food Chem ; 68(1): 390-401, 2020 Jan 08.
Artigo em Inglês | MEDLINE | ID: mdl-31820962

RESUMO

Infrared spectroscopy is often used as a simple, fast, and green method to screen for economically motivated adulteration in spices. However, conventional microscopy remains the reference method. In this research, the combination of microscopy and Fourier-transform infrared spectroscopy in mapping mode, namely, micro-FTIR imaging, along with Principle Component Analysis were used to develop a non-targeted method for detecting a broad range of organic and mineral bulking agents that could potentially be used to adulterate black pepper. This method, based on the spatial distribution of black pepper chemical composition, has been thoroughly validated as a one-class, non-targeted classification method. Results are categorized as Typical or Atypical, where an Atypical result indicates a high probability of adulteration. For an Atypical outcome, a multitool investigational approach is then used for the detection and identification of the potential adulterant.


Assuntos
Contaminação de Alimentos/análise , Piper nigrum/química , Espectrofotometria Infravermelho/métodos , Espectroscopia de Infravermelho com Transformada de Fourier/métodos , Análise de Componente Principal , Sementes/química , Especiarias/análise
17.
Phytochemistry ; 170: 112195, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31743799

RESUMO

In plant spores and pollen, sporopollenin occurs as a structural polymer with remarkable resistance to chemical degradation. This recalcitrant polymer is well-suited to analysis by non-destructive infrared spectroscopy. However, existing infrared characterization of sporopollenin has been limited in scope and occasionally contradictory. This study provides a comprehensive structural analysis of sporopollenin in the Pinus ponderosa pollen exine using infrared spectroscopy, including detailed band assignments, descriptions of chemical reactivity, and comparison to multiple reference substances. We observe that the infrared spectral characteristics of sporopollenin prepared by enzymatic digestion of the polysaccharide-based intine are largely consistent with a copolymer of aliphatic lipids and trans-4-hydroxycinnamic acid, without distinct contributions from α-pyrone or carotenoid substructures.


Assuntos
Biopolímeros/análise , Carotenoides/análise , Compostos Fitoquímicos/análise , Pinus ponderosa/química , Estrutura Molecular , Espectrofotometria Infravermelho
18.
Anal Bioanal Chem ; 412(1): 159-169, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31776642

RESUMO

Attenuated total reflectance-infrared (ATR-IR) spectroscopy is a robust tool for molecular characterisation of matter. Applied to semi-solid formulations, it enables rapid and reliable data collection without pre-analytical requirements. Based on nano-encapsulated Omegalight®, a skin-lightening active cosmetic ingredient (ACI), incorporated in a hydrogel, it is first demonstrated that, despite the high water content and the chemical complexity of the samples (i.e. number of ingredients), the spectral features of the ACI can be detected and monitored. Secondly, with a total of 105 samples divided into a training set (n = 60) and an unknown set (n = 45) covering a 0.5% w/w-5% w/w concentration range, the study further investigates the quantitative performance of ATR-IR coupled with partial least squares regression (PLSR). Through a step-by-step approach in testing different cross-validation protocols, accuracy (root mean square error of cross-validation (RMSECV)) and linearity between the experimental and predicted concentrations (R2) of ATR-IR are consistently evaluated to be respectively 0.097% (w/w) and 0.995 with a lower LOD = 0.067% (w/w). Subsequently, further evaluation of the accuracy (relative error of the predicted concentration compared with the true value, expressed as %) of the analysis was undertaken with the 45 unknown samples that were defined as unknown and analysed by PLSR. The outcome of the analysis demonstrates the ruggedness and the consistency of the determination performed using the ATR-IR data. With an average relative error of 2.5% w/w and only 5 samples out of 45 blind samples exhibiting a relative error above the 5% threshold, high accuracy quantification of the nano-encapsulated ACI can be unambiguously achieved by means of the label-free and non-destructive technique of ATR-IR spectroscopy. Ultimately, the study demonstrates that the analytical capabilities of ATR-IR hold significant potential for applications in the cosmetics industry, and although the path remains long, the present study is one step further to support validation of the technique, albeit for the specific case of Omegalight®.


Assuntos
Cosméticos/química , Espectrofotometria Infravermelho/métodos , Calibragem , Reprodutibilidade dos Testes
19.
Chemosphere ; 243: 125427, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-31778917

RESUMO

The quantization parameters, infrared and Raman spectra of 75 polychlorinated naphthalenes (PCNs) and 42 environmentally friendly CN-56 (CN-56: No. 56 PCN molecule; 1, 2, 3, 7, 8-PentaCN) molecules that are easier to degrade were first calculated via the density functional theory (DFT) method, and the structural characteristics of the molecules were analysed to obtain the substituent characteristics. The principal component analysis method was used to systematically analyse and summarize the effects of macroscopic substituent characteristics, microscopic quantitative parameters and spectral information on the biodegradability of PCNs and 42 environmentally friendly CN-56 molecules, and then the quantitative structure-activity relationship (QSAR), molecular docking and molecular dynamics simulation methods were used to further investigate the biodegradation mechanism from the perspective of molecules and protein receptors. The results showed that PCNs and new PCNs extracted 5 and 6 principal components from 21 kinds of original parameter indicators, respectively, which can effectively explain the original variable information. Besides that, electrostatic activity is the primary factor affecting the degradation of PCNs; reducing the para-substitution logarithm or increasing the total number of substituents and introducing electrostatic groups in the ortho or meta position of PCN molecules can design new PCN derivatives with higher degradability; enhancing the irradiation of Raman light or reducing the irradiation of infrared light properly can increase the biodegradation rate of PCN molecules.


Assuntos
Biodegradação Ambiental , Simulação de Acoplamento Molecular , Simulação de Dinâmica Molecular , Naftalenos/metabolismo , Análise de Componente Principal , Relação Quantitativa Estrutura-Atividade , Naftalenos/análise , Espectrofotometria Infravermelho , Análise Espectral Raman
20.
Bioelectrochemistry ; 132: 107443, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-31869700

RESUMO

Planar asymmetric lipid bilayers composed of phosphatidylethanolamine and phosphatidylglycerol lipids are transferred onto a gold electrode surface. Lipids containing two saturated, one monounsaturated and two monounsaturated hydrocarbon chains compose the model membranes. Results of electrochemically controlled polarization modulation infrared reflection absorption spectroscopy and quartz crystal microbalance with energy dissipation studies reveal two different types of electric potential-dependent structural rearrangements in the bilayers. They are correlated with the geometry of the lipid molecule. Packing parameter correlates the cross-section area of the hydrophobic and hydrophilic parts of amphiphilic molecules. In bilayers composed of lipids with the packing parameter <1, the hydrocarbon chains are tilted with respect to the bilayer plane and the polar head groups are well hydrated. At a threshold potential an abrupt flow of water through the bilayer is connected with membrane dehydration and upward orientation of the chains. In bilayers composed of lipids with packing parameter ≥1, electric potentials have negligible effect on the membrane structure. A simple rule correlating the packing parameter with molecular scale changes occurring at electrified membranes has a large diagnostic implication for biomimetic studies and our understanding of molecular processes occurring in biological cell membranes.


Assuntos
Eletrodos , Lipídeos/química , Membranas Artificiais , Interações Hidrofóbicas e Hidrofílicas , Bicamadas Lipídicas/química , Espectrofotometria Infravermelho/métodos
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA