Hasil untuk "Physical and theoretical chemistry"

G. T. Velde, F. Bickelhaupt, E. Baerends et al.

D. Tasis, N. Tagmatarchis, A. Bianco et al.

E. Tiesinga, Peter J. Mohr, D. Newell et al.

We report the 2018 self-consistent values of constants and conversion factors of physics and chemistry recommended by the Committee on Data of the International Science Council (CODATA). The recommended values can also be found at physics.nist.gov/constants. The values are based on a least-squares adjustment that takes into account all theoretical and experimental data available through 31 December 2018. A discussion of the major improvements as well as inconsistencies within the data is given. The former include a decrease in the uncertainty of the dimensionless fine-structure constant and a nearly two orders of magnitude improvement of particle masses expressed in units of kg due to the transition to the revised International System of Units (SI) with an exact value for the Planck constant. Further, because the elementary charge, Boltzmann constant, and Avogadro constant also have exact values in the revised SI, many other constants are either exact or have significantly reduced uncertainties. Inconsistencies remain for the gravitational constant and the muon magnetic-moment anomaly. The proton charge radius puzzle has been partially resolved by improved measurements of hydrogen energy levels.

M. Ruggenthaler, D. Sidler, A. Rubio

In this review, we present the theoretical foundations and first-principles frameworks to describe quantum matter within quantum electrodynamics (QED) in the low-energy regime, with a focus on polaritonic chemistry. By starting from fundamental physical and mathematical principles, we first review in great detail ab initio nonrelativistic QED. The resulting Pauli-Fierz quantum field theory serves as a cornerstone for the development of (in principle exact but in practice) approximate computational methods such as quantum-electrodynamical density functional theory, QED coupled cluster, or cavity Born–Oppenheimer molecular dynamics. These methods treat light and matter on equal footing and, at the same time, have the same level of accuracy and reliability as established methods of computational chemistry and electronic structure theory. After an overview of the key ideas behind those ab initio QED methods, we highlight their benefits for understanding photon-induced changes of chemical properties and reactions. Based on results obtained by ab initio QED methods, we identify open theoretical questions and how a so far missing detailed understanding of polaritonic chemistry can be established. We finally give an outlook on future directions within polaritonic chemistry and first-principles QED.

D.N. Sokolov, V.S. Myasnichenko, O.V. Polev et al.

The thermal stability of gold nanostars with two types of initial morphology: a great dodecicosacron and a great inverted snub icosidodecahedron was studied. The initial nanostar configurations were obtained using the Atomsk program, followed by structural relaxation. Thermally induced stress was simulated using the Monte Carlo method (Metropolis scheme). Interatomic interactions were described by the tight-binding potential. Critical destabilization temperatures, which increase with increasing size for both types of the initial morphology, were determined. Patterns of structural segregation during thermally induced stress up to the melting temperature were also established. Despite the dominance of the local FCC structure in the central part of the nanostars, the nature of the distribution of local HCP structure differs for the considered types of the initial morphology up to the melting temperature. Thermal degradation was shown to begin with «multiple rays» of nanostars, where the local atomic density is lower than the surface average one. The results allow us to predict the stability of anisotropic nanoparticles for photothermal applications.

Yui FUJIHARA, Takeshi KOBAYASHI

Lithium-ion batteries are used on an increasingly large scale, making their lifetime prediction a critical issue. Especially, a rapid decrease in capacity after the mild degradation period, referred to as the knee point, is often observed, and thus understanding the knee point and its mechanism is a critical issue. Although numerous studies have been dedicated to the analysis of this phenomenon, studies on a commercial large-format lithium-ion battery are lacking. Further studies are required to continuously track changes over time and elucidate the source of knee points during operation. Herein, we conduct degradation cycle tests using a large-format commercial lithium-ion battery (> 50 Wh, LiNi0.5Co0.2Mn0.3O2/graphite) and analyze the knee points during cycling by employing electrochemical impedance spectroscopy (EIS) at different states of charge (SOCs) to track the degradation state over time, in combination with differential analysis and post-mortem methods. As a result, two knee points appear during degradation, caused by increases in resistance that are mainly derived from electrolyte depletion and Li plating at the anode. These observations are described based on the SOC dependency of the EIS results, which can be leveraged to identify the cause of knee points.

K. Oberg, S. Facchini, D. Anderson

Planets form in disks of gas and dust around young stars. The disk molecular reservoirs and their chemical evolution affect all aspects of planet formation, from the coagulation of dust grains into pebbles to the elemental and molecular compositions of the mature planet. Disk chemistry also enables unique probes of disk structures and dynamics, including those directly linked to ongoing planet formation. We review the protoplanetary disk chemistry of the volatile elements H, O, C, N, S, and P; the associated observational and theoretical methods; and the links between disk and planet chemical compositions. Three takeaways from this review are: ▪ The disk chemical composition, including the organic reservoirs, is set by both inheritance and in situ chemistry. ▪ Disk gas and solid O/C/N/H elemental ratios often deviate from stellar values due to a combination of condensation of molecular carriers, chemistry, and dynamics. ▪ Chemical, physical, and dynamical processes in disks are closely linked, which complicates disk chemistry modeling, but they also present an opportunity to develop chemical probes of different aspects of disk evolution and planet formation. Expected final online publication date for the Annual Review of Astronomy and Astrophysics, Volume 61 is August 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Niels Kubitza, Carina Büchner, J. Sinclair et al.

MAX phases are layered solids with unique properties combining characteristics of ceramics and metals. MXenes are their two-dimensional siblings that can be synthesized as van der Waals stacked and multi-/single-layer nanosheets, which possess chemical and physical properties that make them interesting for a plethora of applications. Both families of materials are highly versatile in terms of their chemical composition and theoretical studies suggest that many more members are stable and can be synthesized. This is very intriguing because new combinations of elements, and potentially new structures, can lead to further (tunable) properties. In this review, we focus on the synthesis science (including non-conventional approaches) and structure of members less investigated, namely compounds with more exotic M-, A-, and X-elements, for example nitrides and (carbo)nitrides, and the related family of MAB phases.

Guanyou Lin, Miqin Zhang

ConspectusTheranostic nanoparticles' potential in tumor treatment has been widely acknowledged thanks to their capability of integrating multifaceted functionalities into a single nanosystem. Theranostic nanoparticles are typically equipped with an inorganic core with exploitable physical properties for imaging and therapeutic functions, bioinert coatings for improved biocompatibility and immunological stealth, controlled drug-loading-release modules, and the ability to recognize specific cell type for uptake. Integrating multiple functionalities in a single nanosized construct require sophisticated molecular design and precise execution of assembly procedures. Underlying the multifunctionality of theranostic nanoparticles, ligand chemistry plays a decisive role in translating theoretical designs into fully functionalized theranostic nanoparticles. The ligand hierarchy in theranostic nanoparticles is usually threefold. As they serve to passivate the nanoparticle's surface, capping ligands form the first layer directly interfacing with the crystalline lattice of the inorganic core. The size and shape of nanoparticles are largely determined by the molecular property of capping ligands so that they have profound influences on the nanoparticles' surface chemistry and physical properties. Capping ligands are mostly chemically inert, which necessitates the presence of additional ligands for drug loading and tumor targeting. The second layer is commonly utilized for drug loading. Therapeutic drugs can either be covalently conjugated onto the capping layer or noncovalently loaded onto nanoparticles via drug-loading ligands. Drug-loading ligands need to be equally versatile in properties to accommodate the diversity of drugs. Biodegradable moieties are often incorporated into drug-loading ligands to enable smart drug release. With the aid of targeting ligands which usually stand the tallest on the nanoparticle surface to seek and bind to their corresponding receptors on the target, theranostic nanoparticles can preferentially accumulate at the tumor site to attain a higher precision and quantity for drug delivery. In this Account, the properties and utilities of representative capping ligands, drug-loading ligands, and targeting ligands are reviewed. Since these types of ligands are often assembled in close vicinity to each other, it is essential for them to be chemically compatible and able to function in tandem with each other. Relevant conjugation strategies and critical factors with a significant impact on ligands' performance on nanoparticles are discussed. Representative theranostic nanoparticles are presented to showcase how different types of ligands function synergistically from a single nanosystem. Finally, the technological outlook of evolving ligand chemistry on theranostic nanoparticles is provided.

Shakeel Ahmad, Jalil ur Rehman, Muhammad Usman et al.

Ziad Guerfi, O. Kribaa, H. Djouama

Hydroxyapatite (HAp) is a ceramic composed of calcium phosphate, frequently employed as a bone substitute material due to its biocompatibility and bioactivity. Over the past century, there has been substantial attention in fields such as orthopedics and plastic surgery. Remarkably, synthetic HAp exhibits properties akin to those found in natural bone and teeth. Computational theoretical chemistry focuses on numerically computing molecular electronic structures and interactions. As chemistry education evolves, it's imperative to acknowledge the increasing significance of computational tools in research. Density Functional Theory (DFT) stands out as the most widely adopted method in contemporary computational chemistry. In this study, we synthesized Hydroxyapatite (HAp) via the double decomposition method using synthetic sources. The synthesized materials underwent thorough characterization, including X-ray Diffraction (XRD), UV-visible spectroscopy, and Fourier Transform Infrared (FTIR) spectroscopy under various conditions. Additionally, we performed quantum mechanical computations on the HAp molecule using density functional theory. Our results were then compared with experimental data. Our experimental findings highlight the successful synthesis of HAp, particularly under specific temperature conditions. Moreover, the quantum chemistry calculations exhibited excellent agreement with the experimental results, especially in terms of spectroscopic characterizations.

Bin Qiao, Tao Lv

Titanium and its alloys have been widely adopted in dental prosthetics due to their excellent biocompatibility, light weight, high resilience and good corrosion resistance. The human oral cavity is the second largest microbial host system after the human intestine, with a large number of microbial species. This complex environment of multiple groups of microorganisms promotes the formation of biofilms on the surface of oral implant titanium materials, leading to possible peri-implant inflammation which accelerates the surface corrosion of the titanium implant material. Candida albicans is a common fungus, and the study of the interaction between Candida albicans and titanium alloys is of great importance for the later systematic study of the corrosion effect of the fungus on the metal. In this study, fluorescence microscopy, scanning electron microscopy and electrochemical analysis techniques were adopted to systematically study the formation of microbial films of Candida albicans on the surface of titanium-nickel alloy. The electrochemical behavior of the corrosion of titanium-nickel alloy by Candida albicans were investigated with open circuit potential, potentiodynamic polarization curves and electrochemical impedance spectroscopy. The combined action of metabolites produced by Candida albicans, the extracellular polymer matrix and the formation of microbial film led to the changes in the corrosion electrochemistry of titanium-nickel alloy.

Zhentao Bian, Guangzhen Zhao, Long Chao et al.

Due to the unique physicochemical properties, heteroatom doping of porous carbon has attracted wide attention. However, the complicated synthesis process and high cost limit its mass production. In this work, nitrogen and oxygen co-doped porous carbon materials (N-O-PCMs) derived from pine mushroom (PM) were prepared using a “one-step” carbonization and activation approach with potassium hydroxide (KOH) as active agent and at different PM/KOH mass ratios. The as-prepared hierarchical porous carbon materials are shown to not only contain rich N and O species, but also have an appropriate mesopore ratio and a narrow mesopore size distribution. Among all samples, the sample N-O-PCM-3 exhibits the largest specific surface area (935.8 m2 g−1), greatest total pore volume (0.56 cm3 g−1), highest content of oxygen (20.1 at.%) and nitrogen (4.9 at.%) as well as optimal hierarchical porous structure. The N-O-PCMs were tested in two electrode systems using 1 M Na2SO4 aqueous electrolyte. N-O-PCM-3 shows an energy density of up to 35.9 Wh kg−1 at 360 W kg−1 and an outstanding long-term stability (89.7 % after 10,000 cycles). This work proposes a facile and low-cost method for synthesizing multiple heteroatom-doped hierarchical porous carbon for supercapacitors.

Angelika A. Adamus-Grabicka, Magdalena Markowicz-Piasecka, Marcin Cieślak et al.

A series of 3-benzylidenechrmanones <b>1</b>, <b>3</b>, <b>5</b>, <b>7</b>, <b>9</b> and their spiropyrazoline analogues <b>2</b>, <b>4</b>, <b>6</b>, <b>8</b>, <b>10</b> were synthesized. X-ray analysis confirms that compounds <b>2</b> and <b>8</b> crystallize in a monoclinic system in P2₁/n space groups with one and three molecules in each asymmetric unit. The crystal lattice of the analyzed compounds is enhanced by hydrogen bonds. The primary aim of the study was to evaluate the anti-proliferative potential of 3-benzylidenechromanones and their spiropyrazoline analogues towards four cancer cell lines. Our results indicate that parent compounds <b>1</b> and <b>9</b> with a phenyl ring at C2 have lower cytotoxic activity against cancer cell lines than their spiropyrazolines analogues. Analysis of IC₅₀ values showed that the compounds <b>3</b> and <b>7</b> exhibited higher cytotoxic activity against cancer cells, being more active than the reference compound (4-chromanone or quercetin). The results of this study indicate that the incorporation of a pyrazoline ring into the 3-arylideneflavanone results in an improvement of the compounds’ activity and therefore it may be of use in the search of new anticancer agents. Further analysis allowed us to demonstrate the compounds to have a strong inhibitory effect on the cell cycle. For instance, compounds <b>2</b>, <b>10</b> induced 60% of HL-60 cells to be arrested in G2/M phase. Using a DNA-cleavage protection assay we also demonstrated that tested compounds interact with DNA. All compounds at the concentrations corresponding to cytotoxic properties are not toxic towards red blood cells, and do not contribute to hemolysis of RBCs.

Ilham Elazhary, A. Boutouil, Hicham Ben El Ayouchia et al.

Hendry. I. Elim, L. Chiang

In providing the best nanocarbon-based medicine particularly associated with their multitasking healing system, an advanced knowledge and understanding of physical chemistry engineering is compulsory. Discovery of the first spherical nanocarbon cage C60, namely, fullerene or buckyball by R. Smalley and his colleague in ~1986 at Rice university made the former elected as a chemistry Nobel laureate 10 years later in 1996. Various investigations in conjunction with fullerenes had been tremendously pursued in many interesting research fields, especially, on its characters including nonlinear and optical limiting behaviors, ultrafast dynamics of electrons in 5-level models, and advanced theoretical and computational cooperation system involving fullerenes encapsulated in a carbon nanotube (CNT). This present editorial communication stimulates an alternative view of physical chemistry engineering of fullerene and its derivatives functioning as nanofullerene-based medicine and its potential healing impacts. Our aims focus on the use of such non-toxic nanocarbons for various broad application leading to a number of different medicinal products.

Guanghui Yuan, Huafeng Jin, Yan Zhao

An innovative reduced graphene oxide wrapped sulfur/polypyrrole (S/PPy@RGO) composite is synthesized via a one-pot polymerization of pyrrole monomer in a sulfur/reduced graphene oxide aqueous suspension. This one-pot preparation method is efficient through its inherent simplicity and low cost. The resultant S/PPy@RGO composite was characterized via EDS, XRD, SEM, TEM and electrochemical measurements. In the S/PPy@RGO ternary composite, reduced graphene oxide played a crucial role of coating a thin layer to trap soluble polysulfide intermediates, provide a continuous electrically conducting network and accommodate volume expansion. Meanwhile polypyrrole with its high absorptivity, joins sulfur and RGO as a binding agent, and tether polysulfides into its porous framework. Therefore, the synthesized S/PPy@RGO composite delivers excellent rate ability and highly cycling stability. This composite can retain a specific discharge capacity of 615.3 mAh g-1 at 0.2C, even after 100 cycles.

Jingbo Liu, Jihui Wang, Wenbin Hu

Erosion–corrosion behavior of an X65 steel reducer in oilfield formation water containing quartz sand particles was investigated using circulating loop system and scanning electron microscopy (SEM). The corrosion behavior of the X65 reducer during the erosion–corrosion was determined by electrochemical impedance spectroscopy (EIS), and the erosion behavior of the X65 reducer was simulated and calculated via computational fluid dynamic (CFD) method. By the synergistic interaction between erosion and corrosion, the pure corrosion rate, pure erosion rate, corrosion-enhanced erosion rate and erosion-enhanced corrosion rate of the typical reducer locations in the erosion–corrosion rate were quantified and compared. The experimental and simulation results indicated that with the decreasing of tube diameter the erosion–corrosion rate, erosion rate (total erosion rate, pure erosion rate and corrosion-enhanced erosion rate) and their percentages in erosion–corrosion rate are increased. And the total corrosion rate and erosion-enhanced corrosion rate are also increased with the decreasing of tube diameter, but their percentages in erosion–corrosion rate are reduced. From the location of tube top, tube side to the tube bottom, a similar erosion–corrosion behavior could be obtained except for the reduction of corrosion-enhanced erosion rate and its percentage in erosion–corrosion rate. This erosion–corrosion behavior of the reducer is result from the distribution of flow velocity and sand particle concentration and the synergistic interaction between erosion and corrosion, especially the erosion-enhanced corrosion behavior.

M. Abdallah, E. Gad, J. Al-Fahemi et al.

Bernd Kollmann, Zhongrui Chen, D. Lüftner et al.

We present a combined experimental and theoretical study of electronic and optical properties of dihydro-tetraaza-acenes (DHTAn). Using solvent-free condensation, we are able to synthesize not only DHTA5 but also the longer DHTA6 and DHTA7 molecules. We then investigate their gas-phase electronic structures by means of ab initio density functional calculations employing an optimally tuned range-separated hybrid functional. By comparing with the parent linear oligoacenes (nA) and based on computed ionization potentials and electron affinities, we predict DHTAn molecules to be more stable than acenes of the same length, where we expect DHTAn molecules to be persistent at least up to n = 7 rings. We further exploit the analogy with nA by analyzing the entire intramolecular π-band structure of the DHTAn molecules. This clearly reveals that the additional two electrons donated by the dihydropyrazine group are delocalized over the entire molecule and contribute to its π-electron system. As a consequence, the symmetry of the frontier orbitals of DHTAn differs from that of the parent nA molecule. This also affects the UV–vis absorption spectra which have been measured for DHTA5, 6, and 7 dissolved in dimethyl sulfoxide and analyzed by means of excited state calculations within a time-dependent density functional theory framework.