1921年诺贝尔化学奖获得者——索迪

在探索微观元素的过程中,同位素与放射性元素位移定律的发现无疑具有里程碑式的意义。同位素的发现修正了道尔顿原子学说,元素位移规律的发现使放射化学成为一门独立的学科,为此1921年的诺贝尔化学奖授予了同位素与元素位移定律的发现者—弗雷德里克.索迪,2011年恰逢索迪逝世55周年,特写此文来纪念他对现代放射化学与核物理学做出的贡献。     

Emil Wohlwill's “Entdeckung des Isomorphismus”: A Nineteenth-Century “Material Biography” of Crystallography

Abstract

Eilhard Mitscherlich's experimental work on isomorphism in the crystallisation of many inorganic compounds was regarded by Emil Wohlwill (1835–1912) as a milestone in the history of the atomic–molecular theory. Despite his positivist account, Wohlwill's 1866 survey was primarily concerned with the material conditions that shaped Mitscherlich's theoretical assumptions on iso- and polymorphic crystallisation, narrowing the range of possible alternative models. Following an account of Wohlwill's exposition, and a discussion of his historiographic views, the paper shows how, from a historico-epistemological perspective, technical improvements in crystallography (an emerging branch of early-nineteenth-century mineralogy) were deeply entangled with a new interest in crystal formation as a cutting-edge research field of inorganic chemistry. This had fundamental implications for the development of atomic and molecular theory.     

Tracing Influence in Small Steps: Richard Kirwan's Quantified Affinity Theory

Abstract

This paper presents an attempt to negotiate the familiar historiographical difficulties of tracing influence in science without fear of accusations of whiggishness. Through a close reading of three papers presented to the Royal Society by Richard Kirwan in the early 1780s on specific gravity, proportions and affinity, it seeks to show that the search for the role of influence in the history of science need not be based on a present-centred value judgement of past science. Prevailing historiography tends to link Kirwan's work to notions of definite combining proportions, settling him firmly on the Proust side of the Berthollet–Proust debate and regarding his work as vaguely precursory to Dalton's atomic theory. My reading suggests, however, that these papers may well have had a surprising level of influence on Berthollet's Chemical Statics and should perhaps be viewed through a somewhat different historical lens. I hope to show that the tracing of historical influence can offer valuable insights to historians of science and that when influence is tracked in small steps only, and forwards rather than backwards, we can legitimately follow it without fear of present-centredness clouding our vision.     

The Nature of Chemical Bonds from PNOF5 Calculations

Natural orbital functional theory (NOFT) is used for the first time in the analysis of different types of chemical bonds. Concretely, the Piris natural orbital functional PNOF5 is used. It provides a localization scheme that yields an orbital picture which agrees very well with the empirical valence shell electron pair repulsion theory (VSEPR) and Bent’s rule, as well as with other theoretical pictures provided by valence bond (VB) or linear combination of atomic orbitals–molecular orbital (LCAO‐MO) methods. In this context, PNOF5 provides a novel tool for chemical bond analysis. In this work, PNOF5 is applied to selected molecules that have ionic, polar covalent, covalent, multiple (σ and π), 3c–2e, and 3c–4e bonds.     

A Letter Signed: The Very Beginnings of Dalton's Atomic Theory

Abstract

This paper explores the provenance and content of a previously unknown personal letter by John Dalton (1766–1844), which is dated 12 April 1803. It relates to a startling breakthrough in Dalton's research, which pre-dates by five months the earliest date in his laboratory notebook, namely, 6 September 1803. The author acquired the letter about thirty years ago, and now offers it to the public. He makes no attempt to explain how it contributes to — or even changes — our understanding of Dalton, but leaves that privilege to Dalton scholars.     

本科实验课程中的主观能动性激励方法

本科生实验课程是对理论知识进行实践的重要环节。为提高本科生在实验过程中对实验理论和技能的理性认识,增强自主学习的意识和兴趣,提出了“理论质疑”和“步骤调整”的方法,以激励学生在实验过程中能更好地发挥创造性思维,提升实验操作能力。该方法经过作者在指导本科生基础有机化学实验的过程中证明,学生在实验过程中的积极性得到明显提升,增强了对所学理论知识的认识和理解,更善于提出新的科学问题,能对实验方法的合理性和继续改进提出新的见解,理解了“尽信书不如无书”的道理。     

The possibility of constructing the hydrogen scale of the absolute atomic masses of the elements

The paper presents a scheme for the experimental-empirical construction of the existing chemical, physical, and carbon scales of the relative nonintegral atomic masses of the elements. The quantitative interrelation between the nonintegral relative atomic masses, their minimized fractional positive and negative natural deviations from integral numbers, and their integral parts are reproduced mathematically. Nonisotopic fractional deviations are shown to be a consequence of methodological side effects of the scheme for theoretical processing of the data of thorough physical and chemical measurements performed by Stas and Aston in constructing scales of relative atomic masses. In conformity with the Prout hypothesis, the absolute atomic mass unit and the corresponding Avogadro’s number value are suggested for the construction of the hydrogen scale of absolute atomic masses of nonisotopic elements, individual isotopes, and isotope-containing elements.     

Patterns of cation binding to the aromatic amino acid R groups in Trp,Tyr, and Phe

Previous joint experimental and theoretical work demonstrates that typically soluble peptides will be rendered insoluble in the presence of saturated sodium ions in aqueous solution due to disruption of cation-π interactions between Trp and Lys. The present work utilizes quantum chemical methods including density functional theory, symmetry-adapted perturbation theory, and even coupled cluster theory to determine the strengths of cation-π interactions for the aromatic R groups of Trp, Tyr, and Phe (approximated as skatole, methyl phenol, and toluene) with both alkali and alkaline-Earth atomic cations and electron-accepting R groups from Lys, Arg, and His approximated as methyl ammonium, guanidinium, and imidazolium cations. This work shows that sodium ion is still the most likely disrupter of peptide folding built upon cation-π interactions, since Trp, Tyr, and Phe all bind more strongly to sodium ion than to any of the polyatomic cations. Additionally, the atomic cation complex binding energies decrease with an increase in partial charge on the atomic cation in the complex. However, as the average partial charge increases in the interacting hydrogen atoms in the polyatomic cations, the binding energy increases. The disruption of such peptide–peptide cation-π interactions is certainly relevant for peptide design in β-sheets or β-hairpin structures, but it could also have implications for astrobiology.     

A letter signed: the very beginnings of Dalton's atomic theory

This paper explores the provenance and content of a previously unknown personal letter by John Dalton (1766-1844), which is dated 12 April 1803. It relates to a startling breakthrough in Dalton's research, which pre-dates by five months the earliest date in his laboratory notebook, namely, 6 September 1803. The author acquired the letter about thirty years ago, and now offers it to the public. He makes no attempt to explain how it contributes to--or even changes--our understanding of Dalton, but leaves that privilege to Dalton scholars.     

Exchange energy gradients with respect to atomic positions and cell parameters within the Hartree-Fock Gamma-point approximation

Recently, linear scaling construction of the periodic exact Hartree-Fock exchange matrix within the Gamma-point approximation has been introduced [J. Chem. Phys. 122, 124105 (2005)]. In this article, a formalism for evaluation of analytical Hartree-Fock exchange energy gradients with respect to atomic positions and cell parameters at the Gamma-point approximation is presented. While the evaluation of exchange gradients with respect to atomic positions is similar to those in the gas phase limit, the gradients with respect to cell parameters involve the accumulation of atomic gradients multiplied by appropriate factors and a modified electron repulsion integral (ERI). This latter integral arises from use of the minimum image convention in the definition of the Gamma-point Hartree-Fock approximation. We demonstrate how this new ERI can be computed with the help of a modified vertical recurrence relation in the frame of the Obara-Saika and Head-Gordon-Pople algorithm. As an illustration, the analytical gradients have been used in conjunction with the QUICCA algorithm [K. Nemeth and M. Challacombe, J. Chem. Phys. 121, 2877 (2004)] to optimize periodic systems at the Hartree-Fock level of theory.     

Hall transformation of exp( – r): Correction of the results

Owing to an error in his determination of the repulsion integral and the kinetic energy. Hall's results [1] for the ground state of atomic two-electron systems are wrong. Here these results have been corrected. For Z ≤ 5, the results have been obtained by determining the pertinent integrals numerically: but for Z ≥ 5, these can be found sufficiently accurately from Z expansions.     

John D. Roberts: In His Own Words and Those of His Friends

In honor of the 97th birthday of Professor John D. Roberts, the author has assembled a collection of poignant quotes and anecdotes, mostly written by Roberts himself, which embody his philosophies of life and his wide‐ranging experiences and interests. A brief summary of Roberts’s major scientific accomplishments is also presented.     

Application of integrated computer simulation approach to solid surfaces and interfaces

The atomistic understanding of the structure, reactivity, and electronic properties of solid surfaces and interfaces are essential for the design of novel catalysts and electronics/photonics devices which have high-performance and unexplored properties. Computational chemistry is expected not only to rationalize the experimental results but also to predict new features. We have applied integrated computer simulation methods including quantum chemistry, periodic density functional theory, molecular dynamics, embedded atom method, and atomic force microscopy simulation to various topics related to solid surfaces and interfaces. In the present paper, we reviewed our recent activities on supported metal catalysts, metal clusters, atomic force microscopy simulation, high-temperature superconductors, tribology, Si semiconductor and V₂O₅ catalysts. Our activities also involve the generation of a lot of new computer simulation codes. We emphasize that the integrated computer simulation system provides not only methods for scientific studies but also a key technology for industrial innovations in research and development.     

Multi‐Resolution Simulation of Biomolecular Systems: A Review of Methodological Issues

Theoretical‐computational modeling with an eye to explaining experimental observations in regard to a particular chemical phenomenon or process requires choices concerning essential degrees of freedom and types of interactions and the generation of a Boltzmann ensemble or trajectories of configurations. Depending on the degrees of freedom that are essential to the process of interest, for example, electronic or nuclear versus atomic, molecular or supra‐molecular, quantum‐ or classical‐mechanical equations of motion are to be used. In multi‐resolution simulation, various levels of resolution, for example, electronic, atomic, supra‐atomic or supra‐molecular, are combined in one model. This allows an enhancement of the computational efficiency, while maintaining sufficient detail with respect to particular degrees of freedom. The basic challenges and choices with respect to multi‐resolution modeling are reviewed and as an illustration the differential catalytic properties of two enzymes with similar folds but different substrates with respect to these substrates are explored using multi‐resolution simulation at the electronic, atomic and supra‐molecular levels of resolution.     

Reply to A Computational Evaluation of the Evidence for the Synthesis of 1,3‐Dimethylcyclobutadiene in Solid State and Aqueous Solution—Beyond the Experimental Reality

Following earlier reports on the photochemical synthesis of 1,3‐dimethylcyclobutadiene 8 , 10 in a protective host matrix, theoretical calculations for the formation of that adduct have been recently performed by Rzepa. 13 The author formulated criticisms based mainly on density functional theory calculations of ¹H NMR spectra. According to Rzepa the calculated spectra do not correspond with our measured spectra, which leads him to the conclusion that our interpretation is wrong, and that mainly cyclobutadiene has not been stabilized or even synthesized; we believe, however, that the initial model that Rzepa used for his calculations does not correspond to chemical reality or is at the very least a crude simplification of it, which implies that his calculations cannot match, in every point, our experimental spectra. Rzepa′s simplified models might be ‘reasonable’ from the theoretical point of view; however, in the case of assessment in the solid state, the theoretical setup does not force the system to preserve the confined stabilizing space defined by the crystalline matrix for encapsulated hosts in the solid state. Inversely, in the case of solution modeling, the theoretical setup is too rigid to properly assess the complex equilibria occurring in solution and to accurately determine the NMR spectra of exchanging species in solution. The inconsistency between our experimental results and the results of the theoretical models proposed by Rzepa is such that his conclusions are considered to be too far from experimental reality. Accurate modeling taking in account “reasonable” experimental details would be a worthwhile endeavor.     

Theoretical Investigation of Electrochemical Signal from Nanoscale Systems

In this paper, we report a theoretical study exploring the stochastic signal from electrochemical detection toward the nanometer scale systems. By using a discrete simulation as well as a statistical theory, this work investigates the distribution of the capturing times for redox molecules that released at a given distance from an electrode. We find that the capturing times tend to distribute over a wider range with a larger distance between the molecule’s source and the electrode, and thus the corresponding electrochemical signal would be somewhat less repeatable.     

Response to Geoffrey Neuss on how to teach the 4s and 3d orbital conundrum

In the accompanying article in this issue Neuss challenges the explanation that was first suggested by Schwarz for how to teach the relative occupation and ionization of atomic orbitals in the atoms of metals in the first transition series. The present article is a response to Neuss’ critique which includes a detailed examination of his claim that there is no conclusive evidence for the view that the scandium and other first transition metal atoms lose 4s electrons in preference to those located in 3d orbitals.

     

Ab initio prediction of 15N-NMR chemical shift in α-boron nitride based on an analysis of connectivities

Hydrogen-saturated cut-outs of hexagonal boron nitride have been used to model the solid state. Model compounds have been geometry optimized by means of density functional theory, whereas chemical shift calculations have been carried out at the coupled-perturbed Hartree–Fock level of theory employing gauge-including atomic orbital (GIAO) basis sets. The reliability of results has been tested against experimental values for chemical shifts in stable molecules with similar structural elements. With increasing cluster size, viz. a vanishing influence of the saturating hydrogens on the innermost nitrogen atoms, we find a convergence of ¹⁵N chemical shifts. A classification scheme for the chemical environment of a nitrogen atom has been set up according to its bonding graph including the second coordination sphere. For a given connectivity, chemical shifts vary within a few parts per million, thus enabling us to predict a ¹⁵N-NMR chemical shift of −285 ± 5 ppm for solid α-boron nitride. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 716–725, 1998     

Humphry Davy and the Problem of Analogy

Analogy, the comparison of one set of relations to another, was essential to Humphry Davy’s understanding of chemistry. Throughout his career, Davy used analogical reasoning to direct and to interpret his experimental analyses of the chemical reactions between substances. In his writing, he deployed analogies to organise and to explain his theories about the relations between physical processes and between the properties of different chemical elements and compounds. But Davy also regularly expressed two concerns about analogical comparison: first, that it was founded not on the rational interpretation of facts but on imaginative speculation; and second, that it was a kind of rhetoric, the persuasiveness of which depended not on material evidence but on misleading figures of speech. This article discusses the influences that informed Davy’s ambivalent assessment of the value of analogy, and it examines the distinct yet overlapping ways in which this assessment was expressed in his notebooks, his lectures and treatises on chemistry, his philosophical writings, and his poetry.