H++ is an automated system that computes pK values of ionizable groups in macromolecules and adds missing hydrogen atoms according to the specified pH of the environment. Given a (PDB) structure file on input, H++ outputs the completed structure in several common formats (PDB, PQR, AMBER inpcrd/prmtop) and provides a set of tools for analysis of electrostatic-related molecular properties.

H++是一个自动化系统，可以计算大分子中可电离基团的pK值，并根据环境的指定pH值添加缺失的氢原子。给定输入上的（PDB）结构文件，H++以几种常见格式（PDB、PQR、AMBER inpcrd/prmtop）输出完整的结构，并提供一组用于分析静电相关分子特性的工具。

Structure and function of macromolecules depend critically on the ionization (protonation) states ( pK ) of their acidic and basic groups. For example, affinities of proteins for ligands depend on the pKs of the groups in or near the binding sites; groups with unusual pKs are often found in active sites of enzymes. Atomistic simulations of macromolecules require specification of the protonation state of the titratable groups. Whether or not a given group is protonated depends, in a non-trivial way, on the position of the group within the molecule as well on the characteristics of the surrounding solvent such as its pH and ionic strength.

大分子的结构和功能在很大程度上取决于其酸性和碱性基团的电离（质子化）状态（pK）。例如，蛋白质对配体的亲和力取决于结合位点内或附近基团的pKs；具有异常pKs的组通常存在于酶的活性位点。大分子的原子模拟需要指定可滴定基团的质子化状态。给定的基团是否被质子化，在很大程度上取决于该基团在分子中的位置以及周围溶剂的特性，如pH值和离子强度。

Experimental determination (usually by NMR) of protonation equilibria is expensive and often can not be performed for every group of interest. The most common source of high resolution structures -- X-ray crystallography -- normally does not provide positions of the hydrogen atoms. The gap is bridged by theoretical methods that predict protonation states (pK) of ionizable groups within the macromolecule based on its atomic resolution structure. This web site provides access to a set of tools that automate this process.

质子化平衡的实验测定（通常通过核磁共振）是昂贵的，并且通常无法对每个感兴趣的组进行。高分辨率结构的最常见来源——X射线晶体学——通常不提供氢原子的位置。通过理论方法弥合了这一差距，这些方法根据大分子的原子分辨率结构预测大分子内可电离基团的质子化状态（pK）。此网站提供对一组自动化此过程的工具的访问。