Hasil untuk "Analytical chemistry"

Judith Wurmel, John M. Simmie

Tunnelling reactions of molecules embedded on cryogenic noble-gas matrices are being used in fundamental studies of how reactivity varies with the nature of the supposedly inert matrix as well as pointers to the chemistry occurring in the interstellar medium on ice-grains. To these ends we present chemical kinetic rate constants for the \textit{cis} to \textit{trans} isomerisation of seleno-, thio- and monomeric formic acids and that of their three dimeric species, based on multidimensional calculations in the gas-phase, from 10~K to 300~K as a guide to the matrix reactions.

Amal Raj Veluthedath Nair, Nuala M. Caffrey

As the energy storage ecosystem evolves beyond lithium, MXenes, a versatile family of 2D materials derived from MAX phases, have emerged as promising candidates for next-generation energy storage electrodes due to their tunable surface chemistry, large interlayer spacing, and excellent electronic conductivity. In this work, we use density functional theory to investigate Ti$_3$C$_2$ and V$_2$C MXenes as cathodes in Al-ion batteries. Four stacking configurations of the two-dimensional sheets and two different ion coordination sites are evaluated to understand their influence on ion intercalation and mobility. We find that the stacking configuration and surface chemistry critically impact interlayer spacing and electrochemical performance. O-terminated layers in an octahedral stacking exhibit remarkable structural stability with minimal interlayer expansion upon ion intercalation, particularly for Al intercalation in V$_2$C which exhibits an interlayer expansion of 0.1 angstrom, consistent with experimental findings. While octahedral stacking is observed to be energetically more favourable, it reduces ion mobility compared to prismatic stacking. Furthermore, O-terminated MXenes exhibit high theoretical specific capacities, reaching more than 270 mAh/g. F-terminated MXenes are considerably more unstable after intercalation and as a result exhibit much lower Al capacities. These findings highlight the importance of stacking configurations, termination and intercalant chemistry in MXenes for battery applications.

Marcus D. Liebenthal, Stephen H. Yuwono, Lauren N. Koulias et al.

This article summarizes recent updates to the p$^\dagger$q package, which is a C++ accelerated Python library for generating equations and computer code corresponding to singly-reference many-body quantum chemistry methods such as coupled-cluster (CC) and equation-of-motion (EOM) CC theory. Since 2021, the functionality in \pq has expanded to include boson operators, coupled fermion-boson operators, unitary cluster operators, non-particle-conserving EOM operators, spin tracing, multiple single-particle subspaces, and more. Additional developments allow for the generation of C++ and Python code that minimizes floating-point operations via contraction order optimization, sub-expression elimination, and the fusion of similar terms.

Jan Cvengros, Gerd Kortemeyer

We explore the effectiveness and reliability of an artificial intelligence (AI)-based grading system for a handwritten general chemistry exam, comparing AI-assigned scores to human grading across various types of questions. Exam pages and grading rubrics were uploaded as images to account for chemical reaction equations, short and long open-ended answers, numerical and symbolic answer derivations, drawing, and sketching in pencil-and-paper format. Using linear regression analyses and psychometric evaluations, the investigation reveals high agreement between AI and human graders for textual and chemical reaction questions, while highlighting lower reliability for numerical and graphical tasks. The findings emphasize the necessity for human oversight to ensure grading accuracy, based on selective filtering. The results indicate promising applications for AI in routine assessment tasks, though careful consideration must be given to student perceptions of fairness and trust in integrating AI-based grading into educational practice.

Sura A. A. F. Al Bayati, Sarah A. Salim, Youser H. Al Maged et al.

Context: The human oral microbiota plays a crucial role in maintaining oral and systemic health. Dysbiosis has been implicated in diseases such as periodontitis, diabetes, cardiovascular conditions, and cancers. Aims: This study aimed to evaluate awareness, perception, and knowledge of oral microbiota and its systemic implications among clinical dental students at Gulf Medical University (GMU), UAE. Settings and Design: A descriptive cross-sectional study involving 150 clinical dental students from the third, fourth, and fifth years of the Bachelor of Dental Surgery program. Methods and Materials: A validated, anonymous questionnaire (24 multiple-choice items) was distributed electronically. The survey assessed participants’ demographics, oral hygiene practices, perception of oral microbiota, and its relation to systemic health. Statistical Analysis Used: Data was analyzed using descriptive statistics (frequency and percentages) in Microsoft Excel. Results: Among respondents, 84% recognized the oral cavity as a habitat for diverse microbes, and 88% agreed that microbial imbalance leads to oral diseases. Awareness of the oral microbiota’s systemic links was high (87.3%), particularly with diabetes (70.7%) and cardiovascular diseases (48.7%). However, only 19.3% linked oral microbiota monitoring with early cancer detection. While 72% brushed twice daily, only 34.7% used probiotics. Conclusion: GMU dental students demonstrated substantial awareness of the oral microbiota’s role in oral and systemic health. However, gaps exist in advanced knowledge areas such as diagnostic microbiota testing and therapeutic interventions, indicating a need for curriculum enhancement.

Teddy X. Cai, Nathan H. Williamson, Peter J. Basser

The field of diffusion microstructural magnetic resonance (MR) aims to probe time-dependent diffusion, i.e., an ensemble-averaged mean-squared displacement ⟨r2(t)⟩ that is not linear in time. This time-dependence contains rich information about the surrounding microenvironment. MR methods to measure time-dependent diffusion quantitatively, however, require either non-standard pulse sequences, such as oscillating gradients, or make non-physical assumptions, such as infinitely narrow gradient pulses. Here, we argue that standard spin echo and stimulated echo MR sequences can be used to probe ⟨r2(t)⟩ directly. In particular, we propose a framework in which the log-signal ratio obtained from a pair of measurements with different inter-pulse spacing Δ is proportional to the MSD between these two Δ values along the gradient direction x: ⟨rx2(Δ2)⟩−⟨rx2(Δ1)⟩. The framework is quantitative for short, finite-duration gradient pulses and under the Gaussian phase approximation (GPA). To validate the framework, we consider one-dimensional diffusion between impermeable, parallel planes, as well as periodically-spaced, permeable planes. Excellent agreement is obtained between the estimation and the ground truth in the regime where the GPA is expected to hold. Importantly, the GPA can be made to hold for any underlying microstructure, making the proposed framework widely applicable.

Çiğdem Aybüke Özata, Nevin Erk, Wiem Bouali et al.

Durairaj VTA, Kalpana R

Three-dimensional polymeric networks called hydrogels have drawn a lot of interest in a variety of biomedical applications because of their distinctive qualities, like high water content and biocompatibility. Hydrogels can be strengthened mechanically and become more stable via cross-linking. In this study, we described the synthesis and characterization of a cross-linked hydrogel made of polyethylene glycol (PEG) capable of absorbing drug. The hydrogel was created by using a polymerization procedure to cross-link PEG chains. In order to allay this worry, we added particular functional groups to the hydrogel matrix that had a strong affinity for glutaraldehyde. These functional groups made it easier for excess glutaraldehyde to be absorbed and sequestered inside the hydrogel, lowering its cytotoxic potential. After incubation with the hydrogel, the residual glutaraldehyde concentration in solution was measured in order to assess the glutaraldehyde absorption potential.

M. Monica Gurupriya, K. Divya Barathi, Ashok Viswanath Nalankilli et al.

Background: Children living with perinatal HIV/AIDS (CLWPHA) have a higher prevalence of dental caries and fungal infections. Caries tooth serves as a niche for Candida colonization and it also impairs oral health-related quality of life. The management of dental caries can eliminate the risk factor for Candida colonization and subsequently can promote their quality of life related to oral health. Aim: The aim of our study was to determine the effect of dental caries management on the Candida albicans carriage and oral health-related quality of life among CLWPHA under highly active antiretroviral therapy (HAART). Methodology: This pre- and post-experimental study was conducted with 40 students. Candida colonization was assessed from the participant’s saliva samples. OHRQoL of participants was assessed using the Oral Health Impact Profile-14 questionnaire. Results: The mean value of Candida albicans CFUs in saliva after dental caries management was significantly lower compared with before dental caries management. The mean OHIP-14 score after dental caries management was significantly lower compared with the baseline score. Conclusion: Dental caries management can be effective in reducing the oral Candidal colony count, thereby improving their oral health-related quality of life.

Jorge A. Custodio-Mendoza, Havva Aktaş, Magdalena Zalewska et al.

Anthocyanins, a subclass of flavonoids known for their vibrant colors and health-promoting properties, are pivotal in the nutritional science and food industry. This review article delves into the analytical methodologies for anthocyanin detection and quantification in food matrices, comparing quantitative and topical techniques. Quantitative methods, including High-performance Liquid Chromatography (HPLC) and Mass Spectrometry (MS), offer precise quantification and profiling of individual anthocyanins but require sample destruction, limiting their use in continuous quality control. Topical approaches, such as Near-infrared Spectroscopy (NIR) and hyperspectral imaging, provide rapid, in situ analysis without compromising sample integrity, ideal for on-site food quality assessment. The review highlights the advancements in chromatographic techniques, particularly Ultra-high-performance Liquid Chromatography (UHPLC) coupled with modern detectors, enhancing resolution and speed in anthocyanin analysis. It also emphasizes the growing importance of topical techniques in the food industry for their efficiency and minimal sample preparation. By examining the strengths and limitations of both analytical realms, this article aims to shed light on current challenges and prospective advancements, providing insights into future research directions for improving anthocyanin analysis in foods.

Dragoș Vlad Teodoru, Rodica Olar, Cătălin Maxim et al.

A series of five novel copper(II) complexes with imidazole derivatives having general core Cu(R-Im)₂(Macr)₂ (Macr = methacrylate anion; R-Im = 2-methylimidazole/2-MeIm, 4-methylimidazole/4-MeIm, 2-ethylimidazole/2-EtIm, 2-isopropylimidazole/2-<i>i</i>PrIm) has been synthesized and characterized by elemental analysis, Fourier Transform Infrared spectroscopy (FTIR), electronic reflectance spectroscopy, cyclic voltammetry, thermal analysis and single crystal X-ray diffraction. All complexes crystalize in a monoclinic crystal system and form a complex supramolecular network developed through hydrogen bonds. The stereochemistry of the copper ion is distorted octahedral except for the compound with 4-methylimidazole for which the geometry is square-pyramidal. The imidazole derivatives act as unidentate while methacrylate ions are chelated except for compound with 4-methylimidazole where is unidentate. All ligands and complexes inhibited B16 murine melanoma cells in a micromolar range, but the complex with 2-isopropylimidazole was more active. Furthermore, all species do not affect the healthy BJ cells in the concentration range used for assays.

Kun Xue, Shuhong Kang

Abstract Pseudomonas aeruginosa (P. aeruginosa), a kind of gram-negative pathogenic bacteria, are causative agents of severe infections, such as lower respiratory tract infections in children and cancers. Detecting low levels of P. aeruginosa in clinical samples in an easy-to-operate manner is highly desired but still poses a problem. Herein, we established a target recognition-initiated allosteric probe-based multiple signal amplification strategy for sensitive detection of P. aeruginosa in a wash-free way. This approach involves the allosteric probe’s accurate recognition and binding to target P. aeruginosa, leading to subsequent multiple-cycle amplification. Afterward, the amplified products were translated to induce the aggregation of gold nanoparticles (AuNPs), resulting in color variations. The utilization of the allosteric probe, which is integrated with the aptamer sequences, enables wash-free detection of P. aeruginosa. Taking the merit of multiple signal amplification process, the suggested method showed a strong linear response to the extracted P. aeruginosa within a concentration range of 10–105 cfu/mL, with a low limit of detection for individual P. aeruginosa detection. The proposed technique has considerable clinical promise for early disease diagnosis because to its high sensitivity and wash-free simplicity.

Min Zhang, Runze Mao, Han Li et al.

Stratified premixed combustion, known for its capability to expand flammability limits and reduce overall-lean combustion instability, has been widely adopted to comply with increasingly stringent environmental regulations. Numerous numerical simulations with different combustion models and mesh resolutions have been conducted on laboratory-scale flames to further understand the stratified premixed combustion. However, the trade-off between the high-fidelity and low computational cost for simulating laboratory-scale flames still remains, particularly for those combustion models involving direct coupling of chemistry and flow. In the present study, a GPU-based solver is employed to solve partial differential equations and calculate the thermal and transport properties, while an artificial neural network (ANN) is introduced to replace reaction rate calculation. Particular emphasis is placed on evaluating the proposed GPU-ANN approach through the large eddy simulation of the Cambridge stratified flame. The simulation results show good agreement for the flow and flame statistics between the GPU-ANN approach and the conventional CPU-based solver with direct integration (DI). The comparison suggests that the GPU-ANN approach can achieve the same level of accuracy as the conventional CPU-DI solver. In addition, the overall speed-up factor for the GPU-ANN approach is over two orders of magnitude. This study lays the potential groundwork for fully resolved laboratory-scale flame simulations based on detailed chemistry with much more affordable computational cost.

Nicole Siegel, Hiroaki Hasebe, German Chiarelli et al.

Nanotechnology has revolutionized the fabrication of hybrid species with tailored functionalities. A milestone in this field is the DNA conjugation of nanoparticles, introduced almost 30 years ago, which typically exploits the affinity between thiol groups and metallic surfaces. Over the last decades, developments in colloidal research have enabled the synthesis of an assortment of non-metallic structures, such as high-index dielectric nanoparticles, with unique properties not previously accessible with traditional metallic nanoparticles. However, to stabilize, integrate and provide further functionality to non-metallic nanoparticles, reliable techniques for their functionalization with DNA will be crucial. Here, we combine well-established dibenzylcyclooctyne-azide click-chemistry with a simple freeze-thaw method to achieve the functionalization of silica and silicon nanoparticles, which form exceptionally stable colloids with a high DNA surface density of 0.2 molecules/nm2. Furthermore, we demonstrate that these functionalized colloids can be self-assembled into high-index dielectric optical antennas with a yield of up to 78% via the use of DNA origami. Finally, we extend this method to functionalize other important nanomaterials, including oxides, polymers, core-shell and metal nanostructures. Our results indicate that the method presented herein serves as a crucial complement to conventional thiol functionalization chemistry and thus greatly expands the toolbox of DNA-functionalized nanoparticles currently available.

S. J. van der Walt, L. E. Kristensen, H. Calcutt et al.

(Abridged) Molecular lines are commonly detected towards protostellar sources. However, to get a better understanding of the chemistry of these sources we need unbiased molecular surveys over a wide frequency range for as many sources as possible to shed light on the origin of this chemistry, particularly any influence from the external environment. We present results from the PILS-Cygnus survey of ten intermediate- to high-mass protostellar sources in the nearby Cygnus-X complex, through high angular resolution interferometric observations over a wide frequency range. Using the Submillimeter Array (SMA), a spectral line survey of ten sources was performed in the frequency range 329-361 GHz, with an angular resolution of $\sim$1\farcs5, ($\sim$2000 AU, source distance of 1.3 kpc). Spectral modelling was performed to identify molecular emission and determine column densities and excitation temperatures for each source. We detect CH$_3$OH towards nine of the ten sources, CH$_3$OCH$_3$ and CH$_3$OCHO towards three sources, and CH$_3$CN towards four sources. Towards five sources the chemistry is spatially differentiated (different species peak at different positions and are offset from the peak continuum emission). The chemical properties of each source do not correlate with their position in the Cygnus-X complex, nor do the distance or direction to the nearest OB associations. However, the five sources located in the DR21 filament do appear to show less line emission compared to the five sources outside the filament. This work shows how important wide frequency coverage observations are combined with high angular resolution observations for studying the protostellar environment. Based on the ten sources observed here, the external environment appears to only play a minor role in setting the chemical environment on these small scales ($<$ 2000 AU).

Zahraa Kayali, Reem H. Obaydo, Amir Alhaj Sakur

Shelley Minteer, Jingguang Chen, Song Lin et al.

Cica Gustiani, Richard Meister, Simon C. Benjamin

Variational methods offer a highly promising route to exploiting quantum computers for chemistry tasks. Here we employ methods described in a sister paper to the present report, entitled ab initio machine synthesis of quantum circuits, in order to solve problems using adaptively evolving quantum circuits. Consistent with prior authors we find that this approach can outperform human-designed circuits such as the coupled-cluster or hardware-efficient ansätze, and we make comparisons for larger instances up to 14 qubits. Moreover we introduce a novel approach to constraining the circuit evolution in the physically relevant subspace, finding that this greatly improves performance and compactness of the circuits. We consider both static and dynamics properties of molecular systems. The emulation environments used is QuESTlink; all resources are open source and linked from this paper.

Sabrina Hamla, Pierre-Yves Sacré, Allison Derenne et al.

Glycosylation is considered a critical quality attribute of therapeutic proteins as it affects their stability, bioactivity, and safety. Hence, the development of analytical methods able to characterize the composition and structure of glycoproteins is crucial. Existing methods are time consuming, expensive, and require significant sample preparation, which can alter the robustness of the analyses. In this context, we developed a fast, direct, and simple drop-coating deposition Raman imaging (DCDR) method combined with multivariate curve resolution alternating least square (MCR-ALS) to analyze glycosylation in monoclonal antibodies (mAbs). A database of hyperspectral Raman imaging data of glycoproteins was built, and the glycoproteins were characterized by LC-FLR-MS as a reference method to determine the composition in glycans and monosaccharides. The DCDR method was used and allowed the separation of excipient and protein by forming a “coffee ring”. MCR-ALS analysis was performed to visualize the distribution of the compounds in the drop and to extract the pure spectral components. Further, the strategy of SVD-truncation was used to select the number of components to resolve by MCR-ALS. Raman spectra were processed by support vector regression (SVR). SVR models showed good predictive performance in terms of RMSECV, R²_CV.

L. Chahine, A. López-Sepulcre, R. Neri et al.

Hot corinos are compact regions around solar-mass protostellar objects that are very rich in interstellar complex organic molecules (iCOMs). They are believed to represent the very early phases of our Solar System's birth, which was very likely also characterized by rich organic chemistry. While most of the studied hot corinos are either isolated or born in a loose protocluster, our Sun was born in a densely packed star cluster, near massive stars whose ultraviolet radiation must have contributed to shaping the evolution of the surrounding environment. In addition, internal irradiation from energetic particles ($>$10 Mev), whose imprint is seen today in the products of short-lived radionuclides in meteoritic material, is also known to have occurred during the Solar System formation. How did all these conditions affect the chemistry of the proto-Sun and its surroundings is still an open question. To answer this question, we studied HOPS-108, the hot corino located in the protosolar analogue OMC-2 FIR4. The study was carried out with ALMA at 1.3mm with an angular resolution of $\sim$100 AU. We detected 11 iCOMs such as CH$_{3}$OH HCOOCH$_{3}$ and CH$_{3}$OCH$_{3}$. Our results can be summarized as follows: (1) an enhancement of HCOOCH3 with respect to other hot corinos, (2) a [CH$_{3}$OCH$_{3}$]/[HCOOCH$_{3}$] abundance ratio of $\sim$0.2 marginally deviating from the usual trend seen in other sources ([CH$_{3}$OCH$_{3}$]/[HCOOCH$_{3}$] $\sim$1), (3) a [CH$_{2}$DOH]/[CH$_{3}$OH] ratio of 2.5\% which is lower than what is seen in Perseus and Ophiuchus hot corinos ($\sim$7\%-9\%) and similar to that seen in HH212 another source located in Orion. This might result from different physical conditions in the Orion molecular complex compared to other regions.