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1.
Phys Chem Chem Phys ; 21(41): 22782-22793, 2019 Oct 24.
Artigo em Inglês | MEDLINE | ID: mdl-31595896

RESUMO

The theoretical assignment of electronic spectra of polyatomic molecules is a challenging problem that requires the specification of the character of a large number of electronic states. We propose a procedure for automatically determining the character of electronic transitions and apply it to the study of UV spectra of DNA bases in the gas phase and in the aqueous environment. The procedure is based on the computation of electronic wave function overlaps and accounts for an extensive sampling of nuclear geometries. Novelties of this work are the theoretical assignment of the electronic spectra of DNA bases up to 190 nm and a state specific analysis of solvation effects. By accounting for different effects contributing to the total solvent shift we obtained a good agreement between the computed and experimental spectra. Effects of vibrational averaging, temperature and solvent-induced structural changes shift excitation energies to lower values. Solvent-solute electrostatic interactions are state specific and strongly destabilize nRyd states, and to lesser extent nπ* and πRyd states. Altogether, this results in the stabilization of ππ* states and destabilization of nπ*, πRyd and nRyd states in solution.


Assuntos
Técnicas de Química Analítica/métodos , DNA/química , Solventes/química , Análise Espectral , Gases/química , Eletricidade Estática , Raios Ultravioleta
2.
Phys Chem Chem Phys ; 21(40): 22224-22229, 2019 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-31576857

RESUMO

The application of co-solvents and high pressure has been reported to be an efficient means to tune the kinetics of enzyme-catalyzed reactions. Co-solvents and pressure can lead to increased reaction rates without sacrificing enzyme stability, while temperature and pH operation windows are generally very narrow. Quantitative prediction of co-solvent and pressure effects on enzymatic reactions has not been successfully addressed in the literature. Herein, we are introducing a thermodynamic approach that is based on molecular interactions in the form of activity coefficients of substrate and of enzyme in the multi-component solution. This allowed us to quantitatively predict the combined effect of co-solvent and pressure on the kinetic constants, i.e. the Michaelis constant KM and the catalytic constant kcat, of an α-CT-catalyzed peptide hydrolysis reaction. The reaction was studied in the presence of different types of co-solvents and at pressures up to 2 kbar, and quantitative predictions could be obtained for KM, kcat, and finally even primary Michaelis-Menten plots using activity coefficients provided by the thermodynamic model PC-SAFT.


Assuntos
Quimotripsina/química , Fenilalanina/análogos & derivados , Dimetil Sulfóxido/química , Hidrólise , Cinética , Metilaminas/química , Fenilalanina/química , Pressão , Solventes/química , Termodinâmica , Ureia/química , Água/química
3.
Se Pu ; 37(11): 1209-1214, 2019 Nov 08.
Artigo em Chinês | MEDLINE | ID: mdl-31642274

RESUMO

Radial thin-layer chromatography (RTLC) is a form of chromatography in which the sample and developing agent/solvent are applied at the edge of a circle on the silica-layered TLC plate. The sample components are radially transported from the center of the circle toward the periphery by the solvent flow. RTLC is an efficient separation and semi-preparation method, with the advantages of fast separation, low diffusion, and absence of tailing at a certain distance. Although RTLC isolation has been well documented in the literature, there are only a few qualitative and quantitative reports on this technique. In this study, a self-programming module combined with image processing software was adopted for digital processing of RTLC images, and a digital atlas was created. Qualitative and quantitative verification of RTLC was then conducted. With the aid of computer technology, qualitative and quantitative methods of radially expanded TLC for Yiqing tablets were investigated. The results showed that the qualitative RTLC method has good reliability, but the quantitative RTLC method has inherent drawbacks, which may be associated with the experimental environment. We strongly believe that better separation and data acquisition equipment, as well as the combination of computer image processing and programming methods, will open up infinite possibilities of analysis/separation using RTLC-based techniques. We also believe that TLC will take a new step in the future with the assistance of computer technology.


Assuntos
Cromatografia em Camada Delgada/instrumentação , Medicamentos de Ervas Chinesas/análise , Processamento de Imagem Assistida por Computador , Reprodutibilidade dos Testes , Solventes , Comprimidos
4.
Bioresour Technol ; 294: 122173, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31586730

RESUMO

The simplified direct-transesterification (DT) process was compared to the conventional biodiesel production process based on a reported previous experimental work with economic standpoint. Based on the process flow diagram, capital and operating costs were itemized properly and then unit biodiesel production cost was calculated. The results show the biodiesel production costs were 18.2 $ kg-1 (conventional process) and 12.5 $ kg-1 (DT process), respectively. Sensitivity analysis shows the source of biomass and chemical consumption are the major factors to determine total biodiesel production cost. The affecting factors were a solvent recycling, yield of biodiesel, and plant capacity and these values were varied to evaluate the variation of unit biodiesel production cost. As a result, the maximized biodiesel production cost went down to 3.5 $ kg-1, which is cost-competitive with other reported values of production cost.


Assuntos
Microalgas , Biocombustíveis , Biomassa , Esterificação , Solventes
5.
Top Curr Chem (Cham) ; 377(6): 30, 2019 Oct 19.
Artigo em Inglês | MEDLINE | ID: mdl-31628623

RESUMO

Ionic liquids (ILs) are considered as highly useful materials for potential diverse uses such as greener and more convenient alternatives to volatile organic solvents, reagents, additives, ligands and co-solvents. Thermal stability, negligible vapor pressure and high polarity with ionic environments have possibly conferred some unique physico-chemical properties and a wider electrochemical window on ILs. More importantly, these properties are tuneable, depending on variations in alkyl chains and counter-anions. On the other hand, various transition-metal-catalyzed cross-coupling reactions constitute an important backbone of contemporary organic synthesis. A vast number of C-C and C-heteroatom cross-coupling reactions are reported in the presence of ILs, often showing better performance. The influence of IL on the action of a given catalyst or on the course of a reaction can be relatively complex, and is not understood well enough to be able to draw succinct conclusions. However, there are a few reports in the literature that help understand the role of actual and active catalytic species stabilized in an IL environment. Stabilization, which can be either helpful or detrimental to catalysis depends on specific circumstances. This review article is aimed primarily at summarizing the various applications of ILs during the past decade, focusing as far as possible on the task-specific properties of ILs in transition-metal-catalyzed C-C and C-heteroatom cross-coupling reactions. Several successful achievements and noteworthy progress in this field of research leads to the sensible conclusion that future prospects in this field of research are not only bright but promise new horizons.


Assuntos
Líquidos Iônicos/química , Catálise , Compostos Heterocíclicos/química , Ligantes , Metano/análogos & derivados , Metano/química , Solventes/química , Elementos de Transição/química
6.
J Chromatogr A ; 1604: 460473, 2019 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-31472937

RESUMO

A solvent-assisted vacuum desorption method is developed and combined with gas chromatography-tandem mass spectrometry (GC-MS/MS) for quick determination of soil PAHs. With the assistance of a reduced pressure of 0.0001 kPa and the DMSO/acetone (1:1) mixed solvent, this method allows desorption of PAHs in a moderate temperature of 160 °C. Analytes were trapped in a collection tube and eluted with n-hexan for GC-MS/MS analysis. The entire procedure can be completed within 20 min. In order to validate this method for determining soil PAHs, the solvent-assisted vacuum desorption method, Soxhlet extraction and ASE extraction were applied in different samples of real contaminated soils. Most HMW PAHs showed similar concentrations, yet LMW PAHs with solvent-assisted vacuum desorption presented significantly higher concentrations than those with conventional methods, such as NAP, ANY, ANA and FLU. Further investigation revealed that solvent-assisted vacuum desorption is capable of improving both the extractability and collection efficiency of those four LMW PAHs in real contaminated soil. This method enables desorption of HMW PAHs and provides the additional benefit of improved extractability and collection efficiency for LMW PAHs.


Assuntos
Monitoramento Ambiental/métodos , Cromatografia Gasosa-Espectrometria de Massas , Hidrocarbonetos Policíclicos Aromáticos/análise , Poluentes do Solo/análise , Solo/química , Solventes/química , Vácuo
7.
Shokuhin Eiseigaku Zasshi ; 60(4): 73-81, 2019.
Artigo em Japonês | MEDLINE | ID: mdl-31474654

RESUMO

Multilayer laminated films may contain organic solvents derived from adhesives, printing inks and so on. A headspace-GC/MS analysis method for the simultaneous determination of 30 substances such as toluene, xylene, acetone, methyl ethyl ketone, ethyl acetate, butyl acetate, methanol, ethanol, was developed. A N,N-dimethyl formamide solution containing an internal standard substance was added to the sample. After leaving overnight at room temperature, the headspace gas was analyzed by GC/MS. This method was applicable to a laminate film made of various materials. The organic solvents such as toluene, ethyl acetate, and heptane were detected from 6 out of 42 food packaging bags made from laminated film on Japanese market using this method.


Assuntos
Embalagem de Alimentos , Cromatografia Gasosa-Espectrometria de Massas , Solventes/análise
8.
Phys Chem Chem Phys ; 21(38): 21549-21560, 2019 Oct 02.
Artigo em Inglês | MEDLINE | ID: mdl-31536074

RESUMO

Repetitive cytosine rich i-motif forming sequences are abundant in the telomere, centromere and promoters of several oncogenes and in some instances are known to regulate transcription and gene expression. The in vivo existence of i-motif structures demands further insight into the factors affecting their formation and stability and development of better understanding of their gene regulatory functions. Most prior studies characterizing the conformational dynamics of i-motifs are based on i-motif forming synthetic constructs. Here, we present a systematic study on the stability and structural properties of biologically relevant i-motifs of telomeric and centromeric repeat fragments. Our results based on molecular dynamics simulations and quantum chemical calculations indicate that along with base pairing interactions within the i-motif core the overall folded conformation is associated with the stable C-HO sugar "zippers" in the narrow grooves and structured water molecules along the wide grooves. The stacked geometry of the hemi-protonated cytosine pairs within the i-motif core is mainly governed by the repulsive base stacking interaction. The loop sequence can affect the structural dynamics of the i-motif by altering the loop motion and backbone conformation. Overall this study provides microscopic insight into the i-motif structure that will be helpful to understand the structural aspect of mechanisms of gene regulation by i-motif DNA.


Assuntos
DNA/química , Substâncias Intercalantes/química , Motivos de Nucleotídeos , Solventes/química , Telômero/química , Pareamento de Bases , Citosina/química , Ligações de Hidrogênio , Simulação de Dinâmica Molecular
9.
Chem Pharm Bull (Tokyo) ; 67(9): 906-914, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31474728

RESUMO

An aminoalkyl methacrylate copolymer, Eudragit® E (EUD-E), has gained tremendous attention as a solid dispersion carrier because it efficiently stabilizes drugs in the amorphous state. Furthermore, EUD-E remarkably enhances drug dissolution in water. This review focuses on the interaction between drugs and EUD-E in solution, which contributes to the enhancement of drug concentration. Studies examining interactions between acidic drugs and EUD-E in organic solvents have revealed that the interaction occurs predominantly by electrostatic interaction, including hydrogen bonding and dipolar interactions. Other studies on interactions in aqueous solution found evidence for strong electrostatic interactions between acidic drugs and EUD-E in ion exchange experiments. 1H-NMR studies using high-resolution magic-angle spinning, nuclear Overhauser effect spectroscopy, diffusion, and relaxation time measurements successfully identified the interaction site and strength in aqueous solution. Hydrophobic and ionic interactions occurred between drugs and EUD-E. The conformation of EUD-E, which was affected by the ionic strength and pH of the aqueous media, also influenced the interaction. The knowledge discussed in this review will be helpful in designing solid dispersion formulations with EUD-E, which will efficiently enhance drug concentration and subsequent absorption into the body.


Assuntos
Preparações Farmacêuticas/química , Ácidos Polimetacrílicos/química , Água/química , Ligações de Hidrogênio , Concentração de Íons de Hidrogênio , Interações Hidrofóbicas e Hidrofílicas , Solubilidade , Solventes/química , Eletricidade Estática
10.
Chem Pharm Bull (Tokyo) ; 67(9): 953-958, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31474735

RESUMO

Asymmetric total syntheses of dihydropyran containing natural products, (+)-eurotiumide F and (+)-eurotiumide G have been described. These total syntheses revealed the absolute configuration of eurotiumide F and G, and confirmed the reported structure of eurotiumide F and revised the reported structure of eurotiumide G. Highlight of these syntheses is thermal rearrangement with 4-methoxyisochroman-1-one derivative having propargyl ether on phenolic ether under thermal condition to construct dihydropyran ring. X-Ray crystallographic analysis of (+)-eurotiumide G clarified the stereochemistry at the C1-position.


Assuntos
Produtos Biológicos/química , Piranos/química , Produtos Biológicos/síntese química , Cristalografia por Raios X , Conformação Molecular , Piranos/síntese química , Solventes/química , Estereoisomerismo
11.
BMC Bioinformatics ; 20(1): 464, 2019 Sep 09.
Artigo em Inglês | MEDLINE | ID: mdl-31500562

RESUMO

BACKGROUND: The function of oligomeric proteins is inherently linked to their quaternary structure. In the absence of high-resolution data, low-resolution information in the form of spatial restraints can significantly contribute to the precision and accuracy of structural models obtained using computational approaches. To obtain such restraints, chemical cross-linking coupled with mass spectrometry (XL-MS) is commonly used. However, the use of XL-MS in the modeling of protein complexes comprised of identical subunits (homo-oligomers) is often hindered by the inherent ambiguity of intra- and inter-subunit connection assignment. RESULTS: We present a comprehensive evaluation of (1) different methods for inter-residue distance calculations, and (2) different approaches for the scoring of spatial restraints. Our results show that using Solvent Accessible Surface distances (SASDs) instead of Euclidean distances (EUCs) greatly reduces the assignation ambiguity and delivers better modeling precision. Furthermore, ambiguous connections should be considered as inter-subunit only when the intra-subunit alternative exceeds the distance threshold. Modeling performance can also be improved if symmetry, characteristic for most homo-oligomers, is explicitly defined in the scoring function. CONCLUSIONS: Our findings provide guidelines for proper evaluation of chemical cross-linking-based spatial restraints in modeling homo-oligomeric protein complexes, which could facilitate structural characterization of this important group of proteins.


Assuntos
Reagentes para Ligações Cruzadas/química , Modelos Moleculares , Complexos Multiproteicos/química , Multimerização Proteica , Simulação de Acoplamento Molecular , Subunidades Proteicas/química , Solventes
12.
Bioresour Technol ; 293: 122036, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31479857

RESUMO

To improve the neutral DES (choline chloride/glycerol) pretreatment performance, three environmentally friendly heteropoly acids (phosphotungstic, phosphomolybdic and silicotungstic acids) were used as catalysts. Pretreatment with silicotungstic acid at 120 °C for 3 h resulted in 97.3% of enzymatic digestibility at an enzyme loading of 15FPU/g substrate, which was approximately eight times more than that of raw samples. More importantly, 80% of glucose yield was obtained within 12 h. Simultaneously, 81.8% of ethanol yield was achieved in the SSSF process. The efficient conversion was ascribed to the significant delignification (89.5%), which resulted in the exposure of more accessible specific surface area. This was attributed to that the proton (H+) from heteropoly acids could significantly contribute to the lignin degradation. Intriguingly, trace acetic acid (0.39 g/L) and HMF (0.21-0.95 g/L) in the pretreatment liquor were produced without any significant deleterious effects. These discoveries provide new insights for efficient biomass conversion under mild conditions.


Assuntos
Etanol , Lignina , Biomassa , Fermentação , Hidrólise , Solventes
13.
AAPS PharmSciTech ; 20(7): 273, 2019 Aug 05.
Artigo em Inglês | MEDLINE | ID: mdl-31385126

RESUMO

Orodispersible films (ODFs) are more convenient for paediatric and geriatric patients to take as compared to conventional tablets and capsules. Electrospinning has recently been attempted to produce ODFs. This study investigated the feasibility of formulating poorly water-soluble drug into ODFs using electrospinning technology coupled with the anti-solvent precipitation method. Piroxicam (PX), a poorly water-soluble drug, was chosen as a model drug. Polyvinyl alcohol and polyvinylpyrrolidone were used as film forming polymers. PX microcrystals were prepared using poloxamer as the stabilizer with the anti-solvent precipitation method, and then loaded in ODFs through the electrospinning process. The obtained ODFs were characterized using a scanning electron microscope, X-ray powder diffraction and Fourier transform infrared spectroscopy with respect to the morphology, solid state and potential molecular interaction between the model drug and polymers. The mechanical property, disintegration and dissolution rate of the obtained ODF were evaluated using dynamic mechanical analysis, a customized method and USP2 apparatus. The results showed that PX microcrystals suspended in polymeric solutions could be readily electrospun into fibrous films, where the microcrystals scattered between the fibers. The electrospun fibrous film-based ODFs exhibited satisfactory mechanical behaviour, and fast disintegration upon the polymer selection. In the dissolution tests, almost 90% of PX was dissolved within 6 min from the ODFs, whereas 40% of PX dissolved from physical mixtures in 60 min. This study demonstrated that poorly water-soluble drugs could be formulated into ODFs with satisfactory quality attributes by combining micronization and the electrospinning process.


Assuntos
Anti-Inflamatórios não Esteroides/síntese química , Química Farmacêutica/métodos , Portadores de Fármacos/síntese química , Piroxicam/síntese química , Água/química , Administração Oral , Cristalização , Humanos , Polímeros/química , Álcool de Polivinil/química , Solubilidade , Solventes/química , Espectroscopia de Infravermelho com Transformada de Fourier/métodos , Comprimidos , Difração de Raios X/métodos
14.
Chemistry ; 25(53): 12275-12280, 2019 Sep 20.
Artigo em Inglês | MEDLINE | ID: mdl-31389071

RESUMO

A range of oxobis(phenyl-1,3-butanedione) vanadium(IV) complexes have been successfully synthesized from cheap starting materials and a simple and solvent-free one-pot dry-melt reaction. This direct, straightforward, fast and alternative approach to inorganic synthesis has the potential for a wide range of applications. Analytical studies confirm their successful synthesis, purity and solid-state coordination, and we report the use of such complexes as potential drug candidates for the treatment of cancer. After a 24 hour incubation of A549 lung carcinoma cells with the compounds, they reveal cytotoxicity values elevenfold greater than cisplatin and remain non-toxic towards normal cell types. Additionally, the complexes are stable over a range of physiological pH values and show the potential for interactions with bovine serum albumin.


Assuntos
Antineoplásicos/farmacologia , Cisplatino/toxicidade , Complexos de Coordenação/síntese química , Vanádio/química , Animais , Antineoplásicos/síntese química , Antineoplásicos/química , Bovinos , Cisplatino/química , Complexos de Coordenação/química , Complexos de Coordenação/farmacologia , Humanos , Soroalbumina Bovina/química , Soroalbumina Bovina/metabolismo , Solventes
15.
Pharm Res ; 36(10): 142, 2019 Aug 02.
Artigo em Inglês | MEDLINE | ID: mdl-31376020

RESUMO

BACKGROUND: With the recent approval of the first small interfering RNA (siRNA) therapeutic formulated as nanoparticles, there is increased incentive for establishing the factors of importance for the design of stable solid dosage forms of such complex nanomedicines. METHODS: The aims of this study were: (i) to identify factors of importance for the design of spray-dried siRNA-loaded lipidoid-poly(DL-lactic-co-glycolic acid) hybrid nanoparticles (LPNs), and (ii) to evaluate their influence on the resulting powders by using a quality-by-design approach. Critical formulation and process parameters were linked to critical quality attributes (CQAs) using design of experiments, and an optimal operating space (OOS) was identified. RESULTS: A series of CQAs were identified based on the quality target product profile. The loading (ratio of LPNs to the total solid content) and the feedstock concentration were determined as critical parameters, which were optimized systematically. Mannitol was chosen as stabilizing excipient due to the low water content of the resulting powders. The loading negatively affected the colloidal stability of the LPNs, whereas feedstock concentration correlated positively with the powder particle size. The optimal mannitol-based solid formulation, defined from the OOS, displayed a loading of 5% (w/w), mass median aerodynamic diameter of 3.3 ± 0.2 µm, yield of 60.6 ± 6.6%, and a size ratio of 1.15 ± 0.03. Dispersed micro-embedded LPNs had preserved physicochemical characteristics as well as in vitro siRNA release profile and gene silencing, as compared to non-spray-dried LPNs. CONCLUSION: The optimal solid dosage forms represent robust formulations suitable for higher scale-up manufacturing.


Assuntos
Dessecação/métodos , Lipídeos/química , Nanopartículas/química , Copolímero de Ácido Poliláctico e Ácido Poliglicólico/química , RNA Interferente Pequeno/química , Administração por Inalação , Animais , Composição de Medicamentos , Excipientes/química , Inativação Gênica , Técnicas de Transferência de Genes , Manitol/química , Camundongos , Nanomedicina , Tamanho da Partícula , Pós , Células RAW 264.7 , RNA Interferente Pequeno/administração & dosagem , Solubilidade , Solventes/química
16.
Phys Chem Chem Phys ; 21(35): 19209-19215, 2019 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-31441478

RESUMO

Pure-shift NMR experiments provide highly resolved spectra, which could be perfect for precise monitoring of chemical shift variations under different conditions, such as temperature or concentration. However, their sensitivity is relatively low and signal sampling is time-consuming, which leads to long experimental times, making such serial acquisition problematic. In this paper we present a new method of NMR spectroscopy which improves the speed and sensitivity of serial pseudo-two-dimensional pure-shift experiments. The example of variable-temperature study of atorvastatin reveals the potential of the method in verifying the theoretical predictions of solvent-dependent spectral effects.


Assuntos
Atorvastatina/química , Técnicas de Química Analítica/métodos , Espectroscopia de Ressonância Magnética , Solventes/química , Temperatura Ambiente , Técnicas de Química Analítica/normas
17.
Phys Chem Chem Phys ; 21(35): 19469-19479, 2019 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-31461098

RESUMO

Using all-atom molecular dynamics simulations of aqueous solutions of the globular protein SNase, the dynamic behavior of water molecules and cosolvents (trimethylamine-N-oxide (TMAO) and urea) in the hydration shell of the protein was studied for different solvent compositions. TMAO is a potent protein-stabilizing osmolyte, whereas urea is known to destabilize proteins. For molecules that are initially located in successive narrow layers at a given distance from the protein, the mean displacements and the distribution of displacements for short time intervals are calculated. For molecules that are initially located in solvation shells of a given thickness around the protein, the characteristic residence times in these shells are determined to characterize the dynamic behavior of the solvent molecules as a function of the distance to the protein. A combined consideration of these characteristics allows to reveal additional features of the dynamics of the cosolvents. It is shown that TMAO molecules leave the nearest vicinity of the protein faster than urea molecules, despite the fact that the mobility of TMAO molecules, measured by their mean displacements, is lower than that of urea. Moreover, we show that the rate of release of TMAO molecules from the hydration shell is lower in ternary (TMAO + urea + H2O) solvent mixtures than in the binary ones. This is consistent with a recent observation that the fraction of TMAO near the protein decreases in the presence of urea. From the analysis of the decay of the number of particles initially located in the region of the first peak of the distribution function of solvent molecules around the protein, we estimated that about 20 water molecules and 6-7 urea molecules stay near the protein for more than 1000 ps.


Assuntos
Endodesoxirribonucleases/química , Endodesoxirribonucleases/metabolismo , Metilaminas/química , Simulação de Dinâmica Molecular , Ureia/química , Água/química , Estabilidade Proteica , Solventes/química
18.
Phys Chem Chem Phys ; 21(34): 18727-18740, 2019 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-31424463

RESUMO

The plant stress protein COR15A stabilizes chloroplast membranes during freezing. COR15A is an intrinsically disordered protein (IDP) in aqueous solution, but acquires an α-helical structure during dehydration or the increase of solution osmolarity. We have used small- and wide-angle X-ray scattering (SAXS/WAXS) combined with static and dynamic light scattering (SLS/DLS) to investigate the structural and hydrodynamic properties of COR15A in response to increasing solution osmolarity. Coarse-grained ensemble modelling allowed a structure-based interpretation of the SAXS data. Our results demonstrate that COR15A behaves as a biomacromolecule with polymer-like properties which strongly depend on solution osmolarity. Biomacromolecular self-assembly occurring at high solvent osmolarity is initiated by the occurrence of two specific structural subpopulations of the COR15A monomer. The osmolarity dependent structural selection mechanism is an elegant way for conformational regulation and assembly of COR15A. It highlights the importance of the polymer-like properties of IDPs for their associated biological function.


Assuntos
Proteínas de Arabidopsis/química , Proteínas Intrinsicamente Desordenadas/química , Concentração Osmolar , Conformação Proteica , Espalhamento a Baixo Ângulo , Solventes/química , Raios X
19.
J Phys Chem Lett ; 10(19): 5861-5867, 2019 Oct 03.
Artigo em Inglês | MEDLINE | ID: mdl-31464127

RESUMO

Circularly polarized luminescence (CPL) reflects the excited-state properties of the chiral system. However, compared to the singlet and triplet excited states, there are still many unknowns about CPL from the double excited state. Here, using the self-assembly strategy of a dipeptide substituted naphthalenediimide (NDI-GE) and the photogenerated radical anions, we have explored the ground-state (CD) and excited-state (CPL) chiral characteristics of neutral NDI and NDI•- radical anion assemblies. The neutral gelator assemblies showed CPL with the dissymmetry factor glum on the order of 10-3; the radical anion exhibited an inversed CPL signal with a significantly enhanced glum of 10-1. Time-dependent density functional theory calculation revealed that upon formation of the radical anions, the direction of the dipole moment changed, thus leading to the inversion of CD and CPL. The present work reveals a new platform for developing CPL materials based on the doublet excited state.


Assuntos
Dipeptídeos/química , Imidas/química , Naftalenos/química , Ânions/química , Teoria da Densidade Funcional , Dimerização , Cinética , Luminescência , Modelos Químicos , Modelos Moleculares , Processos Fotoquímicos , Solventes/química
20.
Phys Chem Chem Phys ; 21(32): 17893-17900, 2019 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-31380529

RESUMO

The dispersion interaction was reported to play a critical role in the stabilization of model dipeptide Z-Arg-OH, even greater than the conventional hydrogen bond (HB), which is opposite to the traditional opinion. Here the conformation of Z-Arg-OH has been systematically searched by the effective fragment based step-by-step strategy. All the newly-found low-energy conformers determined at the advanced DSD-PBEP86-D3(BJ)/aug-cc-pVTZ level are clearly in the stretched form with strong conventional HBs, rather than the reported folded structures with emphasis on the dispersion interactions. The simulated IR spectra of the stretched conformers fit better than those of the folded ones compared with the previous experimental observations. Near-edge X-ray absorption fine-structure (NEXAFS) spectra and X-ray photoelectron spectra (XPS) at C, N and O K-edges have also been simulated to unambiguously identify different isomers. This work thus provides valuable insight into the competitions between the conventional HB and the dispersion interactions and demonstrates that the conventional hydrogen bonding is still more important for such small peptides.


Assuntos
Arginina/análogos & derivados , Arginina/química , Dipeptídeos/química , Modelos Moleculares , Ligações de Hidrogênio , Isomerismo , Fenômenos Físicos , Conformação Proteica , Estabilidade Proteica , Solventes/química , Termodinâmica
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