Small Angle X-ray Scattering Techniques Research Articles

Structural Features of the Porous Network of Poly(Urethane) Aerogels via Gas Permeability Measurements.

The permeability for gases through polyurethane (PUR) aerogels prepared from unsorted PUR scraps by means of a recycling technique is measured with a dynamic pressure method. The permeabilities are in the range of 10-15 to 10-13 m2 and thus reflect the pore morphology observed with scanning electron microscopy. The permeability depends on the envelope density and microstructural features of the aerogels and decreases with increasing inner surface area. The comparison of the permeability with the Porod constant, which is obtained independently via small-angle X-ray scattering (SAXS), yields a high consistency with the expected theoretical relationship. However, a calculation of inner surface area based on permeability yields lower results than expected from data based on the established SAXS technique, revealing that the famous Carman-Kozeny law correlates only by trend, which is attributed to additional gas transport through the micro- and mesopores. A possible approach for the correlation of this behavior to the tortuosity is given. Several models accounting for the combined action of viscous flow, Knudsen diffusion, and molecular slip along pore walls are fitted to the experimental data, effectively qualifying the permeability measurement as time-efficient and inexpensive technique for the characterization of structural features ofaerogels.

Synchrotron radiation SAXS study of the species structure evolution in the synthesis process of MCM-56 zeolite

In the process of synthesizing zeolite, the evolution behavior of aluminosilicate species is crucial for investigating the crystallization mechanism and controlling the structure of desired zeolite. Herein, the synthesis process of MCM-56 zeolite was investigated by using the synchrotron radiation Small Angle X-ray Scattering (SAXS) technique. Based on the distance distribution function curves and Porod analysis, the particle distribution of the sol in the synthesis system transformed from a monodisperse spherical particle to a polydisperse lamellar structure. The results indicated that the particle size distribution, fractal dimension, and the evolution behavior of particles in sol vary with the variation of crystallization time. Specifically, the initial step involves the depolymerization of particles forming small particles approximately 1 nm. Subsequently, these small particles polymerize to form structural units ranging in size from 1 to 5 nm, and finally grow to form MCM-56 zeolite crystal by consuming aluminosilicate species. The SAXS results in conjunction with the XRD, SEM, FT-IR, and N2 adsorption-desorption analysis elucidate the evolution of aluminosilicate species and the crystallization process of MCM-56 zeolite at three stages, including the induction/nucleation period (0–84 h), the crystal growth period (84–108 h) and the crystal stability period (108–168 h). By virtue of the understanding for the structural evolution of the sol species, this work is expected to highlight the controllable synthesis of MCM-56 zeolite.

Small-Angle X-ray Scattering (SAXS) Used for the Identification of Nicomorphine Polymorphic Changes at the Early Stage to Avoid Varied Stability and Possible Side Effects.

In this paper, we present the identification of polymorphisms at an early stage, identified by applying non-standard methods such as SAXS. We provide an analytical approach to polymorphism in the quality/purity of an active pharmaceutical ingredient (API), supplied to a generic company by two different suppliers (i.e., manufacturers). Changes in thermodynamic polymorphism firstly become visible in traces in the larger crystal lattices, which are visible on the SAXS spectrum only using the logarithmic scale, as shown in the result figures. Hence, we are here on the trail of the beginning of a new polymorph in nicomorphine, whose crystal waviness at the early stage is visible only in the additional symmetrical peaks identified and calculated using SAXS, while the chemical analyses excluded all kinds of chemical impurities. The chemical and structural properties were studied using the following techniques: SAXS, WAXS, DSC, dissolution, Raman spectroscopy, and FTIR. Only the SAXS technique could identify crucial differences and calculate the additional signals related to giant crystals, whilst a standard method such as WAXS showed none, and nor did the chemical analyses, such as Raman spectroscopy and FT-IR. This means that due to water in crystallization (known in nicomorphine) or thermodynamic waviness, the formation of the new polymorph starts first in traces, which become visible at larger distances from the crystal lattice, detectible only in the SAXS range. This is a very important premise and hypothesis for further research, and we believe that this work lays a new stone in understanding the origin of new unknown polymorphs and their mixtures. Therefore, the aim of this work is to show that the use of non-standard methods (i.e., SAXS) can be of great benefit to API analysis and the identification of polymorphic changes in the early phase, which can cause varied stability, solubility and bioavailability and thus different therapeutic effects or side effects.

Applications of X-ray micro-computed tomography and small-angle X-ray scattering techniques in food systems: A concise review

X-ray micro-computed tomography (X-ray μ-CT) is a non-destructive method that allows visualization of the internal microstructures of materials through the creation of 3D volumetric data in different spatial scales. It has been successfully applied in the field of food science to study the internal microstructures of different food materials, e.g., bread and pastry products, different seeds, and frozen food products among others. Small-angle X-ray scattering (SAXS) is also a powerful non-destructive method used for the micro or nano-structural analysis of dry or partly-hydrated materials, gels, and solutions. It is used to study the particle size and its distribution, shape, molecular orientation and structure of a material. This review reports the applications of X-ray μ-CT and SAXS techniques in food systems and their prospects in the field of food science. Some of the limitations of these techniques are cost and time constraints, image artifacts, and inaccessibility of synchrotron facilities for high-resolution research applications which are also discussed. • X-ray micro-tomography is used to visualize the internal microstructures of food materials. • Small-angle X-ray scattering is used to analyze the structures of food materials. • X-rays generated from synchrotron facilities are more suitable for fast dynamic studies due to the fast measurements possible. • Baked goods, frozen foods, grains and meat products have been studied using X-ray imaging systems. • X-ray imaging methods are excellent tools to understand the structure and compositions of food materials.

Quantitative evaluation of the effect of Ag-addition on the concurrently-existing precipitation kinetics in the aged Al-Cu-Mg(-Ag) alloys

Two Al-Cu-Mg(-Ag) aluminium alloys, having the same base composition of Al-5.11Cu-0.96 Mg-0.58Mn-0.12Zr (wt.%) but different Ag contents, 0 and 0.7 Ag (wt.%), and accordingly denoted 0A and 7A samples, were aged at 185 °C. In early-ageing, the formation of disk-like Mg-Cu and Mg-Ag nano(co–)clusters can be quantitatively examined by Small angle X-ray scattering (SAXS), respectively. In the prolonged ageing of the 0A samples, the thickening in the disk-like θ-precipitates leads to a lower aspect ratio. For S-precipitates, the change in the total surface area and the single-particle surface area indicates that the coalescence mechanism is prevalent from peak-ageing to over-ageing, and then after over-ageing, the precipitate coarsening dominates. The coarsening in S and θ precipitates presumably leads to a lower mechanical strength. Alternatively, in the aged 7A sample, the SAXS technique in conjunction with transmission electron microscopy (TEM) quantitatively reveals Ω-precipitates possessing a nearly constant thickness but an increase in diameter with ageing time. Additionally, the stable behaviors of the total surface and size of S-precipitates illuminate that the coalescence/coarsening mechanisms are significantly slowed down. The concurrently-existing precipitation kinetics of Ω and S have provided an in-depth understanding of the higher strength of the aged 7A sample.

Small angle X-ray scattering and positron annihilation spectroscopy of polyethyleneimine functionalized ordered mesoporous silica SBA-15 microstructure

Owing to its advantages of high specific surface area, large pore volume, adjustable pore size, good thermal stability and relatively low cost, SBA-15 has a wide range of application prospects in adsorption, separation, catalysis, nanomaterials and other fields. And the use of organic functional groups to modify SBA-15 has become one of the hot spots of research on materials, but the introduction of organic functional groups will inevitably affect the pore structure of material, affecting its performance. Therefore, how to more comprehensively characterize the pore structure of material has received much attention. In this work, small angle X-ray scattering (SAXS) technique is used to characterize the pore structure of PEI/SBA-15 mesoporous molecular sieve. The pore structure and periodicity information of PEI/SBA-15 are obtained by using correlation function and string length distribution theory, and compared with those obtained by positron annihilation lifetime spectroscopy (PALS) technique. The results show that the periodic structure of PEI/SBA-15 mesoporous molecular sieve does not change significantly with the increase of PEI mass percent, and the pore size of PEI/SBA-15 mesoporous molecular sieve only decreases from 8.3 nm to 7.6 nm by the chord length distribution function. Two long-life components<i>, τ</i><sub>3</sub> and <i>τ</i><sub>4</sub>, are obtained by PALS, and <i>τ</i><sub>3</sub> reflects the random pores structure in SBA-15 matrix, while <i>τ</i><sub>4</sub> denotes the size of SBA-15 hexagonal pores. Compared with the results of SAXS, the mesoporous pore size obtained by PALS technique shows the same trend. By combining SAXS technique and PALS technique, the evolution of material microstructure can be revealed in more depth, thus providing a unique method for studying the structural characterization of functional nanocomposites in the future.

Development and characterization of nanodispersion-based sildenafil pressurized metered-dose inhaler using combined small-angle X-ray scattering, dynamic light scattering, and impactors

The objectives of this study were to develop and measure the hydrodynamic particle size of sildenafil citrate nanoparticles dispersed in a pressurized metered-dose inhaler (pMDI) using dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS). Aerodynamic properties and charges of aerosolized particles after emission from the pMDI were monitored by next generation impactor (NGI) and electrical low pressure impactor (ELPI). Nanodispersion-based sildenafil citrate pMDI formulated with 0, 1, 5 and 10% poloxamer 188 (P188) as a surfactant namely formulations F1, F2, F3 and F4, respectively. The results showed no precipitated or crystal growth during 6 months. The particle size and polydispersity index of the F3 obtained from the DLS analysis were 9.0 ± 1.6 d nm and 0.421 ± 0.038, respectively. The respective characteristics obtained from the SAXS data were 5.2 ± 1.2 d nm. The results from SAXS were smaller than those obtained from DLS. Larger hydrodynamic shell contributed to the larger size of nanoparticles. The sildenafil citrate content of pMDI was 107–109.5% LA. The mass median aerodynamic diameter (MMAD) from NGI was 1.2–2 μm and the fine particle fraction was 60%. The formulation without P188 (F1) showed particles of 10–100 nm and 0.1–1 μm and exhibited a unipolar charge profile. The formulations with P188 exhibited a bipolar charge profile with the nano-size of 200 (F3) and 300–800 nm (F4). The formulations of pMDI exhibited either a unipolar charge or bipolar charge profile depending on the composition of the formulation. The sildenafil citrate pMDI with 5% P188 generated sub-micronized and nano-sized aerosols with bipolar charged particles. The DLS and SAXS techniques were alternative ways to determine the particle size and size distribution of the pMDI products. The EPLI is also suitable to assess the stability of the MDI products from charge measurement.

Pore Characterization of Alumina Short Fiber Using Small Angle X-Ray Scattering Technique

Umar Abdillah Anwar1, Hafizal Yazid2*, Ruey Shan Chen1, Siti Zaubidah1, Nurulizzati Makhtar1, Maria Sabtu1, M Rawi M Zain2, Roslan Yahya3 and Sahrim Ahmad1 Author Affiliations 1Department of Applied Physics, Universiti Kebangssan Malaysia, Malaysia 2Materials Technology Group, Malaysia 3Plant Assessment Technology Group, Malaysia Received: January 25, 2022 | Published: February 02, 2022 Corresponding author: Hafizal Yazid, Materials Technology Group, Industrial Technology Division, Malaysian Nuclear Agency, 43000 Kajang Selangor, Malaysia DOI: 10.26717/BJSTR.2022.41.006622

Size exclusion chromatography coupled small angle X-ray scattering with tandem multiangle light scattering at the SIBYLS beamline.

Small-angle X-ray Scattering (SAXS) has been a versatile technique for studying biomolecules in solution for several decades now. Developments in SAXS techniques that integrate in situ purification with a high-throughput, multimodal design philosophy have revolutionized the reach and tempo of BioSAXS experiments. The current zenith of the field comes in the form of size exclusion chromatography coupled SAXS with in-line multiangle light scattering (SEC-SAXS-MALS). This technique has been a considerable focus at the Structurally Integrated BiologY for Life Sciences (SIBYLS) beamline at the Advanced Light Source (ALS) in Berkeley, California, over the last 5 years and continues to be a point of active development. In this chapter, we describe the design of the SEC-SAXS-MALS system and general guidelines for collecting, processing, and analyzing SEC-SAXS-MALS data at the SIBYLS beamline.

Monitoring Nuclease Activity by X-Ray Scattering Interferometry Using Gold Nanoparticle-Conjugated DNA.

The biologically critical, exquisite specificity and efficiency of nucleases, such as those acting in DNA repair and replication, often emerge in the context of multiple other macromolecules. The evolved complexity also makes biologically relevant nuclease assays challenging and low-throughput. Meiotic recombination 11 homolog 1 (MRE11) is an exemplary nuclease that initiates DNA double-strand break (DSB) repair and processes stalled DNA replication forks. Thus, DNA resection by MRE11 nuclease activity is critical for multiple DSB repair pathways as well as in replication. Traditionally, in vitro nuclease activity of purified enzymes is studied either through gel-based assays or fluorescence-based assays like fluorescence resonance energy transfer (FRET). However, adapting these methods for a high-throughput application such as inhibitor screening can be challenging. Gel-based approaches are slow, and FRET assays can suffer from interference and distance limitations. Here we describe an alternative methodology to monitor nuclease activity by measuring the small-angle X-ray scattering (SAXS) interference pattern from gold nanoparticles (Au NPs) conjugated to 5'-ends of dsDNA using X-ray scattering interferometry (XSI). In addition to reporting on the enzyme activity, XSI can provide insight into DNA-protein interactions, aiding in the development of inhibitors that trap enzymes on the DNA substrate. Enabled by efficient access to synchrotron beamlines, sample preparation, and the feasibility of high-throughput XSI data collection and processing pipelines, this method allows for far greater speeds with less sample consumption than conventional SAXS techniques. The reported metrics and methods can be generalized to monitor not only other nucleases but also most other DNA-protein interactions.

Influence of egg albumin and whey protein in the co‐encapsulation of betalains and phenolic compounds fromBougainvillea glabrabracts in Ca(II)‐alginate beads

Bougainvillea glabra bracts aqueous extract was co-encapsulated in Ca(II)-alginate beads, with the inclusion of egg albumin and whey protein isolate. Rheological measurements of the dispersions prepared in advance to beads formation showed a viscosity reduction by WPI, however, albumin increased the viscosity due to higher intermolecular association with alginate, as confirmed by FT-IR. The beads supplemented with proteins showed higher encapsulation efficiencies, with values higher than 70% for phenolic compounds and 50% for betalains. Rupture strength varied from 31.1 to 38.9 N for beads containing whey protein and albumin, respectively, indicating that the inclusion of these proteins resulted in beads with different mechanical properties and applications. Thermogravimetric analysis and FT-IR indicated molecular interactions between B. glabra compounds, sodium alginate, and proteins. The beads structural characterization determined by Small Angle X-ray Scattering demonstrated that Ca(II)-alginate microstructure was highly affected by proteins, especially albumin, revealing strong interactions between these biopolymers. Novelty impact statement This study employs a novel matrix to encapsulate phenolic compounds and betalains from B. glabra bracts in Ca(II)-alginate beads using egg albumin and whey protein isolate to reinforce the structure of the beads and improve their chemical stability. Small Angle X-ray Scattering (SAXS) technique showed that proteins affected the beads microstructure, revealing strong interaction with Ca(II)-alginate. The inclusion of egg albumin and whey protein resulted in beads with different mechanical properties allowing their application in several food products.

In vivo effectiveness of hybrid membranes with osteogenic growth peptide for bone regeneration.

Guided bone regeneration (GBR) technique helps to restore bone tissue through cellular selectivity principle. Currently no osteoinductive membrane exists on the market. Osteogenic growth peptide (OGP) acts as a hematopoietic stimulator. This association could improve the quality of bone formation, benefiting more than 2.2 million patients annually. The objective of this work was to develop membranes from ureasil-polyether materials containing OGP. The membranes were characterized by differential scanning calorimetry (DSC) and small angle X-ray scattering (SAXS). OGP was synthesized by the solid phase method. Sterilization results using gamma radiation at 24kGy did not change the structure of the material, as confirmed by DSC. The SAXS technique revealed the structural homogeneity of the matrix. OGP was incorporated in 66.25×10-10 mol and release results showed that the ureasil-PPO400/PEO500 and ureasil-PPO400/PEO1900 membranes released 7% and 21%, respectively, after 48h. In vivo results demonstrated that the amount and quality of bone tissue formed in the bone defects in the presence of ureasil-polyether membranes with OGP were similar to commercial collagen material with BMP. The results allow us to conclude that membranes with OGP have characteristics that make them potential candidates for the GBR.

Mesoporous Carbons of Well-Organized Structure in the Removal of Dyes from Aqueous Solutions.

Mesoporous carbons with differentiated properties were synthesized by using the method of impregnation of mesoporous well-organized silicas. The obtained carbonaceous materials and microporous activated carbon were investigated by applying different methods in order to determine their structural, surface and adsorption properties towards selected dyes from aqueous solutions. In order to verify applicability of adsorbents for removing dyes the equilibrium and kinetic experimental data were measured and analyzed by applying various equations and models. The structural and acid-base properties of the investigated carbons were evaluated by Small-Angle X-ray Scattering (SAXS) technique, adsorption/desorption of nitrogen, potentiometric titration, and Transmission Electron Microscopy (TEM). The results of these techniques are complementary, indicating the type of porosity and structural ordering, e.g., the pore sizes determined from the SAXS data are in good agreement with those obtained from nitrogen sorption data. The SAXS and TEM data confirm the regularity of mesoporous carbon structure. The adsorption experiment, especially kinetic measurements, reveals the utility of mesoporous carbons in dye removing, taking into account not only the adsorption uptake but also the adsorption rate.

The Structure of the Potato Virus A Particles Elucidated by Small Angle X-Ray Scattering and Complementary Techniques

Potato virus A (PVA) protein coat contains on its surface partially unstructured N-terminal domain of the viral coat protein (CP), whose structural and functional characteristics are important for understanding the mechanism of plant infection with this virus. In this work, we investigated the properties and the structure of intact PVA and partially trypsinized PVAΔ32 virions using small-angle X-ray scattering (SAXS) and complimentary methods. It was shown that after the removal of 32 N-terminal amino acids of the CP, the virion did not disintegrate and remained compact, but the helical pitch of the CP packing changed. To determine the nature of these changes, we performed ab initio modeling, including the multiphase procedure, with the geometric bodies (helices) and restoration of the PVA structure in solution using available high-resolution structures of the homologous CP from the PVY potyvirus, based on the SAXS data. As a result, for the first time, a low-resolution structure of the filamentous PVA virus, both intact and partially degraded, was elucidated under conditions close to natural. The far-UV circular dichroism spectra of the PVA and PVAΔ32 samples differed significantly in the amplitude and position of the main negative maximum. The extent of thermal denaturation of these samples in the temperature range of 20-55°C was also different. The data of transmission electron microscopy showed that the PVAΔ32 virions were mostly rod-shaped, in contrast to the flexible filamentous particles typical of the intact virus, which correlated well with the SAXS results. In general, structural analysis indicates an importance of the CP N-terminal domain for the vital functions of PVA, which can be used to develop a strategy for combating this plant pathogen.

Development and characterization of highly structured rinse-off conditioners containing vegetable oils

The appearance of the hair interferes with people's self-esteem and may indicate characteristics about their lifestyle. Due to their importance, hair treatment cosmetics correspond to a significant portion of the sector's sales. This research aimed to develop and characterize highly structured conditioners, prepared with avocado, wheat germ and grape seeds oils. The formulations were developed through a ternary phase diagram, using cationic surfactant (cetyl trimethyl ammonium chloride), oily phase (mineral or vegetable oils) and aqueous phase. The formulations obtained were classified according to their aspect and viscosity, with the most appropriate ones chosen for the intended use. They were evaluated by polarized light microscopy (PLM) to verify the structure of the system and, also, by means of rheology, small angle X-ray scattering (SAXS) and sun protection factor (SPF) determination. After the classification of the formulations, the opaque and uniform ones, with intermediate viscosity, compatible with the application on the hair were chosen, guaranteeing acceptance by possible consumers. PLM offered images indicative of highly structured systems, confirmed by the SAXS technique. Rheology indicated that the use of vegetable oils, compared to mineral oil, generated formulations with slightly lower viscosity, allowing the choice of the formulation (12, of the ternary diagram) with higher viscosity among the others. Finally, the determination of the SPF did not indicate the ability to protect against ultraviolet radiation. Thus, in this study, a highly structured formulation, prepared with cationic surfactant and vegetable oils was developed, offering another possibility of an innovative product to consumers of hair cosmetics.

How Do Surface Properties of Nanoparticles Influence Their Diffusion in the Extracellular Matrix? A Model Study in Matrigel Using Polymer-Grafted Nanoparticles.

Diffusion of nanomedicines inside the extracellular matrix (ECM) has been identified as a key factor to achieve homogeneous distribution and therefore therapeutic efficacy. Here, we sought to determine the impact of nanoparticles' (NPs) surface properties on their ability to diffuse in the ECM. As model nano-objects, we used a library of gold nanoparticles grafted with a versatile polymethacrylate corona, which enabled the surface properties to be modified. To accurately recreate the features of the native ECM, diffusion studies were carried out in a tumor-derived gel (Matrigel). We developed two methods to evaluate the diffusion ability of NPs inside this model gel: an easy-to-implement one based on optical monitoring and another one using small-angle X-ray scattering (SAXS) measurements. Both enabled the determination of the diffusion coefficients of NPs and comparison of the influence of their various surface properties, while the SAXS technique also allowed to monitor the NPs' structure as they diffused inside the gel. Positive charges and hydrophobicity were found to particularly hinder diffusion, and the different results suggested on the whole the presence of NPs-matrix interactions, therefore underlying the importance of the ECM model. The accuracy of the tumor-derived gels used in this study was evidenced by in vivo experiments involving intratumoral injections of NPs on mice, which showed that diffusion patterns in the peripheral tumor tissues were quite similar to the ones obtained within the chosen ECM model.

Understanding the Overcoated Catalyst Using in Situ Synchrotron X-Ray Techniques

Carbonaceous feeds, such as oil, gas, and coal, can be catalytically converted to useful products. Many of these reactions are conducted under harsh conditions, where the metal catalysts will rapidly sinter and lose activity. Overcoating is a methodology which preserves catalyst integrity under reaction conditions by depositing protective layers around the catalysts. Recently, we show that overcoating the metal nanoparticles with alumina using atomic layer deposition (ALD) will reduce the sintering and coking while the lifetime and reactivity of catalyst increase dramatically compared to the catalyst without ALD overcoating. It is believed that nano-sized pore (less than 2 nm) was formed during the calcination of ALD overlayer at high temperature. However, the mechanism of pore formation is still poorly understood due to the limited characterization technique.Understanding the mechanism of the pore formation and further controlling the pore size are crucial for the development of the ALD overcoated catalyst. Recently, we demonstrated that small angle X-ray scattering (SAXS) can be used to characterize these ALD overcoated catalysts. From SAXS analysis, the thermal treatment resulted in the formation of ~ 3.5 nm pores. Moreover, the evolution of pore size was monitored by in situ SAXS technique. The pore size increases with increasing annealing temperature. In this proposal, we aim to investigate the mechanism of pore formation during the calcination using in situ SAXS as well as wide angle X-ray scattering, to understand how the ramping rate, gas used, nature of supports and overcoated materials affect the formation of the pore.

Characterization of materials embedded in thick objects using spectral small-angle x-ray scattering

Small-angle x-ray scattering (SAXS) can identify a material based on its scattering features. However, SAXS techniques have been limited to the study of thin samples in the mm scale. We investigated the use of spectral SAXS (sSAXS) in the 30–45 keV energy range to identify embedded materials in up to 5 cm thick objects. A prototype sSAXS system was built by integrating a polychromatic x-ray source and a 2D spectroscopic detector in a two-pinhole collimation setup. The elastically scattered x-rays at deflection angles smaller than 10° were measured without collimating the scattered rays or filtering the energy spectrum. Using caffeine as a target material in 1 to 5 cm polymethyl methacrylate (PMMA) slabs, we demonstrate the capability of sSAXS technique to identify caffeine targets in all cases with 600 s acquisition times. The distinct Bragg peaks of caffeine at 8.44 and 18.64 nm−1 were recovered with a q-resolution of 0.6 nm−1 after attenuation and background corrections. Furthermore, we show the effect of PMMA thickness and target location to estimate the caffeine amount from the recovered signal using area-under-the-peak (AUP) analysis. We found that AUPs were slightly overestimated due to signal contamination by PMMA when the scattered photons from the caffeine target traverse through 1 to 3 cm PMMA slabs. This effect was more significant in the 5 cm thick PMMA with an average transmission factor of 24%, where the AUP was overestimated approximately by 34%.

K vs. Na Effects on the Self-Assembly of Guanosine 5'-Monophosphate: A Solution SAXS Structural Study+.

The hierarchical process of guanosine (G) self-assembly, leading in aqueous solution and in the presence of metal cations to the formation of G-quadruplexes, represents an intriguing topic both for the biological correlation with telomerase activity and for the nano-technological applications, as demonstrated by the current measured in a quadruplex wire 100 nm long. Similar to G-rich DNA sequences and G-oligonucleotides, the guanosine 5′-monophosphate (GMP) self-aggregates in water to form quadruplexes. However, due to the absence of a covalent axial backbone, this system can be very useful to understand the chemical-physical conditions that govern the guanosine supramolecular aggregation. We have then investigated by in-solution Synchrotron Small Angle X-ray Scattering technique the role of different cations in promoting the quadruplex formation as a function of concentration and temperature. Results show how potassium, with its peculiar biological traits, favours the G-quadruplex elongation process in respect to other cations (Na, but also NH and Li), determining the longest particles in solution. Moreover, the formation and the elongation of G-quadruplexes have been demonstrated to be controlled by both GMP concentration and excess cation content, even if they specifically contribute to these processes in different ways. The occurrence of condensed liquid crystalline phases was also detected, proving that excess cations play also unspecific effects on the effective charges on the G-quadruplex surface.

Characterization of Crystal Microstructure Based on Small Angle X-ray Scattering (SAXS) Technique.

Small-angle X-ray scattering (SAXS) is an effective method to obtain microstructural information of materials. However, due to the influence of crystal surface effects, SAXS has a deviation in the characterization of the crystal microstructure. In order to solve the influence of crystal surface effect on the internal defect signal, the microstructure of Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) crystal was characterized by soaking the sample in the matching solution. We found that the absolute scattering intensity, specific surface and volume fraction of the sample in the matching solution are significantly lower than the initial sample, which solves the influence of the crystal surface effect on the test results. Comparing the scattering results of the samples in different electron density matching solutions, it was found that the best result was obtained when using GPL-107 perfluoropolyether (PFPE) matching solution and the same law was obtained by controlling the experiment with 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (CL-20) crystal. The fitting density was calculated according to the theoretical density and void volume fraction of the sample, and the calculated results are close to the test results of Particle Density Distribution Analyzer (PDDA). Based on this paper, we provide a method to obtain the correct information of crystal microstructure.