Hair relaxation after shaping - A kinetic approach.

OBJECTIVE: Hair fibres have been shaped via either a thermal route or via a chemical route. The time-relaxation transients of the shaped hairs in air, and in water, respectively, were evaluated. The collected data were kinetically modelled in order to reveal information about the rate controlling mechanism of the recovery process. METHODS: Hair fibres were thermally shaped at different temperatures between heated plates and left to relax in an environment of controlled humidity and temperature. Different hair fibres were chemically shaped and left to relax in water of different controlled temperatures. Relaxation data were used for modelling the kinetics of the recovery processes by using exponential and logarithmic kinetic laws. The fitting of the models to the two sets of data has been checked by using the residual sum of squares for matching the proper model to each set of data. RESULTS: The processes of shaping and recovery were assimilated with a sequence of two successive quasi-chemical reactions, occurring at the used temperatures. Based on chemical and physical assumptions, the two groups of experiments were modelled by two different laws: an exponential law, suggesting a first-order process as the rate-determining step of the relaxation of thermally shaped fibres, and a logarithmic law, suggesting a slow relaxation, based on percolation theory, for the chemically shaped fibres. This allowed use of chemical kinetics tools for calculating the values of the activation energy in each case. The evaluated values of activation energy of the relaxation processes for both thermal and chemical shaping were found to be close to each other, in spite of the different methods of shaping. CONCLUSION: The kinetic analysis suggests that despite different reaction sequences occurring during the different shaping-relaxation processes, the rate-controlling mechanism that manages the recovery process is the same in all cases; and this process is proposed to be the thiol-disulphide reformation of intra-protein bonds inside hair.

OBJECTIF: Les fibres capillaires ont été traitées soit par voie thermique, soit par voie chimique. Les variations passagères du temps de relaxation des cheveux traités dans l'eau et dans l'air, respectivement, ont été évaluées. Les données recueillies ont été modélisées cinétiquement afin de révéler des informations sur le mécanisme de contrôle de la vitesse du processus de récupération. MÉTHODES: Les fibres capillaires ont été traitées thermiquement à différentes températures entre des plaques chauffantes et on les a laissées se relâcher dans un environnement où l'humidité et la température étaient contrôlées. Différentes fibres capillaires ont été traitées chimiquement et on les a laissées se relâcher dans l'eau à différentes températures contrôlées. Les données de relâchement ont été utilisées pour modéliser la cinétique des processus de récupération en utilisant des lois cinétiques exponentielles et logarithmiques. L'ajustement des modèles aux deux ensembles de données a été vérifié en utilisant la somme résiduelle des carrés pour faire correspondre le modèle approprié à chaque ensemble de données. RÉSULTATS: Les processus de traitement et de récupération ont été assimilés à une séquence de deux réactions quasi-chimiques successives, survenant aux températures utilisées. Sur la base d'hypothèses chimiques et physiques, les deux groupes d'expériences ont été modélisés selon deux lois différentes : une loi exponentielle, indiquant un processus de premier ordre comme l'étape déterminant la vitesse de relâchement des fibres traitées thermiquement, et une loi logarithmique, indiquant un relâchement lent, sur la base de la théorie de la percolation, pour les fibres traitées chimiquement. Cela a permis d'utiliser des outils de cinétique chimique pour calculer les valeurs de l'énergie d'activation dans chaque cas. Les valeurs évaluées de l'énergie d'activation des processus de relâchement pour le traitement thermique et chimique se sont avérées proches les unes des autres, malgré les différentes méthodes de traitement. CONCLUSION: L'analyse cinétique indique que, malgré les différentes séquences de réaction survenant au cours des différents processus de traitement-relâchement, le mécanisme de contrôle de la vitesse qui gère le processus de récupération est le même dans tous les cas ; et ce processus est proposé comme étant la reformation du thiol/disulfure des liaisons intraprotéiques à l'intérieur du cheve.

Chemical bonds and hair behaviour-A review.

When undertaking any review of the structure of the hair and its mechanical properties it becomes apparent that the overall behaviour of keratin fibres is commonly attributed to the presence of hydrogen, disulfide and ionic bonds. The action of physico-chemical agents used during various cosmetic treatments is viewed as the result of an interaction with these bonds. Thus, the breaking of bonds by chemical agents, or via mechanical or thermal stresses, affects the relative balance of disulfide and hydrogen bonds and the contribution of hydrophobic interactions, which are all important factors that may alter hair behaviour. Generally, these chemical bonds are considered as responding homogeneously to the environmental and cosmetic factors. This unitary image is challenged, however, by evaluating the results of chemical, nanomechanical, tensile and thermal measurements, which suggest that disulfide bonds may be grouped into several types, according to their location within the fibre and the way they respond to various agents. A compensatory effect of newly formed hydrogen bonds for broken disulfide bonds may also be seen, and additionally involves different types of hydrogen bonds. As a result, the picture of chemical bonding in hair appears to be far from a homogeneous one. In addition, it is apparent that further investigation is required for clarifying the action of ionic bonds and hydrophobic interactions within the hair fibre. The present review aims, thus, at offering a deeper background for understanding how the hair behaves under various conditions.

Comme l'indique l'étude de la littérature réalisée dans le cadre de cette revue, le comportement général des fibres kératiniques est généralement attribué à la présence de liaisons hydrogène, disulfure et ioniques. L'action des agents physico­chimiques utilisés au cours de divers traitements cosmétiques est alors considérée comme le résultat d'une interaction avec ces liaisons. Ainsi, la rupture des liaisons par des agents chimiques, ou par des contraintes mécaniques ou thermiques, affecte l'équilibre relatif des liaisons disulfure et hydrogène et la contribution des interactions hydrophobes, qui sont autant de facteurs importants susceptibles d'altérer le comportement du cheveu. En général, on considère que ces liaisons chimiques réagissent de manière homogène aux facteurs environnementaux et cosmétiques. Cette image unitaire est toutefois remise en question par l'évaluation des résultats des mesures chimiques, nanomécaniques, thermiques et de traction, qui suggèrent que les liaisons disulfures peuvent être regroupées en plusieurs types, en fonction de leur emplacement dans la fibre et de la manière dont elles réagissent aux différents agents. Un effet compensatoire des liaisons hydrogène nouvellement formées pour les liaisons disulfures rompues peut également être observé et implique en outre différents types de liaisons hydrogène. Par conséquent, l'image de la liaison chimique dans les cheveux est loin d'être homogène. En outre, il est évident que des recherches supplémentaires sont nécessaires pour clarifier l'action des liaisons ioniques et des interactions hydrophobes au sein de la fibre capillaire. La présente étude vise donc à offrir une base pour une compréhension plus approfondie du comportement du cheveu dans diverses conditions.

Online prediction tools for melanoma survival: A comparison.

BACKGROUND: Breslow thickness, patient age and ulceration are the three most valuable clinical and pathological predictors of melanoma survival. A readily available reliable online tool that accurately considers these and other predictors could be valuable for clinicians managing melanoma patients. OBJECTIVE: To compare online melanoma survival prediction tools that request user input on clinical and pathological features. METHODS: Search engines were used to identify available predictive nomograms. For each, clinical and pathological predictors were compared. RESULTS: Three tools were identified. The American Joint Committee on Cancer tool inappropriately rated thin tumours as higher risk than intermediate tumours. The University of Louisville tool was found to have six shortcomings: a requirement for sentinel node biopsy, unavailable input of thin melanoma or patients over 70 years of age and less reliable hazard ratio calculations for age, ulceration and tumour thickness. The LifeMath.net tool was found to appropriately consider tumour thickness, ulceration, age, sex, site and tumour subtype in predicting survival. LIMITATIONS: The authors did not have access to the base data used to compile various prediction tools. CONCLUSION: The LifeMath.net prediction tool is the most reliable for clinicians in counselling patients with newly diagnosed primary cutaneous melanoma regarding their survival prospects.

Structural, vibrational and electronic properties of α'-Ga2S3 under compression.

We report a joint experimental and theoretical study of the low-pressure phase of α'-Ga2S3 under compression. Theoretical ab initio calculations have been compared to X-ray diffraction and Raman scattering measurements under high pressure carried out up to 17.5 and 16.1 GPa, respectively. In addition, we report Raman scattering measurements of α'-Ga2S3 at high temperature that have allowed us to study its anharmonic properties. To understand better the compression of this compound, we have evaluated the topological properties of the electron density, the electron localization function, and the electronic properties as a function of pressure. As a result, we shed light on the role of the Ga-S bonds, the van der Waals interactions inside the channels of the crystalline structure, and the single and double lone electron pairs of the sulphur atoms in the anisotropic compression of α'-Ga2S3. We found that the structural channels are responsible for the anisotropic properties of α'-Ga2S3 and the A'(6) phonon, known as the breathing mode and associated with these channels, exhibits the highest anharmonic behaviour. Finally, we report calculations of the electronic band structure of α'-Ga2S3 at different pressures and find a nonlinear pressure behaviour of the direct band gap and a pressure-induced direct-to-indirect band gap crossover that is similar to the behaviour previously reported in other ordered-vacancy compounds, including ß-Ga2Se3. The importance of the single and, more specially, the double lone electron pairs of sulphur in the pressure dependence of the topmost valence band of α'-Ga2S3 is stressed.

BONE QUALITY IN A YOUNG COHORT OF HIV-POSITIVE PATIENTS.

CONTEXT: In HIV+ patients, several factors related to patient and antiretroviral therapy (ART) could determine early onset of bone mineral density (BMD) disturbances. OBJECTIVE: Evaluation of bone quality according to gender in patients from the HIV Romanian cohort. DESIGN: A cross-sectional study in "Prof. Dr. Matei Bals" National Institute for Infectious Diseases, Bucharest between 2016-2018. SUBJECT AND METHODS: We collected data regarding HIV infection, ART history, viral hepatitis co-infections and we calculated patients body mass index (BMI). CD4 cell count, HIV viral load (VL), vitamin-D levels were determined. Dual-energy X-ray absorptiometry (DXA) scans were used to evaluate BMD. RESULTS: We enrolled 97 patients with the median age of 26 years. According to the DXA T-scores, 10 males and 8 females had osteopenia and 4 males and 4 females had osteoporosis. According to Z-scores 2 males and 1 female had osteoporosis. Hip DXA T-scores revealed osteopenia in 6 males and 9 females, whereas T and Z-scores showed osteoporosis in 2 males and 3 females. Lumbar spine (LS) T-score diagnosed osteopenia in 9 males and 6 females, while T and Z-scores revealed osteoporosis in 3 males and females. In males, low T-scores were associated with decreased BMI; low LS DXA Z-scores with low vitamin-D levels; low T and Z-scores and LS-BMD with high VL. CONCLUSIONS: Evaluating bone quality in patients with a long history of HIV infection, multiple factors should be taken into account.

Risk of hepatitis B virus reactivation in hepatitis B virus + hepatitis C virus-co-infected patients with compensated liver cirrhosis treated with ombitasvir, paritaprevir/r + dasabuvir + ribavirin.

Hepatitis B virus may reactivate in patients with chronic hepatitis C treated with direct-acting antivirals. The aim of this study was to investigate the risk of hepatitis B virus (HBV) reactivation in HBV + hepatitis C virus (HCV)-co-infected patients with compensated liver cirrhosis treated with paritaprevir/ombitasvir/ritonavir, dasabuvir with ribavirin. We reviewed prospectively gathered data from a national cohort of 2070 hepatitis C virus patients with compensated liver cirrhosis who received reimbursed paritaprevir/ombitasvir/r, dasabuvir with ribavirin for 12 weeks from the Romanian National Health Agency during 2015-2016. Twenty-five patients in this cohort were HBs antigen positive (1.2%); 15 untreated with nucleotide analogues agreed to enter the study. These patients were followed up: ALT monthly, serology for HBV and DNA viral load at baseline, EOT and SVR at 12 weeks. Hepatitis B virus (HBV)-co-infected patients were all genotype 1b and 52% females, with a median age of 60 years (51 ÷ 74); 76% were pretreated with peginterferon + ribavirin; 72% were with severe necroinflammatory activity on FibroMax assessment; 40% presented comorbidities; and all were HBe antigen negative. Hepatitis C virus (HCV) SVR response rate was 100%. Hepatitis B virus (HBV)-DNA viral load was undetectable in 7/15 (47%) before therapy, and for the other 8 patients, it varied between below 20 and 867 IU/mL. Five patients (33%) presented virological reactivation (>2 log increase in HBV-DNA levels) during therapy. One patient presented with hepatitis associated with HBV reactivation, and two started anti-HBV therapy with entecavir. Hepatitis B virus (HBV) virological reactivation was present in 33% in our patients. Generally, HBV-DNA elevations were mild (<20 000 IU/mL); however, we report one case of hepatitis associated with HBV reactivation.

Structural and vibrational properties of corundum-type In2O3 nanocrystals under compression.

This work reports the structural and vibrational properties of nanocrystals of corundum-type In2O3 (rh-In2O3) at high pressures by using angle-dispersive x-ray diffraction and Raman scattering measurements up to 30 GPa. The equation of state and the pressure dependence of the Raman-active modes of the corundum phase in nanocrystals are in good agreement with previous studies on bulk material and theoretical simulations on bulk rh-In2O3. Nanocrystalline rh-In2O3 showed stability under compression at least up to 20 GPa, unlike bulk rh-In2O3 which gradually transforms to the orthorhombic Pbca (Rh2O3-III-type) structure above 12-14 GPa. The different stability range found in nanocrystalline and bulk corundum-type In2O3 is discussed.

The effect of levodopa-carbidopa intestinal gel infusion long-term therapy on motor complications in advanced Parkinson's disease: a multicenter Romanian experience.

Chronic treatment with oral levodopa is associated with an increased frequency of motor complications in the late stages of Parkinson's disease (PD). Continuous administration of levodopa-carbidopa intestinal gel (LCIG-Duodopa(®), Abbott Laboratories), which has been available in Romania since 2009, represents an option for treating patients with advanced PD. Our primary objective was to report changes in motor complications after initiation of LCIG therapy. The secondary objectives were as follows: to determine the impact of LCIG therapy on the daily levodopa dose variation before/and after LCIG, to collect patient self-assessments of quality of life (QoL), and to study the overall tolerability and safety of LCIG administration. A retrospective analysis (2009-2013) of LCIG therapy and the experience in nine neurology centers in Romania was performed. The impact of LCIG therapy was evaluated by analyzing changes in motor fluctuations, dyskinesia and the patients' QoL after initiating therapy. The safety of LCIG therapy was estimated by noting agent-related adverse events (AEs) and medical device-related AEs. In the 113 patients included, we observed a significant improvement in PD symptoms after initiation of LCIG therapy. The "on" period increased, with a mean value of 6.14 h, and the dyskinesia period was reduced, with a mean value of 29.4 %. The quantified non-motor symptoms subsided. The patients exhibited significant improvements in QoL scores. There were few AEs and few cases of LCIG therapy discontinuation. LCIG is an important and available therapeutic option for managing patients with advanced PD.

DSC of human hair: a tool for claim support or incorrect data analysis?

Differential scanning calorimetry (DSC) data are increasingly used to substantiate product claims of hair repair. Decreasing peak temperatures may indicate structural changes and chemical damage. Increasing the DSC, wet peak temperature is, therefore, often considered as proof of hair repair. A detailed understanding of the technique and hair structure indicates that this may not be a sound approach. Surveying the rich literature on the use of dynamic thermal analysis (DTA) and differential scanning calorimetry (DSC) for the analyses of human hair and the effect of cosmetic treatments, we underline some of the problems of hair structure and data interpretation. To overcome some of the difficulties of data interpretation, we advise that DSC acquired data should be supported by other techniques when used for claim substantiation. In this way, one can provide meaningful interpretation of the hair science and robust data for product claims support.

No survival benefit for patients with melanoma undergoing sentinel lymph node biopsy: critical appraisal of the Multicenter Selective Lymphadenectomy Trial-I final report.

BACKGROUND: Sentinel lymph node biopsy (SLNB) was developed in the hope that it would improve outcomes for patients with melanoma. SLNB is an area of discussion and controversy in melanoma medicine. The final trial results of the Multicenter Selective Lymphadenectomy Trial (MSLT-I) have now been published and the authors suggest their long-term results 'clearly validate the use of sentinel-node biopsy in patients with intermediate-thickness or thick primary melanomas'. An accompanying editorial states that MSLT-I is a practice-changing trial. CONCLUSIONS: However, critical appraisal of MSLT-I data does not support the claims of the final report. On the contrary, MSLT-I failed to demonstrate that there is a significant treatment-related difference in the 10-year melanoma-specific survival rate in the overall study population. Furthermore, there was no improvement in overall or melanoma-specific survival of the intermediate-thickness group (1·2-3·5 mm). Completion lymphadenectomy can result in complications in about a third of patients, with a rate of clinically significant lymphoedema following axillary or groin dissection of 5-10%. Unnecessary lymphadenectomy can therefore have a major effect on patient quality of life. The evidence provided by Morton et al. does not support the claim that sentinel lymph node biopsy followed by lymphadenectomy in patients with positive sentinel nodes should be the standard of care in patients with melanoma. Readers are encouraged to check with registration sites to make sure declared primary outcomes are fairly reported. Post-hoc analyses are at best exploratory and cannot be used to form the principal conclusions of a trial.

Lessons learned from Jordan's response to the Syria refugee crisis.

The number of refugees across the world has jumped from 15.7 million to 34.6 million in the past 10 years, and their forced displacement situation remain for an average period of 20 years. To ensure sustainable benefits, health system strengthening through development cooperation should be a priority in parallel to humanitarian aid early on in refugee crises.

Epidemiology of hepatitis D in patients infected with hepatitis B virus in bucharest: a cross-sectional study.

Epidemiological analyses indicate a decreasing level of hepatitis D (HDV) infections in most developed countries during the last 15 years. Romania, however, is one of the European countries that still has high morbidity from HDV; this study was performed in order to estimate the HDV prevalence in the Bucharest area. Three thousand four hundred sixty-one hepatitis B (HBV) infected patients were invited to participate and 1,094 were recruited. Serum anti-HDV IgG was detected in 223 patients indicating a hepatitis D seroprevalence of 20.4% (95% CI = 18.1-22.9) in patients chronically infected with HBV, less than that seen in previous studies. Seroprevalence was not gender related, but patients over 40 years were more likely to have anti-HDV antibodies, RR = 1.9 (1.2; 3.0). Detectable hepatitis D viraemia was found in 67.7% of the patients who were positive for anti-HDV. The HDV genotype was characterized for 40 isolates; all were very similar and belonged to genotype 1. Serum HBV-DNA was detectable less frequently in patients positive for anti-HDV than in patients infected with HBV alone: 68.5% versus 89.3%, OR 3.9 (1.7; 10.0), but the extent of this HDV replicative dominance varies with the sensitivity of the HBV-DNA detection. 19.3% of the subjects who tested positive for anti-HDV IgG had a HBV-DNA level higher than four logs. This high prevalence prompts the need for better HBV vaccination coverage and measures to prevent super infection with HDV in patients infected with HBV.

Iron oxide/hydroxide-nitrogen doped graphene-like visible-light active photocatalytic layers for antibiotics removal from wastewater.

Hybrid layers consisting of Fe oxide, Fe hydroxide, and nitrogen doped graphene-like platelets have been synthesized by an eco-friendly laser-based method for photocatalytic applications. The complex composite layers show high photodecomposition efficiency towards degradation of antibiotic molecules under visible light irradiation. The photodecomposition efficiency was investigated as a function of relative concentrations of base materials, Fe oxide nanoparticles and graphene oxide platelets used for the preparation of target dispersions submitted to laser irradiation. Although reference pure Fe oxide/Fe hydroxide layers have high absorption in the visible spectral region, their photodecomposition efficiency is negligible under the same irradiation conditions. The high photocatalytic decomposition efficiency of the nanohybrid layer, up to 80% of the initial antibiotic molecules was assigned to synergistic effects between the constituent materials, efficient separation of the electron-hole pairs generated by visible light irradiation on the surface of Fe oxide and Fe hydroxide nanoparticles, in the presence of conducting graphene-like platelets. Nitrogen doped graphene-like platelets contribute also to the generation of electron-hole pairs under visible light irradiation, as demonstrated by the photocatalytic activity of pure, reference nitrogen doped graphene-like layers. The results also showed that adsorption processes do not contribute significantly to the removal of antibiotic molecules from the test solutions. The decrease of the antibiotic concentration under visible light irradiation was assigned primarily to photocatalytic decomposition mechanisms.

On the feasibility of using motor imagery EEG-based brain-computer interface in chronic tetraplegics for assistive robotic arm control: a clinical test and long-term post-trial follow-up.

STUDY DESIGN: Survey and long-term clinical post-trial follow-up (interviews/correspondence) on nine chronic, post spinal cord injury (SCI) tetraplegics. OBJECTIVE: To assess feasibility of the use of Electroencephalography-based Brain-Computer Interface (EEG-BCI) for reaching/grasping assistance in tetraplegics, through a robotic arm. SETTINGS: Physical and (neuromuscular) Rehabilitation Medicine, Cardiology, Neurosurgery Clinic Divisions of TEHBA and UMPCD, in collaboration with 'Brain2Robot' (composed of the European Commission-funded Marie Curie Excellence Team by the same name, hosted by Fraunhofer Institute-FIRST), in the second part of 2008. METHODS: Enrolled patients underwent EEG-BCI preliminary training and robot control sessions. Statistics entailed multiple linear regressions and cluster analysis. A follow-up-custom questionnaire based-including patients' perception of their EEG-BCI control capacity was continued up to 14 months after initial experiments. RESULTS: EEG-BCI performance/calibration-phase classification accuracy averaged 81.0%; feedback training sessions averaged 70.5% accuracy for 7 subjects who completed at least one feedback training session; 7 (77.7%) of 9 subjects reported having felt control of the cursor; and 3 (33.3%) subjects felt that they were also controlling the robot through their movement imagination. No significant side effects occurred. BCI performance was positively correlated with beta (13-30 Hz) EEG spectral power density (coefficient 0.432, standardized coefficient 0.745, P-value=0.025); another possible influence was sensory AIS score (range: 0 min to 224 max, coefficient -0.177, standardized coefficient -0.512, P=0.089). CONCLUSION: Limited but real potential for self-assistance in chronic tetraplegics by EEG-BCI-actuated mechatronic devices was found, which was mainly related to spectral density in the beta range positively (increasing therewith) and to AIS sensory score negatively.

Pharyngoesophageal junction neoplasia--therapeutic management.

Not only the anatomy but the treatment and the prognosis of these tumors are intermediate between hypopharyngeal and esophageal tumors. After a portion of the esophagus is removed or complete esophagectomy, a conduit must be established. The authors reviewed the experience of Prof. Cristian Popescu in total pharyngo-laryngectomy and his technique of pharyngoesophageal reconstruction with synthetic esophageal prosthesis. We have some 21 patients who underwent an esophageal reconstruction with Montgomery esophageal tube. This is a very important new, modem, interdisciplinary approach bewteen the head and neck surgeon and the general/thoracic surgeon to treat the pharyngo-laryngo-esofageal neoplasia with one stage reconstruction. The follow up for these patients shows that this reconstruction method is a good, reliable choice with low costs and considerable advantages for the quality of life. Surgery for these patients should be considered primarily palliative and the optimal reconstruction should preserve the quality of life for the duration of survival.

Intestinal perforated malignant melanoma: diagnostic and therapeutic difficulties.

The intestinal malignant melanoma is a rare occurrence in the daily surgical practice, with difficult diagnosis (even on usual pathologic examination) and therapeutic attitude. Most of the lesions are secondary to a cutaneous primary melanoma, but there are cases in which the original site may not be discovered, and are considered as primitive intestinal melanomas. This paper presents the case of a 50 year old male patient, diagnosed and operated as emergency with acute abdomen caused by a tumoral perforation of the small bowel; several tumors, in different stages of local evolution, were discovered during laparotomy. A triple enterectomy with end-to-end entero-enteral anastomosis was performed, with uneventful postoperative recovery. The later postoperative evolution was marked by the occurrence of multiple subcutaneous recurrences and a bulky metastasis in the mediastinum; 18 month after the initial surgery, the patient died due to the melanoma recurrence. Diagnostic and therapeutic difficulties are discussed in this paper, related especially to the differential diagnosis of the origin of the intestinal lesion (a metastatic melanoma with unknown primary site or a primary malignant melanoma of the small bowel), since no other sites of origin were discovered after a thorough examination.

Mössbauer studies of the ferryl, ferrous and ferric states of dehaloperoxidase from A. ornata.

Dehaloperoxidase (DHP) is a multi-functional catalytic globin from the marine worm A. ornata, whose physiological functions include oxygen transport and oxidation of toxic substrates present in its habitat. In the Fe(III) state, DHPA has an isomer shift of 0.42 mm/s, characteristic for high-spin heme proteins. Changes in pH have subtle effects on the electronic structure of DHP in the Fe(III) state detectable in the high-field spectra, which show a pH-dependent mixture of species with different zero-field splittings between 5 and 18 cm-1. The short-lived intermediate obtained by direct reaction of the Fe(III) enzyme with H2O2 has an isomer shift of 0.10 mm/s, indicative of an Fe(IV)-oxo state and of an S = 1 electronic ground state confirmed by variable field studies. The O2-bound state of DHP has an isomer shift of 0.28 mm/s and a high-field spectrum characteristic for diamagnetic heme complexes, similarly to other haemoglobins. Overall, the isomer shift and quadrupole splitting of DHP in the four states studied are expectedly similar to both peroxidases and to myoglobin. The differences in electronic structure between DHP and other heme proteins and enzyme are observed in the high-field Mössbauer spectra of the ferric state, which show pH-dependent zero-field splittings suggesting a heme site in which the ligand field strength at the iron ion is tuned by pH. This tunability is correlated with variable electron-donating properties of the iron, which can perform multiple functions.

Phase stability and dense polymorph of the BaCa(CO3)2 barytocalcite carbonate.

The double carbonate BaCa(CO3)2 holds potential as host compound for carbon in the Earth's crust and mantle. Here, we report the crystal structure determination of a high-pressure BaCa(CO3)2 phase characterized by single-crystal X-ray diffraction. This phase, named post-barytocalcite, was obtained at 5.7 GPa and can be described by a monoclinic Pm space group. The barytocalcite to post-baritocalcite phase transition involves a significant discontinuous 1.4% decrease of the unit-cell volume, and the increase of the coordination number of 1/4 and 1/2 of the Ba and Ca atoms, respectively. High-pressure powder X-ray diffraction measurements at room- and high-temperatures using synchrotron radiation and DFT calculations yield the thermal expansion of barytocalcite and, together with single-crystal data, the compressibility and anisotropy of both the low- and high-pressure phases. The calculated enthalpy differences between different BaCa(CO3)2 polymorphs confirm that barytocalcite is the thermodynamically stable phase at ambient conditions and that it undergoes the phase transition to the experimentally observed post-barytocalcite phase. The double carbonate is significantly less stable than a mixture of the CaCO3 and BaCO3 end-members above 10 GPa. The experimental observation of the high-pressure phase up to 15 GPa and 300 ºC suggests that the decomposition into its single carbonate components is kinetically hindered.