D2O Solutions Research Articles

S‐Aryl Substitution Enhances Acidity of the 1,2,4‐Triazolium Scaffold

AbstractThe 1,2,4‐triazolium scaffold in asymmetric organocatalysis results in remarkable rate accelerations, with reactions typically occurring via N‐heterocyclic carbene (NHC) intermediates. Although the most acidic NHC pre‐catalyst class, there remains scope for further increases in acidity particularly for aqueous organocatalysis applications. The acidity‐enhancing effects of thio‐substituents on carbon acidity are well‐documented but not explored in the 1,2,4‐triazolium scaffold. Herein, we report the synthesis of a large series of N, N‐dialkyl‐C(3)‐S‐aryltriazolium ions and quantitative kinetic evaluation of C(5)‐H acidity. The direct attachment of S‐aryl substituents to the triazolium heterocycle results in substantial increases in protofugalities (kinetic acidities) with second order rate constants (kDO) for C(5)‐H deprotonation by DO− base that are 2.9–60.3 fold higher than for reference 1,4‐dimethyl‐1,2,4‐triazolium iodide in D2O solution. Protofugalities for the N, N‐dialkyl‐C(3)‐S‐aryltriazolium series are similar to commonly used bicyclic N‐aryl‐1,2,4‐triazolium organocatalysts despite having two electron donating N‐alkyl substituents. This highlights the future potential of this NHC design which could enable the introduction of two chiral alkyl substituents close to the C(5) carbenic position with pre‐catalyst acidity controlled by distal C(3)‐S‐aryl substitution. Detailed X‐ray structural data‐protofugality correlations enabled evaluation of the S‐aryl substituent effect origins. C(5)‐H pKa values (16.9–18.6) were calculated by utilisation of experimental protofugalities.

Basic accuracy of a1D NOESY with presaturation method using standard solutions of amino and maleic acids.

1D NOESY with presaturation (NOESY-presat) is the most popular water suppression method. When D2O solutions of L-phenylalanine or L-valine were measured using NOESY, the absolute concentration biases increased with longer mixing and evolution times, reaching a maximum of 54% with respect to the preparation values. At mixing and evolution times of 0ms and 0µs, respectively, the absolute concentration biases were reduced to less than 3%. The remaining biases were caused by the off-resonance effect, which was prevented by setting the frequency offset to an intermediate value between the analyte and internal standard 3-(trimethylsilyl)-1-propanesulfonic acid-d6 (DSS-d6) signals. Nevertheless, NOESY-presat gave maximum absolute biases of 26% and 11% for glycine and maleic acid concentrations, respectively, in three H2O/D2O (90/10 vol%) solutions. The proposed NOESY-dual-presat method reduced the absolute biases to below 4%. However, water suppression was insufficient but was improved by setting the frequency offset to the same as the presaturation offset with the H2O signal, although the absolute biases rose to 5 to 13%. Quantitative analyses using NOESY-presat and NOESY-dual-presat require careful consideration of the off-resonance effect.

Hydrogen/Deuterium Exchange Reaction Rate of Cytochrome c Determined by Droplet Collision Atmospheric Pressure Infrared Laser Ablation Mass Spectrometry.

The hydrogen/deuterium (H/D) exchange rate is an optimal measure for studying the structures and dynamics of hydrogen bonding systems, as it reflects the molecular contact environment and the strength of the hydrogen bonds. A method for rapid measurement of the H/D exchange reaction rates is required to examine the intermolecular environments of molecules in solutions. We developed a droplet collision atmospheric pressure infrared laser ablation mass spectrometry technique for this purpose. We obtained the H/D exchange reaction rate of cytochrome c in a methanol/H2O·D2O solution. We revealed that the first hydration shell of the cytochrome c molecule hinders the penetration of D2O to the surface of the molecule from the rates, which provides a novel method to investigate solution structures by a mass-spectrometric method. The droplet-collision mass spectrometry method developed in the present study can be extended to research on the molecular interactions in solutions, such as the mutual interactions of protein molecules, which are of importance in living cells.

Controlled Reactivity of Viologens in Alkaline Solutions Via Cucurbit[7]uril Complexation

AbstractA series of N‐alkyl‐ and N‐aryl‐viologens has been studied in alkaline solutions. In this work, we evaluated the deuteration rate of the viologens in D2O solutions of pH values ranging from 7.3 to 12.7. Kinetic experiments and computational calculations showed the high reactivity of H−C(2) bonds toward deprotonation of N‐aryl‐pyridinium moieties compared to N‐alkyl‐pyridinium moieties, even in hybrid N‐aryl/N‐alkyl dissymmetric viologens. However this high H−C(2) reactivity in liquid phase contrasted with the proton fragmentation mechanism observed in the gas phase by mass spectrometry. The H/D exchange rate of viologens in very strong alkaline conditions could be significantly reduced using cucurbit[7]uril (CB[7]) as supramolecular protecting group. Ultimately, CB[7] inclusion led to a selective protection of H−C(2) group of N‐aryl‐pyridinium of dissymmetric viologens, and induced a supramolecular regioselective deuteration.

Densities, Excess Molar Volumes and Excess Refractive Indices for Binary Solutions of D2O and H2O

Densities, Excess Molar Volumes and Excess Refractive Indices for Binary Solutions of D2O and H2O

Interaction of electrolyte molecules with the surface of porous carbon: NMR study

Electrochemical double-layer capacitors use porous carbons as the electrode material, and improving their performance requires an understanding of the electrolyte−carbon surface interactions. 13C, 14N, and 11B NMR spectroscopy were used to investigate the behaviour of the electrolytes [C(OCH3)3NH3]+Cl- and [N(CH2CH3)]+BF4- on the surface of porous carbon in D2O solutions. A chemical shift of 13C has been found in the fragments N–C, indicating electron density redistribution between nitrogen atoms and alkyl fragments. The presence of a signal with a chemical shift of d = 7.7 confirms the structuring of the electrolytic layer of water solution [N(CH2CH3)]+BF4-.

High-Performance and Stability Electrochromic Devices with a Water Isotopologue.

In this report, an ammonium metatungstate (AMT) and ferrous chloride [Fe(II)Cl2] electrochromic liquid (ECL) was synthesized using a hydrothermal method, with D2O used as the solvent instead of H2O. The results show that the use of D2O can improve the stability and performance of ECLs. The hydrogen evolution process in electrochromic devices (ECDs) filled with ECL becomes more difficult, while the material exchange process becomes easier. The ECD exhibits a color modulation amplitude of 58%@680 nm at 2 V. After 500 cycles, the device's performance remains above 95% at a current density of 1.5 mA/cm2. Hydrogen bonds in D2O solutions are expected to exhibit stronger forces compared to those in regular H2O solutions. Therefore, we hypothesize that enhancing the strength of hydrogen bonds in H2O solutions is an effective approach for improving the performance and stability of electrochromic solutions.

Effects of spectral density on the azide vibrational transition in water versus D2O

Water and D2O have distinct spectral densities resulting from isotopic shifts associated with their vibrational manifold. Two-dimensional infrared, pump–probe, and transient grating spectroscopies were employed to directly measure the vibrational dynamics for the azide transition of NaN3 within solutions of water and D2O. Although the frequency correlation time revealed minimal variation, a linear correlation between lifetime and the optical density of the solvent background was uncovered. Thus, a predictive model of the lifetime was proposed. These findings highlight the importance of spectral density of the solvent and its role in the pathways of energy dissipation for vibrational probes.

Water distribution in human hair microstructure elucidated by spin contrast variation small-angle neutron scattering

Dynamic nuclear polarization (DNP) is effective for controlling the neutron scattering length of protons and can be utilized for contrast variation in small-angle neutron scattering (SANS). Using the TEMPOL solution soaking method as electron spin doping, the DNP–SANS technique was applied to human hair fiber for the first time. For dry and D2O-swollen hair samples, a drastic change in the SANS profile was observed at high polarization conditions (|P H P N| ∼ 60%, where P H and P N are the proton and neutron spin polarization, respectively). The SANS profile as a function of the magnitude of the scattering vector, q, was composed of a low-q upturn, a middle-q oscillation and a high-q flat region. The low-q upturn was assumed to be a combination of two power-law functions, q −4 due to a large structure interface (Porod's law) and q −2 due to random coil. The middle-q oscillation was well reproduced by numerical calculation based on the structure model of intermediate filaments (IFs) as proposed by Er Rafik et al. [Biophys. J. (2004), 86, 3893–3904]: one pair of keratin coiled-coils is located at the center and surrounded by seven pairs of keratin coiled-coils located in a circle (called the `7 + 1' model), and a collection of IFs is arranged in a quasi-hexagonal manner. For the observed SANS profiles for different P H P N, the IF term contribution maintained a constant q-dependent profile, despite significant changes in intensity. This indicates that the macrofibril is composed of two domains (keratin coiled-coils and matrix). In addition, D2O swelling enhanced the IF term intensity and shifted the polarization-dependent local minimum to higher P H P N. This behavior was reproduced by contrast factor calculation based on the two-domain model. Scattering length densities of keratin coiled-coil and surrounding matrix domains were calculated by use of the known amino acid composition, considering the hydrogen–deuterium exchange reaction during soaking with D2O solution of TEMPOL. As a result, it was found that for keratin coiled-coil domains, about 40% of the peptide backbone amide NH protons were replaced with deuterons. This means that 68% of the α-helix domain is rigid, but the rest is flexible to allow dynamic dissociation of the hydrogen bond. Furthermore, the local mass density of each domain was precisely evaluated. The obtained data are expected to be a guide for further detailed investigation of keratin and keratin-associated protein distribution. This approach is expected to be applied to a wide variety of bio-derived materials, which are water absorbing in general.

Structural Identification and Antioxidant Activity of Loach Protein Enzymatic Hydrolysates.

Loach, rich in nutrients, such as proteins, amino acids, and mineral elements, is being gradually favored by consumers. Therefore, in this study, the antioxidant activity and structural characteristics of loach peptides were comprehensively analyzed. The loach protein (LAP) with a molecular weight between 150 and 3000 Da was graded by ultrafiltration and nanofiltration processes, which exhibited excellent scavenging activity against DPPH radical (IC50 2.91 ± 0.02 mg/mL), hydroxyl radical (IC50 9.95 ± 0.03 mg/mL), and superoxide anion radical (IC50 13.67 ± 0.33 mg/mL). Additionally, LAP was purified by gel filtration chromatography, and two principal components (named as LAP-I and LAP-II) were isolated. A total of 582 and 672 peptides were identified in LAP-I and LAP-II, respectively, through structural analysis. The XRD results revealed that LAP-I and LAP-II had an irregular amorphous structure. The 2D-NMR spectroscopy results suggested that LAP-I had a compact stretch conformation in the D2O solution, while LAP-II had a folded conformation. Overall, the study results suggested that loach peptide could be a potential antioxidant agent and might provide valuable information for chain conformation and antioxidant mechanism research further.

Fresh Dual Presaturation Method for Analyzing H2O-Rich Samples Using Quantitative 1H NMR

A fresh dual presaturation (pre-SAT) method was developed to quantify analytes accurately near the suppressed water signal in 1H NMR spectra obtained from H2O-rich samples. The method includes an extra dummy pre-SAT with a suitable offset for each analyte signal in addition to the water pre-SAT. The residual HOD signal at 4.66 ppm was observed using D2O solutions containing l-phenylalanine (Phe) or l-valine (Val) and an internal standard of 3-(trimethylsilyl)-1-propanesulfonic acid-d6 sodium salt (DSS-d6). When the HOD signal was suppressed using the conventional single pre-SAT method, the measured concentration of Phe from the NCH signal at 3.89 ppm decreased by a maximum of 48%, whereas the dual pre-SAT method gave a reduction in the Phe concentration measured from the NCH signal of less than 3%. The proposed dual pre-SAT method achieved accurate quantification of glycine (Gly) and maleic acid (MA) in a 10 vol % D2O/H2O solution. The measured concentrations of Gly of 513.5 ± 8.9 mg kg-1 and MA of 512.2 ± 10.3 mg kg-1 corresponded to sample preparation values of Gly of 502.9 ± 1.7 mg kg-1 and MA of 506.7 ± 2.9 mg kg-1 (the number after "±" indicates the expanded uncertainty (k = 2)).

Thermal Behavior of Poly(vinyl alcohol) in the Form of Physically Crosslinked Film.

Evaluation and understanding of the thermal behavior of polymers is crucial for many applications, e.g., polymer processing at relatively high temperatures, and for evaluating polymer-polymer miscibility. In this study, the differences in the thermal behavior of poly(vinyl alcohol) (PVA) raw powder and physically crosslinked films were investigated using various methods, such as thermogravimetric analysis (TGA) and derivative TGA (DTGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Various strategies were adopted, e.g., film casting from PVA solutions in H2O and D2O and heating of samples at carefully selected temperatures, in order to provide insights about the structure-properties relationship. It was found that the physically crosslinked PVA film presents an increased number of hydrogen bonds and increased thermal stability/slower decomposition rate compared to the PVA raw powder. This is also depicted in the estimated values of specific heat of thermochemical transition. The first thermochemical transition (glass transition) of PVA film, as for the raw powder, overlaps with mass loss from multiple origins. Evidence for minor decomposition that occurs along with impurities removal is presented. The overlapping of various effects (softening, decomposition, and evaporation of impurities) has led to confusion and apparent consistencies, e.g., from the XRD, it is derived that the film has decreased crystallinity, and apparently this is in agreement with the lower value of heat of fusion. However, the heat of fusion in this particular case has a questionable meaning.

The H-D-isotope effect of heavy water affecting ligand-mediated nanoparticle formation in SANS and NMR experiments.

An isotopic effect of normal (H2O) vs. heavy water (D2O) is well known to fundamentally affect the structure and chemical properties of proteins, for instance. Here, we correlate the results from small angle X-ray and neutron scattering (SAXS, SANS) with high-resolution scanning transmission electron microscopy to track the evolution of CdS nanoparticle size and crystallinity from aqueous solution in the presence of the organic ligand ethylenediaminetetraacetate (EDTA) at room temperature in both H2O and D2O. We provide evidence via SANS experiments that exchanging H2O with D2O impacts nanoparticle formation by changing the equilibria and dynamics of EDTA clusters in solution as investigated by nuclear magnetic resonance analysis. The colloidal stability of the CdS nanoparticles, covered by a layer of [Cd(EDTA)]2- complexes, is significantly reduced in D2O despite the strong stabilizing effect of EDTA in suspensions of normal water. Hence, conclusions about nanoparticle formation mechanisms from D2O solutions reveal limited transferability to reactions in normal water due to isotopic effects, which thus need to be discussed for contrast match experiments.

The effect of alcoholic solutions on the thermomechanical properties of immersed poly(lactic acid) films

AbstractThe effects of aqueous and deuterium oxide (D2O) solutions of alcohols (methanol, ethanol, 1‐propanol, 2‐propanol, and 1‐butanol) on the thermomechanical properties of poly(lactic acid)—PLA—films were assessed by dynamic mechanical analysis. The glass transition temperature (Tg) of PLA films immersed in 25%, 50%, 75%, and 100% (v/v) alcoholic solutions were compared with the Tg of films immersed in 100% water and D2O. The Tg of PLA films immersed in methanol and ethanol aqueous solutions decreased as the concentration of the alcohol solutions increased. For methanol and ethanol, the Tg decreased by 8.6 and 7.6°C per 25% (v/v) increase in alcohol, respectively. When the PLA films were immersed in propanol aqueous solutions and butanol, the Tg reached the lowest value at 75% (v/v) and 100% (v/v), respectively. Tg of PLA films immersed in 1‐propanol and 2‐propanol decreased by 8.6 and 8.9°C for every 25% increase in propanol before reaching the minimum value, respectively. Aqueous and D2O solutions had similar effects on Tg. Selective studies of crystallinity evolution, ethanol sorption, degree of swelling, and Hansen solubility parameters of PLA were conducted. This work assists in developing PLA films intended for contact with aqueous‐alcoholic solutions.

Infrared spectroscopic analysis of hydrogen-bonding interactions in cryopreservation solutions

BackgroundIn this study we investigated hydrogen bonding interactions in hydrated and frozen solutions of different cryoprotective agents (CPAs) including dimethyl sulfoxide, glycerol, ethylene glycol, propylene glycol, and trehalose. We also investigated the effect of CPAs on ice crystal growth during storage and correlated this with storage stability of liposomes. MethodsFTIR spectroscopy was used to study hydrogen bonding interactions in CPA solutions in H2O and D2O, and their thermal response was analyzed using van ’t Hoff analysis. The effect of CPAs on ice crystal growth during storage was investigated by microscopy and correlated with storage stability of liposomes encapsulated with a fluorescent dye. ResultsPrincipal component analyses demonstrated that different CPAs can be recognized based on the shape of the OD band region only. Chemically similar molecules such as glycerol and ethylene glycol closely group together in a principal component score plot, whereas trehalose and DMSO appear as condensed separated clusters. The OH/OD band of CPA solutions exhibits an overall shift to higher wavenumbers with increasing temperature and changed fractions of weak and strong hydrogen interactions. CPAs diminish ice crystal formation in frozen samples during storage and minimize liposome leakage during freezing but cannot prevent leakage during frozen storage. ConclusionsCPAs can be distinguished from one another based on the hydrogen bonding network that is formed in solution. DMSO-water mixtures behave anomalous compared to other CPAs that have OH groups. CPAs modulate ice crystal formation during frozen storage but cannot prevent liposome leakage during frozen storage.

ПРИМЕНЕНИЕ МЕТОДА ГЛАВНЫХ КОМПОНЕНТ ДЛЯ АНАЛИЗА ИК СПЕКТРОВ СЫВОРОТКИ КРОВИ ПАЦИЕНТОВ С ОНКОГЕМАТОЛОГИЧЕСКИМИ ЗАБОЛЕВАНИЯМИ

Multiple myeloma and chronic lymphocytic leukemia are oncological diseases of the blood, which remain incurable today. The paper proposes a method for classifying blood serum samples from patients with multiple myeloma, chronic lymphocytic leukemia and healthy donors based on the analysis of their spectra in the mid-infrared (IR) range. IR spectra of blood serum were recorded using a Tensor 27 IR Fourier spectrometer in D2O solution. To analyze the obtained spectra in this work, a machine learning algorithm was implemented – the principal component analysis. The use of the principal component analysis made it possible to significantly simplify the representation of the array of spectral data. 45 samples of blood serum were analyzed in the work. As a result of applying this approach, the studied set of samples is divided into three disjoint sets corresponding to blood serum samples of patients with multiple myeloma, chronic lymphocytic leukemia and healthy donors. Thus, the principal component method can be successfully applied to classify blood serum samples of patients with diagnoses of multiple myeloma and chronic lymphocytic leukemia. The universality of the proposed algorithm allows us to expect that in the future it is possible to apply a similar approach for other oncohematological diseases.

Hydrogen-deuterium (H/D) exchange reaction of acebutolol hydrochloride in D₂O and CD₃OD solution.

H/D exchange reactions can be observed by NMR spectroscopy of acebutolol (ACE). The results obtained showed deuterium incorporation at α-posi t ion of the carbonyl group of acebutolol, when using deuterium oxide or deuterated methanol as deuterium source and solvent. The spontaneous deuteration is proceeded by the following pathway CH₃→CH₂D→CHD→CD₃, through a keto-enol tautomerization reaction. Furthermore, LC-MS / QTOF analyses have confirmed the proposed H/D exchange. In order to reduce the time of total deuteration observed at the acetyl group alkaline catalysts were employed.

Physico-Chemical Characterization of a Highly Rigid Gd(III) Complex Formed with a Phenanthroline Derivative Ligand.

The discovery of the nephrogenic systemic fibrosis (NSF) and its link with the in vivo dissociation of certain Gd(III)-based contrast agents (CAs) applied in the magnetic resonance imaging (MRI) induced a still growing research to replace the compromised agents with safer alternatives. In recent years, several ligands were designed to exploit the luminescence properties of the lanthanides, containing structurally constrained aromatic moieties, which may form rigid Gd(III) complexes. One of these ligands is (1,10-phenanthroline-2,9-diyl)bis(methyliminodiacetic acid) (H4FENTA) designed and synthesized to sensitize Eu(III) and Tb(III) luminescence. Our results show that the conditional stability of the [Gd(FENTA)]- chelate calculated for physiological pH (pGd = 19.7) is similar to those determined for [Gd(DTPA)]2- (pGd = 19.4) and [Gd(DOTA)]- (pGd = 20.1), routinely used in the clinical practice. The [Gd(FENTA)]- complex is remarkably inert with respect to its dissociation (t1/2 = 872 days at pH = 7 and 25 °C); furthermore, its relaxivity values determined at different field strengths and temperatures (e.g., r1p = 4.3 mM-1s-1at 60 MHz and 37 °C) are ca. one unit higher than those of [Gd(DTPA)]2- (r1p = 3.4 mM-1 s-1) and [Gd(DOTA)]- (r1p = 3.1 mM-1 s-1) under the same conditions. Moreover, significant improvement on the relaxivity was observed in the presence of serum proteins (r1p = 6.9 mM-1 s-1 at 60 MHz and 37 °C). The luminescence lifetimes recorded in H2O and D2O solutions indicate the presence of a water molecule (q = 1) in the inner sphere of the complex directly coordinated to the metal ion, possessing a relatively high water exchange rate (kex298 = 29(2) × 106 s-1). The acceleration of the water exchange can be explained by the steric compression around the water binding site due to the rigid structure of the complex, which was supported by DFT calculations. On the basis of these results, ligands containing a phenanthroline platform have great potential in the design of safer Gd(III) agents for MRI.

Determination of ribose and phosphorus contents in Haemophilus influenzae type b capsular polysaccharide by a quantitative NMR method using a single internal standard.

The ribose and phosphorus contents in Haemophilus influenzae type b (Hib) capsular polysaccharide (CPS) are two important chemical indexes for the development and quality control of Hib conjugate vaccine. A quantitative 1H- and 31P-NMR method using a single internal standard was developed for simultaneous determination of ribose and phosphorus contents in Hib CPS. Hexamethylphosphoramide (HMPA) was successfully utilized as an internal standard in quantitative 1H-NMR method for ribose content determination. The ribose and phosphorus contents were found to be affected by the concentration of polysaccharide solution. Thus, 15-20 mg·L-1 was the optimal concentration range of Hib CPS in D2O solution for determination of ribose and phosphorus contents by this method. The ribose and phosphorus contents obtained by the quantitative NMR were consistent with those obtained by traditional chemical methods. In conclusion, this quantitative 1H- and 31P-NMR method using a single internal standard shows good specificity, accuracy and precision, providing a valuable approach for the quality control of Hib glycoconjugate vaccines.

Photoacid-induced aqueous acid–base reactions probed by femtosecond infrared spectroscopy

Acid-base reactions involving an excited photoacid have typically been investigated at high base concentrations, but the mechanisms at low base concentrations require clarification. Herein, the dynamics of acid-base reactions induced by an excited photoacid, pyranine (DA), were investigated in the presence of azide ion (N3-) in D2O solution using femtosecond infrared spectroscopy. Specifically, the spectral characteristics of four species (DA, electronically excited DA (DA*), the conjugate base of DA* (A*-), and the conjugate base of DA (A-)) were probed in the spectral region of 1400-1670cm-1 in the time range of 1ps-1μs. This broad timescale encompassed all the acid-base reactions initiated by photoexcitation at 400nm; thus, reactions related to both DA* and A- could be probed. Furthermore, changes in the populations of N3- and DN3 were monitored using the absorption bands at 2042 and 2133cm-1, respectively. Following excitation, approximately half of DA* relaxed to DA with a time constant of 0.44 ± 0.04ns. The remainder underwent an acid-base reaction to produce A*-, which relaxed to A- with a time constant of 3.9 ± 0.3ns. The acid-base reaction proceeded via two paths, namely, proton exchange with the added base or simple deuteron release to D2O (protolysis). Notably, all the acid-base reactions were well described by the rate constant at the steady-state limit. Thus, although the acid-base reactions at low base concentrations (< 0.1M) were diffusion controlled, they could be described using a simple rate equation.