Polar Atoms Research Articles

Simulating structure and dynamics in small droplets of 1-ethyl-3-methylimidazolium acetate.

To investigate the structure and dynamics of small ionic liquid droplets in gas phase, we performed a DFT-based ab initio molecular dynamics study of several 1-ethyl-3-methylimidazolium acetate clusters in vacuum as well as a bulk phase simulation. We introduce an unbiased criterion for average droplet diameter and density. By extrapolation of the droplet densities, we predict the experimental bulk phase density with a deviation of only a few percent. The hydrogen bond geometry between cations and anions is very similar in droplets and bulk, but the hydrogen bond dynamics is significantly slower in the droplets, becoming slower with increasing system size, with hydrogen bond lifetimes up to 2000 ps. From a normal mode analysis of the trajectories, we identify the modes of the ring proton C-H stretching, which are strongly affected by hydrogen bonding. From analyzing these, we find that the hydrogen bond becomes weaker with increasing system size. The cations possess an increased concentration inside the clusters, whereas the anions show an excess concentration on the outside. Almost all anions point towards the droplet center with their carboxylic groups. Ring stacking is found to be a very important structural motif in the droplets (as in the bulk), but side chain interactions are only of minor importance. By using Voronoi tessellation, we define the exposed droplet surface and find that it consists mainly of hydrogen atoms from the cation's and anion's methyl and ethyl groups. Polar atoms are rarely found on the surface, such that the droplets appear completely hydrophobic on the outside.

Large-Scale Bose-Einstein Condensation in an Atomic Gas by Applying an Electric Field

Large-scale Bose-Einstein condensation (BEC) of cesium atoms has been observed (T=343K). The technical bottleneck of BEC is very small trapping volume (10-8cm3), which made the number of condensed atoms still stagnant (less than 107), much smaller than normal condensation (more than 1013), large-scale BEC has never been observed. In BEC experiment, scientists have applied magnetic field (used to trap atoms) and laser (used to cool atoms), but never considered applying electric field, because they think that all kinds of atoms are non-polar atoms. The breakthrough of the bottleneck lies in the application of electric field. In theory, despite 6s and 6p states of cesium are not degenerate, but Cs may be polar atom doesn't conflict with quantum mechanics because it is hydrogen-like atom. When an electric field was applied, Cs atoms become dipoles, therefore large-scale BEC can be observed. BEC experiment of cesium has been redone. From the entropy S=0, critical voltage Vc=78V. When V 0; when V > Vc, S Vc, almost all Cs atoms (bosons) are in exactly the same state，according to Feynman, “the quantum physics is the same thing as the classical physics”, so our classical theory can explain BEC experiment satisfactorily. Ultra-low temperature is to make Bose gas phase transition, we used critical voltage to achieve phase transition, ultra-low temperature is no longer necessary. Five innovative formulas were first reported in the history of physics, the publication of this article marking mankind will enter a new era of polar atoms.

The crystal structure of Z-DNA with untypically coordinated Ca2+ ions.

DNA oligomer duplexes with alternating cytosines and guanines in their sequence tend to form helices of the Z-DNA type, where the sugar and phosphate backbone forms a left-handed helix in a zigzag fashion with a repeat of two successive Watson-Crick pairs of nucleotides. Z-DNA duplexes often crystallize in complexes with diverse metal ions interacting with polar DNA atoms in various ways. This work describes the high-resolution crystal structure of a Z-DNA d(CGCGCG)2 duplex in complex with Ca2+ ions, unusually coordinated as an approximate pentagonal bipyramid by two neighboring guanines through their O6 and N7 atoms and a water molecule in the equatorial plane and a phosphate oxygen atom and another water molecule in the apical positions.

Advanced Structure-activity Relationships Applied to Mentha spicata L. Subsp. spicata Essential Oil Compounds as AChE and NMDA Ligands, in Comparison with Donepezil, Galantamine and Memantine – New Approach in Brain Disorders Pharmacology

Alzheimer's disease (AD) therapy is based on several natural and synthetic compounds that act as acetylcholinesterase (AChE) and N-methyl-D-aspartate receptor (NMDA) ligands that have limited efficiency in relieving AD symptoms. Recent studies show that inhibitors isolated from Mentha spicata L. subsp. spicata are promising for AD therapy. We aimed to identify novel and more potent phytopharmaceutical compounds for AD treatment by taking into account the compounds from Mentha spicata L. subsp. spicata essential oil. We generated structure-activity relationship (SAR) models that predict the biological activities of 14 Mentha spicata L. subsp. spicata compounds on AChE and NMDA by comparing their molecular features with those of the three conventional ligands: donepezil, galantamine and memantine. The most relevant descriptors for predicting the biological activities of considered compounds are solvent accessible area and their subdivided, hydrophobicity, energy of frontier molecular orbitals and counts of the aromatic ring and rotatable bounds. 1,8-cineole, the main compound from Mentha spicata L. subsp. spicata essential oil, resulted to be similar with memantine and dissimilar with donepezil in respect to hidrophobicity (logP1,8-cineole=2.95, logPmemantine=2.81, logPdonepezil=4.11), the energy of LUMO (eLUMO1,8-cineole=3.01 eV, eLUMOmemantine=3.35 eV, eLUMOdonepezil=-0.35 eV) and the solvent accessible surface areas over all hydrophobic (SA_H1,8-cineole= 350 Å2, SA_Hmemantine= 358 Å2, SA_Hdonepezil= 655 Å2) or polar atoms (SA_P1,8-cineole= 4 Å2, SA_Pmemantine=10 Å2, SA_Pdonepezil=44.62 Å2). Our results point towards 1,8-cineole as a good candidate for NMDA antagonism, with a weaker AChE inhibitory effect. Our results may be useful in establishing new therapeutic strategies for neurological disorders.

Full Protein Sequence Redesign with an MMGBSA Energy Function.

Computational protein design aims to create proteins with novel properties. A key element is the energy or scoring function used to select the sequences and conformations. We study the performance of an "MMGBSA" energy function, which combines molecular mechanics terms, a generalized Born and surface area (GBSA) solvent model, with approximations that make the model pairwise additive. Our approach is implemented in the Proteus software. The use of a physics-based energy function ensures a certain model transferability and explanatory power. As a first test, we redesign the sequence of nine proteins, one position at a time, with the rest of the protein having its native sequence and crystallographic conformation. As a second test, all positions are designed together. The contributions of individual energy terms are evaluated, and various parametrizations are compared. We find that the GB term significantly improves the results compared to simple Coulomb electrostatics but is affected by pairwise decomposition errors when all positions are designed together. The SA term, with distinct energy coefficients for nonpolar and polar atoms, makes a decisive contribution to obtain realistic protein sequences and can partially compensate for the absence of a GB term. With the best GBSA protocol, we obtain nativelike protein cores and Superfamily recognition of almost all of our sequences.

Solvent selection for explaining the morphology of nitroguanidine crystal by molecular dynamics simulation

In this article, a method was performed to predict the morphology of needle-shaped crystals by analyzing the growth mechanisms for the various crystal faces. As an example, the crystal morphology of a nitroguanidine (NQ) was investigated via molecular dynamics simulations. The modified attachment energy (MEA) model was constructed by introducing surface chemistry terms and the relevant morphology of the habit crystal faces. The results indicate that the growth morphology of NQ in vacuum is dominated by {220}, {040}, {111}, {131} and {311} faces. The {220} and {040} faces are parallel to the elongation direction of the crystal, while the other faces are at the needle tips direction. The atoms or atomic groups exposed in crystal surface were used to analyze the relationship between structure and morphology. Compared to the surrounding faces, the needle tip faces have a large number of polar atoms or atomic groups. The needle tip faces have a high electronegativity on N, O atoms via molecular electrostatic potential (ESP) analysis. Furthermore, the protic solvent was used to reduce the attachment energy of the tip surfaces for achieving the purpose of inhibiting the growth of needle tips. Gamma-butyrolactone as the selected solvent inhibited effectively the growth of the needle tip faces. The predicted result is serviceable for the formation design.

Statistical Analysis, Investigation, and Prediction of the Water Positions in the Binding Sites of Proteins.

Water molecules play a crucial role in biomolecular associations by mediating a hydrogen bond network or filling spaces with van der Waals interactions. Although current drug design technologies have taken water molecule interactions into account, their applications are still limited to their reliance on either excessive computer resources or a particular potential energy model. Here, we introduce a statistical method that is based on experimentally determined water molecules in the binding sites of high-resolution X-ray crystal structures to predict the potential hydration sites in the binding sites of crystal structures of interest. By clustering and analyzing the various interaction patterns of water molecules in the training data set, we derived a tetrahedron-water-cluster model based on a series of residue group triplets that form feature triangles of different shapes. In the tetrahedral-water-cluster model, a triplet of three polar atoms in the residue group triplet acts as the vertices of the bottom triangle of the tetrahedron, and the water molecule that interacts with these three polar atoms is set as the top vertex of the tetrahedron. By comparing the shapes of the bottom triangles in the training data set with the shape of the triangle in the residue group triplets in the crystal structure of interest, we can identify the bottom triangle that is most similar to the one in the residue group triplet of the crystal structure of interest. According to the tetrahedron-water-cluster model, the hydration site for the residue group triplet in the crystal structure of interest can be predicted based on the height of the tetrahedron that has the most similar bottom triangle in the training data set. A test set containing 193 crystal structures was used to evaluate model performance, and extensive comparison with the recently published program Dowser++ revealed that our model is at least as good at providing an accurate set of the potential hydration sites in crystal structures of interest.

Synthesis and evaluation of 1-phenyl-1H-1,2,3-triazole-4-carboxylic acid derivatives as xanthine oxidase inhibitors

This study mainly focused on the modification of the X2 position in febuxostat analogs. A series of 1-phenyl-1H-1,2,3-triazole-4-carboxylic acid derivatives (1a-s) with an N atom occupying the X2 position was designed and synthesized. Evaluation of their inhibitory potency in vitro on xanthine oxidase indicated that these compounds exhibited micromolar level potencies, with IC50 values ranging from 0.21µM to 26.13μM. Among them, compound 1s (IC50=0.21μM) showed the most promising inhibitory effects and was 36-fold more potent than allopurinol, but was still 13-fold less potent than the lead compound Y-700, which meant that a polar atom fused at the X2 position could be unfavorable for potency. The Lineweaver-Burk plot revealed that compound 1s acted as a mixed-type xanthine oxidase inhibitor. Analysis of the structure-activity relationships demonstrated that a more lipophilic ether tail (e.g., meta-methoxybenzoxy) at the 4′-position could benefit the inhibitory potency. Molecular modeling provided a reasonable explanation for the structure–activity relationships observed in this study.

Preparation and electrodeformation of silicone dielectric elastomers containing poly(propylene glycol diacetate) with different molecular weights

ABSTRACTIn this study, poly(propylene glycol diacetate)s (PPGDAs) with different molecular weights were obtained by the esterification reaction of poly(propylene glycol) and acetic anhydride. We effectively reduced the residual moisture and hydrophilicity of PPGDA. Then, poly(dimethyl siloxane) (PDMS) was modified by the addition of only 5 wt % PPGDA, which possessed a high dielectric constant (k) and a large actuated strain at a low electric field. PPGDA was used to enhance the molecular polarity because of the more polar oxygen atoms and the greater number of ester groups. The great increase in k and the low elastic modulus of the PPGDA–PDMS composites lead to a great increase in the electromechanical sensitivity. When the molecular weight of PPGDA was about 4000, the PPGDA–PDMS composites had the largest actuated strain. As a result, compared to the pure silicone elastomer (8.94%), it exhibited a greater strain of 17.31% at a low electric field of 10.5 V/μm (an increase of ca. 1.94 times). © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45329.

Orally Absorbed Cyclic Peptides.

Peptides and proteins are not orally bioavailable in mammals, although a few peptides are intestinally absorbed in small amounts. Polypeptides are generally too large and polar to passively diffuse through lipid membranes, while most known active transport mechanisms facilitate cell uptake of only very small peptides. Systematic evaluations of peptides with molecular weights above 500 Da are needed to identify parameters that influence oral bioavailability. Here we describe 125 cyclic peptides containing four to thirty-seven amino acids that are orally absorbed by mammals. Cyclization minimizes degradation in the gut, blood, and tissues by removing cleavable N- and C-termini and by shielding components from metabolic enzymes. Cyclization also folds peptides into bioactive conformations that determine exposure of polar atoms to solvation by water and lipids and therefore can influence oral bioavailability. Key chemical properties thought to influence oral absorption and bioavailability are analyzed, including molecular weight, octanol-water partitioning, hydrogen bond donors/acceptors, rotatable bonds, and polar surface area. The cyclic peptides violated to different degrees all of the limits traditionally considered to be important for oral bioavailability of drug-like small molecules, although fewer hydrogen bond donors and reduced flexibility generally favored oral absorption.

Diffusion of the small, very polar, drug piracetam through a lipid bilayer: an MD simulation study

One of the major goals to improve drug discovery is to understand the molecular properties that influence oral bioavailability. Molecular dynamics-based methods have been used to understand passive diffusion with atomic detail and to predict diffusivities and permeabilities. In this paper, we explore the structural and dynamic behavior of piracetam, a nootropic drug, using umbrella sampling, as it crosses a 1,2-dioleoyl-sn-glycero-3-phosphocholine bilayer model. This is accompanied with a potential of mean force profile, showing the partition equilibrium within the bilayer. We discuss important molecular properties and their influence to the permeation of this important drug. Piracetam changes its solution-dominant conformation, modifying its polar surface area and forming an internal hydrogen bond, to facilitate penetration into the hydrophobic core. Rotation and orientation patterns, as piracetam diffuses across the membrane, were also analyzed, and we found out that in bulk water and at the membrane center piracetam shows no specific orientation as it rotates quickly and freely, whereas near the phospholipids’ polar head groups its polar atoms are much more oriented and the rotation is slowed down by more than one order of magnitude. Altogether, the study provides a very detailed view of the events mediating the permeation of this small and very polar drug.

Theoretical and Experimental Proof of Alkali-Metal Atom as Polar Atom

In addition to polar molecules, there is no polar atom in the natural world, which is a deep-rooted traditional concept that has lasted for more than a century. However, our research showed that alkali-metal atoms form an exception. In theory, we proved that alkali atom may be polar atom doesn't conflict with quantum mechanics, which is a great breakthrough in measurement theory of quantum mechanics. Variation of the capacitance with temperature and density offers a means of separating polar and nonpolar atom, but no one has done these experiments so far. If alkali atom is nonpolar atom, its capacitance should be independent of temperature and density, because atomic nucleus located at the center of the electron cloud. Our experiments showed that Na, K, Rb and Cs atoms are polar atoms, because their capacitance is not only related to temperature, but also to density. Unlike alkali atoms, the capacitance of Hg gas is independent of temperature and density, so mercury is nonpolar atom. Therefore atoms can be divided into two categories: polar and nonpolar atom, this discovery will lead to an exciting revolution in Bose- Einstein condensation (BEC) research and condensed matter physics. BEC experiments have been carried out for decades, but the number of condensed atoms is still very small (<107) because scientists has never applied an electric field. Our innovation lies in the application of an electric field, we don't need magnetic field and lasers. When V=390 volts, condensates contained up to 2.51 × 1017 sodium atoms; when V=350 volts, condensates contained up to 1.93 × 1017 cesium atoms, large-scale BEC at T=343 K or 353 K has been observed. Now scientists generally assume that polar molecules may be used as candidate materials for quantum computers. In the future, polar atoms will replace polar molecules as candidate materials for quantum computers, because of its very small moment of inertia.

A Machine Learning Approach to Designing Guidelines for Acute Aquatic Toxicity

A support vector classification wrapper feature elimination approach was used to find the most relevant pairs of molecular features that adequately and accurately can predict acute aquatic toxicity. These pairs were then used to derive chemical thresholds or boundaries between chemical properties for toxic and nontoxic organic chemicals that can be used as a “rule of thumb” to design less toxic chemicals. The most relevant pairs were determined to be: Lowest Unoccupied Molecular Orbital (LUMO) and Aqueous Solubility (QPlogS), Difference between the LUMO and HOMO (dE) and Octonal-Water Partition Coefficient (QPlogo.w), and Difference between the LUMO and HOMO (dE) and Van der Waals surface area of polar nitrogen and oxygen atoms (PSA). Projected hyper planes were constructed for each pair and the following thresholds were found: for Lowest Unoccupied Molecular Orbital (LUMO) and Aqueous Solubility (QPlogS) they roughly correspond to QPlogS>-1 and LUMO>1, and for Octonal-Water Partition Coefficient (QPlogo.w) vs. difference between the LUMO and HOMO (dE) they roughly correspond to QPlogo.w 9. This study shows how a statistical approach such as support vector machines can be applied to the rational design of chemicals with reduced toxicity.

Mayer Bond Order as a Metric of Complexation Effectiveness in Lead Halide Perovskite Solutions

One of the most appealing features of solar cells made from hybrid organic–inorganic perovskites is that they can be processed directly from solution, leading to low cost, energy-efficient processing. Numerous studies have shown that the composition of these solutions and the choice of solvent (or solvent blend) affects the efficiency of the resulting solar cell. Despite the importance of this correlation for performance, the choice of solvent(s) used to deposit the perovskite precursors has been largely a matter of experimental trial-and-error. In this work, we present a coherent theory explaining the molecular origin of the efficacy of solvent choice, which lends itself to the creation of a fast quantum mechanical-based screening process that facilitates the design of effective new solvents. We also provide the first theoretical confirmation of complexation of HOIP precursors in solution, including their structure and relative stability. We show that the Mayer bond order of a solvent’s polar atoms predi...

DNA minor groove electrostatic potential: influence of sequence-specific transitions of the torsion angle gamma and deoxyribose conformations

The structural adjustments of the sugar-phosphate DNA backbone (switching of the γ angle (O5′–C5′–C4′–C3′) from canonical to alternative conformations and/or C2′-endo → C3′-endo transition of deoxyribose) lead to the sequence-specific changes in accessible surface area of both polar and non-polar atoms of the grooves and the polar/hydrophobic profile of the latter ones. The distribution of the minor groove electrostatic potential is likely to be changing as a result of such conformational rearrangements in sugar-phosphate DNA backbone. Our analysis of the crystal structures of the short free DNA fragments and calculation of their electrostatic potentials allowed us to determine: (1) the number of classical and alternative γ angle conformations in the free B-DNA; (2) changes in the minor groove electrostatic potential, depending on the conformation of the sugar-phosphate DNA backbone; (3) the effect of the DNA sequence on the minor groove electrostatic potential. We have demonstrated that the structural adjustments of the DNA double helix (the conformations of the sugar-phosphate backbone and the minor groove dimensions) induce changes in the distribution of the minor groove electrostatic potential and are sequence-specific. Therefore, these features of the minor groove sizes and distribution of minor groove electrostatic potential can be used as a signal for recognition of the target DNA sequence by protein in the implementation of the indirect readout mechanism.

Charge Control in Two Isostructural Anionic/Cationic CoII Coordination Frameworks for Enhanced Acetylene Capture.

Two isostructural CoII -based metal-organic frameworks (MOFs) with the opposite framework charges have been constructed, which can be simply controlled by changing the tetrazolyl or triazolyl terminal in two bifunctional ligands. Notably, the cationic MOF 2 can adsorb much more C2 H2 than the anionic MOF 1 with an increase of 88 % for C2 H2 uptake at 298 K in spite of more active nitrogen sites in 1. Theoretical calculations indicate that both nitrate and triazolyl play vital roles in C2 H2 binding and the C2 H2 adsorption isotherm confirms that the enhanced C2 H2 uptake for 2 (225 and 163 cm3 g-1 at 273 and 298 K) is exceptionally high for MOF materials without open metal sites or uncoordinated polar atom groups on the frameworks.

Erratum: Proton solvation in protic and aprotic solvents [J. Comput. Chem. 2015, 37, 1082-1091

The authors were using for dimethyl sulfoxide (DMSO) a value of the dielectric constant of 36.7, which is lower than the correct value of 46.7. We are sorry for this confusion. The purpose of this erratum is to demonstrate the consequences on the results using the correct value of the DMSO dielectric constant. With the larger value of the dielectric constant the individual electrostatic solvation energies of the protonated and deprotonated molecular species are all more negative. However, for the computation of pKA values differences of these solvation energies are used, where these changes are nearly compensated. As final result no change in the value of proton solvation in DMSO was obtained remaining at −266.4 kcal/mol.1 The individual computed pKA values exhibit minor changes (see Table 1) with a root mean square deviation (pKA-RMSD) of 0.42 and a mean signed deviation (pKA-MSDnew-old) of −0.2 between the new and old pKA values. The pKA-RMSD between computed and measured pKA values is with 0.65 (without outliers) slightly smaller than before, where it was 0.75. The value of pKA-MSDcomp-exp remains practically the same.1 Hence, pKA values seem to be robust against moderate deviations (less than 20%) of the dielectric constant used for the computation. It can be expected that this is less the case for variations of atomic radii and atomic partial charges. As an aprotic solvent DMSO does not possess polar hydrogen atoms. Due to the lack of polar hydrogens the atomic charges of the solvent molecules come less close to atoms of solute molecule than in case of a protic solvent like water. To account for this solvation effect the solute atomic radii must be enlarged compared to the atomic radii in water. For this purpose, we use radii enhancement factors, which are determined by minimizing the pKA-RMSD of measured and computed pKA values. Figure 1 shows the dependence of the pKA-RMSD and the proton solvation energy as a function of the enhancement factor α. The optimal value of the enhancement factor is α = 1.28, if the three compounds, 17, 18, 19, involving a sulfur atom are ignored. The resulting proton solvation energy of −266.4 kcal/mol is again in a plateau regime. Considering the three sulfur compounds separately, the optimized sulfur radius is 2.18 Å, which is the same value as before.1 However, when including these three sulfur compounds in the optimization procedure the smallest pKA-RMSD of 0.65 is obtained with the enhancement factor α = 1.25 and the proton solvation energy is −266.4 kcal/mol as obtained before.1 pKA-RMSD value (•, left scale) and proton solvation energy [kcal/mol] (◊, right scale) for DMSO are plotted as a function of the multiplicative atomic radius enhancement factor α. Ignoring the three sulfur compounds (No. 17–19) the optimal enhancement factor is 1.28 yielding a pKA-RMSD value of 0.65. The resulting proton solvation energy is −266.4 kcal/mol.1 Finally we like to correct Table 1 in the referred article, since the references to the literature were skewed. Again we are very sorry for the confusion.

Aromatic Side Chain Water-to-Lipid Transfer Free Energies Show a Depth Dependence across the Membrane Normal.

Quantitating and understanding the physical forces responsible for the interactions of biomolecules are fundamental to the biological sciences. This is especially challenging for membrane proteins because they are embedded within cellular bilayers that provide a unique medium in which hydrophobic sequences must fold. Knowledge of the energetics of protein-lipid interactions is thus vital to understand cellular processes involving membrane proteins. Here we used a host-guest mutational strategy to calculate the Gibbs free energy changes of water-to-lipid transfer for the aromatic side chains Trp, Tyr, and Phe as a function of depth in the membrane. This work reveals an energetic gradient in the transfer free energies for Trp and Tyr, where transfer was most favorable to the membrane interfacial region and comparatively less favorable into the bilayer center. The transfer energetics follows the concentration gradient of polar atoms across the bilayer normal that naturally occurs in biological membranes. Additional measurements revealed nearest-neighbor coupling in the data set are influenced by a network of aromatic side chains in the host protein. Taken together, these results show that aromatic side chains contribute significantly to membrane protein stability through either aromatic-aromatic interactions or placement at the membrane interface.

Blend polymer electrolyte films based on poly(ethyl methacrylate)/poly(vinylidenefluoride-co-hexafluoropropylene) incorporated with 1-butyl-3-methyl imidazolium iodide ionic liquid

Poly(ethyl methacrylate) (PEMA) and poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP) in the weight ratio of 70:30 are chosen as hosts for the development of a polymer blend electrolyte system containing lithium trifluoromethanesulfonate (LiTf) salt as ion provider and 1-butyl-3-methyl imidazolium iodide (BMII) as ionic liquid. The best ambient conductivity is achieved at 4.86×10−5Scm−1 in the polymer blend-salt sample incorporated with 12.5wt.% BMII. The imidazolium (BMI+) cations of BMII have interacted with the oxygen atoms in the ethoxy (O–C2H5) groups of PEMA as well as the fluorine atoms in the CF2 groups of PVdF-HFP. Competition between the Li+ ions and BMI+ ions for the coordination sites at the polar atoms of the polymer blend host exists and plays a role in determining the number density and mobility of the free ions. Thermal gravimetric analysis (TGA) has shown that the BMII-based polymer electrolytes are thermally stable up to about 200°C.

Bose–Einstein condensation in a vapor of sodium atoms in an electric field

Bose–Einstein condensation (BEC) at normal temperature (T=343K) has been observed because an electric field was first applied. There are two ways to achieve phase transition: lower the temperature of Bose gas or increase its density. This article provides more appropriate method: increase the voltage. In theory, 3s and 3p states of sodium are not degenerate, but Na may be polar atom doesnot conflict with quantum mechanics because it is hydrogen-like atom. Our innovation lies in we applied an electric field used for the orientation polarization. Na vapor was filled in a cylindrical capacitor. In order to determine the polarity of sodium, we measured the capacitance at different temperatures. If Na is non-polar atom, its capacitance should be independent of temperature because the nucleus of atom is located at the center of the electron cloud. But our experiment shows that its capacitance is related to temperature, so Na is polar atom. In order to achieve Na vapor phase transition, we measured the capacitance at different voltages. From the entropy of Na vapor S=0, the critical voltage Vc=68volts. When V<Vc, many atoms are in random orientation S>0; when V>Vc, the atoms become aligned with the field S<0, phase transition occurred. When V=390volts »Vc, the capacitance decreased from C=1.9C0 to C≈C0 (C0 is the vacuum capacitance), this result implies that almost all the Na atoms (more than 98%) are aligned with the field, Na vapor entered quasi-vacuum state. We create a BEC with 2.506×1017 atoms, condensate fraction reached 98.9%. This is BEC in momentum space. Our experiment shows that if a Bose gas enters quasi-vacuum state, this also means that it underwent phase transition and generates BEC. Therefore, quasi-vacuum state of alkali gas is essentially large-scale BEC. This is an unexpected discovery. BEC and vacuum theory are two unrelated research areas, but now they are closely linked together. The maximum induced dipole moment dind≤7.8×10−15ecm can be neglected. Ultra-low temperature is in order to make Bose gas phase transition, we achieve the phase transition by the critical voltage, so the ultra-low temperature is not necessary. According to the standard proposed by Ketterle, although we didn’t use laser cooling atoms, our experiment is real ideal BEC. Na material with purity 99.95% was supplied by Strem Chemicals Co., USA. Our experiments are easily repeated because low temperature is not necessary.