OC Interactions Research Articles

Open Circuit Interaction Between Ethanol or 2-Propanol and Oxidized Platinum Surfaces.

The interaction between organic molecules and oxidized catalyst surfaces has frequently been used to study the fuel crossover from the anode to the cathode in direct liquid fuel cells. In such experiments, the oxidized surface is put in contact with the fuel under open circuit conditions, and the evolution of the potential is registered. The open circuit potential (OCP) vs. time features can then inform on the reactivity of the fuel with the oxidized surface and provide valuable information not only to applications in fuel cells but also to the electrochemical reform of those molecules to produce clean hydrogen. In this paper, we present an experimental investigation of the open circuit interaction between ethanol or 2-propanol with oxidized platinum surfaces. Besides the OCP time traces, we have also employed cyclic voltammetry and fast oxide reduction sweep in the presence of the alcohols. Comparable reaction currents are obtained in the cyclic voltammogram, but the electro-oxidation of 2-propanol sets in at considerably lower overpotentials than that of ethanol. At the high potential region, both the magnitude and the potential of the current peak are nearly identical in both cases. In contrast, under open circuit conditions, the interaction of ethanol with the oxidized platinum surface is more pronounced than that found for 2-propanol, and these results are corroborated by the facile reduction of the platinum oxides along the fast backward sweep for the case of the latter.

A Third of Organic Carbon Is Mineral Bound in Permafrost Sediments Exposed by the World's Largest Thaw Slump, Batagay, Siberia

ABSTRACTOrganic carbon (OC) in permafrost interacts with the mineral fraction of soil and sediments, representing < 1% to ~80% of the total OC pool. Quantifying the nature and controls of mineral–OC interactions is therefore crucial for realistic assessments of permafrost‐carbon‐climate feedbacks, especially in ice‐rich regions facing rapid thaw and the development of thermo‐erosion landforms. Here, we analyzed sediment samples from the Batagay megaslump in East Siberia, and we present total element concentrations, mineralogy, and mineral–OC interactions in its different stratigraphic units. Our findings indicate that up to 34 ± 8% of the OC pool interacts with mineral surfaces or elements. Interglacial deposits exhibit enhanced OC–mineral interactions, where OC has undergone greater microbial transformation and has likely low degradability. We provide a first‐order estimate of ~12,000 tons of OC mobilized annually downslope of the headwall (i.e., the approximate mass of 30 large aircrafts), with a maximum of 38% interacting with OC via complexation with metals or associations to poorly crystalline iron oxides. These data imply that over one‐third of the OC exposed by the slump is not readily available for mineralization, potentially leading to prolonged OC residence time in soil and sediments under stable physicochemical conditions.

How minerals impact the storage of organic carbon in our oceans

How minerals impact the storage of organic carbon in our oceans MinOrg set out to increase our understanding of the oceanic carbon cycle, aiding understanding of how Earth’s climate and surface conditions have evolved over time, and pointing to ways that might improve climate change predictions. The project explored why and how OC is preserved in seawater and sediments, testing its hypothesis: OC and minerals interaction promotes carbon preservation in seawater and sediments to an extent that impacts the global carbon cycle and climate.

Effects of erosion and deposition on the extent and characteristics of organic carbon associated with soil minerals in Mollisol landscape

The physicochemical interactions between soil organic carbon (SOC) and minerals are important for the long-term stabilization of OC. However, in the dynamic landscape, the mechanisms of OC stabilized by different types of minerals remains unclear. Herein, we investigated the effects of erosion and deposition on the distribution of SOC pools and the interaction of OC with different minerals in an agricultural Mollisol landscape. We quantified the SOC fractions using a physically separated technique and measured the polyvalent cation bound-OC using a mineral reduction release method. Sorption experiments and specific mineral surface area (SSA) were determined. Results show that 77.6%−96.9% of SOC was mineral-associated OC (MAOC). MAOC contents in the topsoil (0–20 cm) and subsoil (60–80 cm) of the depositional sites were 1.17 and 1.64 times higher than those in the topsoil and subsoil of the eroding sites, respectively. A higher MAOC content in the depositional sites suggests that MAOC in the middle slope migrates directly to the downslope through erosion, and subsequent depositional and burial processes promote OC interactions with minerals. Furthermore, Fe and Al oxides were the main minerals that stabilized OC compounds at each slope, while Ca played a vital role in OC interactions in the depositional sites. The Fe- and Al-bound OC (Fe/Al-OC) showed higher aromaticity, humification, and molecular weight than Ca-OC and bulk soil dissolved OC, which remained unaffected by erosion and deposition. These OC interactions with Fe/Al increased the chemical structural stability of SOC. Furthermore, the depositional sites showed the highest MAOC contents, MAOC loading, BET-C constant, adsorption capacity, and the lowest SSA covered by SOC (%SSASOC-covered). These results indicate that depositional sites have the highest capacities for OC sequestration. Based on these results, the deposition or burying of eroding OC plays a key role in stabilizing soil OC.

Low content of highly reactive iron in sediments from Prydz Bay and the adjacent Southern Ocean: Controlling factors and implications for sedimentary organic carbon preservation

Examining iron (Fe) speciation in marine sediments is critical to understand Fe and carbon biogeochemical cycling in polar regions. In this study, we investigated the speciation of Fe in sediments from Prydz Bay and the adjacent Southern Ocean, and examined the factors controlling Fe speciation and its relationship with total organic carbon (TOC). Our results reveal that unreactive silicate Fe (FeU) is the dominant pool of total Fe (FeT), followed by poorly reactive sheet silicate Fe (FePRS), reducible crystalline Fe oxides (Feox2), easily reducible amorphous/poorly crystalline Fe oxides (Feox1), and magnetite (Femag), with carbonate-associated ferrous Fe (Fecarb) being the smallest pool. The highly reactive Fe (FeHR)/FeT ratios (0.13 ± 0.06) in our study area are among the lowest end-member globally, primarily due to weak bedrock weathering and slow glacier melting. The Feox1/FeT ratios are similar to those in continental shelf and marginal seas containing highly weathered materials, while the Feox2/FeT ratios are significantly lower. This result implicates that low temperature inhibits the aging of iceberg melting-sourced Feox1 potentially, and accordingly the regulation of weathering on the FeHR/FeT ratio is mainly reflected in Feox2/FeT ratio. There are no significant correlations between TOC and FeHR, Fecarb, Feox1 or Feox2 in the research region. Four distinct patterns of TOC/FeHR ratio can be discerned by summarizing the global data set: (a) high TOC/FeHR ratios (> 2.5) are likely the result of high marine primary productivity and low chemically weathered source materials; (b) low TOC/FeHR ratios (< 0.6) are caused by high rates of FeHR inputs and OC remineralization; (c) mid-range TOC/FeHR ratios (0.6 – 2.5) typical of most river particulates and marginal sea sediments indicate the same FeHR and OC sources and/or interactions between each other; (d) both low TOC and FeHR content is the result of low marine primary productivity and weak chemical weathering. Our findings provide new insights into the relationship between FeHR and TOC in polar sediments.

A novel aryl hydrazide nucleator to effectively promote stereocomplex crystallization in high-molecular-weight poly(L-lactide)/poly(D-lactide) blends

Enhancing the interchain CH3⋯OC interactions between poly (l-lactide) (PLLA) and poly (d-lactide) (PDLA) proves effective in promoting stereocomplex (SC) crystallization of high-molecular-weight (HMW) PLLA/PDLA blends and thus endowing SC-type polylactide (PLA) with super physicochemical properties. In this work, a novel aryl hydrazide-type nucleator N,N,N,N′-salicylic tetra(1,2,4,5-benzenetetracarboxylic acid) hydrazide (BAS) with plentiful hydrazide and hydroxyl groups was designed and applied into HMW PLLA/PDLA blends, aiming to enhance the interchain interactions by forming numerous hydrogen bonds with PLA chains. The results indicate that BAS can simultaneously improve the crystallization rate and SC crystallizaion ability of racemic blend. No matter in nonisothermal or isothermal crystallization, the fraction of SC crystallites all exhibits a substantial enhancement as the BAS content increases. More importantly, exclusive SC crystallization with a quite high crystallinity (Xc,SC= 53.0%) is achieved for the ternary blends isothermally crystallized at 160 °C, which is simultaneously accompanied by a extremely fast crystallization rate and high nucleation density. Based on FTIR analysis, the mechanism of BAS facilitated SC crystallization is interpreted to be the largely enhanced enantiomeric interchain attractions derived from the abundant hydrogen bonds between BAS and PLA. We believe this work could provide significant guidance to develop novel efficient SC-type nucleators and fabricate high-performance SC-type PLA materials.

Observation of 3D isostructurality in halogen substituted N-benzoyl-N-phenylbenzamides

The occurrence of 3D isostructurality in six halogen substituted N-benzoyl-N-phenylbenzamides has been reported and this feature has been quantitatively analyzed in this study. 4-fluoro-N-(4-fluorobenzoyl)N-(fluorphenyl)benzamide (1) was observed to be isostructural with 2-fluoro-N-(2-fluorobenzoyl)N-(4-fluorophenyl)benzamide (7), N-(4-bromophenyl)-2-fluoro-N-(2-fluorobenzoyl)benzamide (8) and 2-fluoro-N-(2-fluorobenzoyl)N-(4-iodophenyl)benzamide (9). Similarly, N-(4-chlorophenyl)-4-fluoro-N-(4-fluorobenzoyl)benzamide (2) and N-(4-bromophenyl)-4-fluoro-N-(4-fluorobenzoyl)benzamide (3) was observed to be isostructural with each other. It was clearly evident from the analysis of structural similarity that 3D supramolecular construct present in 2/3 [Set 2] were more identical as compared to those observed in 1/7/8/9 [Set 1]. The molecular packing in both sets of isostructural molecules was observed to be governed by the presence of several CH⋯OC interactions. In addition to that, CH⋯FC and CH⋯π interactions also played an important role in the stabilization. However, 2D Fingerprint analysis revealed that the contribution of CH⋯FC interaction in a given structure was also dependent on the contribution of other hydrogens bonds involving halogens.

Studies on the syntheses, structural Characterization, antimicrobial of the CO-CRYSTAL 1,10-phenanthrolin-1-IUM(1,10-phenH+)-caffeine(caf)-hexafluorophosphate

Co-crystal of 1,10-phenanthrolin-1-ium-caffeine-hexafluorophosphate was synthesized, studied by FTIR, 1H, 13C NMR, DSC and X-ray structure and crystallized in the monoclinic space group C2/c. The unit cell parameters are a = 19.3761 (3), b = 17.9548 (3), c = 13.8074 (3) with β = 117.8132 (10). The final R value is 0.069 for 29,522 measured reflections. The co-crystal structure analysis indicate the 1,10-phenanthroline is protonated by one nitrogen atom and formed the 1,10-phenanthrolin-1-ium cation, which is stabilized by hydrogen bonds N+-H…OC interaction with carbonyl and imidazol ring in caffeine molecule. The intermolecular hydrogen bonds: CH...O, CH...N, NH...O, CH...F and intramolecular hydrogen bond: C1H12...O14, together play a vital role in stabilizing the structure of co-crystal.The X-ray structural analysis confirm the assignments of the structure from infrared, 1H, 13C NMR, spectroscopic data DSC and molar conductivity analysis. The antimicrobial activity of the co-crystal was studied.

Electrophilic substitution of acetyltrimethylsilane with tellurium(IV) halides: A synthetic route to 3-methyl-5-(trimethylsilyl)-1,2-oxatellurol-1-ium halides

The reaction of tellurium tetrahalides, TeX4 (XCl. Br) with acetyltrimethylsilane in CCl4 at ambient temperature, unlike that of the aryltellurium trichlorides, ArTeCl3 that give the expected electrophilic substitution products, Ar(Me3SiCOCH2)TeCl2, (Ar = 1-C10H7, 2; 2,4,6-Me3C6H2, 3), afforded novel silylated heterocycles, 3-methyl-5-(trimethylsilyl)-1,2-oxatellurol-1-ium halides 1a and 1b. These Te(II) heterocyclic compounds undergo halide exchange with sodium iodide and also add dihalogens oxidatively to afford the corresponding iodide, 1c and the Te(IV) trihalides, 5a and 5b respectively. A large lowering of ν(CO) is indicative of strong Te⋯OC interactions among these heterocycles, and is also substantiated by single-crystal X-ray diffraction data for 3-methyl-5-(trimethylsilyl)-1,2-oxatellurol-1-ium chloride. The 125Te chemical shifts for the new 10-Te-3 telluranes and 12-Te-5 pertelluranes that involve tellurium bound to two highly electronegative atoms (O, X) are among the highest (downfield) reported for organotellurium(II) and (IV) compounds.

Further studies on the chemistry of tetramethylthiourea–platinum complexes: Evolution of cis-[PtCl{S[dbnd]C(NMe2)2}(PPh3)2]+ to the dinuclear monothiocarbamato–sulfido complex [Pt2(μ-S){μ-SC(O)NMe2}(PPh3)4

Reaction of cis-[PtCl2(PPh3)2] with tetramethylthiourea (tmtu) in methanol under various conditions has been re-investigated. In the absence of base, the simple ligand substitution product [PtCl(tmtu)(PPh3)2]PF6 can be isolated by addition of excess NH4PF6. The complex was characterised by positive-ion ESI mass spectrometry, NMR spectroscopy and an X-ray structure determination. In refluxing methanol with excess Me3N, cis-[PtCl2(PPh3)2] reacts with tmtu to give a yellow solution containing the dinuclear monothiocarbamato complex [Pt2(μ-S){μ-SC(O)NMe2}(PPh3)4]+; the complex was isolated as BPh4− or PF6− salts. The X-ray structure of [Pt2(μ-S){μ-SC(O)NMe2}(PPh3)4]BPh4·CHCl3 is described. ESI mass spectrometry has been used to identify various reaction intermediates and by-products in the synthesis of [Pt2(μ-S){μ-SC(O)NMe2}(PPh3)4]+. [Pt2(μ-S){μ-SC(O)NMe2}(PPh3)4]+ acts as a metalloligand, e.g. towards PhHg+, but a pure product was unable to be isolated. DFT calculations suggest the presence of a Hg⋯OC interaction.

The effect of organizational culture on knowledge sharing among academic staff holding an administrative position in university

Knowledge sharing is the primary source of gaining competitive advantage and achieving long term success. Knowledge sharing is affected by many factors and the foremost of them is the culture of an organization. Organizational culture will help in developing the knowledge sharing practices among the members of an organization and achieve organizational objectives. The aim of the present study; firstly, to find out how the culture affects knowledge sharing in UTM (Universiti Teknologi Malaysia) and which of the cultural factors are more prevalent in developing knowledge sharing practices; secondly, to determine the level of knowledge sharing among the academic staff holding administrative positions in various faculties and departments of the university. Using quantitative approach, data was collected through survey questionnaire from a sample of 132 respondents. The analysis was carried out using descriptive and inferential statistics. Three of the dimensions of OC, workgroup support, information technology, and social interaction are found to be most significant in UTM, while reward system is found to be insignificant. Knowledge sharing is found to be high among academic staff holding administrative posts. The study concludes that organizational culture factors, workgroup support, information technology and social interaction are the most important factors that are helping in enhancing knowledge sharing in UTM. Finally, some recommendations related to the future studies are also included like investigating all levels and incorporating both administrative and academic staff, comparison with other public sector universities and between public and private sector universities.

Photophysics of indole-2-carboxylic acid (I2C) and indole-5-carboxylic acid (I5C): Heavy atom effect

In this study the effect of carboxylic group substitution in the 2 and 5 position of indole ring on the photophysics of the parent indole chromophore has been studied. The photophysical parameters crucial in triplet state decay mechanism of aqueous indole-2-carboxylic acid (I2C) and indole-5-carboxylic acid (I5C) have been determined applying our previously proposed methodology based on the heavy atom effect and fluorescence and phosphorescence decay kinetics [Kowalska-Baron et al., 2012]. The determined time-resolved phosphorescence spectra of I2C and I5C are red-shifted as compared to that of the parent indole. This red-shift was especially evident in the case of I2C and may indicate the possibility of hydrogen bonded complex formation incorporating carbonyl CO, the NH group of I2C and, possibly, surrounding water molecules. The possibility of the excited state charge transfer process and the subsequent electronic charge redistribution in such a hydrogen bonded complex may also be postulated. The resulting stabilization of the I2C triplet state is manifested by its relatively long phosphorescence lifetime in aqueous solution (912μs). The relatively short phosphorescence lifetime of I5C (56μs) may be the consequence of more effective ground-state quenching of I5C triplet state. This hypothesis may be strengthened by the significantly larger value of the determined rate constant of I5C triplet state quenching by its ground-state (4.4×108M−1s−1) as compared to that for indole (6.8×107M−1s−1) and I2C (2.3×107M−1s−1). The determined bimolecular rate constant for triplet state quenching by iodide kqT1 is equal to 1×104M−1s−1; 6×103M−1s−1 and 2.7×104M−1s−1 for indole, I2C and I5C, respectively. In order to obtain a better insight into iodide quenching of I2C and I5C triplet states in aqueous solution, the temperature dependence of the bimolecular rate constants for iodide quenching of the triplet states has been expressed in Arrhenius form. The linearity of the obtained Arrhenius plots clearly indicated the existence of one temperature-dependent non-radiative process for the de-excitation of I2C and I5C triplet state in the presence of iodide. This process may be attributed to the solute-quenching by iodide and, most probably, proceeds via reversibly formed exciplex. The activation energies obtained from linear Arrhenius plots (1.89kcal/mol for I5C; 2.55kcal/mol for I2C) are smaller as compared to that for diffusion controlled reactions in aqueous solution (about 4kcal/mol), which may indicate the great importance of the electrostatic interactions between solute and iodide ions in lowering the energy barrier needed for the formation of the triplet-quencher complex. Based on the theoretical predictions (at the DFT(CAM-B3LYP)/6-31+G(d,p) level of theory) and careful analysis of the obtained FTIR spectra it may be concluded that in the solid state I2C and I5C molecules form associates by intermolecular NH⋯OC and OH⋯OC hydrogen bonding interactions, whereas the existence of intramolecular NH⋯OC interactions in the solid state of I2C and I5C is highly unlikely.

Synthesis and SAR studies of mono O-prenylated coumarins as potent 15-lipoxygenase inhibitors

All of the mono isopentenyloxy, -geranyloxy and -farnesyloxy derivatives of coumarin were synthesized and their inhibitory potency against soybean 15-lipoxygenase (SLO) and human 15-lipoxygenase-1 (HLO-1) were determined. Amongst the synthetic analogs, 5-farnesyloxycoumarin showed the most potent inhibitory activity against SLO (IC50 = 0.8 μM) while 6-farnesyloxycoumarin was the strongest HLO-1 inhibitor (IC50 = 1.3 μM). The IC50 variations of the farnesyl derivatives for HLO-1 (1.3 to ∼75 μM) were much higher than that observed for SLO (0.8–5.8 μM). SAR studies showed that hydrogen bonding, CH/π, anion-π and S–OC interactions with FeIII–OH, Leu408, Glu357 and Met419 were the distinct intermolecular interactions which can lead to important role of the coumarin substitution site in HLO-1 inhibitory potency, respectively.

Impact of the effort–reward imbalance model on intent to leave among Belgian health care workers: A prospective study

The aim of this study was to analyse the impact of the effort–reward imbalance (ERI) model on intent to leave the current organization (ITL organization) and intent to leave the nursing profession (ITL profession) in a prospective way. A total of 1,531 health care workers who remained in their job filled in a self‐administered questionnaire at baseline and 1 year later. ERI was measured at baseline by a 23‐item questionnaire. Multivariate logistic regression analyses were performed. Within a population with low intent to leave at baseline, we found that an imbalance between high efforts and low rewards (extrinsic hypothesis) increased the risk of high ITL organization (OR 4.98; 95% CI 2.07–11.97) and high ITL profession (OR 1.84; 95% CI 1.03–3.30), 1 year later. A high level of overcommitment (OC; intrinsic hypothesis) was not predictive for both intent to leave outcome variables, neither was the interaction between high efforts/low rewards and a high level of OC (interaction hypothesis). Our results showed that a perceived effort‐reward imbalance (ERI) at work is a significant predictor of intent to leave among health care workers. This contribution concludes with some directions aimed at boosting nurses' retention and recommendations for future research.

Structural Stability and Binding Efficiency of Strong and Weak Interactions in Epidermal Growth Factor Receptor (EGFR) Tyrosine Kinase Domain of Human and Drosophila

Epidermal growth factor receptor (EGFR) is a cell membrane receptor serving as a molecular target for Non Small Cell Lung cancer (NSCLC). The aim of the study was to analyze the weak ion interactions taking place in the tyrosine kinase domain of Human and Drosophila EGFR. This study throws light on the environment preferability, stabilizing residues taking part in weak and strong interactions of EGFR TK domain. Analysis of short, medium and long range contacts showed that the cation-� interactions are mainly formed by long-range contacts, whereas CH…OC interactions are formed by both long and short range interactions. Except Pro, other non-polar hydrophobic amino acids in Drosophila EGFR TK domain were present in buried environment. However, in humans other than Pro and Ala, which were involved in SS (CH…OC) and SM (NH…OC) interactions, other non-polar hydrophobic amino acid preferred to be in buried environment. The results observed in this study will be useful for understanding the contribution of weak and strong interactions to the stability of EGFR TK domain. Further, the weak interactions have distinct roles in the stability of EGFR TK domain in addition to other conventional strong interactions. The results can lead to the identification of novel targets for NSCLC drugs which in turn will serve as a major break through in the treatment of NSCLC. methoxy-6-(3-morpholin-4-ylpropoxy)quinazolin-4-amine), both orally available, low molecular weight, reversible and selective EGFR-TKIs, were used as advanced EGFR- targeted drugs in NSCLC treatment. They blocked signal

Supramolecular Walls from Cyclic Peptides: Modulating Nature and Strength of Weak Interactions

Both macrolactams cyclo-[NH−CH2−C≡C−CH2−C(Me)2-CO]n (n = 3 and n = 2) have been synthesized and crystallized. They have respectively one intramolecular hydrogen bond and no such bond. Both macrocycles self-assemble as parallel supramolecular walls with or without inclusion of solvent between them. The units of the former (n = 3) are held together by NH···π/NH···OC interactions, whereas they are glued by a very dense network of classical parallel-oriented hydrogen bonds, involving all the amides of the rings, in the latter (n = 2). In that case, the bulky C(Me)2 groups are located on the surface of the walls and can be held responsible for the piling process of the layers, by means of attractive van der Waals interactions. This spatial arrangement recalls the 3D structure of cellulose, where all constitutive sheets stack mostly via van der Waals forces.

Appraising the relative strengths of C–H⋯OC and N–H⋯OC interactions from cis-N-methylacetamide multimers

The strength of C-H***O[double bond, length as m-dash]C interactions relative to regular N-H***O[double bond, length as m-dash]C hydrogen bonds is estimated from DFT quantum calculations on multimers of cis-N-methylacetamide (NMA). Assuming transferable hydrogen-bond increments, treatment of various constraint-free NMA dimers and trimers enables us to provide statistical values for (i) the direct energy difference between the two kinds of interaction (calculated around 5 kcal mol(-1)), and (ii) their associated binding energies, hence the ratio of their strengths. Combining the binding energies with other critically-analyzed observables, a relative strength of about 20%-say no more than one fifth-is finally proposed.

How robust is the hydrogen-bonded amide ‘ladder’ motif?

The well-known hydrogen-bonded ladder displayed by amides in the solid state, is readily disrupted and reduced to an R22(8) motif if a competitive hydrogen-bond acceptor is incorporated in the molecular structure of the amide. When a weaker hydrogen-bond acceptor (i.e. –NO2, –CN, –Cl, –Br) is present, the ladder persists in about every other case, whereas if a stronger hydrogen-bond acceptor is introduced (such as a N-heterocycle), the ladder is very unlikely to appear. If a strong hydrogen-bond acceptor is present, the amide⋯amide dimer ‘survives’ a little over 50% of the time. This conclusion is based upon the synthesis and structural characterization of six pyrazole-decorated benzamides in addition to an examination of relevant data from the CSD. The anti hydrogen atom of the amide moiety is much more likely to engage in an N–H⋯N(heterocycle) hydrogen bond instead of an N–H⋯OC (amide) interaction.

Relative importance of X⋯OC vs. X⋯X halogen bonding as structural determinants in 4-halotriaroylbenzenes

The structures of 4-chloro- and 4-bromotribenzoylbenzene, as well as a solid solution prepared from these two components, are isomorphous and dominated by C-X...O=C interactions, whereas type-II I...I interactions are important in the 4-iodo derivative.

Stereoselective Crystallization and Specific Interactions in Polylactides

The stereoselective annealing conditions for polylactides to crystallize as α homocrystals (Tm = 180 °C) and/or higher melting temperature (Tm = 230 °C) η stereocomplex crystals are reported in this paper. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) studies provide evidence of the isothermal annealing conditions in which equimolar mixtures of optically pure poly(l-lactide) and poly(d-lactide) take exclusively the form α, exclusively the form η, or coexist as both α and η crystal polymorphs. Fourier transformed infrared (FTIR) spectroscopy studies reveal a shift to lower wavenumbers in the CO stretching band of polylactides in the stereocomplex with regard to that in the homocrystal. This band shift is accompanied by similar displacements in the C−H spectral bands. These results are interpreted in terms of H-bonding forces causing specific CH3···OC and CαH···OC interactions between both stereoisomers of polylactide. Molecular models support that the suggested hydrogen-bonding arrangement can be accommodated into the stereocomplex crystal lattice. The strength of the interactions has been calculated from both CO and C−H spectral regions, resulting in a mean value of 1.1 kcal/mol, close to that expected according to ab initio calculations.