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1.
J Phys Chem B ; 125(44): 12392-12397, 2021 Nov 11.
Artigo em Inglês | MEDLINE | ID: mdl-34705443

RESUMO

Unexpected hydrogel and coacervate are observed for dilute (1 mM) uranyl peroxide molecular cluster (Li68K12(OH)20[UO2(O2)(OH)]60, U60) solution in the presence of di- or trivalent salts. We report the mechanism as the formation of anisotropic two-dimensional (2-D) single-layer nanosheets, driven by counterion-mediated attraction due to the size disparity between U60 and small counterions. With weak monovalent cations, the nanosheets are bendable, resulting in hollow, spherical blackberry-type supramolecular assemblies in a homogeneous solution. With extra strong divalent or trivalent cations, the tough, free-standing sheets lead to gelation at ∼1 mM U60. These stiff nanosheets are difficult to bend into spherical blackberry-type structures; instead, they stay in solution and form hydrogel based on their significant excluded volumes. At higher ionic strength, the large, thin filmlike nanosheet structures stack together more compactly and consequently lead to the transition from gel phase to a coacervate phase, another surprise since it was formed without the presence of bulky polycations.

2.
Chem Sci ; 12(36): 12130-12137, 2021 Sep 22.
Artigo em Inglês | MEDLINE | ID: mdl-34667578

RESUMO

We report herein that dendron-shaped macromolecules AB n crystallize into well-ordered pyramid-like structures from mixed solvents, instead of spherical motifs with curved structures, as found in the bulk. The design of the asymmetric molecular architecture and the choice of mixed solvents are applied as strategies to manipulate the crystallization process. In mixed solvents, the solvent selection for the Janus macromolecule and the existence of dominant crystalline clusters contribute to the formation of flat nanosheets. Whereas during solvent evaporation, the bulkiness of the asymmetric macromolecules easily creates defects within 2D nanosheets which lead to their spiral growth through screw dislocation. The size of the nanosheets and the growth into 2D nanosheets or 3D pyramidal structures can be regulated by the solvent ratio and solvent compositions. Moreover, macromolecules of higher asymmetry generate polycrystals of lower orderliness, probably due to higher localized stress.

3.
Microb Biotechnol ; 2021 Jul 26.
Artigo em Inglês | MEDLINE | ID: mdl-34310825

RESUMO

Edeines, a group of cationic antimicrobial peptides produced by the soil bacterium Brevibacillus, have broad biological effects, such as antimicrobial, anticancer and immunosuppressive activities. However, the yield of edeines in wild-type (WT) Brevibacillus is extremely low, and chemical synthesis of edeines is a time-consuming process. Genetic engineering has proven to be an effective approach to produce antibiotics with high yield. In this study, the edeine biosynthetic gene cluster (ede BGC), which is involved in edeine production, was identified and characterized in Brevibacillus brevis X23. To improve edeine production in B. brevis X23, the ede BGC promoter was replaced with six different promoters, Pmwp , Pspc , PxylA , Pshuttle-09 , Pgrac or P43 , through double-crossover homologous recombination. The new promoters significantly increased the expression of the ede BGC as well as edeine production by 2.9 ± 0.4 to 20.5 ± 1.2-fold and 3.6 ± 0.1to 8.7 ± 0.7-fold respectively. The highest yield of edeines (83.6 mg l-1 ) was obtained in B. brevis X23 with the Pmwp promoter. This study provides a practical approach for producing high yields of edeines in B. brevis.

4.
Environ Res ; 200: 111715, 2021 09.
Artigo em Inglês | MEDLINE | ID: mdl-34297933

RESUMO

Plant leaves are colonized by a remarkably diverse fungal microbiome, which contributes to host plant growth and health. However, responses of foliar fungal community to phytopathogen invasion and measures of the fungal community taken to resist or assist pathogens remain elusive. By utilizing high-throughput sequencing of internal transcribed spacer (ITS) amplicons, we studied the relationships between the foliar fungal community around the disease spot and the pathogen of brown spot disease. The pathogenic Alternaria was found to follow a dramatically decreased trend from the disease spot to its surrounding fungal communities, whose community structure also diverged substantially away from the disease spot community. With the increase of pathogenic Alternaria, diversity indexes, including Shannon, Pielou and Simpson, showed a trend of increasing first and then decreasing. Total network links and the average path distance exhibited strong negative and positive correlations with Alternaria, respectively. Five keystone members showed direct interactions with pathogenic Alternaria. Members of Botryosphaeria, Paraphoma and Plectosphaerella might act as key 'pathogen facilitators' to increase the severity and development of brown spot disease, while Pleospora and Ochrocladosporium might be important 'pathogen antagonists' to suppress the expansion of pathogenic Alternaria. Our study provides new insights in developing new strategies for leaf disease prediction or prevention.


Assuntos
Alternaria , Micobioma , Folhas de Planta
5.
BMC Microbiol ; 21(1): 184, 2021 06 17.
Artigo em Inglês | MEDLINE | ID: mdl-34139992

RESUMO

BACKGROUND: To investigate the ecological effects of chemical and biological control methods on tobacco wildfire disease, a plot field experiment was conducted to compare the control efficiency and mechanisms of a chemical pesticide (kasugamycin wettable powder, KWP) and a biological control agent (BCA) through high-throughput sequencing of bacterial 16S rRNA genes. RESULTS: The results showed that the BCA displayed better performance in decreasing the disease index and morbidity of tobacco than the chemical pesticide. By monitoring the endophytic community within tobacco leaves, it was found that the control effects of these two methods might be mediated by different changes in the endophytic bacterial communities and community assembly patterns. The application of either method decreased the taxonomic diversity of the leaf endophytic community. Compared to the BCA, KWP showed a more significant effect on the endophytic community structure, while the endophytic community treated with the BCA was able to return to the original state, which presented much lower disease infection. The disease control efficiency of KWP and BCA treatments might be achieved by increasing the abundance of Sphingomonas and Streptophyta, respectively. Furthermore, an analysis of the ecological processes in community assembly indicated that the BCA strengthened the homogeneous and variable selection, while KWP enhanced ecological drift. CONCLUSIONS: The results suggested different control mechanisms between KWP and BCA treatments, which will help in developing diverse ecological strategies for plant disease control.

6.
Environ Microbiol ; 23(7): 3896-3912, 2021 07.
Artigo em Inglês | MEDLINE | ID: mdl-33913568

RESUMO

Alicyclobacillus species inhabit diverse environments and have adapted to broad ranges of pH and temperature. However, their adaptive evolutions remain elusive, especially regarding the role of mobile genetic elements (MGEs). Here, we characterized the distributions and functions of MGEs in Alicyclobacillus species across five environments, including acid mine drainage (AMD), beverages, hot springs, sediments, and soils. Nine Alicyclobacillus strains were isolated from AMD and possessed larger genome sizes and more genes than those from other environments. Four AMD strains evolved to be mixotrophic and fell into distinctive clusters in phylogenetic tree. Four types of MGEs including genomic island (GI), insertion sequence (IS), prophage, and integrative and conjugative element (ICE) were widely distributed in Alicyclobacillus species. Further, AMD strains did not possess CRISPR-Cas systems, but had more GI, IS, and ICE, as well as more MGE-associated genes involved in the oxidation of iron and sulfide and the resistance of heavy metal and low temperature. These findings highlight the differences in phenotypes and genotypes between strains isolated from AMD and other environments and the important role of MGEs in rapid environment niche expansions.


Assuntos
Alicyclobacillus , Alicyclobacillus/genética , Elementos de DNA Transponíveis/genética , Ilhas Genômicas , Mineração , Filogenia
7.
Angew Chem Int Ed Engl ; 60(11): 5833-5837, 2021 Mar 08.
Artigo em Inglês | MEDLINE | ID: mdl-33295092

RESUMO

The accurate distribution of countercations (Rb+ and Sr2+ ) around a rigid, spherical, 2.9-nm size polyoxometalate cluster, {Mo132 }42- , is determined by anomalous small-angle X-ray scattering. Both Rb+ and Sr2+ ions lead to shorter diffuse lengths for {Mo132 } than prediction. Most Rb+ ions are closely associated with {Mo132 } by staying near the skeleton of {Mo132 } or in the Stern layer, whereas more Sr2+ ions loosely associate with {Mo132 } in the diffuse layer. The stronger affinity of Rb+ ions towards {Mo132 } than that of Sr2+ ions explains the anomalous lower critical coagulation concentration of {Mo132 } with Rb+ compared to Sr2+ . The anomalous behavior of {Mo132 } can be attributed to majority of negative charges being located at the inner surface of its cavity. The longer anion-cation distance weakens the Coulomb interaction, making the enthalpy change owing to the breakage of hydration layers of cations more important in regulating the counterion-{Mo132 } interaction.

8.
ACS Appl Mater Interfaces ; 12(50): 56310-56318, 2020 Dec 16.
Artigo em Inglês | MEDLINE | ID: mdl-33269903

RESUMO

We report the mechanism of hydrogel formation in dilute aqueous solutions (>15 mg/mL) by 2 nm metal-organic cages (MOCs). Experiments and all-atom simulations confirm that with the addition of small electrolytes, the MOCs self-assemble into 2D nanosheets via counterion-mediated attraction because of their unique molecular structure and charge distribution as well as σ-π interactions. The stiff nanosheets are difficult to bend into 3-D hollow, spherical blackberry type structures, as observed in many other macroion systems. Instead, they stay in solution and their very large excluded volumes lead to gelation at low (∼1.5 wt %) MOC concentrations, with additional help from hydrophobic and partial π-π interactions similar to the gelation of graphene oxides.

9.
Chem Commun (Camb) ; 56(97): 15341-15344, 2020 Dec 18.
Artigo em Inglês | MEDLINE | ID: mdl-33231249

RESUMO

Zwitterionic Ni(ii)-catalyzed carbonylative copolymerization of ethylene and cyclic ethers for the synthesis of photolytically and hydrolytically degradable polymers is reported. The segmented tetrapolymer products are composed of polyketone segments from alternating enchainments of CO and ethylene and poly(ether-co-ester) segments from non-alternating enchainments of CO, ethylene oxide, and tetrahydrofuran. Plastic and elastic products can be obtained via the general synthetic platform with the appropriate choice of catalyst and polymerization conditions.

10.
J Phys Chem B ; 124(44): 9958-9966, 2020 11 05.
Artigo em Inglês | MEDLINE | ID: mdl-33085899

RESUMO

The role of chiral counterions on the attraction and self-assembly of chiral Pd12L24 metal organic cages (MOCs) with NO3- being the original counterion is studied by laser light scattering and isothermal titration calorimetry. Nitrates can trigger the self-assembly of macrocationic Pd12L24 into hollow spherical blackberry-type supramolecular structures via counterion-mediated attraction. Although chiral counteranions, such as N-(tert-butoxycarbonyl)-alanine (Boc-Ala), have weaker interaction with the MOCs compared to NO3-, they can induce different assembly behaviors between two enantiomeric MOCs by inhibiting the MOC-nitrate binding and weakening the interaction between them. The d-counterions are capable of selectively suppressing and slowing down the assembly of l-MOCs and also considerably decreasing their assembly size due to the much weaker MOC-nitrate interaction. The same scenario is observed for l-counterions when interacting with the d-MOCs. This study unveils the role of weakly associated chiral counterions on the central chiral macroions, especially their supramolecular structure formation, and provides additional evidence on the mechanism of the homochirality phenomenon.

11.
Cancer Cell Int ; 20: 500, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-33061852

RESUMO

Background: Cervical cancer is the second leading cause of death in women 20-39 years old. Because coverage for cervical cancer screening is low, and the vaccination rate of human papillomavirus (HPV) is poor in some countries, potential markers to detect the disease at early stages are needed. E2F transcription factors (E2Fs) are a family of transcription factors that function in cell proliferation, differentiation, apoptosis, and tumorigenesis. As abnormal activation and regulation of E2Fs are related to tumor development and poor prognosis, we performed bioinformatic analyses and in vitro assays to evaluate the role of E2Fs in cervical cancer. Methods: Transcriptional expression of E2Fs was initially evaluated in silico using ONCOMINE and Gene Expression Profiling Interactive Analysis (GEPIA), followed by evaluation of E2F1/2/7/8 protein levels using immunohistochemistry in 88 patient tissues. E2F2 and E2F7 mRNA levels were measured by RT-qPCR. LinkedOmics and Metascape were used to predict functions of E2Fs, and in vitro experiments were performed to assess the tumorigenic role of E2F2 and E2F7. Results: In silico analysis showed that E2F1/2/7/8 were significantly overexpressed in cervical cancer, findings which were confirmed at the protein level using immunohistochemistry. Further, upregulation of E2F1/2/7/8 was associated with different clinicopathological prognostic factors, including positivity for lymph vessel invasion and deep invasion of cervical stroma. Increased expression of E2F1/2/7/8 was also related to shorter overall survival (OS) and disease-free survival (DFS) in patients with cervical cancer. Using multivariate analysis, we confirmed E2F1/2/7/8 as independent prognostic factors for shorter OS of patients with cervical cancer. Finally, in vitro experiments showed that E2F2 and E2F7 are involved in cell proliferation and migration and cell cycle regulation in both HPV-positive and HPV-negative cervical cancer cells. Conclusions: E2F1/2/7/8 may be prognostic biomarkers for survival of patients with cervical cancer. E2F2 and E2F7 are involved in cell proliferation, migration, and cell cycle in both HPV-positive and HPV-negative cervical cancer cells.

12.
Chempluschem ; 85(10): 2316-2319, 2020 10.
Artigo em Inglês | MEDLINE | ID: mdl-33058510

RESUMO

We report a feasible method to control self-recognition during the self-assembly of a hydrophilic macroion, phosphate-functionalized γ-cyclodextrin (γ-CD-P), though host-guest interactions. We confirmed that γ-CD-P can form a host-guest complex with a super-chaotropic anion, namely the B12 F12 2- borate cluster, by using NMR spectroscopy and isothermal titration calorimetry. The loaded γ-CD-P, which has a higher charge density, can be distinguished from the uncomplexed γ-CD-P, leading to self-sorting behavior during the self-assembly process, confirmed by the formation of two types of individual supramolecular structures (Rh of ca. 57 nm and 18 nm, determined by light scattering) instead of hybrid structures in mixed dilute solution. This self-recognition behavior is accounted for by the difference in intermolecular electrostatic interactions arising from the loading.

13.
Chem Commun (Camb) ; 56(84): 12849-12852, 2020 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-32969428

RESUMO

We present a single molecular polyoxometalate cluster (K41[(P2W12Nb6O62)6{Mn3(OH)3(H2O)6}4{Mn3Na(H2O)16}]·26H2O) with controllable release of a large number of protons (∼40 per molecule) in its aqueous solution upon addition of a base. The deprotonation/protonation process is reversible with the clusters remaining intact. This molecule can also absorb up to 11 protons per cluster when an acid, HCl, was added to its original aqueous solution. To the best of our knowledge, such large proton absorption/release capacity along with excellent stability is unprecedented.

14.
J Am Chem Soc ; 142(41): 17508-17514, 2020 10 14.
Artigo em Inglês | MEDLINE | ID: mdl-32965108

RESUMO

Polyoxometalate molybdenum blue (MB) complexes typically exist as discrete multianionic clusters and are composed of repeating Mo building units. MB wheels such as {Mo176} and {Mo154} are made from pentagon-centered {Mo8} building blocks joined by equal number of {Mo1} units as loin, and {Mo2} dimer units as skirt along the ring edge, with the ring sizes of the MB wheels modulated by the {Mo2} units. Herein we report a new class of contracted lanthanide-doped MB structures that have replaced all the {Mo2} units with lanthanide ions on the inner rim, giving the general formula {Mo90Ln10}. We show three examples of this new decameric {Mo90Ln10} (Ln = La, Ce, and Pr) framework synthesized by high temperature reduction and demonstrate that later Ln ions result in {Mo92Ln9} (Ln = Nd, Sm), conserving one {Mo2} linker unit in its structure, as a consequence of the lanthanide contraction. Remarkably the {Mo90Ln10} compounds are the first examples of charge-neutral molybdate wheels as confirmed by BVS, solubility experiments, and redox titrations. We detail our full synthetic optimization for the isolation of these clusters and complete characterization by X-ray, TGA, UV-vis, and ICP studies. Finally, we show that this fine-tuned self-assembly process can be utilized to selectively enrich Ln-MB wheels for effective separation of lanthanides.

15.
Chemistry ; 26(70): 16802-16810, 2020 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-32844449

RESUMO

Keggin clusters are the most widely used polyoxometalate building blocks for the construction advanced materials, but effective methods for precisely recognizing the isostructural analogues of Keggins are still limited. In this study we employed the zwitterionic molecule 4,4'-dipyridyl N,N'-dioxide as a recognition receptor to specifically bind to the three Keggin analogues PW12 O40 3- , PMo12 O40 3- , and SiW12 O40 4- , which separately co-assembled into three different types of spherical charged colloids of different sizes. The recognition phenomena were confirmed by electrochemical methods and their crystallization behavior. Compared with solely anion-cation interaction-driven systems, the synergism with the anion-π interactions between the superchaotropic Keggins and the electron-deficient pyridine rings is believed to enhance the recognition. This observation is intriguing as the long-range solution assembly of Keggins is mainly driven by short-range anion-π interactions. Our results show that the little-noticed hydration shell of Keggins is significantly influenced by the superchaotropic effect, leading to differentiated binding affinity to the receptors and more obvious recognition phenomena between tungsten/molybdenum Keggin analogues.

16.
Langmuir ; 36(35): 10519-10527, 2020 Sep 08.
Artigo em Inglês | MEDLINE | ID: mdl-32787054

RESUMO

Macroions, as soluble ions with a size on the nanometer scale, show unique solution behavior different from those of simple ions and large colloidal suspensions. In macroionic solutions, the counterions are known to be important and well-explored. However, the role of co-ions (ions carrying the same type of charge as the macroions) is often ignored. Here, through experimental and simulation studies, we demonstrate the role of co-ions as a function of co-ion size on their interaction with the macroions (using {Mo72Fe30} and {SrPd12} as models) and the related self-assembly into blackberry-type structures in dilute solutions. Several regimes of unique co-ion effects are clearly identified: small ions (halides, oxoacid ions), subnanometer-scaled bulky ions (lacunary Keggin and dodecaborate ions), and those with sizes comparable to the macroions. Small co-ions have no observable effect on the self-assembly of fully hydrophilic {Mo72Fe30}, while due to hydrophobic interaction and intermolecular hydrogen bonds, the small co-ions show influences on the self-assembly of hydrophobic {SrPd12}. Subnanometer ions, a.k.a. "superchaotropic ions", are still too small to assemble into a blackberry by themselves, but they can coassemble with the macroions, showing a strong interaction with the macroionic system. When the co-ion size is comparable to that of the macroions, they assemble independently instead of assembling with the macroions, leading to the previously reported unique self-recognition phenomenon for macroions.

17.
ACS Omega ; 5(32): 20122-20133, 2020 Aug 18.
Artigo em Inglês | MEDLINE | ID: mdl-32832766

RESUMO

Lysine ubiquitination, a widely studied posttranslational modification, plays vital roles in various biological processes in eukaryotic cells. Although several studies have examined the plant ubiquitylome, no such research has been performed in tobacco, a model plant for molecular biology. Here, we comprehensively analyzed lysine ubiquitination in tobacco (Nicotiana tabacum) using LC-MS/MS along with highly sensitive immune-affinity purification. In total, 964 lysine-ubiquitinated (Kub) sites were identified in 572 proteins. Extensive bioinformatics studies revealed the distribution of these proteins in various cellular locations, including the cytoplasm, chloroplast, nucleus, and plasma membrane. Notably, 25% of the Kub proteins were located in the chloroplast of which 21 were enzymatically involved in important pathways, that is, photosynthesis and carbon fixation. Western blot analysis indicated that TMV infection can cause changes in ubiquitination levels. This is the first comprehensive proteomic analysis of lysine ubiquitination in tobacco, illustrating the vital role of ubiquitination in various physiological and biochemical processes and representing a valuable addition to the existing landscape of lysine ubiquitination.

18.
Exp Cell Res ; 396(1): 112241, 2020 11 01.
Artigo em Inglês | MEDLINE | ID: mdl-32835657

RESUMO

Epithelial-mesenchymal transition (EMT) is an important contributor to drug resistance in ovarian cancer. The aims of this study were to explore the potential role of the miR-302 cluster in modulating EMT and cisplatin resistance in ovarian cancer. We used qRT-PCR and western blotting to show that miR-302 expression was lower in chemoresistant than in chemosensitive cells, and miR-302 was upregulated in chemosensitive, but not chemoresistant ovarian cancer cells in response to cisplatin treatment. We identified ATAD2 as a target of miR-302 and showed that ectopic expression of miR-302 increased cisplatin sensitivity and inhibited EMT and the invasiveness of cisplatin-resistant cells in vitro by targeting ATAD2. Knockdown of ATAD2 restored cisplatin sensitivity and reversed EMT/metastasis in cisplatin-resistant cells, as shown by western blotting and invasion/migration assays. The effect of miR-302 overexpression on EMT and invasiveness was mediated by the modulation of ß-catenin nuclear expression. Immunofluorescence analysis showed that ATAD2 overexpression reversed the miR-302-induced downregulation of nuclear ß-catenin in cisplatin resistant cells. A xenograft tumor model was used to show that miR-302 increases the antitumor effect of cisplatin in vivo. Taken together, these results identify a potential regulatory axis involving miR-302 and ATAD2 with a role in chemoresistance, indicating that activation of miR-302 or inactivation of ATAD2 could serve as a novel approach to reverse cisplatin resistance in ovarian cancer.


Assuntos
ATPases Associadas a Diversas Atividades Celulares/genética , Antineoplásicos/farmacologia , Carcinoma Epitelial do Ovário/genética , Cisplatino/farmacologia , Proteínas de Ligação a DNA/genética , Resistencia a Medicamentos Antineoplásicos/genética , MicroRNAs/genética , Neoplasias Ovarianas/genética , ATPases Associadas a Diversas Atividades Celulares/metabolismo , Animais , Antagomirs/genética , Antagomirs/metabolismo , Carcinoma Epitelial do Ovário/tratamento farmacológico , Carcinoma Epitelial do Ovário/metabolismo , Carcinoma Epitelial do Ovário/patologia , Linhagem Celular Tumoral , Movimento Celular/efeitos dos fármacos , Proliferação de Células/efeitos dos fármacos , Proteínas de Ligação a DNA/metabolismo , Transição Epitelial-Mesenquimal/efeitos dos fármacos , Transição Epitelial-Mesenquimal/genética , Feminino , Regulação Neoplásica da Expressão Gênica , Humanos , Camundongos Endogâmicos BALB C , Camundongos Nus , MicroRNAs/agonistas , MicroRNAs/antagonistas & inibidores , MicroRNAs/metabolismo , Oligorribonucleotídeos/genética , Oligorribonucleotídeos/metabolismo , Neoplasias Ovarianas/tratamento farmacológico , Neoplasias Ovarianas/metabolismo , Neoplasias Ovarianas/patologia , Transdução de Sinais , Carga Tumoral , Ensaios Antitumorais Modelo de Xenoenxerto
19.
Cancer Cell Int ; 20: 396, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32821249

RESUMO

Background: This research aimed to investigate the association between tumor necrosis factor-a-induced protein 8 (TNFAIP8) polymorphisms and ovarian cancer (OC) susceptibility. Methods: A case-control study of 210 patients with OC and 231 healthy controls was conducted to assess the association between TNFAIP8 polymorphisms (rs11064, rs1045241, and rs1045242) and OC risk in Heilongjiang Province of China. The SNaPshot SNP assay was conducted to detect SNP genotype. Logistic regression analysis was applied to illustrate the underlying association. Results: Our research found that TNFAIP8 rs11064 and rs1045242 were significantly connected with the susceptibility of OC. Additionally, rs1045242 increased the risk of OC, while rs11064 performed a protective role in the risk of OC. Data revealed that rs1045242 strongly related with advanced FIGO stage, larger residual tumor, and the presence of recurrence. Conclusions: TNFAIP8 genetic variants, which may play difference roles, were significantly associated with OC susceptibility. The underlying molecular mechanism needs be clarified with scientific evidence.

20.
J Phys Chem B ; 124(29): 6288-6298, 2020 07 23.
Artigo em Inglês | MEDLINE | ID: mdl-32600044

RESUMO

Proteins and their mimics that contain negatively charged sequences are important in natural and biomimetic mineralization. The mechanism by which these sequences affect calcium phosphate mineralization is not well understood. Here, peptides containing different numbers of repeat units of contiguous glutamic acid residues, oligo(l-glutamic acid)n (n = 3, 7, 8, 10), were investigated with regards to the mechanism in delaying the crystallization of amorphous calcium phosphate (ACP) while holding the amount of carboxylic acid groups in solution constant. Increasing peptide chain length increases the stability of ACP at a certain total amount of carboxylic acid groups in solution. This effect is shown to be due to stronger binding as well as binding to more calcium ions per peptide by the longer oligopeptides compared to the shorter ones. It is proposed that these associations delay the structural rearrangement of calcium ions and the dehydration of ACP, which are required for the crystallization of hydroxyapatite. The initial nucleation and the local structure of ACP, however, do not vary with chain length. This second part of a two-part series provides an improved mechanistic understanding of how organic additives, especially those with contiguous acidic amino acid sequences, modulate the kinetics of calcium phosphate precipitation and phase transformation.


Assuntos
Fosfatos de Cálcio , Ácido Glutâmico , Cálcio , Cristalização , Durapatita , Cinética
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