pKs Values Research Articles

서리피해 찻잎 활용 홍차의 성분 함량 및 맛 분석

The yield of premium green tea is reduced when the plants are exposed to abnormally low temperatures caused by climate change. In particular, the damage caused by frost is severe. All frost-damaged tea leaves are discarded after pruning. This study was conducted to partially reduce the decrease in farm household income caused by frost damage using these damaged tea leaves for black tea processing. Frost-damaged tea leaves were harvested in May 2022 and processed into black tea. The changes in the component content were investigated by analyzing the catechin, caffeine, theaflavin, and free amino acids and performing taste analysis using an electronic tongue. The total catechin content was 0.24% and 1.06% in the undamaged and frost-damaged black tea, respectively. The C (catechin) content was particularly high at 0.81% in the frost-damaged black tea. The caffeine levels in undamaged and frost-damaged black tea were 0.84% and 0.42%, respectively, showing an approximately 50% reduction of the caffeine content by frost damage. The total theaflavin content in undamaged and frost-damaged black tea was 0.24% and 0.13%, respectively. The total free amino acid content in undamaged and frost-damaged black tea was 714 mg/100 g and 1,122 mg/100 g, respectively, of which the γ-aminobutyric acid content in undamaged and frost-damaged black tea was 16.9 mg/100 g and 140.4 mg/100 g, respectively. Taste analysis using the electronic tongue revealed high AHS and CPS sensor values in undamaged black tea and high CTS, PKS, NMS, and SCS sensor values in frost-damaged black tea.

Characterization and discrimination of the flavor profiles of Chinese indigenous sheep breeds via electronic sensory, smart instruments and chemometrics

This study was conducted to analyze the flavor profile of six commercially available Chinese indigenous breeds of sheep meat and to distinguish them based on their flavor characteristics. Various techniques such as gas chromatography-mass spectrometry (GC-MS), electronic nose (E-nose), high performance liquid chromatography (HPLC) and electronic tongue (E-tongue) were employed to analyze both volatile and non-volatile compounds in the meat samples. The results showed that, a total of 28 volatile compounds in sheep meat were detected, with 1-octen-3-ol, 1-pentanol, hexanal, octanal, and nonanal identified as the major contributors to its aroma. Tan Sheep and Oula Sheep had significantly higher concentrations of 1-pentanol, nonanal, 1-octen-3-ol, 1-octanol, and hexanoic acid than other breeds. Sweet amino acids were the most abundant free amino acids, comprising 72–85% of the total FAAs, and inosinic acid was the most abundant ATP-related compound. Small-Tailed Han sheep had significantly higher levels of SFAAs, total FAAs, and AMP, while Tan sheep had significantly higher levels of UFAAs, and Oula Sheep had significantly higher levels of GMP. The response values of differential electronic sensors W5S, W1W, NMS, PKS, and SCS were found to be useful in discriminating between breeds of sheep meat. The fusion electronic sensory signals were used to train support vector machine and random forest models, both achieving 100% accuracy in discriminating between sheep breeds.

Two PKs to Protect LSB Method of Data Steganography

LSB method of data steganography is very popular and easy method of data hiding, but it si not secure. In this research paper a simple and easy modifications will be added to LSB method to increase the security level of data hiding. Two PKs will be used to protect the hidden secret message, the first PK1 will be generated using a selected parameter values to run CLMM, this key will be converted to form a lockup table to apply message encryption-decryption. The second PK2 will be used to apply bits’ substitution of the character binary matrix, the two keys will provide a necessary key space, which can resist hacking attacks, the two keys will be sensitive to any minor changes in the PKs contents, any changes in the PKs values in the message retrieving phase will be considered as a hacking attempt. The proposed method will be implemented using various messages and various covering images, the obtained results will be analyzed, several types of results analysis will be performed to prove the quality, performance, security and sensitivity of the proposed method.

Quantitative Evaluation of Rotator Cuff Tears Based on Non-linear Statistical Analysis of Ultrasound Radiofrequency Signals

There is increasing clinical requirement for early and accurate ultrasound diagnosis of rotator cuff tears (RCTs). A method based on non-linear statistical analysis was proposed for the detection of RCTs using ultrasound radiofrequency (RF) signals. One hundred fifty-two patients with shoulder pain were first examined with ultrasound and then diagnosed with magnetic resonance imaging (MRI) as the ground truth. By comparison of the region of interest (ROI) with a part of the supraspinatus with no pathologic change part in the same RF signal frame, the relative Pks value (viz., rPks value) was evaluated to quantify the pathophysiologic changes. The results indicated that the rPks values of all RCTs are <0.7, and the accuracy, sensitivity and specificity of the proposed method can reach 97.5%, 100% and 91.4%, respectively. This computer-aided method was found to perform better diagnostic than the results reported by an experienced radiologist (accuracy = 75.7%, sensitivity = 72.6%, and specificity = 85.7%). The high sensitivity advantage of this method indicates that the prospects for its application in the computer-aided diagnosis of RCTs are good.

Synthesis of Calcium Orthophosphates by Chemical Precipitation in Aqueous Solutions: The Effect of the Acidity, Ca/P Molar Ratio, and Temperature on the Phase Composition and Solubility of Precipitates

Studies on chemical precipitation of the calcium orthophosphates have shown that their phase compositions do not vary depending on molar ratio Ca/P but are sensitive to solutions acidity and temperature. These are two key factors that determine the phase transformation progress of metastable phases into less soluble precipitates of the phosphates. It was proposed to compare calcium orthophosphates solubility products with calcium cations quantities in their formulas. It was found that there was a linear correlation between calcium orthophosphates specific solubility products and their molar ratios Ca/P if hydroxyapatite and its Ca-deficient forms were excluded from consideration. It was concluded that the relatively large deviations of their solubility products from the found correlation should be thought of as erroneous data. That is why solubility products were changed in accordance with correlation dependence: pKS for hydroxyapatite was 155, pKS for Ca-deficient hydroxyapatites was 114–155. The solubility isotherms, which were calculated on the basis of the corrected pKS values, coincided with the experimental data on solid-phase titration by Pan and Darvell.

Surface reactivity of the anaerobic phototrophic Fe(II)-oxidizing bacterium Rhodovulum iodosum: Implications for trace metal budgets in ancient oceans and banded iron formations

It is widely accepted that anoxygenic photosynthetic bacteria (photoferrotrophs) oxidized dissolved Fe(II) in anoxic Archean seawater, leading to the sedimentation of cellular biomass and the Fe(III) minerals that comprised banded iron formations (BIF). However, it remains unknown to which extent the sedimented bacteria may have transported trace metals to BIF through their ability to sorb ions from seawater. We therefore chose the marine anoxygenic photoferrotroph Rhodovulum iodosum to quantify Cd2+, Co2+, Cu2+, Mn2+, Ni2+ and Zn2+ adsorption to bacteria/Fe(III)-oxyhydroxide composites at neutral pH and an ionic strength of 0.1M. Acid base titration data were modeled using a linear programming optimization method to yield pKa values of 4.83±0.13, 6.21±0.18, 7.74±0.24 and 9.28±0.27 and corresponding site densities of 5.7, 12.0, 3.3 and 6.5×10−4mol/g, respectively. FTIR spectroscopy confirmed the presence of carboxyl groups as the most acidic sites corresponding to the lowest pKa values. The analysis of Cd2+ sorption data showed two metal complexing sites with pKS values of 3.44±0.14 and 4.80±0.21 and corresponding binding site concentrations of 1.1±0.3×10−4 and 0.9±0.2×10−4mol/g on the ferrihydrite/R. iodosum composite. The pKS values were used to calculate metal-ligand binding constants, Km. This confirmed Cd2+ binding to the most acidic carboxyl groups on the ferrihydrite/R. iodosum composite surface, as the calculated Km was consistent with reported Cd2+ binding constants for simple organic acids (e.g., lactic, acetic, pyruvic and citric acid). This was used to further calculate the concentration of Co2+, Cu2+, Mn2+, Ni2+ and Zn2+ sorbed to ferrihydrite/R. iodosum composites. The resulting concentrations were ultimately compared to the concentrations of trace elements in BIF to demonstrate that is plausible that the trace metal content in BIF was derived from plankton growing in the ancient ocean's photic zone.

Feature Tracking-Derived Peak Systolic Strain Compared to Late Gadolinium Enhancement in Troponin-Positive Myocarditis: A Case-Control Study.

Cardiac magnetic resonance (CMR) assesses myocardial involvement in myocarditis (MYO). Current techniques are qualitative, subjective, and prone to interpretation error. Feature tracking (FT) analyzes myocardial strain using CMR and has not been examined in MYO. We hypothesize that regional left ventricular (LV) strain is abnormal in MYO. Regional strain by FT was compared to late gadolinium enhancement (LGE) and troponin leak as measures of myocardial involvement. This single-center, retrospective CMR study reviewed patients with clinical MYO and structurally normal hearts who underwent CMR at our institution. Young adults with normal cardiac anatomy, function, and absent LGE served as controls. MYO patients with documented troponin leak and normal global ejection fraction (EF > 50 %) were included in comparison. FT determined regional myocardial peak systolic strain (pkS) in longitudinal and circumferential distributions. T tests compared strain values between cases and controls. Receiver operating characteristic curves determined pkS values with highest sensitivity and specificity for concurrent troponin leak and LGE. FT was performed on 57 patients: 37 MYO and 20 controls. Twenty-eight cases with normal EF, and 20 control patients were included in final analysis. Nearly all cases with normal function demonstrated abnormal regional pkS (27/28, 96 %). Cases had significantly diminished pkS when compared to controls in all regions except the longitudinal 2C distribution. FT-derived longitudinal and circumferential pkS is sensitive and specific in identifying myocardial involvement, namely the presence of troponin leak and LGE. FT may be a useful adjunctive, objective measure of myocardial involvement in patients with MYO and normal LV function.

Thiol groups controls on arsenite binding by organic matter: New experimental and modeling evidence

Although it has been suggested that several mechanisms can describe the direct binding of As(III) to organic matter (OM), more recently, the thiol functional group of humic acid (HA) was shown to be an important potential binding site for As(III). Isotherm experiments on As(III) sorption to HAs, that have either been grafted with thiol or not, were thus conducted to investigate the preferential As(III) binding sites. There was a low level of binding of As(III) to HA, which was strongly dependent on the abundance of the thiols. Experimental datasets were used to develop a new model (the modified PHREEQC-Model VI), which defines HA as a group of discrete carboxylic, phenolic and thiol sites. Protonation/deprotonation constants were determined for each group of sites (pKA=4.28±0.03; ΔpKA=2.13±0.10; pKB=7.11±0.26; ΔpKB=3.52±0.49; pKS=5.82±0.052; ΔpKS=6.12±0.12 for the carboxylic, phenolic and thiols sites, respectively) from HAs that were either grafted with thiol or not. The pKS value corresponds to that of single thiol-containing organic ligands. Two binding models were tested: the Mono model, which considered that As(III) is bound to the HA thiol site as monodentate complexes, and the Tri model, which considered that As(III) is bound as tridentate complexes. A simulation of the available literature datasets was used to validate the Mono model, with logKMS=2.91±0.04, i.e. the monodentate hypothesis. This study highlighted the importance of thiol groups in OM reactivity and, notably, determined the As(III) concentration bound to OM (considering that Fe is lacking or at least negligible) and was used to develop a model that is able to determine the As(III) concentrations bound to OM.

Acid–base property of protic ionic liquid, 1-alkylimidazolium bis(trifluoromethanesulfonyl)amide studied by potentiometric titration

We report the acid–base property of typical protic ionic liquid, 1-alkylimidazolium bis(trifluoromethanesulfonyl)amide ([CnImH+][TFSA−], n: alkyl-chain length), investigated by potentiometric titration. The equilibrium constant, Ks=[CnIm][HTFSA] on the autoprotolysis reaction (CnImH++TFSA−⇄CnIm+HTFSA) was successfully determined for n=2 and 4 systems using an ion-selective field effect transistor (IS-FET) electrode. The pKs values for n=2 and 4 were estimated to be 12.3 and 12.6mol2dm−6, respectively, indicating that the autoprotolysis reaction is almost independent of the alkyl chain length. Temperature dependence of the potentiometric titration was also performed to obtain the reaction enthalpy. The enthalpy value, 41kJmol−1, obtained here is appreciably smaller than that for ethylammonium nitrate (83kJmol−1).

Influence of tempereature on Struvite precipitation by CO2‐deagassing method

AbstractThe present study explores struvite precipitation by degassing method under different temperature (14.5‐35 °C). It is shown that an increase of temperature does not affect the nucleation kinetics but strongly influences the growth rate and the efficiency of the phosphate removal. This was attributed to the effect of temperature on the struvite solubility and then the reached supersaturation coefficient. It was also shown, by using degassing method, that the determined solubility constant (pKs) values of struvite, at 14.5, 20, 25 and 35 °C are 13.00, 12.82, 12.63 and 13.20, respectively, are close to those presented in the literature. The results show that temperature influences the kinetics of precipitation. First‐order kinetics were found to be sufficient to describe the rate data. The rates decreased with increasing temperature and the apparent rate constants for the reaction were determined. Arrhenius plots yielded a relatively apparent high activation energy Ea = 31.0 kJ·mol–1. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Determination of Autoprotolysis Constants of Water-Organic Solvent Mixtures by Potentiometry

This paper describes a potentiometric titra- tion method for the determination of stoichiometric autoprotolysis constants (pKs) in binary mixtures of water with methanol, ethanol, 1-propanol, 2-propanol, dioxane, and acetonitrile. A combined pH electrode modified by replacing its aqueous KCl solution with 0.01 M NaCl þ 0.09 M NaClO4 saturated with AgCl was used for the first time in aqueous organic solvent mixtures. The potentiometric cell was calibrated be- fore each experiment so that the hydrogen ion con- centration rather than the activity was measured. The calibration constants Eand k were determined by titrating a solution of perchloric acid with sodium hydroxide solution for each medium studied at 25 � C and under nitrogen atmosphere. During each titration the concentration of NaClO4 was maintained at 0.1 M and the pKs values were calculated by using this titra- tion data. It is shown that the combined electrode system could be successfully used to determine auto- protolysis constants in water-organic solvent mixtures. Furthermore, the variation of the pKs values with solvent composition is discussed.

Quantitative Structure-Activity Relationships for the Pre-Steady State of Pseudomonas Species Lipase Inhibitions by p-Nirophenyl-N-Substituted Carbamates

The pre-steady states of Pseudomonas species lipase inhibitions by p-nitrophenyl-N-substituted carbamates (1-6) are composed of two steps: (1) formation of the non-covalent enzyme-inhibitor complex (E:I) from the inhibitor and the enzyme and (2) formation of the tetrahedral enzyme-inhibitor adduct (E-I) from the E:I complex. From a stopped-flow apparatus, the dissociation constant for the E:I complex, KS, and the rate constant for formation of the tetrahedral E-I adduct from the E:I complex, k2 are obtained from the non-linear least-squares of curve fittings of first-order rate constant (k(obs)) versus inhibition concentration ([I]) plot against k(obs)=k2+k2[I]/(KS+[I]). Values of pKS, and log k2 are linearly correlated with the sigma* values with the rho* values of -2.0 and 0.36, respectively. Therefore, the E:I complexes are more positive charges than the inhibitors due to the rho* value of -2.0. The tetrahedral E-I adducts on the other hand are more negative charges than the E:I complexes due to the rho* value of 0.36. Formation of the E:I complex from the inhibitor and the enzyme are further divided into two steps: (1) the pre-equilibrium protonation of the inhibitor and (2) formation of the E:I complex from the protonated inhibitor and the enzyme.

Estudo de algumas reações oxoacidobásicas no solvente NaCl fundido entre 1100K e 1200K

Equilibrium constants (K) of some oxoacidbasic reactions in molten NaCl in the temperature range of 1100K to 1200K, have been measured potentiometrically with a calcia stabilized zirconia oxide ion (O2-) indicator electrode. In molten NaCl at 1100K the pKs values (in molality scale) for HCl/H2O and HO-/H2O are respectively 11.0 ± 0.3; 1.6 ± 0.3 and the pKs for CaO is 4.3 ± 0.3. The results have been compared with those determined previously by Combes for the molten equimolar NaCl-KCl mixture and are in good agreement with literature data and gives some qualitative explanation of the comparison of oxoacidbasic properties between molten NaCl and NaCl-KCl.

Chemical Equilibrium Modeling Techniques for the Analysis of High-Resolution Bacterial Metal Sorption Data

An ion selective electrode was used to monitor binding of Cd2+ on two bacteria, Bacillus subtilis (Gram+) and Escherichia coli (Gram−), as a function of increasing pH. A competitive Langmuir sorption isotherm was used in conjunction with a linear programming method (LPM) or FITEQL to fit experimental data. Results obtained with simulated data showed that LPM is less sensitive than FITEQL to variations in sorption data. Application of the LPM to experimental data found three discrete metal binding sites on B. subtilis and E. coli with −log equilibrium constant (pKS) values of −0.80±0.20, 0.63±0.09, and 2.35±0.10, and −0.60±0.10, 0.25±0.19, and 1.93±0.17, respectively, at a constant ionic strength, I=0.1 M (KNO3). The corresponding site densities were 0.09±0.01, 0.07±0.01, and 0.07±0.01, and 0.01±0.002, 0.02±0.01, and 0.04±0.01 μmol of Cd2+/mg of B. subtilis or E. coli. From FITEQL, pKS values of −1.18±0.15, 0.40±0.11, and 2.31±0.32 for B. subtilis and −1.46±0.34, 0.20±0.12, and 1.87±0.12 for E. coli were recovered with site densities of 0.10±0.07, 0.07±0.06, and 0.06±0.02, and 0.02±0.005, 0.02±0.004, and 0.04±0.04 μmol of Cd2+/mg of B. subtilis or E. coli, respectively. Total site densities of 0.22±0.02 and 0.06±0.01 μmol/mg were obtained by LPM for B. subtilis and E. coli, whereas FITEQL yielded values of 0.23±0.02 and 0.08±0.07 μmol/mg. Both LPM and FITEQL produced feasible results, but LPM was less sensitive to error and did not require an a priori assumption of the number of binding sites.

Chemical and electrochemical behaviour of chromium in molten chlorides

The chemical and electrochemical behaviour of chromium ions in the equimolar CaCl2 NaCl mixture at 550°C has been studied by electrochemical techniques (i.e. cyclic and square wave voltammetry, chronopotentiometry, chronoamperometry and potentiometry) using various substrates (Mo, W and glassy carbon) as working electrodes. Some of the results have been compared to data obtained in the eutectic LiClKCl mixture at 450°C. The stable oxidation states of chromium species were found to be the same in both melts. However, in the case of the CaCl2 NaCl melt and when using W substrates, a new electrochemical wave appears, which has been related to an enhancement of the oxidation of trace amounts of O 2 ions on the W material by the presence of Cr ions. Kinetic parameters characterising the mass and charge transfer of the electrochemical reduction and oxidation of Cr(II) ions as well as of the Cr(III) reduction process were also obtained. Chronoamperometric studies did not show evidence of nucleation phenomena in the case of the equimolar CaCl2 NaCl mixture when using any of the substrates. However, in the eutectic LiClKCl it has been shown that nucleation of metallic chromium, especially on glassy carbon substrates, controls the electroreduction process. The electrochemical behaviour of some chromium oxo-anions, i.e. Cr2O7 and CrO4 , has also been studied. The results show that both complexes lead to the same stable Cr(VI) species in the melt, whose reduction at glassy carbon electrodes implies a single one-electron process giving Cr(V) ions which are present in the melt as soluble species. Potentiometric titration of both Cr(III) and Cr(II) solutions were performed by using an oxide selective ion electrode, which consist of a membrane of ZrO2 stabilised with yttrium oxide (YSZME). The values of pKs for the different CrO compounds stable in the melt, i.e. CrO, Cr2O 2 and Cr2O3, were obtained. © 2000 Elsevier Science B.V. All rights reserved.

Exchange Interaction Mediated by O−H···O Hydrogen Bonds: Synthesis, Structure, and EPR Study of the Paramagnetic Organometallic Carboxylic Acid (η7-C7H7)V(η5-C5H4COOH)

Lithiation of trovacene [(η7-tropylium)vanadium(η5-cyclopentadienyl)] (1•) and appropriate subsequent reactions afforded trovacenyl carboxylic acid (η7-C7H7)V(η5-C5H4COOH) (2•) and its anhydride [(η7-C7H7)V(η5-C5H4CO)]2O (3••). The deuterated acid 2•-d1 was also prepared; 2•, 2•-d1, and 3•• were characterized by X-ray structural analysis. The dimeric hydrogen bonded structure of 2• which is found in the crystal also prevails in aprotic, nonpolar solvents and gives rise to a biradical EPR spectrum from which the electron exchange coupling constant J = −0.011 cm-1 can be determined via computer simulation. Thus, exchange interaction across eight bonds is observable even though the spacer contains weak hydrogen bonds. Considerably stronger exchange coupling (J = −0.345 cm-1) is displayed by the anhydride 3••. The EPR spectrum of 2• in toluene is temperature dependent as expected for the equilibrium 2 (2•) ⇌ (2•)2 which leads to the superposition of monomer and dimer spectra at ratios governed by temperature. The enthalpy of dimerization can thus be derived; it amounts to −11.8 kcal mol-1 for 2• and −15.2 kcal mol-1 for 2•-d1. The 1H NMR spectrum of the radical 2• reveals the positive contact shift Δδ = 3 ppm for the carboxylic proton, relative to the chemical shift observed for the diamagnetic organometallic acid Cr(η6-C6H5COOH)2. Conceivably, the finite spin density on the carboxyl group, present in the monomer 2•, contributes to the exchange interaction displayed by the hydrogen bonded dimer (2•)2. The redox potential E1/2 (2+/0) and the hyperfine coupling constant a(51V, 2•) are pH dependent. In the former case, a Nernst−Clark plot furnishes the pKs values of 4.4 for neutral 2• and 1.85 for the cation 2+. A similar value, pKs(2•) = 3.7, is read off the plot a(51V, 2•) versus pH.

Copolymers with periodic comonomer sequences

AbstractThe free radical copolymerization and multipolymerization of olefins with acrylic monomers in the presence of acids has been studied. It was found that Brönsted acids are as suitable complexing agents for the acrylic comonomer as the up to now exclusively used Lewis acids. The effectiveness of the Brönsted acids, e.g. carboxylic acids, for obtaining alternating copolymers increased with the pKs value, and trifluoroacetic acid turned out to be the acid of choice. The variation of the Lewis acid‐type complexation agents was extended by the zinc chloride diethylether complex which is advantageous over ZnCl2 or other Lewis acids because of its good solubility and recycling practicability, which is also a feature of the Brönsted acids. The versatility of the new complexing agent systems was demonstrated in a series of co‐ and multipolymerizations, and ethyl cyanoacrylate was employed for the first time as electron acceptor comonomer. The properties of the copolymers with periodic comonomer sequences varied systematically with their composition, e.g. the glass transition temperature and the degree of crystallinity.

1:1 Metal Complexes of Bivalent Cobalt, Nickel, Copper, Zink, and Cadmium with the Tripodal Ligand tris[2‐(dimethylamino)ethyl]amine: Their stabilities and the X‐ray crystal structure of its copper(II) complex sulfate

AbstractThe complex formation by Co2+, Ni2+, Cu2+, Zn2+, and Cd2+ with tris[2‐(dimethylamino)ethyl]amine (N(CH2CH2NMe2)3, Me6tren) was investigated at 25° and at an ionic strength of 1, using VIS spectroscopy and potentiometric measurements. The stability constants of these complexes are compared with those of tris(2‐aminoethyl)amine (N(CH2CH2NH2)3, tren), obtained under the same conditions. The values of the constants for Me6tren are much lower than those for tren, due to the bulky Me substituents. The values of the constants can be correlated with the ability of the individual metal ions to adopt coordination number 5. This appears to be easier for Cu2+ and Co2+ than for Cd2+ and Zn2+ and is very difficult for Ni2+. The 1:1 complexes [ML(H2O)]2+ are monoprotonic acids whose pKs values are similar or lower than those of the corresponding aquametal ions. The X‐ray crystal structure of the copper(II) complex [Cu(SO4)(Me6tren)] · 8H2O reveals pentacoordination at the central ion. The UV/VIS spectra of the aqueous solutions of the Co2+, Ni2+, and Cu2+ 1:1 complexes confirm that the same coordination number is present also in these complexes.

Solvent effects on the solubilities of reference electrolytes

Solubilities of bis(biphenyl)chromium(I) tetraphenylborate were measured in 25, solubilities of tetraphenylarsonium tetraphenylborate in nine and solubilities of bis(biphenyl)chromium(0) in seven nonaqueous solvents. Linear dependences of the pKs-values for these compounds as well as the pKs values for tetraphenylstibonium tetraphenylborate, tetraphenylmethane and tetraphenylgermane were observed. The relations between the pKs-values of the above mentioned compounds and solvent parameters as well as solvent structure are discussed.

Metall‐π1‐Komplexe von Benzolderivaten, XLI. Bis(η61‐anilin)chrom: Synthese, Redoxverhalten und Brønsted‐Basizität

Metal π Complexes of Benzene Derivatives, XLI[1]. — Bis(η61‐aniline)chromium: Synthesis, Redox Properties and Brønsted BasicityBis(η61‐aniline)chromium (6) has been prepared by protodesilylation of its N,N,N′,N′1‐tetrakis(trimethylsilyl) derivative 5, which is accessible by metal‐atom ligand‐vapor cocondensation (cc). Bis(η61‐dimethylaniline)chromium (3) is obtained directly from cc. The couples 3+/0 and 6+/0 feature the most negative redox potentials E1/2 ever reported for bis(arene)1‐metal complexes. According to EPR spectroscopy, applied to the radical cations 3+· and 6+· the site of oxidation is largely localized on the metal. The pH dependence of E1/2 is cast in Nerst‐Clark plots, whose breaks supply the pKs values of the mono‐and diprotonated forms of 3 and 6. η61‐Coordination to CrI increases the basicity of aniline by three pK units, whereas η61‐coordination to Cr1 effects a decrease by more than seven pK units. The first and second dissociation constants of the organometallic bis(ammonium) ions 3(H+)2 and 6(H+)2 differ by 2.7 pK units. This interval reflects the interaction of the two basic centers in 3 and 6 which approaches that of p1‐phenylenediamine. Thus, conjugation across the bis(η61‐arene)chromium unit is virtually uninhibited.