Twofold Excess Research Articles

The extraction of tin (Sn) from primary tin ore deposits using wet chlorination

More than half of the world’s tin production is from secondary ore deposits. However, along with its depletion, PT Timah Tbk has explored and mined the primary deposits in Belitung, one that is expected to become tin’s new source. Tin was found liberated as cassiterite in the secondary deposits, while in the primary, it was associated with other minerals requiring more complex processing. Therefore, a suitable technology is needed to extract the tin from the primary ore deposits. This research aims to observe the extraction of tin from primary deposits (oxide and skarn ores) using HCl wet chlorination, observed at different temperature (60 – 90°C), HCl concentrations (10 – 50 % excess of stoichiometric amount), leaching time (60 – 300 minutes), and with or without the addition of oxidant (hydrogen peroxide, H2O2). The research found that the highest percentage of tin extraction from oxide and skarn ores was 92.32% and 97.28%, respectively. Both results were achieved at the same optimum condition: temperature of 60°C, 50% excess of HCl, 240 minutes of leaching time, and at two-fold excess of the stoichiometric amount of H2O2. It was concluded that oxidative wet chlorination could be used to recover tin from its primary ore deposits.

Efficiency of regional agriculture state support

The study analyzed data on state support for agricultural production in the Samara region. The regional level is the main source of budgetary funding for the agro-industrial complex. The Samara region is a pilot region in the research field into the results impact effectiveness of support measures on the agricultural organizations activities. The study purpose is to substantiate the need to improve state support in agriculture in the Samara region. It is necessary to solve the following tasks: to analyze the experience of state regulation in the Samara region agro-industrial complex; to classify the existing directions of state support for agriculture; to substantiate the need to correct the existing approach when improving state support for agricultural production. As a result of the consistent policy implementation in the field of agro-industrial complex supporting, agricultural production in the Samara region was able to become quite effective. The twofold excess of taxes in 2019 over the amount of support indicates that agricultural producers were able to switch to expanded reproduction using their resources. If the current situation persists in the long term, then the state role will be reduced to stimulating extremely promising directions for the region’s agro-industrial complex development.

Environmentally Friendly, Photochemical Access to [ ]AuIII Pincer Complexes By Oxidative Addition.

Starting from commercially available DMSAuCl and diazonium salts, cationic [N∧C∧N ]AuIII complexes were synthesized in a selective, photosensitizer‐free, photochemical reaction by irradiation with blue LED light. This new protocol represents the first easy synthesis of these types of pincer complexes in moderate to excellent yield starting from a readily available gold(I) precursor with nitrogen as the only by‐product. Owing to the disadvantages of known protocols, especially the toxicity in the case of a transmetalation with mercury or the necessity for a mostly twofold excess of a gold precursor, this method offers an attractive alternative towards this kind of gold(III) complexes. In addition, the first arylated [N∧C∧N ]Au(III) pincer complex was synthesized by using this technology.

НОВАЯ СПЕКТРОФОТОМЕТРИЧЕСКАЯ МЕТОДИКА ОПРЕДЕЛЕНИЯ ТИТАНА(IV) В ПРИРОДНЫХ ОБЪЕКТАХ

The article considers the interaction of Ti(IV) with 2, 3, 4-trihydroxy-3'-fluoroazobenzene (H3R) in the presence and absence of phenontroline (Phen), α, α'-dipyridine (α, 
 α'-dip), and batophenontroline (B-phen) studied by using a spectrophotometric method. It has been found that the yield of the binary complex is maximum at pHopt = 5 (λmax = 428 nm), and for mixed-ligand complexes, pHopt = 3.0; 4.0; 3.5; λmax = 477 nm, 443 nm, 440 nm Ti(OH)2(H2R)-Phen, 
 Ti (OH)2(H2R)-α, α'-dip and Ti(OH)2(H2R)-B-phen, respectively. It has been investigated that a twofold excess of the reagent is required for complete binding of titanium(IV) into the complex. The influence of time and temperature on the complexation is investigated. The stability constants of binary and mixed-ligand titanium(IV) complexes were calculated: logβ = 8.61 ± 0.05 for Ti(OH)2(H2R)2, logβ = 10.98 ± 0.06 for Ti(OH)2(H2R)-Phen, logβ = 10.85 ± 0.04 for Ti (OH)2(H2R)-α, α'-dip, 
 logβ = 11.26 ± 0.03 for Ti(OH)2(H2R)-B-phen. The ratio of the reacting components in the binary complex is 1 : 2, and in the mixed ligands 1 : 2 : 2. The influence of foreign ions and masking substances on the titanium(IV) complexation with reagents has been studied. The determination is practically not interfered by alkaline, alkaline-earth and some transition elements. Due to these characteristics, the complexes can be used for defining titanium(IV) in different objects.

Hydrogen-Bonded Complexes of Star Polymers.

The effect of molecular architecture, star versus linear, poly(ethylene oxide) (PEO) on the formation of hydrogen-bonded complexes with linear poly(methacrylic acid) (PMAA) is investigated experimentally and rationalized theoretically. Isothermal titration calorimetry reveals that at pH 2.5 interpolymer complexes (IPCs) of PMMA with a 6-arm star PEO (sPEO) contains ≈50% more polyacid than IPCs formed with linear PEO (lPEO). While the enthalpy of IPC formation is positive in both cases, its magnitude is ≈50% larger for sPEO/PMAA complexes that exhibit a lower dissociation constant than lPEO/polyacid complexes. These results are rationalized based on a higher localized density of hydrogen bonds formed between sPEO and the polyacid which prevents penetration of star molecules into PMAA coils. Accordingly, Fourier transform infrared results indicate approximately twofold excess of self-associated >COOH units over intermolecularly bonded >COOH units in sPEO-containing complexes. The excess of PMAA chains in IPCs and the percentage of self-associated carboxylic groups in sPEO/PMAA complexes both increase with polyacid molecular weight. Other findings, including a positive entropy, hysteresis in composition at strongly acidic pH, and progressive equilibration of IPCs at increased pH are consistent with the critical role of charge and release of water molecules in the formation of sPEO/PMAA and lPEO/PMAA complexes.

PTFE-Carbon Nanotubes and Lipase B from Candida antarctica—Long-Lasting Marriage for Ultra-Fast and Fully Selective Synthesis of Levulinate Esters

An effective method for levulinic acid esters synthesis by the enzymatic Fischer esterification of levulinic acid using a lipase B from Candida antarctica (CALB) immobilized on the advanced material consisting of multi-wall carbon nanotubes (MWCNTs) and a hydrophobic polymer—polytetrafluoroethylene (Teflon, PTFE)—as a heterogeneous biocatalyst, was developed. An active phase of the biocatalyst was obtained by immobilization via interfacial activation on the surface of the hybrid material MWCNTs/PTFE (immobilization yield: 6%, activity of CALB: 5000 U∙L∙kg−1, enzyme loading: 22.5 wt.%). The catalytic activity of the obtained biocatalyst and the effects of the selected reaction parameters, including the agitation speed, the amount of PTFE in the CALB/MWCNT-PTFE biocatalyst, the amount of CALB/MWCNT-PTFE, the type of organic solvent, n-butanol excess, were tested in the esterification of levulinic acid by n-butanol. The results showed that the use of a two-fold excess of levulinic acid to n-butanol, 22.5 wt.% of CALB on MWCNT-PTFE (0.10 wt.%) and cyclohexane as a solvent at 20 °C allowed one to obtain n-butyl levulinate with a high yield (99%) and selectivity (>99%) after 45 min. The catalyst retained its activity and stability after three cycles, and then started to lose activity until dropping to a 69% yield of ester in the sixth reaction run. The presented method has opened the new possibilities for environmentally friendly synthesis of levulinate esters.

Comparative evaluation study of polycomplex carriers based on Eudragit® EPO/S100 copolymers prepared in different media

AbstractInterpolymer complexes (IPC) Eudragit® EPO/S100 were prepared in different media (water pH of 7.0 and ethanol). According to the elemental analysis, FTIR spectroscopy, and thermal analysis data, IPC prepared in aqueous media (denoted as interpolyelectrolyte complexes—IPECs) is stabilized predominantly by ionic intermacromolecular bonds and has a composition close to equimolar. However, polycomplexes formed in nonaqueous (ethanol) media (denoted as IPC) are stabilized by both hydrogen and ionic bonds and characterized by an almost twofold excess of Eudragit® S100. All samples do not include free copolymer domains. IPECs and IPCs have different behavior in the buffer media mimicking the gastrointestinal tract. Matrices of IPECs are characterized by the surface erosion and pH‐independent swelling profiles with low values of a swelling degree. Matrices of the IPCs swell significantly in the buffer media with pH 1.2, 5.8, and 6.8 with subsequent decrease in the swelling degree due to the surface erosion. According to the assessment of release of the model active pharmaceutical ingredient (API), IPECs are prospective carriers for sustained delivery of II class Biopharmaceutical Classification System (BCS) drug (diclofenac sodium). At the same time, IPCs provide sustained release of the II class BCS and prolonged release of the I class BCS drug (theophylline).

Human Plasma and Recombinant Hemopexins: Heme Binding Revisited.

Plasma hemopexin (HPX) is the key antioxidant protein of the endogenous clearance pathway that limits the deleterious effects of heme released from hemoglobin and myoglobin (the term “heme” is used in this article to denote both the ferrous and ferric forms). During intra-vascular hemolysis, heme partitioning to protein and lipid increases as the plasma concentration of HPX declines. Therefore, the development of HPX as a replacement therapy during high heme stress could be a relevant intervention for hemolytic disorders. A logical approach to enhance HPX yield involves recombinant production strategies from human cell lines. The present study focuses on a biophysical assessment of heme binding to recombinant human HPX (rhHPX) produced in the Expi293FTM (HEK293) cell system. In this report, we examine rhHPX in comparison with plasma HPX using a systematic analysis of protein structural and functional characteristics related to heme binding. Analysis of rhHPX by UV/Vis absorption spectroscopy, circular dichroism (CD), size-exclusion chromatography (SEC)-HPLC, and catalase-like activity demonstrated a similarity to HPX fractionated from plasma. In particular, the titration of HPX apo-protein(s) with heme was performed for the first time using a wide range of heme concentrations to model HPX–heme interactions to approximate physiological conditions (from extremely low to more than two-fold heme molar excess over the protein). The CD titration data showed an induced bisignate CD Soret band pattern typical for plasma and rhHPX versions at low heme-to-protein molar ratios and demonstrated that further titration is dependent on the amount of protein-bound heme to the extent that the arising opposite CD couplet results in a complete inversion of the observed CD pattern. The data generated in this study suggest more than one binding site in both plasma and rhHPX. Furthermore, our study provides a useful analytical platform for the detailed characterization of HPX–heme interactions and potentially novel HPX fusion constructs.

“Greener” chemical modification of cellulose nanocrystals via oxa-Michael addition with N-Benzylmaleimide

Surface modification of cellulose nanocrystals (CNCs) was conducted by an oxa-Michael addition of primary hydroxyl groups on the CNC surface with N-Benzylmaleimide (BnM). Six principles of green chemistry were used to obtain the hydrophobized CNC. Two catalytic approaches were used, a self-catalyzed reaction where alkyl sulfuric acid on the surface of the CNC was the catalyst, and a base-catalyzed approach using triethylamine (TEA). DMSO was chosen as reaction solvent due to its low cost, low toxicity and ability to disperse native CNC compared to other polar diprotic solvents. NMR and FTIR studies confirmed the successful modification of CNCs in both reaction routes. The TEA-catalyzed reaction showed a higher BnM conversion at 70 ​°C after 72 ​h (46 ​± ​2%) compared to the self-catalyzed reaction at 100 ​°C (24 ​± ​2%). Since BnM was added at a two-fold excess compared to superficial primary –OH groups, these had estimated conversions of 92% and 48%, for the base catalyzed and acid catalyzed routes, respectively. Zeta potential measurements suggest, the sulfate groups were retained after the modification reaction. AFM demonstrated no change in particle morphology after modification. Modified CNCs degraded at a higher temperature (390 ​± ​8 ​°C) when the reaction was catalyzed by TEA compared to native CNCs and the self-catalyzed product (220 ​± ​10 ​°C). Contact angle measurements demonstrated the increased hydrophobicity of the modified nanoparticles. Visual inspection and UV–vis spectroscopy demonstrated the modified CNCs had an increased affinity towards organic solvents like acetone, acetonitrile and toluene.

N-Aroylbenzotriazoles as Efficient Reagents for o-Aroylation in Absence of Organic Solvent

N-Aroylbenzotriazoles have been shown to be efficient reagents for esterification in the absence of organic solvent. Grinding of N-aroylbenzoytiazoles with twofold excess of alcohols for a couple of hours at room temperature gave corresponding esters in high percentage of yields.

The Reaction of (1,3,4-Oxadiazole-Thiolato) Mercury(II) with Triphenyl Phosphine

The reaction of 5-phenyl-1,3,4-oxadiazole-2-thiol with mercury(II) acetate in ethanol led to the isolation of the complex [Hg(L)2] (1). Further reaction of 1 with a twofold molar excess of triphenylphosphine led to the isolation of [Hg(L)2(PPh3)2] (2). The complex 2 was characterized by infrared, ultraviolet–visible and nuclear magnetic resonance spectroscopy techniques, as well as by X-ray diffraction analysis.

Impact of the character of the associative interactions between chitosan and whey protein isolate on the structure, thermodynamic parameters, and functionality of their complexes with essential lipids

The aim of this work is the clarification of the impact of the character of associative interactions (covalent and non-covalent (electrostatic)) between chitosan (CHI) and whey protein isolate (WPI) on the structure, thermodynamic parameters and functionality of their complexes with essential lipids. These lipids included soybean phosphatidylcholine liposomes (PC), originally rich in omega-6 linoleic fatty acid (LA), enriched in omega-3 α-linolenic fatty acid (ALA) to an equimass ratio with LA. Differential scanning calorimetry and laser light scattering indicated that the covalent (WPI–CHI) conjugate had a greater degree of protein unfolding, a more open architecture of a random coil and a lower density compared to the same parameters of the electrostatic (WPI–CHI) complex. These structural features of the covalent conjugate contributed to the formation of the ternary (WPI–CHI) + (PC−ALA) complex particles with a higher molar mass and density as well as a more open architecture compared with the same parameters of the ternary electrostatic group. Similar properties of these ternary complexes are the following: a nanoscale size; a high aqueous solubility in the vicinity of the WPI isoelectric point (at pH = 5.1); ζ-potential ≥ +30 mV; an increase in the microviscosity of the encapsulated (PC−ALA) liposome bilayers as a result of complexation (data of electron paramagnetic resonance spectroscopy); 40% protection of the liposomes from oxidation under the twofold excess of the biopolymers relative to the lipids in the ternary complexes.

Исследование пространственных характеристик излучения квантовых каскадных лазеров для спектрального диапазона 8 μm

The near and far fields of quantum cascade lasers emitting in the spectral range near 8 µm have been studied. Lasing in the fundamental waveguide mode along the "fast" axis with a divergence of ~ 50º was observed in all samples of lasers with stripe widths of 22 and 50 µm in the entire range of pump currents. On the "slow" axis, multimode lasing and competition between the fundamental and higher waveguide modes were observed, which manifests itself for lasers with a 50 µm stripe in an increase of the radiation divergence from ~ 10º near the threshold to > 50º with a two-fold excess of the lasing threshold. The divergence along the slow axis for lasers with a stripe width of 22 µm remained unchanged over the entire range of pump currents and amounted to ~ 50º. The significant contribution of the fundamental mode to the total radiation intensity of quantum cascade lasers, being obvious from the far-field intensity distribution, cannot be established solely from the results of measurements of the near-field.

Highly Efficient Biphasic System for the Synthesis of Alkyl Lactates in the Presence of Acidic Ionic Liquids

Alkyl lactates are produced from lactic acid via esterification, and are used in the production of plastics, paints, solvents and detergents. In the pursuit of an inexpensive, industry-suitable catalyst for this reaction, the application of protic ionic liquids based on nitrogen base and sulphuric acid is proposed. The ionic liquid was synthesised via a simple reaction of triethylamine and a threefold molar excess of sulphuric acid. Water was added to remove the heat of the reaction. Next, the reaction conditions for the model esterification of 2-ethylhexanol with lactic acid without additional solvent were optimised. Exceptionally mild conditions, i.e., a twofold molar excess of alcohol to lactic acid with the addition of an ionic liquid in a catalytic amount (15 mol%) at 60 °C, resulted in high yields of ethyl and 2-ethylhexyl lactates (96–97%). The driving force of this reaction is the production of a biphasic system with immiscible ester during the reaction. This phenomenon makes it possible to overcome the reaction equilibrium. Using an inexpensive ionic liquid, which could be recycled up to five times without diminution in conversion or selectivity, leads to both a greener and a more economically-viable process.

ВІКОВА СТРУКТУРА НАСЕЛЕННЯ КИЇВСЬКОЇ ОБЛАСТІ: ДОСВІД ПРОСТОРОВОЇ ТИПІЗАЦІЇ

New conditions for the development of Ukraine’s economy require increased attention to national and regional labor markets. Already, in some sectors of the economy there are new facts for Ukraine of shortages of labor resources. The basis of this phenomenon, besides economic factors, is the deterioration of the age structure of the population, which determines the presence and qualitative parameters of labor resources by its structure. In modern scientific literature devoted to issues of labor resources and labor markets, a great deal of attention is paid to the analysis of demographic factors. Most authors recognize the decisive role of the age structure of the population in the formation of specific regional labor markets. The age structure of the population serves as the factual basis for forecasting the provision of labor resources of the region and the country. Cluster analysis allowed distinguishing in the Kyiv region a significant spatial differentiation of the age structure of the population. The differentiation of the age structure of the population of the administrative units of the Kyiv region allowed us to distinguish between two types that differ significantly in the ratio of the main age groups. The first type, which predominantly forms the periphery of the Kyiv region, is characterized by a high percentage of the population of the older age group, low share of children and working age population. The second type was formed around Kiev and has a relatively young population structure, with a high proportion of children (on the background of the Kiev region as a whole) and people of working age. Part of administrative units of the second type can be attributed to the transition group between the components of the first and second types. Spatial analysis shows centrifugal, centripetal, peripheral trends in the deteriorated age structure of the population. The main geographic vector of deterioration is observed from Kyiv to the periphery of the region. On the periphery of the region there is a two-fold excess of the share of pensioners over children.

γ-Ketosulfides and Hydroxysulfides from Sodium Methanthiolate of Sulfidic Spent Caustics

Condensation of pentan-3-one, hexan-2-one, 4-methylpentan-2-one, 5-methylhexan-3-one, or 2,6-dimethylheptan-4-one with formaldehyde and sodium methanethiolate, which is present in sulfidic spent caustic from the Orenburg gas processing plant, yields the corresponding mono- and bis[(methylsulfanyl)methyl]-substituted ketones or their mixtures depending on the reactant ketone structure. Alkylthiomethylation of butan-2-one with equimolar amounts of formaldehyde and sodium methanethiolate results in 3-methyl-5-thiahexan-2-one or, in the case of a twofold excess of the reagents, in 2-methyl-1,5-bis(methylsulfanyl)-4-[(methylsulfanyl)methyl]pentan-3-one. On the basis of 3-methyl-5-thiahexan-2-one, new polyfunctional [(methylsulfanyl)methyl]-substituted alcohol, α-hydroxymethylketone, 1,3-diol, and 1,3-dioxane have been obtained.

Energy of the Jets of the Antarctic Circumpolar Current and of Their Eddies in the Surface Layer of the Southern Ocean

The kinetic energy of six jets of the Antarctic Circumpolar Current (ACC) and of the cyclonic and anticyclonic mesoscale eddies generated by these jets is studied in application to the surface layer of Antarctic Circle. The study is based on satellite altimetry data for 1993–2015 available at http://aviso.altimetry.fr . Main results of the study are (a) a fivefold excess of the mean energy of jets proper over the mean total (cyclones plus anticyclones) energy of eddies; (b) the prevalence of the energy of the core jet of the Subantarctic Current over the energy of the rest of the ACC jets in the entire Antarctic Circle; (c) a twofold excess of the mean energy of cyclonic eddies over the energy of anticyclones in the upper ocean layer.

Hydride, alkyl and carbyne derivatives of the unsaturated heterometallic anion [MoWCp2(μ-PCy2)(μ-CO)2

The heterometallic hydride [MoWCp2(μ-H)(μ-PCy2)(CO)4] was prepared in 30% yield through reaction of an equimolar mixture of [Mo2Cp2(CO)6] and [W2Cp2(CO)6] with a two-fold excess of PHCy2 in xylene solution, in a sealed tube at 453 K. The sodium salt of the title anion was then prepared from the latter hydride in a three-step process first involving dehydrogenation with HBF4·OEt2 in dichloromethane to give the cationic derivative [MoWCp2(μ-PCy2)(CO)4](BF4), then reaction of the latter with NaI in refluxing 1,2-dichloroethane to yield the iodide-bridged dicarbonyl complex [MoWCp2(μ-I)(μ-PCy2)(CO)2] and, finally, reaction of the latter with Na(Hg) in tetrahydrofuran solution. Reaction of this anion with (NH4)PF6 gave the hydride [MoWCp2(H)(μ-PCy2)(CO)2], which in solution displays an equilibrium mixture of two isomers, one with terminal carbonyls and the hydride ligand bridging the metal atoms (B), another one with a semibridging carbonyl and the hydride ligand terminally bound to the W atom (T). The prevalence of isomer T was higher than the observed ones in the corresponding homometallic analogues, and there was a clear thermodynamic preference of the hydride ligand for the W site, estimated in some 20 kJ/mol according to density functional theory (DFT) calculations. The title anion reacted selectively with benzyl chloride at room temperature, to give the agostic benzyl-bridged derivative [MoWCp2(μ-κ1:η2-CH2Ph)(μ-PCy2)(CO)2], which displays specific κ1-coordination to the W atom (MoW = 2.580(1) Å), while the analogous reaction with MeI gave a mixture of the related methyl-bridged complex [MoWCp2(μ-κ1:η2-CH3)(μ-PCy2)(CO)2] and its methoxycarbyne-bridged isomer [MoWCp2(μ-COMe)(μ-PCy2)(μ-CO)] in a ratio of ca. 5:1, with the latter corresponding to a chemical behaviour intermediate between those of its homonuclear analogues. Photolysis of the above alkyl complexes with visible-UV light at room temperature resulted in fast decarbonylation followed by dehydrogenation, to give the corresponding carbyne-bridged derivatives [MoWCp2(μ-CR)(μ-PCy2)(μ-CO)] (R = H, Ph) in good yield. This suggests that the cooperative action of Mo and W atoms greatly reduces the thermal barrier of the CH bond cleavage steps required for dehydrogenation of the alkyl ligands in these substrates.

Non-enzymatic transformations of dietary 2-hydroxyalkenyl and aromatic glucosinolates in the stomach of monogastrics

Monogastric animals exhibit different biological responses to structurally diverse glucosinolates and their transformation products, depending on the dietary levels. The transformations of 2-hydroxyalkenyl and aromatic glucosinolates were examined in vitro under gastric conditions, ex vivo in ligated porcine stomachs and in vivo in a rat model.Intact glucosinolates were almost completely transformed in vitro within 1 h at pH 3 (73–88%) and at pH 5 (97–100%) upon addition of Fe2+ ranging from two-fold molar excess. Glucosinolate transformations reached 78–99% when incubated ex vivo in ligated porcine stomachs. Rat in vivo feeding trials showed major reductions (81–84%) in the intact glucosinolate contents upon passage through the gastrointestinal (GI) tract.Non-enzymatic transformations of glucosinolates occur in the stomach, where pH and the level of Fe2+ are primary determinants. This is the first study to show a complex formation between iron-progoitrin and iron-sinalbin, facilitating the transformation into nitriles and thionamides.

Composition and Structure of Hydrates Formed in Aqueous Solutions of Formic Acid

IR spectroscopy and quantum chemical methods are used to study the features of hydration and determine concentration structural areas in the HCOOH-H2O system. Data on the composition and structure of stable heteroassociates (HA) formed in HCOOH aqueous solutions are obtained from the joint analysis of the IR spectra of these solutions and the results of quantum chemical calculations of (HCOOH)m·(H2O)n (m = 1−4, 6, n = 1−10, 14) and HCO 2 − ·(H2O)n (n = 2, 6) complexes. The sequence is established in which these complexes form when pure acid is diluted with water. For HCOOH concentrations from 100% to the ratio HCOOH:H2O = 1:1, all water molecules are involved in the most stable cyclic (HCOOH)2· (H2O)2 HAs with the C2 symmetry. The components of the equimolar solution are almost completely bound into such hydrates. For the HCOOH:H2O ratio ranging from 1:1 to 1:2, less stable (by ∼10%) cyclic HCOOH · (H2O)2 HAs form along with the (HCOOH)2 · (H2O)2 complexes. The solution with a twofold water excess consists of these hydrates. A further increase in the water concentration results in further hydration of HCOOH · (H2O)2 HAs.