Hasil untuk "Analytical chemistry"

J. Kroll, N. Donahue, J. Jimenez et al.

A detailed understanding of the sources, transformations and fates of organic species in the environment is crucial because of the central roles that they play in human health, biogeochemical cycles and the Earth's climate. However, such an understanding is hindered by the immense chemical complexity of environmental mixtures of organics; for example, atmospheric organic aerosol consists of at least thousands of individual compounds, all of which likely evolve chemically over their atmospheric lifetimes. Here, we demonstrate the utility of describing organic aerosol (and other complex organic mixtures) in terms of average carbon oxidation state, a quantity that always increases with oxidation, and is readily measured using state-of-the-art analytical techniques. Field and laboratory measurements of the average carbon oxidation state, using several such techniques, constrain the chemical properties of the organics and demonstrate that the formation and evolution of organic aerosol involves simultaneous changes to both carbon oxidation state and carbon number.

Siegfried Eigler, A. Hirsch

The chemical production of graphene as well as its controlled wet chemical modification is a challenge for synthetic chemists. Furthermore, the characterization of reaction products requires sophisticated analytical methods. In this Review we first describe the structure of graphene and graphene oxide and then outline the most important synthetic methods that are used for the production of these carbon-based nanomaterials. We summarize the state-of-the-art for their chemical functionalization by noncovalent and covalent approaches. We put special emphasis on the differentiation of the terms graphite, graphene, graphite oxide, and graphene oxide. An improved fundamental knowledge of the structure and the chemical properties of graphene and graphene oxide is an important prerequisite for the development of practical applications.

Jun Yao, Mei Yang, Y. Duan

A. Kulmatiski, K. Beard, J. Stevens et al.

C. Burtis

A. Palomo, Krivenko Pavel, I. García-Lodeiro et al.

For many years now the idea of including alkalis in a Portland cement matrix has been regarded as a daft or inexcusably erroneous proposition: despite its absurdity, that opinion has been widely accepted as a basic premise by the scientific and technical community working in the area of the chemistry of cement. In 1957 Glukhovsky proposed a working hypothesis in which he established a close relationship between alkalis and cementitious materials. That hypothesis has become consolidated and has served as a basis for developing a new type of binders, initially called “alkaline cements”. The present paper reviews the most significant theoretical interpretations of the role played by alkalis in the formation of the “stony” structure of cement. It ends with a broad overview of the versatility of this type of materials for industrial applications and a discussion of the possibility of building on the existing legislation to meet the need for the future regulation of alkaline cement and concrete manufacture.

Guan-Hua Chen, Wei-Yu Chen, Y. Yen et al.

Kentaro Yamada, Terence G. Henares, Koji Suzuki et al.

M. Nocita, A. Stevens, B. van Wesemael et al.

Joe Pratt-Johns, Toby St. Clere Smithe, Chris Guiver et al.

We construct a functor that gives a dynamics to an algebraic model of interacting components. The construction generalises a computational model of Fontana and Buss in the field of artificial life known as AlChemy, in which molecules and their chemical interactions are emulated by lambda calculus terms and their application and subsequent reduction. We discuss future directions for the application of category theory to algebraic artificial chemistry as an organisational tool, with a focus on formalising the connection between the algebraic and the dynamical facets of such models.

Akanksha Lahiri, Balamuralidhara V, Hemanth Vikram PR et al.

Introduction: Levodopa, a dopamine precursor, widely prescribed drug in Parkinson’s disease management possesses a side effect of Levodopa-induced dyskinesia (LID). Amantadine hydrochloride, an NMDA receptor antagonist is co-encapsulated along with levodopa and formulates as polymeric nanoparticles (NPs) so as to overcome the side effects and act synergistically to enhance therapeutic outcome. Methodology: In current work, we developed a novel, green Ultra-Fast Liquid Chromatography-Tandem Mass Spectrometry (UFLC-MS/MS) technique for the simultaneous quantification of amantadine and levodopa in polymeric nanoparticles. A triple quadrupole analyser with a multiple reaction monitoring (MRM) scan mode and an atmospheric pressure chemical ionization (APCI) source. A Waters Symmetry C8 column (150 × 4.6 mm, 3.5 μm) maintained at 40 °C was used for the chromatographic separation. In order to ensure sensitive and specific analyte detection, the mobile phase consisted of 0.1 % formic acid in water and methanol (40:60) with a total run time of 5 min. Excellent linearity, recovery, accuracy, and sensitivity were validated by method validation. Greenness assessment was done by AGREE, GAPI and AES metrics. Results: Proposed green UFLC-MS/MS method effectively quantifies Levodopa and Amantadine in polymeric nanoparticles, followed by accurate evaluation of %DL, %DEE, and drug release profiles. %DEE values were observed for Levodopa (89.6%) and Amantadine (90.16 %), with corresponding %DL values of 20.5% and 24.10%, indicating substantial drug loading capacity. The in vitro drug release profiles demonstrated sustained release behaviour, with 91.89% ± 0.362 of Levodopa and 92% ± 0.362 of Amantadine released over the study period. Conclusion: Using GAPI, AGREE, and AES criteria, the created analytical method's greenness was carefully assessed. The outcomes were then compared to previously published methods in the literature. For the simultaneous measurement of amantadine and levodopa in nanoparticles, our innovative UFLC-MS/MS technology offered a dependable and extremely sensitive method.

Nikolay V. Golubev, Mohammed Th. Hassan

How quantum electron and nuclei motions affect biomolecular chemical reactions remains a central challengeable question at the interface of quantum chemistry and biology. Ultrafast charge migration in deoxyribonucleic acid (DNA) has long been hypothesized to play a critical role in photochemistry, genome stability, and long-range biomolecular signaling, however, direct real-time observation of these electronic processes has remained elusive. Here, we present a theoretical investigation and propose the concept of future experimental measurements of laser-driven charge dynamics in the canonical DNA nucleobase pairs thymine_adenine and cytosine_guanine. Attosecond-resolved simulations employing high-level ab initio methods reveal base-dependent ionization mechanisms, directional charge migration pathways, and electronic coherences that govern sub-femtosecond redistribution of electron density across hydrogen-bonded nucleobase interfaces. Accordingly, we propose the concept of a quantum attosecond scanning electron microscope, termed the quantum attomicroscope (Q-attomicroscope), a capable of imaging photoinduced quantum chemistry reactions in attosecond temporal resolution and sub-nanometer spatial precision. As a proof of principle, we propose to image the charge migrations dynamics in DNA which we studied theoretically. Together, our preceptive bridges theory, instrumentation, and control, outlining a pathway toward laser mediated manipulation of DNA structure with implications for repair processes, chemical reactivity, and future personalized medicine.

Sebastian Ehlert, Jan Hermann, Thijs Vogels et al.

Accurate thermochemical data with sub-chemical accuracy (within 1 kcal mol$^{-1}$ of the empirical ground truth) are essential for advancing computational chemistry methods. However, existing datasets that reach this level of accuracy remain limited in size or scope. This hinders the development of data-driven methods with predictive accuracy across the broad chemical space of closed-shell, neutral molecules. Here we present Microsoft Research Accurate Chemistry Collection (MSR-ACC) and its first release, MSR-ACC/TAE25, comprising 73,040 total atomization energies at the CCSD(T)/CBS level obtained with the W1-F12 thermochemical protocol. The dataset is constructed to exhaustively cover the chemical space of closed-shell, charge-neutral, covalently bound equilibrium molecular structures containing up to 5 non-hydrogen atoms drawn from elements up to argon and lacking significant multireference character. The dataset and its canonical train and validation splits are openly available on Zenodo in the QCSchema format under the CDLA Permissive 2.0 license. This first release of MSR-ACC enables data-driven approaches for developing predictive computational chemistry methods with unprecedented accuracy and scope.

M. Van de Sande, M. Gueguen, T. Danilovich et al.

Chemical reaction networks are central to all chemical models. Each rate coefficient has an associated uncertainty, which is generally not taken into account when calculating the chemistry. We performed the first uncertainty analysis of a chemical model of C-rich and O-rich AGB outflows using the Rate22 reaction network. Quantifying the error on the model predictions enables us to determine the need for adding complexity to the model. Using a Monte Carlo sampling method, we quantified the impact of the uncertainties on the chemical kinetic data on the predicted fractional abundances and column densities. The errors are caused by a complex interplay of reactions forming and destroying each species. Parent species show an error on their envelope sizes, which is not caused by the uncertainty on their photodissociation rate, but rather the chemistry reforming the parent after its photodissociation. Using photodissociation models to estimate the envelope size might be an oversimplification. The error on the CO envelope impacts retrieved mass-loss rates by up to a factor of two. For daughter species, the error on the peak fractional abundance ranges from a factor of a few to three orders of magnitude, and is on average about 10\% of its value. This error is positively correlated with the error on the column density. The standard model suffices for many species, e.g., the radial distribution of cyanopolyynes and hydrocarbon radicals around IRC +10216. However, including spherical asymmetries, dust-gas chemistry, and photochemistry induced by a close-by stellar companion are still necessary to explain certain observations.

Brandt A. L. Gaches, Serena Viti

In the past decade, there has been a significant shift in astrochemistry with a renewed focus on the role of non-thermal processes on the molecular interstellar medium, in particular energetic particles (such as cosmic ray particles and fast electrons) and X-ray radiation. This has been brought about in large part due to new observations of interstellar complex organic molecules (iCOMS) in environments that would inhibit their formation, such as cold, dense gas in prestellar cores or in the highly energetic environments in galactic centers. In parallel, there has been a plethora of new laboratory investigations on the role of high-energy radiation and electrons on the chemistry of astrophysical ices, demonstrating the ability of this radiation to induce complex chemistry. In recent years, theoretical models have also begun to include newer cosmic-ray-driven processes in both the gas and ice phases. In this review, we unify aspects of the chemistry driven by X-ray radiation and energetic particles into a ``high-energy astrochemistry'', defining this term and reviewing the underlying chemical processes. We conclude by examining various laboratories where high-energy astrochemistry is at play and identify future issues to be tackled.

Jangil Moon, Yeongcheol Han, Songyi Kim et al.

Abstract Accurate measurement of water vapor isotopes (δ18O and δ2H) is fundamental for advancing our understanding of the hydrological cycle and improving hydrological model accuracy. This study introduces an innovative calibration methodology using a controlled evaporation mixer (CEM) for determining stable isotopic ratios in atmospheric water vapor via cavity ring-down spectroscopy. The CEM technique reliably produces a stable water vapor stream, crucial for enhancing the precision and accuracy of isotopic measurements. Its rapid adaptation to changes in water vapor concentration and compatibility with different water standards enhance calibration reliability. Demonstrated reproducibility in generating water vapor across a broad concentration range from 900 to over 25,000 ppmv, coupled with a substantial reduction in memory effects, makes this approach highly effective in both laboratory and field settings. This calibration advancement greatly enhances research capabilities for continuous atmospheric water vapor analysis, providing deeper insights into hydrological processes and atmospheric dynamics.

Mohammed G. Sghaireen, Mohammad Khursheed Alam, Ahmed Azhari Salih Mohamedeissa et al.

Background: Osseointegration is critical for the success of dental implants. Surface modifications of dental implants play a crucial role in enhancing osseointegration and implant stability. This in-vitro study aims to evaluate the influence of various surface modifications on dental implant stability. Materials and Methods: Dental implants with different surface modifications were prepared and subjected to in-vitro testing. Surface modifications included sandblasting, acid etching, and plasma spraying. Implant stability was assessed using resonance frequency analysis (RFA) and pull-out tests. Statistical analysis was performed to compare the stability of implants with different surface modifications. Results: The results showed that implants with sandblasted and acid-etched surfaces exhibited significantly higher stability compared with those with only a machined surface. The mean RFA values for sandblasted and acid-etched implants were 75 ± 5 and 80 ± 6, respectively, whereas machined implants recorded a mean RFA value of 60 ± 4. Similarly, pull-out tests demonstrated higher maximum tensile strengths for sandblasted and acid-etched implants compared with machined implants. Conclusion: Surface modifications, such as sandblasting and acid etching, significantly enhance dental implant stability in vitro. These modifications promote better osseointegration, which is crucial for the long-term success of dental implants in clinical practice.

Mikuláš Matoušek, Nam Vu, Niranjan Govind et al.

The emerging field of polaritonic chemistry explores the behavior of molecules under strong coupling with cavity modes. Despite recent developments in ab initio polaritonic methods for simulating polaritonic chemistry under electronic strong coupling, their capabilities are limited, especially in cases where the molecule also features strong electronic correlation. To bridge this gap, we have developed a novel method for cavity QED calculations utilizing the Density Matrix Renormalization Group (DMRG) algorithm in conjunction with the Pauli-Fierz Hamiltonian. Our approach is applied to investigate the effect of the cavity on the S0 -S1 transition of n-oligoacenes, with n ranging from 2 to 5, encompassing 22 fully correlated π orbitals in the largest pentacene molecule. Our findings indicate that the influence of the cavity intensifies with larger acenes. Additionally, we demonstrate that, unlike the full determinantal representation, DMRG efficiently optimizes and eliminates excess photonic degrees of freedom, resulting in an asymptotically constant computational cost as the photonic basis increases.

Merel L. R. van 't Hoff, Jennifer B. Bergner

Knowledge of the composition of material that will form planets is crucial to understand planetary diversity and the occurrence of potentially habitable planets. Ultimately, it is the chemistry in circumstellar disks that determines the global make up of planetary systems, as the dust in these disks grows into giant planet cores and rocky planets, the gas becomes incorporated in giant planet atmospheres, and the ices can be delivered to rocky planets by comets and meteorites. With the advent of ALMA a decade ago and the recent launch of JWST, the composition of the disk gas and ice can now be studied in great detail. This review will provide an overview of our current knowledge of the disk chemical structure, focusing on the six elements essential to life on Earth: carbon (C), hydrogen (H), nitrogen (N), oxygen (O), phosphorus (P) and sulfur (S).

Eric W. Fischer, Jan A. Syska, Peter Saalfrank

In the vibrational strong coupling (VSC) regime, molecular vibrations and resonant low-frequency cavity modes form light-matter hybrid states, named vibrational polaritons, with characteristic IR spectroscopic signatures. Here, we introduce a quantum chemistry based computational scheme for linear IR spectra of vibrational polaritons in polyatomic molecules, which perturbatively accounts for nonresonant electron-photon interactions under VSC. Specifically, we formulate a cavity Born- Oppenheimer perturbation theory (CBO-PT) linear response approach, which provides an approximate but systematic description of such electron-photon correlation effects in VSC scenarios, while relying on molecular ab initio quantum chemistry methods. We identify relevant electron-photon correlation effects at second-order of CBO-PT, which manifest as static polarizability-dependent Hessian corrections and an emerging polarizability-dependent cavity intensity component providing access to transmission spectra commonly measured in vibro-polaritonic chemistry. Illustratively, we address electron-photon correlation effects perturbatively in IR spectra of CO$_2$ and Fe(CO)$_5$ vibropolaritonic models qualitatively in sound agreement with non-perturbative CBO linear response theory.